In this work, tris (trimethylsilyl) phosphate (TMSP) is used as an electrolyte additive to improve the cycling performance of Li/LiNi0.5Mn1.5O4 cell upon cycling at high voltage, 4.9 V vs. Li/Li+ at room temperature and elevated temperature (55 °C). The effects of TMSP on the cathode interface and the cycling performance of Li/LiNi0.5Mn1.5O4 cell were investigated via the combination of electrochemical methods, including cycling test, cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). It is found that cells with electrolyte containing TMSP have better capacity retention than that of the cells without TMSP upon cycling at high voltage at room temperature and elevated temperature. The functional mechanism of incorporation of TMSP to the electrolyte to improve the cycling performance is conducted with ex-situ analysis approaches, including X-ray diffraction (XRD), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and ICP-MS. The surface analysis results reveal that more stable and more conductive surface layer is formed on the LiNi0.5Mn1.5O4 electrode with TMSP containing electrolyte, which is a leading factor for the enhanced the cycling performance of Li/LiNi0.5Mn1.5O4 cells upon cycling at high voltage at room temperature and elevated temperature.