Method of restoring capacity of non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

A method of restoring capacity of a non-aqueous electrolyte secondary battery, comprising:

• preparing a liquid composition;
• and
• mixing the liquid composition with an electrolyte solution of the non-aqueous electrolyte secondary battery having an observed capacity loss from a predetermined capacity,
• the liquid composition including a solvent and a dissolved substance,
• the dissolved substance including an ionic compound,
• the ionic compound consisting of a radical anion of an aromatic compound and a metal cation,
• the aromatic compound being a polyacene or a polyphenyl,
• the metal cation being an ion of the same type as carrier ions of the non-aqueous electrolyte secondary battery.