Gel electrolyte composition and secondary battery containing the same

Abstract

The present invention relates to a gel electrolyte composition, comprising: a fluorine-containing copolymer having repeating units represented by Chemical Formula 1 and Chemical Formula 2; a lithium salt; and an organic solvent; and a secondary battery comprising the gel electrolyte composition.

Description

[Technical Field]

[0001] The present invention relates to a flame-retardant gel electrolyte composition and a secondary battery containing the same. [Background technology]

[0002] A secondary battery is a battery that continuously charges and outputs electrical energy, and has traditionally been used as a driving power source or backup power source for mobile phones, notebooks, small portable devices, and the like.

[0003] Currently, the issue of global warming caused by greenhouse gases is attracting attention worldwide, and in an effort to solve this problem, the use of secondary batteries is expected to increase in part or in whole in various fields that use fossil fuels, such as automobiles, ships, aviation, and heating.

[0004] For secondary batteries to be used as alternative energy sources in various fields, they must have high-output characteristics such as high capacity and fast charging, as well as excellent stability and durability. However, conventional secondary batteries have faced a technical conflict in that it is difficult to simultaneously improve both high-output characteristics and stability.

[0005] In particular, explosion and combustion of conventional secondary batteries can occur for various reasons, such as a short circuit occurring between the positive and negative electrodes, which causes a thermal explosion due to high energy released in a short time, or an increase in voltage due to an increase in side reaction between the positive electrode active material and the gel electrolyte when the secondary battery is overcharged.

[0006] On the other hand, the problem of deterioration of secondary batteries is also related to the lifespan of the secondary batteries. Specifically, as the temperature of the secondary battery increases, side reactions increase, which can result in a decrease in the charge / discharge capacity of the secondary battery.

[0007] To solve these stability issues in secondary batteries, active research is being conducted on gel polymer electrolytes, which are manufactured by adding a plasticizer to a polymer matrix instead of liquid electrolytes, which have low thermal stability and the possibility of electrolyte leakage. Gel polymer electrolytes are intermediate electrolytes that can simultaneously improve the low stability of liquid electrolytes and the low ionic conductivity of solid polymer electrolytes by utilizing the principle that lithium ions move quickly through pores formed along polymer fibers entangled in a gel-like state.

[0008] However, development of gel polymer electrolytes that have excellent performance while significantly reducing the risk of explosion and combustion remains limited, and the problem of short circuits between the positive and negative electrodes, which is the biggest factor affecting the stability of secondary batteries, remains unresolved. Furthermore, gel polymer electrolytes generally have poor adhesion to the negative electrode surface, which reduces the workability of the gel polymer electrolytes.

[0009] Therefore, there is a need to develop a gel electrolyte composition that has flame retardancy, excellent workability, and improved adhesion to the surface of the negative electrode so that the stability of the secondary battery can be improved while still exhibiting high output performance. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made to solve the above-mentioned problems, and provides a flame-retardant gel electrolyte composition that includes a fluorine-containing copolymer and can be gelled on the surface of a negative electrode, thereby solving the problem of performance degradation due to deterioration of a secondary battery, making it possible to more easily prepare a gel electrolyte, and providing an energy storage device with excellent stability and performance by manufacturing a secondary battery including the gel electrolyte composition. [Means for solving the problem]

[0011] According to one embodiment of the present invention, there is provided a gel electrolyte composition comprising: a fluorine-containing copolymer having repeating units represented by the following Chemical Formula 1 and Chemical Formula 2; a lithium salt; and an organic solvent.

[0012] [ka] In the above Chemical Formula 1, A1 is *-C(=O)-*, *-C(=O)O-* or *-S(=O) 2- * and R1, R2 and R3 are each independently hydrogen or C1-C6 linear or branched alkyl; X is *-F, [ka] and D1, D2, D3 and D4 are each independently one selected from hydrogen, fluorine, C1-C6 linear or branched alkyl and fluorinated C1-C6 linear or branched alkyl; D5 is fluorine, fluorinated C1-C 12 linear or branched alkyl and fluorinated C1-C 12 is one selected from the group consisting of straight or branched chain alkoxy D6 is hydrogen, fluorine, fluorinated C1-C 12 linear or branched alkyl and fluorinated C1-C 12 is one selected from the group consisting of straight or branched chain alkoxy n is an integer from 0 to 20, y is an integer from 1 to 5;

[0013] [ka] In the above Chemical Formula 2, R4, R5 and R6 are each independently hydrogen or C1-C6 linear or branched alkyl; A2 is a C1-C6 straight or branched chain alkylene.

[0014] According to another embodiment of the present invention, there is provided a secondary battery including a positive electrode, a negative electrode, and the gel electrolyte composition, wherein the gel electrolyte composition forms a layer between the positive electrode and the negative electrode. [Effects of the Invention]

[0015] The gel electrolyte composition of the present invention has excellent flame retardancy due to the inclusion of a fluorine-containing copolymer, thereby preventing fire and explosion problems due to deterioration of a secondary battery containing the gel electrolyte composition and minimizing performance degradation of the secondary battery even after repeated charge and discharge. In addition, when the gel electrolyte composition according to the present invention is used, an electrolyte SEI layer is formed on the negative electrode, which can prevent deterioration of the negative electrode and suppress side reactions with the electrolyte, thereby achieving better life characteristics than conventional secondary batteries. [Brief explanation of the drawings]

[0016] [Figure 1a] 1 is a graph showing the flame retardant properties of the gel electrolyte composition according to Example 1. [Figure 1b] 10 is a graph showing the flame retardant properties of the gel electrolyte composition according to Example 4. [Figure 1c] 10 is a graph showing the flame retardant properties of the gel electrolyte composition according to Example 5. [Figure 2] 1 is a graph showing the specific capacity and coulombic efficiency of the secondary batteries of Examples 11 to 14 and Comparative Example 2 while charging and discharging for 600 cycles. [Figure 3a] 10 is a graph showing a voltage profile according to the progress of cycles of the secondary battery according to Example 11. [Figure 3b] 10 is a graph showing a voltage profile according to the progress of cycles of the secondary battery according to Example 12. [Figure 3c] 12 is a graph showing a voltage profile according to the progress of cycles of the secondary battery according to Example 13. [Figure 3d]10 is a graph showing a voltage profile according to the progress of cycles of the secondary battery according to Example 14. [Figure 3e] 10 is a graph showing a voltage profile according to the progress of cycles of the secondary battery according to Example 15. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, the gel electrolyte composition of the present invention and the secondary battery including the same will be described in detail so that those skilled in the art can easily carry out the present invention.

[0018] According to one embodiment of the present invention, there is provided a gel electrolyte composition comprising: a fluorine-containing copolymer having repeating units represented by the following Chemical Formula 1 and Chemical Formula 2; a lithium salt; and an organic solvent. [ka] In the above Chemical Formula 1, A1 is *-C(=O)-*, *-C(=O)O-*, or *-S(=O) 2- *, wherein R1, R2 and R3 are each independently hydrogen or a C1-C6 straight or branched alkyl, and X is *-F, [ka] D1, D2, D3 and D4 are each independently one selected from hydrogen, fluorine, C1-C6 linear or branched alkyl and fluorinated C1-C6 linear or branched alkyl; D5 is fluorine, fluorinated C1-C6 linear or branched alkyl; 12 linear or branched alkyl and fluorinated C1-C 12 and D6 is one selected from hydrogen, fluorine, fluorinated C1-C 12 linear or branched alkyl and fluorinated C1-C 12 wherein n is an integer from 0 to 20 and y is an integer from 1 to 5. [ka] In the above formula 2, R4, R5 and R6 are each independently hydrogen or a C1-C6 linear or branched alkyl, and A2 is a C1-C6 linear or branched alkylene.

[0019] As used herein, the term "fluorinated" means that at least one hydrogen is replaced with a fluorine.

[0020] According to one embodiment of the present invention, in Formula 1, R1, R2, and R3 are each independently hydrogen or a C1-C3 linear or branched alkyl; and X is [ka] D1, D2, D3 and D4 are each independently one selected from hydrogen, fluorine, C1-C3 linear or branched alkyl and fluorinated C1-C3 linear or branched alkyl, and D5 is fluorine, fluorinated C1-C6 linear or branched alkyl and fluorinated C1-C6 linear or branched alkyl. 12 and D6 is one selected from hydrogen, fluorine, fluorinated C1-C6 straight or branched alkyl, and fluorinated C1-C6 straight or branched alkoxy.

[0021] As a specific example, in the above Chemical Formula 1, X is [ka] and D1, D2, D3 and D4 may be, independently of one another, hydrogen, fluorine, methyl, *-CHF2, *-CH2F or *-CF3.

[0022] According to one embodiment of the present invention, in Formula 2, R4, R5, and R6 may each independently be hydrogen or a C1-C3 linear or branched alkyl, and A2 may be a C1-C3 linear alkylene.

[0023] The gel electrolyte composition according to the present invention includes a fluorine-containing copolymer, which suppresses the reactivity of hole electrons formed in the polymer under conditions where combustion may occur, thereby interrupting the chain reaction of the electrolyte composition and preventing combustion.

[0024] The fluorine-containing copolymer may contain the repeating units represented by Chemical Formula 1 and Chemical Formula 2 in a molar ratio of 1:1 to 1:10, preferably 1:2 to 1:8, and more preferably 1:3 to 1:7. When the molar ratio of the repeating units represented by Chemical Formula 1 and Chemical Formula 2 contained in the fluorine-containing copolymer satisfies the above range, the prepared gel electrolyte may have excellent flame retardancy, and thus the safety and life characteristics of a secondary battery including the gel electrolyte may be improved. Furthermore, the cyano group contained in the fluorine-containing copolymer readily crosslinks inside the secondary battery, thereby improving workability.

[0025] Meanwhile, the fluorine-containing copolymer may further include a repeating unit represented by the following Chemical Formula 3:

[0026] [ka] In the above formula 3, R7, R8 and R9 are each independently hydrogen or a C1-C6 linear or branched alkyl.

[0027] The fluorine-containing copolymer may contain 0 to 30 mol %, preferably 0.5 to 20 mol %, and more preferably 1 to 15 mol % of the repeating unit represented by Chemical Formula 3 relative to the total repeating units contained in the copolymer. When the fluorine-containing copolymer contains the repeating unit represented by Chemical Formula 3 in an amount within the above range, the fluorine-containing copolymer has excellent solubility in organic solvents, and the hydroxyl group contained in the fluorine-containing copolymer can further activate the reaction of a lithium salt with water to form a strong Lewis acid, thereby increasing the crosslinking rate of the fluorine-containing copolymer.

[0028] Specifically, crosslinking of the gel electrolyte composition may occur when a cyano group of a fluorine-containing copolymer bonds with a cyano group of a different fluorine-containing copolymer. Such crosslinking occurs when a lithium salt decomposed at a high temperature reacts with a hydroxy group to form a strong Lewis acid, and the hydroxy group can act as an initiator for crosslinking of the cyano group.

[0029] That is, when the repeating unit of Chemical Formula 3 containing a large amount of hydroxyl groups is contained in the fluorine-containing copolymer within the above range, a large amount of strong Lewis acid derived from the lithium salt can be generated, thereby increasing the crosslinking rate.

[0030] The fluorine-containing copolymer may have a number average molecular weight of 10,000 to 1,000,000 g / mol, preferably 10,000 to 300,000 g / mol, and more preferably 10,000 to 200,000 g / mol. When the number average molecular weight of the fluorine-containing copolymer satisfies this range, a gel electrolyte having excellent ionic conductivity, mechanical strength, heat resistance, vibration resistance, and chemical resistance can be realized.

[0031] The fluorine-containing copolymer may be contained in an amount of 0.1 to 10 parts by weight, preferably 0.1 to 5 parts by weight, and more preferably 1 to 5 parts by weight, based on 100 parts by weight of the gel electrolyte composition. When the gel electrolyte composition contains the fluorine-containing copolymer in this range, it not only has excellent crosslinking reactivity and flame retardancy, but also contains a large amount of liquid electrolyte containing a lithium salt, resulting in excellent lithium mobility and improved electrical conductivity. As a result, a secondary battery manufactured using the gel electrolyte composition can exhibit excellent output, charge, and life characteristics.

[0032] In the gel electrolyte according to the present invention, the fluorine-containing copolymer may be crosslinked in the presence of a lithium salt and an organic solvent, and in particular, the gel electrolyte can be crosslinked in a secondary battery.

[0033] The lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFOB, LiDFBP, LiTFOP, LiPO2F2, LiCl, LiBr, LiI, LiB10Cl10, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, and LiC(CF3SO2)3, preferably at least one selected from the group consisting of LiPF6, LiFSI, and LiDFOB.

[0034] When the gel electrolyte composition contains the lithium salt, the viscosity of the electrolyte can be reduced and the crosslinking property can be more excellent.

[0035] The lithium salt may be dissolved in an organic solvent to a concentration of 0.5 to 3 M, preferably 0.8 to 1.5 M, and more preferably 0.8 to 1.2 M. When the concentration of the lithium salt is within this range, the crosslinking reactivity of the fluorine-containing copolymer contained in the gel electrolyte is more excellent, and thus a secondary battery including the gel electrolyte can achieve excellent charge / discharge capacity.

[0036] The organic solvent may be any compound containing a carbonate group, but excellent secondary battery performance can be achieved by using a mixture of a cyclic carbonate compound and a linear carbonate compound.

[0037] Specifically, the organic solvent may include at least one selected from the group consisting of dimethylcarbonate (DMC), diethylcarbonate (DEC), dipropylcarbonate (DPC), methylpropylcarbonate (MPC), ethylpropylcarbonate (EPC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), propylenecarbonate (PC), and butylenecarbonate (BC), and preferably at least one selected from the group consisting of dimethylcarbonate (DMC), ethylmethylcarbonate (EMC), and ethylenecarbonate (EC).

[0038] Ethylene carbonate (EC) is a cyclic carbonate-based compound, and a gel electrolyte composition including the EC can adjust viscosity, dissociate lithium salt, and have an excellent dielectric constant, thereby improving the charge / discharge capacity of a secondary battery including the gel electrolyte composition.

[0039] Ethyl methyl carbonate (EMC) is a linear carbonate-based compound having a low freezing point and a high boiling point. A gel electrolyte composition containing EMC may have excellent low-temperature characteristics, thereby suppressing low-temperature discharge of a secondary battery and improving the cycle life of the battery.

[0040] For example, the organic solvent may be ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:1 to 1:10, preferably 1:1 to 1:5, and more preferably 1:2 to 1:3. When the ethylene carbonate and ethyl methyl carbonate contained in the organic solvent are mixed in this volume ratio range, the resulting mixture can simultaneously have excellent dielectric constant, lithium salt dissociation properties, and low-temperature properties.

[0041] The gel electrolyte composition may be crosslinked at 20 to 80° C., preferably 30 to 80° C., and more preferably 40 to 70° C. When the crosslinking temperature of the gel electrolyte composition satisfies the above range, not only can the crosslinking reaction rate be increased, but also a gel polymer electrolyte having excellent mechanical properties can be produced.

[0042] The fluorine-containing copolymer may be prepared by reacting a base copolymer containing repeating units represented by the following Chemical Formula 2 and Chemical Formula 3 with a fluorine-containing compound.

[0043] [ka] In the above formula 2, R4, R5 and R6 are each independently hydrogen or a C1-C6 linear or branched alkyl, and A2 is a C1-C6 linear or branched alkylene.

[0044] [ka] In the above formula 3, R7, R8 and R9 are each independently hydrogen or a C1-C6 linear or branched alkyl.

[0045] The fluorine-containing copolymer may be prepared by reacting a hydroxy group contained in a base copolymer with a fluorine-containing compound, and the content of the repeating unit represented by Formula 3 can be adjusted or the repeating unit may not be present, depending on the mass ratio of the base copolymer and the fluorine-containing compound.

[0046] The fluorine-containing compound may contain one or more functional groups selected from a carboxy group (-COOH, -COO[halogen]), a carbonate group (-COO-), and a sulfone group (-SOOH, -SOO[halogen]), and the fluorine-containing copolymer produced by reacting with the base copolymer may be -C(=O)-, -C(=O)O-, or -S(=O) 2- * may include one bond structure selected from

[0047] Specifically, the fluorine-containing compound is 4-(trifluoromethoxy)benzoic acid, pentafluorobenzoic acid, bis(pentafluorophenyl)carbonate, trifluoromethanesulfonylchloride, bis(trifluoromethyl)benzenesulfonylchloride, pentafluorobenzenesulfonylchloride, The compound may include at least one selected from the group consisting of bis(2,2,2-trifluoroethyl)carbonate, pentafluorobenzoylchloride, pentafluorobenzylbromide, heptafluorobutyrylchloride, bis(2,2,2-trifluoroethyl)carbonate, pentafluorobenzoylchloride, bis(pentafluorophenyl)carbonate, trifluoroethylmethacrylate, heptafluoro-1-butanol, 4-(trifluoromethoxy)benzenesulfonylchloride, and 4-(trifluoromethoxy)benzoicacid.

[0048] The fluorine-containing copolymer prepared by substitution with the fluorine-containing compound has a high fluorine content and can exhibit excellent heat resistance and flame retardancy, and therefore, a secondary battery prepared using the fluorine-containing copolymer can have excellent life characteristics and safety.

[0049] The fluorine-containing copolymer may be prepared through an esterification reaction (DCC coupling, reaction of carbonates with alcohol, reaction of sulfonyl chloride with alcohol) between the base copolymer and the fluorine-containing compound. The esterification reaction may be carried out in the presence of a coupling agent.

[0050] The coupling agent may vary depending on the type of functional group of the fluorine-containing compound. For example, dicyclohexylcarbodiimide may be preferred for an ester bond, triethylamine for a carbonate bond, and pyridine for a sorbone bond.

[0051] The coupling agent may be a carbodiimide-based, pyridine-based, or amine-based coupling agent, and specifically may be at least one selected from the group consisting of dicyclohexylcarbodiimide (DCC), ethyldimethylamino-propylcarboximide, hydroxysuccinimide, diisopropylcarbodiimide (DIC), 4-dimethylaminopyridine (DMAP), pyridine, triethylamine, and 2-chloro-1-methylpyridinium iodide, and preferably at least one selected from the group consisting of dicyclohexylcarbodiimide, 4-dimethylaminopyridine, triethylamine, and pyridine.

[0052] The method for producing the fluorine-containing copolymer may include an aprotic organic solvent, which may include at least one selected from the group consisting of acetone, acetonitrile, dichloromethane, dimethylformamide, dimethylpropylene urea, dimethyl sulfoxide, ethyl acetate, hexamethylphosphoric triamide, pyridine, sulfolane, and tetrahydrofuran, but is not necessarily limited thereto as long as the fluorine-containing copolymer can be synthesized using the aprotic organic solvent.

[0053] Examples of the method for producing the fluorine-containing copolymer may be represented by the following production schemes 1 to 7. [ka]

[0054] [ka]

[0055] [ka]

[0056] [ka]

[0057] [ka]

[0058] [ka]

[0059] [ka] The A1 is a C1-C6 alkylene.

[0060] The content of vinyl alcohol repeating units contained in the fluorine-containing copolymer may vary depending on the molar ratio of the base copolymer and the fluorine-containing compound in Preparation Schemes 1 to 7, and may not be present in some cases. Specifically, when the molar ratio of the base copolymer and the fluorine-containing compound is 1:2 to 1:5, the vinyl alcohol repeating units may not be present, and when the molar ratio is 1:1 to less than 1:2, the vinyl alcohol repeating units may be present, but may be the same or different depending on the fluorine-containing compound reacted.

[0061] According to another embodiment of the present invention, there is provided a secondary battery including a positive electrode; a negative electrode; and the gel electrolyte composition, wherein the gel electrolyte composition forms a layer between the positive electrode and the negative electrode.

[0062] The secondary battery includes a flame-retardant gel electrolyte composition having excellent heat resistance and flame retardancy between the positive electrode and the negative electrode, thereby preventing a short circuit between the positive electrode and the negative electrode, and thus exhibiting excellent stability.

[0063] In addition, during charging, the secondary battery forms a solid electrolyte interphase (SEI) layer on the surface of the negative electrode due to a reaction between lithium ions generated by dissociation of lithium salt contained in the gel electrolyte composition and other compounds contained in the gel electrolyte composition. This allows for excellent lithium mobility on the surface of the negative electrode, thereby improving the capacity retention rate of the secondary battery.

[0064] The secondary battery may satisfy the following formula 1: [Formula 1] C 600 / C 1≧ 0.8 In the formula 1, C 600 is the discharge capacity of a secondary battery that has been charged and discharged 600 times, C1 is the discharge capacity of the secondary battery after one charge and discharge.

[0065] Specifically, the formula 1 indicates the charge / discharge capacity of a secondary battery, and C in the formula 1 600 The / C1 value may be 0.85 to 0.98, which may mean that the battery has excellent life characteristics compared to conventional secondary batteries.

[0066] The positive electrode active material contained in the positive electrode may be at least one selected from the group consisting of nickel, cobalt, manganese, tin, silicon, and aluminum, and preferably an alloy of lithium, nickel, manganese, and cobalt in order to overcome the advantages and disadvantages of each metal.

[0067] The negative electrode active material contained in the negative electrode may contain at least one selected from the group consisting of graphite, silicon, germanium, tin, and antimony, and preferably graphite.

[0068] The gel electrolyte composition may be formed by gelation on the surface of the negative electrode. As a result, even when the gel electrolyte composition according to the present invention is used, a stable solid electrolyte interface (SEI) layer can be formed on the negative electrode, thereby preventing decomposition of the electrolyte and promoting smooth movement of lithium ions, thereby improving the performance and lifespan of the lithium secondary battery.

[0069] The present invention will be described in more detail below through examples. However, these examples are merely intended to aid in understanding the present invention and are not intended to limit the scope of the present invention in any way.

[0070] <Example 1> Preparation of gel electrolyte composition 1 In a 50 mL round-bottom flask, add 12 mL of N,N-Dimethylmethanamide (DMF) and Poly[Vinylachol-co-3-(vinyloxy)propanenitrile] (weight-average molecular weight: 1.1058 x 10). 5g / mol, vinyl alcohol repeating unit: 24.2 mol%) was added and stirred.

[0071] Then, 1.36 g (0.066 mol) of 4-(trifluoromethoxy)benzoic acid and 2.26 g (0.011 mol) of N,N'-dicyclohexylcarbodiimide (DCC), which are fluorine-containing compounds listed in Table 1 below, were added to the stirred mixture, and the round-bottom flask containing the mixture was immersed in a water bath containing ice water. After that, 0.0559 g (0.0004572 mol) of DMAP (4-dimethylaminopyridine) was dissolved in 3 mL of DMF, and the solution was slowly added to the round-bottom flask and stirred for 10 minutes.

[0072] After 10 minutes, the mixture was stirred and reacted at room temperature for 24 hours. After the reaction was completed, the precipitate was filtered and the remaining polymer solution was precipitated in ethyl alcohol and then dried in a vacuum oven at 60°C to produce a fluorine-containing copolymer.

[0073] 0.03 g of the prepared fluorine-containing copolymer was added to 1.47 g of an organic solvent (a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7) containing 1 M lithium salt LiPF6, and then crosslinked at a temperature of 60°C to prepare a gel electrolyte composition.

[0074] <Example 2> Preparation of gel electrolyte composition 2 A gel electrolyte composition was prepared in the same manner as in Example 1, except that 0.907 g (0.0044 mol) of 4-(trifluoromethoxy)benzoicacid, a fluorine-containing compound, was added.

[0075] <Example 3> Preparation of gel electrolyte composition 3 A gel electrolyte composition was prepared in the same manner as in Example 1, except that 2.3329 g (0.011 mol) of pentafluorobenzoicacid, a fluorine-containing compound, was added.

[0076] <Example 4> Preparation of gel electrolyte composition 4 A gel electrolyte composition was prepared in the same manner as in Example 1, except that 0.9331 g (0.0044 mol) of pentafluorobenzoicacid, a fluorine-containing compound, was added.

[0077] <Example 5> Preparation of gel electrolyte composition 5 In a 50 mL round-bottom flask, add 15 mL of DMF (N,N-Dimethylmethanamide) and Poly[Vinylachol-co-3-(vinyloxy)propanenitrile] (weight-average molecular weight: 1.1058 x 10). 5 g / mol, vinyl alcohol repeating unit: 24.2 mol%) was added and stirred.

[0078] Then, 2.2 mL (0.0165 mol) of TEA (triethylamine) was added to the stirred mixture, and 3.2514 g (0.00825 mol) of fluorine-containing compound Bis(pentafluorophenyl)carbonate was added, followed by reaction at room temperature for 72 hours.

[0079] After the reaction was completed, the precipitate was filtered and the remaining polymer solution was precipitated in ethyl alcohol and dried in a vacuum oven at 60° C. to prepare a fluorine-containing copolymer.

[0080] 0.03 g of the prepared fluorine-containing copolymer was added to 1.47 g of an organic solvent (a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7) containing 1 M lithium salt LiPF6, and then crosslinked at a temperature of 60°C to prepare a gel electrolyte composition.

[0081] <Example 6> Preparation of gel electrolyte composition 6 In a 50 mL round-bottom flask, add 15 mL of DMF (N,N-Dimethylmethanamide) and Poly[Vinylachol-co-3-(vinyloxy)propanenitrile] (weight-average molecular weight: 1.1058 x 10). 5 g / mol, 1 g (0.0055 mol) of vinyl alcohol: 24.2 mol%) was added and stirred.

[0082] Then, pyridine (2.75 ml, 0.0275 mol) was added to the stirred mixture, and 0.88 mL (1.39 g, 0.00825 mol) of trifluoromethanesulfonyl chloride, a fluorine-containing compound shown in Table 1 below, was slowly added, and the mixture was allowed to react for 46 hours.

[0083] After the reaction was completed, the precipitate was filtered and the remaining polymer solution was precipitated in ethyl alcohol and dried in a vacuum oven at 60° C. to prepare a fluorine-containing copolymer.

[0084] 0.03 g of the prepared fluorine-containing copolymer was added to 1.47 g of an organic solvent (a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7) containing 1 M lithium salt LiPF6, and then crosslinked at a temperature of 60°C to prepare a gel electrolyte composition.

[0085] <Example 7> Preparation of gel electrolyte composition 7 A gel electrolyte composition was prepared in the same manner as in Example 6, except that 2.579 g (0.00825 mol) of Bis(trifluoromethyl)benzenesulfonylchloride was added as the fluorine-containing compound and the mixture was reacted at room temperature for 72 hours.

[0086] <Example 8> Preparation of gel electrolyte composition 8 A gel electrolyte composition was prepared in the same manner as in Example 7, except that 1.2 mL (2.2 g, 0.00825 mol) of pentafluorobenzenesulfonyl chloride was added as the fluorine-containing compound.

[0087] <Example 9> Preparation of gel electrolyte composition 9 A gel electrolyte composition was prepared in the same manner as in Example 5, except that 1.329 mL (0.0165 mol) of pyridine and 0.1 g (0.00825 mol) of DAMP were used instead of TEA as a solvent, and 1.73 g (0.00825 mol) of trifluoroacetic anhydride, a fluorine-containing compound, was added.

[0088] <Example 10> Preparation of gel electrolyte composition 10 A gel electrolyte composition identical to that of Example 9 was prepared, except that 0.58 g (0.00275 mol) of trifluoroacetic anhydride was added as the fluorine-containing compound.

[0089] <Comparative Example 1> Preparation of gel electrolyte composition 11 A gel electrolyte composition was prepared in the same manner as in Example 1, except that the fluorine-containing copolymer was not included.

[0090] <Experimental Example 1> Evaluation of flame retardancy The gel electrolyte compositions according to Examples 1 to 10 and Comparative Example 1 were prepared into 10mm x 10mm x 10mm test pieces, and the process of burning them with a 1.20mm spark for 1 second was repeated four times to observe whether they burned or not. The results are shown in Table 1 below. No combustion was indicated by O, and combustion was indicated by X.

[0091] [Table 1]

[0092] Examples 1 to 10 are gel electrolyte compositions containing a fluorine-containing copolymer, and Comparative Example 1 is a gel electrolyte composition of an acrylonitrile-ethylene oxide copolymer.

[0093] In Table 1, it was confirmed that Examples 1 to 10 all had excellent flame retardancy compared to Comparative Example 1, which can be attributed to the fact that the fluorine-containing copolymers contained in the gel electrolyte compositions of Examples 1 to 10 contain fluorine substituents.

[0094] Meanwhile, the excellent flame retardancy of the gel electrolyte compositions of Examples 1 to 10 indicates that the excellent flame retardancy is achieved regardless of the bonds *-C(=O)O-*, *-OC(=O)O-* and *-S(=O)-* contained in the fluorine-containing copolymer.

[0095] Furthermore, when comparing Examples 1 and 2, Examples 3 and 4, and Examples 9 and 10, which show differences depending on the presence or absence of vinyl alcohol repeating units, it was confirmed that the gel electrolyte compositions of Examples 1 to 10 all had excellent flame retardancy, regardless of the presence or absence of vinyl alcohol repeating units.

[0096] 1a to 1c are photographs showing the evaluation results of flame retardancy of Examples 1, 4 and 5, which contain fluorine-containing copolymers having aryl groups, and show excellent flame retardancy.

[0097] <Example 11> Production of secondary battery containing gel electrolyte 1 As the positive electrode, LiNi 0.6 Co 0.2 Mn 0.2 A secondary battery was fabricated using O2 (NCM622), graphite as a negative electrode, and the gel electrolyte composition according to Example 1.

[0098] The positive electrode of NCM622 is LiNi 0.6 Co 0.2 Mn 0.2O2, PVDF, and super-P were mixed in a mass ratio of 94:3:3 and then uniformly dissolved in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The slurry was applied to aluminum foil and dried in a vacuum oven at 120°C for 24 hours to prepare a cathode. The cathode was coated with 12 mg / cm2 of PVDF and super-P. 2 After loading at a density of 14 mm, the mixture was punched out into a circle with a diameter of 14 mm and used in a coin-type cell.

[0099] The negative electrode was prepared by mixing graphite, PVDF, and carbon black (Superp) in a mass ratio of 94:3:3 and then uniformly dissolving the mixture in N-methyl-2-pyrrolidone (NMP). The slurry was applied to copper foil and dried in a vacuum oven at 120°C for 24 hours to prepare a negative electrode. The negative electrode was prepared at a concentration of 6 mg / cm. 2 After loading at a density of 16 mm, the mixture was punched out into a circle with a diameter of 16 mm and used in a coin-type cell.

[0100] Thereafter, the gel electrolyte composition according to Example 1 was placed between the positive electrode and the negative electrode to complete a coin-type secondary battery.

[0101] It was confirmed that a solid electrolyte interphase (SEI) layer was formed on the surface of the negative electrode and that LiF was contained in the SEI layer.

[0102] <Example 12> Production of secondary battery containing gel electrolyte 2 A secondary battery was manufactured in the same manner as in Example 11, except that the gel electrolyte composition of Example 3 was used instead of the gel electrolyte composition of Example 1.

[0103] <Example 13> Production of secondary battery containing gel electrolyte 3 A secondary battery was manufactured in the same manner as in Example 11, except that the gel electrolyte composition of Example 4 was used instead of the gel electrolyte composition of Example 1.

[0104] <Example 14> Production of secondary battery containing gel electrolyte 4 A secondary battery was manufactured in the same manner as in Example 11, except that the gel electrolyte composition of Example 5 was used instead of the gel electrolyte composition of Example 1.

[0105] <Example 15> Production of secondary battery containing gel electrolyte 5 A secondary battery was manufactured in the same manner as in Example 11, except that the gel electrolyte composition of Example 9 was used instead of the gel electrolyte composition of Example 1.

[0106] <Comparative Example 2> Production of secondary battery containing gel electrolyte 6 The prepared positive and negative electrodes were used to prepare a polymer battery together with a separator consisting of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP) in a conventional manner, and then a non-aqueous electrolyte solution prepared by dissolving LiPF6 electrolyte at a concentration of 1M in a solvent mixed at a volume ratio of EC (ethylene carbonate): DEC (diethyl carbonate): EMC (ethyl methyl carbonate) = 4:3:3 was injected to prepare a lithium secondary battery.

[0107] <Experimental Example 2> Secondary Battery Power Outage Test Method The coin-type secondary battery was charged and discharged once at an operating temperature of 25°C, in a voltage range of 3 to 4.2 V, and at a charge / discharge rate of 0.1 C-rate (165 mA / g), after which the gelation reaction was initiated. It was then charged and discharged 600 times at a rate of 0.5 C-rate, and the discharge capacities after one charge / discharge cycle and after 600 cycles were measured and calculated using the following formula 1. [Formula 1] Capacity retention rate (%) = (discharge capacity after 600 cycles / discharge capacity after 1 cycle) x 100

[0108] The calculation results are shown in Table 2 below. [Table 2]

[0109] The capacity retention rate in Table 2 indicates the change in discharge capacity after 600 charge / discharge cycles, and is a measured value that can be used to estimate the life characteristics of a secondary battery.

[0110] In Table 2, Examples 11 to 15 contained the gel electrolyte compositions of Examples 1, 3 to 5, and 9, respectively, and the capacity retention rate of the secondary batteries was 81% or more, specifically, 85% or more in the cases of Examples 13 to 15. This is because the secondary batteries of Examples 11 to 15 contained the gel electrolyte compositions of Examples 1, 3 to 5, and 9, and thus formed a stable SEI layer, thereby preventing deterioration of the negative electrode and suppressing side reactions with the electrolyte, ultimately resulting in a better capacity retention rate.

[0111] 3a to 3d show capacity-voltage graphs at an initial rate of 0.1 C-rate for Examples 11 to 15. From these graphs, the capacity of the secondary batteries according to Examples 11 to 15 can be compared at the initial stage of charge / discharge. The amount of the SEI layer formed at the initial stage of charge / discharge can be estimated by calculating the Coulombic efficiency, and the overvoltage formed in each battery can be determined. In the capacity range of 0 mAh / g to 10 mAh / g, the lower the voltage, the better, and Example 13 had the lowest voltage. Furthermore, Example 13 also showed the highest capacity retention rate.

[0112] Therefore, the gel electrolyte composition of the present invention can exhibit flame retardancy by containing a fluorine-containing copolymer, and can improve the stability of a secondary battery including the gel electrolyte composition, thereby preventing explosions and fires. Furthermore, the gel electrolyte composition of the present invention can form a stable SEI layer on the negative electrode, preventing deterioration of the negative electrode and suppressing side reactions with the electrolyte, thereby achieving better life characteristics than conventional secondary batteries.

Claims

1. A fluorine-containing copolymer containing repeating units represented by the following chemical formula 1 and chemical formula 2: lithium salts; and an organic solvent. 【Chemistry 1】 In the above Chemical Formula 1, A １ is *-C(=O)-*, *-C(=O)O-* or *-S(=O) ２－ * and R １ , R ２ and R ３ are each independently hydrogen or C １ -C ６ is a straight or branched chain alkyl of X is *-F, 【Chemistry 2】 and D １ , D ２ , D ３ and D ４ are each independently hydrogen, fluorine, C １ -C ６ Linear or branched alkyl and fluorinated C １ -C ６ is one selected from the linear or branched alkyl D ５ is fluorine, fluorinated C １ -C １２ Linear or branched alkyl and fluorinated C １ -C １２ is one selected from the group consisting of straight or branched chain alkoxy D ６ is hydrogen, fluorine, fluorinated C １ -C １２ Linear or branched alkyl and fluorinated C １ -C １２ is one selected from the group consisting of straight or branched chain alkoxy n is an integer from 0 to 20; y is an integer from 1 to 5; 【Transformation 3】 In the above Chemical Formula 2, R ４ , R ５ and R ６ are each independently hydrogen or C １ -C ６ is a straight or branched chain alkyl of A ２ is C １ -C ６ is a straight or branched chain alkylene.

2. 2. The gel electrolyte composition according to claim 1, wherein the fluorine-containing copolymer further comprises a repeating unit represented by the following chemical formula 3: 【Chemistry 4】 In the above Chemical Formula 3, R ７ , R ８ and R ９ are each independently hydrogen or C １ -C ６ is a straight or branched chain alkyl.

3. R １ , R ２ and R ３ are each independently hydrogen or C １ -C ３ is a straight or branched chain alkyl of X is 【Transformation 5】 in, D １ , D ２ , D ３ and D ４ are each independently hydrogen, fluorine, C １ -C ３ Linear or branched alkyl and fluorinated C １ -C ３ is one selected from the linear or branched alkyl D ５ is fluorine, fluorinated C １ -C ６ Linear or branched alkyl and fluorinated C １ -C １２ is one selected from the group consisting of straight or branched chain alkoxy D ６ is hydrogen, fluorine, fluorinated C １ -C ６ Linear or branched alkyl and fluorinated C １ -C ６ 2. The gel electrolyte composition of claim 1, wherein the alkoxy group is one selected from the group consisting of:

4. X is 【Transformation 6】 At least one selected from the group consisting of D １ , D ２ , D ３ and D ４ are each independently hydrogen, fluorine, methyl, *-CHF ２ , *-CH ２ F or *-CF ３ The gel electrolyte composition according to claim 1,

5. R ４ , R ５ and R ６ are each independently hydrogen or C １ -C ３ is a straight or branched chain alkyl of A ２ is C １ -C ３ The gel electrolyte composition according to claim 1 , wherein the alkylene is a straight-chain alkylene.

6. 2. The gel electrolyte composition according to claim 1, wherein the fluorine-containing copolymer contains the repeating units represented by Chemical Formula 1 and Chemical Formula 2 in a molar ratio of 1:1 to 1:

10.

7. 3. The gel electrolyte composition according to claim 2, wherein the fluorine-containing copolymer contains less than 30 mol% of the repeating unit represented by Chemical Formula 3 relative to the total repeating units contained in the copolymer.

8. 2. The gel electrolyte composition according to claim 1, wherein the fluorine-containing copolymer has a number average molecular weight of 10,000 to 1,000,000 g / mol.

9. The gel electrolyte composition according to claim 1 , wherein the fluorine-containing copolymer is contained in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the gel electrolyte composition.

10. The lithium salt is LiPF ６ , LiClO ４ , LiBF ４ , LiFSI, LiTFSI, LiSO ３ CF ３ , LiBOB, LiFOB, LiDFOB, LiDFBP, LiTFOP, LiPO ２ F ２ , LiCl, LiBr, LiI, LiB10Cl10, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiAlCl ４ , C.H. ３ SO ３ Li, CF ３ SO ３ Li, LiSCN and LiC(CF ３ SO ２ ) ３ 2. The gel electrolyte composition according to claim 1, wherein the composition is at least one selected from the group consisting of:

11. 2. The gel electrolyte composition of claim 1, wherein the organic solvent comprises one or more selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

12. The gel electrolyte composition according to claim 1 , wherein the gel electrolyte composition is crosslinked at 20 to 80° C.

13. positive electrode; a negative electrode; and The gel electrolyte composition of claim 1; A secondary battery comprising: The gel electrolyte composition forms a layer between a positive electrode and a negative electrode.

14. The secondary battery according to claim 13 , wherein the secondary battery satisfies the following formula 1: [Formula 1] C ６００ / C １≧ 0.8 In the formula 1, C ６００ is the discharge capacity of a secondary battery that has been repeatedly charged and discharged 600 times, C １ is the discharge capacity of a secondary battery that has been charged and discharged once.

15. 14. The secondary battery according to claim 13, wherein the positive electrode active material contained in the positive electrode contains at least one selected from the group consisting of nickel, cobalt, manganese, tin, silicon, and aluminum.

16. 14. The secondary battery according to claim 13, wherein the negative electrode active material contained in the negative electrode contains at least one selected from the group consisting of graphite, silicon, germanium, tin, and antimony.

17. The secondary battery according to claim 13 , wherein the gel electrolyte composition is formed by gelling on the surface of the negative electrode.

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