Separator for rechargeable lithium battery and rechargeable lithium battery including the same
A separator for a rechargeable lithium battery includes a substrate and a heat-resistant porous layer on at least one side of the substrate. The heat-resistant porous layer includes a crosslinked binder. The crosslinked binder has a cross-linked structure of a crosslinkable compound including a siloxane compound. The siloxane compound includes a siloxane resin including a unit represented by the chemical formula R 1 SiO 3/2 , where R 1 is a curable reactive group, or an organic group having a curable reactive group.
1. A separator for a rechargeable lithium battery, the separator comprising:
a substrate; and
a heat-resistant porous layer on at least one side of the substrate, the heat-resistant porous layer including a crosslinked binder and an ether-based compound,
wherein:
the crosslinked binder has a cross-linked structure of a crosslinkable compound including a siloxane compound, and
the siloxane compound includes a siloxane resin including a unit represented by Chemical Formula 1:
R 1 SiO 3/2 [Chemical Formula 1]
wherein, in Chemical Formula 1, R 1 is a C6 to C20 cycloalkyl group including a fused epoxy structure, a C6 to C20 cycloalkenyl group including a fused epoxy structure, or a C3 to C20 cycloalkynyl group including a fused epoxy structure, and
the ether-based compound is represented by Chemical Formula 9:
wherein m is an integer.
2. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the siloxane resin further includes a unit represented by Chemical Formula 2, a unit represented by Chemical Formula 3, or a combination thereof:
(R 2 )(R 3 )SiO 2/2 [Chemical Formula 2]
(R 4 )(R 5 )(R 6 )SiO 1/2 [Chemical Formula 3]
wherein, in Chemical Formulae 2 and 3, R 2 , R 3 , R 4 , R 5 , and R 6 are independently a curable reactive group, an organic group having a curable reactive group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, or a substituted or unsubstituted C6 to C20 aryl group.
3. The separator for a rechargeable lithium battery as claimed in claim 2 , wherein the siloxane resin includes about 50 mol % to about 99 mol % of the unit represented by Chemical Formula 1.
4. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the siloxane resin has a weight average molecular weight of about 600 g/mol to about 40,000 g/mol.
5. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the siloxane compound further includes a siloxane resin including a unit represented by Chemical Formula 2, a siloxane resin including a unit represented by Chemical Formula 3, or a combination thereof:
(R 2 )(R 3 )SiO 2/2 [Chemical Formula 2]
(R 4 )(R 5 )(R 6 )SiO 1/2 [Chemical Formula 3]
wherein, in Chemical Formulae 2 and 3, R 2 , R 3 , R 4 , R 5 , and R 6 are independently a curable reactive group, an organic group having a curable reactive group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, or a substituted or unsubstituted C6 to C20 aryl group.
6. The separator for a rechargeable lithium battery as claimed in claim 5 , wherein the siloxane resin that includes the unit represented by Chemical Formula 1 is present in the siloxane compound in an amount of about 50 mol % to about 99 mol % based on the total amount of the siloxane compound.
7. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the siloxane compound is included in the crosslinkable compound in an amount of about 50 wt % to about 99 wt % based on the total amount of the siloxane compound and the ether-based compound.
8. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the heat-resistant porous layer further includes a filler, the filler including an inorganic particle, an organic particle, or a combination thereof.
9. The separator for a rechargeable lithium battery as claimed in claim 8 , wherein:
when the filler includes the inorganic particle, the inorganic particle includes Al 2 O 3 , SiO 2 , B 2 O 3 , Ga 2 O 3 , TiO 2 , SnO 2 , or a combination thereof, and
when the filler includes the organic particle, the organic particle includes an acryl-based compound, an imide-based compound, an amide-based compound, or a combination thereof.
10. The separator for a rechargeable lithium battery as claimed in claim 8 , wherein the filler is included in the heat resistant porous layer in an amount of about 50 wt % to about 95 wt % based on the total amount of the crosslinked binder and the filler.
11. The separator for a rechargeable lithium battery as claimed in claim 8 , wherein the heat-resistant porous layer further includes a non-crosslinked binder.
12. The separator for a rechargeable lithium battery as claimed in claim 11 , wherein the non-crosslinked binder includes a vinylidene fluoride-based polymer, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, a polyethylene-vinylacetate copolymer, polyethyleneoxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethylpolyvinyl alcohol, cyanoethyl cellulose, cyanoethylsucrose, pullulan, carboxymethyl cellulose, an acrylonitrile-styrene-butadiene copolymer, or a combination thereof.
13. The separator for a rechargeable lithium battery as claimed in claim 11 , wherein the filler is included in the heat-resistant porous layer in an amount of about 50 wt % to about 99 wt % based on the total amount of the crosslinked binder, the filler, and the non-crosslinked binder.
14. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein a shrinkage ratio in a machine direction (MD) of the separator and a shrinkage ratio in a transverse direction (TD) with respect to the machine direction of the separator are each less than or equal to about 5% according to Equation 1:
Shrinkage ratio (%)=[( L 0− L 1)/ L 0]×100 [Equation 1]
wherein, in Equation 1, L0 indicates an initial length of a separator and L1 indicates a length of a separator after being allowed to stand at 200° C. and for 10 minutes.
15. A rechargeable lithium battery comprising the separator as claimed in claim 1 .
16. The rechargeable lithium battery as claimed in claim 15 , wherein the rechargeable lithium battery is operable at a voltage of about 4.35V to about 4.55V.
17. The separator for a rechargeable lithium battery as claimed in claim 1 ,
wherein the ether-based compound of Chemical Formula 9 has a weight average molecular weight of 500 g/mol.