Positive electrode active material for nonaqueous electrolyte secondary battery, method for producing the same, and nonaqueous electrolyte secondary battery containing the positive electrode active material

1. A positive electrode active material for a nonaqueous electrolyte secondary battery, the positive electrode active material comprising:

a lithium-nickel-cobalt-manganese composite oxide represented by General Formula (1): Li 1+s Ni x Co y Mn z B t M1 u O 2+β (in Formula (1), M1 is an element other than Li, Ni, Co, Mn, and B; and −0.05≤s≤0.20, 0.1≤x≤0.5, 0.1≤y≤0.5, 0.1≤z≤0.5, x+y+z+u=1, 0.025≤t≤0.04, 0≤u≤0.1, and 0≤β≤0.5) and having a hexagonal layered crystal structure, wherein

the lithium-nickel-cobalt-manganese composite oxide contains a secondary particle formed of a plurality of flocculated primary particles and a boron compound containing lithium present at least on part of surfaces of the primary particles, and

a water-soluble Li amount present on the surfaces of the primary particles is up to 0.1% by mass relative to an entire amount of the positive electrode active material.

2. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein the positive electrode active material has an average particle diameter of at least 3 μm and up to 20 μm.

3. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein the primary particles have an average particle diameter of at least 0.2 μm and up to 1.0 μm.

4. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein [(d90−d10)/(an average particle diameter)] as an indicator indicating a spread of particle size distribution of the positive electrode active material is up to 0.60.

5. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein the secondary particle has a hollow structure having a hollow part therewithin.

6. A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, the positive electrode active material comprising a lithium-nickel-cobalt-manganese composite oxide represented by General Formula (1): Li 1+s Ni x Co y Mn z B t M1 u O 2+β (in Formula (1), M1 is an element other than Li, Ni, Co, Mn, and B; and −0.05≤s≤0.20, 0.1≤x≤0.5, 0.1≤y≤0.5, 0.1≤z≤0.5, x+y+z+u=1, 0.025≤t≤0.04, 0≤u≤0.1, and 0≤β≤0.5) and having a hexagonal layered crystal structure, the method comprising:

obtaining nickel-cobalt-manganese composite hydroxide particles represented by General Formula (2): Ni x Co y Mn z M2 u (OH) 2+α (in Formula (2), M2 is an element other than Li, Ni, Co, and Mn; 0.1≤x≤0.5, 0.1≤y≤0.5, 0.1≤z≤0.5, x+y+z+u=1, 0≤u≤0.1, and 0≤α≤0.5) by crystallization;

mixing a lithium compound with the nickel-cobalt-manganese composite hydroxide particles such that a ratio of number of atoms of lithium to a sum of numbers of atoms of metal elements other than lithium is at least 0.95 and up to 1.20 to obtain a lithium mixture;

firing the lithium mixture while being held in an oxidative atmosphere at a temperature of at least 800° C. and up to 1,000° C. for at least 5 hours and up to 20 hours to obtain lithium-nickel-cobalt-manganese composite oxide particles formed of a secondary particle formed of a plurality of flocculated primary particles;

mixing the lithium-nickel-cobalt-manganese composite oxide particles and a boron raw material together to obtain a boron mixture; and

thermally treating the boron mixture in an oxidative atmosphere at a temperature of at least 200° C. and up to 300° C. to form a boron compound containing lithium present at least on part of surfaces of the primary particles, wherein

at the thermally treating, thermal treatment is performed such that a water-soluble Li amount present on the surfaces of the primary particles after the thermal treatment is up to 0.1% by mass relative to an entire amount of the positive electrode active material.

7. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 6 , wherein the boron raw material is at least one of boron oxide and an oxoacid of boron.

8. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 7 , wherein the boron raw material is orthoboric acid.

9. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 6 , further comprising crushing the lithium-nickel-cobalt-manganese composite oxide particles obtained at the firing.

10. A nonaqueous electrolyte secondary battery comprising:

a positive electrode;

a negative electrode;

a separator; and

a nonaqueous electrolyte,

the positive electrode containing the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 .

11. The method for producing the positive electrode active material for the nonaqueous electrolyte secondary battery according to claim 6 , wherein at the thermally treating, the thermal treatment is performed such that the water-soluble Li amount present on surfaces of the primary particles after the thermal treatment is up to 1.3 times the amount before the thermal treatment.