Tris(trimethylsilyl) borate (TMSB) used as new electrolyte additive to improve performance of LiFePO4 based lithium-ion battery is investigated in this paper. The effects of the TMSB on the LiFePO4 electrode are investigated via a combination of electrochemical impedance spectroscopy (EIS), cyclability, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). It is found that the LiFePO4 battery with a composite LiPF6-based electrolyte containing 1wt% TMSB additive exhibits higher discharge retention and better cycling performance than the battery without TMSB additive at both 30°C and 55°C. SEM and XPS measurements show the changes of surface morphology and formation of solid electrolyte interface (SEI). EIS results indicate that the interfacial impedances of the batteries after cycled at 55°C with the electrolyte containing TMSB additive are significantly smaller than the batteries without additive. The improved performances are ascribed to the enhancement of the thermal stability of the electrolyte and the modification of SEI component on the LiFePO4 electrode.