ELECTROLYTE FOR MAGNESIUM ION SECONDARY BATTERY, AND MAGNESIUM ION SECONDARY BATTERY

PROBLEM TO BE SOLVED: To properly perform charge and discharge by reversible dissolution and deposition of magnesium ions, and to ensure the battery safety for putting a magnesium ion battery to practical use.SOLUTION: The electrolyte for a magnesium ion secondary battery comprises: an ether-based solvent; and a flame retardant. The ether-based solvent has an inflammation point of 12°C or lower. The flame retardant includes a bromine-based flame retardant. The ratio of the flame retardant added to a water-insoluble electrolyte is 10 wt% or below. The flame retardant includes one or more of tetrabromobisphenol (TBBA), decabromodiphenyl ether, bispentabromophenylethane, polystyrene bromide, ethylene bistetrabromophthalimide, hexabromocyclododecane, and pentabromobenzylacrylate.