Studies on Capacity Fade of Spinel
based Li-Ion Batteries
by
P. Ramadass , A. Durairajan, Bala S. Haran, R. E. White and B. N. PopovCenter for Electrochemical Engineering
Department of Chemical Engineering, University of South Carolina Columbia, SC 29208
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Motivation
To characterize the capacity fade phenomena of Li-
ion 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.
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
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.
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
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
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
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) (cm2) 436 498
Loading on one side (mg/cm2) 22 10.2
Thickness of the Electrode (m) 91 70
Dimensions of the electrode (cm x cm) 54.5 x 4 58.5 x 4
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Cellbatt is a ‘Prismatic’ type cell
Electrode ReactionsAt anode
charge
dischargeLi C Li Li Cx x δδ δe
At cathode
charge
2-γ γ 4 δ 2-γ γ 4dischargeLi (Mn Li )O Li C Li (Mn Li )O Li Cx x δ
Cell Reaction
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
charge -2-γ γ 4 δ 2-γ γ 4discharge
Li (Mn Li )O Li (Mn Li )O δLi δe
Non-Stoichiometric Spinel
Charging Protocols
Constant current - Constant voltageTotal charging time fixed
Constant voltageCharging done completely at constant voltage
Constant current - Constant voltageCharging stopped when the current reaches a value
of 50 mA during the CV part
Charging done to different cut-off potentials
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Change in discharge capacity for Li-ion cells charged to different potentials
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Capacity (Ah)
3.0
3.2
3.4
3.6
3.8
4.0Cel
l Vol
tage
(V)
4.0, 4.05, 4.10, 4.17, 4.3 V Protocol
1A Discharge
4.054.104.0
4.17
4.3
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
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.Center for Electrochemical Engineering
University of South CarolinaCenter for Electrochemical Engineering
University of South Carolina
Charge curves for CC-CV Protocol
0.0 0.2 0.4 0.6 0.8 1.0
Capacity (Ah)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Cur
rent
(A)
Charge Curve comparison 100 cycles
1 A0.75 A0.5 A0.25 A
0.00 0.25 0.50 0.75 1.003.0
3.3
3.6
3.9
4.2
Potential (V)
Capacity (Ah)
1 A0.75 A0.5 A0.25 A
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Charge and Discharge curves for Li-ion Cell at various Cycles
Capacity Fade 15.4% for C/2 rate
0.00 0.18 0.36 0.54 0.72 0.90 1.08
Capacity (Ah)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Cur
rent
(A)
Vol
tage
(V)
3.3
3.5
3.7
3.9
4.1
0.5 C Protocol
4.17 V0.5 A
1 Cycle
200500
800
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
C/2 Rate
C/2 Rate0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Capacity (Ah)
3.0
3.2
3.4
3.6
3.8
Cel
l Vol
tage
(V)
1 cycle
200500800
0.5 C protocol
Capacity Fade 19% for 1 C rate
Change in CC-CV Profiles with Cycling
0.0 0.2 0.4 0.6 0.8 1.0
Capacity (Ah)
0.0
0.2
0.4
0.6
0.8
1.0
1.2C
urre
nt (
A)
Vol
tage
(V
)
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.17 V1 A
200 cycles
500 cycles
0.56 Ah
0.23 Ah 0.25 Ah
0.52 Ah
0.5 A
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Nyquist plots for Cellbatt cell charged at 0.5 A at different states of charge
0.25 0.26 0.27 0.28 0.29 0.30 0.31 0.32
Real Z ()
0.00
0.01
0.02
0.03
Imag
inar
y Z
()
100 (Charged)3520100
Impedance response as a function of SOC in case of fresh battery
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Nyquist plots for Cellbatt cell charged at 0.5 A during different cycles
0.24 0.25 0.26 0.27 0.28 0.29 0.30
ZRe ()
0.00
0.01
0.02
0.03
ZIm
()
Fresh-0-SOC200-0-SOC600-0-SOCFresh-100-SOC200-100-SOC600-100-SOC
1C 200 & 600
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Nyquist Plots for Spinel and Carbon Electrodes at Discharged state at Various Cycles
0 30 60 90 120 150ZRe (cm2)
0
10
20
30
40
50
ZIm
(cm
2)
200 cycles600 cycles800 cycles
Discharge Impedance LiMn2O4
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
0 20 40 60 80 100 120 140 160 180 200
ZRe (cm2)
0
10
20
30
40
50
60
70
80
90
100
ZIm
(cm
2)
200 cycles600 cycles800 cycles
Discharge Impedance Carbon
Spinel
Carbon
Cyclic Voltammograms of Spinel Electrode after 800 Cycles at various Scan rates
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Cyclic Voltammograms of Carbon Electrode after 800 Cycles at various Scan rates
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Cyclic Voltammograms of Spinel and Carbon Electrodes at Different Cycles
Spinel
CarbonCenter for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
XRD Patterns of Spinel after Different Charge-Discharge Cycles
Cycle "a" (Ao)0 8.17162
400 8.14257800 8.12964
10 25 40 55 70
2
Inte
nsit
y
Fresh
400 cycles
800 cycles222
311
440331
511
111
400
531
X-ray patterns for LiMn2O4 samples taken out of batteries cycled using
05C rate protocol
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
P. G.. Bruce et al., J. Electrochem. Soc., 146, 3649 (1999).
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………
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Capacity Fade in Cellbatt Li-ion cells
Secondary Active Material Degradation(C6 & LiMn2O4)
Structural Degradation of LiMn2O4
Mn Dissolution from Spinel
SEI layer attack on Negative Electrode
HF formation Accumulation of -MnO2 with Cycling
Electrolyte Oxidation(starts from 3.7 V)
2 4 2 22LiMn O 3λ -MnO (solid) + MnO(solution) + Li O(solution)
26 2PF H O POF HF
Salt Hydrolysis
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
J.C.Hunter et al.
E. Wang et al.
Acknowledgements
Financial support provided in part by the Department of Energy (DOE) is gratefully acknowledged.
Center for Electrochemical EngineeringUniversity of South Carolina
Center for Electrochemical EngineeringUniversity of South Carolina
Thank you!
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