Effects of Lithium Salts and Solvents on the Performance of Lithium-ion Batteries with Carbonate-free Electrolytes Comprising Lithium Bis(fluorosulfonyl)imide and Sulfolane

The effects of addition of LiPF6 and various solvents to the electrolyte comprising lithium bis(fluorosulfonyl)imide (LiFSI) and sulfolane (SL) (LiFSI/SL) are investigated to improve the performance of lithium-ion batteries. A partial replacement of LiFSI in LiFSI/SL by LiPF6 does not considerably affect the cycle performance of LiCoO2/graphite cells. The addition of solvents with low dielectric constants or easily reducible solvents to LiFSI/SL degrades the performance. In contrast, an addition of PC increases the capacity of the cell during the initial stage of the cycle test. However, the capacity retention of the cell is lower than that of LiFSI/SL.