Polyamide composite ceramic membrane as well as preparation method and application thereof

Abstract

The invention discloses a polyamide composite ceramic membrane and a preparation method and application thereof, and relates to the technical field of battery diaphragms. The polyamide composite ceramic membrane comprises a microporous base membrane and a polyamide layer located on the surface of the microporous base membrane, and metal hydroxide is contained in pores of the base membrane. According to the polyamide composite ceramic membrane, the polyamide layer is arranged on the surface of the microporous base membrane, the polyamide layer structure with relatively thin wall thickness and relatively low surface density improves the mechanical strength of the membrane, and meanwhile, the polyamide composite ceramic membrane is beneficial to constructing a faster ion channel and improving the ion conductivity and the energy density; and the metal hydroxide is uniformly filled into pores of the microporous base membrane, so that the electrolyte wettability and the heat-resistant stability of the diaphragm can be improved.

Description

Technical Field

[0001] This application relates to the field of battery separator technology, and in particular to a polyamide composite ceramic membrane, its preparation method and application. Background Technology

[0002] Lithium-ion batteries (LIBs) are characterized by high energy density and high power density, and are widely used in electric vehicles, laptops, and digital cameras.

[0003] Battery separators are one of the main materials in lithium-ion batteries, serving to separate the positive and negative electrodes while allowing the electrolyte to pass through. Currently, commercially available lithium-ion battery separators are mostly microporous membranes made of polyolefin materials, primarily high-molecular-weight polyethylene and polypropylene. Products mainly include single-layer polyethylene (PE) membranes, single-layer polypropylene (PP) membranes, and multilayer microporous membranes composed of PP and PE. Polyolefin materials possess advantages such as high strength, good resistance to acid and alkali corrosion, water resistance, chemical resistance, good biocompatibility, and non-toxicity, and their industrial preparation is relatively mature. However, polyolefin separators have low surface energy, resulting in poor wettability of polar liquid electrolytes and insufficient electrolyte absorption, significantly limiting battery performance. Furthermore, polyolefin separators have a melting point in the range of 135°C-165°C, exhibiting poor thermal stability at high temperatures. When the battery heats up, the separator is prone to shrinkage or breakage, leading to internal short circuits and posing a significant safety hazard to lithium-ion batteries.

[0004] To overcome the aforementioned technical problems of battery separators, extensive research has been conducted on the modification of traditional polyolefin separators, primarily focusing on coating the surface of polyolefin separators with a heat-resistant layer. Introducing ceramic coatings into polyolefin membranes is one effective means to improve the thermal stability of the separator. Traditional inorganic coated separators typically use hydrophilic polymers as binders to introduce Al2O3, ZrO2, SiO2, zeolite, and other ceramic particle coatings onto the surface of the polyolefin substrate. However, many ceramic-coated separators still exhibit poor thermal stability because common polymer binders (such as polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polymethyl methacrylate (PMMA), or PVDF) have low melting points. When the battery operating temperature is too high, the binder melts due to the high temperature, causing irregular distribution of ceramic particles within the binder. Prolonged immersion in the electrolyte can also lead to swelling, reducing viscosity and causing the inorganic material coating to detach. In addition to the above problems, ceramic separators obtained through surface coating processes significantly increase in thickness and weight, which may reduce the ion conductivity and energy density of the battery intracellular matrix (LIB). Therefore, designing thinner, lighter membranes with high wettability and thermal stability in a simple way remains a research hotspot.

[0005] To reduce or avoid the use of binders and other additives in inorganic coated membranes, patent CN111509176A proposes a cross-linked polyimide / ceramic composite membrane and its preparation method. This composite membrane includes a microporous base membrane, ceramic particles discontinuously distributed on the surface of the microporous base membrane, and cross-linked polyimide grown in situ on the surface and internal pores of the microporous base membrane and on the surface of the ceramic particles. The preparation method achieves simultaneous coating of the cross-linked polyimide and ceramic through interfacial polymerization and chemical imidization, which can simultaneously improve the adhesion between the polyimide and the base membrane, and the compatibility between the ceramic and the base membrane, avoiding the use of binders and other additives. However, although this ceramic composite membrane has good heat resistance (thermal shrinkage rate at 120℃: MD=0.9-1.8, TD=0.6-1.2), its contact angle is only 14.6-16.9°, and its air permeability is 201-207 s / 100mL, indicating that its wettability and air permeability still need improvement. Summary of the Invention

[0006] To address the shortcomings and defects of existing technologies, a polyamide composite ceramic membrane is provided. This membrane is thin and lightweight, and has excellent heat resistance, wettability, and air permeability.

[0007] Another objective of this invention is to provide a method for preparing a polyamide composite ceramic membrane, which is based on interfacial polymerization and can be prepared in one step. This method is simple and avoids the use of binders.

[0008] Another object of the present invention is to provide a lithium-ion battery comprising the above-described polyamide composite ceramic film.

[0009] This invention protects a polyamide composite ceramic membrane, comprising a microporous base membrane and a polyamide layer located on the surface of the microporous base membrane, wherein the pores of the microporous base membrane contain metal hydroxide.

[0010] The polyamide composite ceramic membrane of the present invention has a polyamide layer on the surface of the microporous base membrane that can improve the mechanical strength of the membrane, while also improving the ion conductivity and energy density; the metal hydroxide filling the inner wall of the microporous base membrane greatly improves the electrolyte wettability and heat resistance stability of the membrane.

[0011] In some embodiments, the metal element concentration inside the pores of the microporous membrane is 3-10 wt%, preferably 3-8 wt%, and more preferably 4-7 wt%. The metal element concentration inside the pores of the microporous membrane of the present invention is determined by EDS method, and the determination method refers to standard GB / T 17359-2012.

[0012] In some embodiments, the concentration of metal elements inside the pores of the base film is derived from metal hydroxide; the metal atoms in the metal hydroxide are selected from at least one of Al, Zr, Mg or La.

[0013] In some embodiments, the metal hydroxide is formed by an in-situ reaction, specifically by the formation of a metal alkoxide through an interfacial hydrolysis reaction. The "interfacial hydrolysis reaction" referred to in this invention refers to a hydrolysis reaction at the interface between the aqueous and oil phases. The in-situ growth of metal hydroxide within the polyamide layer and the pores of the microporous membrane through the metal alkoxide hydrolysis reaction can significantly improve the electrolyte wettability and thermal stability of the membrane.

[0014] In some embodiments, the polyamide layer is filled with metal hydroxide to form a polyamide composite ceramic layer.

[0015] In some embodiments, the polyamide layer is formed by interfacial polymerization of the aqueous and oil phases, using polyamine monomers as the aqueous and oil phase monomers. The polyamide composite ceramic layer prepared by interfacial polymerization exhibits high adhesion to the base film, eliminating the need for polymeric adhesives.

[0016] In some embodiments, the polyamide layer has a thickness of 0.01-0.1 μm; preferably, its thickness is 0.01-0.04 μm. A thinner polyamide layer with lower areal density is beneficial for ionic conductivity and energy density.

[0017] Optionally, the areal density of the polyamide composite ceramic membrane is ≤5.5 g / m³. 2 The preferred areal density is 4.6-4.8 g / m³. 2 .

[0018] In some embodiments, the microporous membrane has a porosity greater than 40% and a median pore size of 30-50 nm; preferably, the porosity is 40-60%, more preferably 45-55%; preferably, the median pore size is 35-45 nm. The thickness of the microporous membrane is not particularly limited and can be arbitrarily selected from conventional sizes in the field of microporous membranes for lithium-ion batteries; preferably, the thickness of the microporous membrane is 7-9 μm.

[0019] The microporous base membrane material of the present invention is not particularly limited and can be arbitrarily selected from conventional battery separator materials in the field of lithium-ion batteries; optionally, the microporous base membrane is a polyolefin separator; specifically, the polyolefin separator is any one of polyethylene (PE) single-layer membrane, polypropylene (PP) single-layer membrane, and PP / PE / PP multilayer microporous membrane composed of PP and PE.

[0020] This invention protects a method for preparing a polyamide composite ceramic membrane, comprising the following steps: S1, dissolve the polyamine monomer in water to obtain an aqueous monomer solution; S2, dissolving polyacrylamide chloride monomers and metal alkoxides in an oil phase solvent to obtain an oil phase monomer solution, wherein the concentration of the metal alkoxide in the oil phase monomer solution is 0.01-0.5 wt%; S3, the microporous base membrane is immersed in an aqueous monomer solution, taken out and excess solution is removed from the surface, then immersed in an oil-phase monomer solution, taken out and heat-treated to obtain the polyamide composite ceramic membrane.

[0021] The method for preparing the polyamide composite ceramic membrane of the present invention involves introducing a specific amount of metal alkoxide solution into the oil phase of an interfacial polymerization system. Simultaneously, as the polyamine monomer and acyl chloride monomer undergo a polycondensation reaction at the interface, the metal alkoxide molecules continuously migrate towards the water / oil interface and hydrolyze, thereby generating a polyamide composite ceramic layer on the surface of the base membrane. This process eliminates the need for polymeric binders, solving the problem in traditional ceramic coating techniques where binder swelling leads to easy detachment of the inorganic material coating and weak adhesion. Furthermore, the metal hydroxide can fill the inner walls of the pores in the polyolefin base membrane, further improving the bulk electrolyte wettability of the membrane.

[0022] Optionally, the concentration of the metal alkoxide in the oil phase monomer solution can be any one of 0.01wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, and 0.5wt%, or any range between two of them.

[0023] In some embodiments, in step S1, the polyamine monomer is selected from at least one of piperazine, m-phenylenediamine, ethylenediamine, p-phenylenediamine, or hexamethylenediamine. Piperazine monomer is preferred.

[0024] In some embodiments, the concentration of the polyamine monomer in the aqueous monomer solution is 1-5 wt%.

[0025] In some embodiments, in step S1, the aqueous monomer solution further includes 0.5-2.0 wt% of an additive; the additive is a surfactant and / or a pore-forming agent.

[0026] Optionally, the surfactant is selected from sodium dodecyl sulfate and / or polyvinylpyrrolidone.

[0027] The pore-forming agent is selected from at least one of polyethylene glycol, polyacrylic acid, or glycerin.

[0028] In some embodiments, in step S2, the polyacrylamide chloride monomer is selected from at least one of pyromellitic trimethylol chloride or isophthalic dimethylol chloride.

[0029] In some embodiments, the concentration of polyacrylamide chloride monomer in the oil phase monomer solution is 0.05-0.5 wt%.

[0030] In some embodiments, the metal alkoxide has the structural formula M(OR). n n represents the valence state of metal M, M is selected from at least one of Al, Zr, Mg or La, and R is selected from C2-C5 alkyl groups.

[0031] In some embodiments, the metal alkoxide is selected from at least one of aluminum isopropoxide, aluminum sec-butoxide, zirconium n-propoxide, zirconium n-butoxide, magnesium tert-butoxide, or lanthanum n-butoxide.

[0032] In some embodiments, the oil phase solvent comprises a nonpolar solvent and a polar solvent in a volume ratio of (10-100):1.

[0033] Optionally, the volume ratio of the nonpolar solvent solution to the polar solvent solution is any one of 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1 or any range between the two.

[0034] Optionally, the nonpolar solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, octane, or chloroform.

[0035] Optionally, the polar solvent is selected from at least one of acetone, N,N-dimethylformamide, dichloromethane, tetrahydrofuran, isopropanol, or tert-butanol.

[0036] Optionally, the metal alkoxide is dissolved in a polar solvent, wherein the concentration of the metal alkoxide in the polar solvent is 0.5-5 wt%.

[0037] The metal alkoxide of the present invention is added to the oil phase monomer solution of a nonpolar system in the form of a polar solvent. The introduction of the polar solution can promote the hydrolysis of a small amount of acyl chloride monomer, while the more polar molecules will accumulate at the interface, triggering a faster polymerization reaction. The rapid self-limiting reaction can effectively hinder the diffusion process of aqueous monomer through the cross-linking network, thereby producing a thinner and looser polyamide layer. This thinner polyamide layer with a lower areal density improves the mechanical strength of the membrane and is also conducive to the construction of faster ion channels, thereby improving ion conductivity and energy density.

[0038] In some embodiments, in step S3, the microporous base membrane further includes a surface pretreatment prior to the immersion treatment, wherein the surface pretreatment is plasma treatment and / or corona treatment. Surface pretreatment improves the adhesion and hydrophilicity of the base membrane, facilitates the uniform distribution of amine monomers on the base membrane surface, and is beneficial for the formation and adhesion of the polyamide layer.

[0039] This invention protects a lithium-ion battery, comprising the polyamide composite ceramic membrane or the polyamide composite ceramic membrane prepared by the method of preparing the polyamide composite ceramic membrane.

[0040] Compared with the prior art, the beneficial effects of the present invention are: The present invention discloses a polyamide composite ceramic membrane, wherein the surface of the porous base membrane has a polyamide layer, which improves the mechanical strength of the membrane, while also increasing the ion conductivity and energy density; the metal hydroxide can fill the pores of the base membrane, significantly improving the electrolyte wettability and heat resistance stability of the membrane.

[0041] This invention discloses a method for preparing a polyamide composite ceramic membrane. A specific amount of metal alkoxide solution is introduced into the oil phase of an interfacial polymerization system. Simultaneously, while the polyamine monomer and acyl chloride monomer undergo condensation at the interface, the metal alkoxide molecules continuously migrate towards the water / oil interface and hydrolyze, thereby generating metal oxide and polyamide layers inside and on the surface of the base membrane. This process eliminates the need for polymeric binders, solving the problem in traditional ceramic coating techniques where binder swelling leads to easy detachment of the inorganic material coating and weak adhesion. Furthermore, the metal hydroxide can fill the pores of the polyolefin base membrane, further improving the bulk electrolyte wettability and thermal stability of the membrane. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of the polyamide composite ceramic membrane prepared in Example 1 of the present invention.

[0043] Figure 2 The images show SEM images of the surface and cross-section of the polyamide composite ceramic film prepared in Example 1 of this invention.

[0044] Figure 3 This is a SEM image of the surface and cross-section of the PE base film (HSV9) in Comparative Example 1 of the present invention.

[0045] Figure 4 This is a cross-sectional EDS elemental distribution diagram of the polyamide composite ceramic membrane prepared in Example 3 of the present invention.

[0046] Figure 5 This is a cross-sectional EDS elemental distribution diagram of the polyamide composite ceramic membrane prepared in Comparative Example 3 of the present invention. Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way.

[0048] Example 1 A polyamide composite ceramic membrane, such as Figure 1As shown, it includes a microporous base membrane 1, a polyamide layer 2 located on the surface of the microporous base membrane 1, and a metal hydroxide 3 in the internal pores of the microporous base membrane 1.

[0049] The microporous base membrane 1 is a PE base membrane, model HSV9, with a porosity of 50.9%.

[0050] The polyamide layer 2 is formed by interfacial polymerization of the aqueous and oil phases using a polyamine monomer as the aqueous phase monomer and a polyacrylamide chloride monomer as the oil phase monomer. Specifically, the polyamine monomer is piperazine and the polyacrylamide chloride monomer is pyromellitic trimethylol chloride.

[0051] The metal hydroxide 3 is formed by an interfacial hydrolysis reaction of a metal alkoxide dissolved in an oil phase containing a polar solvent; the metal alkoxide is aluminum isopropoxide, and the polar solvent is selected from acetone.

[0052] The method for preparing the polyamide composite ceramic membrane includes the following steps: S1, Base film pretreatment: Take PE base film (model HSV9) and perform plasma surface treatment using a plasma cleaner. The treatment conditions are: power 30w, N2 atmosphere, time 60s, and electrode spacing 15cm.

[0053] S2, Preparation of an aqueous monomer solution: Piperazine monomer and additive PEG are dissolved in water to obtain an aqueous monomer solution; the concentration of piperazine monomer in the aqueous monomer solution is 2.0 wt%, and the concentration of PEG is 0.5 wt%. S3, Preparation of oil phase monomer solution: Mix a hexane solution containing 0.10 wt% trimesoyl chloride monomer and an acetone solution containing 1.0 wt% aluminum isopropoxide at a volume ratio of 50:1, and stir evenly at 60°C to obtain an oil phase monomer solution. S4, Interfacial polymerization to prepare polyamide composite ceramic layer: Immerse the PE base film in an aqueous solution and let it stand for 60s. After removing it and removing excess solution from the surface, dry it at room temperature for 1min. Then immerse the PE base film in an oil solution for 30s. After the reaction is complete, remove the PE base film and vacuum dry it at 80°C to obtain a polyamide composite ceramic film with a polyamide composite ceramic layer.

[0054] Example 2 A polyamide composite ceramic membrane differs from Example 1 in that the additive in the aqueous monomer solution of this example is sodium dodecyl sulfate.

[0055] Specifically, the preparation method of the polyamide composite ceramic membrane includes the following steps: S1, Base film pretreatment: Take PE base film (model HSV9) and perform plasma surface treatment using a plasma cleaner. The treatment conditions are: power 30w, N2 atmosphere, time 60s, and electrode spacing 15cm.

[0056] S2, Preparation of an aqueous monomer solution: Piperazine monomer and sodium dodecyl sulfate additive are dissolved in water to obtain an aqueous monomer solution; the concentration of piperazine monomer in the aqueous monomer solution is 2.0 wt%, and the concentration of sodium dodecyl sulfate is 0.5 wt%. S3, Preparation of oil phase monomer solution: Mix a hexane solution containing 0.10 wt% trimesoyl chloride monomer and an acetone solution containing 1.0 wt% aluminum isopropoxide at a volume ratio of 50:1, and stir evenly at 60°C to obtain an oil phase monomer solution. S4, Interfacial polymerization to prepare polyamide composite ceramic layer: Immerse the PE base film in an aqueous solution and let it stand for 60s. After removing it and removing excess solution from the surface, dry it at room temperature for 1min. Then immerse the PE base film in an oil solution for 30s. After the reaction is complete, remove the PE base film and vacuum dry it at 80°C to obtain a polyamide composite ceramic film with a polyamide composite ceramic layer.

[0057] Example 3 A polyamide composite ceramic membrane differs from Example 1 in that the metal alkoxide in this example is zirconium propoxide.

[0058] Specifically, the preparation method of the polyamide composite ceramic membrane includes the following steps: S1, Base film pretreatment: Take PE base film (model HSV9) and perform plasma surface treatment using a plasma cleaner. The treatment conditions are: power 30w, N2 atmosphere, time 60s, and electrode spacing 15cm.

[0059] S2, Preparation of an aqueous monomer solution: Piperazine monomer and additive PEG are dissolved in water to obtain an aqueous monomer solution; the concentration of piperazine monomer in the aqueous monomer solution is 2.0 wt%, and the concentration of PEG is 0.5 wt%. S3, Preparation of oil phase monomer solution: Mix a hexane solution containing 0.10 wt% trimesoyl chloride monomer and an acetone solution containing 1.0 wt% zirconium propoxide at a volume ratio of 50:1, and stir evenly at 60°C to obtain an oil phase monomer solution. S4, Interfacial polymerization to prepare polyamide composite ceramic layer: Immerse the PE base film in an aqueous solution and let it stand for 60s. After removing it and removing excess solution from the surface, dry it at room temperature for 1min. Then immerse the PE base film in an oil solution for 30s. After the reaction is complete, remove the PE base film and vacuum dry it at 80°C to obtain a polyamide composite ceramic film with a polyamide composite ceramic layer.

[0060] Example 4 A polyamide composite ceramic membrane differs from Example 1 in that: the polyamine monomer in this example is selected from m-phenylenediamine; and the polyacrylamide chloride monomer is selected from m-phenylenedimethyl chloride.

[0061] Example 5 A polyamide composite ceramic membrane differs from Example 1 in that the aluminum isopropoxide content in the acetone solution containing aluminum isopropoxide in this example is 4.0 wt%.

[0062] Comparative Example 1 A battery separator differs from that of Example 1 in that the battery separator in this comparative example is a PE-based film (HSV9). No polyamide layer was prepared on the surface of the base film, and no metal hydroxide filling treatment was performed.

[0063] Comparative Example 2 A polyamide composite membrane differs from Example 1 in that the membrane in this comparative example does not contain metal hydroxides.

[0064] The method for preparing the polyamide composite separator includes the following steps: S1, Base film pretreatment: Take PE base film (model HSV9) and perform plasma surface treatment using a plasma cleaner. The treatment conditions are: power 30w, N2 atmosphere, time 60s, and electrode spacing 15cm. S2, Preparation of an aqueous monomer solution: Piperazine monomer and additive PEG are dissolved in water to obtain an aqueous monomer solution; the concentration of piperazine monomer in the aqueous monomer solution is 2.0 wt%, and the concentration of PEG is 0.5 wt%. S3, Preparation of oil phase monomer solution: A hexane solution containing 0.10 wt% trimesoyl chloride monomer is used as the oil phase monomer solution. An acetone solution is mixed at a volume ratio of 50:1 and stirred evenly at 60°C to obtain the oil phase monomer solution. S4, Interfacial polymerization to prepare polyamide layer: Immerse the PE base film in an aqueous solution and let it stand for 60s. After removing it and removing excess solution from the surface, dry it at room temperature for 1min. Then immerse the PE base film in an oil solution for 30s. After the reaction is complete, remove the PE base film and vacuum dry it at 80°C to obtain a polyamide composite membrane with a polyamide layer.

[0065] Comparative Example 3 A polyamide composite ceramic membrane differs from Example 3 in that: metal hydroxide is directly introduced into the membrane of this comparative example, instead of introducing metal alkoxide solution into the oil phase of the interfacial polymerization system in Example 1 to prepare metal hydroxide through interfacial hydrolysis.

[0066] Specifically, the preparation method of the polyamide composite ceramic membrane includes the following steps: S1, Base film pretreatment: Take PE base film (model HSV9) and perform plasma surface treatment using a plasma cleaner. The treatment conditions are: power 30w, N2 atmosphere, time 60s, and electrode spacing 15cm.

[0067] S2, Preparation of aqueous monomer solution: Piperazine monomer, additive PEG, and zirconium hydroxide are added to water and stirred until homogeneous to obtain an aqueous monomer solution; the concentration of piperazine monomer in the aqueous monomer solution is 2.0 wt%, the concentration of PEG is 0.5 wt%, and the concentration of zirconium hydroxide is 1.0 wt%. S3, Preparation of oil phase monomer solution: Use a hexane solution containing 0.10 wt% trimesoyl chloride monomer as the oil phase monomer solution; S4, Interfacial polymerization to prepare polyamide layer: Immerse the PE base film in an aqueous solution and let it stand for 60s. After removing it and removing excess solution from the surface, dry it at room temperature for 1min. Then immerse the PE base film in an oil solution for 30s. After the reaction is complete, remove the PE base film and vacuum dry it at 80°C to obtain a polyamide composite membrane with a polyamide layer.

[0068] Performance testing I. SEM Characterization The membrane materials of Example 1 and Comparative Example 1 were characterized by scanning electron microscopy (SEM), and the results are as follows: Figure 2 and Figure 3 As shown.

[0069] The results show that a polyamide composite ceramic layer was constructed on the surface of the membrane material in Example 1, and the polyamide composite ceramic layer was thin, with an average thickness as low as 0.08 μm.

[0070] II. EDS Characterization Quantitative analysis was performed using the microbeam energy dispersive spectroscopy method according to standard GB / T 17359-2012. This involved combining an X-ray energy dispersive spectroscopy (EDS) instrument with a scanning electron microscope (SEM). The sample surface was bombarded with an electron beam in a vacuum chamber to excite the material and elicit characteristic X-ray emission. Qualitative and semi-quantitative analysis of the cross-sectional elemental distribution of the membrane materials in Example 3 and Comparative Example 3 was conducted. The results are as follows: Figure 4-5 As shown. The results show that uniformly distributed zirconium hydroxide particles were successfully introduced into the pores inside the microporous membrane and the polyamide layer of the present invention, with a zirconium element concentration of 5 wt%. Figure 4 In contrast, when metal hydroxide was directly introduced in Comparative Example 3, the zirconium concentration in the pores of the microporous membrane was only 1 wt%. Figure 5 ).

[0071] III. Material Property Characterization The membrane materials of each embodiment and comparative example were subjected to the following performance tests, referring to the standard GB / T 36363-2018 Test Methods for Polyolefin Separators for Lithium-ion Batteries. The results are shown in Table 1.

[0072] 1. Thickness and areal density: The total thickness of the diaphragm (coating + base film) is measured using a thickness gauge or scanning electron microscope. The mass of the sample is weighed using a precision analytical balance, and the length and width of the diaphragm are measured. The areal density is calculated using the formula ρ = m / (L*b), where m is the mass of the sample, and L and b are the length and width of the diaphragm.

[0073] 2. Contact angle: Cut 5 pieces of film with a size of 10mm×10mm, add 2.0μL of electrolyte, and test the contact angle using a contact angle tester.

[0074] 3. Tensile strength: The test shall be conducted in accordance with GB / T1040.3-2006, using three specimens with a width of 15 mm, an initial distance of 100 mm between the fixtures, and a test speed of 250 mm / min.

[0075] 4. Heat shrinkage rate: Cut three 100mm×100mm films, place the sample between two sheets of quantitative filter paper, and place it in the middle of a blower-type constant temperature chamber. Measure the changes in the longitudinal (MD) and transverse (TD) length of the film before and after heating. Test conditions: temperature 130°C, test duration 1 hour.

[0076] 5. Air permeability: Cut three 100mm x 100mm films and place them in an air permeability testing instrument for testing. Apply a pressure of 1.21 kPa to the testing instrument; the contact area for 100 mL of air passing through is 6.45 cm². 2 The time required for the diaphragm to be in place.

[0077] Table 1

[0078] Referring to Table 1, the polyamide composite ceramic membrane of the present invention has the characteristics of low thickness and areal density, good wettability, high tensile strength, low heat shrinkage and good air permeability; its contact angle is ≤20.1°; tensile strength MD≥258.6MPa, TD≥222.1MPa; heat shrinkage at 130°C / 1h MD≤4.2%, TD≤3.0%; and air permeability ≤177.2s / 100mL.

[0079] Compared to Example 1, the PE base film of Comparative Example 1 did not have a polyamide composite ceramic layer prepared on its surface, resulting in poor wettability and a large thermal shrinkage rate.

[0080] In Comparative Example 2, the polyamide layer does not contain metal hydroxide, resulting in a larger contact angle, poorer wettability, and a larger thermal shrinkage rate. In contrast, in Comparative Example 3, metal hydroxide was directly introduced, but it failed to disperse in the pores of the microporous base film. This not only failed to effectively improve its wettability and thermal shrinkage rate but also led to a decrease in its air permeability.

[0081] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A polyamide composite ceramic membrane, characterized in that, It includes a microporous base membrane and a polyamide layer located on the surface of the microporous base membrane, wherein the pores of the microporous base membrane contain metal hydroxide.

2. The polyamide composite ceramic membrane according to claim 1, characterized in that, The concentration of metal elements inside the pores of the microporous membrane is 3-8 wt%.

3. The polyamide composite ceramic membrane according to claim 1 or 2, characterized in that, The metal atoms in the metal hydroxide are selected from at least one of Al, Zr, Mg or La.

4. The polyamide composite ceramic membrane according to claim 1, characterized in that, The metal hydroxide is formed by the interfacial hydrolysis reaction of a metal alkoxide.

5. The polyamide composite ceramic membrane according to claim 1, characterized in that, The polyamide layer is filled with metal hydroxide.

6. The polyamide composite ceramic membrane according to claim 1, characterized in that, The polyamide layer is formed by interfacial polymerization of the aqueous and oil phases using polyamine monomers as aqueous and polyacrylamide monomers as oil phase monomers.

7. The polyamide composite ceramic membrane according to claim 1, characterized in that, The thickness of the polyamide layer is 0.01-0.1 μm.

8. The polyamide composite ceramic membrane according to claim 1, characterized in that, The microporous base membrane has a porosity greater than 40% and a median pore size of 30-50 nm.

9. A method for preparing a polyamide composite ceramic membrane, characterized in that, Includes the following steps: S1, dissolve the polyamine monomer in water to obtain an aqueous monomer solution; S2, dissolving polyacrylamide chloride monomers and metal alkoxides in an oil phase solvent to obtain an oil phase monomer solution, wherein the concentration of the metal alkoxide in the oil phase monomer solution is 0.01-0.5 wt%; S3, the microporous base membrane is immersed in an aqueous monomer solution, taken out and excess solution is removed from the surface, then immersed in an oil-phase monomer solution, taken out and heat-treated to obtain the polyamide composite ceramic membrane.

10. The method for preparing the polyamide composite ceramic membrane according to claim 9, characterized in that, In step S2, the concentration of the polyacrylamide chloride monomer in the oil phase monomer solution is 0.05-0.5 wt%.

11. The method for preparing the polyamide composite ceramic membrane according to claim 9 or 10, characterized in that, In step S2, the polyacrylamide chloride monomer is selected from at least one of pyromellitic trimethylol chloride or isophthalic dimethylol chloride.

12. The method for preparing the polyamide composite ceramic membrane according to claim 9, characterized in that, In step S1, the polyamine monomer is selected from at least one of piperazine, m-phenylenediamine, ethylenediamine, p-phenylenediamine, or hexamethylenediamine.

13. The method for preparing the polyamide composite ceramic membrane according to claim 9 or 12, characterized in that, The concentration of polyamine monomer in the aqueous monomer solution is 1-5 wt%.

14. The method for preparing the polyamide composite ceramic membrane according to claim 9, characterized in that, The structural formula of the metal alkoxide is M(OR). n n represents the valence state of metal M, M is selected from at least one of Al, Zr, Mg or La, and R is selected from C2-C5 alkyl groups.

15. The method for preparing the polyamide composite ceramic membrane according to claim 9 or 14, characterized in that, The metal alkoxide is selected from at least one of aluminum isopropoxide, aluminum sec-butoxide, zirconium n-propoxide, zirconium n-butoxide, magnesium tert-butoxide, or lanthanum n-butoxide.

16. The method for preparing the polyamide composite ceramic membrane according to claim 9, characterized in that, In step S1, the aqueous monomer solution further includes 0.5-2.0 wt% of additives; the additives are surfactants and / or pore-forming agents.

17. The method for preparing the polyamide composite ceramic membrane according to claim 16, characterized in that, The additive is selected from at least one of sodium dodecyl sulfate, polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, or glycerin.

18. The method for preparing the polyamide composite ceramic membrane according to claim 9, characterized in that, The oil phase solvent includes a nonpolar solvent and a polar solvent in a volume ratio of (10-100):

1.

19. The method for preparing the polyamide composite ceramic membrane according to claim 18, characterized in that, The nonpolar solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, octane, or chloroform; The polar solvent is selected from at least one of acetone, N,N-dimethylformamide, dichloromethane, tetrahydrofuran, isopropanol, or tert-butanol.

20. The method for preparing the polyamide composite ceramic membrane according to claim 9, characterized in that, In step S3, the microporous base membrane further includes a surface pretreatment before immersion treatment, which is plasma treatment and / or corona treatment.

21. A lithium-ion battery, characterized in that, The polyamide composite ceramic membrane includes the polyamide composite ceramic membrane according to any one of claims 1-8 or the polyamide composite ceramic membrane prepared by the method according to any one of claims 9-20.

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