Method for preparing cross-linked ceramic-coated separator containing ionic polymer, ceramic-coated separator prepared by the method, and lithium secondary battery using the same

1. A method for preparing a cross-linked ceramic-coated separator containing an ionic polymer, the method comprising:

(a) preparing a polymer solution by dissolving an ionic polymer in a solvent;

(b) preparing an inorganic dispersion solution by dispersing ceramic particles for improving thermal and mechanical characteristics and a functional inorganic compound for forming a conductive solid electrolyte interface during charge/discharge in a solvent;

(c) preparing a coating material by adding a curing agent and an initiator to the two solutions prepared in steps (a) and (b) and uniformly mixing the resulting solution;

(d) coating the coating material prepared in step (c) on one or both sides of a porous membrane substrate and drying the resulting substrate;

(e) preparing a chemically cross-linked separator by chemically cross-linking the substrate obtained in step (d) by thermal polymerization or ultraviolet irradiation; and

(f) drying the thus prepared separator.

2. The method of claim 1 , wherein the coating material comprises 10 to 90 wt % of the ionic polymer, 10 to 90 wt % of the ceramic particles, and 0.01 to 10 wt % of the functional inorganic compound.

3. The method of claim 1 , wherein the ionic polymer used as a binder is a copolymer containing metal cations and comprising at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, butadiene-acrylic acid copolymer, butadiene-methacrylic acid copolymer, polyvinylsulfonate, chlorosulfonated polyethylene, perfluorosulfonate ionomer, sulfonated polystyrene, styrene-acrylic acid copolymer, and sulfonated butyl rubber.

4. The method of claim 1 , wherein the ceramic particles comprise at least one selected from the group consisting of: SiO 2 , Al 2 O 3 , TiO 2 , SnO 2 , CeO 2 , ZrO 2 , BaTiO 3 , and Y 2 O 3 .

5. The method of claim 4 , wherein the ceramic particles have a diameter in the range of 0.001 to 1 μm.

6. The method of claim 1 , wherein the functional inorganic compound comprises at least one selected from the group consisting of: AlX 3 , MgX 2 , and SnX 2 in which X represents a halogen atom such as F, Cl, Br, and I.

7. The method of claim 1 , wherein the porous membrane substrate comprises at least one selected from the group consisting of: a polyolefin resin, a fluorine resin, a polyester resin, a polyacrylonitrile resin, and a cellulose nonwoven fabric.

8. The method of claim 7 , wherein the porous membrane has a porosity of at least 30% and a thickness of 10 to 100μ.

9. The method of claim 1 , wherein in step (c), a cross-linking agent containing at least two double bonds in a molecule, the cross-linking agent comprising at least one compound selected from the group consisting of: divinylbenzene, diacrylate, triacrylate, tetraacrylate, dimethacrylate, trimethacrylate, tetramethacrylate, diallyl ester, triallyl ester, diglycidyl ester, and polyethylene glycol dimethacrylate.

10. The method of claim 1 , wherein the initiator added to initiate a chemical reaction of the cross-linking agent comprises one selected from the group consisting of: an azo compound, a peroxide compound, and a ketone compound.

11. A method for preparing a cross-linked ceramic-coated separator containing an ionic polymer, the method comprising:

(a) preparing a polymer solution;

(b) preparing an inorganic dispersion solution;

(c) preparing a coating material by mixing prepared solutions (a) and (b);

(d) coating the coating material prepared in step (c) on one or both sides of a porous membrane substrate and drying the resulting substrate; and

(e) preparing a chemically cross-linked separator,

wherein the inorganic dispersion solution is prepared by dispersing ceramic particles for improving thermal and mechanical characteristics and a functional inorganic compound for forming a conductive solid electrolyte interface during charge/discharge in a solvent.

12. The method for preparing the cross-linked ceramic-coated separator of claim 11 , wherein the polymer solution is prepared by dissolving an ionic polymer in a solvent.

13. The method for preparing the cross-linked ceramic-coated separator of claim 11 , wherein the coating material is prepared by adding a curing agent and an initiator to the two solutions prepared in steps (a) and (b) and uniformly mixing the resulting solution.

14. The method for preparing the cross-linked ceramic-coated separator of claim 11 , wherein the chemically cross-linked separator is prepared by chemically cross-linking the substrate obtained in step (d) by thermal polymerization or ultraviolet irradiation.

15. The method for preparing the cross-linked ceramic-coated separator of claim 11 , further comprising the step of drying the prepared separator.

16. The method for preparing the cross-linked ceramic-coated separator of claim 11 , wherein the coating material comprises 10 to 90 wt % of an ionic polymer.

17. The method for preparing the cross-linked ceramic-coated separator of claim 11 , wherein the coating material comprises 10 to 90 wt % of ceramic particles.

18. The method for preparing the cross-linked ceramic-coated separator of claim 11 , wherein the coating material comprises 0.01 to 10 wt % of functional inorganic compound.

19. The method of claim 1 , wherein the porous membrane substrate comprises at least one selected from the group consisting of: polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate and polybutylene terephthalate.

20. The method of claim 1 , wherein the initiator added to initiate a chemical reaction of the cross-linking agent comprises one selected from the group consisting of azobisisobutyronitrile, benzoyl peroxide, and hydroxy ketone.