Positive electrode active material for lithium secondary battery, method for preparing same and lithium secondary battery comprising same

1. A positive active material for a lithium secondary battery, said material comprising a core having a core portion and a surface portion, each portion containing a compound of Formula 1,

Li[Li z A (1-z-a) D a ]E b O 2-b   [Formula 1]

wherein

the compound in the surface portion has a lower L3/L2 intensity ratio of Ni, i.e., the oxidation number of Ni measured by electronic energy loss spectroscopy, than that in the core portion, an L3/L2 intensity ratio of Ni in the surface portion being 1.2 to 1.4, and an L3/L2 intensity ratio of Ni in the core portion being 1.5 to 1.6;

in Formula 1, A is Ni α Co β Mn γ , D is at least one element selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, B, Si, Sn, Mn, Cr, Fe, V, Zr, Nb, and Mo, E is at least one element selected from the group consisting of P, F, and S, −0.05≤z≤0.1, 0≤a≤0.05, 0≤b≤0.05, 0.3≤α≤0.9, 0.05≤β≤0.4, and 0.05≤γ≤0.4.

2. The positive active material for a lithium secondary battery of claim 1 , wherein, in Formula 1, −0.05≤z≤0.05, 0.6≤α≤0.9, 0.05≤β≤0.2, and 0.05≤γ≤0.2.

3. The positive active material for a lithium secondary battery of claim 1 , wherein in Formula 1, D is one element selected from the group consisting of Zr, Ti, Mg, Al, and combinations thereof.

4. The positive active material for a lithium secondary battery of claim 1 , wherein in Formula 1, a mole doping ratio of D is 0.001 to 0.01.

5. The positive active material for a lithium secondary battery of claim 1 , wherein the positive active material further includes a coating layer located outside the core.

6. The positive active material for a lithium secondary battery of claim 5 , wherein the coating layer includes Al and/or B.

7. The positive active material for a lithium secondary battery of claim 5 , wherein a weight ratio of the coating layer to the total weight of the entire positive active material is 0.05 to 0.5.

8. The positive active material for a lithium secondary battery of claim 6 , wherein the coating layer further comprises F.

9. The positive active material for a lithium secondary battery of claim 1 , wherein the compound in the core portion is represented by Formula 2 and the compound in the surface portion is represented by Formula 3:

Li[Li z A (1-z-a) D a ]E b O 2-b   [Formula 2]

in Formula 2, A is Ni α Co β Mn γ , D is at least one element selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, B, Si, Sn, Mn, Cr, Fe, V, Zr, Nb, and Mo, E is at least one element selected from the group consisting of P, F, and S, −0.05≤z≤0.1, 0≤a≤0.01, 0≤b≤0.05, 0.3≤α≤0.9, 0.05≤β≤0.4, and 0.05≤γ≤0.4;

Li[Li z A (1-z-a) D a ]E b O 2-b   [Formula 3]

in Formula 3, A is Ni α Co β Mn γ , D is at least one element selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, B, Si, Sn, Mn, Cr, Fe, V, Zr, Nb, and Mo, E is at least one element selected from the group consisting of P, F, and S, −0.05≤z≤0.1, 0.03≤a≤0.05, 0≤b≤0.05, 0.3≤α≤0.9, 0.05≤β≤0.4, and 0.05≤y≤0.4.

10. A method of producing a positive active material for a lithium secondary battery, the method comprising:

uniformly adhering a D supply material to a surface of a transition metal precursor by dry-mixing the transition metal precursor and the D supply material;

adding a lithium supply material and dry-mixing the mixture; and

sintering the mixture to obtain a core including a core portion and a surface portion, each portion containing a compound of Formula 1:

Li[Li z A (1-z-a) D a ]E b O 2-b   [Formula 1]

wherein

the compound in the surface portion has a lower L3/L2 intensity ratio of Ni, i.e., the oxidation number of Ni measured by electronic energy loss spectroscopy, than that in the core portion, an L3/L2 intensity ratio of Ni in the surface portion being 1.2 to 1.4, and an L3/L2 intensity ratio of Ni in the core portion being 1.5 to 1.6;

in Formula (1), A is Ni α Co β Mn γ , D is at least one element selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, B, Si, Sn, Mn, Cr, Fe, V, Zr, Nb, and Mo, E is at least one element selected from the group consisting of P, F, and S, −0.05≤z≤0.1, 0≤a≤0.05, 0≤b≤0.05, 0.3≤a≤0.9, 0.05≤β≤0.4, and 0.05≤γ≤0.4.

11. The method of producing a positive active material for a lithium secondary battery of claim 10 , further comprising,

dry-mixing the core thus obtained and a coating layer-forming material; and

sintering the mixture to form a coating layer on the surface of the core.

12. The method of producing a positive active material for a lithium secondary battery of claim 10 , wherein, the sintering step is performed at 800 to 1050° C.

13. The method of producing a positive active material for a lithium secondary battery of claim 11 , wherein, the second sintering step is performed at 300 to 450° C.

14. The method of producing a positive active material for a lithium secondary battery of claim 10 , wherein the D supply material comprises Zr, Ti, Mg, Al, or combinations thereof.

15. The method of producing a positive active material for a lithium secondary battery of claim 11 , wherein the coating layer-forming material comprises Al and/or B.

16. A lithium secondary battery, comprising:

a positive electrode including a positive active material for a lithium secondary battery of claim 1 ;

a negative electrode including a negative active material; and

an electrolyte.