Polymer graphite composite anodes for Li-ion batteries

1. Polymer graphite composite anodes for Li-ion batteries Basker Veeraraghavan, Bala Haran, Ralph White and Branko Popov University of South Carolina, Columbia, SC 29208 Plamen Atanassov University of New Mexico, Albuquerque, NM 87131

2. Problem Definition Previous approaches Electrolyte decomposition Solvated lithium intercalation and reduction Irreversible reactions lead to Losses in capacity / active lithium material Lowers cell energy densities, increases cell cost • Modification to the electrolyte • Addition of SO2, CO2 • Other solvents like DMPC • Modification to the electrode • Mild oxidation • Coating with Ni, Pd

3. Objectives To prepare PPy/C composite which will reduce the initial irreversible capacity To improve the conductivity and the coulombic efficiency of the electrode To obtain material with better rate capability and good cycle life Approach • Produce a matrix of PPy which forms a conducting backbone for the graphite particles by in-situ polymerization

4. Preparation of PPy/Graphite composites • Dropwise addition of pyrrole into aqueous slurry of graphite at 0 C with nitric acid acting as an oxidizer for 40 h • Wash repeatedly with water and methanol and vacuum dried at 200C for 24h • Cell Preparation for testing • Electrodes prepared by cold rolling using PTFE binder (10wt%) • Whatman fiber used as separator and Li-foil used as counter and reference electrode • 1M LiPF6 in EC/DMC (1:1 v/v) used as electrolyte Experimental

5. Experimental (Cont’d.) Electrochemical characterizations Charge-discharge and cycling behaviors Arbin Battery test system used for the testing Cycling was performed between 2V and 5 mV at C/15 rate (0.25 mA/cm2) Cyclic Voltammetry CVs were performed from 1.6V to 0.01V at 0.05 mV/s Electrochemical Impedance Spectroscopy (EIS) 100kHz to 1mHz with 5mV PP signal Physical characterizations SEM micrographs TGA and BET analysis

6. TGA analysis of polymer compositeSFG10 samples

7. Charge-discharge curves of polymer composite SFG10 samples

8. Change in irreversible capacity loss with PPy loading at C/15 rate

9. Comparison of surface area and capacity for polymer composite electrodes

10. Cyclic voltammograms of polymer composite SFG10 samples

11. 10 m 10 m SEM pictures of polymer composite SFG10 samples Bare PPy/C

12. Impedance studies of polymer composite SFG10 samples

13. C1 C2 DPE1 DPE2 RW R1 R2 Equivalent circuit used to fit the experimental data RW – ohmic resistance R1 – SEI layer resistance C1 – SEI layer capacitance R2 – Polarization resistance C2 – Double layer capacitance

14. Equivalent circuit parameters for polymer composite electrode

15. Comparison of coulombic efficiencies for SFG10 samples

16. Rate capability studies of composite SFG10 samples

17. Cycle life studies of composite SFG10 samples

18. Charge-Discharge curves of polymer compositeSFG10-15% sn samples

19. Comparison of irreversible capacities for bare and polymer composite SFG10 samples

20. Conclusions Polypyrrole on SFG10 graphite results in high performance anodes for use in Li-ion batteries Irreversible capacity is reduced up to 7.8% PPy composite Charge discharge studies are supported by CV data Reduction in irreversible capacity seen during cathodic scan Polymer composite anodes show better conductivity and lower polarization resistance compared to virgincarbon Polymer composite anode show better rate capability and longer cycle life

21. Acknowledgements This work was funded by the Dept. of Energy division of Chemical Science, Office of Basic Energy Sciences and, in part, by Sandia National Laboratories (Sandia National Laboratories is a multi-program laboratory operated by Sandia corp., a Lockheed Martin Company, for the U.S. Dept. of Energy under Contract DE-AC04-94AL85000.)