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

Abstract

To provide an electrolyte for a rechargeable lithium battery improved in high-temperature lifetime characteristics and high-temperature stability.SOLUTION: The invention relates to an electrolyte for a rechargeable lithium battery, and a rechargeable lithium battery including the same. The electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive. The additive includes a first compound represented by the Chemical Formula 1, and a second compound represented by the Chemical Formula 2. The detailed contents relating to the Chemical Formulas 1 and 2 are as described in the specification.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, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density, high-capacity secondary batteries is rapidly increasing, and research and development efforts to improve the performance of lithium secondary batteries are being 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 by oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated at the cathode and anode.

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

[0005] One embodiment provides an electrolyte for a lithium secondary battery having improved high-temperature life characteristics and high-temperature stability.

[0006] Another embodiment provides a lithium secondary battery comprising the electrolyte solution. [Means for solving the problem]

[0007] One embodiment includes a non-aqueous solvent, a lithium salt, and an additive; The additive comprises a first compound represented by the following chemical formula 1 and a second compound represented by the following chemical formula 2:

[0008] [ka]

[0009] In the above Chemical Formula 1, X 1 may be a fluoro, chloro, bromo, or iodo group; R 1 ~R 6 each independently may be 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; n may be an integer of 0 or 1;

[0010] [ka]

[0011] In the above Chemical Formula 2, L 2A and L 2B each independently may be a single bond, a substituted or unsubstituted C1 to C5 alkylene group, a substituted or unsubstituted C2 to C5 alkenylene group, a substituted or unsubstituted C2 to C5 alkynylene group, or a substituted or unsubstituted C6 to C20 arylene group; A and B may each independently be a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; At least one of A and B may be a group represented by the following chemical formula A:

[0012] [ka]

[0013] In the above chemical formula A, R 7 and R 8 may each independently be hydrogen, halogen, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C3 to C10 cycloalkyl group.

[0014] Another embodiment provides a lithium secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and the lithium secondary battery electrolyte. [Effects of the Invention]

[0015] The electrolyte for a lithium secondary battery according to one embodiment can improve the life characteristics of a lithium secondary battery and reduce the internal resistance of the battery, and these effects are particularly pronounced at high temperatures. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a simplified conceptual diagram of a lithium secondary battery according to one embodiment of the present invention; [Figure 2] 1 is a schematic diagram illustrating a lithium secondary battery according to one embodiment, showing a cylindrical battery configuration. [Figure 3] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, illustrating a prismatic battery configuration. [Figure 4] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, illustrating a pouch-type battery configuration. [Figure 5] 1 is a schematic diagram showing a lithium secondary battery according to an embodiment, illustrating a pouch-type battery configuration. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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 enable those skilled in the art to fully understand the scope of the invention.

[0018] 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.

[0019] Unless otherwise stated herein, the singular may also include the plural. Additionally, unless otherwise stated, "A" or "B" may 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.

[0020] As used herein, "combinations thereof" may refer to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0021] In this specification, unless otherwise defined, the particle size may be the average particle size. Also, the particle size is the average particle size (D ) which means the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution. 50 ) means the average particle size (D 50The average particle diameter (D) can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer, or by using a transmission electron microscope or a scanning electron microscope. Another method is to measure using a measuring device that uses dynamic light-scattering, and then perform data analysis to count the number of particles in each particle size range, and then calculate the average particle diameter (D 50 Alternatively, the measurement may be carried out by using a laser diffraction method. More specifically, when measuring by the laser diffraction method, particles to be measured are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (for example, MT 3000 manufactured by Microtrac), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W. Then, the average particle size (D ) at 50% of the particle size distribution in the measuring device is measured. 50 ) can be calculated.

[0022] In this specification, unless otherwise defined, the term "substituted" means that at least one hydrogen atom in a substituent or compound is replaced with deuterium, a halogen group, 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.

[0023] Specifically, "substituted" may mean that at least one hydrogen atom 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" may mean that at least one hydrogen atom 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" may mean that at least one hydrogen atom 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. As an example, "substituted" may mean that at least one hydrogen in a substituent or compound is replaced with deuterium, a cyano group, a halogen group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0024] 1 is a schematic diagram illustrating a lithium secondary battery according to one embodiment of the present invention, which includes a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte solution ELL.

[0025] The positive electrode 10 and the negative electrode 20 are separated from each other by a separator 30. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 are in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 are immersed in the electrolyte solution ELL.

[0026] The electrolyte ELL may be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions may pass through the separator 30 and migrate toward the positive electrode 10 or the negative electrode 20.

[0027] positive electrode 10 A positive electrode 10 for a lithium secondary battery includes 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.

[0028] As an example, the positive electrode 10 may further include an additive that can act as a sacrificial positive electrode.

[0029] 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.

[0030] 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.

[0031] The conductive material is used to impart conductivity to the electrode and may be any material that is electron-conductive and does not cause a chemical change in the battery. 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. The current collector COL1 can be made of Al, but is not limited to this.

[0032] positive electrode active material The positive electrode active material in the positive electrode active material layer AML1 is 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 are used.

[0033] 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.

[0034] For example, a compound represented by any one of the following chemical formulas can be used: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Ni 1-b-c Co b X c O2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni b Co c L 1 d G e O2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4(0.90≦a≦1.8).

[0035] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 is Mn, Al, or a combination thereof.

[0036] For example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more 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 can realize high capacity and is therefore applicable to high-capacity, high-density lithium secondary batteries.

[0037] negative electrode 20 The lithium secondary battery positive electrode 20 includes 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.

[0038] For example, the negative electrode active material layer AML2 contains 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0039] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] The dry binder may be a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene oxide, or a combination thereof.

[0044] The conductive material is used to impart conductivity to the electrode and may be any material that is electron-conductive and does not cause a chemical change in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0045] As the current collector COL2, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof may be used.

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

[0047] The material capable of reversibly inserting / desorbing the lithium ions is a carbon-based negative electrode active material, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0048] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0049] As the material 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 a combination thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0050] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, the silicon-carbon composite may include secondary particles (cores) formed by combining primary silicon particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The 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 in an amorphous carbon matrix.

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

[0052] The Si-based or Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material.

[0053] In one embodiment, the negative electrode active material may include a carbon-based negative electrode active material and a Si-based negative electrode active material. In other words, the negative electrode active material may include carbon (C) and silicon (Si). For example, the carbon-based negative electrode active material may be graphite, and the Si-based negative electrode active material may be silicon nanoparticles.

[0054] The weight ratio of the silicon nanoparticles to the graphite may be 0.001 to 20, or 1 to 10. When the weight ratio of the silicon nanoparticles to the graphite is within this range, the buffering effect against the volume expansion of the silicon nanoparticles is increased, which may provide excellent electrical conductivity and improve the lifespan.

[0055] The silicon nanoparticles may refer to nano-sized silicon particles. The silicon nanoparticles may have an average particle size of 50 nm to 300 nm, more specifically, an average particle size of 80 nm to 200 nm. Nano-sized silicon particles allow for smooth ingress and egress of lithium ions and low ionic resistance, thereby suppressing volume expansion and improving lifespan.

[0056] 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, but it goes without saying that 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 also be used.

[0057] 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.

[0058] 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 (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0059] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0060] The inorganic material may be inorganic particles selected from, but not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0061] 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.

[0062] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0063] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0064] The non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, a non-quantum solvent, or a combination thereof.

[0065] Examples of the carbonate solvent that may be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0066] As the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, and the like may be used.

[0067] 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 hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and 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, sulfolanes, and propyl propionate (PP).

[0068] The non-aqueous organic solvents may be used alone or in combination of two or more.

[0069] 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.

[0070] 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 electrode and the negative electrode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0071] Hereinafter, the electrolyte of the lithium secondary battery according to one embodiment of the present invention will be described in more detail.

[0072] An electrolyte solution for a lithium secondary battery according to one embodiment includes a non-aqueous organic solvent, a lithium salt, and an additive.

[0073] The additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2:

[0074] [ka]

[0075] In the above Chemical Formula 1, X 1 may be a fluoro, chloro, bromo, or iodo group; R 1 ~R 6 each independently may be 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; n may be an integer of 0 or 1;

[0076] [ka]

[0077] In the above Chemical Formula 2, L 2A and L 2B each independently may be a single bond, a substituted or unsubstituted C1 to C5 alkylene group, a substituted or unsubstituted C2 to C5 alkenylene group, a substituted or unsubstituted C2 to C5 alkynylene group, or a substituted or unsubstituted C6 to C20 arylene group; A and B may each independently be a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; At least one of A and B may be a group represented by the following chemical formula A:

[0078] [ka]

[0079] In the above chemical formula A, R 7 and R 8 may each independently be hydrogen, halogen, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C3 to C10 cycloalkyl group.

[0080] The electrolyte solution may be prepared by dissolving a lithium salt in a non-aqueous organic solvent, adding the first compound and the second compound, and then mixing them. The process of mixing the electrolyte solution is well known in the technical field of electrolytes, and can be appropriately selected and used by those skilled in the art.

[0081] The non-aqueous organic solvent may include one or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and butylene carbonate (BC).

[0082] In one embodiment, the non-aqueous organic solvent may be a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0083] As a specific example, the ethylene carbonate (EC) may be contained in an amount of 10 to 30% by volume based on the total amount of the non-aqueous organic solvent, the ethyl methyl carbonate (EMC) may be contained in an amount of 5 to 20% by volume based on the total amount of the non-aqueous organic solvent, and the dimethyl carbonate (DMC) may be contained in an amount of 50 to 80% by volume based on the total amount of the non-aqueous organic solvent.

[0084] In one embodiment, the lithium salt may be LiPF6.

[0085] The concentration of the lithium salt may be 0.1 M to 2.0 M. Specifically, the concentration of the lithium salt may be 0.5 M or more, or 1.0 M or more. The concentration of the lithium salt may be 2.0 M or less, 1.7 M or less, or 1.5 M or less. In the present invention, when the concentration is 0.1 M to 2.0 M, the conductivity and viscosity of the electrolyte can be appropriately maintained.

[0086] 1st compound A first compound according to one embodiment of the present invention is represented by Chemical Formula 1.

[0087] [ka]

[0088] In the above Chemical Formula 1, X 1 may be a fluoro, chloro, bromo, or iodo group; R 1 ~R 6each independently may be 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; n may be an integer of 0 or 1.

[0089] The first compound can form a solid electrolyte interface (SEI) film on the surface of the negative electrode, which has high high-temperature stability and excellent ionic conductivity. Furthermore, the first compound can reduce gas generation due to decomposition reactions occurring 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 negative ions 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.

[0090] The first compound's effects of improving the life characteristics of lithium secondary batteries at high temperatures and reducing the battery's internal resistance are even more pronounced when used with a high-nickel cathode active material and an anode active material containing graphite and silicon nanoparticles. While silicon particles are used to increase battery capacity, they can cause side reactions with the electrolyte, increasing the battery's internal resistance. By incorporating the first compound as an additive, the side reactions between the silicon particles and the electrolyte can be suppressed, thereby minimizing the increase in battery internal resistance and maximizing the goal of increasing battery capacity.

[0091] The first compound may include a cyclic phosphorane derivative. The cyclic phosphorane derivative can significantly improve the lifespan characteristics of lithium secondary batteries at high temperatures compared to linear phosphorane derivatives. The linear phosphorane derivative may induce side reactions of LiPF6 due to the dissociated -PO2F functional group, which may cause gas generation due to electrolyte decomposition during high-temperature storage.

[0092] In one embodiment, the formula 1 may be represented by the following formula 1-1 or 1-2.

[0093] [ka]

[0094] [ka]

[0095] In the above Chemical Formula 1-1 and Chemical Formula 1-2, X 1 may be a fluoro, chloro, bromo, or iodo group; R 1 ~R 6 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.

[0096] In one embodiment, R in Formula 1-1 3 and R 4 may each be hydrogen; R 5 and R 6 At least one of them 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.

[0097] In one embodiment, the first compound may be at least one selected from the compounds listed in the following first group: 2-fluoro-1,3,2-dioxaphospholane and 2-fluoro-4-methyl-1,3,2-dioxaphospholane.

[0098] [ka]

[0099] The content of the first compound may be 0.2 to 5.0 parts by weight based on 100 parts by weight of the electrolyte solution for lithium secondary batteries. Specifically, the content of the first compound may be 0.5 to 1.5 parts by weight based on 100 parts by weight of the electrolyte solution for lithium secondary batteries. The content of the first compound may refer to the weight of the first compound contained in the electrolyte solution with respect to the total weight of the electrolyte solution. When the content of the first compound satisfies the above range, the effect of forming an excellent SEI film and the effect of reducing gas generation at high temperatures may be maximized.

[0100] 2nd compound The second compound according to an embodiment of the present invention can be represented by Chemical Formula 2.

[0101] [ka]

[0102] In the above Chemical Formula 2, L 2A and L 2B each independently may be a single bond, a substituted or unsubstituted C1 to C5 alkylene group, a substituted or unsubstituted C2 to C5 alkenylene group, a substituted or unsubstituted C2 to C5 alkynylene group, or a substituted or unsubstituted C6 to C20 arylene group; A and B may each independently be a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; At least one of A and B may be a group represented by the following chemical formula A:

[0103] [ka]

[0104] In the above chemical formula A, R 7 and R 8 may each independently be hydrogen, halogen, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C3 to C10 cycloalkyl group.

[0105] The second compound may have the effect of protecting the passivating coating formed on the surfaces of the positive and negative electrodes. The coating formed on the surface of the positive electrode is commonly referred to as a cathode electrolyte interface (CEI) film, and the coating formed on the surface of the negative electrode is commonly referred to as an SEI film. Specifically, the triazole group and sulfone group of the second compound provide unshared electron pairs to stabilize the lithium salt in the electrolyte and protect the coating. This minimizes the problems of reduced battery life and increased resistance that occur when acid, a decomposition product of the lithium salt in the electrolyte, attacks the coating on the surfaces of the positive and negative electrodes. The protective effect of the coating can contribute to improved life characteristics of lithium secondary batteries and reduced internal resistance, especially at high temperatures.

[0106] The second compound has the effect of forming a coating on the surface of the positive electrode. The coating formed on the surface of the positive electrode is commonly referred to in the art as a CEI film. Specifically, the triazole group and sulfone group of the second compound form a coordination bond with the metal contained in the positive electrode active material to form a coating on the surface of the positive electrode. This can reduce gas generation due to side reactions between the positive electrode interface and the electrolyte and may suppress gas generation and transition metal elution caused by decomposition of the positive electrode active material. The coating formation effect may contribute to improving the life characteristics of lithium secondary batteries, especially at high temperatures, and reducing the internal resistance of the battery.

[0107] In addition to the aforementioned effects of protecting the surfaces of the positive and negative electrodes and forming a surface film on the positive electrode, the second compound may also have the effect of strengthening the surface film on the negative electrode. This improves the life characteristics of the lithium secondary battery and reduces the internal resistance of the battery. The coating formed on the surface of the negative electrode is commonly referred to in the industry as an SEI film. The strengthening effect of the coating contributes to improving the life characteristics of the lithium secondary battery and reducing the internal resistance of the battery, especially at high temperatures.

[0108] The second compound may include 1,2,4-triazole. 1,2,4-triazole significantly improves the high-temperature characteristics of lithium secondary batteries compared to 1,2,3-triazole. In particular, 1,2,4-triazole may be more effective when used with a high-nickel positive electrode active material. When 1,2,3-triazole coordinates with the metal contained in the positive electrode active material to form a coating on the surface of the positive electrode, the steric arrangement with nickel may be less efficient than that of 1,2,4-triazole.

[0109] In one embodiment, in Formula 2, the L 2A and L 2B At least one of them may be a substituted or unsubstituted C1 to C5 alkylene group.

[0110] In one embodiment, in Formula 2, the L 2A and L2B may each independently be a substituted or unsubstituted C1 to C5 alkylene group.

[0111] In one embodiment, in Formula 2, the L 2A and L 2B At least one of the groups may be a substituted or unsubstituted C2 to C5 alkylene group.

[0112] In one embodiment, in Formula 2, the L 2A and L 2B may each independently be a substituted or unsubstituted C2 to C5 alkylene group.

[0113] In one embodiment, the formula 2 can be represented by the following formula 2-1.

[0114] [ka]

[0115] In the above Chemical Formula 2-1, Said L 1 and L 2 may each independently be a substituted or unsubstituted C2 to C5 alkylene group; R 21A , R 21B , R 21C , and R 21D may each independently be hydrogen, halogen, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C3 to C10 cycloalkyl group.

[0116] In one embodiment, the second compound may be one selected from the compounds listed in the second group below.

[0117] [ka]

[0118] The content of the second compound may be 1 to 5 parts by weight based on 100 parts by weight of the electrolyte for lithium secondary batteries. The content of the second compound may refer 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 this range, the effect of protecting the coatings formed on the surfaces of the positive and negative electrodes, the effect of forming a coating on the surface of the positive electrode, and the effect of strengthening the coating on the surface of the negative electrode are maximized, thereby maximizing the improvement in life characteristics and the effect of reducing internal resistance of the lithium secondary battery.

[0119] additives The electrolyte for a lithium secondary battery according to the present invention may include a non-aqueous organic solvent, a lithium salt, and an additive, which may include the first compound and the second compound described above.

[0120] When the second compound is used in combination with a fluorinated lithium salt compound structure (e.g., the first compound described above), a synergistic effect can be generated. The combination of the first and second compounds can effectively alleviate the problems of reduced lifespan and increased resistance in lithium secondary batteries. Specifically, the first compound's excellent SEI film formation and gas generation reduction effects, and the second compound's positive electrode transition metal elution inhibition and gas generation reduction effects, can be simultaneously generated, maximizing the improvement of lithium battery characteristics. The synergistic effect may be particularly pronounced at high temperatures.

[0121] The content of the additive may be 1.2 to 10 parts by weight based on 100 parts by weight of the electrolyte for lithium secondary batteries. The content of the additive may refer to the weight of the additive contained in the electrolyte relative to the total weight of the electrolyte. When the content of the additive satisfies the above range, the effects of improving the capacity retention rate of the lithium secondary battery, improving the resistance increase rate, and reducing the amount of transition metal elution can be maximized. The improvement in battery characteristics can be particularly pronounced at high temperatures.

[0122] The weight ratio of the second compound to the first compound in the additive is 0.2 to 25. Specifically, the weight ratio of the second compound to the first compound in the additive is 1 to 5. This weight ratio range can maximize the effect of improving the high-temperature characteristics of the lithium secondary battery. If the weight ratio of the second compound to the first compound is less than this range, the coulombic efficiency may decrease sharply, and if the weight ratio of the second compound to the first compound exceeds this range, a sufficient coating may not be formed on the surface of the positive electrode.

[0123] 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 embodiments, with FIG. 2 illustrating a cylindrical battery, FIG. 3 illustrating a prismatic battery, and FIGS. 4 and 5 illustrating pouch battery types. Referring to FIGS. 2 to 4, a lithium secondary battery 100 includes 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 are impregnated with an electrolyte (not shown). The lithium secondary battery 100 includes a sealing member 60 that seals the housing 50, as shown in FIG. 2. Also, in FIG. 3, the lithium secondary battery 100 includes 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 includes electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0124] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of battery devices, but the present invention is not limited thereto.

[0125] The lithium secondary battery according to the present invention comprises a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and the above-described electrolyte solution for lithium secondary batteries.

[0126] The positive electrode active material includes a lithium composite oxide represented by the following Chemical Formula 3:

[0127] (Chemical Formula 3) Li x M 1 y M 2 z M 3 1-y-z O 2-a X a 0.5 ≦ x ≦ 1.8, 0 ≦ a ≦ 0.05, 0 < y ≦ 1, 0 ≦ z ≦ 1, and 0 ≦ y + z ≦ 1, M 1 , M 2 , and M 3 each independently may contain one or more elements selected from metals such as Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, or La and combinations thereof, X may contain one or more elements selected from F, S, P, or Cl.

[0128] As one embodiment, in Chemical Formula 3, M 1 may be Ni, 0.8 ≦ y ≦ 1, and 0 ≦ z ≦ 0.2. Or, in Chemical Formula 3, M 1 may be Ni, M 2 may be Co, and M 3 may be Al. Or, in Chemical Formula 3, M 1 may be Ni, M 2 may be Co, and M 3 may be Mn.

[0129] The negative electrode active material may be a carbon - based negative electrode active material, a Si - based negative electrode active material, a Sn - based negative electrode active material, or a combination thereof.

[0130] In one embodiment, the negative electrode active material includes a carbon-based negative electrode active material and a Si-based negative electrode active material. The carbon-based negative electrode active material may be graphite, and the Si-based negative electrode active material may be silicon nanoparticles. The weight ratio of the silicon nanoparticles to the graphite may be 0.001 to 20. By satisfying the combination of graphite and silicon nanoparticles and the weight ratio range, the effect of improving the high-temperature performance of the lithium secondary battery can be maximized.

[0131] In a lithium secondary battery according to another embodiment of the present invention, a passivating coating is formed on the surfaces of the positive and negative electrodes as the non-aqueous electrolyte is decomposed during initial charge and discharge, thereby improving high-temperature storage characteristics. The coating is a HF film formed by the thermal decomposition of lithium salts (e.g., LiPF6) widely used in lithium-ion batteries. - and PF5 - Acid attack can cause degradation of the positive electrode due to acids such as nitroxide, nitrate, and nitrate. This acid attack can cause the elution of transition metal elements at the positive electrode, changing the surface structure and increasing the electrode's surface resistance. This can lead to a decrease in the theoretical capacity due to the loss of redox center metal elements, resulting in a decrease in the actual capacity. Furthermore, these eluted transition metal ions can be electrodeposited on the negative electrode, which reacts in a strong reduction potential range. This not only consumes electrons, but also destroys the coating during electrodeposition, exposing the negative electrode surface and potentially triggering further electrolyte decomposition reactions. This can lead to increased negative electrode resistance and an increase in irreversible capacity, resulting in a continuous decrease in cell capacity.

[0132] In the present invention, the -PO2F functional group of the first compound and the triazole group and sulfone group of the second compound provide unshared electron pairs, thereby forming a PF5 - By capturing the acid and stabilizing the LiPF6 salt, it is possible to remove the acid caused by the decomposition of the lithium salt in the electrolyte.

[0133] In addition, the triazole group and sulfone group contained in the second compound described above form a coating on the surface of the positive electrode, thereby suppressing decomposition of the positive electrode active material, thereby making it possible to suppress the generation of gas and the elution of transition metals due to decomposition of the positive electrode active material.

[0134] In addition, the triazole group and sulfone group contained in the second compound further strengthen the SEI film on the surface of the negative electrode, thereby further improving the lifespan characteristics of the battery and reducing the internal resistance of the battery.

[0135] The positive electrode active material of the lithium secondary battery may be a lithium-cobalt-based oxide, a lithium-nickel-based oxide, a lithium-manganese-based oxide, a lithium-iron phosphate-based oxide, a cobalt-free nickel-manganese-based oxide, or a combination thereof. In one embodiment, the positive electrode active material of the lithium secondary battery may include nickel, cobalt, and aluminum. Alternatively, in another embodiment, the positive electrode active material of the lithium secondary battery may include nickel, cobalt, and manganese.

[0136] The negative electrode active material of the lithium secondary battery may be a carbon-based negative electrode active material, a silicon-based negative electrode active material, or a combination thereof. In one embodiment, the negative electrode active material of the lithium secondary battery may include a carbon-based negative electrode active material and a Si-based negative electrode active material. In this case, the carbon-based negative electrode active material may be graphite, and the Si-based negative electrode active material may be silicon nanoparticles. The weight ratio of the silicon nanoparticles to the graphite may be 0.001 to 20. [Example]

[0137] Examples of the present invention and comparative examples are described below, but the following examples are merely examples of the present invention and the present invention is not limited to the following examples.

[0138] Example 1 (1) Preparation of electrolyte An electrolyte solution was prepared by dissolving 1.5 M LiPF6 in a non-aqueous organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:10:70, and adding additives.

[0139] The additive contained 1 part by weight of the first compound based on 100 parts by weight of the electrolyte solution, and 1 part by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0140] The first and second compounds used were those represented by the following Chemical Formula 1A and Chemical Formula 2A.

[0141] [ka]

[0142] [ka]

[0143] (2) Fabrication of lithium secondary batteries LiNi as the positive electrode active material 0.91 Co 0.07 Al 0.02 O2, polyvinylidene fluoride as a binder, and Ketjen black as a conductive material were mixed in a weight ratio of 97:2:1, and dispersed in N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0144] The positive electrode active material slurry was applied to an aluminum current collector to form a coating layer having a thickness of 14 μm, which was then dried at 100° C. and pressed to prepare a positive electrode.

[0145] The negative electrode active material was a mixture of artificial graphite and silicon nanoparticles in a weight ratio of 93:7, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener in a weight ratio of 97:1:2. The mixture was dispersed in distilled water to prepare a negative electrode active material slurry.

[0146] The negative electrode active material slurry was used to form a coating layer on a copper current collector having a thickness of 10 μm, which was then dried at 100° C. and rolled to prepare a negative electrode.

[0147] The positive and negative electrodes were assembled with a 25 μm thick polyethylene separator to prepare an electrode assembly, and an electrolyte solution was injected to prepare a lithium secondary battery.

[0148] Example 2 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the additive contained 1 part by weight of the first compound based on 100 parts by weight of the electrolyte solution and 2 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0149] Example 3 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the additive contained 1 part by weight of the first compound based on 100 parts by weight of the electrolyte solution and 3 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0150] Example 4 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the additive contained 1 part by weight of the first compound based on 100 parts by weight of the electrolyte solution and 4 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0151] Example 5 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the additive contained 1 part by weight of the first compound based on 100 parts by weight of the electrolyte solution and 5 parts by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0152] Comparative Example 1 An electrolyte solution and a lithium secondary battery were produced in the same manner as in Example 1, except that no additives were added.

[0153] Comparative Example 2 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the additive contained 1 part by weight of the first compound based on 100 parts by weight of the electrolyte solution and did not contain any of the second compound.

[0154] Comparative Example 3 An electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the additive did not contain any first compound and contained 1 part by weight of the second compound based on 100 parts by weight of the electrolyte solution.

[0155] Evaluation example 1: Evaluation of capacity retention rate during high-temperature storage To evaluate high-temperature storage characteristics, high-temperature capacity retention was measured. The lithium secondary batteries prepared in the Examples and Comparative Examples were charged to SOC 100 at room temperature (25°C) under constant current-voltage (CC-CV) conditions of 0.33 C, 4.25 V, and 0.025 C cutoff, and then stored at 55°C for 60 days. Next, the discharge capacity was measured and the high-temperature capacity retention was calculated. The results are shown in Table 1 below. The high-temperature capacity retention was calculated according to the following equation 1.

[0156] (Formula 1) Capacity retention rate (%) = (discharge capacity after storage at 55°C for 60 days) / (initial discharge capacity) * 100

[0157] Evaluation example 2: Evaluation of resistance increase rate during high temperature storage The lithium secondary batteries prepared in the Examples and Comparative Examples were charged to SOC 100 at room temperature (25°C) using a constant current-voltage (CC-CV) charger under cutoff conditions of 0.33 C, 4.25 V, and 0.025 C. The initial battery resistance (DC-IR) and the battery resistance (DC-IR) after storage at 55°C for 60 days were measured. The resistance increase rate was calculated, and the results are shown in Table 1 below. The resistance (DC-IR) was calculated from the current difference and voltage difference when different currents were applied. The resistance (DC-IR) was calculated by discharging a battery at a constant current of 1 C for 30 seconds from an initial fully charged state, using ΔR=ΔV / ΔI. The resistance increase rate was calculated according to Equation 2 below.

[0158] (Formula 2) Resistance increase rate (%) = [[Battery resistance (DC-IR) value after 60 days / Initial battery resistance (DC-IR) value] - 1] * 100

[0159] Evaluation example 3: Evaluation of transition metal (Ni) elution amount during high-temperature storage The lithium secondary batteries prepared in the examples and comparative examples were charged to SOC 100 at 55°C and 0.33C charge (CC / CV, 4.25V, 0.025C cut-off), and then left at 55°C for 60 days to measure the amount of nickel (Ni) elution. The results are shown in Table 1 below.

[0160] [Table 1]

[0161] Referring to Table 1, it was confirmed that the use of an electrolyte containing the first compound and the second compound according to the present invention (Examples 1 to 5) had a superior capacity retention rate at a high temperature (55°C) compared to the use of an electrolyte containing no first compound or second compound at all (Comparative Example 1), the use of an electrolyte containing only the first compound (Comparative Example 2), and the use of an electrolyte containing only the second compound (Comparative Example 3). In other words, it was confirmed that Examples 1 to 5 were superior in improving the life characteristics of the battery.

[0162] Continuing to refer to Table 1, it was confirmed that when an electrolyte containing the first compound and the second compound according to the present invention was used (Examples 1 to 5), the resistance increase rate at high temperature (55°C) was lower than when an electrolyte containing no first compound or second compound was used (Comparative Example 1), when an electrolyte containing only the first compound was used (Comparative Example 2), and when an electrolyte containing only the second compound was used (Comparative Example 3). In other words, it was confirmed that Examples 1 to 5 had an excellent resistance reduction effect.

[0163] Further referring to Table 1, it was confirmed that when an electrolyte containing the first compound and the second compound according to the present invention was used (Examples 1 to 5), the amount of transition metal (Ni) eluted at a high temperature (55°C) was lower than when an electrolyte containing no first compound or second compound was used (Comparative Example 1), when an electrolyte containing only the first compound was used (Comparative Example 2), or when an electrolyte containing only the second compound was used (Comparative Example 3). In other words, it was confirmed that Examples 1 to 5 had an excellent effect of inhibiting the elution of the transition metal.

[0164] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be embodied in various modifications within the scope of the claims, the embodiments for implementing the invention, and the accompanying drawings, and it is to be understood that these also fall within the scope of the present invention. [Explanation of symbols]

[0165] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive electrode terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Housing 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】 (In the above Chemical Formula 1, X １ is a fluoro, chloro, bromo, or iodo group; R １ ~R ６ each independently represents 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; n is an integer of 0 or 1; 【Chemistry 2】 In the above Chemical Formula 2, L ２Ａ and L ２Ｂ each independently represents a single bond, a substituted or unsubstituted C1 to C5 alkylene group, a substituted or unsubstituted C2 to C5 alkenylene group, a substituted or unsubstituted C2 to C5 alkynylene group, or a substituted or unsubstituted C6 to C20 arylene group; A and B are each independently a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a substituted or unsubstituted C2 to C20 heteroaryl group; At least one of A and B is a group represented by the following chemical formula A: 【Chemistry 3】 In the above chemical formula A, R ７ and R ８ are each independently hydrogen, halogen, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C3 to C10 cycloalkyl group.

2. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the content of the first compound is 0.2 to 5.0 parts by weight based on 100 parts by weight of the electrolyte for a lithium secondary battery.

3. 2. The electrolyte solution for a lithium secondary battery according to claim 1, wherein the content of the second compound is 1 to 5 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 additive is 1.2 to 10 parts by weight based on 100 parts by weight of the electrolyte solution for a lithium secondary battery.

5. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein a weight ratio of the second compound to the first compound in the additive is 0.2 to 25.

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

7. 2. The electrolyte for a lithium secondary battery according to claim 1, wherein the formula 1 is represented by the following formula 1-1 or 1-2: 【Chemistry 4】 (In the above Chemical Formula 1-1 and Chemical Formula 1-2, X １ is a fluoro, chloro, bromo, or iodo group; R １ ~R ６ 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.

8. R in Formula 1-1 ３ and R ４ are hydrogen, The R ５ and R ６ 8. The electrolyte for a lithium secondary battery according to claim 7, wherein at least one of the groups 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.

9. The electrolyte for a lithium secondary battery according to claim 1 , wherein the first compound is at least one selected from the following first group of compounds: 【Chemistry 5】

10. Said L ２Ａ and L ２Ｂ 2. The electrolyte for a lithium secondary battery according to claim 1, wherein at least one of the groups is a substituted or unsubstituted C1 to C5 alkylene group.

11. Said L ２Ａ and L ２Ｂ 2. The electrolyte for a lithium secondary battery according to claim 1, wherein at least one of the groups is a substituted or unsubstituted C2 to C5 alkylene group.

12. The electrolyte for a lithium secondary battery according to claim 1, wherein the chemical formula 2 is represented by the following chemical formula 2-1: 【Chemistry 6】 (In the above chemical formula 2-1, Said L １ and L ２ are each independently a substituted or unsubstituted C2 to C5 alkylene group; R ２１Ａ , R ２１Ｂ , R ２１Ｃ , and R ２１Ｄ are each independently hydrogen, halogen, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C3 to C10 cycloalkyl group.

13. The electrolyte for a lithium secondary battery according to claim 1 , wherein the second compound is one selected from the compounds listed in the following second group: 【Chemistry 7】

14. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; A lithium secondary battery comprising the electrolyte solution for lithium secondary batteries according to any one of claims 1 to 13.

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

16. In the above formula 3, M １ The lithium secondary battery according to claim 15, wherein is Ni, 0.8≦y≦1, and 0≦z≦0.

2.

17. The lithium secondary battery of claim 14 , wherein the negative electrode active material comprises a carbon-based negative electrode active material, a Si-based negative electrode active material, a Sn-based negative electrode active material, or a combination thereof.

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