A battery with a high battery voltage at charging and improved energy density is provided. A cathode (12) and an anode (14) are laminated with a separator (15) sandwiched therebetween which is impregnated with an electrolyte. The cathode (12) has a cathode active material including a lithium composite oxide which contains lithium, at least either cobalt or nickel, and oxygen. The battery voltage at charging is 4.25 V or more. The total amount of lithium carbonate and lithium sulphate in the cathode (12) to the cathode active material is 1.0 wt % or less, a concentration of protic impurities in the electrolyte, which is converted to a mass ratio of protons to the electrolyte, is 20 ppm or less, or moisture content in the electrolyte is 20 ppm mass ratio or less to the electrolyte. This inhibits metal eluting from the lithium composite oxide even at high voltages.