Composite separator, method for its preparation and its use in semi-solid batteries

Abstract

The application discloses a composite diaphragm, a preparation method thereof and application thereof in a semi-solid battery. The composite diaphragm comprises a base film and a coating layer formed on at least one surface of the base film, and the coating layer comprises polyamide, LATP and an auxiliary agent. The structure of the polyamide contains at least a repeating unit shown in formula I. X, Y and Z are independently selected from a substituted or unsubstituted aromatic ring, an aromatic heterocyclic ring or a heterocyclic ring. n is an integer between 0 and 4. a is greater than or equal to 1, c is greater than or equal to 1, and a+c=b. The composite diaphragm provided in the application has the characteristics of low heat shrinkage and high conductivity, can be applied to the semi-solid battery as a diaphragm, can improve the impact resistance passing rate of the battery, and can improve the low-temperature cycle performance and safety performance of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery separators, and particularly relates to a composite separator and a preparation method thereof, and further relates to application of the composite separator in a semi-solid battery. BACKGROUND

[0002] With the rapid development of new energy automobile and energy storage market, the demand for high-performance batteries is increasing. As a new battery technology between traditional liquid lithium ion batteries and all-solid-state batteries, semi-solid batteries gradually become a research and industrialization hotspot due to their high safety, high energy density and good rate performance. Semi-solid batteries use a part of solid-state electrolyte to replace the traditional liquid electrolyte, thereby reducing the amount of liquid electrolyte, and effectively reducing the risk of battery leakage and thermal runaway. In addition, semi-solid batteries also have the advantages of wide electrochemical window and high energy density, and are considered as an important development direction of future battery technology.

[0003] As one of the key components in semi-solid batteries, the performance of the separator directly affects the safety, cycle life and rate performance of the battery. The traditional liquid lithium ion battery separator is mainly made of polyolefin materials (such as polyethylene and polypropylene), which has good chemical stability and mechanical strength. However, in semi-solid batteries, the porosity and pore size of the traditional separator are small, which is difficult to meet the filling demand of semi-solid electrolyte. Although the composite separator formed by coating a coating layer containing high molecular materials and solid-state electrolyte (such as LATP, etc.) on the surface of the base film can improve the safety and electrochemical performance of the battery to a certain extent, the thermal conductivity and battery thermal runaway threshold still need to be improved. In addition, the difference in thermal expansion coefficient between the solid-state electrolyte and the base film, and the dispersion of the solid-state electrolyte and the high molecular material affect the adhesion between the coating layer and the base film, and further affect the safety and cycle performance of the battery.

[0004] In summary, the composite separator currently applied in semi-solid batteries has the problem of imbalance of "thermal-power-electricity" triple performance, and still has the problems of insufficient ion conductivity, insufficient thermal conductivity, mechanical performance to be improved, and poor cycle performance, especially low-temperature cycle performance. It is of important practical significance to develop a new type of composite separator that can solve the above problems at the same time. SUMMARY

[0005] Therefore, the primary purpose of the present application is to provide a composite separator, which adds a polyamide with a specific structure in the coating layer, and cooperates with LATP (Li 1.3 Al 0.3 Ti 1.7PO4)3, lithium titanium aluminum phosphate), so that the obtained composite diaphragm has excellent performance in heat, force and electricity, and is a composite diaphragm with excellent comprehensive performance, which can significantly improve the performance of the semi-solid battery when applied to the semi-solid battery.

[0006] In order to achieve the above-mentioned purpose, the following technical solutions are adopted in the present application:

[0007] One aspect of the present application provides a composite diaphragm, which comprises a base film and a coating layer formed on at least one surface of the base film, and the coating layer comprises polyamide, LATP and an auxiliary agent, and the polyamide has at least a repeating unit represented by Formula I in its structure:

[0008]

[0009] wherein X, Y and Z are independently selected from substituted or unsubstituted aromatic ring, aromatic heterocycle or heterocycle; n is an integer between 0 and 4; a≥1, c≥1, and a+c=b.

[0010] Another aspect of the present application provides a preparation method of the composite diaphragm as described above, which comprises the following steps:

[0011] adding polyamide, LATP and an auxiliary agent into an organic solvent, mixing uniformly to form a coating liquid;

[0012] coating the coating liquid on at least one surface of the base film, extracting through a coagulation bath and drying to form the composite diaphragm.

[0013] Another aspect of the present application provides the use of the composite diaphragm as described above or prepared by the preparation method in a semi-solid battery.

[0014] Another aspect of the present application provides a semi-solid battery comprising the composite diaphragm as described above or prepared by the preparation method.

[0015] The present application has the following beneficial effects:

[0016] The composite diaphragm in the present application adds polyamide and LATP with specific structures in the coating layer, wherein the polyamide added in the present application has the characteristics of high temperature resistance, high adhesion and easy film formation, which can not only improve the heat resistance of the diaphragm but also increase the bonding force between the coating layer and the base film to avoid powdering of the coating layer; and after adding LATP, on the one hand, the high ionic conductivity of LATP helps to improve the overall conductivity of the diaphragm; on the other hand, both polyamide and LATP have high strength, and the synergistic effect of the two enhances the impact resistance of the battery.

[0017] In summary, the composite separator of the present application integrates the performance of heat, power and electricity, has low thermal shrinkage, high ionic conductivity, strong coating adhesion, and better safety than traditional separators. At the same time, the low temperature performance of the battery is significantly improved, and the cycle performance is improved. In addition, the composite separator of the present application has high resistance to heavy object impact, which is beneficial to reduce the thickness of the current collector, thereby improving the energy density of the battery. DETAILED DESCRIPTION

[0018] The embodiments of the present application will be clearly and completely described below. The technical solutions described in the embodiments below are exemplary, and only some possible technical implementations of the present application, not all possible implementations. Those skilled in the art can combine the embodiments of the present application without creative labor to obtain other embodiments, and these embodiments are also within the protection scope of the present application.

[0019] The first aspect of the present application discloses a composite separator, which comprises a base film and a coating layer formed on at least one surface of the base film, and the coating layer comprises polyamide, LATP and an auxiliary agent, and the structure of the polyamide contains at least a repeating unit represented by Formula I:

[0020]

[0021] wherein X, Y and Z are independently selected from substituted or unsubstituted aromatic ring, aromatic heterocycle or heterocycle; n is an integer between 0 and 4; a≥1, c≥1, and a+c=b.

[0022] In the present application, a specific structure of polyamide and LATP is added to the coating layer. Due to the synergistic effect of each key group in the structure of the polyamide, the composite separator has excellent high temperature resistance, high adhesion and easy film forming characteristics, which can not only improve the heat resistance of the separator, but also increase the bonding force between the coating layer and the base film to avoid powdering of the coating layer. Further, the LATP is compounded in the coating layer to improve the overall conductivity of the composite separator by using the high ionic conductivity of the LATP. At the same time, both the polyamide and the LATP have high strength, and the synergistic effect of the two enhances the impact resistance of the battery. The composite separator of the present application realizes the balance of heat, power and electricity, has low thermal shrinkage, high ionic conductivity, strong coating adhesion, and the low temperature performance of the battery is significantly improved, and the cycle performance is improved. In addition, the composite separator of the present application has high resistance to heavy object impact, which is beneficial to reduce the thickness of the current collector, thereby improving the energy density of the battery.

[0023] In addition, in some specific examples, the coating layer also comprises polyethylene oxide (PEO) to further improve the performance of the separator.

[0024] <base film>

[0025] In the present application, the base film is a thin film made of a porous polymer material, which provides physical separation for the battery to prevent direct contact between the positive and negative electrodes, while allowing the free transmission of metal ions in the electrolyte.

[0026] In some examples, the base film is a polyolefin film, which can be polyethylene (PE), can also be polypropylene (PP), and can also be a multi-layer composite polyolefin film of PE and PP, without special limitation.

[0027] In other examples, in order to obtain excellent thermal stability and mechanical properties, preferably, the base film is a polyolefin film coated with a ceramic layer on at least one surface, wherein the ceramic layer can be an oxide ceramic, and specific examples that can be mentioned include, but are not limited to, at least one of aluminum oxide, silicon dioxide, zirconium oxide. The ceramic layer can also be a nitride ceramic, and specific examples that can be mentioned include, but are not limited to, at least one of silicon nitride, aluminum nitride.

[0028] It can be understood that the thickness of the base film is not particularly required, and the specifications of the base film well known in the art can be used, and the person skilled in the art can select as needed, for example, for a polyolefin film, the thickness is generally 0.5-50 μm, preferably 5-30 μm, more preferably 5-14 μm. For the thickness of the ceramic layer, the single-sided thickness is generally 0.1-5 μm, preferably 0.5-5 μm, more preferably between 1-3 μm.

[0029] < Polyamide >

[0030] In the present application, the polyamide is obtained by copolymerization of a first monomer, a second monomer and a third monomer, wherein:

[0031] The first monomer is at least one of aromatic diacyl chloride, aromatic heterocyclic diacyl chloride, and heterocyclic diacyl chloride;

[0032] The second monomer is an alkyl ether group-containing diamine, and its general structure is shown in formula II:

[0033]

[0034] Wherein, n is an integer between 0-4;

[0035] The third monomer is a sulfone group-containing aromatic, aromatic heterocyclic or heterocyclic diamine, or a mixture thereof with other diamines.

[0036] In some examples, the first monomer is at least one of isophthaloyl chloride, terephthaloyl chloride, naphthalene dicarboxylic acid chloride, 1,3,5-benzene tricarboxylic acid chloride, 4,4'-diphenyl ether dicarboxylic acid chloride, imidazole dicarboxylic acid chloride, furan dicarboxylic acid chloride, and pyridine dicarboxylic acid chloride, but is not limited thereto.

[0037] In some examples, the second monomer is any one of the following compounds A-C:

[0038]

[0039] The specific second monomer can be prepared by commercially available or known methods in the art.

[0040] In some examples, the preparation methods of compounds A, B, and C are as follows, respectively:

[0041] Compound A: Dichloroethane (0.1 mol) is added to DMF (100 mL), p-nitrophenol (0.2 mol), potassium carbonate (0.2 mol), and reacted at 125°C for 5 hours. Filtration and solvent evaporation are performed, and a nitro-containing intermediate is obtained. The nitro-containing intermediate is dissolved in ethanol (100 mL), and palladium-carbon (1 g) is added. The mixture is heated to 45°C under a hydrogen atmosphere of 0.2 MPa for 12 hours. The reaction is stopped, filtration is performed, and the solvent is evaporated. Column chromatography is performed to obtain compound A with the following structure.

[0042] Compound B: 1,2-bis(2-chloroethoxy)ethane (0.1 mol) is added to DMF (100 mL), p-nitrophenol (0.2 mol), potassium carbonate (0.2 mol), and reacted at 125°C for 5 hours. Filtration and solvent evaporation are performed, and a nitro-containing intermediate is obtained. The nitro-containing intermediate is dissolved in ethanol (100 mL), and palladium-carbon (1 g) is added. The mixture is heated to 45°C under a hydrogen atmosphere of 0.2 MPa for 12 hours. The reaction is stopped, filtration is performed, and the solvent is evaporated. Column chromatography is performed to obtain compound B with the following structure.

[0043] Compound C: Dichloroethane (0.1 mol) is added to DMF (100 mL), p-nitrophenol (0.1 mol), m-nitrophenol (0.1 mol), and potassium carbonate (0.2 mol), and reacted at 125°C for 5 hours. Filtration and solvent evaporation are performed, and a nitro-containing intermediate is obtained. The nitro-containing intermediate is dissolved in ethanol (100 mL), and palladium-carbon (1 g) is added. The mixture is heated to 45°C under a hydrogen atmosphere of 0.2 MPa for 12 hours. The reaction is stopped, filtration is performed, and the solvent is evaporated. Column chromatography is performed to obtain compound C with the following structure.

[0044] The third monomer can be a sulfone-containing aromatic, aromatic heterocyclic, or heterocyclic diamine, or a mixture of a sulfone-containing aromatic, aromatic heterocyclic, or heterocyclic diamine and other diamines.

[0045] The sulfone-containing aromatic, aromatic heterocyclic, or heterocyclic diamine is at least one of 4,4-diaminodiphenyl sulfone, 3,4-diaminodiphenyl sulfone, 3,3-diaminodiphenyl sulfone, and 3,6-thioanthracene diamine.

[0046] The other diamines are aromatic, aromatic heterocyclic, heterocyclic or aliphatic diamines without sulfone groups, and specific examples include at least one of m-phenylenediamine, p-phenylenediamine, pyridine diamine, naphthalene diamine, butane diamine, and pentane diamine, but are not limited thereto.

[0047] Further, the amounts of the first monomer, the second monomer and the third monomer can be adjusted according to actual needs, and in some specific embodiments of the present application, the molar ratio of the first monomer n1, the second monomer n2 and the third monomer n2 is n1:(n2+n3)=(0.95-1.05):1, and preferably n1:(n2+n3)=1:1.

[0048] Further, the method for preparing the polyamide in the present application can be prepared by the following method, and the main steps include:

[0049] Under the protection of an inert atmosphere, the organic solvent, the second monomer and the third monomer are sequentially added to the reaction container and stirred, and then the catalyst is added and stirred continuously;

[0050] The temperature is adjusted to 0-10°C, the first monomer is added to the system, the reaction is completed, and the polyarylether sulfone amide is obtained.

[0051] The inert atmosphere refers to the reaction in an oxygen-free environment by introducing an inert atmosphere, and the inert atmosphere used can be one of noble gases or nitrogen, and is not particularly limited.

[0052] Further, the organic solvent can be of a type commonly used in the art, and specific examples include but are not limited to at least one of N,N-dimethylformamide (DMF), dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and dichloromethane. The specific amount can be adjusted according to the actual situation, and in some specific embodiments of the present application, the mass of the organic solvent is 3-10 times the mass of the total diamine.

[0053] Further, the polymerization efficiency of the reaction is improved by adding a catalyst in the reaction, and thus a polyarylether sulfone amide with excellent performance is obtained, and in some specific embodiments of the present application, the catalyst is at least one of tungsten sulfate, tungsten hexachloride, and zirconium sulfate, and the content of the catalyst is 0.5%-5% of the total mass of the diamine.

[0054] Further, after the reaction is completed, the following steps are included:

[0055] A poor solvent for the polyarylether sulfone amide is added to the solution after the reaction is completed, and after stirring, the solution is filtered and dried.

[0056] The poor solvent described herein refers to a poor solvent of the polyarylene ether sulfone amide, and the polyarylene ether sulfone amide is precipitated by adding the poor solvent of the polyarylene ether sulfone amide. In some specific embodiments of the present application, the poor solvent is at least one of methanol, ethanol, isopropanol, acetonitrile, and n-butanol, but is not limited thereto, and the specific amount can be selected according to the amount of the organic solvent. In some specific embodiments of the present application, preferably, the mass of the poor solvent is 1-3 times the mass of the organic solvent.

[0057] <Assistant>

[0058] In the present application, the assistant mainly refers to a functional assistant for improving the uniformity and dispersibility of the coating layer, or for imparting corresponding functions to the composite separator, and specific examples that can be mentioned include, but are not limited to, at least one of a binder, a dispersant, a thickening agent, and a conductive agent. In some examples, the assistant includes at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, polyacrylonitrile, styrene butadiene rubber, and PVDF.

[0059] <Preparation of the composite separator>

[0060] In the present application, the preparation of the composite separator mainly includes the following steps:

[0061] The polyamide, the LATP, and the assistant are added to the organic solvent and mixed uniformly to form a coating liquid;

[0062] The coating liquid is coated on at least one surface of the base film, extracted by a coagulation bath, and dried to form the composite separator.

[0063] The coating liquid is obtained by uniform stirring in a conventional mechanical stirring manner in the art. The organic solvent in the coating liquid is mainly used to dissolve and / or disperse other components in the coating liquid, but it does not react with other components and facilitates removal in the later process. Specific examples that can be mentioned include at least one of N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide, but are not limited thereto.

[0064] The ratio of the components in the coating liquid can be determined by experimental methods in the art. In some examples, the following mass fractions are used: 5-30 parts of polyamide, 1-10 parts of LATP, 1-20 parts of assistant, and 20-100 parts of organic solvent.

[0065] Further, the coating thickness of the coating liquid can be adjusted or optimized as needed. In some examples, the single-sided coating thickness is 0.5-5 μm, and preferably 1-3 μm.

[0066] Further, after coating, the composite separator can be obtained by extraction in a coagulation bath and drying. The coagulation bath is mainly a process of inducing phase separation of the polymer solution and forming a solid film during the preparation of the coating layer by the wet method or phase inversion method, which is generally achieved by a coagulation liquid. The coagulation liquid mainly includes a solvent (such as dimethylformamide DMF or dimethylacetamide DMAC) and a non-solvent (water or ethanol), and can also contain additives, etc. In some examples of the present application, the coagulation liquid used is a mixture of water and DMAC in a mass ratio of 1:1.

[0067] The second aspect of the present application discloses an application of the composite separator described above or prepared by the preparation method described above in a semi-solid battery.

[0068] The third aspect of the present application discloses a semi-solid battery comprising the composite separator described above or prepared by the preparation method described above.

[0069] In the present application, the semi-solid battery refers to a repeatable charge-discharge energy storage device, the electrolyte of which comprises a solid-state electrolyte and a liquid-state electrolyte, and the core components of which include a positive electrode, a negative electrode, a separator and an electrolyte. The separator adopts the composite separator described in the present application. The positive electrode, the negative electrode and the electrolyte can all adopt conventional compositions in the art without special limitations, and those skilled in the art can select or configure them according to the needs, which have such ability, and here is not repeated.

[0070] The following are specific examples of the present application. It should be noted that the following specific examples are for illustrative purposes only and do not limit the scope of the present application in any way.

[0071] 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 the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0072] In addition, unless otherwise specified, the methods without specific conditions or steps are conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0073] Example 1

[0074] A preparation method of a composite separator is disclosed in the present embodiment:

[0075] DMAC (100 g), polyamide (10 g), LATP (8 g), PVDF (1 g) and polyvinyl alcohol (1 g) were sequentially added to the reactor, stirred for 1 h to form a coating liquid;

[0076] The coating liquid is coated on both sides of the base film (PE with a thickness of 5 μm, both sides of which are formed with an aluminum oxide layer, and the thickness of the aluminum oxide single layer is 1 μm), the coating thickness of each side is 2 μm, and the film is extracted through a coagulation bath, the coagulation liquid is a mixture of water and DMAC (mass ratio is 1:1), and the extracted film is dried at 60°C, thereby obtaining the composite separator.

[0077] In the embodiment, the polyamide is prepared from the three monomers described in Table 1 by the following method:

[0078] S1, preparation of compound A

[0079] Dichloroether (0.1 mol), p-nitrophenol (0.2 mol), and potassium carbonate (0.2 mol) are added to DMF (100 mL), and the mixture is reacted at 125°C for 5 hours. The solvent is extracted and dried by rotary evaporation to obtain a nitro-containing intermediate. The nitro-containing intermediate is dissolved in ethanol (100 mL), and palladium-carbon (1 g) is added. The mixture is heated to 45°C under a hydrogen atmosphere of 0.2 MPa and reacted for 12 hours. The reaction is stopped, the mixture is extracted and dried by rotary evaporation, and column chromatography is performed to obtain compound A with the following structure:

[0080]

[0081] S2, preparation of polyamide

[0082] DMAC (200 g), 4,4-diaminodiphenyl sulfone (24.8 g, 0.1 mol), and compound A (28.8 g, 0.1 mol) are added to a reaction kettle under nitrogen protection, and tungsten sulfate (0.5 g) is stirred. After the internal temperature is reduced to 0°C by opening the cooling bath, m-phthaloyl chloride (40.6 g, 0.2 mol) is added, and the mixture is reacted for 1 hour to obtain polyarylether sulfone amide slurry. Methanol (600 g) is added, the mixture is stirred for 1 hour, extracted, and dried by rotary evaporation to obtain the polyamide.

[0083] Examples 2-7

[0084] The preparation method of another composite separator is disclosed in Examples 2-7, and the implementation in Example 1 is referred to, and the only difference is that the structure of the polyamide is different.

[0085] In the embodiment, the polyamide is prepared from the three monomers described in Table 1 by the following method:

[0086] Example 8

[0087] Another preparation method of a composite separator is provided in the embodiment, and the implementation in Example 1 is referred to, and the only difference is that the polyamide is 5 g and the LATP is 1 g.

[0088] Example 9

[0089] Another method for preparing a composite separator is provided in this example, referring to the implementation in Example 1, the only difference being that the polyamide is 30 g and the LATP is 10 g.

[0090] Comparative Example 1

[0091] A method for preparing a composite separator is provided in this comparative example, referring to the implementation in Example 1, the only difference being that the polyamide in the coating layer of Example 1 is replaced with an equal amount of LATP.

[0092] Comparative Example 2

[0093] A method for preparing a composite separator is provided in this comparative example, referring to the implementation in Example 1, the only difference being that the LATP in the coating layer of Example 1 is replaced with an equal amount of polyamide.

[0094] Comparative Example 3

[0095] A composite separator is provided in this comparative example, which is the base film in Example 1, without forming a coating layer on the surface of the base film.

[0096] Comparative Example 4

[0097] A method for preparing a composite separator is provided in this comparative example, referring to the implementation in Example 1, the only difference being that the polyamide in the coating layer of Example 1 is replaced with an equal amount of poly-m-phenylene isophthalamide.

[0098] Table 1 Monomer composition of polyamide in Examples 1-7

[0099]

[0100] Performance Test

[0101] The composite separators in Examples 1-9 and Comparative Examples 1-4 were subjected to the following performance tests, respectively:

[0102] (1) Heat shrinkage test

[0103] A 10 cm x 10 cm size sample was cut from the composite separator, and the longitudinal length (MD1) and transverse length (TD1) before heating were measured. The separator sample was placed in a vacuum oven at a temperature of 150°C for 1 h, taken out, cooled to room temperature, and the longitudinal length (MD2) and transverse length (TD1) were measured again. The heat shrinkage Y was calculated according to the following formula.

[0104]

[0105] (2) Peel strength and conductivity test: tested according to the standard GB / T 36363-2018.

[0106] (3) 100% SOC heavy impact test: refer to GB 31241-2014.

[0107] (4) Low temperature capacity retention: refer to GB 31241-2014, test condition (-10℃, 0.2C, 3.4V).

[0108] Wherein, (3) and (4) are the corresponding tests on the battery after the composite separator is assembled into the battery, wherein the negative electrode of the battery is graphite, the positive electrode sheet is lithium iron phosphate, and the electrolyte is 1M LiPF6 (the electrolyte solvent is a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1). The specific assembly method can be according to the well-known in the art.

[0109] The above test results are shown in Table 2.

[0110] Table 2 Performance test results

[0111]

[0112] From the test results in Table 2, it can be concluded that compared with the comparative example, the composite separator provided in the application example has significantly improved thermal shrinkage, peel strength, 100% SOC heavy impact, electrical conductivity and low temperature cycle performance. This is due to the cooperation of the specific structure of the polyamide and LATP in the coating layer, which not only enhances the heat resistance of the separator and the bonding ability with the base film, but also improves the overall electrical conductivity of the separator. In addition, the polyamide and LATP added in the application both have high strength, and the two of them have synergistic effect, which significantly enhances the impact resistance of the battery. This can reduce the thickness of the current collector in the battery, thereby improving the energy density of the semi-solid battery.

[0113] It should be noted that the application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the application are all included in the technical scope of the application. In addition, within the scope of the application, various modifications of the embodiments that can be thought of by those skilled in the art, as well as other ways of combining part of the components in the embodiments, are also included in the scope of the application.

Claims

1. A composite diaphragm, characterized in that, The composite membrane includes a base membrane and a coating layer formed on at least one surface of the base membrane. The coating layer includes polyamide, LATP, and additives. The polyamide has a structure containing at least one repeating unit as shown in Formula I. ， Where X, Y, and Z are independently selected from substituted or unsubstituted aromatic rings or heterocycles; n is an integer between 0 and 4; a≥1, c≥1, a+c=b; The polyamide is obtained by copolymerization of a first monomer, a second monomer, and a third monomer, wherein: The first monomer is at least one of aromatic diacyl chloride and heterocyclic diacyl chloride; The second monomer is a diamine containing an alkyl ether group, and its general structural formula is shown in Formula II: ， Where n is an integer between 0 and 4; The third monomer is an aromatic or heterocyclic diamine containing a sulfone group, or a mixture thereof with other diamines.

2. The composite diaphragm as described in claim 1, characterized in that, The base membrane is a polyolefin base membrane.

3. The composite diaphragm as described in claim 2, characterized in that, At least one surface of the polyolefin-based film is provided with a ceramic layer.

4. The composite diaphragm as described in claim 2 or 3, characterized in that, The polyolefin-based film is made of at least one of PE and PP.

5. The composite diaphragm as described in claim 3, characterized in that, The ceramic layer includes at least one of oxide ceramics or nitride ceramics.

6. The composite diaphragm as described in claim 5, characterized in that, The oxide ceramic is at least one of alumina, silicon oxide, and zirconium oxide; the nitride ceramic is at least one of silicon nitride and aluminum nitride.

7. The composite diaphragm as described in claim 1, characterized in that, The first monomer is at least one of isophthaloyl chloride, terephthaloyl chloride, naphthaloyl chloride, 1,3,5-benzenetricarboxyl chloride, 4,4'-diphenyl ether carboxyl chloride, imidazole carboxyl chloride, furan carboxyl chloride, and pyridine carboxyl chloride; The second monomer is any one of the following compounds A to C: ； The sulfone-containing aromatic or heterocyclic diamine is at least one of 4,4-diaminodiphenyl sulfone, 3,4-diaminodiphenyl sulfone, 3,3-diaminodiphenyl sulfone, and 3,6-thioanthraphthalene diamine.

8. The composite diaphragm as described in claim 1, characterized in that, The coating also includes polyethylene oxide.

9. The composite diaphragm as described in claim 1, characterized in that, The additives include at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, polyacrylonitrile, styrene-butadiene rubber, and PVDF.

10. A method for preparing a composite separator as described in any one of claims 1-9, characterized in that, Includes the following steps: Polyamide, LATP, and additives are added to an organic solvent and mixed thoroughly to form a coating solution. The coating solution is applied to at least one surface of the base membrane, and then extracted in a coagulation bath and dried to form a composite membrane.

11. The preparation method according to claim 10, characterized in that, The organic solvent is at least one of N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

12. The preparation method according to claim 10 or 11, characterized in that, The coating liquid is composed of the following components in parts by mass: 5-30 parts polyamide, 1-10 parts LATP, 1-20 parts additives, and 20-100 parts organic solvent.

13. The application of the composite separator as described in any one of claims 1-9 or the composite separator prepared by the preparation method as described in any one of claims 10-11 in a semi-solid-state battery.

14. A semi-solid-state battery, characterized in that, It includes the composite membrane according to any one of claims 1-9 or the composite membrane prepared by the preparation method according to any one of claims 10-11.

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