Cathode active material, cathode and lithium secondary battery including the same, and method of preparing cathode active material

1. A cathode active material comprising:

a layered lithium transition metal oxide comprising overlithiated lithium transition metal oxide represented by Formula 1:

Li 1-x [M 1-y M′ y ]O 2±α   Formula 1

Wherein, in Formula 1,

1.1<(1+x)≤1.6, 0<y≤0.0045, and 0≤α<1,

M is at least one transition metal selected from Ni, Co, Mn, and

M′ is at least one metal selected from V, Hf, Pa, U, NP, PU, Ce, Pb, and Ge, wherein the layered lithium transition metal oxide comprises a metal cation having an oxidation number of +4,

wherein the metal cation is selected from V 4+ , Hf 4+ , Pa 4+ , U 4+ , Np 4+ , Pu 4+ , Ce 4+ , Pb 4+ , and Ge 4+ ,

wherein the metal cation is disposed in an octahedral site defined by oxygen atoms of a lattice of the layered lithium transition metal oxide, and

wherein the metal cation having an oxidation number of +4 is included in an amount ranging greater than 0 mole percent to about 0.0045 mole percent, based on 1 mole of a transition metal of the transition metal oxide.

2. The cathode active material of claim 1 , wherein the metal cation having an oxidation number of +4 is V 4+ .

3. The cathode active material of claim 1 , wherein, in Formula 1, 1.32≤(1+x)≤1.52.

4. The cathode active material of claim 1 , wherein, in Formula 1, M′ is V.

5. The cathode active material of claim 1 , wherein the layered lithium transition metal oxide is a spherical particle, and an average particle diameter (D50) of the spherical particle is in a range of about 1 micrometer to about 20 micrometers.

6. The cathode active material of claim 5 , wherein a surface of and an inside of the spherical particle comprises the metal cation having an oxidation number of +4.

7. The cathode active material of claim 6 , wherein a shape of the spherical particle comprising the metal cation having an oxidation number of +4 in the surface of and in the inside of the spherical particle is identical to a shape of a spherical particle not comprising the metal cation having an oxidation number of +4 in a surface of and in an inside thereof.

8. A cathode comprising a cathode active material according to claim 1 .

9. A lithium secondary battery comprising the cathode according to claim 8 .

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

combining a metal cation precursor with a transition metal hydroxide precursor to provide a combination;

precipitating a transition metal hydroxide comprising a metal cation having an oxidation number of +4 from the combination, wherein the metal cation is selected from V 4+ , Hf 4+ , Pa 4+ , U 4+ , Np 4+ , Pu 4+ , Ce 4+ , Pb 4+ , and Ge 4+ ; and wherein the metal cation having an oxidation number of +4 is included in an amount ranging greater than 0 mole percent to about 0.0045 mole percent, based on 1 mole of a transition metal of the transition metal oxide; and

combining the transition metal hydroxide comprising the metal cation having an oxidation number of +4 with a lithium precursor to obtain a mixture; and

thermally treating the mixture to prepare the cathode active material according to claim 1 .

11. The method of claim 10 , wherein the metal cation precursor comprises at least one selected from VOSO 4 .xH 2 O wherein 3≤x≤5, and V(CO 3 ) 2 .

12. The method of claim 10 , wherein the transition metal hydroxide comprises a transition metal hydroxide represented by Formula 2:

[(M1) 1-a (M′1) a ](OH) 2   Formula 2

wherein, in Formula 2,

0≤a≤0.0045,

M1 is at least one transition metal selected from Ni, Co, and Mn, and

M′1 is at least one metal selected from V, Hf, Pa, U, Np, Pu, Ce, Pb, and Ge.

13. The method of claim 10 , wherein the combining of the transition metal hydroxide and the metal cation precursor comprises stirring a mixture of the metal cation precursor and the transition metal hydroxide precursor at a temperature of about 40° C. to about 60° C. and at a rate of about 600 revolutions per minute to about 1000 revolutions per minute.

14. The method of claim 10 , further comprising adding a base during the combining in an amount effective to maintain a pH of the combination in a range of about 11 to about 12.

15. The method of claim 10 , wherein the thermal treating is performed at a temperature of about 500° C. to about 900° C.

16. The method of claim 10 , wherein the thermal treating is performed in an air atmosphere.

17. A cathode active material comprising:

a layered lithium transition metal oxide, wherein the layered lithium transition metal oxide comprises

a metal cation having an oxidation number of +4, and wherein the metal cation is disposed in an octahedral site of a lattice of the layered lithium transition metal oxide, wherein the layered lithium transition metal oxide comprises an overlithiated lithium transition metal oxide represented by Formula 1:

Li 1+x [M 1-y M′ y ]O 2+α   Formula 1

wherein, in Formula 1,

1.1<(1+x)≤1.6, 0<y≤0.0045, and 0≤α<1,

M is at least one transition metal selected from Ni, Co, and Mn, and

M′ is at least one metal selected from V, Zr, Hf, Ti, Pa, U, Np, Pu, Ce, Pb, and Ge.

18. A lithium secondary battery comprising the cathode according to claim 17 .

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

combining a metal cation precursor with a transition metal hydroxide precursor to provide a combination;

precipitating a transition metal hydroxide comprising a metal cation having an oxidation number of +4 from the combination;

combining the transition metal hydroxide comprising the metal cation having an oxidation number of +4 with a lithium precursor to obtain a mixture; and

thermally treating the mixture to prepare the cathode active material, wherein the cathode active material comprises:

a layered lithium transition metal oxide, wherein the layered lithium transition metal oxide comprises

a metal cation having an oxidation number of +4, and wherein the metal cation is disposed in an octahedral site of a lattice of the layered lithium transition metal oxide, and wherein the layered lithium transition metal oxide comprises an overlithiated lithium transition metal oxide represented by Formula 1:

Li 1+x [M 1-y M′ y ]O 2+α   Formula 1

wherein, in Formula 1,

1.1<(1+x)≤1.6, 0<y≤0.0045, and 0≤α<1,

M is at least one transition metal selected from Ni, Co, and Mn, and

M′ is at least one metal selected from V, Zr, Hf, Ti, Pa, U, Np, Pu, Ce, Pb, and Ge.