Positive electrode active material for all-solid-state lithium ion secondary battery and method for manufacturing the same
A positive electrode active material includes a lithium-nickel composite oxide particle and a coating layer. The particle has a crystal structure belonging to a space group R-3m, contains at least Li, Ni, an element M, and Nb, wherein Li:Ni:M:Nb=a:(1-x-y):x:y (0.98≤a≤1.15, 0<x≤0.5, 0<y≤0.03, 0<x+y≤0.5, and the element M is at least one of Co, Al, Mn, Zr, Si, Zn, and Ti), has a crystallite diameter of 140 nm or less, and has an eluted lithium ion amount of 0.30% by mass or more and 1.00% by mass or less. The coating layer is a composite oxide containing Li and at least one of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W.
1 . An all-solid-state lithium ion secondary battery, comprising:
a positive electrode; a negative electrode; and a solid electrolyte, wherein
the positive electrode includes a positive electrode active material comprising a lithium-nickel composite oxide particle and a coating layer coating a surface of the particle,
the lithium-nickel composite oxide particle has a crystal structure belonging to a space group R-3m, which contains at least Li, Ni, an element M, and Nb, a molar ratio among the elements Li, Ni, M, and Nb being represented by a:(1-x-y):x:y, respectively,
wherein
0.98≤a≤1.15,
0<x≤0.5,
0<y≤0.03,
0<x+y≤0.5, and
the element M is at least one selected from the group consisting of Co, Al, Mn, Zr, Si, Zn, and Ti,
the lithium-nickel composite oxide particle has a crystallite diameter of 140 nm or less as calculated by a Scherrer method from a diffraction peak attributed to a (003) plane measured by XRD,
the lithium-nickel composite oxide particle has an eluted lithium ion amount of 0.30% by mass or more and 1.00% by mass or less with respect to a total amount of the lithium-nickel composite oxide particles as determined by neutralization titration,
the coating layer is a composite oxide containing Li and at least one element selected from the group consisting of Al, Si, Ti, V, Ga, Ge, Zr, Nb, Mo, Ta, and W, and
at least one of the positive electrode and the solid electrolyte includes a sulfide solid electrolyte.
2 . The all-solid-state lithium ion secondary battery according to claim 1 , wherein the “y” in the molar ratio satisfies 0.001≤y≤0.012.
3 . The all-solid-state lithium ion secondary battery according to claim 1 , wherein
the element M contains Co and Al,
a molar ratio of Co represented by “x′” in the molar ratio among the elements satisfies 0<x′≤0.3, and
a molar ratio of Al represented by “x″” in the molar ratio among the elements satisfies 0<x″≤0.1.
4 . The all-solid-state lithium ion secondary battery according to claim 1 , wherein the coating layer is a composite oxide containing Li and Nb.