Cathode active material for lithium secondary battery, method of preparing the same, and lithium secondary battery containing the same

1. A cathode active material for a lithium secondary battery, the cathode active material comprising:

a core made of a compound reversibly intercalating and deintercalating lithium; and

a coating layer positioned on at least a portion of a surface of the compound,

wherein the coating layer is a composite coating layer containing Li 3 PO 4 and LiF, and

the core is doped with fluorine.

2. The cathode active material of claim 1 , wherein:

lithium of Li 3 PO 4 , LiF, and/or the lithium metal compound contained in the composite coating layer is derived from Li contained in the compound reversibly intercalating and deintercalating lithium or from a separate Li source material.

3. The cathode active material of claim 1 , wherein:

metals in the lithium metal compound, the metal oxide, and the metal fluoride compound contained in the composite coating layer,

are each independently Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, Zr, or a combination thereof.

4. The cathode active material of claim 1 , wherein:

the lithium metal compound contained in the composite coating layer is Li 2 TiO 3 , LiAlO 2 , Li 2 ZrO 3 , Li 2 SiO 3 , Li 4 SiO 4 , or a combination thereof.

5. The cathode active material of claim 1 , wherein:

the metal oxide contained in the composite coating layer is TiO 2 , Al 2 O 3 , SiO 2 , ZrO 2 , or a combination thereof.

6. The cathode active material of claim 1 , wherein:

the metal fluoride compound contained in the composite coating layer is AlF 3 , TiF 4 , CoF 2 , NiF 2 , MnF 2 , ZrF 4 , SiF 4 , or a combination thereof.

7. The cathode active material of claim 1 , wherein:

fluorine of the metal fluoride compound in the composite coating layer,

is derived from fluorine contained in the core doped with fluorine.

8. The cathode active material of claim 1 , wherein:

a molar doping ratio of fluorine in the core is 0.001 to 0.01.

9. The cathode active material of claim 1 , wherein:

some of oxygen atoms in the core are doped with fluorine.

10. The cathode active material of claim 1 , wherein:

a content of the coating layer is 0.2 to 2.0 wt % based on a total weight of the cathode active material.

11. The cathode active material of claim 1 , wherein:

a content of P in the composite coating layer is 500 to 5000 ppm.

12. The cathode active material of claim 1 , wherein:

the compound reversibly intercalating and deintercalating lithium is at least one selected from the group consisting of Li a A 1-b X b D 2 (0.90≤a≤1.8, 0≤b≤0.5); Li a A 1-b X b O 2-c T c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE 1-b X b O 2-c D c (0≤b≤0.5, 0≤c≤0.05); LiE 2-b X b O 4-c T c (0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Co b X c O 2-α T 2 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mn b X c D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Mn b X c O 2-α T α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α T 2 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni b E c G d O 2-e T e (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1, 0≤e≤0.05); Li a Ni b Co c Mn d G e O 2-f T f (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1, 0≤e≤0.05); Li a NiG b O 2-c T c (0.90≤a≤1.8, 0.001≤b≤0.1, 0≤c≤0.05); Li a CoG b O 2-c (0.90≤a≤1.8, 0.001≤b≤0.1, 0≤c≤0.05); Li a MnG′ b O 2-c T c (0.90≤a≤1.8, 0.001≤b≤0.1, 0≤c≤0.05); Li a Mn 2 G b O 2-c T c (0.90≤a≤1.8, 0.001≤b≤0.1, 0≤c≤0.05); Li a MnG′ b PO 4 (0.90≤a≤1.8, 0.001≤b≤0.1); LiNiVO 4 ; and Li (3-f) J 2 (PO 4 ) 3 (0≤f≤2):

in Chemical Formulas, A is selected from the group consisting of Ni, Co, Mn, and a combination thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and a combination thereof; D is selected from the group consisting of O, F, S, P, and a combination thereof; E is selected from the group consisting of Co, Mn, and a combination thereof; T is selected from the group consisting of F, S, P, and a combination thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and a combination thereof; Q is selected from the group consisting of Ti, Mo, Mn, and a combination thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and a combination thereof; and J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and a combination thereof.

13. A method of preparing a cathode active material for a lithium secondary battery, the method comprising:

preparing a core material containing a compound reversibly intercalating and deintercalating lithium, and doped with fluorine;

preparing a lithium source, a phosphorus source, and/or a metal source;

uniformly attaching the lithium source, the phosphorous source, and/or the metal source onto a surface of the core material by mixing the lithium source, the phosphorous source, and/or the metal source with the core material; and

obtaining a core material of which a composite coating layer containing Li 3 PO 4 and LiF and further containing a lithium metal compound, a metal oxide, a metal fluoride compound, and/or a combination thereof is formed on the surface by heat-treating the core material onto which the lithium source, the phosphorous source, and/or the metal source are attached.

14. The method of claim 13 , wherein:

the preparing of the core material containing the compound reversibly intercalating and deintercalating lithium, and doped with fluorine,

is performed by a method of mixing the compound reversibly intercalating and deintercalating lithium with a fluorine compound and heat-treating the mixture, and

a heat treatment temperature is 800 to 1050° C.

15. The method of claim 13 , wherein:

the fluorine compound used in a method of mixing the compound reversibly intercalating and deintercalating lithium with a fluorine compound and heat-treating the mixture,

is LiF, AlF 3 , MgF 2 , CaF 2 , ZrF 4 , TiF 4 , or a combination thereof.

16. The method of claim 13 , wherein:

in the obtaining of the core material of which the composite coating layer containing Li 3 PO 4 and LiF and further containing the lithium metal compound, the metal oxide, the metal fluoride compound, and/or the combination thereof is formed on the surface by heat-treating the core material onto which the lithium source, the phosphorous source, and/or the metal source are attached,

a heat treatment temperature is 650 to 950° C.

17. A lithium secondary battery comprising:

a cathode containing the cathode active material of claim 1 ;

an anode containing an anode active material; and

an electrolyte.

18. The cathode active material of claim 1 , wherein:

the coating layer further contains a lithium metal compound, a metal oxide, a metal fluoride compound, and/or a combination thereof.