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

Abstract

To provide an electrolyte for a lithium secondary battery excellent in normal temperature life characteristics.SOLUTION: The electrolyte for the lithium secondary battery includes a nonaqueous organic solvent, a lithium salt, a first additive represented by chemical formula 1, and a second additive such as 1, 4-butane sultone and 1, 3-propane sultone.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] One 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, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density, high-capacity secondary batteries has been expanding rapidly. Therefore, 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, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated at the positive electrode and negative electrode. Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide an electrolyte solution for a lithium secondary battery having excellent room temperature life characteristics.

[0005] Another object of the present invention is to provide an electrolyte for a lithium secondary battery that is improved in suppressing gas generation and resistance increase during high-temperature storage.

[0006] Another object of the present invention is to provide a lithium secondary battery containing the above-mentioned electrolyte solution for lithium secondary batteries. [Means for solving the problem]

[0007] The electrolyte for a lithium secondary battery according to the concept of the present invention may include a non-aqueous organic solvent, a lithium salt, a first additive represented by the following Chemical Formula 1, and a second additive represented by the following Chemical Formula 2.

[0008] [ka]

[0009] In chemical formula 1, R1 are the same or different and independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one R1 is an isocyanate group; R2 are the same or different and independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one R2 is an isocyanate group; R3 are the same or different and independently represent hydrogen or a cyclohexyl isocyanate residue; n is an integer from 1 to 10.

[0010] [ka]

[0011] In chemical formula 2, R4 are the same or different and independently represent 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; m is an integer from 0 to 4;

[0012] A lithium secondary battery according to another aspect of the present invention may include 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] According to one embodiment of the present invention, a lithium secondary battery having excellent room temperature life characteristics and improved stability due to suppression of gas generation and resistance increase inside the battery during high temperature storage can be provided. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the lithium secondary battery having a cylindrical battery shape. [Figure 3] 1 is a cross-sectional view showing a lithium secondary battery according to an embodiment. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the battery having a prismatic shape. [Figure 5] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, in the form of a pouch-shaped battery. DETAILED DESCRIPTION OF THE INVENTION

[0015] In order to fully understand the configuration and effects of the present invention, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiment disclosed below, and can be implemented in various forms and can be modified in various ways. The following description is provided solely to fully disclose the present invention and to enable those skilled in the art to fully understand the scope of the invention.

[0016] In this specification, when a component is referred to as being on another component, this expression means that the component may be formed directly on the other component, or a third component may be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the sake of efficient explanation of the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0017] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used herein, the terms "comprise" and / or "comprising" do not exclude the presence or addition of one or more other elements besides the elements mentioned.

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

[0019] Unless otherwise defined herein, particle size 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% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or transmission electron microscope (TEM) or scanning electron microscope (SEM) images. Alternatively, measurement can be performed 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, based on which the average particle size (D50) value can be obtained. Alternatively, measurement can be performed using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., MT3000 manufactured by Microtrac), and ultrasonic waves of approximately 28 kHz are irradiated at an output of 60 W. Then, the average particle size (D50) based on 50% of the particle size distribution can be calculated.

[0020] Unless otherwise defined, the term "substituted" as used herein may mean that at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen, 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, a C1 to C20 alkoxy group, a C1 to C10 fluoroalkyl group, a cyano group, or a combination thereof.

[0021] Specifically, "substituted" can mean that at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen, 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 C10 fluoroalkyl group, or a cyano group. For example, "substituted" can mean that at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen, a C1 to C20 alkyl group, a C6 to C30 aryl group, a C1 to C10 fluoroalkyl group, or a cyano group. Alternatively, "substituted" can mean that at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen, a C1 to C5 alkyl group, a C6 to C18 aryl group, a C1 to C5 fluoroalkyl group, or a cyano group. As an example, "substituted" can mean that at least one hydrogen in a substituent or compound is replaced with deuterium, a cyano group, a halogen, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[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 the electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with the electrolyte solution ELL.

[0024] The electrolyte ELL can function as 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, the positive electrode 10 may further include an additive that can act as a sacrificial positive electrode.

[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 100 wt % of the positive electrode active material layer AML1, and the contents of the binder and conductive material may be 0.5 wt % to 5 wt % each relative to 100 wt % of the positive electrode active material layer AML1.

[0028] The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector COL1. Representative 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)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, and the like.

[0029] The conductive material is used to impart conductivity to the electrode, and any material that is electron-conductive and does not cause chemical changes in the battery that is constructed 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 Al, but is not limited to this.

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

[0032] The composite oxide is a lithium transition metal composite oxide, and specific examples thereof include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, cobalt-nickel-manganese oxide, or a combination thereof.

[0033] As an example, a compound represented by any one of the following chemical 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 L 1 is Mn, Al, or a combination thereof.

[0035] For example, the positive electrode active material may be a lithium transition metal composite oxide, and 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 but 99 mol% or less relative to 100 mol% of metals excluding lithium. 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 negative electrode 20 for a lithium secondary battery includes a current collector COL2 and a negative electrode active material layer AML2 located on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may 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 serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0039] Examples of 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-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester 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 that can impart viscosity. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0042] The dry binder can include a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0043] The conductive material is used to impart conductivity to the electrode, and any material that is electron-conductive without causing 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, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0044] As the current collector COL2, it can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0045] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0046] Examples of materials capable of reversibly intercalating / deintercalating lithium ions include carbon-based negative electrode active materials, such as 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, calcined coke, etc.

[0047] As the alloy of lithium metal, an alloy of lithium and a metal 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 the material capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (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. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0049] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to 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) composed of silicon primary particles and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. 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 disposed on the core.

[0051] The Si-based negative electrode active material or the Sn-based negative electrode active material may 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, and 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 formed from 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, polyacetimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more polymers selected from 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)2, 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 solution ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0059] The non-aqueous organic solvent serves as a medium for the migration of ions involved in the electrochemical reactions of the battery.

[0060] The non-aqueous organic solvent may be an aprotic solvent such as a carbonate, ester, ether, or ketone solvent, or a protic solvent such as an alcohol 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 propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0062] Examples of the ester solvent that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[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 other aprotic solvents that can be used include nitriles represented by R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which 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 kinds.

[0065] In addition, 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 carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0066] Lithium salts are substances dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative 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 integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0067] Hereinafter, the electrolyte for a lithium secondary battery according to an embodiment of the present invention will be described in more detail.

[0068] The electrolyte for a lithium secondary battery according to one embodiment of the present invention may include a non-aqueous organic solvent, a lithium salt, a first additive represented by the following Chemical Formula 1, and a second additive represented by the following Chemical Formula 2.

[0069] The non-aqueous organic solvent may include ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). For example, ethylene carbonate (EC) may be included in an amount of 10 to 30% by volume based on the total amount of the non-aqueous organic solvent. Ethyl methyl carbonate (EMC) may be included in an amount of 20 to 70% by volume based on the total amount of the non-aqueous organic solvent. Dimethyl carbonate (DMC) may be included in an amount of 20 to 70% by volume based on the total amount of the non-aqueous organic solvent.

[0070] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) may have a volume ratio of 1:a:b, where a may be 1 to 3, and b may be 1 to 3. By satisfying this volume ratio range, the additive can have excellent solubility in the non-aqueous organic solvent.

[0071] The lithium salt may include one or more selected from the group consisting of LiPF, LiBF, LiSbF, LiAsF, LiClO, LiAlO, LiAlCl, LiPO, LiCl, LiI, LiN(SOCF), Li(FSO)N, (lithium bis(fluorosulfonyl)imide (LiFSI), and LiCFSO. In one embodiment, the lithium salt may be LiPF.

[0072] The concentration of the lithium salt may be 0.1 M to 2.0 M. For example, the concentration of the lithium salt may be 0.5 M or more, or 1.0 M or more. The concentration of the lithium salt may be 2.0 M or less, 1.7 M or less, or 1.5 M or less. For example, the concentration of the lithium salt may be 1.15 M. When the concentration of the lithium salt is within this range, the conductivity and viscosity of the electrolyte can be appropriately maintained.

[0073] First Additive The first additive according to one embodiment of the present invention may be represented by the following Chemical Formula 1:

[0074] [ka]

[0075] In Formula 1, R1 may be the same or different and may independently be hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R1 may be an isocyanate group.

[0076] R2 may be the same or different and may independently be hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R2 may be an isocyanate group.

[0077] R3 may be the same or different and may independently be hydrogen or a cyclohexyl isocyanate residue.

[0078] n may be an integer from 1 to 10.

[0079] In one embodiment, the first additive may be represented by the following formula 1-1:

[0080] [ka]

[0081] In Chemical Formula 1-1, R1 may be the same or different and may independently be hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R1 may be an isocyanate group.

[0082] R2 may be the same or different and may independently be hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group. At least one of R2 may be an isocyanate group.

[0083] In one embodiment, the first additive may be represented by the following formula 1-2:

[0084] [ka]

[0085] In Formula 1-2, R1 may be the same or different and may independently be hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms.

[0086] R2 may be the same or different and may independently be hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms.

[0087] In one embodiment, the first additive may be represented by the following chemical formula 1-2-1.

[0088] [ka]

[0089] Although the cathode active material, which is lithium-transition metal oxide, has a stable structure, transition metal ions dissolve during charge / discharge processes and storage at high temperatures, causing side reactions with moisture. This leads to deterioration of cell performance, such as increased internal resistance and deterioration of charge / discharge cycle characteristics, during storage at high temperatures.

[0090] The electrolyte for a lithium secondary battery using the first additive can effectively prevent the transition metal ions eluted from the positive electrode from being deposited on the negative electrode surface by controlling moisture, thereby effectively preventing the degradation of cell performance during charge / discharge processes and high-temperature storage.

[0091] The first additive may be included in an amount of 0.01 wt % to 3 wt % based on the total weight of the electrolyte. Specifically, the first additive 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 weight of the electrolyte. The first additive may be included in an amount of 2 wt % or less, or 1.5 wt % or less based on the total weight of the electrolyte. In one embodiment, the first additive may be included in an amount of 0.1 wt % to 1 wt % based on the total weight of the electrolyte. If the content of the first additive is less than 0.01 wt % based on the total weight of the electrolyte, the effect of solving the problem caused by transition metal ions leached from the positive electrode may be insufficient. If the content of the first additive exceeds 3 wt % based on the total weight of the electrolyte, the life characteristics during charge-discharge cycles may be reduced.

[0092] Second Additive The second additive according to one embodiment of the present invention may be represented by the following Chemical Formula 2:

[0093] [ka]

[0094] In chemical formula 2, R4 are the same or different and independently represent 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; m may be an integer from 0 to 4;

[0095] The second additive may include one or more cyclic sulfonate compounds. Specifically, each R4 in Chemical Formula 2 may be hydrogen. The second additive may be a compound represented by the following Chemical Formula 2-1 or 2-2. As an example, the second additive may be 1,4-butane sultone or 1,3-propane sultone.

[0096] The second additive according to one embodiment of the present invention may include at least one selected from the compounds represented by the following Formula 2-1 and Formula 2-2.

[0097] [ka]

[0098] The second additive forms a coating on the surface of the positive electrode, thereby preventing the decomposition of the positive electrode surface and the oxidation reaction of the electrolyte in a high-temperature environment. Specifically, the lone electron pair of the sulfonate group acts as a Lewis acid (e.g., PF5 - ) and stabilize it. In addition, the unshared electron pair can stabilize the transition metal on the surface of the positive electrode or the transition metal released at the surface of the positive electrode. Therefore, the deterioration of the positive electrode can be prevented, and the life characteristics of the battery can be improved.

[0099] The second additive may be included in an amount of 0.01 wt % to 5 wt % based on the total weight of the electrolyte. Specifically, the second additive 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 weight of the electrolyte. The second additive may be included in an amount of 3 wt % or less, or 2 wt % or less based on the total weight of the electrolyte. In one embodiment, the second additive may be included in an amount of 0.5 wt % to 1.5 wt % based on the total weight of the electrolyte. If the content of the second additive is less than 0.01 wt % based on the total weight of the electrolyte, it is difficult to expect an effect of suppressing gas generation inside the battery. If the content of the second additive exceeds 5 wt % based on the total weight of the electrolyte, the initial charge / discharge efficiency and life performance of the battery may decrease with use.

[0100] The second additive can achieve a synergistic effect when used in combination with the first additive. That is, when the first additive and the second additive are used in combination, a stronger coating can be formed on the surfaces of the positive and negative electrodes compared to when each additive is used alone. As a result, the effect of suppressing internal gas generation and resistance increase in the battery in a high-temperature environment can be further improved, and room-temperature life characteristics can be further improved.

[0101] According to one embodiment, the first additive and the second additive may be included in a weight ratio of 5:1 to 1:3. Specifically, this ratio may be 2:1 to 1:3. In one embodiment, the weight ratio of the first additive and the second additive may be 1:1 to 1:3. When the weight ratio of the first additive and the second additive satisfies this range, gas generation during high-temperature storage is effectively suppressed, and a lithium secondary battery with excellent room-temperature life characteristics and an excellent effect of suppressing internal battery resistance at high temperatures and improved high-temperature storage characteristics can be realized.

[0102] Lithium secondary battery

[0103] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating lithium secondary batteries according to an embodiment, with FIG. 2 illustrating a cylindrical type, FIG. 3 illustrating a cross-sectional view, FIG. 4 illustrating a prismatic type, and FIG. 5 illustrating a pouch type. 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 case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). As shown in FIG. 2, the lithium secondary battery 100 may include a sealing member 60 that seals the case 50. As shown in FIG. 3, the lithium secondary battery 100 may also 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 electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0104] A lithium secondary battery according to an embodiment of the present invention may include a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and the electrolyte for a lithium secondary battery described above.

[0105] The positive electrode active material may include, for example, a cobalt-nickel-manganese-based oxide represented by the following Chemical Formula 3.

[0106] Chemical Formula 3 Li a Ni x Mn y M 1 z O 2-b X b

[0107] In Chemical Formula 3, 0.9 ≦ a ≦ 1.8, 0.8 ≦ x < 1, 0 < y ≦ 0.2, 0 ≦ z ≦ 0.2, 0.9 ≦ x + y + z ≦ 1.1, and 0 ≦ b ≦ 0.1, M1 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0108] <​​​​​​​​​​​​The lithium secondary battery according to an embodiment of the present invention can operate at a high voltage of 4.35 V or more. For example, the lithium secondary battery can operate at a voltage of 4.4 V to 4.5 V.

[0112] 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]

[0113] Examples and comparative examples of the present invention will be described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples. Examples and Comparative Examples

[0114] An electrolyte solution and a lithium secondary battery were prepared by the following method.

[0115] Example 1 (1) Preparation of electrolyte An electrolyte solution was prepared by dissolving 1.15 M LiPF6 in a non-aqueous organic solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:40:40, and adding 0.5 wt% of the first additive and 0.5 wt% of the second additive.

[0116] The first additive was a compound represented by the following formula 1A, and the second additive was a compound represented by the following formula 2A.

[0117] [ka]

[0118] (2) Fabrication of lithium secondary batteries LiNi as the positive electrode active material 0.91 Mn 0.09O2, polyvinylidene fluoride as a binder, and carbon 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.

[0119] The positive electrode active material slurry was coated onto an Al current collector having a thickness of 15 μm, dried at 100° C., and then rolled to prepare a positive electrode.

[0120] A mixture of artificial graphite and silicon nanoparticles in a weight ratio of 93:7 was used as the negative electrode active material, and styrene-styrene rubber (SBR) as a binder and carboxymethyl cellulose (CMC) as a thickener in a weight ratio of 97:1:2 were mixed. This mixture was then dispersed in distilled water to prepare a negative electrode active material slurry.

[0121] The negative electrode active material slurry was coated onto a Cu current collector with a thickness of 10 μm, dried at 100° C., and then rolled to prepare a negative electrode.

[0122] The positive and negative electrodes were assembled with a 25 μm thick polyethylene separator to form an electrode assembly, and an electrolyte was injected into the assembly to prepare a lithium secondary battery.

[0123] Example 2 An electrolyte solution was prepared in the same manner as in Example 1, except that 1 wt % of the second additive represented by Chemical Formula 2A was added during preparation of the electrolyte solution, and a lithium secondary battery was fabricated using the electrolyte solution.

[0124] Example 3 An electrolyte solution was prepared in the same manner as in Example 1, except that 1.5 wt % of the second additive represented by Chemical Formula 2A was added during preparation of the electrolyte solution, and a lithium secondary battery was fabricated using the electrolyte solution.

[0125] Comparative Example 1 An electrolyte solution was prepared in the same manner as in Example 1, except that the first additive represented by Chemical Formula 1A and the second additive represented by Chemical Formula 2A were not added, and a lithium secondary battery was fabricated using the electrolyte solution.

[0126] Comparative Example 2 An electrolyte solution was prepared in the same manner as in Example 1, except that the first additive represented by Chemical Formula 1A was not added, and a lithium secondary battery was fabricated using the electrolyte solution.

[0127] Comparative Example 3 An electrolyte solution was prepared in the same manner as in Example 1, except that 0.5 wt % of a compound represented by the following Chemical Formula 4 and 0.5 wt % of a second additive represented by Chemical Formula 2A were added during preparation of the electrolyte solution, and a lithium secondary battery was fabricated using the same method as in Example 1.

[0128] [ka]

[0129] Comparative Example 4 An electrolyte solution was prepared in the same manner as in Example 1, except that 5 wt % of the first additive represented by Chemical Formula 1A was added during preparation of the electrolyte solution, and a lithium secondary battery was fabricated using the electrolyte solution.

[0130] The compositions of the electrolyte solutions of the examples and comparative examples are shown in Table 1 below.

[0131] [Table 1]

[0132] Evaluation example 1: High temperature storage characteristic evaluation For the lithium secondary batteries of the Examples and Comparative Examples, the initial DC resistance (DC-IR) was measured as a ΔV / ΔI (change in voltage / change in current) value, and then the maximum energy state inside the battery was set to a fully charged state (SOC 100%). After storing the batteries in this state at high temperature (60°C) for 30 days, the DC resistance was measured and the DC-IR increase rate (%) was calculated using the following equation 1. The results are shown in Table 2 below.

[0133] formula 1 DC-IR increase rate (%) = (DC-IR after 30 days / initial DC-IR) × 100

[0134] [Table 2]

[0135] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 to 3 had a smaller DC-IR increase rate after 30 days of storage at high temperature than the lithium secondary batteries of Comparative Examples 1 to 4. In particular, it can be seen that the effect of suppressing resistance increase was reduced when an electrolyte solution with a content outside the range of the first additive was used (Comparative Example 4). Therefore, it can be seen that the high-temperature storage characteristics of the battery were further improved through the combination of the first additive and the second additive.

[0136] Evaluation example 2: Room temperature life characteristics evaluation The lithium secondary batteries of the examples and comparative examples were charged and discharged once at 0.2 C to measure the charge and discharge capacity (initial capacity).

[0137] Subsequently, 200 charge / discharge cycles were performed at room temperature (25° C.) between 2.75 V and 4.25 V at a 0.5 CC-rate, and the change in discharge capacity was measured.

[0138] The battery was again charged at a constant current of 0.2 C up to 4.2 V and at a constant voltage with a final current of 0.05 C, and then discharged at a constant current of 0.2 C down to 3.0 V to measure the discharge capacity. The charge / discharge characteristics at this time are defined as recovery characteristics. The charge / discharge capacity at this time was measured, and the ratio of the discharge capacity to the initial capacity is shown in Table 3 below as the capacity recovery rate (%).

[0139] [Table 3]

[0140] Referring to Table 3, it can be seen that the lithium secondary batteries of Examples 1 to 3 have better room temperature charge / discharge cycle characteristics than the lithium secondary batteries of Comparative Examples 1 to 4. In particular, it can be seen that the room temperature cycle characteristics deteriorate when an electrolyte solution with a content outside the range of the first additive (Comparative Example 4) is used. That is, it can be seen that improved room temperature life characteristics are achieved by simultaneously including the first additive and the second additive according to one embodiment of the present invention.

[0141] Evaluation example 3: Gas generation evaluation during high temperature storage The lithium secondary batteries fabricated in the examples and comparative examples were stored at 60°C for 1 day and 7 days, and then the amount of gas generated (mL) was measured using a refinery gas analyzer (RGA). The results are shown in Table 4 below.

[0142] [Table 4]

[0143] Referring to Table 4, it can be seen that the lithium secondary batteries of Examples 1 to 3 not only generated less gas after high-temperature storage but also had a smaller increase in the amount of gas generated, compared to the lithium secondary batteries of Comparative Examples 1 to 4. In particular, the lithium secondary batteries according to embodiments of the present invention contain an isocyanate group but have a high reduction potential and a low oxidation potential, and therefore, unlike Comparative Example 3, which has reduced chemical stability, it can stably control moisture and more effectively suppress gas generation. In addition, it can be seen that when an electrolyte solution with a first additive content outside the range (Comparative Example 4) is used, the gas generation reduction effect is reduced. According to one embodiment of the present invention, a lithium secondary battery with improved swelling characteristics can be provided.

[0144] From the above results, it can be seen that the above-mentioned excellent effects cannot be achieved when none of the additives according to the present invention is contained, when some of the compounds of the additive are replaced with other compounds, or when the composition of the additive deviates from the specific range.

[0145] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is natural that these also fall within the scope of the present invention. [Explanation of symbols]

[0146] 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 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. a non-aqueous organic solvent; A lithium salt, A first additive represented by the following chemical formula 1: and a second additive represented by the following chemical formula 2: 【Chemistry 1】 In the above Chemical Formula 1, R １ are the same or different and independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; R １ at least one of which is an isocyanate group, R ２ are the same or different and independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; R ２ at least one of which is an isocyanate group; R ３ are the same or different and independently represent hydrogen or a cyclohexyl isocyanate residue, n is an integer from 1 to 10; 【Chemistry 2】 In the above Chemical Formula 2, R ４ are the same or different and independently represent 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; An electrolyte for a lithium secondary battery, wherein m is an integer of 0 to 4.

2. The first additive is represented by the following chemical formula 1-1: 【Transformation 3】 In the above Chemical Formula 1-1, R １ are the same or different and independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; R １ at least one of which is an isocyanate group; R ２ are the same or different and independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group; R ２ 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein at least one of the groups is an isocyanate group.

3. The first additive is represented by the following chemical formula 1-2: 【Chemistry 4】 In the above Chemical Formula 1-2, R １ are the same or different and independently represent hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms; R ２ and are the same or different and independently represent hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms.

4. R of Formula 2 ４ 2. The electrolyte for a lithium secondary battery according to claim 1, wherein each of

5. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the second additive comprises at least one selected from the group consisting of compounds represented by the following Formula 2-1 and Formula 2-2: 【Transformation 5】

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

7. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the first additive is contained in an amount of 0.1 to 1 wt % based on the total weight of the electrolyte solution for a lithium secondary battery.

8. The electrolyte solution for a lithium secondary battery according to claim 1 , wherein the second additive 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.

9. The electrolyte for a lithium secondary battery according to claim 1 , wherein the second additive is contained in an amount of 0.5 to 1.5 wt % based on the total weight of the electrolyte for a lithium secondary battery.

10. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the first additive and the second additive are contained in a weight ratio of 5:1 to 1:

3.

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

12. The electrolyte for a lithium secondary battery according to claim 11, wherein the carbonate-based solvent includes ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

13. The ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate have a volume ratio of 1:a:b, a is 1 to 3; 13. The electrolyte solution for a lithium secondary battery according to claim 12, wherein b is an integer of 1 to 3.

14. The lithium salt is LiPF ６ 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein

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

17. 17. The lithium secondary battery according to claim 16, wherein the positive electrode active material comprises a cobalt-pre-nickel manganese oxide.

18. 17. The lithium secondary battery of claim 16, wherein the negative electrode active material comprises a carbon-based negative electrode active material, a Si-based negative electrode active material, a Sn-based negative electrode active material, or a combination thereof.

19. 17. The lithium secondary battery according to claim 16, wherein the lithium secondary battery operates at a high voltage of 4.35 V or higher.

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