Gel polymer electrolyte and electrochemical device comprising the same

1. A composition for a gel polymer electrolyte, the composition comprising:

(i) a cyclic compound as a first crosslinking agent, the cyclic compound containing a cyclic group at the center thereof and having at least three double bonds at the end thereof;

(ii) a linear or branched compound as a second crosslinking agent, the linear or branched compound containing an oxyalkylene group at the center thereof and having at least two (meth)acryl groups at the end thereof;

(iii) an electrolyte solvent;

(iv) an electrolyte salt; and

(v) a polymerization initiator,

wherein (i) the cyclic compound is a compound represented by Formula 1 or Formula 2 below or a mixture thereof:

wherein R 1 is H or a methyl group; R 2 is a C1-C12 alkylene group; n is 0 or 1; and W is a vinyl group or (meth)acrylate group,

wherein R 3 is H or a methyl group; R 4 is a C1-C12 alkylene group; n is 0 or 1; and W is a vinyl group or (meth)acrylate group;

(ii) the linear or branched compound is a compound represented by Formula 3 below:

wherein A is a C1-C12 alkylene group or C1-C12 haloalkylene group; a is an integer of 0 to 30; B is H or a methyl group; b is an integer of 2 to 6; X represents any one of

wherein each of E 1 , E 2 , E 3 and E 4 independently represents H, a C1-C12 alkyl group, C1-C12 haloalkyl group or C1-C12 hydroxyalkyl group; and m is an integer of 0 to 30, and

(v) the polymerization initiator is selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, cumyl hydroperoxide, hydrogen peroxide, 2,2-zaobis(2-cyanobutane), 2,2-azobis(methylbutyronitrile), AIBN (azobis(iso-butyronitrile)) and AMVN (zaobisdimethyl-valeronitrile).

2. The composition for a gel polymer electrolyte as claimed in claim 1 , wherein the cyclic compound as the first crosslinking agent is at least one compound selected from the group consisting of 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-cyclotetrasiloxane, 2,4,6,8-tetramethyl-2,4,6,8-tetraacrylate-cyclotetrasiloxane, 1,3,5-trimethyl-1,3,5-trivinyl-cyclohexane and 1,3,5-trimethyl-1,3,5-triacrylate-cyclohexane.

3. The composition for a gel polymer electrolyte as claimed in claim 1 , wherein the linear or branched compound as the second crosslinking agent is at least one compound selected from the group consisting of tetraethylene glycol diacrylate, polyethylene glycol diacrylate (molecular weight 50 to 20,000), 1,4-butanediol diacrylate, 1,6-hexandiol diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate.

4. The composition for a gel polymer electrolyte as claimed in claim 1 , wherein the cyclic compound as the first crosslinking agent is used in an amount of 0.01 to 0.5 wt % based on the weight of the composition for a gel polymer electrolyte.

5. The composition for a gel polymer electrolyte as claimed in claim 1 , wherein the linear or branched compound as the second crosslinking agent is used in an amount of 1.5 to 10 wt % based on the weight of the composition for a gel polymer electrolyte.

6. The composition for a gel polymer electrolyte as claimed in claim 1 , wherein the electrolyte solvent is at least one solvent selected from the group consisting of cyclic carbonates, linear carbonates, lactones, ethers, esters, sulfoxides, acetonitriles, lactams, ketones and halogen derivatives thereof.

7. The composition for a gel polymer electrolyte as claimed in claim 1 , wherein the electrolyte salt is formed by a combination of:

(i) a cation selected from the group consisting of Li + , Na + and K + ; with

(ii) an anion selected from the group consisting of PF 6 − , BF 4 − , Cl − , Br − , I − , ClO 4 − , AsF 6 − , CH 3 CO 2 − , CF 3 SO 3 − , N(CF 3 SO 2 ) 2 − and C(CF 2 SO 2 ) 3 − .

8. A gel polymer electrolyte formed by polymerizing a composition for a gel polymer electrolyte, the composition comprising:

(i) a cyclic compound as a first crosslinking agent, the cyclic compound containing a cyclic group at the center thereof and having at least three double bonds at the end thereof;

(ii) a linear or branched compound as a second crosslinking agent, the linear or branched compound containing an oxyalkylene group at the center thereof and having at least two (meth)acryl groups at the end thereof;

(iii) an electrolyte solvent;

(iv) an electrolyte salt; and

(v) a polymerization initiator,

wherein (i) the cyclic compound is a compound represented by Formula 1 or Formula 2 below or a mixture thereof:

wherein R 1 is H or a methyl group; R 2 is a C1-C12 alkylene group; n is 0 or 1; and W is a vinyl group or (meth)acrylate group,

wherein R 3 is H or a methyl group; R 4 is a C1-C12 alkylene group; n is 0 or 1; and W is a vinyl group or (meth)acrylate group,

ii) the linear or branched compound is a compound represented by Formula 3 below:

wherein A is a C1-C12 alkylene group or C1-C12 haloalkylene group; a is an integer of 0 to 30; B is H or a methyl group; b is an integer of 2 to 6; X represents any one of

wherein each of E 1 , E 2 , E 3 and E 4 independently represents H, a C1-C12 alkyl group, C1-C12 haloalkyl group or C1-C12 hydroxyalkyl group; and m is an integer of 0 to 30, and

(v) the polymerization initiator is selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, cumyl hydroperoxide, hydrogen peroxide, 2,2-zaobis(2-cyanobutane), 2,2-azobis(methylbutyronitrile), AIBN (azobis(iso-butyronitrile)) and AMVN (zaobisdimethyl-valeronitrile).

9. The gel polymer electrolyte as claimed in claim 8 , which is formed via in-situ polymerization inside an electrochemical device.

10. An electrochemical device comprising a cathode, an anode and the gel polymer electrolyte as defined in claim 8 .

11. The electrochemical device as claimed in claim 10 , which is a lithium secondary battery.

12. The gel polymer electrolyte as claimed in claim 8 , wherein the cyclic compound as the first crosslinking agent is at least one compound selected from the group consisting of 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-cyclotetrasiloxane, 2,4, 6,8-tetramethyl-2,4,6,8-tetraacrylate-cyclotetrasiloxane, 1,3,5-trimethyl-1,3,5-trivinyl-cyclohexane and 1,3,5-trimethyl-1,3,5-triacrylate-cyclohexane.

13. The gel polymer electrolyte as claimed in claim 8 , wherein the linear or branched compound as the second crosslinking agent is at least one compound selected from the group consisting of tetraethylene glycol diacrylate, polyethylene glycol diacrylate (molecular weight 50 to 20,000), 1,4-butanediol diacrylate, 1,6-hexandiol diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate.

14. The gel polymer electrolyte as claimed in claim 8 , wherein the cyclic compound as the first crosslinking agent is present in an amount of 0.01 to 0.5 wt % based on the weight of the composition for a gel polymer electrolyte.

15. The gel polymer electrolyte as claimed in claim 8 , wherein the linear or branched compound as the second crosslinking agent is present in an amount of 1.5 to 10 wt % based on the weight of the composition for a gel polymer electrolyte.