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

Abstract

To provide an electrolyte solution for a lithium secondary battery with excellent safety against overcharging and an excellent high-temperature preservation characteristic.SOLUTION: An electrolyte solution for a lithium secondary battery includes a nonaqueous organic solvent, a lithium salt, and an additive. The additive includes a first compound expressed by Chemical Formula 1, and a second compound expressed by Chemical Formula 2.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. For this reason, research and development for improving the performance of lithium secondary batteries have been actively carried out.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of insertion (intercalation) and desorption (deintercalation) of lithium ions, and an electrolyte, and produces electrical energy by oxidation and reduction reactions when lithium ions are inserted / desorbed between the positive electrode and the negative electrode.

[0004] Recently, for use as a driving power source for hybrid vehicles or electric vehicles, or a power storage power source, etc., active research has been conducted on lithium secondary batteries with ensured high capacity, high energy density, and high safety. [[ID=二十二]]

[0005] In a lithium secondary battery, the electrolyte plays an important role in transmitting lithium ions, contains an organic solvent and a lithium salt, and exhibits very high ionic conductivity. Such an electrolyte plays an important role in determining the safety and performance of a lithium secondary battery.

[0006] When a lithium secondary battery is in an overcharged state, the cell may explode, and the safety of the battery has become a problem. Also, when exposed to high temperatures, there is a problem that the internal resistance of the battery increases.

[0007] For this reason, the development of an electrolyte for realizing a battery excellent in safety even under overcharging and high temperatures is required.

Summary of the Invention

Problems to be Solved by the Invention

[0008] One embodiment of the present invention is an electrolyte for a lithium secondary battery that is excellent in safety under overcharge and has excellent high-temperature storage characteristics.

[0009] Another embodiment of the present invention is a lithium secondary battery including the above electrolyte.

Means for Solving the Problems

[0010] One embodiment of the present invention is an electrolyte for a lithium secondary battery, including a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive includes a first compound represented by the following Chemical Formula 1 and a second compound represented by the following Chemical Formula 2.

[0011]

Chem.

[0012] In Chemical Formula 1, R

[0013] , ,

[0012] , , 2 , , 2 , , , , , 1 ,

[0014] , , 1 , , , and R 2 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and any one or more of R 1 and R<​​​​​​​​​​​​​An electrolyte for lithium secondary batteries according to one embodiment of the present invention can realize a lithium secondary battery that is highly safe under overcharging conditions and has excellent high-temperature storage characteristics. [Brief explanation of the drawing]

[0015] [Figure 1] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 2] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 3] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 4] This figure schematically shows a lithium secondary battery according to one embodiment. [Figure 5] This graph shows the overcharge evaluation results for lithium secondary batteries prepared in Example 1 and Comparative Examples 1 to 3. [Figure 6] This graph shows the results of the high-temperature storage characteristics evaluation of lithium secondary batteries prepared in Example 1 and Comparative Examples 1 to 3. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described in detail below. However, these are presented as examples only and do not limit the present invention, which is defined solely by the scope of the claims described below.

[0017] Unless otherwise specified herein, when a part such as a layer, film, region, or plate is said to be "on top of" another part, this includes not only the case where it is "directly on top of" another part, but also the case where there is yet another part in between.

[0018] Unless otherwise specified herein, singular nouns may also include plural nouns. Similarly, unless otherwise specified, "A or B" may mean "containing A, or containing B, or containing both A and B."

[0019] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0020] Unless otherwise defined herein, particle size may refer to average particle size. Furthermore, particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. Average particle size (D50) can be measured by methods widely known to those skilled in the art. For example, average particle size (D50) can be measured using a particle size analyzer, or by using a transmission electron microscope or scanning electron microscope. Alternatively, a measurement device using dynamic light-scattering can be used, and after data analysis to count the number of particles for each particle size range, the average particle size (D50) can be calculated. Alternatively, it can be measured using the laser diffraction method. When measuring using the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, and then the dispersion is introduced into a commercially available laser diffraction particle size analyzer (for example, the MT3000 from Microtrac). After irradiating the dispersion with ultrasound at approximately 28 kHz at an output of 60 W, the average particle size (D50) based on the 50% particle size distribution in the analyzer can be calculated.

[0021] Here, "substitution" means that, unless otherwise defined, a substituent or at least one hydrogen atom in a compound is substituted with deuterium, halogen, hydroxyl group, amino group, C1-C30 amine group, nitro group, C1-C40 silyl group, C1-C30 alkyl group, C1-C10 alkylsilyl group, C6-C30 arylsilyl group, C3-C30 cycloalkyl group, C3-C30 heterocycloalkyl group, C6-C30 aryl group, C2-C30 heteroaryl group, C1-C20 alkoxy group, C1-C10 fluoroalkyl group, cyano group, or a combination thereof.

[0022] Specifically, "substitution" can mean that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen, a C1-C30 alkyl group, a C1-C10 alkylsilyl group, a C6-C30 arylsilyl group, a C3-C30 cycloalkyl group, a C3-C30 heterocycloalkyl group, a C6-C30 aryl group, a C2-C30 heteroaryl group, a C1-C10 fluoroalkyl group, or a cyano group. For example, "substitution" can mean that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen, a C1-C20 alkyl group, a C6-C30 aryl group, a C1-C10 fluoroalkyl group, or a cyano group. Alternatively, "substitution" can mean that at least one hydrogen atom in a substituent or compound is substituted with deuterium, a halogen, a C1-C5 alkyl group, a C6-C18 aryl group, a C1-C5 fluoroalkyl group, or a cyano group. For example, "substitution" can mean that a substituent or at least one hydrogen atom in a compound is substituted with deuterium, a cyano group, a halogen, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, a biphenyl group, a terphenyl group, a trifluoromethyl group, or a naphthyl group.

[0023] An electrolyte for a lithium secondary battery according to one embodiment comprises a non-aqueous organic solvent, a lithium salt, and an additive, the additive comprising a first compound and a second compound. The first and second compounds are described in detail below.

[0024] When the first compound and the second compound are used in combination, a lithium secondary battery excellent in stability under overcharge and excellent in high-temperature storage characteristics can be realized.

[0025] 1. The first compound The first compound is a sulfoxide-based compound and plays a role in effectively suppressing the heat generation of the battery under overcharge driving conditions.

[0026] The first compound is represented by the following Chemical Formula 1.

[0027]

Chem.

[0028] In Chemical Formula 1, R 1 and R 2 are each independently a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and any one or more of R 1 and R 2 is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.

[0029] In one embodiment, Chemical Formula 1 is represented by the following Chemical Formula 1-1 or Chemical Formula 1-2. As the most specific example, Chemical Formula 1 is represented by the following Chemical Formula 1-1.

[0030]

Chem.

[0031] In Chemical Formula 1-1, R 1a is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, H a ~H eEach of these may independently be hydrogen, halogen, hydroxyl group, cyano group, nitro group, substituted or unsubstituted C1-C20 alkyl group, substituted or unsubstituted C1-C20 alkoxy group, substituted or unsubstituted C2-C20 alkenyl group, substituted or unsubstituted C2-C20 alkynyl group, substituted or unsubstituted C3-C20 cycloalkyl group, substituted or unsubstituted C6-C20 aryl group, or substituted or unsubstituted C2-C20 heteroaryl group.

[0032] As a specific example, H a ~H e Each of these may independently be hydrogen, a halogen, a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C1-C20 alkoxy group.

[0033] [ka]

[0034] In chemical formula 1-2, H a ~H j Each of these may independently be hydrogen, halogen, hydroxyl group, cyano group, nitro group, substituted or unsubstituted C1-C20 alkyl group, substituted or unsubstituted C1-C20 alkoxy group, substituted or unsubstituted C2-C20 alkenyl group, substituted or unsubstituted C2-C20 alkynyl group, substituted or unsubstituted C3-C20 cycloalkyl group, substituted or unsubstituted C6-C20 aryl group, or substituted or unsubstituted C2-C20 heteroaryl group.

[0035] As a specific example, H a ~H j Each of these may independently be hydrogen, a halogen, a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C1-C20 alkoxy group.

[0036] For example, the first compound may be one or more compounds selected from the compounds listed in Group 1 below.

[0037] [ka]

[0038] In one embodiment, the first compound may be present in an amount exceeding 0.05% by weight, or 0.1% by weight or more, with respect to the total weight of the electrolyte for the lithium secondary battery, and may also be present in an amount less than 6% by weight, or 5% by weight or less.

[0039] As a specific example, the first compound may be included in an amount greater than 0.05% by weight but less than 6% by weight of the total weight of the electrolyte for the lithium secondary battery, for example, greater than 0.05% by weight but 5% by weight or less, 0.1% by weight or more but less than 6% by weight, or 0.1% by weight to 5% by weight.

[0040] If the first compound is present in an amount of 0.05% by weight or less relative to the total weight of the electrolyte for lithium secondary batteries, the effect of improving battery safety during overcharging is low. If it is present in an amount of 6% by weight or more, there is a problem that the battery resistance increases excessively, reducing the battery life.

[0041] 2.Second compound The second compound is a bicyclic sulfate compound that improves the thermal stability of lithium secondary batteries at high temperatures by forming a solid electrolyte interface (SEI) layer on the negative electrode surface or a protective layer on the positive electrode surface, thereby improving the battery's lifespan characteristics.

[0042] The second compound is represented by the following chemical formula 2.

[0043] [ka]

[0044] In chemical formula 2, A1, A2, A3, and A4 are each independently a single bond, a substituted or unsubstituted alkylene group, a carbonyl group, or a sulfinyl group having 1 to 5 carbon atoms. However, A1 and A2 are not both single bonds, and A3 and A4 are not both single bonds.

[0045] As an example, one or more of A1, A2, A3, and A4 may be an unsubstituted C1-C5 alkylene group or a substituted C1-C5 alkylene group, and the substituents of the substituted C1-C5 alkylene group may be a halogen-substituted or unsubstituted C1-C20 alkyl group, a halogen-substituted or unsubstituted C2-C20 alkenyl group, a halogen-substituted or unsubstituted C2-C20 alkynyl group, a halogen-substituted or unsubstituted C3-C20 cycloalkenyl group, a halogen-substituted or unsubstituted C3-C20 heterocyclyl group, a halogen-substituted or unsubstituted C6-C40 aryl group, or a halogen-substituted or unsubstituted C2-C40 heteroaryl group.

[0046] As an example, one or more of A1, A2, A3, and A4 are unsubstituted C1-C5 alkylene groups or substituted C1-C5 alkylene groups, and the substituents of the substituted C1-C5 alkylene groups may be halogens, methyl groups, ethyl groups, propyl groups, isopropyl groups, butyl groups, tert-butyl groups, trifluoromethyl groups, tetrafluoroethyl groups, phenyl groups, naphthyl groups, tetrafluorophenyl groups, pyrrolyl groups, or pyridinyl groups, but the substituents are not necessarily limited to these and are all that can be used as substituents of alkylene groups in the art.

[0047] In one embodiment, chemical formula 2 may include one or more compounds represented by the following chemical formulas 2-1 to 2-7.

[0048] [ka] [ka]

[0049] In one embodiment, the second compound may be present in an amount exceeding 0.05% by weight or 0.1% by weight or more, or in an amount less than 6% by weight or 5% by weight or less, relative to the total weight of the electrolyte for the lithium secondary battery.

[0050] As a specific example, the second compound may be included in an amount greater than 0.05% by weight but less than 6% by weight of the total weight of the electrolyte for the lithium secondary battery. For example, it may be included in an amount greater than 0.05% by weight but 5% by weight or less, 0.1% by weight or more but less than 6% by weight, or 0.1% by weight to 5% by weight.

[0051] If the second compound is present in an amount of 0.05% by weight or less relative to the total weight of the lithium secondary battery electrolyte, the high-temperature life characteristics of the battery are not easily improved. If it is present in an amount of 6% by weight or more, there is a problem that the battery's resistance increases excessively, reducing its lifespan.

[0052] In one embodiment, the first compound and the second compound may be present in a weight ratio of 0.01:1 to 100:1, for example, in a weight ratio of 0.05:1 to 100:1, 0.01:1 to 40:1, 0.05:1 to 40:1, 0.05:1 to 20:1, or 0.1:1 to 20:1.

[0053] When the weight ratio of the first compound and the second compound satisfies the above numerical range, a battery can be realized that is highly safe under overcharging conditions and has excellent high-temperature life characteristics.

[0054] The electrolyte for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0055] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of batteries can move.

[0056] The non-aqueous organic solvent may be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0057] Examples of carbonate-based solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of ester-based solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran can be used. As ketone-based solvents, cyclohexanone can be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol can be used, and as aprotic solvents, nitriles represented as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes can be used.

[0058] Non-aqueous organic solvents can be used alone or in mixtures of two or more. Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and these can be mixed in a volume ratio of 1:1 to 1:9.

[0059] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, playing a role in enabling the operation of basic lithium-ion secondary batteries. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 One or more of the following can be selected: SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate) borate (LiBOB).

[0060] A lithium secondary battery according to another embodiment includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator located between the positive electrode and the negative electrode, and the electrolyte described above.

[0061] 3.Cathode active material As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more composite oxides of lithium with metals selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0062] The composite oxide may be a lithium transition metal composite oxide, and specific examples include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free nickel-manganese oxides, or combinations thereof.

[0063] As an 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 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).

[0064] 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, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 These are Mn, Al, or a combination of these.

[0065] For example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more, and 99 mol% or less in a lithium transition metal composite oxide. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0066] 4.Positive electrode A positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material and further include a binder and / or a conductive material.

[0067] As an example, the positive electrode may further contain additives that can act as a sacrificial positive electrode.

[0068] The content of the positive electrode active material may be 90% to 99.5% by weight relative to 100% by weight of the positive electrode active material layer, and the content of the binder and conductive material may be 0.5% to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0069] The binder plays a role in firmly adhering the positive electrode active material particles to each other and firmly adhering the positive electrode active material to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0070] Conductive materials are used to impart conductivity to electrodes, and any material can be used in the battery that is constructed from them as long as it is an electronically conductive material that does not cause chemical changes. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0071] Al can be used as a current collector, but it is not limited to this.

[0072] 5.Negative electrode active material The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material that can be doped and dedoped with lithium, or a transition metal oxide.

[0073] As substances that can reversibly intercalate / deintercalate lithium ions, carbon-based negative electrode active materials can be included, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0074] As alloys of lithium metal, alloys of lithium and metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0075] As substances that can dope and undope lithium, Si-based negative electrode active materials or Sn-based negative electrode active materials can be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or combinations thereof. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0076] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon is also located between the primary silicon particles, for example, the primary silicon particles are coated with amorphous carbon. The secondary particles may be dispersed in the amorphous carbon matrix.

[0077] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, as well as an amorphous carbon coating layer located on the surface of this core.

[0078] Si-based or Sn-based anode active materials can be used in combination with carbon-based anode active materials.

[0079] 6.Negative electrode A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer contains a negative electrode active material and may further contain a binder and / or conductive material.

[0080] For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0081] The binder plays the role of firmly adhering the negative electrode active material particles to each other and firmly adhering the negative electrode active material to the current collector. Non-aqueous binders, aqueous binders, dry binders, or combinations thereof can be used as binders.

[0082] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0083] The aqueous 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, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0084] When using an aqueous binder as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. Na, K, or Li can be used as the alkali metal.

[0085] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0086] Conductive materials are used to impart conductivity to electrodes, and any material can be used in a battery that does not cause chemical changes and is electrically conductive. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials in the form of metal powders or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0087] The negative electrode current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metal, and combinations thereof.

[0088] 7. Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers of these materials. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0089] The separator may include a porous substrate and a coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0090] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as 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 from a copolymer or mixture of two or more of these polymers.

[0091] The organic material may include polyvinylidene fluoride polymers or (meth)acrylic polymers.

[0092] Inorganic materials may include, but are not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and inorganic particles selected from combinations thereof.

[0093] Organic and inorganic materials may exist mixed together in a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are laminated together.

[0094] Lithium-ion rechargeable battery Lithium-ion batteries are classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium-ion battery according to one embodiment, with Figure 1 being cylindrical, Figure 2 being prismatic, and Figures 3 and 4 being pouch-type batteries. Referring to Figures 1 to 4, the lithium-ion battery 100 may include an electrode assembly 40 with a separator 30 between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium-ion battery 100 may include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, as shown in Figure 2, the lithium-ion battery 100 may include a positive electrode lead tab 11 and a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for guiding the current formed in the electrode assembly 40 to the outside.

[0095] A lithium secondary battery according to one embodiment of the present invention can be applied to automobiles, mobile phones, and / or various forms of electrical devices, and the present invention is not limited thereto. [Examples]

[0096] Examples and comparative examples of the present invention are described below. However, the following examples are merely one embodiment of the present invention, and the present invention is not limited to the following embodiments.

[0097] Example 1 A basic electrolyte was prepared by dissolving 1.15 M lithium LiPF6 salt in a non-aqueous organic solvent, which was a mixture of ethylene carbonate (EC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC) in a volume ratio of 20:40:40 in that order.

[0098] An electrolyte solution was prepared by adding compound 1-a as the first compound and the compound represented by the following chemical formula 2-1 as the second compound to the basic electrolyte solution.

[0099] [ka]

[0100] At this time, the first compound was present in a concentration of 2% by weight and the second compound in a concentration of 1% by weight relative to the total electrolyte.

[0101] LiNi 0.91 Co 0.07 Al 0.02 O2, polyvinylidene fluoride as a binder, and Ketjenblack as a conductive material were mixed in a weight ratio of 97:2:1, and this mixture was dispersed in N-methylpyrrolidone to prepare a cathode active material slurry.

[0102] The cathode active material slurry was coated onto a 14 μm thick aluminum foil, dried at 110°C, and then rolled (pressed) to produce the cathode.

[0103] A negative electrode active material slurry was prepared by mixing artificial graphite as the negative electrode active material, styrene-butadiene rubber as the binder, and carboxymethylcellulose as the thickener in a weight ratio of 97:1:2, and dispersing this mixture in distilled water. The negative electrode active material slurry was coated onto a 10 μm thick Cu foil current collector, dried at 100°C, and then rolled to produce the negative electrode.

[0104] An electrode assembly was fabricated by placing a 25 μm thick polyethylene-polypropylene multilayer separator between the fabricated positive and negative electrodes. This assembly was then inserted into a rectangular battery case, and the prepared electrolyte was injected to produce the lithium secondary battery of Example 1.

[0105] Examples 2 to 15 Lithium secondary batteries were prepared according to Examples 2 to 15 in the same manner as in Example 1, except that the content of the first and second compounds in the total electrolyte was adjusted as shown in Table 1 below.

[0106] Comparative Example 1 A lithium secondary battery was prepared in the same manner as in Example 1, except that the first and second compounds were not added to the electrolyte.

[0107] Comparative Example 2 A lithium secondary battery was prepared in the same manner as in Example 1, except that the second compound was not added during the preparation of the electrolyte.

[0108] Comparative Example 3 A lithium secondary battery was prepared in the same manner as in Example 1, except that the first compound was not added during the preparation of the electrolyte.

[0109] (Example of evaluation) Evaluation Example 1: Overcharge Safety Evaluation Overcharge evaluations were performed on the lithium secondary batteries prepared in Examples 1 to 15 and Comparative Examples 1 to 3, and the results are shown in Table 1 below.

[0110] Furthermore, Figure 5 shows the overcharge evaluation results for the lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 to 3.

[0111] A safety protection element was welded to the negative electrode of the lithium secondary battery cell, a tab was welded to the positive electrode, and a thermocouple was fixed to the center of the cell to enable temperature measurement.

[0112] Subsequently, the cells, which had been prepared to a fully charged state of 4.2V, were charged at a rate of 1.0C until the charging voltage reached 6V, and this charging voltage was maintained for 50 minutes. If the battery did not ignite during the period of maintaining the charging voltage and remained in the same state as the battery before evaluation, it was evaluated as "P (Pass)". If the battery ignited, it was evaluated as "F (Fail)". The results are shown in Table 1 below.

[0113] Referring to Table 1, it was confirmed that in Comparative Examples 1 and 3, where the first compound was not added to the electrolyte, the batteries ignited during overcharging.

[0114] Referring to Figure 5, in Example 1, the battery temperature remained constant without increasing even when maintained in an overcharged state for 50 minutes. On the other hand, in Comparative Examples 1 to 3, it was confirmed that the battery temperature reached approximately 600°C after about 35 minutes, causing the battery to ignite.

[0115] Evaluation Example 2: Evaluation of storage characteristics at high temperatures (60°C) For the lithium secondary batteries prepared in Examples 1 to 15 and Comparative Examples 1 to 3, the initial DC-IR was measured using the ΔV / ΔI (voltage change / current change) value. Then, the maximum energy state inside the battery was set to a fully charged state (SOC 100), and the batteries were stored at a high temperature (60°C) for 90 days.

[0116] Furthermore, the batteries were fully recharged at room temperature (25°C) every 30 days, and the DC resistance was measured. The DC-IR increase rate (%) was calculated using the following formula 1. The batteries whose DC resistance was measured were then recharged to 4.2V and SOC 100 and stored at a high temperature (60°C). [Formula 1] DCIR increase rate = ((DC-IR after 30 × n days / initial DC-IR) × 100% (n is a natural number between 1 and 3)

[0117] The results of the high-temperature storage characteristics evaluation are shown in Table 1 and Figure 6 below.

[0118] Referring to Table 1, it can be confirmed that the lithium secondary batteries of Comparative Examples 1 to 3 show a higher rate of resistance increase after high-temperature storage compared to the examples.

[0119] However, in the case of Comparative Example 3, since it contains the second compound, it can be confirmed that the rate of increase in high-temperature resistance is lower compared to the other comparative examples.

[0120] Referring to Figure 6, it can be confirmed that the lithium secondary battery of Example 1 has a significantly lower resistance increase rate after high-temperature storage compared to Comparative Examples 1-3.

[0121] [Table 1]

[0122] Evaluation Example 3: Lifetime Characteristics Evaluation at Room Temperature (25°C) The life characteristics of the lithium secondary batteries fabricated in Examples 1 to 15 were evaluated at room temperature (25°C). Specifically, 800 cycles of 0.33C charge / 0.5C discharge were performed between 2.8V and 4.2V, and the capacity retention rate (%) after 800 cycles relative to the first discharge capacity was calculated. The results are shown in Table 2 below.

[0123] [Table 2]

[0124] Referring to Table 2, it was confirmed that the lithium secondary batteries produced in Examples 1 to 15 exhibited excellent overcharge safety and high-temperature storage characteristics, as well as excellent lifespan characteristics at room temperature, as described above. Specifically, it was confirmed that the capacity retention rate at room temperature was maintained at around 90%.

[0125] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings, and these also naturally fall within the scope of the present invention. [Explanation of symbols]

[0126] 100: Lithium-ion rechargeable battery 10: Positive electrode 11: Positive lead tab 12: Positive terminal 20: Negative electrode 21: Negative lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode Tab 71: Positive Tab 72: Negative electrode tab

Claims

1. It comprises a non-aqueous organic solvent, a lithium salt, and additives. The aforementioned additive comprises a first compound represented by the following chemical formula 1 and a second compound represented by the following chemical formula 2. 【Chemistry 1】 In the above chemical formula 1, R1 is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, and R2 is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms. In the above chemical formula 2, A １ A ２ A ３ and A ４ Each of these is independently a substituent-substituted or unsubstituted alkylene group having 1 to 5 carbon atoms. The first compound is present in an amount greater than 0.05% by weight and less than 6% by weight. The second compound is present in an electrolyte for lithium secondary batteries in an amount greater than 0.05% by weight and less than 6% by weight.

2. The aforementioned chemical formula 1 is represented by the following chemical formula 1-1, 【Chemistry 2】 In the above chemical formula 1-1, R １ａ is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms. H ａ ~H ｅ The electrolyte for lithium secondary batteries according to claim 1, wherein each of them is independently hydrogen, a halogen, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, and a substituted or unsubstituted C3-C20 cycloalkyl group.

3. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound is one or more compounds selected from the compounds listed in Group 1 below. 【Transformation 3】

4. The electrolyte for a lithium secondary battery according to claim 1, wherein the chemical formula 2 comprises one or more compounds represented by the following chemical formulas 2-1 to 2-6. 【Chemistry 4】 【Transformation 5】

5. The lithium secondary battery electrolyte according to claim 1, wherein the first compound is contained in an amount of 0.1% by weight or more and less than 6% by weight of the total weight of the lithium secondary battery electrolyte.

6. The lithium secondary battery electrolyte according to claim 1, wherein the second compound is contained in an amount of 0.1% or more and less than 6% by weight relative to the total weight of the lithium secondary battery electrolyte.

7. The electrolyte for a lithium secondary battery according to claim 1, wherein the first compound and the second compound are contained in a weight ratio of 0.01:1 to 100:

1.

8. Positive electrode containing positive electrode active material, A negative electrode containing negative electrode active material, A separator located between the positive electrode and the negative electrode, and A lithium secondary battery comprising the electrolyte for lithium secondary batteries according to any one of claims 1 to 7.

9. H a to H e are each independently hydrogen, a substituted or unsubstituted C1 to C20 alkyl group, or a substituted or unsubstituted C3 to C20 cycloalkyl group, The electrolyte for lithium secondary batteries according to claim 2, wherein A1, A2, A3, and A4 are each independently a methyl group, a trifluoromethyl group, or a fluorine-substituted or unsubstituted methylene group.

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