Nickel-based active material for lithium secondary battery, method of preparing the same, and lithium secondary battery including positive electrode including the nickel-based active material

1. A nickel-based active material for a lithium secondary battery, the nickel-based active material comprising:

at least one secondary particle comprising at least two primary particle structures,

wherein the at least two primary particle structures each comprise a porous inner portion and an outer portion comprising a radially arranged structure,

wherein the at least one secondary particle comprises at least two radial centers,

wherein the at least two primary particle structures each comprise an agglomeration of at least two primary particles, and

wherein respective ones of the at least two primary particles of each primary particle structure are radially arranged around a respective one of the at least two radial centers.

2. The nickel-based active material of claim 1 , wherein the at least two primary particle structures are aligned in a multicenter isotropic arrangement to form the secondary particle.

3. The nickel-based active material of claim 1 , wherein the at least two primary particle structures have a plurality of particle shapes, and

wherein a sphericity of the most abundant particle shape of the at least two primary particle structures have is in a range of about 0.960 to about 0.985.

4. The nickel-based active material of claim 1 , wherein a size of each of the at least two primary particle structures is in a range of about 2 μm to about 5 μm.

5. The nickel-based active material of claim 1 , wherein a size of the at least one secondary particle is in a range of about 5 μm to about 25 μm.

6. The nickel-based active material of claim 1 , wherein a pore size of the porous inner portion is in a range of about 150 nm to about 1 μm, a porosity of the porous inner portion is in a range of about 5% to about 15%, and a porosity of the outer portion having a radially arranged structure is in a range of about 1% to about 5%.

7. The nickel-based active material of claim 1 , further comprising a plate particle of which a long axis is aligned in a radial direction, and a ratio of a thickness to a length of the plate particle is in a range of about 1:2 to about 1:20.

8. The nickel-based active material of claim 1 , wherein the nickel-based active material comprises a compound represented by Formula 1:

Li a (Ni 1-x-y-z Co x Mn y M z )O 2   Formula 1

wherein, in Formula 1, M is an element selected from the group consisting of boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); and

a, x, y, and z satisfy the following conditions: 0.95≤a≤1.3, x≤(1−x−y−z), y≤(1−x−y−z), 0<x<1, 0≤y<1, 0≤z<1, and 0<(1−x−y−z)<1.

9. The nickel-based active material of claim 8 , wherein an amount of nickel in the nickel-based active material is in a range of about 30 mol % to about 95 mol % based on a total amount of transition metals including nickel, cobalt, and manganese, the amount of nickel being higher than an amount of each of manganese and cobalt.

10. The nickel-based active material of claim 1 , wherein the nickel-based active material comprises LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 , and/or LiNi 0.85 Co 0.1 Al 0.05 O 2 .

11. A method of preparing a nickel-based active material for a lithium secondary battery, the method comprising:

primary heat-treating a mixture of a lithium precursor and a metal hydroxide in an oxidative gas atmosphere at a temperature in a range of about 600° C. to about 850° C.; and

secondary heat-treating the mixture in an oxidative gas atmosphere at a temperature in a range of about 700° C. to about 950° C. to prepare the nickel-based active material of claim 1 .

12. The method of claim 11 , wherein the secondary heat-treating is performed at a temperature higher than that of the primary heat-treating.

13. A lithium secondary battery comprising:

a positive electrode comprising the nickel-based active material of claim 1 ;

a negative electrode; and

an electrolyte between the positive electrode and the negative electrode.

14. The lithium secondary battery of claim 13 , wherein a sphericity of particles in the positive electrode is in a range of about 0.960 to about 0.985.