Positive electrode for lithium secondary battery including insulating layer having excellent wet adhesion and lithium secondary battery including the same

Abstract

The present technology relates to a positive electrode for a lithium secondary battery, which includes an insulating layer having excellent wet adhesion, and a lithium secondary battery including the same, and they have the advantage that the migration of lithium ions in the overlapping area of ​​the electrodes can be prevented by the insulating layer having excellent wet adhesion in a liquid electrolyte to suppress capacity expression and the like.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0100426, filed on July 30, 2021, and Korean Patent Application No. 10-2022-0092191, filed on July 26, 2022, and incorporates the entire contents of these Korean patent applications herein by reference.

[0002] The present technology relates to a positive electrode for a lithium secondary battery, which includes an insulating layer having excellent wet adhesion; a method of manufacturing the same; and a lithium secondary battery including the same. Background Art

[0003] As the technology of mobile devices develops and the demand for mobile devices increases, the demand for secondary batteries as power sources is rapidly increasing, and accordingly, many studies have been conducted on batteries that can meet various demands.

[0004] Typically, in terms of battery shape, thin prismatic and pouch-type batteries applicable to products such as mobile phones and the like are highly desired. In addition, in terms of materials, lithium secondary batteries such as lithium cobalt polymer batteries, which are excellent in energy density, discharge voltage, and safety, are highly desired.

[0005] One of the main research tasks related to secondary batteries is to enhance safety. Accidents related to battery safety are mainly caused by abnormally high temperatures due to short circuits between the positive and negative electrodes. That is, under normal circumstances, electrical insulation is maintained due to the presence of a separator between the positive and negative electrodes. On the other hand, in abnormal circumstances where the battery is overcharged or discharged, dendritic growth of the electrode material occurs, or an internal short circuit is caused by external substances, sharp objects such as nails, screws, and the like penetrate the battery, or the battery is excessively deformed by external forces, and existing separators have these limitations.

[0006] Generally speaking, microporous films formed from polyolefin resins are mainly used as separators, but their heat resistance temperature is about 120°C to 160°C, so their heat resistance is insufficient. Therefore, when an internal short circuit occurs, the separator shrinks due to the heat of the short circuit reaction, and the short circuit portion is magnified, and thermal runaway occurs, generating a large amount of reaction heat. Since this phenomenon mainly occurs at the end of the electrode current collector coated with the electrode active material in the electrode stack, various methods have been tried to reduce the possibility of electrode short circuits caused by external impact or high temperature.

[0007] Specifically, in order to solve the internal short circuit of the battery, a method of attaching an insulating tape to or applying an insulating liquid to the non-coated portion of the electrode and the active material layer to form an insulating layer has been proposed. For example, there is a method of applying an insulating adhesive to the non-coated portion and the active material layer of the positive electrode, or applying an insulating liquid in which a mixture of the adhesive and inorganic particles is dispersed in a solvent to form a coating (hereinafter referred to as an insulating layer).

[0008] Meanwhile, the electrodes in actual secondary batteries exist in a state of being immersed in a liquid electrolyte, and conventional insulating layers exhibit reduced adhesion (hereinafter, referred to as wet adhesion) while immersed in the liquid electrolyte, and thus fail to prevent the migration of lithium ions in the overlay region of the electrodes, resulting in capacity expression (see Figure 1 ). In particular, when the capacity is expressed in the overlapping region of the electrodes, lithium ions may be precipitated, which may lead to a decrease in the stability of the battery cell.

[0009] Therefore, there is a need to develop an insulating layer having excellent wet adhesion. Summary of the Invention

[0010] Technical issues

[0011] The present technology relates to providing a positive electrode for a lithium secondary battery, which includes an insulating layer having excellent wet adhesion; a method of manufacturing the same; and a lithium secondary battery including the same.

[0012] Technical Solution

[0013] In order to solve the above problems, one aspect of the present invention provides a positive electrode for a lithium secondary battery, which includes: a current collector; a positive electrode active material layer formed on one surface or both surfaces of the current collector and including a positive electrode active material, a conductive material, and a non-aqueous binder; and an insulating layer arranged on one side of the active material layer, wherein the insulating layer is formed by an aqueous binder replaced with a non-aqueous solvent.

[0014] In one embodiment, the insulating layer may be provided on the current collector such that the insulating layer covers from a portion of the non-coating portion of the current collector to a portion of the positive active material layer applied to the current collector.

[0015] In a specific embodiment, the insulating layer may be disposed on the current collector so that the insulating layer covers from a portion of the non-coated portion of the current collector to a portion of the sliding area of ​​the positive electrode active material layer applied to the current collector, and the height of the insulating layer formed may vary from 10% to 50% of the height of the positive electrode active material layer.

[0016] In another embodiment, the insulating layer may be provided on the current collector so that the insulating layer covers from a portion of the non-coated portion of the current collector to a portion of the sliding area of ​​the positive active material layer applied to the current collector, and the height of the insulating layer formed may vary from 50% of the height of the positive active material layer to 100% of the height of the positive active material layer.

[0017] For example, the insulating layer may have an average thickness of 1 μm to 50 μm.

[0018] In one embodiment, the insulating layer may further include inorganic particles dispersed in the aqueous binder replaced with the non-aqueous solvent. In addition, the weight ratio of the inorganic particles to the aqueous binder may vary from 1:99 to 95:5.

[0019] The inorganic particles may be one or more selected from the group consisting of AlOOH, Al2O3, γ-AlOOH, Al(OH)3, Mg(OH)2, Ti(OH)4, MgO, CaO, Cr2O3, MnO2, Fe2O3, Co3O4, NiO, ZrO2, BaTiO3, SnO2, CeO2, Y2O3, SiO2, silicon carbide (SIC), and boron nitride (BN).

[0020] In addition, the aqueous binder can be one or more selected from the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetyl cellulose.

[0021] In addition, the non-aqueous binder of the active material layer may be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP, Poly(vinylidene fluoride-co-hexafluoropropene)), polyethylene oxide (PEO, Poly(ethylene oxide)), polyacrylic acid (PAA), polyimide (PI), polyamideimide (PAI), and polyimide-polyamideimide copolymer (PI-PAI).

[0022] In a specific embodiment, the non-aqueous binder may be polyvinylidene fluoride (PVDF). In addition, the aqueous binder may be an aqueous binder replaced with a non-aqueous organic solvent, for example, styrene-butadiene rubber replaced with N-methyl-2-pyrrolidone.

[0023] Meanwhile, in an embodiment of the present invention, the insulating layer may have a composition including both an aqueous binder and a non-aqueous binder replaced with a non-aqueous solvent. For example, the insulating layer may have a composition including the aqueous binder and the non-aqueous binder at a weight ratio of 20:80 to 80:20 or 40:60 to 60:40.

[0024] Another aspect of the present invention provides a lithium secondary battery including the positive electrode for a secondary battery.

[0025] Beneficial effects

[0026] The advantages of the positive electrode for a lithium secondary battery including an insulating layer having excellent wet adhesion according to the present invention and the lithium secondary battery including the same are that the migration of lithium ions in the overlapping area of ​​the electrodes can be prevented by the insulating layer having excellent wet adhesion in the liquid electrolyte to suppress capacity expression and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic image showing the migration of lithium ions in the overlapping region of electrodes.

[0028] Figure 2 is a flow chart of a method for manufacturing a positive electrode for a lithium secondary battery according to the present invention.

[0029] Figure 3 The results of measuring the wet adhesion of the insulating layers of Examples and Comparative Examples are shown.

[0030] Figure 4 This is a graph obtained by measuring the discharge capacity to evaluate the capacity expression (room temperature discharge characteristics) of the battery cells of Examples 5 to 7.

[0031] Figure 5 This is a graph obtained by measuring the discharge capacity to evaluate the capacity expression (high-temperature discharge characteristics) of the battery cells of Examples 5 to 7. DETAILED DESCRIPTION

[0032] Since the present invention allows for various changes and various embodiments, specific embodiments will be described in detail in the detailed description.

[0033] However, this is not intended to limit the present invention to a specific embodiment, and it should be understood that all changes, equivalents, or substitutes within the spirit and technical scope of the present invention are included in the present invention.

[0034] In the present invention, it should be understood that the terms "including" or "having" are only intended to indicate the presence of a feature, quantity, step, operation, component, part, or a combination thereof, and are not intended to exclude the possibility of adding one or more other features, quantities, steps, operations, components, parts, or a combination thereof.

[0035] In addition, in the present invention, when a portion of a layer, film, region, plate, or the like is referred to as being "on" another portion, this includes not only the case where the portion is "directly" "on" another portion, but also the case where another portion is interposed therebetween. Conversely, when a portion of a layer, film, region, plate, or the like is referred to as being "under" another portion, this includes not only the case where the portion is "directly" "under" another portion, but also the case where another portion is interposed therebetween. Furthermore, in this document, being referred to as being "disposed on" may include not only being disposed on an upper portion, but also being disposed on a lower portion.

[0036] As used herein, “insulating layer” refers to an insulating member formed by applying from at least a portion of the non-coated portion of the electrode current collector to at least a portion of the electrode active material layer and drying.

[0037] As used herein, "wet adhesion" refers to the adhesion of an insulating layer as measured in a state immersed in a liquid electrolyte. More specifically, wet adhesion can be measured by immersing a metal coupon including an insulating layer formed therein in a liquid electrolyte, applying ultrasonic waves, and then determining whether the insulating layer swells or detaches.

[0038] As used herein, a "metal coupon" refers to a location where an insulating layer is formed, and may refer to a metal current collector used in manufacturing an electrode, specifically a metal current collector cut into a predetermined width and a predetermined length. For example, the metal coupon may be aluminum, copper, or a lithium alloy.

[0039] As used herein, an "overlapping region" may refer to a region in an electrode where an insulating layer is formed. More specifically, in an electrode where an active material layer is formed, the region where the insulating layer covers at least a portion of the non-coated portion and at least a portion of the active material layer, and where the insulating layer is formed on the active material layer, is referred to as the overlapping region.

[0040] Hereinafter, the present invention will be described in further detail.

[0041] Positive electrode for lithium secondary battery

[0042] One aspect of the present invention provides a positive electrode for a lithium secondary battery, comprising: a current collector; an active material layer formed on one or both surfaces of the current collector and comprising a positive electrode active material, a conductive material, and a non-aqueous binder; and an insulating layer disposed on one side of the active material layer.

[0043] In addition, the insulating layer is formed by replacing the aqueous binder with a non-aqueous solvent. According to the present invention, in forming the insulating layer, the aqueous binder can be applied to increase wet adhesion, and the replacement with the non-aqueous solvent can allow the insulating layer to be applied even more stably to the positive electrode that is susceptible to moisture.

[0044] Since the positive electrode for a secondary battery according to the present invention includes the insulating layer having excellent wet adhesion in a liquid electrolyte, there is an advantage in that migration of lithium ions in the overlapping region of electrodes can be prevented to suppress capacity expression and the like.

[0045] Generally speaking, the electrodes in secondary batteries exist in a state of being immersed in a liquid electrolyte, and accordingly, conventional insulating layers exhibit reduced wet adhesion while being immersed in the liquid electrolyte, and do not prevent the migration of lithium ions in the overlapping region of the positive electrode, resulting in capacity expression. In particular, when the capacity is expressed in the overlapping region of the positive electrode, lithium ions may be precipitated, which may lead to reduced stability of the battery cell. In the present invention, since an aqueous binder replaced with the same non-aqueous solvent as the positive electrode slurry solvent is used to form the insulating layer in the manufacture of the positive electrode for the secondary battery, gelation between the active material layer and the coating layer caused by the difference in binder type is suppressed. In particular, since the insulating layer is dried simultaneously with the solvent of the positive electrode slurry in the drying process, cracks between the active material layer and the insulating layer caused by differences in drying rate or temperature can be prevented.

[0046] Besides, the insulating layer has the effects of increasing electrical insulating properties and thermal safety and suppressing thermal expansion by further including the inorganic particles.

[0047] Meanwhile, the wet adhesion of the insulating layer may be measured by immersing a metal coupon including the insulating layer formed therein in a liquid electrolyte, applying ultrasonic waves, and then determining whether the insulating layer formed in the metal coupon swells or detaches.

[0048] The liquid electrolyte used in the measurement of wet adhesion may include an organic solvent and an electrolyte salt, and the electrolyte salt may be a lithium salt. As the lithium salt, any lithium salt typically used in a non-aqueous liquid electrolyte for a lithium secondary battery may be used without limitation. For example, the anion of the lithium salt may include an organic solvent, an electrolyte salt, a lithium ... - 、Cl - Br - , I - 、NO3 -、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - , and (CF3CF2SO2)2N - Any one or two or more of the groups consisting of.

[0049] As the organic solvent included in the above-mentioned liquid electrolyte, any organic solvent typically used in the liquid electrolyte for lithium secondary batteries can be used without restriction. For example, ether, ester, amide, linear carbonate, cyclic carbonate or the like can be used alone or in combination of two or more thereof. Among them, cyclic carbonate, linear carbonate or a carbonate compound as a mixture thereof can be typically used.

[0050] In the positive electrode for a lithium secondary battery according to the present invention, the insulating layer may include an aqueous binder.

[0051] In a specific embodiment, the water-based adhesive can be selected from one or more of the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetyl cellulose. In a specific embodiment, the water-based adhesive can be selected from one or more of the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber. For example, the water-based adhesive can be styrene-butadiene rubber.

[0052] Conventionally, polyvinylidene fluoride (hereinafter referred to as PVDF) is used as a binder for the insulating layer of the positive electrode, but PVDF shows reduced wet adhesion when immersed in a liquid electrolyte. Accordingly, in the present invention, styrene-butadiene rubber can be used as a binder polymer. Meanwhile, when styrene-butadiene rubber is used as a binder polymer, water can be used as a solvent. However, in this case, when the insulating composition is applied simultaneously with the positive electrode slurry, gelation (gelation) between the insulating composition and the positive electrode slurry caused by the difference in binder type may occur.

[0053] In a specific embodiment, the aqueous adhesive may be an aqueous adhesive replaced with a non-aqueous organic solvent. Here, the non-aqueous organic solvent may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), γ-butyrolactone, methyl alcohol, ethanol, and isopropyl alcohol.

[0054] For example, the aqueous binder may be styrene-butadiene rubber replaced with an NMP solvent. More specifically, the insulating layer may be formed by applying the insulating composition so that the insulating layer covers at least a portion of the non-coated portion and at least a portion of the active material layer, followed by drying at approximately 50°C to 300°C. In this case, the solvent is removed from the insulating layer during the drying process, and the styrene-butadiene rubber dispersed in the solvent is replaced with NMP, resulting in the presence of styrene-butadiene rubber replaced with NMP.

[0055] In addition, the insulating layer can enhance the safety of the battery by including inorganic particles, and the strength of the insulating layer can also be enhanced. The amount of inorganic particles can be suitably adjusted in view of the viscosity, heat resistance, insulating properties, filling effect, dispersibility, stability or the like of the insulating composition. Generally speaking, as the inorganic particle size increases, the viscosity of the composition comprising it increases, and the possibility of sedimentation in the insulating composition increases. In addition, as the inorganic particle size decreases, heat resistance increases. Therefore, considering the above points, the inorganic particles of suitable type and size can be selected, and if necessary, at least two types of inorganic particles can be used.

[0056] In a specific embodiment, the inorganic particles of the insulating layer may be one or more selected from the group consisting of AlOOH, Al2O3, γ-AlOOH, Al(OH)3, Mg(OH)2, Ti(OH)4, MgO, CaO, Cr2O3, MnO2, Fe2O3, Co3O4, NiO, ZrO2, BaTiO3, SnO2, CeO2, Y2O3, SiO2, silicon carbide (SiC), and boron nitride (BN), specifically one or more selected from the group consisting of AlOOH, Al2O3, γ-AlOOH, and Al(OH)3. For example, the inorganic particles may be AlOOH.

[0057] The weight ratio of the inorganic particles to the aqueous binder can vary from 1:99 to 95:5, from 10:90 to 70:30, from 20:80 to 60:40, or from 40:60 to 60:40. For example, the weight ratio of the inorganic particles to the aqueous binder in the insulating composition can be 50:50. At the same time, when the amount of the aqueous binder is too small, it may be difficult to obtain the desired insulating effect of the present invention, and the adhesion to the electrode may be reduced. On the other hand, when the amount of the aqueous binder is too large, the insulating composition may drip out in the overlapping area when the electrode is applied, and thus the safety of the battery cell may be reduced.

[0058] The inorganic particles may have an average particle diameter of 0.1 μm to 100 μm, specifically 0.5 μm to 80 μm, 1 μm to 50 μm, 2 μm to 30 μm, 3 μm to 20 μm, or 5 μm to 10 μm. When the size of the inorganic particles falls within the above range, the inorganic particles can be uniformly applied to the electrode, and the resistance of lithium ions can be minimized to ensure the performance of the lithium secondary battery.

[0059] In another embodiment, the insulating composition may include first and second inorganic particles having different particle diameters and may have a bimodal particle size distribution. This means that the inorganic particles are composed of a mixture of small and large particles, and the small second inorganic particles may fill the empty spaces between the large first inorganic particles, and an appropriate amount of inorganic particles may be dispersed. However, the present invention is not limited thereto.

[0060] Meanwhile, the insulating layer may have a thickness ranging from 0.2 μm to 100 μm, specifically from 1 μm to 50 μm, and more specifically from 1 μm to 30 μm, from 2 μm to 30 μm, from 3 μm to 20 μm, or from 5 μm to 15 μm. When the coating is too thin, it may be difficult to expect the effect of enhancing safety by applying the insulating layer.

[0061] In addition, the active material layer may include a positive electrode active material. In a specific embodiment, any typically used positive electrode active material may be used as the positive electrode active material, and lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide made by combining them may be used, but the present invention is not limited thereto.

[0062] In addition, the amount of the positive electrode active material may be 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight relative to 100 parts by weight of the active material layer.

[0063] In addition, a conductive material may be used to enhance the properties of the positive electrode, such as electrical conductivity, and one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber may be used. For example, the conductive material may include acetylene black.

[0064] In addition, the conductive material may be included in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight or 2 to 6 parts by weight, relative to 100 parts by weight of the active material layer.

[0065] Furthermore, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0066] In addition, the binder may be included in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight or 2 to 6 parts by weight, relative to 100 parts by weight of the active material layer.

[0067] Although there is no particular limitation on the average thickness of the active material layer, the average thickness may be specifically 10 to 500 μm or 50 to 400 μm, and more specifically 50 to 350 μm, 100 to 400 μm, 100 to 400 μm, 200 to 300 μm, or 50 to 250 μm.

[0068] Meanwhile, as a current collector for the positive electrode of a lithium secondary battery according to the present invention, any current collector that does not cause chemical changes in the battery and has high conductivity can be used. For example, stainless steel, aluminum, nickel, titanium, calcined carbon or the like can be used, and aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver or the like can also be used. In addition, fine random bodies can be formed on the surface of the current collector to increase the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous materials, foams, and mesh fabrics are feasible. In addition, the average thickness of the current collector can be suitably applied in the range of 3 μm to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0069] Method for manufacturing positive electrode for lithium secondary battery

[0070] Another aspect of the present invention provides a method for manufacturing a positive electrode for a lithium secondary battery, comprising: applying a positive electrode slurry comprising a positive electrode active material, a conductive material, and a non-aqueous binder to one or both surfaces of a current collector; applying an insulating composition comprising an aqueous binder replaced with a non-aqueous solvent so that the insulating composition covers at least a portion of a non-coated portion of the current collector to the portion of the positive electrode slurry applied to the current collector; and drying the positive electrode slurry and insulating composition applied to the current collector. Furthermore, the positive electrode slurry and insulating composition comprise the same non-aqueous solvent.

[0071] Figure 21 is a flow chart of a method for manufacturing a positive electrode for a lithium secondary battery according to the present invention. Figure 2 In the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention, the positive electrode slurry may be applied to one or both surfaces of the current collector, and the insulating composition may be applied so that the insulating composition covers the portion of the positive electrode slurry applied to the current collector from at least a portion of the non-coated portion of the current collector. At the same time, the insulating composition may be applied when the positive electrode slurry is not dried. Here, the undried slurry may refer to a slurry that has not yet undergone a separate drying process in a drying device or apparatus. In addition, the present invention may include drying the positive electrode slurry and the insulating composition applied to the current collector. In particular, according to the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention, the positive electrode slurry and the insulating composition applied to the current collector are dried simultaneously to increase the adhesion between the positive electrode active material and the insulating layer, and accordingly, the interface resistance therebetween can be reduced, and a dense insulating layer can be formed in which mechanical property problems such as fracture and the like are improved. In addition, the efficiency of the positive electrode manufacturing process can be increased.

[0072] Meanwhile, the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention is characterized in that the positive electrode slurry and the insulating composition include the same non-aqueous organic solvent. When the positive electrode slurry and the insulating composition use the same solvent, gelation caused by using different types of binders or cracks caused by differences in boiling points during the drying process can be resolved.

[0073] The non-aqueous organic solvent may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), γ-butyrolactone, methyl alcohol, ethanol, and isopropyl alcohol.

[0074] In a specific embodiment, the non-aqueous organic solvent may be one or more selected from the group consisting of NMP, DMF, DMAc, and DMSO, specifically one or more selected from the group consisting of NMP, DMF, and DMAc.

[0075] For example, the non-aqueous organic solvent may be an amide-based organic solvent, and the same solvent as that used in preparing the positive electrode slurry may be used. The non-aqueous organic solvent may be NMP.

[0076] When NMP is used as a solvent for the positive electrode slurry, the solvent for the insulating composition may be NMP. In particular, NMP may be used as a solvent for the insulating composition to prevent cracks and the like from occurring at the boundary between the insulating coating and the active material layer in the overlapping region of the electrode. The insulating composition for the electrode of the secondary battery according to the present invention may be applied and dried simultaneously with the positive electrode slurry. In particular, NMP may be used as a displacement solvent in the drying process.

[0077] Hereinafter, the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention will be described in detail.

[0078] Applying the positive electrode slurry to one or both surfaces of the current collector (S10)

[0079] The method of manufacturing a positive electrode for a lithium secondary battery according to the present invention includes applying a positive electrode slurry to one surface or both surfaces of a current collector.

[0080] In this case, as the current collector, any current collector that does not cause chemical changes in the battery and has high conductivity can be used. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or the like can be used, and aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like can also be used. For example, the current collector can be aluminum.

[0081] In addition, as the positive electrode active material in the slurry for the positive electrode active material layer, any positive electrode active material typically used in the positive electrode can be used, and lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide made by combining them can be used, but the present invention is not limited thereto.

[0082] The non-aqueous binder in the slurry for the positive electrode active material layer may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0083] In addition, a conductive material may be used to enhance the properties of the positive electrode, such as electrical conductivity, and one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber may be used. For example, the conductive material may include acetylene black.

[0084] In addition, the solvent used in the positive electrode slurry is a non-aqueous organic solvent, and the non-aqueous organic solvent may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), γ-butyrolactone, methyl alcohol, ethanol, and isopropyl alcohol.

[0085] Applying an insulating composition so that the insulating composition covers from at least a portion of the non-coated portion of the current collector to a portion of the positive electrode slurry applied to the current collector (S20)

[0086] The method of manufacturing a positive electrode for a lithium secondary battery according to the present invention includes applying an insulating composition containing inorganic particles and an aqueous binder so that the insulating composition covers at least a portion of a non-coated portion of a current collector to a portion of a positive electrode slurry applied to the current collector.

[0087] In this case, the positive electrode slurry may be in an undried state. Here, the undried slurry may refer to a slurry that has not yet undergone a separate drying process in a drying device or apparatus.

[0088] The insulating composition can provide excellent wet adhesion by including inorganic particles and an aqueous binder. Accordingly, the migration of lithium ions can be suppressed in the overlapping region of the positive electrode, and lithium ion precipitation can be prevented.

[0089] lithium secondary batteries

[0090] Yet another aspect of the present invention provides a lithium secondary battery comprising the positive electrode for a lithium secondary battery according to the present invention.

[0091] The lithium secondary battery according to the present invention may include the above-described positive electrode according to the present invention, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0092] In particular, the lithium secondary battery according to the present invention has the advantage that the migration of lithium ions in the overlapping region of the electrodes can be prevented by the insulating layer having excellent wet adhesion in the liquid electrolyte to suppress capacity expression and the like. Accordingly, the lithium secondary battery according to the present invention can exhibit enhanced stability.

[0093] In this case, the negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector and including a negative electrode active material. Specifically, the negative electrode is manufactured by applying the negative electrode active material to the negative electrode current collector, followed by drying and pressing, and if necessary, the negative electrode may further include a conductive material, an organic binder polymer, a filler, and the like as described above.

[0094] As the negative electrode active material, for example, carbon and graphite materials such as graphite having a complete layered crystal structure (such as natural graphite), soft carbon having a layered crystal structure with low crystallinity (graphene structure; a structure in which hexagonal honeycomb planes of carbon are arranged in layers), hard carbon in which these structures are mixed with an amorphous portion, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerene, activated carbon, and the like can be used; metal composite oxides such as Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Group 1, Group 2 and Group 3 in the periodic table, halogen; 0<x≤1; 1≤y≤3; 1≤z≤8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene and the like; Li-Co-Ni based materials; titanium oxide; lithium titanium oxide, and the like.

[0095] In one embodiment, the negative electrode active material may include both graphite and silicon (Si)-containing particles. As the graphite, any one or more of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure may be included, and as the silicon (Si)-containing particles, silicon (Si) particles, silicon oxide (SiO2) particles, or a mixture of silicon (Si) particles and silicon oxide (SiO2) particles containing silicon (Si) as a main metal component may be included.

[0096] In this case, the negative electrode active material may include 80 to 95 parts by weight of graphite and 1 to 20 parts by weight of silicon (Si) particles relative to 100 parts by weight of the negative electrode active material. In the present invention, by adjusting the amount of graphite and silicon (Si) particles included in the negative electrode active material within the above range, lithium consumption and irreversible capacity loss during initial charge and discharge of the battery can be reduced, and the charge capacity per unit mass can be enhanced.

[0097] In addition, the negative active material layer may have an average thickness of 100 μm to 200 μm, specifically 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0098] In addition, the negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, nickel, titanium, calcined carbon, or the like can be used, and copper or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like can also be used.

[0099] In addition, similar to the positive electrode current collector, the negative electrode current collector may have fine random bodies formed on its surface to increase the adhesion of the negative electrode active material, and various forms such as films, sheets, foils, nets, porous materials, foams, and mesh fabrics are possible. In addition, the average thickness of the negative electrode current collector can be appropriately applied within the range of 3 μm to 500 μm in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0100] In addition, the separator is inserted between the positive electrode and the negative electrode, and an insulating film with high ion permeability and mechanical strength is used. Although there is no particular limitation on the separator as long as it is typically used in the art, specifically, a sheet or non-woven fabric made of chemically resistant and hydrophobic polypropylene, glass fiber, polyethylene, or the like can be used, and in some cases, a composite separator in which a porous polymer substrate such as a sheet or non-woven fabric is coated with inorganic particles / organic particles by an organic binder polymer can be used. When a solid electrolyte such as a polymer or the like is used as an electrolyte, the solid electrolyte can act as a separator. In addition, the separator can have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0101] Meanwhile, the positive and negative electrodes may be housed in a cylindrical battery, a prismatic battery, or a pouch-type battery while being wound in a jelly roll form, or may be folded or stacked-folded to be housed in a pouch-type battery, but the present invention is not limited thereto.

[0102] In addition, the liquid electrolyte containing lithium salt according to the present invention can be composed of a liquid electrolyte and a lithium salt. As the liquid electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like can be used.

[0103] As the nonaqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfrank, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, or the like can be used.

[0104] As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate polymer, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer including an ion dissociative group, or the like can be used.

[0105] As an inorganic solid electrolyte, for example, nitrides, halides, and sulfates of lithium (Li) such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, or the like can be used.

[0106] Lithium salts are substances that can be easily dissolved in non-aqueous electrolytes, and for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, imide, or the like.

[0107] In addition, in order to improve charge / discharge characteristics, flame retardancy, and the like, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-ethylene glycol dimethyl ether (glyme), hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinones, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, or the like may be added to the non-aqueous electrolyte. In some cases, a halogen-containing solvent such as carbon tetrachloride, trifluoroethylene, or the like may be further included to impart non-flammability, carbon dioxide gas may be further included to enhance high-temperature storage characteristics, and fluoroethylene carbonate (FEC), propylene sultone (PRS), or the like may be further included.

[0108] Meanwhile, yet another aspect of the present invention provides a battery module including the above-mentioned secondary battery as a unit cell and also provides a battery pack including the battery module.

[0109] The battery pack can be used as a power source for medium to large-sized devices that require high-temperature stability and high-rate characteristics such as long cycle characteristics, and specific examples of the medium to large-sized devices include: power tools powered by electric motors; electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and the like; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; power storage systems; and the like, and more specific examples thereof include hybrid electric vehicles (HEV), but the present invention is not limited thereto.

[0110] In addition, the positive electrode and the negative electrode can be housed in a cylindrical battery, a prismatic battery, or a pouch-type battery while being wound in the form of a jelly roll, or can be folded or stacked-folded and housed in a pouch-type battery. For example, the lithium secondary battery according to the present invention can be a pouch-type battery.

[0111] As described above, the lithium secondary battery including the positive electrode active material according to the present invention can be used in a battery module or battery pack including a plurality of batteries as unit cells. Specifically, the lithium secondary battery is useful in the fields of portable devices such as mobile phones, notebook computers, digital cameras, and the like, and electric vehicles such as hybrid electric vehicles (HEVs) and the like.

[0112] Hereinafter, the present invention will be described in further detail with reference to Examples and Experimental Examples.

[0113] However, it should be understood that the following embodiments and experimental examples are given for illustrative purposes only and are not intended to limit the scope of the present invention.

[0114] Example 1

[0115] To 100g of styrene-butadiene rubber (hereinafter referred to as SBR, commercially available from ZEON Chemicals as BM451B) dispersed in water as a solvent at a ratio of 60:40 (parts by weight), 500g of N-methyl-2-pyrrolidone (NMP) solvent was added and stirred. The stirred mixture was then heated at 100°C to 120°C for 2 hours to completely evaporate the water contained therein to prepare an NMP-substituted SBR binder. The NMP-substituted SBR binder and inorganic particles were then mixed and stirred at a weight ratio of 50:50 to prepare an insulating composition. The prepared insulating composition had a viscosity of 5,000 cP.

[0116] Examples 2 to 4 and Comparative Examples 1 and 2

[0117] An insulating composition was obtained in the same manner as in Example 1, except that the amounts of the inorganic particles and the binder were changed in the preparation of the insulating composition.

[0118] The specific compositions of Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0119] [Table 1]

[0120]

[0121]

[0122] Experimental Example 1: Measurement of wet adhesion of insulating layer

[0123] In order to evaluate the adhesion of the insulating layer according to the present invention, an experiment was performed as follows.

[0124] Metal specimen including an insulating layer formed therein

[0125] Each of the insulating compositions prepared in Examples 1 to 4 and Comparative Examples 1 and 2 was applied to an aluminum metal foil and dried to prepare a metal specimen having a 10 μm thick insulating layer formed therein. The metal specimen including the insulating layer formed therein was cut to a size of 2 cm×2 cm using a cutting device for adhesion measurement.

[0126] Application of ultrasonic waves

[0127] 200 g of liquid electrolyte (EC / EMC=3 / 7 (vol%)) was placed in a 250 ml beaker, and the metal sample including the insulating layer formed therein was immersed in the liquid electrolyte. In order to control the movement of the metal sample, the metal sample was fixed with a jig.

[0128] Then, ultrasonic waves were applied to the liquid electrolyte in which the metal sample was immersed using an ultrasonic generator (4200 commercially available from BANDELIN). In this case, the conditions for applying ultrasonic waves were as follows.

[0129] -Frequency: 20kHz

[0130] -Tip diameter: 13mm (TS-113)

[0131] -Amplitude: 100%

[0132] (When using a 13mm tip, peak-to-peak 132μm)

[0133] The results are shown in Tables 2 and Figure 3 middle.

[0134] [Table 2]

[0135]

[0136]

[0137] Figure 3 : is an image showing the results of measuring the wet adhesion of the insulating layers of Examples 1 and 4 and Comparative Examples 1 and 2. Figure 2 The electrode sample of Example 1 did not show swelling or detachment of the insulating layer. However, in the case of Example 1, the measurement was stopped when it reached 109°C because the measurement environment was changed by the evaporation of the solvent due to the increase in the temperature of the liquid electrolyte due to the application of ultrasonic waves and the boiling point of the EMC of 107.5°C.

[0138] Although not shown in the drawings, the electrode samples of Examples 2 and 3 also did not show swelling or detachment of the insulating layer, similar to Example 1. However, when reaching 109°C, the measurement was stopped because the measurement environment was changed by the evaporating solvent due to the boiling point of EMC at 107.5°C.

[0139] In the case of Example 4, no swelling or detachment occurred in the electrode sample during the 15 minutes of ultrasonic wave application to the liquid electrolyte. However, although not shown in the drawings, swelling and detachment occurred in the electrode sample when the temperature of the liquid electrolyte increased to 108° C. due to continued ultrasonic wave application.

[0140] Besides, in the case of Comparative Examples 1 and 2, swelling and detachment occurred in the electrode samples only within 15 minutes of applying ultrasonic waves to the liquid electrolyte.

[0141] From the above results, it can be confirmed that the insulating layer of Example has superior wet adhesion compared to the insulating layers of Comparative Examples 1 and 2.

[0142] Experimental Example 2: Evaluation of Battery Cell Capacity Expression

[0143] In order to evaluate the performance of the positive electrode including the insulating layer according to the present invention, a half cell was manufactured and then the capacity expression was evaluated.

[0144] Semi-cell manufacturing

[0145] 96 parts by weight of LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, 2 parts by weight of polyvinylidene fluoride (PVDF) as a binder, and 2 parts by weight of carbon black as a conductive agent were weighed and mixed in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was then applied to aluminum foil, dried, and rolled to produce a positive electrode including a positive electrode active material layer (average thickness: 130 μm).

[0146] Then, the positive electrode was dip-coated with each of the insulating compositions obtained in Examples 1 to 3 and then dried in a convection oven (130° C.) to form a 10 μm thick insulating layer in the positive electrode. A coin-type half-cell was prepared using aluminum foil as the negative electrode and a liquid electrolyte in which 1 M LiPF6 was added to a solvent (EC:DMC:DEC=1:2:1).

[0147] [Table 3]

[0148] insulation layer Battery Example 1 Example 5 Example 2 Example 6 Example 3 Example 7

[0149] Measurement of discharge capacity

[0150] The discharge characteristics of Examples 5 to 7 were evaluated under the following conditions: In addition, the discharge characteristics were measured at each of room temperature (25° C.) and high temperature (45° C.).

[0151] -Discharge: 0.1C, 0.33C, 0.5C, 1.0C, 2.5V, cut-off

[0152] Meanwhile, in order to compare the capacity expression of each battery, a battery cell including an electrode without an insulating layer was used as Comparative Example 3. The results are shown in Tables 4 and 5 and Figure 4 and Figure 5 middle.

[0153] [Table 4]

[0154]

[0155]

[0156] [Table 5]

[0157]

[0158] Refer to Table 4 and Table 5 and Figure 4 and Figure 5 In the case of high temperature discharge (45°C), the battery of Example 7 partially expresses capacity when discharged at 0.7C, while the batteries of Examples 5 and 6 hardly express capacity when discharged at room temperature (25°C).

[0159] The above results are believed to be due to the fact that the insulating layer, by having excellent wet adhesion in the liquid electrolyte, prevents the migration of lithium ions in the overlapping area of ​​the electrodes, thereby suppressing capacity growth and the like during discharge. Accordingly, in the case of the lithium secondary battery according to the present invention, the decrease in capacity with increasing cycles can be suppressed, and safety can be improved.

[0160] Although the present invention has been described above with reference to exemplary embodiments, it will be understood by those skilled in the art that various modifications and variations may be made without departing from the spirit and technical scope of the invention as described in the appended claims.

[0161] Therefore, the technical scope of the present invention should be defined by the appended claims rather than by the detailed description of this specification.

Claims

1. A positive electrode for a lithium secondary battery, comprising: Current collector; An active material layer formed on one surface or both surfaces of the current collector and comprising a positive electrode active material, a conductive material, and a non-aqueous binder; and an insulating layer disposed on one side of the active material layer, wherein the insulating layer prevents migration of lithium ions in an overlapping region of the electrodes; wherein the insulating layer is formed using an insulating composition comprising an aqueous binder replaced with a non-aqueous solvent; wherein the insulating layer is provided on the current collector such that the insulating layer covers from at least a portion of the non-coated portion of the current collector to at least a portion of a sliding region of the active material layer applied to the current collector.

2. The positive electrode according to claim 1, wherein The insulating layer is formed to have a height ranging from 10% to 50% of the height of the active material layer.

3. The positive electrode according to claim 1, wherein The insulating layer is formed to have a height ranging from 50% to 100% of the height of the active material layer. The positive electrode according to claim 1 , wherein the insulating layer has an average thickness ranging from 1 μm to 50 μm.

5. The positive electrode according to claim 1, wherein the insulating layer further comprises inorganic particles dispersed in the aqueous binder replaced with the non-aqueous solvent, and The weight ratio of the inorganic particles to the aqueous binder varies from 1:99 to 95:

5.

6. The positive electrode according to claim 5, wherein the inorganic particles are one or more selected from the group consisting of AlOOH, Al2O3, Al(OH)3, Mg(OH)2, Ti(OH)4, MgO, CaO, Cr2O3, MnO2, Fe2O3, Co3O4, NiO, ZrO2, BaTiO3, SnO2, CeO2, Y2O3, SiO2, silicon carbide, and boron nitride.

7. The positive electrode according to claim 1, wherein the aqueous binder is one or more selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetyl cellulose. 8 . The positive electrode according to claim 1 , wherein the non-aqueous binder is one or more selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyethylene oxide, polyacrylic acid, polyimide, polyamideimide, and polyimide-polyamideimide copolymer. 9 . The positive electrode according to claim 1 , wherein the non-aqueous binder is polyvinylidene fluoride, and the aqueous binder is styrene-butadiene rubber replaced with N-methyl-2-pyrrolidone.

10. The positive electrode according to claim 1, wherein The active material layer is formed by applying a positive electrode slurry to one surface or both surfaces of the current collector, and The insulating layer is formed by applying the insulating composition while the positive electrode slurry is not dried, so that the insulating composition covers at least a portion of the non-coated portion of the current collector to at least a portion of the positive electrode slurry applied to the current collector. The positive electrode according to claim 5 , wherein the inorganic particles are γ-AlOOH. 12 . A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 1 .

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