POSITIVE ELECTRODE ACTIVE MATERIAL, BATTERY, AND METHOD FOR PRODUCING POSITIVE ELECTRODE ACTIVE MATERIAL

A positive electrode active material includes a primary particle and a coating, wherein the primary particle includes an olivine-type phosphate compound, the coating covers at least part of a surface of the primary particle, the coating includes carbon, and when a filtrate is obtained by a preparation method including immersing 0.5 g of the positive electrode active material in 10 g of pure water and subjecting a resulting immersed liquid to ultrasonic treatment for 10 minutes and stirring for 6 hours followed by filtration, a concentration of a transition metal element in the filtrate detected by ICP-AES is 200 ppm or less in total.