Composite separator and method for manufacturing the same

Abstract

The application discloses a composite diaphragm and a preparation method thereof. The composite diaphragm comprises modified zirconium oxide, modified polyimide and modified polyamide acid, and the modified zirconium oxide, the modified polyimide and the modified polyamide acid each independently has a hydrophilic group, and the hydrophilic group comprises a hydroxyl group. The composite diaphragm provided by the application has good hydrophilicity and gas resistance.

Description

Technical Field

[0001] This application relates to the field of separation membrane technology, specifically to composite membranes and their preparation methods. Background Technology

[0002] In fields such as hydrogen production through water electrolysis, fuel cells, flow batteries, and water treatment, the membrane is a core component, and its performance directly determines the efficiency, stability, and safety of the equipment. Depending on the application scenario, the membrane needs to possess both specific transport and separation functions. However, the hydrophilic and gas-barrier properties of the membrane need further improvement. Summary of the Invention

[0003] The first aspect of this application proposes a composite membrane comprising modified zirconium oxide, modified polyimide, and modified polyamic acid, wherein each of the modified zirconium oxide, modified polyimide, and modified polyamic acid independently has a hydrophilic group, the hydrophilic group including hydroxyl groups.

[0004] This application utilizes an organic-inorganic composite membrane comprising modified zirconium oxide, modified polyimide, and modified polyamic acid, exhibiting high hydrophilic gas barrier properties. Zirconia (ZrO2) readily forms Zr-OH with water, creating hydrophilic sites that can form a hydrogen bond network with water, thus inherently possessing hydrophilic properties. Further modification by introducing hydroxyl groups onto the zirconium oxide surface, resulting in modified zirconium oxide with hydrophilic groups such as hydroxyl groups, further enhances its hydrophilicity. Consequently, the modified polyimide, containing hydrophilic hydroxyl groups, works in conjunction with the modified zirconium oxide to form a hydrogen bond network with water, better performing adsorption and anchoring functions, thereby improving the overall hydrophilicity. This allows liquid water to rapidly wet the composite membrane, filling the pores and increasing the resistance to gas flow within the pores, thus blocking gas diffusion and improving gas barrier performance.

[0005] In some embodiments, the composite diaphragm comprises, by weight percentage: 60%-90% modified zirconium oxide; optionally 70%-90% modified zirconium oxide. 0-40% modified polyimide; optionally 3%-9% modified polyimide; 0-40% modified polyamic acid; optionally 7%-21% modified polyamic acid.

[0006] In some implementations, the composite diaphragm satisfies at least one of the following: (a) The content of hydroxyl groups in the modified polyimide is 2wt%-15wt%; (b) The content of hydroxyl groups in the modified polyamic acid is 1wt%-10wt%; (c) The content of hydroxyl groups in the modified zirconia is 0.5wt%-3.5wt%.

[0007] In some embodiments, the composite membrane structure includes a first membrane layer and a second membrane layer; the porosity of the first membrane layer is less than that of the second membrane layer, and the pore size of the first membrane layer is less than that of the second membrane layer.

[0008] In some embodiments, the composite diaphragm satisfies at least one of the following (A) to (F): (A) The porosity of the first membrane layer is 5%-15%; (B) The pore size of the first film layer is 20nm-100nm; (C) The thickness of the first film layer is 5μm-15μm; (D) The porosity of the second membrane layer is 50%-80%; (E) The pore size of the second membrane layer is 0.3 μm-2 μm; (F) The thickness of the second film layer is 300μm-500μm.

[0009] In some embodiments, the second film layer further includes a framework material; optionally, the framework material satisfies at least one of the following (I) and (II): (I) The skeleton material is a mesh structure with a mesh size of 250-350 mesh; (II) The skeleton material includes one or more of polyphenylene sulfide, polypropylene, and polytetrafluoroethylene.

[0010] In some embodiments, the composite diaphragm satisfies at least one of the following (i) to (iii): (i) The thickness of the composite membrane is 305μm-515μm; optionally 400μm-500μm; (ii) The particle size of the modified zirconium oxide is 50nm-200nm; (iii) The molecular weight of the modified polyamic acid is 40,000-80,000.

[0011] The second aspect of this application discloses a method for preparing a composite membrane, comprising: The slurry is provided, comprising modified polyamic acid, modified zirconia, modified polyimide, and solvent; the modified zirconia, modified polyimide, and modified polyamic acid each independently have hydrophilic groups, including hydroxyl groups; and the amount of modified polyimide added is greater than or equal to 0 parts; The slurry is coated onto the skeleton material; The composite membrane is obtained by curing.

[0012] In some embodiments, the curing process includes heat treatment; optionally, the heat treatment temperature is 50°C-100°C.

[0013] In some implementations, the method satisfies at least one of the following (α) and (β): (α) Methods for coating a slurry onto a skeleton material include casting; (β) The viscosity of the slurry is 0.7 dL / g-1.0 dL / g.

[0014] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 A schematic diagram of the structure of the composite diaphragm provided in some embodiments of this application is shown.

[0016] Figure 2 The surface SEM image of the composite diaphragm obtained in Example 3 of this application is shown.

[0017] Figure 3 The image shows a cross-sectional SEM image of the composite diaphragm obtained in Example 3 of this application.

[0018] Explanation of reference numerals in the attached figures: 101 First film layer; 102 Framework material; 103 Second film layer. Detailed Implementation

[0019] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0020] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0021] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this application.

[0022] In this application, the terms "comprising" or "including" are open-ended expressions, meaning they include the content specified in this application but do not exclude other aspects.

[0023] In fields such as hydrogen production through water electrolysis, fuel cells, flow batteries, and water treatment, the membrane is a core component, and its hydrophilicity and gas barrier properties have a significant impact on the performance of the equipment. Traditional polyimide membranes lack sufficient hydrophilicity.

[0024] Therefore, a first aspect of the present application provides a composite membrane comprising modified zirconium oxide, modified polyimide, and modified polyamic acid, wherein the modified zirconium oxide, modified polyimide, and modified polyamic acid each independently have hydrophilic groups, the hydrophilic groups including hydroxyl groups.

[0025] In this embodiment, an organic-inorganic composite membrane comprising modified zirconium oxide, modified polyimide, and modified polyamic acid exhibits high hydrophilic gas barrier properties. Zirconia (ZrO2) readily forms Zr-OH with water, creating hydrophilic sites that can form a hydrogen bond network with water. Therefore, zirconium oxide itself possesses hydrophilic properties. Further modification by introducing hydroxyl groups onto the zirconium oxide surface to form modified zirconium oxide with hydrophilic groups such as hydroxyl groups further enhances its hydrophilicity. Thus, the modified polyimide, containing hydrophilic hydroxyl groups, works in conjunction with the modified zirconium oxide to form a hydrogen bond network with water, better performing adsorption and anchoring functions, thereby improving the overall hydrophilicity. This allows liquid water to rapidly wet the composite membrane, filling the pores and increasing the resistance to gas flow within the pores, thus blocking gas diffusion and improving gas barrier properties.

[0026] Furthermore, in the embodiments of this application, the modified polyamic acid has hydrophilic groups such as hydroxyl groups. On the one hand, the surface hydrophilic groups such as hydroxyl groups can form hydrogen bonds with water, improving the water adsorption performance, which in turn helps to further improve the hydrophilic gas barrier performance of the composite membrane. On the other hand, the modified polyamic acid with hydroxyl groups exhibits good adhesion properties, acting as a binder in the composite membrane, which helps to improve problems such as coating peeling and material loss, and helps to obtain a structurally stable composite membrane, and also helps the composite membrane to better exert its hydrophilic gas barrier performance.

[0027] In some embodiments of this application, the composite diaphragm comprises, by weight percentage: 60%-90% modified zirconium oxide; optionally 70%-90% modified zirconium oxide. 0-40% modified polyimide; optionally 3%-9% modified polyimide; 0-40% modified polyamic acid; optionally 7%-21% modified polyamic acid.

[0028] As an example, the composite membrane contains 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, or any number between two of these. As an example, the composite separator contains 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 25%, 30%, 35%, 40%, or any number of modified polyimides between two of these. As an example, the composite separator contains 0, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 27%, 30%, 33%, 35%, 37%, 40%, or any number of these values.

[0029] In this embodiment, the modified polyimide exhibits high high-temperature resistance, insulation properties, mechanical strength, chemical corrosion resistance, and flexibility, along with good stability. The modified polyimide also possesses good flexibility and structural strength. The composite diaphragm combines the advantages of both organic and inorganic materials, possessing the flexibility of organic diaphragms and the rigidity of zirconium oxide, making it suitable for various applications. Furthermore, by controlling the content of modified polyamic acid to meet the above conditions, a composite diaphragm with high stability and good flexibility can be obtained.

[0030] In some embodiments of this application, the composite diaphragm satisfies at least one of the following: (a) The content of hydroxyl groups in the modified polyimide is 2wt%-15wt%; (b) The content of hydroxyl groups in the modified polyamic acid is 1wt%-10wt%; (c) The content of hydroxyl groups in the modified zirconia is 0.5wt%-3.5wt%.

[0031] As an example, the content of hydroxyl groups in modified polyimides is 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, etc.

[0032] As an example, the content of hydroxyl groups in modified polyamic acid is 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, etc.

[0033] As an example, the hydroxyl content in modified zirconia is 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, etc.

[0034] In this embodiment, the proportion of hydroxyl groups in the modified polyimide meets the above conditions. While improving the hydrophilicity, the obtained modified polyimide can also maintain high strength, temperature resistance, and chemical corrosion resistance, thereby better improving the overall hydrophilic and gas barrier properties of the composite membrane.

[0035] In this embodiment, the proportion of hydroxyl groups in the modified polyamic acid meets the above conditions, which is beneficial to improving the hydrophilicity of the composite membrane, providing better adhesion, reducing the risk of swelling, and improving the overall stability of the composite membrane.

[0036] In this embodiment, the proportion of hydroxyl groups in the modified zirconium oxide meets the above conditions, which is beneficial to better improve the hydrophilicity and dispersibility of zirconium oxide, and to better balance the hydrophilicity and gas barrier properties of the composite membrane.

[0037] In some embodiments of this application, the composite membrane structure includes a first membrane layer and a second membrane layer; the porosity of the first membrane layer is less than that of the second membrane layer, and the pore size of the first membrane layer is less than that of the second membrane layer.

[0038] In this embodiment, the first membrane layer has a small porosity and pore size, forming a dense layer. This dense structure helps reduce gas permeability, thereby improving gas barrier performance. The modified polyimide, modified zirconium oxide, and modified polyamic acid in the first membrane layer have hydroxyl hydrophilic groups, which can better adsorb and anchor water, improving hydrophilicity. After water is wetted in the pores, it increases the gas diffusion resistance, further improving gas barrier performance. The modified polyimide, modified zirconium oxide, and modified polyamic acid in the second membrane layer also have hydroxyl hydrophilic groups, as mentioned above, providing high hydrophilicity. At the same time, the second membrane layer has a large porosity and pore size, forming a porous layer. This porous network structure provides more and less resistant transport channels for ion transport, thereby improving ion conductivity. Therefore, the synergistic effect of the first and second membrane layers can improve the hydrophilic barrier properties while simultaneously enhancing the ionic conductivity and reducing the resistance of the composite membrane. This helps resolve the industry contradiction of "high resistance due to density and poor gas barrier properties due to porosity," and also facilitates improvements in component permeability and retention. Furthermore, it helps overcome drawbacks such as coating peeling and filler loss, meeting the needs of various applications including membranes for water electrolysis and ultrafiltration.

[0039] In some embodiments of this application, the composite diaphragm satisfies at least one of the following (A) to (F): (A) The porosity of the first membrane layer is 5%-15%; (B) The pore size of the first film layer is 20nm-100nm; (C) The thickness of the first film layer is 5μm-15μm; (D) The porosity of the second membrane layer is 50%-80%; (E) The pore size of the second membrane layer is 0.3 μm-2 μm; (F) The thickness of the second film layer is 300μm-500μm.

[0040] As an example, the porosity of the first membrane layer is 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc.

[0041] As an example, the pore size of the first film layer is 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 100nm, etc.

[0042] As an example, the thickness of the first film layer is 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc.

[0043] In this embodiment, the porosity, pore size, thickness and other structural characteristics of the first membrane layer meet the above conditions, which is beneficial to improving the gas barrier performance of the first membrane layer and also beneficial to improving the retention rate of the composite membrane; at the same time, it also takes into account reducing the obstruction to ion conduction and better improving the resistance of the composite membrane.

[0044] As an example, the porosity of the second membrane layer is 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0045] As an example, the pore size of the second membrane layer is 0.3μm, 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, 1.7μm, 1.9μm, 2.0μm, etc.

[0046] As an example, the thickness of the second film layer is 300μm, 320μm, 340μm, 360μm, 380μm, 400μm, 420μm, 440μm, 460μm, 480μm, 500μm, etc.

[0047] In this embodiment, the porosity, pore size, thickness and other structural characteristics of the second membrane layer meet the above conditions, which is conducive to providing more ion transport channels, reducing the resistance of the composite membrane, and also conducive to increasing the flow rate of the composite membrane; at the same time, it also takes into account reducing the adverse effects on the gas barrier performance.

[0048] In some embodiments of this application, the second film layer further includes a framework material; optionally, the framework material satisfies at least one of the following (I) and (II): (I) The skeleton material is a mesh structure with a mesh size of 250-350 mesh; (II) The skeleton material includes one or more of polyphenylene sulfide, polypropylene, and polytetrafluoroethylene.

[0049] As an example, the mesh count of the mesh structure is 250 mesh, 275 mesh, 300 mesh, 325 mesh, 350 mesh, or any value between the two.

[0050] In this embodiment, a skeleton material is added to the second membrane layer, which helps to exert mechanical reinforcement and physical constraint effects, thereby improving the overall structural stability of the composite membrane.

[0051] Furthermore, the skeleton material can be a mesh structure, such as polyphenylene sulfide (PPS) mesh. The hydrophilic gas barrier layer (second membrane layer, first membrane layer) is formed in the pores and surface of the mesh structure to form a composite structure. When the composite membrane is subjected to stretching, compression or internal stress due to hydrothermal changes (swelling / contraction), the flexible hydrophilic gas barrier layer will transfer the stress to the PPS mesh skeleton with high modulus and high strength. The skeleton material can bear most of the mechanical load, which helps to protect the brittle or creep-prone hydrophilic gas barrier layer from damage.

[0052] Furthermore, materials such as PPS mesh possess high strength, flexibility, and chemical corrosion resistance, and can be combined with hydrophilic barrier materials to facilitate the long-life and high-safety operation of composite diaphragms under complex working conditions (such as high pressure, strong acid, dry and wet cycles).

[0053] In some embodiments of this application, the composite diaphragm satisfies at least one of the following (i) to (iii): (i) The thickness of the composite membrane is 305μm-515μm; optionally 400μm-500μm; (ii) The particle size of the modified zirconium oxide is 50nm-200nm; (iii) The molecular weight of the modified polyamic acid is 40,000-80,000.

[0054] As an example, the thickness of the composite membrane is 200μm, 250μm, 300μm, 350μm, 400μm, 450μm, 500μm, 550μm, 600μm, 650μm, 700μm, 750μm, 800μm, 850μm, 900μm, etc.

[0055] In this embodiment, the thickness of the composite membrane meets the above conditions, which helps to better balance the hydrophilic barrier properties and ion transport properties, improve the overall performance of the composite membrane, and the composite membrane exhibits better retention rate and flow rate.

[0056] As an example, the particle sizes of modified zirconia are 50nm, 70nm, 90nm, 110nm, 130nm, 150nm, 170nm, 190nm, 200nm, etc.

[0057] In this embodiment, the particle size of the modified zirconia meets the above conditions. On the one hand, it is beneficial to provide a larger specific surface area and more hydrophilic interfaces; on the other hand, it is beneficial to form appropriate porosity and pore size, especially to form a porous support for the second membrane layer, thereby improving the ionic conductivity of the composite membrane and reducing the resistance.

[0058] For example, the molecular weights of modified polyamic acid are 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, etc.

[0059] In this embodiment, the molecular weight of the modified polyamic acid meets the above conditions, providing good adhesion properties, and the overall flexibility and film-forming properties of the formed composite membrane fully utilize the role of organic components.

[0060] The provided composite diaphragm combines the advantages of organic and inorganic materials, achieving a balance between low resistance and high gas barrier properties, while also possessing the flexibility of organic diaphragms and the rigidity of zirconium oxide, thus adapting to diverse assembly stresses in different application scenarios.

[0061] A second aspect of this application provides a method for preparing a composite membrane, comprising: The slurry is provided, comprising modified polyamic acid, modified zirconia, modified polyimide, and solvent; the modified zirconia, modified polyimide, and modified polyamic acid each independently have hydrophilic groups, including hydroxyl groups; and the amount of modified polyimide added is greater than or equal to 0 parts; The slurry is coated onto the skeleton material; The composite membrane is obtained by curing.

[0062] This application describes the preparation of a hydrophilic gas-barrier composite diaphragm using a modified polyamic acid and modified zirconia organic-inorganic composite slurry as the main components. The slurry may or may not contain modified polyimide. For example, without modified polyimide, a curing process can be selected to partially imidize the modified polyamic acid during curing, thus converting some of the modified polyamic acid into modified polyimide. Alternatively, with modified polyimide in the slurry, a curing process can be selected without considering imidization. The resulting composite diaphragm can contain modified polyimide, modified polyamic acid, and modified zirconia simultaneously. This method offers a simple preparation process, relatively low raw material costs, and effectively balances the requirements for hydrophilic gas-barrier properties, stability, and cost-effectiveness of the composite diaphragm.

[0063] Furthermore, the modified polyamic acid contains carbon-oxygen double bonds, which can form hydrogen bonds with the hydroxyl groups on the surface of modified zirconia. This improves the dispersion of modified zirconia in the slurry, reduces slurry agglomeration and deposition, and lowers processing difficulty. It also helps improve the distribution of inorganic powders within the composite membrane, reducing the adverse effects of zirconia particle agglomeration, such as stress concentration, decreased gas barrier effect, and increased internal resistance. The synergistic effect between modified polyamic acid and modified zirconia allows the composite membrane to combine the advantages of both organic and inorganic materials, achieving a balance between low resistance and high gas barrier properties. It also possesses the flexibility of organic membranes and the rigidity of modified zirconia, resulting in a composite membrane with high hydrophilic gas barrier performance and low internal resistance.

[0064] In some embodiments of this application, the slurry also includes one or more of a dispersant and a pore-forming agent.

[0065] As an example, the solvent includes, but is not limited to, one or more of N,N-dimethylacetamide, N-methylpyrrolidone, and N,N-dimethylformamide.

[0066] As an example, the adhesive includes one or more of the modified polyamic acids.

[0067] As an example, dispersants include one or more of fish oil, such as triethanolamine, polyacrylamide, and sodium dodecylbenzenesulfonate.

[0068] As an example, pore-forming agents include one or more of polyvinyl alcohol, polyethylene glycol, and starch.

[0069] In some embodiments of this application, the curing process includes heat treatment; optionally, the temperature of the heat treatment is 50°C-100°C.

[0070] In this embodiment, the curing process can be heat treatment. During heat treatment, on the one hand, the solvent, dispersant, pore-forming agent and other components in the slurry volatilize to form the final composite membrane; on the other hand, during heat treatment, the modified polyamic acid can undergo an imidization reaction to form modified polyimide. The degree of imidization can be controlled by controlling the heat treatment temperature, time and other conditions, so that some of the modified polyamic acid is transformed to form modified polyimide in the final composite membrane, while a certain amount of modified polyamic acid can be retained.

[0071] For example, the heat treatment temperatures are 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, etc.

[0072] In this embodiment, the heat treatment temperature meets the above conditions and is relatively low. While achieving slurry curing and molding, it reduces the degree of reaction of modified polyamic acid, causing some of the modified polyamic acid to undergo imidization transformation to form modified polyamic acid. This is especially suitable for cases where no modified polyimide is added to the slurry.

[0073] Furthermore, during the heat treatment and curing process after coating the slurry onto the skeleton material, large particles (such as modified zirconium oxide and pore-forming agents) will deposit and gradually migrate downwards. In the lower layer, a porous structure will form between the zirconium oxide particles, and the abundant pore-forming agent will fully exert its pore-forming effect in the lower layer, thus forming a layered structure with a dense surface and a porous lower layer, i.e., forming a double-layer structure of a dense first film layer and a porous second film layer. Figure 1 As shown, a composite membrane with a double-layer structure is formed, consisting of a dense first membrane layer 101 on the upper layer and a porous second membrane layer 103 on the lower layer. The second membrane layer 103 contains a skeleton material 102, which serves as a skeleton support.

[0074] In some embodiments of this application, the method satisfies at least one of the following (α) and (β): (α) Methods for coating a slurry onto a skeleton material include casting; (β) The viscosity of the slurry is 0.7 dL / g-1.0 dL / g.

[0075] In the embodiments of this application, the slurry can be coated onto the skeleton material using methods known in the art. For example, the casting method can be used.

[0076] For example, the viscosity of the slurry is 0.7 dL / g, 0.8 dL / g, 0.9 dL / g, 1.0 dL / g, etc. This maintains good fluidity, which helps reduce the difficulty of casting and improves the casting effect.

[0077] In some embodiments of this application, the preparation method includes: Prepare casting slurry, which includes modified polyamic acid, modified zirconium oxide, solvent (such as N,N-dimethylacetamide), dispersant (such as fish oil), and pore-forming agent (such as polyvinyl alcohol). The casting paste is cast onto a support material (such as a PPS mesh); The composite membrane is obtained by heat treatment; the heat treatment temperature is 50℃-100℃ and the heat treatment time is 2h-10h.

[0078] As an example, a method for preparing a composite membrane can be: As an example, one or more of the following can be used in the preparation of casting slurry: ball milling assisted treatment and degassing treatment.

[0079] As an example, the cast slurry contains, by weight, 32-53 parts solvent, 8-13 parts modified polyamic acid, 0.5-1.5 parts dispersant, 1.5-2.5 parts pore-forming agent, and 31-57 parts modified zirconium oxide.

[0080] In addition, curing methods also include phase inversion methods, which remove organic solvents inside the membrane through different curing film-forming methods, thereby producing a composite membrane with moderate porosity and uniform pore size distribution.

[0081] In some embodiments of this application, the method for preparing modified polyamic acid includes synthesis from 4,4'-diaminodiphenyl ether (ODA), 4,4'-diamino-4''-hydroxytriphenylmethane (DHTM), and pyromellitic dianhydride (PMDA). DHTM serves as a hydroxyl donor for introducing hydroxyl modification. Specific synthesis steps may include: Under an inert atmosphere, 4,4'-diaminodiphenyl ether and 4,4'-diamino-4''-hydroxytriphenylmethane were added to the solvent N,N-dimethylacetamide and dissolved completely. Pyromellitic dianhydride was added in several portions and stirred to obtain a light yellow, transparent, viscous PAA-OH solution, i.e., a modified polyamic acid solution.

[0082] As an example, modified polyamic acid can be prepared using the following method: In a dry three-necked flask under N2 protection, first add N,N-dimethylacetamide, then add 4,4'-diaminodiphenyl ether and 4,4'-diamino-4''-hydroxytriphenylmethane, and stir at room temperature until completely dissolved. Add pyromellitic dianhydride slowly in 2-4 portions, with intervals of 15-30 minutes, to prevent excessive local concentration and gelation. Stir for 10-12 hours to obtain a pale yellow, transparent, viscous PAA-OH solution. The molar ratio of 4,4'-diaminodiphenyl ether to 4,4'-diamino-4''-hydroxytriphenylmethane is 7:3, and the molar ratio of diamine to dianhydride is 1:1. Here, "diamine" refers to the total amount of 4,4'-diaminodiphenyl ether and 4,4'-diamino-4''-hydroxytriphenylmethane, and "dianhydride" refers to the amount of pyromellitic dianhydride.

[0083] In some embodiments of this application, the method for preparing modified zirconia includes: using an alcohol as a modifier and preparing modified zirconia by wet ball milling. Specifically, it includes: An initial slurry is prepared, comprising zirconium oxide, solvent, modifier, dispersant, and grinding balls; The modified zirconium oxide was obtained by ball milling and then drying.

[0084] As an example, modified zirconium oxide can be prepared using the following method: Using a planetary ball mill, zirconia grinding balls (100μm-15μm diameter) and zirconia powder were added at a ball-to-powder ratio of 2:1. Anhydrous ethanol was used as a solvent, and 1% fish oil by weight of the powder was added as a dispersant, followed by 2%-3% polyethylene glycol by weight of the powder as a modifier. The milling was carried out at 500-700 rpm for 22-24 hours, with a rotation-to-stop time ratio of 4:1 (8 minutes of rotation, 2 minutes of rest, and this cycle was repeated). The milled slurry was dried in an oven at 80℃ for 2-3 hours. The dried powder was then ground in a mortar and sieved to obtain nano-zirconia powder of the desired particle size.

[0085] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0086] [Performance Testing] 1. Hydrophilicity test: A small amount of pure water is dropped onto the surface of the composite membrane to be tested, and the contact angle θ between the water droplet profile and the surface is measured. The smaller the angle, the stronger the hydrophilicity. Judgment criteria: θ < 90°: hydrophilic, θ < 30°: superhydrophilic.

[0087] 2. Gas barrier performance test: After immersing the composite membrane in pure water for 24 hours, fix the pressure difference ΔP between the composite membrane and allow gas to pass through the composite membrane. Record the permeation volume or flux per unit time. Calculate the gas permeability coefficient P.

[0088] P = Q d / A ΔP; Where Q is the gas flux (m³ / s), d is the film thickness (m), A is the effective area (m²), and ΔP is the pressure difference (Pa).

[0089] 3. Surface resistance test: Use AC impedance EIS to measure the impedance difference between the blank electrolyte and the membrane electrolyte, and calculate the true surface resistance of the composite membrane.

[0090] ASR = (R2) R1) A; Where R1 is the impedance of the electrolyte without a membrane, R2 is the impedance of the membrane-coated system, A is the effective electrode area (cm²), and ASR is the surface resistance (Ω). (cm²).

[0091]

Preparation of Composite Separator

[0092] 53 parts N,N-dimethylacetamide were selected as the solvent, 13 parts modified polyamic acid as the binder, 1 part fish oil as the dispersant, 2 parts polyvinyl alcohol as the pore-forming agent, and 31 parts modified zirconia powder were mixed. The mixture was placed in a vacuum degassing device and ball-milled at 1500 rpm for 40 min, followed by vacuum degassing for 8 min to obtain a cast slurry. This slurry was then cast on a PPS mesh at a speed of 3 mm / s on a coating machine and dried in an oven at 80℃ for 6 hours to obtain a composite diaphragm.

[0093] The modified polyamic acid has a hydroxyl content of 23.4 wt% and a viscosity of 0.8 dL / g; the modified zirconia has a hydroxyl content of 2.0 wt%; and the modified zirconia has a particle size of 100 nm-200 nm.

[0094] Example 2-Example 3 The composite diaphragm was prepared using the method of Example 1, except that the content of modified polyamide, modified polyimide, and modified zirconium oxide in the composite diaphragm was controlled by adjusting the content of each component in the casting slurry and the drying parameters (such as temperature and time).

[0095] Comparative Example 1 The composite membrane was prepared using the method of Example 1, with the difference that polyamic acid was used instead of modified polyamic acid. Specifically, the hydroxyl donor 4,4'-diamino-4''-hydroxytriphenylmethane was not added during the preparation of the polyamic acid.

[0096] Comparative Example 2 The composite membrane was prepared using the method of Example 1, except that zirconium oxide was used instead of modified zirconium oxide. Wet ball milling modification was not performed.

[0097] Comparative Example 3 The composite membrane was prepared using the method of Example 1, except that polyamic acid was used instead of modified polyamic acid, and zirconium oxide was used instead of modified zirconium oxide.

[0098] Table 1

[0099] As shown in Table 1, the embodiments of this application utilize the synergistic effect of modified polyamic acid, modified polyimide, and modified zirconium oxide to effectively improve hydrophilicity and gas barrier properties, while also improving ion transport efficiency and reducing surface resistivity.

[0100] In addition, such as Figure 2 and Figure 3 As shown, the composite membrane obtained in Example 3 was characterized by SEM, and the results were obtained. Figure 2 and Figure 3 This forms a thin, dense surface layer (i.e., the first membrane layer) and a thicker porous support layer (i.e., the second membrane layer) below, and the skeleton material can be clearly seen in the porous support layer.

[0101] Example 4-Example 5 The composite membrane was prepared using the method of Example 3, the difference being that the content of hydroxyl groups in the modified polyimide, modified polyamic acid, and modified zirconium oxide in the resulting composite membrane was different.

[0102] Table 2

[0103] As shown in Table 2, the hydroxyl content of each of the modified polyamic acid, modified polyimide, and modified zirconium oxide has a certain impact on the performance of the composite membrane. The hydrophilicity and gas barrier properties can be appropriately controlled by adjusting the hydroxyl content.

[0104] Examples 6-7 The composite membrane was prepared using the method of Example 3, the difference being that the thickness and pore structure parameters of the first membrane layer and the second membrane layer in the resulting composite membrane were different.

[0105] Table 3

[0106] As shown in Table 3, the various structural parameters of the composite membrane have a certain impact on its performance. The hydrophilic gas barrier properties can be appropriately controlled by adjusting parameters such as the porosity and thickness of each sub-membrane layer.

[0107] Example 8 The composite membrane was prepared using the method described in Example 3, the difference being that a phase inversion method was used to achieve the curing process. Specifically: A glass plate is fixed on the coating machine as a diaphragm support plate. The coating machine casts the slurry on a PPS screen at a speed of 3 mm / s. After pre-evaporation in the air, the cast slurry is immersed in deionized water to solidify into a film. After demolding, the composite diaphragm is repeatedly rinsed with deionized water and then stored moist in a sealed bag to obtain the composite diaphragm.

[0108] Table 4

[0109] As shown in Table 4, the phase inversion method can be used to achieve curing treatment, and the imidization of modified polyamic acid can be completed by heat treatment. The resulting composite membrane exhibits good hydrophilic gas barrier properties and low sheet resistance.

[0110] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A composite diaphragm, characterized in that, It includes modified zirconium oxide, modified polyimide, and modified polyamic acid, wherein each of the modified zirconium oxide, the modified polyimide, and the modified polyamic acid independently has a hydrophilic group, and the hydrophilic group includes hydroxyl groups.

2. The composite diaphragm according to claim 1, characterized in that, The composite membrane comprises, by weight percentage: 60%-90% modified zirconium oxide; optionally 70%-90% modified zirconium oxide. 0-40% modified polyimide; optionally 3%-9% modified polyimide; 0-40% modified polyamic acid; optionally 7%-21% modified polyamic acid.

3. The composite diaphragm according to claim 1 or 2, characterized in that, The composite diaphragm satisfies at least one of the following: (a) The content of hydroxyl groups in the modified polyimide is 2wt%-15wt%; (b) The content of hydroxyl groups in the modified polyamic acid is 1wt%-10wt%; (c) The content of hydroxyl groups in the modified zirconium oxide is 0.5wt%-3.5wt%.

4. The composite diaphragm according to claim 1 or 2, characterized in that, The composite membrane comprises a first membrane layer and a second membrane layer; the porosity of the first membrane layer is less than that of the second membrane layer, and the pore size of the first membrane layer is less than that of the second membrane layer.

5. The composite diaphragm according to claim 4, characterized in that, The composite diaphragm satisfies at least one of the following (A) to (F): (A) The porosity of the first membrane layer is 5%-15%; (B) The pore size of the first film layer is 20nm-100nm; (C) The thickness of the first film layer is 5μm-15μm; (D) The porosity of the second membrane layer is 50%-80%; (E) The pore size of the second membrane layer is 0.3 μm-2 μm; (F) The thickness of the second film layer is 300μm-500μm.

6. The composite diaphragm according to claim 4, characterized in that, The second film layer further includes a framework material; optionally, the framework material satisfies at least one of the following (I) and (II): (I) The skeleton material is a mesh structure, and the mesh count of the mesh structure is 250-350 mesh; (II) The skeleton material includes one or more of polyphenylene sulfide, polypropylene, and polytetrafluoroethylene.

7. The composite diaphragm according to claim 1 or 2, characterized in that, The composite diaphragm satisfies at least one of the following (i) to (iii): (i) The thickness of the composite diaphragm is 305μm-515μm; optionally, it is 400μm-500μm. (ii) The particle size of the modified zirconium oxide is 50nm-200nm; (iii) The molecular weight of the modified polyamic acid is 40,000-80,000.

8. A method for preparing a composite diaphragm, characterized in that, include: A slurry is provided, the slurry comprising modified polyamic acid, modified zirconium oxide, modified polyimide and solvent; The modified zirconium oxide, the modified polyimide, and the modified polyamic acid each independently have hydrophilic groups, including hydroxyl groups; and the amount of the modified polyimide added is greater than or equal to 0 parts. The slurry is coated onto the skeleton material; The composite membrane is obtained by performing a curing process.

9. The method according to claim 8, characterized in that, The curing process includes heat treatment; optionally, the temperature of the heat treatment is 50℃-100℃.

10. The method according to claim 8 or 9, characterized in that, The method satisfies at least one of the following (α) and (β): (α) The method of coating the slurry onto the skeleton material includes a casting method; (β) The viscosity of the slurry is 0.7 dL / g-1.0 dL / g.

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