[One][Citation with related applications] [2]This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0107364 filed on August 30, 2019, and all contents disclosed in the Korean Patent Application Document are incorporated as a part of this specification. [3] [4] [Technical field] [5] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to an electrolyte for a lithium secondary battery having excellent high-temperature lifespan characteristics and thermal stability, and a lithium secondary battery including the same. [6] background [7] Lithium secondary batteries generally form an electrode assembly by interposing a separator between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode including a negative electrode active material capable of storing lithium ions, and the electrode It is manufactured by inserting the assembly into the battery case, injecting a non-aqueous electrolyte serving as a medium for transferring lithium ions, and then sealing the assembly. [8] The nonaqueous electrolyte is generally composed of a lithium salt and an organic solvent capable of dissolving the lithium salt, and LiPF 6 and the like are mainly used as the lithium salt. However, in the case of PF 6 − anion, it is very vulnerable to heat, so that when the battery is exposed to high temperatures, it is thermally decomposed to generate Lewis acids such as PF 5 . Lewis acids such as PF 5 not only cause decomposition of organic solvents such as ethyl carbonate, but also destroy the SEI film formed by the reduction reaction on the surface of the active material having an operating voltage that exists outside the electrochemical stability window of the electrolyte, thereby increasing the resistance, There is a problem that the battery performance deteriorates. In addition, heat generation and ignition may occur inside the battery due to an increase in the interfacial resistance of the battery. [9] Accordingly, there is a demand for the development of an electrolyte for a lithium secondary battery having less deterioration of battery performance at high temperatures and excellent thermal stability. [10] DETAILED DESCRIPTION OF THE INVENTION technical challenge [11] An object of the present invention is to provide an electrolyte for a lithium secondary battery capable of implementing excellent high-temperature lifespan characteristics and thermal stability, including a fluorine-based organic solvent and a fluorine-based compound having a specific structure, and a lithium secondary battery including the same. [12] means of solving the problem [13] According to one embodiment, the present invention, a lithium salt; a non-aqueous solvent including a fluorine-based organic solvent; And it provides an electrolyte for a lithium secondary battery comprising a fluorine-based compound represented by the following [Formula 1]. [14] [Formula 1] [15] [16] In Formula 1, n is an integer of 1 to 300, R is hydrogen, a halogen, an alkyl group having 1 to 6 carbon atoms, or a halogen-substituted alkyl group having 1 to 6 carbon atoms, and X is a functional group represented by Formula 2 below. [17] [Formula 2] [18] [19] In Formula 2, m is an integer of 0 to 4, l is an integer of 1 to 3, R 1 and R 2 are each independently hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms, or a halogen-substituted alkyl group having 1 to 6 carbon atoms And , when two or more R 1 and R 2 are present, each of R 1 and R 2 may be the same as or different from each other. [20] According to another embodiment, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the negative electrode and the positive electrode, and the electrolyte for a lithium secondary battery of the present invention. [21] Effects of the Invention [22] Since the electrolyte according to the present invention uses a fluorine-based solvent having excellent flame retardancy, it is possible to suppress heat generation/ignition in the battery and thus has excellent thermal stability. [23] In addition, in the electrolyte according to the present invention, the surface tension of the electrolyte is reduced by using the fluorine-based solvent and the fluorine-based compound having a specific structure together, and thus electrode wetting and adhesion with the electrode are improved. [24] The lithium secondary battery to which the electrolyte of the present invention is applied as described above has excellent high-temperature lifespan characteristics and stability. [25] Best mode for carrying out the invention [26] Hereinafter, the present invention will be described in more detail. [27] [28] electrolyte [29] The electrolyte according to the present invention includes a lithium salt, a non-aqueous solvent including a fluorine-based organic solvent, and a fluorine-based compound. [30] [31] (1) lithium salt [32] As the lithium salt, various lithium salts commonly used in electrolytes for lithium secondary batteries may be used without limitation. For example, the lithium salt includes Li + as a cation, and F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - as an anion. , AlO 4 - , AlCl 4 - , PF 6 - , SbF 6 - , AsF 6 - , B 10 Cl 10 -, BF 2 C 2 O 4 - , BC 4 O 8 - , PF 4 C 2 O 4 - , PF 2 C 4 O 8 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , ( CF 3 ) 4 PF 2 - , (CF 3) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3 - , C 4 F 9 SO 3 - , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , CF 3 CF 2 (CF 3) 2 CO - , (CF 3 SO 2 ) 2 CH - , CH 3 SO 3 - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - and (CF 3 CF 2 SO 2 ) 2 N -It may include at least one selected from the group consisting of. [33] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF 4 , LiClO 4 , LiAlO 4 , LiAlCl 4 , LiPF 6 , LiSbF 6 , LiAsF 6 , LiB 10 Cl 10 , LiBOB (LiB(C 2 O 4 ) 2 ) , LiCF 3 SO 3 , LiTFSI (LiN(SO 2 CF 3 ) 2 ), LiFSI (LiN(SO 2 F) 2 ), LiCH 3 SO 3, LiCF 3 CO 2 , LiCH 3 CO 2 and LiBETI (LiN(SO 2 CF 2 CF 3 ) 2 at least one selected from the group consisting of 2 . Specifically, the lithium salt is LiBF 4 , LiClO 4 , LiPF 6 . , LiBOB (LiB(C 2 O 4 ) 2 ), LiCF 3 SO 3 , LiTFSI (LiN(SO 2 CF 3 ) 2 ), LiFSI (LiN(SO 2 F) 2 )) and LiBETI (LiN(SO 2 CF 2 CF 3 ) 2 A single substance selected from the group consisting of or a mixture of two or more thereof may be included. [34] The lithium salt may be appropriately changed within the range that can be used in general, but to be included in the electrolyte at a concentration of 0.4 M to 4.0 M, specifically, at a concentration of 1.0M to 3.0M, in order to obtain an optimal effect of forming a film for preventing corrosion of the electrode surface. can When the concentration of the lithium salt is less than 0.4 M, the effect of improving the low-temperature output of the lithium secondary battery and improving cycle characteristics during high-temperature storage is insignificant, and when the concentration of the lithium salt exceeds 4.0 M, the viscosity of the electrolyte increases and the electrolyte impregnation property may be reduced. . [35] [36] (2) non-aqueous solvents [37] The electrolyte of the present invention includes a non-aqueous solvent, and the non-aqueous solvent includes a fluorine-based organic solvent. [38] Fluorine-based organic solvents are not easily decomposed at high temperatures and high voltages and have flame retardancy, so when used as a solvent for electrolytes, it is possible to suppress heat generation/ignition phenomena due to gas generation and resistance increase due to electrolyte decomposition reaction. [39] Examples of the fluorine-based organic solvent include fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), fluorodimethyl carbonate (F-DMC), fluoroethyl methyl carbonate (FEMC), 2,2 -bis(trifluoromethyl)-1,3-dioxolane (TFDOL), methyl 2,2,2-trifluoroethyl carbonate (F3-EMC), trifluoroethyl phosphite (TFEPi) , Trifluoroethyl phosphate (TFEPa), 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (1,1,2,2-Tetrafluoroethyl 2,2, 2-trifluoroethyl ether), 1,1,2,2-tetrafluoroethyl 2,2,3,3,-tetrafluoropropyl ether (1,1,2,2-Tetrafluoroethyl 2,2,3,3- tetrafluoropropyl ether), monofluorobenzene (FB), difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentatrifluorobenzene, hexafluorobenzene, 1,1,2,2-tetrafluoro- 3-(1,1,2,2-tetrafluoroethoxy)propane (1,1,2,2-tetrafluoro-3-(1,1,2,2-tetrafluoroethoxy)propane), methyl difluoroacetate (methyl difluoroacetate), ethyl difluoroacetate (ethyl difluoroacetate), difluoroethyl acetate (difluoroethyl acetate), or a mixture thereof may be used. [40] Among them, fluoroethylene carbonate (FEC), methyl 2,2,2-trifluoroethyl carbonate (F3-EMC), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoro Roethyl ether (1,1,2,2-Tetrafluoroethyl 2,2,2-trifluoroethyl ether), 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (1 ,1,2,2-Tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether) or a mixture thereof is particularly preferred. When the above compounds are used, a more stable film (LiF) may be formed on the anode to improve durability such as maintaining cell life and high temperature stability. [41] [42] The fluorine-based organic solvent may be included in an amount of 5 to 100 parts by weight, preferably 10 to 95 parts by weight, more preferably 20 to 90 parts by weight based on 100 parts by weight of the non-aqueous solvent. When the content of the fluorine-based organic solvent satisfies the above range, high temperature/high voltage stability can be improved, and the effect of controlling the exothermic characteristics can be obtained without impairing the ion transfer ability. [43] [44] Meanwhile, the non-aqueous solvent may further include a non-fluorine-based organic solvent in addition to the fluorine-based organic solvent, if necessary for improving physical properties. [45] [46] The non-fluorine-based organic solvent means an organic solvent that does not contain a fluorine atom, and various organic solvents commonly used in electrolytes for lithium secondary batteries may be used without limitation. For example, the non-fluorine-based organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, a linear ester-based organic solvent, a cyclic ester-based organic solvent, or a mixture thereof. [47] The cyclic carbonate-based organic solvent is a high-viscosity organic solvent that has a high dielectric constant and can well dissociate lithium salts in the electrolyte, and specific examples thereof include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene. At least one organic solvent selected from the group consisting of carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate and vinylene carbonate, among them, ethylene carbonate may include [48] In addition, the linear carbonate-based organic solvent is an organic solvent having a low viscosity and a low dielectric constant, and representative examples thereof include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate ( EMC), at least one organic solvent selected from the group consisting of methyl propyl carbonate and ethyl propyl carbonate may be used, and specifically, ethyl methyl carbonate (EMC) may be included. [49] The linear ester-based organic solvent is a specific example of at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate. can be heard [50] In addition, the cyclic ester-based organic solvent may include at least one organic solvent selected from the group consisting of butyrolactone, γ-valerolactone, γ-caprolactone, ε-valerolactone, and ε-caprolactone. there is. [51] The non-fluorine-based organic solvent may be included in an amount of 95 parts by weight or less, preferably 5 to 95 parts by weight, more preferably 10 to 80 parts by weight, based on 100 parts by weight of the non-aqueous solvent. When a non-fluorine-based solvent is additionally added, the effect of improving lithium salt dissociation degree, electrolyte dielectric constant and viscosity characteristics can be obtained. [52] [53] (3) fluorine-based compounds [54] The electrolyte of the present invention includes a fluorine-based compound represented by the following formula (1). [55] [Formula 1] [56] [57] In Formula 1, n is an integer of 1 to 300, preferably an integer of 10 to 100. [58] R is hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms or a halogen-substituted alkyl group having 1 to 6 carbon atoms, preferably hydrogen or a fluorine-substituted alkyl group having 1 to 4 carbon atoms, more preferably hydrogen or -CF 2 CF 3 . [59] X is a functional group represented by the following formula (2). [60] [Formula 2] [61] [62] In Formula 2, m is an integer of 0 to 4, preferably, an integer of 0 to 3, more preferably 1 or 2. [63] 1 is an integer of 1 to 3, preferably 1 or 3. [64] R1 and R2 are each independently hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms or a halogen-substituted alkyl group having 1 to 6 carbon atoms, preferably a hydrogen or fluorine-substituted alkyl group having 1 to 4 carbon atoms, more preferably , hydrogen or —CF 2 CF 3 . Meanwhile, when two or more R 1 and R 2 are present, each of R 1 and R 2 may be the same as or different from each other. [65] The fluorine-based compound represented by the [Formula 1] is a component for improving the wettability of the electrolyte and the electrode adhesion. When a fluorine-based organic solvent is used as in the present invention, an effect of improving high-temperature characteristics and thermal stability can be obtained, but the fluorine-based organic solvent has a higher viscosity than a conventional non-fluorine-based organic solvent used as an electrolyte solvent. There is a problem in that electrode wettability is poor. As a result of repeated research, the present inventors have found that the above problems can be solved by using the compound of Formula 1 together with a fluorine-based organic solvent. [66] Since the compound of Formula 1 coexists with the polar part and the non-polar part in the polymer structure, when it is added, the surface tension of the electrolyte is reduced. Therefore, when the fluorine-based solvent and the fluorine-based compound represented by the above [Formula 1] are used together, the surface tension of the electrolyte is reduced, thereby minimizing deterioration in electrode wettability and electrode adhesion, while improving thermal stability and high temperature characteristics. [67] [68] More specifically, the fluorine-based compound represented by the [Formula 1] may be a compound represented by the following [Formula 1-1] or a compound represented by the following [Formula 1-2]. [69] [Formula 1-1] [70] [71] [Formula 1-2] [72] [73] In the [Formula 1-1] and [Formula 1-2], n is an integer of 1 to 300, preferably an integer of 10 to 100. [74] R is hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms or a halogen-substituted alkyl group having 1 to 6 carbon atoms, preferably hydrogen or a fluorine-substituted alkyl group having 1 to 4 carbon atoms, more preferably hydrogen or -CF2CF3 am. [75] Wherein R 1 , R 1 ' and R 1 "are each independently hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms, or a halogen-substituted alkyl group having 1 to 6 carbon atoms, preferably hydrogen or fluorine-substituted C 1 to 4 carbon atoms. an alkyl group , more preferably hydrogen or -CF 2 CF 3 [76] Meanwhile, the fluorine-based compound represented by Formula 1 may have a weight average molecular weight of 60,000 g/mol or less, preferably 4,000 to 40,000 g/mol, and more preferably 4,000 to 30,000 g/mol. This is because, when the weight average molecular weight of the fluorine-based compound exceeds 600,000 g/mol, solubility in the fluorine-based solvent may decrease. [77] [78] The fluorine-based compound represented by the [Formula 1] may be included in an amount of 0.001 to 30% by weight, preferably 0.01 to 10% by weight, more preferably 0.01 to 5% by weight based on the total weight of the electrolyte. When the content of the fluorine-based compound satisfies the above range, the effect of improving wettability and improving battery stability is excellent. [79] [80] (4) Others [81] The electrolyte according to the present invention may further include an ionic liquid or an additive, if necessary. [82] [83] The ionic liquid is for improving battery stability, and is a compound containing an organic cation and an organic or inorganic anion. The types of cations and anions included in the ionic liquid are not particularly limited. [84] For example, as a cation contained in the ionic liquid, a pyridinium cation, a piperidinium cation, a pyrrolidinium cation, a cation having a pyrroline skeleton, a cation having a pyrrole skeleton, an imidazolium cation, tetrahydropyrimidi an nium cation, a dihydropyrimidinium cation, a pyrazolium cation, a pyrazolinium cation, a tetraalkylammonium cation, a trialkylsulfonium cation, or a tetraalkylphosphonium cation. [85] Anions included in the ionic liquid are F - , Cl - , Br - , I - , NO 3 - , (CN) 2 N - , BF 4 - , ClO 4 - , RSO 3 - (where R is carbon number 1 -9 alkyl group or phenyl group), RCOO - (wherein R is an alkyl group or phenyl group having 1-9 carbon atoms), PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 -, (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , (CF 3 SO 3 - ) 2 , (CF 2 CF 2 SO 3 - ) 2 , (C 2 F 5 SO 2 ) 2 N - , (CF 3 SO 3) 2 N - , (CF 3 SO 2 )(CF 3 CO)N - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 CH - , (SF 5 ) 3 C - , ( CF 3 SO 2 ) 3 C - , CF 3 (CF 2 )) 7 SO 3 - , CF 3 COO - , C 3 F 7 COO - , CF 3 SO 3 - , or C 4 F 9 SO 3 - . [86] Specifically, the ionic compound is 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM FSI), 1-methyl-1-propylpyrrolidinium bis(trifluorosulfonyl) Ponyl) imide (1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide, PYR13 TFSI), or a combination thereof, but is not limited thereto. [87] The ionic liquid may be included in an amount of 30% by weight or less, preferably 1 to 10% by weight, more preferably 1 to 5% by weight based on the total weight of the electrolyte for a lithium secondary battery. When the content of the ionic liquid satisfies the above range, it is possible to obtain the effect of reducing battery heat or improving battery safety without adversely affecting ionic conductivity and viscosity. [88] [89] In addition, the electrolyte according to the present invention prevents the anode from collapsing due to decomposition of the electrolyte in a high-output environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and battery expansion inhibition effect at high temperatures. , and may further include additives. [90] Examples of such additives include a cyclic carbonate-based compound, a halogen-substituted carbonate-based compound, a sultone-based compound, a sulfate-based compound, a phosphate-based compound, a borate-based compound, a nitrile-based compound, a benzene-based compound, an amine-based compound, a silane-based compound, and lithium and at least one selected from the group consisting of salt-based compounds. [91] The cyclic carbonate-based compound may be, for example, vinylene carbonate (VC) or vinylethylene carbonate. [92] The halogen-substituted carbonate-based compound may be, for example, fluoroethylene carbonate (FEC). [93] The sultone-based compound is, for example, 1,3-propane sultone (PS), 1,4-butane sultone, ethensultone, 1,3-propene sultone (PRS), 1,4-butene sultone and 1- It may be at least one compound selected from the group consisting of methyl-1,3-propene sultone. [94] The sulfate-based compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS). [95] The phosphate-based compound is, for example, lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethyl silyl phosphate, trimethyl silyl phosphite, tris(2,2,2-trifluoro It may be at least one compound selected from the group consisting of ethyl) phosphate and tris (trifluoroethyl) phosphite. [96] The borate-based compound may be, for example, tetraphenylborate, lithium oxalyldifluoroborate, or the like. [97] The nitrile-based compound is, for example, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, From the group consisting of 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile It may be at least one or more selected compounds. [98] The benzene-based compound may be, for example, fluorobenzene, etc., the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane. [99] The lithium salt-based compound is a compound different from the lithium salt included in the non-aqueous electrolyte, and may be at least one compound selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalatoborate (LiB(C2O4)2) and LiBF4. . [100] [101] On the other hand, two or more of the additives may be mixed and used, and may be included in an amount of 0.01 to 50% by weight, specifically 0.01 to 10% by weight, preferably 0.05 to 5% by weight based on the total weight of the electrolyte. . When the content of the additive is less than 0.01% by weight, the effect of improving physical properties is insignificant, and when the content of the additive exceeds 50% by weight, there is a possibility that a side reaction may occur excessively during charging and discharging of the battery due to an excessive amount of the additive. [102] [103] lithium secondary battery [104] Next, a lithium secondary battery according to the present invention will be described. [105] A lithium secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the electrolyte according to the present invention. Since the electrolyte has been described above, a description thereof will be omitted, and other components will be described below. [106] [107] (1) Anode [108] The positive electrode according to the present invention may include a positive electrode active material layer including a positive electrode active material, and if necessary, the positive electrode active material layer may further include a conductive material and/or a binder. [109] [110] The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may be a lithium composite metal oxide including lithium and one or more transition metals such as cobalt, manganese, nickel or aluminum. . More specifically, the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO 2 , LiMn 2 O 4 , etc.), a lithium-cobalt-based oxide (eg, LiCoO 2 , etc.), lithium-nickel-based oxide (eg, LiNiO 2 , etc.), lithium-nickel-manganese oxide (eg, LiNi 1-Y Mn Y O 2 (0