Positive electrode active material for secondary battery, and secondary battery comprising the same

1. A positive electrode active material for a secondary battery comprising:

a lithium composite metal oxide particle represented by Formula 1 below,

Li a Ni 1−x−y Co x M1 y M2 z M3 w O 2   [Formula 1]

wherein, in the Formula 1,

M1 is a metal element whose surface energy (ΔE surf ) calculated by Equation 1 below is −0.5 eV or higher,

M2 is a metal element whose surface energy (ΔE surf ) calculated by Equation 1 below is −1.5 eV or higher and less than −0.5 eV,

M3 is a metal element whose surface energy (ΔE surf ) calculated by Equation 1 below is less than −1.5 eV, and

1.0≤a≤1.5, 0<x≤0.5, 0<y≤0.5, 0.002≤w≤0.1, 0<z≤0.05, 0<x+y≤0.7,

Δ

⁢

⁢

E

surf

=

⁢

E

surf

⁢

⁢

2

-

E

surf

⁢

⁢

1

=

⁢

(

E

slab

⁢

⁢

2

-

E

bulk

)

-

(

E

slab

⁢

⁢

1

-

E

bulk

)

[

Equation

⁢

⁢

1

]

wherein, in the Equation 1

E suf2 represents an extent to which a metal element is oriented toward the outermost surface of the lithium composite metal oxide particle,

E suf1 represents an extent to which the metal element is oriented toward a central portion of the lithium composite metal oxide particle,

E slab1 is energy of a slab model of the lithium composite metal oxide particle when the metal element is at the central portion of the lithium composite metal oxide particle,

E slab2 is energy of a slab model of the lithium composite metal oxide when the metal element is at the outermost surface of the lithium composite metal oxide, and

E bulk is energy of a bulk model corresponding to each of the slab models.

2. The positive electrode active material of claim 1 , wherein:

the M1 is distributed such that an average slope of a concentration profile from a surface of the lithium composite metal oxide particle to a central portion section thereof is 0 or positive (+); and

the M2 and M3 are independently distributed such that an average slope of a concentration profile from a surface of the lithium composite metal oxide particle to a central portion section thereof is negative (−).

3. The positive electrode active material of claim 1 , wherein the M1 includes any one or two or more selected from the group consisting of Al, Mg, Y, Zn, In, and Mn.

4. The positive electrode active material of claim 1 , wherein the M2 includes any one or two or more selected from the group consisting of Zr, Ti, Ta, Hf, Sn, Cr, Sb, Ru, Gd, and Os.

5. The positive electrode active material of claim 1 , wherein the M3 includes any one or two or more selected from the group consisting of W, V, Nb, Nd, and Mo.

6. The positive electrode active material of claim 1 , wherein:

the lithium composite metal oxide particle has a core-shell structure including a core and a shell located on a surface of the core;

the M1 is included such that an average slope of a concentration profile from a surface of the lithium composite metal oxide particle to a central portion section thereof is 0;

the M2 is included at a concentration of 1 to 25 mol % in the core and at a concentration of 75 to 99 mol % in the shell; and

the M3 is included at a concentration of 1 to 10 mol % in the core and at a concentration of 90 to 99 mol % in the shell.

7. The positive electrode active material of claim 6 , wherein the core and the shell are included in a volume ratio of 50:50 to 80:20.

8. The positive electrode active material of claim 1 , wherein at least one metal element of nickel and cobalt in Formula 1 exhibits a concentration gradient that changes in the lithium composite metal oxide particle.

9. The positive electrode active material of claim 1 , wherein:

in the Formula 1, nickel and cobalt independently exhibit a concentration gradient that changes throughout the lithium composite metal oxide particle;

the concentration of nickel decreases with a concentration gradient in a direction from a center of the lithium composite metal oxide particle to a surface thereof; and

the concentration of cobalt increases with a concentration gradient in the direction from the center of the lithium composite metal oxide particle to the surface thereof.

10. The positive electrode active material of claim 1 , the positive electrode active material further comprises, on a surface of the positive electrode active material particle, at least one metal element selected from the group consisting of the M2 and M3; or a coating layer including a lithium oxide including the at least one metal element.

11. The positive electrode active material of claim 1 , wherein the positive electrode active material has an average particle size (D 50 ) of 4 μm to 20 μm.

12. The positive electrode active material of claim 1 , wherein the positive electrode active material has a Brunauer-Emmett-Teller (BET) specific surface area of 0.3 m 2 /g to 1.9 m 2 /g.

13. The positive electrode active material of claim 1 , wherein the positive electrode active material has a tap density of 1.7 g/cc to 2.8 g/cc.

14. A positive electrode for a secondary battery comprising the positive electrode active material of claim 1 .

15. A lithium secondary battery comprising the positive electrode of claim 14 .