Research Collection31008/eth-31008-02.pdf · Na konec, d kuji Kristina. Nic víc. VIII. List of...

$: Research Collection31008/eth-31008-02.pdf · Na konec, d kuji Kristina. Nic víc. VIII. List of symbols, ... materials) using advanced in situ x-ray and neutron powder diffraction$
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Doctoral Thesis

In situ synchrotron and neutron diffraction based methodsfor the characterization of cathodic materials for lithium-ionbatteries

Author(s): Rosciano, Fabio

Publication Date: 2008

Permanent Link: https://doi.org/10.3929/ethz-a-005708014

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DISS. ETH NO. 17847

In Situ Synchrotron and Neutron

Diffraction Based Methods for the

Characterization of Cathodic Materials for

Lithium-Ion Batteries

A dissertation submitted to

ETH ZURICH

for the degree of

Doctor of Sciences

presented by

FABIO ROSCIANO

Master of Science, University of Milano Bicocca

born 27.05.1979

citizen of Italy

accepted on the recommendation of

Prof. Dr. A. Wokaun

PD Dr. P. Novák

Prof. Dr. R. Nesper

2008

To My Family

There are two types of chemists:

those who have never worked with lithium

and those who are scared to death by it.

Acknowledgments

AcknowledgmentsThis work has been carried out in the Batteries Group, part of the

Electrochemistry Laboratory of the General Energy Department (ENE) of the Paul

Scherrer Institut, Villigen, Switzerland.

I would like to thank Prof. Alexander Wokaun, my thesis advisor and head of

ENE, for accepting me as a Ph.D. Student and for his continuous assistance and

encouragement. This work could have never been completed without the

constant supervision and the stimulating scientific discussion with PD Dr. Petr

Novák, head of the Batteries Group. Thank you for teaching me the fundamentals

of being a good scientist.

I am also grateful to Prof. Reinhard Nesper at ETHZ for accepting to be part of

the examining commission and for the insightful comments about the

development of NMC materials.

A big thank you goes to my part-time supervisors Dr. Michael Holzapfel and Dr.

Nicolas Tran, who helped through the hard times with encouragement and

guidance. Good luck in your new career, hopefully we'll work again together at

some point.

A huge thank you is for Fabio La Mantia, who shared with me the adventure of

being a Ph.D. Student from day 1 to day 1125. We've been a reciprocal pain in

the neck more often than not, but we'd have never managed to do it without

noisy and agitated arguments. Grazie!

I am grateful to Hermann Kaiser and Werner Scheifele, experts in mechanical

and technical matters in the Batteries Group. Without you pretty much nothing of

this thesis would have happened. Danke, or better, Merci!

Thank you to the whole of the Batteries Group, those who came and those who

went. In particular thanks to Hilmi Buqa for introducing me to the PSI Football

Sport Club, to Pascal Maire for making me notice things I overlooked, to Jean-

François Colin for disclosing me the secrets of Fullprof. Faleminderit, danke, merci,

thank you!

Thank you to the other groups in the Electrochemistry Laboratory, in particular

VI

Acknowledgments

to the Supercaps Group, for the fruitful collaboration. Among others, thank you to

Patrick Ruch for sharing the good and the bad times at the synchrotron; and

Stefan Freunberger for being my first office mate here at PSI. Thanks and danke!

Thank you to the beamline personnel at the Material Science BL X04SA at the

Swiss Light Source (SLS), in particular Dr. Bernd Schmitt and Dr. David Maden.

Without their help setting up the in situ method would have been a total

nightmare. Thank you!

Gratitude goes to the people at the High Resolution Powder Diffractometer for

Thermal Neutrons (HRPT) at the Swiss Spallation Neutron Source (SINQ), in

particular Dr. Denis Cheptiakov and Dr. Vladimir Pomjakushin. I learned more

about neutrons in 5 days with you than in 5 weeks reading books. !��

Also, thanks to all people at PSI who helped to different degrees. In particular

thanks to Dr. Ekaterina Pomjakushina for letting me use the diffractometer and

for the patience whenever I had problems with it; and Anja Weber for her help

with SEM. Thank you also to my german teacher Christian Aeberhard. I won't

embarrass you by writing in german now! and danke!��

Thank you to the PSI Football Sport Club for many hours of great fun and

improved productivity.

A big shout out goes to all of the friends I made here at PSI: thank you to all

the friends of the 15.45h coffee. You know who you are, damn slackers. Thank

you to the people in The List. Things have quite changed in the years, but I'm

sure you're all still going strong. Honorable mention for Mr. Paul Blair (you, sir, are

my benchmark for all that is geek) and Simeon Karagiannidis, for introducing me

to the greeks. It was worth it!

Grazie alla ghenga italiana, in ordine più o meno cronologico: Luca, Antonino,

Valerio, Paolo, Gaia, Stefano, Davide, Alessandra, Salvatore, Andrea, Roberto,

Tara & Ian (ad honorem), Salvatore, Sebastiano, Roberto, Barbara, Davide,

Roberto, Maurizio, Stefania, Dario. Se ho dimenticato qualcuno, peste mi colga.

Andiamo a Berlino!

Grazie anche alla mia famiglia, mamma e papà, mia sorella e tutti gli altri, per

il continuo supporto in questa mia fissazione di fare lo scienziato, invece di

VII

Acknowledgments

imparare un mestiere rispettabile. Grazie anche ai miei amici, in particolare a

Matteo (forza e coraggio) e a Patrizia e Tommaso (insieme ai loro splendidi

cuccioli). Thanks Ali for being the good friend you are.

Na konec, d�kuji Kristina. Nic víc.

VIII

List of symbols, fundamental constants and abbreviations

List of Symbols, Fundamental Constants andAbbreviations

Symbol Name Unit

ai activity of species i mol dm-3 C-rate rate of charge AhC capacitance F m-2

ci concentration of species i mol dm-3

Eo standard electrode potential V or mVEe equilibrium potential V or mV

Eeo

formal electrode potential (i.e.the equilibrium potential when co

= cr)V or mV

E� o, Uo cell potential V or mVF Faraday constant C mol-1

G� o standard Gibbs free energy J mol-1

I electric current Aim specific current A g-1

k Boltzmann constant J K-1

M, mi mass kgMr molar mass kg mol-1

n number of electrons exchanged (dimensionless)NA Avogadro constant mol-1

p specific power W kg-1

Pv power density W dm-3

Q charge capacity C or Ahqth theoretical specific charge

capacityAh kg-1

R Gas constant J mol-1 K-1

R resistance Reff effective series resistance T temperature Kt time sV, Vi volume dm-3

wth theoretical specific energy Wh kg-1

WV.th theoretical energy density Wh dm-3

� dielectric constant (dimensionless)� wavelength of light Nm or � magnetic permeability N A-2

� conductivity S cm-1 or mS cm-1

IX

List of symbols, fundamental constants and abbreviations

Fundamental Constants

Quantity Symbol Value Power of ten Units

speed of light c 2.997 924 58 108 m s-1

elementary charge e 1.602 177 10-19 CFaraday constant F = NA e 9.648 53 104 C mol-1

Boltzmann constant k 1.380 66 10-23 J K-1

Gas constant R = NA k 8.314 51 J K-1 mol-1

Planck constant h 6.626 08 10-34 J s = h/ � 2� 1.054 57 10-34 J s

Avogadro constant NA 6.022 14 1023 mol-1

Abbreviations

AN AcetonitrileASA Active surface areaa.u. arbitrary unitBET Brunaner Emmett TellerCV Cylic voltammetryDEC Diethyl carbonateDEMS Differential electrochemical mass spectrometryDMC Dimethyl carbonateEC Ethylene carbonateEDLC Electrochemical double layer capacitorEMC Ethyl-methyl carbonateEMI 1-ethyl 3-methyl imidazolium saltFWHM Full width at half maximumNPD Neutron powder diffractionOCP Open circuit potentialOCV Open circuit voltagePC Propylene carbonatePEEK PolyetheretherketonePVdF PolyvinyldenedifluorideSEI Solid electrolyte interphaseSEM Scanning electron microscopySHE Standard hydrogen electrodeTEA Tetraethyl ammoniumVC Vinylene carbonateXRD X-ray diffraction

X

Table of Contents

Table of ContentsAcknowledgments......................................................................................VI

List of Symbols, Fundamental Constants and Abbreviations......................IX

Table Of Contents.......................................................................................XI

Abstract...................................................................................................XIII

Riassunto..................................................................................................XV

Chapter 1 - Introduction............................................................................19

1.1 Motivation...........................................................................................21

1.2 Goal of this work.................................................................................22

1.3 Electrochemical energy storage devices.............................................23

1.4 Lithium batteries.................................................................................26

1.4.1 Primary lithium batteries.........................................................................261.4.2 Secondary lithium batteries.....................................................................28

1.4.2.1 Applications of Li-ion batteries...............................................................291.4.2.2 Issues with current batteries..................................................................311.4.2.3 Possible improvements for Li-ion...........................................................31

1.5 Positive electrode materials................................................................33

1.5.1 Layered type oxides................................................................................331.5.2 Spinel type oxides...................................................................................351.5.3 Phosphates..............................................................................................37

1.6 Mixed oxides Li1+x(Ni1-y-zMnyCoz)1-xO2.....................................................38

Chapter 2 - Principles of Diffraction...........................................................41

2.1 Principles of diffraction........................................................................43

2.1.1 Experimental notes.................................................................................462.2 The Rietveld method...........................................................................49

Chapter 3 - Synthesis and Characterization of NMC Materials...................53

3.1 Synthesis of powders..........................................................................55

3.2 Characterization of NMC powders.......................................................56

3.3 Working hypothesis....................................................................................713.3.1 Cycling stability.......................................................................................713.3.2 Origin of O2 evolution..............................................................................71

Chapter 4 - O3 O1 Phase Transition in NMC Materials� ............................73

4.1 Introduction.........................................................................................75

XI

Table of Contents

4.2 In situ method at the SLS synchrotron................................................79

4.2.1 State of the art in situ XRD......................................................................794.2.2 Method development...............................................................................81

4.2.2.1 Synchrotron radiation.............................................................................814.2.2.2 New �coffee bags�.................................................................................824.2.2.3 Sample changer.....................................................................................86

4.3 Results and discussion........................................................................88

4.3.1 Additional results obtained using in situ XRD..........................................95Chapter 5 - Oxygen Evolution from NMC Materials....................................99

5.1 Introduction.......................................................................................101

5.2 In situ method at the SINQ neutron source.......................................102

5.2.1 State of the art in situ NPD....................................................................1025.2.2 Method development.............................................................................103

5.2.2.1 New electrochemical cell.....................................................................1035.2.2.2 Cell optimization..................................................................................105

5.3 Results and discussion......................................................................112

Chapter 6 - Conclusions and Outlook......................................................123

6.1 General conclusions..........................................................................125

6.2 Recommendations for future work....................................................127

6.2.1 NMC materials.......................................................................................1286.2.2 Coffee bag cells and in situ synchrotron method...................................1286.2.3 Neutron cell and in situ neutron diffraction method..............................129

Chapter 7 - Appendix..............................................................................131

7.1 SLS Script..........................................................................................133

Bibliography............................................................................................147

Curriculum Vitae.....................................................................................153

XII

Abstract

AbstractLithium ion batteries (Li-ion) are today's energy source of choice for the market

of portable devices and are ubiquitously found in all sorts of electronic gadgets.

The appearance of new fields of application in more demanding systems such as

those introduced in the automotive industry, pushes Li-ion technology to the next

level. To overcome the shortcomings of current lithium ion batteries,

improvements are needed in electrode materials (both positive and negative),

electrolytes and cell engineering.

Advanced characterization techniques that allow for understanding of the

deepest details of lithium insertion and removal mechanisms from novel

materials are crucial for selecting the best compound for demanding applications.

The combination of x-rays and neutrons allows investigating materials for lithium

ion batteries in a complementary manner, as neutrons permit to directly study

lithium, practically undetectable by x-rays.

This work has been focused on the synthesis and characterization of novel

positive electrode materials with general formula Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 (NMC

materials) using advanced in situ x-ray and neutron powder diffraction

techniques. NMC materials have been indicated as promising substitutes of

LiCoO2 since they provide performance levels at least on par with the standard,

while being safer and having the obvious advantage of containing only 1/3 of

cobalt. Moreover, overlithiated species (compounds with x > 0) seem to have a

better long term cycle stability than the stoichiometric one (compound with x =

0).

Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 powders have been prepared using a soft chemistry

approach by coprecipitation of hydroxides from an aqueous solution and

subsequent high temperature calcination. Structural, morphologic and

electrochemical characterization allowed to individuate particular properties of

Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 that needed further investigation by means of in situ

synchrotron x-rays powder diffraction and in situ neutron powder diffraction.

A method for performing in situ x-ray powder diffraction, revolving around

electrochemical �coffee bag� cells, was developed and implemented at the Swiss

XIII

Abstract

Light Source (SLS) synchrotron. The cheap and versatile �coffee bag� cells were

used to study phase transitions in the NMC materials, and the use of an

automatic sample changer allowed to efficiently examine numerous samples,

therefore optimizing the use of granted beamtime at the beamline.

A completely novel concept for an electrochemical cell that allows for in situ

neutron powder diffraction experiments was also developed and used at the

Swiss Spallation Neutron Source (SINQ). This device was employed to investigate

the origin of oxygen development during the first charge of

Li1.1(Ni1/3Mn1/3Co1/3)0.9O2, a phenomenon that was observed by means of

Differential Electrochemical Mass Spectrometry (DEMS) during the preliminary

characterization of the material and that prompted further study.

The investigation of the structural stability of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 allowed to

find a possible explanation for the improved long term reversible capacity

retention of this compound, correlating the preparation method to the structural

properties that influence lithium insertion and removal. On the other hand, in situ

neutron diffraction experiments were successfully performed but the results did

not give conclusive evidence on the changes in oxygen content of

Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 at potentials positive to 4.5V vs. Li+/Li.

The development of both x-rays and neutron in situ methods was completed

successfully, with both techniques ready to be used in further experiments on

different materials and to be expanded for further applications.

This thesis details the synthesis and preparation of Li1+x(Ni1/3Mn1/3Co1/3)1-xO2

powders and their characterization, as well as the development of the in situ

techniques using both synchrotron x-rays and neutrons and their implementation

at the large facilities (SLS and SINQ) at the Paul Scherrer Institut (PSI). The results

obtained using these novel methods, complemented by traditional investigation

techniques, are also presented, along with the discussion of the obtained data.

Finally, suggestions for further development of the methods and additional

investigations on NMC materials are given.

XIV

Riassunto

RiassuntoLe batterie agli ioni di litio (Li-ion) sono la piú diffusa sorgente energetica

portatile e sono presenti in ogni dispositivo di elettronica di consumo. La crescita

di nuovi campi di applicazione in sistemi piú esigenti come quelli introdotti

dall'industria automobilistica, spingono la tecnologia Li-ion ad un livello superiore.

Per superare i punti deboli delle attuali batterie al litio, sono necessari

miglioramenti nei materiali elettrodici (sia positivi che negativi), negli elettroliti e

nella costruzione delle batterie.

Nuove tecniche di caratterizzazione che permettano di comprendere ogni

dettaglio dei meccanismi di intercalazione e deintercalazione di ioni litio da

materiali innovativi sono di cruciale importanza per selezionare i migliori

composti per applicazioni avanzate. La combinazione di raggi X e neutroni

permette di investigare materiali per batterie al litio in maniera complementare,

dato che i neutroni danno la possibilità di studiare direttamente il litio,

praticamente invisibile ai raggi X.

Questo lavoro si é focalizzato sulla sintesi e la caratterizzazione di nuovi

materiali elettrodici positivi con formula generale Li1+x(Ni1/3Mn1/3Co1/3)1-xO2

(materiali NMC) usando tecniche avanzate in situ di diffrazione di polveri

attraverso raggi X e neutroni. I materiali NMC sono stati indicati come

promettenti sostituti per LiCoO2 poiché hanno prestazioni almeno identiche allo

standard, pur essendo piú sicuri e con l'ovvio vantaggio di contenere solo 1/3 di

cobalto. Inoltre, le specie sovralitiate (composti con x > 0) sembrano avere

migliore stabilitá a lungo termine dell'omologo stechiometrico (x = 0). Polveri di

Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 sono state preparate usando un approccio di chimica

dolce, attraverso la coprecipitazione di idrossidi da una soluzione acquosa,

seguita da calcinazione ad alta temperatura. La caratterizzazione strutturale,

morfologica ed elettrochimica ha permesso di individuare proprietá particolari di

Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 che sono state oggetto di ulteriore investigazione usando

diffrazione di polveri in situ usando luce di sincrotrone (raggi X) e neutroni.

Un metodo per effettuare diffrazione in situ di raggi X, costruito attorno a celle

elettrochimiche �a bustina� (�coffee bag cells�), é stato sviluppato ed

XV

Riassunto

implementato al sincrotrone Sorgente di Luce Svizzera (SLS). Le versatili ed

economiche celle a bustina sono state usate per studiare transizioni di fase da

parte dei materiali NMC e l'utilizzo di un sistema automatizzato per la gestione

dei campioni ha permesso di analizzare efficientemente numerose celle,

ottimizzando cosí l'uso della limitata quantità di tempo macchina al sincrotrone.

Un concetto completamente nuovo per una cella elettrochimica che

permettesse di effettuare misure in situ di diffrazione di neutroni é stato inoltre

sviluppato ed utilizzato alla Sorgente Svizzera di Neutroni a Spallazione (SINQ).

Questo dispositivo é stato usato per investigare l'origine dello sviluppo di

ossigeno durante la prima carica di Li1.1(Ni1/3Mn1/3Co1/3)0.9O2, un fenomeno

osservato durante la caratterizzazione iniziale attraverso l'uso di Spettroscopia di

Massa Differenziale Elettrochimica (DEMS) e che ha richiesto uno studio piú

approfondito.

L'investigazione della stabilità strutturale di Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 ha

permesso di trovare una possibile spiegazione per la migliore reversibilità del

processo di carica � scarica di questo composto rispetto l'omologo

stechiometrico, correlando il metodo di preparazione alle proprietà strutturali che

influenzano il processo di inserzione e rimozione di litio. D'altra parte,

esperimenti di diffrazione di neutroni in situ sono stati effettuati con successo,

ma i dati ottenuti non hanno permesso di trovare prove conclusive su eventuali

cambiamenti dell'occupazione dell'ossigeno in Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 a potenziali

positivi rispetto a 4.5V vs. Li+/Li.

Lo sviluppo di entrambe le tecniche in situ (raggi X e neutroni) é stato

completato con successo. I metodi potranno essere ulteriormente utilizzati per

studiare altri materiali o essere sviluppati per applicazioni successive.

Questa tesi presenta in dettaglio la sintesi, preparazione e caratterizzazione di

polveri di Li1+x(Ni1/3Mn1/3Co1/3)1-xO2; oltre che lo sviluppo e l'implementazione presso

le strutture del Paul Scherrer Institut (SLS e SINQ) di tecniche in situ che sfruttino

raggi X di sincrotrone e neutroni. I risultati ottenuti da questi nuovi metodi,

completati attraverso l'uso di tecniche convenzionali, sono anche presentati

insieme ad una discussione dei dati ottenuti. Infine sono dati suggerimenti per

l'ulteriore sviluppo dei metodi e per successive investigazioni sui materiali NMC.

XVI

Chapter 1

Introduction

Chapter 1 - Introduction

1.1 Motivation

The technological progress that invested the western society in the last fifty

years has provided us with an unprecedented quality of life and wealth of

possibilities that could only be imagined in science fiction only a few decades

earlier. The spreading of the electronic revolution that started with the invention

of the microchip in 1959 has allowed for continuous increase in miniaturization

and creation of more and more complex and powerful devices. The next logical

step has been the introduction of portable devices, from the clumsy first portable

computers and cellphones that could barely fit in bulky suitcases, to the

convergence of multiple devices in objects small enough to fit in a pocket.

The steadily increasing offer in computing power, however, is limited by the

portable energy source these devices are fitted with. The switch from primary

batteries such as alkaline and zinc-air to secondary systems such as Ni-Cd and

NiMH permitted at least not to carry spare replacement batteries along with the

devices, but the real breakthrough came when lithium ion batteries (Li-ion) were

introduced to the market by Sony in 1991. Li-ion had clear advantages over their

nickel based competition: higher capacity and higher nominal voltage, resulting

in higher energy and power densities.

The rise of Li-ion in the market was then unstoppable, resulting in a

predominant position in the portable devices market that seemed to encounter

no obstacle. In recent years though, the commercialization of cheap batteries

manufactured with poor quality starting materials, lead to a spreading mistrust in

the technology: reports of batteries that would swell, catch fire or even explode

have been read in most generic media, sometimes spreading unnecessary and

unsubstantiated panic in the general public.

Today's challenge for those who research the topic of lithium batteries is then

not only the improvement of the technology through new materials and

engineering solutions, but also the responsibility of increasing the safety of Li-ion

powered devices by designing batteries that will overcome the actual weak

points. Additionally, the debate on alternative and renewable energy sources

pushes Li-ion to the next level, both in stationary applications to store the energy

21


obtained from solar and wind sources; and mobile applications, for example in

hybrid and fully electric vehicles.

In this work new cathode materials with general formula Li1+x(Ni1/3Mn1/3Co1/3)1-

xO2 for Li-ion batteries are prepared and characterized, while the development of

novel in situ diffraction techniques using both x-rays and neutrons allows for

discussion of some of the scientific questions arising when studying such

materials. The novel experimental methods are described and compared to

existing state-of-the-art technologies.

1.2 Goal of this workThe development of the next generation of lithium ion batteries is a complex

task that involves the cooperation of many different experts. Among them, the

material scientist is called to invent and perfection new chemical compounds,

ceramics and molecules. These new materials cannot be engineered by mere trial

and error, therefore the understanding of the processes involved in the operation

of a Li-ion battery is of vital importance.

The purpose of this work is the preparation of novel ceramic materials to be

used as cathodic material in lithium ion batteries and the study of their properties

through new analytic techniques. The focus of the thesis is on the investigation of

the high potential properties of a class of materials with general formula

Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 through in situ diffraction methods.

Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 (NMC) encompasses a range of materials that are

regarded as promising substitutes for today's industry standard LiCoO2 because

of their improved electrochemical performance and thermal stability in the

charged state. Nonetheless, their behavior at high potentials (positive to 4.5V vs.

Li+/Li) and their different long term performance for different values of the

lithiation parameter x is still debated. These properties derive from the crystal

structure of the material and from the way it changes during charge and

discharge: phase transitions can occur and they can influence the reversibility of

the lithium insertion.

The obvious tool to study crystal structures is diffraction. This method is

extremely widespread and it's the technique of choice for scientists who routinely

22


work with crystalline samples. Diffraction can be induced with a wide array of

radiations and every different particle used can reveal different details of the

structure under investigation. Among those many possibilities, the focus of this

thesis is the use of x-rays and neutrons, as they complement each other to obtain

a clear picture of the structural changes occurring in electrode materials. In

particular, their use in situ allows for direct investigation of processes while

occurring, as opposed to ex situ and post mortem analysis, when often slim

details are lost in the handling and preparation of the sample.

This thesis details the synthesis of Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 through a soft

chemistry approach, in order to obtain a fast and economic way of producing

pure and crystalline powders of this active material, and the characterization of

the prepared compound.

Later, the scientific questions related to the high potential behavior are

discussed and the steps to answer them are presented, along with the design of

the in situ experiments.

Finally, the results obtained by the use of said techniques implemented at the

Swiss Light Source (SLS) synchrotron and Swiss Spallation Neutron Source (SINQ)

are discussed, together with an outlook on the further improvements of the

experimental technique.

1.3 Electrochemical energy storage devicesStoring energy by electrochemical means, or transforming chemical energy in

usable work, has been known to man for many centuries. The first examples of

sui generis batteries were discovered in 1936 by German archaeologists near

Baghdad, Iraq [1], and are believed to be around 2000 years old: terracotta jars

with two electrodes made of iron and copper were probably immersed in an

electrolyte of natural origin, like lemon juice. The use of these devices is debated,

as they could have been used for electroplating small jewelry with gold or maybe

in religious ceremonies: in fact, they could have been no batteries at all. A real

scientific study of the properties of two metals separated by an electrolyte came

only in the 19th century, through the work of Alessandro Volta (1745-1827). The

Italian scientist first built an electrochemical device (the �Voltaic pile�) by

23


stacking zinc and copper discs separated by cardboard soaked in brine: this was

the first real battery, with a stable potential depending on the metals used and

on the number of layers used in the stack. It was only in 1859 that Gaston Planté

(1834-1889) invented the first rechargeable battery, based on the interaction

between lead and an acidic electrolyte. This concept is still in use today, as lead-

acid batteries are the most widespread batteries on the planet nowadays [2].

Many other researchers worked on the topic through these pioneering years,

notably John Frederic Daniell (1790-1845), Georges Leclanché (1839-1882) and

William Robert Grove (1811-1896).

Sir William Grove is perhaps best known for another electrochemical device

that transforms chemical energy in work: the fuel cell. In 1843 he described his

�Gas voltaic battery� describing how hydrogen and oxygen could be combined

electrochemically to produce a steady current [3].

The third way to store energy using electrochemistry are capacitors, invented

in 1745 by Ewald Jürgen Georg von Kleist (1700-1748). That concept was then

updated and improved in 1957, when General Electric applied for a patent

describing a device that would store larger amounts of energy than conventional

capacitors: supercapacitors or electrochemical double layer capacitors (EDLC)

were born [4].

Despite being based on three diverse principles, batteries, fuel cells and EDLCs

are generally grouped when discussing energy storage systems. Nonetheless all

three serve different purposes, according to their energy and power density

characteristics, often represented in the well known �Ragone chart�. One

example is proposed in figure 1.3.1.

24


Figure 1.3.1: A typical Ragone chart. In this plot, different electrochemical energy storagesystems are compared according to their gravimetric energy and power density [5].

In this chart the characteristics of different electrochemical systems appear

clearly: supercapacitors, in the top-left corner of the plot, provide a little amount

of energy in an extremely short time, and are thus suited for short bursts of

energy, as for example the acceleration of a car at a traffic light sign. Fuel cells

are at the other end of the chart, because of their high energy density delivered

in long times: this makes them suited to provide the energy necessary to cruise

for a long time at a constant speed on a highway. Batteries are somewhere in

between of these systems, providing a bridge between fuel cells and EDLCs and

making them suitable for both substituting or complementing one of the other

technologies. Four different types of rechargeable batteries are plotted in figure

1.3.1, and it is clear that Li-ion is the technology that provides with both the

highest power and energy density.

25


1.4 Lithium batteriesIn a battery, chemical energy is transformed in electricity through oxidation

and reduction processes. When a component in a battery is oxidized, one

electron leaves its bulk, travels through an external circuit making work, and

reenters the battery at the other end, reducing the material at the opposite

electrode. It is then necessary to have materials that are able to be easily

reduced and oxidized: metals are in general the best candidates for this purpose.

The choice of lithium for batteries is not casual, but it is dictated by the fact that

Li is the lightest metal of all, at only 6.941 g/mol: this means that lithium has a

theoretical specific charge1 of 3861mAh/g. Unfortunately lithium, as all alkali

metals, reacts violently and heavily exothermically with water to form hydrogen

gas:

2 Li + 2 H2O � 2 LiOH + H2 [-222 kJ/mol]

and gets oxidated extremely quickly when put in contact with oxygen:

4 Li + O2 � 2 Li2O

2 Li + O2 � Li2O2

Because of its reactivity, lithium metal is not safe in the open atmosphere and

therefore its use in batteries has been subjected to finding suitable ways to

protect it from oxygen and moisture.

As with all types of batteries, lithium batteries can be divided in two families:

1. Primary batteries, not rechargeable, such as the Li-MnO2, Li-SOCl2 and

Li-FeS2 systems

2. Secondary batteries, rechargeable, such as Li-ion or Li-polymer systems.

A third type of lithium battery, the lithium-air battery, has been proposed [6].

Theoretically it has the highest specific capacity of all lithium batteries, but being

in the early steps of its development, it will not be discussed further.

1.4.1 Primary lithium batteriesUnder the definition of primary lithium batteries it is possible to find an

1 The specific charge is a measure of the amount of charge that one gram of a material can exchange. Forcomparison, zinc, at a weight of 65.39 g/mol, provides only 820mAh/g.

26


extremely wide array of different chemistries that employ metallic lithium at the

anode and some kind of reducible compound at the cathode [6].

The most common primary lithium battery employs MnO2 as cathode, and

provides a nominal voltage of 3V. Its electrode reactions can be written as:

Li+ + e- � Li (anode)

MnO2 + e- + Li+ � LiMnO2 (cathode)

This battery uses an organic electrolyte (propylene carbonate with LiClO4) and

is commonly found in wrist watches, calculators, and all sorts of low power � low

drain applications.

The lithium � thionyl chloride battery has been developed by the US Army for

stationary applications because of the wide range of temperature in which it can

be operated (from -55 °C to +85 °C). It is built around a liquid cathode with a

graphite current collector and the electrode reactions are:


2 SOCl2 + 4 e- + 4 Li+ � 4 LiCl + SO2 + S (cathode)

The discharge products (sulphur and sulphur dioxide) are soluble in the

electrolyte, generally lithium aluminum chloride in thionyl chloride. This battery

provides a nominal voltage of 3.5V and an extremely long life, but has a major

drawback in the constituents. Thionyl chloride is extremely toxic and upon deep

discharge the gaseous SO2 can build up a dangerous pressure: therefore they

need to be maintained properly and are not generally available to the general

public.

One last example of primary lithium battery is the iron sulfide battery. This

system is based on the following reactions:


2 FeS2 + 4 Li+ + 4 e- � Fe + 2 Li2S (cathode)

The electrolyte in this cell is an organic solution based on propylene carbonate,

dioxolane and dimethoxyethane. These batteries are the primary lithium

batteries commercialized by many major manufacturers such as Energizer and

provide a nominal voltage of 1.5V: therefore they are suitable to replace normal

27


alkaline batteries, while providing a lifetime up to 2.5 times. This battery is also

called �lithium-iron� and is not to be confused with the rechargeable battery

based on lithium iron phosphate. A similar chemistry can be employed for high

temperature batteries for stationary applications.

1.4.2 Secondary lithium batteriesRechargeable lithium batteries were first proposed by Michael Stanley

Whittingham in 1976, when working for the Exxon company [7]. Whittingham

proposed a system with metallic lithium at the anode and titanium disulfide at

the cathode. The mechanism of the battery was the reversible insertion of lithium

ions into TiS2, but the use of Li at the anode posed great safety concerns. For this

reason it was proposed to use an insertion material also at the anode and in 1981

the first workable graphite anode was patented by the Bell Labs [8]. The work of

John Bannister Goodenough led to the first commercial lithium battery (Li-ion),

commercialized by Sony in 1991. This cell was based on a graphitic anode and on

a lithium cobalt oxide cathode [9]: when assembled, the cell was in the

discharged state, another safety advantage for storage and transport.

Li-ion batteries are based on the reversible insertion (intercalation) and

removal (deintercalation) of lithium ions in and from host materials. For this

property, they are also called �rocking chair batteries�. As electrolyte, a solution

of a lithium salt in an organic solvent is used. A scheme of the functioning

principle is shown in figure 1.4.1 Lithium ions are included in the cathodic

material (LiCoO2 in the example) and they need to be deintercalated from the

cathode to the anode in order to charge the battery. During the charge process

the positive electrode is oxidized, and the negative is reduced following these

reactions:

6 C + x Li+ + x e- � LixC6 (anode)

Li1-xCoO2 + x Li+ + x e- � LiCoO2 (cathode)

The electrodes are separated by a polymeric membrane that is permeable to

the electrolyte but ensures electrical insulation between the anode and the

cathode. The vast majority of today's Li-ion batteries are still built around this

principle.

28


Figure 1.4.1: Schematic representation of a lithium-ion battery. On the left side thepositive electrode is the original source of lithium ions, while on the right side is the

negative electrode, completely without lithium. Upon charge, lithium ions travel from thepositive to the negative electrode, creating the compound Li1-xCoO2 and LixC6. When

discharging the battery, lithium ions are reintercalated in the positive electrode, leadingto the original situation.

1.4.2.1 Applications of Li-ion batteries

Secondary lithium batteries are very versatile and can be combined to satisfy

the energy needs of many different applications.

The environment Li-ion batteries are most commonly found is the portable

applications market. Thanks to their high energy density, it is possible to have a

light and compact energy source that can power electronic devices for several

hours or even days. Figure 1.4.2 contains a comparison of Li-ion with previous

batteries that were used in mobile applications (NiMH and NiCd), that gives a

clear picture of the vast superiority of the lithium technology.

In this plot, lithium based batteries are in the top-right corner of the chart,

showing higher gravimetric and volumetric power density. In comparison with

other secondary systems, Li-ion shows values two or three times higher: it is

possible to pack the same energy in half the weight with respect to a traditional

battery, which represents an enormous advantage when portability is the most

important factor. Lithium ion batteries have found application in stationary

29


applications too: they are used for example in telecommunications to power radio

stations for phone networks when the power network is down.

Figure 1.4.2: Comparison of various types of rechargeable batteries. Li-ion batteries arein the top-right corner, sporting the highest power densities [10].

A different topic is the use of lithium batteries in mobile applications, in

particular in hybrid and fully electric vehicles. Nowadays the most widespread

hybrid vehicles (such as the Toyota Prius) are powered by a dual energy source

with an internal combustion engine coupled with one (or more, such as in the

Lexus RXh SUV) electric engine. The electric engines power the car at low speed

and help the acceleration thanks to the favorable torque at low RPM, while

batteries are recharged when cruising at high speed or when braking.

Li-ion batteries have not been massively introduced into this market because

of the residual perplexities on their safety, but one bright example of a vehicle

fully powered by lithium batteries has been presented by the US company Tesla

Motors [11]. They are now commercializing a sports car capable of a 0-100 km/h

time of less than 4 seconds, an equivalent of 135mpg (57 km/l) and a range of

220 miles (more than 350km). This sort of numbers shows that a fully electric car

that could satisfy most of the daily transportation needs of the majority of the

population is in fact possible, also thanks to Li-ion technology.

30


1.4.2.2 Issues with current batteriesLithium ion batteries are a fairly recent technology, and as such they are not

perfect nor fully established yet. Many issues are still open in all components of

the batteries and on many diverse fronts.

When focusing on electrode materials, performance problems are to be

reckoned with, for example the disparity in practical charge capacity between

positive and negative materials2, or the inherent danger of overcharging a

battery3.

Electrolytes too present issues: in the current technology a solution based on

flammable solvents is used. Steps are being taken towards immobilizing the

liquid into a polymeric matrix (the so-called �lithium-polymer� batteries, or �Li-

PO�) but while these polymers are less flammable than the liquid, they do not

solve the problem at its roots.

1.4.2.3 Possible improvements for Li-ionIt is possible to break down the need for improvement of current Li-ion

materials in three big groups:

� Performance

� Safety

� Environment, toxicity, economy

Regarding performance, the challenge is to enhance both power and energy

density. The former can be improved by finding materials that can guarantee a

higher rate of charge and discharge, the latter by enlarging the potential window

with positive electrode materials that have an intercalation potential at 5V or

plus. This way, though, is heavily limited by the electrolyte: current solvents start

oxidizing around 4.5V and therefore are not stable at high potential. Ionic liquids

have been proposed as possible substitutes [12], and while they present a good

stability, they don't seem to be actually suitable for use in batteries because of

the lack of an SEI formation on the graphite negative electrode during charge. In

2 Graphite can store a charge more than double than LiCoO2, 372 mAh/g versus 150 mAh/g.3 When graphite is intercalated with lithium ions, its potential reaches values near to 0V vs Li+/Li. At this

potential metallic lithium is formed and being lithium reactive towards the electrolyte, hydrogen gas can beformed.

31


order to enhance the energy density new materials with higher specific capacity

are needed. Any improvement would translate in an immediate extension of

battery life.

For safety, two great weak points can be improved. First, substituting the

anode material with some compound with a higher intercalation potential than

graphite would greatly reduce the risk of formation of metallic lithium. Titanium

dioxide is a prime candidate: its intercalation potential lays at about 1.5V vs.

Li+/Li and it has the correct properties for high rate cycling. The second major

improvement is much more complicated to achieve and it regards electrolytes. As

mentioned before, the use of flammable liquids in the electrolyte poses the major

fire hazard in Li-ion batteries: in case of short circuit the large amount of energy

stored in the battery is freed as heat and the organic solvents catch fire. A way of

preventing this to happen would be the use of inorganic solid state electrolytes,

but a ceramic material that would have a conductivity at room temperature high

enough to rival the one of the typical liquid electrolyte4 has yet to be discovered.

Lastly it is important to consider economic and environmental questions, the

most pressing of which is the use of heavy metals in the positive electrode

materials. As mentioned before, most of today's batteries run on cathodes

containing a major percentage of cobalt as transition metal of choice: the price of

this metal has been extremely unstable in the last few years, with a trend to rise

(see figure 1.4.3). Additionally, the main cobalt resources are located in politically

unstable countries, which makes the supply even more unreliable. Moreover,

cobalt is extremely toxic and it should be properly recycled. Other metals can be

used, such as manganese and nickel, that address these problems.

4 The industry standard mixture 1:1 wt% of ethylene carbonate and dimethyl carbonate with 1M LiPF6,commonly referred to as �LP30�, has a conductivity �0 = 9.8 mS/ cm [13].

32


Figure 1.4.3: Cobalt price in US$/kg between 1937 and 2007 [14].

1.5 Positive electrode materialsThe focus of this work is the study of new positive electrode materials for Li-ion

batteries, therefore it is useful to summarize the characteristics of the currently

employed materials.

Positive electrode materials can be divided in three main categories:

� Layered type oxides

� Spinel type oxides

� Phosphates

All of these types of positive electrode materials have strengths and

weaknesses that will be discussed hereafter.

1.5.1 Layered type oxidesLayered oxides are the dominating material on the market today. They all

share a general formula LiMO2, where M can be one or more transition metals,

and they are all isostructural to -NaFeO2. They all belong to the R3-m space

group and the structure can be described as the periodic distribution of layers of

MO6 and LiO6 octahedra stacked in an alternate manner, as shown in figure 1.5.1

33


[15].

Figure 1.5.1: LiCoO2 structure. LiO6 octahedra are lighter, CoO6 darker.

LiCoO2 was recognized by John B. Goodenough in 1980 as a viable positive

electrode material and was subsequently patented. LiCoO2 is only one of the

compositions patented by Goodenough and Mizuchima, as their patent

application [16] contained the following claims:

1. An ion conductor, of the formula AxMyO2 and having the layers of the -

NaCrO2 structure, in which formula A is Li, Na or K; M is a transition metal;

x is less than 1 and y is approximately equal to 1, the A+ cation vacancies

in the ion conductor having been created by A+ cation extraction.

2. An ion conductor according to claim 1, wherein A is Li and M is a

transition metal of atomic number from 23 to 28.

This means that any subsequent material containing any transition metal

ranging from vanadium to nickel was actually covered by this patent (it expired in

2000), including combinations of more different metal species.

LiCoO2, however, is not the perfect material, as many drawbacks affect its

performance. As major disadvantage, it is possible to only extract about half of

the lithium, limiting its charge capacity to 130mAh/g. Above this threshold the

34


structure of Li0.5-xCoO2 starts undergoing phase transitions that heavily hinder its

stability and therefore limit the reversibility of the intercalation process [17].

Trying to address the issue of cost, it was proposed to substitute cobalt with

nickel, but LiNiO2 could not be employed in place of lithium cobalt oxide. Albeit

being isostructural to LiCoO2, the nickel compound showed too many

shortcomings to be practically usable: its synthesis is quite difficult due to lithium

volatility [18] and the resulting compound is often highly disordered, because of

lithium and nickel having similar atomic radii. Moreover, LiNiO2 showed a very low

thermal thermal stability in its charged state, raising serious concern about its

safety in real life applications [19].

Cobalt seemed then almost irreplaceable for a reliable operation of layered

oxides, and this observation led the way for the study of compounds containing

mixed metals. Many different compositions in the range of LiNixCo1-xO2 have been

synthesized and studied [20], and among them LiNi0.7Co0.3O2 showed good

behaviour, with stable energy density up to 500 Wh/kg [21]. Other examples of

cobalt substitution include aluminum [22], chromium [23] and manganese [24].

Along with binary substitutions, a large array of layered oxides containing

multiple transition metals have been prepared and tested, trying to tailor the

electrochemical properties of this class of materials. The class of ternary oxides

Li(Ni1-x-yMnxCoy)O2 will be discussed later in chapter 1.6.

1.5.2 Spinel type oxidesSpinels are a class of compounds with general formula AB2X4, largely occurring

in minerals on a wide range of compositions. The original crystal, after which the

whole class is denominated, is MgAl2O4. They share a cubic unit cell, shown in

figure 1.5.2.

The first spinel to be used as cathode for lithium batteries was LiMn2O4 and it

was proposed by Thackeray and Goodenough in 1983 [25]. This spinel exhibits

two charge plateaus, one around 3V vs. Li+/Li and one around 4V vs. Li+/Li, but in

general only the latter is used in battery operation.

The plateau (figure 1.5.3) at 4V vs. Li+/Li corresponds to a lithium content

limited between x=0 and x=1 in LixMn2O4. When inserting more lithium in the

35


structure (the plateau at 3V vs. Li+/Li), divalent manganese ions are formed and

these ions are very soluble in acidic conditions.

Figure 1.5.2: LiMn2O4 structure. Mn sits in octahedral sites, Li in tetrahedral (not drawn forclarity).

).

Since in general Li-ion batteries electrolytes can contain acidic species, this

leads to a dissolution of the active material in the liquid, causing malfunction in

36


the battery.

The lithium-manganese-oxygen is an extremely complex system, whose

discussion goes beyond the scope of this writing. For a more thorough

description, a comprehensive review was written by Thackeray in 1997 [26].

Another interesting spinel that gained much attention is actually employed as

negative electrode. Li4Ti5O12 has shown interesting properties for lithium

intercalation and advantages over graphite as anodic material [27].

1.5.3 PhosphatesOlivine type phosphates with general formula LiMPO4 (M = Fe, Ni, Co, Mn)

represent the newest form of cathode material for Li-ion batteries. They all share

the same orthorhombic structure presented in figure 1.5.4.

First proposed by Goodenough in 1997 [28], LiFePO4 has practical advantages

such as low cost and low toxicity, thanks to the use of iron as transition metal.

Figure 1.5.4: LiFePO4 structure. PO4 tetrahedra (lighter), FeO6 octahedra (darker) andlithium ions are visible.

Additionally, LiFePO4 has a good charge capacity of about 170 mAh/g, thus

higher than LiCoO2, and great reversibility, with no fading observed over several

37


hundred cycles. One drawback of LiFePO4 is the relatively low discharge potential:

the plateau is observed at about 3.5V vs. Li+/Li (whereas LiCoO2 has its plateau

around 4V vs. Li+/Li), thus lowering the energy that can be extracted from this

electrode material.

Other olivine type phosphates have been proposed, such as LiCoPO4 [29],

LiMnPO4 [30] and LiNiPO4 [31]. All these compounds are isostructural and present

intercalation potential higher than the one of iron, at 4.8V, 4.1V and 5.1V for Co,

Mn and Ni respectively. Unfortunately though they don't seem to allow reversible

lithium extraction and insertion, thus making them unsuitable for consideration

as industrial cathode materials.

1.6 Mixed oxides Li1+x(Ni1-y-zMnyCoz)1-xO2

As it was presented in chapter 1.5.1, it is clear that every transition metal

included in a layered oxide contributes in a characteristic fashion to the overall

performance of the final product. After binary combinations of Mn, Ni and Co were

produced and tested, it was only logical to mix these three metals in various

ratios and test the properties of the ternary oxide.

A range of ternary oxides was first reported by Liu in 1999 [32] and it was

shown that this family of materials retained the layered structure typical of

LiCoO2. The electrochemical performance was dependent on the Mn/Ni/Co ratio,

with Li(Ni0.7Mn0.1Co0.2)O2 having the best long term capacity retention. The

preparation method employed to synthesize the active powders was based on a

mixed hydroxide approach, with subsequent high temperature annealing. While

Liu used a temperature of 750°C, it was later discovered that the optimal

temperature value was between 800°C and 900°C [33]. In 2000 the structure of

the ternary oxide was thoroughly explored [34], reporting for the first time that

manganese was present in the structure as tetravalent ion, therefore being

inactive electrochemically, but strongly stabilizing the structure upon cycling.

The fully symmetric compound Li(Ni1/3Mn1/3Co1/3)O2 was reported in 2001 [35],

showing a reversible capacity of 150 mAh/g when cycled in a narrow potential

window of 2.5V-4.2V vs. Li+/Li. When the potential range was broadened up to

5.0V vs. Li+/Li, the material delivered 220mAh/g but it also showed intense

38


capacity fading. Other studies about the dependence of the synthesis route on

the electrochemical performance showed that spray-drying instead of hydroxides

coprecipitation allows for higher reversible capacity [36].

It has been shown that upon lithium removal the unit cell volume change in

Li(Ni1/3Mn1/3Co1/3)O2 is less than 2% [37], this being a factor that might explain the

high cycle reversibility that this material shows. This low variation happens

without phase transitions, thus further enhancing the stability of the material.

The symmetric compound has been studied in a prismatic cell, mimicking a

commercial battery, and it was found that its performance is at least on par with

that of LiCoO2 at a lower cost, thanks to the use of manganese and nickel, if not

even better [38]. In fact, the higher thermal stability of this material in its

charged state [39] allows for higher cutoff potentials, therefore enabling the cell

to reach up to 20mAh/g more than LiCoO2.

Overlithiated ternary compounds with layered structure and general formula

Li1+xM1-xO2 can be seen as a solid solution of LiCoyNi1-yO2 and Li2MnO3. This latter

compound is particularly interesting because of its unforeseen electrochemical

activity. Li2MnO3 can reversibly deintercalate lithium, but since it is believed that

manganese ions in an octahedral oxygen environment cannot be oxidized further

than 4+ [40], it is not clear how is the lithium removal possible. One proposed

mechanism involves the substitution of Li+ ions with H+ ions coming from the

electrolyte, but this is only possible in an acidic environment. Alongside this ion

exchange, oxygen ions can be removed from the structure, effectively removing

Li2O from the original cathode material [41]. A confirmation of the oxygen

removal theory was later proposed regarding a series of solid solutions between

Li2MnO3 and LiNiO2 with general formula Li[NiyLi(1/3-2y/3)Mn(2/3-y/3)]O2: an irreversible

charge plateau at about 4.5V vs. Li+/Li was associated with the loss of O2 from the

structure, after all Ni2+ ions were oxidized to Ni4+. Upon further experiments it was

discovered that the material with the lowest �y� value (therefore with the highest

excess lithium) showed the best electrochemical performance, peaking at about

200mAh/g [42].

From these results it is clear that many factors can influence the

electrochemical performance of mixed cation layered oxides and each component

39


of the materials give a particular property: manganese seems to be needed for

structure stabilization, nickel offers most of the electrochemical activity, cobalt

tends to help the rate capability and excess lithium increases the capacity [43].

40

Chapter 2

Principles of Diffraction

Chapter 2 � Principles of Diffraction

2.1 Principles of diffraction5

Diffraction is one of the most basic phenomena occurring when a wave (be it

light, particles or sound) interacts with an obstacle. When applied to the study of

solid state matter, Bragg diffraction is generally considered.

In this type of diffraction, the crystal structure of a solid acts as a three

dimensional grating. The waves scattered at various angles interact between

them and the resulting diffracted waves have maximum intensity when they

satisfy the famous Bragg's law:

(2.1.1) 2d sin ��=n�

where d is the distance between two interatomic planes, is the angle at�

which the radiation hits the crystal and is the wavelength of the radiation.�

Bragg's law can be easily derived graphically, as shown in figure 2.1.1:

Figure 2.1.1: Schematic representation of Bragg's law.

Considering two rows of atoms, the distance between them (AB) is equal to the

interplanary distance d. In order to have constructive interference between the

waves 1 and 2, scattered by the two planes, it is needed that the additional path

traveled by wave 2 is an integer number of wavelengths. Therefore it is possible

to write that BC + BD = n and since BC and BD can be estimated from�

5 This coarse introduction cannot and will not cover extensively every aspect of diffraction andcrystallography, but it is intended in order to give a context to many of the terms that will be used later inthe discussion of the experimental work. The reader interested in further details about crystallography anddiffraction is invited to consult more complete books such as �Fundamentals of Crystallography� [44].

43


trigonometry as BC = BD = d sin( ) Bragg's law is obtained as 2d sin( ) = n .� � �

This law was proposed by father and son William Lawrence Bragg and William

Henry Bragg in 1913 and for this discovery they were awarded the Nobel prize in

1915 [45].

Modern crystallography is then a relatively young science, born from the

concurrent discoveries of key components such as that of x-rays by Wilhelm

Conrad Röntgen in 1895. The idea that a crystal could act as a diffraction grating

for x-rays was first proposed by Paul Peter Ewald and Max von Laue in 1912,

given its wavelength comparable in size with interplanary distances, in the order

of magnitude of 1Å (10-10m). Von Laue was the first to shine an x-ray beam on a

crystal and to record the resulting diffraction pattern on a photographic plate. His

work on the crystal structure of solids by interpreting the position of the spots on

the photographic plate obtained by x-ray diffraction was the reason for his Nobel

prize in 1914. In the first decades of 1900 many simple structures were

discovered thanks to x-ray diffraction, with the work of well known scientists such

as Peter Debye and Paul Scherrer, who developed a new technique called

�powder diffraction�. Debye and Scherrer expanded the original theory of

diffraction applied to single crystals by using powdered samples, much easier to

obtain than a perfect crystal big enough to be used as a target for x-ray

irradiation.

Diffraction is a faceted experimental technique that can be implemented with

many different radiations: apart from x-rays, it is possible to use neutrons,

electrons, muons and in general any radiation with a wavelength around 1Å. For

the purpose of this work it is interesting to discuss the differences between x-ray

and neutron diffraction.

Since x-rays and neutrons have different nature, they interact with matter in

diverse ways. X-rays are scattered by the electron clouds surrounding atoms,

while neutrons are scattered by the nuclei. Given that the number of electrons

per atom follows the atomic number, heavy atoms scatter x-rays more strongly

than light ones. With neutrons, there is no direct dependence of Z with the

interaction strength. A qualitative depiction of this property is shown in figure

2.1.2.

44


This difference is extremely useful because species adjacent on the periodic

table cannot be distinguished with x-rays but can have largely different neutron

scattering lengths: for example manganese, cobalt and nickel have almost

identical x-rays scattering factors, but have different neutron scattering lengths,

allowing for more precise identification. Moreover, atoms such as lithium and

hydrogen that are practically invisible to x-rays, have larger neutron detectability.

Another interesting property is the ability of neutrons to discern between isotopes

of the same atomic species: as shown in figure 2.1.2, hydrogen and deuterium

have identical x-ray scattering factors but largely different neutron scattering

lengths.

Figure 2.1.2: Schematic representation of neutron versus x-ray scattering of variousnuclei. The larger the area associated with each nucleus, the larger the scattering. H and

D (deuterium) are shown at different Z values for convenience [46].

The intensity of the interaction between radiation and sample is also very

different between x-rays and neutrons. Photons interact more strongly with

matter, therefore they tend to be absorbed by the bulk of the material. This gives

rise to a stronger diffracted beam, but only a small depth of the sample can be

investigated. Neutrons on the other hand have a weaker interaction with matter:

while the diffracted beam is less intense, therefore needing larger samples and

longer exposure time to obtain a large signal to noise ratio, neutrons can travel

more deeply through samples.

45


2.1.1 Experimental notesDiffraction experiments can be carried out with different geometries and using

diverse types of samples (Chapter 4, [44]).

The biggest distinction that can be made is the one between the use of single

crystal or polycrystalline samples. Single crystal methods are used mainly to

solve molecular structures and in protein crystallography. The need for well

crystallized samples for this technique is often the largest obstacle to obtain high

quality data. For this reason, especially in inorganic chemistry where samples are

easily obtainable as powders, the most used technique is powder diffraction. In a

powder diffraction sample a large collection of randomly distributed crystallites is

irradiated and in order to limit anisotropy effects the sample can be rotated so

that each crystallite assumes additional random orientations.

The first use of x-ray powder diffraction was reported by Debye and Scherrer

[47] when they described their camera for x-ray detection. In their geometry, a

sample is positioned in the center of a cylindrical drum, in which a strip of

photographic paper is put. The sample is irradiated perpendicularly with x-rays

(i.e., the beam travels along the drum axis) and the diffraction maxima are

printed on the photographic plate as arcs. The arcs are segments of diffraction

cones with aperture 2 , therefore the radii of the arcs give the angle values. This�

information, combined with the relative intensity of the arcs on the photographic

plate, allows to work out the structure of the sample. The main problem with this

method is the fact that quite broad diffraction lines are generated, thus heavily

limiting the resolution of the measurement. If a collimator is used to reduce the

width of the lines, the intensity might become so weak that the experiments

could become impractically long in time.

In order to reduce this effect, so called parafocusing methods have been

invented, out of which the most widely used today is the Bragg-Brentano

geometry, visible schematically in figure 2.1.3.

46


Figure 2.1.3: Schematic representation of the Bragg-Brentano parafocusing geometry forx-ray diffractometers [44].

In this setting, a flat sample sits at the tangent of the �focusing circle� and the

sample center is also the center of the �goniometer circle� around which the x-

ray source and the detector are placed. The x-rays are diffracted by the sample

and those reflected towards the detector are recorded as intensity vs. 2�

position.

In order to have the parafocusing effect happening at any 2 value, it is�

needed that the sample is constantly tilted in order to be at the tangent of the

focusing circle at any time. Note that the focusing circle is an imaginary

construction with variable radius, while the goniometer circle is very real and

determined by the position of the sample, around which x-ray tube and detector

revolve. The variation of the radius of the focusing circle is easily determined

geometrically from the figure: if we assume the triangle OSD to be isosceles,

since both S and D points lay on the focusing circle, then we have, considering

that the distance between S and D is the radius of the goniometer circle:

(2.1.2) sin�=1

2

R

r

47


and if we solve to find the radius of the focusing circle r we obtain:

(2.1.3) r=R

2sin�

Additionally to this tilting, the sample can be rotated to minimize anisotropy,

as in the Debye-Scherrer geometry. The motion of the detector can be operated

continuously or in discrete steps, with the former option being more intensive in

computer resources, but yielding better pattern profiles.

A few words can be spent to briefly discuss the importance of sample

preparation when operating a Bragg-Brentano diffractometer. First, it is obvious

that in order to obtain the highest parafocusing effect, the sample needs to be

extremely flat. While it could be tempting to just press powders in a sample

holder to obtain a compact and flat surface, this approach is not advised because

of the high preferred orientation that might ensue in the diffraction pattern. On

the other hand, in case of a textured sample, the incorrect preparation of the

sample can hinder the detection of this property. When a sample presents

preferred orientation, the relative intensities of the diffraction peaks are not

correct, potentially leading to faulty interpretations of the crystal structure.

Second, the size distribution of the powders employed for XRD measurements

can heavily influence the patterns. One of the effects of crystallite size is in fact

peak broadening and if particles are too small (leading to broader peaks) the

resolution of nearby peaks can be hindered. While milling of the powders can be

performed to homogenize the particle size, particular care must be taken for

those samples that might undergo transformations upon the heating and

oxygenation resulting from the mechanical grinding. A possible solution to these

problems is the sieving of the powders prior to the measuring in the

diffractometer. Third, radiation damage can be an issue: while this is mainly a

problem concerning organic samples, it is not to be forgotten that the

concentration of x-rays on the sample can locally raise the temperature and

potentially cause phase transitions and other transformations, such as

dehydration. Nowadays though, complex sample holders that can adjust the

environment around the sample are available to minimize these effects.

Another modern technique for x-ray powder diffraction employs the detection

48


of transmitted diffracted beams from a powder sample enclosed in a capillary

tube sitting at the center of a curved position-sensitive detector. While this

technique can yield more precise results than those obtained in Bragg-Brentano

diffractometers, the tedious sample preparation and the long measuring times

due to the low amount of specimen make this method less preferred for routine

measurements.

The diffracted intensity data collected along a scan of 2 angles is then plotted�

and analyzed in order to determine structural features of the examined sample. A

typical x-ray powder diffraction pattern is shown in figure 2.1.4.

Figure 2.1.4: Simulated x-ray diffraction pattern of anatase, one of the allotropic forms oftitanium dioxide.

Structure solution, i.e. the determination of an unknown crystal structure from

diffraction data, can be performed using direct or probability methods (Chapter 5,

[44]), while the refinement of a known structure can be carried out using the

common Rietveld method, discussed in the next chapter.

2.2 The Rietveld methodX-ray diffraction is modeled by a very elegant theory that explains in detail the

interaction of the photons with the matter and the reasons for the resulting

diffraction patterns (Chapter 3, [44]). When x-rays hit the crystal, they are

scattered by the electrons surrounding the atoms in a process that can be

assimilated to Thomson scattering. Therefore, atoms with higher atomic number

Z will scatter more x-rays and will give stronger signals than light atoms.

49


The intensity of the scattered beam I k� equals the square modulus of the

wavefunction � k� and is proportional to the square modulus of a quantity F k�

called structure factor:

(2.2.1) I �k=��k�2

�F�k�2

The structure factor is defined as following:

(2.2.2) F�k=j

f j e�i�k�r

j

where fj is the atomic form factor, a coefficient defining the scattering ability of

a given atomic species, k is the wavevector of the scattered beam and r� j is the

position of the j-th atom in the unit cell.

In order to evaluate a diffraction pattern, it is needed to match a theoretical

model of the investigated sample with experimental diffraction data. The most

widely used method to perform this fitting is by using the so called �Rietveld

method�, named after its creator, Hugo M. Rietveld. Rietveld described in 1969

his �profile refinement method for nuclear and magnetic structures� [48] and

while originally developed for neutron diffraction experiments, it was later

extended to be used with x-ray diffraction patterns [49]. The method is based on

the refinement of the original structural model by minimizing the quantity

(2.2.3) S= w i�yio� y ic�2

where wi is a weight function defined by:

(2.2.4) �w i��1= i

2= ip

2� ib

2

in which �ip is the standard deviation associated with the peak and �ib is

associated with the background intensity yib. In equation (2.2.3) are also found yio,

which is the observed intensity for each scanned 2 value, and y� ic is the

calculated intensity according to the selected model. This latter intensity is the

sum of various contributions expressed in the equation:

(2.2.5) yic=sk

mk Lk�F k�2G ��ik�� y ib

where s is a scale factor, Lk is the Lorentz-polarization factor for reflection k, Fk

is the structure factor in equation (2.2.2), mk is the multiplicity factor, ��ik=2�i -

50


2�k is the true position of the peak corrected for the detector shift, and G(�� ik) is

the reflection profile function. When the method is applied, parameters relative to

the unit cell (influencing the position of the peaks), atomic positional and thermal

parameters (influencing the intensity of the calculated peaks) and parameters

defining the functions G and yib (Chapter 1, [50]) are refined.

The G function, relative to the peak profile, has to be chosen accordingly to the

radiation used for the measurement: in general, for x-ray measurements, a

mixture of Gaussian and Lorentzian components are chosen (the so called

�Pseudo-Voigt� profile), while when refining neutron measurements an analytical

function can be found to describe the pattern profile. During the refinement it is

needed to refine the FWHM6 because of its dependence from the angular value.

For this the parameters U,V and W are used, according to:

(2.2.6) �FWHM �G2=U tan

2��k ��V tan ��k ��W

for the Gaussian component [51]. When a function involving Lorentzian

components is used, parameters X and Y are also refined [52], according to:

(2.2.7) �FWHM �L=X tan ��k ��Y

cos��k �

Another extremely important part of the fitting procedure is an accurate choice

of the background. This can be achieved by manually selecting some nodes that

will provide with a background line, or by selecting an appropriate function. One

recognized approach is the use of a power series in 2 :�

(2.2.8) yib=n

bn�2�i�n

Finally, the calculated profile is compared to the observed diffraction pattern

and its accuracy is evaluated according to different parameters [53].

This brief introduction about the Rietveld method gives an idea of the main

advantage of this technique of fitting pattern profiles, namely its simple and

effective approach to the problem. Admittedly though, the method has to be

applied cautiously and particular care has to be taken on some aspects (Chapter

8.6, [54]). One, since the Rietveld method is designed to refine a structure and

6 FWHM = Full Width at Half Maximum

51


not to solve it, the starting model needs to be reasonably accurate in order to

index the Bragg peaks of the pattern properly. If the wrong space group is

selected, or if the cell parameters of the model unit cell are too distant from the

true values, the method will not yield meaningful results. Two, the peak shapes

are influenced by many factors including instrumental and sample preparation

issues (Chapter 5.2, [55]). Therefore it is difficult to accurately describe the peak

shapes and be able to discern the influence of specimen characteristics from the

systematic errors induced by the diffractometer. Three, the choice of the

background is crucial to allow for a proper peak approximation. Four, other

undesired influences can be ascribed to sample texturing and preferred

orientation, which can be however minimized by an accurate specimen

preparation.

In order to apply the Rietveld method on powder diffraction data, many

software packages have been developed over the years, some part of

commercial solutions such as Bruker's EVA and Topas or MDI's JADE; and some

available for free to the scientific community, such as Von Dreele's GSAS.

Throughout this work, all x-ray and neutron diffraction data will be analyzed using

Fullprof, written by Juan Rodríguez-Carvajal [56]. Despite being sometimes

clumsy and prone to crashes, Fullprof and its GUI Winplotr proved themselves

invaluable tools to accurately analyze powder diffraction patterns.

52

Chapter 3

Synthesis and Characterization of NMC Materials

Chapter 3 � Synthesis and Characterization of NMC Materials

3.1 Synthesis of powdersTo prepare powders of Li1+x(Ni1/3Mn1/3Co1/3)1-xO2, a soft chemistry approach by

coprecipitation of hydroxides was chosen [32] (flowchart in figure 3.1.1).

All synthesis started from two solutions:

� LiOH (1M) + NH3 (3M) in H2O

� Ni(NO3)2 (1M) + Mn(NO3)2 (1M) + Co(NO3)2 (1M) in CH3CH2OH

The basic lithium solution was prepared in water since ammonia was already in

a 25% wt. aqueous solution, while the metal nitrate solution was prepared in

ethanol in order to speed up the drying in rotavapor.

Stoichiometric amounts of solutions were mixed by slowly dripping the

transition metals solution into the basic lithium solution under magnetic stirring,

in order to achieve uniform cation mixing. Because of the high pH, hydroxides of

the metals would precipitate and the resulting suspension was left overnight

under agitation, obtaining a liquid colored in a very dark shade of brown.

The suspension was later dried in rotavapor until all solvents were removed.

The dried precipitate was additionally kept overnight in vacuum oven at 80°C to

completely remove water. Powders were collected from the glassware by scraping

and later ground in an agate mortar.

The ground powder was put in an alumina crucible and calcined in air following

this heat ramp:

1. Heat from 25°C to the calcination temperature in 6 hours

2. Calcine at 700°C / 850°C / 1000°C for 6 hours

3. Cool down to 25°C in 6 hours

The material was not quenched in order to prevent a high cation disorder and

the powders were again ground in an agate mortar. 9 samples were prepared in

total, by crossing 3 stoichiometries (x=0, x=0.1 x=0.2) and 3 different calcination

temperatures (700°C, 850°C, 1000°C). The characterization of the samples is

presented in chapter 3.2.

55


3.2 Characterization of NMC powdersIn order to individuate the best synthetic conditions, the 9 prepared samples

were investigated through x-ray diffraction, iodometric titrations, SEM imaging

and electrochemical tests. Samples will be identified with the following naming

convention: the first three characters indicate the x stoichiometric coefficient in

Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 (NMC) while the following characters indicate the

56


calcination temperature. Table 3.2.1 summarizes this convention.

Sample name Calcination temperature Lithiation degree

X00700 700°C X = 0

X00850 850°C X = 0.1

X001000 1000°C X = 0.2

X10700 700°C X = 0

X10850 850°C X = 0.1

X101000 1000°C X = 0.2

X20700 700°C X = 0

X20850 850°C X = 0.1

X201000 1000°C X = 0.2

Table 3.2.1: Summary of the samples prepared for preliminary characterization.

X-ray diffraction was used to confirm the purity of the powders and to check

whether they were all crystallized in the correct R3-m layered phase. In figure

3.2.1 the patterns relative to the 9 prepared samples are shown. While all 9

diffraction patterns look very similar, an important difference can be appreciated

in the enlargement shown in figure 3.2.2. The samples calcinated at 700°C are

not fully crystallized in the R3-m phase: the doublet that should appear at about

66° on the Cuk scale is in fact appearing as a single peak. This can be

interpreted as the formation of the spinel phase Fd3m and therefore 700°C was

not believed to be a good calcination temperature to prepare pure layered

oxides. Because of this, further analysis on samples X00700, X10700 and X20700

were dropped.

SEM images were acquired to study the morphology of the remaining samples

and were performed on a Zeiss Supra 55vp microscope on uncoated powder

samples. Images were recorded at 2kV with a secondary electron beam and a

selection of pictures is presented in figure 3.2.3. From the images it is observed

that strong sintering of particles occurred for the samples prepared at 1000°C.

The size of the particles constituting samples X001000, X101000 and X201000 is

very large, in the magnitude order of some micrometers. On the other hand,

particles of X00850, X10850 and X20850 show strong aggregation of finer

particles, situated in the nanometer range. Therefore 850°C was selected as the

optimal calcination temperature. Large particles have a lower surface area than

57


small particles and this plays a very important role in the preparation of

electrodes. Since a liquid electrolyte is used, a large surface area favors the

wetting of the particles with the electrolyte solution, enhancing the lithium ion

exchange with the active material. Albeit the focus of this work is not on the high

rate capabilities of the NMC materials, it was decided to concentrate later efforts

on the samples prepared at 850°C.

Figure 3.2.1: X-ray powder diffraction patterns of the 9 prepared samples.

58


Figure 3.2.2: Enlargement of the 62°-68° region of three XRD patterns. The doubletobserved for the X001000 and X00850 samples is not present in the X00700 powder,

therefore this specimen is not believed to be pure.

Figure 3.2.3: SEM images of X10850 (left) and X101000 (right).

59


The last test to make sure that the remaining samples X00850, X10850 and

X20850 were pure as intended was to estimate the actual lithium content in the

structure. To do this, a redox iodometric titration was performed on the powders.

Iodometric titrations [57] are used to estimate the oxidation degree of the

transition metals in the NMC materials. A small amount of active powder (circa

30mg) was put in a Teflon vial and dissolved in a solution of 5ml HCl (37%) and

5ml KI (10%) in 10ml H2O. Alongside, a reference solution (called �blank�) without

active powders was prepared. The solutions were then agitated and put in an

oven at 60°C overnight to favor complete powders dissolution. The next day they

were titrated with Na2S2O3 (0.01M in H2O) until their orange color disappeared.

The sodium thiosulphate solution volume needed to titrate each vial was noted

and to analyze the results the following method was used. If we assume that the

nominal formula Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 is valid, then the combined oxidation

value of the cations must be 4+, to counterbalance the 4- formal charge of the

oxygen atoms.

Therefore we can write:

(3.2.1) �1�x�1��1�x�d t=4

where dt is the average oxidation degree of the transition metals. Lithium is

assumed to have an oxidation degree of 1+. From this we can easily estimate dt

as:

(3.2.2) d t=3�x1�x

The experimental oxidation degree is calculated using:

(3.2.3)d=2�

[Na2S2O3]�V tit

ms

M�Qmet

where [Na2S2O3] is the concentration of the titrating solution (mol/l), Vtit is the

effective volume of the titrating solution (ml), ms is the mass of the sample (mg),

M is the molar mass of the sample (g/mol) and Qmet is the stoichiometric

coefficient for the metals in the sample (e.g. Qmet = 0.9 for sample X10850). It is

clear that the assumption made here is that the oxygen stoichiometry is actually

60


O2: this was not determined exactly via other analytical methods, therefore in

case of an unknown oxygen defectivity the real composition of the samples would

not be directly connected to the oxidation degree of the transition metals.

Measurements were repeated on 5 specimens per sample and an average of

all values was taken. With these numbers it was possible to obtain the results

summarized in table 3.2.2.

Sample xnomms

(mg)M

(g/mol)Qmet

Vtot

(ml)Vblank

(ml)Vtit

(ml)dT d

X00850 0 35 96.46 1 48 12 36 3 2.99X10850 0.1 30.92 91.39 0.9 51.9 15 36.9 3.22 3.21X20850 0.2 36.54 86.34 0.8 59.5 12 47.5 3.5 3.4

Table 3.2.2: Results of iodometric titrations.

With samples X00850 and X10850 values were obtained for d that confirmed

the expected mean oxidation degree value, therefore the desired lithiation

degree was obtained. For sample X20850, on the other hand, the discrepancy

between the expected and experimental value is too large to say with certainty

that the sample actually contains a 20% overlithiation. This can be explained with

the tendency of lithium to evaporate during calcination at high temperature and

also it is also possible that the structure of the layered oxide is not able to

accommodate such a large overlithiation in a stable manner. The sample

Li1.2(Ni1/3Mn1/3Co1/3)0.8O2 prepared at 850°C was then dropped since after several

synthesis tries it was not possible to obtain a pure sample with the desired

stoichiometry, and subsequent work was focused on the two remaining samples

Li(Ni1/3Mn1/3Co1/3)O2 and Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 both calcinated at 850°C.

XRD analysis of X00850 (�stoichiometric sample�) and X10850 (�overlithiated

sample�) was carried out in order to obtain the structure of these samples. XRD

measurements were performed on a Siemens D500 diffractometer equipped with

a copper x-ray source in Bragg Brentano geometry. The patterns were refined

with a Pseudo-Voigt profile function and the adopted model took into account the

possible migration of nickel ions from the 3b site (MO6 layers) to the 3a site (LiO6

layers). The resulting matched profile are reported in figure 3.2.4 and 3.2.5; while

all crystallographic data are summarized in tables 3.2.3 and 3.2.4.

Both samples appear well crystallized and conforming to the R3-m space

group; while lithium-nickel exchange is about 2-3%.

61


Figure 3.2.4: X-ray powder diffraction pattern of Li(Ni1/3Mn1/3Co1/3)O2. Experimental dataare black dots, solid line is the calculated profile, dashed black line is the difference

between calculated and experimental data. Bragg peaks are also marked.

Figure 3.2.5: X-ray powder diffraction pattern of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2. Experimentaldata are black dots, solid line is the calculated profile, dashed black line is the difference

between calculated and experimental data. Bragg peaks are also marked.

62


Li(Ni1/3Mn1/3Co1/3)O2, Space group R3-m, a=2.8535(5) Å c=14.204(5) Å

Atom x y z Occ

Li (3a) 0 0 0 0.469

Ni (3a) 0 0 0 0.031

Li (3b) 0 0 ½ 0.031

Ni (3b) 0 0 ½ 0.134

Mn (3b) 0 0 ½ 0.165

Co (3b) 0 0 ½ 0.165

O (6c) 0 0 0.241(2) 1.000

Table 3.2.3: Crystallographic data for Li(Ni1/3Mn1/3Co1/3)O2.

Li1.1(Ni1/3Mn1/3Co1/3)0.9O2, Space group R3-m, a=2.8419(6) Å c=14.166(7) Å

Atom x y z Occ

Li (3a) 0 0 0 0.478

Ni (3a) 0 0 0 0.022

Li (3b) 0 0 ½ 0.022

Ni (3b) 0 0 ½ 0.143

Mn (3b) 0 0 ½ 0.165

Co (3b) 0 0 ½ 0.165

O (6c) 0 0 0.242(3) 1.000

Table 3.2.4: Crystallographic data for Li1.1(Ni1/3Mn1/3Co1/3)0.9O2.

X00850 and X10850 were subsequently characterized electrochemically, by

means of cyclic voltammetry and galvanostatic cycling. In a cyclic voltammetry

(CV) a potential scan is performed and the current flowing in the battery is

recorded. The positions on the voltage scale at which peaks are observed

individuate potentials where electrochemical processes take place. In

galvanostatic cycling a battery is tested for its charge and discharge

characteristics. The device is charged and discharged between suitable cutoff

potentials, while the cell potential and the amount of charge flowing through the

cell is recorded.

All following electrochemical measurements were performed in standard two

electrode coin-like cells. The electrolyte used (Ferro) was a 1M solution of LiPF6 in

a 1:1 wt% mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC).

The electrodes were prepared by mixing the active material (82% wt) with

63


graphite (4% wt, Timcal KS6) and carbon black (7% wt, Timcal SuperP) along with

a polymeric binder (PVDF, 7% wt). The mixture was diluted in N-methyl-

pyrrolidone and the fluid suspension was then cast onto an aluminum current

collector. The electrode paste was left to dry in a vacuum oven at 80°C. At the

end of the process, each electrode had a weight of about 30mg. Lithium was

used as counter electrode and glassfiber separators were employed.

The stoichiometric sample was measured in CV mode in the potential range

2.5V - 5.0V vs. Li+/Li at a scan rate of 20�V/s over several cycles and the resulting

current profile is shown in figure 3.2.6.

Figure 3.2.6: Cyclic voltammetry of Li(Ni1/3Mn1/3Co1/3)O2 performed at 20�V/s. The secondcycle is representative for all subsequent cycles.

During the first cycle (solid symbols in figure 3.2.6) there is a first peak at

about 3.8V vs. Li+/Li and a second doublet at more anodic potentials, around 4.8V

vs. Li+/Li. The corresponding reductive peaks appear at about 4.6V and 3.7V vs.

Li+/Li. During the second cycle (empty symbols in figure 3.2.6), on the other

hand, the first oxidative peak seems to be split in two and to be shifted to more

negative potentials, while the second doublet disappears to leave place for a

single peak. The reductive path is remarkably reversible between first and second

cycle. The overlithiated sample was cycled under similar conditions as before and

64


the CV measurements are plotted in figure 3.2.7.

Figure 3.2.7: Cyclic voltammetry of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 performed at 20�V/s . Thesecond cycle is representative for all subsequent cycles.

X10850 shows similar features to X00850, but the intensity difference between

first and second charge at high potentials is much larger in the overlithiated

sample. Similarly as for X00850 though, both reductive scans seem to be rather

reversible. From these measurements it is clear that stoichiometric and

overlithiated samples behave in a similar fashion, but at very positive potentials

some oxidative process is happening, whose intensity is strongly enhanced by

the presence of excess lithium in the structure. While the �baseline� intensity

observed in the stoichiometric sample can be explained with electrolyte

oxidation7, the strong peak measured in the overlithiated sample cannot be

dismissed as an inevitable side reaction.

Subsequent tests were performed galvanostatically to assess the capacity

retention of the two materials. Since the CV showed two different reaction

ranges, it was decided to investigate separately the electrochemical performance

between 3.0V and 4.3V vs. Li+/Li, and later between 3.0V and 5.0V vs. Li+/Li.

7 Ethylene carbonate and dimethyl carbonate are not stable towards oxidation at positive potentials, ingeneral higher than 4.5V vs. Li+/Li [58].

65


Galvanostatic experiments have been performed by Fabio La Mantia [59].

In the first experiment, X00850 and X10850 were charged between 3.0 and

4.3V vs. Li+/Li in a coin like cell, in an analogous setup to the CV experiments. The

results are plotted in figure 3.2.8.

Figure 3.2.8: Galvanostatic cycling of Li(Ni1/3Mn1/3Co1/3)O2 (solid symbols) andLi1.1(Ni1/3Mn1/3Co1/3)0.9O2 (empty symbols) between 3.0V and 4.3V vs. Li+/Li. Only the

reversible charge (discharge process) is shown.

The stoichiometric NMC delivers a higher reversible specific charge when

compared to the overlithiated NMC. This fact can be explained by considering the

complex oxidation state distribution of the transition metals in the two

compounds: as illustrated earlier when discussing iodometric titrations, transition

metals in X00850 have an average oxidation degree of 3+. In X10850 this

average value needs to be 3.22+: the 4- formal charge delivered by the oxygen

atoms is partially compensated by 1.1+ delivered by lithium ions. The remaining

2.9+ has to be split between the transition metals, but only 0.9 formula units of

them are present, therefore 2.9/0.9 = 3.22. As mentioned in chapter 1.6, it has

been demonstrated that in the pristine material Mn ions are present as 4+ and

Co ions are 3+ [35], therefore Ni ions are responsible for the remaining positive

charge. In the stoichiometric material then, all Ni ions are formally 2+ (to

counterbalance Mn4+), but in the overlithiated material not all of the nickel needs

to be fully reduced, therefore this metal is in a mixed state Ni2+/3+. Now let us

consider the charge process: the removal of a Li+ ion is compensated by the

66


oxidation of a transition metal ion. Manganese cannot be oxidized further than

4+, and between cobalt and nickel it is the latter that is more easily [37]

oxidized: the low potential charge/discharge process, then, involves mainly nickel

ions. In the stoichiometric material all Ni2+ are available for the 2+ � 4+ redox

process, but in the overlithiated one a fraction of Ni ions can only contribute a 3+

� 4+ transition, thus lowering the amount of charge that can be extracted at low

potentials from X10850.

A different result was observed when comparing high potential cycling of both

X00850 and X10850, as shown in figure 3.2.9.

High potential cycling of the stoichiometric material induces an extremely

strong fading of the reversible charge, so that after a few cycles its value drops

well below those delivered by the overlithiated material. This result suggests that

the charge capacity retention of X10850 is better than that of X00850, a property

possibly connected to the high potential peaks observed in the CV shown in

figure 3.2.7.

It was then decided to investigate further the behavior of both materials by

means of Differential Electrochemical Mass Spectrometry (DEMS), in order to

assess their interaction with the electrolyte.

Figure 3.2.9: Galvanostatic cycling of Li(Ni1/3Mn1/3Co1/3)O2 (solid symbols) andLi1.1(Ni1/3Mn1/3Co1/3)0.9O2 (open symbols) between 3.0V and 5.0V vs. Li+/Li. Only the

reversible charge (discharge process) is shown.

67


DEMS is a technique that combines electrochemical experiments with mass

spectrometry [60]: a special electrochemical cell allows to charge an electrode

while an argon stream purges the cell from the developed gases. These are then

carried to a mass spectrometer where they are analyzed, and by combining the

electrochemical data with the MS data it is possible to work out which species are

produced at which cell potentials. Both samples were tested in a DEMS cell

against a metallic lithium counter electrode and cycled in CV mode between 2.5V

and 5.5V vs. Li+/Li in the same electrolyte used for previously described

electrochemical experiments. X00850 and X10850 have been tested for both CO2

and O2 evolution, as these gases are those most commonly developed in

oxidative conditions. The following measurements have been performed by Fabio

La Mantia [59].

First, the CO2 production was investigated and the results are reported in figure

3.2.10.

Figure 3.2.10: DEMS detection of carbon dioxide of Li(Ni1/3Mn1/3Co1/3)O2 (solid line) andLi1.1(Ni1/3Mn1/3Co1/3)0.9O2 (dashed line). Cycling was performed between 2.5V and 5.5V vs.

Li+/Li (potential profile in the dash-dotted line) against a metallic lithium counterelectrode. CV performed at 200 V/s in an 1M LiPF6 solution in 1:1 wt% mixture of�

ethylene carbonate and dimethyl carbonate as electrolyte.

68


Analyzing the DEMS results, differences between X00850 and X10850 appear:

the stoichiometric material shows CO2 production during both cycles (the second

cycle is representative for all subsequent cycles), while the overlithiated one

presents a massive CO2 production in the first cycle, but no more peaks during

the second cycle. The residual intensity for X10850 in the second cycle is due to

the delay in response of DEMS measurements, with gas bubbles trapped in the

electrolyte that get released slowly, creating a certain baseline. The small peak

occurring for both materials at 2.5V vs Li+/Li is the formation of CO2 upon

reduction of the SEI-like8 layer on the electrode at more negative potentials. It is

then possible to hypothesize that some kind of protection mechanism occurs at

high potentials on the NMC materials, much more effective in case of

overlithiation.

Oxygen was also detected during the DEMS experiments, and the results are

shown in figure 3.2.11.

Figure 3.2.11: DEMS detection of oxygen of Li(Ni1/3Mn1/3Co1/3)O2 (solid line) andLi1.1(Ni1/3Mn1/3Co1/3)0.9O2 (dashed line). Cycling was performed between 2.5V and 5.5V vs.

Li+/Li (potential profile in the dash-dotted line) against a metallic lithium counterelectrode. CV performed at 200 V/s in an 1M LiPF6 solution in 1:1 wt% mixture of�

ethylene carbonate and dimethyl carbonate as electrolyte.

8 SEI, Solid Electrolyte Interphase, is a protective layer that gets formed on electrodes upon the first fewcycles. It provides a protective function and is particularly critical on graphite negative electrodes [61].

69


In this case the striking difference between X00850 and X10850 is the

completely flat line observed for the stoichiometric material, and the strong peak

detected for the overlithiated one during the first cycle.

In order to rule out the possible influence of the electrolyte on this later result,

another DEMS experiment was performed. In this case, an X10850 electrode was

cycled in a 1M LiPF6 in acetonitrile (AcN) electrolyte against a LiFePO4 electrode. It

is not possible to use AcN with metallic lithium, because the metal would react

with the solvent. LiFePO4 was chosen because its intercalation plateau is

extremely flat, thus providing a useful reference electrode-like function. LiFePO4

was chemically delithiated using NO2BF4 and then used in the form of Li0.5FePO4

as anode. The cell was cycled between 2.0V and 5.5V vs Li+/Li and the resulting

O2 evolution is shown in figure 3.2.12.

Figure 3.2.12: DEMS detection of oxygen Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 (dashed line) inacetonitrile. Cycling was performed between 2.0V and 5.5V vs. Li+/Li (potential profile in

the dash-dotted line) against a metallic lithium counter electrode. CV performed at200 V/s in an 1M LiPF6 solution in 1:1 wt% mixture of ethylene carbonate and dimethyl�

carbonate as electrolyte.

In this experiment the oxygen evolution is detected again, and given the lack

of oxygen atoms in any component of the cell but the positive electrode, the

conclusion is that oxygen is in fact lost by the overlithiated NMC material.

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3.3 Working hypothesisFrom the results obtained on X00850 and X10850 during the preliminary

characterization, it is clear that the overlithiated sample presents some

interesting characteristics over its stoichiometric equivalent. Thus the following

scientific questions ensued:

� What is the reason for the good cycle stability of X10850?

� Where does the oxygen come from upon high potential charging of

X10850?

3.3.1 Cycling stabilityAs it was presented in figure 3.2.9, when NMC materials are cycled at high

potentials, their electrochemical performance degraded differently: the

stoichiometric material had a higher capacity during the first 15 cycles, but upon

further testing the overlithiated material retained more reversible charge. This

property could be explained with an enhanced structural solidity of X10850 with

respect to phase transitions and mechanical stress upon delithiation. It was then

decided to investigate the structural integrity of X10850 during the

charge/discharge process: to do this, a new in situ method to perform XRD at a

synchrotron source was developed, in order to be able to follow the structural

changes occurring in the material upon delithiation. This new method, alongside

with the results obtained with it, will be presented in chapter 4.

3.3.2 Origin of O2 evolutionAfter demonstrating with DEMS that X10850 behaves differently than X00850

at high potentials and that O2 evolution during the first cycle is actually due to

the material and it's not only a side reaction occurring with the electrolyte, it was

necessary to determine the origin of the oxygen. At this point two possible

options were left open:

1. Upon deep delithiation, a surface rearrangement frees some oxygen and

this new structural setting provides the protection needed not to lose

additional O2 in later cycles

2. Once all metal ions are oxidized to M4+, further lithium removal proceeds

71


by losing Li2O (as it was detected for Li2MnO3, see chapter 1.6): this

mechanism could involve bulk oxygen ions

If the latter hypothesis is true, then neutron diffraction would be ideal to

investigate this effect for X10850: as it was presented in chapter 2.1, one of the

advantages of neutron powder diffraction over x-ray powder diffraction is the

ability to detect directly light atoms such as Li and O. In order to study this

possible mechanism of oxygen production a novel in situ neutron powder

diffraction electrochemical cell was designed and developed. It will be described

in chapter 5, alongside with the results of the investigation.

72

Chapter 4

O3 � O1 Phase Transition in NMC Materials

Chapter 4 � O3 � O1 Phase Transition in NMC Materials

4.1 IntroductionLayered oxides as cathode materials for lithium ion battery are in general

characterized by the space group they belong to in their pristine state. The

structural classification of AxMO2 type compounds, as for example LiCoO2 and

LiNiO2, revolves around the possible placement of the A cations [15], as shown in

figure 4.1.1.

Figure 4.1.1: Structural classification of layered oxides AxMO2 after Delmas, Fouassier andHagenmuller. (Adapted from [15]).

In the four settings shown above, metal ions sit in octahedral sites where they

form MO6 edge-shared octahedra arranged in two dimensional layers called slabs.

These metal-oxide layers are then stacked in different ways defining the sites

where A cations can sit: in the �O� structures octahedral sites are found, in the

�T� structures tetrahedral sites are found and in �P� structures prismatic sites are

found. The O3 packing is the well known -NaFeO2 structure, in which LiCoO2 and

LiNiO2 crystallize: lithium ions sit in the 3a sites, metal ions in the 3b sites and

75


oxygen ions in the 6c sites.

In this setting, the alkali ions (Li+ in this specific case) sitting in the interslab

sites define other LiO6 octahedra arranged similarly to the MO6 slabs, creating

other edge-shared octahedral sheets. The ordered arrangement of these

alternating sheets forms a unit cell in which four MO6 slabs and three LiO6 layers

are included, in the hexagonal setting of the rhombohedral space group R3-m

(#166).

Upon electrochemical delithiation, though, both LiCoO2 [17] and LiNiO2 [62] fail

to retain the O3 structure. When the lithium content in the material is lowered at

about 50%, a new structure is observed and it can be classified in the monoclinic

space group C2/m. The relationship between the two structures can be observed

in figure 4.2.2.

Figure 4.2.2: Relationship between hexagonal and monoclinic setting in Li1-xNiO2.(Adapted from [62]).

When concentrating on LiCoO2, the complex system that ensues for

76


compositions between Li0.5CoO2 and Li�CoO2 has been deeply studied and it has

been found [63] that between Li0.4CoO2 and Li0.2CoO2 the O3 phase is restored.

Upon further lithium removal, though, another phase denominated H1-3 appears.

This setting can be seen as the O3 phase in which some of the LiO6 octahedra are

not edge-sharing but face-sharing. The face-sharing layers are generally

characteristic of the phase that appears upon further delithiation, between

Li0.1CoO2 and Li�CoO2, the so called O1 phase [64]. A comparison of the O3, H1-3

and O1 phase is shown in figure 4.2.3.

Figure 4.2.3: Schematic descriptions of the O3, H1-3 and O1 phase. (Adapted from [64]).

LiNiO2 shares some similarities with its cobalt brethren [65] and upon

delithiation the new monoclinic, rhombohedral and hexagonal phases appear. On

the other hand, though, these phase transitions seem to be depending on the

preparation method and the resulting non-stoichiometry and cation mixing of

LiNiO2 [66]. Lithium and nickel have similar ionic radii (Li+=0.76Å, Ni2+=0.69Å)

and therefore when the material is synthesized, if it is cooled too quickly, some

77


nickel ions can end up being in the interslab space (3a sites); while lithium ions

will sit in the slab space (3b sites). If the cation mixing is lower than ~5% then

the monoclinic phase at Li0.5NiO2 is observed, otherwise the whole deintercalation

proceeds without phase transitions and diffraction patterns can be indexed in the

O3 phase throughout the electrochemical delithiation. Additionally, though, it has

been shown that the amount of �disorder� in the structure can have dramatic

influence on the lithium extraction reversibility [67].

When considering NMC compounds, isostructural with LiCoO2 and LiNiO2, it

would be natural to expect similarities. It has been reported previously that when

cation mixing is high (~6%), no phase transition is observed during the first cycle

[37], but with a carefully synthesized sample where the Li-Ni exchange was lower

(~2%-3%), the O3 phase was retained only until Li0.3(Ni1/3Mn1/3Co1/3)O2 [68]. Upon

further lithium extraction the NMC material would change into the O1 phase, and

it was devised that when the material was not delithiated further than

Li0.3(Ni1/3Mn1/3Co1/3)O2 the reversibility of lithium insertion was much better. It

should be noted that the latter work used chemical delithiation and relithiation,

instead of electrochemical operation of the electrode material.

To graphically describe the O3�O1 phase transition (see figure 4.2.3), it is

possible to imagine that when most of the lithium ions are removed from the

interslab space, the MO6 slabs acquire a certain freedom of displacement. When

two layers slide on top of each other, the symmetry is reduced and therefore the

phase transition takes place. On the other hand, if in the interslab space a

quantity of nickel ions are still present, the slabs cannot move and therefore the

transition is hindered. The O3 � O1 transition's role in the on the charge retention

properties of NMC materials is not well understood. Slight changes in the

structural parameters mean that the material is not subjected to strong

mechanical stress, which could be beneficial to the long term cycling stability. On

the other hand, all previous works have focused on short term cycling (mostly the

first cycle), therefore later effects of deep charge and discharge have not been

thoroughly studied yet.

After noticing the better specific charge retention of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2

over the stoichiometric material, it was decided to investigate its properties with

78


three different experiments:

� First cycle charge

� Potentiostatic stress over time

� Galvanostatic stress over time

The goal of combining these measurements was to investigate whether the

probable initial lack of O3 � O1 transition (due to the high Li-Ni exchange in the

synthesized materials) could be induced by electrochemical stress, thus

simulating real life battery operation. First cycle measurements were studied by

means of in situ x-ray powder diffraction using a newly developed method

described in chapter 4.2. The results of this investigation are reported in chapter

4.3.

4.2 In situ method at the SLS synchrotronIn situ x-ray diffraction has been performed in many different electrochemical

fields (for example in electrodeposition [69], fuel cell catalysts [70] or basic

electrochemical experiments [71]), and battery research does not differ. Diverse

ways of combining the electrochemical operation of a battery with the acquisition

of XRD data, both at synchrotron facilities and with conventional laboratory

sources, have been presented over the years and in this section these methods

will be discussed, before presenting the novel approach developed as topic of this

work.

4.2.1 State of the art in situ XRDThe development of new electrode materials brought new issues to be

discussed. In particular, the link between the cycling characteristics of a battery

material with its structural properties has been a constant question, whichever

the investigated material. It was clear from the start that understanding in a

satisfactory manner all fine details of the structural developments upon charging

and discharging was not possible from ex situ and post mortem investigations.

Therefore the need for in situ x-ray diffraction measurement techniques arose in

many research groups. Independent approaches have been published over the

years and a selection of the developed devices is presented here.

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In 1992 Gustafsson et al. introduced a design in which a polymer battery is

used to obtain XRD patterns while cycling it [72]. The battery is a device

composed by a stack of thin layers enclosed in a multilayered foil

(polyester/aluminum/polyethylene) and it uses a polymeric electrolyte. This

device is commonly described as �coffee bag cell�, since the enclosure is the

wrapping actually used for packaging coffee beans and powder. It is suited for Li-

ion battery research because of the high protection it ensures against

permeability of gases through the polymeric membranes, thanks to the central

aluminum layer. The battery is mounted in transmission mode, therefore the x-

ray beam has to travel through the aluminum in the coffee bag and the nickel

current collector, generating additional peaks.

A similar stacked cell was introduced by Bellcore in 1996 [73] and it is known

as �Bellcore battery�. In this cell, plasticized electrodes are pressed onto metal

current collectors and then used to �sandwich� a polymeric electrolyte. The

assembly is then packaged in a metal-plastic bag similar to the aforementioned

coffee bag. The main advantage of this device over the coffee bag cell is that the

industrial process does not require a controlled environment during the

production of the devices, because the moisture sensitive electrolyte is added

only at a second step and not during the stacking of all other components. The

Bellcore setup has been used to perform in situ XRD with conventional laboratory

diffractometers and at synchrotron facilities.

In 1997 Richard et al. presented a cell based on Bellcore electrodes to perform

in situ XRD with a laboratory diffractometer [74]. In this contribution the

electrochemically active elements are not enclosed in a coffee bag but are built

into a conventional coin cell, whose bottom element (the current collector for the

working electrode) is cut in order to accommodate a beryllium window. Beryllium

is chosen because it is the lightest metal stable in air (the lightest metal being

lithium, but as discussed earlier it is not stable in air), therefore its contribution to

the diffraction pattern is minimal, but it still provides electronic conductivity and

doubles as a current collector. This cell was used in Bragg-Brentano geometry,

therefore the beam does not have to go through the whole cell stack. The full

Bellcore design, on the other hand, has been used by Strobel et al. in 1999 [75]

for synchrotron XRD measurements. In this setup the cell is used in transmission

80


mode, similarly to the example of Gustafsson.

Obviously not only soft packaging cells (or some derivatives) have been used

for in situ XRD, but also more solid designs. One example is the laboratory cell

developed by Roberts et al. in which a beryllium window is used to allow x-rays to

reach the working electrode [76]. This cell, operating in the Bragg-Brentano

geometry, presents the obvious advantage that it can be reused by changing the

working electrode and does not need to be disposed of at the end of the

experiment. Another reusable cell, this time to be employed in synchrotron XRD

experiments, was proposed by Baehtz et al. in 2005 and is to be operated in

transmission mode [77]. The stack of electroactive elements is enclosed between

an aluminum current collector (for the working electrode) and the lithium foil, and

the whole stack is contained in a stainless steel body. Two windows are present

and are both made out of kapton foil.

The experience accumulated in these and other contributions was used as

starting point to develop a new method by analyzing first each method's

strengths and weaknesses and then by proposing a new design suitable for in

situ XRD experiments.

4.2.2 Method developmentThis work has been geared towards the resolution of some of the issues

discovered in the contributions presented above and has been particularly

focused on the need to optimize the use of beamtime at synchrotron sources. The

method relies on the combination of the use of synchrotron radiation with an

efficient, reliable and cost effective way of performing electrochemical

experiments, namely coffee bag cells. To exploit beamtime at its fullest the use of

an automatic sample changer is then presented.

4.2.2.1 Synchrotron radiationThe use of synchrotron radiation to perform x-ray diffraction presents some

major advantages over the usual laboratory sources.

To begin with, when operating at a synchrotron it is possible to choose the

wavelength of the x-rays. A conventional lab source has a fixed wavelength that

81


might not be optimal for every sample, in particular because of the fluorescence

that might ensue with some elements. Additionally, given the strong interaction

of x-rays with matter, there could be strong absorption of radiation by some

chemical species. Being able to choose the energy of the x-rays according to the

sample that is being measured is then crucial in order to obtain the clearest

diffraction patterns with the highest intensity. Moreover, the x-rays obtained at a

synchrotron are in general more monochromatic than their conventional

counterpart, removing the need to strip the effect of the stray radiation from the

final diffraction pattern.

Another significant advantage of synchrotron sources over conventional x-ray

tubes is the beam flux that can be achieved by the former. Having a larger

number of photons hitting on the sample allows to perform experiments much

more quickly and with higher overall intensity.

One final advantage of using a synchrotron is the fact that it is possible to

obtain a very focused beam. Having a spot size in the order of magnitude of a

few m� 2 allows for local investigations of large samples, as well as the possibility

to focus on a small portion of the sample, minimizing the effect of possible

inhomogeneities in the specimen.

4.2.2.2 New �coffee bags�Given the large number of existing designs for in situ XRD applied to Li-ion

batteries, it was not needed to reinvent the wheel in order to develop an

electrochemical cell suitable for this technique.

First, it was decided not to use any solution involving beryllium windows.

Beryllium presents three main issues:

1. While being a light element, it is not completely transparent to x-rays,

therefore its weak Bragg peaks are present in the final diffraction pattern,

along with beryllium oxide ones;

2. It is not completely stable against corrosion and given the tendency to

investigate novel materials that present lithium intercalation at very positive

potentials it is not optimal to have it as a current collector or in any case in

electrical contact with the active elements of the cell;

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3. Beryllium presents serious health hazards: it is a recognized carcinogenic

agent and therefore it has to be manipulated very carefully.

As an x-ray window for cells, kapton was selected: while it is not completely

transparent for x-rays (it has a large band at low angles but however no very

strong Bragg peaks), it does not hinder the evaluation of the typical Bragg peaks

of materials of interest for Li-ion research.

Bellcore technology for electrodes and electrolytes presents a certain

sophistication in the preparation of such elements, involving know-how not easily

accessible. On the other hand, it was possible to reuse most of the experience in

preparing electrodes for common laboratory coin-like cells by choosing a design

inspired by the coffee bag cells described by Gustafsson. The design chosen for

the electrochemical cells to be used for in situ x-ray diffraction was then derived

from the �coffee bags� described earlier. In figure 4.2.1 a schematic view of the

coffee bag cell in a two electrode setup is presented.

The working electrode consists of a self-standing active layer pressed onto a

metallic mesh that act as a current collector. The active layer is prepared by

mixing the active powder, be it positive or negative electrode material, with a

conductivity enhancer (if needed) and a polymeric binder (polyvinylidene

fluoride, PVDF). The binder is dissolved in N-methyl pyrrolidone (NMP) and the

whole mixture's thickness is adjusted by adding more NMP. The compound is then

thoroughly mixed and the resulting slurry is spread onto a non adhesive substrate

such as wax paper. The casting is done with the �doctor blade� technique, in

which a blade is passed over the slurry at a constant height, in order to obtain a

homogeneous film. The electrode is then dried in a vacuum oven at 80°C

overnight and when dry it can be cut into the appropriate shape, in general 2cm

x 2cm squares. The current collectors are expanded metal meshes and the

material is chosen according to the experiment to be performed: aluminum is

used for positive working electrodes, while copper is chosen for negative working

electrodes. Counter electrodes, carrying a strip of metallic lithium foil as

electroactive material, are also on the copper mesh.

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Figure 4.2.1: Schematic view of the coffee bag cell for in situ XRD experiments. In theenlargement, PE is polyethylene, Al is aluminum, OPA is oriented polyamide.

Between the electrodes a separator is placed and in coffee bag cells it has to

be as thin as possible. Therefore it was chosen to use a polymeric

�(polypropylene) separator about 25 m thick. While in figure 4.2.1 only one layer

of separator is schematically shown, two more layers of glassfiber separators

were added because of the low wettability of the polymeric separator with

electrolyte. Glassfiber separators, comparably sized to the polymeric one, absorb

electrolyte, creating a buffer layer of solution that helps the homogeneity of the

battery charge and discharge. Since the glassfiber is amorphous, the addition of

two layers to the assembly does not create additional peaks in the diffraction

pattern, however a certain absorption is created, resulting in slightly attenuated

intensities. Any liquid electrolyte (including ionic liquids) can be used in the

coffee bag cell, allowing the study of the effect of different behavior of the

electrodes according to the chosen solution.

The coffee bag foil used for the assembly of the electrochemical cells (Gruber

Folien GmbH) is a multilayered foil composed by two layers of polyethylene (PE),

one layer of aluminum (Al) and one layer of oriented polyamide (OPA). The

presence of a terminal OPA layer makes the coffee bag sealable only on one side.

In order to minimize the impact of aluminum in the final diffraction patters, a

window is cut in correspondence to the electrodes' positions and then covered on

both sides with kapton tape. Kapton is the commercial name of a polyimide

84


commercialized by DuPont and is chosen because of its low interaction with both

x-rays and the chemicals (especially the electrolyte) in the electrochemical cell.

Once all elements of the cell are stacked, it can be sealed: at this point the

device will protect the inner elements from oxygen and moisture in the air for the

time necessary to perform the XRD experiments.

Figure 4.2.2: Picture of an optimized coffee bag cell. The kapton window is visible, as wellas the aluminum (left) and copper (right) current collectors.

Figure 4.2.3: A coffee bag cell enclosed in the sample holder (left) and with solderedcables, ready to be included in the sample changer.

Figure 4.2.2 illustrates the cell in a two electrode configuration, with one

aluminum and one copper current collector. The coffee bag measures

approximately 8cm x 9cm and before being used two cables have to be soldered

to the current collectors, in order to connect it to the potentiostat. It is then

85


placed in an aluminum sample holder as shown in figure 4.2.3. The casing is

coated with a non conductive thin film in order to avoid shortcircuiting of the cells

when placed in the holder. The sample holder has two holes in order to allow for

the x-rays to pass through the coffee bag. Once all samples are enclosed in the

casings, they can be transferred to the sample changer.

4.2.2.3 Sample changerGiven the simple nature of the coffee bag cells, it is easy to build a large

number of samples with different combinations of active materials and

electrolytes. Since one pattern can be acquired in the time frame of a few

seconds (normally between 10s and 60s), it would be unimaginable to effectively

put samples in front of the beam manually. Therefore it was decided to build an

automatic sample changer that would accommodate many different cells that

could be measured in sequence without the need of human intervention over

many hours of operation. It was decided to embrace a design comprising a

carriage (in which the samples would be loaded) performing a �slide show

motion�. This motion can be summarized in 4 movements:

1. The carriage slides in one direction until the slot of the cell to measure

reaches the correct position;

2. A compressed air operated piston pushes the cell in the wall mount;

3. When the x-ray measurement is over, the piston is retracted and the cell

is put back in the carriage;

4. The carriage slides to the next slot to be measured.

A drawing of the sample changer is shown in figure 4.2.4. Up to 32 cells can be

accommodated in the sample changer, and each of them can be x-ray measured

depending on the time passed from the previous measurement, the potential

state, the charge state or simply continuously, without checking for any criteria.

The sample changer and the diffractometer are controlled using a BASH9 script

that follows the flowchart reported in figure 4.2.5. BASH was chosen because it is

commonly found in UNIX-like systems such as the Linux setup of the beam line

and it does not require additional software (such as compilers or interpreters) to

9 BASH, or Bourne Again Shell, is the default shell in many UNIX-like systems such as Linux [78].

86


be run. Being a script, it can be modified by the user at any time with the use of a

text editor. The full script is included in this thesis as Appendix 1, at the end of

the volume.

Figure 4.2.4: Schematic view of the automatic sample changer.

Figure 4.2.5: Flowchart detailing the functioning principle of the controlling software forsynchrotron measurements.

87


4.3 Results and discussionThe structural properties of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 were investigated with x-ray

diffraction and in order to follow the changes during electrochemical

deintercalation ex situ and in situ XRD were used. The strategy to individuate the

O3 � O1 phase transition, as it was described in chapter 4.1, was to compare the

diffraction patterns obtained in situ resulting from the first charge and those

obtained ex situ after extensive potentiostatic and cycling stress.

O3 and O1 phases have different space groups and will thus appear with

different diffraction patterns. In figure 4.3.1 a comparison of simulated XRD

patterns for both phases is shown. The differences between the patterns are

obvious, and a striking diversity is the doublet at 66° in the O3 phase which is not

present in the O1 phase, where only a single peak is visible.

Figure 4.3.1: Simulated x-ray powder diffraction patterns for the O3 (top) and O1(bottom) phases.

In situ XRD experiments were performed at the Material Science beamline at

the Swiss Light Source using a photon energy of 17.5 keV. This energy

corresponds to a wavelength of 0.7085 Å, roughly the half of the one relative to

the Cuk radiation used commonly in laboratory diffractometers. A coffee bag cell

88


was prepared as described in chapter 4.2 with a working electrode composed by

82% wt. Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 (82% wt), graphite (4% wt, Timcal KS6), carbon

black (7% wt, Timcal Super P) and PVDF binder (7% wt, Solef). The counter

electrode was metallic lithium and the electrolyte was a 1M LiPF6 solution in a 1:1

wt% mixture of ethylene carbonate and dimethyl carbonate.

Figure 4.3.2: Potential profile of the coffee bag cell containing an X10850 workingelectrode. Charge performed between OCV and 4.7V vs Li+/Li during the in situ XRD

measurement. Counter electrode is metallic lithium, electrolyte is a 1M LiPF6 solution in a1:1 wt% mixture of ethylene carbonate and dimethyl carbonate. Marked in the circles are

the potentials at which diffraction patterns were recorded.

The battery was charged with a specific current of 45mA/g from OCV up to

4.7V vs. Li+/Li. It was decided not to go up to 5.0V vs. Li+/Li because of the

electrolyte oxidation occurring at high potentials. In the coffee bag cell only a few

�l of electrolyte are present and the risk of quickly decomposing a large part of it

and thus compromising the electrochemical operation of the battery is very high.

Therefore the synchrotron experiment was kept on the safe side and only 4.7V vs.

Li+/Li were reached. A plot of the recorded potential profile is shown in figure

4.3.2.

During the electrochemical delithiation 5 diffraction patterns were recorded

and later analyzed. An example in situ x-ray diffraction pattern is presented in

figure 4.3.3. In the diffraction patterns acquired in situ, additional phases are

present. In particular, peaks relative to the aluminum current collector and to the

separator are recognizable. The additional phases make the XRD data harder to

89


analyze, but the main features of O3 and O1 phases are easily detectable. In

particular, the [003] peak at low angles (at about 8° on the synchrotron 2� scale)

and the doublet formed by the [018] and [101] peaks (at about 28° on the

synchrotron 2� scale) are clearly distinguishable. In figure 4.3.4 all 5 patterns

acquired during the charge of X10850 are compared.

Figure 4.3.3: Sample in situ XRD pattern acquired at the SLS with a wavelength of0.7085Å of X10850 at open circuit voltage. Marked with (°) are peaks relative to the

separator, with (+) those relative to graphite and with (*) those relative to the aluminumcurrent collector.

The XRD patterns shown in figure 4.3.4 have been analyzed to determine the

crystallographic parameters. A summary of the refined values is included in table

4.3.1 along with the data relative to the electrochemical state of the battery at

the moment of the diffraction measurement.

Sample compositionPotential

(V vs.Li+/Li)

Specificcharge(mAh/g)

Spacegroup

a (Å) c (Å)Unit cell volume

(Å3)

Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 OCV 0 R3-m 2.852(6) 14.21(6) 100.1

Li0.86(Ni1/3Mn1/3Co1/3)0.9O2 4.0V 68 R3-m 2.828(5) 14.27(5) 98.84

Li0.52(Ni1/3Mn1/3Co1/3)0.9O2 4.5V 165 R3-m 2.822(5) 14.35(5) 98.97

Li0.40(Ni1/3Mn1/3Co1/3)0.9O2 4.6V 199 R3-m 2.823(5) 14.31(5) 98.76

Li0.32(Ni1/3Mn1/3Co1/3)0.9O2 4.7V 221 R3-m 2.825(6) 14.29(7) 98.76

Table 4.3.1: Summary of crystallographic and electrochemical data relative to the firstcharge of X10850.

90


Figure 4.3.4: Comparison between in situ XRD patterns of X10850 charged from OCV(bottom) to 4.7V vs. Li+/Li (top).

Every pattern could be indexed in the O3 phase (space group R3-m) and the

cell parameter evolution is shown in figure 4.3.5.

Figure 4.3.5: Cell parameter evolution versus cell potential. Open squares are relative tothe �a� cell parameter, solid dots are relative to the �c� cell parameter.

91


Both cell parameters follow a symmetric behavior: prior to 4.5V vs. Li+/Li the

�a� parameter shrinks while the �c� parameter grows; while afterwards the

trends are reversed. It is interesting to note that the unit cell volume showed

small changes, around 1%: the structure is extremely stable and the mechanical

stress on the crystallites induced by the lithium removal is kept to a minimum.

This result seems to confirm that the lithium-nickel exchange detected during the

preliminary characterization of X10850 does not allow the O3�O1 phase

transition, at least in the first cycle until about 70% of lithium ions are removed

from the structure.

For additional investigation, ex situ measurements were performed on

standard electrodes charged in a coin-like cell used for routine laboratory

electrochemical experiments. To build these electrodes, a slurry was prepared by

mixing Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 (82% wt), graphite (4% wt, Timcal KS6), carbon

black (7% wt, Timcal Super P) and PVDF binder (7% wt, Solef) in N-methyl-

pyrrolidone. The slurry was then cast on aluminum foil and dried overnight in a

vacuum oven at 80°C. The dried electrodes were then cut in a circular shape and

transferred into an Ar filled glove box, where they were enclosed into the cells

along with a metallic lithium current collector and 500�l of electrolyte, a 1M LiPF6

solution in a 1:1wt% mixture of ethylene carbonate and dimethyl carbonate. The

electrodes were then subjected to the desired electrochemical treatment:

� Sample A: Full charge to 5.0V vs. Li+/Li, 1st cycle only

� Sample B: Charge to 4.5V vs. Li+/Li and subsequent potentiostatic phase

at 4.5V vs. Li+/Li for 30 days, 1st cycle only

� Sample C: 150 deep charge-discharge cycles at 25 mA/g between 2.0V

and 5.0V vs. Li+/Li

At the end of the conditioning the working electrodes were removed from the

cells and washed in dimethyl carbonate to remove traces of LiPF6 originating from

the electrolyte. The active mass was then separated from the aluminum current

collector (in order to have as little extra phases in the diffraction patterns as

possible) and taped onto a sample holder for a Siemens D500 powder

diffractometer. The resulting diffraction patterns are shown in figure 4.3.6. The

large bump at low angles is due to the beam overflow on the sample holder and

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the peaks visible at about 25° in patterns A and B (marked with �*�) are due to

the graphite present in the electrode.

The typical features of the O3 phase are present in all three patterns,

indicating that the O1 phase was not formed. In the enlargement shown in figure

4.3.7 the doublet at high angles is clearly visible, evidencing the lack of O1 phase

(compare to figure 4.3.1). In pattern B the [003] peak is to lower angles than in

patterns A and C, and [018] and [101] are more separated in B than in A and C.

This is easily explained by examining the results obtained with in situ

measurements (figure 4.3.5). Sample B was charged up to 4.5V, therefore at the

largest size of the �c� cell parameter, thus the [003] peak is shifted to lower

angles that correspond to higher d spacing. At 4.5V the smallest size of the �a�

parameter was also observed, and the [101] peak is shifted at higher angles, thus

smaller d-spacings.

Figure 4.3.6: comparison of XRD patterns obtained for samples A (1st charge at 5.0V vs.Li+/Li), B (potentiostatic stress at 4.5V vs Li+/Li for 30 days) and C (150 cycles between

2.5V and 5.0V vs Li+/Li). All samples are X10850.

From these experiments, then, it was clear that there was no transformation of

the O3 phase in the O1 phase. The ~3% lithium-nickel cationic exchange

detected during the preliminary investigations seems to hinder the transition

between the two phases. Once all lithium ions are removed from the interslab

space, only a few nickel ions are left to lock the MO6 layers in place. They are

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anyway sufficient to block the sliding of the layers on each other, thus not

allowing the creation of the new O1 phase.

The influence of the strong structural stability of the disordered X10850

material can be observed directly in the capacity retention over the long cycling

stress performed on sample C. The results are shown in figure 4.3.8.

In the first charge, the capacity loss is very high. There is an extremely high

charge value and then a much lower discharge value. Later, after the initial fast

fading of the capacity during the first 20 cycles, the electrode charge capacity is

stabilized around 130 mAh/g with irreversible capacity loss around 1% per cycle.

Under such abusive cycling conditions up to 5.0V vs. Li+/Li, though, this result is

far from disappointing, given that LiCoO2 can reach such low values even when

cycled between 2.75V and 4.4V vs. Li+/Li if not properly protected by coating or

modified by doping [79]. It is worth noting that the electrode was not in any way

optimized for electrochemical performance, therefore part of the fading can be

due to this reason. Furthermore, cycling at such high potentials provokes strong

electrolyte oxidation, and this can also be a limiting factor in the cycling behavior.

Figure 4.3.7: Enlargement of figure 4.3.6 showing in detail the features relative of the O3phase and the lack of features relative to phase O1.

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Figure 4.3.8: Cycling behavior of an Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 electrode cycled 150 timesbetween 2.5V and 5.0V vs. Li+/Li. Counter electrode is metallic lithium, electrolyte is a 1M

LiPF6 solution in a 1:1 wt% mixture of ethylene carbonate and dimethyl carbonate. Fulldots are the charging process (lithium removal), open dots are the discharging process

(lithium insertion) and open diamonds represent the irreversible charge between chargeand discharge in every cycle.

In summary, Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 showed some interesting electrochemical

and structural properties that qualify it as a useful candidate for substituting

LiCoO2 as cathode material of choice for the Li-ion battery industry. The material

didn't undergo structural modifications that dramatically disrupted the

reversibility of the charge-discharge process and the low specific charge

observed after 150 cycles can be attributed to the very high cutoff voltage

chosen for the experiment, that is largely beyond the demand of current

commercial batteries. The lack of O3 � O1 phase transition is probably due to the

lithium-nickel cationic exchange detected during the initial characterization, and

therefore the influence of the preparation conditions on the final product can be

quite high.

4.3.1 Additional results obtained using in situ XRD

Coffee bag cells are very versatile, as they can be equipped with all sorts of

electrode materials and electrolytes. Some examples of results obtained from

investigations conducted at the MS beamline at the SLS using the method

described in chapter 4.2 are hereby presented.

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Several materials have been investigated using coffee bag cells, among which

LiFePO4 showed excellent results. In this study, conducted on powders

synthesized in the laboratory of Prof. Reinhard Nesper at ETHZ, the two phase

charge-discharge reaction on the olivine phosphate was followed by in situ XRD.

A depiction of the results is shown in figure 4.3.9.

Figure 4.3.9: In situ XRD measurement of a LiFePO4 electrode. On the left side of thepicture, the diffraction patterns are shown: at the bottom pure LiFePO4 is present (peaks[020] and [301] are marked), then by charging the battery the new FePO4 phase appears

(peaks [211] and [020] in italic). Halfway in the figure only FePO4 is present, and bydischarging the electrode LiFePO4 appears again, until it is the only phase present. Cellcharged at C/6 rate against metallic lithium, LiPF6 1M in 1:1 wt% mixture of ethylene

carbonate and dimethyl carbonate as electrolyte.

The cell was charged from OCV to 3.7V vs. Li+/Li and then discharged down to

3.0V. The flat insertion plateau observed at 3.35V (right side of figure 4.3.9) is

typical of two-phase reactions. In this case, the two phases are both

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orthorhombic (Pnma space group): at OCV only LiFePO4 is present (see left side

of figure 4.3.9), identified by well defined [020] and [301] Bragg peaks. By

removing lithium, thus creating FePO4 a second phase appears, shown by [211]

and [020] Bragg peaks. The intensity of the LiFePO4 peaks diminishes as that of

FePO4 increases. When discharging the electrode the trend is reversed, until only

LiFePO4 is detected in the topmost diffraction pattern.

The coffee bag method has been used to conduct further studies on other

electrochemical systems than lithium-ion batteries. The effect of ion intercalation

in graphitic materials from electrolytes for supercapacitors has been investigated

[80] by monitoring the changes in the [002] peak of graphite, as shown in figure

4.3.10. A graphite working electrode was cycled in CV mode against a carbon

cloth counter electrode (this material is typical for supercapacitors) at a scan rate

of 0.3 mV/s between 0 and 5.2V (first cycle) and 5.5V (second cycle) vs. Li+/Li.

Figure 4.3.10 refers to the first and second anodic cycles. The [002] peak is the

one at 12° and by inserting BF4- ions this peak splits in two, the [00n] and

[00n+1] peak, where n is an index depending on the stage of the intercalation in

graphite. When graphite is intercalated, two new peaks appear: one at about 9°

and another one shifting between 1.5° and 2.5° degrees.

A more detailed description of these phenomena can be read in the

aforementioned reference.

From these examples it is clear that the in situ method developed within this

thesis work is extremely flexible and reliable, and that it can be employed with a

variety of different materials. The large number of diffraction patterns that can be

acquired per sample allows for a detailed elucidation of crystallographic

phenomena without the need to prepare a large number of samples and with the

help of synchrotron radiation these studies can be carried out more quickly than

what would be needed with a conventional laboratory diffractometer.

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Figure 4.3.10: Effect of the intercalation of BF4- ions in graphite from an acetonitrile based

electrolyte (1M (C2H5)4NBF4 in acetonitrile).(Adapted from [80]).

98

Chapter 5

Oxygen Evolution from NMC Materials

Chapter 5 � Oxygen Evolution from NMC Materials

5.1 IntroductionThe detection of oxygen evolution from the overlithiated NMC material

described in chapter 3.2 confirmed the hypothesis made on similar mixed oxides

by other researchers. The study of binary and ternary layered oxides with a

lithium excess produced results similar to those presented in this work, namely

an unknown origin plateau after 4.5V vs Li+/Li and a large irreversible capacity

during the first cycle [81]. The first speculation about the possible oxygen

evolution from a series of overlithiated mixed oxides Li[NixLi(1/3-2x/3)Mn(2/3-x/3)]O2

(x=1/2, x=5/12, x=1/3) lead to the observation that by higher overlithiation

(therefore lower x value) a larger first cycle irreversible capacity was detected

[81]. This mechanism was later investigated by the same researchers [82] and

convincing evidence for the oxygen loss of these mixed oxides was found. As it

was briefly introduced in chapter 1.6, overlithiation can be induced by forming a

solid solution between Li2M'O3 and LiMO2 and the lithium rich phase is responsible

for the oxygen loss. It was demonstrated that the actual electrochemical activity

of Li2M'O3 can be achieved only for M'=Mn, while M'=Ti, Zr didn't provide the

same results [83]. The effect of Li2MnO3 in a solid solution with LiMn0.5Ni0.5O2 was

studied with respect to the role of acid treatment over the irreversible capacity

[84]: it was found that by treating the powders with H2SO4 the irreversible

capacity observed during the first cycle would be reduced, therefore

corroborating the theory that Li+ ions are replaced by H+ ions, thus creating Li1-

xHxMnO3 [85]. Oxygen was later on detected by means of DEMS from the binary

oxide Li[Ni0.2Li0.2Mn0.6]O2 [86]. In this work it was hypothesized that the oxygen

loss is associated with the removal of excess lithium from the slab space (3b

sites). This creates vacancies that are filled by transition metal ions diffusing from

the surface, and the oxygen evolution would end once all vacancies in octahedral

sites are filled by such ions. Ternary oxides in a wide array of compositions were

also studied [87] and yielded similar results with respect to the oxygen evolution,

showing that the presence of cobalt does not seem to inhibit this behavior.

Materials in this class of overlithiated mixed layered oxides show interesting

electrochemical performance, therefore they are regarded as possible substitutes

for LiCoO2. The safety concern arising from the pressure that might ensue in a

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sealed commercial cell was studied after some test coin cells with an

overlithiated positive electrode material vented upon cycling [88]. When the

same material was cycled against a porous graphite counter electrode instead of

a metal lithium one, it was found that with a careful engineering of the cell the

oxygen production in a sealed cell is not a cause of concern [89].

As presented in this short introduction, most of the research on overlithiated

mixed oxides has been focused on binary nickel-manganese compounds. The

findings on Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 sparked the interest of studying the structural

changes in this material upon concurrent lithium and oxygen extraction. The

need to have a direct look at Li and O demanded the use of neutrons as the

diffraction technique of choice and the development of an electrochemical cell for

in situ neutron powder diffraction experiments was started. The cell is presented

in chapter 5.2 and the results of the investigation on the NMC material are

reported in chapter 5.3.

5.2 In situ method at the SINQ neutron sourceWhile in situ x-ray diffraction, as presented in chapter 4, is a well established

research field; in situ neutron powder diffraction (NPD) applied to lithium ion

batteries has never enjoyed large popularity. This is mainly due to the technical

difficulties that arise when considering the use of neutrons, as it was introduced

in chapter 2. The previous attempts at in situ neutron diffraction will be discussed

hereafter, before introducing the method developed during this work.

5.2.1 State of the art in situ NPDThe first electrochemical cell for in situ neutron diffraction was presented in

1998 by Bergstöm et al. [90]. It was modeled after the common cylindrical

sample holders used in NPD and it was constituted by a Pyrex tube (section

10mm) filled with active powder. The inside walls of the glass container were

coated with a gold layer about 100nm thin that serves as current collector for the

positive electrode. In the center of the tube, a lithium rod wrapped in a polymeric

separator was placed, acting as counter electrode. This cell was later used to

study phase transitions in LiMn2O4 electrodes [91].

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In 2004 Rodriguez et al. [92] reported a different approach to in situ NPD: they

simply placed a commercially available battery in front of a neutron beam, thus

simultaneously measuring anode and cathode. While this approach is definitely

easy and convenient, it cannot be neglected that the resulting diffraction

patterns are not only the sum of both anodic and cathodic active materials, but

also of all current collectors, separators and the container of the cell. Additionally,

the presence of commercial electrolyte with high hydrogen content creates a

very large background intensity.

5.2.2 Method developmentWhen analyzing the two methods presented above, it was clear that none of

them was optimal for in situ NPD. The latter method is just too limited: it is not

possible to perform measurements on novel materials, unless a battery is built,

and the resulting diffraction patterns don't seem clear enough to obtain

meaningful data with Rietveld refinement.

Bergstöm's approach is much more flexible and has the advantage of the

cylindrical shape, very important when evaluating the NPD data. The choice of

gold as current collector, though, limits the use of the cell at negative potentials,

since gold and lithium tend to form an alloy at negative potentials. Additionally,

the counter electrode is in the beam at all times, as well as the separator,

producing foreign reflections in the diffraction pattern and strongly absorbing

neutrons.

With these considerations in mind, an electrochemical cell for in situ neutron

diffraction was realized based on a completely new design.

5.2.2.1 New electrochemical cellThe goal for the new cell for in situ NPD measurements was to develop a

device capable of combining electrochemical and diffraction measurements, by

compromising as little as possible the outcome of both experiments. For this

reason it was decided to concentrate on a model based on flat electrodes (just as

in common electrochemical cells) and with as little components as possible in the

beam path. For this reason, the coffee bag model was not suitable and a new

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design had to be implemented.

A cross section of the developed device is shown in figure 5.2.1, where the

main building elements are visible. The cell top (1) encloses two springs (2) that

press on the negative current collector (3). The cell body (4) insulates the top

from the positive current collector (6), which encloses the cavity (5) where the

active material is pressed. The cell top is built from aluminum, as well as the

positive current collector, while the negative current collector is built from copper.

The lower part of the device, the one that contains the electrodes, is the most

important and figure 5.2.2 shows a magnification of that area, along with a

schematic view of the electrode assembly.

The stack that forms the battery starts with the negative current collector (1)

under which a strip of metallic lithium (2, the counter electrode) is found. Under

the lithium there is a glassfiber separator soaked with electrolyte (3) and then a

polymeric separator (4). Another glassfiber separator (5) sits on top of the active

powder (6), which in turn is enclosed in the positive current collector (7). The

choice of using two different types of separators is derived from the experience

with the coffee bag cells: glassfiber separators act as reservoirs of electrolyte,

while the polymeric separator provides a vital barrier against lithium dendrites.

Figure 5.2.1: Schematic representation of the electrochemical cell for in situ neutrondiffraction experiments.

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Figure 5.2.2: Schematic view of the electrode assembly in the in situ cell. Componentsnot in scale.

The working electrode is prepared by dry mixing the active powder with

variable amounts of carbonaceous materials, such as graphite and carbon black.

The active material to carbon ratio should be as high as possible in order to

obtain a good intensity of the diffraction patterns, but it must also be tailored in

order to obtain adequate electrochemical performance, i.e. overpotentials must

be controlled and homogeneous reaction of the active material must be ensured.

The working electrode powders are then pressed in the current collector and

dried in vacuum in order to remove all moisture present on the powders. This

leads to a highly porous electrode that is subsequently soaked with the

electrolyte, which can easily reach the bottom of the electrode by filling the

volume previously occupied by the moisture. All parts of the cell are then

transferred to an argon filled glove box and the device is assembled as illustrated

earlier and tightly secured. When the cell is closed it is airtight and it can be

safely handled in the open laboratory atmosphere.

5.2.2.2 Cell optimizationThe presented device needed a thorough optimization of the working electrode

as first step towards an effective utilization for in situ experiments. As model

material for this work it was decided to use LiNiO2: this compound, while not

being suited for commercial application in Li-ion batteries because of its low

thermal stability [93] and difficult synthesis [18], has a very well known structure

[62] and presents the additional advantage of not being activated when

irradiated with neutrons, allowing for quick and safe removal of the sample when

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tests at the neutron source would be performed.

The main issue to be dealt with during the optimization of the cell was the

working electrode (item 6 in figure 5.2.2). It is in fact very thick (about 5mm) and

this is needed in order to accommodate a sufficient amount of active powders,

given the weak interaction of neutrons with the sample. On the other hand,

though, this electrode size is not optimal for electrochemical operation of the

battery because the exchange of lithium ions from the material might not be

homogeneous throughout the thickness of the powders. In order to assess the

homogeneity of the electrode operation, it was decided to partially charge an

LiNiO2 electrode (up to 75mAh/g, about 50% of the usual charge obtained at the

upper limit of cycleability of the material of 4.5V vs. Li+/Li or Li0.5NiO2),

disassemble the cell, divide the active mass in three slices (top, middle, bottom)

and inspect each layer using XRD. If an inhomogeneity was to be discovered, it

was expected to be a lesser delithiation of the lower part. Being it further away

from the electrode interface with the counter electrode, it was thought that it

would have reacted less than the middle and the top layer, nearer to the lithium

counter electrode. As can be seen in the left side of figure 5.2.3, though, the

lowest layer showed only one phase, while the topmost layer showed the

strongest signs of unreacted material. This was explained with the poor electrical

conductivity of LiNiO2. Since the process of lithium removal from the structure

has to be accompanied by the transfer of one electron through the external

circuit to the counter electrode, the fastest reacting layer is the one in contact

with the largest area of current collector, therefore the lowest. The middle and

the top layer can directly only exchange electrons with the sides of the current

collector, therefore their delithiation reaction is slower and some portions of the

powder (presumably those in the center of the electrode) react very slowly. It was

then decided to adjust the electrical conductivity of the different layers of the

electrode by adding variable quantities of graphite for each layer, thus altering

the active material to carbon ratio. The experiment was repeated with the

optimized electrode and XRD confirmed that all three layers reacted equally: no

traces of unreacted LiNiO2 were detected, as it's visible in the right side of figure

5.2.3.

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Figure 5.2.3: Comparison of not optimized (left) and optimized (right) electrodes ofLi0.75NiO2.

A further step that was taken to ensure proper electrochemical performance of

the cell was to investigate the electrochemical overpotentials. For this purpose,

an electrode was prepared using a 2:1 wt% ratio between LiNiO2 and

carbonaceous materials, and it was charged at a C/50 rate (that is, the selected

current would have charged the material in 50 hours) against a metallic lithium

counter electrode in an electrolyte with 1M LiPF6 dissolved in a 1:1 wt% mixture

of ethylene carbonate and dimethyl carbonate. The charge curve was then

compared with the one obtained from a similar electrode (87% LiNiO2, 8%

carbonaceous materials, 5% polymeric binder) in a conventional coin-like cell

used routinely for laboratory experiments. The result is shown in figure 5.2.4 and

it is clear that the thick electrode has a larger ohmic resistance than the

conventional electrode. Nonetheless, the shapes of the curves are comparable,

indicating that the same processes are occurring in both setups. This proved the

suitability of the in situ cell to be used for meaningful electrochemical

experiments.

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Figure 5.2.4: Comparison of charge curves in a coin-like cell (solid line) and in situ cell(dashed line).

It was then necessary to test the capability of the cell to obtain proper

diffraction patterns when subjected to a neutron beam. In order to have a

comparison, first a neutron diffraction pattern of LiNiO2 was acquired using the

standard sample holder employed during conventional NPD experiments, a

cylindrical vanadium tube. Vanadium is chosen because it has almost no Bragg

peaks and therefore it adds no features to the diffraction patterns. The obtained

pattern is shown in figure 5.2.5.

Later, a neutron powder diffraction pattern was acquired in the in situ cell. The

cell was placed in the beam according to the scheme in figure 5.2.6, mimicking

the setup used for conventional cylindrical sample holders. The axis of the

electrode is in the middle of the detector, exactly where the axis of the vanadium

cylinder is normally placed.

The test of the in situ cell was conducted using a mixed electrode with the

typical composition (LiNiO2 : carbonaceous materials ratio 2:1 wt%) and the

profile is shown in figure 5.2.7. Both measurements were performed at the HRPT

(High Resolution Powder diffractometer for Thermal neutrons) beamline at the

neutron spallation source SINQ at PSI. The wavelength of 1.494Å was selected for

108


the experiments and each diffraction pattern was acquired over 2 hours. In the

obtained diffraction pattern shown in figure 5.2.7 there are multiple phases

included, as expected: graphite and aluminum peaks overlap those of LiNiO2, but

they do not hinder the detection of the main phase. When comparing cell

parameters obtained for both measurements (table 5.2.1) it is clear that data

obtained in the in situ cell are suitable for effective Rietveld refinement of powder

diffraction patterns.

Figure 5.2.5: Neutron powder diffraction pattern of LiNiO2 in a standard vanadium sampleholder.

The cell parameters are consistent between the two measurements and the

difference in value is comparable with the standard deviation. After this test it

was decided to study the impact of the electrolyte on the diffraction patterns. An

electrode was prepared as above, by mixing LiNiO2 and carbonaceous materials

in a 2:1 wt% ratio and soaked in a 1M solution of LiPF6 in a 1:1 wt% mixture of

ethylene carbonate and dimethyl carbonate before being built into an in situ cell.

The result of the measurement is shown in figure 5.2.8.

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Figure 5.2.6: Beamline setup. The in situ cell is placed in the center of the detector and isirradiated on the thin side. The diffracted neutrons are irradiated through the base of the

cell and the transmitted beam is then sent to the beamstop.

Figure 5.2.7: Neutron powder diffraction pattern of the in situ cell with full electrodeconfiguration. From top to bottom: experimental data (dots), calculated profile (solid

line), Bragg peaks (dashes) of LiNiO2, graphite and aluminum, difference betweencalculated and experimental data (dashed line).

110


LiNiO2, space group R3-m, hexagonal setting

Environment Parameter �a� (Å) Parameter �c� (Å)

Vanadium tube 2.8756(4) 14.179(2)

In situ cell 2.8765(6) 14.187(5)

Table 5.2.1: Comparison between cell parameters obtained from the referencemeasurement in the vanadium sample holder (figure 5) and the in situ cell (figure 6).

It is obvious that the presence of H atoms in the solvents (4 atoms per

ethylene carbonate molecule and 6 atoms for dimethyl carbonate molecule)

created an extremely strong background, giving the characteristic bent shape of

the diffraction pattern. Additionally, weaker peaks are now swallowed in the

background, dramatically reducing the possibility of obtaining meaningful

Rietveld refinement results. This result confirmed the absolute need to use

deuterated electrolytes for in situ neutron powder diffraction experiments.

Figure 5.2.8: Neutron diffraction pattern of an LiNiO2 electrode in the in situ cell withorganic electrolyte. Peaks relative to graphite (+) and aluminum (*) are also marked.

From the preliminary tests on the new in situ cell it was possible to assess the

suitability of the device to combine effectively electrochemical experiments with

NPD measurements. Nonetheless, three delicate issues were individuated:

� The charge homogeneity along the thickness of the electrode needs to

be carefully tested

� The ratio between active material and carbonaceous materials needs to

be as high as possible

� Deuterated solvents to prepare electrolytes are necessary in order to

have limited background intensity

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Each of these points had to be considered while preparing the investigations

using the in situ cell.

5.3 Results and discussionThe investigation of oxygen evolution from Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 at high

potentials using in situ neutron powder diffraction required as a first step the

optimization of the sample. As it was shown in chapter 5.2, the working electrode

needs to be carefully optimized in order to obtain the best experimental

conditions before the actual in situ measurements. In particular, this means

investigating the homogeneity of charge throughout the thickness of the working

electrode to make sure that all material is delithiated at the same level. For a true

in situ experiment to take place, it is needed for the diffraction pattern

acquisition to happen at the same time as the electrochemical charging. While

this is easy enough with synchrotron radiation, where a diffraction pattern can be

acquired in a few seconds, the low interaction of neutrons with the sample

complicates considerably the matter. In order to have a large enough intensity, a

considerable amount of active powders is needed but another limiting factor in

the selection of the working electrode composition is the maximum current

selectable in the electrochemical equipment used during this work. Then, of

course, the longer a pattern is accumulated, the higher the signal to noise ratio

will be, but this parameter is limited by the allocated beamtime. The charging

time of the electrode has to be accounted for in the total experiment time at the

beamline, and given the thickness of the sample in the in situ cell, this cannot

happen too quickly or the electrode will not be charged homogeneously.

It was then needed to individuate the best electrode composition and the

highest specific current usable for the charge process. As mentioned before, in

order to have a high signal to noise ratio in the neutron diffraction patterns, it is

needed to prepare electrodes with a large active material content. As a start, an

electrode composition similar to that used for the LiNiO2 tests (2:1 wt% active

mass to carbonaceous materials ratio) was employed and a charge current of

10mA/g was selected. The working electrode was charged in the in situ cell

against a metallic lithium counter electrode in an electrolyte constituted by a 1M

LiPF6 solution in 1:1 wt% mixture of ethylene carbonate and dimethyl carbonate.

112


The resulting charge curve is shown in the top part of figure 5.3.1. The cell was

charged as expected until 4.5V vs. Li+/Li, but upon reaching that value, some

parasitic reaction (probably enhanced by the presence of oxygen) took place,

hindering the further charge of the electrode. In an attempt to reduce this

parasitic effect, it was decided to charge the cell with a lower specific current. A

second working electrode was prepared by modifying the active mass to

carbonaceous material ratio, reaching a 3:1 wt% value.

Figure 5.3.1: Comparison of preliminary tests to obtain a full charge of X10850 from OCVto 5.0V vs. Li+/Li in the in situ cell. At the top, an electrode with a 2:1 wt% ratio betweenX10850 and carbonaceous materials, at the bottom an electrode with a 3:1 wt% ratio.Both electrodes were charged against a metallic lithium counter electrode using a 1M

LiPF6 solution in 1:1 wt% mixture of ethylene carbonate and dimethyl carbonate aselectrolyte.

Given the lower specific current it was possible to use more active mass while

remaining in the working limit of the electrochemical equipment (18mA

maximum). The electrode was built into an in situ cell with the same counter

electrode and electrolyte as before, and it was charged at 7.5mA/g. The resulting

charge curve is shown in the lower part of figure 5.3.1. Neither this configuration

could complete a full charge until 5.0V vs. Li+/Li, stopping similarly as the first

electrode around 4.5V vs. Li+/Li. The critical breaking point of the cell operation

113


was then deemed the amount of active powders, thus the amount of oxygen

released at high potential. For this reason the Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 mass was

reduced and a third electrode with a 1:1 wt% ratio between active material and

carbonaceous materials was prepared. This electrode was charged from OCV to

5.0V vs. Li+/Li with a specific current of 15mA/g. The potential profile relative to

this sample is shown in figure 5.3.2. The electrode could be charged up to 5.0V

vs. Li+/Li and then subsequently discharged without any disturbance and

therefore this sample was chosen to perform further optimization.

Figure 5.3.2: Charge profile of a working electrode 1:1 wt% between X10850 andcarbonaceous materials charged at 15mA/g up to 5.0V vs. Li+/Li and discharged with the

same specific current down to 2.5V vs. Li+/Li. Counter electrode is metallic lithium,electrolyte is a 1M LiPF6 solution in 1:1 wt% mixture of ethylene carbonate and dimethyl

carbonate.

It was then needed to assess the homogeneity of the charging process and to

do this the same method used in the general optimization of the cell (chapter

5.2) was used. The electrode was charged up to 100mAh/g (about 50% of the

reversible charge) and then it was divided in three layers along the thickness.

Topmost, middle and lowest layers were then analyzed by means of x-ray

diffraction to individuate unreacted material or differences in the delithiation

state. The XRD patterns are presented in figure 5.3.3 and the refined

crystallographic parameters are included in table 5.3.1.

114


Layer Cell parameter �a� (Å) Cell parameter �c� (Å)

Top 2.821(2) 14.39(2)

Middle 2.821(2) 14.40(1)

Low 2.820(2) 14.40(2)

Table 5.3.1: Refined cell parameters of the Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 phase extracted froman electrode charged at 100mAh/g in the in situ cell and then divided in three layers.

The data included in table 5.3.1 shows clearly that the material reacted

homogeneously also without an extensive optimization of the conductivity of

each layer, as it had been the case with LiNiO2 during the preliminary

characterization of the in situ cell. The three XRD patterns can be almost

superimposed and this fact gave confidence about the cell operation during the

in situ experiment.

Figure 5.3.3: Comparison of XRD patterns of the three layers obtained dividing an X10850working electrode charged at 15mA/g up to 100mAh/g in the in situ cell.

The in situ experiment was carried out at the HRPT (High Resolution Powder

diffractometer for Thermal neutrons) beamline at the Swiss Spallation Neutron

Source SINQ. An in situ cell was prepared as follows:

� Working electrode: mixed powders 1:1 wt% Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 and

carbonaceous materials

115


� Counter electrode: metallic lithium

� Electrolyte: 1M LiClO4 solution in a 1:1 wt% mixture of deuterated

ethylene carbonate (>98% deuterated) and deuterated dimethyl

carbonate (>98% deuterated)

Lithium perchlorate was used to prepare the electrolyte instead of lithium

hexafluorophosphate because the deuterated solvents were not dry enough. In

general, battery-grade solvents contain < 5ppm of water, while the deuterated

solvents had a content > 30ppm, both H2O and D2O. LiClO4 is less sensitive to

water than LiPF6, thus it was preferred as electrolyte salt for this experiment.

Given the low amount of active material in the electrochemical cell, it was

needed to accumulate neutron patterns for a long time. For this reason, it was

not possible to perform an in situ measurement under constant current

conditions, but it was decided to charge the cell up to selected potential values

with a specific current of 15mA/g, stabilize the electrode potentiostatically for 60

minutes and then perform the neutron powder diffraction experiments in OCV

regime over 6 hours. The current and potential curves are shown in figure 5.3.4.

Figure 5.3.4: Current and potential curves used during the in situ experiment onLi1.1(Ni1/3Mn1/3Co1/3)0.9O2. Marked with �G� are the periods where the cell was subjected to

galvanostatic charging at 15mA/g, marked with �P� are the potentiostatic stabilizations at4.1V, 4.4V, 4.7V and 5.0V vs. Li+/Li and marked with �OCV� are the periods at open circuit

voltage, during which the neutron diffraction patterns have been accumulated.

116


The in situ cell was placed in the beam according to the scheme in figure 5.2.6.

In order to obtain the highest intensity possible, the cell was rotated by some

degrees along its vertical axis, as shown in figure 5.3.5.

This rotation had the effect to allow the beam to travel for a longer path in the

sample holder, thus picking up more active material and generating more intense

diffraction patterns. On the other hand though, some of the glassfiber separator

fell in the beam path, thus creating a large bump at low angles due to the

amorphous nature of the glassfiber. Once the best position of the cell in the beam

was determined, the experiment was started. The first pattern was acquired in

the pristine cell, at open circuit potential and it is shown in figure 5.3.6.

Figure 5.3.5: Schematic depiction of the beam path in the sample holder.

As previously mentioned, the bump at about 20° is due to the glassfiber

separator. Comparing this pattern with the one shown in figure 5.2.8, it is clear

that the use of deuterated electrolyte is extremely beneficial, as the background

is much flatter. Unfortunately though, the intensity of peaks relative to

Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 is very low, when compared to the intensity of graphite

and aluminum.

117


Figure 5.3.6: In situ neutron powder diffraction pattern of pristine Li1.1(Ni1/3Mn1/3Co1/3)0.9O2

at open circuit potential (~ 3.5V vs. Li+/Li). Three sets of Bragg peaks are marked: NMCmaterial (top), graphite (middle) and aluminum (bottom). The bump at about 20° is due

to the amorphous glassfiber separator.

This is due to the fact that in order to achieve a full charge up to 5.0V vs.

Li+/Li, the active material to carbonaceous materials ratio is 1:1, therefore much

lower than the 2:1 ratio with which patterns shown in figures 5.2.7 and 5.2.8 were

accumulated. The absorbing effect of carbon is extremely strong, and the

intensity of the diffracted beam is very low, thus making the evaluation of the

diffraction data very difficult. All collected in situ diffraction patterns are shown in

figure 5.3.7.

None of the strongest peaks are relative to the NMC phase, while the only

identifiable contribution of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 is the [003] peak, visible at

about 18° on the 2� scale. Additionally, the intensity of the contribution to the

pattern of X10850 was found to diminish upon delithiation and removal of

oxygen, thus making more and more complicated the detection of the active

material phase.

Given these data, it was not possible to successfully perform Rietveld

refinement, thus obtaining meaningful information on the oxygen occupation in

118


the crystal structure. The experiment could not repeated in different conditions

because the beamline was not available until the end of this work. With such a

low intensity, some values could be extracted, but they would be riddled with

extremely large standard deviations, thus making them unreliable and finally not

useful. The experiment, though, could be considered successful by analyzing

some qualitative details. First of all, the optimization work done to prepare the

experiment yielded good results, as shown in figure 5.3.8. By considering the

[003] peak of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 in fact, it can be observed its shifting

according to the delithiation state. As it was presented in chapter 4.3, it was

expected to observe an enlargement of the �c� unit cell parameter up to 4.5V vs.

Li+/Li, followed by a shrinkage of the unit cell by further delithiation. This was

observed, and it is interesting to consider how the [003] peak is a well defined

singlet, thus confirming that the active material was charged uniformly.

Figure 5.3.7: In situ neutron diffraction patterns of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 acquiredduring a full charge to 5.0V vs Li+/Li. While all patterns have been acquired over 6 hours,

the difference in intensity is due to the instability of the neutron beam.

119


Figure 5.3.8: Shift of the [003] peak position of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 along charging ofthe in situ cell. The �c� unit cell parameter hits a maximum at about 4.4V vs. Li+/Li and

then shrinks upon further delithiation.

Another expected behavior was observed by considering the [002] peak of

graphite at about 25° on the 2� scale. In fact, at potentials positive to 4.7V vs.

Li+/Li the perchlorate anion was intercalated in the graphite particles of the

working electrode, and the peak shifted to lower angles, at about 22° as shown in

figure 5.3.9.

120


Figure 5.3.9: Shift of the [002] peak of graphite upon ClO4- intercalation at potentials

positive to 4.7V vs. Li+/Li.

While the in situ experiment did not shed light on the original scientific

question on the origin of oxygen development from Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 at high

potentials, it was possible to assess the suitability of the in situ electrochemical

cell for this type of experiments. Many technical caveats have been found that

will be crucial in future experiments, and the experience gained in this campaign

is vital for the further development of the technique.

121


122

Chapter 6

Conclusions and Outlook

Chapter 6 � Conclusions and Outlook

6.1 General conclusionsThe goal of this doctoral thesis was to study novel positive electrode materials

for lithium-ion batteries by means of newly developed in situ powder diffraction

techniques, using synchrotron x-rays and neutrons, with a strong focus on the

method development.

The work revolved around the study of materials with general formula

Li1+x(Ni1/3Mn1/3Co1/3)1-xO2 (NMC materials). An array of powders were prepared by

combining different lithiation degrees (x=0, x=0.1 and x=0.2) with diverse

calcination temperatures (T=700°C, T=850°C and T=1000°C). Pure phases were

obtained at T=850°C, while those prepared at T=700°C were not completely pure

and those prepared at T=1000°C showed strong sintering of the particles. The

three remaining samples (codenamed X00850, X10850 and X20850) were

chemically analyzed to confirm their stoichiometry: X00850 and X10850 were

obtained with the desired composition, while X20850 was not and therefore not

further considered. The electrochemical properties of the stoichiometric material

(Li(Ni1/3Mn1/3Co1/3)O2) and those of the overlithiated material

(Li1.1(Ni1/3Mn1/3Co1/3)0.9O2) were compared. The overlithiated species showed better

long term cycling stability over the stoichiometric one and additionally an

unusual first charge irreversible capacity. The long term cycling stability was

investigated using in situ synchrotron x-ray diffraction, since it was thought that

it was related to the structural properties of the material. The first charge

irreversible capacity was investigated by means of in situ neutron powder

diffraction, since it was demonstrated with DEMS (Differential Electrochemical

Mass Spectrometry) that during the first charge oxygen was released from the

material.

The central topic in the development of the in situ techniques was the design

and implementation of cells that could combine electrochemical and diffraction

experiments. For the synchrotron x-ray method, an electrochemical cell based on

the �coffee bag� design was developed. These cells are composed by a thin stack

of layers through which the x-ray beam is shone. The diffraction pattern is

collected in transmission mode and thanks to the high intensity of synchrotron

radiation a measurement can be completed in a few seconds. In order to

125


efficiently use the limited beamtime on the largest number of samples possible,

an automatic sample changer was also built. Thanks to this device, many cells

(up to 32) can be cycled and x-ray diffraction measured at the same time,

without needing human intervention. The in situ electrochemical cell for neutron

diffraction is a completely new design that is focused on obtaining clear

diffraction patterns by limiting the amount of foreign phases in the neutron

beam. Given the low interaction between neutrons and atoms, it is needed to

have in the neutron beam as much as possible of the material being measured,

and to limit the presence of other components. This leads to large electrodes that

need to be carefully optimized in order to obtain proper electrochemical charge

and discharge.

Long term cycle stability of Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 was investigated with in situ

synchrotron x-ray diffraction and ex situ x-ray diffraction. One possible

explanation of this property was the structural stability of this material, i.e. the

fact that it would not change from the pristine phase (rhombohedral R3-m, O3

phase) to another setting (possibly tetragonal P3-m1, O1 phase). It was found

that the material does not undergo any phase transition during its first charge

and that the cell volume stays almost constant for the whole delithiation process.

The material was subsequently stressed over long periods of time both

potentiostatically (for 30 days) and in deep charge-discharge cycles (150 cycles).

Neither of the treatments caused the material to change phase from O3 to O1.

The cause of this behavior can be individuated in the preparation of the sample:

during the preliminary characterization, it was found that a certain amount of

lithium ions exchanged site with nickel ions, given their similar ionic radius. Since

the transition from O3 to O1 can be seen as the sliding of the layers composing

the material on each other when the lithium ions present in the interlayer space

are removed (see chapter 4.1), the lack of interchange is due to the presence of

residual nickel ions in the interslab space, locking the structure in place. The

preparation of the material, and in particular the cooling after calcination, is then

crucial for the long term performance of the material.

First cycle irreversible capacity was studied by in situ neutron diffraction, since

it was assessed by means of DEMS that oxygen is evolved from the electrode

material during the first charge at potential positive to 4.5V vs. Li+/Li, but left

126


open the question if this oxygen is lost from the surface of the particles or if it is a

bulk effect. If the latter option is true, then it could have been detected by means

of diffraction. Since neutrons are more sensitive to lighter atoms (such as lithium

and oxygen) than x-rays (for which Li and O are practically undetectable), their

use in diffraction would have allowed to detect a lowering of the oxygen

occupation in the structural sites. During the preliminary optimization of the cell,

though, it was found that in order to obtain a full and homogeneous charge of

Li1.1(Ni1/3Mn1/3Co1/3)0.9O2 up to 5.0V vs. Li+/Li, the working electrode had to be

prepared with a 1:1 wt% ratio between active material and carbonaceous

materials, needed for the electrical conductivity. This lowered the intensity of the

NMC phase in the final diffraction patterns (C is a strong neutron absorber) and

therefore they could not be reliably refined using the Rietveld method. The

obtained values were riddled by large standard deviations that rendered them

not useful. The true origin of the oxygen evolution could not be individuated by in

situ neutron diffraction, but the experiment served its purpose as confirmation of

the good design of the electrochemical cell since the electrode could be

homogeneously charged and diffraction patterns could be accumulated reliably.

From this experience, though, it is clear that the amount of active mass must be

carefully adapted for each experiment, and that an extensive preparation is

needed before every in situ measurement. The testing of the work in progress is

though not easy: while some aspects of the experiments can be approximated by

the use of laboratory x-ray diffraction, others can only be guessed or very briefly

tested, since it is very difficult to obtain beamtime at the neutron source, given

the limited availability of beamtime at such facilities.

6.2 Recommendations for future workThe primary goal of this thesis was the development of two in situ diffraction

methods. In the course of the work the concepts were proven and test

experiments performed. All topics discussed in this thesis can therefore be

further extended, as every new finding opened the door for additional scientific

questions and technical improvements. Collected here are some

recommendations to be considered as starting ideas for further work.

127


6.2.1 NMC materialsNMC materials offer many interesting starting points for further research lines,

from the synthetic, structural and chemical point of view:

� What is the effect of the preparation, and in particular the cooling of the

powders after calcination, on the long term cycle stability? Is the ordered

phase (with low Li-Ni exchange) better than the disordered one in capacity

retention?

� What is the cationic distribution on the surface of the particles? Are

there any particular electrochemical effects due to one particular transition

metal, or do Ni, Mn and Co contribute in the same way to the properties of

the material?

� Is lithium reintercalated up to the core of every particle, or is it stored in

a surface layer upon battery discharge? What are the optimal particle size

and shape to obtain the most efficient and reversible lithium insertion?

� Is the oxygen evolution a surface effect or a bulk one? Can the

contribution of a particular cationic species be identified as decisive to the

oxygen loss from the material, and if yes, can this influence be enhanced,

reduced or completely removed?

6.2.2 Coffee bag cells and in situ synchrotron methodCoffee bag cells are extremely versatile and can therefore be further

developed. Technical issues and other uses that can be looked into are, for

example:

� Is the contact between the electrodes optimal? Even though the

synchrotron beam is extremely focused, are inhomogeneities in the

electrode charging affecting the final outcome? Is the amount of

electrolyte in the cell optimal, or should it be stored differently upon

sealing and vacuuming?

� Adding more electrodes to the cell can improve the control over

electrochemical parameters of the electrodes. What is the best way of

adding a third and/or a fourth electrode without hindering the outcome of

128


diffraction experiments?

� Using coffee bag cells, can other techniques (e.g. electrochemical

impedance spectroscopy) be combined with XRD? Would these

combinations bring novel content to the scientific discussion?

6.2.3 Neutron cell and in situ neutron diffraction methodThe in situ cell for neutron powder diffraction still has some rough edges,

where many improvements are needed:

� As of now, about half of the sample is not in the neutron beam and

therefore just adds overhead to the electrochemical measurement without

really contributing to the experiment. Can the size of the cell be reduced,

to better match the size of the neutron beam? Can the electrode thickness

be reduced to reduce overpotentials, but still contain enough active

material to provide intense enough neutron diffraction patterns?

� Currently, to fill the sample holder cavity, carbon black is used. While

this material is electrically conductive and does not have Bragg peaks,

carbon is a strong neutron absorber, therefore reducing the amount of

neutrons contributing to the diffraction pattern. Can a new filler be

individuated, that is substantially electrochemically inert (if not beneficial)

in the potential window useful for Li-ion investigations, not strongly

absorbing and not contributing with additional Bragg peaks to the in situ

measurement?

� The in situ cell has been used with an aluminum sample holder, which is

adequate for positive potentials but not for the study of negative electrode

materials. Can other materials (e.g. vanadium) be found that would allow

the cell to be used for negative electrode materials investigation?

129


130

Chapter 7

Appendix

Appendix

7.1 SLS ScriptThis script was used during the SLS measurements to control the sample

changer and the diffractometer. It is written in the BASH scripting language, since

the whole SLS infrastructure is based on Linux and BASH is the default shell in

the chosen distribution (Scientific Linux).

#!/bin/bash

# Script to control the XRD measurements at SLS. Its goal is to measure a

set of cells defined by the user over time or over potential steps. This is

the first time I write a BASH shell script, so it probably sucks. But at

least it should get the job done.

# This script is released under the GPL License

#

# Changelog

# 0.01: Initial version, 12.05.06

# 0.02: Added some functions, the while loop and changed some stuff,

13.05.06

# 0.03: Added the correct loop structures to change the cell in a proper

way with the array variable DESIRED_CELLS. Looks like I am starting to learn

BASH! 14.05.06

# 0.1: This version is the first that implements all functions and should

work properly in real world. Will test it later, 14.05.06

# 0.11: Change the awk function to check potential step, 15.05.06

# 0.99b1: It works! First beta issued before checking with the SLS guys. I

am proud of myself! Still have to do the absolute value part though!,

15.05.06

# 0.99b2: Added the absolute value check. Not used a function though,

15.05.06

# 0.99b3: Looks like everything (and I mean *everything*) works. Pride,

15.05.06

# 0.99b4: Worked with David Maden ([email protected]) to write the

move_sample function. Should check the electronics with Hermann now,

16.05.06

# 0.99b5: Completely rewritten the concept of it. Now different criteria can

be read and used for cells measurement. Hope I didn't mess up with variable

names, 18.05.06

# 0.99b6: Looks like everything with the new concept works! Should clean up

the code now, 22.05.06

# 0.99b7: Small changes from b6, mostly just cleaned up the code, 22.05.06

# 0.99b8: Implemented the actual move_sample(), 23.05.06

# 0.99b9: Implemented the actual XRD measuring command, 24.05.06

# 1.00: Script to be used during the campaign in May 2007!

#--------------------------

# First things first, let's define some functions we need later

#--------------------------

move_sample ()

{

posit=$(evaluateSliderPosition $1)

retractSlider

moveMagazine $posit

133

Appendix

insertSlider

echo "Cell $1 is in place at $(date)"

}

function retractSlider () {

#================================================

# Note:Check polarity of X04SA-ES2-BI:USR0 signal

#================================================

# Check if cell is in magazine

# IsOut means "out of beam", therefore "in magazine"

# IsIn means "in beam", therefore "out of magazine"

isOut=$(echo $(ca_get X04SA-ES2-BI:USR0) | cut -d" " -f2 | cut -d. -f1)

isIn=$(echo $(ca_get X04SA-ES2-BI:USR1) | cut -d" " -f2 | cut -d. -f1)

if [ $isOut = 0 ] && [ $isIn = 0 ]; then

printf "\007Invalid plunger state.\n"

echo "SOMETHING'S WRONG!" | mail [email protected]


echo "Something is wrong with the plunger, fix it and then press

ENTER"

read JUNK

fi






ENTER"

read JUNK

fi

if [ $isOut = 1 ]; then

# It is, so just enable the motor motion

ca_put X04SA-ES2-USR:MOT5_able 0

# It is, so do nothing

return

fi

# It's not, so retract magazine and wait for it to get there

ca_put X04SA-ES2-FI4D:SET 0

while [ $isOut != 1 ]; do

usleep 100000

isOut=$(echo $(ca_get X04SA-ES2-BI:USR0) | cut -d" " -f2 | cut -d.

-f1)

done

# Finally enable the motor motion


}

function insertSlider () {

#================================================

# Note:Check polarity of X04SA-ES2-BI:USR1 signal

#================================================

134

Appendix

# Check if cell is in magazine

# IsOut means "out of beam", therefore "in magazine"

# IsIn means "in beam", therefore "out of magazine"

isOut=$(echo $(ca_get X04SA-ES2-BI:USR0) | cut -d" " -f2 | cut -d. -f1)

isIn=$(echo $(ca_get X04SA-ES2-BI:USR1) | cut -d" " -f2 | cut -d. -f1)






ENTER"

read JUNK

fi






ENTER"

read JUNK

fi

# Disable the motor motion


if [ $isIn = 1 ]; then

return

fi

# Cell is in magazine so insert cell into beam and wait for it to get

there.

ca_put X04SA-ES2-FI4D:SET 1

while [ $isIn != 0 ]; do

usleep 100000

isIn=$(echo $(ca_get X04SA-ES2-BI:USR0) | cut -d" " -f2 | cut -d.

-f1)

done

}

function cvtToFlt () {

units=$(expr $1 / 10)

deci=$(expr $1 - 10 '*' $units)

echo $units.$deci

}

function moveMagazine () {

ca_put X04SA-ES2-USR:MOT5 $1

dmov=$(echo $(ca_get X04SA-ES2-USR:MOT5.DMOV) | cut -d" " -f2 | cut -d.

-f1)

while [ $dmov != 1 ]; do

usleep 100000

135

Appendix

dmov=$(echo $(ca_get X04SA-ES2-USR:MOT5.DMOV) | cut -d" " -f2 | cut

-d. -f1)

done

}

function evaluateSliderPosition () {

if [ "$1" -lt 1 ] || [ "$1" -gt 34 ]; then

printf "\007Cell number out of range 1 to 34\n"

exit

fi

# Units are 0.1 mm

slotWidth=120

slotZero=0

posit=$(expr $1 '*' $slotWidth + $slotZero)

posit=$(cvtToFlt $posit)

echo $posit

}

function move_sample () {

posit=$(evaluateSliderPosition $1)

retractSlider

moveMagazine $posit

insertSlider

echo "Cell $1 is in place at $(date)"

}

#================================================================

# Function start_xrd_measurement is a fake in place of the actual XRD

measurement software

#================================================================

function start_xrd_measurement () {

echo "Starting XRD measurement for cell $CURRENT_CELL"

K=1

while [ $K -lt 3 ]; do

echo -n "-"

sleep 1

let "K+=1"

done

echo '>'' 'Your pattern is ready!

}

# Function read_dat_file takes out useful information from the .dat file of

the ASTROL

read_dat_file_for_voltage ()

{

CURRENT_VOLTAGE=`tail -n1 $ASTROL_PATH/$CURRENT_CELL.dat | awk 'BEGIN

{ FS=";" } { print $2 }'`

}

136

Appendix

# Function read_dat_file takes out useful information from the .dat file of

the ASTROL

read_dat_file_for_charge ()

{

CURRENT_CHARGE=`tail -n1 $ASTROL_PATH/$CURRENT_CELL.dat | awk 'BEGIN

{ FS=";" } { print $4 }'`

}

# write_cell_info creates a unique file that includes all information about

a certain cell

write_cell_info ()

{

echo $NICE_FILENAME';'$TIMES_MEASURED';'$CURRENT_CRITERIUM_VALUE';'`date`

>> $FILENAME.cell

}

# Function check_old_voltage does exactly what you expect, that is reads

the voltage at which the previous XRD measurement has been carried out for

a certain cell

check_old_voltage ()

{

OLD_VOLTAGE=`tail -n1 $FILENAME.cell | awk 'BEGIN { FS=";" } { print $3 }'`

}

# Function check_old_charge does exactly what you expect, that is reads the

charge at which the previous XRD measurement has been carried out for a

certain cell

check_old_charge ()

{

OLD_CHARGE=`tail -n1 $FILENAME.cell | awk 'BEGIN { FS=";" } { print $3 }'`

}

# Function check_old_time does exactly what you expect, that is reads the

charge at which the previous XRD measurement has been carried out for a

certain cell

check_old_time ()

{

OLD_TIME=`tail -n1 $FILENAME.cell | awk 'BEGIN { FS=";" } { print $3 }'`

}

rename_data ()

{

mv run_100.ang "$NICE_FILENAME"_1.ang

mv run_100.angc "$NICE_FILENAME"_1.angc

mv run_100.data "$NICE_FILENAME"_1.data

mv run_100.datac "$NICE_FILENAME"_1.datac

mv run_100.corr "$NICE_FILENAME"_1.corr

mv test_100.parab "$NICE_FILENAME"_1.parab



137

Appendix



















































138

Appendix



}

#==========================================================================

# Here starts the actual script.

#==========================================================================

echo Welcome to the SLS Measurements control script

if [ -f cell_list.txt ]; then

BACKUP_DIR=backup_`date | sed 's/ /_/g'`

mkdir $BACKUP_DIR

# mv *.txt $BACKUP_DIR > /dev/null

# mv *.dat $BACKUP_DIR > /dev/null

mv *.cell $BACKUP_DIR > /dev/null

# mv *.xrd $BACKUP_DIR > /dev/null

mv *.ang $BACKUP_DIR > /dev/null

mv *.angc $BACKUP_DIR > /dev/null

mv *.data $BACKUP_DIR > /dev/null

mv *.datac $BACKUP_DIR > /dev/null

mv *.corr $BACKUP_DIR > /dev/null

mv *.parab $BACKUP_DIR > /dev/null

fi

ASTROL_PATH=/sls/X04SA/data/e11036/Astrol_Messungen

echo "The ASTROL path is now set to $ASTROL_PATH, to change it please edit

the ASTROL_PATH variable directly in script!"

COUNTER=1

while true; do

echo "Enter cell number, valid cell numbers are 01-->34"

echo -n "Your choice: "

read CELL_NUMBER

DESIRED_CELLS=( "${DESIRED_CELLS[@]}" "$CELL_NUMBER" )

if [ $CELL_NUMBER -gt 34 ]; then

echo "Cell number invalid, please enter a valid number"

echo -n "Your choice, think twice before hitting ENTER: "

read CELL_NUMBER

fi

echo "Please enter a description for this cell, e.g. the name on the ASTROL

file"

echo -n "Description for cell $CELL_NUMBER: "

read CELL_NAME

while true; do

echo "Please select a criterium to measure cell $CELL_NUMBER"

echo "1. [P]otential"

echo "2. [C]harge"

echo "3. [T]ime"

139

Appendix

echo "4. [N]o criterium"

echo -n "Your choice for cell $CELL_NUMBER: "

read CRITERIUM_FOR_CELL

case $CRITERIUM_FOR_CELL in

"1" | "P" )

echo "Enter potential step in V"

read PSTEP

echo

$CELL_NUMBER';'$CELL_NAME';'$CRITERIUM_FOR_CELL';'$PSTEP';'$(date) >>

cell_list.txt

echo

$CELL_NUMBER';'$CELL_NAME';'$CRITERIUM_FOR_CELL';'$PSTEP';'$(date) >>

$CELL_NUMBER'_'$CELL_NAME.cell

break

;;

"2" | "C" )

echo "Enter charge step in mAh/g"

read CSTEP

echo

$CELL_NUMBER';'$CELL_NAME';'$CRITERIUM_FOR_CELL';'$CSTEP';'$(date) >>

cell_list.txt

echo

$CELL_NUMBER';'$CELL_NAME';'$CRITERIUM_FOR_CELL';'$CSTEP';'$(date) >>


break

;;

"3" | "T" )

echo "Enter time step in seconds"

read TSTEP

echo

$CELL_NUMBER';'$CELL_NAME';'$CRITERIUM_FOR_CELL';'$TSTEP';'$(date) >>

cell_list.txt

echo

$CELL_NUMBER';'$CELL_NAME';'$CRITERIUM_FOR_CELL';'$TSTEP';'$(date) >>


break

;;

"4" | "N" )

echo $CELL_NUMBER';'$CELL_NAME';'$CRITERIUM_FOR_CELL';''No

criterium'';'$(date) >> cell_list.txt

echo $CELL_NUMBER';'$CELL_NAME';'$CRITERIUM_FOR_CELL';''No

criterium'';'$(date) >> $CELL_NUMBER'_'$CELL_NAME.cell

break

;;

* )

echo "Unrecognized criterium, please select one of the

options"

;;

esac

done

echo "You selected criterium $CRITERIUM_FOR_CELL for cell $CELL_NUMBER"

echo "Until now you set up $COUNTER cells"

140

Appendix

echo "Would you like to select another cell? [y/n] "

read ANSWER

if [ $ANSWER == n ]; then

break

fi

let "COUNTER+=1"

done

# Let's put in a safe place cell_list.txt

cp cell_list.txt cell_list_$(date | sed 's/ /_/g').txt

# Here starts the infinite loop

while true; do

# Here starts the "for" loop that checks which cells are meant to be

measured

for CURRENT_CELL in ${DESIRED_CELLS[@]}; do

# Read the measurement criterium for current cell

CRITERIUM=$(grep ^$CURRENT_CELL cell_list.txt | awk 'BEGIN { FS=";" }

{ print $3 }')

# Now I want to check if this is the first time that the cell is being XRD

measured.

CELL_NAME=$(grep ^$CURRENT_CELL cell_list.txt | awk 'BEGIN { FS=";" }

{ print $2 }')

FILENAME=ècho $CURRENT_CELL`_ècho $CELL_NAME`

TIMES_MEASURED=`cat $FILENAME.cell | wc -l`

if [ $TIMES_MEASURED -gt 1 ]; then

# For CURRENT_CELL to enter the measuring loop, it needs to fulfill its

criterium

echo Checking criterium for cell $CURRENT_CELL

case $CRITERIUM in

"1" | "P" )

PSTEP=$(grep ^$CURRENT_CELL cell_list.txt | awk

'BEGIN { FS=";" } { print $4 }')

read_dat_file_for_voltage

check_old_voltage

PDIFF=ècho $CURRENT_VOLTAGE - $OLD_VOLTAGE | bc`

PDIFF=àwk "BEGIN {if ($PDIFF >= 0) print $PDIFF ;

else print (0 - $PDIFF) }"`

CHECK=àwk "BEGIN { if ($PDIFF >= $PSTEP) print 0 ;

else print 1 }"`

case $CHECK in

"0" )

141

Appendix

CELLS_TO_BE_MEASURED=( "$

{CELLS_TO_BE_MEASURED[@]}" "$CURRENT_CELL" )

;;

"1" )

usleep 100

;;

esac

;;

"2" | "C" )

CSTEP=$(grep ^$CURRENT_CELL cell_list.txt | awk

'BEGIN { FS=";" } { print $4 }')

read_dat_file_for_charge

check_old_charge

CDIFF=ècho $CURRENT_CHARGE - $OLD_CHARGE | bc`

CDIFF=àwk "BEGIN {if ($CDIFF >= 0) print $CDIFF ;

else print (0 - $CDIFF) }"`

CHECK=àwk "BEGIN { if ($CDIFF >= $CSTEP) print 0 ;

else print 1 }"`

case $CHECK in

"0" )



;;

"1" )

usleep 100

;;

esac

;;

"3" | "T" )

TSTEP=$(grep ^$CURRENT_CELL cell_list.txt | awk

'BEGIN { FS=";" } { print $4 }')

CURRENT_TIME=`date +%s`

check_old_time

TDIFF=$(( $CURRENT_TIME - $OLD_TIME ))

CHECK=àwk "BEGIN { if ($TDIFF >= $TSTEP) print 0 ;

else print 1 }"`

case $CHECK in

"0" )



;;

"1" )

usleep 100

;;

esac

;;

"4" | "N" )

CELLS_TO_BE_MEASURED=( "${CELLS_TO_BE_MEASURED[@]}"

"$CURRENT_CELL" )

;;

esac

else

# If it's the first time $CURRENT_CELL is being measured, we add it to

CELLS_TO_BE_MEASURED without further ado

142

Appendix

case $CRITERIUM in

"1" | "P" )


"$CURRENT_CELL" )

;;

"2" | "C" )


"$CURRENT_CELL" )

;;

"3" | "T" )


"$CURRENT_CELL" )

;;

"4" | "N" )


"$CURRENT_CELL" )

;;

esac

fi

done

#================================================

# "for" loop that does the actual measurements

#================================================

# We have the CELLS_TO_BE_MEASURED array full of numbers. We get rid of

those by measuring the cells in it.

for CURRENT_CELL in ${CELLS_TO_BE_MEASURED[@]}; do

# Finally we move the sample and put it in front of the beam

# Let's move the selected cell in the beam while we do some other stuff. It

takes time.

move_sample $CURRENT_CELL

# Now I want to check if the selected cell has an entry in the ASTROL. If

not, tell the user to make it! When this step is over, the .cell file is

created

if [ -f $ASTROL_PATH/$CURRENT_CELL.dat ]; then

echo "$CURRENT_CELL.dat file found, ready to start the XRD measurement"

else

echo "$CURRENT_CELL.dat file not found. Please start the electrochemical

measurement on the ASTROL box for cell '#'$CURRENT_CELL and press ENTER

when ready"

read JUNK

fi

# Finally we can start the XRD using the existing software. If it accepts

arguments, I should create a variable with a nice filename.

CELL_NAME=$(grep ^$CURRENT_CELL cell_list.txt | awk 'BEGIN { FS=";" }

{ print $2 }')

143

Appendix

FILENAME=ècho $CURRENT_CELL`_ècho $CELL_NAME`

TIMES_MEASURED=`cat $FILENAME.cell | wc -l`

NICE_FILENAME=ècho $FILENAME`_ècho $TIMES_MEASURED`

CRITERIUM=$(grep ^$CURRENT_CELL cell_list.txt | awk 'BEGIN { FS=";" }

{ print $3 }')

echo "Measuring $NICE_FILENAME"

case $CRITERIUM in

"1" | "P" )


CURRENT_CRITERIUM_VALUE=$CURRENT_VOLTAGE

unset CURRENT_VOLTAGE

;;

"2" | "C" )

read_dat_file_for_charge

CURRENT_CRITERIUM_VALUE=$CURRENT_CHARGE

unset CURRENT_CHARGE

;;

"3" | "T" )

CURRENT_CRITERIUM_VALUE=`date +%s`

;;

"4" | "N" )


CURRENT_CRITERIUM_VALUE=$CURRENT_VOLTAGE

unset CURRENT_VOLTAGE

;;

esac

write_cell_info

# Here we do the actual XRD measurement

startrundetektor2pos.awk directory=patrick_mai07/batteries startrun=100

# This function changes all filenames.

sleep 5

rename_data

# Ok, the measurement is over. Let the user know it, or he'll get impatient.

echo Cell '#'$CURRENT_CELL has been measured, starting measurement of the

next one

# It is time to restart the script for the next measurement, the while loop

takes care of that. We ask the user to kill the script if something has got

to be changed.

done # This closes the for loop

unset CELLS_TO_BE_MEASURED

echo -n "You have 2 seconds to pause the script execution. Type P and then

ENTER to pause: "

read -t 2 PAUSE

144

Appendix

case $PAUSE in

"p" | "P" )

echo "Press <ENTER> to resume script execution"

read JUNK

continue

;;

* )

continue

;;

esac

done # This closes the while loop

145

Appendix

146

Bibliography

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152

Curriculum Vitae

Curriculum Vitae

Curriculum Vitae

Personal information

Surname(s) / Firstname(s)

Rosciano, Fabio

Address(es) Zentralstrasse 114, CH-5430 Wettingen

Telephone(s) +41919949635 Mobile: +41765405457

E-mail [email protected]

Nationality Italian / Swiss

Date of birth 27.05.1979

Gender M

Work experience

Dates 01.06.05 � 30.06.08

Occupation or positionheld

Junior Researcher

Main activities andresponsibilities

� Development of the necessary means toefficiently measure diffraction patterns ofelectrodes in Li-Ion batteries systems.

� Design and optimization of electrochemical cells� Development of software solutions� Implementation of innovative methods at

synchrotron sources and neutron facilities� Data analysis and explanation of the ion insertion

mechanisms in matrix materials.

Name and address ofemployer

Paul Scherrer Institut, CH-5232 Villigen

Type of business orsector

R&D / Education

Dates 2002 - 2003

Occupation or positionheld

Teaching assistant

CLV

Curriculum Vitae

Main activities andresponsibilities

� Responsibility for the laboratory of organicchemistry

� Preparation of the laboratory for lessons(chemicals, materials, equipment and safety).

� Tutoring of the students through help inconducting experiments (examples andexplanation of theoretical principles).

Name and address ofemployer

Università Degli Studi Di Milano Bicocca � Milan, Italy

Type of business orsector

Education

Education andtraining

Dates 01.06.05 � 04.06.08

Title of qualificationawarded

PhD Student

Principalsubjects/occupational

skills covered

Enrolled in the Chemistry department with a thesisentitled:

�In Situ Synchrotron and Neutron Diffraction BasedMethods for the Characterization of Cathodic Materials forLithium-Ion Batteries�

Name and type oforganization providingeducation and training

Swiss Federal Institute for Technology (ETH) � Zürich,Switzerland

Level in national orinternationalclassification

Technical University

Dates 1998 - 11.03.05

Title of qualificationawarded

MSc

Principalsubjects/occupational

skills covered

Enrolled in the Materials Science department. Master thesis in electrochemistry:

�Synthesis and characterization of olivine typephosphates as cathodic materials for Li-ion Batteries�

Name and type oforganization providingeducation and training

Università Degli Studi Di Milano Bicocca � Milan, Italy

CLVI

Curriculum Vitae

Level in national orinternationalclassification

University

Personal skills andcompetences

Mother tongue(s) Italian

Other language(s) English, German, French, Spanish

Self-assessment Understanding Speaking

European level (*) Listening

Reading Spokeninteraction

Spokenproduction

English C2 C2 C2 C2

German B2 B2 B2 B2

French B2 B2 B2 B2

Spanish B2 A2 B1 A2

(*) Common European Framework of Reference forLanguages

Organizational skillsand competences

Complete organization of the teaching material(chemicals, scripts, instruments) for the aforementionedtutoring of Organic chemistry students

Technical skills andcompetences

Basic security knowledge for chemicals managementFamiliarity with common chemistry laboratory equipment

Computer skills andcompetences

Proficiency in all major operating systems (MicrosoftWindows, GNU/Linux, Apple MacOSX)Proficiency in all major office suites (Microsoft Office,Openoffice.org)Basic programming skills in Fortran77 and BASH

Driving license Swiss license �B�

CLVII

Curriculum Vitae

Additionalinformation

For references please contact:PD Dr Petr Novák, Paul Scherrer Institut,[email protected]. Claudio Maria Mari, University of MilanoBicocca, [email protected]

List of publications 1. R. Ruffo, C. M. Mari, F. Morazzoni, F. Rosciano and R.Scotti, Electrical and electrochemical behavior of severalLiFexCo1 x� PO4 solid solutions as cathode materials forlithium ion batteries, Ionics (2007), 13(5), 287-291

2. F. Rosciano, M. Holzapfel, H. Kaiser, W. Scheifele, P.Ruch, M. Hahn, R. Kötz and P. Novák, A multi-sampleautomatic system for in situ electrochemical X-raydiffraction synchrotron measurements, J. SynchrotronRad. (2007), 14, 487-491

3. P. Ruch , M. Hahn, F. Rosciano, M. Holzapfel, H. Kaiser,W. Scheifele, B. Schmitt, P. Novák, R. Kötz and A. Wokaun,In situ X-ray diffraction of the intercalation of (C2H5)4N+

and BF4� into graphite from acetonitrile and propylene

carbonate based supercapacitor electrolytes,Electrochimica Acta (2007), 53(3), 1074-1082

4. F. La Mantia, F. Rosciano, N. Tran and P. Novák, Directevidence of oxygen evolution from Li1+x(Ni1/3Mn1/3Co1/3)1-

xO2 at high potentials, J. Appl. Electrochem. (2008), 38,893-8965. F. Rosciano, M. Holzapfel, W. Scheifele and P. Novák, Anovel electrochemical cell for in situ neutron diffractionstudies of electrode materials for lithium-ion batteries, J.Appl. Cryst. (2008), in press6. F. Rosciano, F. La Mantia, N. Tran and P. Novák,Electrochemical stress at high potential to investigatephase transitions in Li1.1(Ni1/3Mn1/3Co1/3)0.9O2, J.Electrochem. Soc. (2008), submitted

CLVIII

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