Cathode active material for lithium secondary battery and lithium secondary battery including the same
A cathode active material for a lithium secondary battery according to an embodiment of the present invention includes a lithium-nickel composite metal oxide in which an oxidation number of nickel is 2.8 or more. The lithium-nickel composite metal oxide includes a first doping element having an oxidation number of +2 and a second doping element having an oxidation number of +4. A ratio of a molar ratio of the second doping element relative to a molar ratio of the first doping element is greater than 1 and less than 5.
1 . A cathode active material for a lithium secondary battery comprising a lithium-nickel composite metal oxide in which an oxidation number of nickel is 2.8 or more,
wherein the lithium-nickel composite metal oxide comprises a first doping element having an oxidation number of +2 and a second doping element having an oxidation number of +4,
the first doping element includes Sr, and
a ratio of a molar ratio of the second doping element relative to a molar ratio of the first doping element is in a range from 1.2 to 4.8.
2 . The cathode active material for a lithium secondary battery according to claim 1 , wherein the first doping element further comprises at least one element selected from the group consisting of Mg, Ca, Ba and Ra.
3 . The cathode active material for a lithium secondary battery according to claim 2 , wherein a molar ratio of Sr in the first doping element is greater than or equal to a molar ratio of the at least one element in the first doping element.
4 . The cathode active material for a lithium secondary battery according to claim 1 , wherein the second doping element comprises Ti or Zr.
5 . The cathode active material for a lithium secondary battery according to claim 1 , wherein the lithium-nickel composite metal oxide further comprises at least one additional doping element selected from the group consisting of B, Al, P, Si, V, Mo, Re, Sn and W.
6 . The cathode active material for a lithium secondary battery according to claim 1 , wherein the lithium-nickel composite metal oxide has a chemical structure represented by Chemical Formula 1 below:
Li
a
Ni
x
Co
y
Mn
z
M
2
d
M
4
e
M
f
′
O
2
+
b
[
Chemical
Formula
1
]
wherein, in Chemical Formula 1, M2 represents the first doping element, M4 represents the second doping element, M′ represents an additional doping element other than M2 and M4, and
0.9
≤
a
≤
1
.
2
,
0
.
8
≤
x
≤
0
.
9
9
,
0
.
0
1
≤
y
+
z
≤
0.2
,
0
<
d
<
0
.
0
5
,
0
<
e
<
0
.
0
5
,
0
≤
f
<
0.05
,
and
-
0.1
≤
b
≤
0
.
1
.
7 . The cathode active material for a lithium secondary battery according to claim 6 , wherein, in Chemical Formula 1, 0.0005<d<0.003 and 0.001<e<0.005.
8 . The cathode active material for a lithium secondary battery according to claim 6 , wherein, in Chemical Formula 1, 0<d<1.7((2x+3(x−z))z)/100.
9 . The cathode active material for a lithium secondary battery according to claim 6 , wherein, in Chemical Formula 1, 0.5((2x+3(x−z))z)/100<d<1.7((2x+3(x−z))z)/100.
10 . The cathode active material for a lithium secondary battery according to claim 6 , wherein, in Chemical Formula 1, 0<e<0.12((2x+3(x−z))/x)/100.
11 . The cathode active material for a lithium secondary battery according to claim 6 , wherein, in Chemical Formula 1, 0.05((2x+3(x−z))/x)/100<e<0.12((2x+3(x−z))/x)/100.
12 . The cathode active material for a lithium secondary battery according to claim 1 , wherein the ratio of the molar ratio of the second doping element relative to the molar ratio of the first doping element is in a range from 1.2 to 2.0 within a range of the oxidation number of nickel from 2.8 to 2.95.
13 . The cathode active material for a lithium secondary battery according to claim 1 , wherein the ratio of the molar ratio of the second doping element relative to the molar ratio of the first doping element is in a range from 2.1 to 4.7, provided that the oxidation number of nickel exceeds 2.95.
14 . The cathode active material for a lithium secondary battery according to claim 13 , wherein the ratio the molar ratio of the second doping element relative to the molar ratio of the first doping element is greater than 2 and less than 3.5, provided that the oxidation number of nickel is greater than 2.95, and less than or equal to 2.98.
15 . The cathode active material for a lithium secondary battery according to claim 13 , wherein the ratio of the molar ratio of the second doping element relative to the molar ratio of the first doping element is in a range from 3.5 to 4.7, provided that the oxidation number of nickel exceeds 2.98.
16 . A lithium secondary battery, comprising:
a cathode comprising a cathode active material layer that comprises the cathode active material for a lithium secondary battery of claim 1 ; and
an anode facing the cathode.