Preparation method of separator having organic-inorganic composite porous coating layer, separator formed therefrom, and electrochemical device containing the same

1. A preparation method of a separator, comprising:

preparing an aqueous slurry comprising pulverized inorganic particles, a binder polymer, and an aqueous medium,

wherein the binder polymer is selected from the group consisting of styrene-butadiene rubber (SBR)-based polymer and acrylate-based polymer, or mixtures thereof,

wherein a weight ratio of the inorganic particles and the binder polymer is in a range between 50:50 and 99:1; and

coating the aqueous slurry on at least one surface of a polyolefin-based porous polymer film substrate to from an organic-inorganic composite porous coating layer,

wherein a thickness of the porous polymer film substrate is from 5 μm to 50 μm, a pore size of the porous polymer film substrate is from 0.01 μm to 50 μm and a porosity of the porous polymer film substrate is from 10% to 95%,

wherein a capillary number of the aqueous slurry is from 0.3 to 65,

the capillary number is determined by the following equation 1:

Capillary number( Ca )=(μ× U )/σ

wherein the viscosity μ is from 0.005 to 0.05 kgf·s/m 2 ,

wherein the coating velocity U is from 0.15 to 2.0 m/s, and

wherein the surface tension σ is from 0.0015 to 0.005 kgf/m.

2. The preparation method of a separator according to claim 1 , wherein the capillary number Ca is from 0.4 to 45.

3. The preparation method of a separator according to claim 1 , wherein the aqueous medium is water, or a mixture of alcohol and water.

4. The preparation method of a separator according to claim 1 , wherein an additive to reduce surface tension is present in an amount of about 0.1 wt % to about 3.0 wt % of the weight of the aqueous slurry and is at least one surfactant selected from the group consisting of polyoxyethylene(10)-hydrogenated castor oil, polyoxyethylene(40)-hydrogenated castor oil, polyoxyethylene(60)-hydrogenated castor oil, siloxane, polysorbate 60, polysorbate 80, and polysorbate 20.

5. The preparation method of a separator according to claim 1 , wherein the polyolefin-based porous polymer film substrate is formed from at least one type of polymer selected from the group consisting of polyethylene, polypropylene, polybutylene, and polypentene.

6. The preparation method of a separator according to claim 1 , wherein the forming of the organic-inorganic composite porous coating layer is performed by a slot coating method.

7. The preparation method of a separator according to claim 1 , wherein the forming of the organic-inorganic composite porous coating layer is performed by a dip coating method.

8. The preparation method of a separator according to claim 1 , wherein an average grain size of the inorganic particles is from 0.001 μm to 10 μm.

9. The preparation method of a separator according to claim 1 , wherein the inorganic particles are inorganic particles selected from the group consisting of inorganic particles having a high dielectric constant greater than or equal to 5, inorganic particles capable of transporting lithium ions, and mixtures thereof.

10. The preparation method of a separator according to claim 9 , wherein the inorganic particles having a high dielectric constant greater than or equal to 5 are inorganic particles of any one selected from the group consisting of BaTiO 3 , Pb(Zr,Ti)O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), wherein 0<x<1, 0<y<1, Pb(Mg 1/3 Nb 2/3 )O 3 —PbTiO 3 (PMN-PT), hafnia (HfO 2 ), SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO, ZrO 2 , SiO 2 , Y 2 O 3 , Al 2 O 3 , boehmite (γ-AlO(OH)), SiC and TiO 2 , or mixtures thereof.

11. The preparation method of a separator according to claim 9 , wherein the inorganic particles capable of transporting lithium ions are inorganic particles of any one selected from the group consisting of lithium phosphate, lithium titanium phosphate, lithium aluminum titanium phosphate, (LiAlTiP) x O y based glass, wherein 0<x<4, 0<y<13, lithium lanthanum titanate, lithium germanium thiophosphate, lithium nitride, SiS 2 based glass, and P 2 S 5 based glass, or mixtures thereof.