To suppress the decomposition of an organic solvent on negative electrode side and improve the charge and discharge efficiency by using a fluorine-containing ester compound as a mixture with a nonaqueous electrolyte, and setting the reduction potential of the fluorine-containing ester compound to a specified value to the oxidation-reduction potential of lithium.

The reduction potential of a fluorine-containing ester compound is set to 1.0-0.7 to the oxidation-reduction potential (Li/Li+) of lithium. The fluorine-containing ester compound is represented by the general formula R1 CFXCOOR2. In the formula, R1 represents hydrogen atom, fluorine atom, or a 1-3C alkyl group, and R2 represents a 1-2C alkyl group. More specifically, CHF2COOCH3, CHF2COOC2H5, and CH3CF2COOCH3 are preferably used. As a carbonic ester organic solvent used together with the fluorine-containing ester compound as an electrolyte, propylene carbonate, ethylene carbonate or the like can be given.