Electrolyte for lithium secondary battery, and lithium secondary battery comprising same

Abstract

The present invention relates to: a lithium secondary battery electrolyte having excellent low-temperature and high-rate performance; and a lithium secondary battery comprising same. Specifically, the present invention relates to: a lithium secondary battery electrolyte capable of solving the problem of irreversible performance degradation, which occurs when batteries are operated at low temperature and charged at high speed, by solvent combination; and a lithium secondary battery that comprises same and thus can exhibit excellent negative electrode reversibility and capacity.

Description

Electrolyte for lithium secondary batteries and lithium secondary batteries including the same

[0001] The present invention relates to an electrolyte for a lithium secondary battery having excellent low-temperature and high-rate performance and a lithium secondary battery including the same. Specifically, the invention relates to an electrolyte for a lithium secondary battery capable of improving the low-temperature characteristics and rate characteristics of the battery by combining a solvent used in the electrolyte to increase the reversibility of lithium ions.

[0002] The applications of lithium-ion batteries are rapidly expanding, not only as portable power sources for mobile phones, laptop computers, digital cameras, and camcorders, but also as medium-to-large power sources for power tools, electric bicycles, hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). With this expansion of application fields, the demand for batteries capable of high-speed charging at room temperature and use in low-temperature environments below 0°C is also increasing.

[0003] Lithium-ion batteries generally use organic electrolytes, but these electrolytes exhibit reduced ion transportability and lithium-ion charge storage reversibility during room-temperature fast charging or in low-temperature environments. Consequently, lithium-ion batteries using organic electrolytes face the problem of insufficient capacity and performance degradation under room-temperature fast charging and low-temperature conditions.

[0004] Therefore, research is needed on electrolytes for lithium secondary batteries that can enhance ion transportability and lithium ion charge storage reversibility so that the battery can operate stably even under room temperature fast charging conditions and low temperature conditions.

[0005] The present invention is designed to solve the above problems, and the objective of the present invention is to provide an electrolyte for a lithium secondary battery capable of increasing the reversibility of lithium ions so that the lithium secondary battery can operate stably even under room temperature fast charging conditions and low temperature conditions, and a lithium secondary battery including the same.

[0006] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof described in the specification.

[0007] To solve the above problem, the present invention provides an electrolyte for a lithium secondary battery comprising a lithium salt and a mixed solvent, wherein the mixed solvent comprises: a first solvent comprising an ether-based solvent; a second solvent comprising an ether-based solvent substituted with an electron-withdrawing group or a substituent causing steric hindrance within the solvent molecule; and a third solvent comprising a sulfonamide-based solvent substituted with an electron-withdrawing group within the solvent molecule.

[0008] In one embodiment of the present invention, based on the total moles of the mixed solvent, the first solvent may be included in an amount of 20 mol% to 40 mol%, and the second solvent and the third solvent may each be included independently in an amount of 10 mol% to 70 mol%.

[0009] In one embodiment of the present invention, the first solvent is a high-coordinate solvent, and the second solvent and the third solvent are low-coordinate solvents, and the high-coordinate solvent and the low-coordinate solvent may be included in a molar ratio of 1:2 to 1:4.

[0010] In one embodiment of the present invention, the electron withdrawer substituted in the molecule of the low-coordinate solvent compound may be a halogen group.

[0011] In one embodiment of the present invention, the electron withdrawer substituted on the molecule of the low-coordination solvent compound may be one or more selected from the group consisting of a monofluoroalkyl group, a difluoroalkyl group, a trifluoroalkyl group, a monochloroalkyl group, a dichloroalkyl group, a trichloroalkyl group, a monofluoroalkyl sulfonyl group, a difluoroalkyl sulfonyl group, a trifluoroalkyl sulfonyl group, a monochloroalkyl sulfonyl group, a dichloroalkyl sulfonyl group, a monochloroalkyl sulfonyl group, a dichloroalkyl sulfonyl group, and a trichloroalkyl sulfonyl group.

[0012] In one embodiment of the present invention, the electrolyte for a lithium secondary battery may further include a carbonate-based solvent.

[0013] In one embodiment of the present invention, the first to third solvents included in the mixed solvent may each include a compound represented by the following chemical formulas 1 to 3.

[0014] [Chemical Formula 1]

[0015]

[0016] [Chemical Formula 2]

[0017]

[0018] [Chemical Formula 3]

[0019]

[0020] In one embodiment of the present invention, the first solvent comprises a compound having a binding energy for lithium ions of 2.5 eV to 3.2 eV, and the second solvent and the third solvent may comprise compounds having a binding energy lower than that of the first solvent.

[0021] The present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte for the lithium secondary battery.

[0022] The means for solving the above problem are not all of the features of the present invention, but may be combined with some embodiments of this specification. Various features of the present invention and the advantages and effects derived therefrom may be understood in more detail by referring to the specific description below.

[0023] The present invention can improve low-temperature performance or rate performance by providing an electrolyte for a lithium secondary battery that can increase ion transportability and the reversibility of charge storage of lithium ions.

[0024] In addition to the effects described above, specific effects of the present invention are described together with the following explanation of specific details for implementing the invention. Furthermore, the effects of the present invention are not limited to those mentioned above and can be easily realized by means and combinations thereof described in the specification.

[0025] Figure 1 is a graph comparing the molecular orbital energy levels of each solvent used in the mixed solvent.

[0026] Figure 2 shows the morphology of lithium electrodeposited on the surface of a copper electrode in the 6th cycle after fabricating a Li||Cu half-cell using the electrolyte of Preparation Example 1 and performing lithium electrodeposition / deposition.

[0027] Figures 3 to 5 show the morphology of lithium electrodeposited on the surface of a copper electrode in the 6th cycle after performing lithium electrodeposition / deposition and fabricating a Li||Cu half-cell using Comparative Manufacturing Examples 1 to 3.

[0028] Figure 6 is a graph showing the results of the Step chronoamperometry test (oxidation stability test) of the electrolytes according to Examples 1-3, Comparative Examples 1-3, 2-3, and 3-3.

[0029] Figure 7 is a graph comparing the solvation structures of electrolytes according to Preparation Example 1 and Comparative Preparation Examples 1 to 3.

[0030] FIG. 8 is a graph comparing the Coulomb efficiency of the batteries in Example 1-1, Comparative Example 1-1, and Comparative Example 6-1 under room temperature fast charging and discharging conditions.

[0031] FIG. 9 is a graph comparing the lifespan performance of the batteries in Example 1-2, Comparative Example 1-2, and Comparative Example 4 under room temperature fast charging and discharging conditions.

[0032] Figure 10 is a graph comparing the lifespan performance of the batteries of Examples 2 to 4 under room temperature fast charging and discharging conditions.

[0033] Figure 11 is a graph comparing the lifespan performance of Comparative Example 2 and Comparative Example 3 batteries under room temperature fast charging and discharging conditions.

[0034] Figure 12 is a graph comparing the lifespan performance of Comparative Example 5 and Comparative Example 6 batteries under room temperature fast charging and discharging conditions.

[0035] FIG. 13 is a graph comparing the Coulomb efficiency of the batteries in Example 1-1, Comparative Example 3-1, and Comparative Example 5-1 under low temperature and low speed charge / discharge conditions.

[0036] FIG. 14 is a graph comparing the lifespan performance of the batteries in Examples 1-2, Comparative Example 3, and Comparative Example 5 under low temperature and low speed charge / discharge conditions.

[0037] The principles of a preferred embodiment of the present invention will be explained in detail below with reference to the attached drawings and description. However, the drawings and descriptions below relate to preferred embodiments among various methods for effectively explaining the features of the present invention, and the present invention is not limited to the drawings and descriptions below.

[0038] Meanwhile, terms such as "first" or "second" may be used to describe various components, but these terms should be interpreted solely for the purpose of distinguishing one component from another. For example, a first component may be named a second component, and similarly, a second component may be named a first component.

[0039] The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, terms such as "comprising" or "having" are intended to specify the existence of the described features, numbers, steps, actions, components, parts, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0040] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this specification.

[0041] The present invention will be described in more detail below.

[0042] The present invention relates to an electrolyte for a lithium secondary battery comprising a lithium salt and a mixed solvent, wherein the mixed solvent comprises: a first solvent comprising an ether-based solvent; a second solvent comprising an ether-based solvent substituted with an electron-withdrawing group or a substituent causing steric hindrance within the solvent molecule; and a third solvent comprising a sulfonamide-based solvent substituted with an electron-withdrawing group within the solvent molecule.

[0043] The present invention enables excellent low-temperature performance and excellent rate capability of a lithium secondary battery by mixing a high-solvating solvent capable of increasing the conductivity of lithium ions with a weakly solvating solvent capable of providing interfacial stability when forming a negative electrode SEI (solid electrolyte interphase) layer. In particular, improved ion transportability, that is, improved lithium ion reversibility, could significantly improve the low-temperature performance and rate capability of the battery.

[0044] In the present invention, the second solvent and the third solvent may be low-coordination solvents having a lower coordination ability than the first solvent. Accordingly, the first solvent may be a relatively high-coordination solvent.

[0045] In the present invention, a weakly solvating solvent refers to a solvent compound having a low binding energy or a high minimum electrostatic potential value for lithium ions. Due to the electron withdrawing groups within the molecule of the weakly solvating solvent compound, it has a low binding energy for lithium ions, thereby enabling the formation of a relatively inorganic-rich, rigid, and stable SEI interface. On the other hand, when the weakly solvating solvent coordinates with lithium ions, the cluster size increases and desolvation becomes difficult due to strong cation-anion bonding.

[0046] Highly solvating solvents refer to solvents that have high binding energy for lithium ions and can solvate lithium salts relatively more than low-solvating solvents, thereby imparting high lithium ion conductivity. However, they form a relatively organic-rich SEI, which reduces the stability of the cathode interface.

[0047] By composing an electrolyte using a mixed solvent that appropriately combines low-coordinate solvents and high-coordinate solvents, which have distinct advantages and disadvantages as described above, the reversibility of lithium ions (adsorption / desorption or insertion / extraction) can be improved during high-speed or low-temperature charging and discharging processes of the electrolyte at room temperature.

[0048] In a preferred embodiment of the present invention, based on the total moles of the mixed solvent, the first solvent may be included in an amount of 20 mol% to 40 mol%, and the second solvent and the third solvent may each be included independently in an amount of 10 mol% to 70 mol%.

[0049] The first solvent is a solvent compound not substituted with a halogen group and belongs to the high-coordination solvent category, while the second and third solvents are compounds substituted with a halogen group and belong to the low-coordination solvent category. By mixing the first, second, and third solvents in the above molar ratio, the reversibility of lithium ions can be improved, and at the same time, a rigid and stable SEI interface can be formed.

[0050] In one embodiment of the present invention, a first solvent belonging to a high-coordinate solvent, a second solvent belonging to a low-coordinate solvent, and a third solvent may be mixed in a molar ratio of 1:2 to 1:4 (mol of the first solvent: mol of the second solvent + mol of the third solvent).

[0051] In a preferred embodiment of the present invention, the low-coordinate solvent comprises a solvent compound substituted with an electron-withdrawing group within the molecule, and preferably may include one or more electron-withdrawing groups within the molecule, preferably including a halogen group, more preferably fluorine or chlorine.

[0052] Meanwhile, another electron withdrawer may be one or more selected from the group consisting of monofluoroalkyl group, difluoroalkyl group, trifluoroalkyl group, monochloroalkyl group, dichloroalkyl group, trichloroalkyl group, monofluoroalkyl sulfonyl group, difluoroalkyl sulfonyl group, trifluoroalkyl sulfonyl group, monochloroalkyl sulfonyl group, dichloroalkyl sulfonyl group, and trichloroalkyl sulfonyl group.

[0053] In the electron withdrawer above, the alkyl group may each independently be an alkyl group having 1 to 8 carbon atoms and may include a linear or branched alkyl group. For example, it may be one selected from the group consisting of methyl, ethyl, propyl, isopropyl, tert-butyl, and neopentyl, and is not limited to a specific alkyl group.

[0054] In a preferred embodiment of the present invention, the second solvent and the third solvent may contain substituents that cause steric hindrance within the solvent molecules. When substituents that cause steric hindrance within the molecules are included, the effect of stabilizing ions by the solvent is weakened, so the coordination ability of the solvent may be reduced. Substituents that cause steric hindrance include methyl groups, ethyl groups, propyl groups, isopropyl groups, tert-butyl groups, neopentyl groups, cyclopentyl groups, cyclohexyl groups, etc.

[0055] In a preferred embodiment of the present invention, the ether-based solvent may be, for example, 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), or diethyl ether (DEE).

[0056] In a preferred embodiment of the present invention, the electrolyte for a lithium secondary battery of the present invention may further include various carbonate solvents in addition to the first to third solvents.

[0057] In a preferred embodiment of the present invention, the first to third solvents may each include a compound represented by the following chemical formulas 1 to 3.

[0058] [Chemical Formula 1]

[0059]

[0060] [Chemical Formula 2]

[0061]

[0062] [Chemical Formula 3]

[0063]

[0064] The first solvent comprises a compound having a binding energy to lithium ions of 2.5 eV to 3.2 eV, and the second and third solvents may comprise compounds having binding energies lower than those of the first solvent.

[0065] In the present invention, the magnitude of the binding energy of the solvent can be calculated through Density Functional Theory (DFT), and the program conditions used are as follows.

[0066] the Gaussian 16 software package with the B3LYP functional and 6-311++G(d,p) basis set, under vacuum conditions (no solvation model applied)

[0067] In a preferred embodiment of the present invention, the mixed solvent may be a mixed solvent of three or more types, more specifically three to five or fewer types, by further mixing an additional solvent corresponding to the first to third solvents.

[0068] In one embodiment of the present invention, the electrolyte comprises lithium bis(fluorosulfonyl)imide (LiFSI) as a lithium salt.

[0069] In addition to LiFSI, lithium salts that may be included include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB, which are commonly used in electrolytes. 10 Cl 10 LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiC4BO8, LiCF3CO2, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC4F9SO3, LiC(CF3SO2)3, (CF3SO2)2NLi, lithium chloroborate, lithium lower aliphatic carboxylate, lithium tetraphenylborate, lithium imide, etc. are possible.

[0070] At this time, the total concentration of LiFSI and other lithium salts may be 0.5 M (mol / L) to 4.0 M, preferably 1.0 M to 3.0 M.

[0071] Meanwhile, the electrolyte of the present invention may additionally include additives to improve the electrochemical performance of the battery as needed. Additives usable in the present invention include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), lithium nitrate, lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiBOB), and lithium difluoro(oxalato)borate. LiFOB) Lithium bis(fluorosulfonyl)imide (LiFSI), Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Lithium difluorobisoxalato phosphate (WCA), Lithium bis(pentafluoroethylsulfonyl)amide (LiBETI), Lithium (malonato oxalato) borate (LiMOB), LiPF2C4O8, LiSO3CF3, LiPF4(C2O4), LiP(C2O4)3, LiC(SO2CF3)3, LiBF3(CF3CF2), LiPF3(CF3CF2)3, Li2B 12 F 12, 1,3-propane sultone, 1,3-propene sultone, biphenayl, cyclohexyl benzene, 4-fluorotoluene, succinic anhydride, ethylene sulfate anhydride, tris(methylsilyl)borate, cyclic sulfites, saturated sultones, unsaturated sultones, acyclic sulfones, etc., may be used individually or in a mixture of two or more types, but are not limited thereto. The above additives may be included in an amount of 0.5% to 10% by weight relative to the total weight of the electrolyte.

[0072] Meanwhile, the present invention also provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte of the present invention.

[0073] anode

[0074] The anode according to the present invention may include an anode current collector and an anode active material layer disposed on at least one surface of the anode current collector. The anode active material layer may include an anode active material, a conductive material, and an anode binder.

[0075] The positive current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. At this time, the positive current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric with fine irregularities formed on its surface so as to increase adhesion with the positive active material.

[0076] The above-mentioned cathode active material is a compound capable of reversible lithiation and delithiation of lithium, and specifically, may include a lithium composite metal oxide comprising lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2(where, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2Examples include )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are each atomic fractions of independent elements, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1)), and any one or more of these compounds may be included.

[0077] Among these, the lithium composite metal oxides mentioned above include LiCoO2, LiMnO2, LiNiO2, and lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel-cobalt-aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 It could be )O2 etc.

[0078] The conductive material used in the anode above can improve conductivity between active material particles or with a metal current collector and prevent the binder from acting as an insulator. The conductive material may be, for example, a mixture of one or more conductive materials selected from the group consisting of graphite, carbon black, carbon fiber, metal fiber, metal powder, conductive whiskers, conductive metal oxide, activated carbon, and polyphenylene derivatives, and more specifically, may be a mixture of one or more conductive materials selected from the group consisting of natural graphite, artificial graphite, Super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0079] The above anode binder is, for example, poly(vinylidene fluoride), poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-trichloroethylene), poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), polyacrylonitrile, poly(vinylpyrrolidone), poly(vinyl acetate), ethylene vinyl acetate copolymer, poly(ethylene-co-vinyl acetate), poly(ethylene oxide). It may be at least one selected from polyacrylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl poly(vinyl alcohol), cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxymethylcellulose, but is not limited thereto.

[0080] cathode

[0081] The cathode according to the present invention may include a cathode current collector and a cathode active material layer disposed on at least one surface of the cathode current collector. Additionally, the cathode may use a metal electrode. When a metal electrode is used as the cathode, lithium metal (Li metal) or lithium-coated copper foil (Cu foil) may be used.

[0082] The above cathode active material layer may include a cathode active material, a conductive material, and a cathode binder.

[0083] The above-mentioned negative current collector can serve as a channel to transfer electrons from the outside to cause an electrochemical reaction to occur in the negative active material, or to receive electrons from the negative active material and send them to the outside. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., may be used as the negative current collector, and specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used as the current collector. For example, the thickness of the above-mentioned negative current collector may be 6㎛ to 20㎛, but the thickness of the above-mentioned negative current collector is not limited thereto.

[0084] The above-mentioned negative electrode active material can perform the role of storing or releasing lithium ions and generating electricity. For example, the above-mentioned negative electrode active material may include at least one of silicon-based active material particles and graphite-based active material particles.

[0085] The above silicon-based active material particles are Si, SiO x (0 <x≤2), Si-C 복합체 및 Si-Y 합금(Y는 알칼리금속, 알칼리토금속, 전이금속, 13족 원소, 14족 원소 및 희토류 원소로 이루어진 군에서 선택된 어느 하나의 원소이다)으로 이루어진 군에서 선택되는 1종 이상을 사용할 수 있다.

[0086] The graphite-based active material particles may include one or more selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fibers, and graphitized mesocarbon micro beads.

[0087] The content of the above-mentioned negative electrode active material may be 80 to 97 weight percent based on the total solid content included in the above-mentioned negative electrode active material layer.

[0088] The conductive material can improve conductivity between active material particles or with a metal current collector at the electrode and prevent the binder from acting as an insulator. The conductive material may be, for example, a mixture of one or more conductive materials selected from the group consisting of graphite, carbon black, carbon fiber, metal fiber, metal powder, conductive whiskers, conductive metal oxide, activated carbon, and polyphenylene derivatives; more specifically, it may be a mixture of one or more conductive materials selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermo black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0089] The above-mentioned cathode binder can suppress separation between cathode active material particles, or between the cathode and the current collector. As the above-mentioned cathode binder, a polymer commonly used for electrodes in the relevant technical field may be used. These cathode binders are, but are not limited to, poly(vinylidene fluoride cohexafluoropropylene), poly(vinylidene fluoride-co-trichloroethylene), poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinyl acetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), polyacrylate, cellulose acetate, and cellulose acetate butyrate. It may be cellulose acetate propionate, cyano ethyl pullulan, cyano ethyl poly(vinyl alcohol), cyanoethylcellulose, cyano ethylsucrose, pullulan, and carboxyl methyl cellulose, but is not limited thereto.

[0090] Separator

[0091] The separator according to the present invention includes a porous substrate to electrically insulate the cathode and the anode to prevent a short circuit.

[0092] As long as the constituent material of the above porous substrate is an organic or inorganic material having electrical insulation properties, it may be used without particular limitation. The above porous substrate may include, for example, at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, and specifically may include polyolefin. Polyolefin not only has excellent coating properties but also allows for a thinner separator thickness, thereby increasing the proportion of the electrode active material layer within the battery and increasing the capacity per volume. Specifically, the weight-average molecular weight (Mw) of the above polyolefin may be 100,000 to 500,000 g / mol. If the weight-average molecular weight of the above polyolefin is below the above numerical range, it may be difficult to secure sufficient mechanical properties, and if it exceeds the above numerical range, the shutdown function may not be implemented or molding may be difficult. The shutdown function refers to a function in which, when the temperature of the secondary battery rises, the thermoplastic resin melts to close the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery.

[0093] The thickness of the porous substrate may be, for example, 3 to 12 μm or 5 to 12 μm. If the thickness of the porous substrate is less than the numerical range, the function of the conductive barrier may not be sufficient, and if it exceeds the numerical range, the resistance of the separator may increase excessively.

[0094] The average diameter of the pores included in the porous substrate may be, for example, 10 to 100 nm. The pores included in the porous substrate have a structure in which they are interconnected, so that gas or liquid can pass from one side of the porous substrate to another side.

[0095] According to some embodiments of the present invention, a coating layer may be disposed on at least one surface of the porous substrate. Specifically, the coating layer can improve the mechanical strength and heat resistance of the separator and increase the ion conductivity in the secondary battery.

[0096] The coating layer according to the present invention may include a binder polymer and inorganic particles.

[0097] The binder polymer according to the present invention can connect inorganic particles and stably fix them. The above binder polymer is, for example, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, poly(ethylene-co-vinyl acetate), polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, One or more selected from the group consisting of cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxymethylcellulose, acrylonitrile-styrene butadiene copolymer, and polyimide may be used in combination.

[0098] According to another embodiment of the present invention, the weight ratio of the inorganic particles to the binder polymer (inorganic particles:binder polymer) may be 50:50 to 99:1, specifically 70:30 to 95:5. If the content ratio of inorganic particles to the binder polymer is less than the above numerical range, the content of the binder polymer increases, which may reduce the performance of improving the thermal safety of the separator membrane, and the pore size and porosity decrease due to the reduction of empty spaces formed between the inorganic particles, which may cause a decrease in the performance of the final battery, and if it exceeds the above numerical range, the content of the binder polymer is too low, which may weaken the peel resistance of the coating layer.

[0099] The inorganic particles according to the present invention can contribute to improving the mechanical strength and heat resistance of a separator for a secondary battery. Specifically, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are applicable within the operating voltage range of the secondary battery (e.g., Li / Li). + It is not specifically limited as long as oxidation and / or reduction reactions do not occur at a standard of 0~5V.

[0100] For example, when using inorganic particles with a high dielectric constant as inorganic particles, the ionic conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of salts, such as lithium salts, within the liquid electrolyte. For the reasons mentioned above, the inorganic particles may be inorganic particles having a dielectric constant of 5 or higher, inorganic particles having lithium ion transport capability, or a mixture thereof.

[0101] The above inorganic particles having a dielectric constant of 5 or greater are Al2O3, SiO2, ZrO2, AlO(OH), Al(OH)3, Mg(OH)2, BaSO4, TiO2, BaTiO3, Pb(Zr x Ti 1-x )O3(PZT, where 0 <x<1), Pb 1-x La x Zr 1-y Tiy O3(PLZT, where, 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-x It may be one or more mixtures selected from the group consisting of PbTiO3 (PMN-PT, where 0 < x < 1), HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO and SiC.

[0102] For example, the average particle size (D) of the above inorganic particles 50 The particle size may be 1 nm to 10 µm for the formation of a coating layer of uniform thickness and appropriate porosity, specifically 10 nm to 2 µm, and more specifically 50 nm to 1 µm. The "average particle size (D50)" refers to the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size. The average particle size can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, the particle size distribution can be calculated by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and measuring the difference in diffraction patterns according to particle size as the particles pass through the laser beam.

[0103] Hereinafter, specific examples and experimental results will be cited to provide a detailed explanation of the effects of the present invention. The following examples are merely illustrative to help understand the embodiments of the present invention and do not limit the scope of the present invention. Readers of this specification should understand that a person skilled in the art may implement the present invention by adding other components or deleting or substituting non-essential components, excluding the essential components of the present invention, and that such implementations are easily derived from the description in this specification and are also within the scope of the present invention.

[0104] <Example>

[0105] Preparation Example 1: Electrolyte using a three-type mixed solvent

[0106] As solvents, a mixed solvent (trisol) was prepared by mixing DME (1,2-dimethoxyethane, with a binding energy of approximately 2.84 eV with lithium ions) having the structure of Chemical Formula 1, TFDMP (1,1,1-trifluoro-2,3-dimethoxypropane, with a binding energy of approximately 2.40 eV with lithium ions) having the structure of Chemical Formula 2, and DMTMSA (N,N-dimethyltrifluoromethane-sulfonamide, with a binding energy of approximately 1.86 eV with lithium ions) having the structure of Chemical Formula 3 in a molar ratio of 2.5 : 4.08 : 1.36, respectively.

[0107] [Chemical Formula 1]

[0108]

[0109] [Chemical Formula 2]

[0110]

[0111] [Chemical Formula 3]

[0112]

[0113] An electrolyte for a lithium secondary battery was prepared by dissolving the lithium salt LiFSI (Lithium bis(fluorosulfonyl)imide) in the above mixed solvent at a concentration of 2.0 M.

[0114] Preparation Example 2: Electrolyte using a three-type mixed solvent

[0115] The electrolyte was prepared in the same manner as the electrolyte of Preparation Example 1, except that a mixture of three solvents—DME, TFDMP, and DMTMSA—in a molar ratio of 2.5:2.8:2.8 (trisol) was used as the mixed solvent.

[0116] Preparation Example 3: Electrolyte using a three-type mixed solvent

[0117] The electrolyte was prepared in the same manner as the electrolyte of Preparation Example 1, except that the mixed solvent consisted of three types of solvents, DME, TFDMP, and DMTMSA, mixed in a molar ratio of 2.5:3.7:1.85 (trisol).

[0118] Preparation Example 4: Electrolyte using a three-type mixed solvent

[0119] The electrolyte was prepared in the same manner as the electrolyte of Preparation Example 1, except that the mixed solvent consisted of three types of solvents, DME, TFDMP, and DMTMSA, mixed in a molar ratio of 2.5:4.5:0.9 (trisol).

[0120] Comparative Preparation Example 1: Electrolyte using a single solvent

[0121] The electrolyte was prepared in the same manner as the electrolyte of Preparation Example 1, except that DME alone was used as the solvent (Monosol E).

[0122] Comparative Preparation Example 2: Electrolyte using a single solvent

[0123] The electrolyte was prepared in the same manner as in Preparation Example 1, except that TFDMP was used as the sole solvent (Monosol T).

[0124] Comparative Preparation Example 3: Electrolyte using a single solvent

[0125] The electrolyte was prepared in the same manner as the electrolyte of Preparation Example 1, except that DMTMSA was used as the sole solvent (Monosol D).

[0126] Comparative Preparation Example 4: Electrolyte using a two-type mixed solvent

[0127] The electrolyte was prepared in the same manner as the electrolyte of Preparation Example 1, except that a mixture of two solvents, DME and TFDMP, in a molar ratio of 2.5:5.25 (disol) was used as the mixed solvent.

[0128] Comparative Preparation Example 5: Electrolyte using a two-type mixed solvent

[0129] The electrolyte was prepared in the same manner as the electrolyte of Preparation Example 1, except that a mixture of two solvents, DME and DMTMSA, in a molar ratio of 2.5:6.03 (disol) was used as the mixed solvent.

[0130] Comparative Preparation Example 6: Electrolyte using a two-type mixed solvent

[0131] The electrolyte was prepared in the same manner as the electrolyte of Preparation Example 1, except that a mixture of two solvents, TFDMP and DMTMSA, in a molar ratio of 5.49:1.83 (disol) was used as the mixed solvent.

[0132] Comparative Preparation Example 1 Comparative Preparation Example 2 Comparative Preparation Example 3 Comparative Preparation Example 4 (mol) Comparative Preparation Example 5 (mol) Comparative Preparation Example 6 (mol) 1st solvent used alone--2.5 2.5 - 2nd solvent- used alone-5.25 - 5.49 3rd solvent-- used alone-6.03 1.83

[0133] Preparation Example 1 (mol) Preparation Example 2 (mol) Preparation Example 3 (mol) Preparation Example 4 (mol) First solvent 2.5 2.5 2.5 2.5 Second solvent 4.0 8 2.8 3.7 4.5 Third solvent 1.3 6 2.8 1.8 5 0.9

[0134] Example 1-1 (Half-cell)

[0135] A half-cell was prepared using the electrolyte of Preparation Example 1 and a 300 μm thick lithium metal and copper foil as the counter electrode.

[0136] Example 1-2 (Complete paper)

[0137] NCM811, polyvinylidene fluoride (PVDF) binder, and carbon black conductive material were mixed in a weight ratio of 94:3:3 and added to an N-methyl-2-pyrrolidone (NMP) solvent to prepare an anode slurry with a solid content of approximately 54.5 wt%. The anode slurry was coated onto an aluminum foil (Al foil) and dried to produce an anode.

[0138] A battery was manufactured by stacking the above anode, lithium metal cathode, and polyethylene separator (SB16C) in sequence and introducing the electrolyte of Manufacturing Example 1.

[0139] Examples 1-3 (half-cells)

[0140] A half-cell was manufactured using the electrolyte of Preparation Example 1 and a lithium metal and aluminum foil with a thickness of 300 μm as the counter electrode.

[0141] Example 2

[0142] A battery was manufactured in the same manner as in Examples 1-2, except that the electrolyte of Manufacturing Example 2 was used.

[0143] Example 3

[0144] A battery was manufactured in the same manner as in Examples 1-2, except that the electrolyte of Manufacturing Example 3 was used.

[0145] Example 4

[0146] A battery was manufactured in the same manner as in Examples 1-2, except that the electrolyte of Manufacturing Example 4 was used.

[0147] Comparative Example 1-1

[0148] A battery was manufactured in the same manner as in Example 1-1, except that the electrolyte of Comparative Manufacturing Example 1 was used.

[0149] Comparative Example 1-2

[0150] A battery was manufactured in the same manner as in Examples 1-2, except that the electrolyte of Comparative Manufacturing Example 1 was used.

[0151] Comparative Examples 1-3

[0152] A battery was manufactured in the same manner as in Examples 1-3, except that the electrolyte of Comparative Manufacturing Example 1 was used.

[0153] Comparative Example 2

[0154] A battery was manufactured in the same manner as Comparative Example 1-2, except that the electrolyte of Comparative Example 2 was used.

[0155] Comparative Example 2-3

[0156] A battery was manufactured in the same manner as in Examples 1-3, except that the electrolyte of Comparative Manufacturing Example 2 was used.

[0157] Comparative Example 3-1

[0158] A battery was manufactured in the same manner as Comparative Example 1-1, except that the electrolyte of Comparative Manufacturing Example 3 was used.

[0159] Comparative Example 3

[0160] A battery was manufactured in the same manner as Comparative Example 1-2, except that the electrolyte of Comparative Example 3 was used.

[0161] Comparative Example 3-3

[0162] A battery was manufactured in the same manner as in Examples 1-3, except that the electrolyte of Comparative Manufacturing Example 3 was used.

[0163] Comparative Example 4

[0164] A battery was manufactured in the same manner as Comparative Example 1-2, except that the electrolyte of Comparative Example 4 was used.

[0165] Comparative Example 5-1

[0166] A battery was manufactured in the same manner as Comparative Example 1-1, except that the electrolyte of Comparative Example 5 was used.

[0167] Comparative Example 5

[0168] A battery was manufactured in the same manner as Comparative Example 1-2, except that the electrolyte of Comparative Example 5 was used.

[0169] Comparative Example 6-1

[0170] A battery was manufactured in the same manner as Comparative Example 1-1, except that the electrolyte of Comparative Manufacturing Example 6 was used.

[0171] Comparative Example 6

[0172] A battery was manufactured in the same manner as Comparative Example 1-2, except that the electrolyte of Comparative Example 6 was used.

[0173] <Experimental Example>

[0174] Experimental Example 1: Reversibility of Lithium Ions

[0175] Li||Cu half-cells were fabricated using the electrolytes of Preparation Example 1 and Comparative Preparation Examples 1 to 3, and the electrodeposition / desorption reaction of lithium was performed. Subsequently, SEM images of the morphology of lithium electrodeposited on the copper electrode surface in the 6th cycle are shown in FIGS. 2 to 5.

[0176] Referring to FIGS. 2 to 5, unlike the batteries using the electrolytes of Comparative Manufacturing Examples 1 to 3, it can be seen that lithium is electrodeposited very uniformly on the surface of the copper electrode of the battery using the electrolyte of Manufacturing Example 1.

[0177] Experimental Example 2: Oxidation Stability Test (Step chronoamperometry; step-CA test)

[0178] The leakage current was measured by applying voltage for a certain period of time to the batteries according to Examples 1-3, Comparative Examples 1-3, Comparative Examples 2-3, and Comparative Example 3-3, and is shown in FIG. 6.

[0179] Referring to FIG. 6, the electrolyte of Preparation Example 1, prepared by mixing three types of solvents, has a voltage of 5.0 V (vs. Li / Li + It can be confirmed that oxidation stability is very high, as no large oxidation current occurs even up to ). On the other hand, the electrolyte of Comparative Example 1 (Monosol E), which uses DME alone, is 4.2V (vs. Li / Li + As the oxidation current increased significantly from ), it was confirmed that the oxidation stability of the electrolyte was low.

[0180] Experimental Example 3: Raman Spectrum Test

[0181] The Raman spectra of the electrolytes according to Preparation Example 1 and Comparative Preparation Examples 1 to 3 were measured, and the peak areas exhibited by the lithium salt in the SSIP (Solvent-Separated Ion Pairs), CIP (Contact Ion Pairs), and AGG (Aggregates) states were compared and shown in FIG. 7.

[0182] Referring to Fig. 7, it can be seen that the electrolyte of Comparative Example 1 (Monosol E) mostly consists of lithium salts forming an SSIP state. Consequently, an organic-rich SEI is formed at the interface with the cathode, which has the disadvantage of lowering the stability of the interface.

[0183] Comparative Manufacturing Examples 2 (Monosol T) and 3 (Monosol D) have a low proportion of the SSIP state and a high proportion of the AGG state, so there is a disadvantage that performance deteriorates when operating the battery under high-speed charging conditions and low-temperature conditions where the kinetic factor becomes important.

[0184] The electrolyte of Preparation Example 1 has SSIP, CIP, and AGG states in appropriate proportions, which improves oxidation stability and lithium ion reversibility, and at the same time forms an inorganic-rich SEI, thereby forming a rigid and stable SEI interface. Therefore, a battery using the electrolyte of Preparation Example 1 can achieve excellent low-temperature performance and rate performance.

[0185] Experimental Example 4

[0186] (1) Half-cell test

[0187] A fast charging performance test was performed on the batteries of Example 1-1, Comparative Example 6-1, and Comparative Example 1-1.

[0188] 16 mA cm during charging -2 At an electrodeposition rate, the electrodeposition cutoff capacity is 1.6 mAh cm -2 Set to, and 16 mA cm during discharge -2 Detachment cutoff voltage of 1.0 V (vs. Li / Li) with a detachment rate + It was set to ). Charging and discharging were performed for approximately 180 cycles, and the Coulomb efficiency was measured for each cycle and is shown in Fig. 8.

[0189] (2) Complete test

[0190] A high-speed charging performance test was performed on the batteries of the examples and comparative examples.

[0191] Specifically, a fast charging performance test was performed on the batteries of Examples 1-2, Comparative Examples 1-2 and Comparative Example 4, and the results are shown in FIG. 9.

[0192] In addition, a fast charging performance test was performed on the batteries of Examples 2 to 4, and the results are shown in FIG. 10; a fast charging performance test was performed on the batteries of Comparative Examples 2 and 3, and the results are shown in FIG. 11; and a fast charging performance test was performed on the batteries of Comparative Examples 5 and 6, and the results are shown in FIG. 12.

[0193] Fast charging was performed under 10 C-rate constant current and constant voltage conditions, with the cutoff current set to 0.05 C and the total charging time set to 6 minutes during constant voltage charging. Charging and discharging were performed for 400 cycles, and the discharge capacity was measured for each cycle.

[0194] Referring to FIGS. 8 to 12, it can be seen that when a three-type mixed electrolyte is used, the reversibility of lithium ion deposition / desorption or insertion / desorption is improved compared to when a one-type or two-type mixed electrolyte is used, and thus the Coulomb efficiency and lifespan performance are greatly improved.

[0195] Experimental Example 5

[0196] (1) Half-cell test

[0197] A low-temperature performance (-20 ℃) ​​test was performed on the batteries of Example 1-1, Comparative Example 3-1, and Comparative Example 5-1.

[0198] When charging, 1 mA cm -2 At an electrodeposition rate, the electrodeposition cutoff capacity is 1 mAh cm -2 Set to, and 1 mA cm during discharge -2The detachment cutoff voltage was set to 1.0 V with a detachment rate. Charge / discharge was performed for approximately 250 cycles, and the Coulomb efficiency was measured for each cycle and is shown in Fig. 13.

[0199] (2) Complete test

[0200] A low-temperature performance (-20 ℃) ​​test was performed on the batteries of Examples 1-2, Comparative Example 3, and Comparative Example 5.

[0201] 1. Charging was performed under C-rate constant current and constant voltage conditions, with the cutoff current set to 0.05C during constant voltage charging. Charging and discharging were performed for approximately 100 cycles, and the capacity was measured for each cycle and is shown in Fig. 14.

[0202] Referring to Figures 13 and 14, it can be seen that when a three-type mixed electrolyte is used, the reversibility of lithium ion adsorption / desorption or insertion / desorption is improved compared to when a one-type or two-type mixed electrolyte is used, and thus Coulomb efficiency and lifespan performance are greatly improved even at low temperatures.

[0203] The embodiments described above are illustrative in all respects and should be understood as not limiting; the scope of the invention is defined by the claims set forth below rather than by the detailed description, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the invention.

[0204] [National R&D projects that supported this invention]

[0205] [Project ID] 2710003963

[0206] [Project No.] RS-2024-00335274

[0207] [Ministry Name] Ministry of Science and ICT

[0208] [Name of Project Management (Specialized) Agency] National Research Foundation of Korea

[0209] [Research Project Name] Mid-career Researcher Program

[0210] [Research Project Title] Development of High-Capacity, Long-Life Lithium Secondary Battery Anodes

[0211] [Name of Project Performing Organization] Seoul National University

[0212] [Research Period] 2021.03.01 ~ 2024.02.29

[0213] [National R&D projects that supported this invention]

[0214] [Project ID] 2710009616

[0215] [Project No.] 2022M3J1A1054151

[0216] [Ministry Name] Ministry of Science and ICT

[0217] [Name of Project Management (Specialized) Agency] National Research Foundation of Korea

[0218] [Research Project Name] Original Technology Development Project

[0219] [Project Title] Battery Design-Based 600Wh / L Class Large-Area All-Solid State Battery Bridge for EVs

[0220] Technology development

[0221] [Name of Project Performing Organization] Seoul National University

[0222] [Research Period] May 24, 2022 ~ January 23, 2025

[0223] [National R&D projects that supported this invention]

[0224] [Project ID] 2710002815

[0225] [Project No.] RS-2023-00261543

[0226] [Ministry Name] Ministry of Science and ICT

[0227] [Name of Project Management (Specialized) Agency] National Research Foundation of Korea

[0228] [Research Project Name] Innovation Research Center (IRC)

[0229] [Research Project Title] Development of Core Element Technologies for Next-Generation Secondary Batteries

[0230] [Name of Project Performing Organization] Seoul National University

[0231] [Research Period] 2023.09.01 ~ 2026.02.28

[0232] [National R&D projects that supported this invention]

[0233] [Project ID] 1711185103

[0234] [Assignment No.] 2021M3H4A3A02086100

[0235] [Ministry Name] Ministry of Science and ICT

[0236] [Name of Project Management (Specialized) Agency] National Research Foundation of Korea

[0237] [Research Project Name] Nano and Materials Technology Development Project

[0238] [Research Project Title] Development of High-Elasticity Binders for Silicon Anodes Using Supramolecular Structures

[0239] [Name of Project Performing Organization] Seoul National University

[0240] [Research Period] July 26, 2021 ~ December 31, 2025

[0241] [National R&D projects that supported this invention]

[0242] [Project ID] 2710010904

[0243] [Assignment No.] 2020M3H4A3081891

[0244] [Ministry Name] Ministry of Science and ICT

[0245] [Name of Project Management (Specialized) Agency] National Research Foundation of Korea

[0246] [Research Project Name] Nano and Materials Technology Development Project

[0247] [Research Project Title] Bin for Lithium-ion Battery High-voltage Cathode Material Based on Structural Design

[0248] Further core technology development

[0249] [Name of Project Performing Organization] Seoul National University

[0250] [Research Period] May 15, 2020 ~ December 31, 2024

[0251] [National R&D projects that supported this invention]

[0252] [Project ID] 1415186254

[0253] [Assignment No.] 20012341

[0254] [Ministry Name] Ministry of Trade, Industry and Energy

[0255] [Name of Project Management (Specialized) Agency] Korea Institute of Industrial Technology Planning and Evaluation

[0256] [Research Project Name] Development of Performance Enhancement and Manufacturing Technology for Lithium-based Next-Generation Secondary Batteries

[0257] [Research Project Title] Design and Manufacturing Technology of High Energy Density Sulfur Electrode (7 mAh / ㎠, 85 wt%)

[0258] development

[0259] [Name of Project Performing Organization] Seoul National University

[0260] [Research Period] 2024.01.01 ~ 2024.12.31

[0261] [National R&D projects that supported this invention]

[0262] [Project ID] 2710006479

[0263] [Project No.] RS-2024-00429941

[0264] [Ministry Name] Ministry of Science and ICT

[0265] [Name of Project Management (Specialized) Agency] National Research Foundation of Korea

[0266] [Research Project Name] Original Technology International Cooperation Development Project (R&D)

[0267] [Research Project Title] Hybrid Aqueous Zinc Secondary Battery via Artificial Intelligence Machine Learning

[0268] Development of high-entropy electrolytes

[0269] [Name of Project Performing Organization] Seoul National University

[0270] [Research Period] May 1, 2024 ~ December 31, 2028

Claims

1. Lithium salt; and In an electrolyte for a lithium secondary battery comprising a mixed solvent, The above mixed solvent is, A first solvent comprising an ether-based solvent; A second solvent comprising an ether-based solvent substituted with an electron-withdrawing group or a steric hindrance substituent within the solvent molecule; and A third solvent comprising a sulfonamide-based solvent in which an electron-withdrawing group is substituted within the solvent molecule; Electrolyte for lithium secondary batteries.

2. In Paragraph 1, Based on the total moles of the mixed solvent, the first solvent is included in an amount of 20 mol% to 40 mol%, and the second solvent and the third solvent are each independently included in an amount of 10 mol% to 70 mol%. Electrolyte for lithium secondary batteries.

3. In Paragraph 1, The first solvent mentioned above is a high-coordination solvent, and The above second solvent and third solvent are low-coordinate solvents, and The high-coordination solvent and the low-coordination solvent are included in a molar ratio of 1:2 to 1:4, Electrolyte for lithium secondary batteries.

4. In Paragraph 3, The electron withdrawer substituted in the molecule of the above low-coordinate solvent compound is a halogen group, Electrolyte for lithium secondary batteries.

5. In Paragraph 3, The electron withdrawer substituted on the molecule of the above low-coordination solvent compound is one or more selected from the group consisting of a monofluoroalkyl group, a difluoroalkyl group, a trifluoroalkyl group, a monochloroalkyl group, a dichloroalkyl group, a trichloroalkyl group, a monofluoroalkyl sulfonyl group, a difluoroalkyl sulfonyl group, a trifluoroalkyl sulfonyl group, a monochloroalkyl sulfonyl group, a dichloroalkyl sulfonyl group, a dichloroalkyl sulfonyl group, and a trichloroalkyl sulfonyl group. Electrolyte for lithium secondary batteries.

6. In Paragraph 1, The above electrolyte for a lithium secondary battery further comprises a carbonate-based solvent, Electrolyte for lithium secondary batteries 7. In Paragraph 1, The first to third solvents included in the above mixed solvent each comprise a compound represented by the following chemical formulas 1 to 3, Electrolyte for lithium-ion batteries: [Chemical Formula 1] [Chemical Formula 2] [Chemical Formula 3] 8. In Paragraph 1, The first solvent comprises a compound having a binding energy for lithium ions of 2.5 eV to 3.2 eV, and The second solvent and the third solvent comprise a compound having a lower bond energy than the first solvent, Electrolyte for lithium secondary batteries.

9. Anode; A cathode; a separator interposed between the anode and the cathode; and A lithium secondary battery comprising an electrolyte for a lithium secondary battery according to any one of claims 1 to 8.

Images