Cathode active material for lithium secondary battery

1. A cathode active material, comprising:

cathode active material particles having an average particle diameter D50 of 3 to 20 μm, said cathode active material particles comprising an agglomerated structure of an aggregate of microfine particles which have an average particle diameter D90 of 0.01 to 8 μm, said microfine particles comprising a lithium nickel-manganese-cobalt oxide represented by Formula 1, wherein the lithium nickel-manganese-cobalt oxide has a nickel content of at least 40% among overall transition metals; and

polypyrrole coated on a surface of said cathode active material particles:

Li x M y O 2   (1)

wherein M is Ni 1-a-b Mn a Co b (0.05≦a≦0.4, 0.1≦b≦0.4, 0.4≦(1-a-b)≦0.9), x+y is about 2 and 0.95≦x≦1.15; and

wherein a coating amount of polypyrrole coated on an exposed surface of the agglomeration of said cathode active material particles ranges from 0.5 to 10% by weight relative to a total weight of the active material; and

a coating thickness ranges from 0.1 to 10 μm.

2. A cathode active material according to claim 1 , wherein the polypyrrole has a melting point of 80 to 300° C.

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

4. The lithium secondary battery according to claim 3 , 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.

5. The cathode active material according to claim 1 , wherein the lithium nickel-manganese-cobalt oxide is LiNi 0.53 Mn 0.27 Co 0.2 O 2 .

6. The cathode active material according to claim 1 , wherein the lithium nickel-manganese-cobalt oxide is LiNi 0.5 Mn 0.3 Co 0.2 O 2 .

7. A cathode active material composition comprising:

the cathode active material according to claim 1 ;

a conductive material; and

a binder.