[One]This application claims the benefit of the filing date of Korean Patent Application No. 10-2019-0102520, filed with the Korean Intellectual Property Office on August 21, 2019, the entire contents of which are incorporated herein by reference. [2] The present invention relates to a non-aqueous electrolyte for a lithium secondary battery comprising an additive having an excellent effect of removing decomposition products generated from a lithium salt, and to a lithium secondary battery having improved high temperature durability by including the same. background [3] As personal IT devices and computer networks are developed due to the development of the information society, and the overall society's dependence on electric energy increases accordingly, technology development for efficiently storing and utilizing electric energy is required. [4] Among the technologies developed for this purpose, the most suitable technology for various uses is a secondary battery-based technology. In the case of a secondary battery, interest in it is rising because it can be miniaturized enough to be applied to personal IT devices, and can also be applied to electric vehicles and power storage devices. Lithium ion batteries are in the spotlight as a battery system with the highest theoretical energy density among these secondary battery technologies, and are currently being applied to various devices. [5] A lithium ion battery consists of a positive electrode made of a transition metal oxide containing lithium, a negative electrode made of a carbon-based material such as graphite that can store lithium, an electrolyte solution as a medium for transferring lithium ions, and a separator. Proper selection of these components is important in order to improve the electrochemical properties. [6] On the other hand, lithium ion batteries have disadvantages in that performance deteriorates due to an increase in resistance and a decrease in capacity during charging and discharging or storage at high temperatures. One of the causes of this problem is a side reaction that occurs due to deterioration of the electrolyte at a high temperature, especially deterioration due to the decomposition of lithium salts. [7] As the lithium salt, LiPF 6 is mainly used in order to obtain suitable characteristics of the secondary battery . In the case of the PF 6 - anion of the lithium salt, it is very vulnerable to heat, and due to thermal decomposition when the battery is exposed to high temperature, PF 5 - It is known to generate Lewis acid. [8] PF 5 − formed in this way not only causes a decomposition reaction of organic solvents such as ethylene carbonate, but also destroys the solid electrolyte interphase (SEI) formed on the surface of an active material such as graphite, which has an operating voltage that exists outside the electrochemical stability window of the electrolyte. It causes additional decomposition of the electrolyte, thereby increasing the resistance of the battery and deterioration of the lifespan. [9] Accordingly, various methods have been proposed for removing PF 5 generated by thermal decomposition of LiPF 6 based salt , maintaining the passivation ability of the SEI film when exposed to heat, and suppressing the deterioration behavior of the battery. DETAILED DESCRIPTION OF THE INVENTION technical challenge [10] An object of the present invention is to provide a non-aqueous electrolyte for a lithium secondary battery comprising an additive having an excellent effect of removing decomposition products generated from lithium salts that may be generated inside the electrolyte. [11] In addition, an object of the present invention is to provide a lithium secondary battery having an improved effect of improving high temperature durability by including the non-aqueous electrolyte for a lithium secondary battery. means of solving the problem [12] In one embodiment of the present invention for achieving the above object, [13] lithium salt; [14] organic solvents; [15] A compound represented by the following formula (1) as a first additive; and [16] Provided is a non-aqueous electrolyte for a lithium secondary battery comprising lithium difluorophosphate (LiDFP) as a second additive. [17] [Formula 1] [18] [19] In Formula 1, [20] R is a substituted or unsubstituted C 1 to C 5 alkyl group. [21] [22] Another embodiment of the present invention provides a lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of the present invention. Effects of the Invention [23] The non-aqueous electrolyte of the present invention contains a Lewis base and a material capable of forming SEI as a first additive, thereby removing decomposition products generated by thermal decomposition of lithium salts (scavenging) and strengthening the SEI film, thereby improving the performance of the SEI film during high-temperature storage. Passive ability can be secured. Furthermore, in the non-aqueous electrolyte of the present invention, by combining the second additive having an excellent film-forming effect with the first additive, a desirable film is formed on the surfaces of the positive electrode and the negative electrode, thereby suppressing the initial resistance of the battery. Therefore, by using the non-aqueous electrolyte of the present invention, it is possible to manufacture a lithium secondary battery having an improved effect of improving high temperature durability. Brief description of the drawing [24] 1 is a graph showing the resistance increase rate of the secondary battery of Example 1 and the secondary battery of Comparative Example 1 after high temperature (60° C.) storage. [25] FIG. 2 is a graph showing the resistance increase rate of the secondary battery of Example 1 and the secondary battery of Comparative Example 1 at a high temperature (45° C.) for 200 cycles. Best mode for carrying out the invention [26] Hereinafter, the present invention will be described in more detail. [27] The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention. [28] [29] In the lithium secondary battery, as the non-aqueous electrolyte is decomposed during initial charging and discharging, a film having passivation ability is formed on the surfaces of the positive and negative electrodes to improve high-temperature storage characteristics. However, the film may be deteriorated by acids such as HF − and PF 5 − generated by thermal decomposition of lithium salts (LiPF 6 etc.) widely used in lithium ion batteries . As the transition metal element is eluted from the anode by this acid attack, the surface resistance of the electrode increases due to a change in the structure of the surface, and the theoretical capacity decreases as the metal elements, which are the redox centers, disappear, so the expression capacity may decrease. can In addition, the eluted transition metal ions are electrodeposited on the negative electrode reacting in the strong reduction potential band, and not only consume electrons, but also destroy the film when electrodeposited, thereby exposing the surface of the negative electrode, thereby causing an additional electrolyte decomposition reaction. As a result, there is a problem in that the capacity of the cell is continuously decreased as the resistance of the negative electrode increases and the irreversible capacity increases. [30] Therefore, in the present invention, the non-aqueous electrolyte component includes a Lewis salt-based compound and an additive capable of forming SEI, thereby removing acid caused by the decomposition of lithium salt and preventing deterioration of the SEI film or elution of transition metal from the positive electrode during high-temperature storage An object of the present invention is to provide a non-aqueous electrolyte capable of strengthening the SEI film on the surface of an anode and a lithium secondary battery including the same. [31] [32] Non-aqueous electrolyte for lithium secondary battery [33] First, a non-aqueous electrolyte for a lithium secondary battery according to the present invention will be described. [34] The non-aqueous electrolyte for a lithium secondary battery of the present invention comprises (1) a lithium salt, (2) an organic solvent, (3) a compound represented by the following formula 1 as a first additive, and (4) lithium difluorophosphate as a second additive ( LiDFP). [35] [Formula 1] [36] [37] In Formula 1, [38] R is a substituted or unsubstituted C 1 to C 5 alkyl group. [39] [40] (1) lithium salt [41] First, in the non-aqueous electrolyte for a lithium secondary battery according to an embodiment of the present invention, the lithium salt may be used without limitation, those commonly used in the electrolyte for a lithium secondary battery, for example, Li + as a cation, and an anion. F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , 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 -At least one selected from the group consisting of may be mentioned. 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 3SO 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 ) or a mixture of two or more thereof. [42] 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 0.8 M to 3.0 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 [43] When the concentration of the lithium salt is less than 0.8 M, the mobility of lithium ions may decrease, and thus capacity characteristics may be deteriorated. When the concentration of the lithium salt exceeds the concentration of 3.0 M, the viscosity of the non-aqueous electrolyte may excessively increase, thereby reducing electrolyte impregnability and reducing the film-forming effect. [44] [45] (2) organic solvents [46] As the organic solvent, various organic solvents commonly used in lithium electrolytes may be used without limitation. For example, the organic solvent may include a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, or a mixed organic solvent 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 organic solvent may include a cyclic carbonate organic solvent and a linear carbonate organic solvent in a volume ratio of 1:9 to 5:5, specifically 2:8 to 4:6 by volume, in order to prepare an electrolyte solution having high ionic conductivity. [50] In addition, the organic solvent may further include a cyclic carbonate-based organic solvent and/or a linear carbonate-based organic solvent and a linear ester-based organic solvent and/or a cyclic ester-based organic solvent commonly used in electrolytes for lithium secondary batteries as needed. may [51] Specific examples of the linear ester-based organic solvent include 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 [52] The cyclic ester-based organic solvent is, for example, any one or two selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone and ε-caprolactone. The above organic solvents are mentioned. [53] Meanwhile, as the organic solvent, an ether-based organic solvent or a nitrile-based organic solvent may be further mixed and used as needed in addition to the carbonate-based organic solvent or the ester-based organic solvent. [54] As the ether-based organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used. [55] The nitrile solvent is acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile and at least one selected from the group consisting of difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile. [56] [57] (3) first additive [58] The non-aqueous electrolyte of the present invention includes a compound represented by the following Chemical Formula 1 as a first additive. [59] [Formula 1] [60] [61] In Formula 1, [62] R is a substituted or unsubstituted C 1 to C 5 alkyl group. [63] [64] In Formula 1, R may be a substituted or unsubstituted C 1 to C 3 alkyl group. Specifically, the compound represented by Formula 1 may be a compound represented by Formula 1a below. [65] [Formula 1a] [66] [67] [68] The compound represented by Formula 1 may be included in an amount of 0.1 wt% to 5 wt%, specifically 0.1 wt% to 4 wt%, and 1 wt% to 3 wt% based on the total weight of the non-aqueous electrolyte. [69] When the content of the compound represented by the formula (1) satisfies the above range, while minimizing disadvantages such as side reactions, capacity reduction and resistance increase due to additives, the effect of removing decomposition products of lithium salts is excellent, and overall performance is further improved. battery can be manufactured. [70] If the content of the first additive is less than 0.1% by weight, HF - or PF 5 - may be removed, but the removal effect may be insignificant as time passes. In addition, when the content of the first additive exceeds 5.0% by weight, the viscosity of the electrolyte solution increases due to the excessive amount of the additive, and the ionic conductivity decreases due to the increase in viscosity, which adversely affects the mobility of ions in the battery, resulting in a high temperature During storage, the rate characteristics or low temperature life characteristics may be deteriorated. In addition, due to the decomposition of excessive additives, the resistance of the battery may increase. [71] As described above, the non-aqueous electrolyte of the present invention contains a Lewis base-based compound including a C=S functional group like the compound represented by Formula 1, and thus a by-product that causes deterioration of the battery at high temperatures, such as lithium Lewis acids (eg, HF − or PF 5 − ) generated due to decomposition of salts can be easily removed. Therefore, since it is possible to suppress the deterioration behavior of the film due to the chemical reaction of the film on the surface of the anode or cathode caused by Lewis acid, it is possible to prevent further decomposition of the electrolyte in the battery due to the destruction of the film, and furthermore, to alleviate the self-discharge of the secondary battery, high temperature Storage characteristics can be improved. [72] In particular, since the compound represented by Formula 1 included as the non-aqueous electrolyte additive has a functional group of a double bond and a C=S bond, a more robust SEI may be formed. That is, since the compound represented by Formula 1 of the present invention does not have a C = S bond, which is an electron-rich functional group instead of a C = O bond, when the compound is reduced to form SEI, an interface containing sulfur (S) is formed. can be formed Therefore, the initial resistance can be lowered compared to the case in which the compound represented by the following formula (3) is included. Moreover, the compound represented by Chemical Formula 1 has a smaller molecular weight than a compound containing an ionic bond such as SO 3 − represented by Chemical Formula 4, and has an ester bond, so it is suitable for organic solvents applied to lithium ion batteries. There is an advantage in that it is easier to function as an additive because of its high solubility. [73] [Formula 3] [74] [75] [Formula 4] [76] [77] [78] (4) second additive [79] The non-aqueous electrolyte of the present invention includes lithium difluorophosphate (LiDFP) represented by the following Chemical Formula 2 as a second additive. [80] [Formula 2] [81] [82] The lithium difluorophosphate (LiDFP) is a component for realizing the effect of improving the long-term lifespan characteristics of a secondary battery, and the lithium ion component generated by decomposition during initial charging is electrochemically decomposed on the surface of the anode to form a stable SEI film. there is. By forming the SEI film, it is possible to not only improve the mobility of Li to the cathode, but also lower the interfacial resistance. In addition, difluorophosphate anions generated by decomposition during initial charging are present on the surface of the anode, improving cathode stabilization and discharging characteristics. Accordingly, it is possible to realize the effect of improving the long-term cycle life characteristics of the secondary battery. [83] The second additive, lithium difluorophosphate (LiDFP), is 0.1 wt% to 5 wt%, specifically 0.5 wt% to 3 wt%, more specifically 1 wt% to 3 wt%, based on the total weight of the non-aqueous electrolyte may be included. [84] When the content of lithium difluorophosphate (LiDFP) satisfies the above range, a strong SEI film forming effect and a film forming effect can be obtained. [85] If the content of lithium difluorophosphate (LiDFP) exceeds 5% by weight, the viscosity of the electrolyte solution increases due to the surplus compound, and an excessively thick film is formed on the electrode surface, resulting in increased resistance and deterioration of capacity characteristics. can occur If the content of lithium difluorophosphate (LiDFP) is less than 0.1 wt %, the effect of forming a film on the electrode surface may be insignificant. [86] On the other hand, in the non-aqueous electrolyte of the present invention, the weight ratio of the first additive to the second additive may be 1:1 to 1:10, specifically 1:1 to 1:5, more specifically 1:1 to 1:3. there is. [87] When the first additive and the second additive are mixed in the above ratio, the wettability of the electrolyte may be improved by lowering the surface tension. In addition, by forming a stable SEI film without an increase in resistance, a side reaction between the electrode and the electrolyte can be suppressed during charging at a high temperature. [88] If the ratio of the second additive to the first additive exceeds 10 weight ratio, an excessively thick film is formed on the surface of the electrode and the initial interface resistance is increased, and thus output may be reduced. In addition, when the second additive is included in less than 1 weight ratio with respect to the first additive, the effect of forming an SEI film is insignificant, and the effect of inhibiting side reactions between the electrode and the electrolyte may be reduced. [89] [90] (5) additional additives [91] In addition, the non-aqueous electrolyte for a lithium secondary battery of the present invention prevents the anode from disintegrating due to decomposition of the non-aqueous electrolyte in a high-output environment, or has low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and battery expansion inhibition effect at high temperature. In order to improve it, additional third additives may be further included in the non-aqueous electrolyte if necessary. [92] Representative examples of these third 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, and a silane-based compound It may include at least one additive selected from the group consisting of compounds and lithium salt-based compounds. [93] The cyclic carbonate-based compound may include vinylene carbonate (VC) or vinylethylene carbonate. [94] The halogen-substituted carbonate-based compound may include fluoroethylene carbonate (FEC)). [95] The sultone-based compound includes 1,3-propane sultone (PS), 1,4-butane sultone, ethenesultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3 - at least one compound selected from the group consisting of propene sultone. [96] The sulfate-based compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS). [97] The phosphate-based compound includes lithium difluoro(bisoxalato)phosphate, tetramethyl trimethyl silyl phosphate, trimethyl silyl phosphite, tris(2,2,2-trifluoro) in addition to lithium difluorophosphate included as the second additive. and at least one compound selected from the group consisting of roethyl)phosphate and tris(trifluoroethyl)phosphite. [98] The borate-based compound may include tetraphenylborate and lithium oxalyldifluoroborate. [99] The nitrile-based compound is succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzo At least one selected from the group consisting of nitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile compounds can be mentioned. [100] The benzene-based compound may include fluorobenzene, the amine-based compound may include triethanolamine or ethylenediamine, and the silane-based compound may include tetravinylsilane. [101] The lithium salt-based compound is a compound different from the lithium salt included in the non-aqueous electrolyte, and is selected from the group consisting of LiPO 2 F 2 , LiODFB, LiBOB (lithium bisoxalatoborate (LiB(C 2 O 4 ) 2 ) and LiBF 4 ). one or more compounds. [102] Among these additional additives, when vinylene carbonate, vinylethylene carbonate, or succinonitrile is included, a stronger SEI film may be formed on the surface of the anode during the initial activation process of the secondary battery. [103] When the LiBF 4 is included, generation of a gas that may be generated due to the decomposition of the electrolyte at a high temperature is suppressed, thereby improving the high-temperature stability of the secondary battery. [104] Meanwhile, two or more kinds of the third additive 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% by weight, based on the total weight of the non-aqueous electrolyte. to 5% by weight. When the content of the additional additive is less than 0.01% by weight, the effect of improving the low-temperature output and high-temperature storage characteristics and high-temperature lifespan characteristics of the battery is insignificant, and when the content of the additional additive exceeds 50% by weight, charging and discharging of the battery There is a possibility that side reactions in the electrolyte solution may occur excessively. In particular, when the third additive is added in excess, it may not be sufficiently decomposed at a high temperature, and thus may remain unreacted or precipitated in the electrolyte at room temperature. Accordingly, a side reaction in which the lifespan or resistance characteristic of the secondary battery is deteriorated may occur. [105] [106] lithium secondary battery [107] In another embodiment of the present invention, there is provided a lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of the present invention. [108] On the other hand, the lithium secondary battery of the present invention can be manufactured by forming an electrode assembly in which a positive electrode, a negative electrode, and a separator are sequentially stacked between the positive and negative electrodes, stored in a battery case, and then adding the non-aqueous electrolyte of the present invention. [109] The method for manufacturing the lithium secondary battery of the present invention may be manufactured and applied according to a conventional method known in the art, and will be described in detail below. [110] [111] (1) Anode [112] The positive electrode may be prepared by coating a positive electrode slurry including a positive electrode active material, a binder, a conductive material and a solvent on a positive electrode current collector, followed by drying and rolling. [113] The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. [114] The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and may include a lithium transition metal oxide including lithium and one or more metals selected from cobalt, manganese, nickel, and aluminum, Specifically, lithium-manganese oxides, lithium iron phosphate, and lithium-nickel-manganese-cobalt oxides (eg, Li(Ni p Co q Mn r1 )O having high capacity characteristics and safety of batteries) 2 (herein, 0