POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM ION SECONDARY BATTERY AND LITHIUM ION SECONDARY BATTERY

A positive electrode active material is constituted by lithium transition metal-containing composite oxide particles having a layered rock salt type crystal structure and are composed of secondary particles each formed of an aggregation of primary particles. The secondary particles have a d50 of 3.0 to 7.0 μm, a BET specific surface area of 1.8 to 5.5 m/g, a pore peak diameter of 0.01 to 0.30 μm, and a log differential pore volume [dV/d(log D)] of 0.2 to 0.6 ml/g within a range of the pore peak diameter. In each of a plurality of primary particles having a primary particle size of 0.1 to 1.0 μm, a coefficient of variation of the concentration of an additive element M is 1.5 or less.