Cathode active material and lithium secondary battery for controlling impurity or swelling including the same and method of preparing cathode active material with enhanced productivity
Disclosed are a cathode active material represented by Formula 1 below and including a metal cation having a greater ionic radius than a Ni cation and represented by M of Formula 1 at a Li cation site or in an empty space within a crystal lattice so as to prevent mixing of Ni cations into a Li layer, a lithium secondary battery including the same, and a method of preparing the cathode active material which has improved productivity. Li a Ni x Mn y Co z M w O 2−t A t (1) wherein a, x, y, w, M, A, z, and t are the same as defined in the specification.
1. A cathode active material represented by Formula 1 below and comprising a metal cation having a greater ionic radius than a Ni cation and represented by M of Formula 1 at a Li cation site or in an empty space within a crystal lattice so as to prevent mixing of Ni cations into a Li layer,
wherein the cathode active material further comprises a Li-containing compound,
wherein an amount of the Li-containing compound is greater than 0 and less than or equal to 0.161 wt % based on a total weight of the cathode active material and the Li-containing compound is Li 2 CO 3 and/or LiOH:
the cathode active material is prepared by a method comprising the steps of sintering a mixture of a transition metal source and a lithium source in air, wherein the mixture comprises an alkaline earth metal source having an oxidation number of +2 so that the sintering is performed at 890° C. to 930° C., and
the alkaline earth metal is Sr or Ba:
Li a Ni x Mn y Co z M w O 2−t A t (Formula 1)
wherein
0≤a≤1.2, 0<x≤0.9, 0<y≤0.9, 0<z≤0.9, 0<w≤0.3, 2≤a+x+y+z+w≤2.3, x>y, x>z, and 0≤t<0.2;
M is Sr 2+ or Ba 2+ ; and
A is at least one monovalent or divalent anion.
2. The cathode active material according to claim 1 , wherein, in Formula 1, y+z≤0.6.
3. The cathode active material according to claim 2 , wherein, in Formula 1, y+z≤0.44.
4. The cathode active material according to claim 1 , wherein M is Sr +2 .
5. The cathode active material according to claim 1 , wherein M is Ba 2+ .
6. The cathode active material according to claim 1 , wherein the Ni cation is Ni 2+ .
7. The cathode active material according to claim 1 , wherein an X-ray diffraction peak ratio (003)/(014) of the cathode active material of Formula 1 is greater than that of a cathode active material represented by Formula 2 below prepared under the same sintering temperature conditions:
Li a Ni x Mn y Co z O 2−t A t (2)
wherein
0≤a≤1.2, 0<x≤0.9, 0<y≤0.9, 0<z≤0.9, a+x+y+z=2, x>y, x>z, and 0≤t<0.2;
and
A is at least one monovalent or divalent anion.
8. A cathode mixture for secondary batteries, comprising the cathode active material according to claim 1 .
9. A cathode for secondary batteries in which the cathode mixture according to claim 8 is coated on a current collector.
10. A lithium secondary battery comprising the cathode according to claim 9 .
11. The lithium secondary battery according to claim 10 , wherein the lithium secondary battery has a capacity retention ratio with respect to initial capacity of 85% or more at 50 cycles performed under the following conditions: at 45° C., charging at 0.5 C and discharging at 1.0 C.
12. A battery module comprising the lithium secondary battery according to claim 10 as a unit cell.
13. A battery pack comprising the battery module according to claim 12 .
14. A device using the battery pack according to claim 13 as a power source.