A hydrofluoroether, 2-trifluoromethyl-3-methoxyperfluoropentane (TMMP), was investigated as a nonflammable electrolyte for lithium-ion batteries. This paper reports on the psychochemical properties of the TMMP-mixed electrolyte [1 M lithium bis(pentafluoroethylsulfonyl (imide) LiBETI/ethylene carbonate + diethyl carbonate (EC + DEC) + TMMP (5:45:50)] in relation with the battery performances. The TMMP-mixed electrolyte showed effective nonflammability with prolonged ignition time (150s). No differences in oxidative and reductive decomposition currents were observed in the operation voltage range of lithium-ion batteries (0-4.2 V vs Li/Li+) for the electrolytes with and without TMMP. At a high rate of 12 C, 75% of the capacity (obtained at 0.2 C) was obtained for the TMMP-mixed electrolyte, while less than 40% was obtained for the electrolytes without TMMP [1 M LiBETI/EC + DEC (50:50) and EC + DEC (5:95)]. The low-temperature performance and cyclability were also significantly improved for the TMMP-mixed electrolyte. (c) 2009 The Electrochemical Society. [DOI: 10.1149/1.3073552] All rights reserved.