A separator includes a non-woven fabric substrate having pores, fine thermoplastic powder located inside the pores of the non-woven fabric substrate, and a porous coating layer disposed on at least one surface of the non-woven fabric substrate. The fine thermoplastic powder has an average diameter smaller than that of the pores and a melting point lower than the melting or decomposition point of the non-woven fabric substrate. The porous coating layer includes a mixture of inorganic particles and a binder polymer whose melting point is higher than the melting or decomposition point of the fine thermoplastic powder. In the porous coating layer, the inorganic particles are fixedly connected to each other by the binder polymer and the pores are formed by interstitial volumes between the inorganic particles. Previous filling of the large pores of the non-woven fabric substrate with the fine thermoplastic powder makes the porous coating layer uniform.