Lithium metal composite oxide, positive electrode active material for lithium secondary batteries, positive electrode and lithium secondary battery

1 . A lithium metal composite oxide composed of secondary particles that are aggregates of primary particles, and single particles that exist independently from the secondary particles,

wherein the primary particles are particles with an average particle size of less than 0.5 μm, and are particles which constitute part of secondary particles, and the single particles are particles with an average particle size of at least 1.0 μm but not more than 5.0 μm, and

wherein the lithium metal composite oxide is represented by a compositional formula (1) shown below, and satisfies requirements (A), (B) and (C) described below:

Li[Li x (Ni (1-y-z-w) CO y Mn z M w ) 1-x ]O 2   (1)

wherein M is at least one element selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga and V, −0.1≤x≤0.2, 0<y≤0.4, 0≤z≤0.4 and 0≤w≤0.1,

(A) a BET specific surface area of the lithium metal composite oxide is less than 2 m 2 /g,

(B) the lithium metal composite oxide has at least two peaks in a circularity distribution in which a circularity is determined using a formula (2) shown below:

Circularity=4 πS/L 2   (2)

wherein S is a projected surface area in a projected image of a particle that constitutes the lithium metal composite oxide, and L is a circumference of the particle, and

(C) an average particle size D 50 of the lithium metal composite oxide is at least 2 μm but not more than 20 μm,

wherein the circularity distribution is obtained by plotting the circularity along a horizontal axis and a number of particles along a vertical axis, the horizontal axis has a circularity range from 0 to 1.0 divided into 20 data ranges having equal intervals of 0.05, and each peak in the circularity distribution represents a location of the circularity, and

wherein the circularity distribution has a first peak within a circularity range in which the circularity is at least 0.4 but not more than 0.7, and has a second peak within a circularity range in which the circularity is at least 0.75 but not more than 0.95.

2 . The lithium metal composite oxide according to claim 1 , wherein an average circularity is at least 0.4 but not more than 0.8.

3 . The lithium metal composite oxide according to claim 1 , wherein in the circularity distribution, a circularity distribution standard deviation is at least 0.1 but not more than 0.4.

4 . The lithium metal composite oxide according to claim 1 , wherein the first peak is a peak attributable to the single particles, and the second peak is a peak attributable to the secondary particles.

5 . A positive electrode active material for a lithium secondary battery, the active material comprising the lithium metal composite oxide according to claim 1 .

6 . A positive electrode having the positive electrode active material for a lithium secondary battery according to claim 5 .

7 . A lithium secondary battery having the positive electrode according to claim 6 .

8 . A positive electrode active material for a lithium secondary battery, the active material comprising the lithium metal composite oxide according to claim 2 .

9 . A positive electrode having the positive electrode active material for a lithium secondary battery according to claim 8 .

10 . A lithium secondary battery having the positive electrode according to claim 9 .

11 . The lithium metal composite oxide according to claim 3 , wherein the first peak is a peak attributable to the single particles, and the second peak is a peak attributable to the secondary particles.

12 . The lithium metal composite oxide according to claim 1 , wherein an average circularity is at least 0.45 but not more than 0.75.