POSITIVE ELECTRODE ACTIVE MATERIAL FOR NONAQUEOUS ELECTROLYTE SECONDARY BATTERIES, METHOD FOR PRODUCING SAME, AND NONAQUEOUS ELECTROLYTE SECONDARY BATTERY

Provided is a positive electrode active material with which a nonaqueous electrolyte secondary battery can be obtained that achieves both high energy density and output characteristics and thermal stability at the time of short-circuit owing to low conductivity. A positive electrode active material for a nonaqueous electrolyte secondary battery contains a lithium-nickel-manganese composite oxide containing a secondary particle formed of a plurality of flocculated primary particles. The lithium-nickel-manganese composite oxide is represented by General Formula (1): LiNiMnMNbO, at least part of niobium is solid-solved in the primary particles, and a maximum niobium concentration within the primary particles is at least one time and up to three times an average niobium concentration within the primary particles.