Comparison of the thermal and electrochemical properties of LiPF6 and LiN(SO2C2F5)2 salts in organic electrolytes

Thermal and electrochemical properties of LiPF6 and LiN(SO2C2F5)2, known as LiBETI, are compared in binary mixtures of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Thermal stability of these electrolytes was tested between 50 and 120 °C at 10 °C intervals. The electrolytes were kept at temperature for 1 week and every other day they were taken out of the oven and checked visually for any discoloration. Visual inspection showed discoloration of the LiPF6-containing electrolyte even at 60 °C (straw brown to dark brown at 120 °C) while the electrolyte containing LiBETI showed no or very little discoloration even at 120 °C. In lithium-ion "Tee" cells the electrolyte with LiBETI cycled equally well or better than the electrolyte containing LiPF6 at room temperature. Tee cells containing LiBETI showed lower cathode impedance than and comparable anode impedance to the cells containing electrolytes with LiPF6. In a full cell the electrodes performed equally well.