Process for manufacturing positive electrode active material for lithium ion secondary battery, positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery

A process for manufacturing a positive electrode active material for a lithium ion secondary battery including secondary particles in which a plurality of primary particles are aggregated with each other, the process comprising:

• a mixing process of mixing a lithium-transition metal composite oxide having a crystal structure of a layered structure with lithium phosphate;
• a milling process of applying a mechanical stress to a mixture obtained in the mixing process to form the lithium-transition metal composite oxide having the crystal structure of the layered structure and the lithium phosphate into an amorphous or low-crystalline NiO-like rock-salt type crystal structure;
• and
• a heat treatment process of subjecting the mixture having the amorphous or low-crystalline NiO-like rock-salt type crystal structure obtained in the milling process to a heat treatment to obtain a lithium-transition metal composite oxide having a layered rock-salt type crystal structure in which lithium phosphate is finely crystallized and dispersed,
• wherein the lithium-transition metal composite oxide is represented by a general formula:
• LisNi1-x-y-zCoxMnyMzO2+α (where 0≤x≤0.35, 0≤y≤0.35, 0≤z≤0.10, 1.00≤s≤1.30, 0≤α≤0.2, and M is at least one element selected from V, Mg, Mo, Nb, Ti, W, and Al), and
• the finely crystallized lithium phosphate covers a surface of a primary particle of the lithium-transition metal composite oxide having the layered rock-salt type crystal structure, and is dispersed inside or on a surface of a secondary particle of the lithium-transition metal composite oxide having the layered rock-salt type crystal structure.