Novel silane compounds as electrolyte solvents for Li-ion batteries

Novel silane compounds such as {2-[2-(2-methoxyethoxy)ethoxy]ethoxy} trimethylsilane (1), bis{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}dimethylsilane (2), {3-[2-(2-(2-methoxyethoxy)ethoxy)ethoxy]-propyl}trimethylsilane (3) and {[2-(2-(2-methoxyethoxy)ethoxy)ethoxy]-methyl} trimethylsilane (4) have been synthesized and used as non-aqueous electrolyte solvents in lithium-ion batteries. These silane molecules can easily dissolve most lithium salts including lithium bis(oxalato)borate (LiBOB), LiPF6, LiBF4, and lithium trifluoromethylsulfonimide. The LiBOB salt was found to be very appropriate for these silane molecules because, unlike LiPF6, LiBOB can provide a good passivation film on a graphite anode. Cyclic voltammetry analyses show that silane-based electrolytes with a 0.8 M LiBOB salt concentration are stable to 4.4 V; they also exhibit very high lithium-ion conductivities up to 1.29 × 10−3 S/cm at room temperature. Full cell performance tests with LiNi0.08Co0.15Al0.05O2 as the positive electrode and MCMB graphite as the negative electrode have shown excellent cyclability both at room temperature and at 40 °C. Cells with these new silane electrolytes exhibit long calendar life; they show no impedance rise after aging at 80% state of charge and 55 °C for one year. The results suggest that silane-based electrolytes have great potential for use in lithium-ion batteries.