Positive electrode active material for lithium ion secondary battery, lithium ion secondary battery, and method for producing positive electrode active material for lithium ion secondary battery

1. A positive electrode active material for a lithium ion secondary battery, comprising lithium-nickel composite oxide particles and a coating layer that covers at least a part of surfaces of the lithium-nickel composite oxide particles, wherein

components other than oxygen of the lithium-nickel composite oxide are represented by Li:Ni:Co:M=t:1−x−y:x:y (where, M is at least one element selected from the group consisting of Mg, Al, Ca, Si, Ti, V, Fe, Cu, Cr, Zn, Zr, Nb, Mo, or W, 0.95≤t≤1.20, 0<x≤0.22, and 0≤y≤0.15), and

the coating layer contains a Ti compound, wherein a Ti amount per 1 m 2 surface area of the lithium-nickel composite oxide is 7.0 μmol or more and 60 μmol or less.

2. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein a quotient of an amount ratio (Tis/Nis) of Ti to Ni that are present on a surface of the positive electrode active material for a lithium ion secondary battery and a ratio (Nib/(Nib+Cob+Mb)) of an amount of Ni to a sum of amounts of Ni, Co, and M in an entire positive electrode active material is 0.07 or more and 0.30 or less.

3. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein a carbon content is 0.05% by mass or more and 0.40% by mass or less with respect to 100% by mass of the entire positive electrode active material for a lithium ion secondary battery.

4. The positive electrode active material for a lithium ion secondary battery according to claim 3 , wherein the carbon content is 0.08% by mass or less.

5. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein a specific surface area of the lithium-nickel composite oxide is 0.1 m 2 /g or more and 1.0 m 2 /g or less.

6. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein the lithium-nickel composite oxide is a layered rock-salt type compound particle having a crystal structure belonging to a space group R-3m.

7. A lithium ion secondary battery comprising at least a positive electrode containing the positive electrode active material for a lithium ion secondary battery according to claim 1 , a negative electrode, a separator, and a non-aqueous electrolyte solution.

8. A method for producing a positive electrode active material for a lithium ion secondary battery comprising lithium-nickel composite oxide particles and a coating layer that covers at least a part of surfaces of the lithium-nickel composite oxide particles, the method comprising at least:

a precursor crystallization process for preparing a nickel composite hydroxide that is a precursor of the lithium-nickel composite oxide by a crystallization reaction;

an oxidizing roasting process for oxidizing and roasting the nickel composite hydroxide obtained in the precursor crystallization process to obtain a nickel composite oxide;

a lithium-nickel composite oxide synthesis process for mixing the nickel composite oxide obtained in the oxidizing roasting process with a lithium compound to obtain a mixture and firing the mixture to obtain a lithium-nickel composite oxide; and

a coating process for forming the coating layer containing a Ti compound on at least a part of surfaces of particles of the lithium-nickel composite oxide obtained in the lithium-nickel composite oxide synthesis process.

9. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 8 , wherein

a Ti compound is added so that a Ti amount attributed to the Ti compound is 7.0 μmol or more and 60 μmol or less per 1 m 2 surface area of the lithium-nickel composite oxide in the coating process,

components other than oxygen of the lithium-nickel composite oxide obtained in the coating process are represented by Li:Ni:Co:M=t:1−x−y:x:y (where, M is at least one element selected from the group consisting of Mg, Al, Ca, Si, Ti, V, Fe, Cu, Cr, Zn, Zr, Nb, Mo, or W, 0.95≤t≤1.20, 0<x≤0.22, and 0≤y≤0.15), and

a quotient of an amount ratio (Tis/Nis) of Ti to Ni that are present on a surface of the positive electrode active material for a lithium ion secondary battery and a ratio (Nib/(Nib+Cob+Mb)) of an amount of Ni to a sum of amounts of Ni, Co, and M in an entire positive electrode active material is 0.07 or more and 0.30 or less.

10. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 8 , wherein firing is performed at a temperature of 700° C. or more and 800° C. or less in an oxygen-containing atmosphere in the lithium-nickel composite oxide synthesis process.