Electrolyte for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The present invention relates to an electrolyte for a rechargeable lithium battery and a rechargeable lithium battery including same. The electrolyte for a rechargeable lithium battery includes: a non-aqueous organic solvent; a lithium salt; and an additive, wherein the additive includes a first additive represented by chemical formula 1. The rechargeable lithium battery includes the electrolyte for a rechargeable lithium battery.

Description

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

[0001] The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery containing the same.

[0002]

[0003] Recently, accompanied by the rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries is rapidly increasing. Accordingly, research and development to improve the performance of lithium-ion batteries is actively underway.

[0004] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of lithium ion intercalation and deintercalation, and an electrolyte, which produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated or deintercalated from the positive and negative electrodes.

[0005] The electrolyte for these lithium secondary batteries consists of a lithium salt dissolved in a non-aqueous organic solvent. The characteristics of a lithium secondary battery are determined by complex reactions between the anode and the electrolyte, and between the cathode and the electrolyte. Therefore, the use of an appropriate electrolyte is one of the important variables for improving the performance of a lithium secondary battery.

[0006]

[0007] One embodiment provides an electrolyte for a lithium secondary battery that provides a room temperature life, a high temperature life, a low resistance increase rate after high temperature storage, and a low gas generation amount after high temperature storage.

[0008] Another embodiment provides an electrolyte for a lithium secondary battery that provides a room temperature life at high voltage, a high temperature life, a low resistance increase rate after high temperature storage, and a low gas generation amount after high temperature storage.

[0009] Another embodiment provides an electrolyte for a lithium secondary battery having a cobalt-free positive electrode active material, which provides a room temperature life, a high temperature life, a low resistance increase rate after high temperature storage, and a low gas generation amount after high temperature storage.

[0010] Another embodiment provides a lithium secondary battery comprising the above electrolyte.

[0011]

[0012] One embodiment provides an electrolyte for a lithium secondary battery.

[0013] 1. An electrolyte for a lithium secondary battery comprises a non-aqueous organic solvent; a lithium salt; and an additive, wherein the additive comprises a first additive represented by the following chemical formula 1:

[0014] [Chemical Formula 1]

[0015]

[0016] (In the above chemical formula 1,

[0017] R 1 , R 2 , R 3 , and R 4 is the same as defined in the description of the invention below).

[0018] In 2.1, R 1 , R 2 and R 3 An electrolyte for a lithium secondary battery, wherein each is independently a substituted or unsubstituted C1 to C5 alkylene group, a substituted or unsubstituted C2 to C5 alkenylene group, or a substituted or unsubstituted C2 to C5 alkynylene group.

[0019] In 3.1 to 2, R 4 An electrolyte for a lithium secondary battery, wherein is a halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, or a substituted or unsubstituted C2 to C20 alkynyl group.

[0020] 4.1 to 3, wherein the first additive is one or more of the following chemical formulas 1-2 to 1-8, an electrolyte for a lithium secondary battery:

[0021] [Chemical Formula 1-2]

[0022]

[0023] [Chemical Formula 1-3]

[0024]

[0025] [Chemical Formula 1-4]

[0026]

[0027] [Chemical Formula 1-5]

[0028]

[0029] [Chemical Formula 1-6]

[0030]

[0031] [Chemical Formula 1-7]

[0032]

[0033] [Chemical Formula 1-8]

[0034]

[0035] 5.1 to 4, the electrolyte for a lithium secondary battery, wherein the first additive is included in an amount of 0.05 to 5 weight% with respect to the total amount of the electrolyte.

[0036] 6.1 to 5, the electrolyte for a lithium secondary battery further comprising a second additive in addition to the first additive.

[0037] 7.1 to 6, the electrolyte for a lithium secondary battery comprising the second additive, saccharin or a saccharin derivative.

[0038] 8.1 to 7, wherein the saccharin or saccharin derivative comprises one or more of the following chemical formulas 2-1 and 2-2, an electrolyte for a lithium secondary battery:

[0039] [Chemical Formula 2-1]

[0040]

[0041] [Chemical Formula 2-2]

[0042]

[0043] (In the above chemical formulas 2-1 and 2-2,

[0044] is a hydrogen cation, alkali metal cation, ammonium cation, phosphonium cation, or sulfonium cation).

[0045] 9.1 to 8, an electrolyte for a lithium secondary battery, wherein the first additive and the second additive in the electrolyte are included in a weight ratio of 10:90 to 90:10 of the total weight of the first additive and the second additive in an amount of 100 parts by weight.

[0046] 10.1 to 9, the electrolyte for a lithium secondary battery, wherein the second additive is included in an amount of 0.05 to 5 weight% with respect to the total amount of the electrolyte.

[0047] 11.1 to 10, the electrolyte for a lithium secondary battery, wherein the non-aqueous organic solvent is a mixture containing ethylene carbonate (EC): ethylmethyl carbonate (EMC): dimethyl carbonate (DMC) in a volume ratio of 10 to 30: 20 to 50: 20 to 50.

[0048] 12.1 to 11, an electrolyte for a lithium secondary battery, wherein the concentration of the lithium salt in the electrolyte is 0.1M to 3.0M.

[0049] 13.1 to 12, the lithium salt is one or more selected from the group consisting of LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFBP, LiTFOP, LiPO2F2, LiSbF6, LiAsF6, LiAlO2, LiAlCl4, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N, and LiC4F9SO3, an electrolyte for a lithium secondary battery.

[0050] 14.1 to 13, an electrolyte for a lithium secondary battery, wherein the additive comprises 95% by weight or more of the total additive of the electrolyte.

[0051] Another embodiment provides a lithium secondary battery.

[0052] 15. A lithium secondary battery comprises a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, wherein the electrolyte comprises electrolytes 1 to 14.

[0053] In 16.15, the above positive active material is a cobalt-free positive active material, a lithium secondary battery.

[0054] 17.15 to 16, the cobalt-free positive electrode active material comprises a cobalt-free nickel-manganese-based oxide, in a lithium secondary battery.

[0055] 18.15 to 17, wherein the cobalt-free nickel-manganese-based oxide comprises a lithium composite oxide represented by the following chemical formula 6, a lithium secondary battery:

[0056] [Chemical Formula 6]

[0057] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0058] In the above chemical formula 6, 0.9≤a4≤1.8, 0.8≤x4<1, 0 <y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, 및 0≤b4≤0.1이고 M 5 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0059] 19.15 to 18, a lithium secondary battery wherein the negative electrode active material comprises at least one of graphite and a Si composite.

[0060] A lithium secondary battery, wherein, in 20.15 to 19, the driving voltage of the lithium secondary battery is 4.45 V or higher.

[0061]

[0062] An electrolyte according to one embodiment can exhibit the effect of improving lifespan characteristics and stability under high voltage and / or high temperature conditions when activating a secondary battery in a lithium secondary battery.

[0063] An electrolyte according to one embodiment can have the effect of improving lifespan characteristics and stability under high voltage and / or high temperature conditions when activating a lithium secondary battery containing a cobalt-free cathode active material.

[0064]

[0065] FIG. 1 is a conceptual diagram briefly illustrating a lithium secondary battery according to one embodiment of the present invention.

[0066] FIGS. 2 to 5 are cross-sectional views schematically illustrating a lithium secondary battery according to one embodiment.

[0067]

[0068] In order to fully understand the structure and effects of the present invention, preferred embodiments of the present invention are described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various modifications can be made. The description of these embodiments is provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention.

[0069] In this specification, when a component is described as being on another component, it means that it may be formed directly on the other component or that a third component may be interposed between them. Additionally, in the drawings, the thicknesses of the components are exaggerated for the effective description of the technical content. Throughout the specification, parts indicated by the same reference numeral represent the same components.

[0070] Unless otherwise specified in this specification, the singular form may also include the plural. Additionally, unless otherwise specified, "A or B" may mean "comprising A, comprising B, or comprising A and B." As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components to the mentioned components.

[0071] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0072] In this specification, "substitution" means that, unless otherwise defined, at least one hydrogen of a substituent or compound is substituted with a 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.

[0073] Specifically, "substitution" may mean that at least one hydrogen in the substituent or compound is substituted 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, "substitution" may mean that at least one hydrogen in the substituent or compound is substituted 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, "substitution" may mean that at least one hydrogen in the substituent or compound is substituted with a 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. For example, "substitution" may mean that at least one hydrogen in the substituent or compound is substituted with a 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.

[0074] Unless otherwise defined in this specification, "*" means a part connected to the same or different atoms or chemical formulas.

[0075] Unless otherwise specifically stated in the formulas described in this specification, hydrogen may be bonded in the structure of the formulas. Unless otherwise defined in this specification, the halogen may be F, Cl, Br, or I.

[0076] FIG. 1 is a conceptual diagram briefly illustrating a lithium secondary battery according to embodiments of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode (10), a negative electrode (20), a separator (30), and an electrolyte (ELL).

[0077] The positive electrode (10) and the negative electrode (20) may be spaced apart from each other with a separator (30) in between. 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 come into contact with an electrolyte (ELL). The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated within the electrolyte (ELL).

[0078] The electrolyte (ELL) may be a medium for transferring lithium ions between the positive electrode (10) and the negative electrode (20). Within the electrolyte (ELL), the lithium ions may pass through a separator (30) and move toward the positive electrode (10) or the negative electrode (20).

[0079] positive electrode (10)

[0080] A positive electrode (10) for a lithium secondary battery may include a current collector (COL1) and a positive electrode active material layer (AML1) formed on the current collector (COL1). The positive electrode active material layer (AML1) may include a positive electrode active material and may further include a binder and / or a conductive material.

[0081] For example, the anode (10) may further include an additive that can serve as a sacrificial anode.

[0082] The content of the positive active material in the positive active material layer (AML1) may be 90% to 99.5% by weight with respect to 100% by weight of the positive active material layer (AML1). The content of the binder and the conductive material may each be 0.5% to 5% by weight with respect to 100% by weight of the positive active material layer (AML1).

[0083] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector (COL1). Representative 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)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0084] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0085] Al can be used as the current collector (COL1), but is not limited thereto.

[0086] positive electrode active material

[0087] As the positive active material in the positive active material layer (AML1), a compound capable of reversible intercalation and deintercalation of lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0088] The above composite oxide may be a lithium transition metal composite oxide, and specific examples include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0089] As an example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li aNiG 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).

[0090] 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; L 1 is Mn, Al, or a combination thereof.

[0091] For example, the above-mentioned 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 in the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0092] Negative electrode (20)

[0093] A negative electrode (20) for a lithium secondary battery comprises 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) comprises a negative electrode active material and may further comprise a binder and / or a conductive material.

[0094] 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.

[0095] The above binder serves to effectively bond the negative electrode active material particles to each other and also to effectively bond 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.

[0096] Examples of the above-mentioned 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.

[0097] The above-mentioned water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0098] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0099] The above dry binder is a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0100] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0101] 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, and combinations thereof may be used.

[0102] cathode active material

[0103] The negative electrode active material in the negative electrode active material layer (AML2) comprises 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.

[0104] A material capable of reversibly intercalating / deintercalating the above lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0105] As the above 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.

[0106] As a material capable of doping and undoping the above 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 (wherein Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0107] 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 amorphous carbon coated on the surface of the silicon particles. For example, it may include a secondary particle (core) assembled from silicon primary particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particle. The amorphous carbon may also be located between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0108] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0109] The above Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0110] Separator (30)

[0111] Depending on the type of lithium secondary battery, a separator (30) may be present between the positive electrode (10) and the negative electrode (20). As such a separator (30), polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and of course, 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.

[0112] The 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.

[0113] The porous substrate may be a polymer membrane formed from any one of the following: polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyacetal; polyamide; polyimide; polycarbonate; polyetherketone; polyaryletherketone; polyetherimide; polyamideimide; polybenzimidazole; polyethersulfone; polyphenylene oxide; cyclic olefin copolymer; polyphenylene sulfide; polyethylene naphthalate; glass fiber; Teflon; and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0114] The above organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0115] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include, but is not limited to, inorganic particles selected from SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0116] The above organic and inorganic materials may exist mixed in a single coating layer, or may exist in a stacked form with a coating layer containing organic materials and a coating layer containing inorganic materials.

[0117] Electrolyte (ELL)

[0118] The electrolyte (ELL) for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0119] The above-mentioned non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0120] The above-mentioned non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0121] The above carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc.

[0122] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0123] As ether-based solvents, dibutyl ether, tetraglame, diglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Additionally, as ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. may be used.

[0124] The above-mentioned non-aqueous organic solvent can be used alone or in a mixture of two or more types.

[0125] In addition, when using a carbonate-based solvent, a mixture of cyclic carbonates and chain carbonates can be used, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0126] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and facilitating the movement of lithium ions between the anode and cathode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N, LiFSI, LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 It may include one or more selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFOP), and lithium bis(oxalate)borate (LiBOB).

[0127] lithium secondary battery

[0128] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, coin, etc., depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, where FIG. 2 is a cylindrical battery, FIG. 3 is a prismatic battery, and FIGS. 4 and 5 are pouch-type batteries. Referring to FIGS. 2 to 5, the lithium secondary battery (100) may include an electrode assembly (40) with a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is housed. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as in FIG. 2. In addition, in FIG. 3, the lithium secondary battery (100) may include a positive lead tab (11) and a positive terminal (12), a negative lead tab (21) and a negative terminal (22). As shown in FIG. 4 and FIG. 5, the lithium secondary battery (100) may include electrode tabs (70), namely a positive tab (71) and a negative tab (72), which serve as electrical passages for inducing current formed in the electrode assembly (40) to the outside.

[0129] [Electrolyte]

[0130] Hereinafter, the electrolyte of a lithium secondary battery according to one embodiment of the present invention will be described in more detail.

[0131] An electrolyte for a lithium secondary battery according to one embodiment comprises the above-described non-aqueous organic solvent; a lithium salt; and an additive, wherein the additive comprises an additive to be described below.

[0132] The above electrolyte can be prepared by dissolving a lithium salt in a non-aqueous organic solvent, adding the above additive, and then performing a mixing process. The process of mixing the electrolyte is widely known in the field of electrolyte manufacturing, and a person skilled in the art would be able to appropriately select and use it.

[0133] A non-aqueous organic solvent according to one embodiment of the present invention may include one or more of the non-aqueous organic solvents described above.

[0134] In one embodiment, 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 to 30: 20 to 50: 20 to 50. Here, the volume ratio is a value based on 100 volume% of the total of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC). Within the above range, it is easy to implement the effect of the additive described below, and the reductive decomposition rate of the cathode in a lithium secondary battery containing the cobalt-free cathode active material described below is slowed down, thereby further improving the battery life.

[0135] A lithium salt according to one embodiment of the present invention may include one or more selected from the group consisting of LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFBP, LiTFOP, 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.

[0136] The concentration of the lithium salt in the above electrolyte may be 0.1M to 3.0M. Specifically, the concentration of the lithium salt may be 0.5M or higher and 1.0M or higher. The concentration of the lithium salt may be 3.0M or lower, 2.5M or lower, and 2.0M or lower. In the present invention, when the concentration of the lithium salt is 0.1M to 2.0M, the conductivity and viscosity of the electrolyte can be appropriately maintained.

[0137] additives

[0138] An additive according to one embodiment of the present invention comprises a first additive represented by the following chemical formula 1:

[0139] [Chemical Formula 1]

[0140]

[0141] (In the above chemical formula 1,

[0142] R 1 , R 2 and R 3 Each is independently 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, and

[0143] R 4 is hydrogen, halogen, 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).

[0144] In one specific example, R 1 , R 2 and R 3 Each may independently be a substituted or unsubstituted C1 to C5 alkylene group, a substituted or unsubstituted C2 to C5 alkenylene group, or a substituted or unsubstituted C2 to C5 alkynylene group. For example, R 1 , R 2 and R 3 Each may independently be a propylene group including a methylene group, an ethylene group, an n-propylene group, an iso-propylene group, etc.

[0145] In one specific example, R 4may be a halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, or a substituted or unsubstituted C2 to C20 alkenyl group. For example, R 4 may be a halogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, or a substituted or unsubstituted C2 to C10 alkynyl group. For example, R 4 It can be a methyl group, an ethyl group, a propyl group including an n-propyl group, an iso-propyl group, etc., a butyl group including an n-butyl group, an iso-butyl group, a tert-butyl group, etc., a halogen, a trifluoromethyl group, a vinyl group, a metavinyl group, an allyl group, or a metaallyl group, etc.

[0146] For example, the first additive may be one or more of the following chemical formulas 1-2 to 1-8:

[0147] [Chemical Formula 1-2]

[0148]

[0149] [Chemical Formula 1-3]

[0150]

[0151] [Chemical Formula 1-4]

[0152]

[0153] [Chemical Formula 1-5]

[0154]

[0155] [Chemical Formula 1-6]

[0156]

[0157] [Chemical Formula 1-7]

[0158]

[0159] [Chemical Formula 1-8]

[0160]

[0161] The above-mentioned first additive can be synthesized using conventional methods known to those skilled in the art.

[0162] The first additive is a cyclic organophosphite ester having a non-covalent electron pair at P and additionally having a -P(-O)3 structure. Due to the non-covalent electron pair at P, it has basicity, which improves defects in the battery and can suppress the deterioration of the anode by capturing oxygen radicals in the electrolyte. In addition, the first additive can improve the performance of the battery at high temperatures by forming a film on the cathode while undergoing reductive decomposition. Furthermore, the first additive can reduce the reductive decomposition of the anode caused by ethylene carbonate in the electrolyte.

[0163] In particular, in lithium secondary batteries containing cobalt-free cathode active materials, such as nickel-manganese-based cathode active materials, electrolyte decomposition is accelerated as nickel activity increases, and the surface of the anode is reduced after a large amount of nickel is leached, which can accelerate the deterioration of lifespan. Additionally, the reductive decomposition of the cathode can be accelerated by receiving electrons from ethylene carbonate as a non-aqueous organic solvent in the electrolyte. When the first additive is applied to a lithium secondary battery containing a cobalt-free cathode active material, it may provide excellent effects in terms of room temperature lifespan, high temperature lifespan, low resistance increase rate after high-temperature storage, and low gas generation amount after high-temperature storage. In particular, the first additive can improve the battery lifespan of a lithium secondary battery containing a cobalt-free cathode active material under high voltage of 4.45V or higher, and significantly improve battery performance even under high-temperature conditions.

[0164] The first additive may be included in an amount of 95% by weight or more of the total additives of the electrolyte, for example, 95 to 100% by weight or 100% by weight. Within this range, the effect of the additive described above is realized, and side reactions of the electrolyte can be suppressed.

[0165] The first additive may be included in an amount of 0.05 to 5 weight percent relative to the total amount of the electrolyte. Within this range, the effect of the first additive may be realized. Specifically, the first additive may be included in an amount of 0.05 to 3 weight percent or 0.1 to 3 weight percent relative to the total amount of the electrolyte. Within this range, the effect of the first additive is significantly enhanced, and there may be an additional effect of not increasing the resistance of the battery.

[0166] The above additive may further include a second additive in addition to the first additive.

[0167] The second additive mentioned above may be saccharin or a saccharin derivative. Saccharin or a saccharin derivative has phenyl groups and S(=O)2, which can increase the reliability of the battery after high-temperature storage by forming a film on the anode.

[0168] The above saccharin or saccharin derivative may include one or more of the following chemical formulas 2-1 and 2-2.

[0169] [Chemical Formula 2-1]

[0170]

[0171] [Chemical Formula 2-2]

[0172]

[0173] (In the above chemical formulas 2-1 and 2-2,

[0174] is a hydrogen cation, alkali metal cation, ammonium cation, phosphonium cation, or sulfonium cation).

[0175] The ammonium cation may be selected from the group consisting of pyridinium, piperidinium, pyrrolidinium, pyrroline cation, pyrrole cation, imidazolium, tetrahydropyrimidinium, dihydropyrimidinium, pyrazolium, pyrazolinium, monoalkyl, dialkyl, trialkyl, or tetraalkylammonium having 1 to 40 carbon atoms, and those in which the alkyl groups thereof are substituted with alkenyl, alkoxyl, or epoxy groups.

[0176] The phosphonium cation may be selected from the group consisting of tetramethylphosphonium, tetraethylphosphonium, tetrabutylphosphonium, tetrapentylphosphonium, tetrahexylphosphonium, tetraheptylphosphonium, tetraoctylphosphonium, triethylmethylphosphonium, tributylmethylphosphonium, tributylethylphosphonium, and trimethyldecylphosphonium.

[0177] The sulfonium cation may be selected from the group consisting of trimethylsulfonium, triethylsulfonium, tributylsulfonium, trihexylsulfonium, diethylmethylsulfonium, dibutylethylsulfonium, and dimethyldecylsulfonium.

[0178] The second additive may be included in an amount of 0.05 to 5 weight percent relative to the total amount of the electrolyte. Within this range, the effect of the second additive may be realized. Specifically, the second additive may be included in an amount of 0.05 to 3 weight percent or 0.1 to 3 weight percent relative to the total amount of the electrolyte. Within this range, the effect of the second additive is significantly enhanced, and there may be an additional effect of not increasing the resistance of the battery.

[0179] The first additive of Formula 1 above can provide a synergistic effect in the lifespan (room temperature lifespan and high temperature lifespan) and stability of the battery by significantly improving the lifespan characteristics and stability of the battery under high voltage and / or high temperature conditions when combined with the second additive above. In particular, the first additive of Formula 1 above can provide a synergistic effect in the lifespan (high temperature lifespan) and stability under high voltage and / or high temperature conditions when activating the secondary battery in a lithium secondary battery containing a cobalt-free cathode active material by significantly improving the lifespan characteristics and stability under high voltage and / or high temperature conditions.

[0180] In one embodiment, the first additive and the second additive in the electrolyte may be included in a weight ratio of 10:90 to 90:10 in 100 parts by weight of the total sum of the first additive and the second additive. Within this range, it may be easy to implement the effect of the mixture of the additives. Specifically, the weight ratio may be included in a weight ratio of 20:80 to 80:20 or 30:70 to 70:30.

[0181] In one embodiment, the mixture of the first additive and the second additive among the total additives of the electrolyte may be included in an amount of 95% by weight or more, for example, 95 to 100% by weight, or 100% by weight.

[0182] In one embodiment, the mixture of the first additive and the second additive may be included in the electrolyte in an amount of 0.1 to 5 weight%, for example, 0.1 to 3 weight%. Within this range, it may be easy to achieve the effect of the mixture of additives.

[0183] [Lithium Secondary Battery]

[0184] In another embodiment of the present invention, a lithium secondary battery may be provided comprising: a positive electrode comprising a positive active material; a negative electrode comprising a negative 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 first additive of Formula 1.

[0185] The above additive may further include the above second additive.

[0186] The above-mentioned lithium secondary battery may be applied to automobiles, mobile phones, and / or various types of electric devices, etc., but the present invention is not limited thereto.

[0187] The above-mentioned positive electrode active material may be a lithium transition metal composite oxide, and specific examples of the above-mentioned positive electrode active material may include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-based oxide, or a combination thereof.

[0188] As an example, the above-mentioned positive active material may use a compound represented by any one of the following chemical formulas. 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 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).

[0189] 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; L 1 is Mn, Al, or a combination thereof.

[0190] The above positive active material may include, for example, a lithium nickel-based oxide represented by the following chemical formula 3, a lithium cobalt-based oxide represented by the following chemical formula 4, a lithium iron phosphate-based compound represented by the following chemical formula 5, a cobalt-free lithium nickel-based oxide represented by the chemical formula 6, or a combination thereof.

[0191] [Chemical Formula 3]

[0192] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0193] In the above chemical formula 2, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, and M 1 and M 2 Each is independently one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0194] In the above chemical formula 3, 0.6≤x1≤1, 0≤y1≤0.4, and 0≤z1≤0.4, or 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2.

[0195] [Chemical Formula 4]

[0196] Li a2 Co x2 M 3 y2 O 2-b2 X b2

[0197] In the above chemical formula 4, 0.9≤a2≤1.8, 0.7≤x2≤1, 0≤y2≤0.3, 0.9≤x2+y2≤1.1, and 0≤b2≤0.1, and M 3 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0198] [Chemical Formula 5]

[0199] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3

[0200] In the above chemical formula 4, 0.9≤a3≤1.8, 0.6≤x3≤1, 0≤y3≤0.4, and 0≤b3≤0.1, and M 4 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0201] [Chemical Formula 6]

[0202] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4

[0203] In the above chemical formula 6, 0.9≤a4≤1.8, 0.8≤x4<1, 0 <y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, 및 0≤b4≤0.1이고 M 5 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0204] In one embodiment, the positive electrode active material may include a cobalt-free positive electrode active material. In one embodiment, the cobalt-free positive electrode active material may include a cobalt-free lithium nickel-based oxide represented by Chemical Formula 6, for example, a cobalt-free lithium nickel manganese-based oxide.

[0205] It is possible to have a coating layer on the surface of the above-mentioned lithium composite oxide, or to use a mixture of the above-mentioned lithium composite oxide and a compound having a coating layer. This coating layer may include at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers may be amorphous or crystalline. As coating elements included in the above-mentioned coating layer, Mg, Al, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof may be used. For the coating layer formation process, any coating method may be used as long as the compound can be coated using these elements in a way that does not adversely affect the physical properties of the cathode active material (e.g., spray coating, immersion method, etc.). Since this is a matter that is well understood by those skilled in the art, a detailed explanation is omitted.

[0206] In one embodiment, the cobalt-free lithium nickel-based oxide, for example, the cobalt-free nickel manganese-based oxide, may be included in the positive electrode active material in an amount of 95% or more by weight, for example, 95 to 100% by weight or 100% by weight.

[0207] In a specific embodiment, the negative electrode active material may include at least one of graphite and a Si composite.

[0208] When the above-mentioned cathode active material includes a Si composite and graphite together, the Si composite and graphite may be included in the form of a mixture, in which case the Si composite:graphite may be included in a weight ratio of 1:99 to 50:50 based on a total of 100 parts by weight. More specifically, the Si composite:graphite may be included in a weight ratio of 3:97 to 20:80, 4:96 to 20:80, or 5:95 to 20:80.

[0209] The above Si composite comprises a core containing Si-based particles and an amorphous carbon coating layer, for example, the Si-based particles are a Si-C composite, SiO x It may include one or more of (0 < x ≤ 2) and Si alloys. 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, natural graphite, artificial graphite, or a mixture thereof.

[0210] When the positive electrode contains a cobalt-free lithium nickel-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 voltage of the lithium secondary battery of the above combination is 4.45V or higher, and the battery may operate even at high voltage.

[0211] In one embodiment, the lithium secondary battery may be a cylindrical battery.

[0212]

[0213] Examples and comparative examples of the present invention are described below. However, the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0214]

[0215] Examples and Comparative Examples

[0216] (1) Preparation of electrolyte

[0217] An electrolyte was prepared by dissolving 1.15 M LiPF6 in a carbonate-based solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:40:40 (based on a total volume of 100 volumes), adding an additive, and mixing. Specifically, the amount of additive used is shown in Table 1 below.

[0218] The molar concentration (M) of the lithium salt LiPF6 refers to the amount (number of moles) of the lithium salt dissolved per 1 L of electrolyte, and the volume ratio of the non-aqueous organic solvent refers to the volume ratio of EC:EMC:DMC. The content of the additive (unit: weight%) in Table 1 below refers to the weight of the additive in 100 weight% of the total electrolyte (lithium salt + non-aqueous organic solvent + additive).

[0219] The above additives used were the following chemical formulas 1-2 (CAS No. 824-11-3) and 7.

[0220] [Chemical Formula 1-2]

[0221]

[0222] [Chemical Formula 7]

[0223]

[0224] (2) Manufacturing of lithium secondary batteries

[0225] LiNi as a positive electrode active material 0.75 Mn 0.23 Al 0.02An anode slurry was prepared by mixing O297 wt%, 0.5 wt% artificial graphite powder and 0.8 wt% carbon black (Ketjenblack) as conductive materials, 0.2 wt% acrylonitrile rubber, and 1.5 wt% polyvinylidene fluoride (PVdF) as a binder, adding the mixture to N-methyl-2-pyrrolidone, and stirring for 30 minutes using a mechanical stirrer. The slurry was applied to a thickness of about 60 μm on a 20 μm thick aluminum foil using a doctor blade, dried in a hot air dryer at 100 ℃ for 0.5 hours, dried once more under vacuum conditions at 120 ℃ for 4 hours, and then rolled to produce an anode.

[0226] A cathode slurry was prepared by mixing 98 wt% of a cathode active material, in which a graphite and Si composite was mixed in a weight ratio of 95.8:4.2, 1 wt% of styrene-butadiene rubber (SBR), and 1 wt% of carboxymethylcellulose (CMC), adding the mixture to distilled water, and stirring for 60 minutes using a mechanical stirrer. The slurry was applied to a thickness of about 60 μm on a 10 μm thick copper foil using a doctor blade, dried in a hot air dryer at 100 °C for 0.5 hours, dried once more under vacuum conditions at 120 °C for 4 hours, and then rolled to produce a cathode.

[0227] An electrode assembly was manufactured by assembling the above positive electrode and the above negative electrode with a polyethylene separator having a thickness of 16 μm, and a circular (4.45 V class) lithium secondary battery was manufactured by injecting the above electrolyte.

[0228]

[0229] Evaluation 1: Evaluation of Room Temperature Charge / Discharge Cycle Characteristics (Room Temperature Life) (Unit: %)

[0230] Room temperature charge-discharge characteristics were evaluated for lithium secondary batteries according to the examples and comparative examples. To this end, 200 charge-discharge cycles of the lithium secondary batteries were performed under 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 recovery rate (unit: %) was calculated according to the following formula.

[0231] Capacity recovery rate (%) = (Discharge capacity after 200 cycles / Discharge capacity after 1 cycle) × 100.

[0232]

[0233] Evaluation 2: High Temperature (45℃) Charge / Discharge Cycle Characteristics Evaluation (High Temperature Life) (Unit: %)

[0234] High-temperature charge-discharge characteristics were evaluated for lithium secondary batteries according to the examples and comparative examples. To this end, 200 charge-discharge cycles of the lithium secondary battery were performed under 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 recovery rate (unit: %) was calculated according to the following formula.

[0235] Capacity recovery rate (%) = (Discharge capacity after 200 cycles / Discharge capacity after 1 cycle) × 100.

[0236]

[0237] Evaluation 3: High-temperature storage characteristics evaluation, DCIR (direct current internal resistance) increase rate

[0238] For the lithium secondary batteries according to the examples and comparative examples, the initial DC resistance (unit: mΩ) was measured using the △V / △I (change in voltage / change in current) value, the maximum energy state inside the battery was made to a fully charged state (SOC (state of charge) 100%), and after storing it at 60°C for 30 days in this state, the DC resistance (unit: mΩ) was measured, and the DCIR increase rate (%) was calculated according to the following formula.

[0239] [ceremony]

[0240] DCIR growth rate (%) = (DCIR after 30 days at 60℃ / Initial DCIR) × 100.

[0241]

[0242] Evaluation 4: Evaluation of High Temperature (60℃) Gas Generation Characteristics

[0243] High-temperature gas generation characteristics were evaluated for lithium secondary batteries according to the examples and comparative examples. The maximum energy state inside the battery was set to a fully charged state (SOC 100%). In this state, the amount of gas generated (unit: mL) was evaluated after storing at 60°C for 1 day (initial), 60°C for 1 day, and 60°C for 7 days, respectively. The amount of gas generated was calculated by measuring the volume change before and after high-temperature storage and converting it into a mass change using Archimedes' method.

[0244]

[0245] The results of the above evaluation are shown in Table 1 below.

[0246] Chemical Formula 1-2 Chemical Formula 7 Room Temperature Life High Temperature Life DCIR Gas Generation Amount Initial 60℃ 30 Days DCIR Growth Rate Initial 1 Day 7 Days Example 10.50 92.38 9.34 0.9 48.91 19 0.01 20.01 80.071 Example 20.10 91.58 8.74 1.15 0.51 23 0.01 20.02 40.083 Example 31.00 90.98 8.34 2.15 2.11 24 0.01 30.02 90.081 Example 43.00 90.58 7.94 3.45 3.81 24 0.01 20.02 40.083 Example 50.05090.187.642.552.71240.0120.0270.084Comparative Example 10089.181.142.3531250.0120.0330.092Comparative Example 200.590.487.643.153.91250.0120.0310.090

[0247]

[0248] synthesis

[0249] Referring to Table 1 above, the electrolyte of the example provided room temperature life, high temperature life, a low resistance increase rate after high temperature storage, and a low gas generation amount after high temperature storage under high voltage, based on the results of evaluations 1 to 4. In particular, the electrolyte of the example provided room temperature life, high temperature life, a low resistance increase rate after high temperature storage, and a low gas generation amount after high temperature storage in a lithium secondary battery having a cobalt-free cathode active material.

[0250] However, referring to Table 1 above, Comparative Example 1, which does not contain the additive of the present invention, and Comparative Example 2, which has a cyclic additive not having a -P(-O)3 structure, provided lower effects compared to the electrolyte of the example in terms of room temperature life, high temperature life, resistance increase rate after high temperature storage, and gas generation amount after high temperature storage under high voltage.

[0251]

[0252] Examples and Comparative Examples

[0253] (1) Preparation of electrolyte

[0254] An electrolyte was prepared by dissolving 1.15 M LiPF6 in a carbonate-based solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:40:40 (based on a total volume of 100 volumes), adding an additive, and mixing. Specifically, the amount of additive used is shown in Table 2 below.

[0255] The molar concentration (M) of the lithium salt LiPF6 refers to the amount (number of moles) of the lithium salt dissolved per 1 L of electrolyte, and the volume ratio of the non-aqueous organic solvent refers to the volume ratio of EC:EMC:DMC. The content of the first additive and the second additive in Table 2 below (unit: weight%) refers to the weight of the additive in 100 weight% of the total electrolyte (lithium salt + non-aqueous organic solvent + additive).

[0256] The following chemical formulas 2-3, 1-2 (CAS No. 824-11-3), 8, and 7 were used as the above additives.

[0257] [Chemical Formula 2-3]

[0258]

[0259] [Chemical Formula 1-2]

[0260]

[0261] [Chemical Formula 8]

[0262]

[0263] [Chemical Formula 7]

[0264]

[0265]

[0266] (2) Manufacturing of lithium secondary batteries

[0267] LiNi as a positive electrode active material 0.75 Mn 0.23 Al 0.02An anode slurry was prepared by mixing O297 wt%, 0.5 wt% artificial graphite powder as a conductive material, 0.8 wt% carbon black (Ketjenblack), 0.2 wt% acrylonitrile rubber, and 1.5 wt% polyvinylidene fluoride (PVdF) as a binder, adding the mixture to N-methyl-2-pyrrolidone, and stirring for 30 minutes using a mechanical stirrer. The slurry was applied to a thickness of about 60 μm on a 20 μm thick aluminum foil using a doctor blade, dried in a hot air dryer at 100 ℃ for 0.5 hours, dried once more under vacuum conditions at 120 ℃ for 4 hours, and then rolled to produce an anode.

[0268] A cathode slurry was prepared by mixing 98 wt% of a cathode active material, in which a graphite and Si composite was mixed in a weight ratio of 95.8:4.2, 1 wt% of styrene-butadiene rubber (SBR), and 1 wt% of carboxymethylcellulose (CMC), adding the mixture to distilled water, and stirring for 60 minutes using a mechanical stirrer. The slurry was applied to a thickness of about 60 μm on a 10 μm thick copper foil using a doctor blade, dried in a hot air dryer at 100 °C for 0.5 hours, dried once more under vacuum conditions at 120 °C for 4 hours, and then rolled to produce a cathode.

[0269] An electrode assembly was manufactured by assembling the above positive electrode and the above negative electrode with a separator made of polyethylene material with a thickness of 16 μm, and the above electrolyte was injected to manufacture a prismatic (4.45 V class) lithium secondary battery.

[0270]

[0271] Evaluation 1: High-temperature storage characteristics evaluation DCIR (direct current internal resistance) increase rate (Unit: %)

[0272] For the lithium secondary batteries according to the examples and comparative examples, the initial DC resistance (unit: mΩ) was measured using the △V / △I (change in voltage / change in current) value, the maximum energy state inside the battery was made to a fully charged state (SOC (state of charge) 100%), and after storing it at 60°C for 30 days in this state, the DC resistance (unit: mΩ) was measured, and the DCIR increase rate (%) was calculated according to the following formula.

[0273] [ceremony]

[0274] DCIR growth rate (%) = (DCIR after 30 days at 60℃ / Initial DCIR) × 100.

[0275]

[0276] Evaluation 2: Capacity retention rate after high-temperature storage (Unit: %)

[0277] The lithium secondary batteries of the examples and comparative examples were charged at 25°C with 0.5C CC / CV charging (4.45V, 0.05C CUT-OFF) and discharged at 0.5C CC (2.8V CUT-OFF) twice, and the second discharge capacity C1 (unit: Ah) was measured. After storing the charged lithium secondary batteries at 60°C for 30 days, they were left at room temperature for an additional 30 minutes, and discharged at 0.33C CC (2.8V CUT-OFF) to measure the discharge capacity C2 (unit: Ah). The capacity retention rate was calculated using the following formula.

[0278] [ceremony]

[0279] Capacity retention rate (%) = C2 / C1 × 100.

[0280]

[0281] Evaluation 3: Evaluation of High Temperature (60℃) Gas Generation Characteristics

[0282] High-temperature gas generation characteristics were evaluated for lithium secondary batteries according to the examples and comparative examples. The maximum energy state inside the battery was set to a fully charged state (SOC 100%). In this state, the amount of gas generated (unit: mL) was evaluated before storage at 60°C for 30 days (initial) and after storage at 60°C for 30 days, respectively. The amount of gas generated was calculated by measuring the volume change before and after high-temperature storage and converting it into a change in mass using Archimedes' method.

[0283] The gas generation rate (unit: %) was calculated according to the following formula.

[0284] Gas generation rate (%) = ((Gas generated after 30 days of storage at 60℃ - Initial (pre-storage) gas generation) / Initial (pre-storage) gas generation) × 100.

[0285]

[0286] Evaluation 4: Room Temperature Life Evaluation

[0287] Room temperature charge-discharge characteristics were evaluated for lithium secondary batteries according to the examples and comparative examples. To this end, 300 charge-discharge cycles of the lithium secondary batteries were performed under conditions of 25°C, 0.5C charge (CC / CV, 4.45V, 0.025C Cut-off) / 1.0C discharge (CC, 2.5V Cut-off). The capacity recovery rate (unit: %) was calculated according to the following formula.

[0288] [ceremony]

[0289] Capacity recovery rate (%) = (Discharge capacity after 300 cycles / Discharge capacity after 1 cycle) × 100.

[0290]

[0291] Evaluation 5: High-temperature life evaluation

[0292] High-temperature charge-discharge characteristics were evaluated for lithium secondary batteries according to the examples and comparative examples. To this end, 300 charge-discharge cycles of the lithium secondary battery were performed under conditions of 45°C, 0.5C charge (CC / CV, 4.45V, 0.025C Cut-off) / 1.0C discharge (CC, 2.5V Cut-off). The capacity recovery rate (unit: %) was calculated according to the following formula.

[0293] [ceremony]

[0294] Capacity recovery rate (%) = (Discharge capacity after 300 cycles / Discharge capacity after 1 cycle) × 100.

[0295]

[0296] The results of the above evaluation are shown in Table 3 below.

[0297] Chemical Formula 2-3 Chemical Formula 1-2 Chemical Formula 8 Chemical Formula 7 Example 60.50.500 Example 70.30.500 Example 80.50.300 Comparative Example 30000 Comparative Example 40.5000 Comparative Example 50.500.50 Comparative Example 60.5000.5

[0298]

[0299] DCIR Initial Capacity High Temperature Storage Capacity Capacity Retention Rate Gas Generation Rate Room Temperature Life High Temperature Life Initial High Temperature Storage Growth Rate Example 6 12.3 213.0 810 6.2 6.3 46.2 398.3 12.5 892.8 89.6 Example 7 12.19 13.12 10 7.6 6.3 36.1 89 7.6 13.0 591.9 88.4 Example 8 12.27 13.27 10 8.1 6.3 46.1 89 7.4 13.27 92.1 88.6 Comparative Example 3 13.0 215.4 211 8.4 6.3 25.8 392.2 17.2 283.9 78.4 Comparative Example 412.5513.93111.26.325.9794.414.1088.283.9 Comparative Example 512.4813.92111.56.325.9994.815.0588.485.3 Comparative Example 612.3913.64110.16.326.0495.614.9888.986.2

[0300]

[0301] synthesis

[0302] Referring to Table 3 above, the electrolyte of the example provided room temperature life, high temperature life, a low resistance increase rate after high temperature storage, and a low gas generation amount after high temperature storage under high voltage according to the evaluation results. In particular, the electrolyte of the example provided room temperature life, high temperature life, a low resistance increase rate after high temperature storage, and a low gas generation amount after high temperature storage in a lithium secondary battery having a cobalt-free cathode active material.

[0303] In addition, although not shown in Table 3 above, Example 5 can provide synergistic effects in capacity retention rate, room temperature life, and high temperature life compared to Comparative Example 3.

[0304] However, referring to Table 3 above, Comparative Example 3, which does not contain both the first and second additives of the present invention, showed a significantly higher DCIR increase rate and a low capacity retention rate, and also showed a significantly higher gas generation rate, and was not as effective as the example in both room temperature life and high temperature life. Comparative Example 4, which contains the second additive of the present invention but does not contain the first additive of the present invention; Comparative Example 5, which contains the second additive of the present invention but includes an additive other than the first additive of the present invention (including an additive having a -P(-O)3 structure but not cyclic); and Comparative Example 6, which contains the second additive of the present invention but includes an additive other than the first additive of the present invention (including an additive that is cyclic but does not have a -P(-O)3 structure), were also not as effective as the example in terms of DCIR increase rate, capacity retention after high temperature storage, gas generation rate, and both room temperature life and high temperature life.

[0305]

[0306] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

1. A non-aqueous organic solvent; a lithium salt; and an additive, comprising, The above additive is an electrolyte for a lithium secondary battery comprising a first additive represented by the following chemical formula 1: [Chemical Formula 1] (In the above chemical formula 1, R 1 , R 2 and R 3 Each is independently 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, and R 4 is hydrogen, halogen, 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).

2. In Paragraph 1, R 1 , R 2 and R 3 An electrolyte for a lithium secondary battery, wherein each is independently a substituted or unsubstituted C1 to C5 alkylene group, a substituted or unsubstituted C2 to C5 alkenylene group, or a substituted or unsubstituted C2 to C5 alkynylene group.

3. In Paragraph 1, R 4 An electrolyte for a lithium secondary battery, wherein is a halogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, or a substituted or unsubstituted C2 to C20 alkynyl group.

4. An electrolyte for a lithium secondary battery according to claim 1, wherein the first additive is one or more of the following chemical formulas 1-2 to 1-8: [Chemical Formula 1-2] [Chemical Formula 1-3] [Chemical Formula 1-4] [Chemical Formula 1-5] [Chemical Formula 1-6] [Chemical Formula 1-7] [Chemical Formula 1-8] .

5. An electrolyte for a lithium secondary battery according to claim 1, wherein the first additive is included in an amount of 0.05 to 5 weight% with respect to the total amount of the electrolyte.

6. An electrolyte for a lithium secondary battery according to claim 1, wherein the additive further comprises a second additive in addition to the first additive.

7. In paragraph 6, the second additive comprises saccharin or a saccharin derivative, an electrolyte for a lithium secondary battery.

8. An electrolyte for a lithium secondary battery according to claim 7, wherein the saccharin or saccharin derivative comprises one or more of the following chemical formulas 2-1 and 2-2: [Chemical Formula 2-1] [Chemical Formula 2-2] (In the above chemical formulas 2-1 and 2-2, is a hydrogen cation, alkali metal cation, ammonium cation, phosphonium cation, or sulfonium cation).

9. An electrolyte for a lithium secondary battery according to claim 6, wherein the first additive and the second additive in the electrolyte are included in a weight ratio of 10:90 to 90:10 of the total weight of the first additive and the second additive, in an amount of 100 parts by weight.

10. An electrolyte for a lithium secondary battery according to claim 6, wherein the second additive is included in an amount of 0.05 to 5 weight% with respect to the total amount of the electrolyte.

11. An electrolyte for a lithium secondary battery according to claim 1, wherein the non-aqueous organic solvent is a mixture comprising ethylene carbonate (EC): ethylmethyl carbonate (EMC): dimethyl carbonate (DMC) in a volume ratio of 10 to 30: 20 to 50: 20 to 50.

12. An electrolyte for a lithium secondary battery according to claim 1, wherein the concentration of the lithium salt in the electrolyte is 0.1M to 3.0M.

13. An electrolyte for a lithium secondary battery according to claim 1, wherein the lithium salt is one or more selected from the group consisting of LiPF6, LiClO4, LiBF4, LiFSI, LiTFSI, LiSO3CF3, LiBOB, LiFOB, LiDFBP, LiTFOP, LiPO2F2, LiSbF6, LiAsF6, LiAlO2, LiAlCl4, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N, and LiC4F9SO3.

14. An electrolyte for a lithium secondary battery according to claim 1, wherein the additive comprises 95% by weight or more of the total additive of the electrolyte.

15. Anode comprising a positive active material; A cathode comprising a cathode active material; and A lithium secondary battery comprising an electrolyte according to any one of claims 1 to 14.

16. A lithium secondary battery, wherein the positive electrode active material in paragraph 15 is a cobalt-free positive electrode active material.

17. In paragraph 16, the above cobalt-free positive electrode active material comprises a cobalt-free nickel-manganese-based oxide, in a lithium secondary battery.

18. In claim 17, the above-mentioned cobalt-free nickel-manganese-based oxide comprises a lithium composite oxide represented by the following chemical formula 6, in a lithium secondary battery: [Chemical Formula 6] Li a4 Ni x4 Mr y4 M 5 z4 O 2-b4 X b4 In the above chemical formula 6, 0.9≤a4≤1.8, 0.8≤x4<1, 0 <y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, 및 0≤b4≤0.1이고, M 5 is one or more elements selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

19. A lithium secondary battery according to claim 15, wherein the negative electrode active material comprises at least one of graphite and a Si composite.

20. A lithium secondary battery according to claim 15, wherein the operating voltage of the lithium secondary battery is 4.45 V or higher.

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