Separator for rechargeable lithium battery and rechargeable lithium battery including the same
A separator for a rechargeable lithium battery and a rechargeable lithium battery including the same, the separator including 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 a non-crosslinked binder, wherein the crosslinked binder has a cross-linked structure of at least one crosslinkable compound, the at least one crosslinkable compound including a multi-functional urethane-based compound, and the crosslinked binder and the non-crosslinked binder are included in a weight ratio of about 3:7 to about 8:2.
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 a non-crosslinked binder,
wherein:
the crosslinked binder has a cross-linked structure of at least one crosslinkable compound, the at least one crosslinkable compound including a multi-functional urethane-based compound,
the crosslinked binder and the non-crosslinked binder are included in different amounts, and in a weight ratio of about 3:7 to 4:6 or 6:4 to about 8:2, and
the at least on crosslinkable compound includes:
at least one multi-functional urethane-based compound having at least six curable functional groups, or
a mixture of multi-functional urethane-based compound having at least two curable functional groups and at least one multi-functional compound having as many curable functional group as will make a total of at least six curable functional groups among the multi-functional urethane-based compound together with the multi-functional compound.
2. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the crosslinked binder and the non-crosslinked binder are included in a weight ratio of 4:6 or 6:4.
3. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the at least one crosslinkable compound includes at least six curable functional groups.
4. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the at least one crosslinkable compound includes 6 to 30 curable functional groups.
5. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the multi-functional urethane-based compound includes a urethane group and at least two curable functional groups.
6. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the multi-functional urethane-based compound has a molecular weight or a weight average molecular weight of about 500 g/mol to about 80,000 g/mol.
7. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the at least one crosslinkable compound further includes a multi-functional compound including at least three curable functional groups.
8. The separator for a rechargeable lithium battery as claimed in claim 3 , wherein the curable functional group includes a (meth)acrylate group, a vinyl group, a hydroxy group, an ester group, a cyanate group, a carboxyl group, a thiol group, a C1 to C10 alkoxy group, a heterocyclic group, an amino group, or a combination thereof.
9. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the at least one crosslinkable compound includes:
at least one multi-functional urethane acrylate having at least six (meth)acrylate groups, or
a mixture of a multi-functional urethane acrylate having at least two (meth)acrylate groups and at least one multi-functional compound having as many (meth)acrylate groups as will make a total of at least six (meth)acrylate groups among the multi-functional urethane-based compound together with the multi-functional compound.
10. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the non-crosslinked binder includes a swellable polymer.
11. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the non-crosslinked binder includes a vinylidenefluoride-based polymer, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-vinylacetate copolymer, polyethyleneoxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethyl cellulose, cyanoethylsucrose, pullulan, carboxylmethyl cellulose, an acrylonitrile-styrene-butadiene copolymer, or a combination thereof.
12. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the non-crosslinked binder includes a vinylidenefluoride-based polymer, the vinylidenefluoride-based polymer including a polyvinylidene fluoride (PVdF) homopolymer, a polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer, or a combination thereof.
13. The separator for a rechargeable lithium battery as claimed in claim 12 , wherein the vinylidenefluoride-based polymer has a weight average molecular weight of about 300,000 g/mol to about 1,500,000 g/mol.
14. 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.
15. The separator for a rechargeable lithium battery as claimed in claim 14 , wherein:
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
the organic particle includes an acryl-based compound, an imide-based compound, an amide-based compound, or a combination thereof.
16. The separator for a rechargeable lithium battery as claimed in claim 14 , wherein the filler is included in an amount of about 50 wt % to about 99 wt %, based on a total weight of the crosslinked binder, the non-crosslinked binder, and the filler.
17. The separator for a rechargeable lithium battery as claimed in claim 14 , wherein:
the at least one crosslinkable compound includes:
at least one multi-functional urethane acrylate having at least six (meth)acrylate groups, or
a mixture of a multi-functional urethane acrylate having at least two (meth)acrylate groups and at least one multi-functional compound having as many (meth)acrylate groups as will make a total of at least six (meth)acrylate groups among the multi-functional urethane-based compound together with the multi-functional compound,
the non-crosslinked binder includes a vinylidenefluoride-based polymer, the vinylidenefluoride-based polymer including a polyvinylidene fluoride (PVdF) homopolymer, a polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer, or a combination thereof, and
the filler includes the inorganic particle.
18. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein each of a shrinkage ratio in a machine direction (MD) of the separator and a shrinkage ratio in a transverse direction (TD) of the separator is less than or equal to about 5%, when calculated 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 the separator and L1 indicates a length of the separator after being allowed to stand at 200° C. for 10 minutes.
19. A rechargeable lithium battery comprising the separator as claimed in claim 1 .
20. The separator for a rechargeable lithium battery as claimed in claim 1 , wherein the multi-functional urethane-based compound includes:
a multi-functional urethane acrylate having nine acrylate groups and a weight average molecular weight of 3,500 g/mol,
a multi-functional urethane acrylate having fifteen acrylate groups and a weight average molecular weight of 20,000 g/mol, or
a multi-functional urethane acrylate having two acrylate groups and a weight average molecular weight of 16,000 g/mol.