Non-aqueous electrolyte solution for secondary batteries, and lithium ion secondary battery

A non-aqueous electrolyte solution, comprising:

• an electrolyte salt which comprises a lithium salt;
• and a liquid composition, the non-aqueous electrolyte solution comprising either one or both of monofluorophosphate anions and difluorophosphate anions derived from at least part of the electrolyte salt,
• wherein the liquid composition comprises:
• at least one fluorine-containing solvent (α) comprising a fluorine-containing ether compound, and optionally one selected from the group consisting of a fluorine-containing chain carboxylic acid ester compound and a fluorine-containing chain carbonate compound, in an amount of from 54.3 to 80 mass % with respect to 100 mass % of the non-aqueous electrolyte solution;
• at least one compound (β) selected from the group consisting of a saturated cyclic carbonate compound, a saturated chain carbonate compound having no fluorine atom, a saturated cyclic sulfone compound, which is not a lithium salt, and a phosphoric acid ester compound, in an amount of from 0.01 mass % to 30 mass % with respect to 100 mass % of the non-aqueous electrolyte solution;
• and
• a cyclic carboxylic acid ester compound which comprises at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone and ϵ-caprolactone,
• wherein the fluorine-containing ether compound comprises CF3CH2OCF2CHF2, CF3CH2OCF2CHFCF3, CHF2CF2CH2OCF2CHF2, CH3CH2CH2OCF2CHF2, CH3CH2OCF2CHF2, CHF2CF2CH2OCF2CHFCF3, or a mixture thereof, and
• wherein the ratio of the mass of the fluorine-containing ether compound to the total mass of the at least one fluorine-containing solvent (a) is from 70 to 100 mass %.