studies on capacity fade of spinel based li-ion batteries by p. ramadass, a. durairajan, bala s....

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


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.



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.



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



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



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



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



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



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



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



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



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



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



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



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



Cyclic Voltammograms of Carbon Electrode after 800 Cycles at various Scan rates



Cyclic Voltammograms of Spinel and Carbon Electrodes at Different Cycles

Spinel

CarbonCenter 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



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………



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



J.C.Hunter et al.

E. Wang et al.

Acknowledgements

Financial support provided in part by the Department of Energy (DOE) is gratefully acknowledged.



Thank you!

studies on capacity fade of spinel based li-ion batteries by p. ramadass, a. durairajan, bala s....

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