Preparation method of separator having organic-inorganic composite porous coating layer, separator formed therefrom, and electrochemical device containing the same
A preparation method of a separator according to the present disclosure includes preparing an aqueous slurry including inorganic particles, a binder polymer, and an aqueous medium, and coating the aqueous slurry on at least one surface of a porous polymer substrate to form an organic-inorganic composite porous coating layer, wherein capillary number of the aqueous slurry has a range between 0.3 and 65.
1. A preparation method of a separator, comprising:
preparing an aqueous slurry comprising inorganic particles, a binder polymer, and an aqueous medium; and
coating the aqueous slurry on at least one surface of a polyolefin-based porous polymer film substrate to form 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 capillary number of the aqueous slurry is from 4.2 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 0.2 m/s 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 4.2 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 a weight ratio of the inorganic particles and the binder polymer is in a range between 50:50 and 99:1.
9. The preparation method of a separator according to claim 1 , wherein the binder polymer comprises acrylate-based polymer.
10. The preparation method of a separator according to claim 1 , wherein the binder polymer comprises styrene-butadiene rubber (SBR)-based polymer.
11. The preparation method of a separator according to claim 1 , wherein the binder polymer comprises at least one of styrene-butadiene rubber (SBR)-based polymer and acrylate-based polymer.
12. 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.
13. 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.
14. The preparation method of a separator according to claim 13 , 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 , Pb 1-x La x Zr 1-y Ti y O 3 , wherein 0<x<1, 0<y<1, Pb(Mg 1/3 Nb 2/3 )O 3 —PbTiO 3 , hafnia, SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, ZnO, ZrO 2 , SiO 2 , Y 2 O 3 , Al 2 O 3 , boehmite, SiC and TiO 2 , or mixtures thereof.
15. The preparation method of a separator according to claim 13 , wherein the inorganic particles capable of transporting lithium ions are inorganic particles of any one selected from the group consisting of lithium phosphate of formula Li 3 PO 4 , lithium titanium phosphate of formula Li x Ti y (PO 4 ) 3 , wherein 0<x<2, 0<y<3, lithium aluminum titanium phosphate of formula Li x Al y Ti z (PO 4 ) 3 , wherein 0<x<2, 0<y<1, 0<z<3, (LiAlTiP) x O y based glass, wherein 0<x<4, 0<y<13, lithium lanthanum titanate of formula Li x La y TiO 3 , wherein 0<x<2, 0<y<3, lithium germanium thiophosphate of formula Li x Ge y P z S w , wherein 0<x<4, 0<y<1, 0<z<1, 0<w<5, lithium nitride of formula Li x N y , 0<x<4, 0<y<2, SiS 2 based glass of formula Li x Si y S z , wherein 0<x<3, 0<y<2, 0<z<4, and P 2 S 5 based glass of formula Li x P y S z , wherein 0<x<3, 0<y<3, 0<z<7, or mixtures thereof.