Electrolyte for lithium secondary batteries and lithium secondary batteries containing the same

Abstract

This invention provides an electrolyte that can improve the lifespan and high-temperature performance of lithium secondary batteries containing cobalt-free positive electrode active material under high-voltage conditions. [Solution] The present invention relates to an electrolyte for lithium secondary batteries and a lithium secondary battery containing the same. The electrolyte comprises a non-aqueous organic solvent, a lithium salt, and an additive, the additive comprising a mixture of a first additive represented by the following chemical formula 1 and a second additive having a sulfonyl group and a triazole group. JPEG2026068701000021.jpg6045

Description

[Technical Field]

[0001] This application claims priority and interest in Korean Patent Application No. 10-2024-0137952, filed with the Korean Intellectual Property Office on 10 October 2024, all of which are incorporated herein by reference. [Background technology]

[0002] One embodiment of the present invention relates to an electrolyte for lithium secondary batteries and a lithium secondary battery containing the same. [Overview of the project] [Problems that the invention aims to solve]

[0003] In recent years, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries has been rapidly increasing. As a result, research and development to improve the performance of lithium-ion rechargeable batteries is being actively pursued.

[0004] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode containing an active material that allows for the insertion and deintercalation of lithium ions, and an electrolyte. It produces electrical energy through oxidation and reduction reactions that occur when lithium ions are inserted into and deintercalated at the positive and negative electrodes.

[0005] The electrolyte in such lithium secondary batteries is a solution of lithium salt dissolved in a non-aqueous organic solvent. The characteristics of a lithium secondary battery are determined by complex reactions between the positive electrode and electrolyte, and the negative electrode and electrolyte. Therefore, the use of an appropriate electrolyte is one of the important variables for improving the performance of a lithium secondary battery. [Means for solving the problem]

[0006] One embodiment of the present invention provides an electrolyte for lithium secondary batteries that can improve the lifespan and high-temperature performance of lithium secondary batteries containing a cobalt-free positive electrode active material under high-voltage conditions.

[0007] Another embodiment is to provide a lithium secondary battery containing the above-mentioned electrolyte.

[0008] One embodiment provides an electrolyte for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive comprises a mixture of a first additive represented by the following chemical formula 1 and a second additive represented by the following chemical formula 2.

[0009] [ka]

[0010] In chemical formula 1, R 1 ~R 6 Each of these is independently hydrogen, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group. R 7 These are substituted or unsubstituted C1-C20 alkoxy groups, n is an integer, either 0 or 1.

[0011] [ka]

[0012] In chemical formula 2, L 1 and L 2Each of these is independently a single bond, a substituted or unsubstituted C1-C5 alkylene group, a substituted or unsubstituted C2-C5 alkenylene group, a substituted or unsubstituted C2-C5 alkynylene group, or a substituted or unsubstituted C6-C20 arylene group. A and B are each independently a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group. At least one of A and B is a group represented by the following chemical formula A,

[0013] [ka]

[0014] In chemical formula A, L 3 and L 4 Each of these is independently hydrogen, a halogen, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C3-C10 cycloalkyl group.

[0015] Another embodiment provides a lithium secondary battery comprising the above-mentioned electrolyte, a positive electrode containing a cobalt-free positive electrode active material, and a negative electrode containing a negative electrode active material.

[0016] The electrolyte according to one embodiment can improve the lifespan and stability of a lithium secondary battery containing a cobalt-free positive electrode active material under high voltage conditions during activation. [Brief explanation of the drawing]

[0017] [Figure 1] This is a conceptual diagram schematically showing a lithium secondary battery according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment of the present invention. [Figure 3] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment of the present invention. [Figure 4]This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment of the present invention. [Figure 5] This is a schematic cross-sectional view showing a lithium secondary battery according to one embodiment of the present invention. [Modes for carrying out the invention]

[0018] To fully understand the structure and effects of the present invention, preferred embodiments 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 modified in many ways. Furthermore, the following description is provided to complete the disclosure of the present invention through the description of these embodiments and to fully inform a person with ordinary skill in the art to which the invention pertains of the invention of the scope of the invention.

[0019] In this specification, when a component is referred to as being on another component, it means that the component may be formed directly on the other component, or a third component may be interposed between them. Furthermore, in the drawings, the thickness of components is exaggerated for the sake of effective illustration of the technical content. Throughout the specification, the same reference numeral refers to the same component.

[0020] Unless otherwise specified herein, a singular representation of a component may include multiple components. Furthermore, unless otherwise specified, "A or B" means "including A, or including B, or including A and B." As used herein, "including ()" does not exclude the presence or addition of one or more other components by the referred component.

[0021] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0022] In this specification, "substituted" means that, unless otherwise defined, at least one hydrogen atom of a substituent or compound is substituted with deuterium, halogen, hydroxyl group, amino group, C1-C30 amino group, nitro group, C1-C40 silyl group, C1-C30 alkyl group, C1-C10 alkylsilyl group, C6-C30 arylsilyl group, C3-C30 cycloalkyl group, C3-C30 heterocycloalkyl group, C6-C30 aryl group, C2-C30 heteroaryl group, C1-C20 alkoxy group, C1-C10 fluoroalkyl group, cyano group, or a combination thereof.

[0023] Specifically, "substitution" can mean that at least one hydrogen atom of a substituent or compound is substituted with deuterium, halogen, C1-C30 alkyl, C1-C10 alkylsilyl, C6-C30 arylsilyl, C3-C30 cycloalkyl, C3-C30 heterocycloalkyl, C6-C30 aryl, C2-C30 heteroaryl, C1-C10 fluoroalkyl, or cyano group. For example, "substitution" can mean that at least one hydrogen atom of a substituent or compound is substituted with deuterium, halogen, C1-C20 alkyl, C6-C30 aryl, C1-C10 fluoroalkyl, or cyano group. Also, "substitution" can mean that at least one hydrogen atom of a substituent or compound is substituted with deuterium, halogen, C1-C5 alkyl, C6-C18 aryl, C1-C5 fluoroalkyl, or cyano group. For example, "substitution" may mean that at least one hydrogen atom of a substituent or compound is substituted with deuterium, a cyano group, a halogen, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0024] In this specification, unless otherwise defined, "*" means a portion that is bonded to the same or different atoms or groups of atoms. In the chemical formulas described herein, unless otherwise specified, hydrogen can be assumed to be bonded to *.

[0025] Figure 1 is a schematic conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention. Referring to Figure 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0026] The positive electrode 10 and the negative electrode 20 may be separated from each other via a separator 30. The separator 30 may be placed 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 ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with the electrolyte ELL.

[0027] The electrolyte ELL may be a medium for transporting lithium ions between the positive electrode 10 and the negative electrode 20. Within the electrolyte ELL, lithium ions may move towards the positive electrode 10 or the negative electrode 20 by passing through the separator 30.

[0028] positive electrode 10 The positive electrode 10 for the 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.

[0029] As an example, the positive electrode 10 may further contain an additive that can act as a sacrificial positive electrode.

[0030] The content of the positive electrode active material in the positive electrode active material layer AML1 may be 90% to 99.5% by weight relative to 100% by weight of the positive electrode active material layer AML1. The content of the binder and conductive material may be 0.5% to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer AML1.

[0031] The binder plays a role in firmly adhering the positive electrode active material particles to each other and further firmly adhering the positive electrode active material to the current collector COL1. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0032] Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that makes up the battery can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, and carbon nanotubes; powdered or fibrous metallic materials containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0033] Aluminum may be used as the current collector COL1, but it is not limited to this.

[0034] positive electrode active material As the positive electrode active material in the positive electrode active material layer AML1, a compound capable of reversible intercalation and deintercalation of lithium (a lithium intercalation compound) may be used. Specifically, at least one composite oxide of lithium with a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0035] The composite oxide may be a composite oxide of lithium and a transition metal. Specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0036] As an example, a compound represented by any of the following general 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 Mn2G bO4(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).

[0037] In the above general formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, 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; L 1 This is Mn, Al, or a combination of these.

[0038] For example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or less, among the composite oxide of lithium and transition metal. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0039] negative electrode 20 The negative electrode 20 for the 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.

[0040] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of negative electrode active material, 0.5% to 5% by weight of binder, and 0% to 5% by weight of conductive material.

[0041] The binder plays the role of firmly adhering the negative electrode active material particles to each other and further firmly adhering the negative electrode active material to the current collector COL2. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof may be used.

[0042] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0043] 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, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0044] When an aqueous binder is used as the negative electrode binder, the negative electrode binder may further contain a cellulosic compound that can impart viscosity. This cellulosic compound may be a mixture of at least one of carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. As the alkali metal, Na, K, or Li may be used.

[0045] The dry binder is a fibrous polymeric material, which may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0046] Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that makes up the battery can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, and carbon nanotubes; powdered or fibrous metallic materials containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0047] The current collector COL2 can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and combinations thereof.

[0048] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0049] Examples of materials capable of reversibly intercalating / deintercalating lithium ions include carbon-based anode active materials, such as crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, while examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, and calcined coke.

[0050] As the lithium metal alloy, 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 may be used.

[0051] As the substance capable of doping and 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, SiO x (0 < x < 2), a Si-Q alloy (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.

[0052] 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 amorphous carbon is coated on the surface of silicon particles. For example, it may include secondary particles (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles. For example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0053] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0054] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used by being mixed with a carbon-based negative electrode active material.

[0055] 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 containing two or more layers of these materials may be used, 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.

[0056] The separator 30 may include a porous substrate and a coating layer containing organic matter, inorganic matter, or a combination thereof located on one or both sides of the porous substrate.

[0057] The porous substrate may be a polymer film formed from any polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, glass fiber, Teflon®, and polytetrafluoroethylene, or from copolymers or mixtures of two or more of these polymers.

[0058] The organic material may include polyvinylidene fluoride polymers or (meth)acrylic polymers.

[0059] The inorganic materials may include, but are not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, bohemite, and inorganic particles selected from combinations thereof.

[0060] Organic and inorganic materials may be mixed together in a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0061] Electrolyte (ELL) The electrolyte for lithium secondary batteries (ELL) contains a non-aqueous organic solvent and a lithium salt.

[0062] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reaction of batteries can move.

[0063] The non-aqueous organic solvent may be a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0064] Examples of carbonate-based solvents that may be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0065] Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0066] As ether-based solvents, dibutyl ether, tetraglyceride, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran may be used. As ketone-based solvents, cyclohexanone may be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol may be used. As aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double bond, aromatic ring, or ether group), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes may be used.

[0067] Non-aqueous organic solvents may be used individually or in combination of two or more.

[0068] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates may be mixed and used together, and the cyclic carbonates and linear carbonates may be mixed in a volume ratio of 1:1 to 1:9.

[0069] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI)), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (where x and y are integers from 1 to 20), may contain one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethersulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFOP), and lithium bis(oxalate)borate (LiBOB).

[0070] Lithium-ion rechargeable battery Lithium secondary batteries may be classified into cylindrical, rectangular, pouch-shaped, coin-shaped, etc., depending on their form. Figures 2 to 5 are schematic diagrams showing a lithium secondary battery according to one embodiment, with Figure 2 showing a cylindrical battery, Figure 3 showing a rectangular battery, and Figures 4 and 5 showing a pouch-shaped battery. Referring to Figures 2 to 4, the lithium secondary battery 100 may include an electrode assembly 40 with a separator 30 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, negative electrode 20 and separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in Figure 2. Also, in Figure 3, the lithium secondary battery 100 may include a positive electrode lead tab 11 and a positive electrode terminal 12, a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in Figures 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which function as electrical pathways for guiding the current formed in the electrode assembly 40 to the outside.

[0071] The following describes in more detail the electrolyte of a lithium secondary battery according to one embodiment of the present invention.

[0072] An electrolyte for a lithium secondary battery according to one embodiment comprises the above-mentioned non-aqueous organic solvent, lithium salt, and additives, wherein the additives include a mixture of a first additive represented by chemical formula 1 (described later) and a second additive represented by chemical formula 2 (described later).

[0073] The electrolyte may be manufactured by dissolving a lithium salt in a non-aqueous organic solvent, adding a first additive and a second additive, and then mixing the mixture. The mixing step of the electrolyte may use any step that is widely known in the field of electrolyte manufacturing.

[0074] A non-aqueous organic solvent according to one embodiment of the present invention may contain at least one of the above-mentioned non-aqueous organic solvents.

[0075] In one specific example, the non-aqueous organic solvent may be a mixture containing ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) in a volume ratio of 10-30:20-50:20-50. Here, the volume ratio is based on a total of 100% by volume of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC). By satisfying this range, the effects of the additive mixture described later can be easily realized, and in lithium secondary batteries containing nickel-manganese-based positive electrode active materials described later, the reductive decomposition rate of the positive electrode can be reduced, further improving the battery life.

[0076] A lithium salt according to one embodiment of the present invention may include at least one selected from the group consisting of LiPF6, LiClO4, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiSO3CF3, LiBOB, LiFOB (Lithium difluoro(oxalato)borate), LiDFBP (lithium bis(oxyallyl)dlfluorophosphate, Lithium difluoro(bisoxalato) phosphate), LiTFOP (Lithium Tetrafluoro Oxalato Phosphate), LiPO2F2, LiSbF6, LiAsF6, LiAlO2, LiAlCl4, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N, and LiC4F9SO3. According to one embodiment, LiPF6 may be used as the lithium salt.

[0077] The lithium salt concentration may be between 0.1 M and 3.0 M. Specifically, the lithium salt concentration may be 0.5 M or higher, or 1.0 M or higher. The lithium salt concentration may be 3.0 M or lower, 2.5 M or lower, or 2.0 M or lower. In this invention, when the lithium salt concentration is between 0.1 M and 2.0 M, the conductivity and viscosity of the electrolyte can be appropriately maintained.

[0078] additives An additive according to one embodiment of the present invention includes a first additive and a second additive, which will be described later.

[0079] First additive A first additive according to one embodiment of the present invention is represented by the following chemical formula 1.

[0080] [ka]

[0081] R 1 ~R 6 Each of these is independently hydrogen, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group, R 7 n is a substituted or unsubstituted C1-C20 alkoxy group, and n is an integer of 0 or 1.

[0082] An additive according to another embodiment of the present invention is represented by the following chemical formula 1-1.

[0083] [ka]

[0084] In chemical formula 1-1, R 3 ~R 6 Each of these is independently hydrogen, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group, R 7 These are substituted or unsubstituted C1-C20 alkoxy groups.

[0085] In one embodiment, in chemical formula 1 and chemical formula 1-1, R 7 This may be a substituted or unsubstituted linear or branched C1-C5 alkoxy group.

[0086] For example, the first additive may be at least one of the following chemical formulas 1-3 to 1-6.

[0087] [ka]

[0088] Second additive A second additive according to one embodiment of the present invention is represented by the following chemical formula 2.

[0089] [ka]

[0090] In chemical formula 2, L 1 and L 2A and B are each independently single-bonded, substituted or unsubstituted C1-C5 alkylene groups, substituted or unsubstituted C2-C5 alkenylene groups, substituted or unsubstituted C2-C5 alkylylene groups, or substituted or unsubstituted C6-C20 arylene groups, and A and B are each independently substituted or unsubstituted C1-C20 alkyl groups, substituted or unsubstituted C6-C20 aryl groups, or substituted or unsubstituted C2-C20 heteroaryl groups, and at least one of A and B is a group represented by the following chemical formula A.

[0091] [ka]

[0092] In chemical formula A, L 3 and L 4 Each of these is independently hydrogen, a halogen, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C3-C10 cycloalkyl group.

[0093] In one embodiment, L 1 and L 2 At least one of these may be a substituted or unsubstituted C1-C5 alkylene group.

[0094] In one embodiment, L 1 and L 2 Each of these may independently be a substituted or unsubstituted C1-C5 alkylene group.

[0095] In one embodiment, L 1 and L 2 At least one of these may be a substituted or unsubstituted C2-C5 alkylene group.

[0096] In one embodiment, L 1 and L 2 Each of these may independently be a substituted or unsubstituted C2-C5 alkylene group.

[0097] For example, the second additive is represented by the following chemical formula 2-1.

[0098] [ka]

[0099] In chemical formula 2-1, L 1 and L 2 Each of these is independently a substituted or unsubstituted C2-C5 alkylene group, L 3A , L 3B , L 4A and L 4B Each of these is independently hydrogen, a halogen, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C3-C10 cycloalkyl group.

[0100] In one embodiment, the second additive may include at least one of the following chemical formulas 2-2 and 2-3.

[0101] [ka]

[0102] An additive according to one embodiment of the present invention comprises a mixture of a first additive and a second additive.

[0103] Lithium secondary batteries containing cobalt-free positive electrode active materials, such as nickel-manganese-based positive electrode active materials, may experience accelerated electrolyte decomposition due to increased nickel activity. This can lead to reduction of the negative electrode surface after significant nickel leaching, resulting in accelerated battery life degradation. Additionally, the positive electrode may accept electrons from ethylene carbonate, a non-aqueous organic solvent electrolyte, accelerating the reductive decomposition of the positive electrode.

[0104] A mixture of the first and second additives, when applied as an additive to a lithium secondary battery containing a nickel-manganese-based cathode active material, can improve battery life under high voltage and significantly improve battery performance even under high temperature conditions. In particular, this mixture can improve the life of a lithium secondary battery containing a nickel-manganese-based cathode active material under high voltages of 4.35V or higher and significantly improve battery performance even under high temperature conditions.

[0105] In one embodiment, this mixture may be included in the electrolyte additive at an amount of 95% by weight or more, for example, 95-100% by weight or 100% by weight. By satisfying this range, the effects of the mixture described above can be realized, and side reactions of the electrolyte can be suppressed.

[0106] The first additive may be present in an amount of 0.05 to 5% by weight relative to the total amount of electrolyte. By satisfying this range, the effects of the mixture described above can be achieved. Specifically, the first additive may be present in an amount of 0.1 to 5% by weight or 0.05 to 3% by weight relative to the total amount of electrolyte. When the content of the first additive is within this range, the effects of the mixture described above are significantly enhanced, and the effect of preventing an increase in battery resistance can also be achieved.

[0107] The second additive may be present in an amount of 0.05 to 5% by weight relative to the total weight of the electrolyte. By satisfying this range, the effects of the mixture described above can be achieved. Specifically, the second additive may be present in an amount of 0.05 to 3% by weight or 0.1 to 1% by weight relative to the total amount of the electrolyte. When the content of the first additive is within this range, the effects of the mixture described above are significantly enhanced, improving the rapid charging effect and preventing an increase in battery resistance.

[0108] In the electrolyte, the ratio (by weight) of the content of the first additive to the content of the second additive may be between 9:1 and 0.5:1. By satisfying this range, the effects of the mixture described above can be easily achieved.

[0109] According to one embodiment, the ratio (by weight) of the content of the first additive to the content of the second additive may be 5:1 to 0.5:1 or 5:1 to 1:1. By satisfying this range, a resistance suppression effect at high temperatures is achieved, and the problem of a rapid decrease in the lifespan of lithium secondary batteries can be resolved. For example, the weight ratio may be 2:1 to 0.5:1. By satisfying this range, the resistance suppression effect at high temperatures and the improvement in lifespan become significant.

[0110] The electrolyte according to the present invention, by combining the aforementioned non-aqueous organic solvent and lithium salt, includes a mixture of the first and second additives, thereby suppressing the increase in resistance during high-temperature storage in lithium secondary batteries containing cobalt-free cathode active materials, particularly nickel-manganese-based cathode active materials, and enabling the realization of lithium secondary batteries with improved lifespan and stability.

[0111] In another embodiment of the present invention, a lithium secondary battery can be provided, comprising a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, wherein the electrolyte comprises a non-aqueous organic solvent, a lithium salt, and an additive, and the additive comprises a mixture of the first additive and the second additive described above.

[0112] Lithium-ion batteries may be applied to automobiles, mobile phones, and / or various forms of electrical devices, but the present invention is not limited thereto.

[0113] The positive electrode active material may include a cobalt-free positive electrode active material.

[0114] In one embodiment, the cobalt-free cathode active material may contain a nickel-manganese oxide.

[0115] In this specification, a cobalt-free nickel-manganese oxide functioning as a positive electrode active material can mean a positive electrode active material that does not contain cobalt and is composed mainly of nickel and manganese.

[0116] In one embodiment, the cobalt-free nickel-manganese oxide may contain at least one lithium composite oxide represented by the following general formula. Li a Ni x Mn y M1 z M2 w O 2±b X c

[0117] In the above general formula, 0.9≦a<1.2, 0≦b<0.1, 0≦c<0.1, 0≦w<0.1, 0.05≦x<1.0, 0 <y<0.4、0≦z<0.1、w+x+y+z=1であり、 M1 and M2 are each independently at least one element selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Nb, Si, Ba, Ca, Ce, Cr, Fe, and Nb, and X is at least one element selected from S, F, P, and Cl.

[0118] In the general formula above, 0.05 ≤ x ≤ 0.95 is also acceptable.

[0119] It is also possible to use a lithium composite oxide having a coating layer on its surface, or to use a mixture of a lithium composite oxide and a compound constituting the coating layer. This coating layer may contain at least one coating element compound selected from the group consisting of an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, and a hydroxycarbonate of the coating element. The compounds constituting these coating layers may be amorphous or crystalline. As the coating element contained in the coating layer, Mg, Al, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. The coating layer forming step may use any coating method as long as the compound constituting the coating layer can be coated by a method that does not adversely affect the physical properties of the positive electrode active material (for example, spray coating, dipping method, etc.). Since this is a matter that can be understood by those skilled in the art, detailed description thereof is omitted.

[0120] In one example, the cobalt-free nickel manganese-based oxide is represented by the following general formula. Li a Ni x1 Mn y1 Al z1 M2 w1 O 2±b X c

[0121] In the above general formula, 0.9 ≦ a < 1.2, 0 ≦ b < 0.1, 0 ≦ c < 0.1, 0 ≦ w1 < 0.1, 0.05 ≦ x1 < 1.0, 0 < y1 < 0.4, 0 ≦ z1 < 0.1, and w1 + x1 + y1 + z1 = 1. M2 is at least one element independently selected from Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Nb, Si, Ba, Ca, Ce, Cr, Fe, and Nb, and X is at least one element selected from S, F, P, and Cl.

[0122] In the above general formula, 0.05 ≦ x1 ≦ 0.95 may also be applicable.

[0123] In one embodiment, the cobalt-free nickel manganese-based oxide may be contained in an amount of 95% by weight or more, for example, 95 to 100% by weight or 100% by weight, based on the positive electrode active material.

[0124] In a specific embodiment, the negative electrode active material may include at least one of graphite and a Si composite.

[0125] When the negative electrode active material includes a Si composite and graphite, the Si composite and graphite may be contained in the form of a mixture. In this case, the weight ratio of the Si composite to graphite may be 1:99 to 50:50. More specifically, the weight ratio of the Si composite to graphite may be 3:97 to 20:80, 4:96 to 20:80, or 5:95 to 20:80.

[0126] The Si composite includes a core containing Si-based particles and an amorphous carbon coating layer. For example, the Si-based particles may include at least one of a Si-C composite, SiO x (0 < x ≤ 2) and a Si alloy. For example, the Si-C composite may include a core containing Si particles and crystalline carbon, and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0127] When the positive electrode contains a cobalt-free nickel manganese-based oxide and the negative electrode contains graphite, the effect of improving the high-temperature stability of the lithium secondary battery can be maximized. The operating driving voltage of this combination of lithium secondary batteries is 4.35 V or more, and it can operate even at a high voltage.

Examples

[0128] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0129] Examples and Comparative Examples (1) Preparation of Electrolyte 1.15 M of LiPF6 was dissolved in a non-aqueous organic solvent in which carbonate solvents were mixed at the volume ratios shown in Table 1 below. After adding the first additive and the second additive, they were mixed to prepare an electrolyte. The electrolytes according to the examples and comparative examples were prepared with the compositions shown in Table 1 below.

[0130] As the first additive, a compound represented by Chemical Formula 1-3 below was used. As the second additive, the one represented by Chemical Formula 2-2 below was used.

[0131]

Chemical Formula

[0132] (2) Fabrication of Lithium Secondary Battery As the positive electrode active material, 97% by weight of LiNi 0.75 Mn 0.23 Al 0.02 O2, 0.5% by weight of artificial graphite powder as a conductive material, 0.8% by weight of carbon black (Ketjenblack), 0.2% by weight of acrylonitrile rubber, and 1.5% by weight of polyvinylidene fluoride (PVdF) were mixed. After adding this mixture to N-methyl-2-pyrrolidone (NMP), it was stirred for 30 minutes using a mechanical stirrer to prepare a positive electrode active material slurry. This slurry was applied to an aluminum current collector with a thickness of 20 μm to a thickness of about 60 μm using a doctor blade, dried for 0.5 hours with a hot air dryer at 100 °C, and then further dried for 4 hours under vacuum and at 120 °C, and rolled to fabricate a positive electrode.

[0133] 98% by weight of a negative electrode active material in which a graphite and Si composite were mixed at a weight ratio of 95.8:4.2, 1% by weight of styrene-butadiene rubber (SBR), and 1% by weight of carboxymethyl cellulose (CMC) were mixed. After adding this mixture to distilled water, it was stirred for 60 minutes using a mechanical stirrer to prepare a negative electrode active material slurry. This slurry was applied to a copper current collector with a thickness of 10 μm to a thickness of about 60 μm using a doctor blade, dried for 0.5 hours with a hot air dryer at 100 °C, and then further dried for 4 hours under vacuum and at 120 °C, and rolled to fabricate a negative electrode.

[0134] An electrode assembly was fabricated by assembling a positive electrode, a negative electrode, and a polyethylene separator with a thickness of 16 μm, and a circular lithium secondary battery was fabricated by injecting the electrolyte solution.

[0135] (3) Evaluation of lithium secondary batteries Lithium-ion batteries were evaluated using the following method.

[0136] Evaluation 1: Volume retention rate (Retention, Ret) and volume recovery rate (Rec) after high-temperature storage. The lithium secondary batteries of the examples and comparative examples were subjected to 0.5C CC / CV charging (3.65V, 0.05C CUT-OFF) and 0.5C CC discharge (2.5V CUT-OFF) three times at 25°C, and the discharge capacity C1 was measured on the third discharge. After the charged lithium secondary batteries were stored at 60°C for 7 or 21 days, they were left at room temperature for 30 minutes, and then discharged at 0.5C CC (2.5V CUT-OFF) to measure the discharge capacity C2. The capacity retention rate was calculated according to the following formula and is shown in Table 1 below. Capacity maintenance rate (%)=C2 / C1×100(%)

[0137] After measuring the capacity retention rate of the lithium secondary batteries of the examples and comparative examples using the method described above, they were charged at 0.5C-rate CC / CV (3.65V, 0.05C cut-off) and discharged at 0.5C-rate CC (2.5V cut-off) to measure their discharge capacity.

[0138] As can be seen from the following formula, the capacity recovery rate was calculated by dividing the discharge capacity after the capacity retention rate measurement by the initial capacity. Capacity recovery rate (%) = (Discharge capacity after capacity retention rate measurement / Initial capacity) × 100

[0139] Evaluation 2: Evaluation of room temperature charge / discharge cycle characteristics The room-temperature charge-discharge characteristics of lithium secondary batteries were evaluated for the examples and comparative examples. Specifically, 200 charge-discharge cycles were performed on the lithium secondary batteries under the conditions of 25°C, 0.33C charging (CC / CV, 4.45V, 0.025C Cut-off) / 1.0C discharging (CC, 2.5V Cut-off). The capacity retention rate was calculated using the following formula. Capacity retention rate (%) = (Discharge capacity after 200 cycles / Discharge capacity after 1 cycle) × 100

[0140] Evaluation 3: High-temperature (45°C) charge / discharge cycle characteristics evaluation High-temperature charge-discharge characteristics were evaluated for lithium secondary batteries in the examples and comparative examples. Specifically, 200 charge-discharge cycles were performed on the lithium secondary batteries under the conditions of 45°C, 0.33C charging (CC / CV, 4.45V, 0.025C Cut-off) / 1.0C discharging (CC, 2.5V Cut-off). The capacity retention rate was calculated using the following formula. Capacity retention rate (%) = (Discharge capacity after 200 cycles / Discharge capacity after 1 cycle) × 100

[0141] Evaluation 4: Evaluation of gas generation characteristics at high temperature (60°C) High-temperature gas generation characteristics were evaluated for lithium secondary batteries based on examples and comparative examples. Specifically, the maximum energy state within the battery was set to a fully charged state (SOC 100%), and the amount of gas generated (unit: mL) was evaluated in this state initially (before storage at high temperature (60°C)) and after storage at high temperature (60°C) for 7 days. The gas generation ratio was calculated by measuring the volume change before and after high-temperature storage and converting it to mass change using the Archimedes method.

[0142] The results for ratings 1 through 4 are shown in Table 1 below.

[0143] [Table 1]

[0144] In Table 1, EC stands for ethylene carbonate, EMC for ethyl methyl carbonate, and DMC for dimethyl carbonate. The weight ratios represent the weight ratio of the additive represented by chemical formulas 1-3 to the additive represented by chemical formulas 2-2. The additives represented by chemical formula 5 are as follows:

[0145] [ka]

[0146] In Table 1, the molar concentration (M) of lithium salt refers to the amount (number of moles) of lithium salt dissolved in 1 L of electrolyte; the volume ratio of non-aqueous organic solvent refers to the volume ratio of EC:EMC:DMC; and the weight % of additive refers to the relative weight of the additive to 100% by weight of the total electrolyte (lithium salt + non-aqueous organic solvent) excluding the additive.

[0147] Consideration As can be seen from Table 1, the electrolytes of the examples, according to the results of Evaluation 1 to Evaluation 4, are considered to be able to significantly improve the lifespan at high voltages and high-temperature performance in lithium secondary batteries containing cobalt-free positive electrode active materials.

[0148] However, referring to Table 1, Comparative Examples 1 to 3, which do not contain at least one of the first and second additives, and Comparative Example 4, which contains a different additive instead of the first additive, show relatively high gas generation rates according to the results of Evaluations 1 to 4. Compared to the examples, these comparative examples are expected to be significantly inferior in terms of high-voltage life and high-temperature performance of lithium secondary batteries containing cobalt-free cathode active material.

[0149] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings, and these also naturally fall within the scope of the present invention. [Explanation of Symbols]

[0150] 10: Positive electrode for secondary battery, 11: Positive electrode lead tab, 12: Positive electrode terminal, 20: Negative electrode for lithium secondary battery, 21: Negative electrode lead tab, 22: Negative electrode terminal, 30: Separator, 40: Electrode assembly, 50: Case, 60: Sealing material, 70: Electrode tab, 71: Positive electrode tab, 72: Negative electrode tab, 98: Negative electrode active material, 100: Lithium secondary battery

Claims

1. It comprises a non-aqueous organic solvent, a lithium salt, and additives. The aforementioned additive comprises a mixture of a first additive represented by the following chemical formula 1 and a second additive represented by the following chemical formula 2. 【Chemistry 1】 R １ ~R ６ Each of these is independently a hydrogen atom, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group. R ７ These are substituted or unsubstituted C1-C20 alkoxy groups, n is an integer, either 0 or 1. 【Chemistry 2】 L １ and L ２ Each of these is independently a single bond, a substituted or unsubstituted C1-C5 alkylene group, a substituted or unsubstituted C2-C5 alkenylene group, a substituted or unsubstituted C2-C5 alkynylene group, or a substituted or unsubstituted C6-C20 arylene group. A and B are each independently a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group. At least one of A and B is a group represented by the following chemical formula A, 【Transformation 3】 L ３ and L ４ An electrolyte for lithium secondary batteries, wherein each is independently hydrogen, halogen, substituted or unsubstituted C1-C10 alkyl group, or substituted or unsubstituted C3-C10 cycloalkyl group.

2. The first additive is represented by the following chemical formula 1-1, 【Chemistry 4】 R ３ ~R ６ are each independently hydrogen, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group, R ７ The electrolyte for lithium secondary batteries according to claim 1, wherein is a substituted or unsubstituted C1-C20 alkoxy group.

3. The electrolyte for a lithium secondary battery according to claim 1, wherein the first additive is represented by at least one of the following chemical formulas 1-3 to 1-6. 【Transformation 5】

4. The second additive is represented by the following chemical formula 2-1, 【Transformation 6】 L １ and L ２ These are, independently, substituted or unsubstituted C2-C5 alkylene groups, L ３Ａ , L ３Ｂ , L ４Ａ and L ４Ｂ The electrolyte for lithium secondary batteries according to claim 1, wherein each of them is independently hydrogen, a halogen, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C3-C10 cycloalkyl group.

5. The electrolyte for a lithium secondary battery according to claim 1, wherein the second additive is represented by at least one of the following chemical formulas 2-2 and 2-3. 【Transformation 7】

6. The first additive is included in an amount of 0.05 to 5% by weight relative to the total amount of the electrolyte. The electrolyte for a lithium secondary battery according to claim 1, wherein the second additive is contained in an amount of 0.05 to 5% by weight relative to the total amount of the electrolyte.

7. The electrolyte for a lithium secondary battery according to claim 1, wherein the ratio of the weight of the first additive to the weight of the second additive in the electrolyte is 9:1 to 0.5:

1.

8. The electrolyte for lithium secondary batteries according to claim 1, wherein the mixture contains 95% by weight or more of the additives of the electrolyte.

9. The electrolyte for a lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent is a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 10 to 30:20 to 50:20 to 50.

10. The lithium salt is LiPF ６ LiClO ４ LiBF ４ Lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, LiSO ３ CF ３ Lithium bis(oxalate) borate, 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 The electrolyte for lithium secondary batteries according to claim 1, comprising at least one selected from the group consisting of the following.

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

12. Positive electrode containing positive electrode active material, A negative electrode containing a negative electrode active material, and The electrolyte is described in any one of claims 1 to 11, The aforementioned positive electrode active material includes a cobalt-free positive electrode active material in a lithium secondary battery.

13. The lithium secondary battery according to claim 12, wherein the cobalt-free positive electrode active material includes a cobalt-free nickel-manganese oxide.

14. The aforementioned cobalt-free nickel-manganese oxide includes a lithium composite oxide represented by the following general formula: Li ａ ii ｘ 7N ｙ 71 ｚ 72 ｗ 9 ２±ｂ 8 ｃ In the above general formula, 0.9 ≤ a < 1.2, 0 ≤ b < 0.1, 0 ≤ c < 0.1, 0 ≤ w < 0.1, 0.6 ≤ x < 1.0, 0 < y < 0.4, 0 ≤ z < 0.1, and w + x + y + z = 1. M1 and M2 are each independently at least one element selected from Al, Mg, Ti, Zr, Cr, Sr, V, B, W, Mo, Nb, Si, Ba, Ca, Ce, Cr, Fe, and Nb. The lithium secondary battery according to claim 13, wherein X is at least one element selected from S, F, P, and Cl.

15. The lithium secondary battery according to claim 14, wherein in the above general formula, 0.05 ≤ x ≤ 0.

95.

16. The lithium secondary battery according to claim 12, wherein the negative electrode active material comprises at least one of graphite and a Si composite.

17. The lithium secondary battery according to claim 12, wherein the driving voltage of the lithium secondary battery is 4.35V or higher.

18. The lithium secondary battery according to claim 12, wherein the lithium secondary battery is cylindrical, angular, pouch-shaped, or coin-shaped.

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