COMPOSITE METAL OXIDE, PROCESS FOR PRODUCING THE COMPOSITE METAL OXIDE, POSITIVE ACTIVE MATERIAL FOR SODIUM SECONDARY BATTERY, POSITIVE ELECTRODE FOR SODIUM SECONDARY BATTERY, AND SODIUM SECONDARY BATTERY

摘要

Provided are: a composite metal oxide with which it is possible to improve the performance of a sodium secondary battery; a process for producing the composite metal oxide; a positive active material which comprises the composite metal oxide; a positive electrode produced using the positive active material; and a sodium secondary battery including the positive electrode. The composite metal oxide is represented by the following formula: NaxFeyMn1-yO2. The composite metal oxide is constituted of an oxide having a P2 structure and a lamellar oxide, with some extent of stacking faults, having an octahedral structure and/or a triangular-prism structure. The lamellar oxide preferably is an oxide having an O3 structure.