Electrode assembly and method of manufacturing the same, battery cell, battery, and electric device

Abstract

The application relates to the technical field of batteries, in particular to an electrode assembly and a preparation method thereof, a battery monomer, a battery and a power utilization device; the electrode assembly comprises a positive electrode, a negative electrode and a separator arranged between the positive electrode and the negative electrode; the separator comprises a base material layer and a bonding layer arranged on at least one side surface of the base material layer in the thickness direction, the thickness variation rate of the bonding layer is less than or equal to 50%, and the peeling force of the separator is greater than or equal to 1.5 N / m. Compared with the prior art, the thickness of the bonding layer in the electrode assembly is relatively uniform, the gaps and uneven stress in the bonding process are avoided, the effective contact area of the bonding layer is increased, the peeling force of the separator in the electrode assembly is ensured to reach certain bonding requirements, good interaction is realized as a whole, the dislocation and wrinkles between the electrode plate and the separator can be effectively avoided, the separator is tightly bonded with the electrode plate, the performance of the electrode assembly is good and stable, and the overall electrical performance, safety and cycle life of the battery monomer are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to an electrode assembly and its preparation method, a battery cell, a battery, and an electrical device. Background Technology

[0002] A power battery cell is a power source that provides power to tools, primarily referring to the battery cells that power electric vehicles, electric trains, electric bicycles, golf carts, and similar vehicles. Power battery cells are also a core component of new energy vehicles and represent an important direction for future energy transition.

[0003] Traditional power battery cells generally consist of positive and negative electrodes, a separator, and an electrolyte. Bonding the separator to the electrodes (positive and negative) creates a mechanically stable "sandwich" assembly (positive electrode-separator-negative electrode), which plays a crucial role in improving the performance, safety, and cycle life of the battery cell. However, in existing technologies, misalignment or wrinkles frequently occur between the electrodes and the separator, significantly affecting the tight adhesion between them and further impacting the performance of the electrode assembly. To address these technical issues, some researchers have adopted techniques to increase the bonding strength between the separator and the electrodes, but the challenges of misalignment and wrinkles remain unresolved. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides an electrode assembly and its preparation method, a battery cell, a battery, and an electrical device. By setting the thickness of the adhesive layer in the electrode assembly to be relatively uniform at various points and ensuring that the separator peel force meets certain adhesion requirements, misalignment and wrinkles between the electrode and the separator can be effectively avoided, resulting in a tight bond between the separator and the electrode, thereby ensuring good and stable performance of the electrode assembly.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0006] According to one aspect of the present invention, an electrode assembly is provided, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The separator includes a substrate layer and an adhesive layer disposed on at least one surface of the substrate layer along its thickness direction. The thickness variation rate of the adhesive layer is ≤50%, and the peel strength of the separator is ≥1.5 N / m.

[0007] In some embodiments, the thickness of the adhesive layer is 1 μm to 3 μm.

[0008] In some embodiments, the surface of the adhesive layer includes a plurality of adhesive points; among the plurality of adhesive points, the content of adhesive points with a diameter of 200μm to 300μm is ≥70%.

[0009] In some embodiments, the electrode assembly is a wound electrode assembly.

[0010] According to another aspect of the present invention, a method for preparing an electrode assembly is provided, comprising the following steps:

[0011] a) A first adhesive, a second adhesive, and a solvent are mixed to obtain a slurry; the slurry is then coated onto at least one side of the substrate layer along the thickness direction, and after drying, an adhesive layer is formed to obtain a diaphragm; the bonding temperature of the first adhesive is >90℃, and the bonding temperature of the second adhesive is -20℃ to 10℃;

[0012] b) The diaphragm obtained in step a) is placed between the positive and negative electrodes, assembled, and then pressed to obtain the electrode assembly.

[0013] In some of these implementations, in step a):

[0014] The first adhesive includes at least one of polyvinylidene fluoride, a copolymer of hexafluoropropylene and polyvinylidene fluoride, and polymethyl methacrylate;

[0015] And / or, the second adhesive comprises at least one of modified polyvinylidene fluoride, modified ethylene-vinyl acetate copolymer, and perfluoroacrylate modified ethyl acrylate;

[0016] And / or, the mass ratio of the first adhesive to the second adhesive is (20~50):(50~80);

[0017] And / or, the solvent includes at least one of water, N-methylpyrrolidone, and cyclohexanone;

[0018] And / or, the amount of solvent used is 1 to 8 times the total mass of the first adhesive and the second adhesive;

[0019] And / or, the mixing temperature is 15℃~35℃, the rotation speed is 1000rpm~2000rpm, and the time is 60min~180min;

[0020] And / or, the content of particles with a diameter of 4μm to 5μm in the slurry is 60% to 80%;

[0021] And / or, the viscosity of the slurry is 40 mPa·s to 100 mPa·s;

[0022] And / or, the coating method is spraying;

[0023] And / or, the amount of coating is 0.3 g / m 2 ~0.5g / m 2 ;

[0024] And / or, the drying temperature is 35°C to 60°C.

[0025] In some embodiments, the first adhesive is polyvinylidene fluoride; the second adhesive is perfluorobutyl ethyl acrylate modified ethyl acrylate; and the mass ratio of the first adhesive to the second adhesive is 30:70.

[0026] In some of these implementations, in step b):

[0027] The assembly method is either winding or stacking;

[0028] And / or, the pressing method is cold pressing; the temperature of the cold pressing is 15℃~35℃, the pressure is 5MPa~10MPa, and the time is 20s~30s.

[0029] According to another aspect of the present invention, the present invention provides a battery cell comprising the electrode assembly described in the above technical solution or the electrode assembly prepared by the preparation method described in the above technical solution.

[0030] According to another aspect of the present invention, the present invention provides a battery comprising the battery cell described in the above technical solution.

[0031] According to another aspect of the present invention, an electrical device is provided, comprising the battery described in the above technical solution.

[0032] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0033] 1. This invention sets the thickness of the adhesive layer in the electrode assembly to be relatively uniform, avoiding gaps and uneven stress during the bonding process, increasing the effective contact area of ​​the adhesive layer, and ensuring that the peel force of the separator in the electrode assembly meets certain bonding requirements. The whole assembly achieves better interaction, effectively avoiding misalignment and wrinkles between the electrode and the separator, and making the separator and the electrode tightly bonded. This results in good and stable performance of the electrode assembly, which is beneficial to improving the overall electrical performance, safety and cycle life of the battery cell.

[0034] 2. Furthermore, by adjusting the diameter and content of the slurry particles, this invention can improve the dispersibility of the particles, prevent uneven agglomeration of the particles in the adhesive layer, reduce porosity caused by uneven agglomeration, ensure suitable bonding points in the adhesive layer, and further improve the thickness uniformity of the adhesive layer.

[0035] 3. The electrode assembly preparation method provided by the present invention is simple, mild and easy to control, with low raw material and equipment costs, and does not use organic solvents or other raw materials, making it more environmentally friendly and with broad application prospects.

[0036] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0037] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0038] Figure 1 This is a SEM image of the adhesive layer surface in Example 1.

[0039] Figure 2 This is a SEM image of the adhesive layer surface in Comparative Example 1.

[0040] Figure 3 This is a SEM image of the adhesive layer surface in Comparative Example 3.

[0041] Figure 4 This is a schematic diagram of the thickness change rate test.

[0042] Figure 5 This is a schematic diagram of the wrinkle-free version of Example 1.

[0043] Figure 6 This is a schematic diagram of the octopus fold, a type of fold.

[0044] Figure 7 This is a schematic diagram of the thinned zone fold in the fold type.

[0045] Figure 8 This is a schematic diagram of a large-area fold in the fold type.

[0046] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0047] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0048] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0049] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0050] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0051] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0052] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0053] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0054] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0055] Currently, the inventors of this invention have discovered during the research and development process that misalignment and / or wrinkles frequently occur between the electrode plates and the diaphragm in the electrode assembly. This greatly affects the tight adhesion between the diaphragm and the electrode plates, and further affects the various performance characteristics of the electrode assembly. However, the existing technology does not yet have a clear technical solution for how to better solve the technical problem of misalignment and / or wrinkles between the diaphragm and the electrode plates.

[0056] Based on this, the inventors of this invention have effectively avoided misalignment and wrinkles between the electrode and the separator by ensuring that the thickness of the adhesive layer in the electrode assembly is relatively uniform throughout and that the peel force of the separator meets certain adhesion requirements. This results in a tight bond between the separator and the electrode, thereby ensuring good and stable performance of the electrode assembly. Specifically, this invention adopts the following technical solution:

[0057] According to one aspect of the present invention, an electrode assembly is provided, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The separator includes a substrate layer and an adhesive layer disposed on at least one surface of the substrate layer along its thickness direction. The thickness variation rate of the adhesive layer is ≤50%, and the peel strength of the separator is ≥1.5 N / m.

[0058] In a specific embodiment of the present invention, the diaphragm of the provided electrode assembly is disposed between the positive electrode and the negative electrode; the diaphragm includes a substrate layer and an adhesive layer, wherein the substrate layer can be any diaphragm substrate well known to those skilled in the art, and the present invention does not have any special restrictions on the type and source of the substrate layer, such as polyethylene (PE) base film, polypropylene (PP) base film, etc., and a ceramic layer can also be disposed on the above base film, and the present invention does not have any special restrictions on this.

[0059] In a specific embodiment of the present invention, the adhesive layer is disposed on at least one surface of the substrate layer along the thickness direction, preferably on both surfaces of the substrate layer along the thickness direction.

[0060] In this invention, the thickness variation rate of the adhesive layer is ≤50%, preferably ≤10%; the thickness variation rate here refers to the thickness variation rate of each layer and each layer of the inner and outer rings included in the electrode assembly, and the thickness variation rate = (maximum thickness - minimum thickness) / minimum thickness × 100%; a smaller thickness variation rate results in a more uniform thickness of the adhesive layer and better adhesion.

[0061] In addition to meeting the above-mentioned requirement for the change rate of adhesive layer thickness, the present invention further limits the peel force of the diaphragm to ≥1.5N / m, preferably ≥3N / m, thereby ensuring good adhesion performance.

[0062] Based on this, the present invention makes the thickness of the adhesive layer in the electrode assembly relatively uniform, avoiding gaps and uneven stress during the bonding process, increasing the effective contact area of ​​the adhesive layer, and ensuring that the separator peel force meets certain bonding requirements. The two achieve good overall interaction, thereby effectively avoiding misalignment and wrinkles between the electrode and the separator. More importantly, under the above technical effects, the separator and the electrode are tightly bonded, so that the various performances of the electrode assembly are good and stable, which is conducive to improving the overall electrical performance, safety and cycle life of the battery cell.

[0063] In a specific embodiment of the present invention, the thickness of the adhesive layer is preferably 1μm to 3μm. If the thickness is too large, the wettability is reduced, and the electrolyte will have difficulty fully wetting the adhesive surface during the subsequent preparation of battery cells, resulting in reduced strength of the separator adhesive layer, poor adhesion, and the possibility of wrinkles. If the thickness is too small, it is difficult to achieve a uniform thickness during the coating process due to process deviations.

[0064] In a specific embodiment of the present invention, the surface of the adhesive layer preferably includes a plurality of adhesive points; among the plurality of adhesive points, the content of adhesive points with a diameter of 200μm~300μm is preferably ≥70%, more preferably ≥77%. In the present invention, when the adhesive points are obtained according to the preferred spraying embodiment, they can also be called spray points, that is, microsphere aggregates formed on the surface of the adhesive layer after spraying. In the present invention, the above-mentioned content can be expressed by testing the percentage of the number of adhesive points in a certain area of ​​the adhesive layer surface that meet the corresponding diameter range to the total number of adhesive points in that area, which is convenient for actual testing and obtaining; at the same time, the test result can also reflect the overall condition of the adhesive layer surface. In the present invention, when the content of adhesive points with a diameter of 200μm~300μm meets the above-mentioned limitation, it can better play the bonding role, and the adhesive points are evenly dispersed, making the thickness of the adhesive layer more uniform throughout, and is conducive to the tight adhesion between the diaphragm and the electrode.

[0065] The present invention does not impose any special restrictions on the positive and negative electrodes; conventional technical solutions for positive and negative electrode plates that are well known to those skilled in the art can be used.

[0066] In a specific embodiment of the present invention, the positive electrode is specifically a positive electrode sheet, including a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector along the thickness direction; wherein, the positive electrode current collector may be a metal foil, foamed metal, or a composite current collector. For example, as a metal foil, silver-surfaced aluminum or stainless steel, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, or titanium, etc., may be used; the foamed metal may be foamed nickel, foamed copper, foamed aluminum, foamed alloy, etc.; the composite current collector may include a polymer material base layer and a metal layer, and the composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0067] In a specific embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material. The present invention does not impose any particular limitation on the specific type of the positive electrode active material; any active material known in the art that can be used as the positive electrode of a battery cell can be used. Those skilled in the art can select according to actual needs. Specifically, the positive electrode active material may include, but is not limited to, at least one of lithium transition metal oxides, lithium phosphates with an olivine structure, and their respective modified compounds; examples of lithium transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds; examples of lithium phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. These materials are all commercially available.

[0068] In specific embodiments of the present invention, the positive electrode active material layer may also include a positive electrode binder, a positive electrode conductive agent, and other optional additives. For example, the positive electrode binder may include at least one of styrene-butadiene rubber (SBR), waterborne acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB); the positive electrode conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers. These materials are all commercially available.

[0069] In a specific embodiment of the present invention, the preparation method of the positive electrode sheet adopts a method well known to those skilled in the art: first, the raw materials are mixed in a solvent in a certain proportion to form a slurry, and then the positive electrode slurry is coated on the positive electrode current collector. After drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0070] In a specific embodiment of the present invention, the negative electrode is specifically a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector along the thickness direction; wherein, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil; the composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate, and the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0071] In a specific embodiment of the present invention, the negative electrode active material layer includes a negative electrode active material. The present invention does not impose any particular limitation on the specific type of the negative electrode active material; any active material known in the art that can be used as the negative electrode of a battery cell can be used. Those skilled in the art can select according to actual needs. Specifically, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc.; wherein, the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys; the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. These materials are all commercially available.

[0072] In specific embodiments of the present invention, the negative electrode active material layer may also include a negative electrode binder, a negative electrode conductive agent, and other optional additives. For example, the negative electrode binder may include at least one of polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), and carboxymethyl chitosan (CMCS); the negative electrode conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers; other optional additives include thickeners (such as sodium carboxymethyl cellulose (CMC-Na)). These materials are all commercially available.

[0073] In a specific embodiment of the present invention, the method for preparing the negative electrode sheet adopts a method well known to those skilled in the art: first, the raw materials are mixed in a solvent in a certain proportion to form a slurry, and then the negative electrode slurry is coated on the negative electrode current collector. After drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0074] In a specific embodiment of the present invention, the electrode assembly is preferably a wound electrode assembly; compared with the stacked electrode assembly, the wound electrode assembly of the present invention has a simpler processing technology. Specifically: the above-mentioned positive electrode sheet, separator, and negative electrode sheet are arranged in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet, and then wound to form a wound structure. The shape of the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0075] In a specific embodiment of the present invention, the electrode assembly is provided with tabs, which can conduct current from the electrode assembly; the tabs include a positive tab and a negative tab.

[0076] According to another aspect of the present invention, a method for preparing an electrode assembly is provided, comprising the following steps:

[0077] a) Mix the adhesive and solvent to obtain a slurry; then coat the slurry onto at least one side of the substrate layer along the thickness direction, and after drying, form an adhesive layer to obtain a diaphragm;

[0078] b) The diaphragm obtained in step a) is placed between the positive and negative electrodes, assembled, and then pressed to obtain the electrode assembly.

[0079] This invention first mixes an adhesive and a solvent to obtain a slurry; then, the slurry is coated onto at least one surface of a substrate layer along its thickness direction, and after drying, an adhesive layer is formed to obtain a diaphragm; wherein the adhesive includes, but is not limited to, a first adhesive and / or a second adhesive well known to those skilled in the art. In a preferred embodiment of this invention, the adhesive includes a first adhesive and a second adhesive; based on this, this invention first mixes the first adhesive, the second adhesive, and a solvent to obtain a slurry.

[0080] In a specific embodiment of the present invention, the bonding temperature of the first adhesive is >90°C; the first adhesive preferably includes at least one of polyvinylidene fluoride (PVDF), hexafluoropropylene-polyvinylidene fluoride copolymer (HFP-PVDF), and polymethyl methacrylate (PMMA), more preferably polyvinylidene fluoride (PVDF); its microspheres have an initial particle size between 150 nm and 200 nm. The present invention does not impose any special restrictions on the source of the first adhesive; commercially available products well known to those skilled in the art can be used.

[0081] In a specific embodiment of the present invention, the bonding temperature of the second adhesive is -20℃ to 10℃; the second adhesive preferably includes at least one of modified polyvinylidene fluoride (modified PVDF), modified ethylene-vinyl acetate copolymer (modified EVA), and perfluoroacrylate modified ethyl acrylate, more preferably perfluoroacrylate modified ethyl acrylate; wherein, modified PVDF includes, but is not limited to, acrylic acid modified PVDF, methacrylic acid modified PVDF, and butyl acrylate modified PVDF; modified EVA includes, but is not limited to, maleic anhydride modified EVA and glycidyl methacrylate modified EVA; and perfluoroacrylate modified ethyl acrylate includes, but is not limited to, perfluoroalkyl ethyl acrylate modified ethyl acrylate, perfluorobutyl ethyl acrylate modified ethyl acrylate, perfluorohexyl ethyl acrylate modified ethyl acrylate, and perfluorooctyl ethyl acrylate modified ethyl acrylate. The present invention does not impose any special restrictions on the source of the second adhesive; commercially available products well known to those skilled in the art can be used.

[0082] It should be noted that the bonding temperature described in this invention is the lowest temperature at which the adhesive can achieve a bonding effect.

[0083] In a specific embodiment of the present invention, the preferred mass ratio of the first adhesive to the second adhesive is (20~50):(50~80); specifically, it can be 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, or 50:50, etc. By using the above-mentioned ratio of the first adhesive to the second adhesive, the present invention can achieve better uniformity of adhesive layer thickness and bonding performance.

[0084] In a preferred embodiment of the present invention, the first adhesive is polyvinylidene fluoride (PVDF), and the second adhesive is perfluorobutyl ethyl acrylate modified ethyl acrylate, with a mass ratio of 30:70 between the first adhesive and the second adhesive. The present invention employs the above-mentioned optimal material types and ratios, resulting in superior adhesive layer thickness uniformity and bonding performance.

[0085] In a specific embodiment of the present invention, the solvent preferably includes at least one of water, N-methylpyrrolidone (NMP), and cyclohexanone, more preferably water; the present invention does not have any particular limitation on this, as long as it can be mixed with the above-mentioned first binder and second binder to obtain a slurry.

[0086] In a specific embodiment of the present invention, the amount of solvent is preferably 1 to 8 times the total mass of the first binder and the second binder; specifically, it can be 1, 2, 3, 4, 5, 6, 7, or 8 times, etc. Based on this, a slurry with a suitable viscosity can be obtained.

[0087] In a specific embodiment of the present invention, the viscosity of the slurry is preferably 40 mPa·s to 100 mPa·s, specifically 40 mPa·s, 50 mPa·s, 60 mPa·s, 70 mPa·s, 80 mPa·s, 90 mPa·s, or 100 mPa·s. Lower slurry viscosity results in better rheology, higher process adaptability, better mixing, conveying, and coating, reduced coating defects, improved coating uniformity and yield, and improved uniformity of the adhesive layer thickness. However, if the viscosity is too low, the slurry stability is poor, and particles are more prone to agglomeration and unevenness. Conversely, if the viscosity is too high, it hinders bubbles from rising to the surface and breaking down, leaving a large number of bubbles inside the slurry, affecting the identification function of the coating equipment, causing inaccurate flow rates, and resulting in uneven coating thickness.

[0088] In a specific embodiment of the present invention, the mixing process is preferably carried out under stirring; the mixing temperature is preferably 15℃~35℃, the rotation speed is preferably 1000rpm~2000rpm, and the time is preferably 60min~180min; the present invention uses the above conditions and parameters to ensure that the first binder and the second binder are mixed and dispersed evenly in the solvent, thereby obtaining the desired slurry.

[0089] In a specific embodiment of the present invention, the content of particles with a diameter of 4μm to 5μm in the slurry is preferably 60% to 80%. In this invention, the above content can be expressed as the percentage of the number of particles with a diameter of 4μm to 5μm in a test portion of the slurry relative to the total number of particles in the test slurry, facilitating actual testing and obtaining the results. Simultaneously, the test results can also reflect the overall condition of the slurry. In this invention, when the particle diameter is within this range, it can better play a bonding role. If the diameter is too large, it is easy to cause excessively high local thickness, making it difficult to control the uniformity of the thickness; if the diameter is too small, the surface tension of the particles is large, and the particles are easily attracted to each other and aggregate together. When the content of particles with a diameter of 4μm to 5μm is within the above range, the particle dispersion is relatively uniform, and the thickness of the bonding layer is also relatively uniform throughout.

[0090] This invention improves particle dispersibility by controlling the particle diameter and particle content of the slurry, prevents uneven agglomeration of particles in the adhesive layer, reduces porosity caused by uneven agglomeration, ensures suitable bonding points in the adhesive layer, and further improves the thickness uniformity of the adhesive layer.

[0091] After obtaining the slurry, the present invention coats the slurry onto at least one surface of the substrate layer along the thickness direction, and after drying, forms an adhesive layer to obtain a diaphragm; preferably, the present invention coats the slurry onto both surfaces of the substrate layer along the thickness direction, and after drying, forms adhesive layers on the upper and lower surfaces of the substrate layer respectively to obtain a diaphragm.

[0092] In a specific embodiment of the present invention, the coating method is preferably spraying. In the present invention, spraying is a non-contact coating, which avoids scratches and indentations introduced by physical contact. Spraying atomizes the liquid into tiny particles through ultrasonic vibration, which further enhances the uniformity of particle dispersion, improves the thickness uniformity and adhesion effect of the adhesive layer, and avoids the risk of peeling caused by excessively large particles in traditional coating. Uniform spraying also reduces defects such as pinholes and fisheyes in the coating caused by slurry aggregation or bubbles. The resulting separator has a higher surface quality and fewer defects, which improves the overall reliability of the separator and the safety of the battery cell (reducing the risk of short circuits caused by separator defects).

[0093] In a specific embodiment of the present invention, the coating amount is preferably 0.3 g / m 2 ~0.5g / m 2 This invention does not impose any special limitations on this.

[0094] In specific embodiments of the present invention, the present invention does not have any special restrictions on the type and source of the substrate layer, and any membrane substrate well known to those skilled in the art can be used; for example, it can be a polyethylene (PE) base film, a polypropylene (PP) base film, etc., and a ceramic layer can also be provided on the above base film. The present invention does not have any special restrictions on this, such as the material of the ceramic layer being alumina well known to those skilled in the art.

[0095] In a specific embodiment of the present invention, the drying temperature is preferably 35℃~60℃; the time is adjusted according to the actual situation until the surface is dry; thereby obtaining the adhesive layer; the thickness of the adhesive layer is preferably 1μm~3μm.

[0096] After obtaining the diaphragm, the present invention places the diaphragm between the positive and negative electrodes, assembles them, and then presses them to obtain the electrode assembly. In the present invention, the positive and negative electrodes are the same as those described in the above technical solution, and will not be repeated here.

[0097] In a specific embodiment of the present invention, the assembly method is preferably winding or stacking, more preferably winding; after assembly, an initial electrode is formed, and then pressed to obtain an electrode assembly.

[0098] In a specific embodiment of the present invention, the pressing method is preferably cold pressing; the temperature of the cold pressing is preferably 15℃~35℃, specifically 15℃, 20℃, 25℃, 30℃ or 35℃, etc.; the pressure of the cold pressing is preferably 5MPa~10MPa, specifically 5MPa, 6MPa, 7MPa, 8MPa, 9MPa or 10MPa, etc.; the time of the cold pressing is preferably 20s~30s, specifically 20s, 25s or 30s, etc.

[0099] The electrode assembly preparation method provided by this invention is simple, mild and easy to control, has low raw material and equipment costs, and does not use organic solvents or other raw materials, making it more environmentally friendly and with broad application prospects.

[0100] According to another aspect of the present invention, a battery cell is provided, comprising the electrode assembly described in the above-described technical solutions or the electrode assembly prepared by the preparation method described in the above-described technical solutions. Thus, the battery cell possesses all the features and advantages of the electrode assembly described in the above-described technical solutions, which will not be repeated here. Specifically, the electrode assembly is manufactured from a positive electrode, a negative electrode, and a separator through a winding process or a stacking process.

[0101] In a specific embodiment of the present invention, the number of electrode components contained in the battery cell can be one or more, and those skilled in the art can select according to specific actual needs.

[0102] In a specific embodiment of the present invention, the battery cell further includes an electrolyte. During the charging and discharging process of the battery cell, active ions repeatedly insert and extract between the positive and negative electrodes; the electrolyte plays a role in conducting ions between the positive and negative electrodes; the separator is disposed between the positive and negative electrodes, mainly to prevent short circuits between the positive and negative electrodes, while allowing ions to pass through.

[0103] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This invention does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0104] In a specific embodiment of the present invention, the electrolyte is an electrolyte solution; the electrolyte solution comprises an electrolyte salt and a solvent; wherein, the electrolyte salt preferably comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate, more preferably lithium hexafluorophosphate; the solvent preferably... The ester may include one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone, more preferably ethylene carbonate and diethyl carbonate.

[0105] In a specific embodiment of the present invention, the electrolyte preferably further includes film-forming additives, such as negative electrode film-forming additives and positive electrode film-forming additives, and may also include additives that can improve certain properties of battery cells, such as additives that improve the overcharge performance of battery cells, additives that improve the high-temperature or low-temperature performance of battery cells, etc.

[0106] In a specific embodiment of the present invention, the battery cell may include an outer packaging, which can be used to encapsulate the aforementioned electrode assembly and electrolyte. The outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. Specifically, the hard shell may include a housing and a cover plate, wherein the housing may include a bottom plate and a side plate connected to the bottom plate, the bottom plate and the side plate forming a receiving cavity, the housing having an opening communicating with the receiving cavity, and the cover plate being able to cover the opening to close the receiving cavity, the electrode assembly being encapsulated in the aforementioned receiving cavity, and the electrolyte being immersed in the electrode assembly; it may also be a soft package, such as a pouch soft package; the material of the soft package may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0107] The present invention does not impose any particular restrictions on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape, and those skilled in the art can choose according to specific practical needs.

[0108] According to another aspect of the present invention, a battery is provided, comprising the battery cell described in the above-described technical solution. Thus, the battery possesses all the features and advantages of the battery cell described in the above-described technical solution, which will not be repeated here.

[0109] In a specific embodiment of the present invention, the battery can be a battery module assembled from individual battery cells. The battery module can contain one or more battery cells, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In the battery module, the multiple battery cells can be arranged sequentially along the length of the battery module; of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells can be fixed using fasteners. The battery module may also include a housing with a receiving space, in which the multiple battery cells are received.

[0110] In the description of this invention, "a plurality of" means two or more.

[0111] In a specific embodiment of the present invention, the battery can also be a battery pack assembled from the aforementioned battery modules. The battery pack may contain one or more battery modules, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack. Specifically, the battery pack may include a battery box and multiple battery modules disposed within the battery box; the battery box includes an upper box and a lower box, the upper box covering the lower box and forming a closed space for accommodating the battery modules. The multiple battery modules can be arranged in the battery box in any manner.

[0112] According to another aspect of the present invention, an electrical device is provided, comprising the battery described in the above-described technical solution. Thus, the electrical device possesses all the features and advantages of the battery described in the above-described technical solution, which will not be repeated here. Specifically, the battery can serve as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, and energy storage systems.

[0113] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0114] Example 1

[0115] S1: Preparation of slurry: The first binder and the second binder are mixed and dispersed in solvent water at a mass ratio of 30:70. The mixing and dispersion temperature is 25℃, the rotation speed is 1500rpm, and the time is 120min to obtain the slurry. The first binder is PVDF with a bonding temperature of 140℃, and the second binder is perfluorobutyl ethyl acrylate modified ethyl acrylate with a bonding temperature of -18℃. The amount of solvent used is 4.0 times the total mass of the first binder and the second binder. The viscosity of the slurry is 60mPa·s. The content of particles with a diameter of 4μm~5μm in the slurry is shown in Table 2 below.

[0116] S2: The slurry obtained in step S1 is sprayed onto both sides of the substrate layer along its thickness direction. The substrate layer includes a base film and a ceramic layer disposed on the base film. The base film is made of PE, and the ceramic layer is made of alumina. The thickness of the base film is 7 μm, and the thickness of the ceramic layer is 2 μm. The coating amount is 0.40 g / m². 2Dry at 50°C to form a diaphragm containing an adhesive layer, wherein the thickness of the adhesive layer is 3.0 μm.

[0117] S3: The positive electrode, negative electrode and the separator obtained in step S2 are arranged in sequence, so that the separator is located between the positive and negative electrodes, and after being wound, an initial electrode assembly is formed; then the initial electrode assembly is subjected to cold pressing treatment at a temperature of 25°C, a pressure of 6MPa and a time of 20s to obtain the electrode assembly.

[0118] Among them, the positive electrode current collector is aluminum foil, the positive electrode active material layer is positive electrode active material (lithium iron phosphate): positive electrode conductive agent (SP): positive electrode binder (PVDF) = 97.0:1:2.

[0119] Negative electrode: The negative electrode current collector is copper foil, and the negative electrode active material layer is composed of negative electrode active material (graphite): negative electrode conductive agent (SP): negative electrode binder (PAN) = 96.7:1:2.3.

[0120] Example 2

[0121] The preparation method provided in Example 1 was adopted, with the only difference being that in S1, the first binder was replaced with PMMA and the bonding temperature was 105°C, and the second binder was replaced with maleic anhydride modified EVA and the bonding temperature was -15°C; finally, the electrode assembly was obtained.

[0122] Example 3

[0123] The preparation method provided in Example 1 is used, with the only difference being that in S1, the mass ratio of the first binder and the second binder is 20:80; finally, the electrode assembly is obtained.

[0124] Example 4

[0125] The preparation method provided in Example 1 is used, with the only difference being that in S1, the mass ratio of the first binder and the second binder is 50:50; and finally, the electrode assembly is obtained.

[0126] Example 5

[0127] The preparation method provided in Example 1 was used, with the only difference being that in S1, the amount of solvent used was 4.5 times the total mass of the first binder and the second binder, and the viscosity of the slurry was 40 mPa·s; finally, the electrode assembly was obtained.

[0128] Example 6

[0129] The preparation method provided in Example 1 is adopted, with the only difference being that in S1, the amount of solvent is 3.0 times the total mass of the first binder and the second binder, and the viscosity of the slurry is 100 mPa·s; finally, the electrode assembly is obtained.

[0130] Example 7

[0131] The preparation method provided in Example 1 is adopted, with the only difference being that in S3, the initial electrode assembly is subjected to cold pressing treatment at a temperature of 15°C, a pressure of 6 MPa, and a time of 20 s; the electrode assembly is finally obtained.

[0132] Example 8

[0133] The preparation method provided in Example 1 is adopted, with the only difference being that in S3, the initial electrode assembly is subjected to cold pressing treatment at a temperature of 35°C, a pressure of 6 MPa, and a time of 20 s; the electrode assembly is finally obtained.

[0134] Example 9

[0135] The preparation method provided in Example 1 is used, with the difference including steps S1 and S2: PVDF is dissolved in acetone, mixed with alumina to form a slurry, and the slurry is coated on both sides of the base film to a thickness of 1.5 μm and a coating weight of 0.30 g / m². 2 Then, extract and create pores using a water-based material tank, and dry in an oven to obtain an oily PVDF membrane; step S3 is the same as in Example 1, and finally the electrode assembly is obtained.

[0136] Comparative Example 1

[0137] The preparation method provided in Example 1 is adopted, with the difference including step S1: the first binder and the auxiliary binder are mixed and dispersed in solvent water at a mass ratio of 80:20 to obtain a slurry. The first binder is PVDF with a bonding temperature of 140°C, the auxiliary binder is acrylic acid-acrylonitrile copolymer (PAA-PAN) binder with a bonding temperature of 110°C, the amount of solvent is 4.0 times the total mass of the first binder and the auxiliary binder, and the viscosity of the slurry is 70 mPa·s. The content of particles with a diameter of 4μm~5μm in the slurry is shown in Table 2 below.

[0138] Steps S2 and S3 are the same as in Example 1, and the electrode assembly is finally obtained.

[0139] Comparative Example 2

[0140] The preparation method provided in Example 1 is used, with the only difference being that in S1, the mass ratio of the first binder and the second binder is 15:85; finally, the electrode assembly is obtained.

[0141] Comparative Example 3

[0142] The preparation method provided in Example 1 is used, with the only difference being that in S1, the mass ratio of the first binder and the second binder is 60:40; and finally, the electrode assembly is obtained.

[0143] Comparative Example 4

[0144] The preparation method provided in Example 1 is used, except that in S2, the coating method is changed from spraying to roller coating; finally, the electrode assembly is obtained.

[0145] Test method:

[0146] Percentage of particles with a diameter of 4μm to 5μm in the slurry: percentage of particle size measured by particle size testing instrument.

[0147] The content of bonding points with a diameter of 200μm~300μm on the surface of the adhesive layer was measured by SEM.

[0148] Peel strength: The coated diaphragm is wound together with the positive and negative electrode sheets by a winding machine and pressed. The diaphragm and electrode sheets are then sampled and placed in an electrolyte solvent (the electrolyte solvent is composed of ethylene carbonate (EC), diethyl carbonate (DEC), propyl propionate (PP), and propylene carbonate (PC), with a mass ratio of EC:DEC:PP:PC of 2:2:3:3) and immersed at 45°C for 24 hours. The 180° peel strength of the electrode sheets and diaphragm is then tested using a universal tensile testing machine.

[0149] Thickness change rate: See Figure 4 As shown, the MD direction is the winding direction of the electrode assembly diaphragm, and the TD direction is the width direction of the electrode assembly diaphragm. Multiple thickness detection points are set for the adhesive layer with different numbers of turns in the electrode assembly to obtain the thickness data at each point. The thickness change rate is calculated according to the following formula:

[0150] Thickness change rate = (maximum thickness - minimum thickness) / minimum thickness × 100%.

[0151] Battery cell cycle capacity retention rate: The battery cell is charged at a constant temperature of 25℃ and constant current and constant voltage at 1 / 3C to 3.65V, with a cutoff current of 0.05C; it is then left to stand for 30 minutes and discharged at 1 / 3C to 2.5V. The above steps are repeated to continuously perform charge and discharge cycles. The capacity retention rate = discharge capacity of the 1000th cycle / discharge capacity of the first cycle.

[0152] Test results:

[0153] Table 1. Data on the thickness variation rate of the adhesive layer

[0154]

[0155]

[0156] Table 2. Content of particles with diameters of 4μm~5μm in the slurry, content of bonding points with diameters of 200μm~300μm on the surface of the adhesive layer, and data on cycle retention rate.

[0157]

[0158] The SEM image of the adhesive layer surface in Example 1 is shown below. Figure 1 As shown, the SEM image of the adhesive layer surface in Comparative Example 1 can be found in [reference needed]. Figure 2 As shown, the SEM image of the adhesive layer surface in Comparative Example 3 is available in [reference]. Figure 3 As shown in the above SEM image, the influence of different particle size distributions in the slurry on the uniformity of bonding points on the surface of the adhesive layer can be seen.

[0159] Table 3. Data on peeling force, misalignment, and wrinkling.

[0160]

[0161] Note: When the wrinkle length is greater than 1 / 5 of the electrode width, it is an obvious defective product and is not included in the wrinkle grade classification; when the wrinkle length is less than or equal to 1 / 5 of the electrode width, the wrinkle grade classification shall be carried out in accordance with Table 4.

[0162] Table 4 Classification of Fold Grades

[0163]

[0164] Note: If two or more fold types meet this level, it is determined to be at this level; see the schematic diagram of no folds in Example 1. Figure 5 As shown, see the schematic diagrams for each type of fold. Figures 6-8 As shown, the octopus is a type of folding, and its shape is similar to that of an octopus, extending in all directions.

[0165] Experimental results show that the thickness change rate of the adhesive layer in Examples 1-9 is ≤10%. Comparison of Examples 1, 7, and 8 shows that the lower the cold pressing temperature, the worse the fluidity of the adhesive, the lower the molecular activity, and the less likely it is to rapidly rearrange to form a sufficiently dense and strong network structure under this temperature condition, resulting in low cohesive strength and a reduced thickness compression ratio. In Comparative Example 1, the particle size distribution of the conventional hot-pressing adhesive slurry is uneven, the thickness of the sprayed diaphragm varies greatly, and the thickness rebounds after winding and cold pressing, with little change in thickness after cold pressing compared to the initial sprayed thickness. In Comparative Example 4, the roller coating process results in uneven coating thickness distribution, large differences in film thickness, and small particles arranged individually on the base film surface, which easily causes pore blockage on the base film surface and excessive air permeability. In addition, in Example 9, the oily diaphragm uses organic solvents such as acetone. Although the thickness consistency and adhesion are good, the preparation conditions require high environmental conditions and are not environmentally friendly, resulting in high coating costs.

[0166] In summary, this invention achieves relatively uniform thickness of the adhesive layer of the separator in the electrode assembly, avoiding voids and stress unevenness during the bonding process, increasing the effective contact area of ​​the adhesive layer, and ensuring that the peel force of the separator in the electrode assembly meets certain bonding requirements, resulting in better overall interaction and effectively preventing misalignment and wrinkles between the electrode and the separator. Simultaneously, by controlling the diameter and content of the slurry particles, the dispersibility of the particles can be improved, preventing uneven agglomeration in the adhesive layer, reducing porosity caused by uneven agglomeration, and ensuring suitable bonding points in the adhesive layer, further improving the thickness uniformity of the adhesive layer. Furthermore, the cycle retention data shows that the electrode assembly provided by this invention also has good electrical performance, which is beneficial to improving the overall electrical performance, safety, and cycle life of the battery cell.

[0167] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0168] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0169] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0170] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wound electrode assembly, characterized in that, The device includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The separator includes a substrate layer and an adhesive layer disposed on at least one surface of the substrate layer along the thickness direction. The thickness variation rate of the adhesive layer is ≤10%. The peel strength of the separator is ≥1.5 N / m. The method for testing the thickness change rate includes: setting multiple thickness detection points for the adhesive layer with different numbers of turns in the wound electrode assembly, obtaining the thickness data at each point, and calculating the thickness change rate according to the following formula: Thickness change rate = (maximum thickness - minimum thickness) / minimum thickness × 100%; The adhesive layer comprises a first adhesive and a second adhesive in a mass ratio of (20~50):(50~80); the bonding temperature of the first adhesive is >90℃, and the bonding temperature of the second adhesive is -20℃~10℃.

2. The wound electrode assembly according to claim 1, characterized in that, The thickness of the adhesive layer is 1μm to 3μm.

3. The wound electrode assembly according to claim 1, characterized in that, The surface of the adhesive layer includes a plurality of adhesive points; among the plurality of adhesive points, the content of adhesive points with a diameter of 200μm to 300μm is ≥70%.

4. A method for preparing a wound electrode assembly according to any one of claims 1 to 3, characterized in that, Includes the following steps: a) A first adhesive, a second adhesive, and a solvent are mixed to obtain a slurry; the slurry is then coated onto at least one side of the substrate layer along the thickness direction, and after drying, an adhesive layer is formed to obtain a diaphragm; the bonding temperature of the first adhesive is >90℃, and the bonding temperature of the second adhesive is -20℃ to 10℃; b) The diaphragm obtained in step a) is placed between the positive and negative electrodes, assembled, and then pressed to obtain a wound electrode assembly.

5. The preparation method according to claim 4, characterized in that, In step a), at least one item satisfies the sequence number range: (1) The first adhesive comprises at least one of polyvinylidene fluoride, a copolymer of hexafluoropropylene and polyvinylidene fluoride, and polymethyl methacrylate; (2) The second adhesive includes at least one of modified polyvinylidene fluoride, modified ethylene-vinyl acetate copolymer, and perfluoroacrylate modified ethyl acrylate; (3) The mass ratio of the first adhesive to the second adhesive is (20~50):(50~80); (4) The solvent includes at least one of water, N-methylpyrrolidone, and cyclohexanone; (5) The amount of solvent used is 1 to 8 times the total mass of the first adhesive and the second adhesive; (6) The mixing temperature is 15℃~35℃, the rotation speed is 1000rpm~2000rpm, and the time is 60min~180min; (7) The content of particles with a diameter of 4μm to 5μm in the slurry is 60% to 80%; (8) The viscosity of the slurry is 40 mPa·s to 100 mPa·s; (9) The coating method is spraying; (10) The amount of coating is 0.3 g / m 2 ~0.5g / m 2 ; (11) The drying temperature is 35℃~60℃.

6. The preparation method according to claim 5, characterized in that, The first adhesive is polyvinylidene fluoride; the second adhesive is perfluorobutyl ethyl acrylate modified ethyl acrylate; the mass ratio of the first adhesive to the second adhesive is 30:

70.

7. The preparation method according to claim 4, characterized in that, In step b): The pressing method is cold pressing; the temperature of the cold pressing is 15℃~35℃, the pressure is 5MPa~10MPa, and the time is 20s~30s.

8. A single battery cell, characterized in that, This includes the wound electrode assembly as described in any one of claims 1 to 3 or the wound electrode assembly prepared by the preparation method described in any one of claims 4 to 7.

9. A battery, characterized in that, Includes the battery cell as described in claim 8.

10. An electrical appliance, characterized in that, Includes the battery as described in claim 9.

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