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

The use of LiN(SO2CF3)2 as salt in lithium-ion secondary cells was considered to be a promising alternative to LiPF6 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 Li4Ti5O12 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 LiSO3CF3 (LiTf) or LiN(SO2CF3)2 (LiTFSI) or LiN(SO2C2F5)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 (ER) 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 LiCO2 as cathodic material on aluminium current collectors.