Electrolytic solution for lithium secondary battery, and lithium secondary battery comprising the same

Abstract

To provide a lithium secondary battery improved in lifetime and high-temperature storage characteristics.SOLUTION: An electrolytic solution for a lithium secondary battery includes a non-aqueous organic solvent, a lithium salt, and an additive. The additive includes: a first compound represented by the chemical formula in the figure; and a second compound such as 2-fluoro-1,3,2-dioxaphospholane and 2-fluoro-4-methyl-1,3,2-dioxaphospholane.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 containing the same. [Background technology]

[0002] Recently, the demand for high-energy-density, high-capacity secondary batteries has been increasing rapidly due to the rapid spread of battery-powered electronic devices such as mobile phones, notebook computers, and electric vehicles. Therefore, research and development efforts to improve the performance of lithium secondary batteries have been actively conducted.

[0003] A lithium secondary battery is a battery that includes a 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 from the cathode and anode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 11,437,647 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a lithium secondary battery having improved life and high-temperature storage characteristics. [Means for solving the problem]

[0006] The electrolyte 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 may include a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2:

[0007] [ka] chemical formula 1 In the above chemical formula 1, R1 to R8 are each independently hydrogen or a substituted or unsubstituted C1 to C10 alkyl group, and n may be an integer from 1 to 8.

[0008] [ka] chemical formula 2

[0009] In the above chemical formula 2, X1 is a fluoro group, a chloro group, a bromo group, or an iodo group; R9 to R14 are each independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group, and m may be 0 or 1.

[0010] A lithium secondary battery according to another embodiment of the present invention may include a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte solution for lithium secondary batteries. [Effects of the Invention]

[0011] The lithium secondary battery according to one embodiment can improve the life characteristics and suppress an increase in battery resistance when stored at high temperatures. [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 cross-sectional view schematically illustrating a lithium secondary battery according to one embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to one embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to one embodiment. [Figure 5] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to one embodiment. [Figure 6] 1 is a graph showing the capacity retention rates of the lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3. 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 may be embodied in various forms and may undergo various modifications. However, the description of the present embodiments is provided to complete the disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0014] In this specification, when a component is referred to as being on top of another component, it means that it may be formed directly on the other component, or that a third component may be interposed between them. Also, in the drawings, the thickness of the components is exaggerated for the purpose of effectively explaining the technical content. Throughout the specification, parts designated with the same reference numerals refer to the same components.

[0015] Unless otherwise stated herein, the singular can also include the plural. Additionally, unless otherwise stated, "A" or "B" can mean "including A but also including B, or including A and B." As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements to the referenced element.

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

[0017] Unless otherwise defined, the term "substituted" used herein means that at least one hydrogen atom in a substituent or compound has been replaced with a deuterium atom, 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.

[0018] Specifically, "substituted" means that at least one hydrogen in a substituent or compound is replaced with deuterium, a halogen 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 C10 fluoroalkyl group, or a cyano group. For example, "substituted" means that at least one hydrogen in a substituent or compound is replaced with deuterium, a halogen group, a C1 to C20 alkyl group, a C6 to C30 aryl group, a C1 to C10 fluoroalkyl group, or a cyano group. Alternatively, "substituted" means that at least one hydrogen in a substituent or compound is replaced with deuterium, a halogen group, a C1 to C5 alkyl group, a C6 to C18 aryl group, a C1 to C5 fluoroalkyl group, or a cyano group. By way of example, "substituted" means that at least one hydrogen in a substituent or compound has been 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 an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in 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. Within the electrolyte ELL, the lithium ions may pass through the separator 30 and migrate toward the positive electrode 10 or the negative electrode 20.

[0022] positive electrode 10 The lithium secondary battery positive electrode 10 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 % respectively 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)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0026] The conductive material is used to impart conductivity to the electrode and can be any material that does not cause chemical changes in the constructed battery and is electronically conductive. 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 may 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 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.

[0029] The composite oxide may be a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based oxide, cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0030] For example, a compound represented by any one of the following chemical formulas may 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 a Ni 1-b-c Co b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2), Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5,0<α<2), Li a Ni b Co c L 1 d G e O2 (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1), Li a NiG b O2 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a CoG b O2 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a Mn 1-b G b O2 (0.90≦a≦1.8, 0.001≦b≦0.1), Li a Mn2Gb 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).

[0031] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L1 is Mn, Al, or a combination thereof.

[0032] 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 to 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 may realize high capacity and therefore may be applied to high-capacity, high-density lithium secondary batteries.

[0033] negative electrode 20 The lithium secondary battery positive electrode 20 may include a current collector COL2 and a negative electrode active material layer AML2 formed on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0034] 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.

[0035] The binder serves to firmly adhere the negative active material particles to each other and to firmly adhere the negative 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.

[0036] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0037] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyether resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0038] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound to 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.

[0039] The dry binder may be a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or a combination thereof.

[0040] The conductive material is used to impart conductivity to the electrode and may be any material that does not cause a chemical change in the constructed battery and is electronically conductive. 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.

[0041] The current collector COL2 may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0042] 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, a lithium metal alloy, a material capable of doping or dedoping lithium, or a transition metal oxide.

[0043] The material capable of reversibly inserting / extracting lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous graphite, such as natural graphite or artificial graphite. Examples of amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0044] The lithium metal alloy may be 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.

[0045] As the substance capable of doping or undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, 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.

[0046] 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) combined with 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, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0047] The silicon-carbon composite may further include 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.

[0048] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used by mixing with a carbon-based negative electrode active material.

[0049] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. Such separator 30 may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, or a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0050] Separator 30 may 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.

[0051] The porous substrate may be a polymer membrane made of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0052] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0053] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH), boehmite, and combinations thereof.

[0054] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

[0055] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent, a lithium salt, and an electrolyte additive.

[0056] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0057] The non-aqueous organic solvent may be an ester-based, carbonate-based, ether-based, ketone-based, or alcohol-based solvent, a non-quantum solvent, or a combination thereof.

[0058] The carbonate solvent may be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl pyrrolyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or the like.

[0059] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate (PP), decanolide, mevalonolactone, valerolactone, and caprolactone.

[0060] Examples of ether-based solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone-based solvents that can be used include cyclohexanone. Examples of alcohol-based solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of non-quantum solvents that can be used include nitriles such as R-CN (where R is a 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.

[0061] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0062] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain cyclic carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0063] The lithium salt is dissolved in an organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting 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 positive numbers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0064] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to an embodiment, with FIG. 2 illustrating a cylindrical battery, FIG. 3 illustrating a prismatic battery, and FIGS. 4 and 5 illustrating pouch-type batteries. Referring to FIGS. 2 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a housing 50 in which the electrode assembly 40 is embedded. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the housing 50, as shown in FIG. 2. Also, in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include 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 positive electrode assembly 40 to the outside.

[0065] A lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

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

[0067] According to one embodiment, the electrolyte for a lithium secondary battery includes 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] [ka] chemical formula 1

[0069] In the above chemical formula 1, R1 to R8 are each independently hydrogen or a substituted or unsubstituted C1 to C10 alkyl group, and n may be an integer from 1 to 8.

[0070] [ka] chemical formula 2

[0071] In the above chemical formula 2, X1 is a fluoro group, a chloro group, a bromo group, or an iodo group; R9 to R14 are each independently hydrogen, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group, and m may be 0 or 1.

[0072] The non-aqueous organic solvent according to an embodiment of the present invention may be a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0073] As a specific example, the ethylene carbonate (EC) solvent may be contained in an amount of 5 to 40% by volume, or 10 to 30% by volume, based on the total amount of non-aqueous organic solvents. The ethyl methyl carbonate (EMC) solvent may be contained in an amount of 5 to 20% by volume, or 5 to 15% by volume, based on the total amount of non-aqueous organic solvents. The dimethyl carbonate (DMC) solvent may be contained in an amount of 50 to 90% by volume, or 60 to 80% by volume, based on the total amount of non-aqueous organic solvents.

[0074] The electrolyte according to an embodiment of the present invention may include LiPF6 as the lithium salt.

[0075] The concentration of the lithium salt may be 0.1 M or more and 2.0 M or less. 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 or more and 2.0 M or less, the conductivity and viscosity of the electrolyte can be appropriately maintained.

[0076] 1st compound The first compound according to one embodiment of the present invention can be represented by the following Chemical Formula 1:

[0077] [ka] chemical formula 1

[0078] In the above chemical formula 1, R1 to R8 are each independently hydrogen or a substituted or unsubstituted C1 to C10 alkyl group, and n may be an integer from 1 to 8.

[0079] Specifically, each of R1 to R8 may be hydrogen, and the compound may be represented by Chemical Formula 1A. The first compound may be 1,4-butane sultone.

[0080] [ka] Chemical formula 1A

[0081] The first compound can protect the coating on the positive and negative electrode surfaces and reduce side reactions in the electrolyte. Specifically, the lone pair electron of the sulfonate group can act on and stabilize Lewis acids (e.g., PF5-) present in the electrolyte. The lone pair electron can also stabilize transition metals on the positive electrode surface or transition metals released from the positive electrode surface. This can prevent positive electrode degradation and improve battery life.

[0082] The content of the first compound may be from 0.5 to 5.0 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery. Specifically, the content of the first compound may be from 1.0 to 3.0 parts 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, not only can the electrode coating be effectively protected, but also the interaction with the second compound described below can be maximized.

[0083] 2nd compound The second compound according to one embodiment of the present invention can be represented by the following Chemical Formula 2:

[0084] [ka] chemical formula 2

[0085] In chemical formula 2, X1 is a fluoro group, a chloro group, a bromo group, or an iodo group; R9 to R14 are each independently a hydrogen atom, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; and m may be 0 or 1.

[0086] The second compound can form a solid electrolyte interface (SEI) film on the negative electrode surface that has high high-temperature stability and excellent ionic conductivity. The second compound can also reduce gas generation due to decomposition reactions in the electrolyte during high-temperature storage. Specifically, the -PO2F functional group of the first compound can stabilize the thermal decomposition products of lithium salts such as LiPF6 or anions dissociated from the lithium salt, thereby reducing the generation of gases such as HF. The excellent SEI film formation and gas generation reduction effects can contribute to improved life characteristics and reduced internal resistance of lithium secondary batteries, especially at high temperatures.

[0087] The second compound's effects of improving the lifespan characteristics and reducing the internal resistance of lithium secondary batteries at high temperatures are even more pronounced when used with a high-nickel cathode active material and an anode active material containing graphite and silicon nanoparticles. Specifically, silicon particles are used to increase battery capacity, but they can cause side reactions with the electrolyte, increasing the battery's internal resistance. When the second compound is introduced as an additive, it suppresses the side reactions between the silicon particles and the electrolyte, thereby minimizing the increase in the battery's internal resistance and maximizing the goal of increasing battery capacity.

[0088] The second compound may include a cyclic phosphorane derivative. Compared to linear phosphite derivatives, cyclic phosphorane derivatives can significantly improve the lifespan characteristics of lithium secondary batteries at high temperatures. The linear phosphite derivatives may induce side reactions of LiPF6 through the dissociated -PO2F functional group, thereby inducing gas generation due to the decomposition reaction of the electrolyte during high-temperature storage.

[0089] In one embodiment, Chemical Formula 1 can be represented by the following Chemical Formula 2-1 or 2-2.

[0090] [ka] Chemical formula 2-1 [ka] Chemical formula 2-2

[0091] In Chemical Formula 2-1 and Chemical Formula 2-2, X1 is a fluoro group, a chloro group, a bromo group, or an iodo group; R9 to R14 may each independently be hydrogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

[0092] In one embodiment, R9 and R10 in Chemical Formula 2A are each hydrogen, and at least one of R13 and R14 may be a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

[0093] In one embodiment, the second compound may be at least one selected from the compounds represented by the following Chemical Formula 2C and Chemical Formula 2D, i.e., at least one selected from 2-fluoro-1,3,2-dioxaphospholane and 2-fluoro-4-methyl-1,3,2-dioxaphospholane.

[0094] [ka] Chemical formula 2C Chemical formula 2D

[0095] The content of the second compound may be from 0.2 to 2.0 parts by weight based on 100 parts by weight of the electrolyte for lithium secondary batteries. Specifically, the content of the second compound may be from 0.5 to 1.5 parts by weight based on 100 parts by weight of the electrolyte for lithium secondary batteries. 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, excellent SEI film formation effects and gas generation reduction effects at high temperatures can be maximized.

[0096] The content of the additive, including both the first compound and the second compound, may be 0.7 to 7 parts by weight, 1.2 to 5 parts by weight, or 2 to 5 parts by weight, based on 100 parts by weight of the electrolyte. When the content of the additive satisfies the above range, the effects of improving the resistance increase of the secondary battery and preventing the elution of transition metals can be maximized, while side reactions caused by the excessive addition of the additive can be prevented. The effect of improving battery characteristics can be significant at high temperatures.

[0097] The weight ratio of the first compound to the second compound in the additive may be 1 to 5, more preferably 1 to 3. When the first compound and the second compound have such a weight ratio, a strong film can be formed and the formed film can be effectively protected.

[0098] Examples and comparative examples of the present invention will be described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0099] Examples and Comparative Examples An electrolyte and a lithium secondary battery were manufactured as follows.

[0100] Example 1 (1) Electrolyte production An electrolyte solution was prepared by dissolving 1.5 M LiPF in a non-aqueous organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 20:10:70, and adding 0.5 wt % of the first compound and 1 wt % of the second compound as additives.

[0101] The first compound was represented by the following chemical formula 1A, and the second compound was represented by the following chemical formula 2D.

[0102] [ka] Chemical formula 1A

[0103] [ka] chemical formula 2d

[0104] (2) Manufacture of lithium secondary batteries A positive electrode active material slurry was prepared by mixing LiNi0.91Co0.07Al0.02O2 as a positive electrode active material, polyvinylidene fluoride as a binder, and carbon black as a conductive material in a weight ratio of 97:2:1 and dispersing the mixture in N-methylpyrrolidone.

[0105] The positive electrode active material slurry was coated on an Al current collector with a thickness of 14 μm, dried at 110° C., and then pressed to prepare a positive electrode.

[0106] The negative electrode active material was prepared by mixing artificial graphite and silicon nanoparticles in a weight ratio of 93:7, and the binder was mixed with styrene-styrene rubber (SBR) and thickener carboxymethyl cellulose (CMC) in a weight ratio of 97:1:2. The mixture was dispersed in distilled water to prepare a negative electrode active material slurry.

[0107] The negative electrode active material slurry was coated on a Cu current collector with a thickness of 10 μm, dried at 100° C., and then pressed to prepare a negative electrode.

[0108] The positive and negative electrodes were assembled with a 25 μm thick polyethylene separator to prepare an electrode assembly, and an electrolyte was injected to prepare a lithium secondary battery.

[0109] Example 2 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 1 wt % of the first compound and 1 wt % of the second compound were added as additives when preparing the electrolyte solution.

[0110] Example 3 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 2 wt % of the first compound and 1 wt % of the second compound were added as additives when preparing the electrolyte solution.

[0111] Example 4 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 3 wt % of the first compound and 1 wt % of the second compound were added as additives when preparing the electrolyte solution.

[0112] Example 5 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 5 wt % of the first compound and 1 wt % of the second compound were added as additives when preparing the electrolyte solution.

[0113] Comparative Example 1 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that no additives were added during the preparation of the electrolyte solution.

[0114] Comparative Example 2 An electrolyte solution and a lithium secondary battery were manufactured in the same manner as in Example 1, except that only 1 wt % of the first compound was added as an additive when preparing the electrolyte solution.

[0115] Comparative Example 3 An electrolyte solution and a lithium secondary battery were manufactured in the same manner as in Example 1, except that only 1 wt % of the second compound was added as an additive when preparing the electrolyte solution.

[0116] Comparative Example 4 An electrolyte and a lithium secondary battery were prepared in the same manner as in Example 1, except that 1 wt % of a compound represented by Formula 2D and 1 wt % of a compound represented by Formula 3 were added as additives when preparing the electrolyte.

[0117] [ka] chemical formula 3

[0118] Comparative Example 5 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 1 wt % of the compound represented by Formula 2D and 2 wt % of the compound represented by Formula 3 were added as additives when preparing the electrolyte solution.

[0119] Comparative Example 6 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 1 wt % of the compound represented by Formula 2D and 3 wt % of the compound represented by Formula 3 were added as additives when preparing the electrolyte solution.

[0120] Evaluation example 1: Evaluation of resistance increase rate during high temperature storage The lithium secondary batteries prepared in the examples and comparative examples were charged to SOC100 at room temperature (25°C) using a constant current-constant voltage (CC-CV) charger under conditions of 0.33 C, 4.25 V, and 0.025 C cutoff. The initial battery resistance (DC-IR) was measured, as was the resistance (DC-IR) after storage at 60°C for 90 days. The resistance increase rate was calculated, and the results are shown in Table 1 below. The resistance (DC-IR) was calculated from the difference in current and voltage when different currents were applied. The battery was initially fully charged and discharged at a constant current of 1 C for 30 seconds, and the calculation was performed using ΔR=ΔV / ΔI. The resistance increase rate was calculated according to Equation 1 below.

[0121] Resistance increase rate (%) = [battery resistance (DC-IR) value after 90 days / initial battery resistance (DC-IR) value] * 100

[0122] [Table 1] Referring to Table 1, it can be seen that the lithium secondary batteries according to Examples 1 to 5, which contain the compound represented by Chemical Formula 1A and the compound represented by Chemical Formula 2D as additives, have smaller initial resistances and smaller resistance increase rates after exposure to high temperatures than the secondary batteries according to Comparative Examples 1 to 6.

[0123] Evaluation example 2: High-temperature life capacity retention rate evaluation The secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 6 were continuously charged and discharged up to 300 cycles at 45° C. under 0.5 C charge and 0.5 C discharge conditions, and the capacity retention rates after 300 cycles are shown in Table 2 below. A graph of some of the capacity retention rates of the Comparative Examples and Examples is shown in FIG. 6.

[0124] The capacity retention rate was calculated according to the following formula 2: Capacity retention rate (%) = (discharge capacity at 300th cycle - initial discharge capacity) * 100

[0125] [Table 2] Referring to Table 2 and FIG. 6, it can be seen that the lithium secondary batteries according to Examples 1 to 5, which contain the compound represented by Chemical Formula 1A and the compound represented by Chemical Formula 2D as additives, have a higher capacity retention rate after 300 cycles than the secondary batteries according to Comparative Examples 1 to 6.

[0126] 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]

[0127] 100 Lithium Rechargeable 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, 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 1】 Chemical formula 1 (In the above Chemical Formula 1, R1 to R8 are each independently hydrogen or a substituted or unsubstituted C1 to C10 alkyl group; n is an integer from 1 to 8. 【Chemistry 2】 chemical formula 2 (In the above Chemical Formula 2, X1 is a fluoro group, a chloro group, a bromo group, or an iodo group; R9 to R14 are each independently a hydrogen atom, a cyano group, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; m is 0 or 1.

2. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the content of the first compound is 0.5 parts by weight to 5.0 parts by weight based on 100 parts by weight of the electrolyte solution for a lithium secondary battery.

3. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the content of the first compound is 1.0 to 3.0 parts by weight based on 100 parts by weight of the electrolyte solution for a lithium secondary battery.

4. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the content of the second compound is 0.2 parts by weight to 2.0 parts by weight based on 100 parts by weight of the electrolyte solution for a lithium secondary battery.

5. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the content of the second compound is 0.5 to 1.5 parts by weight based on 100 parts by weight of the electrolyte solution for a lithium secondary battery.

6. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the content of the additive is 0.7 to 7 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery.

7. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the weight ratio of the first compound to the second compound in the additive is 1 to 5.

8. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein each of R1 to R8 in Formula 1 is hydrogen.

9. The electrolyte for a lithium secondary battery according to claim 1 , wherein the first compound is represented by the following Chemical Formula 1A: 【Chemistry 3】 Chemical formula 1A

10. The electrolyte for a lithium secondary battery according to claim 1 , wherein the Chemical Formula 2 is represented by the following Chemical Formula 2A or 2B: 【Chemistry 4】 Chemical formula 2A 【Chemistry 5】 Chemical formula 2B In Formulas 2A and 2B, X1 is a fluoro group, a chloro group, a bromo group, or an iodo group; R9 to R14 are each independently hydrogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

11. R9 and R10 in Formula 2A are each hydrogen; 11. The electrolyte solution for a lithium secondary battery according to claim 10, wherein at least one of R13 and R14 is a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkoxy group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group.

12. The electrolyte for a lithium secondary battery according to claim 1 , wherein the second compound comprises at least one selected from the group consisting of compounds represented by the following Formula 2C and Formula 2D: 【Chemistry 6】 Chemical formula 2C Chemical formula 2D

13. 2. The electrolyte for a lithium secondary battery of claim 1, wherein the additive further comprises at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, vinylethylene carbonate (VEC), adiponitrile (AN), succinonitrile (SN), 1,3,6-hexanetricyanide (HTCN), propene sultone (PST), propane sultone PS, lithium tetrafluoroborate (LiBF), lithium difluorophosphate (LiPOF), and 2-fluorobiphenyl (2-FBP).

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

15. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the lithium salt includes LiPF6.

16. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the concentration of the lithium salt is 0.1 M or more and 2.0 M or less.

17. 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.

18. 18. The lithium secondary battery of claim 17, wherein the positive electrode active material comprises a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-precious nickel-manganese-based oxide, or a combination thereof.

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

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