Insulating composition for electrode and method for preparing same

Abstract

The present technology relates to an insulating composition having excellent wet adhesion and a method for preparing the same, and since an insulating coating layer has excellent wet adhesion in a liquid electrolyte, the advantage is that migration of lithium ions in overlapping regions of electrodes can be prevented 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 / 011197, the Chinese national phase application number is 202280005584.4, the application date is July 29, 2022, and the invention title is "Insulating composition for electrodes with excellent wet adhesion and method for preparing the same". Technical Field

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0100879, filed on July 30, 2021, and Korean Patent Application No. 10-2022-0090835, filed on July 22, 2022, the entire contents of which are incorporated herein by reference.

[0003] This invention relates to an insulating composition for electrodes with excellent wet adhesion and a method for preparing 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 electrodes to form an insulating coating. 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 coating).

[0009] Meanwhile, in actual secondary batteries, the electrodes exist in a submerged state in the liquid electrolyte, and conventional insulating coatings 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 overlay region of the electrodes and consequently not affecting capacity expression (see [link to relevant documentation]). 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 reduction in the safety of the battery cell.

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

[0011] [Technical Issues]

[0012] This invention relates to providing an insulating composition for electrodes with excellent wet adhesion and a method for preparing the same.

[0013] [Technical Solution]

[0014] To address the aforementioned problems, one aspect of the present invention provides an insulating composition for an electrode, comprising: an aqueous binder replaced with a non-aqueous solvent; and inorganic particles. In one embodiment, the weight ratio of the inorganic particles to the aqueous binder varies from 1:99 to 95:5.

[0015] In a specific implementation, the weight ratio of the inorganic particles to the aqueous adhesive can be varied from 45:55 to 90:10.

[0016] In a specific embodiment, the non-aqueous organic solvent may be one or more selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), 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, methyl alcohol, ethanol, and isopropyl alcohol.

[0017] In another embodiment, 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).

[0018] In another embodiment, the aqueous adhesive may be selected from one or more of the group consisting of styrene-butadiene rubber, acrylated 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.

[0019] For example, in the insulating composition for electrodes according to the invention, the non-aqueous organic solvent may be N-methylpyrrolidone (NMP), and the aqueous adhesive may be styrene-butadiene rubber.

[0020] In one embodiment, the inorganic particles may have an average particle diameter ranging from 0.01 μm to 100 μm.

[0021] In a more specific embodiment, the insulating composition according to the invention 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.

[0022] For example, the insulating composition may have a viscosity of 50 cP to 50,000 cP at 25°C.

[0023] In one embodiment, the insulating composition according to the invention may be applied to the positive electrode of a secondary battery.

[0024] Another aspect of the present invention provides a method for preparing the above-described insulating composition for electrodes. In one embodiment, the method for preparing the insulating composition for electrodes according to the present invention includes: mixing an aqueous binder dispersed in water with a non-aqueous solvent; and performing solvent displacement by removing the water through heat treatment.

[0025] In one embodiment, the method may further include allowing the inclusion of inorganic particles after the solvent replacement.

[0026] In a specific implementation, the weight ratio of the inorganic particles to the aqueous adhesive can vary from 1:99 to 95:5.

[0027] In another embodiment, the heat treatment in the solvent replacement can be performed at 80°C to 150°C.

[0028] [Beneficial Effects]

[0029] An insulating composition for electrodes with excellent wet adhesion according to the invention and a method for preparing the same are provided. The advantage of the insulating composition having excellent wet adhesion in liquid electrolytes is that the migration of lithium ions in the overlapping region of the electrodes can be prevented to suppress capacity expression and the like. Attached Figure Description

[0030] Figure 1 This is a schematic image showing the migration of lithium ions in the overlapping region of the electrodes.

[0031] Figure 2 The results of measuring the wet adhesion of coatings formed from the insulating compositions in the examples and comparative examples are shown.

[0032] Figure 3 The graphs are obtained by measuring the discharge capacity to evaluate the capacity expression (room temperature discharge characteristics) of the battery cells of Examples 5 to 7.

[0033] Figure 4 The graphs are obtained by measuring the discharge capacity to evaluate the capacity expression (high-temperature discharge characteristics) of the battery cells in Examples 5 to 7. Detailed Implementation

[0034] Since the present invention allows for various modifications and implementations, specific implementations will be described in detail in the detailed description.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] As used herein, "insulating coating" refers to an insulating element formed by applying it from at least a portion of the uncoated portion of an electrode current collector to at least a portion of the electrode active material layer and drying it.

[0039] As used herein, “wet adhesion” refers to the adhesion of an insulating coating, as measured in a liquid electrolyte in an immersed state. More specifically, wet adhesion can be measured by immersing a metal sample, including an insulating coating formed therein, in a liquid electrolyte, applying ultrasound, and then determining whether the insulating coating swells or detaches.

[0040] As used herein, "metal specimen" refers to a location where an insulating coating 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 specimen can be an aluminum, copper, or lithium alloy.

[0041] As used herein, "overlapping region" can refer to a region in an electrode in which an insulating coating is formed. More specifically, in an electrode in which an active material layer is formed, the region in which the insulating coating 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 the insulating coating is formed on the active material layer, is referred to as the overlapping region.

[0042] The invention will be described in further detail below.

[0043] Insulating Composition

[0044] One aspect of the present invention provides an insulating composition for an electrode, comprising: an aqueous binder replaced with a non-aqueous solvent; and inorganic particles. Specifically, the weight ratio of the inorganic particles to the aqueous binder varies from 1:99 to 95:5.

[0045] Because the insulating composition for electrodes according to the invention has excellent wet adhesion in liquid electrolytes, it is advantageous that the migration of lithium ions in the overlapping regions of the electrodes can be prevented to suppress capacity expression and the like.

[0046] Generally, the electrodes in secondary batteries exist in a submerged state in a liquid electrolyte. Correspondingly, conventional insulating coatings exhibit reduced wet adhesion while submerged in the liquid electrolyte, failing to prevent lithium-ion migration in the overlapping regions of the electrodes and thus not contributing to capacity expression. In particular, when capacity is expressed in the overlapping regions of the electrodes, lithium-ions may deposit, which can lead to reduced cell stability.

[0047] In this invention, an insulating composition for electrodes can be provided, comprising an aqueous binder replaced by a non-aqueous solvent used as an electrode slurry solvent and inorganic particles dispersed therein, to enhance wet adhesion in a liquid electrolyte. That is, the insulating composition enhances wet adhesion when applied to the electrode, thereby suppressing lithium ion migration in the overlapping regions of the electrodes and preventing lithium ion deposition. Accordingly, when applied to the electrodes of a secondary battery, the insulating composition enhances the stability of the secondary battery.

[0048] In a specific embodiment, the insulating composition for electrodes according to the invention has a composition in which inorganic particles and an aqueous binder are mixed in a ratio of 1:99 to 95:5. When the insulating coating is formed from this insulating composition for electrodes, wet adhesion is excellent.

[0049] Meanwhile, the wet adhesion of the insulating coating can be measured by immersing a metal sample containing the insulating coating formed therein in a liquid electrolyte, applying ultrasound, and then determining whether the insulating coating formed in the metal sample swells or detaches.

[0050] 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.

[0051] 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.

[0052] In addition, the insulating composition for the electrode according to the invention can be applied to the positive electrode, and the non-aqueous organic solvent can 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.

[0053] 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.

[0054] 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.

[0055] In a specific embodiment, when the insulating coating serving as the positive electrode is applied, the insulating composition according to the invention can be applied and dried simultaneously with the positive electrode active material layer. In this case, when the same solvent as the solvent for the positive electrode slurry is used as the solvent for the insulating composition, the difference in drying rate and the like is reduced, and thus cracks and the like occurring at the boundary between the insulating coating and the positive electrode active material layer can be prevented. In particular, NMP solvent can be used as a displacement solvent, and an aqueous binder can be present as an NMP-displaced binder.

[0056] In addition, the waterborne adhesive may be one or more selected from the group consisting of styrene-butadiene rubber, acrylated 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 a specific embodiment, the waterborne adhesive may be one or more selected from the group consisting of styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber. For example, the waterborne adhesive may be styrene-butadiene rubber.

[0057] Conventionally, polyvinylidene fluoride (hereinafter referred to as PVDF) is used as a binder for the insulating coating used on the positive electrode, but PVDF exhibits reduced wet adhesion when immersed in liquid electrolyte. Accordingly, in this invention, styrene-butadiene rubber (SBR) can be used as the binder polymer. Water can also be used as the solvent when SBR is used as the binder polymer. However, in this case, when the insulating composition is applied simultaneously with the positive electrode slurry, gelation of the PVDF, which acts as the organic binder used as the positive electrode binder, can occur between the insulating composition and the positive electrode slurry. Therefore, cracks can occur at the boundary between the insulating composition used on the electrode and the positive electrode slurry.

[0058] In addition, the insulating composition can enhance battery safety and the strength of the insulating coating 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.

[0059] In specific embodiments, 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), 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.

[0060] The weight ratio of inorganic particles to aqueous binder can be varied from 1:99 to 95:5, specifically from 45:55 to 90:10 or from 50:50 to 90:10. 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 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, thus potentially reducing the safety of the battery cell.

[0061] The inorganic particles can have an average particle diameter of 0.01 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.

[0062] 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.

[0063] Meanwhile, in the insulating composition for electrodes according to the present invention, inorganic particles and SBR may be included in amounts of 1 to 50 parts by weight, 5 to 40 parts by weight, or 10 to 40 parts by weight relative to 100 parts by weight of NMP solvent.

[0064] The insulating composition may have a viscosity at 25°C of 50 cP to 50,000 cP, 100 cP to 45,000 cP, 1,000 cP to 40,000 cP, 2,000 cP to 35,000 cP, 3,000 cP to 30,000 cP, 4,000 cP to 20,000 cP, or 5,000 cP to 10,000 cP. Within the above ranges, adhesion to the electrode active material layer can be enhanced, and coatability, processability, and the like can be improved.

[0065] In one embodiment, the insulating composition for electrodes according to the invention is prepared by mixing an aqueous binder dispersed in water with a non-aqueous solvent; and by performing solvent displacement by removing water through heat treatment. In the invention, an insulating coating comprising the aqueous binder, which is replaced with a non-aqueous solvent, can be applied to a moisture-sensitive positive electrode by forming an aqueous binder.

[0066] In another embodiment, the method further includes allowing the inclusion of inorganic particles after solvent replacement. Specifically, the weight ratio of inorganic particles to the aqueous binder varies from 1:99 to 95:5. The mixing ratio of inorganic particles to the aqueous binder is as described above.

[0067] In one embodiment, the heat treatment in solvent displacement can be performed at 80°C to 150°C. The heat treatment is intended to remove the water component contained in the water-based adhesive by evaporation. The heat treatment can be performed at atmospheric pressure (1 atm), and can also be performed under vacuum or reduced pressure conditions (0.1 atm or greater but less than 1 atm) for rapid evaporation of water. The heat treatment is intended to effectively evaporate water and can be performed at 80°C to 150°C or 100°C to 130°C.

[0068] Electrodes for secondary batteries

[0069] Another aspect of the present invention provides an electrode for a secondary battery, comprising:

[0070] Metal current collector;

[0071] An active material layer disposed on the metal current collector; and

[0072] An insulating coating that covers at least a portion of the uncoated portion, where the active material layer is not present, to at least a portion of the active material layer.

[0073] The metal current collector includes the uncoated portion, and

[0074] The insulating coating comprises inorganic particles and an aqueous adhesive replaced with a non-aqueous organic solvent.

[0075] The electrode for secondary batteries according to the invention has the advantage of inhibiting capacity expression by including an insulating coating with excellent wet adhesion, which prevents the migration of lithium ions in the overlapping region of the electrode.

[0076] In specific embodiments, the inorganic particles of the insulating coating 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.

[0077] In addition, the waterborne adhesive may be one or more selected from the group consisting of styrene-butadiene rubber, acrylated 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 a specific embodiment, the waterborne adhesive may be one or more selected from the group consisting of styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber. For example, the waterborne adhesive may be styrene-butadiene rubber.

[0078] In specific embodiments, the aqueous adhesive can be an aqueous adhesive replaced with a non-aqueous organic solvent, or a styrene-butadiene rubber replaced with an amide-based solvent, such as a styrene-butadiene rubber replaced with NMP solvent. More specifically, the insulating coating can be formed by applying the above-described insulating composition for the electrode of a secondary battery, such that the insulating composition covers at least a portion of the uncoated portion to at least a portion of the active material layer, and drying it at about 50°C to 300°C. In this case, in the insulating coating, the solvent is removed during the drying process, and the styrene-butadiene rubber dispersed in the solvent is replaced with NMP, thus allowing for the presence of NMP-replaced styrene-butadiene rubber.

[0079] In one embodiment, the insulating coating may 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 desired effect of enhancing safety by applying the insulating coating.

[0080] In addition, the electrode used for secondary batteries can be the positive electrode.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] Although there is no particular limitation on the average thickness of the active material layer, the average thickness can be specifically 0.1 μm to 20 μm, more specifically 0.1 μm to 15 μm, 0.1 μm to 10 μm, 2 μm to 10 μm, 4 μm to 10 μm, or 5 μm to 9 μm.

[0088] 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. Furthermore, fine random particles 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. Moreover, 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.

[0089] Lithium secondary batteries

[0090] Another aspect of the present invention provides a lithium secondary battery comprising the electrodes for a secondary battery described above according to the present invention.

[0091] As described above, the electrode for a secondary battery according to the present invention can be used as the positive electrode in the lithium secondary battery.

[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 coating 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 composition was obtained in the same manner as in Example 1, except that the amounts of inorganic particles and binder were varied during 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 insulating coatings

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

[0124] Metal samples including those with insulating coatings 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 coating was formed. For adhesion measurement, the metal sample, including the insulating coating formed therein, was cut to a size of 2 cm × 2 cm using a cutting device.

[0126] Application of ultrasound

[0127] 200g of liquid electrolyte (EC / EMC = 3 / 7 (vol%)) was placed in a 250ml 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: 20kHz

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

[0131] - Amplitude: 100%

[0132] (Peak-to-peak 132μm when using a 13mm 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 coatings of Examples 1 and 4, and Comparative Examples 1 and 2. Refer to Table 2 and... Figure 2 The electrode sample of Example 1 does not show swelling or detachment of the insulating coating. 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 coating. 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 coating of the embodiment has superior wet adhesion compared to the insulating coatings 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 coating 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 slurry for the positive electrode active material layer. The positive electrode slurry was then applied to 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 compositions obtained in Examples 1 to 3, and then dried in a convection oven (130°C) to form a 10 μm thick insulating coating 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 in a solvent (EC:DMC:DEC = 1:2:1).

[0146] [Table 3]

[0147] Insulating coating Battery Example 1 Example 5 Example 2 Example 6 Example 3 Example 7

[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 insulating coating 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 0.7C, 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 coating, 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. An insulating composition for an electrode, comprising: Water-based adhesives that replace non-aqueous organic solvents; and Inorganic particles, The weight ratio of the inorganic particles to the aqueous adhesive replaced by a non-aqueous organic solvent is 1:99 to 95:

5. The aqueous adhesive is an aqueous adhesive that has undergone solvent replacement with a non-aqueous organic solvent in the following manner: Aqueous binders dispersed in water are mixed with non-aqueous organic solvents; and Solvent replacement is performed by removing the water through heat treatment.

2. The insulating composition of claim 1, wherein the weight ratio of the inorganic particles to the aqueous adhesive replaced with a non-aqueous organic solvent is from 45:55 to 90:

10.

3. The insulating composition of claim 1, wherein the non-aqueous organic solvent is selected from one or more of the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate, 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, ethanol, and isopropanol.

4. The insulating composition of claim 1, 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 (SiC), and boron nitride (BN).

5. The insulating composition of claim 1, wherein the aqueous adhesive is selected from one or more of the group consisting of styrene-butadiene rubber, acrylated 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.

6. The insulating composition of claim 1, wherein the non-aqueous organic solvent is N-methylpyrrolidone, and the aqueous adhesive is styrene-butadiene rubber.

7. The insulating composition of claim 1, wherein the inorganic particles have an average particle diameter of 0.01 μm to 100 μm.

8. The insulating composition of claim 7, wherein the insulating composition comprises a first inorganic particle and a second inorganic particle having different particle diameters from each other, and has a bimodal particle size distribution.

9. The insulating composition of claim 1, wherein the insulating composition has a viscosity of 50 cP to 50,000 cP at 25°C.

10. The insulating composition of claim 1, wherein the non-aqueous organic solvent in the insulating composition is the same as the solvent in the slurry used to prepare the positive electrode.

11. A method for preparing an insulating composition for an electrode according to any one of claims 1 to 10, comprising: Aqueous adhesives dispersed in water are mixed with non-aqueous solvents; and Solvent replacement is performed by removing the water through heat treatment.

12. The method of claim 11, further comprising allowing the inclusion of inorganic particles after the solvent displacement.

13. The method of claim 12, wherein the weight ratio of the inorganic particles to the aqueous adhesive is 1:99 to 95:

5.

14. The method of claim 11, wherein the heat treatment in the solvent replacement is performed at 80°C to 150°C.

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