Cathode active material for secondary battery

1. A cathode active material for secondary batteries comprising a compound having a transition metal layer containing lithium as at least one compound selected from the following Formula 1:

Li(Li 3x±y M 1−y P x )O 2+z   (1)

wherein M is an element stable for a six-coordination structure, which is at least one selected from transition metals that belong to the first and second period elements;

0<x<0.1;

0<y<0.3;

−4x<z≦4x; and

3x>y is satisfied in a case of 3x−y.

2. The cathode active material according to claim 1 , wherein the content of P satisfies the condition of 0<x≦0.05.

3. The cathode active material according to claim 1 , wherein the content of Li in the transition metal layer satisfies the condition of 0.015≦3x±y≦0.3.

4. The cathode active material according to claim 1 , wherein the M is at least one selected from the group consisting of Ni, Mn, Co, Cr, Fe, V and Zr.

5. The cathode active material according to claim 4 , wherein the M contains Ni and Mn as essential elements and contains Co as an optional element.

6. The cathode active material according to claim 5 , wherein the M has a composition of the following formula 2:

M=Ni a Mn b Co c   (2)

wherein 0.10<a<0.85, 0.10<b<0.85, and 0≦c<0.5.

7. A cathode for second batteries comprising the cathode active material according to claim 1 .

8. A lithium secondary battery comprising the cathode according to claim 7 .

9. A battery pack comprising the lithium secondary battery according to claim 8 as a unit battery.

10. The cathode active material according to claim 1 , wherein the oxygen in Formula 1 may be substituted with an anion in an amount of 0.1 moles or less based on the total amount of oxygen.