Copolymer for polymer electrolyte, and gel polymer electrolyte and lithium secondary battery which include the same

1 . A composition for a polymer electrolyte, comprising a copolymer, a non-aqueous electrolyte solution, and a polymerization initiator,

wherein an amount of the copolymer is 25 wt % or more based on a total weight of the composition when a weight-average molecular weight of the copolymer is 12,000 g/mole,

the amount of the copolymer is 0.01 wt % to 25 wt % based on the total weight of the composition when the weight-average molecular weight of the copolymer is less than 15,000 g/mole, and

the amount of the copolymer is 0.01 wt % to 10 wt % based on the total weight of the composition when the weight-average molecular weight of the copolymer is greater than 100,000 g/mole and equal to or less than 200,000 g/mol, and

the copolymer is represented by Formula 2:

wherein, in Formula 2,

R a1 to R f1 are each independently hydrogen, a fluorine element, or an alkyl group having 1 to 10 carbon atoms,

R 4a to R 4d are each independently hydrogen or a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms,

R 5 is a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms,

R 6a to R 6d are each independently an alkyl group having 1 to 15 carbon atoms which is substituted or unsubstituted with at least one halogen element; an alkenyl group having 2 to 15 carbon atoms which is substituted or unsubstituted with at least one halogen element; a cyclic alkyl group having 3 to 10 carbon atoms; a heterocyclic group having 3 to 10 carbon atoms; a cyclic ether group having 3 to 10 carbon atoms; a heterocyclic ether group having 3 to 10 carbon atoms; —(CH 2 ) d —(CR 18 R 19 ) e —OH, wherein R 18 and R 19 are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, and d and e are each independently an integer of 0 to 10, but are not 0 at a same time; —(R 7 ) g —O—(R 8 ) h —CH 3 , wherein R 7 and R 8 are each independently a substituted or unsubstituted alkylene group having 1 to 15 carbon atoms, and g and h each are an integer of 1 to 10; an aryl group having 6 to 12 carbon atoms; —(CH 2 ) f —CN, wherein f is an integer of 0 to 10;—(CH 2 ) i —O—CH 2 ═CH 2 , wherein i is an integer of 0 to 10;—(CH 2 ) j —Si(R 10 ) k (OCH 2 CH 3 ) 3-k , wherein R 10 is hydrogen (H), j is an integer of 1 to 10, and k is an integer of 1 to 3;—(CH 2 ) w —NCO, wherein w is an integer of 1 to 10;—CH 2 CH 2 —N(CH 3 ) 2 ; —(CH 2 ) x —A, wherein A is —OC(═O)(CH 2 ) y COOH (y is an integer of 1 to 10) or A is —C(═O)(CH 2 ) z COOH (z is an integer of 1 to 10);

m is an integer of 0 to 10,

o1 is an integer of 0 to 400,

p1 is an integer of 0 to 400,

q1′ is an integer of 1 to 300,

g2′ is an integer of 0 to 300,

with the proviso that o1 and q2′ are not 0 at a same time,

n is an integer of 1 to 2,000,

n1 is an integer of 0 to 2,000,

n2 is an integer of 0 to 2,000, and

n3 is an integer of 0 to 2,000.

2 . The composition of claim 1 , further comprising a multifunctional crosslinking agent.

3 . The composition of claim 2 , wherein the multifunctional crosslinking agent comprises at least one selected from the group consisting of an isocyanate crosslinking agent, an epoxy crosslinking agent, an aziridine crosslinking agent, an alcohol crosslinking agent, an amine-based crosslinking agent, and a vinyl-based crosslinking agent.

4 . The composition of claim 1 , further comprising at least one additive selected from the group consisting of vinylene carbonate, LiBF 4 , vinylethylene carbonate, 1,3-propane sultone, 1,3-propene sultone, succinonitrile, adiponitrile, fluoroethylene carbonate, ethylene sulfate, LiPO 2 F 2 , methyl trimethylene sulfate, lithium difluorooxalatoborate (LiODFB), lithium bis-(oxalato)borate (LiBOB), tetraphenylborate, 3-trimethoxysilanyl-propyl-N-aniline, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl)phosphite.

5 . A gel polymer electrolyte prepared by thermal polymerization of the composition of claim 1 .

6 . A lithium secondary battery comprising the gel polymer electrolyte of claim 5 .

7 . The composition of claim 1 , wherein the polymerization initiator includes a polymerization initiator selected from the group consisting of 2-hydroxy-2-methylpropiophenone (HMPP), 1-hydroxy-cyclohexylphenyl-ketone, benzophenone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, oxy-phenylacetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester, oxy-phenyl-acetic 2-[2-hydroxyethoxy]-ethyl ester, alpha-dimethoxy-alpha-phenylacetophenone, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide, bis(2,4,6-trimethylbenzoyl) -phenylphosphine oxide, bis(eta 5-2,4-cyclopentadiene-1-yl), bis[2,6-difluoro-3-(1H-pyrrol-1-yl) phenyl]titanium, 4-isobutylphenyl-4′-methylphenyl iodonium, hexafluorophosphate, and methyl benzoylformate.

8 . The composition of claim 1 , wherein the polymerization initiator includes a thermal polymerization initiator selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, hydrogen peroxide, 2,2′-azobis(2-cyanobutane), 2,2′-azobis(methylbutyronitrile), 2,2′-azobis(iso-butyronitrile) (AIBN), and 2,2′-azobisdimethyl-valeronitrile (AMVN).

9 . The composition of claim 1 , wherein an amount of the polymerization initiator is 0.01 part by weight to 5 parts by weight based on 100 parts by weight of the copolymer.

10 . The composition of claim 2 , wherein an amount of the multifunctional crosslinking agent is 1 part by weight to 1,000 parts by weight based on 100 parts by weight of the copolymer.

11 . The composition of claim 1 , wherein the copolymer includes at least one selected from the group consisting of:

polychlorotrifluoroethylene-g-poly(butyl acrylate);

polychlorotrifluoroethylene-g-poly(pentenyl acrylate);

polychlorotrifluoroethylene-g-poly(butyl acrylate-r-hydroxybutyl acrylate-r-acryloyloxyethyl isocyanate);

polychlorotrifluoroethylene-g-poly(butyl acrylate-r-ethoxyethyl acrylate-r-hydroxybutyl acrylate-r-acryloyloxyethyl isocyanate);

polychlorotrifluoroethylene-g-poly(butyl acrylate-r-tetrahydrofurfuryl acrylate);

polychlorotrifluoroethylene-g-poly(butyl acrylate-r-tetrahydrofurfuryl acrylate-r-trifluoroethyl acrylate);

polychlorotrifluoroethylene-g-poly(butyl acrylate-r-tetrahydrofurfuryl acrylate-r-perfluorooctyl acrylate);

polyvinylidene fluoride-g-poly(butyl acrylate);

polyvinylidene fluoride-co-(polychlorotrifluoroethylene-g-poly(butyl acrylate))-co-polytrifluoroethylene;

polyvinylidene fluoride-co-polychlorotrifluoroethylene-g-poly(butyl acrylate); and

polychlorotrifluoroethylene-g-poly(butyl acrylate-r-hydroxybutylacrylate).

12 . The composition of claim 1 , wherein the copolymer includes polychlorotrifluoroethylene-g-poly(butyl acrylate) (PCTFE-g-P(BA)) represented by the following Formula 3a;

in Formula 3a,

q1′, q2′, and n are the numbers of repeating units,

wherein q1′ is an integer of 1 to 300,

q2′ is an integer of 0 to 300, and

n is an integer of 1 to 2,000.

13 . The composition of claim 1 , wherein the copolymer includes polyvinylidene fluoride-g-poly(butyl acrylate) (PVDF-g-P (BA)) represented by the following Formula 3b;

in Formula 3b,

o1, q1′, and n are the numbers of repeating units,

wherein o1 is an integer of 1 to 400,

q1′ is an integer of 1 to 300, and

n is an integer of 1 to 2,000.