Cyclic voltammetry for LiCoO2 deposited on Fsi (Flat-Si) and ESi (Etched-Si)

1
Cyclic voltammetry for LiCoO2 deposited on Fsi
(Flat-Si) and ESi (Etched-Si)
Cyclic voltammetry with slow scan rate Basic
electrochemical characterization

• Li oxidation-reduction peak of LiCoO2 deposited
  on the
• FSi 3.917 and 3.9005 V and
• ESi 3.916 and 3.9002 V, respectively

The symmetric current peaks about potential axis

• High reversible reaction of LiCoO2
• No differences in basic electrochemical
  characteristics between two electrodes

2
Continued
Cyclic voltammetry with variation of scan-rate
Scan rate 0.1 2 mV/sec

• 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

3
Rate-capability for LiCoO2 deposited on FSi and
ESi
Current density range 10 ?A/cm2 1 mA/cm2
4
SEM photos for LiCoO2 deposited on FSi and ESi
Deposition time for both films 8 hrs
5
Electrical resistance of current collector
Sample Length ? With (cm) Resistance (?)
Pt on the FSi substrate 2.5 ? 1 2.4
Pt on the ESi substrate 2.5 ? 1 4.1
Pt on the alumina substrate 2.5 ? 1 4.3
6
Cyclic voltammetry for LiCoO2 deposited on
alumina substrate

• No differences in basic electrochemical
  characteristics between two electrodes
• The largest peak potential divergence for alumina
  substrate

7
Rate-capability for LiCoO2 deposited on FSi and
ESi

• Alumina
• At 1 mA/cm2, 80 capacity retention
• The worst rate-capability among three substrates
• Similar capacity at 10 ?A/cm2 to the FSi

8
SEM photos for LiCoO2 deposited on alumina
substrate
9
Cyclability of LiCoO2 deposited on the FSi and
alumina substrate
Current density 50 ?A/cm2

• Good cyclability of LiCoO2 deposited on both
  substrate at low current density (50 ?A/cm2)

10
Rate-capability of LiCoO2 as a function of film
thickness
Charge-discharge variation 10 ?A/cm2 1
mA/cm2 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

11
Electrochemical Impedance Spectroscopy (EIS) for
LiCoO2 deposited on the Fsi substrate
12
Li-ion diffusion coefficient measured by EIS and
CV

• 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

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

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

15
Charge-discharge properties for anode and
full-cell
Amorphous-Si anode
Full-cell
Current density 50 ?A/cm2 Thickness 350 Å
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