Nickel-manganese composite hydroxide, method for producing the same, positive electrode active material for nonaqueous electrolyte secondary battery, method for producing the same, and nonaqueous electrolyte secondary battery
A positive electrode active material reduces an eluted lithium amount when used for a nonaqueous electrolyte secondary battery, and a nickel-manganese composite hydroxide as a precursor. A nickel-manganese composite hydroxide contains a secondary particle formed of a plurality of mutually flocculated primary particles and is represented by Formula (1): Ni x1 Mn y1 M z1 (OH) 2+α (0.70≤x1≤0.95, 0.05≤y1≤0.30, x1+y1+z1=1.0, and 0≤α≤0.4 are satisfied; and M is at least one element selected from Co, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W). The nickel-manganese composite hydroxide has a manganese-rich layer from a particle surface to a particle inner part of the secondary particle. The manganese-rich layer is represented by Formula (2): Ni x2 Mn y2 M z2 (OH) 2+α . The thickness of the manganese-rich layer is at least 5% and up to 20% of the radius of the secondary particle.
1 . A nickel-manganese composite hydroxide comprising a secondary particle formed of a plurality of mutually flocculated primary particles, wherein the nickel-manganese composite hydroxide is represented by General Formula (1): Ni x1 Mn y1 M z1 (OH) 2+α (in the formula (1), 0.70≤x1≤0.95, 0.05≤y1≤0.30, x1+y1+z1=1.0, and 0≤α≤0.4 are satisfied; and M is at least one element selected from Co, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W), wherein
the nickel-manganese composite hydroxide comprises a central part of the secondary particle and a manganese-rich layer from a particle surface to a particle inner part of the secondary particle,
the manganese-rich layer is represented by General Formula (2) below, and a thickness of the manganese-rich layer is at least 5% and up to 20% of a radius of the secondary particle:
Ni x2 Mn y2 M z2 (OH) 2+α General Formula(2):
(in the formula (2), x2+z2=0 and y2=1 are satisfied or y2/(x2+z2)≥0.6 is satisfied; 0.35≤x2 is satisfied; 0≤z2≤0.40, x2+y2+z2=1.0, and 0≤α≤0.4 are satisfied; and M is at least one element selected from Co, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W),
wherein the manganese-rich layer is formed of one layer having a uniform composition, and
the nickel-manganese composite hydroxide has a [(D90−D10)/Mv] indicating a particle diameter variation index calculated from an accumulated 90 volume % diameter (D90), an accumulated 10 volume % diameter (D10), and the volume average particle diameter (Mv) of at least 0.60 in particle size distribution measured by laser diffraction scattering,
wherein the manganese-rich layer is formed from a particle surface to the central part of the secondary particle, and the central part of the secondary particle has a uniform composition.
2 . The nickel-manganese composite hydroxide according to claim 1 , the nickel-manganese composite hydroxide has a volume average particle diameter (Mv) of at least 4 μm and up to 20 μm.
3 . The nickel-manganese composite hydroxide according to claim 1 , the nickel-manganese composite hydroxide has a tap density of at least 1.8 g/cm 3 and up to 3.2 g/cm 3 .
4 . A method for producing the nickel-manganese composite hydroxide as claimed in claim 1 , the method comprising:
generating particles of a nickel-manganese composite hydroxide by continuously supplying a first mixed aqueous solution containing at least a nickel salt and a manganese salt to a reaction aqueous solution to be subjected to neutralization crystallization using a reaction tank for continuous crystallization, and collecting the particles by overflowing slurry containing the particles from a reaction tank; and
forming the manganese-rich layer on surfaces of the particles by subjecting a reaction aqueous solution containing the collected particles and a second mixed aqueous solution having a molar ratio of Ni, Mn, and M similar to that in the manganese-rich layer to neutralization crystallization.
5 . The method for producing the nickel-manganese composite hydroxide according to claim 4 , wherein at the generating and the forming, an ammonia concentration of the reaction aqueous solution is adjusted to at least 5 g/L and up to 25 g/L.
6 . The method for producing the nickel-manganese composite hydroxide according to claim 4 , wherein at the generating and the forming, a temperature of the reaction aqueous solution is adjusted to a range of at least 35° C. and up to 60° C.
7 . The method for producing the nickel-manganese composite hydroxide according to claim 4 , wherein at the forming, a pH value measured with a liquid temperature of 25° C. as a basis of the reaction aqueous solution is adjusted to a range of at least 10.0 and up to 13.0.
8 . 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 (3): Li 1+t Ni x3 Mn y3 M z3 O 2+β (in the formula (3), −0.05≤t≤0.5, 0.70≤x3≤0.95, 0.05≤y3≤0.30, x3+y3+z3=1.0, and 0≤β≤0.5 are satisfied; and M is at least one element selected from Co, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W) and having a hexagonal layered structure, the method comprising:
mixing the nickel-manganese composite hydroxide according to claim 1 and a lithium compound together to form a lithium mixture; and
firing the lithium mixture in an oxidative atmosphere at a temperature of at least 800° C. and up to 950° C. to obtain a lithium-nickel-manganese composite oxide in which the manganese in the manganese-rich layer is diffused.
9 . The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 8 , wherein a value obtained by dividing an accumulated 50 volume % diameter (D50) of the lithium-nickel-manganese composite oxide after the firing by an accumulated 50 volume % diameter (D50) of the nickel-manganese composite hydroxide before the firing is up to 1.2 in particle size distribution measured by laser diffraction scattering.
10 . The nickel-manganese composite hydroxide according to claim 1 , wherein [(D90−D10)/Mv] is 0.7 or more.
11 . The nickel-manganese composite hydroxide according to claim 1 , wherein the thickness of the manganese-rich layer is at least 5% and less than 10% of a radius of the secondary particle.