Method for Manufacturing Crosslinked Structure-Containing Separator for Lithium Secondary Battery, Crosslinked Structure-Containing Separator for Lithium Secondary Battery Obtained Thereby, and Lithium Secondary Battery Including the Same

A method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery includes supplying polyolefin and a diluting agent to an extruder to extrude a polyolefin composition; molding and orienting the extruded polyolefin composition into the form of a sheet; dipping the oriented sheet in an extraction solution to extract the diluting agent, thereby providing a polyolefin-based porous support; and irradiating ultraviolet rays to the polyolefin-based porous support, wherein the extraction solution has an upper layer and a lower layer, the lower layer includes a photoinitiator and a solvent for the photoinitiator, the upper layer includes a non-solvent for the photoinitiator, and the photoinitiator is present in an amount of 0.01-0.3 parts by weight based on 100 parts by weight of the solvent for the photoinitiator. Also provided is a crosslinked structure-containing separator for a lithium secondary battery and a lithium secondary battery including the crosslinked structure-containing separator.