LITHIUM METAL COMPOSITE OXIDE, POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY, POSITIVE ELECTRODE FOR LITHIUM SECONDARY BATTERY, AND LITHIUM SECONDARY BATTERY
The present invention relates to a lithium metal composite oxide comprising a plurality of secondary particles which are aggregates of primary particles, wherein: at least a part of the secondary particles have voids therein; with respect to outline shape of the voids exposed in cross-sections of the secondary particles having voids therein, an area-weighted average aspect ratio of the voids with an equivalent circle diameter of 0.2 μm or more is 1.8 or more and 5.0 or less; and a ratio of number of the secondary particles having the voids with an equivalent circle diameter of 0.5 μm or more to total number of the secondary particles is 3% or more and 95% or less.
1 . A lithium metal composite oxide comprising a plurality of secondary particles which are aggregates of primary particles, wherein:
at least a part of the secondary particles have voids therein,
with respect to outline shape of the voids exposed in cross-sections of the secondary particles having voids therein, an area-weighted average aspect ratio of the voids with an equivalent circle diameter of 0.2 μm or more is 1.8 or more and 5.0 or less, and
a ratio of number of the secondary particles having the voids with an equivalent circle diameter of 0.5 μm or more to total number of the secondary particles is 3% or more and 95% or less.
2 . The lithium metal composite oxide according to claim 1 , wherein an average value of equivalent circle diameters of the voids with an equivalent circle diameter of 0.2 μm or more is 0.3 μm or more.
3 . The lithium metal composite oxide according to claim 1 , wherein an area-weighted average major axis of the voids with an equivalent circle diameter of 0.2 μm or more is 0.2 μm or more and 15 μm or less.
4 . The lithium metal composite oxide according to claim 1 , wherein the area-weighted average aspect ratio of the voids with an equivalent circle diameter of 0.2 μm or more is 1.0 or more and 5.0 or less.
5 . The lithium metal composite oxide according to claim 1 , wherein a ratio of an area-weighted average major axis of the voids with an equivalent circle diameter of 0.2 μm or more to an area-weighted average major axis of the secondary particles having the voids with an equivalent circle diameter of 0.2 μm or more is 0.001 or more and 0.9 or less.
6 . The lithium metal composite oxide according to claim 1 , which has a volume-based 50% cumulative particle size D 50 of 5 μm or more and 20 μm or less.
7 . The lithium metal composite oxide according to claim 1 , which comprises Li and Ni, and optionally comprises at least one element selected from the group consisting of Co and Mn, wherein a molar percentage of Co relative to a total molar number of elements other than Li and oxygen contained in the lithium metal composite oxide is 5% or less.
8 . The lithium metal composite oxide according to claim 1 , which is represented by composition formula (I) below:
Li
[
Lix
(
Ni
(
1
-
y
-
z
)
M
1
yM
2
z
)
1
-
x
]
O2
,
(
I
)
wherein M1 represents at least one element selected from the group consisting of Co, Mn, and A1; M2 represents at least one element selected from the group consisting of Fe, Cu, Ti, Mg, W, Mo, Nb, Zn, Sn, Zr, Ga, B, Si, S, and P; and the composition formula (I) satisfies −0.1≤x≤0.2, 0<y<1, 0≤z≤0.2, and y+z<1.
9 . The lithium metal composite oxide according to claim 1 , wherein, in a powder X-ray diffraction measurement using CuKα radiation, I D /I E is 0.8 or more, wherein I D is a peak area of a diffraction peak present in a range of 20=18.5±1, and I E is a peak area of a diffraction peak present in a range of 2θ=44.5±1°.
10 . A lithium secondary battery cathode active material, comprising the lithium metal composite oxide of claim 1 .
11 . A lithium secondary battery cathode, comprising the lithium secondary battery cathode active material of claim 10 .
12 . A lithium secondary battery, comprising the lithium secondary battery cathode of claim 11 .
13 . The lithium metal composite oxide according to claim 2 , wherein an area-weighted average major axis of the voids with an equivalent circle diameter of 0.2 μm or more is 0.2 μm or more and m or less.
14 . The lithium metal composite oxide according to claim 2 , wherein the area-weighted average aspect ratio of the voids with an equivalent circle diameter of 0.2 μm or more is 1.0 or more and 5.0 or less.
15 . The lithium metal composite oxide according to claim 3 , wherein the area-weighted average aspect ratio of the voids with an equivalent circle diameter of 0.2 μm or more is 1.0 or more and 5.0 or less.
16 . The lithium metal composite oxide according to claim 2 , wherein a ratio of an area-weighted average major axis of the voids with an equivalent circle diameter of 0.2 μm or more to an area-weighted average major axis of the secondary particles having the voids with an equivalent circle diameter of 0.2 μm or more is 0.001 or more and 0.9 or less.
17 . The lithium metal composite oxide according to claim 3 , wherein a ratio of an area-weighted average major axis of the voids with an equivalent circle diameter of 0.2 μm or more to an area-weighted average major axis of the secondary particles having the voids with an equivalent circle diameter of 0.2 μm or more is 0.001 or more and 0.9 or less.
18 . The lithium metal composite oxide according to claim 4 , wherein a ratio of an area-weighted average major axis of the voids with an equivalent circle diameter of 0.2 μm or more to an area-weighted average major axis of the secondary particles having the voids with an equivalent circle diameter of 0.2 μm or more is 0.001 or more and 0.9 or less.