The electrolyte based on ionic liquid and sulfone with lithium difluoro(oxalate)borate (LiODFB) was prepared for high voltage lithium-ion battery because of its high conductivity, wide electrochemical window and non-flammability. High voltage cathodes and carbonaceous anodes were used as electrodes to evaluate the electrochemical properties of cells with the electrolyte. Li/Li1.2Ni0.2Mn0.6O2 and Li/MCMB cells with LiODFB–PP14TFSI/TMS exhibit good cycling performance, which retain capacities of above 220mAhg−1 and 338.6mAhg−1 after 50 cycles, respectively. The solid-electrolyte interphase (SEI) formation were characterized by ab initio simulations and X-ray photoelectron spectroscopy. The results indicate that LiODFB can be preferably oxidized during charging and reduced during discharging process. The nano reaction products pile up to form the SEI layers on the surfaces of electrodes. The SEI layers which prevent the electrolyte and electrode materials ensure the good electrochemical performance of the cells.