POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM ION SECONDARY BATTERIES, METHOD FOR PRODUCING POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM ION SECONDARY BATTERIES, AND LITHIUM ION SECONDARY BATTERY

A positive electrode active material for a lithium-ion secondary battery containing secondary particles in which a plurality of primary particles are aggregated with each other contains a lithium-transition metal complex oxide having a layered rock-salt type structure. In a crystal structure of the lithium-transition metal complex oxide, a percentage of an element other than Li occupying an Li site (3b site) is 2% or more and 8% or less. A composition of the lithium-transition metal complex oxide is represented by general formula (1) below: General formula (1): LiNiO (where 0.02≤x≤0.08 and -0.1≤α≤0.1).