Lithium secondary battery

1. A lithium secondary battery, comprising:

a cathode formed from a cathode active material including a first cathode active material particle and a second cathode active material particle;

an anode; and

a separation layer interposed between the cathode and the anode,

wherein the first cathode active material particle includes a lithium metal oxide in which at least one metal forms a concentration gradient region,

wherein the second cathode active material particle includes a lithium metal oxide having at least two metal elements except for lithium, and concentrations of the at least two metal elements except lithium are constant from a central portion to a surface,

wherein the second cathode active material particle includes primary particles being aggregated with each other, the primary particles having different shapes or crystalline structures from each other,

wherein the different shapes include a first shape including a granular shape or a spherical shape and a second shape including a rod shape or a needle shape,

wherein the first shape is arranged in a central region of the second cathode active material particle, and the second shape is arranged in a peripheral region of the second cathode active material particle surrounding the central region.

2. The lithium secondary battery according to claim 1 , wherein the central region of the second cathode active material particle includes an area within a region corresponding to 20% to 80% of a radius from a center of the second cathode active material particle.

3. The lithium secondary battery according to claim 1 , wherein the first cathode active material particle includes a core portion, a shell portion, and a concentration gradient region between the core portion and the shell portion,

wherein the concentration gradient is formed in the concentration gradient region.

4. The lithium secondary battery according to claim 3 , wherein the core portion and the shell portion each includes a fixed composition.

5. The lithium secondary battery according to claim 1 , wherein the first cathode active material particle includes a continuous concentration gradient region formed from a center of the first cathode active material particle to a surface of the first cathode active material particle.

6. The lithium secondary battery according to claim 1 , wherein the first cathode active material particle is represented by the following Chemical Formula 1:

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

wherein in Chemical Formula 1, M1, M2 and M3 independently include at least one element selected from a group consisting of Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga and B,

0<x≤1.1, 1.98≤y≤2.02, 0<a<1, 0<b<1, 0<c<1, and 0<a+b+c<1.

7. The lithium secondary battery according to claim 6 , wherein 0.6≤a≤0.95 and 0.05≤b+c≤0.4 in the Chemical Formula 1.

8. The lithium secondary battery according to claim 6 , wherein 0.7≤a≤0.9 and 0.1≤b+c≤0.3 in the Chemical Formula 1.

9. The lithium secondary battery according to claim 6 , wherein M1 is nickel (Ni), M2 is manganese (Mn), and M3 is cobalt (Co).

10. The lithium secondary battery according to claim 1 , wherein the second cathode active material particle is represented by the following 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 element selected from a group consisting of Ti, Zr, Al, Mg, and Cr; and M5 includes at least one element selected from a group consisting of Sr, Y, W, and Mo; and

0<x<1.5, 1.98≤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.

11. The lithium secondary battery according to claim 1 ,

wherein one of the at least two metal elements includes nickel, and a content or a molar ratio of nickel is the largest among the at least two metal elements in the lithium metal oxide.

12. The lithium secondary battery according to claim 1 , wherein the second cathode active material particle is represented by the following Chemical Formula 3:

Li x Ni α ,Co β Mn γ M4 δ M5 ε O y   [Chemical Formula 3]

wherein in Chemical Formula 3, M4 includes at least one element selected from a group consisting of Ti, Zr, Al, Mg, and Cr; and M5 includes at least one element selected from a group consisting of Sr, Y, W, and Mo; and

0<x<1.1, 1.98≤y≤2.02, 0.48≤α≤0.52 0.18≤β≤0.27, 0.24≤γ≤0.32, 0≤δ≤0.03, 0≤ε≤0.03, and 0.98≤α+β+γ≤1.02.

13. The lithium secondary battery according to claim 12 , wherein 0.49≤α≤0.51 0.18≤β≤0.22, and 0.28≤γ≤0.32 in the Chemical Formula 3.

14. The lithium secondary battery according to claim 1 , wherein a blending weight ratio of the first cathode active material particle and the second cathode active material particle is in a range from 9:1 to 1:9.

15. The lithium secondary battery according to claim 1 , wherein an exothermic peak of the second cathode active material particle is 40 J/g or less at 200° C. or more in a Differential Scanning Calorimetry (DSC) measurement.

16. The lithium secondary battery according to claim 1 , wherein the first cathode active material particle or the second cathode active material particle further includes a coating on a surface thereof, and the coating includes at least one selected from a group consisting of Al, Ti, Ba, Zr, Si, B, Mg, P, an alloy thereof and an oxide thereof.

17. The lithium secondary battery according to claim 1 , wherein the first cathode active material particle or the second cathode active material particle further includes a dopant including at least one selected from a group consisting of Al, Ti, Ba, Zr, Si, B, Mg, P, an alloy thereof and an oxide thereof.