Electrolyte solution for lithium secondary battery, and lithium secondary battery

Abstract

To provide an electrolyte solution for a lithium secondary battery, in which the saving characteristic and the stability at high temperature are improved.SOLUTION: An electrolyte solution for a lithium secondary battery includes a nonaqueous organic solvent, lithium salt, and an additive represented by the following Chemical Formula 1. In Chemical Formula 1, R1 to R4 are independently selected from the group consisting of a halogen atom, C1 to C20 alkyl groups, C1 to C20 halide alkyl groups, C3 to C30 cycloalkyl groups, C6 to C30 aryl groups, a hydroxyl group, C1 to C10 alkoxy groups, a carboxyl group, a formyl group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonate group, and derivatives of these.SELECTED DRAWING: Figure 1

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 expanded rapidly. Therefore, research and development to improve the performance of lithium secondary batteries has been actively conducted.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, 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 cathode and anode.

[0004] The electrolyte used in such lithium secondary batteries is a lithium salt dissolved in a non-aqueous organic solvent. In lithium secondary batteries, the battery's characteristics are determined by complex reactions between the positive electrode and the electrolyte, the negative electrode and the electrolyte, etc. Therefore, the use of an appropriate electrolyte is one of the key factors for improving the performance of lithium secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one embodiment is to provide an electrolyte solution for a lithium secondary battery having improved storage characteristics and stability at high temperatures.

[0006] It is an object of another embodiment to provide a lithium secondary battery including an electrolyte. [Means for solving the problem]

[0007] One embodiment provides an electrolyte solution for a lithium secondary battery, including a non-aqueous organic solvent, a lithium salt, and an additive represented by the following Chemical Formula 1:

[0008] [ka]

[0009] In Chemical Formula 1, R1 to R4 are each independently selected from the group consisting of a halogen atom, a C1 to C20 alkyl group, a C1 to C20 halogenated alkyl group, a C3 to C30 cycloalkyl group, a C6 to C30 aryl group, a hydroxy group, a C1 to C10 alkoxy group, a carboxyl group, a formyl group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonic acid group, and derivatives thereof.

[0010] Another embodiment provides a lithium secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte solution, the electrolyte solution including a non-aqueous organic solvent, a lithium salt, and an additive represented by Chemical Formula 1 above. [Effects of the Invention]

[0011] The electrolyte for a lithium secondary battery according to an embodiment may exhibit the effect of improving storage characteristics and stability at high temperatures by suppressing the elution of transition metals in the positive electrode and forming a stable positive electrode film. [Brief explanation of the drawings]

[0012] [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

[0013] 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. Here, the description of the present embodiments is provided solely to fully disclose the present invention and to enable those skilled in the art to understand the scope of the invention.

[0014] In this specification, when a component is referred to as being on another component, it may be formed directly on the other component, or a third component may be interposed therebetween. 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.

[0015] 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, "including" and / or "comprising" does not exclude the presence or addition of one or more other elements other than the elements mentioned.

[0016] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0017] As used herein, unless otherwise defined, the term "substituted" means that at least one hydrogen atom in a substituent or compound has been 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 group, a C1 to C20 alkoxy group, a C1 to C10 fluoroalkyl group, a cyano group, or a combination thereof.

[0018] Specifically, "substituted" can mean that at least one hydrogen in a substituent or compound is replaced with deuterium, halogen, C1 to C30 alkyl group, C1 to C10 alkylsilyl group, C6 to C30 arylsilyl group, C3 to C30 cycloalkyl group, C3 to C30 heterocycloalkyl group, C6 to C30 aryl group, C2 to C30 heteroaryl group, C1 to C10 fluoroalkyl group, or cyano group. For example, "substituted" can mean that at least one hydrogen in a substituent or compound is replaced with deuterium, halogen, C1 to C20 alkyl group, C6 to C30 aryl group, C1 to C10 fluoroalkyl group, or cyano group. Alternatively, "substituted" can mean that at least one hydrogen in a substituent or compound is replaced with deuterium, halogen, C1 to C5 alkyl group, C6 to C18 aryl group, C1 to C5 fluoroalkyl group, or cyano group. As an example, "substituted" may mean that at least one hydrogen atom in a substituent or compound is replaced with deuterium, cyano, halogen, methyl, ethyl, propyl, butyl, phenyl, biphenyl, terphenyl, trifluoromethyl, or naphthyl.

[0019] 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.

[0020] 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.

[0021] The electrolyte ELL may be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. The lithium ions can move toward the positive electrode 10 or the negative electrode 20 through the separator 30 impregnated with the electrolyte ELL.

[0022] positive electrode 10 The positive electrode 10 for a lithium secondary battery may 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 may further include a binder and / or a conductive material.

[0023] For example, the positive electrode 10 may further include an additive that can act as a sacrificial positive electrode.

[0024] 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.

[0025] 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.

[0026] 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 electronically conductive can be used. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0027] The current collector COL1 can be made of Al, but is not limited to this.

[0028] 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 composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0029] 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-nickel-manganese-based oxides, and combinations thereof.

[0030] As an example, a compound represented by any one of the following chemical formulas can be used.

[0031] 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 a Ni 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), Lia 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).

[0032] 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.

[0033] 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 but 99 mol% or less relative to 100 mol% of metals excluding lithium in the lithium transition metal composite oxide. The high-nickel positive electrode active material can achieve high capacity, and therefore can be applied to high-capacity, high-density lithium secondary batteries.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The water-based binder can 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.

[0039] 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.

[0040] 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.

[0041] 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 electronically 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.

[0042] The current collector COL2 may be one or more 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.

[0043] 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, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0044] The material capable of reversibly intercalating / deintercalating lithium ions is a carbon-based negative electrode active material, and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0045] 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.

[0046] As a substance that can be doped and undoped with 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 a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0047] 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 are coated with amorphous carbon on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by condensation of primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, so that, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles can exist dispersed in an amorphous carbon matrix.

[0048] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0049] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used mixed with a carbon-based negative electrode active material.

[0050] 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, 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 can also be used.

[0051] 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.

[0052] 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 selected from these.

[0053] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0054] The inorganic materials can include, but are 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.

[0055] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a form in which a coating layer containing an organic material and a coating layer containing an inorganic material are laminated.

[0056] Electrolyte ELL The electrolyte solution ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0057] The non-aqueous organic solvent serves as a medium for the migration of ions involved in the electrochemical reactions of the battery.

[0058] The non-aqueous organic solvent may be an aprotic solvent such as a carbonate-based, ester-based, ether-based, or ketone-based solvent, a protic solvent such as an alcohol-based solvent, or a combination thereof.

[0059] 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).

[0060] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0061] 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 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.

[0062] The non-aqueous organic solvents can be used alone or in combination of two or more kinds.

[0063] 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.

[0064] 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+1SO2) (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).

[0065] Lithium secondary battery. Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating lithium secondary batteries according to embodiments, 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.

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

[0067] An electrolyte for a lithium secondary battery according to one embodiment includes a non-aqueous organic solvent, a lithium salt, and an additive.

[0068] The additive according to one embodiment of the present invention may be represented by the following Chemical Formula 1:

[0069] [ka]

[0070] In Chemical Formula 1, R1 to R4 may each independently be selected from the group consisting of a halogen atom, a C1 to C20 alkyl group, a C1 to C20 halogenated alkyl group, a C3 to C30 cycloalkyl group, a C6 to C30 aryl group, a hydroxy group, a C1 to C10 alkoxy group, a carboxyl group, a formyl group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonic acid group, and derivatives thereof.

[0071] In the additive according to one embodiment of the present invention, R1 to R4 in Chemical Formula 1 may each independently be one selected from the group consisting of a methyl group, an ethyl group, a phenyl group, and a carboxyl group.

[0072] The additives may have structures with the same functional groups or structures with different functional groups. For example, Chemical Formula 1 may be represented by the following Chemical Formulas 1-1 to 1-3.

[0073] [ka]

[0074] In Chemical Formula 1, at least one of R1 to R4 may be a fluorine-containing substituent or a fluorine element.

[0075] The additive according to one embodiment of the present invention may have a structure in which the substituents are partially or completely fluorinated. For example, the compound represented by Chemical Formula 1 may be a compound represented by the following Chemical Formulas 1A-1 to 1A-4.

[0076] [ka]

[0077] In Chemical Formulae 1A-1 to 1A-4, R1 to R3 can each independently be selected from the group consisting of a C1 to C20 alkyl group, a C1 to C20 halogenated alkyl group, a C3 to C30 cycloalkyl group, a C6 to C30 aryl group, a hydroxy group, a C1 to C10 alkoxy group, a carboxyl group, a formyl group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonic acid group, and derivatives thereof.

[0078] The additive according to one embodiment of the present invention may be a compound with a linear structure containing multiple nitrile groups.

[0079] The nitrile group has a strong negative charge, so it is adsorbed on the surface of the positive electrode and Ni 4+ , Ni 3+ By neutralizing the charge of the transition metals such as ZnO, the decomposition of the electrolyte solvent, which is a side reaction, can be suppressed.

[0080] The additive according to one embodiment of the present invention has a structure in which a functional group that is effective in inhibiting the elution of transition metals is substituted on the carbon atom connecting two nitrile groups.

[0081] The additive represented by Chemical Formula 1 has a structure in which functional groups are introduced as R1 to R4, and therefore forms a coating on the surface of the positive electrode to suppress decomposition of the positive electrode active material, thereby suppressing gas generation and elution of transition metals due to decomposition of the positive electrode active material.

[0082] Therefore, the additive according to one embodiment of the present invention can more effectively contribute to the stability and cycle life characteristics of a lithium battery at high voltage by taking the structure of Chemical Formula 1 described above.

[0083] The additive may be included in an amount of 0.01 wt % to 10 wt % based on the total amount of the electrolyte. Specifically, the additive may be included in an amount of 0.05 wt % to 3 wt % based on the total amount of the electrolyte. If the additive content is below this range, a problem may occur in which a coating cannot be sufficiently formed on the lithium-based positive electrode and negative electrode. If the additive content exceeds this range, a problem may occur in which the resistance of the positive electrode and negative electrode increases, resulting in a decrease in the capacity and lifespan of the battery.

[0084] The additive represented by Chemical Formula 1's effect of improving the high-temperature stability of lithium secondary batteries is even more pronounced when used with a high-nickel cathode active material and an anode active material containing a silicon-carbon composite. Specifically, silicon particles are used to increase battery capacity, but they can cause side reactions with the electrolyte, increasing the battery's internal resistance. The additive suppresses the side reactions between the silicon particles and the electrolyte, thereby minimizing the increase in internal resistance and maximizing the effect of increasing battery capacity.

[0085] The electrolyte solution may be prepared by dissolving a lithium salt in a non-aqueous organic solvent, adding an additive, and mixing the resulting mixture. The electrolyte solution mixing process may be appropriately selected from processes widely known in the field of electrolyte solution manufacturing.

[0086] The non-aqueous organic solvent may include one or more selected from the group consisting of ethyl methyl carbonate (EMC), ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate PC, propyl propionate PP, diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and butylene carbonate BC.

[0087] As a specific example, the non-aqueous organic solvent may be a mixed solvent of ethyl methyl carbonate (EMC), ethylene carbonate (EC), and dimethyl carbonate (DMC).

[0088] For example, ethyl methyl carbonate (EMC) can be contained in an amount of 5 to 30% by volume relative to the total amount of the non-aqueous organic solvent, ethylene carbonate (EC) can be contained in an amount of 10 to 30% by volume relative to the total amount of the non-aqueous organic solvent, and dimethyl carbonate (DMC) can be contained in an amount of 50 to 80% by volume relative to the total amount of the non-aqueous organic solvent.

[0089] The lithium salt may include one or more selected from the group consisting of LiPF, LiClO, LiBF, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiSOCF, LiBOB, LiFOB, LiDFBP, LiTFOP, LiPOF, LiSbF, LiAsF, LiAlO, LiAlCl, LiCl, LiI, LiN(SOCF), Li(FSO)N, and LiCFSO. According to one embodiment, LiPF may be used as the lithium salt.

[0090] The concentration of the lithium salt may be 0.1 M to 3.0 M. Specifically, the concentration of the lithium salt is 0.5 M or more, and may be 1.0 M or more. The concentration of the lithium salt may be 3.0 M or less, 2.5 M or less, or 2.0 M or less. In an embodiment of 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.

[0091] In another embodiment of the present invention, a lithium secondary battery may be provided, which includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte solution, the electrolyte solution including a non-aqueous organic solvent, a lithium salt, and an additive represented by Chemical Formula 1 above.

[0092] The lithium secondary battery can be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0093] The positive electrode active material can include a lithium composite oxide represented by the following Chemical Formula 2. Chemical Formula 2 Li x M 1 y M 2 z M 3 1-y-z O 2-a X<000​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0097] As an embodiment, the Si-based negative electrode active material may be a silicon-carbon composite. The Si-based negative electrode active material may include a core containing silicon-based particles and a coating layer containing amorphous carbon. The silicon-based particles may include one or more selected from silicon particles, Si-C composites, SiOx (0 < x ≦ 2), and Si alloys.

[0098] When the positive electrode contains a high-nickel-based positive electrode active material and the negative electrode contains a silicon-carbon composite, the improvement effect of the high-temperature stability of the lithium secondary battery can be maximized. The lithium secondary battery of the above combination can also operate at a high voltage of 4.2 V or higher.

Examples

[0099] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only one example of the present invention, and the present invention is not limited to the following examples.

[0100] Examples and Comparative Examples Example 1 (1) Preparation of electrolyte 1.5 M of LiPF6 was dissolved in a non-aqueous organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 20:10:70, and 0.25 wt% of an additive was added to obtain an electrolyte solution. preparation prepared.

[0101] As the additive, the compound represented by the following Chemical Formula 1-1 was used.

[0102]

Chemical Formula

[0103] (2) Fabrication of lithium secondary batteries As the positive electrode active material, NCA (LiNi 0.91 Co 0.08 Al 0.01A mixture of 97% O2, 0.5% artificial graphite powder as a conductive material, 0.8% carbon black (Ketjenblack), 0.2% acrylonitrile rubber, and 1.5% polyvinylidene fluoride (PVdF) was added to N-methyl-2-pyrrolidone and stirred for 30 minutes using a mechanical stirrer to prepare a cathode active material slurry. The slurry was then coated onto a 20μm thick aluminum current collector using a doctor blade to a thickness of approximately 60μm, dried in a hot air dryer at 100°C for 0.5 hours, and then dried again under vacuum at 120°C for 4 hours. The cathode was then fabricated by rolling.

[0104] Anode active material (98 wt%), consisting of graphite and silicon composite in a weight ratio of 95.8:4.2, 1 wt% styrene-styrene rubber (SBR), and 1 wt% carboxymethyl cellulose (CMC), was mixed and added to distilled water. The mixture was stirred for 60 minutes using a mechanical stirrer to prepare anode active material slurry. The slurry was applied to a 10 μm-thick copper current collector using a doctor blade to a thickness of approximately 60 μm. The mixture was then dried in a hot air dryer at 100°C for 0.5 hours, then dried again under vacuum at 120°C for 4 hours, and rolled to prepare anodes.

[0105] An electrode assembly was prepared by assembling a positive electrode, a negative electrode, and a 16 μm thick polyethylene separator, and an electrolyte solution was injected into the electrode assembly to prepare a lithium secondary battery.

[0106] Example 2 An electrolyte solution was prepared in the same manner as in Example 1, except that 2.0 wt % of the additive was used, and a lithium secondary battery was fabricated.

[0107] Example 3 An electrolyte solution was prepared in the same manner as in Example 1, except that 5.0 wt % of the additive was used, and a lithium secondary battery was fabricated.

[0108] Example 4 An electrolyte solution was prepared in the same manner as in Example 1, except that an additive represented by the following Chemical Formula 1-2 was used instead of the additive represented by Chemical Formula 1-1, and a lithium secondary battery was fabricated.

[0109] [ka]

[0110] Example 5 An electrolyte solution was prepared in the same manner as in Example 1, except that an additive represented by the following Chemical Formula 1-3 was used instead of the additive represented by Chemical Formula 1-1, and a lithium secondary battery was fabricated.

[0111] [ka]

[0112] Example 6 An electrolyte solution was prepared in the same manner as in Example 1, except that an additive represented by the following Chemical Formula 1A-4 was used instead of the additive represented by Chemical Formula 1-1, and a lithium secondary battery was fabricated.

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[0114] Comparative Example 1 An electrolyte solution was prepared in the same manner as in Example 1, except that the compound represented by Chemical Formula 1-1 was not used, and a lithium secondary battery was fabricated using the electrolyte solution.

[0115] Comparative Example 2 An electrolyte solution was prepared in the same manner as in Example 1, except that an additive represented by the following Chemical Formula 3-1 was used instead of the additive represented by Chemical Formula 1-1, and a lithium secondary battery was fabricated.

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[0117] Comparative Example 3 An electrolyte solution was prepared in the same manner as in Example 1, except that an additive represented by the following Chemical Formula 3-2 was used instead of the additive represented by Chemical Formula 1-1, and a lithium secondary battery was fabricated.

[0118] [ka]

[0119] Comparative Example 4 An electrolyte solution was prepared in the same manner as in Example 1, except that an additive represented by the following Chemical Formula 3-3 was used instead of the additive represented by Chemical Formula 1-1, and a lithium secondary battery was fabricated.

[0120] [ka]

[0121] Comparative Example 5 An electrolyte solution was prepared in the same manner as in Example 1, except that an additive represented by the following Chemical Formula 3-4 was used instead of the additive represented by Chemical Formula 1-1, and a lithium secondary battery was fabricated.

[0122] [ka]

[0123] Evaluation example The lithium secondary batteries were evaluated by the following methods.

[0124] Evaluation 1: ICP-OES analysis (evaluation of transition metal elution) The lithium secondary batteries according to the examples and comparative examples were charged and discharged, and after storing them at 60°C for one day, the amount of eluted metal ions (Ni) was measured by the following method. The charge and discharge were performed at 45°C under the conditions of 1.0 C charge (CC / CV, 4.25 V cut-off) / 1.0 C discharge (CC, 2.5 V cut-off).

[0125] The lithium secondary battery was disassembled and the positive electrode was separated. The separated positive electrode was then placed in a 10 mL Teflon container together with the electrolyte, sealed, and the Ni content was measured by ICP-OES analysis. The results are shown in Table 1 below.

[0126] Evaluation 2: Positive electrode XRD results The lithium secondary batteries prepared in the examples and comparative examples were charged and discharged, and then stored at a high temperature of 60°C for 30 days. After that, the lithium secondary batteries were disassembled and the positive electrodes were separated. The charging and discharging were performed at 45°C under the conditions of 1.0 C charge (CC / CV, 4.25 V cut-off) / 1.0 C discharge (CC, 2.5 V cut-off).

[0127] Next, X-ray diffraction analysis (XRD) was performed on the separated positive electrode, and (I 003 ) / (I 104 The peak ratios were measured, and the results are shown in Table 1 below.

[0128] Evaluation 3: High-temperature storage characteristics evaluation The lithium secondary batteries according to the examples and comparative examples were charged and discharged, and after storing them at 60° C. for 1 day and 30 days, the discharge capacity was measured and the capacity retention rate was calculated. The results are shown in Table 1 below.

[0129] Charge and discharge were performed at 45°C under the conditions of 1.0 C charge (CC / CV, 4.25 V cut-off) / 1.0 C discharge (CC, 2.5 V cut-off).

[0130] The capacity retention rate was calculated using the following formulas 1 and 2. formula 1 Discharge capacity retention rate immediately after high temperature storage (%) = (discharge capacity after 1 day of high temperature storage / initial discharge capacity) * 100 formula 2 High temperature storage discharge capacity retention rate (%) = (discharge capacity after 30 days of high temperature storage / initial discharge capacity) * 100

[0131] [Table 1]

[0132] Consideration Referring to Table 1, it was confirmed that when an electrolyte solution containing an additive according to an embodiment of the present invention was used (Examples 1 to 6), the high temperature (60°C) storage characteristics were improved compared to when an electrolyte solution without an additive according to an embodiment of the present invention was used (Comparative Example 1).

[0133] Furthermore, it was confirmed that the nitrile-based additive (Example 1) in which all of R1 to R4 in the above-mentioned Chemical Formula 1 are substituents other than hydrogen can provide a secondary battery with excellent high-temperature (60°C) storage characteristics compared to the nitrile-based additive (Comparative Example 5) in which only some of R1 to R4 are substituents other than hydrogen.

[0134] Furthermore, referring to Table 1, it can be seen that the lithium secondary battery fabricated according to the embodiment has a significantly lower amount of Ni elution from the positive electrode than the comparative example. Therefore, it can be said that the lithium secondary battery according to the embodiment is effective in suppressing the elution of transition metals during high-temperature storage and suppressing the deterioration of the positive electrode.

[0135] Also, in Table 1 (I 003 ) / (I 104 ) peak ratio, it was confirmed that the lithium secondary battery fabricated according to the embodiment suppresses structural deterioration due to strong charge neutrality on the positive electrode surface and suppression of transition metal elution, compared to the comparative example.

[0136] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this and can be implemented in various modified forms within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is natural that this also falls within the scope of the present invention. [Explanation of symbols]

[0137] 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, and an additive represented by the following chemical formula 1: 【Chemistry 1】 In Formula 1, R 1 ~R 4 are each independently selected from the group consisting of a halogen atom, a C1 to C20 alkyl group, a C1 to C20 halogenated alkyl group, a C3 to C30 cycloalkyl group, a C6 to C30 aryl group, a hydroxy group, a C1 to C10 alkoxy group, a carboxyl group, a formyl group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonic acid group, and derivatives thereof.

2. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the additive is represented by the following Chemical Formulas 1-1 to 1-3. 【Chemistry 2】

3. In Formula 1, R 1 ~R 4 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein at least one of the groups is a fluorine-containing substituent or a fluorine atom.

4. The additive is represented by the following chemical formulas 1A-1 to 1A-4: 【Transformation 3】 In the formulas 1A-1 to 1A-4, R 1 ~R 3 are each independently selected from the group consisting of a C2 to C20 alkyl group, a C1 to C20 alkyl group, a C1 to C20 halogenated alkyl group, a C3 to C30 cycloalkyl group, a C6 to C30 aryl group, a hydroxy group, a C1 to C10 alkoxy group, a carboxyl group, a formyl group, an epoxy group, a cyano group, a nitro group, an amino group, a sulfonic acid group, and derivatives thereof.

5. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the additive is contained in the electrolyte solution in an amount of 0.01 to 10% by weight.

6. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent comprises at least one selected from the group consisting of ethyl methyl carbonate (EMC), ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), propyl propionate (PP), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and butylene carbonate (BC).

7. The lithium salt is LiPF 6 , LiClO 4 , LiBF 4 , lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (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 LiC 4 F 9 SO 3 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the electrolyte solution is one or more selected from the group consisting of:

8. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the concentration of the lithium salt is 0.1M to 3.0M.

9. 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 claim 1.

10. The positive electrode active material includes a lithium composite oxide represented by the following chemical formula 2: chemical formula 2 Li x M 1 y M 2 z M 3 1-y-z O 2-a X a In the above Chemical Formula 2, 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 Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, and La; 10. The lithium secondary battery according to claim 9, wherein X comprises one or more elements selected from F, S, P, or Cl.

11. 11. The lithium secondary battery according to claim 10, wherein in Chemical Formula 2, M1 is Ni, 0.8≦y≦1, and 0≦z≦0.

2.

12. The lithium secondary battery according to claim 9 , 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.

13. The lithium secondary battery according to claim 12, wherein the Si-based negative electrode active material is a silicon-carbon composite.

14. 10. The lithium secondary battery according to claim 9, which operates at a high voltage of 4.2 V or higher.

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