박막및 전지재료연구실 강원대학교 1 Cyclic voltammetry for LiCoO 2 deposited on Fsi (Flat-Si) and ESi (Etched-Si) Scan rate = 0.1 mV/sec ESi FSi Cyclic voltammetry with slow scan rate: Basic electrochemical characterization Li oxidation-reduction peak of LiCoO 2 deposited on the (a) FSi: and V and (b) ESi: and V, respectively The symmetric current peaks about potential axis  High reversible reaction of LiCoO 2  No differences in basic electrochemical characteristics between two electrodes

박막및 전지재료연구실 강원대학교 2 Cyclic voltammetry with variation of scan-rate  Higher anodic and lower cathodic peak potential for ESi than FSi with increase in scan rates.  Larger ionic and electronic resistance for film on ESi substrate than on FSi substrate Continued Scan rate: 0.1 ~ 2 mV/sec

박막및 전지재료연구실 강원대학교 3 Rate-capability for LiCoO 2 deposited on FSi and ESi Current density range: 10  A/cm 2 ~ 1 mA/cm 2  FSi: Even at 1 mA/cm 2, 93% capacity retention  ESi: At 1 mA/cm 2, 89% capacity retention  Low capacity for ESi at 10  A/cm 2 (about 70% of FSi)  Better rate-capability for FSi than ESi Microstructure effect attributed to the difference in substrate roughness

박막및 전지재료연구실 강원대학교 4 SEM photos for LiCoO 2 deposited on FSi and ESi FSi ESi 1  m Deposition time for both films = 8 hrs  FSi: Uniform and very small (about 80 ~ 100 nm) crystallites Larger surface area than ESi  ESi: Non-uniform and mixed size of crystallites Reduced surface area than FSi  Large surface area lessens the effective current densities High rate-capability

박막및 전지재료연구실 강원대학교 5 Electrical resistance of current collector Sample Length  With (cm)Resistance (  ) Pt on the FSi substrate 2.5  Pt on the ESi substrate 2.5  Pt on the alumina substrate 2.5   Non-uniform thickness of current collector on the alumina substrate 1000 ~ 3000 Å  Another contribution to the low rate-capability at high current density discharge

박막및 전지재료연구실 강원대학교 6 Cyclic voltammetry for LiCoO 2 deposited on alumina substrate Alumina FSi  No differences in basic electrochemical characteristics between two electrodes  The largest peak potential divergence for alumina substrate

박막및 전지재료연구실 강원대학교 7 Rate-capability for LiCoO 2 deposited on FSi and ESi  Alumina: At 1 mA/cm 2, 80% capacity retention The worst rate-capability among three substrates  Similar capacity at 10  A/cm 2 to the FSi

박막및 전지재료연구실 강원대학교 8 SEM photos for LiCoO 2 deposited on alumina substrate 4 hrs8 hrs 1  m  The largest particle size among three substrates  Intra-particle micro-cracks observed. Originated in the thermo-mechanical property of alumina

박막및 전지재료연구실 강원대학교 9 Cyclability of LiCoO 2 deposited on the FSi and alumina substrate Current density = 50  A/cm 2  Good cyclability of LiCoO 2 deposited on both substrate at low current density (50  A/cm 2 )

박막및 전지재료연구실 강원대학교 10 Rate-capability of LiCoO 2 as a function of film thickness Charge-discharge variation: 10  A/cm 2 ~ 1 mA/cm 2 Film-thickness variation: 1500 ~ 6000 Å  Diffusion length for Li ion  film thickness Film thickness   Rate-capability  ??? however,  Film thickness   Rate-capability  !!! Diffusion kinetics as a function of film thickness

박막및 전지재료연구실 강원대학교 11 Electrochemical Impedance Spectroscopy (EIS) for LiCoO 2 deposited on the Fsi substrate FSi 4 hrsFSi 8 hrsFSi 12 hrs

박막및 전지재료연구실 강원대학교 12 Li-ion diffusion coefficient measured by EIS and CV  By EIS method = angular velocity at the transition point from semi-infinite to finite diffusion h = film thickness  By CV method  Similar trend “ by EIS at 3.9 V ” and “ by CV ”  Diffusion coefficient increases with equilibrium voltage and film thickness  Deintercalation of Li  generates the intercalation-induced stress

박막및 전지재료연구실 강원대학교 13 Stress measurement by optical cantilever method  Negative sign on deflection angle: compressive stress  Increase in charge current density  decrease in deflection angle  Decrease in expansion depth by steep concentration gradient

박막및 전지재료연구실 강원대학교 14 Calculated tress field assumed linear distribution Stress induced by charge reaction Stress field divided by film thickness  Stress calculation: by Stoney equation   Amount of stress induced by charge reaction  Increase with film thickness, however  Decrease with film thickness for stress field induced by charge reaction Diffusion coefficient decrease with film thickness

박막및 전지재료연구실 강원대학교 15 Charge-discharge properties for anode and full-cell Current density = 50  A/cm 2 Thickness = 350 Å Amorphous-Si anode Full-cell

박막및 전지재료연구실 강원대학교 16 Operation of digital clock by all-solid-state Li microbattery  The first cell in the world using an amorphous-Si anode  Back-up for about 7 hrs upon 1 charge  Showing the possibility of practical utilization of microbattery All-Solid-State Li Secondary Microbattery