Composite separator

Abstract

The utility model provides a kind of composite diaphragm, the composite diaphragm includes substrate and the coating layer being arranged in the substrate at least one surface;The substrate includes mesh base and the composite coating layer being arranged in the mesh base at least one side, the composite coating layer includes inorganic particle and the composite coating layer formed by at least one polymer in polysulfone, polyethersulfone or poly aryl sulfone;The coating layer includes first coating layer and second coating layer sequentially arranged, the first coating layer is close to substrate one side;The first coating layer is the coating layer formed by polymer microsphere in substrate surface dot distribution;The second coating layer includes anion transport function layer.The bubble point of the composite diaphragm is high, and the air isolation performance is good, and it can also ensure good ion transport performance, stability, and can also operate under higher pressure, reduce power consumption and cost.

Description

Technical Field

[0001] This utility model belongs to the field of water electrolysis for hydrogen production technology, and specifically relates to a composite membrane. Background Technology

[0002] The alkaline composite membrane is a key component of a water electrolysis hydrogen production unit. Its main function is to isolate the hydrogen and oxygen produced during the electrocatalytic process, preventing them from mixing, and allowing the free movement of ions within the electrolyzer's circuitry. The membrane's structure directly affects the purity of the hydrogen and oxygen and the power consumption.

[0003] Currently, the alkaline composite membranes widely used in the industry are composite structures formed by a porous support and a coating layer. The pore size distribution in the thickness direction of the porous support and the coating layer is irregular, which makes the alkaline composite membrane have poor gas barrier ability and a low bubble point (around 2 bar). In the actual process of water electrolysis to produce hydrogen, hydrogen and oxygen may cross-contaminate, causing safety problems, especially when high pressure is applied to both sides of the membrane, the problem will be more serious.

[0004] Therefore, developing a composite membrane with a high bubble point and good gas-barrier performance is an urgent problem to be solved in this field. Utility Model Content

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a composite diaphragm with a high bubble point, good gas barrier properties, and excellent ion transport performance and stability. It can also operate under higher pressures, reducing power consumption and costs.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a composite membrane, the composite membrane comprising a substrate and a coating layer disposed on at least one surface of the substrate; the substrate comprising a mesh substrate and a composite coating disposed on at least one side of the mesh substrate, the composite coating comprising inorganic particles and a composite coating formed of at least one polymer selected from polysulfone, polyethersulfone, or polyarylsulfone; the coating layer comprising a first coating layer and a second coating layer disposed sequentially, the first coating layer being located on the side closer to the substrate; the first coating layer being a coating layer formed by polymer microspheres distributed in a dotted pattern on the surface of the substrate; the second coating layer comprising an anion transport functional layer.

[0008] In this invention, the composite structure of the first coating layer and the second coating layer helps to increase the bubble point of the composite diaphragm, enhance its gas isolation effect, reduce gas crosstalk during actual operation, and ensure good ion transport performance. The first coating layer helps to tightly bond the second coating layer and the substrate together, preventing coating peeling and improving the stability of the composite diaphragm. It also controls the overall pore size distribution of the composite diaphragm, further improving its bubble point and gas isolation performance. The composite diaphragm adopts a specific structural design, which not only has a high bubble point, excellent gas isolation performance, and good ion transport performance, but also better increases the safety of the composite diaphragm during operation in the tank, allowing it to operate under higher pressures and reducing power consumption and cost.

[0009] In this invention, the coating layer is located on the side of the composite coating in the substrate; specifically, the first coating layer is located on the side of the composite coating in the substrate.

[0010] In this invention, the composite coating can be a coating formed of multiple materials, and does not specifically refer to a multi-layer structure.

[0011] In this invention, the pore size of the composite membrane decreases sequentially along the direction from the substrate to the coating layer. That is, in the direction of composite membrane thickness, the pore size of the substrate, the first coating layer, and the second coating layer decreases sequentially.

[0012] In this invention, the substrate satisfies at least one of the following conditions.

[0013] (a) The pore size of the substrate is 20 to 500 nm, for example, it can be a range of 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 460 nm, 480 nm, 500 nm or any combination thereof.

[0014] (b) The thickness of the substrate is 200 to 650 μm, for example, it can be a range of 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, 550 μm, 600 μm, 650 μm or any combination thereof.

[0015] In this invention, the substrate is a material known in the prior art, such as Zirfon UTP500 and UTP 500+ produced by Agfa, and KX550 from Shenzhen Kexin Hydrogen Materials Co., Ltd. It may include a mesh substrate, the material of which includes, but is not limited to, porous polymer membranes or nonwoven fabrics formed from at least one of the following polymer resins: polyolefin, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, or polyethylene naphthalate; the polyolefin includes, but is not limited to, polyethylene, polypropylene, etc. A composite coating is disposed on at least one side of the mesh substrate. The composite coating includes inorganic particles and a composite coating formed from at least one polymer selected from polysulfone, polyethersulfone, or polyarylsulfone, wherein the inorganic particles are materials known in the prior art and may include one or more of zirconium oxide, silicon nitride, magnesium oxide, aluminum oxide, zinc oxide, barium titanate, carbon nanotubes, or titanium oxide. The thickness of the substrate can be achieved using commercially available substrates that meet the requirements. The pore size of the substrate can be adjusted by selecting commercially available substrates that meet the application requirements, or by using existing substrates through chemical etching, laser drilling, or high-temperature heat treatment. It is understood that this is merely to clearly disclose the possible structural composition of the substrate, and is not a limitation on the constituent materials, as long as the substrate can be used as a separator for hydrogen production via water electrolysis.

[0016] In this invention, the thickness of the first coating layer is 0.5 to 3 μm, for example, it can be a range of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, or any two of these ranges.

[0017] In this invention, the average particle size of the polymer microspheres in the first coating layer is 500 nm to 2 μm, for example, it can be a range of 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm or any combination thereof.

[0018] In this invention, the average particle size of the polymer microspheres can be obtained by testing with a Malvern Zeta potential and particle size analyzer ZEN3690. The polymer microsphere material with a specific particle size can be purchased from existing commercially available materials, or existing microspheres can be screened using existing techniques such as centrifugation sedimentation.

[0019] In this invention, the coverage of polymer microspheres in the first coating layer is 10% to 30%, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, or 30%.

[0020] In this invention, the coverage of the polymer microspheres is within the above-mentioned range, which is beneficial for bonding with the second coating layer. At the same time, it controls the overall pore size pattern of the composite membrane, so that the composite membrane has both high bubble point, excellent gas barrier performance and good ion transport performance.

[0021] In this invention, the coverage of the polymer microspheres can be measured using an optical microscope (model OLYMPUS MX51) at 2.5x magnification. Three equidistant positions are selected horizontally and three equidistant positions are selected vertically, with a reference length interval of 3cm, for a total of nine positions. The coverage of the polymer coating is calculated using OLYMPUS software, and the average value is taken for testing.

[0022] In this invention, the coverage of the first coating layer can be controlled by adjusting the slurry solid content of the first coating layer, for example, by controlling the slurry solid content of the first coating layer to be 1-10%, or by using commonly used processes in the field such as roller coating, spraying, dot coating, and ultrasonic coating.

[0023] In this invention, the polymer microspheres are materials known in the prior art, including polyacrylate polymer microspheres; the polymer monomers of the polyacrylate polymer microspheres include acrylate monomers and / or a second monomer; the acrylate monomers include, but are not limited to, methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, ethyl methacrylate, etc.; the second monomers include, but are not limited to, styrene, acrylonitrile, vinyl acetate, vinylidene chloride, etc.

[0024] In this invention, the pore size of the second coating layer is ≤15nm, for example, it can be a range of 1nm, 2nm, 4nm, 6nm, 8nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, or any combination thereof. The pore size of the second coating layer can be controlled by the coating process, such as adjusting the concentration of the second coating slurry, the temperature and humidity of the environment during coating, the coating speed, or using a multi-coating method and the drying method after coating, etc.

[0025] In this invention, the thickness of the second coating layer is 1 to 10 μm, for example, it can be a range of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any combination thereof.

[0026] In this invention, the thickness of the second coating layer and the thickness of the first coating layer satisfy the following formula relationship: 1≤T2 / T1≤6; where T1 is the thickness of the first coating layer, T2 is the thickness of the second coating layer, and the units of T1 and T2 are μm; where T2 / T1 can be, for example, a range of 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, 5.2, 5.4, 5.6, 5.8, 6 or any two of them.

[0027] In this invention, the thickness of the second coating layer is within a specific range from the thickness of the first coating layer, and simultaneously satisfies the aforementioned specific relationship. This is beneficial for further improving the bubble point and gas barrier performance of the composite membrane, as well as ensuring the adhesion between the coating layer and the substrate.

[0028] In this invention, the specific surface area of ​​the second coating layer is 1×10⁻⁶. 11 ~4×10 12 m 2 / g, for example, can be 1×10 11 m 2 / g, 2×10 11 m 2 / g, 4×10 11 m 2 / g, 6×10 11 m 2 / g, 8×10 11 m 2 / g, 1×10 12 m 2 / g, 2×10 12 m 2 / g, 3×10 12 m 2 / g, 3.5×10 12 m 2 / g, more preferably 1.67×10 11 ~1.33×10 12 m 2 / g. The specific surface area of ​​the second coating layer can be controlled by adjusting the concentration of the second coating slurry, the thickness of the doctor blade or slit, the coating speed (e.g., the speed of doctor blade coating, the rotation speed of spin coating), and the drying method.

[0029] In some implementations, a combination of rotary spraying and drying can be used to control the pore size or specific surface area of ​​the second coating layer; the rotary spraying speed can be 2000–6000 rpm; the ambient humidity for drying can be 40–60%, and the drying temperature can be 20–80°C. By controlling the drying temperature and humidity, the pore size or specific surface area of ​​the second coating layer can be adjusted.

[0030] In this invention, the material of the second coating layer, namely the anion transport material, is a material known in the prior art. The ionic conductivity of the anion transport material is 0.01 to 0.1 S / cm, for example, it can be 0.01 S / cm, 0.02 S / cm, 0.04 S / cm, 0.06 S / cm, 0.08 S / cm, 0.1 S / cm or any combination thereof.

[0031] In this invention, the material of the second coating layer includes at least one of the following: anionic polymers, covalent organic framework materials (COF) containing functional groups, porous aromatic framework materials (PAF), anion exchange resins, inorganic materials (such as hydrotalcite, phosphates, mesoporous silica containing organic functional groups, etc.), and organic-inorganic hybrid materials.

[0032] In this invention, the anionic ionomer is composed of a main chain and functional groups. The main chain is usually an aromatic polymer or a polyolefin. Aromatic polymers include biphenyl, polystyrene, polyethersulfone, polyphenylene ether, polyether ether ketone, polybenzimidazole, etc., and polyolefins include polyethylene, polypropylene, etc. The functional groups include quaternary ammonium groups, guanidinium groups, imidazole onium salt groups, quaternary phosphorus groups, metal complexes, N-spirocyclic quaternary ammonium salt groups, piperidinium groups, pyrrole groups, etc.

[0033] In this invention, the material of the second coating layer also includes polymers and their derivatives such as polyvinyl chloride, polychlorinated polyethylene, polyvinyl alcohol, cellulose, polyvinyl acetate, polyacrylic acid resin, polyurethane, epoxy resin, urea-formaldehyde resin, linear polyolefin, and natural or synthetic rubber, as well as other materials known in the prior art.

[0034] In this invention, the composite diaphragm can be prepared using conventional methods. For example, the preparation method includes the following steps:

[0035] (1) Provide the substrate;

[0036] (2) The first coating layer slurry and the second coating layer slurry are sequentially coated on at least one surface of the substrate and dried to obtain the composite diaphragm.

[0037] In this invention, the slurry of the first coating layer comprises a first solvent and polymer microspheres; the solid content of the slurry of the first coating layer is 1-10%; the first solvent comprises water; the slurry of the second coating layer comprises anion transport material and a second solvent; the solid content of the slurry of the second coating layer is 5-40%; the second solvent comprises at least one of alcohols, N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP).

[0038] In this invention, after the slurry for coating the first coating layer in step (2) is dried, the slurry for coating the second coating layer can be applied. It is understood that other preparation methods can also be used in other embodiments, as long as the composite membrane structure defined in this invention can be formed.

[0039] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0040] In this invention, the composite diaphragm employs a specific structural design, which not only possesses a high bubble point, excellent gas barrier properties, and good ion transport performance, but also significantly enhances the safety of the composite diaphragm during operation in the tank, enabling it to operate under higher pressures while reducing power consumption and costs. In a preferred embodiment, the composite diaphragm of this invention can increase the bubble point by more than 50% compared to existing composite diaphragms without a significant increase in surface resistivity. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the composite diaphragm provided in Embodiment 2 of this utility model.

[0042] Wherein, 1-substrate; 21-first coating layer; 22-second coating layer.

[0043] Figure 2 This is a schematic diagram of the structure of the substrate of the composite diaphragm provided in Embodiment 2 of this utility model.

[0044] Among them, 11-mesh substrate; 12-composite coating. Detailed Implementation

[0045] It should be understood that in the description of this utility model, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing this utility model and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this utility model, unless otherwise stated, "a plurality of" means two or more.

[0046] It should be noted that, in the description of this utility model, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0047] It should be understood that the material processes described in the specific embodiments are merely examples of methods for preparing composite membranes with specific structures, and the preparation methods for these specific structures are clearly disclosed. The technical solution of this utility model will be further explained below with reference to the accompanying drawings and specific embodiments.

[0048] Example 1

[0049] This embodiment provides a composite diaphragm, comprising a substrate, a first coating layer, and a second coating layer arranged sequentially. The substrate is Zirfon UTP 500 purchased from Agfa, with a thickness of 500 μm and a pore size of 190 nm. It includes a mesh substrate and composite coatings on both sides of the mesh substrate. The composite coating is adjacent to the first coating layer. The first coating layer is a coating layer formed by polyacrylate microspheres distributed in a dotted pattern on the surface of the substrate, with a thickness of 1 μm. The average particle size of the polyacrylate microspheres (purchased from Hunan Gaorui Power Materials Co., Ltd.) is 800 nm, and the coverage of the polyacrylate microspheres is controlled at 28% using a regular dotted coating method. The second coating layer is a PiPerION anionic polymer coating layer purchased from Versogen, with a thickness of 6 μm. It is coated using a spin-spraying and drying method, with the spin-spraying speed controlled at 6000 rpm, the ambient humidity during drying at 40%, and the drying temperature at 25°C. The pore size of the second coating layer is controlled at 6 nm, and the specific surface area is 1.67 × 10⁻⁶. 11 m 2 / g; the ratio of the thickness of the second coating layer (T2) to the thickness of the first coating layer (T1) is 6.

[0050] Example 2

[0051] This embodiment provides a composite diaphragm, the structural schematic of which is shown below. Figure 1 As shown, it includes a substrate 1, a first coating layer 21, and a second coating layer 22 arranged sequentially; a schematic diagram of the substrate structure is shown below. Figure 2 As shown, it includes a mesh substrate 11 arranged sequentially and a composite coating 12 disposed on both sides of the mesh substrate; the difference from Example 1 is that the thickness of the first coating layer is 1.5 μm, the average particle size of the polyacrylate polymer microspheres in the first coating layer is 1.2 μm, and the coverage of the first coating layer is controlled to be 22% by a regular dot coating method; a spin coating combined with drying method is used, the spin coating speed is controlled to be 4000 rpm, the ambient humidity during drying is 50%, the drying temperature is 35℃, and the pore size of the second coating layer is controlled to be 10 nm, the thickness is 5 μm, and the specific surface area is 2 × 10⁻⁶. 11 m 2 / g; the ratio of the thickness of the second coating layer (T2) to the thickness of the first coating layer (T1) is 3.33.

[0052] Example 3

[0053] This embodiment provides a composite membrane, comprising a substrate, a first coating layer, and a second coating layer sequentially disposed therefrom. The difference from Embodiment 1 is that the thickness of the first coating layer is 3 μm, the average particle size of the polyacrylate microspheres in the first coating layer is 1.8 μm, and the coating coverage of the polyacrylate microspheres is controlled at 11% using a regular dot-coating method. A rotary spraying combined with drying method is used, with the rotary spraying speed controlled at 3000 rpm, the ambient humidity during drying at 60%, and the drying temperature at 45°C. The second coating layer is controlled to have a pore size of 15 nm, a thickness of 3 μm, and a specific surface area of ​​3.3 × 10⁻⁶. 11 m 2 / g; the ratio of the thickness of the second coating layer (T2) to the thickness of the first coating layer (T1) is 1.

[0054] Example 4

[0055] This embodiment provides a composite membrane, which differs from Embodiment 1 only in that the coverage of polyacrylate microspheres in the first coating layer is 5%, while the other structures are the same as in Embodiment 1.

[0056] Example 5

[0057] This embodiment provides a composite membrane, which differs from Embodiment 1 only in that the coverage of polyacrylate microspheres in the first coating layer is 40%, while the other structures are the same as in Embodiment 1.

[0058] Example 6

[0059] This embodiment provides a composite membrane, which differs from Embodiment 1 only in that the total thickness of the first and second coating layers remains unchanged, T2 / T1 is 13, and the specific surface area of ​​the second coating layer is 1.54 × 10⁻⁶. 11 m 2 / g, and the other structures are the same as in Example 1.

[0060] Example 7

[0061] This embodiment provides a composite membrane, which differs from Embodiment 1 only in that the total thickness of the first and second coating layers remains unchanged, T2 / T1 is 0.5, the average particle size of the polyacrylate microspheres in the first coating layer is 1.8 μm, the pore size of the second coating layer is 10 nm, and the specific surface area is 4.35 × 10⁻⁶. 11 m 2 / g, and the other structures are the same as in Example 1.

[0062] Example 8

[0063] This embodiment provides a composite diaphragm, which differs from Embodiment 1 only in that, by controlling the rotary spraying speed to 1000 rpm, the specific surface area of ​​the second coating layer is made to be 0.8 × 10⁻⁶. 11 m 2 / g, and the other structures are the same as in Example 1.

[0064] Example 9

[0065] This embodiment provides a composite diaphragm, which differs from Embodiment 1 only in that, by controlling the rotary spraying speed to 8000 rpm, the specific surface area of ​​the second coating layer is made to be 5 × 10⁻⁶. 12 m 2 / g, and the other structures are the same as in Example 1.

[0066] Comparative Example 1

[0067] This comparative example provides a composite membrane, which differs from Example 1 only in that it lacks a first coating layer, and the second coating layer has a thickness of 7 μm and a specific surface area of ​​2 × 10⁻⁶. 11 m 2 / g, and the other structures are the same as in Example 1.

[0068] Comparative Example 2

[0069] This comparative example provides a composite diaphragm, which differs from Example 1 only in that it does not have a second coating layer; all other structures are the same as in Example 1.

[0070] Performance testing

[0071] (1) Bubble point: Referring to GB / T 32361-2015, the composite diaphragm is completely immersed in high-purity water. The fully immersed wet membrane sample is placed in the membrane holder. Tighten the locking ring of the membrane holder and inject high-purity water into the storage tank, keeping the liquid level 2mm to 3mm above the membrane surface. Slowly increase the gas pressure and record the pressure at which the first string of continuous bubbles appears in the center of the storage tank. This is the bubble point pressure, expressed in bar.

[0072] (2) Sheet resistance: Referring to SJ / T 10171-2016, the resistance value of the composite diaphragm of a specified area immersed in a 30% potassium hydroxide solution and the resistance value of a potassium hydroxide solution of the same concentration and area are measured respectively. The product of the difference between the two and the test area of ​​the diaphragm is the sheet resistance of the composite diaphragm, expressed in Ω·cm. 2 express.

[0073] The specific test results are shown in Table 1.

[0074] Table 1

[0075]

[0076]

[0077] As shown in Table 1, the composite diaphragm in this invention employs a specific structural design, which not only possesses a high bubble point, excellent gas barrier properties, and good ion transport performance, but also enhances the safety of the composite diaphragm during operation in the tank, enabling it to operate under higher pressures while reducing power consumption and costs. The bubble point of the composite diaphragm is ≥3.8 bar, which is more than 80% higher than that of Comparative Example 1, while also exhibiting low surface resistance, ≤0.261 Ω·cm. 2 .

[0078] As can be seen from Comparative Examples 1 and 2, the bubble point is significantly reduced in the composite membranes that do not have a first coating layer or a second coating layer.

[0079] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite separator, characterized by, The composite membrane includes a substrate and a coating layer disposed on at least one surface of the substrate; the substrate includes a mesh substrate and a composite coating disposed on at least one side of the mesh substrate, the composite coating comprising inorganic particles and a composite coating formed of at least one polymer selected from polysulfone, polyethersulfone or polyarylsulfone; The coating layer includes a first coating layer and a second coating layer disposed sequentially, wherein the first coating layer is located on the side closest to the substrate; The first coating layer is a coating layer formed by polymer microspheres distributed in a dotted pattern on the surface of the substrate; The second coating layer includes an anion transport functional layer.

2. The composite separator of claim 1, wherein Along the direction from the substrate to the coating layer, the pore size of the composite membrane decreases sequentially.

3. The composite separator of claim 1, wherein The substrate satisfies at least one of the following: (a) The thickness of the substrate is 200-650 μm; (b) The pore size of the substrate is 20 to 500 nm.

4. The composite separator of claim 1, wherein The thickness of the first coating layer is 0.5 to 3 μm.

5. The composite separator of claim 1, wherein The average particle size of the polymer microspheres in the first coating layer is 500 nm to 2 μm.

6. The composite separator of claim 1, wherein The coverage of polymer microspheres in the first coating layer is 10-30%.

7. The composite separator of claim 1, wherein The pore size of the second coating layer is ≤15nm.

8. The composite separator of claim 1, wherein The thickness of the second coating layer is 1 to 10 μm.

9. The composite separator of claim 1, wherein The thickness of the second coating layer and the thickness of the first coating layer satisfy the following formula relationship: 1≤T2 / T1≤6; where T1 is the thickness of the first coating layer, T2 is the thickness of the second coating layer, and the units of T1 and T2 are μm.

10. The composite separator of claim 1, wherein The specific surface area of the second coating layer is 1 x 10 11 ~ 4 x 10 12 m 2 / g.

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