POSITIVE ELECTRODE ACTIVE MATERIAL

To provide a positive electrode active material capable of improving cycle characteristics of a lithium ion secondary battery and achieving a desirable discharge capacity. A positive electrode active material that is an aggregate of lithium compounds each including a lithium-containing transition metal oxide, includes particles having a surface on which a solid film including a plurality of types of lithium salts is formed. The solid film preferably includes a fluorine compound and a phosphorus compound. The solid film preferably contains 70 mol % or more of fluorine atoms with respect to the total number of moles of the fluorine atoms and phosphorus atoms.