Supporting Information

Dendrite- and Oxygen-Proof Protective Layer for Lithium Metal in Lithium-Oxygen Batteries

Won-Jin Kwak,a Jiwon Park,b Trung Thien Nguyen,a Hun Kim,a Hye Ryung Byon,b Minchul Jangc and Yang-Kook Sun*a

a.Department of Energy Engineering, Hanyang University, Seoul 04763, Republic of Korea.

b.Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), and KAIST Institute for

NanoCentury, Daejeon 34141, Republic of Korea

c.Batteries R&D, LG Chem Ltd., Daejeon 34122, Republic of Korea

*Correspondence author: yksun@hanyang.ac.kr

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2019

Supplementary Figures

Fig. S1 Scanning electron microscopy (SEM) images of (A) Li metal, (B–D) NCL-coated Li metal,

and (E, F) Nafion-coated Li metal without Al2O3. Inset photographs in Fig. S1 (A, B, and D) are

representative of Li metal, NCL-coated Li metal, and Nafion-coated Li metal, respectively.

200 μm

20 μm

200 μm

2 μm

A B

C D

200 μm 20 μm

E F

Fig. S2 SEM image of a composite protective layer (CPL, Al2O3-PVdF mixture)-coated Li metal.

There are no morphological differences between NCL and CPL.

20 μm

Fig. S3 Gas evolution profiles during charge of Li-O2 cells with (A, C) CPL and (B, D) NCL for Li-

metal protection with 1 M LiTFSI in TEGDME. A TEMPO (0.3 M) redox mediator was

additionally included in (C) and (D). Before charging process, discharge was performed at a

fixed capacity of 1000 mAh g–1. The blue and red dotted lines, and grey dashed lines denote

the O2, CO2, and H2 evolution profiles, respectively. The horizontal dashed line refers to an e–

/O2 gas evolution with the rate of 2.

0 200 400 600 800 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

Specific capacity (mAh g-1)

e-/O

2 = 2.00

NCL coated Li metal + TEMPO

O2

CO2

H2

Gas e

vo

luti

on

(mm

ol A

-1 m

in-1)

0 200 400 600 800 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

Specific capacity (mAh g-1)

e-/O

2 = 2.00

CPL coated Li metal

O2

CO2

H2

Gas e

vo

luti

on

(mm

ol A

-1 m

in-1)

A B

0 200 400 600 800 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

Specific capacity (mAh g-1)

e-/O

2 = 2.00

CPL coated Li metal + TEMPO

O2

CO2

H2

Gas e

vo

luti

on

(mm

ol A

-1 m

in-1)

C D

0 200 400 600 800 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

Specific capacity (mAh g-1)

e-/O

2 = 2.00

NCL coated Li metal

O2

CO2

H2

(mm

ol A

-1 m

in-1)

Gas e

vo

luti

on

Fig. S4 The OEMS gas analysis of Li–O2 cell where a naked Li metal was used during discharge

with a fixed capacity of 1000 mAh g–1. This Li anode was replaced with a CPL-coated Li metal

in an Ar-filled glove box after discharge, and charge process was continuously carried out. (A)

Cumulative evolution of O2 gas and (B) gas evolution profiles during charge. The blue, red and

grey dotted lines in (B) denote the O2, CO2, and H2 evolution profiles, respectively. The dashed

line in (A) indicates the ideal amount of O2 gas. The horizontal dashed line in (B) refers to an

e–/O2 gas evolution with the rate of 2.

0 200 400 600 800 10000.0

0.1

0.2

0.3

0.4

0.5

0.6

Specific capacity (mAh g-1)

e-/O

2 = 2.00

Pre-discharge with Li metal and

recharge with CPL coated Li metal

O2

CO2

H2

Gas

ev

olu

tio

n

(mm

ol

A-1 m

in-1)

0 200 400 600 800 10000.0

5.0

10.0

15.0

20.0

O2 (5.29 μmol)

Specific capacity (mAh g-1)

Ideal line

CPL coated Li metal (for recharge)

after pre-discharge using Li metal

n

(μ

mo

l O

2)

A B

Fig. S5 UV-Vis spectra of discharged electrodes (0.1 mA – 20 h) immersed in a Ti4+ solution for

titration of Li2O2. The electrodes were made of Li metal, NCL-coated Li metal, or CPL (PVdF-

based)-coated Li metal.

380 420 460 500 540 580 620 660 700

0.0

0.2

0.4

0.6

Cathode before discharge (absence of Li2O

2)

Amount of Li2O

2 on discharged cathode

Li metal

NCL coated Li metal

CPL (PVdF base) coated Li metal

Ab

so

rba

nc

e (

a.u

.)

Wavelength (nm)

Fig. S6 ATR-FTIR spectra of the protective layers in Li-O2 batteries before and after cycle tests

to check the stability of (A) PVdF-based CPL-coated Li metal, and (B) NCL-coated Li metal in

Li-O2 batteries. All the data were used without fitting to exhibit changes in the peaks clearly.

1600 1400 1200 1000 800

PVdF (in CPL) on Li metal

before test

after 1st cycle

Inte

ns

ity (

a.u

.)

Wavenumbers (cm-1)

A

*** ** * * *

*

* PVDF

1600 1400 1200 1000 800

Nafion (in NCL) on Li metal

before test

after 1st cycle

Inte

ns

ity (

a.u

.)

Wavenumbers (cm-1)

B* Nafion

*

* *

**

*

Fig. S7 (A) SEM analysis of PEO-based CPL (Al2O3-PEO mixture)-coated Li metal. This layer has

the same morphology as NCL and PVdF-based CPL. (B) UV-Vis spectra of discharged electrodes

(0.1 mA – 20 h) immersed in a Ti4+ solution for titration of Li2O2. The electrodes were made of

Li metal, NCL-coated Li metal, or CPL (PEO-based)-coated Li metal.

(C) C 1s XPS spectra and (D) ATR-FTIR spectra of the protective layers in Li-O2 batteries before

and after cycle tests to check the stability of PEO-based CPL-coated Li metal in Li-O2 batteries.

All the data were used without fitting to exhibit changes in the peaks clearly.

20 μm

1600 1400 1200 1000 800

PEO (in CPL) on Li metal

before test

after 1st cycleIn

ten

sit

y (

a.u

.)

Wavenumbers (cm-1)

D

*

* PEO

**** * *

***

296 294 292 290 288 286 284 282

PEO (in CPL) on Li metal

before test

after 1st cycle

Inte

ns

ity (

a.u

.)

Binding Energy (eV)

C 1sC

C-O / C-C

380 420 460 500 540 580 620 660 700

0.0

0.2

0.4

0.6

Ab

so

rba

nc

e (

a.u

.)

Wavelength (nm)

Amount of Li2O

2 on discharged cathode

Li metal

NCL coated Li metal

CPL (PEO base) coated Li metal

Cathode before discharge (absence of Li2O

2)

BA

Fig. S8 Voltage profiles during galvanostatic cycling test of a Li-O2 pouch cell using (A) Li metal

and (B) Nafion-coated Li metal as anodes at the same conditions as the pouch cell in Fig. 4b.

Poorer cycling performance of Li-O2 pouch cell using Nafion-coated Li metal (Fig. S8B) than

that of Li metal without coating material (Fig. S8A) results from mechanically unstable

protective layer (NL without Al2O3) which causes deterioration of the cell due to abnormal

accumulation of decomposed byproduct on the metal surface.

0 400 800 1200 1600 20001.0

2.0

3.0

4.0

5.0

1st cyc 2nd cyc 3rd cyc

5th cyc 7th cyc 8th cyc

Vo

lta

ge

(V

)

Specific capacity (mAh g-1)

Nafion coated Li metal

0 400 800 1200 1600 20001.0

2.0

3.0

4.0

5.0

1st cyc 2nd cyc 3rd cyc

5th cyc 7th cyc 10th cyc

15th cyc 17th cyc

Vo

lta

ge

(V

)

Specific capacity (mAh g-1)

Li metal without protective layerA B

Fig. S9 SEM images of (A) Nafion-coated Li metal without Al2O3 and (B) CPL (PVdF-based)-

coated Li metal after the cycling test of Li-O2 cells.

A B

400 μm 400 μm