Composite cathode active material, cathode and lithium battery including the composite cathode active material and method of preparing the composite cathode active material

1. A composite cathode active material, comprising:

a first metal oxide having a first layered crystal structure; and

a second metal oxide having a second layered crystal structure,

wherein the second metal oxide comprises a layered double oxide.

2. The composite cathode active material of claim 1 comprising:

a core, which comprises the first metal oxide; and

a coating layer, which comprises the second metal oxide and is disposed on a surface of the core.

3. The composite cathode active material of claim 2 , wherein the coating layer is disposed on a portion of an outer surface of the core.

4. The composite cathode active material of claim 1 , wherein the second metal oxide is attached to the first metal oxide by a chemical bond.

5. The composite cathode active material of claim 1 ,

wherein a structure of the first metal oxide has a first space group,

wherein a structure of the second metal oxide has a second space group, and

wherein the first space group and the second space group are different.

6. The composite cathode active material of claim 1 ,

wherein the structure of the first metal oxide belongs to space group C2/m, and

wherein structure of the second metal oxide belongs to space group R3m.

7. The composite cathode active material of claim 1 ,

wherein the second metal oxide comprises a metal, and

wherein the metal occupies a crystallographic site of the second metal oxide having octahedral coordination.

8. The composite cathode active material of claim 1 , wherein the second metal oxide comprises a layered double hydroxide that is represented by Formula 1:

M1 a M2 b M3 c O 4   Formula 1

wherein, in Formula 1,

0≤a≤2, 0<c≤2, and b+c=3;

M1 is an alkali metal,

M2 is a metal and comprises an element of Groups 2, 9, 10, 11, or 12, and

M3 is a metal and comprises an element of Groups 3, 4, 5, 8, or 13.

9. The composite cathode active material of claim 1 , wherein the second metal oxide comprises a layered double oxide that is represented by Formula 2:

Li a M2 b M3 c O 4   Formula 2

wherein, in Formula 2,

0≤a≤2, 0<c≤2, b>c, and b+c=3;

M2 is a metal and comprises Co, Mg, Ni, Cu, or Zn, and

M3 is a metal and comprises Ce, Al, Fe, V, Ti, or Ga.

10. The composite cathode active material of claim 1 , wherein the layered double oxide of the second metal oxide comprises LiCo 2 CeO 4 , LiMg 2 CeO 4 , LiNi 2 CeO 4 , LiCu 2 CeO 4 , LiZn 2 CeO 4 , LiCo 2 AlO 4 , LiMg 2 AlO 4 , LiNi 2 AlO 4 , LiCu 2 AlO 4 , LiZn 2 AlO 4 , LiCo 2 FeO 4 , LiMg 2 FeO 4 , LiNi 2 FeO 4 , LiCu 2 FeO 4 , LiZn 2 FeO 4 , LiCo 2 VO 4 , LiMg 2 VO 4 , LiNi 2 VO 4 , LiCu 2 VO 4 , LiZn 2 VO 4 , LiCo 2 TiO 4 , LiMg 2 TiO 4 , LiNi 2 TiO 4 , LiCu 2 TiO 4 , LiZn 2 TiO 4 , LiCo 2 GaO 4 , LiMg 2 GaO 4 , LiNi 2 GaO 4 , LiCu 2 GaO 4 , LiZn 2 GaO 4 , or a combination thereof.

11. The composite cathode active material of claim 1 , wherein an interval between metal oxide layers of the layered double oxide is in a range of about 1 Angstrom to about 10 Angstroms.

12. The composite cathode active material of claim 1 , wherein an amount of the second metal oxide is in a range of about 0.05 parts to about 20 parts by weight, based on 100 parts by weight of the first metal oxide.

13. The composite cathode active material of claim 2 , wherein a thickness of the coating layer is 200 nanometers or less.

14. The composite cathode active material of claim 1 , wherein a caloric value of the composite is 90% or less of a caloric value of the first metal oxide.

15. The composite cathode active material of claim 1 , wherein an amount of lithium remaining on the surface of the composite is 90% or less than an amount of lithium remaining on the surface of the first metal oxide.

16. The composite cathode active material of claim 1 , wherein a zeta potential of the composite is in a range of about −20 millivolts to about +20 millivolts at a pH in a range of about 9 to about 11.

17. The composite cathode active material of claim 1 , wherein the composite has a vibration peak in a range of about 730 cm′ to about 770 cm′ in an IR-spectrum of the composite.

18. The composite cathode active material of claim 1 , wherein a Raman shift of a peak corresponding to an Eg band of the Raman spectrum of the composite is greater than a Raman shift of a peak corresponding to an Eg band of the first metal oxide.

19. The composite cathode active material of claim 1 , wherein the first metal oxide comprises a compound that is represented by Formula 3:

Li x M y O z   Formula 3

wherein, in Formula 3,

0≤x≤3, 1≤y≤3, and 2≤z≤8; and

M comprises an element of Group 2 to Group 13, or a combination thereof.

20. The composite cathode active material of claim 1 , wherein the first metal oxide comprises a compound that is represented by one of Formulas 4 to 6:

Li x Co 1−y M y O 2−α X α   Formula 4

Li x Ni 1−y Me y O 2−α X α   Formula 5

Li x Ni 1−y−z Mn y Ma z O 2−α X α   Formula 6

wherein, in Formulas 4 to 6,

0.90≤x≤1.1, 0≤y≤0.9, 0<z≤0.2, and 0≤α≤2;

M comprises Ni, Mn, Zr, Al, Mg, Ag, Mo, Ti, V, Cr, Fe, Cu, B, or a combination thereof,

Me comprises Co, Zr, Al, Mg, Ag, Mo, Ti, V, Cr, Mn, Fe, Cu, B, or a combination thereof,

Ma comprises Co, Zr, Al, Mg, Ag, Mo, Ti, V, Cr, Fe, Cu, B, or a combination thereof, and

X comprises O, F, S, P, or a combination thereof.

21. The composite cathode active material of claim 1 , wherein the first metal oxide comprises a compound that is represented by Formula 7:

Li x Ni 1−y−z Mn y Co z O 2   Formula 7

wherein, in Formula 7,

0.90≤x≤1.1, 0≤y≤0.2, 0<z≤0.2, and 0.7≤1−y−z≤0.99.

22. The composite cathode active material of claim 1 , wherein the first metal oxide comprises a compound that is represented by one of Formulas 8 to 10:

Li[Li 1−a Me a ]O 2+d   Formula 8

wherein, in Formula 8,

0.8≤a<1 and 0≤d≤0.1; and

Me comprises Ni, Co, Mn, Al, V, Cr, Fe, Zr, Re, B, Ge, Ru, Sn, Ti, Nb, Mo, Pt, or a combination thereof,

Li[Li 1−x−y−z Ma x Mb y Mc z ]O 2+d   Formula 9

wherein, in Formula 9,

0.8≤x+y+z<1, 0<x<1, 0<y<1, 0<z<1, and 0≤d<0.1; and

Ma, Mb, and Mc each independently comprise Mn, Co, Ni, Al, or a combination thereof,

Li[Li 1−x−y−z Ni x Co y Mn z ]O 2+d   Formula 10

wherein, in Formula 10,

0.8≤x+y+z<1; 0<x<1, 0<y<1, 0<z<1, and 0≤d≤0.1.

23. A cathode comprising the composite cathode active material of claim 1 .

24. A lithium battery comprising the cathode of claim 23 .

25. A method of preparing a composite cathode active material, the method comprising:

contacting a layered double hydroxide and a first metal oxide having a first layered crystal structure to prepare a mixture; and

calcining the mixture to prepare the composite cathode active material, wherein the composite cathode active material comprises

a core, which comprises the first metal oxide, and

a coating layer on the core, wherein the coating layer comprises a layered double oxide.

26. The method of claim 25 , wherein the contacting of the layered double hydroxide and the first metal oxide comprises dry mixing.

27. The method of claim 25 , wherein the calcining of the mixture is performed at a temperature of 500° C. or greater.

28. The method of claim 25 , wherein the calcining of the mixture is performed in an oxidizing atmosphere.

29. The method of claim 25 , wherein the method further comprises attaching the layered double hydroxide to a surface of the first metal oxide by an electrostatic force.

30. The method of claim 25 , wherein the layered double hydroxide is represented by Formula 11:

[M2 2+ 1−x M3 3+ x (OH) 2 ] x+ [A n− ] x/n .yH 2 O  Formula 11

wherein, in Formula 11,

0.1≤x≤0.4, 0<y,

M2 2+ comprises Co 2+ , Mg 2+ , Ni 2+ , Cu 2+ , or Zn 2+ ,

M3 3+ comprises Ce 3+ , Al 3+ , Fe 3+ , V 3+ , Ti 3+ , or Ga 3+ ,

A n− comprises NO 3 2− , SO 4 2− , CO 3 2− , PO 4 2− , Cl − , or a combination thereof, and

n is a valence of the anion.