Positive electrode active material for nonaqueous electrolyte secondary batteries, method for producing same, and nonaqueous electrolyte secondary battery

A method for producing a positive electrode, active material for a nonaqueous electrolyte secondary battery, the positive electrode active material comprising a lithium-nickel-manganese composite oxide represented by General Formula (1):

• LidNi1-a-b-cMnaMbNbcO2+γ (in Formula (1), M is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, and Ta;
• and 0.05≤a≤0.60, 0≤b≤0.60, 0.0003≤c≤0.03, 0.95≤d≤1.20, and 0≤γ≤0.5) and containing a secondary particle formed of a plurality of flocculated primary particles, at least part of niobium being solid-solved in the primary particles,
• the method comprising:
• preparing a lithium-niobium mixture containing one or more selected from nickel-manganese composite hydroxide particles represented by General Formula (2):
• Ni1-a-b-cMnaMb(OH)2+α (in Formula (2), M is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, and Ta;
• and 0.05≤a≤0.60, 0≤b≤0.60, and 0≤a≤0.4) and nickel-manganese composite oxide particles represented by General Formula (3):
• Ni1-a-b-cMnaMbO1+β (in Formula (3), M is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Ti, Cr, Zr, and Ta;
• and 0.05≤a≤0.60, 0≤b≤0.60, and 0≤β≤0.41, a niobium compound, and a lithium compound;
• and
• firing the lithium-niobium mixture in an oxidative atmosphere at at least 750° C. and up to 1,000° C. to obtain the lithium-nickel-manganese composite oxide.