Positive electrode active material for lithium secondary batteries, positive electrode for lithium secondary batteries, and lithium secondary battery
A positive electrode active material for a lithium secondary battery, comprising a lithium-containing composite metal oxide in the form of secondary particles formed by aggregation of primary particles capable of being doped and undoped with lithium ions, each of the secondary particles having on its surface a coating layer, the positive electrode active material satisfying the following requirements (1) to (3): (1) the metal oxide has an α-NaFeO 2 type crystal structure of following formula (A): Li a (Ni b Co c M 1 1-b-c )O 2 (A) wherein 0.9≤a≤1.2, 0.9≤b<1, 0<c≤0.1, 0.9<b+c≤1, and M 1 represents at least one optional metal selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In and Sn; (2) the coating layer comprises Li and M 2 , wherein M 2 represents at least one optional metal selected from Al, Ti, Zr and W; and (3) the active material has an average secondary particle diameter of 2 to 20 μm, a BET specific surface area of 0.1 to 2.5 m 2 /g, and a value of 1.0 to 2.0 as a tamped density/untamped density ratio of the active material.
1. A positive electrode active material powder for a lithium secondary battery, consisting of a lithium-containing composite metal oxide in a form of secondary particles formed by aggregation of primary particles capable of being doped and undoped with lithium ions, each of the secondary particles having on its surface a coating layer, the positive electrode active material powder satisfying the following requirements (1) to (3):
(1) the lithium-containing composite metal oxide has an α-NaFeO 2 type crystal structure represented by the following formula (A):
Li a (Ni b Co c M 1 1-b-c )O 2 (A)
wherein 0.9≤a≤1.2, 0.9≤b<1, 0<c≤0.1, 0.9<b+c≤1, and M 1 represents at least one metal selected from the group consisting of Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In and Sn;
(2) the coating layer consisting of a metal composite oxide of Li and M 2 , wherein M 2 represents at least one metal selected from the group consisting of Al, Ti, Zr and W; and
(3) the positive electrode active material powder having an average secondary particle diameter of 2 μm to 20 μm, a BET specific surface area of 0.1 m 2 /g to 2.5 m 2 /g, a value of 1.0 to 2.0 as a quotient of a tamped density of the positive electrode active material powder and an untamped density of the positive electrode active material powder, wherein the tamped density is a tapped bulk density in accordance with JIS R 1628:1997, and the untamped density is an initial stage bulk density in accordance with JIS R 1628:1997; and
wherein a value of [diameter D90 of the positive electrode active material powder/diameter D10 of the positive electrode active material powder] is 1 to 3.
2. The positive electrode active material powder according to claim 1 , wherein M 1 is at least one metal selected from the group consisting of Mg, Al, Ca, Ti, Mn, Zn, Ga, Zr and Sn.
3. The positive electrode active material powder according to claim 1 , wherein M 1 is at least one metal selected from the group consisting of Mg, Al, Mn, Zn and Sn.
4. The positive electrode active material powder according to claim 1 , wherein the tamped density is 1.0 g/cm 3 to 3.5 g/cm 3 .
5. The positive electrode active material powder according to claim 1 , wherein an atomic ratio of M 2 is 0.1 to 5 mol %, relative to a sum of atomic ratios of Ni, Co and M 1 .
6. The positive electrode active material powder according to claim 1 , wherein M 2 is Al.
7. The positive electrode active material powder according to claim 1 , wherein the coating layer is formed of lithium aluminate.
8. The positive electrode active material powder according to claim 1 , wherein an atomic ratio of M 2 is 0.1 to 3 mol %, relative to a sum of atomic ratios of Ni, Co and M 1 .