Electrolyte for lithium secondary battery and lithium secondary battery

Abstract

To provide an electrolyte for a lithium secondary battery capable of improving life characteristics of the battery and improving storage performance of the battery at a high temperature.SOLUTION: The electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive, and the additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2. The first compound may be included in an amount of about 0.01 wt% to about 5 wt%, and the second compound may be included in an amount of about 0.01 wt% to about 5 wt%, based on the total weight of the electrolyte for a rechargeable lithium battery. [Chemical Formula 1] [Chemical Formula 2] SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrolyte solution 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. This has led to active research and development into improving the performance of lithium secondary batteries.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode, each containing an active material capable of inserting and extracting lithium ions, and an electrolyte. Electrical energy is generated through oxidation and reduction reactions that occur when lithium ions are inserted and extracted from the positive electrode and the negative electrode.

[0004] These lithium secondary batteries use an electrolyte in which lithium salt is dissolved in a non-aqueous organic solvent. The characteristics of lithium secondary batteries change due to complex reactions between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte. Therefore, the use of an appropriate electrolyte is one of the key factors for improving the performance of lithium secondary batteries. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Chinese Patent Application Publication No. 110544765 [Patent Document 2] Chinese Patent Application Publication No. 117013070 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide an excellent electrolyte solution for a lithium secondary battery which improves the life characteristics of the battery and improves the storage performance of the battery at high temperatures.

[0007] Another problem to be solved by the present invention is to provide a lithium secondary battery having excellent performance at high temperatures. [Means for solving the problem]

[0008] An electrolyte solution for a lithium secondary battery according to one embodiment of the present invention includes a non-aqueous organic solvent, a lithium salt, and an additive, and the additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2:

[0009] [Chemical formula 1] [ka]

[0010] In chemical formula 1, R1 are the same or different and each independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one of R1 is an isocyanate group; R2 are the same or different and each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one of R2 is an isocyanate group; R3 are the same or different and each independently represent hydrogen or a cyclohexyl isocyanate residue; n is an integer from 1 to 10.

[0011] [Chemical formula 2] [ka]

[0012] In chemical formula 2, R4 to R7 are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

[0013] A lithium secondary battery according to another embodiment of the present invention includes 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]

[0014] The electrolyte for a lithium secondary battery according to the present invention can improve the life characteristics of the battery and the storage performance of the battery at high temperatures, thereby providing a lithium secondary battery with excellent performance. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which is a cylindrical battery. [Figure 3] 1 is a cross-sectional view showing a lithium secondary battery according to an embodiment. [Figure 4] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which has a prismatic battery shape. [Figure 5] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, which is a pouch-shaped battery. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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 can be implemented in various forms and can be modified in various ways. 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.

[0017] 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 efficient explanation of the technical content. Throughout the specification, the same reference numerals refer to the same components, and duplicate descriptions may be omitted for convenience of explanation.

[0018] In this specification, unless otherwise specified, the singular may include the plural. Furthermore, unless otherwise specified, "A or B" may mean "including A and not including B," "excluding A and including B," or "including A and B." As used in this specification, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements other than the elements mentioned.

[0019] As used herein, "combinations thereof" may refer to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0020] 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% 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 a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, measurement can be performed using a measuring device that utilizes dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, from which the average particle size (D50) value can be calculated. 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 placed in a commercially available laser diffraction particle size measuring device (e.g., MT3000 manufactured by Microtrac), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0021] 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.

[0022] Specifically, "substituted" means that at least one hydrogen atom in a substituent or compound is 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 is 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 is 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. 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 group, 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.

[0023] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention, which may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte solution ELL.

[0024] The positive electrode 10 and the negative electrode 20 can be separated from each other by a separator 30. The separator 30 can be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 can be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated in the electrolyte solution ELL.

[0025] 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 migrate toward the positive electrode 10 or the negative electrode 20.

[0026] <Positive electrode 10> The positive electrode 10 for a lithium secondary battery can include a positive electrode current collector COL1 and a positive electrode active material layer AML1 formed on the positive electrode 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.

[0027] As an example, the cathode 10 can further include an additive that can function as a sacrificial cathode.

[0028] The content of the positive electrode active material in the positive electrode active material layer AML1 may be 90 wt % to 99.5 wt % based on 100 wt % of the total weight 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 based on 100 wt % of the total weight of the positive electrode active material layer AML1.

[0029] The binder improves adhesion between particles of the positive electrode active material and also improves adhesion between the positive electrode active material and the positive electrode 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)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0030] The conductive material is used to impart conductivity to the electrode, and any material that does not cause a chemical change in the constructed battery and is electron-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.

[0031] The positive electrode current collector COL1 can be made of aluminum (Al), but is not limited to this.

[0032] (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.

[0033] The composite oxide is a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, and combinations thereof.

[0034] 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);Li aNi 1-b-c Co b X c O 2- αDα(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- αDα(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).

[0035] 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.

[0036] 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.

[0037] <Negative electrode 20> The negative electrode 20 for a lithium secondary battery may include a negative electrode current collector COL2 and a negative electrode active material layer AML2 formed on the negative electrode 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.

[0038] 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.

[0039] 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 negative electrode current collector COL2. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0040] 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.

[0041] 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.

[0042] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound may be further included 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.

[0043] The dry binder is a polymeric material that can be fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0044] The conductive material is used to impart conductivity to the electrode, and any material that does not cause a chemical change in the constructed battery and is electron-conductive 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.

[0045] As the negative electrode current collector COL2, those 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 can be used.

[0046] (Negative electrode active material) The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0047] Examples of the material capable of reversibly inserting / desorbing 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 calcined coke, etc. The carbon-based negative electrode active material can include, for example, a mixture of natural graphite and artificial graphite.

[0048] 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.

[0049] 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 is silicon, a silicon-carbon composite, SiO x (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 may also be used. As the Sn-based negative electrode active material, Sn, SnO x(0 < x ≤ 2, for example, SnO2), an Sn-based alloy, or a combination thereof may also be used.

[0050] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it may include secondary particles (cores) formed by aggregation of primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be present dispersed in an amorphous carbon matrix.

[0051] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0052] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0053] <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. As such a separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used. Needless to say, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc. can be used.

[0054] The separator 30 may include a porous substrate and a coating layer located on one or both surfaces of the porous substrate and containing an organic substance, an inorganic substance, or a combination thereof.

[0055] 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 of these.

[0056] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0057] 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.

[0058] 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.

[0059] <Electrolyte ELL> The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent functions as a medium through which ions involved in the electrochemical reaction of the battery can migrate. The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0060] 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).

[0061] As the ester-based solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, propyl propionate (PP), or the like can be used.

[0062] 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 aprotic solvents that can be used include nitriles such as R-CN (where 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.

[0063] The non-aqueous organic solvents can be used alone or in combination of two or more kinds.

[0064] In addition, when a carbonate-based solvent is used, a mixture of a cyclic carbonate and a chain carbonate can be used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9 (= cyclic carbonate: chain carbonate).

[0065] Lithium salts are dissolved in organic solvents and function as a source of lithium ions in batteries, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Specific 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, and 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 tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoro(oxalato)phosphate (LiOTFP), and lithium bis(oxalato)borate (LiBOB).

[0066] Hereinafter, the electrolyte of the lithium secondary battery according to the embodiment of the present invention will be described in more detail.

[0067] An electrolyte solution for a lithium secondary battery according to an embodiment may include a non-aqueous organic solvent, a lithium salt, and an additive, and the additive may include a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2:

[0068] [Chemical formula 1] [ka]

[0069] In chemical formula 1, R1 are the same or different and each independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one of R1 is an isocyanate group; R2 are the same or different and each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one of R2 is an isocyanate group; R3 are the same or different and each independently represent hydrogen or a cyclohexyl isocyanate residue; n is an integer from 1 to 10.

[0070] [Chemical formula 2] [ka]

[0071] In chemical formula 2, R4 to R7 are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

[0072] The additives will be described in detail below.

[0073] The electrolyte solution can be prepared by dissolving a lithium salt in a non-aqueous organic solvent, adding an additive containing a first compound represented by Chemical Formula 1 and a second compound represented by Chemical Formula 2, and mixing the resulting mixture. The process of mixing the electrolyte solution is well known in the field of electrolyte solution preparation, and can be appropriately selected and used by those skilled in the art.

[0074] The non-aqueous organic solvent may include a carbonate-based solvent. In one embodiment, the non-aqueous organic solvent may include one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and butylene carbonate (BC).

[0075] In one embodiment, the non-aqueous organic solvent can include ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0076] In one embodiment, 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 30% to 50% by volume, based on the total amount of the non-aqueous organic solvent. Dimethyl carbonate (DMC) may be included in an amount of 30% to 50% by volume, based on the total amount of the non-aqueous organic solvent. In another embodiment, ethylene carbonate (EC) may be included in an amount of 15% to 25% by volume, based on the total amount of the non-aqueous organic solvent. Ethyl methyl carbonate (EMC) may be included in an amount of 35% to 45% by volume, based on the total amount of the non-aqueous organic solvent. Dimethyl carbonate (DMC) may be included in an amount of 35% to 45% by volume, based on the total amount of the non-aqueous organic solvent. The above volume ranges allow the additive to achieve optimal solubility, thereby achieving optimal effects.

[0077] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) may have a volume ratio of 1:a:b (=EC:EMC:DMC), where a may be 1 to 3, and b may be 1 to 3. Within the above volume ratio range, the additive achieves optimal solubility, thereby achieving optimal effects.

[0078] In one embodiment, LiPF6 can be used as the lithium salt.

[0079] The concentration of the lithium salt may be 0.1 M to 2.0 M. Specifically, 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. In the present invention, when the concentration of the lithium salt is 0.1 M to 2.0 M, the conductivity and viscosity of the electrolyte can be appropriately maintained.

[0080] <Additives> The additive according to the present invention may include a first compound represented by the above-mentioned Chemical Formula 1 and a second compound represented by the above-mentioned Chemical Formula 2.

[0081] In one embodiment, the first compound represented by Chemical Formula 1 may be a compound represented by Chemical Formula 1-1 below.

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

[0083] In chemical formula 1-1, R1 are the same or different and each independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one of R1 is an isocyanate group; R2's may be the same or different and each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and at least one of R2's is an isocyanate group.

[0084] In one embodiment, the first compound represented by Chemical Formula 1 may be a compound represented by Chemical Formula 1-2 below.

[0085] [Chemical formula 1-2] [ka]

[0086] In chemical formula 1-2, R1 are the same or different and each independently represents hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms; R2 may be the same or different and each independently represents hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms.

[0087] The content of the first compound represented by Chemical Formula 1 may be 0.01 to 5 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery. Specifically, the content of the first compound represented by Chemical Formula 1 may be 0.05 to 3 parts by weight, or 0.01 to 1 part by weight, based on 100 parts by weight of the electrolyte for a lithium secondary battery. The content of the first compound refers to the weight of the first compound contained in the electrolyte relative to the total weight of the electrolyte. When the content of the first compound satisfies the above range, the effect of improving the life characteristics of the battery and the effect of improving the storage performance of the battery at high temperatures can be optimized.

[0088] The content of the second compound represented by Chemical Formula 2 may be 0.01 to 5 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery. Specifically, the content of the second compound represented by Chemical Formula 2 may be 0.05 to 3 parts by weight, or 0.01 to 1 part by weight, based on 100 parts by weight of the electrolyte for a lithium secondary battery. The content of the second compound refers to the weight of the second compound contained in the electrolyte relative to the total weight of the electrolyte. When the content of the second compound satisfies the above range, the effects of improving the life characteristics of the battery and improving the storage performance of the battery at high temperatures can be optimized.

[0089] The additive may contain the first compound and the second compound in a weight ratio of 5:1 to 1:5 (=first compound:second compound). Specifically, the additive may contain the first compound and the second compound in a weight ratio of 3:1 to 1:3. Alternatively, the additive may contain the first compound and the second compound in a weight ratio of 2:1 to 1:2. Specifically, the additive may contain the first compound and the second compound in a weight ratio of 1.5:1 to 1:1.5.

[0090] The first compound represented by Chemical Formula 1 and the second compound represented by Chemical Formula 2 have a moisture-controlling function and can prevent transition metals eluted from the positive electrode from causing side reactions. They also can protect the negative electrode by preventing the transition metals eluted from the positive electrode from being reduced at the negative electrode interface. This effectively prevents cell performance degradation during charge / discharge processes and high-temperature storage.

[0091] When the first compound represented by Chemical Formula 1 and the second compound represented by Chemical Formula 2 are used simultaneously, a synergistic effect can be achieved. Specifically, when the first compound and the second compound are mixed and added so as to satisfy the content range of the embodiment, a better effect can be achieved than when the first compound is added alone, and a better effect can be achieved than when the second compound is added alone.

[0092] The above-described effects of the additive including the first compound and the second compound can be more significantly realized when used together with a positive electrode active material including at least one selected from the group consisting of a lithium iron phosphate-based positive electrode active material and a lithium nickel-based positive electrode active material.

[0093] <Lithium secondary battery> Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, coin, and other types depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating lithium secondary batteries according to embodiments of the present invention, with FIG. 2 illustrating a cylindrical battery, FIG. 4 illustrating a prismatic battery, and FIG. 5 illustrating a pouch-type battery. FIG. 3 is a cross-sectional view of a lithium secondary battery. 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 housing the electrode assembly 40. 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 case 50, as shown in FIG. 2. As shown 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 electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which function as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0094] The lithium secondary battery according to the embodiment of the present invention can be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0095] In the lithium secondary battery according to the embodiment of the present invention, a coating functioning as a passivation is formed on the surfaces of the positive and negative electrodes as the non-aqueous electrolyte is decomposed during initial charge and discharge, thereby improving storage performance at high temperatures. Generally, the coating is formed by the thermal decomposition of HF, which is generated by the thermal decomposition of lithium salts (e.g., LiPF6) widely used in lithium ion batteries. - and PF5 -The positive electrode can be deteriorated by acids such as . This acid attack dissolves transition metal ions from the positive electrode, causing changes in the surface structure and increasing the surface resistance of the electrode. As a result, the redox center metal element disappears, reducing the theoretical capacity and resulting in a decrease in the actual capacity. The dissolved transition metal ions are then electrodeposited on the cathode, which reacts in a strong reduction potential range. This not only consumes electrons, but also destroys the coating during electrodeposition, exposing the cathode surface and causing additional electrolyte decomposition reactions. As a result, the resistance of the negative electrode increases, increasing the irreversible capacity and resulting in a constant decrease in the cell's capacity.

[0096] In the present invention, the first compound represented by Chemical Formula 1 and the second compound represented by Chemical Formula 2 can prevent transition metals eluted from the positive electrode from causing side reactions. Furthermore, the transition metals eluted from the positive electrode can be prevented from being reduced at the negative electrode interface, thereby protecting the negative electrode. As a result, the above-mentioned problems can be prevented, and the effect of improving the life characteristics and storage performance of the battery can be achieved. The effect is even more pronounced at high temperatures. [Example]

[0097] 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.

[0098] Example 1 (1) Electrolyte production An electrolyte solution was prepared by dissolving 1.5 M LiPF6 in a non-aqueous organic solvent, which was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:40:40, and adding additives.

[0099] The additive was prepared so as to contain 0.25 parts by weight of the first compound based on 100 parts by weight of the electrolyte solution, and 0.5 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0100] The first compound was a compound represented by the following chemical formula 1-3, and the second compound was a compound represented by the following chemical formula 2-1.

[0101] [Chemical formula 1-3] [ka]

[0102] [Chemical formula 2-1] [ka]

[0103] (2) Manufacture of lithium secondary batteries LiFePO4 as a positive electrode active material, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed in a weight ratio of 96:3:1 (= LiFePO4:polyvinylidene fluoride:Ketjen black), and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0104] The positive electrode active material slurry was coated onto an aluminum current collector having a thickness of 15 μm, dried at 100° C., and then pressed to prepare a positive electrode.

[0105] Artificial graphite was used as the negative electrode active material, styrene-styrene rubber (SBR) was used as the binder, and carboxymethyl cellulose (CMC) was used as the thickener in a weight ratio of 98:1:1 (= artificial graphite:SBR:CMC), and the mixture was dispersed in distilled water to prepare a negative electrode active material slurry.

[0106] The negative electrode active material slurry was coated onto a copper current collector with a thickness of 10 μm, dried at 100° C., and then pressed to prepare a negative electrode.

[0107] The prepared positive and negative electrodes were assembled with a 10 μm thick polyethylene separator to prepare an electrode assembly, and an electrolyte solution was injected to prepare a lithium secondary battery.

[0108] Example 2 An electrolyte solution and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the additive contained 0.5 parts by weight of the first compound based on 100 parts by weight of the electrolyte solution and 0.25 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0109] Example 3 An electrolyte solution and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the additive contained 0.5 parts by weight of the first compound based on 100 parts by weight of the electrolyte solution and 0.5 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0110] (Comparative Example 1) An electrolyte solution and a lithium secondary battery were produced in the same manner as in Example 1, except that the additive did not contain the first compound and the second compound.

[0111] (Comparative Example 2) An electrolyte solution and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the additive contained 0.5 parts by weight of the first compound based on 100 parts by weight of the electrolyte solution and 10 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0112] (Comparative Example 3) An electrolyte solution and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the additive contained 10 parts by weight of the first compound based on 100 parts by weight of the electrolyte solution and 0.5 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0113] Comparative Example 4 An electrolyte solution and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the additive contained 0.2 parts by weight of the first compound based on 100 parts by weight of the electrolyte solution and 2 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0114] (Comparative Example 5) An electrolyte solution and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the additive contained 2 parts by weight of the first compound based on 100 parts by weight of the electrolyte solution and 0.2 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0115] <Evaluation> (Evaluation example 1: Room temperature performance evaluation) The lithium secondary batteries manufactured in the examples and comparative examples were subjected to 1,000 charge / discharge cycles, and the capacity retention rate and resistance (DC-IR) change rate were calculated. The charging conditions were 25°C, 0.5C, 4.2V, and 0.2C cut-off. The discharging conditions were 25°C, 0.5C, and 2.5V cut-off. The resistance was measured using electrochemical alternating current impedance (EIS). The capacity retention rate was calculated using the following equation 1, and the DC-IR change rate was calculated using the following equation 2. The results are shown in Table 1 below.

[0116] [Formula 1] Capacity retention rate (%) = (discharge capacity after 1000 cycles / discharge capacity after 1 cycle) × 100

[0117] [Formula 2] DC-IR change rate (%) = {(DC-IR after 1000 cycles / DC-IR after 1 cycle)} × 100

[0118] (Evaluation example 2: High temperature performance evaluation) The lithium secondary batteries manufactured in the examples and comparative examples were charged under the conditions of 60°C, 0.33C, 4.2V, and 0.02C cut-off, and the initial capacity of the battery was measured. The lithium secondary batteries were left at 60°C for 60 days, and then the capacity was measured. The resistance was measured using electrochemical alternating current impedance (EIS). The capacity recovery rate and DC-IR change rate were calculated using the following Equations 3 and 4, respectively. The results are shown in Table 1 below.

[0119] [Formula 3] Capacity recovery rate (%) = (Capacity after leaving for 60 days / Initial capacity) x 100

[0120] [Formula 4] DC-IR change rate (%) = {(DC-IR after 60 days / initial DC-IR)} × 100

[0121] [Table 1]

[0122] Referring to Table 1, it can be seen that the examples of the present invention had better performance evaluation results at high temperatures than the comparative examples, which confirms that the additives of the present invention have a superior effect of improving battery performance at high temperatures.

[0123] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention may be embodied in other ways without changing the technical spirit or essential features thereof. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting. [Explanation of symbols]

[0124] 10: Positive electrode 20: Negative electrode 30: Separator ELL: Electrolyte

Claims

1. a non-aqueous organic solvent; A lithium salt, an additive, The additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2: Electrolyte for lithium secondary batteries. [Chemical formula 1] 【Chemistry 1】 (In the above chemical formula 1, The R 1 are the same or different and each independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and 1 at least one of which is an isocyanate group, The R 2 are the same or different and each independently represent hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, or an isocyanate group, and 2 at least one of which is an isocyanate group, The R 3 are the same or different and each independently represents hydrogen or a cyclohexyl isocyanate residue, The n is an integer from 1 to 0. [Chemical formula 2] 【Chemistry 2】 (In the above chemical formula 2, The R 4 ~R 7 are each independently a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

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

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

4. the additive comprises the first compound and the second compound in a weight ratio of 5:1 to 1:5; The electrolyte solution for a lithium secondary battery according to claim 1.

5. the additive comprises the first compound and the second compound in a weight ratio of 2:1 to 1:2; The electrolyte solution for a lithium secondary battery according to claim 1.

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

7. The first compound includes a compound represented by the following Chemical Formula 1-2: The electrolyte solution for a lithium secondary battery according to claim 1. [Chemical formula 1-2] 【Chemistry 4】 (In the above chemical formula 1-2, The R 1 are the same or different and each independently represent hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms; The R 2 are the same or different and each independently represent hydrogen, halogen, or an alkyl group having 1 to 10 carbon atoms.

8. The lithium salt is LiPF 6 , LiClO 4 , LiBF 4 , LiTFSI, LiSO 3 CF 3 , LiBOB, LiFOB, LiDFBP, LiTFOP, LiPO 2 F 2 , LiSbF 6 , LiAsF 6 , LiAlO 2 , LiAlCl 4 , LiCl, LiI, LiN(SO 3 C 2 F 5 ) 2 , Li(FSO 2 ) 2 N, and LiN(C x F 2x+1 SO 2 ) (C y F 2y+1 SO 2 ) (wherein x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfate, and LiC 4 F 9 SO 3 one or more selected from the group consisting of: The electrolyte solution for a lithium secondary battery according to any one of claims 1 to 7.

9. The lithium salt is LiPF 6 Including, The electrolyte solution for a lithium secondary battery according to claim 1.

10. The concentration of the lithium salt is 0.1M to 2.0M. The electrolyte solution for a lithium secondary battery according to claim 1.

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

12. The carbonate solvent includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). The electrolyte solution for a lithium secondary battery according to claim 11.

13. the ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) have a volume ratio of 1:a:b; a is 1 to 3, b is 1 to 3; The electrolyte solution for a lithium secondary battery according to claim 12.

14. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; The lithium secondary battery electrolyte solution according to any one of claims 1 to 13, Lithium secondary battery.

15. The positive electrode active material includes a lithium iron phosphate-based positive electrode active material or a lithium composite oxide represented by the following chemical formula 3: The lithium secondary battery according to claim 14. [Chemical formula 3] Li x M 1 y M 2 z M 3 1-y-z O 2-a X a (0.5≦x≦1.8, 0≦a≦0.05, 0<y≦1, 0≦z≦1, and 0<y+z≦1, M 1 , M 2 , and M 3 each independently contain one or more elements selected from the group consisting of Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, and La; X includes one or more elements selected from the group consisting of F, S, P, and Cl.

16. The negative electrode active material includes at least one of a carbon-based negative electrode active material, a Si-based negative electrode active material, and a Sn-based negative electrode active material. The lithium secondary battery according to claim 14.

17. The lithium secondary battery according to claim 14 , wherein the negative electrode active material is at least one of natural graphite and artificial graphite.

18. The lithium secondary battery is a cylindrical, prismatic, pouch, or coin battery. The lithium secondary battery according to claim 14.

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