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

A positive electrode active material for a lithium-ion secondary battery includes a lithium nickel complex oxide having a hexagonal crystalline layered structure and containing secondary particles in which a plurality of primary particles are aggregated. The lithium nickel complex oxide contains Li, Ni, B, and element M (M) at a ratio by mole of Li:Ni:B:M=a:b:c:d (where 0.95≤a≤1.10, 0.50≤b