The present invention provides a crosslinked polyolefin film for a lithium secondary battery separator, characterized in that the Si atoms are contained in an amount of 500 to 1,000 ppm based on the crosslinked polyolefin film, and as a method of manufacturing the crosslinking agent and the side reaction of the initiator and the diluent and the initiator As an aspect of a method capable of inhibiting side reactions, (S1) a polyolefin, a diluent, an initiator, a carbon-carbon double bond-containing alkoxy silane, and a step of introducing and mixing a crosslinking catalyst into an extruder, wherein the initiator is the carbon-carbon A mixture of a double bond group-containing alkoxy silane and a diluent, and the initiator is added in an amount of 0.1 to 2.0 parts by weight based on 100 parts by weight of the total amount of the carbon-carbon double bond-containing alkoxy silane; (S2) preparing a silane-grafted polyolefin composition by reacting and extruding the resultant mixture in the step (S1); (S3) forming and stretching the reaction-extruded silane-grafted polyolefin composition in a sheet form; (S4) extracting a diluent from the stretched sheet to prepare a porous membrane; (S5) heat-setting the porous membrane; And (S6) crosslinking the heat-set porous membrane in the presence of moisture; characterized in that it comprises a method for producing a crosslinked polyolefin film for a lithium secondary battery separator according to claim 1, wherein A method for manufacturing a crosslinked polyolefin film for a lithium secondary battery separator is provided.
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