Composite separator, preparation method therefor, and use thereof

Abstract

The present application relates to the technical field of separators, and provides a composite separator, a preparation method therefor, and a use thereof. The composite separator comprises a porous layer. The porous layer comprises an organic polymer resin, inorganic particles, and polymer fibers, the polymer fibers being polymer fibers modified with hydrophilic groups. In the present application, by adding polymer fibers into the porous layer, mechanical support is provided to the porous layer, such that the separator is resistant to bending, thereby improving the mechanical strength of the separator. In addition, hydrogen bond interactions are formed between the hydrophilic groups modified on the polymer fibers and the inorganic particles. Considering also the strong interactions between the polymer fibers and the organic polymer resin, this arrangement helps to fix the inorganic particles within the organic polymer resin, thereby effectively reducing detachment of inorganic particles from the porous layer. As a result, the separator has good air tightness, which helps to maintain the stability and safety of the separator.

Description

Composite membranes, their preparation methods, and applications

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 2024119972723, filed on December 31, 2024, entitled "Composite diaphragm and preparation method thereof, application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of diaphragm technology, specifically to a composite diaphragm, its preparation method, and its application. Background Technology

[0004] An alkaline water electrolysis electrolyzer for hydrogen production mainly consists of a water splitting electrode and a diaphragm. During the water electrolysis process, oxygen is generated at the anode electrode and hydrogen is generated at the cathode electrode. The diaphragm's function is to prevent hydrogen and oxygen from mixing, thus ensuring the purity of the hydrogen. Simultaneously, the diaphragm must allow ions in the electrolyte to pass through, ensuring the continuous operation of the electrolysis process. Summary of the Invention

[0005] In view of this, in order to at least partially solve the aforementioned technical problems, this application provides a composite diaphragm, its preparation method, and its application.

[0006] According to one embodiment of this application, a composite membrane is provided, comprising a porous layer; the porous layer comprises an organic polymer resin, inorganic particles, and polymer fibers, wherein the polymer fibers are polymer fibers modified with hydrophilic groups.

[0007] According to another embodiment of this application, a method for preparing a composite membrane as described above is provided, comprising: mixing an organic polymer resin, inorganic particles, polymer fibers and a solvent to obtain a casting solution; coating the casting solution onto a substrate or a porous support, and performing a phase inversion to obtain a composite membrane.

[0008] According to another embodiment of this application, a composite separator as described above is provided for use in alkaline water electrolysis for hydrogen production, lithium batteries, zinc-air batteries, and flow batteries.

[0009] According to embodiments of this application, by adding polymer fibers to the porous layer, mechanical support is provided, making the membrane more resistant to bending and improving its mechanical strength. Furthermore, the hydrophilic groups modified with the polymer fibers form hydrogen bonds with the inorganic particles. Combined with the strong interaction between the polymer fibers and the organic polymer resin, this helps to fix the inorganic particles within the organic polymer resin, effectively reducing the shedding of inorganic particles from the porous layer. This results in better airtightness of the membrane, contributing to its stability and safety. Attached Figure Description

[0010] The above and other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0011] Figure 1 is a flowchart of the preparation method of the composite diaphragm in the embodiment of this application. Detailed Implementation

[0012] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0013] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0014] When using expressions such as "at least one of A, B, and C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, and C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). Similarly, when using expressions such as "at least one of A, B, or C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, or C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0015] In the process of producing hydrogen through water electrolysis, hydrogen and oxygen are typically produced separately from the cathode and anode with relatively low energy consumption. A diaphragm is placed between the cathode and anode to prevent the two gases from mixing, ensuring the purity of the hydrogen while retaining ion transport capabilities. This creates a current loop in the electrolysis process, thus guaranteeing the stability and continuity of the electrolyzer. During the use of the electrolyzer, the diaphragm also needs to possess good mechanical strength to withstand the impact of the electrolyte and generated gases over extended periods.

[0016] The composite membranes in related technologies have poor mechanical strength and are not resistant to bending. In addition, during long-term use, inorganic particles are prone to falling off from the porous layer, which reduces the airtightness of the membrane and affects the stability and safety of the water electrolysis hydrogen production device. It is difficult to simultaneously achieve the performance of ion permeability, mechanical strength and airtightness.

[0017] In realizing the concept of this application, it was discovered that by adding polymer fibers into the porous layer, hydrogen bonds are formed between the hydrophilic groups on the polymer fibers and the inorganic particles. Combined with the strong interaction between the polymer fibers and the organic polymer resin, it helps to fix the inorganic particles in the organic polymer resin.

[0018] Specifically, according to one aspect of the present application, a composite membrane is provided, comprising a porous layer having a plurality of micropores, the porous layer comprising an organic polymer resin, inorganic particles and polymer fibers, wherein the polymer fibers are polymer fibers modified with hydrophilic groups.

[0019] It should be noted that inorganic particles and organic polymer resins are crucial materials for forming the porous layer of the composite membrane. If these particles or resins leak or detach from the composite membrane, voids or cracks will appear, reducing its ability to isolate gases. For example, in the process of producing hydrogen through water electrolysis, hydrogen or oxygen may permeate through the membrane, reducing the purity of the hydrogen and potentially compromising the safety of the water electrolysis hydrogen production unit.

[0020] This application incorporates polymer fibers into a composite membrane. Hydrogen bonds are formed between the hydrophilic groups in the polymer fibers and the groups on the surface of inorganic particles (e.g., hydroxyl, amino groups). Combined with the strong interaction between the polymer fibers and the organic polymer resin, the inorganic particles are fixed onto a porous layer. The high strength of the polymer fibers provides excellent support, strengthening the bond between the inorganic particles and the polymer fibers. This further ensures that the inorganic particles are firmly anchored to the porous layer by the polymer fibers, guaranteeing good ion permeability and airtightness of the membrane, thus improving its stability and safety.

[0021] Furthermore, since polymer fibers have high strength, dispersing them in a porous layer can provide good support, making the composite membrane less prone to defects during use and giving it high mechanical strength and aging resistance.

[0022] According to one or more embodiments of this application, the hydrophilic group includes at least one selected from sulfonic acid group (-SO3H), carboxylic acid group (-COOH), phosphate group (-PO(OH)3), phosphonic acid group (-PO(OH)2), and hypophosphonic acid group (-PO(OH)-). These hydrophilic groups not only form good hydrogen bond interactions with the groups in the inorganic particles, but also help adsorb and transfer ions in the electrolyte, promoting ion migration to form a current loop, and further improving the ion transport performance of the composite membrane.

[0023] According to one or more embodiments of this application, the diameter of the polymer fiber is 10–5000 nm, for example, it can be 10 nm, 50 nm, 100 nm, 300 nm, 500 nm, 700 nm, 900 nm, 1000 nm, 1500 nm, 2000 nm, 3000 nm, 4000 nm, or 5000 nm, preferably 100–1000 nm. If the diameter of the polymer fiber is too short, it is difficult to form a certain supporting effect; if the diameter is too wide, it is easy to precipitate during the preparation process and is difficult to disperse in the solvent, resulting in poor dispersion of the polymer fiber on the prepared porous layer, which further affects the fixation of inorganic particles, resulting in poor airtightness and mechanical strength of the composite membrane. The length of the polymer fiber is 0.5–10 μm, for example, it can be 0.5 μm, 1 μm, 3 μm, 5 μm, 7 μm, 8 μm, 9 μm, or 10 μm. If the fiber length is too long, it easily forms a coiled structure like silk threads, which is prone to agglomeration and poor dispersibility, making it difficult to achieve uniform fixation of inorganic particles. If the length is too short, the supporting effect is relatively limited. Adjusting the diameter and length of the polymer fiber within a reasonable range helps to disperse the polymer fiber in the casting solution during the preparation process, so that its fiber structure provides uniform support, is less prone to defects, and helps to further enhance the mechanical strength and bending resistance of the composite membrane.

[0024] Furthermore, the polymer fiber is selected from sulfonated polymer fiber, carboxylated polymer fiber, phosphorylated polymer fiber, phosphonic polymer fiber, and hypophosphonic polymer fiber.

[0025] According to one or more embodiments of this application, the organic polymer resin is a casting polymer. In this application, it is understood that the casting polymer is a polymer used to form the matrix during the formation of the composite diaphragm. Using the organic polymer resin as the matrix facilitates the uniform dispersion of polymer fibers and inorganic particles, and helps to improve the bonding strength between the polymer fibers and inorganic particles.

[0026] According to one or more embodiments of this application, the hydrophilic groups account for less than or equal to 50% of the molar percentage of the polymer fiber. Based on the polymer fiber's good strength, alkali resistance, resistance to high and low temperature changes, and good insulation properties, adjusting the molar percentage of the hydrophilic groups within the above range can prevent them from dissolving in the solvent during preparation and from swelling in the solvent, thus ensuring that the polymer fiber provides uniform support to the porous layer.

[0027] Furthermore, when the hydrophilic group is a sulfonic acid group, the molar percentage of the sulfonic acid group in the polymer fiber is less than or equal to 10%, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 5%, 6%, 7%, 8%, 9%, or 10%. When the hydrophilic group is a carboxylic acid group, phosphate group, phosphonic acid group, or hypophosphonic acid group, the molar percentage of the carboxylic acid group, phosphate group, phosphonic acid group, or hypophosphonic acid group in the polymer fiber is less than or equal to 50%, preferably less than 30%, for example, it can be 1%, 3%, 5%, 7%, 9%, 10%, 15%, 20%, 25%, or 29%. When the molar percentage of different hydrophilic groups is limited to the above ranges, it helps to stably disperse the polymer fiber in the solvent, providing uniform support. When preparing a composite membrane, it can enhance the mechanical strength of the composite membrane, making the composite membrane more resistant to bending, and further reducing the possibility of inorganic particles falling off from the porous layer.

[0028] The molar percentage of hydrophilic groups in the polymer fiber can be determined by titration, elemental analysis, nuclear magnetic resonance spectroscopy, infrared absorption spectroscopy, or other methods known in the art. During determination, the molar amount of the polymer fiber can be calculated from its mass and average molecular weight.

[0029] According to one or more embodiments of this application, based on the organic polymer values ​​of the porous layer and the mass of the polymer fibers, the mass percentage of hydrophilic groups is less than or equal to 10%, for example, it can be 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0030] Polymer fibers modified with hydrophilic groups can be prepared by introducing hydrophilic groups into polymer fibers that do not possess hydrophilic groups, or by polymerizing monomers containing hydrophilic groups and then spinning the resulting polymer with hydrophilic groups into fibers. The introduction can be achieved using methods known in the art, such as sulfonation to introduce sulfonic acid groups into polymer fibers, for example, using sulfonating agents such as concentrated sulfuric acid or fuming sulfuric acid. Phosphoric acid groups can be introduced into polymer fibers via nucleophilic phosphineization, for example, by reacting diethyl phosphite with a halogenated polymer. Alternatively, polymers containing carboxylic acids can be prepared by copolymerizing unsaturated carboxylic acid monomers (such as acrylic acid) with olefin monomers containing carbon-carbon double bonds (such as styrene), and then spinning these polymers into fibers containing carboxylic acids.

[0031] According to embodiments of this application, the polymer fiber includes at least one of polyphenylene sulfide, polyetheretherketone, polypropylene, and polytetrafluoroethylene. The aforementioned polymer fiber possesses good strength, high alkali resistance, high and low temperature resistance, and good insulation properties, and is easily modified with hydrophilic groups. According to embodiments of this application, the polymer fiber may, for example, be sulfonated polyphenylene sulfide, sulfonated polypropylene, carboxylated polypropylene, sulfonated polyetheretherketone, phosphorylated polyetheretherketone, or sulfonated polytetrafluoroethylene.

[0032] According to one or more embodiments of this application, the mass percentage of polymer fibers in the porous layer is 0.01% to 10%, for example, it can be 0.01%, 0.1%, 1%, 2%, 3%, 4%, 4.5%, 5%, 6%, 8%, or 10%, preferably 0.1% to 6%. If the polymer fibers in the porous layer are excessive, although the mechanical strength is improved, the ionic conductivity will decrease, which is not conducive to the formation of a current loop. Especially when the polymer fibers exceed 10%, the decrease in ionic conductivity is significant. If the polymer fibers are too few, such as below 0.01%, the support for the porous layer is limited due to the insufficient amount added, and it is difficult to provide uniform support, resulting in an insignificant effect on the bending resistance of the composite membrane.

[0033] According to one or more embodiments of this application, the composite membrane further includes a porous support; a porous layer covers the surface of the porous support and fills the through-pores of the porous support. By adding a porous support to the composite membrane, the support and mechanical strength of the composite membrane are further improved through the synergy of the porous layer and the porous support.

[0034] The porous support is made of polyethylene, polypropylene, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfide, polyketone, polyimide, polyetherimide, fluorinated resin, etc.

[0035] Fluorine-based resins include ethylene-tetrafluoroethylene copolymers, polyvinylidene fluoride, polyvinyl fluoride, vinylidene fluoride-hexafluoropropylene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, polychlorotrifluoroethylene, and tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers. Preferred resins are at least one of polypropylene and polyphenylene sulfide.

[0036] The porous support may contain only one of the listed materials such as polyethylene, polypropylene, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfone, polyphenylene sulfide, polyketone, polyimide, polyetherimide, and fluorinated resin, or it may contain two or more. From the perspective of excellent heat resistance and alkali resistance, at least one of polypropylene and polyphenylene sulfide is preferred, and more preferably polyphenylene sulfide.

[0037] According to one or more embodiments of this application, the shape of the porous support is not limited, and it can be at least one of nonwoven fabric, woven fabric, woven mesh, and porous membrane, such as a mixture of nonwoven fabric and woven fabric, preferably a woven mesh. The porous support preferably comprises a woven mesh of polyphenylene sulfide.

[0038] When the porous support is in the form of a woven mesh, the mesh size of the porous support is 40 to 200 mesh, for example, it can be 40 mesh, 50 mesh, 80 mesh, 100 mesh, 150 mesh or 200 mesh, preferably 50 mesh, so as to provide a more uniform and stable support effect.

[0039] The thickness of the porous support when it is in sheet form is not limited, for example, it is 30 to 2000 μm, and can be 30 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, 1100 μm, 1200 μm, 1300 μm, 1400 μm, 1500 μm, 1600 μm, 1700 μm, 1800 μm, 1900 μm or 2000 μm, preferably 50 to 1000 μm, more preferably 80 to 500 μm, and even more preferably 80 to 300 μm.

[0040] The thickness of the porous support can be determined by observing the cross-section using a field emission scanning electron microscope (FE-SEM). For example, the average thickness at any five points can be taken as the thickness of the porous support.

[0041] According to one or more embodiments of this application, inorganic particles may include metal hydroxides, metal oxides, metal nitrides, metal inorganic salts, etc.

[0042] Inorganic particles may include one of the listed metal hydroxides, metal oxides, metal nitrides, or metal inorganic salts, or may include two or more.

[0043] The metal elements in the metal hydroxides, metal oxides, and metal nitrides are selected from magnesium, zirconium, titanium, zinc, aluminum, tantalum, hafnium, and cerium; preferably, the inorganic particles are selected from metal hydroxides or metal oxides of magnesium, zirconium, titanium, zinc, aluminum, and tantalum; sulfates of calcium, barium, lead, and strontium; and nitrides of titanium, zirconium, and hafnium.

[0044] The inorganic metal salt is selected from calcium sulfate, barium sulfate, lead sulfate, strontium sulfate, barium titanate, and potassium titanate, with barium sulfate being preferred. From the perspective of improving the ion conductivity of the composite membrane, metal hydroxides or metal oxides are preferred, more preferably magnesium hydroxide, zirconium hydroxide, titanium hydroxide, zirconium oxide, titanium oxide, magnesium oxide, and cerium oxide, with zirconium oxide being particularly preferred.

[0045] Inorganic particles can be surface-treated, for example using known surface treatment agents such as silane coupling agents, stearic acid, oleic acid, and phosphate esters. The shape of the inorganic particles is not limited and can be amorphous, granular, sheet-like, plate-like (such as hexagonal plates), or fibrous. From the perspective of improving the interaction with polymer fibers, granular, sheet-like, and plate-like shapes are preferred, and sheet-like and plate-like shapes are more preferred. From the perspective of improving the strength of the composite separator, sheet-like and plate-like shapes are preferred, and sheet-like shapes are more preferred.

[0046] From the perspective of improving the strength and hydrophilicity of the composite membrane, the average particle size of the inorganic particles is preferably 0.01 to 2.0 μm, for example, it can be 0.01 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.5 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm or 2 μm. More preferably, it is 0.08 μm or more and 1.5 μm or less, and even more preferably, it is 0.1 μm or more and 1 μm or less.

[0047] The average particle size refers to the volume average particle size (D50) determined by particle size distribution measurement using laser diffraction. Specifically, the particle size distribution is measured using a laser diffraction / scattering particle size distribution measuring device, and the median particle size (D50) in the volume-based particle size distribution is taken as the average particle size. It should be noted that the particles are mixed in ethanol, ultrasonically dispersed, and the resulting mixture is used as the test sample.

[0048] From the perspective of composite membranes with excellent alkali resistance, durability, and good strength, zirconium oxide is the preferred inorganic particle. The average particle size of zirconium oxide is preferably 0.01–2.0 μm, as described above.

[0049] According to one or more embodiments of this application, the organic polymer resin includes polyethylene terephthalate, polybutylene terephthalate, polynaphthalic acid, butylene glycol ester, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylene sulfone, polyarylate, polyetherimide, polyimide, polyamide-imide, polyphenylene ether, polyarylene ether nitrile, etc. The organic polymer resin may be one of the above materials or may contain two or more. From the perspective of excellent heat resistance and alkali resistance, it is preferably selected from at least one of polysulfone, polyethersulfone, polyarylene ether ketone, polyphenylene ether, and polyarylene ether nitrile; from the perspective of easy solubility in solvents, polysulfone is further preferred.

[0050] The average molecular weight of organic polymer resins is greater than 35,000, for example, it can be 35,000, 40,000, etc., which will not be elaborated here. When the average molecular weight of organic polymer resins exceeds 35,000, they have better mechanical strength.

[0051] Considering heat resistance, alkali resistance, and ease of solvent solubility, polysulfone is the preferred organic polymer resin. The average molecular weight of polysulfone, as mentioned above, is greater than 35,000.

[0052] According to one or more embodiments of this application, the porous layer may further include a hydrophilic additive, which may be an organic or inorganic hydrophilic additive. The organic hydrophilic additive is a water-soluble polymer such as polyvinylpyrrolidone, polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyethyleneimine with a molecular weight less than 100,000, or polyacrylic acid; the inorganic hydrophilic additive is a water-soluble salt, preferably a metal chloride such as calcium chloride, magnesium chloride, lithium chloride, sodium chloride, or potassium chloride. The addition of the above-mentioned hydrophilic additives helps to improve the hydrophilicity of the composite membrane, thereby improving the ion conduction effect of the composite membrane and facilitating the formation of a current loop.

[0053] The mass content of the hydrophilic additive in the composite membrane is preferably 0.001 to 20% relative to 100% of the inorganic particles, for example, 0.001%, 0.005%, 0.01%, 0.1%, 1%, 5%, 10%, 15% or 20%, and more preferably 0.01 to 10%.

[0054] According to one or more embodiments of this application, the thickness of the composite membrane is 10–1000 μm, for example, it can be 10 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, or 1000 μm, preferably 400–500 μm. The porosity is 40–80%, for example, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%, preferably 55–65%. Maintaining the thickness and porosity of the composite membrane within the above ranges helps to maintain good mechanical strength, good airtightness, and high ion conductivity.

[0055] According to one or more embodiments of this application, the preferred mass ratio of organic polymer resin, inorganic particles, and polymer fibers is (10-30):(20-50):(0.01-10), for example, 10:20:0.01, 15:25:0.1, 12.1:40.7:4.5, 12:45:2, 15:40:3, 20:50:5, 25:50:4, 30:50:10, etc. Adjusting the mass ratio of the three components to the above range helps to better fix the inorganic particles in the organic polymer resin through the polymer fibers, effectively preventing the inorganic particles from falling off the porous layer and improving the stability of the composite membrane.

[0056] It should be noted that composite membranes may contain other additives as needed.

[0057] According to another aspect of this application, a method for preparing a composite membrane as described above is provided. Figure 1 is a flowchart of the method for preparing a composite membrane according to an embodiment of this application. As shown in Figure 1, the method includes operations S101 to S102.

[0058] In operation S101, organic polymer resin, inorganic particles, polymer fibers and solvent are mixed to prepare casting solution.

[0059] Operation S101 is the process of preparing a casting solution by mixing several raw materials with a solvent. The mixing method and procedure are not limited. The mixing method can be a known method, such as using a mixer, ball mill, jet mill, disperser, sand mill, roller mill, or can mill. The mixing procedure can be arbitrary. For example, the three components—organic polymer resin, inorganic particles, and polymer fibers—can be mixed simultaneously or in any order in the solvent. Alternatively, the organic polymer resin, inorganic particles, and polymer fibers can be mixed separately in the solvent, and then their mixtures can be combined.

[0060] From the perspective of easily dissolving organic polymer resins and better dispersing the three raw materials, the solvent can be at least one of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0061] In operation S102, the casting solution is coated onto the substrate or porous support to undergo phase transformation and obtain a composite membrane.

[0062] Operation S102 is the process of coating the casting solution obtained in operation S101 onto a substrate or porous support to form a composite diaphragm. Methods for coating the casting solution onto the substrate include die coating, spin coating, gravure coating, spray coating, and methods using a coating machine.

[0063] The substrate is a film or sheet, glass plate, etc., made of resins such as polybutylene terephthalate, polyethylene naphthalate, polypropylene, polyethylene, polyvinyl chloride, polyvinyl alcohol acetal, polymethyl methacrylate, and polycarbonate.

[0064] The methods for applying casting solution to porous supports include direct coating and dip coating, for example, a coating machine can be used. Direct coating can be understood as applying the casting solution directly onto the porous support, while dip coating can be understood as immersing the porous support in the casting solution.

[0065] The coating can be applied to one side or both sides of the porous support. The coating can be entirely deposited on the surface of the porous support, or partially impregnated within the porous support with the remainder deposited on its surface. When the coating is impregnated within the porous support, it can penetrate to a certain depth along the thickness direction of the porous support, or it can penetrate along the entire thickness direction of the porous support. The degree of coating impregnation within the porous support can be adjusted by appropriately modifying the coating method and the viscosity of the casting solution. The coating thickness can be controlled by regulating the coating process.

[0066] Phase inversion is a method of preparing a porous layer from a coating, for example, by using a solvent-inducing phase inversion method. When a liquid containing a solvent comes into contact with the coating, the solvent diffuses into the coating. At this time, the solvent soluble in the coating dissolves out of the coating, causing the organic polymer resin insoluble in the solvent to solidify and form a porous layer.

[0067] Without polymer fibers in the coating, the interaction between the organic polymer resin and inorganic particles in the coating is not particularly strong. This application addresses this by adding polymer fibers to the casting solution, thereby firmly fixing the inorganic particles within the organic polymer resin using the polymer fibers.

[0068] The method of bringing the coating film into contact with a liquid containing a non-solvent is to immerse the coating film in a liquid containing a non-solvent (coagulation bath).

[0069] It should be noted that "non-solvent" can be understood as having the property of being substantially insoluble in organic polymer resins. The coating film is brought into contact with a non-solvent, or immersed in a liquid containing a non-solvent. "Substantially insoluble in organic polymer resins" means that the solubility of the polymer resin relative to 100g of solvent is less than 100mg at 25°C. Non-solvents can be pure water, distilled water, ion-exchanged water, etc.; lower alcohols such as methanol, ethanol, propanol, etc.; or mixtures thereof. From the perspective of facilitating post-processing, water is preferred, and ion-exchanged water is more preferred.

[0070] There is no temperature limit for the non-solvent-containing liquid in contact with the coating. For the purpose of facilitating uniform solidification of the coating, a temperature of 10-50°C is acceptable. There is no time limit for immersing the coating in the non-solvent-containing liquid. The porosity, pore structure, and pore size of the porous layer can be controlled by adjusting the process conditions of the solidification bath.

[0071] Optionally, the coating film can be pre-evaporated before the coagulation bath, as needed. It is understood that the prepared coating film is exposed to a non-solvent vapor containing an organic polymer resin.

[0072] There is no temperature limit for the gas containing non-solvent when it comes into contact with the coating. The preferred contact time between the coating and the gas containing non-solvent is 10-80 seconds.

[0073] Through the above operations S101-S102, a porous layer containing organic polymer resin, inorganic particles, and polymer fibers is obtained, which can be used as a composite membrane. As can be seen from the above process, the porous layer may contain non-solvent or solvent components from the coating. The porous layer can be further dried as needed.

[0074] In addition to the above operations, known processes such as pressing can be performed as needed to make the density of the composite diaphragm more uniform.

[0075] The composite membrane has a porous layer comprising organic polymer resin, inorganic particles, and polymer fibers. Preferably, it also includes a porous support.

[0076] In one specific embodiment, the composite membrane is prepared without the addition of a porous support as follows:

[0077] Polysulfone was dissolved in a certain amount of N-methylpyrrolidone (NMP) and mechanically stirred for 12 hours to fully dissolve it. A certain amount of zirconium oxide was added and dispersed for another 24 hours using a high-speed disperser. A certain amount of sulfonated polyphenylene sulfide fiber was then added and ultrasonically dispersed for another 24 hours. The mixture was then coated using a doctor blade, pre-evaporated, and immersed in a coagulation bath to form a porous membrane.

[0078] In one specific embodiment, with the addition of a porous support, the preparation process of the composite membrane is as follows:

[0079] Polysulfone was dissolved in a certain amount of N-methylpyrrolidone and mechanically stirred for 12 hours to fully dissolve it. A certain amount of zirconium oxide was added and the mixture was dispersed for another 24 hours using a high-speed disperser. A certain amount of sulfonated polyphenylene sulfide fiber was then added and ultrasonically dispersed for another 24 hours. The mixture was then coated onto a 50-mesh polyphenylene sulfide (PPS) support mesh using a coating machine. After pre-evaporation, the membrane was immersed in a coagulation bath to form a porous membrane.

[0080] According to another embodiment of this application, a composite separator as described above is provided for use in alkaline water electrolysis for hydrogen production, lithium batteries, zinc-air batteries, and flow batteries.

[0081] It is understood that the composite membrane prepared in this application has good ion conductivity and gas barrier properties, as well as high mechanical strength. When applied to alkaline water electrolysis for hydrogen production, it has alkali resistance and high and low temperature resistance. Furthermore, due to the addition of polymer fibers, it has good mechanical strength, effectively reducing the shedding of inorganic particles and improving the safety and stability in alkaline water electrolysis for hydrogen production.

[0082] In lithium batteries, composite separators help prevent short circuits because the modification of hydrophilic groups helps reduce the interfacial resistance of the composite separator, improve the lithium-ion migration rate, and improve the overall performance of the battery.

[0083] When applied to zinc-air batteries, the modification of the composite membrane with hydrophilic groups helps to introduce catalytic active sites, which can promote the oxygen reduction reaction. At the same time, the porosity of the composite membrane can be appropriately adjusted to optimize the oxygen transport path.

[0084] When applied to flow batteries, it helps to improve the selective passage of target ions. Because flow batteries operate in harsh environments, the composite separator of this application exhibits good stability and corrosion resistance, enabling long-term use and improving the reliability and lifespan of the flow battery.

[0085] The present application is further illustrated below through embodiments, accompanying drawings, and related test experiments and results. In the following detailed description, numerous specific details are set forth for ease of explanation to provide a comprehensive understanding of the embodiments of the present application. However, it is apparent that one or more embodiments may be implemented without these specific details. Moreover, the details in the following embodiments can be arbitrarily combined to form other feasible embodiments without conflict.

[0086] It should be noted that the specific embodiments described below are merely illustrative examples, and the scope of protection of this application is not limited thereto. The chemicals and raw materials used in the following embodiments are all commercially available or prepared using recognized processing methods.

[0087] It should be noted that the tensile strength, sheet resistivity, and bubble point tests of the composite separator all use national standard test methods. Sheet resistivity can be understood as the resistance value per unit width and unit length, and bubble point can be understood as the pressure value at which liquid is forced out of the material's largest pore size to form the first continuous bubble. Tensile strength testing follows the test method described in GB / T1040.3 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films / Sheets". Sheet resistivity testing follows the area resistivity test method described in SJ / T 10171 "General Test Methods for Basic Properties of Alkaline Battery Separators". Bubble point testing follows the test method described in GB / T32361 "Test Methods for Pore Size of Separating Membranes - Bubble Point and Average Flow Rate Method". Porosity is tested using the mercury porosimetry method, measuring the amount of mercury adsorbed by the material using a mercury porosimeter to calculate the porosity and pore size distribution. Stability testing employed accelerated aging. During the test, a diaphragm weighing W1 was placed in a hydrothermal reactor containing 30 wt% KOH and heated at 120°C for 50 hours. Afterward, the diaphragm was removed, washed three times with deionized water, dried, and weighed; the weight was recorded as W2. The weight retention rate of the diaphragm after accelerated aging can be determined by… calculate.

[0088] Example 1:

[0089] In Example 1, the raw materials consist of 12.1% polysulfone, 4.5% sulfonated polyphenylene sulfide fiber, 40.7% zirconium oxide (average particle size 100nm), and 42.7% NMP by mass. The sulfonated polyphenylene sulfide fiber has a sulfonic acid group molar content of 8%, a fiber diameter of 100nm, and a length of 8μm.

[0090] Preparation process: Polysulfone was dissolved in NMP and mechanically stirred for 12 hours to fully dissolve. Zirconia was added and dispersed for 24 hours using a high-speed disperser. Sulfonated polyphenylene sulfide fiber was added and ultrasonically dispersed for 24 hours. The mixture was then coated using a doctor blade, pre-evaporated, and immersed in a coagulation bath to form a porous membrane 1.

[0091] Example 2:

[0092] The formula of raw materials in this Example 2 is the same as that in Example 1.

[0093] Preparation process: Polysulfone was dissolved in a certain amount of N-methylpyrrolidone and mechanically stirred for 12 hours to fully dissolve. Zirconia was added and dispersed for 24 hours using a high-speed disperser. Sulfonated polyphenylene sulfide fiber (SPPS) was added and ultrasonically dispersed for 24 hours. The mixture was then coated onto a 50-mesh polyphenylene sulfide (PPS) support mesh using a coating machine. After pre-evaporation, the membrane was immersed in a coagulation bath to form a porous membrane 2.

[0094] Comparative Example 1:

[0095] The preparation process of Comparative Example 1 is largely the same as that of Example 1, except that sulfonated polyphenylene sulfide fibers were not added in Comparative Example 1 to form a porous membrane 1'.

[0096] Comparative Example 2:

[0097] The preparation process of Comparative Example 2 is largely the same as that of Example 2, except that sulfonated polyphenylene sulfide fibers were not added in Comparative Example 2 to form a porous membrane 2'.

[0098] Examples 1-2 and Comparative Examples 1-2 of this application were tested respectively, and the relevant test results are shown in Table 1 below.

[0099] Comparative Example 3:

[0100] The preparation process of Comparative Example 1 is largely the same as that of Example 1, except that in Comparative Example 1, sulfonated polyphenylene sulfide fibers are replaced with polyphenylene sulfide fibers with a diameter of 100 nm and a length of 8 μm to form a porous membrane 3'.

[0101] Table 1. Performance of porous membranes prepared in the examples and comparative examples.

[0102] As shown in Table 1, comparing Example 1 and Comparative Example 1, it can be seen that the porous membrane prepared after adding sulfonated polyphenylene sulfide fiber has higher tensile strength, higher bubble point pressure, and higher sheet resistivity. After accelerated aging test, the porous membrane of Example 1 has better stability. Comparing Example 2 and Comparative Example 2, it can be seen that the performance of both porous membranes was effectively improved after further adding PPS support mesh, but the performance of Example 2 improved more significantly and was better than that of Comparative Example 2. Comparing the results of Example 1 and Example 2, it can be seen that further adding porous support mesh based on Example 1 resulted in a significant increase in tensile strength, and the bubble point pressure and sheet resistivity were also improved to varying degrees, while the accelerated aging effect was still maintained.

[0103] Comparing Example 1 and Comparative Example 3, it can be seen that the use of sulfonated polyphenylene sulfide fiber can achieve the fixation of zirconium oxide by relying on the interaction between sulfonic acid groups and zirconium oxide, combined with the strong interaction between sulfonated polyphenylene sulfide fiber and polysulfone. This results in Example 1 having better tensile strength, bubble point pressure and sheet resistivity than Comparative Example 3. At the same time, Example 1 has superior anti-aging properties and can be widely promoted in composite membranes.

[0104] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite membrane, comprising a porous layer, The porous layer comprises organic polymer resin, inorganic particles, and polymer fibers, wherein the polymer fibers are polymer fibers modified with hydrophilic groups.

2. The composite diaphragm according to claim 1, wherein, The hydrophilic group includes at least one of sulfonic acid group, carboxylic acid group, phosphate group, phosphonic acid group, and hypophosphonic acid group.

3. The composite separator according to any one of claims 1-2, wherein, The polymer fiber has a diameter of 10–5000 nm, preferably 100–1000 nm; The polymer fiber has a fiber length of 0.5 to 10 μm.

4. The composite separator according to any one of claims 1-3, wherein, The organic polymer resin is a casting polymer.

5. The composite separator according to any one of claims 1-4, wherein, The polymer fiber is selected from sulfonated polymer fiber, carboxylated polymer fiber, phosphorylated polymer fiber, phosphonic polymer fiber, and hypophosphonic polymer fiber.

6. The composite separator according to any one of claims 1 to 5, wherein, The hydrophilic groups constitute less than or equal to 50% of the molar percentage of the polymer fiber.

7. The composite diaphragm according to claim 6, wherein, The hydrophilic group is a sulfonic acid group, and the sulfonic acid group accounts for less than or equal to 10% of the molar percentage of the polymer fiber; or The hydrophilic groups are carboxylic acid groups, phosphate groups, phosphonic acid groups, or hypophosphonic acid groups, and the molar percentage of carboxylic acid groups, phosphate groups, phosphonic acid groups, or hypophosphonic acid groups in the polymer fiber is less than or equal to 50%, preferably less than 30%.

8. The composite diaphragm according to any one of claims 1 to 5, wherein, The polymer fibers in the porous layer account for 0.01 to 10% by mass, preferably 0.1 to 6%.

9. The composite diaphragm according to any one of claims 1 to 5, wherein, The polymer fiber includes at least one of polyphenylene sulfide, polyetheretherketone, polypropylene, and polytetrafluoroethylene.

10. The composite separator according to any one of claims 1 to 5, wherein, The composite membrane also includes a porous support; The porous layer covers the surface of the porous support and fills the through holes of the porous support.

11. The composite diaphragm according to claim 10, wherein, The porous support comprises at least one of polyethylene, polypropylene, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfone, polyketone, polyimide, polyetherimide, and fluorinated resins, preferably at least one of polypropylene and polyphenylene sulfide.

12. The composite diaphragm according to claim 10 or 11, wherein, The porous support can be formed by at least one of the following: nonwoven fabric, woven fabric, woven mesh, and porous membrane. The thickness of the porous support is 30–2000 μm, preferably 50–1000 μm, more preferably 80–500 μm, and even more preferably 80–250 μm.

13. The composite diaphragm according to claim 12, wherein, The porous support is in the form of a woven mesh, and the mesh size of the porous support is 40 to 200 mesh.

14. The composite separator according to any one of claims 1 to 5, wherein, The inorganic particles include at least one of metal hydroxides, metal oxides, metal nitrides, and inorganic metal salts.

15. The composite diaphragm according to any one of claims 14, wherein, The inorganic particles have an average particle size of 0.01–2 μm, preferably 0.08–1.5 μm, and more preferably 0.1–1 μm.

16. The composite diaphragm according to claim 14, wherein, The metal elements in the metal hydroxides, metal oxides, and metal nitrides are selected from magnesium, zirconium, titanium, zinc, aluminum, tantalum, hafnium, and cerium; The inorganic metal salt is selected from calcium sulfate, barium sulfate, lead sulfate, strontium sulfate, barium titanate, and potassium titanate; Preferably, the inorganic particles are selected from metal hydroxides or metal oxides of magnesium, zirconium, titanium, zinc, aluminum, and tantalum; sulfates of calcium, barium, lead, and strontium; and nitrides of titanium, zirconium, and hafnium.

17. The composite diaphragm according to claim 14, wherein, The inorganic particles are selected from magnesium hydroxide, zirconium hydroxide, titanium hydroxide, zirconium oxide, titanium oxide, cerium oxide, barium sulfate, and magnesium oxide.

18. The composite diaphragm according to any one of claims 1 to 5, wherein, The organic polymer resin includes at least one of polyethylene terephthalate, polybutylene terephthalate, polynaphthalic acid, butylene glycol ester, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylene sulfone, polyarylate, polyetherimide, polyimide, polyamide imide, polyphenylene ether, and polyaryletheronitrile, preferably at least one of polysulfone, polyethersulfone, polyaryletherketone, polyphenylene ether, and polyaryletheronitrile; The average molecular weight of the organic polymer resin is greater than 35,000.

19. The composite diaphragm according to any one of claims 1 to 5, wherein, The porous layer further includes a hydrophilic additive, and the mass percentage of the hydrophilic additive is 0.001 to 20%, preferably 0.01 to 10%, based on the mass of the inorganic particles. The hydrophilic additive includes organic hydrophilic additives or inorganic hydrophilic additives, wherein the organic hydrophilic additive is a water-soluble polymer, and the inorganic hydrophilic additive is a water-soluble salt.

20. The composite diaphragm according to any one of claims 1 to 5, wherein, The thickness of the composite membrane is 10–1000 μm, preferably 400–500 μm; the porosity is 40–80%, preferably 55–65%.

21. The composite diaphragm according to any one of claims 1 to 5, wherein, The mass ratio of the organic polymer resin, inorganic particles, and polymer fiber is (10-30):(20-50):(0.01-10).

22. A method for preparing a composite separator as described in any one of claims 1 to 21, comprising: An organic polymer resin, inorganic particles, polymer fibers, and solvent are mixed to prepare a casting solution. The casting solution is coated onto a substrate or porous support, and a phase transformation is performed to obtain the composite membrane.

23. The application of a composite separator as described in any one of claims 1 to 21 in alkaline water electrolysis for hydrogen production, lithium batteries, zinc-air batteries, and flow batteries.

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