A separator comprising: a porous substrate having a plurality of pores; and a pair of porous coating layers formed on both surfaces of the porous substrate, and including a plurality of inorganic particles and a binder polymer disposed partially or totally on the surface of the inorganic particles to connect and fix the inorganic particles with each other, wherein the amount of the binder polymer and the amount of the inorganic particles in one porous coating layer are the same as those in the other porous coating layer, the binder polymer is used in an amount of 5-40 wt% based on the total weight of the porous coating layer, the inorganic particles include boehmite particles and non-boehmite particles, and the boehmite particles and the binder polymer are used at a weight ratio of 1:1-1:5, wherein the non-boehmite particles comprise inorganic particles having a dielectric constant of 5 or more, inorganic particles capable of transporting lithium ions or a mixture thereof, wherein the inorganic particles having a dielectric constant of 5 or more comprise BaTiO 3, Pb(Zr,Ti)O 3, Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), PB(Mg 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, Y 2 O 3, Al 2 O 3, TiO 2, SiC or a mixture thereof, and the inorganic particles capable of transporting lithium ions comprise 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 -based 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 -based glass (Li x Si y S z, 0<x<3, 0<y<2, 0<z<4), P 2 S 5 -based glass (Li x P y S z, 0<x<3, 0<y<3, 0<z<7) or a mixture thereof. a porous substrate having a plurality of pores; and a pair of porous coating layers formed on both surfaces of the porous substrate, and including a plurality of inorganic particles and a binder polymer disposed partially or totally on the surface of the inorganic particles to connect and fix the inorganic particles with each other, wherein the amount of the binder polymer and the amount of the inorganic particles in one porous coating layer are the same as those in the other porous coating layer, the binder polymer is used in an amount of 5-40 wt% based on the total weight of the porous coating layer, the inorganic particles include boehmite particles and non-boehmite particles, and the boehmite particles and the binder polymer are used at a weight ratio of 1:1-1:5, wherein the non-boehmite particles comprise inorganic particles having a dielectric constant of 5 or more, inorganic particles capable of transporting lithium ions or a mixture thereof, wherein the inorganic particles having a dielectric constant of 5 or more comprise BaTiO 3, Pb(Zr,Ti)O 3, Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), PB(Mg 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, Y 2 O 3, Al 2 O 3, TiO 2, SiC or a mixture thereof, and the inorganic particles capable of transporting lithium ions comprise 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 -based 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 -based glass (Li x Si y S z, 0<x<3, 0<y<2, 0<z<4), P 2 S 5 -based glass (Li x P y S z, 0<x<3, 0<y<3, 0<z<7) or a mixture thereof.