Title of the invention: Electrolyte for lithium secondary battery and lithium secondary battery including the same Technical field [One] Mutual citation with related applications [2] This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0067431 filed on June 12, 2018, and all contents disclosed in the documents of the Korean patent application are included as 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 that improves battery performance by suppressing side reactions by a lithium salt, and a lithium secondary battery including the same. . [6] Background [7] As personal IT devices and computer networks are developed due to the development of the information society, the overall society's dependence on electric energy increases, and there is a demand for technology development to efficiently store and utilize electric energy. [8] Among the technologies developed for this, the most suitable technology for various uses is the technology based on secondary batteries. In the case of a secondary battery, it can be miniaturized enough to be applied to personal IT devices, and it can be applied to electric vehicles and power storage devices. Among these secondary battery technologies, a lithium-ion battery, which is a battery system with the highest energy density in theory, is in the spotlight, and is currently applied to various devices. [9] In the case of lithium-ion battery systems, unlike the early days when lithium metal was directly applied to the system, transition metal oxide materials containing lithium are used as cathode materials, and carbon-based materials such as graphite and alloy-based materials such as silicon are used as anode materials. It is implemented as a system in which lithium metal is not directly used inside the battery, such as applying a material as a negative electrode. [10] In the case of such a lithium ion battery, a positive electrode composed of a transition metal oxide largely containing lithium, a negative electrode capable of storing lithium, an electrolytic solution serving as a medium for transferring lithium ions, and a separator are composed of the battery. As it is known as a constituent that has a great influence on stability and safety, many studies are being conducted on this. [11] In the case of an electrolyte for a lithium ion battery, it is composed of a lithium salt, an organic solvent that dissolves it, and a functional additive. In order to improve the electrochemical properties of the battery, proper selection of these components is important. Representative lithium salts currently used include LiPF 6 , LiBF 4 , LiFSI (lithium fluorosulfonyl imide, LiN(SO 2 F) 2 ), LiTFSI (lithium (bis)trifluoromethanesulfonyl imide, LiN(SO 2 CF 3 ) 2 ) or LiBOB ( Lithium bis(oxalate) borate and LiB(C 2 O 4 ) 2 ) are used, and in the case of an organic solvent, an ester-based organic solvent or an ether-based organic solvent is used. [12] In the case of such a lithium-ion battery, an increase in resistance and a decrease in capacity during charge/discharge or storage at high temperatures are suggested as major problems in performance degradation, and one of the causes of such problems is the degradation of electrolyte at high temperatures. It is a side reaction that occurs as a result of decomposition of salts at high temperatures. When the by-products of these salts decompose the film formed on the surface of the anode and the cathode after activation, there is a problem that the passivation ability of the film is degraded, and this causes additional decomposition of the electrolyte and the accompanying self-discharge. There is. [13] Among the electrode materials of lithium-ion batteries, especially for negative electrodes, graphite-based negative electrodes are used in most cases, and the operating potential of graphite-based negative electrodes is 0.3 V ( vs. Li/Li + ) or less, and the electricity of the electrolyte used in lithium-ion batteries. Lower than the chemical stability window, the currently used electrolyte is reduced and decomposed on the cathode. The electrolytic solution product decomposed by reduction in this way allows lithium ions to permeate, but forms a solid electrolyte interphase (SEI) film that can suppress further decomposition reactions of the electrolytic solution. [14] In this case, when the SEI film is incompletely formed and the further decomposition reaction of the electrolyte is not suppressed, the graphite-based negative electrode is self-discharged, and the potential of the entire battery may be lowered. [15] Therefore, in order to stably form and maintain the SEI film, an additive containing double or triple bonds that can better cause a reduction decomposition reaction is introduced, or decomposition products of lithium salts generated by heat/moisture in the battery are removed. Thus, it is possible to devise a method to suppress damage to the SEI membrane. [16] Meanwhile, one of the factors that damage the SEI film is a by-product generated by the decomposition reaction of lithium salts. For example, when LiPF 6 is used as a lithium salt , LiPF 6 is reduced and decomposed by heat/moisture in the battery, and by- products such as HF and PF 5 are formed, and the by-products act as Lewis acids, and the positive electrode It can react with the active material. At this time, the transition metal is eluted from the positive electrode active material, the battery capacity decreases, the resistance in the battery may increase, and the eluted transition metal is electrodeposited on the negative electrode to induce a chain electrolyte decomposition reaction. [17] Therefore, research on additives that can remove by-products generated by decomposition of lithium salts is urgent. [18] (Patent Document 1) Korean Patent Application Publication No. 10-2015-0114460 [19] Detailed description of the invention Technical challenge [20] The present invention provides an electrolyte for a lithium secondary battery and a lithium secondary battery with improved high temperature safety and capacity characteristics of a lithium secondary battery by suppressing side reactions caused by removing decomposition products of lithium salts to solve the above problems. It is to do. [21] Means of solving the task [22] In one aspect, the present invention provides an electrolyte for a lithium secondary battery including a lithium salt, an additive including a compound represented by the following Formula 1, and an organic solvent. [23] [Formula 1] [24] [25] In Formula 1, R is hydrogen, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, m is an integer of 0 to 2, and A is a hetero element selected from the group consisting of nitrogen, oxygen and sulfur elements It is a substituted or unsubstituted C 4 to C 6 hetero ring containing. [26] In this case, the compound represented by Formula 1 may be a compound represented by Formula 1-1 below. [27] [Formula 1-1] [28] [29] In Formula 1-1, R 1 and R 2 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and A is a group consisting of nitrogen, oxygen and sulfur elements It is a substituted or unsubstituted C 4 -C 6 hetero ring containing at least one hetero element selected from. [30] Meanwhile, A may include a nitrogen element as a hetero element. [31] In addition, A may further include an oxygen element as a hetero element. [32] In one embodiment, the compound represented by Formula 1 may be at least one selected from the group consisting of a compound represented by Formula 1-2 and a compound represented by 1-3. [33] [Formula 1-2] [34] [35] In Formula 1-2, R 3 and R 4 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms. [36] [Formula 1-3] [37] [38] In Formula 1-3, R 5 and R 6 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms. [39] In another embodiment, the compound represented by Formula 1 may be a compound represented by Formula 1-4 below. [40] [Formula 1-4] [41] [42] In Formula 1-4, R 7 and R 8 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms. [43] Meanwhile, the additive may be included in an amount of 0.1 to 3 parts by weight based on 100 parts by weight of the electrolyte for the lithium secondary battery. [44] The lithium salt may include at least one selected from the group consisting of LiPF 6 and LiBF 4 . [45] In another aspect, the present invention provides a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte for the lithium secondary battery. [46] Effects of the Invention [47] The electrolyte for a lithium secondary battery according to the present invention includes an additive capable of reacting with a decomposition by-product of a lithium salt, suppressing side reactions caused by a decomposition by-product of a lithium salt, thereby improving the self-discharge phenomenon due to the elution of the positive electrode active material, and By preventing an increase in resistance, high-temperature safety and capacity characteristics of the battery can be improved. [48] Brief description of the drawing [49] 1 is a graph showing an elution amount of a transition metal (Mn) eluted from a positive electrode active material after high temperature storage of a lithium secondary battery according to Experimental Example 1. [50] Best mode for carrying out the invention [51] Hereinafter, the present invention will be described in more detail. [52] The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of ​​the present invention based on the principle that there is. [53] The terms used in the present specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. [54] In the present specification, terms such as "comprises", "includes" or "have" are intended to designate the presence of implemented features, numbers, steps, components, or a combination thereof, and one or more other features or It is to be understood that the possibility of the presence or addition of numbers, steps, elements, or combinations thereof is not preliminarily excluded. [55] [56] [57] The electrolyte for a lithium secondary battery according to the present invention includes a lithium salt, an additive including a compound represented by the following Formula 1, and an organic solvent. [58] [59] Lithium salt [60] First, the lithium salt will be described. [61] The lithium salt is used as an electrolyte salt in a lithium secondary battery, and is used as a medium for transferring ions. Typically, the lithium salt is Li cation + to include, and the anion is 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 ) 2It may include at least one or more compounds selected from the group consisting of N. For a specific example, the lithium salt may include at least one selected from the group consisting of LiPF 6 and LiBF 4 , but is not limited thereto. [62] The lithium salt may be contained in a concentration of 0.1 M to 10.0 M , more preferably 0.5 M to 5.0 M, and further 1.0 M to 3.0 M with respect to the electrolyte for a lithium secondary battery . When the lithium salt is included within the above range, lithium ions in the electrolyte are dissociated to a certain level or more, so that the battery can be charged and discharged smoothly, and the viscosity of the battery can be maintained at a constant level. I can. [63] [64] additive [65] Next, the additive will be described. The additive includes a compound represented by the following formula (1). [66] [Formula 1] [67] [68] In Formula 1, R is hydrogen, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, m is an integer of 0 to 2, and A is a hetero element selected from the group consisting of nitrogen, oxygen and sulfur elements It is a substituted or unsubstituted C 4 to C 6 hetero ring containing. [69] The electrolyte for a lithium secondary battery uses a lithium salt for the conduction of lithium ions. Among lithium salts, lithium salts having a large anion size are mainly used to achieve a high transmission number of lithium ions and increase solubility. As examples of such anions are Hexafluorophosphate (PF 6 - ) or Tetrafluoroborate (BF 4 - to a representative like). However, when the lithium salt, is included in the electrolyte or be degraded by moisture, which is embedded in the electrode, can be a by-product, such as the HF generation, while decomposing at a high temperature PF 5 , or BF 3 as the Lewis acid by-products are degradation products, such as It can also be formed. [70] At this time, the decomposition product of the lithium salt causes a decomposition reaction of an organic solvent such as ethylene carbonate, which induces the deterioration of the electrolyte itself. There is a problem of deteriorating the performance of the battery by causing a reaction with the passivation film formed on the surface. [71] For example, when LiPF 6 is used as a lithium salt , PF 6 -which is an anion is thermally decomposed to generate PF 5 , and the following reaction may proceed in a chain. [72] [73] When the above reaction proceeds in a chain, decomposition reactions of organic solvents may be caused by by-products such as HF and PF 5 generated during the reaction. Can cause a serious side reaction. [74] In addition, by-products such as HF may react with a lithium transition metal oxide used as a cathode active material for a lithium secondary battery to elute transition metal ions. When the transition metal ions are eluted, the transition metal ions are electrodeposited on the negative electrode to destroy the SEI film formed on the surface of the negative electrode, and may involve an additional electrolyte decomposition reaction on the SEI film, further deteriorating the performance of the battery. . [75] At this time, the compound represented by Formula 1 acts as a Lewis base, and thus Lewis acid by-products such as HF or PF 5 may be removed. Therefore, when an electrolyte using the present additive is used, the battery performance can be improved by preventing an additional side reaction from occurring in a chain. [76] [77] In this case, A may include a nitrogen element as a hetero element, and A may further include an oxygen element as a hetero element. [78] As another embodiment, when A includes a nitrogen element as a hetero element, the nitrogen element may be positioned at a point where the hetero ring is connected. [79] Oxygen connected by a double bond to a cyclohexenol ring other than A of the compound represented by Chemical Formula 1 has a property of pushing electrons, and when a nitrogen atom is located at a point where it is connected to a double bond in the cyclohexenol ring , The nitrogen atom having an unshared electron pair can donate more electrons to the C=O functional group, thereby enhancing the nature of the C=O functional group as a Lewis base. Therefore, when A contains a nitrogen element as a hetero element, it is preferable that the nitrogen element is located at a point where the hetero ring is connected. [80] For example, the compound represented by Formula 1 may be a compound represented by Formula 1-1 below. [81] [Formula 1-1] [82] [83] In Formula 1-1, R 1 and R 2 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and A is a group consisting of nitrogen, oxygen and sulfur elements It is a substituted or unsubstituted C 4 -C 6 hetero ring containing at least one hetero element selected from. [84] For another example, the compound represented by Formula 1 may be one or more selected from the group consisting of a compound represented by Formula 1-2 and a compound represented by 1-3. [85] [Formula 1-2] [86] [87] In Formula 1-2, R 3 and R 4 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms. [88] [Formula 1-3] [89] [90] In Formula 1-3, R 5 and R 6 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms. [91] For another example, the compound represented by Formula 1 may be a compound represented by Formula 1-4 below. [92] [Formula 1-4] [93] [94] In Formula 1-4, R 7 and R 8 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms. [95] [96] Meanwhile, the additive may be included in an amount of 0.1 to 5 parts by weight, preferably 0.1 to 3 parts by weight, and more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the electrolyte for the lithium secondary battery. When the additive is included within the above range, deterioration of battery performance can be minimized by effectively removing by-products of lithium salts, and ionic conductivity in the electrolyte can be maintained at a certain level by minimizing an increase in viscosity. [97] [98] Organic solvent [99] Next, the organic solvent will be described. [100] In the present invention, the organic solvent is a solvent commonly used in lithium secondary batteries, for example, an ether compound, an ester compound, an amide compound, a linear carbonate or cyclic carbonate compound, a nitrile compound, etc. Can be used. [101] For example, as the cyclic carbonate compound, ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3- A single compound or a mixture of at least two or more selected from the group consisting of pentylene carbonate, vinylene carbonate, and halides thereof may be used. 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 or a mixture of at least two or more may be used. [102] In addition, the ester compounds include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone and ε -A single compound selected from the group consisting of caprolactone or a mixture of at least two or more can be used. [103] On the other hand, the electrolyte for a lithium secondary battery according to an embodiment of the present invention may optionally further contain other additives known in the art to implement such physical properties in order to impart an effect of reducing the resistance in the battery in addition to the above-described components. I can. As the other additives, for example, VC (Vinylene Carbonate), VEC (vinyl ethylene carbonate), Propane sultone, SN (succinonitrile), AdN (Adiponitrile), ESa (ethylene sulfate), PRS (Propene Sultone), FEC ( Fluoro Ethylene carbonate), LiPO 2 F 2 , LiODFB(Lithium difluoro(oxalate)borate), LiBOB(Lithium bis-(oxalato)borate), TMSPa(3-trimethoxysilanyl-propyl-N-aniline), TMSPi(Tris(trimethylsilyl)) Phosphite) and other additives may be used. [104] [105] [106] Next, a lithium secondary battery according to the present invention will be described. A lithium secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte for the lithium secondary battery. Meanwhile, since the electrolyte for a lithium secondary battery is the same as described above, a detailed description is omitted. [107] [108] The positive electrode may be prepared by coating a positive electrode active material slurry including a positive electrode active material, a binder, a conductive material, and a solvent on the positive electrode current collector. [109] The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , Nickel, titanium, silver, or the like may be used. [110] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium composite metal oxide containing lithium and at least one metal 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 oxide (eg, LiCoO 2, etc.), a lithium-nickel oxide (E.g., LiNiO 2 ), lithium-nickel-manganese oxide (e.g., LiNi 1-Y1 Mn Y1 O 2 (here, 0