PURPOSE: To increase heavy load discharge performance by containing a positive active material comprising β-MnO2 obtained by oxidizing γ-MnOOH at high temperature and a conductive material comprising oil furnace black in a positive electrode.

CONSTITUTION: β-MnO2 obtained by oxidizing γ-MnOOH at high temperature is used as a positive active material. Liquid hydrocarbon is partially oxidized in a furnace in the existence of molecular-state oxygen and steam, and by- product carbon produced together with synthetic gas is dried, then heated to obtain oil furnace black having a specific surface area of 90-150m2/g. This oil furnace black is used as a positive conductive material. Conductivity and electrolyte retaining capability in a positive electrode are increased, and heavy load discharge performance of a battery is also increased.