Tris(2,2,2-trifluoroethyl) phosphite (TTFEP) is investigated as an electrolyte additive to improve the electrochemical performance of LiNi1/3Co1/3Mn1/3O2 cathode at high operating voltage (4.6V). Charge/discharge measurements demonstrate that TTFEP is effective to improve the cycling stability and rate capability of LiNi1/3Co1/3Mn1/3O2 cathode. The capacity retention of LiNi1/3Co1/3Mn1/3O2/Li cell with 1% TTFEP-containing electrolyte reaches up to 85.4% after 100 cycles at 0.5C (1C=160mAg−1), while that of the cell with the baseline electrolyte (1M LiPF6 in EC/DMC electrolyte) only remains 74.2%. Moreover, the discharge capacity of the cathode with 1% TTFEP-containing electrolyte could maintain around 112.0mAhg−1 at 4C. Based on the characterization of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), a protective interphase film formed on the cathode surface can be found due to the preferential oxidation of TTFEP, which inhibits the electrolyte decomposition and mitigates the cathode structural destruction, leading to the improved electrochemical performance of LiNi1/3Co1/3Mn1/3O2 cathode at high voltage.