Dimethyl methylphosphonate (DMMP) was used as a cosolvent to reformulate the nonflammable electrolyte of I M LiPF6/EC + DEC + DMMP (1: 1:2 wt.) in order to improve the safety characteristics of lithium-ion batteries. The flammability, cell performance, low-temperature performance and thermal stability of the DMMP-based electrolyte were compared with the electrolyte of I M LiPF6/EC + DEC (1: 1 wt.). The nonflammable electrolyte exhibits good oxidation stability at the LiCoO2 cathode and poor reduction stability at the mesocarbon microbead (MCMB) and surface-modified graphite (SMG) anodes. The addition of vinyl ethylene carbonate (VEC) to the DMMP-based electrolyte provided a significant improvement in the reduction stability at the carbonaceous electrodes. Furthermore, it was found that the addition of DMMP resulted in optimized low-temperature performance and varied thermal stability of the electrolytes. All of the results indicated the novel DMMP-based electrolyte is a promising nonflammable electrolyte to resolve the safety concerns of lithium-ion batteries. (C) 2007 Elsevier B.V. All rights reserved.