Investigation of Lithium Tetrafluorooxalatophosphate [LiPF[sub 4](C[sub 2]O[sub 4])] as a Lithium-Ion Battery Electrolyte for Elevated Temperature Performance

The thermal stability of lithium tetrafluorooxalatophosphate [LiPF 4(C2O4)] electrolyte was investigated. Although the thermal stabilities of the solid LiPF4(C2O 4) and LiPF6 were comparable, the thermal stability of the liquid LiPF4(C2 O4)/carbonate electrolyte was better than LiPF6/carbonate electrolytes. Lithium-ion cells containing LiPF4(C2 O4) electrolyte had better capacity retention than LiPF6 electrolyte containing cells upon cycling after storage at 65°C for 2 weeks. Ex situ analysis of the electrodes before and after storage at 65°C and cycling suggested that differences in the structures of the anode and cathode surface films contributed to the superior performance of cells containing LiPF4(C 2O4) electrolyte.