Abstract: A lithium ion secondary battery that operates at a high voltage, has a high cycle life, and generates less gas, and an electrolytic solution for such a lithium ion secondary battery. An electrolytic solution for a non-aqueous energy storage device, comprising: a non-aqueous solvent; a lithium salt (A) having no boron atom; a predetermined lithium salt (B) containing a boron atom; and a compound (C) in which at least one of hydrogen atoms in an acid selected from the group consisting of proton acids having a phosphorus atom and/or a boron atom, sulfonic acids, and carboxylic acids is replaced with a substituent represented by formula (3): wherein R3, R4, and R5 each independently represent an organic group which has 1 to 10 carbon atoms and which may have a substituent.