| 摘要 |
PROBLEM TO BE SOLVED: To provide a material that can be obtained using an abundant raw material as resources and, when used as a positive electrode active material for a sodium ion secondary battery, has excellent charge/discharge performance as compared with the conventional materials.SOLUTION: A sodium ferrite-based composite oxide is represented by a composition formula: Na(FeM)O(where, M represents one or two or more elements having an average valence in the range of 2.5-3.5, and 0≤x≤0.5 is satisfied), has a crystal structure of a hexagonal crystal layered rock-salt-type structure, and has a half-value width at a diffraction peak of a (003) face at around a diffraction angle 2&thetas;=16.3° obtained by an X-ray diffraction method using a Cu-Kα line of 0.13° or less. The sodium ferrite-based composite oxide has high discharge capacity, high initial charge/discharge efficiency, and favorable cycle characteristics, as a positive electrode active material for a sodium ion secondary battery. |
