Lithium-philic PCOF-PMIA composite nanofiber membrane as well as preparation method and application of lithium-philic PCOF-PMIA composite nanofiber membrane

Abstract

The invention relates to the technical field of lithium batteries, in particular to a lithium-loving PCOF-PMIA composite nanofiber membrane and a preparation method and application thereof.According to the preparation method, the lithium-loving PCOF-PMIA composite nanofiber membrane is obtained by means of an electrostatic spinning technology and a room-temperature in-situ growth technology, and the mechanical strength of the fiber membrane is greatly improved; the COF nanoparticles are prepared by a room-temperature stirring synthesis process, and the method has the advantages of mild reaction conditions, simplicity in operation, short time consumption and the like; the lithium-loving PCOF-PMIA composite nanofiber membrane has a uniform net-shaped nanofiber structure, and COF particles on the surface and in the fiber can be effectively connected at the same time, so that the maximum utilization of the COF can be achieved. The PMIA and the PCOF are simultaneously introduced into the composite nanofiber membrane provided by the invention, so that the ionic conductivity and the lithium ion transference number of the solid electrolyte are favorably improved, and the composite nanofiber membrane is expected to be applied to preparation of the solid composite electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a lithium-philic PCOF-PMIA composite nanofiber membrane, a preparation method and an application thereof. Background Art

[0002] As an important technology in the current energy storage field, the development of lithium-ion batteries is driven by the consumption of non-renewable energy and environmental problems, and is gradually evolving towards higher energy density, higher safety and longer life. However, traditional liquid lithium-ion batteries still have limitations in terms of energy density, safety and cycle life. For example, there are problems such as easy leakage of the electrolyte and limited specific capacity of the graphite negative electrode.

[0003] To overcome these problems, researchers have proposed the concept of all-solid-state lithium-metal batteries. Such batteries use solid electrolytes to replace traditional liquid electrolytes and use lithium metal as the negative electrode material, and have advantages such as high theoretical capacity (3860 mAh·g -1 ), low electrochemical potential (3.04 V relative to the standard hydrogen electrode), etc., which can significantly improve the energy density of the battery. In addition, the introduction of solid electrolytes effectively solves the safety hazards such as flammability and easy leakage of liquid electrolytes, and at the same time inhibits the growth of lithium dendrites, improving the overall stability of the battery.

[0004] At present, the research and development of solid electrolytes mainly focuses on two major categories: solid polymer electrolytes and solid inorganic electrolytes. Solid polymer electrolytes have been widely studied due to their advantages such as good flexibility, light weight, easy processing and good interface compatibility, but problems such as low room temperature ionic conductivity and poor lithium salt dissociation ability limit their performance improvement. Although solid inorganic electrolytes have high ionic conductivity and excellent mechanical properties, problems such as poor interface wettability, complex preparation and instability in air need to be solved urgently.

[0005] Covalent Organic Frameworks (COFs), as a new type of material, show great potential in the energy storage field due to their high crystallinity, good thermal stability, adjustable pore size and easy modification. The interlayer π electron cloud and open pores of COFs provide diverse paths for high-speed charge carrier ion transfer, and are considered to be one of the research directions for future fast ion conductors. However, at present, the synthesis of COFs mainly relies on the solvothermal method, which has a complex procedure and takes a long time, limiting its large-scale application.

[0006] All-solid-state lithium-metal batteries are expected to solve many problems of traditional lithium-ion batteries by combining high-energy-density lithium-metal negative electrodes and high-performance solid electrolytes. However, to achieve this goal, breakthroughs still need to be made in aspects such as the interface stability of solid electrolytes, ion transport efficiency and preparation processes. Summary of the Invention

[0007] The present invention aims to solve at least one of the technical problems existing in the related art. To this end, the first object of the present invention is to provide a method for preparing a lithiumophilic PCOF-PMIA composite nanofiber membrane; the second object of the present invention is to provide a lithiumophilic PCOF-PMIA composite nanofiber membrane; the third object of the present invention is to provide an application of the lithiumophilic PCOF-PMIA composite nanofiber membrane.

[0008] To achieve the first object, the technical solution adopted by the present invention is as follows: A method for preparing a lithiumophilic PCOF-PMIA composite nanofiber membrane, comprising the following steps: S100. Using electrospinning technology to prepare a meta-aramid spinning precursor doped with tetraminophenyl porphyrin, and the mass ratio of tetraminophenyl porphyrin to meta-aramid in the spinning precursor is 1:50 to 1:10; S200. Respectively prepare solution A and solution B, add solution B to solution A, stir and react for 23 to 25 h, then add a terminator, and continue to stir for 0.5 to 1.5 h to obtain a fiber membrane; Among them, the preparation process of solution A is as follows: Dissolve tetraminophenyl porphyrin in a mixed solution composed of acetonitrile and acetic acid, stir evenly, then add the spinning precursor, and stir evenly to obtain solution A; The preparation process of solution B is as follows: Dissolve terephthalaldehyde in acetonitrile to obtain a terephthalaldehyde acetonitrile solution; S300. Wash the fiber membrane with acetonitrile and deionized water 2 to 4 times respectively, at 25 to 35 °C, and dry for 23 to 25 h to obtain a lithiumophilic PCOF-PMIA composite nanofiber membrane; Among them, PCOF is the abbreviation of porphyrin-based covalent organic framework, and PMIA is the abbreviation of meta-aramid.

[0009] In the preparation method provided by the present invention, the porphyrin molecule centered on the central nitrogen atom (Lewis base) can undergo π-π interaction and metal-ligand coordination with lithium salt after being modified by tetraphenylamino to construct a stable ion channel; at the same time, by using porphyrin-based covalent organic frameworks (Covalent Organic Frameworks, COFs), the dual advantages of porphyrin and COF structures can be obtained, which have the dual functions of promoting lithium ion transfer and uniform lithium deposition.

[0010] The preparation method provided by this application can achieve the rapid synthesis of nanoscale COF particles at room temperature. At the same time, as a filler, COFs are prone to aggregation due to excess, resulting in the inability to exert the structural advantages of COFs. Combining COFs with nanofibers using electrospinning technology can effectively prevent the aggregation of COF particles, increase the specific surface area of COFs, and play an important role in regulating the growth sequence of COFs.

[0011] In the actual application process, it is found that due to the coating of nanofibers, it is impossible to fully utilize the COF particles inside the fibers. At the same time, the surface of the fibers shows spindle or bead structures due to some of the doped COF particles being too large, which will lead to a decrease in the mechanical properties of the fibers. In the prior art, the self-standing nanofibers of COFs prepared by the template sacrifice method lose the supporting effect of flexible fibers and have poor overall mechanical properties. Meta-aramid (PMIA) fibers have excellent mechanical properties, chemical stability, and thermal stability. Using PMIA as the supporting substrate for COFs can provide higher mechanical strength. At the same time, the hydrogen atoms in the amide bonds inside the meta-aramid can undergo protonation and other interactions with the nitrogen atoms inside the tetraaminophenyl porphyrin molecule, anchoring the porphyrin-based COF on the surface and inside the fibers, thereby enabling the uniform anchoring of COF and preventing it from falling off during use, significantly improving the utilization rate of porphyrin-based covalent organic framework (PCOF) nanoparticles.

[0012] Further, S100 includes the following steps: S110: Dissolve tetraaminophenyl porphyrin in N,N-dimethylacetamide, then add the PMIA stock solution, and continuously stir for 11 - 13 h to obtain a spinning solution. S120: Spray the spinning solution through a spinning needle at a speed of 0.5 - 1.5 ml / h to obtain a spinning precursor.

[0013] Further, in step S110, the content of PMIA in the spinning solution is 11 - 13 wt%.

[0014] Further, the terminator in step S200 is selected from benzaldehyde.

[0015] Further, in step S200, the volume ratio of acetonitrile to acetic acid in the mixed solution is 7:1 - 5:1.

[0016] Further, in step S200, the concentration of the phthalaldehyde acetonitrile solution is 0.188 mg / ml - 1.88 mg / ml.

[0017] To achieve the second object, the technical solution adopted by the present invention is as follows: A lithiumophilic PCOF-PMIA composite nanofiber membrane is prepared by using the preparation method of the lithiumophilic PCOF-PMIA composite nanofiber membrane described in any one of the above.

[0018] To achieve the third object, the technical solution adopted by the present invention is as follows: An application of a lithiumophilic PCOF-PMIA composite nanofiber membrane, wherein a solid composite electrolyte is prepared by using the lithiumophilic PCOF-PMIA composite nanofiber membrane described in any one of the above; Wherein, the solid composite electrolyte includes a PCOF-PMIA composite nanofiber membrane, polyethylene oxide and lithium bis(trifluoromethanesulfonyl)imide, and the polyethylene oxide and lithium bis(trifluoromethanesulfonyl)imide are coated on the surface of the PCOF-PMIA composite nanofiber membrane; Wherein, the molar ratio of the ethylene oxide groups in the polyethylene oxide to the lithium ions in the lithium bis(trifluoromethanesulfonyl)imide is 18:1 to 10:1.

[0019] Further, the preparation of the solid composite electrolyte includes the following steps: S410. Add dry polyethylene oxide and lithium bis(trifluoromethanesulfonyl)imide to an organic solvent and dissolve them to obtain an organic solution of polyethylene oxide and lithium bis(trifluoromethanesulfonyl)imide; S420. Scrape the organic solution on both sides of the PCOF-PMIA composite nanofiber membrane, and dry it at a temperature of 45-55 °C for 23-25 h. After removing the organic solvent, the solid composite electrolyte is obtained by a hot pressing method.

[0020] One or more of the above technical solutions in the embodiments of the present invention have at least one of the following technical effects: The preparation method of the lithiumophilic PCOF-PMIA composite nanofiber membrane provided by the present invention uses electrospinning technology and room temperature in-situ growth process to obtain a lithiumophilic PCOF-PMIA composite nanofiber membrane. Compared with the existing self-supporting COF fiber membrane, the present invention uses PMIA as the substrate, which greatly improves the mechanical strength of the fiber membrane. The preparation method provided by the present invention can not only anchor COF nanoparticles on the surface and inside of the fiber, but also, as a building unit of COF nanoparticles, tetraminophenylporphyrin (TAPP) makes it easy for protonation and other interactions to occur between the amide bond in the meta-aramid and the nitrogen atom in the TAPP ring through protonation, which provides chemical support for the anchoring of in-situ grown PCOF nanoparticles.

[0021] The preparation method of the lithiumophilic PCOF-PMIA composite nanofiber membrane provided by the present invention can prepare an electrospinning solution by mixing a meta-aramid spinning solution and a soluble building monomer, and can prepare a uniform network nanofiber network structure without beads and spindles. This network structure can effectively connect the COFs particles on the surface and inside the fiber at the same time, so as to maximize the utilization of COFs.

[0022] The preparation method of the lithiumophilic PCOF-PMIA composite nanofiber membrane provided by the present invention prepares COF nanoparticles through a room-temperature stirring synthesis process, which has the advantages of mild reaction conditions, simple operation, and short time consumption.

[0023] The lithiumophilic PCOF-PMIA composite nanofiber membrane provided by the present invention uses electrospun nanofibers as carriers, which improves the dispersibility of COFs particles. It can not only prevent the aggregation of COFs particles, but also increase the contact surface area between COF and reactants. At the same time, the designed COF nanoparticles have good lithiumophilicity and electron-rich properties, which are beneficial to the improvement of lithium ion transport ability.

[0024] The lithiumophilic PCOF-PMIA composite nanofiber membrane provided by the present invention selects meta-aramid nanofibers with excellent mechanical properties as non-sacrificial templates, which can effectively improve the mechanical strength of the composite fibers.

[0025] The lithiumophilic PCOF-PMIA composite nanofiber membrane provided by the present invention simultaneously introduces PMIA and PCOF, which can simultaneously achieve the dissociation of lithium salts and the weakening of the coordination effect between lithium ions and the ether oxygen bonds of polyethylene oxide (PEO). This dual effect helps to improve the ionic conductivity and lithium ion transference number of solid electrolytes, so it can effectively improve the ion transport ability in solid composite electrolytes and is thus expected to be applied to the preparation of solid composite electrolytes.

[0026] Additional aspects and advantages of the present invention will be given in part in the following description, will become apparent in part from the following description, or will be understood through the practice of the present invention. Description of the Drawings

[0027] Figure 1 It is an SEM image of the spinning precursor provided in Example 1 of the present invention.

[0028] Figure 2 It is an SEM image of the lithiumophilic PCOF-PMIA composite nanofiber membrane provided in Example 1 of the present invention.

[0029] Figure 3 It is an SEM image of the spinning precursor provided in Example 2 of the present invention.

[0030] Figure 4 It is the SEM image of the lithiumophilic PCOF-PMIA composite nanofiber membrane provided in Example 2 of the present invention.

[0031] Figure 5 It is the SEM image of the spinning precursor provided in Example 3 of the present invention.

[0032] Figure 6 It is the SEM image of the lithiumophilic PCOF-PMIA composite nanofiber membrane provided in Example 3 of the present invention.

[0033] Figure 7 It is the SEM image of the spinning precursor provided in Example 4 of the present invention.

[0034] Figure 8 It is the SEM image of the lithiumophilic PCOF-PMIA composite nanofiber membrane provided in Example 4 of the present invention.

[0035] Figure 9 It is the SEM image of the spinning precursor provided in Example 5 of the present invention.

[0036] Figure 10 It is the SEM image of the lithiumophilic PCOF-PMIA composite nanofiber membrane provided in Example 5 of the present invention.

[0037] Figure 11 It is the SEM image of the spinning precursor provided in Comparative Example 1 of the present invention.

[0038] Figure 12 It is the SEM image of the PCOF-PMIA composite nanofiber membrane provided in Comparative Example 1 of the present invention.

[0039] Figure 13 It is the Fourier transform infrared spectrum of the PCOF-PMIA composite nanofiber membrane provided in Example 1 of the present invention, the nano PCOF particles and PMIA provided in Comparative Example 1.

[0040] Figure 14 It is the relationship diagram of the ionic conductivity of different material systems provided in the examples and comparative examples of the present invention varying with temperature.

[0041] Figure 15 It is the schematic diagram of the electrochemical window of the solid composite electrolyte provided in Example 2 of the present invention and the PEO control group at 50°C.

[0042] Figure 16 It is the LiFePO of the solid composite electrolyte provided in Example 2 of the present invention at 50°C and 0.5C conditions 4 / / Li battery cycle performance diagram. Detailed implementation manners

[0043] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0044] In the following examples, the experimental methods used are conventional methods unless otherwise specified, and are carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used are all commercially available unless otherwise specified.

[0045] Example 1 1. Prepare PMIA spinning precursor doped with TAPP using electrospinning technology. The process is as follows: TAPP (20 mg) was dissolved in N, N-dimethylacetamide (DMAC) (3.33 g), and the solution was stirred continuously until the color of the solution was uniform. Then, PMIA stock solution (5 g, solid content 20 wt%) was added to the above solution, and the solution was stirred continuously for 12 h to obtain a uniform spinning solution (PMIA content was 12 wt%). Then, the spinning solution was ejected through an 18G spinning needle at a speed of 1 ml / h. During the electrospinning process, a voltage of 25 kV was applied, the speed of the receiving roller was 65 rpm, and the distance between the needle tip and the receiving roller was set to 15 cm. The PMIA spinning precursor was collected and then placed in a vacuum oven at 50 ° C for 12 h to remove the residual solvent to obtain a PMIA spinning precursor doped with TAPP. The mass ratio of TAPP to PMIA in the spinning precursor was 1:50. The electron microscope image of the spinning precursor is shown as follows. Figure 1 As shown; The electron microscope shooting parameters are as follows: acceleration voltage is 10.0 kV; working distance is 12.4 mm, magnification is 20000; 2. Preparation of PCOF-PMIA composite nanofiber membrane by in-situ growth under room temperature conditions. The process is as follows: Preparation of solution A: Dissolve TAPP (21.1 mg) in a mixed solution consisting of 7.5 ml acetonitrile (ACN) and 1 ml acetic acid, stir continuously for 30 min, then add the spinning precursor prepared above (132.6 mg, of which the content of TAPP is 2.6 mg), stir evenly to obtain solution A; Among them, the total amount of TAPP in solution A was 23.7 mg; Prepare Solution B: Dissolve terephthalaldehyde (TPA) (9.4 mg, 0.07 mmol) in ACN (5 ml), and continuously stir until the solution becomes clear to obtain Solution B; Add Solution B to Solution A, continuously stir at a speed of 1100 rpm for 24 h, then add benzaldehyde (1 μl), and continue to stir for 1 h to obtain a PCOF-PMIA composite nanofiber membrane. Take it out, wash it three times with acetonitrile and deionized water respectively, and dry it at 30 °C for 24 h to obtain a lithium-philic PCOF-PMIA composite nanofiber membrane. The electron micrograph of the PCOF-PMIA composite nanofiber membrane is shown as Figure 2 follows; Among them, the electron microscopy shooting parameters are as follows: the acceleration voltage is 10.0 kV; the working distance is 12.7 mm, and the magnification is 40000; III. Prepare a PCOF-PMIA / PEO / LiTFSI solid composite electrolyte by combining solution casting and hot pressing processes. The process is as follows: Add dried polyethylene oxide (PEO) with a molecular weight of 3×10 5 g·mol -1 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (purity 99.99%) into anhydrous acetonitrile (99.80%) and dissolve to obtain an acetonitrile solution of PEO and LiTFSI; Among them, the molar ratio of the ethylene oxide groups in the added PEO to the lithium ions in the added LiTFSI is 15:1; Use a glass rod (not limited to a glass rod) to cast the above-mentioned acetonitrile solution of PEO and LiTFSI on the surface of the PCOF-PMIA composite nanofiber membrane, and dry it at 50 °C for 24 h to remove the solvent; Finally, obtain a solid composite electrolyte with a thickness of about 50 μm by hot pressing.

[0046] Place the prepared solid composite electrolyte in a glove box filled with argon and further dry it (≥36 h) to obtain a PCOF-PMIA / PEO / LiTFSI solid composite electrolyte.

[0047] Example 2 The difference between this example and Example 1 is that: I. In the process of preparing a PMIA spinning precursor doped with TAPP using electrospinning technology: The amount of TAPP added is 40 mg; during electrospinning, the applied voltage is 30 kV, the distance between the needle tip and the receiving roller is set to 18 cm, and the mass ratio of TAPP to PMIA in the spinning precursor is 1:25. The electron micrograph of the spinning precursor is as shown in Figure 3 shown; Among them, the electron microscopy shooting parameters are as follows: The acceleration voltage is 10.0 kV; the working distance is 13.0 mm, and the magnification is 20,000; II. In the process of in-situ growth and preparation of PCOF-PMIA composite nanofiber membrane at room temperature: When preparing solution A, the amount of TAPP added is 18.96 mg, and the amount of PMIA spinning precursor added is 123.24 mg. The electron micrograph of the PCOF-PMIA composite nanofiber membrane is as shown in Figure 4 shown; Among them, the electron microscopy shooting parameters are as follows: The acceleration voltage is 10.0 kV; the working distance is 12.7 mm, and the magnification is 40,000; III. In the process of preparing PCOF-PMIA / PEO / LiTFSI solid composite electrolyte by combining solution casting and hot pressing processes: The molar ratio of the ethylene oxide groups in the added PEO to the lithium ions in the added LiTFSI is 10:1.

[0048] The remaining processes are the same as those in Example 1.

[0049] Example 3 The difference between this example and Example 1 is as follows: I. In the process of preparing a PMIA spinning precursor doped with TAPP using electrospinning technology: The amount of TAPP added is 60 mg; during electrospinning, the applied voltage is 30 kV, the distance between the needle tip and the receiving roller is set to 17 cm, and the mass ratio of TAPP to PMIA in the spinning precursor is 3:50. The electron micrograph of the spinning precursor is as shown in Figure 5 shown; Among them, the electron microscopy shooting parameters are as follows: The acceleration voltage is 10.0 kV; the working distance is 12.7 mm, and the magnification is 40,000; II. In the process of in-situ growth and preparation of PCOF-PMIA composite nanofiber membrane at room temperature: When preparing solution A, the amount of TAPP added is 21.33 mg, and the amount of PMIA spinning precursor added is 46.5 mg. The electron micrograph of the PCOF-PMIA composite nanofiber membrane is as shown in Figure 6 shown; Among them, the electron microscopy shooting parameters are as follows: The acceleration voltage is 10.0 kV; the working distance is 12.8 mm, and the magnification is 40,000K; III. In the process of preparing the PCOF-PMIA / PEO / LiTFSI solid composite electrolyte by combining solution blade coating and hot pressing processes: The molar ratio of the ethylene oxide groups in the added PEO to the lithium ions in the added LiTFSI is 12:1.

[0050] The remaining processes are the same as those in Example 1.

[0051] Example 4 The difference between this example and Example 1 is as follows: I. In the process of preparing the PMIA spinning precursor doped with TAPP by electrospinning technology: The amount of TAPP added is 80 mg, and the mass ratio of TAPP to PMIA in the spinning precursor is 2:25. The electron micrograph of the spinning precursor is shown as Figure 7 shown; Among them, the electron microscopy shooting parameters are as follows: the acceleration voltage is 10.0 kV; the working distance is 12.7 mm, and the magnification is 40,000; II. In the process of in-situ growth preparation of the PCOF-PMIA composite nanofiber membrane at room temperature: When preparing Solution A, the amount of the spinning precursor added is 35.1 mg. The electron micrograph of the PCOF-PMIA composite nanofiber membrane is shown as Figure 8 shown; Among them, the electron microscopy shooting parameters are as follows: the acceleration voltage is 10.0 kV; the working distance is 12.8 mm, and the magnification is 40,000; III. In the process of preparing the PCOF-PMIA / PEO / LiTFSI solid composite electrolyte by combining solution blade coating and hot pressing processes: The molar ratio of the ethylene oxide groups in the added PEO to the lithium ions in the added LiTFSI is 18:1.

[0052] The remaining processes are the same as those in Example 1.

[0053] Example 5 The difference between this example and Example 1 is as follows: I. In the process of preparing the PMIA spinning precursor doped with TAPP by electrospinning technology: The amount of TAPP added is 100 mg, and the mass ratio of TAPP to PMIA in the spinning precursor is 1:10. The electron micrograph of the spinning precursor is shown as Figure 9 shown; Among them, the electron microscopy shooting parameters are as follows: the acceleration voltage is 10.0 kV; the working distance is 12.8 mm, and the magnification is 40,000; II. During the in-situ growth and preparation of the PCOF-PMIA composite nanofiber membrane at room temperature: When preparing Solution A, the amount of the spinning precursor added is 28.6 mg. The electron micrograph of the PCOF-PMIA composite nanofiber membrane is as shown in Figure 10 shown; Among them, the electron microscopy shooting parameters are as follows: the acceleration voltage is 10.0 kV; the working distance is 12.7 mm, and the magnification is 40,000; III. During the preparation of the PCOF-PMIA / PEO / LiTFSI solid composite electrolyte by combining the solution casting and hot pressing processes: The molar ratio of the ethylene oxide groups in the added PEO to the lithium ions in the added LiTFSI is 18:1.

[0054] The remaining processes are the same as those in Example 1.

[0055] Comparative Example 1 I. Prepare the PMIA spinning precursor without doped TAPP by electrospinning technology, and the process is as follows: Add the meta-aramid stock solution (PMIA, solid content 20%) to N,N-dimethylacetamide (DMAC) (3.33 g), and continuously stir for 12 h to obtain a uniform spinning solution (the content of PMIA is 12%); then, spray the aforementioned spinning solution through an 18G spinning needle at a speed of 1 ml / h. During the electrospinning process, apply a voltage of 25 kV, the receiving roller speed is 65 rpm, and the distance between the needle tip and the receiving roller is set to 15 cm. Collect the PMIA spinning precursor, and then place it in a vacuum oven at 50 °C for 12 h to remove the residual solvent, obtaining the PMIA spinning precursor without doped TAPP. The electron micrograph of the spinning precursor is as shown in Figure 11 shown; Among them, the electron microscopy shooting parameters are as follows: the acceleration voltage is 10.0 kV; the working distance is 12.8 mm, and the magnification is 40,000; II. Prepare nano-PCOF particles at room temperature, and the process is as follows: Prepare Solution A: Dissolve TAPP (23.7 mg, 0.035 mmol) in a mixed solution composed of 7.5 ml of acetonitrile (ACN) and 1 ml of acetic acid, and continuously stir for 30 min to obtain Solution A; Prepare Solution B: Dissolve terephthalaldehyde (TPA) (9.4 mg, 0.07 mmol) in ACN (5 ml), and continuously stir until the solution color is clear to obtain Solution B; Add solution B to solution A, continuously stir at a speed of 1100 rpm for 24 h, add benzaldehyde (1 μl), continue to stir for 1 h, then centrifuge to obtain a precipitate, wash it three times with acetonitrile and deionized water respectively, and dry it at 30 °C for 24 h to obtain nano-porphyrin-based (PCOF) particles.

[0056] III. In-situ growth preparation of PCOF-PMIA composite nanofiber membrane at room temperature, the process is as follows: Dissolve TAPP (23.7 mg, 0.035 mmol) in a mixed solution composed of 7.5 ml of acetonitrile (ACN) and 1 ml of acetic acid, continuously stir for 30 min, then add the spinning precursor (68.47 mg), and stir evenly to obtain solution A; Dissolve TPA (9.4 mg, 0.07 mmol) in ACN (5 ml), continuously stir until the solution is clear, then add it to solution A, continuously stir at a speed of 1100 rpm for 24 h, add benzaldehyde (1 μl), and continue to stir for 1 h to obtain a PCOF-PMIA composite nanofiber membrane. Take it out, wash it three times with acetonitrile and deionized water respectively, and dry it at 30 °C for 24 h to obtain a PCOF-PMIA composite nanofiber membrane. The electron micrograph of the PCOF-PMIA composite nanofiber membrane is as Figure 12 shown; Among them, the electron microscopy shooting parameters are as follows: the acceleration voltage is 10.0 kV; the working distance is 12.7 mm, and the magnification is 40000; III. Preparation of PCOF-PMIA / PEO / LiTFSI solid composite electrolyte by combining solution blade coating and hot pressing process, the process is as follows: Add dry polyethylene oxide (PEO) with a molecular weight of 3×10 5 g·mol -1 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (purity 99.99%) into anhydrous acetonitrile (99.80%) to dissolve, and obtain an acetonitrile solution of PEO and LiTFSI; Among them, the molar ratio of the ethylene oxide groups in the added PEO to the lithium ions in the added LiTFSI is 15:1; Use a glass rod (not limited to a glass rod) to blade coat the above-mentioned acetonitrile solution of PEO and LiTFSI on the surface of the lithiumophilic PCOF-PMIA composite nanofiber membrane, and dry it at 50 °C for 24 h to remove the solvent, and then obtain a solid composite electrolyte with a thickness of about 50 μm by hot pressing method.

[0057] After the prepared solid composite electrolyte was placed in a glove box filled with argon for further drying (≥36 h), a PCOF-PMIA / PEO / LiTFSI solid composite electrolyte was obtained.

[0058] As Figure 13 shown, the Fourier transform infrared spectra of the PCOF-PMIA composite nanofiber membrane provided in Example 1, the nano-PCOF particles provided in Comparative Example 1, and PMIA indicate that PCOF grows on the surface of PMIA fibers and does not completely cover the fiber surface.

[0059] The test results of the mechanical properties of the lithiumophilic PCOF-PMIA composite nanofiber membrane and PMIA nanofibers provided in Example 2 are shown in Table 1: Table 1 Test results of the mechanical properties of different materials

[0060] As can be seen from Table 1, the lithiumophilic PCOF-PMIA composite nanofiber membrane provided by the present invention has excellent mechanical strength, with a tensile strength of 22.29 MPa and an elongation at break of 36.71%.

[0061] The ionic conductivities of the PCOF-PMIA / PEO / LiTFSI solid composite electrolytes, pure polyethylene oxide (PEO) electrolytes, and PEO / PMIA nanofiber composite electrolytes provided in Examples 1 to 5 were tested. The results are as Figure 14 shown. It can be seen from the figure that the ionic conductivities of the electrolytes all increase with the increase in temperature. Compared with the ionic conductivity of the pure PEO electrolyte, the ionic conductivity of the PCOF-PMIA / PEO / LiTFSI solid composite electrolyte is improved and can reach 7.09677×10 -4 S·cm -1 −4 at 50 °C. This result shows that the charge aggregation effect inside PCOF can promote the dissociation of lithium salts and the rapid migration of lithium ions. The porphyrin monomers in PCOF can also coordinate with lithium ions to further promote the dissociation of lithium salts. At the same time, the three-dimensional interconnected network structure constructed by PCOF pores and PMIA nanofibers also provides a faster lithium ion transport channel with a more continuous and lower migration energy barrier inside the electrolyte.

[0062] As Figure 15As shown, it is a schematic diagram of the electrochemical window of the composite electrolyte and pure PEO electrolyte provided in Example 2 of this application at 50°C. It can be seen from the figure that as the voltage increases, the current of both materials gradually increases. However, after the voltage exceeds 5V, the current of the PEO / PCOF-PMIA / LiTFSI composite solid electrolyte is significantly higher than that of the pure PEO electrolyte, indicating better electrochemical performance. Therefore, it meets the conditions for matching with high-voltage cathode materials.

[0063] As Figure 16 shown, it is a cycle performance graph of the LiFePO4 / / Li battery with the PEO / PCOF-PMIA / LiTFSI composite solid electrolyte provided in Example 2 of this application at 50°C and 0.5C. It can be seen from the figure that the battery can stably cycle more than 450 times, which shows that the composite solid electrolyte exhibits excellent long-cycle performance in all-solid-state lithium metal batteries.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a lithium-philic PCOF-PMIA composite nanofiber membrane, characterized in that: The steps include: S100, preparing a meta-aramid spinning precursor doped with tetraaminophenylporphyrin by using an electrospinning technique, wherein the mass ratio of tetraaminophenylporphyrin to meta-aramid in the spinning precursor is 1:50 to 1:10; S200, preparing solution A and solution B respectively, adding solution B to solution A, stirring for reaction for 23 to 25 hours, adding a terminator, and continuing stirring for 0.5 to 1.5 hours to obtain a fiber membrane; The preparation process of solution A is as follows: dissolving tetraaminophenylporphyrin in a mixed solution of acetonitrile and acetic acid, stirring evenly, adding the spinning precursor, stirring evenly, and obtaining solution A; The preparation process of solution B is as follows: dissolving terephthalaldehyde in acetonitrile to obtain terephthalaldehyde acetonitrile solution; S300, washing the fiber membrane with acetonitrile and deionized water for 2 to 4 times, respectively, at 25 to 35° C., and drying for 23 to 25 hours to obtain a lithiophilic PCOF-PMIA composite nanofiber membrane; Among them, PCOF is the abbreviation of porphyrin-based covalent organic framework, and PMIA is the abbreviation of meta-aramid.

2. The method for preparing the lithium-philic PCOF-PMIA composite nanofiber membrane according to claim 1, characterized in that: S100 includes the following steps: S110, dissolving tetraaminophenylporphyrin in N,N-dimethylacetamide, then adding meta-aramid stock solution, and continuously stirring for 11 to 13 hours to obtain a spinning solution; S120, ejecting the spinning solution through a spinning needle at a speed of 0.5 to 1.5 ml / h to obtain a spinning precursor.

3. The method for preparing the lithium-philic PCOF-PMIA composite nanofiber membrane according to claim 2, characterized in that: In step S110, the content of PMIA in the spinning solution is 11-13 wt%.

4. The method for preparing the lithium-philic PCOF-PMIA composite nanofiber membrane according to claim 1, characterized in that: The terminator in step S200 is selected from benzaldehyde.

5. The method for preparing the lithium-philic PCOF-PMIA composite nanofiber membrane according to claim 1, characterized in that: In step S200, the volume ratio of acetonitrile to acetic acid in the mixed solution is 7:1 to 5:

1.

6. The method for preparing the lithium-philic PCOF-PMIA composite nanofiber membrane according to claim 1, characterized in that: In step S200, the concentration of the phthalaldehyde acetonitrile solution is 0.188 mg / ml to 1.88 mg / ml.

7. A lithiophilic PCOF-PMIA composite nanofiber membrane, characterized in that: The nanofiber membrane is prepared by the method for preparing the lithiophilic PCOF-PMIA composite nanofiber membrane as described in any one of claims 1 to 6.

8. An application of a lithium-philic PCOF-PMIA composite nanofiber membrane, characterized in that: A solid composite electrolyte is prepared using the lithium-philic PCOF-PMIA composite nanofiber membrane as claimed in claim 7; Wherein, the solid composite electrolyte comprises a PCOF-PMIA composite nanofiber membrane, polyethylene oxide and lithium bis(trifluoromethanesulfonyl imide), and the polyethylene oxide and lithium bis(trifluoromethanesulfonyl imide are coated on the surface of the PCOF-PMIA composite nanofiber membrane; The molar ratio of the ethylene oxide groups in the polyethylene oxide to the lithium ions in the lithium bis(trifluoromethanesulfonyl)imide is 18:1 to 10:

1.

9. The use of the lithiophilic PCOF-PMIA composite nanofiber membrane as claimed in claim 8, characterized in that: The preparation of the solid composite electrolyte comprises the following steps: S410, adding dried polyethylene oxide and lithium bis(trifluoromethanesulfonyl imide) into an organic solvent to dissolve them, thereby obtaining an organic solution of polyethylene oxide and lithium bis(trifluoromethanesulfonyl imide); S420, coating the organic solution on both sides of the PCOF-PMIA composite nanofiber membrane, drying at 45-55° C. for 23-25 ​​hours, removing the organic solvent, and obtaining the solid composite electrolyte by hot pressing.

10. The use of the lithiophilic PCOF-PMIA composite nanofiber membrane as claimed in claim 9, characterized in that: The organic solvent is selected from acetonitrile.

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