Cathode active material and the secondary battery comprising the same

1. A cathode active material comprising a lithium nickel manganese composite oxide with a spinel structure represented by the following Formula 1 which is suitable for use in high-voltage batteries having a mean voltage of 4.7V, wherein the cathode active material is surface-coated with a silane compound, and a silicon content of the silane compound is 0.01 to 5% by weight, based on the total amount of the cathode active material:

Li x M y Mn 2−y O 4−x A z   (1)

wherein 0.9≦x≦1.2, 0<y<2, and 0≦z<0.2;

M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi; and

A is at least one monovalent or bivalent anion.

2. The cathode active material according to claim 1 , wherein the silane compound is represented by the following Formula a:

R 1 —Si(R 2 )(R 3 )—R 4   (a)

wherein one or more of R 1 , R 2 , R 3 and R 4 are each independently hydrogen, a halogen, alkylamino, dialkylamino, alkyl alcohol, C 1 -C 20 alkyl, C 1 -C 20 alkenyl, C 1 -C 20 alkynyl, C 1 -C 20 alkoxy, C 1 -C 20 alkoxy carbonyl, C 1 -C 20 acyl, C 3 -C 20 cycloalkyl, C 6 -C 18 aryl, C 2 -C 18 allyl, nitrile, silazane or phosphate.

3. The cathode active material according to claim 2 , wherein, in the silane compound of Formula a, one or more of R 1 to R 3 are a halogen, silazane, C 1 -C 20 alkoxy, C 6 -C 18 aryl, or C 2 -C 18 allyl, and R 4 is C 1 -C 20 alkyl, nitrile, fluorine or phosphate.

4. The cathode active material according to claim 2 , wherein, in the silane compound of Formula a, R 1 and R 2 are a halogen, silazane or C 1 -C 10 alkoxy, C 6 -C 18 aryl, or C 2 -C 18 allyl, and R 3 and R 4 are C 1 -C 20 alkyl, nitrile, fluorine or phosphate.

5. The cathode active material according to claim 2 , wherein, in the silane compound of Formula a, one or more of R 1 to R 3 are C 1 -C 20 alkyl or C 1 -C 20 alkoxy, and R 4 is silazane.

6. The cathode active material according to claim 5 , wherein the silane compound of Formula a is hexamethyldisilazane.

7. The cathode active material according to claim 1 , wherein a silicon content of the silane compound is 0.01 to 3% by weight with respect to the total weight of the cathode active material.

8. The cathode active material according to claim 1 , wherein the lithium metal oxide is represented by the following Formula 2:

Li x Ni y Mn 2−y O 4   (2)

wherein 0.9≦x≦1.2, and 0.4≦y≦0.5.

9. The cathode active material according to claim 8 , wherein the lithium metal oxide is LiNi 0.5 Mn 1.5 O 4 or LiNi 0.4 Mn 1.6 O 4 .

10. A secondary battery comprising the cathode active material according to claim 1 , wherein said secondary battery is suitable for use in high-voltage batteries having a mean voltage of 4.7V.

11. The secondary battery according to claim 10 , wherein the secondary battery is a lithium secondary battery.

12. A battery module comprising the secondary battery according to claim 10 as a unit battery.

13. A battery pack comprising the battery module according to claim 12 .

14. A device comprising the battery pack according to claim 13 .

15. The device according to claim 14 , wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or a power storage system.