Covalent organic framework / conducting film composite material as well as preparation method and application thereof

Abstract

The invention provides a covalent organic framework / conducting film composite material as well as a preparation method and application thereof, and belongs to the technical field of covalent organic framework materials. The conductive film is used as the substrate of the diaphragm, and the conductivity of the diaphragm is improved by utilizing the high conductivity of the conductive film, so that the electrochemical performance of the lithium-sulfur battery is improved; in addition, the conductive film has adsorption and catalysis effects on polysulfide, and shuttling of the polysulfide can be inhibited; cOFs are subjected to in-situ growth on the surface of the conductive film through two times of electrochemical deposition, polysulfide is limited in a pore channel by using a pore channel structure of the COFs, and shuttling of the polysulfide is inhibited; by adjusting the monomer concentration of two times of electrochemical deposition, the COFs structure is regular, and the electrochemical performance of the lithium-sulfur battery is further improved.

Description

Technical Field

[0001] This invention belongs to the field of covalent organic framework materials technology, and particularly relates to a covalent organic framework / conductive film composite material, its preparation method and application. Background Technology

[0002] Covalent organic frameworks (COFs) are organic polymers linked by strong covalent bonds, possessing a porous crystalline structure and primarily composed of light elements (such as carbon, hydrogen, nitrogen, and oxygen). COFs offer advantages such as tunable pore size, large specific surface area, and ease of functionalization, making them ideal materials for preparing functional membranes that promote lithium-ion transport and suppress the polysulfide shuttle effect in lithium-sulfur batteries. However, COFs themselves have poor electronic conductivity, hindering the full and effective utilization of active materials and reducing the initial discharge specific capacity and cycle performance of lithium-sulfur batteries. Summary of the Invention

[0003] The purpose of this invention is to provide a covalent organic framework / conductive film composite material, its preparation method, and its applications. The covalent organic framework / conductive film composite material prepared by the method provided by this invention can improve the initial discharge specific capacity and cycle performance of lithium-sulfur batteries.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing a covalent organic framework / conductive film composite material, comprising the following steps:

[0006] (1) Dissolve the monomer and catalyst in a solvent to obtain an electrolyte; the monomer includes a pyromellitic tricarboxylate aldehyde monomer and an aromatic compound containing a diamino group; the molar ratio of the pyromellitic tricarboxylate aldehyde monomer to the aromatic compound containing a diamino group is (0.5-1):1.

[0007] (2) The conductive film is subjected to a first electrochemical deposition in the electrolyte obtained in step (1) to obtain a conductive film with crystal nuclei grown on the surface;

[0008] (3) Add monomers to the electrochemical reaction system of step (2), and then perform a second electrochemical deposition to obtain a membrane material; the initial concentration of monomers in the electrolyte during the second electrochemical deposition is greater than the initial concentration of monomers in the electrolyte during the first electrochemical deposition.

[0009] (4) The membrane material obtained in step (3) is subjected to ion exchange in a lithium salt solution to obtain a covalent organic framework / conductive membrane composite material.

[0010] Preferably, the total concentration of monomers in the electrolyte of step (1) is 0.04 mg / mL to 0.08 mg / mL.

[0011] Preferably, the mass of the monomer added in step (3) is 8 to 10 times the mass of the monomer in the electrolyte in step (1).

[0012] Preferably, in step (1), the pyromellitic aldehyde monomer is 1,3,5-tricarboxymethyl pyrogallol, 2-hydroxy-1,3,5-pyromellitic aldehyde, 2,4-dihydroxy-1,3,5-pyromellitic aldehyde, or pyromellitic aldehyde.

[0013] Preferably, the aromatic compound containing a diamino group in step (1) is 1,4-diaminobenzenesulfonic acid, benzidine, or phenylenediamine.

[0014] Preferably, the conductive film in step (2) is a carbon nanotube film or MXene.

[0015] Preferably, the catalyst in step (1) is a saturated monocarboxylic acid.

[0016] Preferably, the catalyst is octanoic acid, acetic acid, or propionic acid.

[0017] The present invention also provides the covalent organic framework / conductive film composite material described in the above technical solution.

[0018] The present invention also provides the application of the covalent organic framework / conductive film composite material described above in lithium-sulfur batteries.

[0019] This invention provides a method for preparing a covalent organic framework / conductive membrane composite material, comprising the following steps: (1) dissolving monomers and catalysts in a solvent to obtain an electrolyte; wherein the monomers include pyromellitic tricarboxyaldehyde aldehyde monomers and aromatic compounds containing diamino groups; the molar ratio of the pyromellitic tricarboxyaldehyde aldehyde monomers to the aromatic compounds containing diamino groups is (0.5-1):1; (2) performing a first electrochemical deposition on the conductive membrane in the electrolyte obtained in step (1) to obtain a conductive membrane with surface-grown crystal nuclei; (3) supplementing the electrochemical reaction system of step (2) with monomers, and then performing a second electrochemical deposition to obtain a membrane material; wherein the initial concentration of monomers in the electrolyte during the second electrochemical deposition is greater than the initial concentration of monomers in the electrolyte during the first electrochemical deposition; (4) performing ion exchange on the membrane material obtained in step (3) in a lithium salt solution to obtain a covalent organic framework / conductive membrane composite material. This invention uses a conductive film as the substrate for the separator, leveraging its high conductivity to improve the separator's conductivity, thereby enhancing the electrochemical performance of the lithium-sulfur battery. Furthermore, the conductive film exhibits adsorption and catalytic effects on polysulfides, inhibiting polysulfide shuttle. Covalent organic frameworks (COFs) are grown in situ on the conductive film surface through two electrochemical deposition processes. The porous structure of the COFs confines polysulfides within the pores, suppressing their shuttle. By adjusting the monomer concentration during the two electrochemical deposition processes, the COF structure is made more regular, further improving the electrochemical performance of the lithium-sulfur battery. The results of the embodiments show that the covalent organic framework / conductive film composite material provided by this invention, when used in a lithium-sulfur battery, achieves an initial discharge specific capacity of 1123.9 mAh·g at a current density of 0.1C. -1 After 100 cycles, it still has 842.8 mAh·g -1 After 300 cycles at a current density of 0.5C, it still retains 597.5 mAh·g. -1 The capacity decays by only 0.13% per cycle, with a capacity retention rate of 60.8%. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the reaction process for preparing the covalent organic framework / conductive film composite material in Example 1 of the present invention;

[0021] Figure 2 This is a 10,000x magnified SEM image of the covalent organic framework / conductive film composite material prepared in Example 1 of the present invention.

[0022] Figure 3 This is a 25,000x magnified SEM image of the covalent organic framework / conductive film composite material prepared in Example 2 of the present invention.

[0023] Figure 4 This is a 25,000x magnified SEM image of the carbon nanotube film provided in Comparative Example 1 of this invention.

[0024] Figure 5 The graphs show the 0.1C cyclic charge-discharge test results of Application Example 1 and Comparative Application Example of the present invention;

[0025] Figure 6 The graphs show the 0.5C cyclic charge-discharge test results of Application Example 1 and Comparative Application Example of the present invention. Detailed Implementation

[0026] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0027] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses industrial pure raw materials or raw materials with purity commonly used in the field of oil and gas production enhancement and transformation.

[0028] This invention provides a method for preparing a covalent organic framework / conductive film composite material, comprising the following steps:

[0029] (1) Dissolve the monomer and catalyst in a solvent to obtain an electrolyte; the monomer includes a pyromellitic tricarboxylate aldehyde monomer and an aromatic compound containing a diamino group; the molar ratio of the pyromellitic tricarboxylate aldehyde monomer to the aromatic compound containing a diamino group is (0.5-1):1.

[0030] (2) The conductive film is subjected to a first electrochemical deposition in the electrolyte obtained in step (1) to obtain a conductive film with crystal nuclei grown on the surface;

[0031] (3) Add monomers to the electrochemical reaction system of step (2), and then perform a second electrochemical deposition to obtain a membrane material; the initial concentration of monomers in the electrolyte during the second electrochemical deposition is greater than the initial concentration of monomers in the electrolyte during the first electrochemical deposition.

[0032] (4) The membrane material obtained in step (3) is subjected to ion exchange in a lithium salt solution to obtain a covalent organic framework / conductive membrane composite material.

[0033] The present invention dissolves monomers and catalysts in a solvent to obtain an electrolyte.

[0034] In this invention, the monomer includes a trimellitic aldehyde monomer, preferably 1,3,5-tricarboxymethyl phloroglucinol, 2-hydroxy-1,3,5-trimethyl phosphonic acid, 2,4-dihydroxy-1,3,5-trimethyl phosphonic acid, or trimellitic acid. In this invention, the monomer also includes an aromatic compound containing a diamino group, preferably 1,4-diaminobenzenesulfonic acid, benzidine, or phenylenediamine. This invention uses trimellitic aldehyde monomers and aromatic compounds containing diamino groups as monomers, which can undergo a Schiff base reaction to form COFs.

[0035] In this invention, the molar ratio of the trimesin aldehyde monomer to the diamino-containing aromatic compound is (0.5–1):1, preferably (0.6–0.8):1. As one embodiment of this invention, the molar ratio of the trimesin aldehyde monomer to the diamino-containing aromatic compound can be 0.5:1, 0.6:1, 0.67:1, 0.7:1, 0.8:1, 0.9:1, or 1:1. By limiting the molar ratio of the trimesin aldehyde monomer to the diamino-containing aromatic compound to the above range, the generated COFs can suppress polysulfide shuttling, thereby improving the electrochemical performance of lithium-sulfur batteries.

[0036] In this invention, the catalyst is preferably a saturated monocarboxylic acid, more preferably octanoic acid, acetic acid, or propionic acid. Using the above-mentioned catalyst, this invention can adjust the surface area of ​​the monomer synthesis reaction, confining the reaction to the solid-liquid interface, which is beneficial for COF synthesis.

[0037] The present invention does not impose a particular limitation on the amount of catalyst used; it can be added according to the conventional dosage in the art. In one embodiment of the present invention, the dosage relationship between the catalyst and the monomer can be 1 μL: (0.04–0.08) mg; in an embodiment of the present invention, the dosage relationship between the catalyst and the monomer is 100 μL: 6 mg.

[0038] This invention does not have any particular requirements regarding the type of solvent, as long as it can dissolve the monomer without affecting the monomer reaction or dissolving the product. In one embodiment of this invention, the solvent can be a saturated hydrocarbon monohydric alcohol, specifically methanol, ethanol, or propanol.

[0039] This invention does not have specific requirements regarding the specific method of dissolution, as long as an electrolyte can be obtained. As one embodiment of this invention, different monomers can be dissolved separately in a solvent, then mixed, and then a catalyst can be added to the mixture.

[0040] In this invention, the total concentration of monomers in the electrolyte is preferably 0.04 mg / mL to 0.08 mg / mL, more preferably 0.05 mg / mL to 0.07 mg / mL; as one embodiment of this invention, the monomer concentration in the electrolyte can be 0.04 mg / mL, 0.05 mg / mL, 0.06 mg / mL, 0.07 mg / mL, or 0.08 mg / mL. A monomer concentration within the above range is beneficial for the formation of well-defined COF crystal nuclei, thereby improving the composite material's suppression effect on polysulfide shuttle.

[0041] After obtaining the electrolyte, the present invention performs a first electrochemical deposition of the conductive film in the electrolyte to obtain a conductive film with crystal nuclei grown on the surface.

[0042] In this invention, the conductive film is preferably a carbon nanotube film or MXene. This invention does not impose any particular limitations on the specifications of the conductive film; the specifications can be selected according to application requirements.

[0043] In this invention, the conductive film is preferably subjected to ultraviolet ozone treatment before use. This invention uses ultraviolet ozone treatment to thoroughly remove organic contaminants from the surface of the conductive film, which is beneficial for further improving the deposition of COFs on the conductive film surface. This invention does not have special requirements for the apparatus and parameters of the ultraviolet ozone treatment, as long as the organic contaminants on the surface of the conductive film are thoroughly removed. As one embodiment of this invention, the ultraviolet ozone treatment can be performed in an ultraviolet ozone cleaning machine, and the treatment time can be 5–15 minutes.

[0044] As one embodiment of the present invention, an electrode can be assembled by combining a conductive film with a platinum sheet, with the platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode, and immersed in an electrolyte to obtain an electrochemical reaction system.

[0045] This invention does not have a particular requirement for the time of the first electrochemical deposition, as long as a conductive film with surface-grown crystal nuclei can be obtained. In an embodiment of this invention, the time of the first electrochemical deposition is 1 hour.

[0046] After obtaining a conductive film with surface-grown crystal nuclei, the present invention adds monomers to the electrolyte and then performs a second electrochemical deposition to obtain the film material.

[0047] In this invention, the initial concentration of monomers in the electrolyte during the second electrochemical deposition is greater than that during the first electrochemical deposition. The electrochemical deposition of this invention exhibits typical negative feedback characteristics, self-healing, and self-inhibition effects. As the electrochemical time increases, the current gradually decreases. This is because COFs are non-conductive; during electrochemical deposition, the film thickness increases rapidly as defects heal. After a complete COF film is formed, conductivity decreases, slowing the increase in film thickness. Therefore, a higher monomer concentration in the electrolyte during the second electrochemical deposition than during the first can prevent powder formation during the first electrochemical deposition, resulting in well-structured crystal nuclei, and improve the film formation rate during the second electrochemical deposition.

[0048] In this invention, the mass of the supplementary monomer is preferably 8 to 10 times the mass of the monomer in the initial electrolyte, more preferably 9 times. A mass of supplementary monomer within this range is beneficial for further improving the polysulfide suppression effect of the composite material.

[0049] In one embodiment of the present invention, the method of supplementing the monomers may be as follows: dissolving different monomers in solvents to obtain monomer solutions, and then adding the monomer solutions to the electrolyte; the total concentration of monomers in the monomer solutions may be 2.6 mg / mL to 2.8 mg / mL.

[0050] This invention does not have specific requirements regarding the time of the second electrochemical deposition, as long as a COFs-deposited film material can be obtained. In an embodiment of this invention, the time for the second electrochemical deposition is 3 hours.

[0051] In one embodiment of the present invention, the first electrochemical deposition and the second electrochemical deposition can be carried out using a constant voltage deposition method, and the voltage of the first electrochemical deposition and the second electrochemical deposition can be 4V to 9V or 6V to 8V.

[0052] After obtaining the membrane material, this invention performs ion exchange on the obtained membrane material in a lithium salt solution to obtain a covalent organic framework / conductive membrane composite material. This invention performs ion exchange on the membrane material in a lithium salt solution, replacing impurity ions in the membrane material with lithium ions, thus avoiding the consumption of lithium ions in the electrolyte during application of the composite material, and improving the permeability of lithium ions.

[0053] The present invention preferably involves cleaning the membrane material before ion exchange. This invention removes residual monomers by cleaning the membrane material. The present invention does not have particular requirements for the cleaning solvent, as long as it can remove residual monomers without affecting the membrane material itself. As one embodiment of the present invention, the cleaning may be performed sequentially using N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and acetone.

[0054] This invention does not have particular requirements regarding the type and concentration of the lithium salt solution, as long as it can replace impurity ions in the membrane material with lithium ions. In one embodiment of this invention, the lithium salt solution can be an aqueous solution of lithium acetate, and the concentration of lithium acetate in the aqueous solution can be 2 mol / L to 5 mol / L.

[0055] This invention uses a conductive film as the substrate of the separator, leveraging its high conductivity to improve the separator's conductivity, thereby enhancing the electrochemical performance of the lithium-sulfur battery. Furthermore, the conductive film exhibits adsorption and catalytic effects on polysulfides, inhibiting polysulfide shuttle. COFs are grown in situ on the conductive film surface through two electrochemical deposition processes, utilizing the porous structure of the COFs to confine polysulfides within the pores and suppress polysulfide shuttle. By adjusting the monomer concentration during the two electrochemical deposition processes, the COFs structure is made more regular, further improving the electrochemical performance of the lithium-sulfur battery.

[0056] The present invention also provides the covalent organic framework / conductive film composite material described in the above technical solution, comprising a conductive film and a covalent organic framework layer grown in situ on the surface of the conductive film.

[0057] The present invention also provides the application of the covalent organic framework / conductive film composite material described above in lithium-sulfur batteries.

[0058] This invention does not impose any particular limitation on the application of the covalent organic framework / conductive film composite material; conventional application methods in the art are acceptable. As one application method of this invention, the covalent organic framework / conductive film composite material can be directly used as a separator in a lithium-sulfur battery.

[0059] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0060] Example 1

[0061] A method for preparing a covalent organic framework / conductive film composite material, the schematic diagram of the synthesis reaction process is shown below. Figure 1 As shown, the specific steps are as follows:

[0062] (1) After treating the carbon nanotube film (CNT) with ultraviolet ozone for 10 min, the electrodes were assembled.

[0063] (2) Weigh 2.5 mg of 1,3,5-tricarboxymethyl pyrogallol (Tp) and 3.5 mg of 1,4-diaminobenzenesulfonic acid (Pa-SO3H) and dissolve them in 50 mL of methanol respectively. Pour the two solutions into an electrolytic cell, add 100 μL of n-octanoic acid, and mix well.

[0064] (3) Use the constant voltage deposition method, set the voltage to 7V, and the deposition time to 1h;

[0065] (4) Weigh 22.5 mg Tp and 31.3 mg Pa-SO3H and dissolve them in 10 mL of methanol respectively, then pour them into the electrolytic cell;

[0066] (5) Using the constant voltage deposition method, set the voltage to 7V and deposit again for 3 hours;

[0067] (6) After deposition, the membrane material is thoroughly cleaned with DMF, NMP and acetone in sequence to remove residual monomers;

[0068] (7) Ion exchange was carried out in a 2 mol / L lithium acetate solution to obtain a covalent organic framework / conductive membrane composite material, denoted as CNT@TpPa-SO3Li membrane.

[0069] Example 2

[0070] A method for preparing a covalent organic framework / conductive film composite material, comprising the following steps:

[0071] (1) Ti3C2T x After MXene is treated with ultraviolet ozone for 10 minutes, the electrodes are assembled.

[0072] (2) Weigh 2.5 mg Tp and 3.5 mg Pa-SO3H and dissolve them in 50 mL methanol respectively, and add 100 μL of octanoic acid. Pour the two solutions into the electrolytic cell and mix them evenly.

[0073] (3) Use the constant voltage deposition method, set the voltage to 7V, and the deposition time to 1h;

[0074] (4) Weigh 22.5 mg Tp and 31.3 mg Pa-SO3H and dissolve them in 10 mL of methanol solvent, then pour them into the electrolytic cell;

[0075] (5) Using the constant voltage deposition method, set the voltage to 7V and deposit again for 3 hours;

[0076] (6) After deposition, the membrane material is thoroughly cleaned with DMF, NMP and acetone in sequence to remove residual monomers;

[0077] (7) Ion exchange was carried out in a 2 mol / L lithium acetate solution to obtain a covalent organic framework / conductive membrane composite material, denoted as MXene@TpPa-SO3Li membrane.

[0078] Comparative Example 1

[0079] This comparative example is the CNT in Example 1.

[0080] Comparative Example 2

[0081] This comparative example uses a commercially available polypropylene Celgard 2500 membrane.

[0082] Application Example 1

[0083] A lithium sheet was used as the counter electrode, the CNT@TpPa-SO3Li film prepared in Example 1 was used as the separator, 1 mol / L LiTFSI (DOL / DME, 1:1, v / v, 2% LiNO3) was used as the electrolyte, and a conductive carbon black / sulfur electrode was used as the positive electrode with a sulfur loading of 1.4 mg·cm³. -1The CR-2032 button cell was assembled, and the entire assembly process was carried out in a glove box filled with argon gas.

[0084] Application Example 2

[0085] Using the MXene@TpPa-SO3Li membrane prepared in Example 2 as the separator, a lithium-sulfur battery was assembled according to the method of Application Example 1.

[0086] Comparative application examples

[0087] Using the separator provided in Comparative Example 2, a lithium-sulfur battery was assembled according to the method in Application Example 1.

[0088] Test Example 1

[0089] The microstructure of the membrane materials provided in Examples 1, 2, and Comparative Example 1 was observed using a scanning electron microscope, and SEM images were obtained, as shown below. Figures 2-4 As shown. From Figure 2 It can be seen that the CNT@TpPa-SO3Li film prepared in Example 1 has a smooth and flat surface. Figure 3 It can be seen that the MXene@TpPa-SO3Li film prepared in Example 2 has a smooth and flat surface. Figure 4 As can be seen, a large number of carbon nanotubes are exposed on the surface of CNTs (the tubular structures in the image are all carbon nanotubes). This can be observed through comparison. Figure 2 and Figure 4 This indicates that TpPa-SO3Li grows uniformly on the surface of CNTs. Similarly, Figure 3 TpPa-SO3Li was uniformly grown on the surface of MXene.

[0090] Test Example 2

[0091] The batteries assembled in Application Example 1 and the comparative application example were placed on the Land CT2001A battery testing system for electrochemical performance testing. The test temperature was 25°C, and the voltage range was 1.7–2.8V. Long-cycle charge-discharge tests were performed at current densities of 0.1C and 0.5C, and the charge-discharge test curves were obtained, as shown below. Figure 5 , Figure 6 As shown.

[0092] from Figure 5 It can be seen that, at a current density of 0.1C, the initial discharge specific capacity of the lithium-sulfur batteries assembled using the CNT@TpPa-SO3Li membrane prepared in Example 1 and the Celgard 2500 separator provided in Comparative Example 2 are 1123.9 mAh·g, respectively. -1 and 717.3mAh·g -1This indicates that the lithium-sulfur battery using the CNT@TpPa-SO3Li film prepared in Example 1 has a higher sulfur utilization efficiency. After 100 charge-discharge cycles, the lithium-sulfur battery using the CNT@TpPa-SO3Li film prepared in Example 1 still has a capacity of 842.8 mAh·g. -1 The reversible cycle specific capacity of the lithium-sulfur battery was significantly improved, while the capacity of the lithium-sulfur battery using the comparative 2Celgard 2500 separator rapidly decreased to 345.8 mAh·g. -1 .

[0093] from Figure 6 It can be seen that after 300 cycles using the CNT@TpPa-SO3Li film prepared in Example 1 at a current density of 0.5C, the specific capacity of the battery is still 597.5 mAh·g. -1 The capacity decay per cycle was only 0.13%, with a capacity retention rate of 60.8%. In contrast, the lithium-sulfur battery assembled with the comparative 2Celgard 2500 separator showed a rapid decrease in battery capacity with increasing cycle count, reaching a specific capacity of only 346.5 mAh·g after 300 cycles. -1 This indicates that the CNT@TpPa-SO3Li film prepared in Example 1 has good cycle stability, and the polysulfides are effectively confined to the positive electrode side, improving the utilization rate of active materials and effectively improving the electrochemical performance of lithium-sulfur batteries.

[0094] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a covalent organic framework / conductive film composite material, comprising the following steps: (1) Dissolve the monomer and catalyst in a solvent to obtain an electrolyte; the monomer includes a pyromellitic tricarboxylate aldehyde monomer and an aromatic compound containing a diamino group; the molar ratio of the pyromellitic tricarboxylate aldehyde monomer to the aromatic compound containing a diamino group is (0.5-1):

1. (2) The conductive film is subjected to a first electrochemical deposition in the electrolyte obtained in step (1) to obtain a conductive film with surface-grown crystal nuclei; (3) Add monomers to the electrochemical reaction system of step (2), and then perform a second electrochemical deposition to obtain a membrane material; the initial concentration of monomers in the electrolyte during the second electrochemical deposition is greater than the initial concentration of monomers in the electrolyte during the first electrochemical deposition. (4) The membrane material obtained in step (3) is subjected to ion exchange in a lithium salt solution to obtain a covalent organic framework / conductive membrane composite material.

2. The preparation method according to claim 1, characterized in that, The total concentration of monomers in the electrolyte in step (1) is 0.04 mg / mL to 0.08 mg / mL.

3. The preparation method according to claim 1, characterized in that, The mass of the monomer added in step (3) is 8 to 10 times the mass of the monomer in the electrolyte in step (1).

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step (1), the pyromellitic aldehyde monomer is 1,3,5-tricarboxymethyl pyrogallol, 2-hydroxy-1,3,5-pyromellitic aldehyde, 2,4-dihydroxy-1,3,5-pyromellitic aldehyde, or pyromellitic aldehyde.

5. The preparation method according to any one of claims 1 to 3, characterized in that, The aromatic compound containing diamino groups in step (1) is 1,4-diaminobenzenesulfonic acid, benzidine, or phenylenediamine.

6. The preparation method according to claim 1, characterized in that, In step (2), the conductive film is a carbon nanotube film or MXene.

7. The preparation method according to claim 1, characterized in that, The catalyst in step (1) is a saturated monocarboxylic acid.

8. The preparation method according to claim 7, characterized in that, The catalyst is octanoic acid, acetic acid, or propionic acid.

9. The covalent organic framework / conductive film composite material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the covalent organic framework / conductive film composite material of claim 9 in lithium-sulfur batteries.

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