Triphenyl phosphite (TPPi) was investigated as an electrolyte additive for high-voltage lithium-ion batteries using lithium-rich layered oxide cathode in this paper. The cyclic stability of Li1.16Ni0.2Co0.1Mn0.54O2 was improved significantly with the adoption of 0.2wt. % TPPi. The capacity retention of Li1.16Ni0.2Co0.1Mn0.54O2 was improved significantly, especially at elevated temperature, from 69.0% to 89.6% after 90 cycles. Electrochemical and physical characterizations indicated that TPPi was oxidized at 4.2V (vs. Li/Li+), which was lower than that of the solvents and lithium extraction from Li1.16Ni0.2Co0.1Mn0.54O2, and the oxidization resulting in an artificial cathode interface film, which effectively inhibited the decomposition of traditional electrolyte and protected Li1.16Ni0.2Co0.1Mn0.54O2 material from destruction.