[One]Cross-Citation with Related Application(s) [2]This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0039269 dated April 03, 2019, and all contents disclosed in the literature of the Korean patent application 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 capable of improving battery life characteristics and resistance characteristics by including boron and sulfur in a film formed on an electrode, and a lithium secondary battery including the same. background [6] 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. [7] The secondary battery-based technology is the most suitable technology for various uses, and can be applied to personal IT devices because it can be miniaturized, and can also be applied to large devices such as power storage devices. [8] Among secondary battery technologies, a lithium secondary battery, which is a battery system theoretically having the highest energy density per weight and volume, is in the spotlight. [9] A lithium secondary battery is generally composed of a positive electrode composed of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte serving as a medium for transferring lithium ions, and a separator. As it is known as a component that has a great influence on stability, safety, etc., many studies are being conducted on it. [10] In general, the electrolyte is preferably used by mixing a lithium salt with high thermal and chemical stability and an organic solvent while maintaining electrochemical stability within the operating voltage range. However, in general, the reduction voltage of the organic solvent is higher than the operating potential of the negative electrode such as graphite/silicon, and thus a reduction decomposition reaction may occur, and an oxidative decomposition reaction may occur on the surface of the anode. Therefore, controlling this decomposition reaction is an important factor in improving battery performance. [11] By this decomposition reaction, organic/inorganic decomposition products are generated on the surface of the anode/cathode to form a film. When it is formed on the surface of the cathode, it is called SEI (Solid-Electrolyte Interphase), and when it is formed on the anode, it is called a passivation film. [12] The film formed on the electrode surface can move lithium ions while suppressing further decomposition of the electrolyte. Recently, when only lithium salts and organic solvents are used as electrolytes, various additives are added to the electrolyte to form a better film. [13] In particular, since the lifespan characteristics and resistance characteristics of the battery are greatly dependent on the characteristics of the film formed on the electrode surface, there is an urgent need to study an electrolyte for forming a film having a more robust and excellent electrical properties during the charging reaction. [14] (Prior art document) Republic of Korea Patent Publication No. 10-2017-0134258 DETAILED DESCRIPTION OF THE INVENTION technical challenge [15] The present invention is to solve the above problems, and the electrolyte for a lithium secondary battery capable of improving the life characteristics and resistance characteristics of the battery by including boron and sulfur in the film formed on the electrode during the charging and discharging process of the battery and the same An object of the present invention is to provide a lithium secondary battery including means of solving the problem [16] In order to achieve the above object, the present invention provides an electrolyte for a lithium secondary battery comprising a lithium salt, an organic solvent, and an additive, wherein the additive includes a compound represented by the following formula (1). [17] [Formula 1] [18] [19] In Formula 1, R 1 and R 2 are each independently an alkyl group having 1 to 3 carbon atoms. [20] For another example, the present invention provides a lithium secondary battery including a positive electrode, a negative electrode, and the electrolyte for the lithium secondary battery. [21] On the other hand, at least one electrode selected from the group consisting of the anode and the cathode may have a film including boron and sulfur on the electrode surface. Effects of the Invention [22] When the electrolyte for a lithium secondary battery according to the present invention is used, a film containing boron (B) and sulfur (S) can be formed on the surface of the electrode by the decomposition reaction of the electrolyte generated during charging and discharging of the battery. The film containing boron and sulfur effectively suppresses an additional decomposition reaction of the electrolyte, thereby providing an excellent lithium secondary battery with improved lifespan characteristics and resistance characteristics. Brief description of the drawing [23] The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the above-described content of the present invention, so the present invention is limited to the matters described in those drawings It should not be construed as being limited. [24] 1 is a graph showing the initial resistance measured according to Experimental Example 1. [25] 2 is a graph showing the initial dose measured according to Experimental Example 2. [26] 3 is a graph showing a capacity retention rate according to the number of cycles measured according to Experimental Example 3. Best mode for carrying out the invention [27] Hereinafter, the present invention will be described in more detail. [28] The terms or words used in the present specification and claims are not to 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. [29] The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. [30] In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the presence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, elements, or combinations thereof. [31] [32] [33] The electrolyte for a lithium secondary battery according to the present invention includes a lithium salt, an organic solvent, and an additive, wherein the additive provides an electrolyte for a lithium secondary battery including a compound represented by the following formula (1). [34] [Formula 1] [35] [36] In Formula 1, R 1 and R 2 are each independently an alkyl group having 1 to 3 carbon atoms. [37] [38] (1) lithium salt [39] The lithium salt is used to sufficiently supply lithium ions to improve lithium ion yield (Li+ transference number) and degree of dissociation of lithium ions. [40] Specifically, as the lithium salt, any compound capable of providing lithium ions used in a lithium secondary battery may be used without particular limitation. Specifically, the lithium salt includes Li + as a cation and F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , AlO 4 as an anion. - , AlCl 4 - , PF 6 - , SbF 6 - , AsF 6 - , BF 2 C 2 O 4 - , BC 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 9SO 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 - , CF 3 (CF 2 ) 7SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - and (CF 3 CF 2 SO 2 ) 2 N - One selected from the group consisting of or a mixture of two or more may be used as needed. have. [41] 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 [42] 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. [43] [44] (2) organic solvents [45] As the organic solvent, various organic solvents commonly used in electrolytes for lithium secondary batteries 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. [46] The cyclic carbonate-based organic solvent is, for example, ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene any one selected from the group consisting of carbonate, 2,3-pentylene carbonate, vinylene carbonate, difluoroethylene carbonate (DFFC), and fluoroethylene carbonate (FEC), or a mixture of two or more thereof. [47] In addition, the linear carbonate-based organic solvent may include, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate. Any one selected from the group consisting of, or a mixture of two or more thereof may be mentioned. [48] In addition, the organic solvent may be used by further mixing an ether organic solvent, an ester organic solvent, an amide organic solvent, and the like, if necessary. [49] In addition, the ether organic solvent may include 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, The present invention is not limited thereto. [50] The ester organic solvent may be a linear ester such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate or butyl propionate; and any one selected from the group consisting of cyclic esters such as γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone, or a mixture of two or more thereof. However, the present invention is not limited thereto. [51] [52] (3) additives [53] The electrolyte for a lithium secondary battery according to the present invention may include a compound represented by the following Chemical Formula 1 as an additive. [54] [Formula 1] [55] [56] In Formula 1, R 1 and R 2 are each independently an alkyl group having 1 to 3 carbon atoms. [57] [58] During the charging/discharging process of the battery, the electrolyte decomposition reaction occurs on the surface of the electrode. This electrolyte reduction and decomposition product forms a film on the electrode surface to suppress the movement of electrons required for the electrode-electrolyte reaction, thereby further decomposing the electrolyte. suppress the reaction. In general, the film formed on the cathode is defined as a solid-electrolyte interphase (SEI), and the film formed on the anode is defined as a passivation film. At this time, depending on the type of additive added to the electrolyte, the type of the decomposition reaction product of the electrolyte may vary, and accordingly, the component of the film formed may also vary. [59] The compound represented by Formula 1 included as the electrolyte additive may form a film containing boron and sulfur on the electrode by decomposition of the electrolyte during charging and discharging of the battery. As such, when a film containing boron and sulfur is formed on the electrode, the passivation ability is improved, and the lifespan and resistance characteristics of the battery are improved compared to the film formed when an electrolyte composed only of an organic solvent and lithium salt is used. can be improved. [60] In addition, the components (eg, organic solvent components) included in the compound represented by Formula 1 and/or the electrolyte are decomposed together, and the decomposition products are combined with each other to form a polymer, and the polymer is formed within the film. may be included. As a result, a more stable and firm film can be formed. [61] The alkyl group (R 1 and/or R 2 ) substituted for the sulfur atom (S) of the compound of Formula 1 is a factor affecting the size of the polymer included in the film, and when the alkyl group has 1 to 3 carbon atoms, Resistance characteristics can be further improved. [62] For example, in Formula 1, R 1 and R 2 are each independently -CH 3 , -C 2 H 5 , -C 3 H 7 , and -CH(CH 3 ) 2 To be selected from the group consisting of can [63] As a more specific example, the compound represented by Formula 1 may be selected from the group consisting of compounds represented by Formulas 1A to 1J. [64] [Formula 1A] [65] [66] [67] [Formula 1B] [68] [69] [70] [Formula 1C] [71] [72] [73] [Formula 1D] [74] [75] [76] [Formula 1E] [77] [78] [79] [Formula 1F] [80] [81] [82] [Formula 1G] [83] [84] [85] [Formula 1H] [86] [87] [88] [Formula 1I] [89] [90] [91] [Formula 1J] [92] [93] [94] On the other hand, the compound represented by Formula 1 is included in an amount of 0.1 parts by weight to 2 parts by weight, preferably 0.3 parts by weight to 2 parts by weight, more preferably 0.3 parts by weight to 1 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery. can When the compound represented by Formula 1 is included in excess of the above range, side reactions with other compounds included in the electrolyte may occur due to the residue that does not participate in the film formation reaction. In addition, when included below the above range, boron and sulfur are not sufficiently included on the electrode surface, so that the lifespan characteristics and resistance characteristics of the battery cannot be significantly improved. [95] [96] (4) additional additives [97] The electrolyte for a lithium secondary battery of the present invention does not significantly increase the initial resistance, and forms a stable film on the surfaces of the negative electrode and the positive electrode, suppresses the decomposition of the solvent in the non-aqueous electrolyte, and serves as a complement to improve the mobility of lithium ions. Compounds that may be used may be further included as additional additives. [98] These additional additives include, for example, a vinyl silane-based compound, a phosphate or a phosphite-based compound, a sulfite-based compound, a sulfone-based compound, a sulfate-based compound, a sultone-based compound, a halogen-substituted carbonate-based compound, a nitrile-based compound, and a borate It may further include one or more compounds selected from the group consisting of compound, and lithium salt compound. [99] The vinyl silane compound may be electrochemically reduced on the surface of the negative electrode to form a stable film, thereby improving battery durability. More specifically, the vinyl silane-based compound may include tetravinyl silane and the like. [100] The phosphate or phosphite-based compound is a component that is electrochemically decomposed on the surfaces of the positive electrode and the negative electrode to help form a film, and can improve the lifespan characteristics of the secondary battery. More specifically, lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethyl silyl phosphate (TMSPa), trimethyl silyl phosphite (TMSPi), tris(2,2,2-trifluoro and at least one compound selected from the group consisting of ethyl) phosphate (TFEPa) and tris (trifluoroethyl) phosphite (TFEPi). [101] The sulfite-based compound is ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfite at least one compound selected from the group consisting of phite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, and 1,3-butylene glycol sulfite may include [102] The sulfone-based compound may include at least one compound selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methylethyl sulfone, and methylvinyl sulfone. [103] The sulfate-based compound may include at least one compound selected from the group consisting of ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS). . [104] The sultone-based compound is 1,3-propane sultone (PS), 1,4-butane sultone, ethenesultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1; at least one compound selected from the group consisting of 3-propene sultone. [105] As the halogen-substituted carbonate-based compound, fluoroethylene carbonate (FEC)) may be included. [106] In addition, the nitrile-based compound is succinonitrile (SN), adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptannitrile, cyclopentane carbonitrile, cyclohexane Carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile It may include one or more compounds selected from the group consisting of. [107] The borate-based compound may include lithium oxalyldifluoroborate and the like. [108] 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 ). It may include one or more compounds. [109] The additional additive may be included in an amount of 20 parts by weight or less, preferably 10 parts by weight or less, based on 100 parts by weight of the electrolyte for a lithium secondary battery. If the content of the additives exceeds the above range, side reactions in the electrolyte may excessively occur during charging and discharging, and may not be sufficiently decomposed at high temperatures, and may exist as unreacted or precipitated substances in the non-aqueous electrolyte, and thus the lifespan of the secondary battery Alternatively, the resistance characteristic may be deteriorated. [110] [111] [112] Next, a lithium secondary battery according to the present invention will be described. [113] A lithium secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and an electrolyte for the lithium secondary battery, and optionally includes a separator interposed between the positive electrode and the negative electrode. In this case, since the electrolyte for a lithium secondary battery is the same as the above-described content, a detailed description thereof will be omitted. [114] [115] (1) Anode [116] The positive electrode may be prepared by coating a positive electrode active material slurry including a positive electrode active material, a binder for an electrode, a conductive material for an electrode, a solvent, and the like on a positive electrode current collector. [117] 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. In this case, the positive electrode current collector may form fine irregularities on the surface to strengthen the bonding force of the positive electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body. [118] The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically includes a lithium composite metal oxide including lithium and one or more metals such as cobalt, manganese, nickel, aluminum or iron. can do. [119] More specifically, the lithium composite metal oxide is a lithium-iron-based oxide having an olivine structure (as a specific example, LiFePO 4 ), a lithium-manganese oxide (eg, LiMnO 2 , LiMn 2 O 4 , etc.), lithium- Cobalt-based oxide (eg, LiCoO 2 , etc.), lithium-nickel-based oxide (eg, LiNiO 2 , etc.), lithium-nickel-manganese-based oxide (eg, LiNi 1-Y1 Mn Y1 O 2 (here where 0