Separator, lithium secondary battery including separator, and manufacturing method thereof

A lithium secondary battery, comprising:

• a positive electrode;
• a negative electrode;
• and
• a separator interposed between the positive electrode and the negative electrode,
• wherein the separator comprises a non-crosslinked polyolefin layer facing the positive electrode, and a crosslinked polyolefin layer disposed on one surface of the non-crosslinked polyolefin layer and having at least one crosslinking bond represented by the following Chemical Formula 1, and an outermost non-crosslinked polyolefin layer on a surface of the crosslinked polyolefin layer such that the crosslinked polyolefin layer is interposed between the non-crosslinked polyolefin layer and the outermost non-crosslinked polyolefin layer, wherein the outermost non-crosslinked polyolefin layer faces the negative electrode,
• wherein the non-crosslinked polyolefin layer comprises a combination of polyethylene and polypropylene:
• —Si—O—Si— [Chemical Formula 1].