Positive electrode active material, battery, and method of producing positive electrode active material

A method of producing a positive electrode active material, the method comprising:

• (a) wet grinding a manganese carbonate aqueous solution in a vacuum to form a first slurry, where the manganese carbonate aqueous solution is obtained by bubbling carbon dioxide into an aqueous solution containing a manganese compound;
• (b) wet grinding a mixture of a second slurry, the first slurry, and a phosphate compound, in a vacuum to form a third slurry, where the second slurry is obtained by mixing an iron compound, a lithium compound, and a solvent;
• (c) stirring the third slurry while bubbling carbon dioxide thereinto to form a fourth slurry;
• (d) forming precursor particles by spray pyrolysis of the fourth slurry;
• and
• (e) performing heat treatment of the precursor particles to produce an olivine-type phosphate compound, wherein
• the olivine-type phosphate compound includes lithium manganese iron phosphate, and
• the manganese compound and the iron compound are prepared in such amounts that a molar fraction of a content of manganese relative to contents of manganese and iron in the lithium manganese iron phosphate falls within the range of 0.4 to 0.9.