Transcript Studies on Capacity Fade of Spinel based Li

Studies on Capacity Fade of Spinel
based Li-Ion Batteries
by
P. Ramadass , A. Durairajan, Bala S. Haran,
R. E. White and B. N. Popov
Center for Electrochemical Engineering
Department of Chemical Engineering, University of South Carolina
Columbia, SC 29208
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Motivation
 To characterize the capacity fade phenomena of Liion batteries.
 To decrease the capacity fade on both positive and
negative electrode by optimizing the DC and pulse
charging protocol.
 To develop mathematical model which will explain
the capacity fade in the spinel system.
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Objectives
 To study the change in capacity of commercially
available spinel based Li-ion Cells (Cellbatt cells).
 Study the performance of Li-ion cells under DC
charging at different rates.
 Use impedance spectroscopy to analyze the change in
cathode and anode resistance with cycling.
 Determine experimentally which electrode is more
important in contributing to capacity fade.
 Do material characterization to study changes in
electrode structure with cycling.
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Capacity Fade may Result from

Overcharge Phenomena

Lithium deposition on negative electrodes

Electrolyte oxidation on positive electrode

Passivation (Interfacial film formation)

Self discharge

Electrolyte Reduction

Active Material Dissolution

Phase Change
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Physical Characteristics of Cellbatt
Lithium Ion Battery Electrodes
Characteristics
Positive Spinel Negative Carbon
Mass of the electrode material (g)
9.592
5.0865
Geometric area (both sides) (cm 2)
436
498
Loading on one side (mg/cm 2)
22
10.2
Thickness of the Electrode (m)
91
70
54.5 x 4
58.5 x 4
Dimensions of the electrode (cm x cm)
Cellbatt is a ‘Prismatic’ type cell
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Electrode Reactions
At anode
Li xC  δLi

ch arg e
 δe

   
  
d isch arg e
Li xδ C
At cathode

 



Li  (M n 2 -γ Li γ )O 4 
Li
(M
n
Li
)O

δLi

δe

 δ
2-γ
γ
4
discharge
charge
Non-Stoichiometric Spinel
Cell Reaction
 


 Li
L i  (M n 2 -γ L i γ )O 4  L i x C 

  δ (M n 2-γ L i γ )O 4  L i x  δ C
discharge
charge
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Charging Protocols
Constant current - Constant voltage
 Total charging time fixed
Constant voltage
 Charging done completely at constant voltage
Constant current - Constant voltage
 Charging stopped when the current reaches a value
of 50 mA during the CV part
 Charging done to different cut-off potentials
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Change in discharge capacity for Li-ion
cells charged to different potentials
4.0
4.3
3.8
Cel l V o l t ag e (V )
4.17
3.6
3.4
3.2
4.05
4.0
3.0
0.0
0.1
0.2
0.3
0.4
0.5
4.10
0.6
0.7
0.8
0.9
1.0
C ap aci t y (A h )
4 . 0 , 4 . 0 5 , 4 . 1 0 , 4 . 1 7 , 4 . 3 V P ro t o co l
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Experimental
 Full Cell studies on CellBatt® Li-ion Cells
 Galvanostatic charge-discharge
• 0.25 A, 0.5 A, 0.75 A, 1 A - (3.0-4.17 V)
 Cyclic Voltammograms - 0.05 mV/s, 2.5-4.2 V
 T-cell (half cell) studies
 Glove Box - Disk electrodes – 1.2 cm 
 Counter, Reference electrodes – Li metal
 Cyclic Voltammograms - 0.05, 0.1 and 0.2 mV/s, 3-4.5 V
vs. Li/Li+ for spinel and 0-1.2V vs. Li/Li+ for carbon
 Impedance Analysis - 100 kHz ~ 1 mHz ±5 mV.
 XRD studies of spinel electrode at various cycles.
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Charge curves for CC-CV Protocol
1.2
1 A
0.75 A
0.5 A
0.25 A
Cu rren t (A )
1.0
0.8
0.6
0.4
0.2
4.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
C h a rg e C u rv e c o m p a ri so n 1 0 0 c y c l e s
Po t en t i al (V )
3.9
C ap aci t y (A h )
3.6
1 A
0.75 A
0.5 A
0.25 A
3.3
3.0
0.00
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0.25
0.50
C ap aci t y (A h )
0.75
1.00
Charge and Discharge curves for Liion Cell at various Cycles
0.6
4.17 V
0.5
4.1
0.4
3.9
0.3
1 C y cl e
3.7
0.2
V o l t ag e (V )
Cu rren t (A )
0.5 A
3.5
0.1
800
500
200
3.3
0.0
0.18
0.36
C/2 Rate
0.54
0.72
0.90
1.08
3.8
C ap aci t y (A h )
0 . 5 C P ro t o co l
Capacity Fade 15.4% for C/2 rate
C ell V o ltag e (V )
0.00
3.6
3.4
1 cy cle
3.2
Capacity Fade 19% for 1 C rate
800
0.0
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500 200
3.0
C/2 Rate
0.1
0.2
0.3
0.4
0.5
0.6
C ap acity (A h )
0.7
0.8
0.9
1.0
Change in CC-CV Profiles with Cycling
1.2
4.2
1 A
0.8
0 .2 3 A h
C urre nt (A )
4.0
0.5 A
3.8
0 .2 5 A h
0.6
3.6
0 .5 6 A h
0.4
0 .5 2 A h
3.4
200 cycles
V olta ge (V )
1.0
4.17 V
0.2
3.2
500 cycles
0.0
3.0
0.0
0.2
0.4
0.6
0.8
1.0
C apacity (Ah)
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Nyquist plots for Cellbatt cell charged
at 0.5 A at different states of charge
Imag i n ary Z ( )
0.03
100 ( Cha r ge d)
35
20
10
0
0.02
0.01
0.00
0.25
0.26
0.27
0.28
0.29
0.30
0.31
0.32
R eal Z ( )
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Nyquist plots for Cellbatt cell charged
at 0.5 A during different cycles
0.03
Z Im ( )
0.02
F res h -0 -S O C
2 0 0 -0 -S O C
6 0 0 -0 -S O C
F res h -1 0 0 -S O C
2 0 0 -1 0 0 -S O C
6 0 0 -1 0 0 -S O C
0.01
0.00
0.24
0.25
0.26
0.27
0.28
0.29
0.30
Z R e ( )
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Nyquist Plots for Spinel and Carbon Electrodes
at Discharged state at Various Cycles
50
2 0 0 cy cl es
6 0 0 cy cl es
8 0 0 cy cl es
Z Im ( cm 2 )
40
30
20
10
100
2 0 0 cy cl es
6 0 0 cy cl es
8 0 0 cy cl es
90
0
30
Spinel
D i s ch arg e Im p ed an ce L i M n 2 O 4
60
ZRe
90
2
( cm )
120
80
150
70
Z Im ( cm 2 )
0
60
50
40
30
20
10
0
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Carbon
0
20
40
60
80
100
120
2
Z R e ( cm )
140
160
180
200
Cyclic Voltammograms of Spinel Electrode
after 800 Cycles at various Scan rates
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Cyclic Voltammograms of Carbon Electrode
after 800 Cycles at various Scan rates
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Cyclic Voltammograms of Spinel and Carbon
Electrodes at Different Cycles
Spinel
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Carbon
XRD Patterns of Spinel after Different
Charge-Discharge Cycles
111
400
311
8 0 0 cy cl es
511 440
531
331
In t en s i t y
222
4 0 0 cy cl es
Cycle
0
400
800
"a" (Ao )
8.17162
8.14257
8.12964
F re s h
P. G.. Bruce et al., J. Electrochem. Soc., 146, 3649 (1999).
10
25
40
2 
55
70
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Conclusions
 Varying the charging rate affects the overall capacity of
the cell.
 Impedance studies reveal no significant increase in
resistance at both electrodes after 800 cycles.
 XRD studies of Spinel electrode reveal the formation of
an additional phase with cycling.
 Capacity fade in the case of Cellbatt cells can be
summarized as………
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Capacity Fade in Cellbatt
Li-ion cells
Secondary Active Material
Degradation(C6 & LiMn2O4)
Mn Dissolution
from Spinel
SEI layer attack on
Negative Electrode
HF formation
E. Wang et al.
Structural Degradation
of LiMn2O4
Accumulation of -MnO2 with Cycling
2L iM n 2 O 4  3 λ - M nO 2 (solid) + M nO (solution) + L i 2 O (so lution)
J.C.Hunter et al.
Salt Hydrolysis
P F6

Electrolyte Oxidation
(starts from 3.7 V)
 H 2O  P O F  2 H F
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Acknowledgements
Financial support provided in part by the
Department of Energy (DOE) is gratefully
acknowledged.
Thank you!
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