Positive active material for rechargeable lithium battery, method of preparing same and rechargeable lithium battery including same

1. A positive active material for a rechargeable lithium battery, the positive active material comprising:

secondary particles including agglomerated primary particles of a nickel-based compound, the primary particles having an average particle diameter ranging from 0.1 μm to 2.0 μm,

wherein the positive active material has a specific surface area that is 0.77 m 2 /g or greater and less than 2.0 m 2 /g and an average particle diameter ranging from 5.5 μm to 7.5 μm;

wherein a metal oxide layer is on at least one surface of the primary particles and the secondary particles, and

wherein the nickel-based compound is represented by the following Chemical Formula 1 or 2:

Li x MO 2-z L z   [Chemical Formula 1]

wherein, M is M′ 1-k A k (M′ is N 1-d-e Mn d Co e , 0.3≤d+e≤0.7, 0.1≤e≤0.4, A is a dopant, and 0≤k<0.05);

L is F, S, P, or a combination thereof,

0.95≤x≤1.05, and

0≤z≤2,

Li x Ni y T 1-y O 2-z L z   [Chemical Formula 2]

wherein, T is Al, Co, Mn, Cr, Fe, Mg, Sr, a rare earth element, or a combination thereof,

L is F, S, P, or a combination thereof,

0.95≤x≤1.05,

0.3≤y≤0.7, and

0≤z≤2.

2. The positive active material as claimed in claim 1 , wherein a pore channel is between the primary particles.

3. The positive active material as claimed in claim 1 , wherein the metal oxide layer includes a metal that is Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof.

4. The positive active material as claimed in claim 1 , wherein the metal oxide layer has a thickness ranging from 1 nm to 50 nm.

5. A method of preparing the positive active material as claimed in claim 1 , the method comprising:

preparing a transition element composite precursor by agitating and reacting a metal-mixed liquid including a nickel compound, a cobalt compound, and a manganese compound;

spray-drying the transition element composite precursor under a pressure greater than 0.5 MPa and less than or equal to 1.0 MPa to prepare a porous transition element composite precursor;

mixing the porous transition element composite precursor with a lithium salt; and

heat-treating the mixture.

6. The method as claimed in claim 5 , further comprising coating the transition element composite precursor with a metal oxide to form a metal oxide layer thereon.

7. The method as claimed in claim 5 , wherein the coating of the transition element composite precursor with a metal oxide to form the metal oxide layer thereon is carried out after the heat treatment.

8. The method as claimed in claim 5 , wherein the spray-drying process is performed at a temperature ranging from 150° C. to 250° C.

9. The method as claimed in claim 5 , wherein the heat treatment is performed at a temperature ranging from 750° C. to 990° C.

10. A rechargeable lithium battery, comprising

a positive electrode comprising the positive active material as claimed in claim 1 ;

a negative electrode comprising a negative active material; and

an electrolyte.

11. The positive active material as claimed in claim 1 , wherein the primary particles have an average particle diameter ranging from 0.1 μm to 1.0 μm.

12. The positive active material as claimed in claim 1 , wherein the primary particles have an average particle diameter ranging from 0.1 μm to 0.5 μm.

13. The positive active material as claimed in claim 1 , wherein the nickel-based compound is represented by Chemical Formula 2.