Abstract: Provided is an electrolytic solution that includes: an electrolyte containing lithium salt; and a nonaqueous solvent containing cyclic alkylene carbonate and methyl propionate, the electrolyte contains lithium salt other than LiPF6 in an amount of not less than 30 mol % with respect to a total amount of the lithium salt, and the nonaqueous solvent contains 75 volume % or more of the methyl propionate.

Abstract: Provided are an electrolytic solution suitable for a lithium ion secondary battery that includes a positive electrode which has a positive electrode active material having an olivine structure, and includes a negative electrode having graphite as a negative electrode active material, and a superior lithium ion secondary battery having the electrolytic solution. The lithium ion secondary battery includes: a positive electrode that includes a positive electrode active material having an olivine structure; a negative electrode having graphite as a negative electrode active material; and an electrolytic solution. The electrolytic solution contains LiPF6, a cyclic alkylene carbonate selected from ethylene carbonate and propylene carbonate, methyl propionate, and an additive that starts reductive degradation at a potential higher than a potential at which the above components of the electrolytic solution start reductive degradation.