Positive electrode active material and positive electrode for nonaqueous electrolyte secondary battery
Provided is a positive electrode active material which inhibits a decrease in discharge capacity while improving output in a low SOC region. The positive electrode active material includes: first particles that each consist of a first lithium transition metal composite oxide, the first lithium transition metal composite oxide having a layered structure and having a ratio of a number of moles of nickel to a total number of moles of metals other than lithium in a composition thereof being 0.7 or greater and smaller than 1; second particles that have a volume average particle diameter smaller than a volume average particle diameter of the first particles, the second particles each consisting of a second lithium transition metal composite oxide having a layered structure; and third particles that each consist of a third lithium transition metal composite oxide, the third lithium transition metal composite oxide having a layered structure, having a ratio of number of moles of nickel to total number of moles of metals other than lithium in a composition thereof being 0.4 to 0.6, and having a ratio of a number of moles of cobalt to the total number of moles being 0.35 to 0.55. The first particle content is 60 mass % or higher and lower than 100 mass %, and the third particle content is 10 mass % or lower, to a total content of the first particles, the second particles, and the third particles.
1 . A positive electrode active material comprising:
first particles that each consist of a first lithium transition metal composite oxide, the first lithium transition metal composite oxide having a layered structure and having a ratio of a number of moles of nickel to a total number of moles of metals other than lithium in a composition thereof being 0.7 or greater and smaller than 1;
second particles that have a volume average particle diameter smaller than a volume average particle diameter of the first particles, the second particles each consisting of a second lithium transition metal composite oxide having a layered structure; and
third particles that each consist of a third lithium transition metal composite oxide, the third lithium transition metal composite oxide having a layered structure, having a ratio of a number of moles of nickel to a total number of moles of metals other than lithium in a composition of the third particles being 0.4 or greater and 0.6 or smaller, and having a ratio of a number of moles of cobalt to the total number of moles being 0.35 or greater and 0.55 or smaller, wherein
a content of the first particles is 60% by mass or higher and lower than 100% by mass to a total content of the first particles, the second particles, and the third particles, and
a content of the third particles is higher than 0% and 10% by mass or lower to the total content of the first particles, the second particles, and the third particles, wherein the second particles consist of the second lithium transition metal composite oxide having a composition that has a ratio of a number of moles of nickel to a total number of moles of metals other than lithium being 0.33 or greater and smaller than 1, and a ratio of a number of moles of cobalt to the total number of moles being 0.01 or greater and 0.35 or smaller.
2 . The positive electrode active material according to claim 1 , wherein the content of the third particles is higher than 0% and 8% by mass or lower to the total content of the first particles, the second particles, and the third particles.
3 . The positive electrode active material according to claim 2 , wherein
the content of the first particles is 70% by mass or higher and 90% by mass or lower to the total content of the first particles, the second particles, and the third particles, and
a content of the second particles is 1% by mass or higher and lower than 30% by mass to the total content of the first particles, the second particles, and the third particles.
4 . The positive electrode active material according to claim 3 , wherein the third particles have a volume average particle diameter that is smaller than the volume average particle diameter of the first particles.
5 . The positive electrode active material according to claim 4 , wherein
the volume average particle diameter of the first particles is 8 μm or larger and 20 μm or smaller,
the volume average particle diameter of the second particles is 2 μm or larger and smaller than 8 μm, and
the volume average particle diameter of the third particles is 2 μm or larger and smaller than 8 μm.
6 . The positive electrode active material according to claim 5 , wherein
a ratio of the volume average particle diameter of the first particles to the volume average particle diameter of the second particles is 1.3 or greater and 10 or smaller.
7 . The positive electrode active material according to claim 6 , wherein
the second particles each consist of a second lithium transition metal composite oxide having a composition that has a ratio of a number of moles of nickel to a total number of moles of metals other than lithium being 0.7 or greater and smaller than 1.
8 . The positive electrode active material according to claim 1 , wherein
the content of the first particles is 70% by mass or higher and 90% by mass or lower to the total content of the first particles, the second particles, and the third particles, and
a content of the second particles is 1% by mass or higher and lower than 30% by mass to the total content of the first particles, the second particles, and the third particles.
9 . The positive electrode active material according to claim 1 , wherein
the third particles have a volume average particle diameter that is smaller than the volume average particle diameter of the first particles.
10 . The positive electrode active material according to claim 1 , wherein
the volume average particle diameter of the first particles is 6 μm or larger and 30 μm or smaller,
the volume average particle diameter of the second particles is 1 μm or larger and 10μm or smaller, and
the volume average particle diameter of the third particles is 1 μm or larger and 10 μm or smaller.
11 . The positive electrode active material according to claim 1 , wherein
the volume average particle diameter of the first particles is 8 μm or larger and 20 μm or smaller,
the volume average particle diameter of the second particles is 2 μm or larger and smaller than 8 μm, and
the volume average particle diameter of the third particles is 2 μm or larger and smaller than 8 μm.
12 . The positive electrode active material according to claim 1 , wherein
a ratio of the volume average particle diameter of the first particles to the volume average particle diameter of the second particles is 1 . 3 or greater and 10 or smaller.
13 . The positive electrode active material according to claim 1 , wherein
the second particles each consist of a second lithium transition metal composite oxide having a composition that has a ratio of a number of moles of nickel to a total number of moles of metals other than lithium being 0.7 or greater and smaller than 1.
14 . The positive electrode active material according to claim 4 , wherein
the first lithium transition metal composite oxide has a composition represented by Formula (1) below,
Li p1 Ni x1 Co y1 M 1 z1 M 2 w1 O α1 (1)
and wherein
p1, x1, y1, z1, w1, and α1 satisfy 0.95≤p1≤1.5, 0.7≤x1<1, 0<y1≤0.3, 0≤z1≤0.3, 0≤w1≤0.02, x1+y1+z1+w1=1, and 1.5≤α1≤2.5,
where
M 1 represents at least one of Mn and Al, and
M 2 represents at least one selected from the group consisting of Ca, Zr, Ti, Mg, Ta, Nb, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu.
15 . The positive electrode active material according to claim 1 , wherein
the second lithium transition metal composite oxide has a composition represented by Formula (2) below,
Li p2 Ni x2 Co y2 M 1 z2 M 2 w2 O α2 (2)
and wherein
p2, x2, y2, z2, w2, and α2 satisfy 0.95≤p2≤1.5, 0.33≤x2<1, 0.01≤y2≤0.35, 0≤z2≤0.6, 0≤w2≤0.02, x2+y2+z2+w2=1, and 1.5≤α2≤2.5, where
M 1 represents at least one of Mn and Al, and
M 2 represents at least one selected from the group consisting of Ca, Zr, Ti, Mg, Ta, Nb, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu.
16 . The positive electrode active material according to claim 1 , wherein
the third lithium transition metal composite oxide has a composition represented by Formula (3) below,
Li p3 Ni x3 Co y3 M 1 z3 M 2 w3 O α3 (3)
and wherein
p3, x3, y3, z3, w3, and α3 satisfy 0.95≤p3≤1.5, 0.4≤x3≤0.6, 0.35≤y3≤0.55, 0≤z3≤0.25, 0≤w3≤0.02, x3+y3+z3+w3=1, and 1.5≤α3≤2.5, where
M 1 represents at least one of Mn and Al, and
M 2 represents at least one selected from the group consisting of Ca, Zr, Ti, Mg, Ta, Nb, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu.
17 . A positive electrode for a nonaqueous electrolyte secondary battery, the positive electrode comprising the positive electrode active material according to claim 1 .