Gel electrolyte composition and secondary battery including 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 including the same. [Background technology]

[0002] A secondary battery refers to a battery that continuously charges and outputs electrical energy, and has traditionally been used as a driving power source or a 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] In order 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 reactions between the positive electrode active material and the gel electrolyte when the secondary battery is overcharged.

[0006] On the other hand, the deterioration problem 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 the stability problem of 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 using the principle that lithium ions move quickly through pores formed along polymer fibers intertwined in a gel form.

[0008] However, there is still little progress in developing gel polymer electrolytes that have excellent performance and have a significantly reduced risk of explosion and combustion, and the problem of short-circuiting between the positive and negative electrodes, which is the biggest factor in the stability of secondary batteries, has not been fundamentally resolved. In addition, gel polymer electrolytes generally have poor adhesion to the surface of the negative electrode, which reduces the workability of the gel polymer electrolyte.

[0009] For this reason, 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 achieving 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 having 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 Formula 1 and Formula 2; a lithium salt; and an organic solvent.

[0012] [ka] 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 group of X is *-F, [ka] 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 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.

[0013] [ka] 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 group of A 2 is C 1 -C 6 is a 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. Effect of the Invention

[0015] The gel electrolyte composition of the present invention has excellent flame retardancy by including a fluorine-containing copolymer, and therefore, not only can it prevent fire and explosion problems due to deterioration of a secondary battery including the gel electrolyte composition, but also can minimize deterioration in performance of the secondary battery even after repeated charging and discharging. 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 description 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] 1 is a graph showing the flame retardant properties of the gel electrolyte composition according to Example 4. [Figure 1c] 1 is a graph showing the flame retardant properties of the gel electrolyte composition according to Example 5. [Diagram 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 them for 600 cycles. [Figure 3a] 13 is a graph showing a voltage profile according to the progress of cycles of the secondary battery according to Example 11. [Figure 3b] 13 is a graph showing a voltage profile according to the progress of cycles of the secondary battery according to Example 12. [Figure 3c] 13 is a graph showing a voltage profile according to the progress of cycles of the secondary battery according to Example 13. [Figure 3d] 13 is a graph showing a voltage profile according to the progress of cycles of the secondary battery of Example 14. [Figure 3e] 13 is a graph showing a voltage profile according to the progress of cycles of the secondary battery of Example 15. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the gel electrolyte composition and the secondary battery including the same according to the present invention 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 Formula 1 and Formula 2; a lithium salt; and an organic solvent. [ka] 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 X is a straight or branched chain alkyl group represented by the formula: [ka] 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 and D is one selected from the linear or branched alkyl 5 Fluorine, fluorinated C 1 -C 12 Linear or branched alkyl and fluorinated C 1 -C 12 and D is a straight or branched chain alkoxy group. 6 is hydrogen, fluorine, fluorinated C 1 -C 12 Linear or branched alkyl and fluorinated C 1 -C 12 linear or branched chain alkoxy, n is an integer from 0 to 20, and y is an integer from 1 to 5. [ka] In the above formula 2, R 4 , R 5 and R 6 are each independently hydrogen or C 1 -C 6 A is a straight or branched chain alkyl group. 2 is C 1 -C 6 is a straight or branched chain 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, R 1 , R 2 and R 3 are each independently hydrogen or C1 -C 3 and X is a straight or branched chain alkyl of the formula: [ka] and 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 and D is one selected from the linear or branched alkyl 5 Fluorine, fluorinated C 1 -C 6 Linear or branched alkyl and fluorinated C 1 -C 12 and D is a straight or branched chain alkoxy group. 6 is hydrogen, fluorine, fluorinated C 1 -C 6 Linear or branched alkyl and fluorinated C 1 -C 6 The alkoxy group may be one selected from the group consisting of straight chain or branched chain alkoxy.

[0021] As a specific example, in the above Chemical Formula 1, X is [ka] At least one selected from the group consisting of 1 , D 2 , D 3 and D. 4 are each independently hydrogen, fluorine, methyl, *-CHF 2 , *-CH 2 F or *-CF 3 It may be that

[0022] According to one embodiment of the present invention, in Formula 2, R 4 , R 5 and R 6are each independently hydrogen or C 1 -C 3 A2 is a straight or branched alkyl group of the formula C 1 -C 3 It may be a straight chain 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 Formula 1 and Formula 2 in a molar ratio of 1:1 to 1:10, preferably 1:2 to 1:8, more preferably 1:3 to 1:7. When the molar ratio of the repeating units represented by Formula 1 and Formula 2 contained in the fluorine-containing copolymer satisfies the above numerical range, the prepared gel electrolyte may have excellent flame retardancy, and thus the safety and life characteristics of the secondary battery including the gel electrolyte may be improved, and the workability may be improved since the cyano group contained in the fluorine-containing copolymer is immediately crosslinked inside the secondary battery.

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

[0026] [ka] 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.

[0027] The fluorine-containing copolymer may contain 0 to 30 mol%, preferably 0.5 to 20 mol%, more preferably 1 to 15 mol% of the repeating unit represented by Formula 3 relative to the total repeating units contained in the copolymer. When the fluorine-containing copolymer contains the repeating unit represented by Formula 3 in an amount within the above range, the solubility of the fluorine-containing copolymer in an organic solvent is excellent, and the hydroxyl group contained in the fluorine-containing copolymer can further activate the reaction of a lithium salt reacting 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 hydroxyl group to form a strong Lewis acid, and the hydroxyl 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 group is contained in the fluorine-containing copolymer in the above range, a strong Lewis acid derived from lithium salt can be generated in a large amount, and the crosslinking rate can be increased.

[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, more preferably 10,000 to 200,000 g / mol. When the number average molecular weight of the fluorine-containing copolymer satisfies the above numerical range, a gel electrolyte having excellent ion conductivity, mechanical strength, heat resistance, vibration resistance and chemical resistance can be realized.

[0031] The gel electrolyte composition may contain 0.1 to 10 parts by weight, preferably 0.1 to 5 parts by weight, and more preferably 1 to 5 parts by weight, of the fluorine-containing copolymer based on 100 parts by weight of the gel electrolyte composition. By containing the fluorine-containing copolymer in the above range, the gel electrolyte composition not only has excellent crosslinking reactivity and flame retardancy, but also contains a large amount of a liquid electrolyte containing a lithium salt, resulting in excellent lithium mobility, and thus the electrical conductivity may be improved, and thus a secondary battery manufactured using the gel electrolyte composition may exhibit excellent output, charging 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 is capable of crosslinking in a secondary battery.

[0033] 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, C.F. 3 SO 3 Li, LiSCN and LiC(CF 3 SO 2 ) 3 At least one selected from the group consisting of, preferably LiPF 6 , 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 have 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 satisfies the above range, the crosslinking reactivity of the fluorine-containing copolymer contained in the gel electrolyte is more excellent, and thus the secondary battery including the gel electrolyte can realize excellent charge / discharge capacity.

[0036] The organic solvent may be any compound containing a carbonate group, but a mixture of a cyclic carbonate compound and a linear carbonate compound may be used to achieve excellent secondary battery performance.

[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 includes at least one selected from the group consisting of dimethylcarbonate (DMC), ethylmethylcarbonate (EMC), and ethylenecarbonate (EC).

[0038] The ethylene carbonate (EC) is a cyclic carbonate-based compound, and a gel electrolyte composition including the EC can adjust viscosity, dissociate lithium salt, and has an excellent dielectric constant, so that the charge / discharge capacity of a secondary battery including the gel electrolyte composition can be improved.

[0039] The ethyl methyl carbonate (EMC) is a linear carbonate-based compound having a low freezing point and a high boiling point, and a gel electrolyte composition containing the same 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 the above volume ratio range, the organic solvent may have excellent dielectric constant, lithium salt dissociation characteristics, and low temperature characteristics at the same time.

[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 numerical range, not only the crosslinking reaction rate is 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 including repeating units represented by the following Formula 2 and Formula 3 with a fluorine-containing compound.

[0043] [ka] In the above formula 2, R 4 , R 5and R 6 are each independently hydrogen or C 1 -C 6 A is a straight or branched chain alkyl group. 2 is C 1 -C 6 is a straight or branched chain alkylene.

[0044] [ka] 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.

[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 may be adjusted or may not be included 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, 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 realize excellent heat resistance and flame retardancy, and thus, a secondary battery prepared including the fluorine-containing copolymer can have excellent life characteristics and safety.

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

[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 ester bonds, triethylamine for carbonate bonds, and pyridine for sorbone bonds.

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

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

[0054] [ka]

[0055] [ka]

[0056] [ka]

[0057] [ka]

[0058] [ka]

[0059] [ka] The above A 1 is C 1 -C 6 is an alkylene.

[0060] The content of the vinyl alcohol repeat unit contained in the fluorine-containing copolymer may vary depending on the molar ratio of the base copolymer and the fluorine-containing compound in the synthesis formulas 1 to 7, and may not be contained at all 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 repeat unit may not be contained, and when the molar ratio is 1:1 to less than 1:2, the vinyl alcohol repeat unit may be contained, but may be the same or different depending on the reacted fluorine-containing compound.

[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 has excellent stability.

[0063] In addition, in the secondary battery, a solid electrolyte interphase (SEI) layer is formed on the surface of the negative electrode due to a reaction between lithium ions generated by dissociation of a lithium salt contained in the gel electrolyte composition and other compounds contained in the gel electrolyte composition during charging. 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 above formula 1, C 600 is the discharge capacity of a secondary battery that has been charged and discharged 600 times, C 1 is the discharge capacity of a secondary battery that has been charged and discharged once.

[0065] Specifically, the formula 1 indicates the charge / discharge capacity of a secondary battery, and C in the formula 1 600 / C 1 The value may be from 0.85 to 0.98, which may mean superior 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 view of overcoming 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 contains graphite.

[0068] The gel electrolyte composition may be formed by gelling on the surface of the negative electrode. Thus, even if the gel electrolyte composition according to the present invention is applied, a stable solid electrolyte interface (SEI) layer can be formed on the negative electrode, which can prevent decomposition of the electrolyte and promote smooth movement of lithium ions, thereby improving the performance and life of the lithium secondary battery.

[0069] The present invention will be described in more detail with reference to the following examples. However, these examples are merely intended to aid in the understanding of 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. Then, 0.0559 g (0.0004572 mol) of DMAP (4-dimethylaminopyridine) was dissolved in 3 mL of DMF, which 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] The fluorine-containing copolymer thus prepared (0.03 g) was dissolved in 1M lithium salt LiPF 6 Then, 1.47 g of an organic solvent (an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7) containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) was mixed at a volume ratio of 3:7) was added and mixed. Then, a crosslinking reaction was carried out 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 and reacted 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 then dried in a vacuum oven at 60° C. to prepare a fluorine-containing copolymer.

[0080] The fluorine-containing copolymer thus prepared (0.03 g) was dissolved in 1M lithium salt LiPF 6 Then, 1.47 g of an organic solvent (an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7) containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) was mixed at a volume ratio of 3:7) was added and mixed. Then, a crosslinking reaction was carried out 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, vinyl alcohol: 24.2 mol%) 1 g (0.0055 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, which is a fluorine-containing compound shown in Table 1 below, was slowly added thereto, 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 then dried in a vacuum oven at 60° C. to prepare a fluorine-containing copolymer.

[0084] The fluorine-containing copolymer thus prepared (0.03 g) was dissolved in 1M lithium salt LiPF 6 Then, 1.47 g of an organic solvent (an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7) containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) was mixed at a volume ratio of 3:7) was added and mixed. Then, a crosslinking reaction was carried out 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 a 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 was prepared in the same manner as in Example 9, 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 10 mm x 10 mm x 10 mm test pieces, and the process of burning with a 1.20 mm spark for 1 second was repeated 4 times to observe whether or not combustion occurred. The results are shown in Table 1 below. If no combustion occurred, it was marked with O, and if combustion occurred, it was marked with 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 is confirmed that Examples 1 to 10 all have excellent flame retardancy compared to Comparative Example 1. This 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 according to 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] In addition, when comparing Examples 1 and 2, Examples 3 and 4, and Examples 9 and 10, which show differences due to 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 include 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 O 2 A secondary battery was manufactured using (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 0.2 O 2PVDF: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 prepared slurry was applied onto aluminum foil and dried in a vacuum oven at 120°C for 24 hours to prepare a positive electrode. The prepared positive electrode had a density of 12 mg / cm. 2 After loading at a density of 14 mm, the mixture was punched out into a 14 mm diameter circle for use 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 dissolving the mixture in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. 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 with a concentration of 6 mg / cm. 2 After loading at a density of 16 mm, the mixture was punched out into a 16 mm diameter circle for use 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 the SEI layer contained LiF.

[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 according to Example 3 was used instead of the gel electrolyte composition according to 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 positive and negative electrodes were then used to fabricate a polymer battery using a conventional method together with a separator made of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP). LiPF was then added to a solvent that was mixed in a volume ratio of EC (ethylene carbonate):DEC (diethyl carbonate):EMC (ethyl methyl carbonate) = 4:3:3. 6 A non-aqueous electrolyte solution prepared by dissolving the electrolyte in the above-mentioned mixture at a concentration of 1M was poured into the battery to prepare a lithium secondary battery.

[0107] <Experimental Example 2> Secondary battery power failure test method The coin-type secondary battery was charged and discharged once at an operating temperature of 25°C, with a voltage range of 3 to 4.2V and a charge / discharge rate of 0.1C-rate (165mA / g), after which the gelation reaction was initiated. After that, the battery was charged and discharged 600 times at a rate of 0.5C-rate, and the discharge capacity after one charge / discharge and the discharge capacity after 600 charge / discharges were measured and calculated using the following formula 1. [Formula 1] Capacity retention rate (%) = (discharge capacity after 600 times / discharge capacity after 1 time) 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 for inferring the life characteristics of a secondary battery.

[0110] In Table 2, it was confirmed that Examples 11 to 15, which respectively contain the gel electrolyte compositions according to Examples 1, 3 to 5, and 9, have a capacity retention rate of 81% or more, and specifically, in the case of Examples 13 to 15, it is 85% or more. This is because the secondary batteries according to Examples 11 to 15 contain the gel electrolyte compositions according to Examples 1, 3 to 5, and 9, and thus form a stable SEI layer, which can prevent deterioration of the negative electrode and suppress side reactions with the electrolyte, and ultimately have a better capacity retention rate.

[0111] Meanwhile, Figures 3a to 3d show capacity-voltage graphs at an initial rate of 0.1C-rate for Examples 11 to 15. From this, the amount of SEI layer formed at the beginning of charging and discharging can be inferred through a comparison of the capacities of the secondary batteries according to Examples 11 to 15 at the beginning of charging and discharging and a calculation of the Coulombic efficiency, and the amount of overvoltage formed in each battery can be confirmed. In the capacity range of 0mAh / g to 10mAh / g, the lower the voltage, the better, and Example 13 had the lowest voltage. Also, Example 13 showed the highest value for capacity retention rate.

[0112] Therefore, the gel electrolyte composition of the present invention can realize flame retardancy by containing a fluorine-containing copolymer, and can improve the stability of a secondary battery including the gel electrolyte composition to prevent explosion and fire. In addition, the gel electrolyte composition of the present invention can form a stable SEI layer on the negative electrode to prevent deterioration of the negative electrode, and can realize better life characteristics than conventional secondary batteries by suppressing side reactions with the electrolyte.

Claims

1. A fluorine-containing copolymer comprising 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 group 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 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. 【Chemistry 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 group of A ２ is C １ -C ６ is a straight or branched chain alkylene.

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 group of X is 【Chemistry 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 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 【Chemistry 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 group of A ２ is C １ -C ３ 2. The gel electrolyte composition according to claim 1, wherein the alkylene is a straight chain alkylene.

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

8. 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, C.F. ３ SO ３ Li, LiSCN and LiC(CF ３ SO ２ ) ３ 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 according to claim 1, wherein the organic solvent comprises one or more 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).

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 A gel electrolyte composition according to any one of claims 1 to 12; 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 above 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 a surface of a negative electrode.

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