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

The positive electrode active material for a lithium ion secondary battery contains a lithium-nickel composite oxide, in which the lithium-nickel composite oxide contains lithium, nickel, manganese, titanium, niobium, and optionally an element M1, an amount of substance ratio of the respective elements is represented as Li:Ni:Mn:M:Ti:Nb=a:(1−x1−y1−b−c):x1:y1:b:c (provided that, 0.95≤a≤1.25, (1−x1−y1−b−c)