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
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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)
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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)
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
(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)
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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)
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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)
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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)
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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
(a) Cu foil (raw) (b) Cu foil (etched with A solution)(c) Cu foil (etched with B solution )
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
Substrate morphology effect : Surface MorphologySubstrate morphology effect : Surface Morphology
FESEM ImagesFESEM Images
After 18 cyclesAfter 18 cycles
(a) (b) (c)
(a) Cu foil (raw) (b) Cu foil (etched with A solution)(c) Cu foil (etched with B solution )
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
Adhesion layer effect : Surface MorphologyAdhesion layer effect : Surface Morphology
FESEM ImagesFESEM Images
After 18 cyclesAfter 18 cycles
(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 )
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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
Thin Film & Battery Materials Lab.National Research Lab.
Kangwon Nat’l Univ.
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.