NON-AQUEOUS SOLVENT, NON-AQUEOUS ELECTROLYTE COMPOSITIONS, AND NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY

Provided are a nonaqueous solvent to prevent the deterioration of discharge capacity holding ratio in case of repeated charge/discharge, a nonaqueous electrolyte composition containing the nonaqueous solvent, and a nonaqueous electrolyte secondary battery containing the nonaqueous electrolyte composition. The nonaqueous solvent comprises 5-60 wt% of ethylene carbonate; 40 wt% or less of propylene carbonate; and 40 wt% or more of diethyl carbonate. The nonaqueous electrolyte composition comprises an electrolyte salt; the nonaqueous solvent; optionally an unsaturated cyclic carbonate ester; and optionally a polymer compound. Preferably the unsaturated cyclic carbonate ester is vinylene carbonate and/or vinyl ethylene carbonate; and the polymer compound is at least one selected from poly(vinyl formal), polyacrylate and polyfluorovinylidene.