Provided herein is a separator used for an electrochemical device such as a lithium-ion battery. The separator disclosed herein comprises a porous base material, and a protective porous layer coated on one or both surfaces of the porous base material disclosed herein, wherein the protective porous layer comprises an organic binder and an inorganic filler, and wherein the inorganic filler comprises a whisker-type material selected from the group consisting of Al2O3, SiO2, TiO2, ZrO2, BaOx, ZnO, CaCO3, TiN, AlN, MTiO3, K2O·nTiO2, Na2O·mTiO2, and combinations thereof, wherein x is 1 or 2; M is Ba, Sr or Ca; n is 1, 2, 4, 6 or 8; and m is 3 or 6. Also provided herein is a lithium-ion battery including the separator disclosed herein. The separator disclosed herein is excellent in terms of safety, ion permeability, and cycle characteristics.