The Li-S batteries have been rewarded as the one of the most promising candidates due to their high energy densities. In this study, the common nonflammable solvent triethyl phosphate (TEP) is used for the first time as a co-solvent in Li-S battery. In the highly safe electrolyte system of 1 M LiBOB/TEP + FEC (7 : 3, v/v), the sulfur composite cathodes show enhanced cycling performance with a satisfactory capacity retention of 91.3% after 500 cycles at 1C.