To provide a flame retardant non-aqueous electrolyte solution for secondary batteries, with which a lithium ion secondary battery which is less likely to undergo thermal runaway and which is excellent in the high temperature storage properties can be obtained; and a lithium ion secondary battery using the non-aqueous electrolyte solution for secondary batteries.A non-aqueous electrolyte solution for secondary batteries, comprising an electrolyte salt and a liquid composition,which contains either one or both of monofluorophosphate anions and difluorophosphate anions derived from at least part of the electrolyte salt,wherein at least a lithium salt is contained as one type of the electrolyte salt, andthe liquid composition comprises at least one fluorine-containing solvent (α) selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound and a fluorine-containing chain carbonate compound, and a cyclic carboxylic acid ester compound. A lithium ion secondary battery using the non-aqueous electrolyte solution for secondary batteries.