Cross-Citation with Related Application(s) [2] This application claims the benefit of priority based on Korean Patent Application No. 2018-0160981 dated December 13, 2018 and Korean Patent Application No. 2019-0164881 dated December 11, 2019, and all The content is incorporated 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 having improved high temperature performance and fast charging performance, and 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. In order to meet these demands, the battery components must stably realize the performance of the battery under the condition that a large current flows. [7] A lithium secondary battery is manufactured by using a material capable of intercalating and deintercalating lithium ions as a negative electrode and a positive electrode, optionally including a separator between the two electrodes, and placing an electrolyte between both electrodes, and lithium in the negative electrode and the positive electrode Electricity is generated or consumed by redox reactions according to the insertion and desorption of ions. [8] On the other hand, with the recent expansion of application fields, the utility and importance of lithium secondary batteries are gradually increasing, and in particular, the need for R&D for rapid charging while excellent high-temperature performance of lithium secondary batteries is emerging. However, in the case of shortening the charging time of the currently commercialized lithium secondary battery, the capacity and lifespan characteristics of the battery are deteriorated, making it difficult to commercialize. Limitations exist. [9] Therefore, it is necessary to study an electrolyte for a lithium secondary battery with improved fast charging performance so that the charging time can be shortened while maintaining the high-temperature capacity performance and output performance of the existing lithium secondary battery. [10] Prior art literature [11] Korean Patent Publication No. 10-2016-0040127 DETAILED DESCRIPTION OF THE INVENTION technical challenge [12] An object of the present invention is to provide an electrolyte for a lithium secondary battery having excellent high-temperature performance and improved fast charging performance of a lithium secondary battery, and a lithium secondary battery including the same in order to solve the above problems. means of solving the problem [13] In one aspect, the present invention is a lithium salt having a molar concentration of 1.5 M to 2.0M; an oligomer including a unit represented by the following formula (1) and including an acrylate group at the terminal; A first additive represented by the following formula (2); and an organic solvent; provides an electrolyte for a lithium secondary battery comprising. [14] [Formula 1] [15] [16] In Formula 1, Ra, Rb, Rc and Rd are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms unsubstituted or substituted with an element fluorine, and p is an integer of 1 to 50. [17] [Formula 2] [18] [19] In Formula 2, R 1 to R 4 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms. [20] [21] In addition, the present invention provides a lithium secondary battery comprising the electrolyte for a lithium secondary battery of the present invention. Effects of the Invention [22] The electrolyte for a lithium secondary battery according to the present invention has excellent high-temperature performance, and contains specific oligomers and additives, so that the rapid charging performance of the battery can also be improved. Best mode for carrying out the invention [23] Hereinafter, the present invention will be described in more detail. [24] 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. It should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention based on the principle that there is. [25] 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. [26] In this specification, terms such as "comprises", "comprises" 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 the presence or addition of numbers, steps, elements, or combinations thereof does not preclude in advance the possibility of addition. [27] In the present specification, the weight average molecular weight may mean a value converted to standard polystyrene measured by gel permeation chromatography (GPC), and unless otherwise specified, the molecular weight may mean a weight average molecular weight. can For example, in the present invention, the measurement is performed using Agilent's 1200 series under GPC conditions, and the column used at this time may be an Agilent's PL mixed B column, and the solvent may be THF. [28] [29] Electrolyte for Lithium Secondary Battery [30] The present invention is a lithium salt having a molar concentration of 1.5 M to 2.0M; an oligomer including a unit represented by the following formula (1) and including an acrylate group at the terminal; A first additive represented by the following formula (2); and an organic solvent; provides an electrolyte for a lithium secondary battery comprising. [31] [Formula 1] [32] [33] In Formula 1, Ra, Rb, Rc and Rd are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms unsubstituted or substituted with an element fluorine, and p is an integer of 1 to 50. [34] [35] [Formula 2] [36] [37] In Formula 2, R 1 to R 4 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms. [38] [39] (1) lithium salt [40] The lithium salt may be included in the electrolyte for a lithium secondary battery in a molar concentration of 1.5 M to 2.0 M, preferably 1.5 M to 1.9 M, more preferably 1.5 M to 1.8 M. [41] When the lithium salt is included within the molar concentration range, lithium ions may be sufficiently supplied, so that a lithium ion yield (Li+ transference number) and a degree of dissociation of lithium ions may be improved, thereby improving output characteristics of the battery. [42] The lithium salt is a compound that can provide a lithium ion can be used without particular limitation, and specifically Li as the cation used in the lithium secondary battery + as an anion contains, F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , AlO 4 - , 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 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 - , 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 - One selected from the group consisting of or a mixture of two or more may be used as needed. [43] Specifically, the lithium salt may include LiPF 6 and lithium imide salt. [44] In this case, the lithium imide salt may be at least one selected from the group consisting of Li(CF 3 SO 2 ) 2 N, Li(FSO 2 ) 2 N, and Li(CF 3 CF 2 SO 2 ) 2 N. [45] On the other hand, when the lithium salt includes LiPF 6 and a lithium imide salt, the LiPF 6 and the lithium imide salt are 1:1 to 1:5, preferably 1:1 to 1:4, more preferably 1: It may be mixed in a molar ratio of 1 to 1:3. When the two types of salts are mixed in the molar ratio, corrosion in the battery caused by the electrolyte can be minimized, and the output characteristics of the battery can be improved. [46] [47] (2) oligomers [48] The electrolyte for a lithium secondary battery of the present invention includes a unit represented by the following formula (1), and includes an oligomer including an acrylate at the terminal. [49] [Formula 1] [50] [51] In Formula 1, [52] Wherein Ra, Rb, Rc and Rd are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms substituted or unsubstituted with an elemental fluorine, and p is an integer of 1 to 50. [53] Since the oligomer including the unit represented by Formula 1 and including an acrylate group at the terminal contains an ethylene group substituted with a fluorine element having low reactivity with lithium ions, a side reaction of lithium ions and lithium salts It is possible to control the decomposition reaction and the like, and it is possible to suppress side reactions occurring when a high concentration of lithium salt is used. In addition, since the oligomer contains elemental fluorine having excellent flame retardancy, when an electrolyte including the oligomer is used, heat generation and ignition of the lithium secondary battery are suppressed, and high temperature safety can be improved. [54] On the other hand, since the oligomer includes a hydrophobic unit containing a fluorine element and a hydrophilic acrylate group at the end, it serves as a surfactant to lower the surface resistance with the electrode interface, and a lithium secondary battery of the wetting effect (wetting) can be improved. [55] Specifically, the oligomer may be an oligomer represented by the following Chemical Formula 1A. [56] [Formula 1A] [57] [58] In Formula 1A, [59] Wherein Ra, Rb, Rc and Rd are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms unsubstituted or substituted with an elemental fluorine, Re is an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and Rf is a fluorine element substituted or an unsubstituted alkylene group having 1 to 5 carbon atoms, R' is hydrogen or an alkyl group having 1 to 3 carbon atoms, o is an integer from 1 to 3, p is an integer from 1 to 50, and q is 1 It is an integer from 15 to 15. In this case, p may be an integer of preferably 1 to 45, more preferably an integer of 1 to 40. [60] In the oligomer represented by Formula 1A, the aliphatic hydrocarbon group includes an alicyclic hydrocarbon group or a linear hydrocarbon group. [61] The alicyclic hydrocarbon group is a substituted or unsubstituted cycloalkylene group having 4 to 20 carbon atoms; a substituted or unsubstituted C4-C20 cycloalkylene group containing an isocyanate group (NCO); a substituted or unsubstituted C4-C20 cycloalkenylene group; And it may include at least one selected from the group consisting of a substituted or unsubstituted heterocycloalkylene group having 2 to 20 carbon atoms. [62] The linear hydrocarbon group is a substituted or unsubstituted C 1 to C 20 alkylene group; A substituted or unsubstituted C1-C20 alkylene group containing an isocyanate group (NCO); A substituted or unsubstituted C1-C20 alkoxyl group; a substituted or unsubstituted alkenylene group having 2 to 20 carbon atoms; and at least one selected from the group consisting of a substituted or unsubstituted alkynylene group having 2 to 20 carbon atoms. [63] In addition, in the oligomer represented by Formula 1A, the aromatic hydrocarbon group may be a substituted or unsubstituted C 6 to C 20 arylene group; Or it may include a substituted or unsubstituted heteroarylene group having 2 to 20 carbon atoms. [64] As a specific example, the oligomer represented by Formula 1A may be an oligomer represented by Formula 1A-1. [65] [Formula 1A-1] [66] [67] In Formula 1A-1, p is an integer from 1 to 50, and q is an integer from 1 to 15. The p may be an integer of preferably 1 to 45, more preferably an integer of 1 to 40. [68] [69] Alternatively, the oligomer may be an oligomer represented by the following Chemical Formula 1B. [70] [Formula 1B] [71] [72] In Formula 1B, wherein Ra, Rb, Rc and Rd are each independently a fluorine element or an alkyl group having 1 to 3 carbon atoms unsubstituted or substituted with an elemental fluorine element, and Re is an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and Rf is an alkylene group having 1 to 5 carbon atoms substituted or unsubstituted with a fluorine element, o' is an integer from 1 to 2, o" is an integer from 1 to 3, and p is an integer from 1 to 50, The q is an integer from 1 to 15. The p is preferably an integer from 1 to 45, more preferably an integer from 1 to 40. [73] [74] As a specific example, the oligomer represented by Formula 1B may be an oligomer represented by Formula 1B-1. [75] [Formula 1B-1] [76] [77] In Formula 1B-1, p is an integer from 1 to 50, and q is an integer from 1 to 15. In this case, p is preferably an integer of 1 to 45, more preferably an integer of 1 to 40. [78] Meanwhile, the weight average molecular weight (MW) of the oligomer may be controlled by the number of repeating units, and may be about 500 to 200,000, specifically 1,000 to 150,000, and more specifically 2,000 to 100,000. When the weight average molecular weight of the oligomer is within the above range, it has a high affinity with an organic solvent and can be well dispersed, can improve the wettability of the electrolyte by lowering the surface tension to a certain level or less, and suppress the decomposition reaction of the lithium salt and lithium ions can be prevented from causing side reactions. [79] In this case, the oligomer may be included in an amount of 0.1 part by weight to 1 part by weight, preferably 0.1 part by weight to 0.9 part by weight, more preferably 0.1 part by weight to 0.8 part by weight based on 100 parts by weight of the lithium secondary electrolyte. When the oligomer is included within the above range, it is possible to minimize the interfacial resistance in the battery by acting as a surfactant while maintaining the mobility and ionic conductivity of lithium ions above a certain level to suppress side reactions. [80] [81] (3) the first additive [82] Next, the first additive represented by the following formula (2) will be described. [83] [Formula 2] [84] [85] In Formula 2, R 1 to R 4 are each independently selected from the group consisting of hydrogen and a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms. [86] In the case of the first additive represented by Chemical Formula 2, the lowest unoccupied molecular orbita (LUMO), which is the lowest energy orbital among molecular orbitals that do not contain electrons, is low, so the reduction decomposition at the cathode is fast, and the carbon-carbon triple bond is eliminated. A propargyl group including a propargyl group forms a SEI (Solid Electrolyte Interphase) film on the surface of the anode to prevent metal ions eluted from the cathode active material from adhering to the anode, thereby improving the performance of the battery. . [87] As a specific example, the first additive may be represented by the following Chemical Formula 2A. [88] [Formula 2A] [89] [90] [91] Meanwhile, the first additive may be included in an amount of 0.1 part by weight to 1 part by weight, preferably 0.1 part by weight to 0.8 part by weight, more preferably 0.1 part by weight to 0.6 part by weight based on 100 parts by weight of the lithium secondary electrolyte. When the first additive is included within the above range, it is possible to stably form an SEI film on the surface of the negative electrode while minimizing the increase in resistance, and to prevent metal ions eluted from the positive electrode active material from adhering to the negative electrode. [92] [93] (4) organic solvents [94] Next, the organic solvent will be described. [95] As the organic solvent, those commonly used in electrolytes for lithium secondary batteries may be used without limitation. For example, a cyclic carbonate compound, a linear carbonate compound, an ether compound, an ester compound, or an amide compound may be used alone or in combination of two or more. [96] 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, There is any one selected from the group consisting of 2,3-pentylene carbonate, vinylene carbonate and fluoroethylene carbonate (FEC), or a mixture of two or more thereof. [97] In addition, as a specific example of the linear carbonate compound, dimethyl carbonate (DMC) may be used. As a linear carbonate compound, there are ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate in addition to dimethyl carbonate, but in the case of dimethyl carbonate, the molecular size is small compared to other linear carbonate compounds and has a low viscosity characteristic. , it is possible to further improve the ionic conductivity of the electrolyte than when other linear carbonate compounds are used. [98] In particular, as a high-viscosity organic solvent among the carbonate-based organic solvents, a cyclic carbonate such as ethylene carbonate, which is known to well dissociate lithium salts in an electrolyte due to a high dielectric constant, may be used. If the dielectric constant linear carbonate is mixed in an appropriate ratio and used, an electrolyte having high electrical conductivity can be prepared. [99] In addition, as the ether compound, 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, but It is not limited. [100] Examples of the ester compound include linear esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and 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. [101] [102] (5) second additive [103] Meanwhile, the electrolyte for a lithium secondary battery according to the present invention may further include a second additive. As a specific example of the second additive, vinylene carbonate (VC), 1,3-propanesultone (PS), ethylene sulfate ((Ethylene Sulfate; Esa), fluorinated benzene (FB) and LiBF 4 selected from the group consisting of In particular, when the above-listed compounds are used together as the second additive, a stable film can be formed on the positive electrode and the negative electrode at the same time. At this time, the film formed on the negative electrode , it is possible to suppress the decomposition of the electrolyte even under high-temperature and high-pressure conditions, as well as suppress the elution of transition metals contained in the positive electrode by the film formed on the positive electrode, thereby improving the high-temperature and high-pressure characteristics and stability of the battery. have. [104] In this case, the second additive may be included in an amount of 1 part by weight to 15 parts by weight, preferably 1 part by weight to 12 parts by weight, more preferably 1 part by weight to 11 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery. . When the second additive is included within the above range, it is possible to stably form a film on the electrode and suppress the ignition phenomenon during overcharging, but side reactions may occur during the initial activation process of the secondary battery, or the additive may remain or precipitate. it can be prevented [105] [106] lithium secondary battery [107] Next, a lithium secondary battery according to the present invention will be described. [108] A lithium secondary battery according to an embodiment of the present invention includes at least one positive electrode, at least one negative electrode, a separator selectively interposed between the positive electrode and the negative electrode, and an electrolyte for the lithium secondary battery. At this time, since the electrolyte for the lithium secondary battery is the same as the above description, a detailed description thereof will be omitted. [109] [110] (1) Anode [111] The positive electrode may be prepared by coating a positive electrode active material slurry including a positive electrode active material, an electrode binder, an electrode conductive material, and a solvent on a positive electrode current collector. [112] 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, and the like. [113] 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