The cathode/electrolyte interface stability is the key factor for the cycle life and the safety performance of lithium-ion battery. Triphenylphosphine(TPP) is studied as an additive for film-formation on the cathode electrode. TPP additive can be preferably oxidized than the solvent and then a solid electrolyte interphase (SEI) layer is in-situ formed on the cathode surface and it greatly improves the cycle stability of the cathode at high voltage. The capacity retention for the LiMn2O4 cathode, which is cycled up to 4.8V, is improved from 82% in the blank electrolyte to 93% in the TPP-containing electrolyte after 100 times at the current density of 148mA/g(1C).