박막및 전지재료연구실

강원대학교

1

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

3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2-125

-100

-75

-50

-25

0

25

50

75

100

125

Cur

rent

den

sity

/ A

cm-2

Potential vs. Li/Li+ / V

Scan rate = 0.1 mV/sec

ESiFSi

Cyclic voltammetry with slow scan rate: Basic electrochemical characterization

Li oxidation-reduction peak of LiCoO2 deposited

on the

(a) FSi: 3.917 and 3.9005 V and

(b) 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

박막및 전지재료연구실

강원대학교

2

Cyclic voltammetry with variation of scan-rate

0.0 0.5 1.0 1.5 2.03.80

3.82

3.84

3.86

3.88

3.90

3.92

3.94

3.96

3.98

4.00

Flat-Si Etched-Si

Cathodic scan

Anodic scan

Pea

k po

tent

ial v

s. L

i/Li+ /

V

Scan rate / mVsec-1

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 LiCoO2 deposited on FSi and ESi

0 2 4 6 8 103.5

3.6

3.7

3.8

3.9

4.0

4.1

1 mA/cm2

500 A/cm2

20 A/cm2

10 A/cm2

Etched-Si substrate

Vo

ltag

e /

V

Discharge capacity / Ah

0 2 4 6 8 10 123.5

3.6

3.7

3.8

3.9

4.0

4.1

Flat-Si substrate

1 mA/cm2

500 A/cm2

20 A/cm2

10 A/cm2

Vo

ltag

e /

V

Discharge capacity / Ah

Current density range: 10 A/cm2 ~ 1 mA/cm2

10 100 10000.5

0.6

0.7

0.8

0.9

1.0

Flat-Si Etched-Si

Deposition time = 8h

No

rma

lize

d d

isch

arg

e c

ap

aci

ty

Discharge rate / Acm-2

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

박막및 전지재료연구실

강원대학교

4

SEM photos for LiCoO2 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 densitiesHigh rate-capability

박막및 전지재료연구실

강원대학교

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

Non-uniform thickness of current collector on the alumina substrate1000 ~ 3000 Å

Another contribution to the low rate-capability at high current density discharge

박막및 전지재료연구실

강원대학교

6

Cyclic voltammetry for LiCoO2 deposited on alumina substrate

3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2-40.0

-30.0

-20.0

-10.0

0.0

10.0

20.0

30.0

40.0

Scan rate = 0.1mVsec-1

Cur

rent

den

sity

/

Acm

-2

Potential vs. Li/Li+ / V

AluminaFSi

0.0 0.5 1.0 1.5 2.03.80

3.82

3.84

3.86

3.88

3.90

3.92

3.94

3.96

3.98

4.00

Flat-Si Etched-Si Alumina

Cathodic scan

Anodic scan

Pea

k po

tent

ial v

s. L

i/Li+ /

VScan rate / mVsec-1

No differences in basic electrochemical characteristics between two electrodes

The largest peak potential divergence for alumina substrate

박막및 전지재료연구실

강원대학교

7

Rate-capability for LiCoO2 deposited on FSi and ESi

0 2 4 6 8 103.5

3.6

3.7

3.8

3.9

4.0

4.1

Alumina substrate

1 mA/cm2

500 A/cm2

20 A/cm2

10 A/cm2

Vol

tage

/ V

Discharge capacity / Ah

10 100 10000.5

0.6

0.7

0.8

0.9

1.0

Flat-Si Etched-Si Alumina

Deposition time = 8h

No

rma

lize

d d

isch

arg

e c

ap

aci

ty

Discharge rate / Acm-2

Alumina:At 1 mA/cm2, 80% capacity retentionThe worst rate-capability among three substrates

Similar capacity at 10 A/cm2 to the FSi

박막및 전지재료연구실

강원대학교

8

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

박막및 전지재료연구실

강원대학교

9

Cyclability of LiCoO2 deposited on the FSi and alumina substrate

0.0 5.0 10.0 15.0 20.0 25.0 30.0

3.6

3.8

4.0

4.2

Flat-Si substrate

501

150501

Vo

ltag

e /

V

Capacity / Ahcm-2m-1

3.6

3.8

4.0

4.2

Alumina substrate

150

0 50 100 1500.0

0.2

0.4

0.6

0.8

1.0

1.2

Nor

mal

ized

dis

char

ge c

apac

ity

Cycles

Current density = 50 A/cm2

Good cyclability of LiCoO2 deposited

on both substrate at low current density (50 A/cm2)

박막및 전지재료연구실

강원대학교

10

Rate-capability of LiCoO2 as a function of film thickness

10 100 10000.80

0.85

0.90

0.95

1.00

Flat-Silicon 4 hrs Flat-Silicon 6 hrs Flat-Silicon 8 hrs Flat-Silicon 12 hrs

Nor

mal

ized

dis

char

ge c

apac

ity

Discharge rate / Acm-2

10 100 10000.5

0.6

0.7

0.8

0.9

1.0

Alumina 4 hrs Alumina 6 hrs Alumina 8 hrs

Nor

mal

ized

dis

char

ge c

apac

ity

Discharge rate / Acm-2

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

박막및 전지재료연구실

강원대학교

11

Electrochemical Impedance Spectroscopy (EIS) for LiCoO2 deposited on the Fsi substrate

10 20 30 40 500

10

20

30

40

4.1V

4.0V

3.95V

3.9V

3.8V

3.7V

3.5V

ZRe

/ ohm

-Zim

/ o

hm

20 25 30 35 40 45 500

5

10

15

20

25

30

4.05V

4.0V

3.95V

3.9V3.8V

3.7V3.5V

ZRe

/ ohm

ZIm

/ o

hm

0 20 40 60 80 100 120 1400

20

40

60

80

100

120

140

4.0V

3.95V

3.9V

3.8V3.7V

-ZIm

/ o

hm

ZRe

/ ohm

10-2 10-1 100 101 102 103 104 105100

101

102

103

104

105

106

4.0V3.95V3.9V

3.8V

3.7V

Frequency / Hz

ZIm

/ o

hm

10-1 100 101 102 103 104 10510-1

100

101

102

103

104

4.1V4.0V3.95V

3.9V

3.8V

3.7V

3.5V

Frequency / HzZ

Im /

10-2 10-1 100 101 102 103 104 105

100

101

102

103

104

105

4.1V4.0V3.95V

3.9V

3.8V

3.7V

3.5V

Frequency / Hz

ZIm

/ o

hm

FSi 4 hrs FSi 8 hrs FSi 12 hrs

박막및 전지재료연구실

강원대학교

12

Li-ion diffusion coefficient measured by EIS and CV

4 6 8 10 12

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

by CV by EIS at 3.9V by EIS at 3.95V by EIS at 4.0V

Diff

usi

on

co

eff

icie

nt /

cm

2 sec-1

Deposition time / Hr

By EIS method

2

2

h

DT

T = angular velocity at the transition point from semi-infinite to finite diffusionh = film thickness

By CV method

2/12/12/1 )/(4463.0 RTnFnFACDip

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

0 5 10 15 20 25 30 353.4

3.5

3.6

3.7

3.8

3.9

4.0

4.1

4.2

1 mA/cm2

500 A/cm2

100 A/cm2

50 A/cm2

20 A/cm210 A/cm2

Capacity / Ah

Ce

ll vo

ltag

e /

V

-7.0x10-3

-6.0x10-3

-5.0x10-3

-4.0x10-3

-3.0x10-3

-2.0x10-3

-1.0x10-3

0.0

1.0x10-3

Deposition time = 8 hrs

De

flectio

n a

ng

le / ra

d

0 5 10 15 20 25 30 353.4

3.5

3.6

3.7

3.8

3.9

4.0

4.1

4.2

Capacity / Ah

Ce

ll vo

ltag

e /

V

-8.0x10-3

-6.0x10-3

-4.0x10-3

-2.0x10-3

0.0

2.0x10-3

1 mA/cm2

500 A/cm2

100 A/cm2

50 A/cm2

20 A/cm210 A/cm2

Deposition time = 12 hrs

De

flectio

n a

ng

le / ra

d

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

10 100 1000

100

200

300

400

500

600

700

800

Lin

ea

r st

ress

gra

die

nt

/ M

Pa

m

-1

Charge current density / Acm-2

8 hrs 12 hrs

10 100 100050

100

150

200

250

300

350

400

Co

mp

ress

ive

str

ess

/ M

Pa

Charge current density / Acm-2

8 hrs 12 hrs

Stress induced by charge reactionStress induced by charge reaction Stress field divided by film thicknessStress 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

fs

ssf d

dE

L )1(6

2

박막및 전지재료연구실

강원대학교

15

Charge-discharge properties for anode and full-cell

0 10 20 30 400.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Vo

ltag

e /

V

Capacity / Ah

0 5 10 15 20 250

20

40

60

80

100

Nor

mal

ized

cha

rge

capa

city

Cycle number

0 1 2 3 4 5 6 72.0

2.5

3.0

3.5

4.0

4.5

Current density = 10 A/cm2

Vo

ltag

e /

V

Discharge capacity / Ah

Current density = 50 A/cm2

Thickness = 350 Å

0 2 4 6 8 10 12 14 16 18 200

1

2

3

4

5

6

7

8

Cut-off = 4.0 ~ 2.0 V

Dis

cha

rge

ca

pa

city

Cycle numbers

Amorphous-Si anodeAmorphous-Si anode Full-cellFull-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 Microbat

tery