Cathode active material with whole particle concentration gradient for lithium secondary battery, method for preparing same, and lithium secondary battery having same

1. A cathode active material for a lithium secondary battery with whole particle concentration gradient comprises:

the core expressed by the following formula 1; and

the surface part expressed by the following formula 2,

Li a1 M1 x1 M2 y1 M3 z1 M4 w O 2+δ   [Formula 1]

Li a2 M1 x2 M2 y2 M3 z2 M4 w O 2+δ   [Formula 2]

wherein,

the concentrations of the M1, the M2 and the M3 have continuous concentration gradient from the core to the surface;

M1, M2 and M3 are selected from the group consisting of Ni, Co, Mn and a combination thereof;

M4 is selected from the group consisting of Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and a combination thereof; 0<a1≦1.1, 0<a2≦1.1, 0≦x1≦1, 0≦x2≦1, 0≦y1≦1, 0≦y2≦1, 0≦z1≦1, 0≦z2≦1, 0≦w≦0.1, 0.0≦δ≦0.02, 0<x1+y1+z1≦1, 0<x2+y2+z2≦1, x1≦x2, y1≦y2 and z2≦z1;

the concentrations of all metals making up the cathode active material show continuous concentration gradient in the entire region, from the particle core to the surface part,

the particle core is within the diameter 0.2 μm from the center of the active material particle, and

wherein the concentration of Co change from the particle core to the surface part is more than 0 but equal or less than 0.83 mol % per μm.

2. The cathode active material according to claim 1 , wherein the concentration of M1 is increased from the core to the surface part with continuous concentration gradient, the concentration of M2 is increased from the core to the surface part with continuous concentration gradient, and the concentration of the M3 is decreased from the core to the surface part with continuous concentration gradient.

3. The cathode active material according to claim 2 , wherein M1 is Co, M2 is Mn and M3 is Ni.

4. The cathode active material-according to claim 2 , wherein the concentration range of M3 at the core, z1 is 0.6≦z1≦1, and the concentration difference between the core and the surface part of the M3 is 0.2≦|z2−z1|≦0.4.

5. The cathode active material according to claim 2 , wherein the concentration range of M1 at the core, x1 is 0≦x1≦0.2, and the concentration difference between the core and the surface part of the M1 is 0.05≦|x2−x1|≦0.1.

6. The cathode active material according to claim 2 , wherein the concentration range of M2 at the core, y1 is 0≦y1≦0.1, and the concentration difference between the core and the surface part of M2 is 0.2≦|y2−y1≦0.4.

7. The cathode active material according to claim 1 , wherein the concentration gradients of M1, M2 and M3 are constant from the particle core to the surface part.

8. A lithium secondary battery comprising the cathode active material of claim 1 .

9. The cathode active material according to claim 1 , wherein the surface part of the particle is within the radius 0.2 μm from the outermost shell of the active material particle.

10. A method for preparing a cathode active material according to claim 1 comprises:

a first step of preparing a metal salt aqueous solution for forming the core and a metal salt aqueous solution for forming the surface part, which contain M1, M2 and M3 as a metal salt aqueous solution, wherein the concentrations of M1, M2 and M3 are different each other;

a second step of forming precipitates by mixing the metal salt aqueous solution for forming the core and the metal salt aqueous solution for forming the surface part at a mixing ratio from 100 v %: 0 v % to 0 v %: 100 v % with gradual change and by mixing a chelating agent and a basic aqueous solution to a reactor at the same time, wherein the concentrations of M1, M2 and M3 have continuous concentration gradient from the core to the surface part;

a third step of preparing an active material precursor by drying or heat-treating the obtained precipitates; and

a fourth step of mixing the active material precursor and a lithium salt and then heat-treating thereof.

11. The method according to claim 10 , wherein the molar ratio of the chelating agent and the metal salt aqueous solution is 0.2 to 1.0:1.

12. The method according to claim 10 , wherein the heat-treating process after mixing the active material precursor and the lithium salt is conducted at 700 to 1100° C.

13. The method according to claim 10 , which further comprises a pre-calcining process by maintaining at 250 to 650° C. for 5 to 20 hours, before heat-treating after mixing the active material precursor and the lithium salt.

14. The method according to claim 10 , wherein in the second step, pH is within 10 to 12.5, reaction temperature is within 30 to 80° C., and reaction stirring speed is within 100 to 2000 rpm under nitrogen flow.