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 under thermal exposure.SOLUTION: An electrolyte solution for a lithium secondary battery in an embodiment includes a nonaqueous organic solvent, a lithium salt, and an additive. The additive includes a first compound expressed by Chemical Formula 1 below, and a second compound that is a nitrile compound containing three or more cyano groups. In Chemical Formula 1, R1 and R2 independently represent a substituted or non-substituted alkyl group with 1 to 20 carbons, or a substituted or non-substituted aryl group with 6 to 30 carbons, and any one or more of R1 and R2 represent a substituted or non-substituted aryl group with 6 to 30 carbons.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an electrolyte for lithium secondary batteries and a lithium secondary battery containing the same. [Background technology]

[0002] Recently, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for rechargeable batteries with high energy density and high capacity has been rapidly increasing. As a result, research and development to improve the performance of lithium-ion rechargeable batteries is being actively pursued.

[0003] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material that allows for the insertion and deintercalation of lithium ions, and an electrolyte, which produces electrical energy through oxidation and reduction reactions when lithium ions are inserted / deintercalated at the positive and negative electrodes.

[0004] Recently, there has been active research into lithium-ion secondary batteries that offer high capacity, high energy density, and high safety for use as power sources for hybrid and electric vehicles, or for power storage.

[0005] In lithium-ion batteries, the electrolyte plays a crucial role in transporting lithium ions and can exhibit very high ionic conductivity by containing organic solvents and lithium salts. Such electrolytes play a vital role in determining the safety and performance of lithium-ion batteries.

[0006] When lithium-ion batteries are exposed to overcharge conditions or high temperatures, they rapidly generate heat and gas, raising concerns about battery safety due to the risk of cell explosion.

[0007] Therefore, there is a need to develop an electrolyte that provides superior safety even under overcharging and thermal exposure.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] One embodiment of the present invention provides an electrolyte for a lithium secondary battery having excellent safety under overcharge and thermal exposure.

[0010] Another embodiment of the present invention provides a lithium secondary battery including the electrolyte.

Means for Solving the Problems

[0011] One embodiment of the present invention provides 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 which is a nitrile compound containing three or more cyano groups.

[0012]

Chem.

[0013] 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 one or more of R 1 and R 2 is a substituted or unsubstituted aryl group having 6 to 30 carbon atoms.

[0014] Another embodiment of the present invention provides a lithium secondary battery comprising 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 an electrolyte. [Effects of the Invention]

[0015] The electrolyte for lithium secondary batteries according to one embodiment of the present invention can realize a battery with excellent safety under overcharging and thermal exposure conditions. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram showing a lithium secondary battery according to one embodiment. [Figure 2] This is a schematic diagram showing a lithium secondary battery according to one embodiment. [Figure 3] This is a schematic diagram showing a lithium secondary battery according to one embodiment. [Figure 4] This is a schematic diagram showing a lithium secondary battery according to one embodiment. [Figure 5] This graph shows the overcharge evaluation results for lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 to 3. [Figure 6] This graph shows the thermal exposure evaluation results for lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 to 3. [Modes for carrying out the invention]

[0017] 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.

[0018] 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.

[0019] 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."

[0020] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0021] 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, such as using a particle size analyzer, or by using a transmission electron microscope or scanning electron microscope. Alternatively, it can be measured using a dynamic light-scattering device, and after performing data analysis to count the number of particles for each particle size range, the average particle size (D50) value 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, then introduced into a commercially available laser diffraction particle size analyzer (for example, the MT3000 from Microtrac), and after irradiating with ultrasound at approximately 28 kHz at an output of 60 W, the average particle size (D50) based on the 50% standard of the particle size distribution in the analyzer can be calculated.

[0022] Here, "substitution" means that, unless otherwise defined, a substituent or at least one hydrogen atom in a compound is substituted with deuterium, a halogen group, a hydroxyl group, an amino group, a carbon-1 to carbon-30 amine group, a nitro group, a carbon-1 to carbon-40 silyl group, a carbon-1 to carbon-30 alkyl group, a carbon-1 to carbon-10 alkylsilyl group, a carbon-6 to carbon-30 arylsilyl group, a carbon-3 to carbon-30 cycloalkyl group, a carbon-3 to carbon-30 heterocycloalkyl group, a carbon-6 to carbon-30 aryl group, a carbon-2 to carbon-30 heteroaryl group, a carbon-1 to carbon-20 alkoxy group, a carbon-1 to carbon-10 fluoroalkyl group, a cyano group, or a combination thereof.

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

[0024] The electrolyte for a lithium secondary battery according to an embodiment includes a non-aqueous organic solvent, a lithium salt, and an additive, and the additive includes a first compound and a second compound. The first compound and the second compound will be described in detail below.

[0025] When the first compound and the second compound are used in combination, it is possible to effectively achieve both the stability of the battery under overcharge and the safety of the battery under thermal exposure.

[0026] 1st compound The first compound is a sulfoxide-based compound and plays a role in effectively suppressing the heat generation temperature of the battery under overcharge driving conditions.

[0027] The first compound is represented by the following Chemical Formula 1.

[0028]

Chemical Formula

[0029] 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 3,0 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.

[0030] In one embodiment, Chemical Formula 1 is represented by the following Chemical Formula 1-1 or Chemical Formula 1-2. As a most specific example, Chemical Formula 1 is represented by the following Chemical Formula 1-1.

[0031]

Chemical Formula

[0032] In Chemical Formula 1-1, R 1aThese are substituted or unsubstituted alkyl groups having 1 to 20 carbon atoms. H a ~H e Each of these may independently be hydrogen, a halogen group, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group.

[0033] As a specific example, H a ~H e Each of these may independently be hydrogen, a halogen group, a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C1-C20 alkoxy group.

[0034] [ka]

[0035] In the above chemical formulas 1 and 2, H a ~H j Each of these may independently be hydrogen, a halogen group, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group.

[0036] As a specific example, H a ~H jEach of these may independently be hydrogen, a halogen group, a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C1-C20 alkoxy group.

[0037] As an example, the first compound may be one or more compounds selected from the compounds listed in Group 1 below.

[0038] [ka]

[0039] In one embodiment, the first compound may be present in an amount greater than 0.05% by weight or 0.1% by weight or more, and less than 6% by weight or 5% by weight or less, relative to the total weight of the electrolyte for the lithium secondary battery.

[0040] As a specific example, the first compound may be included in an amount greater than 0.05% by weight and less than 6% by weight relative to 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 and 5% by weight or less, 0.1% by weight or more and less than 6% by weight, or 0.1% by weight or more and 5% by weight or less.

[0041] When the first compound is included in an amount of 0.05% by weight or less relative to the total weight of the electrolyte for lithium secondary batteries, its effect on improving battery safety during overcharging is minimal. However, when it is included in an amount of 6% by weight or more, there are problems such as an excessive increase in battery thickness or an excessive increase in battery resistance.

[0042] 2nd compound The second compound is a nitrile compound containing three or more cyano groups (-CN), and plays a role in improving the safety of lithium secondary batteries when they are exposed to high temperatures.

[0043] The second compound is represented by the following chemical formula 2.

[0044] [ka]

[0045] In the above chemical formula 2, L is a substituted linear or branched alkylene group having 1 to 20 carbon atoms, and the substituted alkylene group may be one in which at least one hydrogen atom of the alkylene is substituted with a cyano group (-CN).

[0046] As an example, the substituted alkylene group may be one in which at least one hydrogen atom of the alkylene is further substituted with an isocyano group (-NC) or a thiocyano group (-SCN).

[0047] As an example, the second compound may be one or more compounds selected from the compounds listed in Group 2 below.

[0048] [ka]

[0049] In one of the most specific embodiments, the additive contained in the electrolyte for a lithium secondary battery may be a composition comprising at least one of the compounds listed in Group 1 as the first compound and at least one of the compounds listed in Group 2 as the second compound.

[0050] As an example, the additive contained in the electrolyte for lithium secondary batteries may be a composition containing compound 1-a from group 1 as the first compound and compound 2-a as the second compound.

[0051] In one embodiment, the second compound may be present in an amount greater than 0.05% by weight or 0.1% by weight or more, and less than 6% by weight or 5% by weight or less, relative to the total weight of the electrolyte for the lithium secondary battery.

[0052] As a specific example, the second compound may be included in an amount greater than 0.05% by weight and less than 6% by weight relative to 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 and 5% by weight or less, 0.1% by weight or more and less than 6% by weight, or 0.1% by weight or more and 5% by weight or less.

[0053] When the second compound is included in an amount of 0.05% by weight or less relative to the total weight of the electrolyte for lithium secondary batteries, its effect on improving battery safety during thermal exposure is minimal. However, when it is included in an amount of 6% by weight or more, there is a problem of excessively increasing the battery's resistance.

[0054] In one embodiment, the first compound and the second compound may be included in a weight ratio of 0.01:1 to 50:1, 0.01:1 to 40:1, 0.05:1 to 40:1, or 0.05:1 to 20:1.

[0055] When the weight ratio of the first compound and the second compound satisfies the above numerical range, a battery with excellent safety in terms of overcharging and thermal exposure can be realized.

[0056] The electrolyte for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0057] The aforementioned non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0058] The 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.

[0059] 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 (EP), propyl propionate (PP), 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 such 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.

[0060] The aforementioned non-aqueous organic solvents can be used alone or in combination of two or more.

[0061] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and the cyclic carbonates and linear carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0062] The aforementioned lithium salts dissolve in organic solvents and act as a source of lithium ions within the battery, enabling the basic operation of lithium secondary batteries and promoting the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (where x and y are integers from 1 to 20) may contain one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate) borate (LiBOB).

[0063] Another embodiment of the lithium secondary battery 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.

[0064] positive electrode active material As the positive electrode active material, a lithium-intercalated compound capable of reversible intercalation and deintercalation can be used. Specifically, one or more composite oxides of lithium with metals selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0065] The aforementioned composite oxide may be a lithium transition metal composite oxide, and specific examples include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, cobalt-free nickel-manganese oxide, or a combination thereof.

[0066] 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 GeO2 (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).

[0067] 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.

[0068] As an 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.

[0069] 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.

[0070] As an example, the positive electrode may further include an additive that can act as a sacrificial positive electrode.

[0071] The content of the positive electrode active material may be 90% by weight or more and 99.5% by weight or less based on 100% by weight of the positive electrode active material layer, and the content of the binder and conductive material may be 0.5% by weight or more and 5% by weight or less, each based on 100% by weight of the positive electrode active material layer.

[0072] The binder plays a role in ensuring that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well 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.

[0073] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes can be used in the battery that is constructed. 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 powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0074] Al can be used as the current collector, but is not limited to it.

[0075] 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.

[0076] As the substance capable of reversibly intercalating / deintercalating the lithium ions, a carbon-based negative electrode active material can be used, for example, it can include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0077] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0078] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material is silicon, a silicon-carbon composite, SiO x (0 < x < 2), a Si-Q alloy (where 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 may be used. The Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0079] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which amorphous carbon is coated on the surface of silicon particles. For example, it 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. The 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 an amorphous carbon matrix.

[0080] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of this core.

[0081] The Si-based or Sn-based anode active material can be used in combination with a carbon-based anode active material.

[0082] 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 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0083] For example, the negative electrode active material layer 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.

[0084] The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other and that the negative electrode active material adheres well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0085] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0086] 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.

[0087] When an aqueous binder is used 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. The alkali metal can be Na, K, or Li.

[0088] 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.

[0089] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes can be used in the battery that is constructed. 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 containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0090] As the negative electrode current collector, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be selected.

[0091] 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.

[0092] The separator may include a porous substrate and a coating layer comprising organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0093] The porous substrate may be a polymer film formed from any 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.

[0094] The aforementioned organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0095] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0096] The 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.

[0097] Lithium-ion battery Lithium secondary 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 secondary battery according to one embodiment, where Figure 1 may be cylindrical, Figure 2 rectangular, and Figures 3 and 4 pouch-type batteries. Referring to Figures 1 to 4, the lithium secondary battery 100 may include an electrode assembly 40 with a separator 30 between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, in Figure 2, the lithium secondary battery 100 may include a positive electrode lead tab 11 and a positive electrode terminal 12, a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in Figures 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.

[0098] 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.

[0099] 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. [Examples]

[0100] Example 1 A basic electrolyte was prepared by dissolving 1.3 M lithium LiPF6 salt in a non-aqueous organic solvent, which was a mixture of ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) in a volume ratio of 10:15:30:45 in that order.

[0101] The electrolyte was prepared by adding compound 1-a as the first compound and compound 2-a as the second compound to the aforementioned basic electrolyte.

[0102] [ka] [ka]

[0103] At this time, the first compound is present in an amount of 2% by weight and the second compound in an amount of 3% by weight relative to the entire electrolyte.

[0104] A cathode active material slurry was prepared by mixing LiCoO2 as the cathode active material, polyvinylidene fluoride as the binder, and Ketjenblack as the conductive material in a weight ratio of 97:2:1, and dispersing the mixture in N-methylpyrrolidone.

[0105] The cathode active material slurry was coated onto a 10 μm thick Al foil, dried at 110°C, and then rolled (pressed) to produce the cathode.

[0106] 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 the 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 a negative electrode.

[0107] An electrode assembly was fabricated by placing a 25 μm thick polyethylene-polypropylene multilayer separator between the positive and negative electrodes manufactured as described above. This assembly was then inserted into a pouch-type battery case, and the prepared electrolyte was injected to produce the lithium secondary battery of Example 1.

[0108] Examples 2 to 9 Lithium secondary batteries according to Examples 2 to 9 were manufactured in the same manner as in Example 1, except that the content of the first and second compounds relative to the total electrolyte was adjusted as shown in Table 1 below.

[0109] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the first and second compounds were not added to the electrolyte.

[0110] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the second compound was not added during the production of the electrolyte.

[0111] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the first compound was not added during the production of the electrolyte.

[0112] [Table 1]

[0113] (Example of evaluation) Evaluation Example 1: Overcharge Safety Evaluation Overcharge evaluations were performed on the lithium secondary batteries manufactured in Examples 1 to 9 and Comparative Examples 1 to 3, and the results are shown in Table 2 and Figure 5 below.

[0114] A safety protection element is welded to the negative electrode portion of the lithium secondary battery cell, a tab is welded to the positive electrode portion, and a thermocouple is attached to the center of the cell to enable temperature measurement.

[0115] Afterward, the cell is thoroughly surrounded with insulating material, then charged at a rate-limiting 2.0C until it reaches 10V, and exposed to this voltage for 450 minutes.

[0116] After conducting a total of three experiments, if the battery did not ignite during the aforementioned exposure time and remained in the same state as before evaluation, it was evaluated as "P (Pass)". If the battery ignited, it was evaluated as "F (Fail)", and the results are shown in Table 2 below.

[0117] Furthermore, Figure 5 shows the overcharge evaluation results for lithium secondary batteries in Example 1 and Comparative Examples 1 to 3 in a graph. In Figure 5, the line located at the upper end shows the voltage change over time, and the line located at the lower end shows the temperature change over time.

[0118] Referring to Table 2, in Comparative Examples 1 and 3, where the first compound was not added to the electrolyte, it can be confirmed that the cell temperature rose to 200°C and the cell voltage reached 10V within approximately 350-400 minutes. When the cell voltage reaches 10V, it means that the cell explodes and the potential difference between the positive and negative electrodes cannot be measured.

[0119] Referring to Figure 5, in Example 1, the battery temperature remained constant even after being exposed to an overcharged state for 450 minutes, whereas in Comparative Example 1, the battery temperature rose to approximately 200°C around 370 minutes, and in Comparative Example 3, the battery temperature rose to approximately 175°C around 380 minutes.

[0120] Evaluation Example 2: Thermal Exposure Safety Evaluation The lithium secondary batteries manufactured in Examples 1 to 9 and Comparative Examples 1 to 3 were fully charged at a charge rate of 0.5C with a cutoff condition of 4.47V / 3hr while discharged at 3.0V, and then thermal exposure evaluation was performed.

[0121] After placing the lithium secondary batteries manufactured in Examples 1 to 9 and Comparative Examples 1 to 3 into a chamber, the temperature was increased from room temperature (25°C) to 140°C, 141°C, 142°C, 143°C, 144°C, and 145°C at a rate of 5°C per minute, and the changes in the lithium secondary batteries were observed while maintaining the temperature at the above temperatures for about 1 hour.

[0122] After a total of three experiments, if thermal runaway does not occur while maintaining the temperature, it is marked "P (Pass)". If thermal runaway occurs when exposed to high temperatures, it is marked "F (Fail)", as shown in Table 2 below.

[0123] Furthermore, Figure 6 shows a graph of the thermal exposure evaluation results at 143°C for the lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 to 3. In Figure 6, the line located at the upper end shows the voltage change over time, and the line located at the lower end shows the temperature change over time.

[0124] Referring to Table 2, it can be confirmed that in Comparative Examples 1 and 2, where the second compound was not added to the electrolyte, thermal runaway occurred upon thermal exposure to 141°C.

[0125] Referring to Figure 6, a sharp voltage drop is observed in the lithium secondary batteries of Example 1 and Comparative Examples 1 to 3. When a pouch-type battery is suddenly exposed to high temperatures, gas is generated, increasing the internal pressure, which activates the battery protection circuit (CID), causing a sharp voltage drop. The occurrence of a sharp voltage drop indicates that the protection circuits of the lithium secondary batteries of Example 1 and Comparative Examples 1 to 3 were activated due to gas generation caused by high-temperature exposure.

[0126] Specifically, it can be confirmed that the lithium secondary battery according to Example 1 maintains a temperature of 143°C even when exposed to a temperature of 143°C, and does not experience thermal runaway.

[0127] On the other hand, in Comparative Example 1, it was confirmed that the battery temperature rose to over 450°C at approximately 35 minutes, and in Comparative Example 2, it was confirmed that the battery temperature rose to over 370°C at approximately 36 minutes.

[0128] [Table 2]

[0129] (In Table 2 above, the parts marked with "-" indicate either a case where thermal runaway occurred (Fail) and no further evaluation is required, or a case where thermal runaway did not occur at a specific temperature (Pass) and no further evaluation is required at temperatures below that temperature.)

[0130] Evaluation Example 3: AC Internal Resistance (Alternative Current-Internal Resistance, AC-IR) Evaluation For the lithium secondary batteries in pouch cell form manufactured in Examples 1 to 9, the cell thickness (mm) and AC-IR (mΩ) in the charged state (SOC, state of charge = 100%) were measured and are shown in Table 3 below.

[0131] [Table 3]

[0132] Referring to Table 3, it can be confirmed that in the examples, the cell thickness is 6.04 mm or less, and in particular, the cell thickness characteristics are excellent in Examples 2, 3, 8, and 9.

[0133] Furthermore, referring to Table 3, it can be confirmed that the AC-IR of the examples is 29.3 mΩ or less, and in particular, the AC-IR is low in Examples 2, 3, 6, and 7.

[0134] 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]

[0135] 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 contains a non-aqueous organic solvent, a lithium salt, and an additive. The aforementioned additive comprises a first compound represented by the following chemical formula 1-1 or chemical formula 1-2, and a second compound which is a nitrile compound containing three or more cyano groups, represented by the following chemical formula 2. The first compound is included in an amount of 0.1% by weight or more and less than 6% by weight relative to the total weight of the electrolyte for lithium secondary batteries. The second compound is present in an electrolyte for lithium secondary batteries in an amount of 0.05% by weight or more and less than 6% by weight relative to the total weight of the electrolyte for lithium secondary batteries. 【Chemistry 1】 In the aforementioned chemical formula 1-1, R1a is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms. H a to H e are each independently hydrogen, halogen group, 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. 【Chemistry 2】 In the above chemical formula 1-2, H a to H j are each independently hydrogen, a halogen group, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C1-C20 alkoxy group, a substituted or unsubstituted C2-C20 alkenyl group, a substituted or unsubstituted C2-C20 alkynyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, a substituted or unsubstituted C6-C20 aryl group, or a substituted or unsubstituted C2-C20 heteroaryl group. 【Transformation 3】 In the aforementioned chemical formula 2, L is a substituted linear or branched alkylene group having 1 to 20 carbon atoms, wherein at least one hydrogen atom of the alkylene is substituted with a cyano group (-CN).

2. 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. 【Chemistry 4】

3. The electrolyte for a lithium secondary battery according to claim 1, wherein the second compound is one or more compounds selected from the compounds listed in Group 2 below. 【Transformation 5】

4. 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 5% by weight or less based on the total weight of the lithium secondary battery electrolyte.

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

6. 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 50:

1.

7. 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, A lithium secondary battery comprising the electrolyte according to any one of claims 1 to 6.

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