Polyolefin Separator and Method for Manufacturing the Same

A polyolefin separator is provided in the present disclosure. The polyolefin separator includes a polyolefin porous substrate including a plurality of fibrils and pores formed by the fibrils draped across one another. A coating layer surrounding the outer side of the fibrils is contained in the polyolefin porous substrate and the coating layer includes a crosslinked polymer, wherein the polyolefin separator having the coating layers has a change in air permeability of 20% or less and a change in basis weight of 4% or less, as compared to the polyolefin porous substrate. A method for manufacturing the polyolefin separator and a secondary battery including the polyolefin separator are also disclosed.