METHOD FOR FORMING POSITIVE ELECTRODE ACTIVE MATERIAL, METHOD FOR MANUFACTURING SECONDARY BATTERY, AND SECONDARY BATTERY

A positive electrode active material with high capacity and excellent charge and discharge cycle performance, a positive electrode active material with high productivity, a positive electrode active material that suppresses a decrease in capacity, or the like is provided. Alternatively, a high-capacity secondary battery, a secondary battery with excellent charge and discharge characteristics, a highly safe or reliable secondary battery, or the like is provided. The positive electrode active material is obtained by a first heating step of heating a mixture of a first material, a second material, and a third material and a second heating step of heating a mixture which is a mixture of the mixture, a fourth material, and a fifth material and has a total amount of 15 g or more. The first material is a halogen compound including an alkali metal, the second material includes magnesium, the third material is a metal oxide including a metal A and cobalt, the fourth material includes nickel, and the fifth material includes aluminum. Each heating is performed in an atmosphere including oxygen. A temperature in the first heating step is lower than a temperature in the second heating step by 20° C. or more.