Asymmetric Imides as Electrolyte Additive for Lithium-Ion Batteries with NCM111 Cathode

The synthesis, spectroscopic and electrochemical characterization of Li[N(SiMe3)(SO2RF)] (R-F=CF3, n-C4F9) as well their behavior as electrolyte additive in lithium ion batteries (LIBs) is reported. The lithium salts were obtained by deprotonation of the corresponding acids HN(SiMe3)(SO2RF) with n-butyllithium in n-pentane. The electrochemical investigations suggested potential as additives for LIBs. Thus, NCM111/graphite cells (NCM111=Li[Ni0.33Co0.33Mn0.33]O-2) with LP57 as electrolyte (LP57=1.0 M LiPF6 in EC/EMC 3 : 7) were built to test the performance. Cells with Li[N(SiMe3)(SO2RF)] as additives show coulombic efficiencies of over 99.6 %, less capacity fading over 55 cycles and a significantly lower cell impedance built up.