METHOD FOR PRODUCING POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM ION SECONDARY BATTERY

The method for producing a positive electrode active material for a lithium ion secondary battery includes preparing a mixture containing at least a nickel-manganese composite compound, a lithium compound, and optionally one or both of a titanium compound and a niobium compound. The method also includes firing the mixture from 750° C. to 1000° C. so as to obtain the lithium-nickel-manganese composite oxide, in which the nickel-manganese composite compound contains at least nickel, manganese, and an element M, an amount of substance ratio (z) of titanium and an amount of substance ratio (w) of niobium to a total amount of substance of nickel, manganese, the element M, titanium, and niobium in the mixture satisfy 0.005≤z≤0.05, 0.001w, and at least a part of the niobium is segregated to a grain boundary between primary particles.