Lithium secondary battery and non-aqueous electrolyte solution used therein

The present invention provides a non-aqueous electrolyte solution for a secondary battery, the non-aqueous electrolyte solution containing at least a non-aqueous solvent and a lithium salt, the non-aqueous electrolyte solution having lithium difluorophosphate added therein, the content of the lithium difluorophosphate in the whole non-aqueous electrolyte solution being 10 ppm or more, the non-aqueous solvent constituting the electrolyte solution contains at least one asymmetric chain carbonate, the content ratio of the asymmetric chain carbonate in the whole non-aqueous solvent is 5-90% by volume, the non-aqueous solvent constituting the electrolyte solution further contains ethylene carbonate, and the total of cyclic carbonates and chain carbonates accounts for 80% by volume or more in the non-aqueous solvent, the capacity of the cyclic carbonate is 35% or less relative to the total of the cyclic carbonate and the chain carbonate, the asymmetric chain carbonate in the non-aqueous solvent constituting the ele