PURPOSE: To improve battery performance while preventing the increase in internal resistance of a positive electrode active material as well as increasing the filling amount of said material by covering the surface of said active material grains with an electrically-conductive material.

CONSTITUTION: A positive electrode active material made of power whose surface is covered with an electrically-conductive material is used. For instance, manganese dioxide is heated under reduced pressure or in the atmosphere, and carbon is deposited on the manganese dioxide powder surface through e.g., sputtering process. A battery is constructed by adding a binder to this manganese dioxide as a positive electrode black mixture. Hereby, it is possible to sufficiently fill the positive electrode active material by a fraction by which the conductive material is essentially reduced, while reducing contact resistance between the active material and the conductive material since the conductive material is added not in the state of mixture but exists in a state where the grain surface is covered thus allowing a battery excellent in discharge performance to be obtained.