Composite diaphragm, preparation method thereof, battery and electric device

Abstract

This invention provides a composite separator, its preparation method, a battery, and an electrical device. The composite separator includes a base film layer and a functional modification layer disposed on at least one surface of the base film layer. The functional modification layer includes modified ceramics and modified sepiolite fibers. The modified ceramics include ceramic particles and polydopamine coated on the surface of the ceramic particles. The modified sepiolite fibers include sepiolite fibers and a silane coupling agent coated on the surface of the sepiolite fibers. The composite separator not only exhibits excellent heat resistance but also high mechanical strength, high peel strength, and excellent ionic conductivity, while demonstrating outstanding cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a composite separator and its preparation method, as well as a battery and an electrical device. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and many other fields due to their advantages such as high energy density and long cycle life. The separator, as one of the key components of the battery, plays a crucial role in isolating the positive and negative electrodes and providing microporous channels for ion transport; its performance is closely related to the electrochemical performance of the lithium-ion battery. An ideal separator should possess high electrolyte wettability and excellent electrochemical and thermal stability. Currently, commercially available separator materials largely focus on polyolefin materials, such as polyethylene (PE) and polypropylene (PP), mainly due to their low cost, suitable mechanical strength, and good chemical and electrochemical stability. However, the poor thermal stability and electrolyte wettability of polyolefin materials limit their broader application potential.

[0003] To address this issue, modification methods for this material have been developed, with surface coating modification considered a relatively effective means to improve the electrolyte wetting performance and heat resistance of polyolefin separators. However, current coatings still suffer from poor mechanical strength and weak adhesion to the substrate, posing a risk of detachment from the substrate during battery charge-discharge cycles and aging, which could potentially lead to battery performance degradation.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] In view of the above, this application provides a composite separator, a method for preparing the same, a battery, and an electrical device to solve at least one problem existing in the prior art.

[0006] A first aspect of the present invention provides a composite separator, the composite separator comprising a base film layer and a functional modification layer disposed on at least one surface of the base film layer; wherein,

[0007] The functional modification layer includes modified ceramics and modified sepiolite fibers; the modified ceramics include ceramic particles and polydopamine coated on the surface of the ceramic particles; the modified sepiolite fibers include sepiolite fibers and silane coupling agents coated on the surface of the sepiolite fibers.

[0008] Preferably, the composite membrane satisfies at least one of the following features (1) to (7):

[0009] (1) The base membrane is a polyolefin microporous membrane, which is selected from at least one of polyethylene membrane, polypropylene membrane, and composite membrane of polyethylene and polypropylene;

[0010] (2) The ceramic particles in the modified ceramic are selected from at least one of alumina, boehmite, zirconium oxide, silicon oxide, magnesium oxide, titanium oxide, zinc oxide, calcium oxide, barium sulfate, aluminum hydroxide, magnesium hydroxide, silicon nitride, boron nitride, aluminum nitride, silicon carbide, LATP, LAGP, LLZO, and LCZP; the particle size of the modified ceramic is 100 nm to 3 μm.

[0011] (3) The silane coupling agent is selected from at least one of vinyltriethoxysilane, vinyltrimethoxysilane, methacryloxytrimethoxysilane, methacryloxytriethoxysilane, propenyltrimethoxysilane, and propenyltriethoxysilane;

[0012] (4) In the modified sepiolite fiber, the length of the sepiolite fiber is 0.5μm to 2μm and the diameter of the sepiolite fiber is 5nm to 50nm;

[0013] (5) The mass ratio of the modified ceramic to the modified sepiolite fiber is (10-17):(0.5-8);

[0014] (6) The thickness of the base film layer is 3μm to 20μm;

[0015] (7) The thickness of the modified functional layer is 0.5μm to 5.5μm.

[0016] A second aspect of the present invention provides a method for preparing the composite membrane described in the first aspect of the present invention, the method comprising the following steps:

[0017] S1: Preparation of the modified ceramic: Add the modifier to a mixed solution of ethanol and Tris buffer to obtain a modifier solution, add ceramic particles to obtain the modified ceramic;

[0018] Preparation of the modified sepiolite fiber: Add silane coupling agent to anhydrous ethanol, then add sepiolite fiber to obtain sepiolite fiber suspension, adjust pH, react, and obtain the modified sepiolite fiber.

[0019] S2: Add the modified ceramic and modified sepiolite fiber obtained in step S1 to deionized water, and then add an adhesive to obtain a suspension.

[0020] S3: Add crosslinking agent and catalyst to the suspension obtained in step S2 to obtain functional modified layer slurry;

[0021] S4: The functional modified layer slurry obtained in step S3 is coated on at least one side of the base membrane layer to obtain the composite membrane.

[0022] Preferably, the step of preparing the modified ceramic satisfies at least one of the following features (1) to (3):

[0023] (1) The volume ratio of the ethanol to the Tris buffer is (0.5-2):1;

[0024] (2) The concentration of the modifier in the modifier solution is 2mM to 15mM, and the modifier is dopamine hydrochloride;

[0025] (3) After the step of adding ceramic particles, the steps of stirring, filtering, washing and drying are also included.

[0026] Preferably, the step of preparing the modified sepiolite fiber satisfies at least one of the following features (1) to (4):

[0027] (1) In the sepiolite fiber suspension, the mass ratio of the silane coupling agent to the sepiolite fiber is (5-15):1; the sepiolite fiber accounts for 20%-40% of the total mass of the sepiolite fiber suspension;

[0028] (2) The pH adjustment is performed by using ammonia water to adjust the pH, and the pH of the sepiolite fiber suspension after adjustment is 9 to 11;

[0029] (3) The reaction is carried out under heating conditions, the heating temperature is 70℃~90℃, and the heating time is 2h~3h;

[0030] (4) The reaction also includes washing, filtering and drying steps.

[0031] Preferably, step S2 satisfies at least one of the following features (1) to (5):

[0032] (1) The modified ceramic and modified sepiolite fiber account for 20% to 50% of the total mass of the suspension;

[0033] (2) Based on the total mass of solids in the suspension being 100%, the mass percentage of the modified sepiolite fiber is 5% to 40%, the mass percentage of the modified ceramic is 50% to 90%, and the mass percentage of the adhesive is 3% to 10%.

[0034] (3) The adhesive is selected from one or more of polyvinyl alcohol, polymethyl methacrylate, polybutyl methacrylate, polyacrylonitrile, polyethyl acrylate, polyvinyl acetate, polyacrylate, polyurethane, and urethane to form a mixture or copolymer;

[0035] (4) The substances added simultaneously with the adhesive also include a thickener; the mass percentage of the thickener is 0.01% to 5% based on the total mass of solids in the suspension being 100%; the thickener is selected from at least one of sodium carboxymethyl cellulose, sodium hydroxypropyl methyl cellulose, sodium hydroxyethyl cellulose, sodium alginate, and guar gum;

[0036] (5) The substances added at the same time as the adhesive also include additives; the mass percentage of the additives is 0.01% to 0.5% based on the total mass of solids in the suspension being 100%; the additives are selected from at least one of fatty alcohol polyoxyethylene ether, sodium butadiene naphthalene sulfonate, sodium hydroxyethyl sulfonate, sodium dodecylbenzene sulfonate, stearic acid, and fatty acid glycerides.

[0037] Preferably, in step S3, the crosslinking agent is selected from at least one of glutaraldehyde, formaldehyde, paraformaldehyde, and epichlorohydrin, and the amount of the crosslinking agent added accounts for 5% to 20% of the total mass of the suspension.

[0038] Preferably, in step S3, the catalyst is selected from at least one of hydrochloric acid, oxalic acid, and phosphoric acid, and the amount of catalyst added accounts for 0.01% to 10% of the total mass of the suspension.

[0039] Preferably, in step S4, after the coating is completed, a drying step is further included, wherein the drying temperature is 40℃~90℃ and the drying time is 10min~80min;

[0040] Preferably, in step S4, the coating method is microgravure coating, extrusion coating, wire rod coating, dip coating, or slot coating.

[0041] A third aspect of the present invention provides a battery comprising a separator, wherein the separator is a composite separator as described in the first aspect of the present invention or a composite separator prepared by the preparation method described in the second aspect of the present invention.

[0042] A fourth aspect of the present invention provides an electrical device comprising the battery described in the third aspect of the present invention.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] This invention provides a composite separator, its preparation method, a battery, and an electrical device. The composite separator not only possesses excellent heat resistance, but also high mechanical strength, high peel strength, and excellent ionic conductivity, while exhibiting outstanding cycle stability. Specific features are as follows:

[0045] (1) The functional modification layer of the composite membrane includes a ceramic material coated with polydopamine and sepiolite fiber coated with a silane coupling agent. The surfaces of these two materials are rich in polar functional groups such as hydroxyl and amino groups, which effectively improves the wettability of the composite membrane to the electrolyte and its ionic conductivity.

[0046] (2) Ceramic particles, polydopamine, and sepiolite fibers all have excellent thermal stability, and their combined effect significantly improves the heat resistance of the composite membrane.

[0047] (3) To address the problem of sepiolite fibers being prone to agglomeration due to their high surface energy, this invention employs a silane coupling agent for modification, effectively improving the dispersibility of sepiolite fibers and their compatibility and adhesion with polydopamine. Under the action of the crosslinking agent, a stable three-dimensional structure is formed between polydopamine, sepiolite fibers, and the adhesive, thereby significantly improving the puncture resistance of the diaphragm.

[0048] (4) The surface of sepiolite fiber has abundant Lewis acid sites, which can effectively fix anions in lithium salt (such as hexafluorophosphate anions) through acid-base interaction, promote the transport of lithium ions, facilitate the uniform deposition of lithium ions, and thus inhibit the growth of lithium dendrites, significantly improving the cycle stability of the battery.

[0049] (5) In addition, sepiolite fibers are rich in interconnected pore structures, which can effectively absorb HF and inhibit Fe. 2+ The leaching from the lithium iron phosphate cathode further improves the cycle stability of the battery. Detailed Implementation

[0050] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below by listing specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0051] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0052] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0053] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0054] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0055] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0056] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0057] [Composite diaphragm]

[0058] The first aspect of the present invention provides a composite membrane, the composite membrane comprising a base film layer and a functional modification layer disposed on at least one surface of the base film layer;

[0059] The functional modified layer comprises modified ceramics and modified sepiolite fibers; the modified ceramics comprise ceramic particles and polydopamine coated on the surface of the ceramic particles; the modified sepiolite fibers comprise sepiolite fibers and silane coupling agents coated on the surface of the sepiolite fibers.

[0060] In the composite separator provided by this invention, the surfaces of the modified ceramic and modified sepiolite fibers are rich in polar functional groups such as hydroxyl and amino groups, which can effectively improve the wettability and ionic conductivity of the composite separator to the electrolyte. Simultaneously, the synergistic effect of the ceramic particles, polydopamine, and sepiolite fibers significantly improves the heat resistance of the separator. Furthermore, the surface of the sepiolite fibers contains abundant Lewis acidic sites, which can effectively fix hexafluorophosphate anions through acid-base interactions, promoting lithium-ion transport and facilitating uniform lithium-ion deposition, thereby inhibiting lithium dendrite growth and significantly improving the cycle stability of the battery. The interconnected pore structure abundant on the sepiolite fibers can effectively absorb HF and inhibit Fe... 2+ Dissolution from the lithium iron phosphate cathode further improves the battery's cycle stability.

[0061] In some embodiments, the base membrane is a polyolefin microporous membrane, which is selected from at least one of polyethylene membrane, polypropylene membrane, and composite membrane of polyethylene and polypropylene.

[0062] In some embodiments, the base membrane is a polyethylene microporous membrane.

[0063] In some embodiments, the ceramic particle material in the modified ceramic is selected from at least one of alumina, boehmite, zirconium oxide, silicon oxide, magnesium oxide, titanium oxide, zinc oxide, calcium oxide, barium sulfate, aluminum hydroxide, magnesium hydroxide, silicon nitride, boron nitride, aluminum nitride, silicon carbide, LATP, LAGP, LLZO, and LCZP.

[0064] In some embodiments, the ceramic particles in the modified ceramic are selected from alumina.

[0065] In some embodiments, the particle size of the modified ceramic is 100 nm to 3 μm, for example, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm or 3 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0066] In some embodiments, the silane coupling agent is selected from at least one of vinyltriethoxysilane, vinyltrimethoxysilane, methacryloxytrimethoxysilane, methacryloxytriethoxysilane, propenyltrimethoxysilane, and propenyltriethoxysilane.

[0067] In some embodiments, the silane coupling agent is selected from vinyltriethoxysilane.

[0068] In some embodiments, the length of the modified sepiolite fiber is 0.5 μm to 2 μm, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0069] In some embodiments, the modified sepiolite fiber has a diameter of 5nm to 50nm, such as 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] In some embodiments, the mass ratio of the modified ceramic to the modified sepiolite fiber is (10-17):(0.5-8), for example, 10:0.5, 10:1, 10:2, 10:3, 10:4, 10:5, 10:6, 10:7, 10:8, 11:0.5, 11:1, 11:2, 11:3, 11:4, 11:5, 11:6, 11:7, 11:8, 12:0.5, 12:1, 12:2, 12:3, 12:4, 12:5, 12:7, 12:8, 13:0.5, 13:1, 13:2, 13:3, 13:4. 13:5, 13:6, 13:7, 13:8, 14:0.5, 14:1, 14:2, 14:3, 14:4, 14:5, 14:6, 14:8, 15:0.1, 15:1, 15:2, 15:4, 15:6, 15:7, 15:8, 16:0.5, 16:1, 16:2, 16:3, 16:5, 16:6, 16:7, 17:0.5, 17:1, 17:2, 17:3, 17:4, 17:5, 17:6, 17:7, or 17:8, but not limited to the listed ratios; other unlisted ratios within the range also apply. Therefore, when the mass ratio of the modified ceramic to the modified sepiolite fiber is within this range, it can ensure that the composite membrane has both good heat resistance and excellent ionic conductivity.

[0071] In some embodiments, the thickness of the base film layer is 3μm to 20μm, such as 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] In some embodiments, the thickness of the modified functional layer is 0.5 μm to 5.5 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or 5.5 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0073] [Preparation method of composite membrane]

[0074] A second aspect of the present invention provides a method for preparing the composite membrane described in the first aspect of the present invention, the method comprising the following steps:

[0075] S1: Preparation of the modified ceramic: Add the modifier to a mixed solution of ethanol and Tris buffer to obtain a modifier solution, add ceramic particles to obtain the modified ceramic;

[0076] Preparation of the modified sepiolite fiber: Add silane coupling agent to anhydrous ethanol, then add sepiolite fiber to obtain sepiolite fiber suspension, adjust pH, react, and obtain the modified sepiolite fiber.

[0077] S2: Add the modified ceramic and modified sepiolite fiber obtained in step S1 to deionized water, and then add an adhesive to obtain a suspension.

[0078] S3: Add crosslinking agent and catalyst to the suspension obtained in step S2 to obtain functional modified layer slurry;

[0079] S4: The functional modified layer slurry obtained in step S3 is coated on at least one side of the base membrane layer to obtain the composite membrane.

[0080] Under the action of the cross-linking agent, a stable three-dimensional structure is formed between polydopamine, sepiolite fibers and adhesive, thereby greatly improving the puncture resistance of the diaphragm.

[0081] In some embodiments, in the step of preparing the modified ceramic, the volume ratio of the ethanol to the Tris buffer is (0.5–2):1.

[0082] In some embodiments, during the preparation of the modified ceramic, the concentration of the modifier in the modifier solution is 2mM to 15mM, for example, 2mM, 3mM, 4mM, 5mM, 6mM, 7mM, 8mM, 9mM, 10mM, 11mM, 12mM, 13mM, 14mM or 15mM, but not limited to the listed values; other unlisted values ​​within the range are also applicable.

[0083] In some embodiments, the modifier used in the step of preparing the modified ceramic is dopamine hydrochloride.

[0084] In some embodiments, during the preparation of the modified ceramic, the mass ratio of the modifier to the ceramic particles is (5–15):1, for example, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, or 15:1, but not limited to the listed ratios; other unlisted ratios within this range are also applicable. Therefore, when the mass ratio of the modifier to the ceramic particles is within this range, it ensures that the ceramic particles are completely coated with the modifier, while avoiding problems such as insufficient coating or detachment due to unstable polymer structure of the modifier.

[0085] In some embodiments, the steps of preparing the modified ceramic, after the step of adding ceramic particles, further include stirring, filtering, washing, and drying; the stirring is mechanical stirring, and the stirring time is 10h to 14h, for example, 10h, 12h, or 14h, but not limited to the listed values, and other unlisted values ​​within the range are also applicable; the washing is done using deionized water; the drying time is 10h to 14h, for example, 10h, 12h, or 14h, but not limited to the listed values, and other unlisted values ​​within the range are also applicable; the drying temperature is 50 to 70℃, for example, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, or 70℃, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0086] In some embodiments, in the step of preparing the modified sepiolite fiber, the mass ratio of the silane coupling agent to the sepiolite fiber in the sepiolite fiber suspension is (5-15):1.

[0087] In some embodiments, in the step of preparing the modified sepiolite fiber, the mass ratio of the silane coupling agent to the sepiolite fiber in the sepiolite fiber suspension is (8-12):1, for example 8:1, 9:1, 10:1, 11:1 or 12:1, but not limited to the listed ratios, and other unlisted ratios within the range are also applicable.

[0088] In this application, as the amount of silane coupling agent (vinyltriethoxysilane) added varies, the dispersion and bonding ability of sepiolite fibers in polydopamine-modified ceramics is enhanced, and the cross-linked network structure formed between coating particles and fibers, as well as between particles and fibers, is more uniformly distributed, which can improve the strength and ionic conductivity of the separator. However, when the amount of silane coupling agent added is too high or too low, it will lead to the self-polymerization of the coupling agent, affecting the dispersibility of sepiolite fibers and causing a decrease in separator performance and battery electrochemical performance. But when the amount of silane coupling agent (vinyltriethoxysilane) added is within the above range, the resulting separator has both high strength and excellent ionic conductivity, and the battery containing it also has excellent electrochemical performance.

[0089] In some embodiments, during the step of preparing the modified sepiolite fiber, the sepiolite fiber accounts for 20% to 40% of the total mass of the sepiolite fiber suspension, for example, 20%, 25%, 30%, 35% or 40%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0090] In some embodiments, in the step of preparing the modified sepiolite fiber, the pH adjustment is performed by using ammonia water to adjust the pH, and the pH of the adjusted sepiolite fiber suspension is 9 to 11, for example 9, 9.5, 10, 10.5 or 11, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0091] In some embodiments, in the step of preparing the modified sepiolite fiber, the reaction condition is heating, and the heating temperature is 70℃~90℃, for example 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃ or 90℃, but not limited to the listed values, and other unlisted values ​​within the range are also applicable; the heating time is 2h~3h, for example 2h, 2.5h or 3h, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0092] In some embodiments, the preparation of the modified sepiolite fiber further includes washing, filtering, and drying steps after the reaction; the washing is performed three times with anhydrous ethanol; the drying time is 10h to 14h, for example, 10h, 12h, or 14h, but not limited to the listed values, and other unlisted values ​​within the range are also applicable; the drying temperature is 70 to 90℃, for example, 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃, or 90℃, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0093] In some embodiments, in step S2, the modified ceramic and modified sepiolite fiber account for 20% to 50% of the total mass of the suspension, for example, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, but are not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0094] In some embodiments, in step S2, based on the total mass of solids in the suspension being 100%, the mass percentage of the modified sepiolite fiber is 5% to 40%, the mass percentage of the modified ceramic is 50% to 90%, and the mass percentage of the adhesive is 3% to 10%.

[0095] In some embodiments, in step S2, the adhesive is selected from one or more of polyvinyl alcohol, polymethyl methacrylate, polybutyl methacrylate, polyacrylonitrile, ethyl polyacrylate, polyvinyl acetate, polyacrylate, polyurethane, and urethane, forming a mixture or copolymer.

[0096] In some embodiments, in step S2, the adhesive is selected from polyvinyl alcohol.

[0097] In some embodiments, in step S2, the substance added simultaneously with the adhesive also includes a thickener; the mass percentage of the thickener is 0.01% to 5% based on the total mass of solids in the suspension being 100%.

[0098] In some embodiments, in step S2, the thickener is selected from at least one of sodium carboxymethyl cellulose, sodium hydroxypropyl methyl cellulose, sodium hydroxyethyl cellulose, sodium alginate, and guar gum.

[0099] In some embodiments, in step S2, the thickener is selected from sodium carboxymethyl cellulose.

[0100] In some embodiments, in step S2, the substance added simultaneously with the adhesive also includes an additive; the mass percentage of the additive is 0.01% to 0.5% based on the total mass of solids in the suspension being 100%.

[0101] In some embodiments, in step S2, the additive is selected from at least one of fatty alcohol polyoxyethylene ether, sodium butylbenzene sulfonate, sodium hydroxyethyl sulfonate, sodium dodecylbenzene sulfonate, stearic acid, and fatty acid glycerides.

[0102] In some embodiments, in step S2, the additive is selected from fatty alcohol polyoxyethylene ether.

[0103] In some embodiments, step S2, after adding the adhesive, further includes a stirring and dispersing step, wherein the stirring and dispersing is performed using a mixer.

[0104] In some embodiments, step S2 is: adding the modified ceramic and modified sepiolite fiber obtained in step S1 to deionized water, and then adding adhesive, thickener and additives to obtain a suspension.

[0105] In some embodiments, in step S2, based on the total mass of solids in the suspension being 100%, the modified sepiolite fiber has a mass percentage of 5% to 40%, the modified ceramic has a mass percentage of 50% to 90%, the thickener has a mass percentage of 0.01% to 5%, the adhesive has a mass percentage of 3% to 10%, and the additives have a mass percentage of 0.01% to 0.5%.

[0106] In some embodiments, in step S2, based on a total solid mass of 100% in the suspension, the modified sepiolite fiber has a mass percentage of 20%, the modified ceramic has a mass percentage of 73.8%, the thickener has a mass percentage of 1%, the adhesive has a mass percentage of 5%, and the additives have a mass percentage of 0.2%.

[0107] In some embodiments, in step S2, based on a total solid mass of 100% in the suspension, the modified sepiolite fiber has a mass percentage of 5%, the modified ceramic has a mass percentage of 88.8%, the thickener has a mass percentage of 1%, the adhesive has a mass percentage of 5%, and the additives have a mass percentage of 0.2%.

[0108] In some embodiments, in step S2, based on the total mass of solids in the suspension being 100%, the mass percentage of the modified sepiolite fiber is 40%, the mass percentage of the modified ceramic is 53.8%, the mass percentage of the thickener is 1%, the mass percentage of the adhesive is 5%, and the mass percentage of the additives is 0.2%.

[0109] In some embodiments, in step S3, the crosslinking agent is selected from at least one of glutaraldehyde, formaldehyde, paraformaldehyde, and epichlorohydrin.

[0110] In some embodiments, in step S3, the crosslinking agent is selected from glutaraldehyde.

[0111] In some embodiments, in step S3, the amount of crosslinking agent added accounts for 5% to 20% of the total mass of the suspension, for example, 5%, 10%, 15% or 20%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0112] In some embodiments, in step S3, the catalyst is selected from at least one of hydrochloric acid, oxalic acid, and phosphoric acid.

[0113] In some embodiments, in step S3, the catalyst is selected from hydrochloric acid.

[0114] In some embodiments, in step S3, the amount of catalyst added accounts for 0.01% to 10% of the total mass of the suspension, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 3%, 5%, 7%, 10%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0115] In some embodiments, step S4 further includes a drying step after the coating is completed. The drying temperature is 40℃ to 90℃, for example, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, or 90℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The drying time is 10min to 80min, for example, 10min, 20min, 30min, 40min, 50min, 60min, 70min, or 80min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0116] In some embodiments, in step S4, the coating method is microgravure coating, extrusion coating, wire rod coating, dip coating, or slot coating.

[0117] In some embodiments, in step S4, the coating method is bar coating.

[0118] [Battery]

[0119] A third aspect of the present invention provides a battery comprising a composite separator provided in the first aspect of the present invention or a composite separator prepared by a preparation method provided in the second aspect of the present invention.

[0120] In some embodiments, the battery can be a secondary battery or a primary battery, preferably a secondary battery. For example, the battery can be a lithium-ion battery, but it is not limited to this. The battery structures of this application include, but are not limited to, pouch-type lithium-ion batteries, prismatic hard-shell batteries, or cylindrical hard-shell batteries.

[0121] In some embodiments, the battery further includes a positive electrode, a negative electrode, and an electrolyte. Typically, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, with the separator disposed between the positive and negative electrodes. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0122] The positive electrode sheet includes a positive current collector and a layer of positive active material disposed on the positive current collector. The positive current collector can be aluminum foil, copper foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The positive active material layer includes a positive active material. The positive active material suitable for this invention can be any known positive active material used in lithium-ion batteries, capable of reversibly inserting and de-intercalating lithium ions. The positive active material can be selected from composite oxides containing lithium and at least one selected from cobalt, manganese, nickel, and iron, preferably lithium-containing composite oxides. The lithium-containing composite oxide is preferably LiMnO2. x O y and LiM x One or more of PO4, wherein M is a combination of one or more transition metals, 0 < x ≤ 3, 0 < y ≤ 4. Examples of positive electrode active materials include lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium iron phosphate (LiFePO4), etc. In some embodiments, the positive electrode active material includes NCM (811).

[0123] The positive electrode active material layer may also include one or both selected from conductive agents and binders. The conductive agent is used to improve the electrode conductivity. Examples of conductive agents for the positive electrode include one or more of conductive carbon black, carbon fiber (CF), acetylene black, Ketjen black, graphene, and carbon nanotubes. The binder for the positive electrode improves the adhesion between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of binders for the positive electrode include at least one of fluoropolymers, polypropylene resins, fiber-type binders, rubber-type binders, and polyimide-type binders. In some embodiments, the conductive agent in the positive electrode active material layer is conductive carbon black and single-walled carbon nanotubes, and the binder is polyvinylidene fluoride. The mass ratio of the components in the positive electrode active material layer can be conventional.

[0124] The positive electrode active material layer is obtained by coating a positive electrode slurry containing the components of the positive electrode active material layer and a solvent onto a positive electrode current collector, followed by rolling and slitting. The solvent for the positive electrode slurry can be N-methylpyrrolidone (NMP).

[0125] The negative electrode includes a negative current collector and a layer of negative active material disposed on the negative current collector. The negative current collector can be aluminum foil, copper foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The negative active material layer includes the negative active material. The negative active material can include materials capable of reversibly inserting / deintercalating lithium ions, lithium metal, lithium metal alloys, materials capable of doping / dedoping lithium, or transition metal oxides. Examples of negative active materials include lithium metal, structured lithium metal, graphite (e.g., natural graphite, artificial graphite), mesophase carbon spheres, hard carbon, soft carbon, silicon, silicon-oxygen materials (e.g., silicon dioxide, silicon suboxide), silicon-carbon composites (Si / C composites), Li-Sn alloys, Li-Sn-O alloys, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Examples include Li-Al alloys. In some implementations, the negative electrode active material includes graphite.

[0126] The negative electrode active material layer may also include one or both selected from conductive agents and binders. Conductive agents are used to improve electrode conductivity. Examples of negative electrode conductive agents include conductive carbon black, conductive graphite, vapor-deposited carbon fiber (VGCF), carbon nanotubes, graphene, etc. The binder of the negative electrode improves the adhesion between negative electrode active material particles and between the negative electrode active material particles and the current collector. Examples of negative electrode binders include polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC-Na), cyclodextrin, gelatin, polyvinyl alcohol, polyacrylate, acrylonitrile copolymers, etc. In some embodiments, the conductive agent in the negative electrode active material layer is acetylene black, and the binder is styrene-butadiene rubber and sodium carboxymethyl cellulose. The mass ratio of the components in the negative electrode active material layer can be conventional.

[0127] The negative electrode active material layer is obtained by coating a negative electrode slurry containing the components of the negative electrode active material layer and a solvent onto a negative electrode current collector, followed by rolling and slitting. The solvent for the negative electrode slurry can be a conventional solvent in the art, such as deionized water.

[0128] Electrolytes consist of organic solvents and electrolyte salts.

[0129] The organic solvent suitable for the electrolyte of the present invention may include carbonate solvents, carboxylic acid ester solvents, ether solvents, or other aprotic solvents. In some embodiments, the electrolyte includes a carbonate solvent. In the electrolyte of the present invention, the mass of the carbonate solvent may be 80% to 100% of the total mass of the organic solvent, for example, 85%, 90%, or 95%. Examples of carbonate solvents include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, etc. In some embodiments, the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate. In some embodiments, the organic solvent comprises at least one cyclic carbonate and at least one linear carbonate. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butenyl carbonate, γ-butyrolactone, etc. Examples of linear carbonates include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc.

[0130] The electrolyte salt may include or be selected from lithium salts. The lithium salt may be selected from one or more organic and inorganic lithium salts. In some embodiments, the electrolyte salt is selected from at least one of LiPF6, LiBF4, LiFSI, LiTFSI, LiBOB, LiODFB, and LiPO2F2. In some embodiments, the concentration of the electrolyte salt in the electrolyte is 0.5–2 mol / L, for example, 1 mol / L or 1.5 mol / L.

[0131] The battery of this application also includes a packaging shell for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for lithium-ion batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging shell; it can be a packaging shell known in the art, as long as it can achieve the purpose of this application.

[0132] This invention does not impose any special restrictions on the battery preparation method; any technical solution known to those skilled in the art for preparing a battery, such as a secondary battery, from a negative electrode material can be used.

[0133] It should be understood that since the battery provided in this application includes the composite separator provided in the first aspect of the present invention or the composite separator prepared by the preparation method provided in the second aspect of the present invention, the beneficial effects of the composite separator or preparation method described in any of the above embodiments are applicable to the battery.

[0134] [Electrical appliances]

[0135] A fourth aspect of the present invention provides an electrical device, the electrical device comprising the battery provided in the third aspect of the present invention.

[0136] The application of the battery in this application is not particularly limited, and it can be used in any electrical device known in the prior art. In some embodiments, the battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, drones, and lithium-ion capacitors, etc.

[0137] It should be understood that, since the electrical device provided in this application includes the battery described in the third aspect of the present invention, the beneficial effects of the composite separator described in any of the above embodiments are applicable to the electrical device.

[0138] The method of the present invention will be described below through specific embodiments. It should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0139] Example 1

[0140] S101: Preparation of modified ceramics: Ethanol and Tris buffer were mixed at a volume ratio of 1:1 to obtain a mixed solvent. Dopamine was added and stirred for 12 hours to prepare a dopamine solution with a concentration of 8 mM. Then, alumina (the solid content of alumina in the solution was 10%) was added and mechanically stirred for 12 hours. The stirred material was then washed with deionized water and placed in a vacuum oven at 60°C for 12 hours to obtain modified alumina (i.e., modified ceramics).

[0141] Preparation of modified sepiolite fiber: Vinyltriethoxysilane was dispersed in anhydrous ethanol and stirred for 30 minutes to prepare a 10% solution. Then, sepiolite fiber (the mass ratio of vinyltriethoxysilane to sepiolite fiber was 10:1) was added and stirred to obtain a 30% sepiolite fiber suspension. Ammonia was added to adjust the pH to 10. The sepiolite fiber suspension was then heated to 80℃ and reacted for 2.5 hours. The powder was washed with anhydrous ethanol and filtered three times. Finally, it was dried at 80℃ for 12 hours to obtain the modified sepiolite fiber.

[0142] S102: The modified aluminum fluoride and modified sepiolite fiber obtained in step S101 are added to deionized water and mechanically stirred to form a suspension with a concentration of 40%. Then, a thickener (sodium carboxymethyl cellulose), an adhesive (polyvinyl alcohol), and an auxiliary agent (fatty alcohol polyoxyethylene ether) are added, and a 35% suspension is prepared using a high-speed disperser. The solid content of the suspension comprises 73.8% by mass of modified alumina, 20% by mass of modified sepiolite fiber, 5% by mass of adhesive, 1% by mass of sodium carboxymethyl cellulose, and 0.2% by mass of auxiliary agent.

[0143] S103: Add a crosslinking agent (glutaraldehyde) and a catalyst (hydrochloric acid) to the suspension obtained in step S102, and stir to obtain a coating liquid (i.e., functional modified layer slurry). The amount of glutaraldehyde added accounts for 10% of the mass of the suspension, and the amount of hydrochloric acid added accounts for 0.5% of the mass of the suspension.

[0144] S104: The coating solution obtained in step S103 is applied to one side of a 7μm thick polyethylene film using a wire rod coating method. After baking at 60℃ for 60 minutes, the composite diaphragm is obtained. The thickness of the functional modification layer is measured to be 3μm using a micrometer.

[0145] Example 2

[0146] The only difference between Example 2 and Example 1 is that in step S101, the mass ratio of vinyltriethoxysilane to sepiolite fiber is 5:1.

[0147] Example 3

[0148] The only difference between Example 3 and Example 1 is that in step S101, the mass ratio of vinyltriethoxysilane to sepiolite fiber is 15:1.

[0149] Example 4

[0150] The only difference between Example 4 and Example 1 is that in step S101, the concentration of the dopamine solution prepared is 2 mM.

[0151] Example 5

[0152] The only difference between Example 5 and Example 1 is that in step S101, the concentration of the dopamine solution prepared is 15 mM.

[0153] Example 6

[0154] The only difference between Example 6 and Example 1 is that in step S102, the mass percentage of modified alumina in the solid content of the suspension is 88.8%, and the mass percentage of modified sepiolite is 5%.

[0155] Example 7

[0156] The only difference between Example 7 and Example 1 is that in step S102, the mass percentage of modified alumina in the solid content of the suspension is 53.8%, and the mass percentage of modified sepiolite is 40%.

[0157] Comparative Example 1

[0158] The only difference between Comparative Example 1 and Example 1 is that in step S102, the modified alumina accounts for 93.8% of the solid content of the suspension, and no modified sepiolite fiber is added.

[0159] Comparative Example 2

[0160] The only difference between Comparative Example 2 and Example 1 is that in step S102, the modified alumina is replaced with unmodified alumina; the mass percentage of unmodified alumina in the solid content of the suspension is 93.8%, and no modified sepiolite fiber is added.

[0161] Diaphragm performance testing

[0162] The membranes obtained in Examples 1-7 and Comparative Examples 1-2 were subjected to membrane performance tests, and the test results are shown in Table 1. The test items included needle penetration strength, peel strength, heat shrinkage rate, and ionic conductivity.

[0163] - Needle penetration strength, heat shrinkage rate and ionic conductivity test: The test was performed in accordance with the national standard GB / T 36363 2018 "Polyolefin separator for lithium-ion batteries";

[0164] - Peel strength test: Cut the diaphragm into strips of 25mm*200mm, stick the coated side to the surface of 3M tape, and use a universal tensile testing machine to test at a rate of 50mm / min.

[0165] Electrochemical performance testing

[0166] Preparation of lithium-ion batteries:

[0167] (1) Positive electrode sheet: First, the positive electrode active material (LFP), PVDF and polyphosphate dispersant are mixed in a mass ratio of 97.88:2:0.12. The solvent N-methylpyrrolidone is added and stirred under vacuum until the system is homogeneous. Then, it is coated on the surface of the positive electrode current collector aluminum foil, dried at room temperature, transferred to an oven for further drying, and then cold-pressed and slit to obtain the positive electrode sheet.

[0168] (2) Negative electrode sheet: First, artificial graphite, conductive carbon black (Super P), sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96.5:1:1:1.5. Deionized water is added as a solvent and stirred under vacuum until the system is homogeneous. The mixture is then coated onto the surface of the copper foil of the negative electrode current collector, dried at room temperature, and transferred to an oven for further drying. Finally, the negative electrode sheet is obtained by cold pressing and slitting.

[0169] (3) Electrolyte: Ethyl carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 as a solvent, and LiPF6 was added to prepare the electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0170] (4) Separator: The composite diaphragms obtained in Examples 1 to 7 and Comparative Examples 1 to 2 were used as diaphragms.

[0171] (5) Assembly: The positive electrode, separator and negative electrode are stacked in sequence, then wound into a cell and installed in an aluminum shell. After liquid injection, encapsulation and formation processes, a 5Ah soft pack battery is obtained.

[0172] The batteries with separators from Examples 1-7 or Comparative Examples 1-2 were subjected to a 1C / 1C cycle 1000-cycle capacity retention test: using the Blue Battery Test System, at 25°C, the batteries were discharged at a 1C rate with constant current to 2.0V, then charged at a 1C current with constant current to 3.65V, and then charged at a constant voltage of 3.65V until the current reached 0.05C and cut off. The charging capacity at this point was recorded as the first cycle charging capacity, which constitutes one cycle. This process was repeated for 1000 cycles, and the charging capacity of the 1000th cycle was recorded. The capacity retention rate was calculated as: (1000th cycle charging capacity / first cycle charging capacity) * 100%. The test results are shown in Table 1.

[0173] Table 1

[0174]

[0175] As can be seen from Table 1, compared with Comparative Example 2, the composite membranes prepared in Examples 1-7 all have excellent mechanical strength and heat resistance, ionic conductivity and adhesion between the ceramic coating and the substrate, and the assembled lithium-ion batteries also have better cycle performance.

[0176] Compared to Example 1, the composite membranes of Examples 2 and 3 showed a decrease in strength, heat resistance, ionic conductivity, and cycle performance. This indicates that with changes in the amount of silane coupling agent (vinyltriethoxysilane), the dispersion and bonding ability of sepiolite fibers in the polydopamine-modified ceramic is enhanced, and the cross-linked network structure formed between coating particles, fibers, and between particles and fibers is more uniformly distributed, thus improving the membrane's strength and ionic conductivity. However, when the amount of silane coupling agent added is too high or too low, it can lead to the self-polymerization of the coupling agent, affecting the dispersibility of the sepiolite fibers and causing a decrease in membrane performance and battery electrochemical performance.

[0177] By comparing Examples 1, 4, and 5, it can be found that the content of polydopamine coated on the ceramic surface affects the ionic conductivity of the separator, the bonding force with the substrate, the heat resistance, and the cycle performance of the battery.

[0178] By comparing Examples 1, 6, and 7, it can be found that the strength of the separator is not significantly different; however, when the sepiolite fiber content is too high, the heat resistance of the separator decreases significantly; and as the sepiolite fiber content increases, the ionic conductivity of the separator and the battery cycle performance increase accordingly.

[0179] It should be understood that the above embodiments are exemplary and are not intended to encompass all possible implementations included in the claims. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A method for preparing a composite diaphragm, characterized in that, The preparation method includes the following steps: S1: Preparation of modified ceramics: Add the modifier to a mixed solution of ethanol and Tris buffer to obtain a modifier solution, add ceramic particles to obtain modified ceramics; Preparation of modified sepiolite fiber: Add silane coupling agent to anhydrous ethanol, then add sepiolite fiber to obtain sepiolite fiber suspension, adjust pH, react to obtain modified sepiolite fiber. S2: Add the modified ceramic and modified sepiolite fiber obtained in step S1 to deionized water, and then add an adhesive to obtain a suspension. S3: Add crosslinking agent and catalyst to the suspension obtained in step S2 to obtain functional modified layer slurry; S4: The functional modified layer slurry obtained in step S3 is coated on at least one side of the base membrane layer to obtain a composite membrane; The modifier is dopamine hydrochloride.

2. The method for preparing the composite diaphragm according to claim 1, characterized in that, The steps for preparing the modified ceramics satisfy at least one of the following features (1) to (3): (1) The volume ratio of the ethanol to the Tris buffer is (0.5-2):1; (2) The concentration of the modifier in the modifier solution is 2 mM to 15 mM; (3) After the step of adding ceramic particles, the steps of stirring, filtering, washing and drying are also included.

3. The method for preparing the composite diaphragm according to claim 1, characterized in that, The step of preparing modified sepiolite fiber satisfies at least one of the following characteristics (1) to (4): (1) In the sepiolite fiber suspension, the mass ratio of the silane coupling agent to the sepiolite fiber is (5-15):1; the sepiolite fiber accounts for 20%-40% of the total mass of the sepiolite fiber suspension; (2) The pH adjustment is performed by using ammonia water to adjust the pH, and the pH of the sepiolite fiber suspension after adjustment is 9 to 11; (3) The reaction is carried out under heating conditions, the heating temperature is 70℃~90℃, and the heating time is 2h~3h; (4) The reaction also includes washing, filtering and drying steps.

4. The method for preparing the composite diaphragm according to claim 1, characterized in that, Step S2 satisfies at least one of the following features (1) to (5): (1) The modified ceramic and the modified sepiolite fiber account for 20% to 50% of the total mass of the suspension; (2) Based on the total mass of solids in the suspension being 100%, the mass percentage of the modified sepiolite fiber is 5% to 40%, the mass percentage of the modified ceramic is 50% to 90%, and the mass percentage of the adhesive is 3% to 10%. (3) The adhesive is selected from one or more of polyvinyl alcohol, polymethyl methacrylate, polybutyl methacrylate, polyacrylonitrile, ethyl polyacrylate, polyvinyl acetate, polyacrylate, polyurethane, and urethane to form a mixture or copolymer; (4) The substances added at the same time as the adhesive also include a thickener; the mass percentage of the thickener is 0.01% to 5% based on the total mass of solids in the suspension being 100%; the thickener is selected from at least one of sodium carboxymethyl cellulose, sodium hydroxypropyl methyl cellulose, sodium hydroxyethyl cellulose, sodium alginate, and guar gum; (5) The substances added at the same time as the adhesive also include additives; the mass percentage of the additives is 0.01% to 0.5% based on the total mass of solids in the suspension being 100%; the additives are selected from at least one of fatty alcohol polyoxyethylene ether, sodium butadiene naphthalene sulfonate, sodium hydroxyethyl sulfonate, sodium dodecylbenzene sulfonate, stearic acid, and fatty acid glycerides.

5. The method for preparing the composite diaphragm according to claim 1, characterized in that, In step S3, the crosslinking agent is selected from at least one of glutaraldehyde, formaldehyde, paraformaldehyde, and epichlorohydrin, and the amount of the crosslinking agent added accounts for 5% to 20% of the total mass of the suspension. The catalyst is selected from at least one of hydrochloric acid, oxalic acid, and phosphoric acid, and the amount of the catalyst added accounts for 0.01% to 10% of the total mass of the suspension.

6. The method for preparing the composite diaphragm according to claim 1, characterized in that, In step S4, after the coating is completed, a drying step is also included. The drying temperature is 40℃~90℃ and the drying time is 10min~80min. The coating method is microgravure coating, extrusion coating, wire rod coating, dip coating or slot coating.

7. A composite diaphragm is prepared by any one of claims 1-6.

8. The composite diaphragm according to claim 7, characterized in that, The ceramic particles are made of alumina; the modified sepiolite fiber has a length of 0.5μm to 2μm and a diameter of 5nm to 50nm.

9. The composite diaphragm according to claim 7, characterized in that, The composite membrane satisfies at least one of the following characteristics (1) to (6): (1) The base membrane layer is a polyolefin microporous membrane, and the polyolefin microporous membrane is selected from at least one of polyethylene membrane, polypropylene membrane, and composite membrane of polyethylene and polypropylene; (2) The particle size of the modified ceramic is 100 nm to 3 μm; (3) The silane coupling agent is selected from at least one of vinyltriethoxysilane, vinyltrimethoxysilane, methacryloxytrimethoxysilane, methacryloxytriethoxysilane, propenyltrimethoxysilane, and propenyltriethoxysilane; (4) The mass ratio of the modified ceramic to the modified sepiolite fiber is (10-17):(0.5-8); (5) The thickness of the base film layer is 3μm to 20μm; (6) The thickness of the functional modification layer is 0.5μm to 5.5μm.

10. A battery, characterized in that, The battery includes a separator, which is a composite separator prepared by the preparation method according to any one of claims 1-6 or a composite separator according to any one of claims 7-9.

11. An electrical appliance, characterized in that, The electrical device includes the battery as described in claim 10.

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