Cycle performance of Si-based Thin Film Anodes for Li-ion Batteries

Thin Film & Battery Materials Lab.National Research Lab.

Kangwon Nat’l Univ.

Cycle performance of Si-based Thin Film Anodes for Li-ion BatteriesCycle performance of Si-based Thin Film Anodes for Li-ion Batteries

Kwan-Soo Lee, Jae-Bum Kim, Bong-Suk Jun and Sung-Man Lee

Kangwon Nat’l Univ., Chunchon, Korea



Negative Electrodes for Thin Film MicrobatteryNegative Electrodes for Thin Film Microbattery

1983 1992 1993 1995 1998 2002

Negative electrode

SiTONSn, SiSnO, SnO2Sn3N4, Zn3N2

Year

Li SilicideSn Alloy

Low melting point (181 )℃Very strong reactivity with moisture

Limits application area

Li metal Oxide or NitrideFormation of Li2O or Li3N

Irreversible capacity loss at the 1st cycle

High capacity (~4000mAh/g)

Little irreversible capacityVery large volume expansion during cycling

Si : Candidate material

Little reactivity with air (respectively Li)



ObjectivesObjectives

Adhesion effect between substrate and deposited thin film on the Adhesion effect between substrate and deposited thin film on the cycle properties of Si-based thin-film electrodecycle properties of Si-based thin-film electrode

Deposition condition effect

The variation of thin film deposition condition

• Without negative d.c. bias • With negative d.c. bias

Substrate effect

Morphology

• Chemically-etched Cu foil• Flat-Cu foil

Adhesion layer effect

Insertion of adhesion layer

• Zr-deposited Cu foil• Bare-Cu foil



Experimental processExperimental process

Thin Film Deposition• Substrate : Ni, Cu foil ( 12 mm dia. )• Substrate rotation : 13 ~ 14 rpm. • Targets : Si ( 2 in. )• Deposition Conditions : - Sputtering method - Base pressure : 2 10-6 Torr - Working pressure : 5 10-3 Torr ( Ar ) - Negative DC bias ( - 100 V )

Substrate etching

Characterization

• Substrate : Cu foil ( 12 mm dia. )• Etchant : A Solution ( FeCl3 + HCl + H2O ), B Solution ( HNO3 + H2O )

• Structure analysis - XRD ( X-ray diffraction )• Surface roughness analysis - AFM ( Atomic Force Microscope )• Surface morphology observation - FESEM ( Field-Emission Scanning Electron Mocroscopy ) - SEM ( Scanning Electron Mocroscopy )• Electrochemical analysis - CR2016 Coin Cells - Counter Electrode : Li metal - Electrolyte : 1 M LiPF6 dissolved in EC/DEC(1:1 Vol)



(a) No Bias(b) Bias applied (-100 V) Substrate : Si-wafer

Bias effect : MorphologyBias effect : Morphology

Img. RMS : 0.188 nm

Img. RMS : 0.860 nm

FESEM ImagesFESEM Images AFM ImagesAFM Images

(a) (b)

(a) (b)

(a)

(b)



Bias effect : Electrochemical propertiesBias effect : Electrochemical properties

The 1The 1stst and 2 and 2ndnd cycle cycleDischarge/charge curvesDischarge/charge curves

(a)

(b)

After 1After 1stst cycle discharge/charge cycle discharge/charge

EDAX mappingEDAX mapping

(a) No Bias (b) Bias applied (-100 V)

0 100 200 300 400 500 6000.0

0.5

1.0

1.5

2.0

2.50.0

0.5

1.0

1.5

2.0

2.5

(b)

Vo

ltag

e (V

vs.

Li/L

i+ )

Capacity (Ah)

1st Cycle

2nd Cycle

(a)



After 10 cyclesAfter 10 cycles

Bias effect : Surface morphologyBias effect : Surface morphology

0 2 4 6 8 100

200

400

600 Bias applied (- 100 V) No Bias

Cap

acit

y (

Ah

)

Cycle No.

Cycle performanceCycle performance

(a) (b)

EDAX mappingEDAX mapping

(a) No Bias (b) Bias applied (-100 V)



A Solution : FeCl3 + HCl + H2O B Solution : HNO3 + H2O

Substrate morphology effect : Surface MorphologySubstrate morphology effect : Surface Morphology

FESEM ImagesFESEM Images(Substrate)(Substrate)

(a) Cu foil (raw) (b) Cu foil (etched with A solution)(c) Cu foil (etched with B solution )

(a) (b) (c)



0 2 4 6 8 10 12 14 16 18 200

200

400

600

800

(a) (b) (c)

Cap

acit

y (

Ah

)

Cycle No.

Substrate morphology effect : Electrochemical PropertiesSubstrate morphology effect : Electrochemical Properties

0 100 200 300 400 500 6000.0

0.5

1.0

1.5

2.0

2.50.0

0.5

1.0

1.5

2.0

2.50.0

0.5

1.0

1.5

2.0

2.5

(a)

Capacity (Ah)

(b)

Vo

ltag

e (V

vs.

Li/L

i+ )

1st Cycle

2nd Cycle(c)

The 1The 1stst and 2 and 2ndnd cycle cycleDischarge/charge curvesDischarge/charge curves Cycle performanceCycle performance




Substrate morphology effect : Surface MorphologySubstrate morphology effect : Surface Morphology

FESEM ImagesFESEM Images


(a) (b) (c)




Adhesion layer effect : Electrochemical PropertiesAdhesion layer effect : Electrochemical Properties

0 2 4 6 8 10 12 14 16 18 200

200

400

600

800 (a) (b)

Cap

acit

y (

Ah

)

Cycle No.

0 2 4 6 8 10 12 14 16 18 200

200

400

600

800 (a) (b)

Cap

acit

y (

Ah

)

Cycle No.

0 2 4 6 8 10 12 14 16 18 200

200

400

600

800 (a) (b)

Cap

acit

y (

Ah

)

Cycle No.

Cycle performanceCycle performance

Cu foil (raw) Cu foil (etched with A solution) Cu foil (etched with B solution )

(a) Cu / Zr / Si(b) Cu / Si



Adhesion layer effect : Surface MorphologyAdhesion layer effect : Surface Morphology

FESEM ImagesFESEM Images


(a)

(b)

(a)

(b)

(a)

(b)

(a) Cu / Zr / Si(b) Cu / Si

Cu foil (raw) Cu foil (etched with A solution) Cu foil (etched with B solution )



Adhesion layer effect : Cross-sectional imagesAdhesion layer effect : Cross-sectional images

EDAX mappingEDAX mappingSEM ImagesSEM ImagesAfter 18 cyclesAfter 18 cycles After 18 cyclesAfter 18 cycles

Reverse &Schematic diagram



ConclusionsConclusions

The cyclability of Si thin film anode can be improved by applying negative d.c bias and adhesion property between substrate and deposited thin film anode is enhanced.

The variation of substrate morphology has an effect on the cyclability of Si thin film anodes.

For Si thin film anodes, electrochemical cycling performance is improved with the addition of Zr adhesion layer.

Cycle performance of Si-based Thin Film Anodes for Li-ion Batteries

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