Separator and electrochemical device having the same

1. A separator, comprising a porous substrate; and a porous coating layer formed on at least one surface of the porous substrate and comprising a mixture of inorganic particles and a binder polymer, wherein the separator has a value of a porosity×an air permeability per thickness in the range of 5 to 40, the porosity and the air permeability per thickness being defined by Formula (I) and Formula (II), respectively:

Porosity=1−(the weight ratio of the inorganic particles/the density of the inorganic particles+the weight ratio of the binder polymer/the density of the binder polymer)  [Formula (I)]

Air Permeability per thickness=(the air permeability of the separator−the air permeability of the porous substrate)/(the thickness of the separator−the thickness of the porous substrate)  [Formula (II)]

wherein the porosity ranges from equal to or greater than 0.5 to less than 1, and the air permeability per thickness ranges from 5 to 80, and

the binder polymer is selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl alcohol, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, a low molecular compound having a molecular weight of 10,000 g/mol or less, and a mixture thereof

wherein the porous coating layer is prepared from a slurry wherein the binder polymer is dissolved and the inorganic particles are included, and

wherein the separator has an ionic conductivity of 3.7 to 6.4×10 −4 S/cm.

2. The separator according to claim 1 , wherein the porous substrate is made of a polyolefin-based polymer.

3. The separator according to claim 2 , wherein the porous substrate is made of a polyolefin-based polymer selected from the group consisting of polyethylene, polypropylene, polybutylene and polypentene.

4. The separator according to claim 1 , wherein the inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of 5 or higher, inorganic particles having the ability to transport lithium ions, and a mixture thereof.

5. The separator according to claim 4 , wherein the inorganic particles having a dielectric constant of 5 or higher are selected from the group consisting of BaTiO 3 , Pb(Zr x ,Ti 1-x )O 3 (PZT, 0<x<1), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT, 0<x<1, 0<y<1), (1−x)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PMN-PT, 0<x<1), 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 , SiC, TiO 2 inorganic particles and a mixture thereof.

6. The separator according to claim 4 , wherein the inorganic particles having the ability to transport lithium ions are selected from the group consisting of lithium phosphate (Li 3 PO 4 ), lithium titanium phosphate (Li x Ti y (PO 4 ) 3 , 0<x<2, 0<y<3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO 4 ) 3 , 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O y type glass (0<x<4, 0<y<13), lithium lanthanum titanate (Li x La y TiO 3 , 0<x<2, 0<y<3), lithium germanium thiophosphate (Li x Ge y P z S w , 0<x<4, 0<y<1, 0<z<1, 0<w<5), lithium nitride (Li x N y , 0<x<4, 0<y<2), SiS 2 type glass (Li x Si y S z , 0<x<3, 0<y<2, 0<z<4), P 2 S 5 type glass (Li x P y S z , 0<x<3, 0<y<3, 0<z<7) particles, and a mixture thereof.

7. An electrochemical device, comprising a cathode, an anode and a separator interposed between the cathode and the anode,

wherein the separator is defined in claim 1 .

8. The electrochemical device according to claim 7 , which is a lithium secondary battery.