Cathode active material for lithium battery and method of manufacturing the same
A cathode active material for a lithium secondary battery is provided which comprises a first region and a second region. The first region is represented by Chemical Formula1 wherein M1, M2 and M3 are constant: Li a1 M1 x1 M2 y1 M3 z1 O 2+δ . The second region is formed around the first regions and is represented by Chemical Formula 2 Li a2 M1 x2 M2 y2 M3 z2 M4 w O 2+δ . The concentrations of M1, M2 and M3 are changed from Chemical Formula 1. In both Chemical Formula 1 and 2, M1, M2 and M3 is selected from a group including Ni, Co, Mn and combinations thereof, M4 is selected from a group including Fe, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B and combinations 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.
1. A cathode active material for a lithium secondary battery, the cathode active material comprising:
a first region represented by following Chemical Formula 1, wherein concentrations of M1, M2 and M3 are constant, and wherein the first region is a core with radius R1; and
a second region formed around the first region, wherein a thickness of the second region is D2, and wherein concentrations of M1, M2, M3 and M4 are changed from the composition shown in the Chemical Formula 1 into the following composition shown in Chemical Formula 2, thereby the second region shows the composition of the Chemical Formula 2 at the outer shell,
Li a1 M1 x1 M2 y1 M3 z1 O 2+δ [Chemical Formula 1]
Li a2 M1 x2 M2 y2 M3 z2 M4 w O 2+δ [Chemical Formula 2]
(wherein in Chemical Formula 1 and Chemical Formula 2, each of M1, M2 and M3 is selected from the group consisting of Ni, Co, Mn and combinations thereof, M4 is Al, 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, 0.003≤w≤0.0075, 0.0≤δ≤0.02, 0<x1+y1+z1≤1, and 0<x2+y2+z2≤1).
2. The cathode active material of claim 1 , wherein M4 shows concentration gradient in at least a portion of a particle.
3. The cathode active material of claim 1 , wherein M4 shows concentration gradient from a portion of the second region to the outer shell of the second region.
4. The cathode active material of claim 3 , wherein the concentration of M4 increases as going to the outer shell of the second region from a portion of the second region.
5. The cathode active material of claim 1 , wherein x1≠c2, y1≠y2 and z1≠z2.
6. The cathode active material of claim 1 , wherein the concentration gradients of M1, M2 and M3 are constant in the second region.
7. The cathode active material of claim 1 , wherein the second region comprises a region M1-1 and a region M1-2 of which concentration gradients of M1 are different from each other.
8. The cathode active material of claim 1 , wherein the second region comprises a region M2-1 and a region M2-2 of which concentration gradients of M2 are different from each other.
9. The cathode active material of claim 1 , wherein the second region comprises a region M3-1 and a region M3-2 of which concentration gradients of M3 are different from each other.
10. The cathode active material of claim 1 , wherein at least one of M1, M2, and M3 has constant concentration gradient at an entire region which has concentration gradient of M4.
11. A cathode active material for a lithium secondary battery, wherein average composition of total particles are represented by following Chemical Formula 4,
Li a M1 x M2 y M3 z M4 w O 2+δ , [Chemical Formula 4]
wherein each of M1, M2 and M3 is selected from the group consisting of Ni, Co, Mn and combinations thereof,
wherein M4 is Al, and
wherein at least one of M1, M2 and M3 has concentration gradient in at least a portion of the particle, and
wherein 0≤x≤1, 0≤y≤1, 0≤z≤1, 0.003≤w≤0.0075 and 0.0≤δ≤0.02.
12. The cathode active material of claim 11 , wherein at least one of M1, M2 and M3 shows concentration gradient in the whole particle.
13. The cathode active material of claim 11 , wherein one of M1, M2 and M3 shows constant concentration in the whole particle.
14. The cathode active material of claim 11 , wherein M4 shows concentration gradient in at least a portion of the particle.
15. The cathode active material of claim 11 , wherein concentration of M4 decreases as going to the center of the particle from the surface of the particle.
16. The cathode active material of claim 11 , wherein at least one of M1, M2 and M3 has constant concentration gradient at an entire region which has concentration gradient of M4.