AQUEOUS ELECTROLYTE SOLUTION FOR ENERGY STORAGE DEVICES AND ENERGY STORAGE DEVICE COMPRISING THIS AQUEOUS ELECTROLYTE SOLUTION

According to the present invention, an electrolyte is composed of one or more lithium salts of asymmetric imides each having a perfluoroalkyl group, or a mixed salt of a lithium salt of an asymmetric imide having a perfluoroalkyl group and a lithium salt of a symmetric imide having a perfluoroalkyl group. The composition ratio of the one or more lithium salts and the mixed salt is expressed by (lithium salt of asymmetric imide)(lithium salt of symmetric imide)(wherein x is from 0.1 to 1.0) in terms of the molar ratio; the asymmetric imide lithium salt is (CFSO) (CFSO)NLi or (CFSO) (CFSO)NLi; the symmetric imide lithium salt is (CFSO)NLi; and the composition of an electrolyte solution according to the present invention contains 1.0 mole or more but less than 2 moles of a solvent per 1 mole of the one or more lithium salts or the lithium salts of the mixed salt.