The invention claimed is:
1. A nickel-manganese composite hydroxide represented by General Formula (1): Ni x Mn y M z (OH) 2+α (in Formula (1), M is at least one additional element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W; and x, y, z, and α satisfy 0.1≤x≤0.8, 0.1≤y≤0.6, 0≤z≤0.8, x+y+z=1.0, and 0≤α≤0.4) and containing a secondary particle formed of a plurality of flocculated primary particles, wherein
the primary particles have an aspect ratio of at least 3, and at least some of the primary particles are disposed radially in a direction from a central part of the secondary particle to an outer circumference thereof, and
the secondary particle has a ratio (I(101)/I(001)) of a diffraction peak intensity I(101) of a 101 plane to a diffraction peak intensity I(001) of a 001 plane, measured by an X-ray diffraction measurement, of up to 0.15.
2. The nickel-manganese composite hydroxide according to claim 1 , wherein in an area within 50% of a radius of the secondary particle from the outer circumference of the secondary particle toward the central part thereof, at least 50% of the primary particles in number relative to a total number of the primary particles present within this area are disposed radially.
3. The nickel-manganese composite hydroxide according to claim 1 , wherein a total pore volume in a pore volume distribution is at least 0.015 cm 3 /g and up to 0.03 cm 3 /g.
4. The nickel-manganese composite hydroxide according to claim 1 , wherein a volume-average particle diameter MV is at least 5 μm and up to 20 μm, and [(D90−D10)/average particle diameter] that is an indicator to represent a spread of particle size distribution is at least 0.7.
5. A method for producing a nickel-manganese composite hydroxide represented by General Formula (1): Ni x Mn y M z (OH) 2+α (in Formula (1), M is at least one additional element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W; and x, y, z, and α satisfy 0.1≤x≤0.8, 0.1≤y≤0.6, 0≤z≤0.8, x+y+z=1.0, and 0≤α≤0.4) and containing a secondary particle formed of a plurality of flocculated primary particles,
the method comprising a crystallization process of forming a nickel-manganese composite hydroxide by neutralizing a salt containing at least nickel and a salt containing at least manganese in an aqueous reaction solution, wherein
in the crystallization process, a dissolved nickel concentration in the aqueous reaction solution is controlled in a range of at least 300 mg/L and up to 1,500 mg/L, a dissolved oxygen concentration is controlled in a range of at least 0.5 mg/L and up to 3.5 mg/L, and a stirring power applied to the aqueous reaction solution is controlled in a range of at least 4 kW/m 3 and up to 8 kW/m 3 .
6. The method for producing a nickel-manganese composite hydroxide according to claim 5 , wherein the crystallization process includes continuously adding a mixed aqueous solution including nickel and manganese into a reaction vessel and overflowing slurry including nickel-manganese composite hydroxide particles formed by neutralization to recover the particles.
7. The method for producing a nickel-manganese composite hydroxide according to claim 6 , wherein in the crystallization process, a residence time of the mixed aqueous solution in the reaction vessel is at least 3 hours and up to 15 hours.
8. A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, the method comprising:
a process of mixing the nickel-manganese composite hydroxide according to claim 1 and a lithium compound to obtain a mixture; and
a process of firing the mixture to obtain a lithium-nickel-manganese composite oxide.
9. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 8 , wherein the nickel-manganese composite hydroxide is obtained by the method comprising a crystallization process of forming a nickel-manganese composite hydroxide by neutralizing a salt containing at least nickel and a salt containing at least manganese in an aqueous reaction solution,
wherein, in the crystallization process, a dissolved nickel concentration in the aqueous reaction solution is controlled in a range of at least 300 mg/L and up to 1,500 mg/L, a dissolved oxygen concentration is controlled in a range of at least 0.5 mg/L and up to 3.5 mg/L, and a stirring power applied to the aqueous reaction solution is controlled in a range of at least 4 kW/m 3 and up to 8 kW/m 3 .