Method for preparing composite separator including controlling amount of non-solvent supplied during hot-air drying, composite separator including porous substrate with fluorine-based resin porous layer with more small-diameter pores than large-diameter pores, and lithium battery comprising composite separator

Abstract

A method of preparing a composite separator for a lithium battery includes: coating a binder composition on one side or both sides of a porous substrate; hot-air drying the porous substrate coated with the binder composition; and supplying a non-solvent during the hot-air drying, such that a porous layer is on one side or both sides of the porous substrate, wherein the binder composition includes a good-solvent, a binder, and inorganic particles, an amount of the non-solvent supplied during the hot-air drying is from 12 g/mto 17 g/m, and a ratio (e) of the hot-air supply speed to the moving speed of the porous substrate per unit transit time in the hot-air dryer is from 2.2 to 5.0.