Physicochemical and Electrochemical Properties of the Organic Solvent Electrolyte with Lithium Bis(fluorosulfonyl)Imide (LiFSI) As Lithium-Ion Conducting Salt for Lithium-Ion Batteries

The basic physicochemical and electrochemical properties for organic solvent electrolyte dissolving lithium bis(fluorosulfonyl)imide (LiFSI) was studied. Ionic conductivity of 1M LiFSI in EC/DEC (3/7, v/v) was 7.2 mScm^-1 at 20 ^oC, it is almost same value of 1M LiPF₆ in EC/DEC (3/7,v/v). At lower temperature, however, the ionic conductivity of LiFSI was higher than that of LiPF₆. Degree of ionic disassociation of LiFSI-electrolyte was 0.42 (20 ^oC) and 0.35 (-20 ^oC). Then the concentration of Li-ion is lower than LiPF₆-electrolyte. On the other hand, diffusion coefficient of Li-ion in LiFSI-electrolyte is 1.8 cm²s^-1 that is 1.3 times larger value comparing to LiPF₆. This ratio gradually becomes big when it was low temperature, and reaches double at -20^oC. From these results, it is assumed that the ionic conductivity is strongly affected by diffusion behavior.