Preparation method of fast ion conduction puncture-resistant ultra-thin diaphragm based on concentric three-layer gradient structure carbon nanofiber

Abstract

The application provides a preparation method of a fast-ion-conducting puncture-resistant ultra-thin diaphragm based on a concentric three-layer gradient structure carbon nanometer fiber, comprising the following steps: step 1, blending polyacrylonitrile and aldehyde monomers in a solvent A to prepare an aldehyde-containing spinning solution; step 2, spinning the spinning solution to prepare an aldehyde-containing fiber membrane; step 3, in-situ growing a multi-level pore COF intermediate layer in the aldehyde-containing fiber membrane in an amino monomer, a catalyst and a solvent B to prepare a porous COF fiber; step 4, sequentially performing pre-oxidation and high-temperature isostatic carbonization on the porous COF fiber to prepare a dense COF carbonized fiber membrane; and step 5, loading a titanium source gel layer on the upper and lower surfaces of the dense COF carbonized fiber membrane, and converting the gel into a titanium dioxide nanocrystal outer layer in a solvent C to prepare a puncture-resistant carbon nanometer fiber ultra-thin diaphragm. The diaphragm has the advantages of an ultra-thin thickness, excellent mechanical strength, ultra-high ion conductivity and dendritic puncture resistance, and is suitable for a high-safety long-service-life battery system.

Description

Technical Field

[0001] This invention relates to the fields of extreme condition new energy materials, battery separators and high-safety long-life batteries based on carbon nanofibers, and specifically to a method for preparing a fast ion conduction puncture-resistant ultrathin separator based on concentric three-layer gradient carbon nanofibers. Background Technology

[0002] With the rapid iteration of the new energy industry, high-safety, long-life, and high-energy-density batteries have become the core development direction in the new energy field. As a key component that separates the positive and negative electrodes, conducts ions, and prevents short circuits, the battery separator's comprehensive performance directly determines the battery's safety, cycle stability, and upper limit of energy density. Polyacrylonitrile (PAT), a high-performance polymer material, is widely used in the preparation of battery separator substrate materials due to its regular structure, good fiber-forming properties, and ability to form stable carbon fibers after carbonization. Carbon fiber separators prepared using PAT possess excellent mechanical strength, heat resistance, and chemical stability, making them an important research platform for high-performance battery separators.

[0003] Covalent organic frameworks (COFs), as a class of novel porous materials with regular pore structures, high specific surface areas, and good chemical stability, have received widespread attention in the field of battery separator modification in recent years. Due to their unique pore structure, which can build efficient ion transport channels, and their good interfacial compatibility, they are often used for coating modification of separator surfaces to improve the ionic conductivity, interfacial stability, and corrosion resistance of the separator. Meanwhile, titanium dioxide, as a common inorganic functional material, is often prepared as a coating for surface functional modification of battery separators due to its excellent chemical stability, oxidation resistance, and certain dendrite suppression potential, in an attempt to improve the puncture resistance and safety of the separator.

[0004] Currently, while some research progress has been made in battery separators based on polyacrylonitrile and its carbon fibers, and they have been initially applied in some conventional battery systems, many technical bottlenecks remain insurmountable in the field of high-performance and high-safety batteries. During the preparation of polyacrylonitrile-based carbon fiber separators, factors such as raw material purity and process control precision can easily lead to problems such as fiber agglomeration, uneven pore structure, and disordered pore size distribution. This results in obstructed ion transport channels, significantly limiting the improvement of ionic conductivity and making it difficult to meet the requirements of high-rate charge and discharge. Simultaneously, the single carbon fiber separator itself has a certain degree of brittleness, making it difficult to effectively balance mechanical strength, flexibility, and ultra-thin characteristics. If the thickness is too thin, the mechanical strength is insufficient, making it prone to breakage during battery assembly and cycling; if the thickness is too large, it increases the battery's internal resistance and reduces its energy density. The contradiction between thickness and overall performance is quite prominent. In addition, existing carbon fiber separators modified with COF coating or titanium dioxide coating often have problems such as weak bonding between the modified layer and the carbon fiber substrate, easy detachment, and poor coating uniformity. Moreover, most of them use a single modification method, which makes it difficult to synergistically leverage the unique regular channel transport advantages of COF material and the dendrite suppression and puncture resistance advantages of titanium dioxide coating. This makes it impossible to meet the comprehensive requirements of high-performance batteries for separators that are ultra-thin, high-strength, high-conductivity, and high-safety.

[0005] In the current field of battery separators, the mechanical advantages of polyacrylonitrile (PAC) and its derived carbon fibers, the rapid ion conduction advantage imparted by the hierarchical gradient channels of carbon-fiber composites (COF), and the functional advantages of titanium dioxide coatings are all key challenges. Addressing the issues of poor synergy among these three factors, weak bonding of modified layers, and insufficient overall separator performance remains a critical technical hurdle for the industry. Currently, various modified separators still struggle to simultaneously meet the comprehensive requirements of ultra-thin thickness, excellent mechanical strength, high ionic conductivity, and good dendrite puncture resistance, failing to fully adapt to the application needs of high-safety, long-life battery systems. Therefore, developing a novel battery separator capable of achieving synergistic advantages among these three factors and its preparation method has significant theoretical research value and broad prospects for industrial application. Summary of the Invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing a fast ion conduction and puncture-resistant ultrathin separator based on a concentric three-layer gradient carbon nanofiber structure, in order to meet the urgent needs of cutting-edge electrochemical energy storage fields such as next-generation high-safety and long-life power batteries, large-scale energy storage systems and aerospace for separator materials with dimensional stability, high ion conduction efficiency, excellent mechanical properties and long-term cycle stability under extreme temperature environments.

[0007] This method includes the following steps:

[0008] Step 1: Prepare an aldehyde-containing spinning solution by blending polyacrylonitrile and aldehyde monomer in solvent A;

[0009] Step 2: Spin the spinning solution obtained in Step 1 to prepare an aldehyde-containing fiber membrane;

[0010] Step 3: The aldehyde-containing fiber membrane obtained in Step 2 is used to grow a multi-level porous COF intermediate layer in situ in amino monomer, catalyst and solvent B to prepare porous COF fibers.

[0011] Step 4: The porous COF fibers obtained in Step 3 are subjected to pre-oxidation and high-temperature isostatic pressing carbonization in sequence to prepare a dense COF carbonized fiber membrane.

[0012] Step 5: Load the upper and lower surfaces of the dense COF carbon fiber membrane obtained in Step 4 with titanium source gel layers, and gel transform them in solvent C to form an outer layer of titanium dioxide nanocrystals, thus preparing a puncture-resistant carbon nanofiber ultrathin diaphragm.

[0013] In step 1, the aldehyde monomer is terephthalaldehyde, isophthalaldehyde, o-phthalaldehyde, 2,5-dihydroxyterephthalaldehyde, 2,5-dimethoxyterephthalaldehyde, 4,4'-biphenyldialdehyde, 2,2'-biphenyldialdehyde, 1,4-naphthalenedicarboxyl, 2,6-naphthalenedicarboxyl, anthracenedialdehyde, pyrenedialdehyde, 1,3,5-benzenetrialdehyde, tris(4-formylphenyl)amine, tris(4-aldehydephenyl)triazine, trialdehyde-resorcinol, tetra(4-aldehyde-resorcinol), etc. One or more of the following: phenyl)ethylene, tetraaldehyde calix[4] aromatic hydrocarbon, pyrene tetracarboxaldehyde, glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, hexanedialdehyde, cyclohexanedialdehyde, norbornene dicarboxaldehyde, 2,5-thiophene dicarboxaldehyde, 2,6-pyridine dicarboxaldehyde, 3,4-ethylenedioxythiophene dicarboxaldehyde, cyanotricarboxaldehyde, tetrafluoroterephthalaldehyde, 2-fluoroterephthalaldehyde, and 2-chloroterephthalaldehyde; the molar ratio of polyacrylonitrile to aldehyde monomer is 100:1 to 1:2.

[0014] In step 1, solvent A is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, hexamethylphosphoramide, sulfolane, tetrahydrofuran, acetone, ethyl acetate, chloroform, dichloromethane, 1,4-dioxane, methanol, ethanol, isopropanol, n-butanol, tert-butanol, acetic acid, formic acid, dimethyl sulfone, formamide, and acetamide; the mass fraction of polyacrylonitrile in the spinning solution is 5-25%.

[0015] In step 2, the spinning method is one or more of the following: high-voltage electrospinning, dry spinning, wet spinning, high-speed centrifugal spinning, melt spinning, solution spinning, gel spinning, phase separation spinning, airflow spinning, eddy spinning, triboelectric spinning, electrostatic meltblown spinning, conjugate spinning, island spinning, composite spinning, dry and wet spinning, cryogenic spinning, electrostatic spray spinning, template spinning, and melt electrospinning.

[0016] In step 3, the amino monomer is p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 4,4'-biphenylenediamine, 3,3'-biphenylenediamine, 2,2'-biphenylenediamine, 1,4-naphthylenediamine, 1,5-naphthylenediamine, 2,6-naphthylenediamine, anthracene diamine, pyrene diamine, 1,3,5-phenyltriamine, tris(4-aminophenyl)amine, tris(4-aminophenyl)triazine, tetra(4-aminophenyl)ethylene, tetraaminocalix[4]arene, pyrene tetramine, ethylenediamine, propylenediamine, butanediamine, pentanediamine, hexanediamine, cyclohexanediamine, norbornenediamine, 2,5-thiophenediamine, 2,6-pyridinediamine, 3 One or more of the following: 4-ethylenedioxythiophene diamine, melaminetriamine, 4-aminobenzaldehyde, 2-aminobenzaldehyde, 3-aminobenzaldehyde, p-aminophenol, m-aminophenol, o-aminophenol, tetrafluorop-phenylenediamine, 2-fluorop-phenylenediamine, 2-chlorop-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,2'-diaminodiphenylpropane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, polyethylene glycol, and polypropylene glycol.

[0017] The catalyst is one or more of the following: trifluoroacetic acid, formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, p-toluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, fluoroboric acid, trifluoromethanesulfonic acid, pyridine, 4-dimethylaminopyridine, triethylamine, diethylamine, ethylamine, tributylamine, diisopropylethylamine, imidazole, 1-methylimidazolium, 2-methylimidazolium, 4-methylimidazolium, triphenylphosphine, ferrocene, ferric chloride, cobalt chloride, nickel chloride, copper chloride, zinc chloride, ferric nitrate, cobalt nitrate, nickel nitrate, copper nitrate, zinc nitrate, ferric acetate, cobalt acetate, nickel acetate, copper acetate, zinc acetate, palladium on carbon, platinum on carbon, rhodamine B, rhodamine 6G, tetrabutyl titanate, titanium chloride, titanium sulfate, zinc oxide, alumina, titanium dioxide, silicon dioxide, montmorillonite, kaolin, zeolite, molecular sieve, and ionic liquid catalyst.

[0018] The molar ratio of aldehyde monomer to amino monomer is 20:1 to 1:20, and the molar ratio of the total amount of aldehyde monomer and amino monomer to catalyst is 100:1 to 3:1.

[0019] In step 3, solvent B is one or more of the following: N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, hexamethylphosphoramide, sulfolane, tetrahydrofuran, 1,4-dioxane, chloroform, dichloromethane, chloroform, toluene, benzene, xylene, ethylbenzene, cumene, acetone, methyl ethyl ketone, ethyl acetate, propyl acetate, butyl acetate, methanol, ethanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, propylene glycol, butanediol, pyridine, dioxane, acetonitrile, propionitrile, butyronitrile, formamide, acetamide, dimethyl sulfone, dimethyl carbonate, diethyl carbonate, and propylene carbonate.

[0020] The total mass ratio of aldehyde monomers and amino monomers to solvent B is 1:5 to 1:500; the reaction temperature is 20 to 100℃, and the reaction time is 2 to 120 h.

[0021] In step 4, the pre-oxidation conditions are as follows: the atmosphere includes air, oxygen, oxygen-enriched air (oxygen volume fraction 21%~100%), and an air-inert gas mixed atmosphere (the inert gas is one or more of nitrogen, argon, and helium, with an air-inert gas volume ratio of 1:9~9:1); the heating rate is 0.5~10℃ / min; the pre-oxidation temperature is 150~300℃; the holding time is 1~12 h; and the pre-oxidation pressure is 0.1~1.0 MPa.

[0022] In step 4, the conditions for isostatic carbonization are as follows: the atmosphere is one or more of nitrogen, argon, helium, neon, and krypton; the isostatic pressure is 5~200 MPa; the heating rate is 0.5~8℃ / min; the carbonization temperature is 600~1500℃; the holding time is 0.1~10 h; and the cooling rate is 1~10℃ / min.

[0023] In step 5, the titanium source is one or more of the following: tetrabutyl titanate, isopropyl titanate, ethyl titanate, methyl titanate, titanium tetrachloride, titanium trichloride, titanium sulfate, titanium nitrate, titanium dichlorodicyclopentadiene, titanium acetylacetone, titanium lactate, titanium ethylene glycol, tetraisopropyl titanate, ammonium fluorotitanate, and potassium fluorotitanate. The solvent C is one or more of the following: anhydrous ethanol, methanol, isopropanol, n-propanol, tert-butanol, ethylene glycol, propylene glycol, glycerol, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, acetonitrile, acetone, methyl ethyl ketone, tetrahydrofuran, 1,4-dioxane, acetic acid, ethyl acetate, and deionized water.

[0024] The mass fraction of the titanium source in solvent C is 0.5-10%, the gel transition temperature is 150-500℃, and the time is 0.5-6h.

[0025] In step 5, the puncture-resistant carbon nanofiber ultrathin diaphragm has a thickness of 5-20 μm, a tensile strength of 30-150 MPa, an elongation at break of 5-25%, and a room temperature lithium-ion conductivity of [missing information]. The high-frequency impedance is 10~80Ω·cm 2 .

[0026] The present invention also provides a puncture-resistant carbon nanofiber ultrathin separator obtained by the aforementioned preparation method and its application in high-safety power batteries and extreme environment energy storage systems.

[0027] The beneficial effects of the present invention are as follows: (1) By combining spinning technology with COF in-situ growth, isostatic carbonization and sol-gel modification, and using aldehyde-containing fiber membrane as template, a coaxial three-layer integrated carbon fiber / COF / titanium dioxide composite membrane was successfully constructed. It not only inherits the excellent mechanical flexibility of polyacrylonitrile-based carbon fiber, the high specific surface area and regular channels of COF material and the good electrochemical stability of titanium dioxide, but also achieves complementary performance through the three-layer synergistic structure, achieving the unity of ultra-thin thickness, high ionic conductivity and excellent mechanical strength, effectively overcoming the bottlenecks of traditional carbon fiber membranes with high brittleness, low ionic conductivity and single function of modified membranes. (2) An innovative step-by-step assembly strategy is adopted, which involves first functionalizing the spinning, then in-situ coating with COF, followed by pre-oxidation and isostatic pressing carbonization, and finally the transformation of titanium dioxide into a gel. This achieves uniform and controllable growth of the COF coating layer on the fiber surface, structural stability of the carbon fiber substrate, and dense coating of the titanium dioxide nanocrystal outer layer. The interfaces of each layer are tightly bonded, the preparation process is controllable and reproducible, and it is easy to scale up for industrial production. (3) Through the synergistic effect of the mechanical support of the carbon fiber substrate, the efficient ion transport of the COF layer, and the dendrite suppression of the titanium dioxide layer, a multi-level functional synergistic system is formed, which significantly improves the ionic conductivity, mechanical stability, dendrite puncture resistance, and electrode interface compatibility of the composite separator. (4) This puncture-resistant carbon nanofiber ultrathin separator can effectively suppress lithium dendrite growth and puncture, avoid battery short circuits caused by separator damage, and meet the performance requirements of high-safety and long-life battery systems. It also has excellent compatibility with electrolytes and electrode materials, providing reliable material support for the practical application of high-energy-density and high-safety batteries.

[0028] This invention proposes an ultrathin, high-conductivity flexible carbon fiber separator with a coaxial three-layer integrated structure. This separator features well-organized ion transport channels, a synergistic three-layer functional structure, excellent mechanical properties, and high safety adaptability. Under harsh electrochemical energy storage conditions, such as high-rate charge-discharge, long-cycle operation, and lithium dendrite growth, it exhibits excellent structural stability and long-term operational potential. This provides a highly efficient, stable, and innovative composite separator solution with significant practical application value and industrialization prospects, addressing current challenges in the battery separator field, including the difficulty in balancing ultrathinness and high strength, low ion conductivity, high risk of lithium dendrite puncture, and insufficient overall performance. Attached Figure Description

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0030] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0031] Figure 2 This is a scanning electron microscope image of the puncture-resistant carbon nanofiber ultrathin diaphragm in Example 1.

[0032] Figure 3 This is an elemental distribution diagram of the puncture-resistant carbon nanofiber ultrathin diaphragm in Example 1.

[0033] Figure 4 This is the Fourier transform infrared spectrum of the puncture-resistant carbon nanofiber ultrathin diaphragm in Example 1.

[0034] Figure 5 This is a scanning electron microscope image of the puncture-resistant carbon nanofiber ultrathin diaphragm in Example 2.

[0035] Figure 6 This is a scanning electron microscope image of the puncture-resistant carbon nanofiber ultrathin diaphragm in Example 3.

[0036] Figure 7 This is a scanning electron microscope image of the puncture-resistant carbon nanofiber ultrathin diaphragm in Example 4. Detailed Implementation

[0037] like Figure 1As shown, Embodiment 1 of the present invention provides a method for preparing a puncture-resistant carbon nanofiber ultrathin membrane, comprising the following steps: Step S11, preparing an aldehyde-containing fiber membrane: polyacrylonitrile and terephthalaldehyde are mixed in N,N-dimethylformamide to prepare an aldehyde-containing spinning solution (the mass fraction of polyacrylonitrile in the spinning solution is 15%, and the molar ratio of polyacrylonitrile to terephthalaldehyde is 2:1); Step S12, preparing an aldehyde-containing fiber membrane: the spinning solution obtained in S11 is subjected to high-voltage electrospinning (spinning voltage is 20kV, feed rate is 1.5mL / h, spinning distance is 20cm, spinning temperature is 30℃, spinning humidity is 40%RH, and reciprocating speed is 10cm / min) to prepare an aldehyde-containing fiber membrane; Step S13, preparing porous COF fibers. A multi-level porous COF intermediate layer was in situ grown in p-phenylenediamine, trifluoroacetic acid, and N,N-dimethylformamide using the aldehyde-containing fiber membrane obtained in S12 (molar ratio of terephthalaldehyde to p-phenylenediamine 1:1, molar ratio of the sum of terephthalaldehyde and p-phenylenediamine to p-trifluoroacetic acid 30:1, mass ratio of the sum of terephthalaldehyde and p-phenylenediamine to N,N-dimethylformamide 1:100; reaction temperature 60℃, reaction time 72h). Porous COF fibers were prepared in step S14. Dense COF carbonized fiber membrane: The porous COF fibers obtained in S13 were sequentially pre-oxidized (atmosphere: oxygen, heating rate: 2℃ / min, pre-oxidation temperature: 250℃, holding time: 2h, pre-oxidation pressure: 0.4). A dense COF carbonized fiber membrane was prepared by high-temperature isostatic pressing (argon atmosphere, isostatic pressure 20 MPa, heating rate 1℃ / min, carbonization temperature 800℃, holding time 2 h, cooling rate 1.5℃ / min). Step S15: Preparation of a puncture-resistant carbon nanofiber ultrathin membrane: A tetrabutyl titanate gel layer was loaded onto the surface of the dense COF carbonized fiber membrane obtained in S14, and a titanium dioxide nanocrystalline outer layer was formed by gel transformation in anhydrous ethanol (the mass fraction of tetrabutyl titanate in anhydrous ethanol was 2%, the gel transformation temperature was 200℃, and the time was 2 h), thus preparing a puncture-resistant carbon nanofiber ultrathin membrane. The resulting puncture-resistant carbon nanofiber ultrathin membrane had a membrane thickness of 5 μm, a tensile strength of 150 MPa, an elongation at break of 25%, and a room temperature lithium-ion conductivity of [missing value]. The high-frequency impedance is 10Ω·cm 2 .

[0038] like Figure 2 As shown in the scanning electron microscope image of the puncture-resistant carbon nanofiber ultrathin diaphragm obtained in Example 1 of the present invention, the diaphragm has a continuous self-supporting uniform porous network structure with a smooth surface and no obvious defects. The polyacrylonitrile-based carbon fiber has a uniform diameter ultrafine linear structure with a smooth surface. It is uniformly coated with a dense, continuous, and non-shedding porous COF intermediate layer, and the outermost layer is a titanium dioxide nanocrystal outer layer with uniform particle size, uniform dispersion, and dense adhesion.

[0039] Figure 3 As shown in the figure, the elemental distribution diagram of the puncture-resistant carbon nanofiber ultrathin diaphragm obtained in Example 1 of the present invention shows that carbon element, as the characteristic element of the inner polyacrylonitrile-based carbon fiber and the middle COF coating layer, has a continuous and uniform surface distribution, and the signal is strongest in the fiber region. Nitrogen element corresponds to the middle COF coating layer. Titanium element and oxygen element, as the characteristic elements of the outer titanium dioxide nanocrystal outer layer, have a uniform and dense surface distribution and similar signal intensities.

[0040] like Figure 4 As shown, the Fourier transform infrared spectrum of the puncture-resistant carbon nanofiber ultrathin diaphragm obtained in Example 1 of this invention indicates the presence of absorption peaks representing CH stretching vibrations, aromatic ring skeleton stretching vibrations, CN stretching vibrations, and Ti-O-Ti stretching vibrations in its structure. The presence of stretching vibration absorption peaks.

[0041] Example 2 of this invention provides a method for preparing a puncture-resistant carbon nanofiber ultrathin membrane, comprising the following steps: Step S21, preparing an aldehyde-containing fiber membrane: Polyacrylonitrile and 2,5-dihydroxyterephthalaldehyde are blended in N-methylpyrrolidone to prepare an aldehyde-containing spinning solution (the mass fraction of polyacrylonitrile in the spinning solution is 12%, and the molar ratio of polyacrylonitrile to 2,5-dihydroxyterephthalaldehyde is 1:1); Step S22, preparing an aldehyde-containing fiber membrane: The spinning solution obtained in S21 is subjected to high-speed centrifugal spinning (centrifugal speed is 8000 rpm, feed rate is...). A aldehyde-containing fiber membrane was prepared using a spinning rate of 5 mL / h, a nozzle parameter of 1.0 mm, a receiving speed of 300 rpm, and a spinning temperature of 60℃. Step S23: Preparation of porous COF fibers: A hierarchical porous COF intermediate layer was grown in situ in 4,4'-biphenyldiamine, formic acid, and N,N-dimethylacetamide using the aldehyde-containing fiber membrane obtained in S22. (The molar ratio of 2,5-dihydroxyterephthalaldehyde to 4,4'-biphenyldiamine was 1:2, and the molar ratio of the sum of 2,5-dihydroxyterephthalaldehyde and 4,4'-biphenyldiamine to formic acid was 10:1.) The total mass ratio of 5-dihydroxyterephthalaldehyde and 4,4'-biphenyldiamine to N,N-dimethylacetamide was 1:50; the reaction temperature was 30℃ and the reaction time was 24h to prepare porous COF fibers; Step S24, Dense COF carbonized fiber membrane: The porous COF fibers obtained in S23 were subjected to pre-oxidation (atmosphere: air, heating rate: 1℃ / min, pre-oxidation temperature: 200℃, holding time: 1h, pre-oxidation pressure: 0.2MPa) and high-temperature isostatic pressing carbonization (atmosphere: nitrogen, isostatic pressure: ... A dense COF carbonized fiber membrane was prepared by heating at 8 MPa, a heating rate of 0.5℃ / min, a carbonization temperature of 700℃, a holding time of 1 h, and a cooling rate of 0.5℃ / min. Step S25: Preparation of a puncture-resistant carbon nanofiber ultrathin membrane: An isopropyl titanate gel layer was loaded onto the surface of the dense COF carbonized fiber membrane obtained in S24, and a titanium dioxide nanocrystalline outer layer was formed by gel transformation in methanol (the mass fraction of isopropyl titanate in methanol was 1%, the gel transformation temperature was 170℃, and the time was 1 h), thus preparing a puncture-resistant carbon nanofiber ultrathin membrane. The resulting puncture-resistant carbon nanofiber ultrathin membrane had a membrane thickness of 7 μm, a tensile strength of 123 MPa, an elongation at break of 17%, and a room temperature lithium-ion conductivity of [missing value]. The high-frequency impedance is 34Ω·cm 2 .

[0042] like Figure 5As shown in the scanning electron microscope image of the puncture-resistant carbon nanofiber ultrathin diaphragm obtained in Example 2 of the present invention, the diaphragm has a continuous self-supporting uniform porous network structure with a smooth surface and no obvious defects. The polyacrylonitrile-based carbon fiber has a uniform diameter ultrafine linear structure with a smooth surface. It is uniformly coated with a dense, continuous, and non-shedding porous COF intermediate layer, and the outermost layer is a titanium dioxide nanocrystal outer layer with uniform particle size, uniform dispersion, and dense adhesion.

[0043] Example 3 of this invention provides a method for preparing a puncture-resistant carbon nanofiber ultrathin membrane, comprising the following steps: Step S31, preparing an aldehyde-containing fiber membrane: Polyacrylonitrile and 4,4'-biphenyldicarboxaldehyde are mixed in N-methylpyrrolidone to prepare an aldehyde-containing spinning solution (the mass fraction of polyacrylonitrile in the spinning solution is 18%, and the molar ratio of polyacrylonitrile to 4,4'-biphenyldicarboxaldehyde is 5:1); Step S32, preparing an aldehyde-containing fiber membrane: The spinning solution obtained in S31 is spun by a high-speed airflow (feed rate is 10 mL / h, feed pressure is 0.1 MPa, airflow velocity is 100 m / s, receiving rotation speed is 300 rpm, and nozzle parameters are 0.5). A aldehyde-containing fiber membrane was prepared by spinning at a 30° angle (mm). Step S33: Preparation of porous COF fibers: A hierarchical porous COF intermediate layer was grown in situ in 1,4-naphthyldiamine, acetic acid, and N-methylpyrrolidone using the aldehyde-containing fiber membrane obtained in S32 (molar ratio of 4,4'-biphenyldicarboxaldehyde to 1,4-naphthyldiamine was 3:1, molar ratio of the total of 4,4'-biphenyldicarboxaldehyde and 1,4-naphthyldiamine to acetic acid was 50:1, and mass ratio of the total of 4,4'-biphenyldicarboxaldehyde and 1,4-naphthyldiamine to N-methylpyrrolidone was 1:200; reaction temperature was 80℃, and reaction time was 84h). Step S34: Dense COF carbonized fiber membrane: The porous COF fibers obtained in S33 were pre-oxidized sequentially (atmosphere: oxygen volume fraction 50%). A dense COF carbonized fiber membrane was prepared by heating in oxygen-rich air at a heating rate of 4℃ / min, a pre-oxidation temperature of 280℃, a holding time of 3h, and a pre-oxidation pressure of 0.6MPa, followed by high-temperature isostatic pressing carbonization (atmosphere: helium, isostatic pressure: 40MPa, heating rate: 2℃ / min, carbonization temperature: 900℃, holding time: 3h, cooling rate: 2℃ / min). Step S35: Preparation of puncture-resistant carbon nanofiber ultrathin membrane: A tetraethyl titanate gel layer was loaded onto the surface of the dense COF carbonized fiber membrane obtained in S34, and a titanium dioxide nanocrystalline outer layer was formed by gel transformation in N,N-dimethylformamide (the mass fraction of tetraethyl titanate in N,N-dimethylformamide was 3%, the gel transformation temperature was 250℃, and the time was 3h). The obtained puncture-resistant carbon nanofiber ultrathin separator has a thickness of 14 μm, a tensile strength of 67 MPa, an elongation at break of 11%, and a room temperature lithium-ion conductivity of [missing value]. The high-frequency impedance is 58Ω·cm. 2 .

[0044] like Figure 6 As shown in the scanning electron microscope image of the puncture-resistant carbon nanofiber ultrathin diaphragm obtained in Example 3 of the present invention, the diaphragm has a continuous self-supporting uniform porous network structure with a smooth surface and no obvious defects. The polyacrylonitrile-based carbon fiber has a uniform diameter ultrafine linear structure with a smooth surface. It is uniformly coated with a dense, continuous and non-shedding porous COF intermediate layer, and the outermost layer is a titanium dioxide nanocrystal outer layer with uniform particle size, uniform dispersion and dense adhesion.

[0045] Example 4 of this invention provides a method for preparing a puncture-resistant carbon nanofiber ultrathin membrane, comprising the following steps: Step S41, preparing an aldehyde-containing fiber membrane: Polyacrylonitrile and trialdehyde-based phloroglucinol are blended in N-methylpyrrolidone to prepare an aldehyde-containing spinning solution (the mass fraction of polyacrylonitrile in the spinning solution is 20%, and the molar ratio of polyacrylonitrile to trialdehyde-based phloroglucinol is 10:1); Step S42, preparing an aldehyde-containing fiber membrane: The spinning solution obtained in S41 is subjected to melt electrospinning (melting temperature is 250℃, melting pressure is 0.1MPa). A aldehyde-containing fiber membrane was prepared by feeding at a rate of 5 mL / h, spinning voltage of 30 kV, receiving speed of 500 rpm, and spinning distance of 25 cm. Step S43: Preparation of porous COF fibers: A hierarchical porous COF intermediate layer was grown in situ in p-aminophenol, p-toluenesulfonic acid, and acetonitrile using the aldehyde-containing fiber membrane obtained in S42. (The molar ratio of trialdehyde-based phloroglucinol to p-aminophenol was 10:1, the molar ratio of the sum of trialdehyde-based phloroglucinol and p-aminophenol to p-toluenesulfonic acid was 80:1, and the molar ratio of trialdehyde-based phloroglucinol to p-aminophenol was...) The total mass ratio of COF to acetonitrile was 1:400; the reaction temperature was 100℃ and the reaction time was 96h, to prepare porous COF fibers; Step S44, Dense COF carbonized fiber membrane: The porous COF fibers obtained in S43 were subjected to pre-oxidation (atmosphere: air-argon mixture with a volume ratio of 5:5, heating rate: 5℃ / min, pre-oxidation temperature: 300℃, holding time: 6h, pre-oxidation pressure: 0.8MPa) and high-temperature isostatic pressing carbonization (atmosphere: neon, isostatic pressure: 100MPa ...0.8MPa, pre-oxidation temperature: 300℃, holding time: 6h, pre-oxidation pressure: 0.8MPa) and high-temperature isostatic pressing carbonization. A dense COF carbonized fiber membrane was prepared by heating at a rate of 4℃ / min, carbonizing at a temperature of 1200℃, holding for 5 hours, and cooling at a rate of 5℃ / min. Step S45: Preparation of a puncture-resistant carbon nanofiber ultrathin membrane: An acetylacetone titanium gel layer was loaded onto the surface of the dense COF carbonized fiber membrane obtained in S44. A gel transformation was then performed in deionized water to form a titanium dioxide nanocrystalline outer layer (the mass fraction of acetylacetone titanium in deionized water was 8%, the gel transformation temperature was 400℃, and the time was 6 hours), thus preparing a puncture-resistant carbon nanofiber ultrathin membrane. The resulting puncture-resistant carbon nanofiber ultrathin membrane had a membrane thickness of 20 μm, a tensile strength of 30 MPa, an elongation at break of 5%, and a room temperature lithium-ion conductivity of [missing value]. The high-frequency impedance is 80 Ω·cm 2 .

[0046] like Figure 7 As shown in the scanning electron microscope image of the puncture-resistant carbon nanofiber ultrathin diaphragm obtained in Example 4 of the present invention, the diaphragm has a continuous self-supporting uniform porous network structure with a smooth surface and no obvious defects. The polyacrylonitrile-based carbon fiber has a uniform diameter ultrafine linear structure with a smooth surface. It is uniformly coated with a dense, continuous and non-shedding porous COF intermediate layer, and the outermost layer is a titanium dioxide nanocrystal outer layer with uniform particle size, uniform dispersion and dense adhesion.

[0047] Comparative Example 1 of this invention provides a method for preparing a puncture-resistant carbon nanofiber ultrathin membrane, which basically adopts the method of Example 1 to prepare the puncture-resistant carbon nanofiber ultrathin membrane. The difference is that in this example, the aldehyde monomer and polyacrylonitrile are not mixed beforehand to prepare an aldehyde-containing spinning solution and an aldehyde-containing fiber membrane. Specifically, polyacrylonitrile is dissolved in N,N-dimethylformamide to prepare a polyacrylonitrile spinning solution (the mass fraction of polyacrylonitrile in the spinning solution is 15%); the obtained polyacrylonitrile spinning solution is subjected to high-voltage electrospinning (spinning voltage is 20kV, feed rate is 1.5mL / h, spinning distance is 20cm, spinning temperature is 30℃, spinning humidity is 40%RH, reciprocating speed is 10cm / min) to prepare a fiber precursor membrane; a hierarchical porous COF intermediate layer (terephthalaldehyde and p-phenylenediamine) is grown in situ in p-phenylenediamine, trifluoroacetic acid, and N,N-dimethylformamide. Porous COF fibers were prepared by reacting terephthalaldehyde and p-phenylenediamine in a 1:1 molar ratio, p-trifluoroacetic acid in a 30:1 molar ratio, and N,N-dimethylformamide in a 1:100 mass ratio (reaction temperature: 60℃, reaction time: 72h). The obtained porous COF fibers were then subjected to pre-oxidation (oxygen atmosphere, heating rate: 2℃ / min, pre-oxidation temperature: 250℃, holding time: 2h, pre-oxidation pressure: 0.4MPa) and high-temperature isostatic pressing (argon atmosphere, isostatic pressure: 20 MPa). A dense COF carbonized fiber membrane was prepared by heating at a rate of 1℃ / min, carbonizing at 800℃, holding for 2 hours, and cooling at a rate of 1.5℃ / min. A tetrabutyl titanate gel layer was then loaded onto the surface of the obtained dense COF carbonized fiber membrane, and a titanium dioxide nanocrystalline outer layer was formed by gel transformation in anhydrous ethanol (the mass fraction of tetrabutyl titanate in anhydrous ethanol was 2%, the gel transformation temperature was 200℃, and the time was 2 hours). This process was used to prepare a puncture-resistant carbon nanofiber ultrathin separator. The resulting puncture-resistant carbon nanofiber ultrathin separator had a thickness of 45 μm, a tensile strength of 10 MPa, an elongation at break of 2%, and a room temperature lithium-ion conductivity of [missing value]. The high-frequency impedance is 279 Ω·cm 2 .

[0048] Comparative Example 2 of this invention provides a method for preparing a puncture-resistant carbon nanofiber ultrathin membrane, which basically adopts the method of Example 2 to prepare the puncture-resistant carbon nanofiber ultrathin membrane. The difference is that this example does not use pre-oxidation to cause polyacrylonitrile to undergo cyclization and dehydrogenation to form a heat-resistant trapezoidal structure, but directly performs high-temperature isostatic pressing carbonization. Specifically, an aldehyde-containing spinning solution was prepared by blending polyacrylonitrile and 2,5-dihydroxyterephthalaldehyde in N-methylpyrrolidone (the mass fraction of polyacrylonitrile in the spinning solution was 12%, and the molar ratio of polyacrylonitrile to 2,5-dihydroxyterephthalaldehyde was 1:1). The resulting spinning solution was then subjected to high-speed centrifugal spinning (centrifugal speed 8000 rpm, feed rate 5 mL / h, nozzle parameters 1.0 mm, receiving speed 300 rpm, spinning temperature 60℃) to prepare an aldehyde-containing fiber membrane. A hierarchical porous COF intermediate layer was then grown in situ in 4,4'-biphenyldiamine, formic acid, and N,N-dimethylacetamide (the molar ratio of 2,5-dihydroxyterephthalaldehyde to 4,4'-biphenyldiamine was 1:2, and the molar ratio of the total amount of 2,5-dihydroxyterephthalaldehyde and 4,4'-biphenyldiamine to the molar ratio of formic acid was 1:2). Porous COF fibers were prepared by reacting 2,5-dihydroxyterephthalaldehyde and 4,4'-biphenyldiamine in a ratio of 10:1, with a mass ratio of 1:50 between the total amount of 2,5-dihydroxyterephthalaldehyde and N,N-dimethylacetamide; the reaction temperature was 30℃ and the reaction time was 24h. The obtained porous COF fibers were then subjected to high-temperature isostatic pressing carbonization (nitrogen atmosphere, isostatic pressure of 8MPa, heating rate of 0.5℃ / min, carbonization temperature of 700℃, holding time of 1h, and cooling rate of 0.5℃ / min) to prepare a dense COF carbonized fiber membrane. A titanium isopropyl titanate gel layer was loaded onto the surface of the obtained dense COF carbonized fiber membrane, and a titanium dioxide nanocrystal outer layer was formed by gel transformation in methanol (the mass fraction of titanium isopropyl titanate in methanol was 1%, the gel transformation temperature was 170℃, and the time was 1h) to prepare a puncture-resistant carbon nanofiber ultrathin membrane. The resulting puncture-resistant carbon nanofiber ultrathin separator has a thickness of 69 μm, a tensile strength of 9 MPa, an elongation at break of 2%, and a room temperature lithium-ion conductivity of [missing value]. The high-frequency impedance is 361 Ω·cm 2 .

[0049] Comparative Example 3 provides a method for preparing a puncture-resistant carbon nanofiber ultrathin membrane, which basically adopts the method of Example 3. The difference is that this example does not perform high-temperature isostatic pressing carbonization treatment to graphitize and densify the film, but only uses a pre-oxidation treatment. Specifically, an aldehyde-containing spinning solution was prepared by blending polyacrylonitrile (PAC) and 4,4'-biphenyldicarboxaldehyde (4,4'-biphenyldicarboxaldehyde) in N-methylpyrrolidone (PAC) with PA was 18% by mass and the molar ratio of PAC to 4,4'-biphenyldicarboxaldehyde was 5:1). The resulting spinning solution was then spun using a high-speed airflow (feed rate 10 mL / h, feed pressure 0.1 MPa, airflow velocity 100 m / s, receiving speed 300 rpm, nozzle parameters 0.5 mm, spinning angle 30°) to prepare an aldehyde-containing fiber membrane. A hierarchical porous COF interlayer was then grown in situ in 1,4-naphthyldiamine, acetic acid, and N-methylpyrrolidone (the molar ratio of 4,4'-biphenyldicarboxaldehyde to 1,4-naphthyldiamine was 3:1, and the molar ratio of the sum of 4,4'-biphenyldicarboxaldehyde and 1,4-naphthyldiamine to acetic acid was 5:1). Porous COF fibers were prepared by reacting the total of 0:1,4,4'-biphenyldicarboxaldehyde and 1,4-naphthyldiamine with N-methylpyrrolidone in a mass ratio of 1:200; the reaction temperature was 80℃ and the reaction time was 84h. The obtained porous COF fibers were then pre-oxidized (in an oxygen-enriched air atmosphere with an oxygen volume fraction of 50%, a heating rate of 4℃ / min, a pre-oxidation temperature of 280℃, a holding time of 3h, and a pre-oxidation pressure of 0.6MPa) to prepare a dense COF carbon fiber membrane. A tetraethyl titanate gel layer was loaded onto the surface of the obtained dense COF carbon fiber membrane, and a titanium dioxide nanocrystal outer layer was formed by gel transformation in N,N-dimethylformamide (the mass fraction of tetraethyl titanate in N,N-dimethylformamide was 3%, the gel transformation temperature was 250℃, and the time was 3h) to prepare a puncture-resistant carbon nanofiber ultrathin membrane. The obtained puncture-resistant carbon nanofiber ultrathin separator has a thickness of 84 μm, a tensile strength of 6 MPa, an elongation at break of 3%, and a room temperature lithium-ion conductivity of [missing value]. The high-frequency impedance is 415 Ω·cm 2 .

[0050] The structural characterization and performance testing are as follows.

[0051] Scanning electron microscopy observation: The microstructure of the puncture-resistant carbon nanofiber ultrathin diaphragm was observed using a field emission scanning electron microscope (model JSM-7900F, NEC). Figure 2 , Figure 5 , Figure 6 , Figure 7 ).

[0052] Surface element distribution testing: The surface element distribution of the puncture-resistant carbon nanofiber ultrathin membrane was recorded using an energy-dispersive X-ray spectrometer (model Vario EL, NEC). Figure 3 ).

[0053] Functional group structure testing: The functional groups of the puncture-resistant carbon nanofiber ultrathin diaphragm were recorded using an infrared spectrometer (model VERTEX 70, Bruker, USA). Figure 4 ).

[0054] Mechanical property testing: The tensile strength and elongation at break of the COF / ionic liquid integrated solid electrolyte were recorded using a universal testing machine (model GT-7010, China High Speed ​​Rail Testing Instruments Co., Ltd.).

[0055] Electrochemical performance testing: The room temperature lithium-ion conductivity and high-frequency impedance of the COF / ionic liquid integrated solid electrolyte were recorded using an electrochemical workstation (model CHI660F, China Huachen).

[0056] Experimental results: such as Figure 2 , Figure 5 , Figure 6 and Figure 7 As shown, the obtained puncture-resistant carbon nanofiber ultrathin diaphragm has a continuous, self-supporting, uniform porous network structure with a smooth surface and no obvious defects. The polyacrylonitrile-based carbon fiber has a uniform diameter, ultra-fine linear structure with a smooth surface. It is uniformly coated with a dense, continuous, and non-shedding porous COF intermediate layer, and the outermost layer is a titanium dioxide nanocrystal outer layer with uniform particle size, uniform dispersion, and dense adhesion.

[0057] like Figure 3 As shown, carbon elements in the obtained puncture-resistant carbon nanofiber ultrathin diaphragm are characterized by a continuous and uniform surface distribution as the inner polyacrylonitrile-based carbon fiber and the middle COF coating layer, with the strongest signal in the fiber region. Nitrogen elements correspond to the middle COF coating layer, while titanium and oxygen elements are characterized by a uniform and dense surface distribution as the outer titanium dioxide nanocrystal outer layer, with similar signal intensities.

[0058] like Figure 4 As shown, the obtained puncture-resistant carbon nanofiber ultrathin diaphragm structure contains characteristic absorption peaks representing CH stretching vibrations, aromatic ring skeleton stretching vibrations, CN stretching vibrations, and Ti-O-Ti stretching vibrations. The presence of stretching vibration absorption peaks.

[0059] Table 1 compares the puncture-resistant carbon nanofiber ultrathin diaphragms obtained in the examples and comparative examples, showing the diaphragm thickness, tensile strength, elongation at break, room temperature lithium-ion conductivity, and high-frequency impedance results.

[0060] Table 1

[0061]

[0062] Examples 1-4 exhibit thinner membrane thicknesses (5-20 μm), higher tensile strengths (30-150 MPa), and larger elongation at break (5-25%). This is because the aldehyde monomers are pre-dispersed uniformly and precisely within the fiber through spinning. During COF growth, the precise bonding and crystallization of the aldehyde and amino monomers promotes uniform and controllable in-situ growth. Further continuous pre-oxidation induces cyclization and dehydrogenation of polyacrylonitrile to form a heat-resistant trapezoidal structure. Simultaneously, isostatic carbonization promotes graphitization and densification of the fiber membrane, resulting in superior room-temperature lithium-ion conductivity and high-frequency impedance. Comparative Examples 1-3 have membrane thicknesses of 45-84 μm, tensile strengths of 6-10 MPa, and elongation at break of 2-3%. This is because the in-situ growth process and method of COF were not effectively controlled, making controlled Schiff base condensation impossible, and continuous pre-oxidation and isostatic carbonization were not performed.

[0063] The room-temperature lithium-ion conductivity and high-frequency impedance of puncture-resistant carbon nanofiber ultrathin separators are related to separator thickness, tensile strength, and elongation at break. Examples 1-4, which possess thinner separator thickness, higher tensile strength, and larger elongation at break, all exhibit room-temperature lithium-ion conductivity within [specific parameters]. All of the above have a high-frequency impedance of 80Ω·cm. 2 The following exhibit good ion transport performance and good dendrite puncture resistance. Among them, Example 1, with the thinnest separator thickness, highest tensile strength, and largest elongation at break, performed the best in battery testing, with a room temperature lithium-ion conductivity of [missing value]. The high-frequency impedance is 10Ω·cm 2 This is significantly higher than that of comparative examples 1-3, which have thicker diaphragms, lower tensile strength, and lower elongation at break (room temperature lithium-ion conductivity ≤ 100%). High-frequency impedance ≥279Ω·cm 2 ).

[0064] This invention provides a method for preparing a fast ion-conducting, puncture-resistant ultrathin diaphragm based on a concentric three-layer gradient carbon nanofiber structure. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a fast ion-conducting, puncture-resistant ultrathin diaphragm based on a concentric three-layer gradient carbon nanofiber structure, characterized in that, Includes the following steps: Step 1: Prepare an aldehyde-containing spinning solution by blending polyacrylonitrile and aldehyde monomer in solvent A; Step 2: Spin the spinning solution obtained in Step 1 to prepare an aldehyde-containing fiber membrane; Step 3: The aldehyde-containing fiber membrane obtained in Step 2 is used to grow a multi-level porous COF intermediate layer in situ in amino monomer, catalyst and solvent B to prepare porous COF fibers. Step 4: The porous COF fibers obtained in Step 3 are subjected to pre-oxidation and high-temperature isostatic pressing carbonization in sequence to prepare a dense COF carbonized fiber membrane. Step 5: Load the upper and lower surfaces of the dense COF carbon fiber membrane obtained in Step 4 with titanium source gel layers, and gel transform them in solvent C to form an outer layer of titanium dioxide nanocrystals, thus preparing a puncture-resistant carbon nanofiber ultrathin diaphragm.

2. The method according to claim 1, characterized in that, In step 1, the aldehyde monomer is terephthalaldehyde, isophthalaldehyde, o-phthalaldehyde, 2,5-dihydroxyterephthalaldehyde, 2,5-dimethoxyterephthalaldehyde, 4,4'-biphenyldialdehyde, 2,2'-biphenyldialdehyde, 1,4-naphthalenedicarboxyl, 2,6-naphthalenedicarboxyl, anthracenedialdehyde, pyrenedialdehyde, 1,3,5-benzenetrialdehyde, tris(4-formylphenyl)amine, tris(4-aldehydephenyl)triazine, trialdehyde-resorcinol, tetra(4-aldehyde-resorcinol), etc. One or more of the following: phenyl)ethylene, tetraaldehyde calix[4] aromatic hydrocarbon, pyrene tetracarboxaldehyde, glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, hexanedialdehyde, cyclohexanedialdehyde, norbornene dicarboxaldehyde, 2,5-thiophene dicarboxaldehyde, 2,6-pyridine dicarboxaldehyde, 3,4-ethylenedioxythiophene dicarboxaldehyde, cyanotricarboxaldehyde, tetrafluoroterephthalaldehyde, 2-fluoroterephthalaldehyde, and 2-chloroterephthalaldehyde; the molar ratio of polyacrylonitrile to aldehyde monomer is 100:1 to 1:

2.

3. The method according to claim 2, characterized in that, In step 1, solvent A is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, hexamethylphosphoramide, sulfolane, tetrahydrofuran, acetone, ethyl acetate, chloroform, dichloromethane, 1,4-dioxane, methanol, ethanol, isopropanol, n-butanol, tert-butanol, acetic acid, formic acid, dimethyl sulfone, formamide, and acetamide; the mass fraction of polyacrylonitrile in the spinning solution is 5-25%.

4. The method according to claim 3, characterized in that, In step 2, the spinning method is one or more of the following: high-voltage electrospinning, dry spinning, wet spinning, high-speed centrifugal spinning, melt spinning, solution spinning, gel spinning, phase separation spinning, airflow spinning, eddy spinning, triboelectric spinning, electrostatic meltblown spinning, conjugate spinning, island spinning, composite spinning, dry and wet spinning, cryogenic spinning, electrostatic spray spinning, template spinning, and melt electrospinning.

5. The method according to claim 4, characterized in that, In step 3, the amino monomer is p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 4,4'-biphenylenediamine, 3,3'-biphenylenediamine, 2,2'-biphenylenediamine, 1,4-naphthylenediamine, 1,5-naphthylenediamine, 2,6-naphthylenediamine, anthracene diamine, pyrene diamine, 1,3,5-phenyltriamine, tris(4-aminophenyl)amine, tris(4-aminophenyl)triazine, tetra(4-aminophenyl)ethylene, tetraaminocalix[4]arene, pyrene tetramine, ethylenediamine, propylenediamine, butanediamine, pentanediamine, hexanediamine, cyclohexanediamine, norbornenediamine, 2,5-thiophenediamine, 2,6-pyridinediamine, 3 One or more of the following: 4-ethylenedioxythiophene diamine, melaminetriamine, 4-aminobenzaldehyde, 2-aminobenzaldehyde, 3-aminobenzaldehyde, p-aminophenol, m-aminophenol, o-aminophenol, tetrafluorop-phenylenediamine, 2-fluorop-phenylenediamine, 2-chlorop-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,2'-diaminodiphenylpropane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, polyethylene glycol, and polypropylene glycol. The catalyst is one or more of the following: trifluoroacetic acid, formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, p-toluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, fluoroboric acid, trifluoromethanesulfonic acid, pyridine, 4-dimethylaminopyridine, triethylamine, diethylamine, ethylamine, tributylamine, diisopropylethylamine, imidazole, 1-methylimidazolium, 2-methylimidazolium, 4-methylimidazolium, triphenylphosphine, ferrocene, ferric chloride, cobalt chloride, nickel chloride, copper chloride, zinc chloride, ferric nitrate, cobalt nitrate, nickel nitrate, copper nitrate, zinc nitrate, ferric acetate, cobalt acetate, nickel acetate, copper acetate, zinc acetate, palladium on carbon, platinum on carbon, rhodamine B, rhodamine 6G, tetrabutyl titanate, titanium chloride, titanium sulfate, zinc oxide, alumina, titanium dioxide, silicon dioxide, montmorillonite, kaolin, zeolite, molecular sieve, and ionic liquid catalyst. The molar ratio of aldehyde monomer to amino monomer is 20:1 to 1:20, and the molar ratio of the total amount of aldehyde monomer and amino monomer to catalyst is 100:1 to 3:

1.

6. The method according to claim 5, characterized in that, In step 3, solvent B is one or more of the following: N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, hexamethylphosphoramide, sulfolane, tetrahydrofuran, 1,4-dioxane, chloroform, dichloromethane, chloroform, toluene, benzene, xylene, ethylbenzene, cumene, acetone, methyl ethyl ketone, ethyl acetate, propyl acetate, butyl acetate, methanol, ethanol, isopropanol, n-butanol, tert-butanol, ethylene glycol, propylene glycol, butanediol, pyridine, dioxane, acetonitrile, propionitrile, butyronitrile, formamide, acetamide, dimethyl sulfone, dimethyl carbonate, diethyl carbonate, and propylene carbonate. The total mass ratio of aldehyde monomers and amino monomers to solvent B is 1:5 to 1:500; the reaction temperature is 20 to 100℃, and the reaction time is 2 to 120 h.

7. The method according to claim 6, characterized in that, In step 4, the pre-oxidation conditions are as follows: the atmosphere includes air, oxygen, oxygen-enriched air (oxygen volume fraction 21%~100%), and an air-inert gas mixed atmosphere (the inert gas is one or more of nitrogen, argon, and helium, with an air-inert gas volume ratio of 1:9~9:1); the heating rate is 0.5~10℃ / min; the pre-oxidation temperature is 150~300℃; the holding time is 1~12 h; and the pre-oxidation pressure is 0.1~1.0 MPa.

8. The method according to claim 7, characterized in that, In step 4, the conditions for isostatic carbonization are as follows: the atmosphere is one or more of nitrogen, argon, helium, neon, and krypton; the isostatic pressure is 5~200 MPa; the heating rate is 0.5~8℃ / min; the carbonization temperature is 600~1500℃; the holding time is 0.1~10 h; and the cooling rate is 1~10℃ / min.

9. The method according to claim 8, characterized in that, In step 5, the titanium source is one or more of the following: tetrabutyl titanate, isopropyl titanate, ethyl titanate, methyl titanate, titanium tetrachloride, titanium trichloride, titanium sulfate, titanium nitrate, titanium dichlorodicyclopentadiene, titanium acetylacetone, titanium lactate, titanium ethylene glycol, tetraisopropyl titanate, ammonium fluorotitanate, and potassium fluorotitanate. The solvent C is one or more of the following: anhydrous ethanol, methanol, isopropanol, n-propanol, tert-butanol, ethylene glycol, propylene glycol, glycerol, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, acetonitrile, acetone, methyl ethyl ketone, tetrahydrofuran, 1,4-dioxane, acetic acid, ethyl acetate, and deionized water. The mass fraction of the titanium source in solvent C is 0.5-10%, the gel transition temperature is 150-500℃, and the time is 0.5-6 h.

10. The method according to any one of claims 1 to 9, characterized in that, In step 5, the puncture-resistant carbon nanofiber ultrathin diaphragm has a thickness of 5-20 μm, a tensile strength of 30-150 MPa, an elongation at break of 5-25%, and a room temperature lithium-ion conductivity of [missing information]. The high-frequency impedance is 10~80 Ω·cm 2 .

Images