NEW ELECTROLYTES FOR LITHIUM-ION SECONDARY BATTERIES

摘要

Electrolytes based on ethylene carbonate (EC)/linear carbonates with LiPF,, dissolved as a salt are often employed in lithium-ion secondary batteries. LiPF_6 shows a high ionic conductivity, but it undergoes hydrolysis easily and decomposes at a moderate temperature. Linear carbonates have low flash points and high volatile behaviors. Therefore, we have focussed on both γ-butyrolactone (GBL) as solvent and a new Li imide as salt. GBL has high flash point, high ionic conductivity and low viscosity. Li imide has high thermal stability and high ionic conductivity, though Al corrosion occurs. In this study, we will report the features of new Li imide salt, LiFSI, which has small molecular weight. LiFSI shows a high oxidation potential (5.2 V vs. Li/Li~+), with Al corrosion suppressed by mixing with LiPF_6. Cells with LiFSI/GBL as a battery electrolyte show good rate performances as compared to those with LiPF_6/GBL.