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

Abstract

The present technology relates to a positive electrode for a lithium secondary battery comprising an insulating layer having excellent wet adhesion, and a lithium secondary battery comprising the same, and their advantage is that migration of lithium ions in overlapping regions of the electrodes can be blocked by an insulating layer having excellent wet adhesion in the liquid electrolyte to suppress capacity expression and the like.

Description

[0001] This application is a divisional application. The international application number of the original application is PCT / KR2022 / 011204, the Chinese national phase application number is 202280005627.9, the application date is July 29, 2022, and the invention title is "Positive electrode for lithium secondary battery including an insulating layer with excellent wet adhesion and lithium secondary battery including the same". Technical Field

[0002] This application claims 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, the entire contents of which are incorporated herein by reference.

[0003] This technology relates to a positive electrode for a lithium secondary battery, comprising an insulating layer having excellent wet adhesion; a method for manufacturing the same; and a lithium secondary battery comprising the same. Background Technology

[0004] As mobile device technology advances and the demand for mobile devices increases, the need for secondary batteries as power sources is rapidly growing, and correspondingly, much research has been conducted on batteries that can meet various needs.

[0005] Typically, in terms of battery shape, there is a high demand for thin prismatic and pouch-shaped batteries suitable for use in products such as mobile phones and the like. Furthermore, in terms of materials, there is a high demand for lithium-ion rechargeable batteries such as lithium-cobalt polymer batteries with excellent energy density, discharge voltage, and safety.

[0006] One of the main research tasks related to secondary batteries is to enhance safety. Battery safety-related accidents are mainly caused by abnormally high temperatures resulting from short circuits between the positive and negative electrodes. Under normal circumstances, electrical insulation is maintained due to the separator between the positive and negative electrodes. However, under abnormal conditions such as overcharging or discharging, dendritic growth occurs in the electrode materials, or internal short circuits are caused by external substances, such as sharp objects like nails, screws, or similar objects piercing the battery, or the battery being excessively deformed by external forces. Existing separators have limitations in addressing these issues.

[0007] Generally, microporous membranes formed from polyolefin resins are mainly used as separators, but their heat resistance is insufficient, with a temperature range of approximately 120°C to 160°C. Therefore, when an internal short circuit occurs, the separator shrinks due to the heat generated by the short circuit reaction, thus amplifying the short circuit and leading to thermal runaway, which generates a large amount of heat. Since this phenomenon mainly occurs at the ends of the electrode current collectors coated with electrode active material in electrode stacks, various methods have been attempted to reduce the likelihood of electrode short circuits caused by external impacts or high temperatures.

[0008] Specifically, to address internal short circuits in batteries, methods have been proposed for attaching insulating tape to or applying insulating liquid to the uncoated portions and active material layers of the electrode to form an insulating layer. For example, there are methods for applying insulating adhesive to the uncoated portions and active material layers of the positive electrode or applying an insulating liquid in which a mixture of adhesive and inorganic particles is dispersed in a solvent to form a coating (hereinafter referred to as an insulating layer).

[0009] Meanwhile, in actual secondary batteries, the electrodes exist in a submerged state in the liquid electrolyte, and conventional insulating layers exhibit reduced adhesion (hereinafter referred to as wet adhesion) while submerged in the liquid electrolyte, thus failing to prevent the migration of lithium ions in the electrode overlay and consequently not affecting capacity expression (see [link to battery description]). Figure 1 In particular, when capacity is expressed in the overlapping region of the electrodes, lithium ions may be deposited, which can lead to a decrease in the stability of the battery cell.

[0010] Therefore, there is a need to develop an insulating layer with excellent wet adhesion. Summary of the Invention

[0011] [Technical Issues]

[0012] This 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.

[0013] [Technical Solution]

[0014] To address the aforementioned problems, 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, wherein the insulating layer is formed by an aqueous binder replaced with a non-aqueous solvent.

[0015] In one embodiment, the insulating layer may be disposed on the current collector such that the insulating layer covers from a portion of the uncoated portion of the current collector to a portion of the active material layer applied to the current collector.

[0016] In a specific embodiment, the insulating layer may be disposed on the current collector such that the insulating layer covers from the uncoated portion of the current collector to the sliding area of ​​the active material layer applied to the current collector, and the height of the formed insulating layer may vary from 10% to 50% of the height of the active material layer.

[0017] In another embodiment, the insulating layer may be disposed on the current collector such that the insulating layer covers a portion of the uncoated portion of the current collector to a portion of the sliding area of ​​the active material layer applied to the current collector, and the height of the formed insulating layer may vary from 50% to 100% of the height of the active material layer.

[0018] For example, the insulating layer may have an average thickness of 1 μm to 50 μm.

[0019] In one embodiment, the insulating layer may further comprise inorganic particles dispersed in the aqueous adhesive replaced with a non-aqueous solvent. Furthermore, the weight ratio of the inorganic particles to the aqueous adhesive may vary from 1:99 to 95:5.

[0020] 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).

[0021] In addition, the waterborne adhesive may 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, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetylcellulose.

[0022] Furthermore, the non-aqueous adhesive of the active material layer may be one or more of the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), polyethylene oxide (PEO), polyacrylic acid (PAA), polyimide (PI), polyamide-imide (PAI), and polyimide-polyamide-imide copolymer (PI-PAI).

[0023] In a specific embodiment, the non-aqueous adhesive may be polyvinylidene fluoride (PVDF). Alternatively, the aqueous adhesive may be an aqueous adhesive with a non-aqueous organic solvent replaced, such as styrene-butadiene rubber with N-methyl-2-pyrrolidone replaced.

[0024] Furthermore, in embodiments of the present invention, the insulating layer may have a composition comprising both an aqueous adhesive and a non-aqueous adhesive replaced with a non-aqueous solvent. For example, the insulating layer may have a composition comprising an aqueous adhesive and a non-aqueous adhesive in a weight ratio of 20:80 to 80:20 or 40:60 to 60:40.

[0025] Another aspect of the present invention provides a lithium secondary battery including the above-described positive electrode for a secondary battery.

[0026] [Beneficial Effects]

[0027] The advantages of the positive electrode for a lithium secondary battery, which includes an insulating layer with 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 region of the electrodes can be prevented by the insulating layer with excellent wet adhesion in the liquid electrolyte to suppress capacity expression and the like. Attached Figure Description

[0028] Figure 1 This is a schematic image showing the migration of lithium ions in the overlapping region of the electrodes.

[0029] Figure 2 This is a flowchart of a method for manufacturing a positive electrode for a lithium secondary battery according to the present invention.

[0030] Figure 3 The results of measuring the wet adhesion of the insulating layers in the embodiments and comparative examples are shown.

[0031] Figure 4 The graphs are obtained by measuring the discharge capacity to evaluate the capacity expression (room temperature discharge characteristics) of the battery cells in Examples 4 to 6.

[0032] Figure 5 The graph is obtained by measuring the discharge capacity to evaluate the capacity expression (high temperature discharge characteristics) of the battery cells in Examples 4 to 6. Detailed Implementation

[0033] Since the present invention allows for various modifications and implementations, specific implementations will be described in detail in the detailed description.

[0034] However, this is not intended to limit the invention to a particular implementation, and it should be understood that all changes, equivalents, or alternatives within the spirit and scope of the invention are included in the invention.

[0035] In this invention, it should be understood that the terms "comprising" or "having" are intended only to indicate the presence of features, quantities, steps, operations, components, parts, or combinations thereof, and are not intended to exclude the possibility of adding one or more other features, quantities, steps, operations, components, parts, or combinations thereof.

[0036] Furthermore, in this 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 "on," 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 "below" another portion, this includes not only the case where the portion is "directly" below "below," but also the case where another portion is interposed therebetween. Moreover, in this document, being referred to as being "on" may include not only being disposed on the upper part, but also being disposed on the lower part.

[0037] As used herein, "insulating layer" refers to an insulating element formed by applying from at least a portion of the uncoated portion of an electrode current collector to at least a portion of an electrode active material layer and drying it.

[0038] As used herein, “wet adhesion” refers to the adhesion of an insulating layer as measured in a liquid electrolyte while submerged. More specifically, wet adhesion can be measured by immersing a metal sample, including an insulating layer formed therein, in a liquid electrolyte, applying ultrasound, and then determining whether the insulating layer swells or detaches.

[0039] As used herein, "metal sample" refers to a location where an insulating layer is formed, and can also refer to a metal current collector used in the manufacture of electrodes, specifically a metal current collector cut to a predetermined width and length. For example, a metal sample can be an aluminum, copper, or lithium alloy.

[0040] As used herein, "overlapping region" can refer to a region in an electrode in which an insulating layer is formed. More specifically, in an electrode in which an active material layer is formed, the region in which an insulating layer extends from at least a portion of the uncoated portion to at least a portion of the active material layer, and the region in which an insulating layer is formed on the active material layer, is called the overlapping region.

[0041] The invention will be described in further detail below.

[0042] Positive electrode for lithium secondary batteries

[0043] 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.

[0044] In addition, the insulating layer is formed by an aqueous adhesive that has been replaced with a non-aqueous solvent. According to the present invention, an aqueous adhesive can be applied during the formation of the insulating layer to increase wet adhesion, and the replacement with a non-aqueous solvent allows the insulating layer to be applied more stably even to the positive electrode, which is susceptible to moisture.

[0045] Since the positive electrode for secondary batteries according to the invention includes an insulating layer with excellent wet adhesion in the liquid electrolyte, it is advantageous that the migration of lithium ions in the overlapping region of the electrodes can be prevented to suppress capacity expression and the like.

[0046] Generally, electrodes in secondary batteries exist in a submerged state in a liquid electrolyte. Correspondingly, conventional insulating layers, while submerged in the liquid electrolyte, exhibit reduced wet adhesion and do not prevent the migration of lithium ions in the overlapping region of the positive electrode, thus failing to ensure capacity expression. In particular, when capacity is expressed in the overlapping region of the positive electrode, lithium ions may precipitate, which can lead to reduced battery cell stability. In this invention, since an aqueous binder, using 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 secondary batteries, gelation between the active material layer and the coating layer due to differences in binder type is suppressed. In particular, since the insulating layer and the solvent of the positive electrode slurry are dried simultaneously during the drying process, cracks between the active material layer and the insulating layer caused by differences in drying rate or temperature are prevented.

[0047] In addition, the insulating layer further incorporates inorganic particles, which enhances electrical insulation properties and thermal safety, as well as suppresses thermal expansion.

[0048] Meanwhile, the wet adhesion of the insulating layer can be measured by immersing a metal sample containing the insulating layer formed therein in a liquid electrolyte, applying ultrasound, and then determining whether the insulating layer formed in the metal sample swells or detaches.

[0049] 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 non-aqueous liquid electrolytes for lithium secondary batteries may be used without limitation. For example, the anion of the lithium salt may include those selected from F… - 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, two, or more of the members in the group.

[0050] As an organic solvent included in the aforementioned liquid electrolyte, any organic solvent typically used in liquid electrolytes for lithium secondary batteries may be used without limitation. For example, ethers, esters, amides, linear carbonates, cyclic carbonates, or the like may be used alone or in combination of two or more thereof. Among them, cyclic carbonates, linear carbonates, or carbonate compounds as mixtures thereof may be used typically.

[0051] In the positive electrode red of the lithium secondary battery according to the present invention, the insulating layer may include an aqueous adhesive.

[0052] In specific embodiments, the waterborne adhesive may 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, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetylcellulose. In specific embodiments, the waterborne adhesive may be one or more selected from the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber. For example, the waterborne adhesive may be styrene-butadiene rubber.

[0053] Conventionally, polyvinylidene fluoride (hereinafter referred to as PVDF) is used as a binder for the insulating layer of the positive electrode, but PVDF exhibits reduced wet adhesion when immersed in liquid electrolyte. Accordingly, in this invention, styrene-butadiene rubber can be used as the binder polymer. Simultaneously, when styrene-butadiene rubber is used as the binder polymer, water can be used as the solvent. However, in this case, when the insulating composition is applied simultaneously with the positive electrode slurry, gelation can occur between the insulating composition and the positive electrode slurry due to the difference in binder type.

[0054] In a specific embodiment, the aqueous adhesive may be an aqueous adhesive in which a non-aqueous organic solvent is replaced. Here, the non-aqueous organic solvent may be one or more selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butenyl carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), γ-butyrolactone, methanol, ethyl alcohol, and isopropyl alcohol.

[0055] For example, the aqueous adhesive can be styrene-butadiene rubber replaced with NMP solvent. More specifically, the insulating layer can be formed by applying an insulating composition such that the insulating layer covers at least a portion of the uncoated portion to at least a portion of the active material layer, and then drying it at about 50°C to 300°C. In this case, the solvent is removed in the drying process, and the styrene-butadiene rubber dispersed in the solvent is replaced with NMP, thus allowing the presence of NMP-replaced styrene-butadiene rubber.

[0056] In addition, the insulating layer can enhance battery safety and strength by including inorganic particles. The amount of inorganic particles can be appropriately adjusted taking into account the viscosity, heat resistance, insulating properties, filling effect, dispersibility, stability, or similar factors of the insulating composition. Generally, as the size of the inorganic particles increases, the viscosity of the composition containing them increases, and the possibility of sedimentation in the insulating composition increases. Furthermore, as the size of the inorganic particles decreases, the heat resistance increases. Therefore, taking these points into consideration, suitable types and sizes of inorganic particles can be selected, and if necessary, at least two types of inorganic particles can be used.

[0057] In specific embodiments, 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.

[0058] The weight ratio of inorganic particles to aqueous binder can be varied 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 inorganic particles to aqueous binder in the insulating composition can be 50:50. However, if the amount of aqueous binder is too small, it may be difficult to obtain the desired insulating effect in this invention, and the adhesion to the electrode may be reduced. On the other hand, if the amount of aqueous binder is too large, the insulating composition may drip out in the overlapping areas during electrode coating, and therefore the safety of the battery cell may be reduced.

[0059] The inorganic particles can 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 in the electrode, and the resistance of lithium ions can be minimized to ensure the performance of the lithium secondary battery.

[0060] In another embodiment, the insulating composition may include a first inorganic particle and a second inorganic particle having different particle diameters from each other, and may have a bimodal particle size distribution. This means that the inorganic particles consist of a mixture of small-sized and large-sized particles, and the small-sized second inorganic particles can fill the empty spaces between the large-sized first inorganic particles, and can disperse a suitable amount of inorganic particles. However, the invention is not limited thereto.

[0061] Meanwhile, the insulating layer can have a thickness varying 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 this insulating layer.

[0062] Furthermore, the active material layer may include a positive electrode active material. In specific embodiments, 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 lithium composite oxides made by combining them may be used, but the invention is not limited thereto.

[0063] In addition, the amount of positive electrode active material can 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 active material layer.

[0064] Furthermore, conductive materials can be used to enhance properties of the positive electrode, such as electrical conductivity, and can be selected from one or more of the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers. For example, conductive materials may include acetylene black.

[0065] 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.

[0066] In addition, the adhesive 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 adhesive may include polyvinylidene fluoride.

[0067] In addition, the adhesive 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.

[0068] Although there is no particular limitation on the average thickness of the active material layer, the average thickness can be specifically 10 μm to 500 μm or 50 μm to 400 μm, and more specifically 50 μm to 350 μm, 100 μm to 400 μm, 100 μm to 400 μm, 200 μm to 300 μm, or 50 μm to 250 μm.

[0069] Meanwhile, as the 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 surfaces have 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, meshes, porous materials, foams, and woven fabrics are feasible. Furthermore, 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.

[0070] Method for manufacturing the positive electrode for lithium secondary batteries

[0071] 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, such that the insulating composition covers at least a portion of the uncoated portion of the current collector to a portion of the positive electrode slurry applied to the current collector; and drying the positive electrode slurry and the insulating composition applied to the current collector. Furthermore, the positive electrode slurry and the insulating composition comprise the same non-aqueous solvent.

[0072] Figure 2This is a flowchart of a method for manufacturing a positive electrode for a lithium secondary battery according to the present invention. (Refer to...) Figure 2 In the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention, a positive electrode slurry may be applied to one or both surfaces of a current collector, and an insulating composition may be applied such that the insulating composition covers at least a portion of the uncoated portion of the current collector to the portion of the positive electrode slurry applied to the current collector. Simultaneously, the insulating composition may be applied while the positive electrode slurry is undried. Here, undried slurry may refer to slurry that has not yet undergone a separate drying process in a drying apparatus or device. Furthermore, in the present invention, drying the positive electrode slurry and the insulating composition applied to the current collector may be included. In particular, in 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 simultaneously dried to increase the adhesion between the positive electrode active material and the insulating layer, and accordingly, the interfacial resistance can be reduced, and a dense insulating layer in which mechanical property problems such as breakage and the like are improved can be formed. Furthermore, the efficiency of the positive electrode manufacturing process can be increased.

[0073] 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 comprise the same non-aqueous organic solvent. When the positive electrode slurry and the insulating composition use the same solvent, gelation caused by the use of different types of binders or cracking caused by boiling point differences during the drying process can be resolved.

[0074] The non-aqueous organic solvent may be one or more of the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butenyl carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), γ-butyrolactone, methanol, ethyl alcohol, and isopropyl alcohol.

[0075] In a specific embodiment, the non-aqueous organic solvent may be one or more of the group consisting of NMP, DMF, DMAc, and DMSO, specifically one or more of the group consisting of NMP, DMF, and DMAc.

[0076] For example, the non-aqueous organic solvent can be an amide-based organic solvent, and can be the same solvent used in preparing the cathode slurry. The non-aqueous organic solvent can be NMP.

[0077] When NMP is used as a solvent for the positive electrode slurry, the solvent for the insulating composition can also be NMP. In particular, NMP can be used as a solvent for the insulating composition to prevent cracks and the like at the boundary between the insulating coating and the active material layer in the overlapping area of ​​the electrode. The insulating composition for the electrode of a secondary battery according to the invention can be applied and dried simultaneously with the positive electrode slurry. In particular, NMP can be used as a displacement solvent in the drying process.

[0078] The method for manufacturing a positive electrode for a lithium secondary battery according to the present invention will be described in detail below.

[0079] The positive electrode slurry is applied to one or both surfaces of the current collector (S10).

[0080] 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 or both surfaces of a current collector.

[0081] In this case, 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 surfaces have been treated with carbon, nickel, titanium, silver, or the like can also be used. For example, the current collector can be aluminum.

[0082] In addition, any positive electrode active material typically used in positive electrodes can be used as the positive electrode active material in the slurry used for the positive electrode active material layer, and lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or lithium composite oxides made by combining them can be used, but the present invention is not limited thereto.

[0083] The non-aqueous binder in the slurry used 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.

[0084] In addition, conductive materials can be used to enhance properties of the positive electrode such as electrical conductivity, and can be selected from one or more of the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber. For example, conductive materials may include acetylene black.

[0085] Furthermore, 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-methylpyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butenyl carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), γ-butyrolactone, methanol, ethyl alcohol, and isopropyl alcohol.

[0086] An insulating composition is applied such that it covers at least a portion of the uncoated portion of the current collector to the portion of the positive electrode paste applied to the current collector (S20).

[0087] 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, such that the insulating composition covers at least a portion of the uncoated portion of the current collector to a portion of the positive electrode slurry applied to the current collector.

[0088] In this case, the positive electrode slurry can be in an undried state. Here, undried slurry can refer to slurry that has not yet undergone a separate drying process in a drying device or apparatus.

[0089] The insulating composition can provide excellent wet adhesion by including inorganic particles and an aqueous binder. Accordingly, lithium ion migration can be suppressed in the overlapping region of the positive electrode, and lithium ion deposition can be prevented.

[0090] Lithium secondary batteries

[0091] Another aspect of the present invention provides a lithium secondary battery comprising the above-described positive electrode for a lithium secondary battery according to the present invention.

[0092] The lithium secondary battery according to the present invention may include the positive electrode, negative electrode and separator inserted between the positive electrode and the negative electrode as described above.

[0093] In particular, the lithium secondary battery according to the invention has the advantage that the migration of lithium ions in the overlapping region of the electrodes can be prevented by an insulating layer with excellent wet adhesion in the liquid electrolyte to suppress capacity expression and the like. Accordingly, the lithium secondary battery according to the invention can exhibit enhanced stability.

[0094] In this case, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector and including a negative electrode active material. Specifically, the negative electrode is manufactured by applying a negative electrode active material to the negative electrode current collector, followed by drying and pressing, and where necessary, the negative electrode may selectively further include conductive materials, organic binder polymers, fillers, and the like as described above.

[0095] As anode active materials, carbon and graphite materials can be used, such as graphite with a fully layered crystal structure (e.g., natural graphite), soft carbon with a low-crystallinity layered crystal structure (graphene structure; a hexagonal honeycomb planar layered structure of carbon), hard carbon in which these structures are mixed with amorphous portions, artificial graphite, expanded graphite, carbon fibers, non-graphitizable carbon, carbon black, carbon nanotubes, fullerenes, activated carbon, and the like; 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, Group 1, 2 and 3 elements in the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; 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.

[0096] In one embodiment, the negative electrode active material may include both graphite and silicon (Si) particles. The graphite may include any one or more of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure, while the silicon (Si) particles may include silicon (Si) particles, silicon oxide (SiO2) particles, or a mixture of silicon (Si) particles and silicon oxide (SiO2) particles containing silicon (Si) as the main metal component.

[0097] In this case, the negative electrode active material may comprise 80 to 95 parts by weight of graphite and 1 to 20 parts by weight of silicon (Si) particles per 100 parts by weight of the negative electrode active material. In this 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 the initial charging and discharging of the battery can be reduced, and the charging capacity per unit mass can be enhanced.

[0098] In addition, the negative electrode 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.

[0099] Furthermore, there are no particular restrictions on the negative current collector, 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 similar materials can be used, and copper or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or similar materials can also be used.

[0100] In addition, similar to the positive electrode current collector, the negative electrode current collector can 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, meshes, porous materials, foams, and woven fabrics are feasible. Furthermore, the average thickness of the negative electrode 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 negative electrode to be manufactured.

[0101] Furthermore, a separator is inserted between the positive and negative electrodes and uses an insulating film with high ion permeability and mechanical strength. While there are no particular limitations on the separator as long as it is typically used in the art, specifically, sheets or nonwoven fabrics made of chemically resistant and hydrophobic polypropylene, glass fiber, polyethylene, or the like can be used, and in some cases, composite separators in which a porous polymer substrate, such as a sheet or nonwoven fabric, is coated with inorganic / organic particles by an organic adhesive polymer. When a solid electrolyte, such as a polymer or the like, is used as the electrolyte, the solid electrolyte can act as the separator. Furthermore, 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.

[0102] Meanwhile, the positive and negative electrodes can be contained in a cylindrical battery, a prismatic battery, or a pouch battery while being wound in the form of a jelly roll, or they can be folded or stacked-folded and contained in a pouch battery, but the invention is not limited thereto.

[0103] In addition, the lithium-containing liquid electrolyte according to the present invention can be composed of a liquid electrolyte and a lithium salt. As the liquid electrolyte, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, or similar materials can be used.

[0104] As a non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyflavone, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, or similar solvents may be used.

[0105] As organic solid electrolytes, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, agitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymers including ion-dissociating groups, or the like can be used.

[0106] As an inorganic solid electrolyte, lithium (Li) nitrides, halides, and sulfates, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, or similar, can be used.

[0107] Lithium salts are substances that are readily soluble in non-aqueous electrolytes, and for example, LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB can be used. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acids, lithium tetraphenylborate, imide, or similar.

[0108] In addition, to improve charge / discharge characteristics, flame retardancy, and the like, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-ethylene glycol dimethyl ether (glyme), triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolium ketones, 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, halogenated solvents 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), propene sultone (PRS), or the like may be further included.

[0109] Meanwhile, 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.

[0110] Battery packs can be used as power sources for medium to large-sized devices that require high-temperature stability and high-rate characteristics such as long cycle life. Specific examples of medium to large-sized devices include: power tools powered by electric motors; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles including e-bikes and e-scooters; electric golf carts; energy storage systems; and the like, with more specific examples including hybrid electric vehicles (HEVs), but the invention is not limited thereto.

[0111] Furthermore, the positive and negative electrodes can be housed in a cylindrical, prismatic, or pouch-type battery while being wound in the form of a jelly roll, or they can be folded or stacked—folded in a pouch-type battery. For example, the lithium secondary battery according to the present invention can be a pouch-type battery.

[0112] As described above, lithium secondary batteries incorporating the positive electrode active material according to the present invention can be used in battery modules or battery packs comprising multiple batteries as unit cells. Specifically, lithium secondary batteries are useful in portable devices such as mobile phones, laptop computers, digital cameras, and the like, and in electric vehicles such as hybrid electric vehicles (HEVs) and the like.

[0113] The invention will be described in further detail below with reference to embodiments and experimental examples.

[0114] 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 invention.

[0115] Example 1

[0116] 500 g of N-methyl-2-pyrrolidone (NMP) solvent was added to 100 g of styrene-butadiene rubber (hereinafter referred to as SBR, commercially available from ZEON Chemicals BM451B) dispersed in water as a solvent at a ratio of 60:40 (parts by weight), and the mixture was stirred. The stirred mixture was then heated at 100°C to 120°C for 2 hours to completely evaporate the water contained therein, thereby preparing an NMP-substituted SBR adhesive. The NMP-substituted SBR adhesive and inorganic particles were then mixed at a weight ratio of 50:50 and stirred to prepare an insulating composition. The prepared insulating composition had a viscosity of 5,000 cP.

[0117] Examples 2 to 4 and Comparative Examples 1 and 2

[0118] The insulating coating liquid was obtained in the same manner as in Example 1, except that the amounts of inorganic particles and binder were varied in the preparation of the insulating composition.

[0119] The specific compositions of Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0120] [Table 1]

[0121]

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

[0123] To evaluate the adhesion of the insulating layer according to the present invention, the following experiments were performed.

[0124] Metal sample including the insulating layer formed therein

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

[0126] Application of ultrasound

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

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

[0129] - Frequency: 20 kHz

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

[0131] - Amplitude: 100%

[0132] (Peak-to-peak 132 μm when using a 13 mm tip)

[0133] The results are shown in Table 2 below and Figure 2 middle.

[0134] [Table 2]

[0135]

[0136] Figure 2 These are images showing the results of measuring the wet adhesion of the insulating layers in Examples 1 and 4, and Comparative Examples 1 and 2. Refer to Table 2 and... Figure 2 In Example 1, the electrode sample did not show swelling or detachment of the insulating layer. However, in the case of Example 1, the measurement stopped when 109°C was reached because the measurement environment was altered by the evaporation of the solvent due to the increased temperature of the liquid electrolyte caused by the application of ultrasound and the EMC boiling point of 107.5°C.

[0137] Although not shown in the accompanying drawings, similar to Examples 1, 2, and 3, the electrode samples also do not show swelling or detachment of the insulating layer. However, the measurement stopped when 109°C was reached because the measurement environment was altered by the evaporation of the solvent due to the EMC boiling point of 107.5°C.

[0138] In Example 4, no swelling or detachment occurred in the electrode sample during the 15 minutes of ultrasonic application to the liquid electrolyte. However, although not shown in the figures, swelling and detachment occurred in the electrode sample when the temperature of the liquid electrolyte reached 108°C due to the continuous application of ultrasonic waves.

[0139] In addition, in Comparative Examples 1 and 2, swelling and detachment occurred in the electrode sample within 15 minutes of applying ultrasound to the liquid electrolyte.

[0140] Based on the above results, it can be confirmed that the insulating layer of the embodiment has superior wet adhesion compared to the insulating layers of Comparative Examples 1 and 2.

[0141] Experiment Example 2: Evaluation of Battery Cell Capacity Expression

[0142] To evaluate the performance of the positive electrode including the insulating layer according to the present invention, a half cell is manufactured, and then the capacity expression is evaluated.

[0143] Semi-cell manufacturing

[0144] 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 an aluminum foil, dried, and rolled to manufacture a positive electrode including a positive electrode active material layer (average thickness: 130 μm).

[0145] The positive electrode was then dip-coated with each of the insulating coating solutions 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-shaped half-cell was manufactured 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).

[0146] [Table 3]

[0147]

[0148] Measurement of discharge capacity

[0149] The discharge characteristics of Examples 5 to 7 were evaluated under the following conditions. Furthermore, the discharge characteristics were measured at room temperature (25°C) and at high temperature (45°C).

[0150] - Discharge: 0.1C, 0.33C, 0.5C, 1.0C, 2.5V, Cutoff

[0151] Meanwhile, to compare the capacity expression of each battery, a battery cell including electrodes without an insulating layer was used as Comparative Example 3. The results are shown in Tables 4 and 5. Figure 3 and Figure 4 middle.

[0152] [Table 4]

[0153]

[0154] [Table 5]

[0155]

[0156] Refer to Tables 4 and 5 and Figure 3 and Figure 4 Under high-temperature discharge (45°C), the battery of Example 7 partially expressed its capacity when discharged at 0.7 C, while the batteries of Examples 5 and 6 had difficulty expressing their capacity when discharged at room temperature (25°C).

[0157] The above results are attributed to the fact that the insulating layer, by exhibiting excellent wet adhesion in the liquid electrolyte, prevents the migration of lithium ions in the overlapping regions of the electrodes, thereby suppressing capacity expression during discharge and the like. Accordingly, in the case of the lithium secondary battery according to the invention, the decrease in capacity with increasing cycling can be suppressed, and safety can be improved.

[0158] Although the invention has been described above with reference to exemplary embodiments, it will be understood by those skilled in the art that various modifications and changes can be made without departing from the spirit and scope of the invention as set forth in the appended claims.

[0159] Therefore, the scope of the present invention should be defined by the appended claims and not by the detailed description herein.

Claims

1. A positive electrode for a lithium secondary battery, comprising: 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; The insulating layer is formed using an insulating composition comprising an aqueous adhesive replaced with a non-aqueous solvent; The insulating layer is disposed on the current collector such that the insulating layer covers at least a portion of the uncoated portion of the current collector to at least a portion of the sliding region of the active material layer applied to the current collector; The aqueous adhesive is an aqueous adhesive that has undergone solvent replacement with a non-aqueous solvent in the following manner: Aqueous adhesives dispersed in water are mixed with non-aqueous solvents; and Solvent replacement is performed by heating the water to completely evaporate it.

2. The positive electrode according to claim 1, wherein, The insulating layer prevents lithium ions from migrating in the overlapping region of the electrodes.

3. The positive electrode according to claim 1, wherein, The height of the formed insulating layer varies from 10% to 50% of the height of the active material layer.

4. The positive electrode according to claim 1, wherein, The height of the formed insulating layer varies from 50% to 100% of the height of the active material layer.

5. The positive electrode according to claim 1, wherein the insulating layer has an average thickness ranging from 1 μm to 50 μm.

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

5.

7. The positive electrode according to claim 6, wherein the inorganic particles are selected from one or more of 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.

8. The positive electrode according to claim 1, wherein the aqueous binder is selected from one or more of 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, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetylcellulose.

9. The positive electrode according to claim 1, wherein the non-aqueous binder is selected from one or more of the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyethylene oxide, polyacrylic acid, polyimide, polyamide-imide, and polyimide-polyamide-imide copolymers.

10. 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.

11. The positive electrode according to claim 1, wherein, The active material layer is formed by applying the positive electrode slurry to one or both surfaces of the current collector, and The insulating layer is formed by applying the insulating composition while the positive electrode slurry is undried, such that the insulating composition covers at least a portion of the uncoated portion of the current collector to at least a portion of the positive electrode slurry applied to the current collector.

12. The positive electrode according to claim 6, wherein the inorganic particles are γ-AlOOH.

13. A lithium secondary battery, comprising a positive electrode for a lithium secondary battery according to any one of claims 1 to 12.

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