Separator for rechargeable battery, method of preparing the same and rechargeable lithium battery including the same

A method of preparing a separator, the method comprising:

• preparing a composition for forming a coating layer by dispersing a fluorine-containing binder, a filler, and an additive in a solvent;
• coating the composition for forming the coating layer on one or both surfaces of a porous substrate to form at least one coating layer;
• and
• drying it under a humidified atmosphere of about 40° C. to about 80° C. and an absolute aqueous vapor amount of about 10 g/m3 to about 25 g/m3, wherein:
• the additive is a hydrocarbon polymer compound that includes a head group including a carboxyl group and a tail group including a substituted or unsubstituted aliphatic hydrocarbon polymer structure,
• the fluorine-containing binder is included in an amount of about 20 wt % to about 30 wt %,
• the additive is included in an amount of greater than 0.35 wt % to less than 1.25 wt %, the wt % being based on a total weight of the at least one coating layer,
• the fluorine-containing binder has a crystallinity degree of 51% to 58%,
• the fluorine-containing binder has a concentration gradient in which a concentration thereof in the at least one coating layer increases toward an outer surface of the separator in a thickness direction of the separator, and
• a weight average molecular weight of the hydrocarbon polymer compound is about 5,000 g/mol to about 15,000 g/mol.

A separator for a rechargeable battery, the separator comprising:

• a porous substrate;
• and
• at least one coating layer on one surface of the porous substrate, wherein:
• the at least one coating layer includes a fluorine-containing binder having a crystallinity degree of 51% to 58%, a filler, and an additive,
• the fluorine-containing binder has a concentration gradient in which a concentration thereof in the at least one coating layer increases toward an outer surface of the separator in a thickness direction of the separator,
• the additive is a hydrocarbon polymer compound that includes a head group including a carboxyl group and a tail group including a substituted or unsubstituted aliphatic hydrocarbon polymer structure,
• the fluorine-containing binder is included in an amount of about 20 wt % to about 30 wt %,
• the additive is included in an amount of greater than 0.35 wt % to less than 1.25 wt %, the wt % being based on a total weight of the at least one coating layer, and
• a weight average molecular weight of the hydrocarbon polymer compound is about 5,000 g/mol to about 15,000 g/mol.