An amorphous solid solution of V.sub.2 O.sub.5, CoO.sub.2, P.sub.2 O.sub.5, MO (wherein M represents an alkaline earth metal element) and at least one lithium compound selected from the group consisting of lithium-oxygen compounds, lithium halides and lithium oxygen acid salts is formed by melting precursor materials therefore, then the melt is put into water or pressed with metal plates to quench it, and the solid solution is heat treated above its glass transition temperature, the resulting solid solution being used as a cathode material for a lithium battery, thereby obtaining the lithium battery preventing the capacity of a carbon anode from lowering and excellent in long-term cycle stability.