[One]Cross-Citation with Related Application(s) [2] This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0051437 dated May 02, 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 and a lithium secondary battery including the same, and more particularly, to an electrolyte for a lithium secondary battery capable of improving lifespan characteristics and capacity characteristics even under high voltage driving, and to a lithium secondary battery including the same. background [6] Lithium secondary batteries are used not only as portable power sources for mobile phones, notebook computers, digital cameras and camcorders, but also as power tools, electric bicycles, hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles. Its application is rapidly expanding to medium and large power sources such as HEVs and PHEVs). The external shape and size of the battery are also changing in various ways according to the expansion of the application field and the increase in demand, and better performance and stability than the characteristics required for the existing small battery are required. A lithium secondary battery is manufactured by using a material capable of inserting and deintercalating lithium ions as anode and anode, installing a porous separator between the two electrodes, and then injecting a liquid electrolyte, and inserting and deintercalating lithium ions in the cathode and cathode Electricity is generated or consumed by redox reactions following desorption. [7] Meanwhile, the demand for high energy density of lithium secondary batteries is increasing with the recent expansion of application fields. In order to achieve this, it is necessary to drive the lithium secondary battery under high voltage. However, there is a problem in that the surface of the anode is damaged by the oxidative decomposition reaction of the anode under high voltage, and transition metal ions in the anode are eluted. At this time, the eluted transition metal ions are reduced on the surface of the negative electrode to generate dendrites on the surface of the negative electrode, thereby accelerating performance degradation of the lithium secondary battery. [8] Accordingly, there is a demand for development of an electrolyte for a lithium secondary battery capable of controlling the elution of positive transition metal ions by suppressing the oxidative decomposition reaction of the positive electrode even when the lithium secondary battery is driven under a high voltage. [9] Prior art literature [10] International Patent Publication No. 2018/073694 DETAILED DESCRIPTION OF THE INVENTION technical challenge [11] The present invention is to solve the above problems, even when driving a lithium secondary battery under high voltage and high temperature conditions, it is possible to minimize the decomposition reaction on the surface of the positive electrode, thereby suppressing the elution of transition metal ions in the positive electrode. To provide an electrolyte for a lithium secondary battery and a lithium secondary battery including the same. means of solving the problem [12] According to one embodiment, the present invention is a lithium salt; organic solvents; and a cyanosilane-based compound, wherein the cyanosilane-based compound provides an electrolyte for at least one lithium secondary battery selected from the group consisting of a compound represented by Formula 1 to a compound represented by Formula 3 below. [13] [Formula 1] [14] [15] In Formula 1, R 1 is selected from the group consisting of hydrogen, a cyano group, and an alkyl group having 1 to 5 carbon atoms. [16] [17] [Formula 2] [18] [19] In Formula 2, R 2 and R 3 are each independently a direct bond or an alkylene group having 1 to 3 carbon atoms, and at least one of R 2 and R 3 is an alkylene group having 1 to 3 carbon atoms. [20] [21] [Formula 3] [22] [23] In Formula 3, R 4 is a direct bond, carbon, or an alkenyl group having 2 to 5 carbon atoms. [24] [25] According to another embodiment, the present invention provides a positive electrode; cathode; and an electrolyte for the lithium secondary battery. Effects of the Invention [26] The electrolyte for a lithium secondary battery according to the present invention minimizes the oxidative decomposition reaction that occurs on the surface of the positive electrode even when the lithium secondary battery is driven under high voltage and suppresses the elution of transition metal ions in the positive electrode, thereby improving battery energy density , it is possible to improve the capacity characteristics and safety of the lithium secondary battery. 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] According to one embodiment, the present invention is a lithium salt; organic solvents; and a cyanosilane-based compound, wherein the cyanosilane-based compound provides an electrolyte for at least one lithium secondary battery selected from the group consisting of a compound represented by Formula 1 to a compound represented by Formula 3 below. [34] [35] (1) lithium salt [36] First, the lithium salt will be described. [37] The lithium salt is used as a medium for transferring ions in the lithium secondary battery. Typically, the lithium salt is LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , CF 3 SO 3 Li, LiC(CF ) 3 SO 2 ) 3 , LiC 4 BO 8 , LiTFSI, LiFSI and LiClO 4It may include at least one compound selected from the group consisting of. [38] In this case, the lithium salt is preferably contained in the electrolyte for a lithium secondary battery at a concentration of 0.1M to 3M, preferably 0.5M to 2.5M, more preferably, 0.5M to 2M concentration. When the lithium salt is included in the above range, while minimizing by-products generated by dissolution in the electrolyte, when the battery is driven under high voltage, the SEI (Solid Electrolyte Interphase, SEI) film formed on the electrode interface is prevented from being decomposed from decomposing the battery It can prevent my resistance from rising. [39] [40] (2) organic solvents [41] Next, the organic solvent will be described. [42] In the present invention, the organic solvent is a solvent commonly used in lithium secondary batteries, for example, an ether compound, an ester (Acetate, Propionate) compound, an amide compound, a linear carbonate or a cyclic carbonate compound, a nitrile compound, etc. alone or a mixture of two or more. [43] Among them, a carbonate-based electrolyte solvent including a carbonate compound that is a cyclic carbonate, a linear carbonate, or a mixture thereof may be typically used. [44] Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene There is a single compound or a mixture of at least two or more selected from the group consisting of carbonate, vinylene carbonate, and halides thereof. In addition, specific examples of the linear carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC) and ethylpropyl carbonate (EPC) A compound selected from the group consisting of or a mixture of at least two or more may be representatively used, but the present invention is not limited thereto. [45] In particular, among the carbonate-based electrolyte solvents, propylene carbonate and ethylene carbonate, which are cyclic carbonates, are highly viscous organic solvents and have a high dielectric constant and thus well dissociate lithium salts in the electrolyte. Alternatively, when a low-viscosity, low-dielectric constant linear carbonate such as dimethyl carbonate is mixed in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and thus it can be used more preferably. [46] In addition, esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, and δ-valerolactone. and a single compound or a mixture of at least two or more selected from the group consisting of ε-caprolactone, but is not limited thereto. [47] [48] (3) cyano silane compound [49] Next, a cyanosilane-based compound will be described. [50] The cyanosilane-based compound includes at least one cyanosilane-based compound selected from the group consisting of compounds represented by the following Chemical Formula 1 to the compounds represented by Chemical Formula 3 below. [51] [Formula 1] [52] [53] In Formula 1, R 1 is selected from the group consisting of hydrogen, a cyano group, and an alkyl group having 1 to 5 carbon atoms. [54] [55] [Formula 2] [56] [57] In Formula 2, R 2 and R 3 are each independently a direct bond or an alkylene group having 1 to 3 carbon atoms, and at least one of R 2 and R 3 is an alkylene group having 1 to 3 carbon atoms. [58] [59] [Formula 3] [60] [61] In Formula 3, R 4 is a direct bond, carbon, or an alkenyl group having 2 to 5 carbon atoms. [62] Specifically, the cyano silane-based compound may include a compound represented by Formula 1 above. [63] [64] On the other hand, in the case of the compound represented by Formula 1 to the cyanosilane-based compound represented by Formula 3, it contains three or more cyano groups (CN). Since the cyano group is an electron withdrawing group having a high dipole moment, a cyano group When three or more are included in one compound, they strongly bind to the transition metal exposed on the surface of the electrode active material. In particular, a protective film is formed on the surface of the anode by the bonding, thereby suppressing a side reaction between the cathode and the electrolyte. In addition, when transition metal ions are eluted from the positive electrode active material under high voltage, the transition metal ions and the cyanosilane-based compound react preferentially to suppress reduction of transition metal ions on the surface of the negative electrode. [65] On the other hand, when a cyano group is attached to the silicon element (Si), the reactivity with the transition metal ion is further increased due to the abundant electrons of the silicon atom, and thus it is possible to effectively suppress the suppression of the elution of the transition metal ion. [66] [67] Specifically, in Formula 1, R 1 may be selected from the group consisting of hydrogen, a cyano group, and an alkyl group having 1 to 4 carbon atoms. In addition, in Formula 1, R 1 may be selected from the group consisting of hydrogen, a cyano group, -CH 3 , -CH 2 CH 3 , -CH(CH 3 ) 2 and -C(CH 3 ) 3 . [68] More specifically, the cyanosilane-based compound represented by Chemical Formula 1 may include at least one cyanosilane-based compound selected from the group consisting of compounds represented by the following Chemical Formulas 1-1 to 1-3. have. [69] [Formula 1-1] [70] [71] [72] [Formula 1-2] [73] [74] [75] [Formula 1-3] [76] [77] [78] Meanwhile, the cyanosilane-based compound represented by Formula 2 may include at least one cyanosilane-based compound selected from the group consisting of compounds represented by Formulas 2-1 to 2-4. [79] [Formula 2-1] [80] [81] [82] [Formula 2-2] [83] [84] [85] [Formula 2-3] [86] [87] [88] [Formula 2-4] [89] [90] [91] Meanwhile, the cyanosilane-based compound represented by Chemical Formula 3 may include one or more cyanosilane-based compounds selected from the group consisting of cyanosilane-based compounds represented by the following Chemical Formulas 3-1 to 3-3. [92] [Formula 3-1] [93] [94] [95] [Formula 3-2] [96] [97] [98] [Formula 3-3] [99] [100] [101] The cyano silane compound may be included in an amount of 0.1 parts by weight to 10 parts by weight, preferably 0.5 parts by weight to 5 parts by weight, more preferably 1 part by weight to 4 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery. . When the cyanosilane-based compound is included within the above range, it is possible to effectively suppress the elution of transition metal ions while minimizing the increase in resistance in the battery. [102] [103] (4) other additives [104] On the other hand, the electrolyte for a lithium secondary battery according to an embodiment of the present invention forms a stable film on the surface of the negative electrode and the positive electrode without significantly increasing the initial resistance in addition to the effect expressed by the cyanosilane-based compound, or for a lithium secondary battery It may further include other additives capable of inhibiting the decomposition of the solvent in the electrolyte and serving as a complement to improve the mobility of lithium ions. [105] These other additives are not particularly limited as long as they are additives capable of forming a stable film on the surfaces of the positive and negative electrodes. Representative examples thereof include vinylene carbonate-based compounds, phosphate-based compounds, phosphite-based compounds, sulfite-based compounds, sulfone-based compounds, sulfate-based compounds, sultone-based compounds, halogen-substituted carbonate-based compounds, nitrile-based compounds, borate-based compounds, and at least one selected from the group consisting of lithium salt-based compounds. [106] The vinylene carbonate-based compound is a component that is electrochemically decomposed on the surface of the positive electrode and the negative electrode to help form the SEI film, and through this, it is possible to implement the effect of improving the long-term cycle life characteristics of the secondary battery. Representative examples of this compound may be vinylene carbonate (VC) and vinyl ethylene carbonate (VEC). [107] The phosphate-based compound is electrochemically decomposed on the surface of the positive electrode and the negative electrode to help form the SEI film, and through this, it is possible to implement the effect of improving the long-term cycle life characteristics of the secondary battery. Representative examples of such phosphate-based compounds include lithium difluoro (bisoxalato) phosphate, lithium difluorophosphate, tetramethyl trimethyl silyl phosphate (TMSPa), and tris (2,2,2-trifluoroethyl) phosphate. and at least one compound selected from the group consisting of (TFEPa). [108] The phosphite-based compound is electrochemically decomposed on the surface of the anode and the cathode to help form an SEI film, and typical examples thereof include trimethyl silyl phosphite (TMSPi) or tris (trifluoroethyl) phosphite (TFEPi). can be heard [109] 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 can be [110] The sulfone-based compound may be at least one compound selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methylethyl sulfone, and methylvinyl sulfone. [111] The sulfate-based compound may be ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS). [112] 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; It may be at least one compound selected from the group consisting of 3-propene sultone. [113] The halogen-substituted carbonate-based compound may be fluoroethylene carbonate (FEC). [114] 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 be at least one compound selected from the group consisting of. [115] The borate-based compound may include LiBOB (lithium bisoxalatoborate (LiB(C 2 O 4 ) 2 ) or lithium oxalyldifluoroborate. [116] 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 LiPO 2 F 2 and LiBF 4 . [117] On the other hand, as other additives, the compounds listed above may be included alone or in mixture of two or more types. Specifically, the total additive content of the cyano silane compound and the other additives is 20 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery. It may be included in an amount of not more than 10 parts by weight, specifically, not more than 10 parts by weight. If the total additive content of the additive and other additives exceeds 20 parts by weight, side reactions in the electrolyte may excessively occur during charging and discharging of the battery, and additives that are not sufficiently decomposed at high temperature are present or precipitated unreacted, resulting in lithium secondary By increasing the initial resistance of the battery, the lifespan characteristics of the battery may be deteriorated. [118] [119] [120] Next, a lithium secondary battery according to the present invention will be described. [121] The 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 may further include a separator that can be selectively interposed between the positive electrode and the negative electrode. At this time, since the electrolyte for the lithium secondary battery is the same as the above-described content, a detailed description thereof will be omitted. [122] [123] Meanwhile, the driving voltage of the lithium secondary battery according to the present invention is 4 V to 5 V, preferably 4.2 V to 5 V, and more preferably 4.3 V to 5 V. When the driving voltage range of the lithium secondary battery is within the above range, the capacity available to the positive electrode is maximized to increase the capacity of the lithium secondary battery, thereby improving the energy density. Even when the driving voltage is within the above range, since the lithium secondary battery according to the present invention uses an electrolyte for a lithium secondary battery containing the cyanosilane-based compound represented by Chemical Formulas 1 to 3, the positive electrode is caused by the high dipole moment of the compound. By strongly bonding with the transition metal on the surface to form a film on the surface of the anode, side reactions between the anode and the electrolyte can be minimized. In addition, transition metal ions are easily eluted from the anode during high voltage driving, and the transition metal ions and the cyanosilane-based compound react preferentially to suppress the reduction of the transition metal ions on the surface of the anode, so capacity reduction and It can contribute to the minimization of precipitation and side reactions. [124] [125] 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. [126] 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. [127] The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium composite metal oxide including lithium and one or more metals such as cobalt, manganese, nickel or aluminum. have. 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-Y1 Mn Y1 O 2 (here, 0