For example, an Li ion battery is known as a high-voltage and high-energy density battery. The Li ion battery is a cation-based battery utilizing a reaction between an Li ion and a cathode active material and a reaction between an Li ion and an anode active material. Meanwhile, as an anion-based battery, a fluoride ion battery utilizing a reaction of a fluoride ion is known.
Also, it is known that an ionic liquid is used for a liquid electrolyte. For example, in Patent Literature 1, a nonaqueous electrolyte secondary battery provided with an electrolyte having an ionic liquid and a lithium salt is disclosed. In addition, as the ionic liquid, an ionic liquid containing fluoride complex anions such as 1-butylpyridinium tetrafluoroborate is disclosed.
Also, in Patent Literature 2, a fluoride ion battery provided with an electrolyte dissolving a fluoride salt in a solvent and an addition agent including a fluoride composite producing species is disclosed. In addition, examples of the solvent include an ionic liquid (claim 14). Also, examples of the fluoride composite producing species include tris(pentafluorophenyl)borane (claim 3).