강원대학교
Cyclic voltammetry for LiCoO2 deposited on Fsi (Flat-Si)
and ESi (Etched-Si)
Cyclic voltammetry with slow scan rate: Basic electrochemical characterization
125
Current density /
Acm-2
100
Li oxidation-reduction peak of LiCoO2
Scan rate = 0.1 mV/sec
deposited on the
75
50
(a) FSi: 3.917 and 3.9005 V and
25
(b) ESi: 3.916 and 3.9002 V, respectively
0
-25
-50
-75
The symmetric current peaks about potential axis
ESi
FSi
-100
 High reversible reaction of LiCoO2
-125
3.5
3.6
3.7
3.8
3.9
Potential vs. Li/Li
1
4.0
+
/V
4.1
4.2
 No differences in basic electrochemical
characteristics between two electrodes
박막및 전지재료연구실
강원대학교
Continued
Cyclic voltammetry with variation of scan-rate
4.00
+
Peak potential vs. Li/Li / V
3.98
Flat-Si
Etched-Si
3.96
Scan rate: 0.1 ~ 2 mV/sec
Anodic scan
 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
3.94
3.92
3.90
3.88
3.86
3.84
Cathodic scan
3.82
3.80
0.0
0.5
1.0
1.5
2.0
-1
Scan rate / mVsec
2
박막및 전지재료연구실
강원대학교
Rate-capability for LiCoO2 deposited on FSi and ESi
Current density range: 10 A/cm2 ~ 1 mA/cm2
4.1
4.1
Flat-Si substrate
3.9
2
3.8
1 mA/cm
2
500 A/cm
3.7
3.6
3.5
2
20 A/cm
2
10 A/cm
0
2
4
6
8
10
12
Discharge capacity / Ah
Normalized discharge capacity
Flat-Si
Etched-Si
Deposition time = 8h
0.6
0.5
10
100
Discharge rate / Acm
3
3.8
2
3.7
1 mA/cm
2
500 A/cm
3.6
20 A/cm
2
10 A/cm
3.5
2
0
2
4
6
8
10
 FSi:
Even at 1 mA/cm2, 93% capacity retention
 ESi:
At 1 mA/cm2, 89% capacity retention
 Low capacity for ESi at 10 A/cm2 (about 70% of
FSi)
 Better rate-capability for FSi than ESi
Microstructure effect attributed to the difference in
substrate roughness
0.9
0.7
3.9
Discharge capacity / Ah
1.0
0.8
Etched-Si substrate
4.0
Voltage / V
Voltage / V
4.0
1000
-2
박막및 전지재료연구실
강원대학교
SEM photos for LiCoO2 deposited on FSi and ESi
Deposition time for both films = 8 hrs
FSi
ESi
1 m
 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
4
박막및 전지재료연구실
강원대학교
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
 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
5
박막및 전지재료연구실
강원대학교
Cyclic voltammetry for LiCoO2 deposited on
alumina substrate
4.00
40.0
Scan rate = 0.1mVsec
-1
3.98
Peak potential vs. Li/Li / V
20.0
+
Current density / Acm
-2
30.0
10.0
0.0
-10.0
-20.0
-30.0
Alumina
FSi
Anodic scan
3.96
3.94
3.92
3.90
Cathodic scan
3.88
3.86
Flat-Si
Etched-Si
Alumina
3.84
3.82
-40.0
3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
+
Potential vs. Li/Li / V
3.80
0.0
0.5
1.0
1.5
2.0
-1
Scan rate / mVsec
 No differences in basic electrochemical characteristics between
two electrodes
 The largest peak potential divergence for alumina substrate
6
박막및 전지재료연구실
강원대학교
Rate-capability for LiCoO2 deposited on FSi and ESi
1.0
Voltage / V
4.0
Normalized discharge capacity
4.1
Alumina substrate
3.9
3.8
2
1 mA/cm
3.7
2
500 A/cm
2
20 A/cm
2
10 A/cm
3.6
3.5
0
2
4
6
8
Discharge capacity / Ah
10
0.9
0.8
0.7
Flat-Si
Etched-Si
Alumina
Deposition time = 8h
0.6
0.5
10
100
1000
Discharge rate / Acm
-2
 Alumina:
At 1 mA/cm2, 80% capacity retention
The worst rate-capability among three substrates
 Similar capacity at 10 A/cm2 to the FSi
7
박막및 전지재료연구실
강원대학교
SEM photos for LiCoO2 deposited on alumina substrate
4 hrs
8 hrs
1 m
 The largest particle size among three substrates
 Intra-particle micro-cracks observed.
Originated in the thermo-mechanical property of alumina
8
박막및 전지재료연구실
강원대학교
Cyclability of LiCoO2 deposited on the FSi and
alumina substrate
Current density = 50 A/cm2
1.2
Normalized discharge capacity
4.2
4.0
Voltage / V
3.8
Alumina substrate
1
50
150
3.6
4.2
0.8
0.6
0.4
0.2
0.0
50
100
150
 Good cyclability of LiCoO2 deposited
Flat-Si substrate
3.8
on both substrate at low current
150
50
1
3.6
0.0
0
Cycles
4.0
5.0
10.0
15.0
density (50 A/cm2)
20.0
-2
Capacity / Ahcm m
9
1.0
25.0
30.0
-1
박막및 전지재료연구실
강원대학교
Rate-capability of LiCoO2 as a function of film thickness
1.00
0.95
0.90
0.85
Flat-Silicon 4 hrs
Flat-Silicon 6 hrs
Flat-Silicon 8 hrs
Flat-Silicon 12 hrs
0.80
10
100
Discharge rate / Acm

1000
Normalized discharge capacity
Normalized discharge capacity
Charge-discharge variation: 10 A/cm2 ~ 1 mA/cm2
Film-thickness variation: 1500 ~ 6000 Å
1.0
0.9
0.8
0.7
0.6
0.5
10
-2
Diffusion length for Li ion
Alumina 4 hrs
Alumina 6 hrs
Alumina 8 hrs
100
1000
Discharge rate / Acm
-2
 film thickness
Film thickness   Rate-capability  ??? however,

Film thickness   Rate-capability 
!!! Diffusion kinetics as a function of film thickness
10
박막및 전지재료연구실
강원대학교
Electrochemical Impedance Spectroscopy (EIS) for
LiCoO2 deposited on the Fsi substrate
FSi 4 hrs
FSi 8 hrs
FSi 12 hrs
30
40
140
3.7V
3.7V 3.8V
120
3.9V
30
3.95V
3.95V
4.0V
-Zim / ohm
3.9V
80
60
40
20
3.8V
ZIm / ohm
100
-ZIm / ohm
25
3.5V
20
4.0V
4.1V
15
4.05V
4.0V
3.95V
3.9V
3.5V
3.7V
3.8V
10
10
5
20
0
0
20
40
60
80
100
120
0
10
140
20
30
ZRe / ohm
10
0
20
50
25
30
35
40
45
50
ZRe / ohm
ZRe / ohm
6
5
10
10
40
5
3.5V
3.7V
10
4
10
3
10
2
10
1
10
0
3.5V
4
10
3.7V
4
10
10
2
10
1
ZIm / ohm
ZIm / ohm
3.8V
3
3.7V
3.8V
3
3.9V
3.95V
4.0V
10
3.8V
ZIm / 
10
2
10
3.95V
4.0V
4.1V
1
10
4.1V
4.0V
3.95V
3.9V
3.9V
0
10
0
10 -2
10
10
-1
10
0
10
1
10
2
10
Frequency / Hz
11
3
10
4
10
5
10
-2
10
-1
0
10
1
10
2
10
3
10
Frequency / Hz
4
10
5
10
10
-1
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
Frequency / Hz
박막및 전지재료연구실
강원대학교
1x10
by CV
by EIS at 3.9V
by EIS at 3.95V
by EIS at 4.0V
-6
2
Diffusion coefficient / cm sec
-1
Li-ion diffusion coefficient measured by EIS and CV
1x10
-7
1x10
-8
1x10
-9
1x10
 By EIS method
T 
2D
h2
T = angular velocity at the transition point
from semi-infinite to finite diffusion
h = film thickness
 By CV method
i p  0.4463nFACD1/ 2 (nF / RT )1/ 2 1/ 2
-10
4
6
8
10
12
Deposition time / Hr
 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
12
박막및 전지재료연구실
강원대학교
Stress measurement by optical cantilever method
4.2
4.2
2
-3
2
10 A/cm 20 A/cm
4.1
1.0x10
4.1 10 A/cm2 20 A/cm2
2.0x10
-3
0.0
-3
-2.0x10
3.8
-3
2
1 mA/cm
3.7
-3
-4.0x10
2
500 A/cm
-3
-5.0x10
2
100 A/cm
3.6
2
50 A/cm
3.5
3.4
-3.0x10
-3
-6.0x10
Deposition time = 8 hrs -7.0x10-3
0
5
10
15
20
Capacity / Ah
25
30
35
Cell voltage / V
Cell voltage / V
3.9
4.0
0.0
3.9
1 mA/cm
3.8
500 A/cm
2
-2.0x10
-3
-4.0x10
-3
-6.0x10
-3
-8.0x10
-3
2
3.7
2
100 A/cm
3.6
50 A/cm
3.5
3.4
2
Deposition time = 12 hrs
0
5
10
15
20
25
30
Deflection angle / rad
-3
-1.0x10
Deflection angle / rad
4.0
35
Capacity / Ah
 Negative sign on deflection angle: compressive stress
 Increase in charge current density  decrease in deflection angle
 Decrease in expansion depth by steep concentration gradient
13
박막및 전지재료연구실
강원대학교
Calculated tress field assumed linear distribution
Stress induced by charge reaction
8 hrs
12 hrs
Compressive stress / MPa
350
300
250
200
150
100
50
10
100
Linear stress gradient / MPa m
-1
400
Stress field divided by film thickness
800
8 hrs
12 hrs
700
600
500
400
300
200
100
1000
10
100
-2
Charge current density / Acm
 Stress calculation: by Stoney equation
1000
Charge current density / Acm

 Amount of stress induced by charge reaction
-2

Es d s2
f 
6 L (1   s )d f
 Increase with film thickness, however
 Decrease with film thickness for stress field induced by charge reaction
Diffusion coefficient decrease with film thickness
14
박막및 전지재료연구실
강원대학교
Charge-discharge properties for anode and full-cell
Amorphous-Si anode
Full-cell
4.5
1.6
2
Current density = 10 A/cm
4.0
1.4
Voltage / V
Voltage / V
1.2
1.0
0.8
0.6
0.4
3.5
3.0
2.5
0.2
0.0
2.0
0
10
20
30
0
40
1
2
3
4
5
6
7
Discharge capacity / Ah
Capacity / Ah
8
7
80
60
Current density = 50 A/cm2
Thickness = 350 Å
40
20
6
5
Cut-off = 4.0 ~ 2.0 V
4
3
2
1
0
0
5
10
15
Cycle number
15
Discharge capacity
Normalized charge capacity
100
20
25
0
0
2
4
6
8
10
12
14
16
18
20
Cycle numbers
박막및 전지재료연구실
강원대학교
Operation of digital clock by all-solid-state Li
microbattery
All-Solid-State Li
Secondary
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
16
박막및 전지재료연구실