Cathode active material exhibiting improved property in high voltage

1. A cathode active material comprising:

a lithium transition metal oxide based on at least one transition metal selected from the group consisting of Ni, Mn and Co, wherein the lithium transition metal oxide contains fluorine, 50 to 99.9% of a total weight of fluorine contained in the active material is present on a surface of the lithium transition metal oxide, and at least one metal selected from a group consisting of Mg, Ti, Zr, Al and Fe as well as sulfur (S) are further contained in the lithium transition metal oxide,

wherein a content of the sulfur ranges from 0.005 to 5 wt. % relative to a total weight of the lithium transition metal oxide,

wherein the lithium transition metal oxide is represented by the following Formula 1:

Li 1+a Mn (1-w-x-y-z) Ni w Co x D 1y (D 2 ,D 3 ) Z O 2 *D 1 ′ y (D 2 ′,D 3 ′) Z′   (1)

wherein, −0.3≦a≦0.3; 0≦w<0.8; 0<x<0.8; 0.001<y<0.02; 0.005<z<0.1; 0≦(1−w−x−y−z)<0.5;

D 1 is fluorine;

D 2 is at least one or two selected from a group consisting of Mg, Ti, Zr, Al and Fe;

D 3 is sulfur;

y denotes a doping amount of D 1 ;

z denotes the sum of doping amounts of D 2 and D 3 ;

D 1 ′, D 2 ′ and D 3 ′ denote D 1 , D 2 and D 3 present on the surface of the lithium transition metal oxide, respectively;

y′ denotes a coating amount of D 1 , provided that the sum of y′ and y ranges from 0.01 to 7 wt. % relative to a total weight of lithium transition metal oxide; and

z′ denotes the sum of coating amounts of D 2 ′ and D 3 ′, provided that the sum of z′ and z ranges from 0.01 to 10 wt. % relative to a total weight of lithium transition metal oxide.

2. The cathode active material according to claim 1 , wherein a content of fluorine in the lithium transition metal oxide is 10 wt. % or less relative to a total weight of the lithium transition metal oxide.

3. The cathode active material according to claim 2 , wherein fluorine is doped inside the lithium transition metal oxide.

4. The cathode active material according to claim 2 , wherein the at least one metal includes Mg.

5. The cathode active material according to claim 1 , wherein 0.01 to 7 wt. % of fluorine relative to a total weight of the lithium transition metal oxide is coated on the surface of the lithium transition metal oxide.

6. The cathode active material according to claim 1 , wherein the fluorine has a concentration profile from higher concentration at the surface of the lithium transition metal oxide to lower concentration inside the lithium transition metal oxide.

7. The cathode active material according to claim 1 , wherein metal is present on the surface of the lithium transition metal oxide while the remainder of the metal is doped inside the lithium transition metal oxide.

8. The cathode active material according to claim 1 , wherein a content of the metal ranges from 0.01 to 10 wt. % relative to a total weight of the lithium transition metal oxide.

9. The cathode active material according to claim 1 , wherein some sulfur is present on the surface of the lithium transition metal oxide while the remainder of the sulfur is doped inside the lithium transition metal oxide.

10. The cathode active material according to claim 1 , wherein the lithium transition metal oxide is a lithium nickel-manganese-cobalt oxide having a nickel content of 40 to 70% relative to a total amount of nickel-manganese-cobalt.

11. A lithium secondary battery comprising the cathode active material according to claim 1 .

12. The lithium secondary battery according to claim 11 , wherein an electrolyte further contains propene sultone (PRS) and/or fluoro-ethylene carbonate (FEC) as an additive.

13. The cathode active material according to claim 1 , wherein the at least one metal is Mg,

wherein the amount of Mg doped inside the lithium transition metal oxide is 80-8300 ppm,

wherein the amount of Mg coated to the surface of the lithium transition metal oxide is 20-3500 ppm, and

wherein the amount of Mg doped inside the lithium transition metal oxide is greater than an amount of Mg applied to the surface thereof.

14. The cathode active material according to claim 1 , wherein the content of the sulfur ranges from 0.01 to 5 wt. % relative to a total weight of the lithium transition metal oxide.

15. A method for preparing a lithium transition metal oxide according to claim 1 , the method comprising:

mixing a lithium precursor, a transition metal precursor and fluoride as a doping metal precursor (‘doping metal fluoride’) and

sintering the mixture.

16. The method according to claim 15 , wherein the transition metal precursor is a transition metal oxide.

17. The method according to claim 16 , further comprising addition of sulfuric acid or sulfate.