1. 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

2. 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.

3. 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.

4. 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

5. Physical Characteristics of Cellbatt  Lithium Ion Battery Electrodes Cellbatt  is a ‘Prismatic’ type cell

6. Electrode Reactions At anode At cathode Cell Reaction Non-Stoichiometric Spinel

7. 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

8. Change in discharge capacity for Li-ion cells charged to different potentials

9. 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.

10. Charge curves for CC-CV Protocol

11. Charge and Discharge curves for Li- ion Cell at various Cycles Capacity Fade 15.4% for C/2 rate C/2 Rate Capacity Fade 19% for 1 C rate

12. Change in CC-CV Profiles with Cycling

13. Nyquist plots for Cellbatt  cell charged at 0.5 A at different states of charge

14. Nyquist plots for Cellbatt  cell charged at 0.5 A during different cycles

15. Nyquist Plots for Spinel and Carbon Electrodes at Discharged state at Various Cycles Spinel Carbon

16. Cyclic Voltammograms of Spinel Electrode after 800 Cycles at various Scan rates

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

18. Cyclic Voltammograms of Spinel and Carbon Electrodes at Different Cycles Spinel Carbon

19. XRD Patterns of Spinel after Different Charge-Discharge Cycles P. G.. Bruce et al., J. Electrochem. Soc., 146, 3649 (1999).

20. 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………

21. Capacity Fade in Cellbatt  Li-ion cells Secondary Active Material Degradation(C 6 & LiMn 2 O 4 ) Structural Degradation of LiMn 2 O 4 Mn Dissolution from Spinel SEI layer attack on Negative Electrode HF formation Accumulation of -MnO 2 with Cycling Electrolyte Oxidation (starts from 3.7 V) Salt Hydrolysis J.C.Hunter et al. E. Wang et al.

22. Acknowledgements Financial support provided in part by the Department of Energy (DOE) is gratefully acknowledged. Thank you!