Cathode active material for secondary battery with enhanced lifespan characteristics and method of preparing the same

1. A cathode active material comprising coexisting (1) lithium cobalt oxide particles including particle boundaries and (2) manganese (Mn) -containing lithium transition metal oxide particles provided by a manganese-containing compound selected from MnO 2 , MnCO 3 , MnOOH, Mn(CH 3 COO) 3 , Mn(CH 3 COO) 2 , MnSO 4 , and Mn(NO 3 ) 2 ,

wherein said manganese-containing lithium transition metal oxide particles are present inside the particle boundaries of the lithium cobalt oxide particles,

wherein the lithium cobalt oxide particles have a diameter of 5 μm to 30 μm, and include a lithium deficiency layer of Li x CoO 2 (x<1.0),

wherein the Mn-containing lithium transition metal oxide particles have a diameter of 5 μm or less,

wherein the diameter of the Mn-containing lithium transition metal oxide particles is smaller than the diameter of the lithium cobalt oxide particles,

wherein the Mn-containing lithium transition metal oxide particles are inserted into the particle boundaries of lithium cobalt oxide particles, and

wherein the Mn-containing lithium transition metal oxide particles comprise Li 2 MnO 3 having a layered crystal structure and Mn exists as a stable tetravalent cation, whereby phase transition does not occur during high-rate charge and discharge.

2. The cathode active material according to claim 1 , wherein the cathode active material further comprises an electrochemically inert lithium compound on outer surfaces of the lithium cobalt oxide particles.

3. The cathode active material according to claim 2 , wherein the lithium compound is LiOH.

4. The cathode active material according to claim 2 , wherein the lithium compound is Li 2 CO 3 .

5. A lithium secondary battery comprising the cathode active material according to claim 1 .

6. A battery module comprising the lithium secondary battery according to claim 5 as a unit battery.

7. A battery pack comprising the battery module according to claim 6 .

8. A device using the battery pack according to claim 7 as a power source.

9. The device according to claim 8 , wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a device for storing power.