Cathode active material for secondary battery and lithium secondary battery comprising the same
View Patent ↗Disclosed are a cathode active material for secondary batteries and a lithium secondary battery including the same. More particularly, a cathode active material for secondary batteries having an operating voltage area of 2.50 V to 4.35 V, including a lithium cobalt-based oxide and a surface-treated lithium nickel-based oxide and having high rolling density by a bimodal form in which an average diameter of the cobalt-based oxide and an average diameter of the lithium nickel-based composite oxide are different, and a lithium secondary battery including the same are disclosed.
1. A cathode active material for secondary batteries having an operating voltage area of 2.50 V to 4.35 V, comprising a lithium cobalt-based oxide and a surface-treated lithium nickel-based oxide, wherein the cathode active material has high rolling density by a bimodal form in which an average diameter of the cobalt-based oxide and an average diameter of the lithium nickel-based composite oxide are different;
wherein the lithium nickel-based oxide forms a coating layer over a whole surface of the lithium nickel-based oxide by reacting with a fluorine-containing polymer, and the coating layer comprises 1000 to 2000 ppm of fluorine based on the total weight of the lithium nickel-based oxide; and
wherein a whole surface of the lithium cobalt-based oxide is coated with Al2O3 and the amount of Al is 0.001 to 2000 ppm based on a total amount of the lithium cobalt-based oxide.
2. The cathode active material according to claim 1 , wherein the rolling density of the cathode active material is 3.8 to 4.0 g/cc.
3. The cathode active material according to claim 1 , wherein an average diameter of the lithium cobalt-based oxide is 16 to 25 μm and an average diameter of the lithium nickel-based oxide is 2 to 10 μm.
4. The cathode active material according to claim 1 , wherein an average diameter of the lithium cobalt-based oxide is 2 to 10 μm and an average diameter of the lithium nickel-based oxide is 16 to 25 μm.
5. The cathode active material according to claim 1 , wherein the lithium cobalt-based oxide is represented by Formula 1 below:
Li(Co(1- a )M a )O2 (1)
wherein 0.1≦a≦0.2, and
M is at least one element selected the group consisting of Mg, Ti, Zr, Al and Si.
6. The cathode active material according to claim 5 , wherein M is Mg and/or Ti.
7. The cathode active material according to claim 1 , wherein the amount of Al is 350 to 500 ppm.
8. The cathode active material according to claim 1 , wherein a coating thickness of Al2O3 is 0.5 to 2 nm.
9. The cathode active material according to claim 1 , wherein Al2O3 is coated on a surface of the lithium cobalt-based oxide through wet coating.
10. The cathode active material according to claim 1 , wherein the lithium nickel-based oxide is represented by Formula 2 below and comprised in an amount of 10 to 50 wt % based on a total amount of the cathode active material:
Li1+ x Ni a Mn b Co1−( a+b )O2 (2)
wherein −0.2≦x≦0.2, 0.5≦a≦0.6, and 0.2≦b≦0.3.
11. The cathode active material according to claim 10 , wherein the lithium nickel-based oxide is comprised in 20 to 40 wt % based on a total amount of the cathode active material.
12. The cathode active material according to claim 1 , wherein the fluorine-containing polymer is PVdF or PVdF-HFP.
13. The cathode active material according to claim 12 , wherein the fluorine-containing polymer is PVdF.
14. The cathode active material according to claim 1 , wherein a whole surface of the lithium nickel-based oxide is coated with a metal oxide, and an amount of the metal is 0.001 to 3000 ppm based on the total weight of the lithium nickel-based oxide.
15. The cathode active material according to claim 14 , wherein the metal oxide is Al2O3.
16. The cathode active material according to claim 1 , wherein the coating is performed to a thickness of 0.5 to 2 nm.
17. The cathode active material according to claim 1 , wherein the coating is performed through wet coating or dry coating.
18. A lithium secondary battery comprising the cathode active material according to claim 1 , wherein an operating voltage area is 2.50 V to 4.35 V.
19. The cathode active material according to claim 14 , wherein an amount of the metal is 1000 to 2000 ppm based on the total weight of the lithium nickel-based oxide.
20. The cathode active material according to claim 14 , wherein the coating is performed to a thickness of 0.5 to 2 nm.
21. The cathode active material according to claim 14 , wherein the coating is performed through wet coating or dry coating.