Positive electrode active material having improved safety and lifetime characteristics and lithium secondary battery comprising the same

1. A lithium secondary battery comprising a positive electrode active material represented by the following Chemical Formula 1:

Li{Li a Mn x M 1-a-x-y M′ y }O 2   [Chemical Formula 1]

where 0<a≦0.2, x>(1−a)/2, and 0.05≦y<0.2(1−a), and M is simultaneously applied by two elements of nickel (Ni) and cobalt (Co), and M′ is a metal having an ion diameter of 70 pm or more with an oxidation number of 4 as well as a six-coordinate octahedral structure,

wherein the positive electrode active material further comprises any one or two or more lithium-containing metal oxides selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide, lithium cobalt-nickel-manganese oxide, lithium-containing olivine-type phosphate, lithium-containing manganese spinel, and lithium-containing metal oxide having other element(s) substituted or doped thereto;

wherein the battery is prepared by performing a formation process comprising charging at a voltage from 4.4V to 5.0 V based on a positive electrode potential and degassing after the formation process; and wherein a generation of gas is completed in an initial formation process and the gas is not generated during a subsequent charge and discharge cycle.

2. The lithium secondary battery of claim 1 , wherein M′ in Chemical Formula 1 is simultaneously applied by any one element or two or more elements selected from the group consisting of titanium (Ti), vanadium (V), and iron (Fe).

3. The lithium secondary battery of claim 2 , wherein M′ in Chemical Formula 1 is Fe.

4. The lithium secondary battery of claim 1 , wherein M′ in Chemical Formula 1 is added in an amount ranging from 0.01 mol % to 20 mol % based on a total amount of metals comprised in the positive electrode active material excluding lithium.

5. The lithium secondary battery of claim 1 , wherein M′ in Chemical Formula 1 is added in an amount ranging from 0.05 mol % to 10 mol % based on the total amount of metals comprised in the positive electrode active material excluding lithium.

6. The lithium secondary battery of claim 1 , wherein the other element(s) is any one element or two or more elements selected from the group consisting of aluminum (Al), magnesium (Mg), Mn, Ni, Co, chromium (Cr), vanadium (V), and Fe.

7. The lithium secondary battery of claim 1 , wherein the lithium-containing metal oxide is present in an amount less than or equal to 50 wt % based on a total amount of the positive electrode active material.

8. The lithium secondary battery of claim 1 , wherein the lithium secondary battery is used as a unit cell of a battery module, a power source of a medium or large sized device.

9. The lithium secondary battery of claim 8 , wherein the medium or large sized device is a power tool; an electric vehicle (EV) including an electric car, a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); an electric two-wheeled vehicle including an E-bike and an E-scooter; an electric golf cart; an electric truck; and an electric commercial vehicle or a power storage system.