Nickel manganese composite hydroxide, production method for nickel manganese composite hydroxide, positive electrode active material for non-aqueous electrolyte secondary battery, production method for positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

A method for producing a nickel-manganese composite hydroxide represented by General Formula (1):

• NixMnyMz(OH)2+α (in Formula (1), M is at least one element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W;
• x satisfies 0.1≤x≤0.9, y satisfies 0.05≤y≤0.8, z satisfies 0≤z≤0.8, and x+y+z=1.0;
• and α satisfies 0≤α≤0.4) and containing a secondary particle formed of a plurality of flocculated primary particles,
• the method comprising a crystallization process of generating a nickel-manganese composite hydroxide by neutralizing a salt containing at least nickel and a salt containing at least manganese in a reaction aqueous solution, wherein
• in the crystallization process, a dissolved oxygen concentration in the reaction aqueous solution is adjusted to fall within a range of greater than 4.6 mg/L and up to 6.0 mg/L, and a dissolved nickel concentration in the reaction aqueous solution is adjusted to fall within a range of at least 300 mg/L and up to 800 mg/L.

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 (2):
• Li1+tNixMnyMzO2+β (in Formula (2), M is at least one element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W;
• t satisfies −0.05≤t≤0.5, x satisfies 0.1≤x≤0.9, y satisfies 0.05≤y≤0.8, z satisfies 0≤z≤0.8, and x+y+z=1.0;
• and β satisfies 0≤β≤0.5) and containing a secondary particle formed of flocculated primary particles, wherein
• the positive electrode active material for a nonaqueous electrolyte secondary battery has a degree of sparsity/density represented by [(a void area within the secondary particle/a cross section of the secondary particle)×100](%) of at least 10% and up to 25% and has a DBP absorption amount measured in compliance with JIS K6217-4:2008 of greater than 20 cm3/100 g and up to 28 ml/100 g.