A method for producing positive active material particles includes a contacting step of bringing a phosphate compound solution prepared into contact with untreated positive active material particles, the phosphate compound solution being prepared by dissolving phosphate compound into a first dispersion medium. The phosphate compound is at least one of inorganic phosphoric acid, a salt of inorganic phosphoric acid, organic phosphoric acid, and a salt of organic phosphoric acid. The method further includes a particle drying step, after the contacting step, of drying contacted-undried positive active material particles wetted with the phosphate compound solution to obtain positive active material particles each formed with a coating that contains phosphorus at each particle surface.