Composite diaphragm, preparation method thereof and battery

Abstract

The invention relates to a composite diaphragm, a preparation method thereof and a battery. The composite diaphragm comprises a base membrane, a first coating arranged on at least one side surface of the base membrane in the thickness direction, and a second coating arranged on one side surface, far away from the base membrane, of the first coating, the first coating comprises first silk fibroin, and the second coating comprises second silk fibroin and ceramic particles; the content of the beta-folded structure in the first silk fibroin is lower than that of the beta-folded structure in the second silk fibroin; the ceramic particles comprise modified ceramic particles, the modified ceramic particles comprise organic functional groups, and the organic functional groups comprise amino groups and / or epoxy groups. Therefore, through the combination of the first coating and the second coating, the electrolyte wettability, the electrolyte retention performance, the flexibility, the puncture resistance and the thermal stability of the composite diaphragm can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a composite separator, a preparation method thereof and a battery. BACKGROUND

[0002] Lithium ion batteries are widely used in portable electronic devices, electric vehicles and energy storage systems due to their high energy density, long cycle life and other advantages. The separator is one of the key components of the lithium ion battery, which mainly plays the role of isolating the positive and negative electrodes to prevent short circuit and allowing lithium ions to pass through as well as absorbing and retaining electrolyte. The performance of the separator (such as electrolyte wettability, mechanical strength, thermal stability, etc.) directly affects the performance of the battery.

[0003] At present, the common technology to improve the thermal stability of the separator is to coat a ceramic coating (mainly containing inorganic ceramic particles such as alumina, silicon oxide, boehmite, etc.) on the separator base film. After coating the ceramic coating, the shrinkage of the separator at high temperature can be effectively inhibited, the thermal shutdown temperature is improved, and the safety of the battery is enhanced.

[0004] However, the separator coated with the ceramic coating still has the following deficiencies: first, the ceramic coating is usually brittle and lacks flexibility, which is prone to cracks or even peeling during the winding or charging and discharging of the battery; second, the interfacial bonding force between the inorganic ceramic particles and the organic polymer base film is usually weak; third, the electrolyte affinity of the ceramic coating is poor, resulting in poor electrolyte wettability and liquid retention capacity of the separator. SUMMARY

[0005] Therefore, the present application provides a composite separator, a preparation method thereof and a battery to solve at least one problem in the background art.

[0006] In a first aspect, the present application provides a composite separator, comprising a base film, a first coating layer arranged on at least one side surface of the base film in the thickness direction, and a second coating layer arranged on the side surface of the first coating layer away from the base film. The first coating layer comprises a first silk fibroin, and the second coating layer comprises a second silk fibroin and ceramic particles; the content of β-sheet structure in the first silk fibroin is lower than the content of β-sheet structure in the second silk fibroin; the ceramic particles comprise modified ceramic particles, and the modified ceramic particles comprise an organic functional group, and the organic functional group comprises an amino group and / or an epoxy group.

[0007] In combination with the first aspect of the present application, in an optional implementation, the composite separator satisfies at least one of the following characteristics: (1) the content of β-sheet structure in the first silk fibroin is 15% to 30%; (2) the content of β-sheet structure in the second silk fibroin is 60% to 70%; (3) the ceramic particles include at least one of alumina, boehmite, zirconia, silica, magnesia, titania, zinc oxide, calcium oxide; (4) a mass ratio of the second silk fibroin to the ceramic particles is (1-3): 1.

[0008] In combination with the first aspect of the present application, in an optional implementation, the composite diaphragm satisfies at least one of the following characteristics: (1) a thickness of the first coating layer is 0.5-3 μm; (2) a thickness of the second coating layer is 1-3 μm; (3) the second coating layer further includes a dispersant and a binder, and a ratio of a total mass of the second silk fibroin and the ceramic particles, a mass of the dispersant, and a mass of the binder is (75-95):(2-15):(3-15).

[0009] In a second aspect, the embodiments of the present application provide a preparation method of a composite diaphragm, and the method includes the following steps: S1: dissolving silk fibroin in a first solvent to obtain a silk fibroin solution, and then dialyzing the silk fibroin solution in deionized water to obtain a first slurry; the first slurry includes first silk fibroin; S2: dissolving second silk fibroin in a second solvent, and then adding ceramic particles, a dispersant, and a binder in sequence, and after being uniformly dispersed, a second slurry is obtained; a content of β-sheet structure in the first silk fibroin is lower than a content of β-sheet structure in the second silk fibroin; the ceramic particles include modified ceramic particles, the modified ceramic particles include an organic functional group, and the organic functional group includes an amino group and / or an epoxy group; S3: coating the first slurry on at least one side surface of a base film in a thickness direction, and after drying, a first coating layer is formed; S4: coating the second slurry on the first coating layer, and after drying, a second coating layer is formed.

[0010] In combination with the second aspect of the present application, in an optional implementation, step S1 satisfies at least one of the following characteristics: (1) the first solvent includes a mixture of calcium chloride, ethanol, and water or lithium bromide; (2) the silk fibroin is dissolved in the first solvent at a temperature of 50-65°C; (3) a mass ratio of the deionized water to the silk fibroin solution is (100-150):(1-2); (4) a temperature of the dialysis treatment is 2-4°C; (5) a time of the dialysis treatment is 72-100 h; (6) the mass fraction of the first silk fibroin in the first slurry is 10% to 15%; (7) the content of the beta-sheet structure in the first silk fibroin is 15% to 30%.

[0011] In combination with the second aspect of the present application, in an optional implementation, step S2 satisfies at least one of the following features: (1) the content of the beta-sheet structure in the second silk fibroin is 60% to 70%; (2) the second solvent comprises deionized water; (3) the ceramic particles comprise at least one of alumina, boehmite, zirconia, silica, magnesium oxide, titanium oxide, zinc oxide, and calcium oxide; (4) the mass ratio of the second silk fibroin to the second solvent is (1 to 3) : (10 to 20); (5) the mass ratio of the second silk fibroin to the ceramic particles is (1 to 3) : 1; (6) the ratio of the total mass of the second silk fibroin and the ceramic particles, the mass of the dispersant, and the mass of the binder is (75 to 95) : (2 to 15) : (3 to 15).

[0012] In combination with the second aspect of the present application, in an optional implementation, the preparation method of the second silk fibroin comprises: mixing an initial silk fibroin solution with an ethanol solution, stirring to react, and then standing and precipitating to obtain a silk fibroin product, washing and drying the silk fibroin product, and then performing heat treatment on the silk fibroin product, and crushing the silk fibroin product after the heat treatment to obtain the second silk fibroin.

[0013] In combination with the second aspect of the present application, in an optional implementation, the preparation method of the second silk fibroin satisfies at least one of the following features: (1) the mass fraction of the silk fibroin in the initial silk fibroin solution is 10% to 15%; (2) the mass fraction of the ethanol solution is 85% to 95%; (3) the volume ratio of the initial silk fibroin solution to the ethanol solution is (1 to 3) : (1 to 3); (4) the reaction time is 2h to 4h; (5) the standing and precipitating time is 12h to 16h; (6) the heat treatment temperature is 160°C to 180°C; (7) the heat treatment time is 1h to 2h.

[0014] In combination with the second aspect of the present application, in an optional embodiment, the method satisfies at least one of the following features: (1) before the first slurry is coated, at least one of plasma treatment, corona treatment, chemical treatment is performed on the surface of the base film to be coated with the first slurry; (2) the coating speed of the first slurry is 2 m / min to 5 m / min; (3) the thickness of the first coating layer is 0.5 μm to 3 μm; (4) the coating speed of the second slurry is 2 m / min to 5 m / min; (5) the thickness of the second coating layer is 1 μm to 3 μm.

[0015] In a third aspect, the embodiments of the present application provide a battery comprising the composite separator of any one of the first aspect or the composite separator prepared by the method of any one of the second aspect.

[0016] Compared with the prior art, the embodiments of the present application have the following beneficial effects: The composite diaphragm provided by the embodiment of the present application, the preparation method thereof and the battery, the composite diaphragm comprises a base film, a first coating layer arranged on at least one side surface of the base film along the thickness direction, and a second coating layer arranged on the side surface of the first coating layer away from the base film; the first coating layer comprises first silk fibroin, and the second coating layer comprises second silk fibroin and ceramic particles; the content of the beta-sheet structure in the first silk fibroin is lower than the content of the beta-sheet structure in the second silk fibroin; the ceramic particles comprise modified ceramic particles, the modified ceramic particles comprise an organic functional group, and the organic functional group comprises an amino group and / or an epoxy group. In the embodiment of the present application, the first coating layer comprises the first silk fibroin with a relatively low content of beta-sheet structure, the first silk fibroin has good flexibility and film-forming property, which is conducive to realizing good adhesion of the first coating layer to the base film, forming a strong and tough bonding interface, effectively buffering stress, and improving the overall flexibility of the composite diaphragm, thereby effectively improving the problem of cracking or even peeling of the coating layer in the bending or winding process of the composite diaphragm; the inherent hydrophilicity of the silk fibroin is conducive to improving the affinity of the composite diaphragm to the electrolyte, and the first silk fibroin in the first coating layer has better hydrophilicity than the second silk fibroin, can form a super-hydrophilic network, and can enhance the infiltration and permeation of the electrolyte, thereby improving the wettability and liquid retention performance of the composite diaphragm to the electrolyte and promoting the transmission of active ions. The ceramic particles in the second coating layer comprise modified ceramic particles, the organic functional group in the modified ceramic particles can form chemical bonds and / or hydrogen bonds with active groups (such as amino groups, hydroxyl groups, carboxyl groups, etc.) in the second silk fibroin, realize strong connection between the ceramic particles and the silk fibroin, significantly improve the interfacial bonding strength between the two, reduce interfacial defects, and effectively prevent the agglomeration of the ceramic particles, so that the ceramic particles are uniformly dispersed, thereby effectively inhibiting the shrinkage and melting of the composite diaphragm at high temperature, improving the mechanical strength and thermal stability of the composite diaphragm; that is, through the combination of the first coating layer and the second coating layer in the embodiment of the present application, the wettability and liquid retention performance, flexibility, puncture resistance and thermal stability of the composite diaphragm can be effectively improved.

[0017] Additional aspects and advantages of the present application will be made apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings, which are included to provide a further understanding of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and together with the description serve to explain the present application. In the drawings: Figure 1 A flowchart of a preparation method of a composite diaphragm provided by the embodiment of the present application. DETAILED DESCRIPTION

[0019] In order to make the technical solutions and beneficial effects of the present application more obvious and easy to understand, the following will be described in detail by combining the drawings and listing specific examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application. The experimental methods not specified in the following examples are generally carried out according to the conventional experimental conditions. The reagents and raw materials used in the present application are commercially available unless otherwise specified.

[0020] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without one or more of these specific details. In other instances, well-known features have not been described in detail in order to avoid obscuring the present application. In the following description, the terms "couple" and "coupled" refer to an operational coupling, whether mechanical, electrical, or magnetic, between two components, and does not require that there be any physical contact between them.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0022] For a thorough understanding of the present application, detailed steps and detailed structures will be presented in the following description in order to illustrate the technical solutions of the present application. The preferred embodiments of the present application are described in detail as follows, however, in addition to these detailed descriptions, the present application can also have other implementation manners.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0024] The experimental methods not specified in the following examples are generally carried out according to the conventional techniques described in the literature or according to the product instructions and manufacturer's recommended conditions. The numerical ranges in the following examples include the end point values.

[0025] Silk fibroin (SF) is a natural polymer protein extracted from silk, which has good biocompatibility, degradability, excellent mechanical flexibility, film-forming property and excellent hydrophilicity. The molecular chain of silk fibroin contains a large number of hydrophilic groups (such as hydroxyl, amino and carboxyl), and has strong affinity for polar solvents (such as electrolyte). However, when silk fibroin is used alone as a coating of a separator, the thermal stability and mechanical strength of the separator are difficult to meet the safety performance requirements of the battery.

[0026] Based on this, the embodiment of the present application provides a composite separator, which comprises a base film, a first coating layer arranged on at least one side surface of the base film in the thickness direction, and a second coating layer arranged on the side surface of the first coating layer away from the base film; the first coating layer comprises first silk fibroin, and the second coating layer comprises second silk fibroin and ceramic particles; the content of β-sheet structure in the first silk fibroin is lower than that in the second silk fibroin; the ceramic particles comprise modified ceramic particles, and the modified ceramic particles comprise an organic functional group, and the organic functional group comprises an amino group and / or an epoxy group.

[0027] The β-sheet structure is an important secondary structure in silk fibroin, and is the nature of silk fibroin itself. The silk fibroin with a lower content of β-sheet structure has a lower crystallinity, better flexibility and better surface hydrophilicity than the silk fibroin with a higher content of β-sheet structure, and the silk fibroin with a higher content of β-sheet structure has a higher strength than the silk fibroin with a lower content of β-sheet structure. In the embodiments of the present application, the first coating layer includes the first silk fibroin with a relatively low content of β-sheet structure, and the first silk fibroin has good flexibility and film-forming property, which is conducive to achieving good adhesion between the first coating layer and the base film, forming a strong and tough bonding interface, effectively buffering stress, and improving the overall flexibility of the composite separator, thereby effectively improving the problem of cracking or even peeling of the coating layer during the bending or winding process of the composite separator. The inherent hydrophilicity of the silk fibroin is conducive to improving the affinity of the composite separator to the electrolyte, and the first silk fibroin in the first coating layer has better hydrophilicity than the second silk fibroin, can form a super-hydrophilic network, and can enhance the infiltration and permeation of the electrolyte, thereby improving the wettability and liquid retention performance of the composite separator to the electrolyte and promoting the transmission of active ions. The ceramic particles in the second coating layer include modified ceramic particles, and the organic functional groups in the modified ceramic particles can form chemical bonds and / or hydrogen bonds with the active groups (such as amino groups, hydroxyl groups, and carboxyl groups) in the second silk fibroin, thereby achieving strong connection between the ceramic particles and the silk fibroin, significantly improving the interfacial bonding strength between the two, reducing interface defects, and effectively preventing the agglomeration of the ceramic particles, so that the ceramic particles are uniformly dispersed, thereby effectively inhibiting the shrinkage and melting of the composite separator at high temperatures, and improving the mechanical strength and thermal stability of the composite separator. That is, through the combination of the first coating layer and the second coating layer in the embodiments of the present application, the wettability and liquid retention performance, flexibility, puncture resistance, and thermal stability of the composite separator can be effectively improved.

[0028] In the embodiments of the present application, the first coating layer and the second coating layer arranged in layers can be arranged on one side surface of the base film in the thickness direction, or can be arranged on both side surfaces of the base film in the thickness direction.

[0029] In the embodiments of the present application, the base film mainly plays a mechanical support role. For example, the base film can include a polyethylene film (PE film) and / or a polypropylene film (PP film). The thickness of the base film can be 5 μm to 15 μm, for example, can be 5 μm, 7 μm, 9 μm, 10 μm, 12 μm, 15 μm, or any value within the range between any two of the above values.

[0030] In some embodiments, the content of β-sheet structure in the first silk fibroin can be 15% to 30%.

[0031] The first coating layer includes the first silk fibroin, which can enable the separator to quickly and uniformly absorb electrolyte, improve the electrolyte infiltration rate (significantly reduce the contact angle), and meanwhile, the porous structure and water retention capacity of the silk fibroin can help the composite separator to retain more electrolyte during the circulation process and reduce the dry-out phenomenon. Controlling the content of the β-sheet structure in the first silk fibroin in the above range can help improve the electrolyte wettability and liquid retention performance of the composite separator as well as the flexibility.

[0032] In some embodiments, the content of the β-sheet structure in the second silk fibroin can be 60% to 70%.

[0033] The second coating layer includes the second silk fibroin and ceramic particles, which can provide excellent thermal barrier effect, effectively inhibit the shrinkage and melting of the composite separator at high temperature, and significantly improve the thermal stability and mechanical strength of the composite separator. Controlling the content of the β-sheet structure in the second silk fibroin in the above range can help improve the puncture resistance and thermal stability of the composite separator while taking into account the liquid absorption and liquid retention capacity of the composite separator. In addition, the second coating layer includes the second silk fibroin with a relatively high content of β-sheet structure, and the tightly stacked β-sheet crystal regions not only have relatively high strength but also can selectively intercept by-products such as HF (size > 0.5 nm), thereby further improving the performance of the composite separator.

[0034] In some embodiments, the content of the β-sheet structure in the first silk fibroin is 15% to 30%, and the content of the β-sheet structure in the second silk fibroin is 60% to 70%.

[0035] In the embodiments of the present application, the first silk fibroin in the first coating layer and the second silk fibroin in the second coating layer have a gradient design of the content of the β-sheet structure, which can increase the electrolyte permeation and promote the transmission of active ions (such as lithium ions, sodium ions, etc.). Controlling the content of the β-sheet structure in the first silk fibroin and the second silk fibroin in the above range can help promote the full permeation of the electrolyte and promote the efficient transmission of active ions.

[0036] It can be understood that when the mass ratio of the second silk fibroin to the ceramic particles is too large, it is not conducive to the improvement of the mechanical strength and thermal stability of the composite separator; and when the mass ratio of the second silk fibroin to the ceramic particles is too small, it is not conducive to the improvement of the electrolyte wettability and liquid retention performance of the composite separator as well as the flexibility. Therefore, in some specific embodiments, the mass ratio of the second silk fibroin to the ceramic particles can be (1 to 3): 1, for example, 1:1, 2:1, 3:1, or any value range between any two of the above values.

[0037] Exemplarily, the ceramic particles can include at least one of alumina, boehmite, zirconia, silica, magnesia, titania, zinc oxide, calcium oxide. The modified ceramic particles can be obtained by modifying the above ceramic particles by a silane coupling agent, so as to introduce an organic functional group into the ceramic particles.

[0038] In some embodiments, the second coating further includes a dispersant and a binder, and the ratio of the total mass of the second silk fibroin and the ceramic particles, the mass of the dispersant, and the mass of the binder can be (75-95):(2-15):(3-15). In this way, the connection stability of the second coating and the first coating can be taken into account while ensuring the mechanical strength and thermal stability of the second coating, so as to further improve the comprehensive performance of the composite separator.

[0039] Exemplarily, the dispersant can include sodium polyacrylate (PAAS) and / or polyvinylpyrrolidone (PVP); specifically, the dispersant is PAAS and / or PVP. The binder can include polyvinyl alcohol (PVA) and / or styrene-butadiene rubber (SBR) emulsion; specifically, the binder can be PVA and / or SBR emulsion.

[0040] In some embodiments, the thickness of the first coating can be 0.5-3 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any value within the range between any two of the above values. In this way, the electrolyte wettability and liquid retention performance and flexibility of the composite separator can be improved.

[0041] In some embodiments, the thickness of the second coating can be 1-3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or any value within the range between any two of the above values. In this way, the puncture resistance and thermal stability of the composite separator can be improved.

[0042] The present application also provides a preparation method of a composite separator, please refer to Figure 1 The preparation method of the composite separator provided by the present application includes the following steps: S1: dissolving silk fibroin in a first solvent to obtain a silk fibroin solution, and then dialyzing the silk fibroin solution in deionized water to obtain a first slurry; the first slurry includes a first silk fibroin; S2: dissolving a second silk fibroin in a second solvent, and then sequentially adding ceramic particles, a dispersant and a binder, and uniformly dispersing to obtain a second slurry; the content of the β-sheet structure in the first silk fibroin is lower than the content of the β-sheet structure in the second silk fibroin; the ceramic particles include modified ceramic particles, and the modified ceramic particles include an organic functional group, and the organic functional group includes an amino group and / or an epoxy group; S3: applying the first slurry on at least one side surface of the base film along the thickness direction, and after drying, forming a first coating layer; S4: applying the second slurry on the first coating layer, and after drying, forming a second coating layer.

[0043] In the embodiments of the present application, the first coating layer formed includes a first silk fibroin with a relatively low content of β-sheet structure, and the first silk fibroin has good flexibility and film-forming property, which is conducive to achieving good adhesion of the first coating layer to the base film, forming a strong and tough bonding interface, effectively buffering stress, and improving the overall flexibility of the composite separator, thereby effectively improving the problem of cracking or even peeling of the coating layer during the bending or winding process of the composite separator; the inherent hydrophilicity of silk fibroin is conducive to improving the affinity of the composite separator to the electrolyte, and the first silk fibroin in the first coating layer has better hydrophilicity than the second silk fibroin, which can form a super-hydrophilic network, enhance the infiltration and permeation of the electrolyte, and thus improve the wettability and liquid retention performance of the composite separator to the electrolyte, and promote the transmission of active ions; the ceramic particles in the second coating layer formed include modified ceramic particles, and the organic functional groups in the modified ceramic particles can form chemical bonds and / or hydrogen bonds with active groups (such as amino groups, hydroxyl groups, carboxyl groups, etc.) in the second silk fibroin, realizing strong connection between the ceramic particles and the silk fibroin, significantly improving the interfacial bonding strength between the two, reducing interface defects, and effectively preventing the agglomeration of the ceramic particles, so that they are uniformly dispersed, thereby effectively inhibiting the shrinkage and melting of the composite separator at high temperatures, and improving the mechanical strength and thermal stability of the composite separator; that is, through the combination of the first coating layer and the second coating layer in the embodiments of the present application, the electrolyte wettability and liquid retention performance, flexibility, puncture resistance, and thermal stability of the composite separator can be effectively improved.

[0044] In step S1, the silk fibroin is dissolved in a first solvent to obtain a silk fibroin solution, and then the silk fibroin solution is subjected to dialysis treatment in deionized water to obtain a first slurry; the first slurry includes a first silk fibroin.

[0045] In the actual preparation process, the silk fibroin can be dissolved in the first solvent at a temperature of 50°C to 65°C; in this way, the dissolution of the silk fibroin can be ensured. The first solvent may, for example, include a mixture of calcium chloride, ethanol, and water (CaCl2 / EtOH / H2O) or lithium bromide (LiBr).

[0046] The silk fibroin can be obtained by degumming the cocoon, for example. For example, the cocoon can be degummed by using a sodium bicarbonate-sodium carbonate buffer solution (concentration: 0.01 mol / L-0.03 mol / L, pH=8-10). Specifically, the sodium bicarbonate-sodium carbonate buffer solution can be heated to boiling and then added to the cocoon shell, and the mixture is boiled for 30-50 min. Then the cocoon silk is taken out and washed with deionized water. The above boiling and washing steps can be repeated multiple times. Finally, the obtained cocoon silk is dried in an oven at 55-65°C to obtain the silk fibroin.

[0047] In a specific example, the degummed silk fibroin is added to a calcium chloride-ethanol-water solution with a concentration of 8-10 mol / L, wherein the molar ratio of calcium chloride, ethanol and water is (1-3):(1-3):(8-12). The mixture is dissolved at 50-65°C for 30-50 min to obtain a silk fibroin solution.

[0048] In some embodiments, the mass ratio of deionized water to silk fibroin solution can be (100-150):(1-2).

[0049] In some embodiments, the temperature of the dialysis treatment can be 2-4°C.

[0050] In some embodiments, the dialysis treatment time can be 72-100 h.

[0051] Through the dialysis treatment, Ca 2+ , Cl - , ethanol and other residual small molecules in the silk fibroin solution can be removed. Controlling one or more of the mass ratio of deionized water to silk fibroin solution, the temperature of the dialysis treatment, and the dialysis treatment time in the above range can help improve the effect of the dialysis treatment.

[0052] In actual preparation process, atomic absorption spectrometer can be used to detect the content of Ca 2+ to determine the end time of dialysis; for example, when no Ca 2+ is detected, the dialysis treatment can be ended. After the dialysis treatment is completed, the solution in the dialysis device is taken out to obtain a first slurry.

[0053] In some embodiments, the mass fraction of the first silk fibroin in the first slurry can be 10%-15%.

[0054] In the embodiments of the present application, Ca 2+ is removed through the dialysis treatment. Since Ca 2+ can induce the formation of β-sheet structure, removing Ca 2+The first silk fibroin with a low content of β-sheet structure (which can also be referred to as a β-sheet degree) can be obtained. In some embodiments, the content of β-sheet structure in the first silk fibroin is 15% to 30%.

[0055] In step S2, the second silk fibroin is dissolved in a second solvent, and then ceramic particles, a dispersant, and a binder are sequentially added and uniformly dispersed to obtain a second slurry. The content of β-sheet structure in the first silk fibroin is lower than that in the second silk fibroin. The ceramic particles include modified ceramic particles, and the modified ceramic particles include an organic functional group, which includes an amino group and / or an epoxy group.

[0056] In the actual preparation process, first, the second silk fibroin and deionized water (the second solvent) can be mixed in a mass ratio of (1 to 3) to (10 to 20) to form a solution, and then the modified ceramic particles are added and uniformly dispersed by stirring or ultrasonic treatment, where the mass ratio of the second silk fibroin to the ceramic particles can be (1 to 3) to 1. Next, the dispersant and the binder are added, and ultrasonic treatment is performed for 30 to 50 minutes to ensure uniform dispersion, forming a stable second slurry. The mass ratio of the total mass of the second silk fibroin and the ceramic particles, the mass of the dispersant, and the mass of the binder can be (75 to 95) to (2 to 15) to (3 to 15).

[0057] In some embodiments, the preparation method of the second silk fibroin can include: mixing an initial silk fibroin solution with an ethanol solution, stirring to react, and then standing and precipitating to obtain a silk fibroin product. After washing and drying treatment, the silk fibroin product is subjected to heat treatment, and the silk fibroin product after heat treatment is subjected to crushing treatment to obtain the second silk fibroin.

[0058] In the actual preparation process, the initial silk fibroin solution and the ethanol solution can be mixed, and stirring is performed at room temperature (about 25°C) for 2 to 4 hours for sufficient reaction, so that the α-helix structure in the silk fibroin molecules in the initial silk fibroin solution is gradually destroyed, and β-sheet structures are induced between molecules. Next, the silk fibroin is allowed to stand and precipitate for 12 to 16 hours, the silk fibroin precipitate is collected, washed with deionized water for 2 to 3 times to remove residual ethanol, and then the washed silk fibroin precipitate is placed in an oven and dried at 50°C to 80°C for 12 to 16 hours to obtain a silk fibroin product. Next, the dried silk fibroin product is placed in a high-temperature furnace and subjected to heat treatment at 160°C to 180°C for 1 to 2 hours to further promote the formation of β-sheet structures. Finally, the silk fibroin product after heat treatment (high-temperature treatment) is cooled to room temperature, and is ground into a powder (crushing treatment) using a mortar to obtain the second silk fibroin (silk fibroin with a high β-sheet degree).

[0059] The mass fraction of the initial silk fibroin solution can be 10% to 15%. The initial silk fibroin solution can be prepared according to the preparation method of the first slurry in the above embodiment, which is not described here. The mass fraction of the ethanol solution can be 85% to 95%; in some specific embodiments, the volume ratio of the initial silk fibroin solution to the ethanol solution can be (1 to 3):(1 to 3). In a specific example, the volume ratio of the initial silk fibroin solution to the ethanol solution is 1:1.

[0060] In some embodiments, the content of the beta-sheet structure in the second silk fibroin can be 60% to 70%.

[0061] In some embodiments, the preparation method of the modified ceramic particles can include: Step 1: Mix the silane coupling agent with the solvent (deionized water and / or ethanol) according to a mass ratio of 1:(9 to 20), add a catalyst (including at least one of acetic acid, nitric acid, and acetic acid), adjust the pH value of the solution to 4 to 5, stir for 10 minutes to 30 minutes, promote the hydrolysis of the silane coupling agent, and obtain a mixed solution. Exemplarily, the silane coupling agent can include γ-aminopropyl triethoxysilane (KH550) and / or γ-glycidyl ether oxypropyl trimethoxysilane (KH560). The silicon-oxygen bond (Si-O) in the silane molecule is broken under the action of water to form silanol (Si-OH). This process can be represented by the following chemical equation: R-Si(OR')3+3H2O→R-Si(OH)3+3R'OH; wherein R is a non-hydrolysable organic functional group, which is the core functional part of the silane coupling agent molecule; R' is a hydrolysable alkyl group, which is a hydrolysable group connected to the silicon atom through an oxygen atom.

[0062] Step 2: Add the ceramic particles to the mixed solution obtained in Step 1, the mass ratio of the ceramic particles to the silane coupling agent in the mixed solution is (10 to 15):1, stir for 1 hour to 2 hours to ensure sufficient contact between the two; next, heat at 60°C to 80°C for 2 hours to 4 hours to promote the condensation reaction; next, dry at 80°C to 100°C for 2 hours to 4 hours to obtain the modified ceramic particles.

[0063] In the embodiments of the present application, the organic functional groups (amino and / or epoxy) in the silane coupling agent are introduced into the ceramic particles to obtain modified ceramic particles. The organic functional groups in the modified ceramic particles can form chemical bonds and / or hydrogen bonds with active groups (such as amino, hydroxyl, and carboxyl) in the second silk fibroin, achieving strong connection between the ceramic particles and the silk fibroin, significantly improving the interfacial bonding strength between the two, reducing the interfacial defects, and effectively preventing the agglomeration of the ceramic particles, so that the composite separator can effectively inhibit the shrinkage and melting of the composite separator at high temperatures, and improve the mechanical strength and thermal stability of the composite separator.

[0064] The silane coupling agent can react with the ceramic and the silk fibroin respectively, thereby connecting the silk fibroin and the ceramic. The reaction chemical equation of the silane coupling agent with the silk fibroin can be as follows: R-Si(OH)3+ H2N-[C 15 H 23 N3O5] n → R-Si(OH)2-NH-[C 15 H 23 N3O5] n + H2O; wherein n is 60-500.

[0065] Exemplarily, the ceramic particles can include at least one of alumina, boehmite, zirconia, silica, magnesia, titania, zinc oxide, calcium oxide, for example.

[0066] Taking the ceramic particles as alumina as an example, the chemical equation of the above condensation reaction is as follows: R-Si(OH)3+ 3(HO-Al) → R-Si(O-Al)3+ 3H2O.

[0067] In step S3, the first slurry is coated on at least one side surface of the base film in the thickness direction, and after drying, a first coating layer is formed.

[0068] In the embodiments of the present application, the base film mainly plays a mechanical support role. Exemplarily, the base film can include a polyethylene film (PE film) and / or a polypropylene film (PP film). The thickness of the base film can be 5 μm-15 μm, for example, can be 5 μm, 7 μm, 9 μm, 10 μm, 12 μm, 15 μm or any value within any two of the above numerical ranges.

[0069] In some embodiments, before the first slurry is coated, at least one of plasma treatment, corona treatment, chemical treatment can be performed on the surface of the base film to be coated with the first slurry. In this way, the surface energy of the treated surface of the base film can be improved, thereby improving the bonding force between the base film and the first coating layer.

[0070] In the actual preparation process, at least one of a doctor blade coating, a micro-gravure coating, a spraying, a slot die coating can be used to uniformly coat the first slurry on the surface to be coated of the base film; then, the coated base film is dried at 60-80°C to form a porous silk fibroin layer (first coating layer). Specifically, the coating speed of the first slurry can be 2-5 m / min.

[0071] In some embodiments, the first coating layer can have a thickness of 0.5 μm to 3 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or any value within a range between any two of the above values. This is beneficial to improve the electrolyte wettability and liquid retention performance of the composite separator and the flexibility.

[0072] In step S4, the second slurry is coated on the first coating layer, and after drying, the second coating layer is formed.

[0073] In actual preparation process, the second slurry can be uniformly coated on the surface of the first coating layer by at least one of blade coating, micro-gravure coating and slot coating. Then, the coated base film is dried at 60 °C to 80 °C to form the second coating layer. Specifically, the coating speed of the second slurry can be 2 m / min to 5 m / min.

[0074] In some embodiments, the second coating layer can have a thickness of 1 μm to 3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or any value within a range between any two of the above values. This is beneficial to improve the puncture resistance and thermal stability of the composite separator.

[0075] In actual application, the prepared composite separator can also be subjected to post-processing, such as slitting, winding and the like.

[0076] The embodiments of the present application also provide a battery comprising the composite separator according to any one of the above embodiments or the composite separator prepared by the preparation method according to any one of the above embodiments.

[0077] It can be understood that the beneficial effects of the composite separator according to any one of the above embodiments are applicable to the battery. The battery can be a secondary battery, for example, a lithium ion battery. Since the composite separator according to any one of the above embodiments has high electrolyte wettability and high liquid retention performance, high flexibility, high puncture resistance and high thermal stability, it can avoid short circuit between the positive and negative electrodes and promote the transmission of active ions, and therefore, the battery according to the embodiments of the present application has high safety, high energy density and high cycle performance.

[0078] Specifically, the battery further comprises a positive electrode sheet and a negative electrode sheet, and the composite separator is located between the positive electrode sheet and the negative electrode sheet. During the charging and discharging of the battery, the active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The composite separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time, to allow the active ions to pass through.

[0079] In some embodiments, the preparation method of the battery can comprise: winding or laminating the negative electrode sheet, the composite separator, and the positive electrode sheet to obtain an electrode assembly, placing the electrode assembly in a shell (for example, an aluminum plastic film, an aluminum steel shell, etc.), drying, electrolyte injection, packaging, formation, and capacity distribution, to obtain the battery.

[0080] The technical solutions of the present application will be further described below in combination with multiple embodiments and comparative examples.

[0081] Embodiment 1

[0082] The preparation method of the composite separator in this embodiment comprises the following steps: Step S101: Take 10 g of cocoon, boil and degum in a 0.5% (w / v) Na2CO3 solution for 30 min, twice, and then wash with water and dry to obtain pure silk fibroin; dissolve 5 g of pure silk fibroin in 50 ml of 9.3 M LiBr solution, stir at 60°C for 4 h, to obtain a silk fibroin solution; place the silk fibroin solution in a dialysis bag (MWCO 3500 Da, i.e., retain substances with a molecular weight greater than 3500 Da), dialyze in deionized water for 3 days (72 h), and change the water multiple times in between, to obtain a regenerated silk fibroin aqueous solution with a mass fraction of 15% (first slurry), wherein the content of β-sheet structure in the first silk fibroin in the regenerated silk fibroin aqueous solution is 20%; Step S102: Mix the prepared silk fibroin aqueous solution with a mass fraction of 15% (preparation method as in step S101) with an ethanol solution with a mass fraction of 95% at a volume ratio of 1:1, stir the mixed solution at room temperature, and continue stirring for 2 h, so that the α-helix structure within the silk fibroin molecules is gradually destroyed, and β-sheet structure is induced between molecules; after stirring is completed, let the mixed solution stand for 12 h, so that the silk fibroin precipitates; collect the precipitated silk fibroin after standing, wash it with deionized water 3 times to remove residual ethanol, and place the washed silk fibroin precipitate in an oven and dry it at 60°C for 12 h; place the dried silk fibroin in a high-temperature furnace and treat it at 170°C for 1 h to further promote the formation of β-sheet structure; after cooling the silk fibroin treated at high temperature to room temperature, grind the cooled silk fibroin into powder with a mortar, to obtain silk fibroin with high β-sheet degree (second silk fibroin with a content of β-sheet structure of 60%); Step S103: Mix silane coupling agent KH550 and deionized water solvent according to a mass ratio of 1:9, add catalyst acetic acid, adjust the pH value to 4.5, stir for 30 min, promote the hydrolysis of the silane coupling agent, and obtain a mixed solution; the silicon-oxygen bond (Si-O) in the silane molecule is broken under the action of water to form silanol (Si-OH); add alumina to the mixed solution according to a ratio of 15:1, stir for 2 h to ensure sufficient contact; heat at 60°C for 4 h to promote the condensation reaction; and then dry at 80°C for 4 h to obtain modified alumina.

[0083] Step S104: Mix the second silk fibroin prepared in step S102 and deionized water according to a mass ratio of 1:10, then add the modified alumina prepared in step S103 (the mass ratio of the second silk fibroin to the ceramic particles is 3:1), uniformly disperse by stirring, then add a dispersant and a binder (the mass ratio of the total mass of the second silk fibroin and the ceramic particles, the mass of the dispersant, and the mass of the binder is 92:5:3), and uniformly disperse by ultrasonic treatment for 50 min to form a stable SF / Al2O3 composite slurry (second slurry). Step S105: Use a PE-based film with a thickness of 7 μm, and perform corona treatment on one side; use a micro-gravure coater to coat the first slurry prepared in step S101 on the corona-treated side of the film, wherein the coating speed is 5 m / min; next, dry at 70°C for 5 min under conditions of a relative humidity of 50% to form a first coating layer with a thickness of 1 μm; next, use a knife coater to coat the second slurry prepared in step S104 on the side surface of the first coating layer away from the film, and dry in a 100°C oven for 10 min to form a second coating layer with a thickness of 3 μm.

[0084] Example 2

[0085] The preparation method of the composite separator in this example is basically the same as that in example 1, except that: The thickness of the first coating layer formed in step S105 is 0.5 μm.

[0086] Example 3

[0087] The preparation method of the composite separator in this example is basically the same as that in example 1, except that: The thickness of the first coating layer formed in step S105 is 1.5 μm.

[0088] Example 4

[0089] The preparation method of the composite separator in this example is basically the same as that in example 1, except that: The thickness of the first coating layer formed in step S105 is 2 μm.

[0090] Example 5

[0091] The preparation method of the composite separator in this example is basically the same as that in Example 1, except that: The thickness of the PE base film used in step S105 is 9 μm.

[0092] Example 6

[0093] The preparation method of the composite separator in this example is basically the same as that in Example 1, except that: The thickness of the PE base film used in step S105 is 12 μm.

[0094] Example 7

[0095] The preparation method of the composite separator in this example is basically the same as that in Example 1, except that: The thickness of the second coating layer formed in step S105 is 1.5 μm.

[0096] Example 8

[0097] The preparation method of the composite separator in this example is basically the same as that in Example 1, except that: The thickness of the second coating layer formed in step S105 is 2.5 μm.

[0098] Comparative Example 1

[0099] The preparation method of the composite separator in this example omits step S101 compared to Example 1, and accordingly, step S105 directly coats the second slurry on the corona-treated surface of the base film to form a second coating layer with a thickness of 4 μm. The other steps are consistent with Example 1.

[0100] Comparative Example 2

[0101] The preparation method of the composite separator in this example omits steps S102-S104 compared to Example 1, and accordingly, step S105 only forms a first coating layer with a thickness of 4 μm on the corona-treated surface of the base film, without forming a second coating layer on the side surface of the first coating layer away from the base film. The other steps are consistent with Example 1.

[0102] Comparative Example 3

[0103] In this comparative example, a commercially available PE film (same as the PE base film in Example 1) is used as the separator.

[0104] The electrolyte wettability, thermal stability, and puncture resistance of the separators in each of the above examples and comparative examples are tested. The specific tests are as follows: (1) Electrolyte wettability test: the wettability of the separator is tested by the wetting height method, and the test steps are as follows: a) cut the separator to be tested into a sample to be tested with a fixed size, which is a long strip with a size of 20mm*260mm; b) prepare the wettability test instrument, including a container for containing electrolyte, a clamp for immersing the sample into the electrolyte, a suspension device to ensure that the separator can be vertically suspended; c) install the sample to be tested on the clamp of the wettability test instrument, and ensure that the surface of the sample to be tested in contact with the electrolyte is completely exposed; use double-sided tape to fix the sample to be tested in the grooves on the upper and lower ends of the suspension device, and ensure that the sample to be tested is straight without bending; d) add enough electrolyte in the container of the wettability test instrument, and the liquid level is slightly lower than the height of the shell; wherein, the configuration method of the electrolyte is: mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, and then dissolving lithium salt LiPF6 in the above mixed organic solvent in a proportion of 1 mol / L; e) slowly immerse the clamp with the sample to be tested into the electrolyte until one end of the sample to be tested is immersed in the electrolyte; f) record the initial time and the height of the electrolyte liquid level, and record the climbing height of the electrolyte in the sample to be tested every 30 seconds, and record the climbing height of the electrolyte at 90 seconds, which is recorded as the 90-second electrolyte wettability height.

[0105] (2) Separator thermal response test: three circular samples are cut from the separator to be tested, and the samples are placed in a vacuum drying oven and dried at 120°C for more than 2h to completely remove water and residual solvent; cool the dried samples to room temperature (about 20°C~25°C) in a desiccator and weigh the mass of each dried sample in air, which is recorded as m1 (unit: g). Turn on the high-temperature constant temperature box and the density measuring device, heat and stabilize the immersion liquid (high-boiling point silicone oil) at 120±2°C; immerse the weighed sample into the 120°C immersion liquid; in order to ensure that the immersion liquid completely fills the pores of the separator, the container containing the sample and the immersion liquid is subjected to vacuum treatment for 5min~10min until no bubbles overflow. Use the special support of the high-temperature densimeter to completely immerse the sample saturated with the immersion liquid in the 120°C immersion liquid (high-boiling point silicone oil) without touching the container wall and bottom, and record the mass when the reading is stable, which is recorded as m2 (unit: g), which is equivalent to the buoyancy of the saturated sample in the high-temperature immersion liquid; the average value of the test results of the three parallel samples is taken as the final measurement value. The calculation steps of the porosity of the sample are as follows: Calculate the apparent density (p a ): p a = (m1 / (m1-m2)) * p liq ; wherein, p aThe apparent density of the sample at 120°C (unit: g / cm3); m1 is the mass of the dried sample in air (unit: g); m2 is the apparent mass of the sample saturated with the impregnating liquid in the impregnating liquid (unit: g); p liq The density of the impregnating liquid at 120°C (unit: g / cm3).

[0106] The porosity (P) of the sample is calculated: P = (1 - p a / p i ) * 100%; wherein P is the porosity of the sample (unit: %); p a is the calculated apparent density (unit: g / cm3); p i is the skeleton density of the separator material (unit: g / cm3), the p i of the polypropylene (PP) based film is 0.91 g / cm3, and the p i of the polyethylene (PE) based film is 0.96 g / cm3.

[0107] (3) Puncture resistance test: cut the test separator to obtain a circular test sample with a diameter of 50 mm, and the surface of the test sample should be flat, wrinkle-free and damage-free; install the puncture clamp on the upper and lower clamp seats of the electronic tensile testing machine, and ensure that the clamp is securely installed and the center is aligned; install the puncture needle on the clamp to ensure that it is perpendicular to the clamp plane; place the test sample flat on the lower clamp of the puncture clamp, and use the clamp to clamp the test sample, and the clamping force should be moderate; set the test parameters on the operating interface of the electronic tensile testing machine, the test speed is 50 mm / min, and the data acquisition frequency is 50 Hz; start the electronic tensile testing machine, and the puncture needle moves downward at the set speed and penetrates the test sample. The sensor of the electronic tensile testing machine will collect force and displacement data in real time, and display the force-displacement curve. When the puncture needle completely penetrates the test sample, record the maximum force value, which is the puncture resistance of the separator.

[0108] The test results are shown in Table 1.

[0109] The separators in the above examples and comparative examples are assembled into batteries, and the internal resistance and energy density of the batteries are tested.

[0110] The preparation method of the battery comprises the following steps: 1) preparation of a negative electrode sheet: a negative electrode active material (graphite), a conductive agent (conductive carbon black), and a binder (CMC) are mixed in a mass ratio of 90:2:8 to obtain a mixed material, the mixed material is fully stirred in deionized water to obtain a negative electrode slurry, the obtained negative electrode slurry is coated on a copper foil, and after drying and rolling, a negative electrode sheet is obtained; 2) preparation of a positive electrode sheet: a positive electrode active material (lithium iron phosphate), a conductive agent (conductive carbon black), and a binder (PVDF) are mixed in a mass ratio of 95:3:2 to obtain a mixed material, the mixed material is fully stirred in NMP to obtain a positive electrode slurry, the obtained positive electrode slurry is coated on an aluminum foil, and after drying and rolling, a positive electrode sheet is obtained; 3) assembly of a 2032 type button cell in an Ar-filled glove box, and the assembly sequence of the battery from top to bottom is as follows: a negative electrode shell, a gasket, a gasket, a negative electrode sheet, a separator, a positive electrode sheet, and a positive electrode shell, to obtain a button cell.

[0111] The test results of the battery's internal resistance and energy density are as follows: (1) Internal resistance test: the internal resistance of the battery is measured using a battery internal resistance tester.

[0112] (2) Energy density test: first, the weight of the battery is measured and recorded as m, then the battery is charged at 0.33C constant current to 3.65V at 25°C, and then charged at 3.65V constant voltage until the current is less than or equal to 0.05C, and then left for 5 minutes, and then discharged at 0.33C constant current to 2.0V, to obtain the discharge energy Q, and the battery energy density is calculated as Q / m.

[0113] The test results are shown in Table 1.

[0114] Table 1

[0115] As can be seen from the data in Table 1, in Comparative Example 1, only a second coating layer is formed on the surface of the base film, although the puncture resistance of the separator is at a relatively high level, the electrolyte wettability of the separator is obviously poor, the internal resistance of the corresponding battery is large, and the energy density of the battery is low. In Comparative Example 2, only a first coating layer is formed on the surface of the base film, although the electrolyte wettability of the separator is at a relatively high level, the puncture resistance of the separator is obviously poor, the internal resistance of the corresponding battery is large, and the energy density of the battery is low. In Comparative Example 3, a commercially available PE film is directly used as the separator, and the electrolyte wettability and puncture resistance of the separator are both poor, the internal resistance of the corresponding battery is large, and the energy density of the battery is low. Therefore, it is difficult to simultaneously improve the electrolyte wettability and puncture resistance of the separator by separately providing a first coating layer or a second coating layer on the base film.

[0116] As can be seen from the data in Table 1, the composite separator in Embodiment 1 to Embodiment 8 not only has higher electrolyte wettability, but also has higher puncture resistance, and the corresponding battery has lower internal resistance and higher energy density. Thus, it is shown that, in the present application, the combination of the first coating layer and the second coating layer can effectively improve the electrolyte wettability, liquid retention performance and puncture resistance of the composite separator. In addition, the porosity of the composite separator in Embodiment 1 to Embodiment 8 is at a moderately appropriate level, which can guarantee higher thermal shrinkage and higher ionic conductivity, so that the composite separator has higher safety performance and higher electrochemical performance.

[0117] The present application proposes a novel composite separator structure, which adopts a unique double-layer coating structure of silk fibroin inner layer (first coating layer) / ceramic + silk fibroin outer layer (second coating layer). This structure can combine the excellent thermal stability and mechanical strength of ceramic materials, and the good flexibility, interface bonding force, electrolyte affinity of silk fibroin, so that the composite separator has high safety, good flexibility, strong interface bonding force, excellent electrolyte wettability and excellent ion conductivity.

[0118] It should be noted that the composite separator embodiments, the preparation method embodiments of the composite separator and the battery embodiments provided by the present application belong to the same concept; the technical features in the technical solutions recorded in each embodiment can be arbitrarily combined without conflict.

[0119] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations. Various modifications and changes can also be made to the above embodiments without departing from the scope of the present disclosure. Similarly, any combination of the technical features of the above embodiments can be made to form additional embodiments of the present application that have not been explicitly described. Therefore, the above embodiments only express several implementation manners of the present application, and do not limit the protection scope of the patent of the present application.

Claims

1. A composite diaphragm, characterized in that, It includes a base film, a first coating disposed on at least one side surface of the base film along the thickness direction, and a second coating disposed on the side surface of the first coating away from the base film; The first coating comprises a first silk fibroin, and the second coating comprises a second silk fibroin and ceramic particles; the content of β-sheet structure in the first silk fibroin is lower than the content of β-sheet structure in the second silk fibroin; the ceramic particles comprise modified ceramic particles, the modified ceramic particles comprise organic functional groups, the organic functional groups comprising amino and / or epoxy groups.

2. The composite diaphragm according to claim 1, characterized in that, The composite diaphragm satisfies at least one of the following characteristics: (1) The content of β-sheet structure in the first silk fibroin is 15%~30%; (2) The content of β-sheet structure in the second silk fibroin is 60%~70%; (3) The ceramic particles include at least one of alumina, boehmite, zirconium oxide, silicon oxide, magnesium oxide, titanium oxide, zinc oxide, and calcium oxide; (4) The mass ratio of the second silk fibroin to the ceramic particles is (1~3):

1.

3. The composite diaphragm according to claim 1, characterized in that, The composite diaphragm satisfies at least one of the following characteristics: (1) The thickness of the first coating is 0.5 μm to 3 μm; (2) The thickness of the second coating is 1μm~3μm; (3) The second coating also includes a dispersant and a binder, and the ratio of the total mass of the second silk fibroin to the ceramic particles, the mass of the dispersant and the mass of the binder is (75~95):(2~15):(3~15).

4. A method for preparing a composite diaphragm, characterized in that, The method includes the following steps: S1: Dissolve silk fibroin in a first solvent to obtain a silk fibroin solution, and then place the silk fibroin solution in deionized water for dialysis to obtain a first sizing agent; the first sizing agent includes a first silk fibroin. S2: Dissolve the second silk fibroin in the second solvent, then add ceramic particles, dispersant and binder in sequence, and disperse evenly to obtain the second slurry; the content of β-sheet structure in the first silk fibroin is lower than the content of β-sheet structure in the second silk fibroin; the ceramic particles include modified ceramic particles, the modified ceramic particles include organic functional groups, and the organic functional groups include amino and / or epoxy groups; S3: The first slurry is coated on at least one side surface of the base film along the thickness direction, and after drying, a first coating is formed; S4: The second slurry is coated onto the first coating, and after drying, a second coating is formed.

5. The method for preparing the composite diaphragm according to claim 4, characterized in that, Step S1 satisfies at least one of the following characteristics: (1) The first solvent includes calcium chloride, a mixture of ethanol and water, or lithium bromide; (2) Dissolve the silk fibroin in the first solvent at a temperature of 50°C to 65°C; (3) The mass ratio of the deionized water to the silk fibroin solution is (100~150):(1~2); (4) The temperature of the dialysis treatment is 2℃~4℃; (5) The dialysis treatment time is 72h~100h; (6) The mass fraction of the first silk fibroin in the first slurry is 10%~15%; (7) The content of β-sheet structure in the first silk fibroin is 15%~30%.

6. The method for preparing the composite diaphragm according to claim 4, characterized in that, Step S2 satisfies at least one of the following characteristics: (1) The content of β-sheet structure in the second silk fibroin is 60%~70%; (2) The second solvent includes deionized water; (3) The ceramic particles include at least one of alumina, boehmite, zirconium oxide, silicon oxide, magnesium oxide, titanium oxide, zinc oxide, and calcium oxide; (4) The mass ratio of the second silk fibroin to the second solvent is (1~3):(10~20); (5) The mass ratio of the second silk fibroin to the ceramic particles is (1~3):1; (6) The ratio of the total mass of the second silk fibroin and the ceramic particles, the mass of the dispersant and the mass of the binder is (75~95):(2~15):(3~15).

7. The method for preparing the composite diaphragm according to claim 4, characterized in that, The preparation method of the second silk fibroin includes: The initial silk fibroin solution is mixed with an ethanol solution, stirred and reacted, and then allowed to stand to precipitate, resulting in a silk fibroin product. After washing and drying, the silk fibroin product is subjected to heat treatment, and then the heat-treated silk fibroin product is pulverized to obtain the second silk fibroin.

8. The method for preparing the composite diaphragm according to claim 7, characterized in that, The method for preparing the second silk fibroin satisfies at least one of the following characteristics: (1) The mass fraction of silk fibroin in the initial silk fibroin solution is 10%~15%; (2) The mass fraction of the ethanol solution is 85%~95%; (3) The volume ratio of the initial silk fibroin solution to the ethanol solution is (1~3):(1~3); (4) The reaction time is 2h~4h; (5) The settling time is 12h~16h; (6) The temperature of the heat treatment is 160℃~180℃; (7) The heat treatment time is 1h~2h.

9. The method for preparing the composite diaphragm according to any one of claims 4 to 8, characterized in that, The method satisfies at least one of the following characteristics: (1) Before coating the first slurry, the surface of the base film to be coated with the first slurry is subjected to at least one of plasma treatment, corona treatment, and chemical treatment; (2) The coating speed of the first slurry is 2m / min to 5m / min; (3) The thickness of the first coating is 0.5μm~3μm; (4) The coating speed of the second slurry is 2m / min to 5m / min; (5) The thickness of the second coating is 1μm~3μm.

10. A battery, characterized in that, The composite membrane includes the composite membrane according to any one of claims 1 to 3 or the composite membrane prepared by the method according to any one of claims 4 to 9.

Images