Composite cathode active material, cathode and lithium battery including the composite cathode active material, and method of preparing the composite cathode active material
A composite cathode active material, and a cathode and a lithium battery each including the composite cathode active material. The composite cathode active material includes: a core including a first lithium transition metal oxide represented by Formula 1, Li a MO 2 wherein, in Formula 1, M includes Ni and at least one non-nickel Group 4 to Group 13 element, a content of Ni is about 70 mol % or greater, based on a total content of M, 0.9≤a≤1.1, and wherein the first lithium transition metal oxide has a layered crystal structure belonging to an R 3 m space group; and a shell on a surface of the core, the shell having a spinel crystal structure and including a dopant.
1. A composite cathode active material comprising:
a polyhedral primary particle comprising
a core comprising a first lithium transition metal oxide represented by Formula 1,
a shell on a surface of the core, the shell having a spinel crystal structure and comprising a dopant, and
a polyhedral pore extending from a first surface to an opposite second surface of the polyhedral primary particle:
Li a MO 2 Formula 1
wherein, in Formula 1,
M comprises Ni and at least one non-nickel Group 4 to Group 13 element, wherein a content of Ni is about 70 mole percent or greater, based on a total content of M, 0.9≤a≤1.1, and
wherein the first lithium transition metal oxide has a layered crystal structure belonging to an R 3 m space group.
2. The composite cathode active material of claim 1 , wherein the dopant comprises at least one non-nickel Group 4 to Group 13 element.
3. The composite cathode active material of claim 1 , wherein the shell comprises a second lithium transition metal oxide represented by Formula 2:
Li 1−x M″ y M′ z O 2 Formula 2
wherein, in Formula 2,
M″ comprises Ni and at least one non-nickel Group 4 to Group 13 element,
M′ comprises at least one non-nickel Group 4 to Group 13 element, and
0≤x≤0.05, 0≤z≤0.06, 1.0≤(y+z)≤1.06.
4. The composite cathode active material of claim 3 , wherein M′ comprises Co, Zn, Fe, Cu, Mn, Zr, Ti, Mg, or a combination thereof.
5. The composite cathode active material of claim 3 , wherein the second lithium transition metal oxide has electrochemical activity.
6. The composite cathode active material of claim 1 , wherein the shell has a thickness of about 100 nanometers or less.
7. The composite cathode active material of claim 1 , wherein a content of the shell is about 6 weight percent or less, based on a total weight of the composite cathode active material.
8. The composite cathode active material of claim 1 , wherein the spinel crystal structure belongs to an Fd 3 m space group.
9. The composite cathode active material of claim 1 , wherein a peak intensity ratio of an intensity of a (003) peak to an intensity of a (104) peak of the composite cathode active material is less than a peak intensity ratio of an intensity of a (003) peak to an intensity of a (104) peak of the core.
10. The composite cathode active material of claim 1 , wherein a maximum peak intensity in a Raman spectrum of the composite cathode active material is positioned at about 530 inverse centimeters or greater.
11. The composite cathode active material of claim 1 , wherein a peak intensity ratio of an intensity of a peak at about 530 electron volts to 533 electron volts to an intensity of a peak at about 528 electron volts to about 530 electron volts in a surface X-ray photoelectron spectrum of the composite cathode active material is about 2 or less.
12. The composite cathode active material of claim 1 , wherein the composite cathode active material comprises mesopores having a diameter of about 1 nanometer to about 100 nanometers, and wherein the mesopores have an average volume of about 0.001 cubic centimeters per gram.
13. The composite cathode active material of claim 1 , wherein the composite cathode active material has a specific surface area of about 0.48 square meters per gram or greater.
14. A composite cathode active material comprising:
a primary particle comprising
a core comprising a first lithium transition metal oxide represented by Formula 1,
a shell on a surface of the core, the shell having a spinel crystal structure and comprising a dopant, and
a polyhedral pore extending from a first surface to an opposite second surface of the polyhedral primary particle:
Li a MO 2 Formula 1
wherein, in Formula 1, M comprises Ni and at least one non-nickel Group 4 to Group 13 element, wherein a content of Ni is about 70 mole percent or greater, based on a total content of M, and 0.9≤a≤1.1,
wherein the first lithium transition metal oxide has a layered crystal structure belonging to an R 3 m space group; and
wherein a sum of peak intensities defined as
(Dopant peak intensity+Co peak intensity)/(Mn peak intensity)
before and after Ar + sputtering when analyzed by surface X-ray photoelectron spectroscopy of the composite cathode active material is about 5 or greater.
15. The composite cathode active material of claim 14 , wherein the dopant comprises at least one non-nickel Group 4 to Group 13 element.
16. The composite cathode active material of claim 14 , wherein the shell comprises a second lithium transition metal oxide represented by Formula 2:
Li 1−x M″ y M′ z O 2 Formula 2
wherein, in Formula 2,
M″ comprises Ni and at least one non-nickel Group 4 to Group 13 element,
M′ comprises at least one non-nickel Group 4 to Group 13 element,
0≤x≤0.05, 0≤z≤0.06, and 1.0≤(y+z)≤1.06.
17. The composite cathode active material of claim 14 , wherein M′ comprises Co, Zn, Fe, Cu, Mn, Zr, Ti, Mg, or a combination thereof.
18. The composite cathode active material of claim 14 , wherein the first lithium transition metal oxide is represented by Formula 3:
Li a Ni b M1 c M2 d M3 e O 2 Formula 3
wherein, in Formula 3,
M1, M2, and M3 are different and each independently comprises manganese, vanadium, chromium, iron, cobalt, zirconium, rhenium, aluminum, boron, germanium, ruthenium, tin, titanium, niobium, molybdenum, or platinum,
0.9≤a≤1.1, 0.7<b<1.0, 0<c<0.3, 0<d<0.4, 0≤e<0.3, and b+c+d+e=1.
19. The composite cathode active material of claim 14 , wherein the first lithium transition metal oxide is represented by Formula 4:
Li a Ni b Co c Mn d M3′ e O 2 Formula 4
wherein, in Formula 4, M3′ comprises vanadium, chromium, iron, zirconium, rhenium, aluminum, boron, germanium, ruthenium, tin, titanium, niobium, molybdenum, or platinum,
0.9≤a≤1.1, 0.7<b<1.0, 0<c<0.3, 0<d<0.4, 0≤e<0.3, and b+c+d+e=1.
20. A cathode comprising a composite cathode active material according to claim 1 .
21. A lithium battery comprising:
the cathode of claim 20 ,
an anode, and
an electrolyte between the cathode and the anode.
22. A method of preparing a composite cathode active material, the method comprising:
mixing a metal-organic framework and a first lithium transition metal oxide represented by Formula 1 to prepare a mixture
Li a MO 2 Formula 1
wherein, in Formula 1,
M comprises Ni and at least one non-nickel Group 4 to Group 13 element,
a content of Ni is about 70 mole percent or greater, based on a total content of M, and
0.9≤a≤1.1, and
wherein the first lithium transition metal oxide has a layered crystal structure belonging to an R 3 m space group; and
thermally treating the mixture under an oxidizing atmosphere at about 650° C. to about 800° C. for about 3 hours to about 20 hours to prepare the composite cathode active material,
wherein the composite cathode active material comprises a polyhedral primary article comprising:
a core comprising the first lithium transition metal oxide,
a shell on a surface of the core, the shell having a spinel crystal structure and comprising a dopant, and
a polyhedral pore extending from a first surface to an opposite second surface of the polyhedral primary particle.
23. The method of claim 22 , wherein the metal-organic framework comprises Co, Zn, Fe, Cu, Ni, Mn, Zr, Ti, Mg, or a combination thereof.
24. The method of claim 22 , wherein the metal-organic framework comprises a polyhedral primary particle, and wherein the polyhedral primary particle has a particle diameter of about 2 nanometers to about 300 nanometers.
25. The method of claim 22 , wherein an amount of the metal-organic framework in the mixture is about 6 parts by weight or less, based on 100 parts by weight of the first lithium transition metal oxide.
26. The composite cathode active material of claim 14 , wherein the shell is a reaction product of the first lithium oxide and a metal organic framework.