Electrolyte for lithium secondary battery, and lithium secondary battery

Abstract

To provide an electrolyte for a lithium secondary battery, which is excellent in lifetime characteristics, high-temperature characteristics and stability.SOLUTION: The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, wherein the electrolyte for the lithium secondary battery includes a non-aqueous organic solvent, a lithium salt, lithium bis(oxalato)borate (LiBOB), a first compound expressed by the following chemical formula 1, and a second compound expressed by a specific formula.SELECTED DRAWING: None

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same. [Background technology]

[0002] In recent years, the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles has led to a rapid increase in demand for high-energy-density, high-capacity secondary batteries. Accordingly, research and development efforts to improve the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode containing active materials capable of inserting and extracting lithium ions, and an electrolyte, and generates electrical energy through an oxidation-reduction reaction that occurs when lithium ions are inserted and extracted at the positive electrode and the negative electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2024 / 0128507 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one embodiment is to provide an electrolyte solution for a lithium secondary battery that has excellent life characteristics, high-temperature characteristics, and stability.

[0006] Another embodiment of the present invention provides a lithium secondary battery including the above-mentioned electrolyte solution for lithium secondary batteries. [Means for solving the problem]

[0007] One embodiment provides an electrolyte solution for a lithium secondary battery, including a non-aqueous organic solvent, a lithium salt, lithium bis(oxalato)borate (LiBOB), a first compound represented by the following Chemical Formula 1, and a second compound represented by the following Chemical Formula 2:

[0008] [Chemical formula 1] [ka]

[0009] In chemical formula 1, R 1a ~R 8a each independently represents hydrogen, halogen, a substituted or unsubstituted C1 to C20 (meaning 1 to 20 carbon atoms; the same applies hereinafter) alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C2 to C30 heterocyclic group, k is 0 or 1.

[0010] [ka]

[0011] In chemical formula 2, A 1 is O or C(R 1b )R 2b and A 2 is O or C(R 3b )(R 4b ) and B 1 is C(R 5b )(R 6b ) or a carbonyl group, B 2 is C(R 7b )(R 8b ) or a carbonyl group, B 3 is C(R 9b )(R 10b ) or a carbonyl group, B 4 is C(R 11b )(R 12b ) or a carbonyl group, R 1b ~R 12b are each independently hydrogen, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C2 to C30 heterocyclic group; n1, n2, m1, and m2 are each independently an integer of 0 or 1; n1+m1≧1, n2+m2≧1.

[0012] Another embodiment provides a lithium secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and the above-described electrolyte solution for lithium secondary batteries. [Effects of the Invention]

[0013] By using the electrolyte solution for a lithium secondary battery according to an embodiment, an increase in the resistance of the battery during high-temperature storage can be suppressed, thereby realizing a lithium secondary battery with excellent life characteristics and stability. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a simplified conceptual diagram of a lithium secondary battery according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and may be embodied in various suitable forms. The description of the embodiments is an example of the present invention and is provided to enable those skilled in the art to fully understand the scope of the present invention.

[0016] In this specification, a description that a component is above another component means that the component may be directly above the other component, or that a third component may be interposed between them. Also, in the drawings, the thickness of components may be exaggerated for the purpose of effectively explaining the technical content. Throughout the specification, the same reference numerals refer to the same components, and duplicate descriptions may be omitted for the sake of convenience.

[0017] In this specification, unless otherwise stated, the singular can include the plural. Also, unless otherwise stated, "A or B" can mean "including A and not including B," "not including A and including B," or "including A and B." As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components.

[0018] As used herein, "combinations thereof" may refer to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0019] Unless otherwise defined, particle size herein may refer to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. The average particle size (D50) can be measured using methods well known to those skilled in the art, such as a particle size analyzer, or a transmission electron microscope or scanning electron microscope. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, followed by calculation to obtain the average particle size (D50) value. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. When measuring by the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, then placed in a commercially available laser diffraction particle size measuring device (e.g., MT 3000 manufactured by Microtrac), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. After that, the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0020] As used herein, unless otherwise defined, the term "substituted" means that at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen atom, a hydroxyl group, an amino group, a C1 to C30 amine group, a nitro group, a C1 to C40 silyl group, a C1 to C30 alkyl group, a C1 to C10 alkylsilyl group, a C6 to C30 arylsilyl group, a C3 to C30 cycloalkyl group, a C3 to C30 heterocycloalkyl group, a C6 to C30 aryl group, a C2 to C30 heteroaryl group, a C1 to C20 alkoxy group, a C1 to C10 fluoroalkyl group, a cyano group, or a combination thereof.

[0021] Specifically, "substituted" means that at least one hydrogen atom in a substituent or compound can be replaced with deuterium, a halogen group, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group, or a cyano group. For example, "substituted" means that at least one hydrogen atom in a substituent or compound can be replaced with deuterium, a halogen group, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group, or a cyano group. Alternatively, "substituted" means that at least one hydrogen atom in a substituent or compound can be replaced with deuterium, a halogen group, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group, or a cyano group. For example, "substituted" means that at least one hydrogen in a substituent or compound can be replaced with deuterium, cyano, halogen, methyl, ethyl, propyl, butyl, phenyl, biphenyl, terphenyl, trifluoromethyl, or naphthyl.

[0022] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte solution ELL.

[0023] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0024] The electrolyte ELL may be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0025] <Positive electrode 10> The lithium secondary battery positive electrode 10 can include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and can further include a binder and / or a conductive material.

[0026] For example, cathode 10 can further include an additive that can function as a sacrificial cathode.

[0027] The content of the positive electrode active material in the positive electrode active material layer AML1 may be 90 wt % to 99.5 wt % relative to the total weight of the positive electrode active material layer AML1 (100 wt %). The contents of the binder and the conductive material may be 0.5 wt % to 5 wt % each relative to the total weight of the positive electrode active material layer AML1 (100 wt %).

[0028] The binder improves adhesion between the positive electrode active material particles and between the positive electrode active material and the current collector COL1. Specific examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0029] The conductive material is used to impart electrical conductivity to the electrode, and any material that does not cause a chemical change in the constructed battery and is electronically conductive can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0030] The current collector COL1 can be made of aluminum (Al), but is not limited to this.

[0031] (Cathode active material) The positive electrode active material in the positive electrode active material layer AML1 may be a compound capable of reversibly inserting and extracting lithium (lithiated intercalation compound). Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0032] The composite oxide may be a lithium transition metal composite oxide, but specific examples include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate oxide, cobalt-free nickel-manganese oxide, or a combination thereof.

[0033] For example, a compound represented by any one of the following formulas can be used: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Lia Ni 1-b-c Co b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5,0<α<2);Li a Ni b Co c L 1 d G e O2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4(0.90≦a≦1.8).

[0034] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L1 is Mn, Al, or a combination thereof.

[0035] For example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less relative to 100 mol% of metals excluding lithium from the lithium transition metal composite oxide. High-nickel positive electrode active materials can achieve high capacity, and therefore can be applied to high-capacity, high-density lithium secondary batteries.

[0036] <Negative electrode 20> The lithium secondary battery positive electrode 20 can include a current collector COL2 and a negative electrode active material layer AML2 formed on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and can further include a binder and / or a conductive material.

[0037] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0038] The binder has the function of improving the adhesion between the negative electrode active material particles and also improving the adhesion between the negative electrode active material and the current collector COL2. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0039] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0040] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyether resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0041] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound to impart viscosity. Examples of the cellulose-based compound include carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. Examples of the alkali metal include sodium, potassium, and lithium.

[0042] The dry binder may be a polymeric material that can be fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or combinations thereof.

[0043] The conductive material is used to impart conductivity to the electrode, and any material that is electron-conductive and does not cause a chemical change in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0044] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof can be used.

[0045] (Negative electrode active material) The negative electrode active material in the negative electrode active material layer AML2 includes substances that can reversibly insert / desorb lithium ions, lithium metal, alloys of lithium metal, substances that can be doped or undoped with lithium, or transition metal oxides.

[0046] Examples of substances that can reversibly insert / desorb lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, or fired coke, etc.

[0047] As alloys of lithium metal, alloys of lithium and metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0048] As substances that can be doped or undoped with lithium, Si-based negative electrode active materials or Sn-based negative electrode active materials can be used. The Si-based negative electrode active material is silicon, a silicon-carbon composite, SiO x (0 < x < 2), Si-Q alloys (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or combinations thereof may also be used. As the Sn-based negative electrode active material, Sn, SnO2, Sn-based alloys, or combinations thereof may also be used.

[0049] The silicon-carbon composite may be a composite of silicon and amorphous carbon. In one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, it may include secondary particles (cores) formed by the aggregation of silicon primary particles and amorphous carbon coating layers (shells) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the silicon primary particles, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0050] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0051] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0052] <Separator 30> Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. Such separator 30 may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, but it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0053] Separator 30 can include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0054] The porous substrate may be a polymer membrane made of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0055] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0056] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH), boehmite, and combinations thereof.

[0057] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer containing an organic material and a coating layer containing an inorganic material may be laminated.

[0058] <Electrolyte ELL> The electrolyte ELL for lithium secondary batteries includes a non-aqueous organic solvent, a lithium salt, and an electrolyte additive.

[0059] The non-aqueous organic solvent functions as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0060] The non-aqueous organic solvent may be an ester-based, carbonate-based, ether-based, ketone-based, or alcohol-based solvent, a non-quantum solvent, or a combination thereof.

[0061] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl pyrrolyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0062] As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate (PP), decanolide, mevalonolactone, valerolactone, caprolactone, or the like can be used.

[0063] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of non-quantum solvents that can be used include nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double bond, an aromatic ring, or an ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes.

[0064] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0065] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain cyclic carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0066] Lithium salts are substances dissolved in organic solvents and function as a source of lithium ions in batteries, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive and negative electrodes. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are positive numbers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0067] Hereinafter, an electrolyte solution for a lithium secondary battery according to an embodiment will be described.

[0068] An electrolyte solution for a lithium secondary battery according to one embodiment may include a non-aqueous organic solvent, a lithium salt, lithium bis(oxalato)borate (LiBOB), a first compound represented by the following Chemical Formula 1, and a second compound represented by the following Chemical Formula 2:

[0069] Lithium bis(oxalato)borate (LiBOB) may be an amphoteric lithium salt additive that assists in the replenishment and absorption of lithium in positive and negative electrodes and promotes lithium insertion and desorption from positive and negative electrode active materials, thereby improving the charge and discharge characteristics of batteries. Furthermore, compared with the first and second compounds, which are sulfate- or sulfonate-based compounds, lithium bis(oxalato)borate (LiBOB) begins reductive decomposition under relatively low voltage conditions to form a coating at the positive and negative electrode interfaces, thereby effectively preventing the leaching of transition metals caused by corrosion products of sulfate- or sulfonate-based compounds. As a result, a lithium secondary battery electrolyte containing lithium bis(oxalato)borate (LiBOB) can improve the life characteristics of lithium secondary batteries when used with a sulfide-based additive.

[0070] Lithium bis(oxalato)borate (LiBOB) may be contained in an amount of 0.01 to 2 wt % based on the total amount of the electrolyte for lithium secondary batteries. Specifically, lithium bis(oxalato)borate (LiBOB) may be contained in an amount of 0.05 wt % or more, 0.1 wt % or more, or 0.5 wt % or more based on the total amount of the electrolyte for lithium secondary batteries. Lithium bis(oxalato)borate (LiBOB) may be contained in an amount of 1 wt % or less based on the total amount of the electrolyte for lithium secondary batteries. When the above range is satisfied, excessive formation of a coating film can be prevented, a rapid increase in initial resistance can be suppressed, and the life characteristics of the lithium secondary battery can be improved.

[0071] The first compound can be represented by the following Chemical Formula 1.

[0072] [Chemical formula 1] [ka]

[0073] In chemical formula 1, R 1a ~R 8amay each independently be hydrogen, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C2 to C30 heterocyclic group.

[0074] k can be 0 or 1.

[0075] The first compound may include one or more cyclic sulfonate compounds. When k is 0 in Chemical Formula 1, the first compound has a five-membered ring structure, and when k is 1, the first compound has a six-membered ring structure.

[0076] In one embodiment, the first compound may include at least one of compounds represented by the following chemical formula 1-1 or 1-2.

[0077] [Chemical formula 1-1] [ka]

[0078] [Chemical formula 1-2] [ka]

[0079] In chemical formulas 1-1 and 1-2, R 1a ~R 8amay each independently be hydrogen, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C2 to C30 heterocyclic group.

[0080] In chemical formulas 1-1 and 1-2, R 1a ~R 8a may all be hydrogen.

[0081] In one embodiment, the first compound may include at least one of compounds represented by the following chemical formula 1-1-1 or 1-2-1.

[0082] [Chemical formula 1-1-1] [ka]

[0083] [Chemical formula 1-2-1] [ka]

[0084] The first compound contains a cyclic sulfonate compound, which forms a coating on the positive electrode. The formation of this coating on the positive electrode can suppress the oxidative decomposition of non-aqueous organic solvents at the positive electrode in high-temperature environments. The oxalate by-product (oxalate moiety) derived from lithium bis(oxalato)borate (LiBOB) can react with moisture in the electrolyte at high voltages and generate gas (carbon dioxide, CO2). The first compound forms an oxide coating on the positive electrode, which prevents the oxalate moiety from reacting with moisture in the electrolyte at the positive electrode, thereby suppressing gas generation.

[0085] In one embodiment, the first compound may be contained in an amount of 0.01 to 5 wt % relative to the total amount of the electrolyte solution for lithium secondary batteries. Specifically, the first compound may be contained in an amount of 0.1 wt % or more, 0.5 wt % or more, or 1 wt % or more relative to the total amount of the electrolyte solution for lithium secondary batteries. The first compound may be contained in an amount of 3 wt % or less, or 2 wt % or less relative to the total amount of the electrolyte solution for lithium secondary batteries. When the above range is satisfied, the gas generation suppression effect can be improved.

[0086] The second compound can be represented by the following Chemical Formula 2.

[0087] [Chemical formula 2] [ka]

[0088] In chemical formula 2, A 1 is O or C(R 1b )R 2b and A 2 is O or C(R 3b )(R 4b ) and B 1 is C(R 5b )(R 6b ) or a carbonyl group, B 2 is C(R 7b )(R 8b ) or a carbonyl group, B 3 is C(R 9b )(R 10b ) or a carbonyl group, B 4 is C(R 11b )(R 12b ) or a carbonyl group, R 1b ~R 12bare each independently hydrogen, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C2 to C30 heterocyclic group; n1, n2, m1, and m2 are each independently an integer of 0 or 1; It is also possible that n1+m1≧1 and n2+m2≧1.

[0089] The second compound is a bicyclic sulfate or bicyclic sulfonate compound. The second compound can be reduced even at a voltage of 2.7 V to form a reduced film on the negative electrode. The film formed by the second compound can suppress an increase in resistance and improve output characteristics.

[0090] In one embodiment, the second compound may include at least one of compounds represented by the following chemical formulas 2-1 to 2-4.

[0091] [Chemical formula 2-1] [ka]

[0092] [Chemical formula 2-2] [ka]

[0093] [Chemical formula 2-3] [ka]

[0094] [Chemical formula 2-4] [ka]

[0095] In chemical formulas 2-1 to 2-4, B 1 is C(R 5b )(R 6b ) or a carbonyl group, B 2 is C(R 7b )(R 8b ) or a carbonyl group, B 3 is C(R 9b )(R 10b ) or a carbonyl group, B 4 is C(R 11b )(R 12b ) or a carbonyl group, R 1b ~R 12b may each independently be hydrogen, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C2 to C30 heterocyclic group.

[0096] In one embodiment, the second compound may include at least one of compounds represented by the following Chemical Formulas 2-1-1 to 2-4-1.

[0097] [Chemical formula 2-1-1] [ka]

[0098] [Chemical formula 2-2-1] [ka]

[0099] [Chemical formula 2-3-1] [ka]

[0100] [Chemical formula 2-4-1] [ka]

[0101] In chemical formulas 2-1-1 to 2-4-1, B 1 is C(R 5b )(R 6b ) or a carbonyl group, B 2 is C(R 7b )(R 8b ) or a carbonyl group, B 3 is C(R 9b )(R 10b ) or a carbonyl group, B 4 is C(R 11b )(R 12b ) or a carbonyl group, R 1b ~R 12b may each independently be hydrogen, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C2 to C30 heterocyclic group.

[0102] In one embodiment, the second compound can include at least one of the compounds listed in Group 1 below.

[0103] [Group 1] [ka]

[0104] The second compound contains a cyclic sulfate compound, which forms a coating on the negative electrode. The formation of this coating on the negative electrode reduces the initial resistance and the rate of increase in resistance. The transition metal contained in the positive electrode active material is dissolved into the electrolyte during high-voltage operation. The dissolved transition metal ions are electrodeposited on the negative electrode, degrading the negative electrode and increasing the initial resistance and the rate of increase in resistance. The second compound forms a reduced coating on the negative electrode, which prevents the dissolved transition metal ions from being electrodeposited on the negative electrode, thereby reducing the initial resistance and the rate of increase in resistance.

[0105] In one embodiment, the second compound may be included in an amount of 0.01 to 5 wt % based on the total amount of the electrolyte solution for lithium secondary batteries. Specifically, the second compound may be included in an amount of 0.1 wt % or more, 0.5 wt % or more, or 1 wt % or more based on the total amount of the electrolyte solution for lithium secondary batteries. The second compound may be included in an amount of 3 wt % or less, or 2 wt % or less based on the total amount of the electrolyte solution for lithium secondary batteries. When the above range is satisfied, the initial resistance and the resistance increase rate can be reduced.

[0106] An electrolyte for a lithium secondary battery according to an embodiment may include lithium bis(oxalato)borate (LiBOB) and the first compound in a weight ratio of 1:1 to 1:20. Specifically, the lithium bis(oxalato)borate (LiBOB) and the first compound may be included in a weight ratio of 1:1 to 1:10, a weight ratio of 1:1 to 1:4, or a weight ratio of 1:1 to 1:2. When the above range is satisfied, the first compound can sufficiently prevent the oxalate moiety derived from lithium bis(oxalato)borate (LiBOB) from reacting with moisture in the electrolyte at high voltage, thereby suppressing gas generation.

[0107] An electrolyte solution for a lithium secondary battery according to an embodiment may include lithium bis(oxalato)borate (LiBOB) and the second compound in a weight ratio of 1:1 to 1:20. Specifically, the lithium bis(oxalato)borate (LiBOB) and the second compound may be included in a weight ratio of 1:1 to 1:10, a weight ratio of 1:1 to 1:4, or a weight ratio of 1:1 to 1:2. When the above range is satisfied, the second compound can sufficiently prevent transition metal ions eluted from the positive electrode active material from being electrodeposited on the negative electrode, thereby reducing the initial resistance and the rate of increase in resistance.

[0108] The electrolyte solution for a lithium secondary battery according to one embodiment may contain the first compound and the second compound in a weight ratio of 1:0.2 to 1:5. Specifically, the first compound and the second compound may be contained in a weight ratio of 1:0.5 to 1:2. When the above range is satisfied, an oxide film is formed on the positive electrode and a reduction film is formed on the negative electrode, thereby suppressing gas generation and reducing the initial resistance and the rate of increase in resistance.

[0109] <Lithium secondary battery> Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing a lithium secondary battery according to an embodiment, with FIG. 2 showing a cylindrical battery, FIG. 3 showing a prismatic battery, and FIGS. 4 and 5 showing pouch-type batteries. Referring to FIGS. 2 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a housing 50 in which the electrode assembly 40 is embedded. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the housing 50, as shown in FIG. 2. Also, in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include an electrode tab 70, or a positive electrode tab 71 and a negative electrode tab 72, which function as an electrical path for conducting the current formed in the electrode assembly 40 to the outside.

[0110] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto. [Example]

[0111] Examples of the present invention and comparative examples are described below. However, the examples described below are merely examples of the present invention, and the present invention is not limited to the examples described below.

[0112] <Preparation of Examples and Comparative Examples> An electrolyte solution and a lithium secondary battery were prepared in the following manner.

[0113] Example 1 (1) Preparation of electrolyte An electrolyte solution was prepared by dissolving 1.0 M LiPF6 and 0.1 wt% LiBOB in a non-aqueous organic solvent consisting of ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) in a volume ratio of 20:40:40, and adding additives.

[0114] The additives were prepared by mixing a compound represented by the following chemical formula 1a in an amount of 1 wt % relative to 100 wt % of the total amount of the electrolyte solution, and a compound represented by the following chemical formula 2a in an amount of 1 wt % relative to 100 wt % of the total amount of the electrolyte solution.

[0115] [Chemical formula 1a] [ka] 1,4-Butanesultone (CAS No. 1633-83-6)

[0116] [Chemical formula 2a] [ka]

[0117] (Preparation Example 1: Synthesis of Compound Represented by Chemical Formula 2a) [Reaction Scheme 1] [ka]

[0118] (Step 1: Synthesis of Intermediate A) A 1:1 volumetric mixture of tetrahydrofuran (THF) and dichloromethane (DCM, CHCl) was added with 68.0 g (0.499 mol) of pentaerythritol and 100 g of Type 4A molecular sieves and refluxed for 20 minutes. Subsequently, 110 ml (2.8 equivalents, 1.40 mol) of thionyl chloride (SOCl) was added and refluxed for 8 hours until all the pentaerythritol had reacted, yielding a pale yellow solution. The resulting pale yellow solution was filtered and concentrated to yield a residue containing a pale yellow solid. 1 L of saturated sodium bicarbonate (NaHCO) solution was added directly to the residue at a rate that minimized foaming, yielding a suspension. The resulting suspension was stirred vigorously for 20 minutes. The suspension was then filtered, and the filtered solid was added to 1 L of purified water to prepare a mixture. The prepared mixture was vigorously stirred for 20 minutes, then filtered under reduced pressure (suction filtration) and dried in air to recover 104.61 g (0.458 mol, 92% yield) of intermediate A.

[0119] Intermediate A 1 H and 13 The C NMR data were consistent with literature values.

[0120] (Step 2: Synthesis of the compound represented by chemical formula 2a) As shown in Reaction Scheme 1, the compound represented by Chemical Formula 2a was synthesized from Intermediate A according to the method disclosed in Canadian Journal of Chemistry, 79, 2001, page 1042.

[0121] The synthesized compound was recrystallized in a solvent consisting of 1,2-dichloroethane and acetonitrile in a volume ratio of 2:1 to obtain the target compound.

[0122] (2) Fabrication of lithium secondary batteries LiNi as the positive electrode active material 0.88 Co 0.07 Al 0.05 O2, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed in a weight ratio of 97:2:1 and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0123] The prepared positive electrode active material slurry was coated on an Al foil with a thickness of 14 μm, dried at 110° C., and pressed to prepare a positive electrode.

[0124] A mixture of artificial graphite and Si-C composite in a weight ratio of 93:7 was used as the negative electrode active material, styrene-styrene rubber as the binder, and carboxymethyl cellulose as the thickener in a weight ratio of 97:1:2. The mixture was dispersed in distilled water to prepare a negative electrode active material slurry.

[0125] The Si-C composite is a core containing artificial graphite and silicon particles, and the surface of the core is coated with coal-based pitch.

[0126] The prepared negative electrode active material slurry was coated on a Cu foil with a thickness of 10 μm, dried at 100° C., and pressed to prepare a negative electrode.

[0127] The produced positive and negative electrodes were assembled with a 25 μm thick polyethylene separator to produce an electrode assembly, and an electrolyte was poured into the assembly to produce a prismatic cell having a thickness of 10 mm, thereby producing a lithium secondary battery.

[0128] Example 2 A lithium secondary battery was fabricated in the same manner as in Example 1, except that 0.5 wt % of LiBOB was dissolved in the non-aqueous organic solvent.

[0129] Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1, except that 1 wt % of LiBOB was dissolved in the non-aqueous organic solvent.

[0130] Example 4 A lithium secondary battery was fabricated in the same manner as in Example 2, except that the compound represented by Chemical Formula 2a was mixed as an additive in an amount of 0.1 wt % relative to 100 wt % of the total amount of the electrolyte solution.

[0131] Example 5 A lithium secondary battery was fabricated in the same manner as in Example 2, except that the compound represented by Chemical Formula 2a was mixed as an additive in an amount of 2 wt % relative to the total amount of the electrolyte solution (100 wt %).

[0132] Example 6 A lithium secondary battery was fabricated in the same manner as in Example 2, except that the compound represented by Chemical Formula 1a was mixed as an additive in an amount of 0.1 wt % relative to 100 wt % of the total amount of the electrolyte solution.

[0133] Example 7 A lithium secondary battery was fabricated in the same manner as in Example 2, except that the compound represented by Chemical Formula 1a was mixed as an additive in an amount of 2 wt % relative to 100 wt % of the total amount of the electrolyte solution.

[0134] Example 8 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the compound represented by Chemical Formula 2b was mixed as an additive in an amount of 1 wt % relative to the total amount of the electrolyte solution (100 wt %).

[0135] [Chemical formula 2b] [ka]

[0136] (Preparation Example 2: Synthesis of Compound Represented by Chemical Formula 2b) [Reaction Scheme 2] [ka]

[0137] (Step 1: Synthesis of Intermediate B) To a solution of 10.34 g (0.156 mol) of KOH dissolved in 200 ml of ethanol, 50 g (0.154 mol) of pentaerythritol tribromide was added dropwise and refluxed for 0.5 hours to react. After cooling to room temperature with KBr, the ethanol was evaporated and the remaining residue was distilled to obtain 28 g (0.115 mol) of intermediate B (3,3-bis(bromomethyl)oxacyclobutane).

[0138] (Step 2: Synthesis of Intermediate C) 28 g (0.115 mol) of intermediate B was dissolved in 28 ml of water in 94 ml of methanol, and the solution was added dropwise to a solution of 44.8 g (0.358 mol) of Na2SO3 in 252 ml of water. The mixture was refluxed for 3.5 hours, and the solvent was removed in vacuo from the mixture containing intermediate C, NaBr, and Na2SO3. The mixture from which the solvent was removed was treated with HCl at room temperature and then filtered with NaCl.

[0139] (Step 3: Synthesis of compound represented by chemical formula 2b) The sulfonic acid solution was evaporated under vacuum, and the residual oil was heated at 210-220°C for 2 hours at a pressure of 2 mmHg (i.e., 2 Torr). The residue was refluxed with acetone, cooled to room temperature, and filtered. The remaining solid was extracted with ethyl acetate using a Soxhlet apparatus, and the ethyl acetate suspension containing the compound represented by formula 2b was cooled to room temperature and filtered (yield: 10 g).

[0140] Example 9 A lithium secondary battery was fabricated in the same manner as in Example 8, except that 0.5 wt % of LiBOB was dissolved in the non-aqueous organic solvent.

[0141] Example 10 A lithium secondary battery was fabricated in the same manner as in Example 8, except that 1 wt % of LiBOB was dissolved in the non-aqueous organic solvent.

[0142] Example 11 A lithium secondary battery was fabricated in the same manner as in Example 9, except that the compound represented by Chemical Formula 2b was mixed as an additive in an amount of 0.1 wt % relative to 100 wt % of the total amount of the electrolyte solution.

[0143] Example 12 A lithium secondary battery was fabricated in the same manner as in Example 9, except that the compound represented by Chemical Formula 2b was mixed as an additive in an amount of 2 wt % relative to 100 wt % of the total amount of the electrolyte solution.

[0144] Example 13 A lithium secondary battery was fabricated in the same manner as in Example 9, except that the compound represented by Chemical Formula 1a was mixed as an additive in an amount of 0.1 wt % relative to 100 wt % of the total amount of the electrolyte solution.

[0145] Example 14 A lithium secondary battery was fabricated in the same manner as in Example 9, except that the compound represented by Formula 1a was mixed as an additive in an amount of 2 wt % relative to the total amount of 100 wt % of the electrolyte solution.

[0146] (Comparative Example 1) A lithium secondary battery was fabricated in the same manner as in Example 2, except that no additive was added.

[0147] (Comparative Example 2) A lithium secondary battery was fabricated in the same manner as in Example 2, except that LiBOB was not added and the compound represented by Chemical Formula 1a was not added as an additive.

[0148] (Comparative Example 3) A lithium secondary battery was fabricated in the same manner as in Example 2, except that LiBOB was not added and the compound represented by Chemical Formula 2a was not added as an additive.

[0149] Comparative Example 4 A lithium secondary battery was fabricated in the same manner as in Example 2, except that the compound represented by Chemical Formula 1a was not added as an additive.

[0150] (Comparative Example 5) A lithium secondary battery was fabricated in the same manner as in Example 2, except that the compound represented by Chemical Formula 2a was not added as an additive.

[0151] (Comparative Example 6) A lithium secondary battery was fabricated in the same manner as in Example 2, except that LiBOB was not added.

[0152] Table 1 shows the compositions of the examples and comparative examples.

[0153] [Table 1]

[0154] <Evaluation 1: Evaluation of room temperature life characteristics and DC internal resistance increase rate> The lithium secondary batteries fabricated in Examples 1 to 14 and Comparative Examples 1 to 6 were charged and discharged once at 0.2 C, and the charge-discharge capacity (initial capacity) was measured.

[0155] The lithium secondary batteries fabricated in Examples 1 to 14 and Comparative Examples 1 to 6 were charged and discharged for 100 cycles at room temperature (25°C) at 0.5 C in the range of 2.75 V to 4.25 V, and the change in discharge capacity was measured to calculate the discharge capacity (capacity retention) after 100 cycles relative to the initial capacity. Table 2 shows the capacity retention (%).

[0156] For the lithium secondary batteries fabricated in Examples 1 to 14 and Comparative Examples 1 to 6, the initial direct current internal resistance (DCIR) was measured as ΔV / ΔI (change in voltage / change in current), and then the maximum energy state inside the battery was changed to a fully charged state (SOC 100%) and stored in this state at room temperature (25°C) for 30 days, after which the direct current internal resistance was measured and the DCIR increase rate (%) was calculated according to Equation 1. The results are shown in Table 2.

[0157] [Formula 1] DCIR increase rate (%) = (DCIR after 30 days / initial DCIR) x 100

[0158] <Evaluation 2: Evaluation of the rate of increase in high-temperature DC resistance> The lithium secondary batteries fabricated in Examples 1 to 14 and Comparative Examples 1 to 6 were charged and discharged once at 0.2 C, and the charge-discharge capacity (initial capacity) was measured.

[0159] The lithium secondary batteries manufactured in Examples 1 to 14 and Comparative Examples 1 to 6 were charged and discharged at 0.5 C at a high temperature (60°C) from 2.75 V to 4.25 V for 100 cycles, and the change in discharge capacity was measured to calculate the discharge capacity (capacity retention) at 100 cycles relative to the initial capacity.

[0160] The battery was also recharged to 4.2 V at 0.2 C under conditions of constant current, 0.05 C cutoff, and constant voltage, and then discharged to 3.0 V at 0.2 C under constant current conditions to measure the discharge capacity. The charge / discharge characteristics at this time are considered recovery characteristics. The charge / discharge capacity at this time was measured, and the ratio of the discharge capacity to the initial capacity (capacity recovery rate) was calculated. Table 2 shows the capacity recovery rate (%).

[0161] For the lithium secondary batteries fabricated in Examples 1 to 14 and Comparative Examples 1 to 6, the initial direct current internal resistance (DCIR) was measured as ΔV / ΔI (change in voltage / change in current), and then the maximum energy state inside the battery was changed to a fully charged state (SOC 100%) and stored in this state at high temperature (60°C) for 30 days, after which the direct current internal resistance was measured and the DCIR increase rate (%) was calculated according to Equation 1. The results are shown in Table 2.

[0162] [Formula 1] DCIR increase rate (%) = (DCIR after 30 days / initial DCIR) x 100

[0163] <Evaluation 3: Evaluation of high-temperature gas generation> The lithium secondary batteries fabricated in Examples 1 to 14 and Comparative Examples 1 to 6 were left at 60° C. for 30 days, and then the thickness increase rate (%) was calculated according to Equation 2. The results are shown in Table 2.

[0164] [Formula 2] Thickness increase rate (%) = (cell thickness after 30 days / initial cell thickness) x 100

[0165] [Table 2]

[0166] Referring to Table 2, it can be seen that, compared to the lithium secondary batteries fabricated in Comparative Examples 1 to 6, the lithium secondary batteries fabricated in Examples 1 to 14 have better capacity retention rates and DC internal resistance increase suppression effects at room temperature (25°C), as well as better capacity recovery rates and DC internal resistance increase suppression effects at high temperature (60°C).

[0167] Referring to Table 2, it can be seen that the lithium secondary batteries fabricated in Examples 1 to 4 did not have a high rate of thickness increase at high temperatures (60°C) compared to the lithium secondary batteries fabricated in Comparative Examples 1 to 4 and 4. According to one embodiment, by including LiBOB and Compound 2 together with Compound 1, it can be seen that the lithium secondary battery has excellent storage characteristics, suppresses gas generation, and improves swelling.

[0168] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention. [Explanation of symbols]

[0169] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Cabinet 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. a non-aqueous organic solvent; A lithium salt, Lithium bis(oxalato)borate (LiBOB), A first compound represented by the following chemical formula 1: and a second compound represented by the following chemical formula 2: [Chemical formula 1] 【Chemistry 1】 (In the above chemical formula 1, R １ａ ~R ８ａ are each independently hydrogen, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C2 to C30 heterocyclic group; k is 0 or 1. [Chemical formula 2] 【Chemistry 2】 (In the above chemical formula 2, A １ is O or C(R １ｂ ) R ２ｂ and A ２ is O or C(R ３ｂ ) (R ４ｂ ) and B １ is C(R ５ｂ ) (R ６ｂ ) or a carbonyl group, B ２ is C(R ７ｂ ) (R ８ｂ ) or a carbonyl group, B ３ is C(R ９ｂ ) (R １０ｂ ) or a carbonyl group, B ４ is C(R １１ｂ ) (R １２ｂ ) or a carbonyl group, R １ｂ ~R １２ｂ are each independently hydrogen, halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 cycloalkenyl group, a substituted or unsubstituted C3 to C20 cycloalkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C2 to C30 heterocyclic group; n1, n2, m1, and m2 each independently represent an integer of 0 or 1; n1 + m1 ≧ 1, n2 + m2 ≧ 1.

2. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the lithium bis(oxalato)borate (LiBOB) is contained in an amount of 0.01 to 2 wt % based on the total amount of the electrolyte solution for a lithium secondary battery.

3. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the first compound is contained in an amount of 0.01 to 5 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

4. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound comprises at least one of compounds represented by the following Chemical Formula 1-1 or 1-2: [Chemical formula 1-1] 【Transformation 3】 [Chemical formula 1-2] 【Chemistry 4】 (In the above chemical formulas 1-1 and 1-2, R １ａ ~R ８ａ The definitions are as set forth in claim 1.

5. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound comprises at least one of compounds represented by the following chemical formulas 1-1-1 or 1-2-1: [Chemical formula 1-1-1] 【Transformation 5】 [Chemical formula 1-2-1] 【Transformation 6】

6. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the second compound is contained in an amount of 0.01 to 5 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

7. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the second compound includes at least one of compounds represented by the following Chemical Formulas 2-1 to 2-4: [Chemical formula 2-1] 【Transformation 7】 [Chemical formula 2-2] 【Transformation 8】 [Chemical formula 2-3] 【Chemistry 9】 [Chemical formula 2-4] 【Chemistry 10】 (In the above chemical formulas 2-1 to 2-4, B １ ~B ４ and R １ｂ ~R １２ｂ The definitions are as set forth in claim 1.

8. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the second compound includes at least one of compounds represented by the following Chemical Formulas 2-1-1 to 2-4-1: [Chemical formula 2-1-1] 【Chemistry 11】 [Chemical formula 2-2-1] 【Chemistry 12】 [Chemical formula 2-3-1] 【Chemistry 13】 [Chemical formula 2-4-1] 【Chemistry 14】 (In the above chemical formulas 2-1-1 to 2-4-1, R １ｂ ~R １２ｂ The definitions are as set forth in claim 1.

9. The electrolyte solution for a lithium secondary battery according to claim 1 , wherein the second compound includes at least one of the compounds listed in Group 1 below. [Group 1] 【Chemistry 15】

10. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the lithium bis(oxalato)borate (LiBOB) and the first compound are contained in a weight ratio of 1:1 to 1:

20.

11. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the lithium bis(oxalato)borate (LiBOB) and the first compound are contained in a weight ratio of 1:1 to 1:

20.

12. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the first compound and the second compound are contained in a weight ratio of 1:0.2 to 1:

5.

13. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent comprises a carbonate-based solvent.

14. 14. The electrolyte solution for a lithium secondary battery according to claim 13, wherein the carbonate-based solvent includes dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and ethylene carbonate (EC).

15. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the concentration of the lithium salt is 0.1 to 2.0M.

16. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; A lithium secondary battery comprising the electrolyte solution for lithium secondary batteries according to any one of claims 1 to 14.

17. The lithium secondary battery according to claim 16 , wherein the positive electrode active material is represented by the following chemical formula 3: [Chemical formula 3] Li ａ Ni １－ｂ－ｃ Co ｂ X ｃ O ２－α D α (In the above chemical formula 3, satisfying 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, and 0<α<2; X comprises at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D includes at least one of O, F, S, P, or a combination thereof.

18. the positive electrode further comprises a current collector; 17. The lithium secondary battery according to claim 16, wherein the current collector comprises Al.

19. The lithium secondary battery according to claim 16 , wherein the negative electrode active material comprises a carbon-based negative electrode active material or a Si-based negative electrode active material.

20. The lithium secondary battery according to claim 16, which operates at a high voltage of 4.2 V or more.

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