A separator for a secondary cell includes a porous polymer substrate having a first surface, a second surface opposing the first surface, and a plurality of pores connecting the first surface to the second surface; and heat-resistant coating layers formed on at least one of the first surface and the second surface of the porous polymer substrate and on internal surfaces of the pores using an atomic layer deposition process (ALD). Pores having a non-coated region are present in the internal surfaces of the pores.