PURPOSE: To suppress the reduction of battery voltage at the initial stage of the discharge and to improve the battery performance by using a complex oxide of manganese and copper as a positive electrode active substance.

CONSTITUTION: A complex oxide of manganese and copper Cu2Mn3O6, CuMnO2, or CuMn2O4 is used as a positive electrode active substance, to make it possible to increase the surface area of the positive electrode, to reduce the positive electrode resistance, and to suppress an expansion of the positive electrode, and a drop of the battery voltage at the initial stage of discharge is suppressed. When such a positive electrode active substance is manufactured, a manganese salt solution, a copper salt solution, and an alkaline solution are mixed and reacted to produce a mixture of copper hydroxide, and then, the copper hydroxide is pyrolyzed to obtain a complex oxide of manganese and copper, which is used as a positive electrode active substance.