CN115819818A - Composite diaphragm for hydrogen production by alkaline water electrolysis and preparation method thereof - Google Patents

Abstract

The invention discloses a composite diaphragm for hydrogen production by alkaline water electrolysis and a preparation method thereof. The composite separator includes: weaving a plain mesh film and forming a composite coating layer on at least one surface of the woven plain mesh film, characterized in that a coating liquid for forming the composite coating layer comprises hydrophilic inorganic particles, a binder resin, a pore-forming agent, a solvent and a dispersant: the content of the hydrophilic inorganic particles is 80 to 90wt% based on the total mass of the hydrophilic inorganic particles and the binder resin; the total content of the hydrophilic inorganic particles and the binder resin is 50 to 78.5wt% based on the total mass of the coating liquid; based on the total mass of the coating liquid, the content of the pore-forming agent is 1-6 wt%; the content of the dispersant is 0.5 to 1wt% based on the mass of the hydrophilic inorganic particles. The composite diaphragm is simple in preparation process and low in production cost, and has low surface resistance, high current density and good gas barrier property.

Description

Composite diaphragm for hydrogen production by alkaline water electrolysis and preparation method thereof

technical field

The invention belongs to the field of materials, and in particular relates to a composite diaphragm for hydrogen production by electrolysis of alkaline water and a preparation method thereof.

Background technique

With the development of the economy and the growth of the population, the fossil energy represented by oil and coal will bring a serious energy crisis due to its non-renewability and limited reserves, so it is more and more urgent to develop clean and renewable new energy resources. energy. At present, under the guidance of the goal of "carbon neutrality", the tide of clean energy replacing fossil energy has been fully launched. Hydrogen energy, as a clean energy source with high calorific value and low pollution and greenhouse gas emissions, is considered to achieve the goal of carbon neutrality. important way. Hydrogen production by water electrolysis has become popular in recent years. On the one hand, it is because hydrogen production by water electrolysis can achieve "zero carbon emissions" and obtain truly clean "green hydrogen"; on the other hand, it is also possible to convert intermittent, Unstable renewable energy (wind energy, photovoltaic, nuclear energy, etc.) is converted and stored into chemical energy to promote the consumption of new energy and electricity, which can bring greater ecological and environmental benefits and economic benefits. Hydrogen production by alkaline water electrolysis is currently the main way to produce green hydrogen in China. In alkaline water electrolyzer equipment, a diaphragm is required to separate the positive and negative electrodes to prevent short circuits between electrodes, prevent H ₂ (formed at the cathode) and O ₂ (formed at the anode) permeates through the membrane; at the same time, the membrane acts as a moving channel for the electrolyte, facilitating the transport of OH ^- from the cathode to the anode.

Asbestos diaphragm has long been used as the main raw material for water electrolyzer diaphragm, but due to its high resistance, poor stability and toxicity, its application is strictly limited, and new non-asbestos diaphragm has become one of the research directions. At present, the existing diaphragms include PPS woven cloth diaphragms, but due to their high energy consumption and low current density, their application is limited; AGFA's ZIRFON series diaphragms have low energy consumption and high current density, which have attracted widespread attention, but It's expensive. Therefore, there is an urgent need to provide a separator for hydrogen production by alkaline water electrolysis with excellent performance and low cost.

Contents of the invention

The present invention aims to solve one of the technical problems in the related art at least to a certain extent. Therefore, an object of the present invention is to propose a composite diaphragm for hydrogen production by electrolysis of alkaline water and a preparation method thereof. The composite diaphragm not only has simple preparation process and low production cost, but also has low surface resistance, high current density and good gas barrier performance.

In one aspect of the present invention, the present invention provides a composite diaphragm for hydrogen production by electrolysis of alkaline water. According to an embodiment of the present invention, the composite diaphragm includes: a braided flat mesh membrane and a composite coating formed on at least one surface of the braided flat mesh membrane, characterized in that the coating solution for forming the composite coating includes hydrophilic inorganic particles, viscose Synthetic resins, porogens, solvents and dispersants:

Based on the total mass of the hydrophilic inorganic particles and the binder resin, the content of the hydrophilic inorganic particles is 80-90 wt %;

Based on the total mass of the coating solution, the total content of the hydrophilic inorganic particles and the binder resin is 50-78.5 wt %;

Based on the total mass of the coating liquid, the content of the pore-forming agent is 1-6wt%;

Based on the mass of the hydrophilic inorganic particles, the content of the dispersant is 0.5-1 wt%.

According to the above-mentioned embodiments of the present invention, the composite diaphragm for hydrogen production by alkaline water electrolysis has at least the following beneficial effects: 1) By adding hydrophilic inorganic particles in the coating liquid, the hydrophilic performance of the composite coating can be improved, which is beneficial to the composite coating. A moving channel for ions is formed in the coating, thereby improving the electrical performance of the composite diaphragm; the inorganic particles can be fixed by adding the binding resin, which is beneficial to ensure that the composite diaphragm has a high mechanical strength; The dosage is in the above-mentioned range, not only helps to improve the hydrophilicity of this composite membrane, reduces resistance, also helps to improve the flexibility of composite membrane, control cost; 2) not only can control the rheology of coating liquid by adjusting solvent consumption, It is also possible to form micropores on the composite coating by solvent volatilization and/or water washing to provide a path for ion transmission and reduce electrolytic internal resistance; further, controlling the amount of solvent in the above range can effectively avoid the formation of If the pores are too large, the toughness of the composite diaphragm will be reduced, and even the risk of hole collapse will occur. On the other hand, it will help control the viscosity of the coating liquid and improve the smoothness of the composite diaphragm surface; 3) by adding a pore-forming agent to the coating liquid , it is beneficial to further improve the hydrophilic performance of the composite diaphragm, reduce the resistance of ions passing through the composite diaphragm, and improve the electrical properties of the composite diaphragm. Further, by controlling the amount of pore-forming agent in the above range, it is beneficial to control the thickness of the composite coating surface cortex Moderate, it is not only beneficial to avoid the increase of the surface resistance due to the excessive thickness of the surface skin of the composite coating, but also can effectively avoid the deterioration of the gas barrier performance caused by the large maximum pore size of the surface skin of the composite coating, which is conducive to taking into account the electrical properties of the composite separator. performance and gas barrier properties; 4) By adding a dispersant to the coating liquid, it is beneficial to improve the dispersion effect of the inorganic particles, reduce the processing time of the coating liquid (such as the grinding time of the inorganic particles), and improve the production efficiency of the composite diaphragm. Reduce the processing cost, further, by controlling the amount of the dispersant in the above range, the present invention not only helps to ensure the dispersion effect of the inorganic particles, but also can effectively prevent it from hindering the combination of the inorganic particles and the binder resin, which is beneficial to ensure that the composite diaphragm has High mechanical strength and internal structure stability; (5) Through the synergistic effect of each component, the composite separator can have low surface resistance, high current density and good gas barrier performance.

In addition, the composite diaphragm for hydrogen production by alkaline water electrolysis according to the above embodiments of the present invention may also have the following additional technical features:

In some embodiments of the present invention, the woven flat mesh has a pore size of 350-500 μm and an opening ratio of 42-58%; the adhesive resin contains -SO ₂ - groups; the solvent includes At least one of N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylformamide, dimethylsulfoxide, N,N-dimethylacetamide; the pore-forming agent includes polyethylene Pyrrolidone; the dispersant includes anionic surfactant or nonionic surfactant.

In some embodiments of the present invention, the woven flat mesh film includes one of polypropylene, polyethylene, polystyrene, polyphenylene sulfide, and polytetrafluoroethylene; the hydrophilic inorganic particles include zirconium dioxide And/or barium sulfate; The binding resin includes polysulfone resin and/or polyethersulfone resin; The solvent includes N-methylpyrrolidone; The pore-forming agent includes Povidone K30 and/or Povidone K90 ; The dispersant includes alkylphenol polyoxypropylene ether ester salt or fatty alcohol polyoxyethylene ether ester salt.

In some embodiments of the present invention, the woven flat mesh film includes polypropylene or polyphenylene sulfide; the D50 particle size of the hydrophilic inorganic particles is not greater than 0.7 μm; the molecular weight of the binding resin is not less than 70000g/ mol, tensile strength not less than 70MPa, heat distortion temperature not less than 170°C, glass transition temperature not less than 190°C, heat shrinkage rate not greater than 0.7%; the dispersant includes fatty alcohol polyoxyethylene ether carboxylate , fatty alcohol polyoxyethylene ether sulfate, fatty alcohol polyoxyethylene ether sulfonate, fatty alcohol polyoxyethylene ether phosphate, alkylphenol polyoxyethylene ether carboxylate, alkylphenol polyoxyethylene ether sulfate, Alkylphenol polyoxyethylene ether sulfonate, alkylphenol polyoxyethylene ether phosphate, cardanol polyoxyethylene ether sulfate, nonylphenol polyoxyethylene ether sulfate, dimer nonylphenol polyoxyethylene ether Sulphate, n-octyl alcohol ethoxylate carboxylate, lauryl ethoxylate carboxylate, laureth ethoxylate sulfonate, ethylene glycol ethoxylate One of the sulfonate salts, wherein the salt is selected from at least one of sodium salt, potassium salt and ammonium salt; the thickness of the composite diaphragm is 200-800 μm.

In some embodiments of the present invention, the dispersant includes an alkoxylate salt of a block copolymer containing an acidic group, wherein the salt is selected from at least one of sodium salt, potassium salt, and ammonium salt.

In some embodiments of the present invention, the dispersant includes an alkoxylated ammonium salt of a block copolymer containing an acidic group; the thickness of the composite separator is 480-520 μm.

In another aspect of the present invention, the present invention proposes a method for preparing the composite diaphragm described in any one of the above. According to an embodiment of the present invention, the method includes: (1) mixing an adhesive resin, a pore forming agent, and a solvent to obtain a resin solution; (2) mixing hydrophilic inorganic particles, a dispersant, and the resin solution performing ball milling treatment to obtain a coating solution; (3) coating the coating solution on at least one surface of the braided flat mesh membrane, performing phase inversion treatment and water washing-boiling treatment in sequence to obtain a composite diaphragm. The features and effects described above for the composite diaphragm for hydrogen production by alkaline water electrolysis are also applicable to this method, and will not be repeated here. In general, compared with the existing technology, this method is not only simple in process, easy to operate, and low in cost, but also the prepared composite diaphragm can be used for alkaline water electrolysis to produce hydrogen, with lower energy consumption and higher current Density and good gas barrier properties.

In addition, the method for preparing a composite diaphragm according to the above-mentioned embodiments of the present invention may also have the following additional technical features:

In some embodiments of the present invention, in step (1), the mixing treatment is carried out under stirring conditions, the temperature of the mixing treatment is 80-90°C, and the time is 4-6h; the mixing treatment includes heating and reflux treatment .

In some embodiments of the present invention, in step (2), the ball milling process is carried out using a planetary ball mill, the speed of the ball milling process is 400-600 rpm, and the time is 8-12 hours; after the ball milling process Also includes: filter processing.

In some embodiments of the present invention, in step (3), the coating temperature of the coating liquid is 40-60°C; the phase inversion treatment includes gas phase inversion and liquid phase inversion in sequence, and the gas phase inversion The relative humidity is 60 to 80%, and the time is 5 to 15s. The liquid phase conversion is carried out in a coagulation bath, and the coagulation bath adopts an aqueous solution of N-methylpyrrolidone with a concentration of 5 to 30 wt%. The liquid phase conversion The temperature is 40-60°C, and the time is 3-10 minutes.

Additional aspects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and comprehensible from the description of the embodiments in conjunction with the following drawings, wherein:

Fig. 1 is a schematic structural view of a composite diaphragm for hydrogen production by alkaline water electrolysis according to an embodiment of the present invention;

Fig. 2 is a flowchart of a method for preparing a composite membrane according to an embodiment of the present invention.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

In one aspect of the present invention, the present invention provides a composite diaphragm for hydrogen production by electrolysis of alkaline water. According to an embodiment of the present invention, in conjunction with Fig. 1, the composite diaphragm includes: a woven flat mesh membrane and a composite coating formed on at least one surface of the woven flat mesh membrane, wherein the coating solution for forming the composite coating includes an hydrophilic Water inorganic particles, binder resin, pore forming agent, solvent and dispersant: based on the total mass of hydrophilic inorganic particles and binder resin, the content of hydrophilic inorganic particles is 80-90wt%; based on the total mass of coating liquid Based on mass, the total content of hydrophilic inorganic particles and binder resin is 50-78.5wt%; based on the total mass of coating liquid, the content of pore-forming agent is 1-6wt%; based on the mass of hydrophilic inorganic particles As a basis, the content of the dispersant is 0.5-1 wt%.

According to the above-mentioned embodiments of the present invention, the composite diaphragm for hydrogen production by alkaline water electrolysis has at least the following beneficial effects: 1) By adding hydrophilic inorganic particles in the coating liquid, the hydrophilic performance of the composite coating can be improved, which is beneficial to the composite coating. A moving channel for ions is formed in the coating, thereby improving the electrical performance of the composite diaphragm; the inorganic particles can be fixed by adding the binding resin, which is beneficial to ensure that the composite diaphragm has a high mechanical strength; The dosage is in the above-mentioned range, not only helps to improve the hydrophilicity of this composite membrane, reduces resistance, also helps to improve the flexibility of composite membrane, control cost; 2) not only can control the rheology of coating liquid by adjusting solvent consumption, It is also possible to form micropores on the composite coating by solvent volatilization and/or water washing to provide a path for ion transmission and reduce electrolytic internal resistance; further, controlling the amount of solvent in the above range can effectively avoid the formation of If the pores are too large, the flexibility of the composite diaphragm will be reduced, and even the risk of hole collapse will occur. On the other hand, it will help control the viscosity of the coating liquid and improve the smoothness of the composite diaphragm surface; agent, which is conducive to further improving the hydrophilic performance of the composite diaphragm, reducing the resistance of ions passing through the composite diaphragm, and improving the electrical properties of the composite diaphragm. Moderate thickness is not only beneficial to avoid the increase of the surface resistance due to the excessive thickness of the surface skin of the composite coating, but also can effectively avoid the deterioration of the gas barrier performance caused by the large maximum pore size of the composite diaphragm skin, which is conducive to taking into account the electrical properties of the composite diaphragm and gas barrier properties; 4) By adding a dispersant to the coating liquid, it is beneficial to improve the dispersion effect of the inorganic particles, reduce the processing time of the coating liquid (such as the grinding time of the inorganic particles), improve the production efficiency of the composite diaphragm, and reduce the Processing cost, further, by controlling the amount of dispersant in the above range, the present invention not only helps to ensure the dispersion effect of inorganic particles, but also can effectively avoid it from hindering the combination of inorganic particles and adhesive resin, which is beneficial to ensure that the composite diaphragm has a relatively high High mechanical strength and internal structure stability; (5) Through the synergistic effect of each component, the composite separator can have low surface resistance, high current density and good gas barrier performance.

The composite separator for hydrogen production by alkaline water electrolysis in the above embodiments of the present invention will be described in detail below.

Woven flat omentum

According to the embodiment of the present invention, it can be understood with reference to FIG. 1 that the braided flat mesh membrane 10 has a porous structure, which can provide a path for ion transmission in the electrolyte and reduce the internal resistance of electrolysis. The contact area between the omentum and the composite coating improves the bonding strength of the composite coating on the woven flat omentum. Specifically, the pore diameter of the braided flat mesh 10 may be 350-500 μm, such as 360 μm, 380 μm, 420 μm, 450 μm or 480 μm, etc., and the opening ratio may be 42-58%, such as 44%, 48%, 52% % or 56% etc. The inventors found that if the aperture of the braided flat mesh is too large or the opening ratio is too large, the airtightness of the composite diaphragm will be affected; if the aperture of the braided flat mesh is too small or the opening ratio is too small, it will affect or hinder the ion transmission. By controlling the pore diameter and porosity of the omentum in the above range, the invention is beneficial to make the composite diaphragm take into account better gas barrier properties and lower internal resistance. It should be noted that the present invention has no particular limitation on the specific material of the braided flat mesh, which can be flexibly selected by those skilled in the art according to the actual situation, for example, it can include polypropylene, polyethylene, polystyrene, polyphenylene sulfide, polytetrafluoroethylene One of vinyl fluoride, specifically, according to some specific examples of the present invention, if it is necessary to work under the condition of less than 80°C, the material of the braided flat mesh membrane can preferably be polypropylene, and if it is required to work under the condition of not less than 80°C, The material of the braided flat mesh may preferably be polyphenylene sulfide.

composite coating

According to an embodiment of the present invention, in conjunction with Fig. 1 understanding, the composite coating 20 is formed on at least one surface of the braided flat mesh 10, forms a composite diaphragm together with the braided flat mesh, can improve the hydrophilic performance of the composite diaphragm, and improve the composite membrane. The compatibility of the separator and the electrolyte reduces the internal resistance of the electrolysis, which is beneficial to make the composite separator have both good gas barrier and ion permeability.

According to the embodiment of the present invention, in the present invention, by selecting hydrophilic inorganic particles, the composite coating can be made hydrophilic, so that the prepared composite coating can form a channel for water molecules to move, and provide ^OH- from the cathode to the anode. ion channel. In the coating solution of the composite coating 20, the hydrophilic inorganic particles can be zirconium dioxide and/or barium sulfate, both of which can improve the hydrophilic performance of the composite diaphragm, and are more conducive to being the electrolyte in the composite coating. Ion transport provides access to improve the efficiency of hydrogen production. According to some specific examples of the present invention, the D50 particle size of the hydrophilic inorganic particles used to prepare the composite coating may not be greater than 0.7 μm, wherein the original average particle size may be 10-30 nm. The inventors found that if the particle size of the inorganic particles If it is too large, it may hinder the transmission of ions, increase the resistance of the composite diaphragm, and cause the overall electrical performance of the composite diaphragm to decrease; further, the D50 particle size of the hydrophilic inorganic particle raw material can be preferably 0.3-0.7 μm, because the particle size is relatively small Small inorganic particles are more difficult to process, and the price is higher. Selecting the hydrophilic inorganic particles with the above-mentioned preferred particle size is more conducive to controlling the production cost on the basis of ensuring that the composite separator has good electrical properties. In addition, it should be noted that there are no special restrictions on the specific grades of inorganic particles in the present invention, those skilled in the art can choose flexibly according to the actual situation, for example, nano zirconia provided by Xuancheng Jingrui New Material Co., Ltd. can be selected. The crystal form is monoclinic, the original average particle size is 20-30nm, the specific surface area is 25-50m ² /g, and the D50 particle size is 0.7μm; AY-JB53 model sulfuric acid provided by Foshan Anyi Nano Materials Co., Ltd. can also be used Barium, its particle shape is spherical, amorphous, and its D50 particle size is 0.3 μm. In addition, according to some specific examples of the present invention, in the prepared coating solution, the particle size of the hydrophilic inorganic particles may not be greater than 1 μm, that is, the fineness of the coating solution may not be greater than 1 μm. The inventors found that if the particle size of the inorganic particles in the coating solution is too large, on the one hand, the uniformity of the composite coating will be deteriorated, and in the process of hydrogen production by water electrolysis, it is easy to cause the local resistance to be too large, which will lead to a decrease in gas purity. Decrease, even local overheating will affect the service life of the composite diaphragm; on the other hand, the particle size of the inorganic particles is too large will reduce the performance stability of the composite diaphragm. By controlling the particle size of the inorganic particles in the coating liquid within the above range, the invention is beneficial to ensure the uniformity of the composite diaphragm, improve the electrical performance of the composite diaphragm and prolong its service life.

According to an embodiment of the present invention, in the coating solution of the composite coating 20, by adding an adhesive resin to fix the hydrophilic inorganic particles, it is beneficial to ensure that the composite diaphragm has a higher mechanical strength, wherein the adhesive resin used It can be a resin containing -SO ₂ - group, because the sulfur atom in the -SO ₂ - group is in the highest oxidation state, O=S=O can be produced with the hydroxyl group on the surface of zirconium dioxide or the barium ion in barium sulfate Bonding to form a relatively stable chemical structure, which is conducive to ensuring the stability of inorganic particles in the composite coating. For example, according to some specific examples of the present invention, the binder resin can be polysulfone resin and/or polyethersulfone resin, etc. Both polysulfone resin and polyethersulfone resin have good alkali resistance, and can be used at 80-90°C Under the long-term corrosion resistance of high-concentration lye, the two also have high mechanical strength and low thermal shrinkage performance, which is conducive to improving the mechanical properties and service stability of the composite diaphragm. It should be noted that in the present invention, there are no special restrictions on the performance parameters of the adhesive resin, and those skilled in the art can flexibly choose according to the actual situation. For example, the molecular weight (M _w ) of the adhesive resin can be not less than 70000g/mol, The tensile strength may not be less than 70MPa, the heat distortion temperature may not be less than 170°C, the glass transition temperature may not be less than 190°C, and the heat shrinkage rate may not be greater than 0.7%. In addition, there is no special restriction on the specific brand of the adhesive resin in the present invention. For example, the coating type polysulfone resin from Haisu Plastic Chemical Raw Materials Co., Ltd., the P160S polysulfone resin from Huachang Polymer Co., Ltd. of East China University of Science and Technology or Polyethersulfone P260S, etc.

According to an embodiment of the present invention, based on the total mass of the hydrophilic inorganic particles and the binding resin, the content of the hydrophilic inorganic particles may be 80-90 wt%, such as 82 wt%, 84 wt%, 86 wt% or 88 wt%, etc. . The inventors have found that if the content of inorganic particles is too low, the hydrophilicity of the composite diaphragm will decrease, the surface resistance will increase, and the production efficiency and purity of hydrogen will be reduced; if the content of inorganic particles is too high, not only will the production cost be increased, but the As a result, the brittleness of the composite diaphragm increases and the flexibility decreases. By controlling the relative content of the hydrophilic inorganic particles and the binding resin within the above range, the present invention not only helps to control the production cost of the composite separator, but also enables it to have better electrical and mechanical properties.

According to an embodiment of the present invention, based on the total mass of the coating liquid, the total content of the hydrophilic inorganic particles and the binder resin may be 50-78.5 wt%, for example, 55 wt%, 65 wt%, 70 wt% or 75 wt%. wait. The inventors have found that if the total content of the inorganic particles and the binding resin is too low, it will easily lead to too much solvent in the coating solution, so that the solvent will volatilize or the holes formed in the composite coating will be larger after washing, which will not only reduce the composite coating. The toughness of the diaphragm will also increase the risk of hole collapse; if the total content of inorganic particles and binder resin is too high, it will easily lead to high viscosity of the coating liquid, which will not only increase the difficulty of coating, but also may cause the surface of the composite diaphragm to be smooth Poorness and uniformity. By controlling the total content of the hydrophilic inorganic particles and the binding resin within the above range, the present invention is beneficial to control the pore size of the composite diaphragm and the uniformity of the surface of the composite diaphragm, and further helps to improve the electrical performance and service stability of the composite diaphragm.

According to the embodiments of the present invention, through the adjustment of the amount of solvent, not only is it beneficial to control the rheological properties of the coating liquid, but also can form micropores on the composite coating through solvent volatilization or water washing, providing a path for ion transmission and reducing electrolysis. internal resistance. There is no particular limitation on the specific type of solvent in the present invention, and those skilled in the art can choose flexibly according to the actual situation. For example, according to some specific examples of the present invention, the solvent can include N-methylpyrrolidone, N-ethylpyrrolidone, At least one of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, preferably N-methylpyrrolidone can be used, which helps to recycle it, further Control costs and reduce pollution.

According to the embodiment of the present invention, by adding a pore-forming agent to the coating solution, it is beneficial to further improve the hydrophilic performance of the composite diaphragm, reduce the resistance of ions (OH ^- ) passing through the composite diaphragm, and improve the electrical performance of the composite diaphragm. According to some specific examples of the present invention, the pore forming agent may include polyvinylpyrrolidone (PVP), such as povidone K30 (PVP-K30) and/or povidone K90 (PVP-K90).

According to an embodiment of the present invention, based on the total mass of the coating solution, the content of the pore forming agent may be 1-6 wt%, such as 2 wt%, 3 wt%, 4 wt% or 5 wt%. The inventors have found that if the amount of pore-forming agent used is too small, it is easy to reduce the internal porosity of the composite coating, and the skin layer on the surface of the composite coating becomes thinner, resulting in a decrease in the gas barrier property of the composite diaphragm; if the amount of pore-forming agent used is too much, it is easy to The thickness of the surface cortex of the composite coating is significantly increased, resulting in an increase in the resistance of the composite diaphragm, which affects its electrical properties. The present invention is beneficial to controlling the moderate thickness of the surface cortex of the diaphragm by controlling the amount of the pore-forming agent in the above range, so that the composite diaphragm can take into account Good electrical properties and gas barrier properties.

According to the embodiments of the present invention, by adding a dispersant to the coating liquid, it is beneficial to improve the dispersion effect of the hydrophilic inorganic particles, reduce the processing time of the coating liquid (such as the grinding time of the inorganic particles), and improve the production efficiency of the composite diaphragm , reduce processing costs. According to some specific examples of the present invention, when the hydrophilic inorganic particles used are zirconium dioxide and/or barium sulfate, the dispersant used in the present invention can include anionic surfactant and/or nonionic surfactant, the dispersant The molecular chain can contain acid radicals and hydroxyl functional groups at the same time. At this time, the acid radicals preferentially bond with the hydroxyl groups on the surface of the zirconium dioxide particles and/or the barium ions in the barium sulfate, thereby realizing the acid radicals in the dispersant. Coating on the surface of zirconium dioxide and/or barium sulfate particles, while the hydroxyl functional group is far away from the particle surface, thereby improving the dispersion effect of inorganic particles and reducing or avoiding the agglomeration between inorganic particles. It should be noted that, in the present invention, there is no special restriction on the specific type of acid ion in the dispersant, those skilled in the art can flexibly choose according to the actual situation, for example, it can include a group selected from sulfate, sulfonate, phosphate, carboxylate at least one. The dispersant can include alkylphenol polyoxypropylene ether ester salt and/or fatty alcohol polyoxyethylene ether ester salt, specifically can include fatty alcohol polyoxyethylene ether carboxylate, fatty alcohol polyoxyethylene ether sulfate , fatty alcohol polyoxyethylene ether sulfonate, fatty alcohol polyoxyethylene ether phosphate, alkylphenol polyoxyethylene ether carboxylate, alkylphenol polyoxyethylene ether sulfate, alkylphenol polyoxyethylene ether sulfonic acid Salt, Alkylphenol Polyoxyethylene Ether Phosphate, Cardanol Polyoxyethylene Ether Sulfate, Nonylphenol Polyoxyethylene Ether Sulfate, Dipoly Nonylphenol Polyoxyethylene Ether Sulfate, n-octanol Polyoxyethylene One of ether carboxylate, lauryl alcohol polyoxyethylene ether carboxylate, lauryl alcohol polyoxyethylene ether sulfonate, oxalamide lauryl polyoxyethylene ether sulfonate; or The dispersant may also include an alkoxylate salt of a block copolymer containing an acidic group, wherein the specific type of the salt is not particularly limited, for example, may include at least one selected from sodium salt, potassium salt, and ammonium salt. According to some specific examples of the present invention, the dispersant can preferably be an alkoxylated ammonium salt of a block copolymer containing an acidic group, for example, BYK’s BYK180, BYK181, BYK182, BYK110, BYK111 or Yike Chemical’s YCK- 2240, etc., more preferably BYK180, BYK111, YCK-2240, etc., which can further improve the dispersion effect of inorganic particles. In addition, it should be noted that the dispersant in the present invention can be applied to water, solvent or solvent-free systems, all of which have better dispersion effects on inorganic particles.

According to an embodiment of the present invention, in the coating solution, based on the mass of the hydrophilic inorganic particles, the content of the dispersant may be 0.5-1 wt%, such as 0.6 wt%, 0.7 wt%, 0.8 wt% or 0.9 wt%. wt% etc. The inventors have found that if the content of the dispersant in the coating liquid is too low, the dispersion effect on the inorganic particles will be reduced; if the content of the dispersant in the coating liquid is too high, it will be difficult to completely remove the dispersant in the subsequent washing process. Increases the risk of dispersant residues in composite coatings. The present invention not only helps to improve the dispersing effect of the inorganic particles by controlling the amount of the dispersant in the above range, but also can effectively prevent the dispersant from remaining in the composite coating and affect the hydroxyl groups on the surface of the inorganic particles and the O=S in the binding resin. The chemical bonding of the =O bond is beneficial to ensure the structural stability inside the composite membrane.

According to an embodiment of the present invention, the thickness of the composite diaphragm can be 200-800 μm, for example, 300 μm, 400 μm, 500 μm, 600 μm or 700 μm, which can satisfy the application of the electrolytic cell. Furthermore, the thickness of the composite separator is preferably 480-520 μm, for example, 490 μm, 510 μm or 515 μm, etc., thereby further ensuring that the composite separator has better electrical properties and gas barrier properties.

In another aspect of the present invention, the present invention proposes a method for preparing the composite diaphragm described in any one of the above. According to an embodiment of the present invention, understood in conjunction with FIG. 2, the method includes:

S100: Mix the binding resin, pore forming agent and solvent to obtain a resin solution

According to the embodiments of the present invention, the dispersion uniformity of the binding resin in the coating liquid can be improved and the subsequent ball milling treatment time can be reduced by first mixing the binding resin, the pore forming agent and the solvent. According to some specific examples of the present invention, the mixing treatment can be carried out under stirring conditions, the temperature of the mixing treatment can be 80-90° C., and the time can be 4-6 hours. The stirring and heating treatment is beneficial to improve the dissolution rate of the adhesive resin and improve Processing efficiency. In addition, the mixing treatment can also include heating and reflux treatment. Specifically, the binding resin, pore-forming agent and solvent can be added in proportion to the reflux device, stirred and refluxed at 80-90°C for 4-6 hours, and the obtained resin solution is Yellow transparent solution. It should be noted that, before subsequent processing, the obtained resin solution can be sealed and stored to avoid contamination.

S200: Mix the hydrophilic inorganic particles, dispersant and resin solution and perform ball milling to obtain a coating solution

According to the embodiment of the present invention, the grinding and dispersion of the inorganic particles can be realized by mixing the hydrophilic inorganic particles, the dispersant and the resin solution and then performing ball milling, so as to improve the uniformity of the coating liquid. According to some specific examples of the present invention, the ball milling treatment can be carried out using a planetary ball mill, the speed of the ball milling treatment can be 400-600 rpm, and the time can be 8-12 hours, and finally a coating solution with a fineness of no more than 1 μm can be obtained. This can effectively avoid the influence of the uniformity of the composite coating due to the excessive fineness of the coating solution, and avoid or reduce the risk of affecting the gas purity or reducing the service life of the composite diaphragm due to the excessive local resistance of the composite diaphragm during the hydrogen production process. Furthermore, after the ball milling treatment, filtration treatment may also be included, thereby further improving the uniformity of fineness of the coating liquid. For example, as a specific example, the hydrophilic inorganic particles, dispersant, and dissolved resin solution can be added in proportion to the planetary ball mill jar for grinding and dispersing. After grinding for 10 hours at 500 rpm, the fineness of the coating solution The density is less than 1 μm, and the inorganic-organic composite coating solution is obtained after filtration, and stored after defoaming.

S300: Coating the coating solution on at least one surface of the woven flat mesh membrane, performing phase inversion treatment and water washing-boiling treatment in sequence to obtain a composite diaphragm

According to an embodiment of the present invention, after the coating solution is applied to the braided flat mesh, the coating solution can be converted into a solid-phase composite coating with a porous structure through phase inversion treatment, and the coating solution can be converted into a solid-phase composite coating with a porous structure through water washing-boiling treatment. Small molecules such as solvents and dispersants remaining in the coating liquid are removed to prevent them from affecting the electrical properties and stability of the composite diaphragm.

According to an embodiment of the present invention, the coating temperature of the coating liquid can be 40-60°C, such as 45°C, 50°C or 55°C, etc. The inventors found that at a temperature of 40-60°C, the coating liquid The viscosity is moderate, which is more convenient for coating operation, and the coating appearance is better at the same time.

According to an embodiment of the present invention, the phase inversion treatment may include gas phase inversion and liquid phase inversion in sequence. During the gas phase inversion process, the solvent in the coating liquid volatilizes, and the surface layer coating liquid is gradually separated from a single homogeneous phase into two homogeneous phases. The dispersed phase of the coating liquid forms a porous skin layer structure, and then the solvent in the coating liquid and the non-solvent in the coagulation bath diffuse each other through liquid phase inversion, so that phase separation occurs inside the coating liquid to form a solid phase with a porous structure Composite coating. Specifically, the relative humidity of the gas-phase conversion can be 60-80%, for example, 65%, 70% or 75%, etc., and the time of the gas-phase conversion can be 5-15s, for example, 8s, 10s, 12s or 14s. The inventors found that if the relative humidity of the gas-phase conversion is too low, the pores of the cortex are likely to become smaller; If the time is too short, the formed skin layer will be thinner. If the gas phase conversion time is too long, the formed skin layer will be too thick, which will increase the surface resistance of the composite diaphragm. In the present invention, by controlling the relative humidity and time of the gas phase transformation within the above range, it is beneficial to obtain a porous skin layer structure with moderate micropore size and uniform distribution. On the other hand, liquid phase conversion can be carried out in coagulation bath, and coagulation bath can be the N-methylpyrrolidone aqueous solution of 5～30wt%, for example the concentration of N-methylpyrrolidone can be 10wt%, 15wt%, 20wt% or 25wt% % etc., the temperature of liquid phase transformation can be 40-60°C, such as 45°C, 50°C or 55°C, etc., and the time of liquid phase transformation can be 3-10min, such as 5min, 7min or 9min, etc. The inventors found that if the concentration of the coagulation bath is too low, the risk of powder loss may occur during the liquid phase transformation in the coagulation bath, and if the concentration of the coagulation bath is too high, the thickness of the skin layer may be too large, which may increase the surface resistance of the composite diaphragm; If the temperature of the liquid phase conversion is too low, the internal pore size of the composite membrane will become smaller; if the temperature of the liquid phase conversion is too high, the replacement speed of N-methylpyrrolidone and the solvent will be too fast, which will affect the particle size and distribution of the membrane pores. Uniformity; if the time of liquid phase conversion is too short, there is a risk of incomplete phase conversion; if the time of liquid phase conversion is too long, production efficiency will be reduced and energy will be wasted. By controlling the coagulation bath concentration, temperature and conversion time of the liquid phase conversion, the invention is beneficial to obtain a composite diaphragm with complete phase conversion, appropriate skin thickness, moderate membrane hole size and uniform distribution. In addition, it should be noted that in the present invention, the solvent used in the coagulation bath can be controlled to be the same as the solvent in the coating solution, which is beneficial to its further recycling, and can also reduce production costs while protecting the environment.

According to an embodiment of the present invention, the small molecules remaining in the composite coating can be further removed by performing washing-boiling treatment on the composite coating after the phase inversion, wherein the specific time and times of the washing-boiling treatment in the present invention There is no special limitation, and those skilled in the art can choose flexibly according to the actual situation, for example, it can be 3 times, 5 times, etc. After the last washing-boiling treatment, the washing water can have a transparent texture and no air bubbles on the surface, so it can be It shows that the removal of small molecules such as solvents and dispersants remaining in the coating solution is relatively thorough, which is conducive to further improving the electrical properties and service stability of the composite separator.

According to a specific example of the present invention, a coating solution at 50±10° C. can be applied on both sides of the braided flat screen film, and gas phase conversion is carried out for 5 to 15 seconds at a relative humidity of 60 to 80%, and at 40 to 60° C. The phase inversion is carried out in the coagulation bath of 5-30wt% NMP aqueous solution for 3-10 minutes, and then washed with water-boiled for several times until the water surface has no bubbles and the water quality becomes transparent, and the alkaline water electrolysis hydrogen production composite diaphragm is obtained, which can Further improve the electrical performance and service stability of the composite diaphragm.

In summary, the method for preparing the composite diaphragm in the present invention has all the technical features and effects of the above-mentioned composite diaphragm for hydrogen production by alkaline water electrolysis, and will not be repeated here. In general, compared with the existing technology, this method is not only simple in process, easy to operate, and low in cost, but also the prepared composite separator can be used for alkaline water electrolysis to produce hydrogen, with lower surface resistance and higher current Density and good gas barrier properties.

Embodiments of the present invention are described in detail below. The embodiments described below are exemplary only for explaining the present invention and should not be construed as limiting the present invention. If no specific technique or condition is indicated in the examples, it shall be carried out according to the technique or condition described in the literature in this field or according to the product specification. The reagents or instruments used were not indicated by the manufacturer, and they were all commercially available conventional products.

Example 1

(1) Put 15.0g of P160S polysulfone resin (Huachang Polymer of East China University of Science and Technology), 5.0g of polyvinylpyrrolidone PVP90 (Ronghe New Material), and 55.0g of N-methylpyrrolidone (NMP) at 80°C Dissolve in a reflux device, wherein the polysulfone resin is added in multiple additions, and the dissolution time is 5 hours to obtain polysulfone resin solution 1, which is sealed and preserved;

(2) Add 85g of zirconium dioxide (Tianxing new material TPG-M560, D50 particle size is 0.7μm), 0.4g of BYK180 and polysulfone resin solution 1 obtained in step (1) into a planetary ball mill for grinding, After ball milling at a speed of 500 rpm for 12 hours, the fineness of the particles was measured to be no more than 1 μm, and the inorganic-organic composite coating solution 1 was obtained after filtration, which was left to stand for defoaming and stored for later use;

(3) After coating the coating solution 1 with a wet thickness of 320 μm at about 50 ± 10 ° C on both sides of the woven flat screen film PPSP40 (Shanghai Shangsie Wire Mesh Manufacturing Co., Ltd.), the relative humidity (RH) is 60% in turn. Gas phase inversion was carried out for 10 seconds under the same conditions, phase inversion was carried out in 15wt% NMP aqueous solution at 45°C for 8 minutes, and finally water washing and boiling were performed three times until the water surface was free of bubbles and the water quality became transparent, and a 505 μm thick alkaline water electrolysis system was obtained. Composite membrane for hydrogen1.

Example 2

(1) Dissolve 10.0g of polysulfone resin (Haisu Plastic Chemical Co., Ltd., coating type), 1.8g of polyvinylpyrrolidone PVP30 (Ronghe New Material), and 48.0g of NMP in a reflux device at 85°C, wherein, The method of adding polysulfone resin is multiple additions, and the dissolution time is 5 hours to obtain polysulfone resin solution 2, which is sealed and stored;

(2) Add 90.0 g of barium sulfate (Foshan Anyi Nanomaterials AY-JB53, D50 particle size is 0.3 μm), 0.5 g of BYK180 and polysulfone resin solution 2 obtained in step (1) into a planetary ball mill for grinding, After ball milling at a speed of 500 rpm for 12 hours, the fineness of the particles was measured to be no more than 1 μm, and the inorganic-organic composite coating solution 2 was obtained after filtration, which was left to stand for defoaming and stored for later use;

(3) After coating the coating liquid 2 with a wet thickness of 320 μm at about 50±10°C on both sides of the woven flat screen film PPSP50 (Shanghai Shangsie Wire Mesh Manufacturing Co., Ltd.), the gas phase conversion was carried out at 70% RH for 5s in sequence , carried out phase inversion in a 5wt% NMP aqueous solution at 55°C for 6 minutes, and finally washed and boiled three times until the water surface was free of bubbles and the water quality became transparent, and a 490 μm thick alkaline water electrolysis hydrogen production composite diaphragm 2 was obtained.

Example 3

(1) Dissolve 20g of polyethersulfone P260S (Huachang Polymer of East China University of Science and Technology), 8.5g of polyvinylpyrrolidone PVP30 (Ronghe New Material), and 60g of NMP in a reflux device at 90°C. Polysulfone The resin addition method is multiple additions, and the dissolution time is 5 hours to obtain polysulfone resin solution 3, which is sealed and stored;

(2) Add 80g of zirconium dioxide (Xuancheng Jingrui new material VK-R30Y8, D50 particle size is 0.7μm), 0.9g of BYK111 dispersant and polysulfone resin solution 3 obtained in step (1) to the planetary ball mill Grinding in the medium, after ball milling at a speed of 500 rpm for 12 hours, the fineness of the particles was measured to be no more than 1 μm, and the inorganic-organic composite coating solution 3 was obtained after filtration, which was left to stand for defoaming and stored for later use;

(3) After coating the coating liquid 3 with a wet thickness of 320 μm at about 50 ± 10 ° C on both sides of the woven flat screen film PP50 (Shanghai Shangsie Wire Mesh Manufacturing Co., Ltd.), the gas phase conversion is carried out under 80% RH conditions for 15 seconds in sequence, Phase inversion was carried out in 25wt% NMP aqueous solution at 50°C for 5 minutes, and finally washed and boiled three times until the surface of the water was free of bubbles and the water quality became transparent to obtain a 520 μm thick alkaline water electrolytic hydrogen production composite membrane 3 .

Example 4

(1) Dissolve 12.5g of P160S polysulfone resin (Huachang Polymer of East China University of Science and Technology), 3.0g of polyvinylpyrrolidone PVP90 (Ronghe New Material), and 51g of NMP in a reflux device at 80°C. Polysulfone The resin addition method is multiple additions, and the dissolution time is 5 hours to obtain polysulfone resin solution 4, which is sealed and stored;

(2) Add 82.5g of barium sulfate (Foshan Anyi Nanomaterials AY-JB61, D50 particle size is 0.7μm), 0.8g of BYK111 and the polysulfone resin solution 4 obtained in step (1) into a planetary ball mill for grinding After ball milling at a speed of 500 rpm for 12 hours, the fineness of the particles was measured to be no more than 1 μm, and the inorganic-organic composite coating solution 4 was obtained after filtration, which was left standing for defoaming and stored for later use;

(3) After coating the coating liquid 4 with a wet thickness of 320 μm at about 50 ± 10 ° C on both sides of the woven flat screen film PP60 (Shanghai Shangsie Wire Mesh Manufacturing Co., Ltd.), the gas phase conversion is carried out under 65% RH conditions for 8 seconds, Perform phase inversion in 20wt% NMP aqueous solution at 60°C for 3 minutes, and finally wash and boil three times until the surface of the water has no bubbles and the water quality becomes transparent to obtain a 500 μm thick alkaline water electrolysis hydrogen production composite diaphragm 4 .

Example 5

(1) Dissolve 17.5g of polysulfone resin (Haisu Plastic Chemical Co., Ltd., coating type), 6.8g of polyvinylpyrrolidone PVP90 (Ronghe New Material), and 58g of NMP in a reflux device at 90°C. The method of adding the sulfone resin is multiple additions, and the dissolution time is 5 hours to obtain the polysulfone resin solution 5, which is sealed and preserved;

(2) Add 82g of barium sulfate (Foshan Anyi Nanomaterials AY-JB61, D50 particle size is 0.7μm), 0.7g of YCK2240 (Yike Chemical) and the polysulfone resin solution 5 obtained in step (1) to the planetary Grinding in a ball mill, ball milling at a speed of 500 rpm for 12 hours, the particle fineness is measured to be no more than 1 μm, and the inorganic-organic composite coating solution 5 is obtained after filtration, which is left to stand for defoaming and stored for later use;

(3) After coating the coating solution 5 with a wet thickness of 320 μm at about 50 ± 10 ° C on both sides of the woven flat screen film PPSP60 (Shanghai Shangsie Wire Mesh Manufacturing Co., Ltd.), carry out gas phase conversion under the condition of 75% RH for 12 seconds in sequence, Perform phase inversion in 30wt% NMP aqueous solution at 40°C for 8 minutes, and finally wash and boil three times until the surface of the water has no bubbles and the water quality becomes transparent to obtain a 480 μm thick alkaline water electrolysis hydrogen production composite diaphragm 5 .

Comparative example 1

Zirfonutp 500 from Agfa.

Comparative example 2

The difference from Example 1 is that in step (2), BYK180 is not added.

Performance Testing:

Under the same conditions, the coating solutions or composite diaphragms prepared in Examples 1-5 and Comparative Examples 1-2 were characterized by the following methods, and the characterization results are shown in Table 1.

Test Methods:

(i) Fineness of coating solution: measure the coating solution with a scraper fineness meter with a measuring range of 25 μm;

(ii) Composite diaphragm thickness: measure the wet thickness of the composite diaphragm with reference to the national electronics industry standard SJ-T 10171.1-1991. The specific steps are as follows: (a) Cut the composite diaphragm into 20mm×20mm samples, a total of 5 pieces; ( b) soak the sample in deionized water for 24 hours, and then vibrate for 2 hours with an ultrasonic oscillator; (c) measure the thickness of the sample, accurate to 0.01mm, and take the average value of 5 samples as the measurement result;

(iii) Average pore size and bubble point pressure: use the BSD-PB bubble pressure method membrane pore size analyzer to detect with reference to GB/T 32361-2015 "Separation Membrane Pore Size Test Method Bubble Point and Average Flow Method"; and the same sample three Test after cutting different parts, and record the range of data changes;

(iv) Surface resistance of the composite diaphragm: The surface resistance of the composite diaphragm is the difference between the resistance of the composite diaphragm per unit area in the electrolyte and the resistance of the electrolyte (equal to the volume of the composite diaphragm), and the unit is Ω·cm ² . A two-electrode system is used to measure the surface resistance by the electrochemical impedance method. A 20.1mm×20.1mm square window is opened in the middle of two 75mm×75mm×8mm PTFE plates, and two 20mm×20mm×0.5 mm foil, a composite diaphragm is placed in the middle of the platinum sheet, and the distance between the composite diaphragm and the platinum sheet is 3mm. Secure the Teflon plate tightly with Teflon screws and nuts. Put it into a beaker filled with 30wt% KOH solution, put the beaker into a water bath with a constant temperature of 80-90°C, and measure the electrochemical impedance with an electrochemical workstation. And cut and test three different parts of the same sample, record the range of data changes, the calculation of the surface resistance of the composite diaphragm is: R _S = (R ₁ -R ₀ )S, where: R _S -- the surface resistance of the composite diaphragm , (Ω·cm ² ); R ₀ --the solution resistance between the two electrodes when there is no composite diaphragm, (Ω); R ₁ --the resistance between the cells after adding the composite diaphragm, (Ω); S --- electrode or Composite diaphragm area, (cm ² ).

The test result contrast of table 1 embodiment 1～5 and comparative example 1～2

Results and discussion:

Combining the test results of Examples 1-5 and Comparative Examples 1-2, it can be seen that the properties of the composite diaphragms prepared in Examples 1-5 are close to those of Comparative Example 1, but the ball milling required to achieve the fineness of the coating solution is not greater than 1 μm. The time is greatly shortened, so it can be seen that the composite diaphragm obtained by adopting the above-mentioned embodiments of the present invention not only has better electrical properties, but also has lower production costs and higher production efficiency; comparative example 2 is compared with embodiment 1 , without adding a dispersant, when ball milling is carried out under the same conditions, even if the ball milling time is prolonged, it is difficult to obtain a coating solution with an ideal fineness, indicating that the dispersion effect and efficiency of inorganic particles can be effectively improved by adding a dispersant. To sum up, the composite diaphragm obtained by adopting the above-mentioned preparation method of the present application with the above-mentioned raw material composition of the present application not only has simple process and low production cost, but also has low surface resistance and good gas barrier performance, and can be applied to Alkaline water electrolysis hydrogen production.

In the description of this specification, descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structure, material or characteristic is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention, those skilled in the art can make the above-mentioned The embodiments are subject to changes, modifications, substitutions and variations.

Claims (10)

1. A composite diaphragm for hydrogen production by alkaline water electrolysis, comprising: a braided flat mesh film and a composite coating formed on at least one surface of the braided flat mesh film, characterized in that the coating solution forming the composite coating comprises Hydrophilic inorganic particles, binder resins, pore formers, solvents and dispersants: Based on the total mass of the hydrophilic inorganic particles and the binder resin, the content of the hydrophilic inorganic particles is 80-90 wt %; Based on the total mass of the coating liquid, the total content of the hydrophilic inorganic particles and the binder resin is 50-78.5 wt%; Based on the total mass of the coating liquid, the content of the pore-forming agent is 1-6wt%; Based on the mass of the hydrophilic inorganic particles, the content of the dispersant is 0.5-1 wt%. 2. The composite diaphragm according to claim 1, characterized in that: The woven flat mesh has a pore size of 350-500 μm and a porosity of 42-58%; The binder resin contains -SO ₂ -groups; The solvent includes at least one selected from N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylformamide, dimethylsulfoxide, N,N-dimethylacetamide; The pore forming agent includes polyvinylpyrrolidone; The dispersant includes anionic surfactant or nonionic surfactant. 3. The composite diaphragm according to claim 1, characterized in that: The braided flat mesh includes one of polypropylene, polyethylene, polystyrene, polyphenylene sulfide, and polytetrafluoroethylene; The hydrophilic inorganic particles include zirconium dioxide and/or barium sulfate; The binding resin includes polysulfone resin and/or polyethersulfone resin; The solvent includes N-methylpyrrolidone; The pore-forming agent comprises povidone K30 and/or povidone K90; The dispersant includes alkylphenol polyoxypropylene etherate or fatty alcohol polyoxyethylene etherate. 4. The composite diaphragm according to any one of claims 1 to 3, characterized in that: The braided flat mesh comprises polypropylene or polyphenylene sulfide; The D50 particle size of the hydrophilic inorganic particles is not greater than 0.7 μm; The molecular weight of the binder resin is not less than 70000g/mol, the tensile strength is not less than 70MPa, the heat distortion temperature is not less than 170°C, the glass transition temperature is not less than 190°C, and the heat shrinkage rate is not more than 0.7%; The dispersant includes fatty alcohol polyoxyethylene ether carboxylate, fatty alcohol polyoxyethylene ether sulfate, fatty alcohol polyoxyethylene ether sulfonate, fatty alcohol polyoxyethylene ether phosphate, alkylphenol polyoxyethylene ether Vinyl ether carboxylate, Alkylphenol ethoxylate sulfate, Alkylphenol ethoxylate sulfonate, Alkylphenol ethoxylate phosphate, Cardanol ethoxylate sulfate, Nonylphenol Polyoxypropylene ether sulfate, dipolynonylphenol polyoxyethylene ether sulfate, n-octyl alcohol polyoxyethylene ether carboxylate, lauryl alcohol polyoxyethylene ether carboxylate, lauryl alcohol polyoxyethylene One of vinyl ether sulfonate and ethylene glycol polyoxyethylene lauryl sulfonate, wherein the salt is selected from at least one of sodium salt, potassium salt, and ammonium salt; The thickness of the composite separator is 200-800 μm. 5. The composite diaphragm according to any one of claims 1 to 3, wherein the dispersant comprises an alkoxyl salt of a block copolymer containing an acidic group, wherein the salt is selected from sodium salts , potassium salt, ammonium salt at least one. 6. The composite diaphragm according to claim 5, wherein the dispersant comprises an alkoxyl ammonium salt of a block copolymer containing an acidic group; The thickness of the composite diaphragm is 480-520 μm. 7. A method for preparing the composite diaphragm according to any one of claims 1 to 6, characterized in that, comprising: (1) mixing the binding resin, the pore forming agent and the solvent to obtain a resin solution; (2) ball-milling the hydrophilic inorganic particles, the dispersant and the resin solution to obtain a coating solution; (3) Coating the coating liquid on at least one surface of the braided flat mesh, and performing phase inversion treatment and water washing-boiling treatment in sequence to obtain a composite diaphragm. 8. The method according to claim 7, characterized in that in step (1), the mixing process is carried out under stirring conditions, the temperature of the mixing process is 80-90° C., and the time is 4-6 hours; The mixing treatment includes heating and reflux treatment. 9. The method according to claim 7, characterized in that in step (2), the ball milling process is carried out using a planetary ball mill, the speed of the ball milling process is 400 to 600 rpm, and the time is 8 to 12 hours ; After the ball milling treatment, it also includes: filtering treatment. 10. The method according to claim 7, characterized in that, in step (3), the coating temperature of the coating liquid is 40-60°C; The phase inversion treatment includes sequential gas phase inversion and liquid phase inversion, the relative humidity of the gas phase inversion is 60-80%, and the time is 5-15s; the liquid phase inversion is carried out in a coagulation bath, and the coagulation bath An aqueous solution of N-methylpyrrolidone with a concentration of 5-30 wt % is used, and the temperature of the liquid phase transformation is 40-60° C. and the time is 3-10 min.

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