Non-corrosive electrolyte compositions containing perfluoroalkylsulfonyl imides for high power Li-ion batteries

Abstract

The use of LiN(SO 2CF 3) 2 as salt in lithium-ion secondary cells was considered to be a promising alternative to LiPF 6 salt. However, in practice this salt has never been used in rechargeable batteries due to the severe corrosion it causes to the aluminium current collector. The spinel Li 4Ti 5O 12 has been a focus of attention for the major battery manufacturers as an alternative material for anodes instead of graphite; for cells employing this material, new electrolyte compositions can be considered which solve the corrosion problem and allow the use of imide-type salts. This work reports electrochemical studies characterizing the corrosion of aluminium electrodes polarized at high voltages in aprotic solvents containing LiSO 3CF 3 (LiTf) or LiN(SO 2CF 3) 2 (LiTFSI) or LiN(SO 2C 2F 5) 2 (LiBETI) salts. Despite the observation that in common battery solvents LiTFSI causes severe corrosion of the aluminium current collector at potential around 3.7 V (vs. Li), solvents having a cyano-group showed a repassivation potential ( E R) around 4.15 V (vs. Li). Based on the experimental observations made and previous literature reports, a mechanism to explain the inhibiting properties of nitriles is proposed. The nitrile-based electrolytes allow the final usage of LiTFSI in commercial batteries using LiCO 2 as cathodic material on aluminium current collectors.