Nonstoichiometry of sintered oxide Ca0.9La0.1MnO3-delta and its cathodic properties in alkaline solutions

The nonstoichiometry (3-delta) of perovskite-type oxide Ca0.9La0.1MnO3-delta was detected by thermal gravimetric analysis (TGA) to be 2.97 at room temperature in air, which means that 84% of the manganese was tetravalent. The electrical conductivity of sintered porous oxide Ca0.9La0.1MnO3-delta (porosity: ca. 60%) prepared as the active material was 35 S cm(-1) at room temperature, which was high enough to use it as a conductive cathode material. The sintered ceramic behaved as the cathode material with no conductive powder such as graphite in alkaline solutions. The discharge capacity depended on the concentration and the kind of alkali and was largest in 5% LiOH solution (750 C g(-1)), indicating that manganese in the oxide was reduced partly from Mn4+ to Mn2+. This discharge capacity was almost comparable to that of electrolytic MnO2 if one includes the necessary conductive material (such as graphite) in the latter case.