1. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Cycle 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

2. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Negative Electrodes for Thin Film Microbattery 1983199219931995 1998 2002 Negative electrode SiTON Sn, Si SnO, SnO 2 Sn 3 N 4, Zn 3 N 2 Year Li Silicide Sn Alloy Low melting point (181 ℃ ) Very strong reactivity with moisture Limits application area Li metal Oxide or Nitride Formation of Li 2 O or Li 3 N Irreversible capacity loss at the 1st cycle High capacity (~4000mAh/g) Little irreversible capacity Very large volume expansion during cycling Si : Candidate material Little reactivity with air (respectively Li)

3. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Objectives Adhesion effect between substrate and deposited thin film on the cycle 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

4. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Experimental 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 ( FeCl 3 + HCl + H 2 O ), B Solution ( HNO 3 + H 2 O ) 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)

5. 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 : Morphology Img. RMS : 0.188 nm Img. RMS : 0.860 nm FESEM Images AFM Images (a) (b) (a) (b) (a) (b)

6. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Bias effect : Electrochemical properties The 1 st and 2 nd cycle Discharge/charge curves (a) (b) After 1 st cycle discharge/charge EDAX mapping (a) No Bias (b) Bias applied (-100 V)

7. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. After 10 cycles Bias effect : Surface morphology Cycle performance (a)(b) EDAX mapping (a) No Bias (b) Bias applied (-100 V)

8. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. A Solution : FeCl 3 + HCl + H 2 O B Solution : HNO 3 + H 2 O Substrate morphology effect : Surface Morphology FESEM Images (Substrate) (a) Cu foil (raw) (b) Cu foil (etched with A solution) (c) Cu foil (etched with B solution ) (a)(b)(c)

9. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Substrate morphology effect : Electrochemical Properties The 1 st and 2 nd cycle Discharge/charge curves Cycle performance (a) Cu foil (raw) (b) Cu foil (etched with A solution) (c) Cu foil (etched with B solution )

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

11. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Adhesion layer effect : Electrochemical Properties Cycle performance Cu foil (raw)Cu foil (etched with A solution)Cu foil (etched with B solution ) (a) Cu / Zr / Si (b) Cu / Si

12. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Adhesion layer effect : Surface Morphology FESEM Images After 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 )

13. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Adhesion layer effect : Cross-sectional images EDAX mapping SEM Images After 18 cycles Reverse & Schematic diagram

14. Thin Film & Battery Materials Lab. National Research Lab. Kangwon Nat’l Univ. Conclusions 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.