Composite cathode active material, cathode and lithium battery including the composite cathode active material, and preparation method thereof
In an aspect, a composite cathode active material a cathode and a lithium battery including the composite cathode active material, and a method of preparing the composite cathode active material is disclosed.
1. A composite cathode active material comprising:
particles, wherein each particle has a core; and
a single coating layer formed on the core of each particle,
wherein the single coating layer includes transition metals and the core includes nickel-based lithium transition metal oxide, the single coating layer completely covers the core, and the single coating layer is one body.
2. The composite cathode active material of claim 1 , wherein the single coating layer includes cobalt as a main component among said transition metals at about 50% or more.
3. The composite cathode active material of claim 1 , wherein the single coating layer has a surface and a concentration of cobalt has a gradient continuously decreasing from the surface of the single coating layer to a center of the core.
4. The composite cathode active material of claim 1 , wherein a thickness of the single coating layer is about 100 nm or more.
5. The composite cathode active material of claim 1 , wherein the thickness of the single coating layer is in a range of about 200 nm to about 1000 nm.
6. The composite cathode active material of claim 1 , wherein an average particle diameter of the core is in a range of about 3 μm to about 30 μm.
7. The composite cathode active material of claim 1 , wherein the core is a one-body particle.
8. The composite cathode active material of claim 1 , wherein the core is a secondary particle obtained by agglomeration of primary particles.
9. The composite cathode active material of claim 1 , wherein the single coating layer includes cobalt.
10. The composite cathode active material of claim 1 , wherein the single coating layer includes lithium cobalt oxide.
11. The composite cathode active material of claim 10 , wherein the lithium cobalt oxide is LiCoO 2 .
12. The composite cathode active material of claim 1 , wherein the single coating layer comprises a solid solution of nickel-based lithium transition metal oxide and lithium cobalt oxide.
13. The composite cathode active material of claim 1 , wherein the nickel-based lithium transition metal oxide has a bulk formula expressed as Chemical Formula 1:
Li x Co a Ni b M c O 2+α Chemical Formula 1
where 0.9<x<1.5, 0<a<0.5, 0<b<1, 0<c<1, and −0.1≦a≦0.1, and
M is at least one element selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), tungsten (W), zinc (Zn), aluminum (Al), silicon (Si), manganese (Mn), chromium (Cr), iron (Fe), magnesium (Mg), and vanadium (V).
14. The composite cathode active material of claim 1 , wherein the nickel-based lithium transition metal oxide has a bulk formula expressed as Chemical Formula 3:
Li x Co a Ni b Mn c O 2+α Chemical Formula 3
where 0.9<x<1.1, 0<a<0.5, 0.4<b<1, 0<c<0.5, and −0.1≦a≦0.1.
15. A cathode comprising: a current collector; and the composite cathode active material of claim 1 on the current collector.
16. A lithium battery comprising the cathode of claim 15 ; an anode; and an electrolyte.