Bis(2,2,2-Trifluoroethyl) ethylphosphonate (TFEP) is first synthesized as a flame retardant additive for conventional carbonate electrolyte to improve the safety of lithium ion batteries. The inflammability and electrochemical stability of the TFEP containing electrolyte are studied. The self-extinguishing time test shows that TFEP provides a significant suppression of the flammability of the electrolyte. When adding 20% TFEP, the electrolyte cannot be ignited, exhibiting superior flame retardancy. Cyclic voltammetry and electrochemical charge/discharge tests show that TFEP has insignificant impact on the electrodes’ electrochemical performance. The results demonstrate that TFEP can be used as a novel highly effective safety additive for lithium ion batteries.