Use of nonflammable methyl nonafluorobuyl ether (MFE) has been studied to develop an inherently safe electrolyte for lithium secondary batteries. A no flash point (NFP) solution was prepared by mixing a proper amount of MFE with a common electrolyte solvent such as dimethyl carbonate or ethyl methyl carbonate (EMC) and the NFP electrolyte was obtained by dissolving organic lithium salts (e.g., Li[SO2C2F5](2); LiBETI) in the NFP solution. Cell capacities with NFP electrolyte of 1 mol dm(-3) (M) LiBETI-MFE/EMC (80:20 vol %) were limited by the charge-discharge process on the graphite anode. Electrolyte components were investigated in terms of modifying the solid electrolyte interface film to improve the charge-discharge performance and cycle life of NFP electrolyte. Adding cyclic carbonate (e.g., ethylene carbonate, EC) and LiPF6 to the electrolyte reduced the interfacial resistance in a graphite/Li cell. A 18650 cylindrical cell with EC and LiPF6 added to 1 M LiBETI-MFE/EMC (80:20) electrolyte discharged more than 90% of its capacity at a 1 C current rate (vs. the capacity at the 0.1 C) and kept more than 80% of its initial capacity after 560 cycles at the 1 C current rate and room temperature. Effects of these additives on charge-discharge capacities in a graphite/Li cell were also investigated in terms of electrochemical spectroscopy, X-ray photoelectron spectroscopy, solid-state Li-7 nuclear magnetic resonance, and attenuated total reflection infrared spectroscopy. (C) 2003 The Electrochemical Society.