Positive electrode active material with concentration gradient of dopant for lithium secondary battery
Provided is a positive electrode active material including lithium transition metal oxide for a lithium secondary battery, in which the lithium transition metal oxide includes a dopant diffusing from the surface of the lithium transition metal oxide particle, and the dopant is distributed with a concentration gradient from the center of the particle toward the surface thereof.
1. A positive electrode active material for a lithium secondary battery, the positive electrode active material comprising lithium transition metal oxide represented by the following Chemical Formula 1,
Li a Co 1-x M x O 2 (1)
wherein 0.95≤a≤1.05; 0<x≤0.2, and
M is Al
wherein the lithium transition metal oxide includes a dopant diffusing from a surface of a lithium transition metal oxide particle, and the dopant is distributed with a concentration gradient from a center of the lithium transition metal oxide particle toward the surface thereof, and
wherein 95% or more of the dopant is distributed within the depth range of 100 nm from the surface of the lithium transition metal oxide particle toward the center thereof.
2. The positive electrode active material of claim 1 , wherein 90% or more of the dopant is distributed in the range of 0.5 r to 1 r, based on a mean radius (r) of the lithium transition metal oxide particle.
3. The positive electrode active material of claim 1 , wherein the dopant is distributed within the depth range of 500 nm from the surface of the lithium transition metal oxide particle toward the center thereof.
4. The positive electrode active material of claim 1 , wherein 90% or more of the dopant is distributed within the depth range of 50 nm from the surface of the lithium transition metal oxide particle toward the center thereof.
5. The positive electrode active material of claim 1 , wherein the dopant shows a decreasing concentration gradient from the surface of the lithium transition metal oxide particle toward the center thereof.
6. The positive electrode active material of claim 5 , wherein the concentration gradient of the dopant shows a decreasing graph of a quadratic function of a content change of the dopant versus a distance (L) from the surface of the lithium transition metal oxide particle toward the center thereof.
7. The positive electrode active material of claim 1 , wherein the lithium transition metal oxide shows Li-deficiency on the surface of the particle.
8. The positive electrode active material of claim 1 , wherein the lithium transition metal oxide exhibits charge/discharge characteristics at 3.0 V to 4.55 V.
9. A method of preparing the positive electrode active material of claim 1 , the method comprising:
(a) preparing a lithium transition metal oxide particle and a doping precursor;
(b) coating the surface of the lithium transition metal oxide particle with the doping precursor by mixing the lithium transition metal oxide particle and the doping precursor; and
(c) calcining the doping precursor-coated lithium transition metal oxide particle.
10. The method of claim 9 , wherein the doping precursor is one or more selected from the group consisting of a metal, metal oxide, and a metal salt.
11. The method of claim 9 , wherein in (c), the dopant of the doping precursor diffuses into the lithium transition metal oxide particles.
12. The method of claim 9 , wherein the calcination temperature of (c) is 500° C. to 1000° C.
13. The method of claim 9 , wherein the calcination time of (c) is 3 hours to 20 hours.
14. A positive electrode for a secondary battery, the positive electrode comprising the positive electrode active material of claim 1 .
15. A lithium secondary battery comprising the positive electrode of claim 14 , a negative electrode, and an electrolyte.