Cathode active material and lithium secondary battery containing the same

1. A cathode active material, comprising:

cathode active material particles, comprising a lithium nickel oxide represented by Formula 1, wherein the lithium nickel oxide has a nickel content of at least 40 molar percent among overall transition metals and wherein the cathode active material particles are coated with a compound not reacting with an electrolyte (“non-reactive material”), which is Al 2 O 3 , as well as a carbon material, at a surface of the lithium nickel oxide;

Li x Ni y M 1-y O 2   (1)

wherein 0.95≦x≦1.15, 0.4≦y≦0.9, and

M is (1) Mn, (2) Co, and (3) a stable element of Mg or stable elements of Mg and Al; and

wherein a content of the stable element(s) is less than 0.03,

wherein the carbon material is at least one selected from the group consisting of carbon black, acetylene black, and ketchen black,

wherein a nickel content is greater than a manganese content, and the manganese content is greater than a cobalt content, and

wherein a coating amount ranges from 0.5 to 4% by weight relative to a total weight of the cathode active material.

2. The cathode active material according to claim 1 , wherein the cathode active material particles have an average particle diameter D50 of 3 to 20 μm.

3. The cathode active material according to claim 1 , wherein the cathode active material particles are in a secondary particle form comprising agglomerated primary particles, and the primary particles have an average particle diameter of 0.01 to 8 μm while the secondary particles have an average particle diameter of 3 to 20 μm.

4. The cathode active material according to claim 1 , wherein either the non-reactive material or the carbon material has an average particle diameter D50 equal to 50% or less of an average particle diameter D50 of the cathode active material particles.

5. The cathode active material according to claim 1 , wherein a relative content ratio of the non-reactive material to the carbon material ranges from 90:10 to 10:90 (wt. %).

6. The cathode active material according to claim 1 , wherein the non-reactive material as well as the carbon material are combined with the surface of the cathode active material particles by physical bonding.

7. The cathode active material according to claim 1 , wherein the non-reactive material and the carbon material are each independent phases applied to a surface of the cathode active material particles.

8. The cathode active material according to claim 1 , wherein the non-reactive material and the carbon material are applied to the surface of the cathode active material particles, in a combination form thereof.

9. The cathode active material according to claim 1 , wherein 20 to 80% of an overall surface of the cathode active material particles are coated with the non-reactive material and the carbon material.

10. A lithium secondary battery including the cathode active material as set forth in claim 1 .

11. The lithium secondary battery according to claim 10 , wherein the lithium secondary battery is used as a power supply for a power tool, an electric vehicle, an electric two-wheel vehicle and/or an electric golf cart.

12. A cathode composition comprising:

the cathode active material according to claim 1 ;

a conductive material; and

a binder.

13. A cathode, comprising:

a cathode collector; and

the cathode composition according to claim 12 applied to the current collector.