Method of preparing a separator for a battery with a gel polymer layer

The present invention discloses a separator for a battery, which comprises a gel polymer layer formed on a substrate, the gel polymer layer including a plurality of three-dimensional open pores interconnected with each other wherein the gel polymer layer has a solubility parameter of 15 to 45 MPa. The invention is also related to a method of preparing said separator as well as a lithium secondary battery.