Triphenyl phosphite (TPPi) is reported as a phosphorous additive for lithium-ion batteries. It is found that TPPi can depress the flammability of electrolyte. Moreover, a passivation layer formed on the surface of the LiFePO4 electrode as the Li/LiFePO4 cell was overcharged in the electrolyte containing TPPi. TPPi can be used as an additive for the overcharge protection of LiFePO4 cathode for lithium-ion batteries. The cycle performance of the Li/LiFePO4 cell decreases slightly in the electrolyte containing 10 wt % TPPi after 40 cycles.