NEGATIVE ELECTRODE ACTIVE MATERIAL AND NEGATIVE ELECTRODE FOR SODIUM SECONDARY BATTERY USING MOLTEN SALT ELECTROLYTE, AND SODIUM SECONDARY BATTERY USING MOLTEN SALT ELECTROLYTE

摘要

An object of the present invention is to provide a negative electrode active material etc. which have a high capacity density and which can improve cycle characteristics of a sodium secondary battery using a molten salt electrolyte. The negative electrode active material for a sodium secondary battery using a molten salt electrolyte includes tricobalt tetroxide. In the negative electrode active material, the tricobalt tetroxide preferably has an average particle size d₅₀ of 10 μm or less and a maximum particle size d_max of 30 μm or less.