Positive electrode active material and method for preparing the same

1. A positive electrode active material comprising:

particles having the composition of Formula 1 below; and

a coating layer formed on surfaces of the particles and having the composition of Formula 3 below:

Li[Co 1-a M 1 a ]O 2   [Formula 1]

wherein, in Formula 1 above,

M 1 is one or more selected from the group consisting of B, Mg, Ca, Al, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta, and W, and 0≤a<0.1,

Li[Ni f Co g Mn h M 3 i ]O 2   [Formula 3]

wherein, in Formula 3 above,

M 3 is one or more selected from the group consisting of B, Ca, V, Cr, Fe, Zn, Ga, Y, Nb, Mo, and Ta, and 0<f≤0.4, 0≤g≤0.6, 0≤h≤0.6, 0≤i<0.1, and f+g+h+i=1,

wherein the thickness of the coating layer is 1 nm to 500 nm.

2. The positive electrode active material of claim 1 , wherein the surfaces of the particles are completely surrounded by the coating layer.

3. The positive electrode active material of claim 1 , wherein the thickness of the coating layer is 1 nm to 200 nm.

4. A positive electrode for a lithium secondary battery, the positive electrode comprising the positive electrode active material according to claim 1 .

5. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 4 .

6. The positive electrode active material of claim 1 , wherein the coating layer consists of the composition of Formula 3.

7. A method for preparing the positive electrode active material of claim 1 , comprising:

reacting a coating precursor preparation solution comprising a metal solution containing metal ions and a chelating agent to prepare a coating precursor, wherein the coating precursor is a complex in which the metal ions and the chelating agent are combined; and

dry-mixing particles having the composition of Formula 1 below and the coating precursor to obtain a mixture, followed by firing the mixture to form a coating layer having the composition of Formula 3 below on surfaces of the particles:

Li[Co 1-a M 1 a ]O 2   [Formula 1]

wherein, in Formula 1 above,

M 1 is one or more selected from the group consisting of B, Mg, Ca, Al, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta, and W, and 0≤a<0.1,

Li[Ni f Co g Mn h M 3 i ]O 2   [Formula 3]

wherein, in Formula 3 above, M 3 is one or more selected from the group consisting of B, Mg, Ca, Al, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta, and W, and 0<f≤0.4, 0≤g≤0.6, 0≤h≤0.6, 0≤i<0.1, and f+g+h+i=1, and

wherein the thickness of the coating layer is 1 nm to 500 nm.

8. The method of claim 7 , wherein the chelating agent is a Lewis acid compound including a carboxylic acid group or a nitrogen element.

9. The method of claim 8 , wherein the chelating agent is one or more selected from the group consisting of citric acid, polyvinylpyrrolidone, and glycolic acid.

10. The method of claim 7 , wherein the coating precursor preparation solution is prepared by adding the metal solution containing ions and the chelating agent to a solvent, followed by mixing.

11. The method of claim 10 , wherein the solvent is one or more selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, and 2,3-butanediol.

12. The method of claim 7 , wherein the average particle diameter (D 50 ) of the coating precursor is 1 nm to 500 nm.

13. The method of claim 7 , wherein the reacting the coating precursor preparation solution is performed at 200° C. to 300° C.

14. The method of claim 7 , wherein the firing is performed at a temperature 800° C. to 900° C.

15. The method of claim 14 , wherein the firing is performed after raising the temperature to 800° C. to 900° C. at a rate of 5° C./min to 10° C./min.