Lithium secondary battery

1. A lithium secondary battery, comprising:

a cathode including a first cathode active material and a second cathode active material;

an anode; and

a separator interposed between the cathode and the anode,

wherein the first cathode active material includes a lithium metal oxide particle containing nickel, cobalt and manganese, and the first cathode active material has a secondary particle structure,

wherein the nickel included in the first cathode active material has a concentration gradient region in which a concentration decreases from a central portion to a surface portion of the lithium metal oxide particle,

wherein the second cathode active material includes a lithium metal oxide particle containing nickel, cobalt and manganese and having a single particle structure, and each of nickel, cobalt and manganese in the second cathode active material has a uniform concentration throughout an entire particle, and

wherein a content of nickel included in the first cathode active material is greater than a content of nickel included in the second cathode active material.

2. The lithium secondary battery according to claim 1 , wherein the single particle structure includes a single crystalline structure.

3. The lithium secondary battery according to claim 1 , wherein the first cathode active material includes a first lithium metal oxide represented by Chemical Formula 1:

Li x M1 a M2 b M3 c O y   [Chemical Formula 1]

wherein in Chemical Formula 1, at least one of M1, M2 and M3 has a concentration gradient region between a central portion of the first metal oxide and a surface portion of the first metal oxide, and M1 is nickel, M2 is cobalt and M3 is manganese,

0< x≤ 1.1, 2≤ y≤ 2.02, 0≤ a≤ 1,0≤ b≤ 1, 0≤ c≤ 1, and 0< a+b+c≤ 1.

4. The lithium secondary battery according to claim 3 , wherein 0.6≤a≤0.95 and 0.05≤b+c≤0.4 in Chemical Formula 1.

5. The lithium secondary battery according to claim 3 , wherein 0.7≤a≤0.9 and 0.1≤b+c≤0.3 in Chemical Formula 1.

6. The lithium secondary battery according to claim 1 , wherein the second cathode material includes a second lithium metal oxide represented by Chemical Formula 2:

Li x Ni a Co b Mn c M4 d M5 c O y   [Chemical Formula 2]

wherein, in Chemical Formula 2, M4 includes at least one selected from Ti, Zr, Al, Mg or Cr, M5 includes least one selected from Sr, Y, W or Mo, 0<x<1.5, 2≤y≤2.02, 0.313≤a≤0.353, 0.313≤b≤0.353, 0.313≤c≤0.353, 0≤d≤0.03, 0≤e≤0.03 and 0.98≤a+b+c≤1.02.

7. The lithium secondary battery according to claim 6 , wherein the second lithium metal oxide includes Li 1.0 Ni 1/3 Co 1/3 Mn 1/3 O 2 .

8. The lithium secondary battery according to claim 1 , wherein the second cathode active material has a primary particle shape.

9. The lithium secondary battery according to claim 1 , wherein the second cathode active material shows an exothermic peak of 25 J/g or less at 320° C. or more in a DSC measurement.

10. The lithium secondary battery according to claim 1 , wherein a blending weight ratio of the first cathode active material and the second cathode active material is in a range from 80:20 to 10:90.

11. The lithium secondary battery according to claim 1 , wherein a blending weight ratio the first cathode active material and the second cathode active material is in a range from 50:50 to 10:90.

12. The lithium secondary battery according to claim 1 , wherein the first cathode active material further includes a doping containing at least one selected from the group consisting of Al, Ti, Ba, Zr, Si, B, Mg, P, V and W.

13. The lithium secondary battery according to claim 1 , wherein the first cathode active material further includes a coating layer containing at least one selected from the group consisting of Al, Ti, Ba, Zr, Si, B, Mg and P.