Organosilicon functionalized quaternary ammonium ionic liquids as electrolytes for lithium-ion batteries

Organosilicon-functionalized quaternary ammonium ionic liquids (ILs) with oligo(ethylene oxide) substituent are designed and synthesized. Such properties as viscosity, conductivity, and thermal/electrochemical stability of these ILs are characterized. These ILs are miscible with the commercial carbonate electrolyte (EC: DEC = 1:1(w/w), 1 M LiPF6) and are used as cosolvents to form hybrid electrolytes in proportions up to 30 vol%. By using such hybrid electrolytes, the LiFePO4/Li half cells exhibit no deterioration in specific capacity and cyclability, and the graphite/Li half cells show improved compatibility in the presence of lithium oxalyldifluoroborate. These hybrid electrolytes exhibit less flammability compared with the commercial baseline electrolyte, and thus improved safety for use in lithium-ion batteries.