A lithium secondary battery includes a cathode containing, as an active material, a material that can be doped/undoped with lithium ions; an anode containing, as an active material, a lithium metal, a lithium alloy or a material that can be doped/undoped with lithium ions; and a liquid or solid electrolyte. In this lithium secondary batter, the active material used in the cathode is lithiated nickel dioxide containing gallium. As a result, the lithium secondary battery attains excellent cycle and overcharge resistance characteristics and has a high energy density.