POSITIVE ELECTRODE ACTIVE MATERIAL AND SECONDARY BATTERY PROVIDED WITH POSITIVE ELECTRODE ACTIVE MATERIAL

The present disclosure provides a positive electrode active material having a spinel-type crystal structure that can reduce an increase in resistance and a decrease in capacity retention rate due to repeated charging and discharging of a non-aqueous electrolyte secondary battery. The positive electrode active material disclosed herein is configured of a lithium manganese composite oxide having a spinel-type crystal structure, wherein the lithium manganese composite oxide includes secondary particles in which a plurality of primary particles are aggregated, an average particle diameter of the secondary particles based on a SEM image is 10 μm or more and 20 μm or less, an average particle diameter of the primary particles based on a SEM image is 4 μm or more and 8 μm or less, and nickel atoms are provided in the surface layer portion of the secondary particles.