Separator for rechargeable battery and rechargeable lithium battery including the same

A separator for a rechargeable battery, the separator comprising:

• a porous substrate and a heat resistance layer on at least one surface of the porous substrate, wherein:
• the heat resistance layer includes an acryl-based copolymer, an alkali metal, and a filler, repeating units of the acryl-based copolymer consisting of (i) a unit derived from (meth)acrylate or (meth)acrylic acid, (ii) a cyano group-containing unit, and (iii) a sulfonate group-containing unit, wherein:
• the unit derived from (meth)acrylate or (meth)acrylic acid is represented by Chemical Formula 1, Chemical Formula 2, Chemical Formula 3, or a combination thereof:
• wherein, in Chemical Formula 1, Chemical Formula 2, R1, R2, and R3 are independently hydrogen or a methyl group, and in Chemical Formula 2, M is an alkali metal;
• and
• the sulfonate group-containing unit is represented by Chemical Formula 5, Chemical Formula 6, Chemical Formula 7, or a combination thereof:
• wherein, in Chemical Formula 5, Chemical Formula 6, and Chemical Formula 7, R5, R6, and R7 are independently hydrogen or a C1 to C3 alkyl group, L3, L5, and L7 are independently —C(═O)—, —C(═O)O—, —OC(═O)—, —O—, or —C(═O)NH—, L4, L6, and L8 are independently substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, and a, b, c, d, e, and f are independently an integer ranging from 0 to 2, and in Chemical Formula 6, M′ is an alkali metal,
• the acryl-based copolymer has a glass transition temperature of 232° C. to about 280° C., and
• the sulfonate group-containing unit is included in an amount of more than or equal to about 0.1 mol % and less than about 10 mol %.