A multi-element doped modified carbon-based composite material and a preparation method thereof

Abstract

The present application relates to the field of carbon-based composite materials, and particularly relates to a multi-element doped modified carbon-based composite material and a preparation method thereof, which is used to solve the problems of poor cycle performance and low rate performance of existing carbon-based composite materials as anodes; the carbon-based composite material adds thiophene pyridine anthracene COFs to load carbon quantum dots, carbon quantum dots are obtained by carbonizing chitosan and citric acid, a dithiole pyridine anthracene COFs is obtained by synthesizing a dithiole pyridine anthracene and reacting with p-phenylenediamine, the carbon quantum dots are doped into the thiophene pyridine anthracene COFs to obtain the thiophene pyridine anthracene COFs loaded carbon quantum dots, the carbon quantum dots are uniformly loaded in the COFs channels to form a three-dimensional conductive network, the high conductivity of the three-dimensional conductive network can accelerate the charge transfer, meanwhile, the elastic properties of the carbon quantum dots can relieve the volume expansion of the COFs in the charging and discharging process, prolong the cycle life, and thus the use effect and the life of the sodium ion battery are improved.

Description

Technical Field

[0001] This invention relates to the field of carbon-based composite materials, and more specifically to a multi-element doped modified carbon-based composite material and its preparation method. Background Technology

[0002] Sodium-ion batteries, due to their abundant raw materials and low cost, have become an important research direction in the search for alternatives to traditional lithium-ion batteries. The core components of a sodium-ion battery include positive electrode materials, negative electrode materials, electrolytes, and separators, among which the performance of the negative electrode material has a significant impact on the overall energy density and cycle stability of the battery. Existing sodium-ion battery negative electrode materials are mainly amorphous carbon and hard carbon, which, due to volume changes caused by the exchange of sodium ions with the electrode material during charge and discharge, easily lead to deterioration in cycle performance and poor rate performance. Therefore, this invention provides a multi-element doped modified carbon-based composite material and its preparation method to improve its electrochemical activity and cycle life during charge and discharge. Summary of the Invention

[0003] In order to overcome the above-mentioned technical problems, the present invention aims to provide a multi-element doped modified carbon-based composite material and its preparation method, which solves the problems of poor cycle performance and low rate performance of existing carbon-based composite materials as negative electrodes.

[0004] The objective of this invention can be achieved through the following technical solutions: In a first aspect, this application provides a multi-element doped modified carbon-based composite material, comprising the following parts by weight: Thiophenepyridine anthracene COFs supported on 20-30 parts of carbon quantum dots and 5-10 parts of multi-walled carbon nanotubes The thiophenepyridine anthracene COFs-loaded carbon quantum dots are prepared by the following steps: Step A1: 9,10-Dibromoanthracene, 5-bromothiophene-2-boronic acid, anhydrous sodium carbonate, tetra(triphenylphosphine)palladium, and N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer, and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 10-20 min. The reaction was carried out at 100 °C for 8-10 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. Anhydrous sodium sulfate was added for drying. The filtrate was filtered and evaporated to dryness under reduced pressure. The filtrate was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent as eluent to obtain dibromothiophene anthracene.

[0005] Step A2: Dibromothiophene anthracene, 2-bromopyridin-5-boronic acid, anhydrous sodium carbonate, tetrakis(triphenylphosphine)palladium, and N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer, and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 10-20 min. The reaction was carried out at 100 °C for 12 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. Anhydrous sodium sulfate was added for drying. The filtrate was filtered and evaporated to dryness under reduced pressure. The mixture was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent as eluent to obtain dibromopyridinylthiophene anthracene.

[0006] Step A3: Dibromopyridylthiophene anthracene, 3,5-dicarboxyphenylboronic acid, 1,4-dioxane and N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and thermometer. The mixture was stirred for 5-10 min, potassium carbonate aqueous solution was added dropwise, and the mixture was purged with nitrogen three times. Tetra(triphenylphosphine)palladium was added and stirred for 5-10 min. The mixture was stirred at 100 °C for 24 h. The mixture was then filtered, and the residue was washed with ethyl acetate to obtain dialdehydepyridylthiophene anthracene.

[0007] Step A4: Add chitosan, acetic acid aqueous solution, and cellulase to a three-necked flask equipped with a thermometer and stirrer. Stir for 5-10 minutes and enzymatically hydrolyze at 50°C for 4 hours. Adjust the pH to 5 with sodium hydroxide aqueous solution. Centrifuge, add the supernatant, anhydrous citric acid, and deionized water to a beaker, add sodium dodecyl sulfate, sonicate for 30 minutes, transfer to a high-pressure reactor, purge with nitrogen three times, react at 120°C for 2 hours, react at 160°C for 2 hours, and react at 180°C for 4 hours. Cool, transfer through a filter membrane to a dialysis bag, place in distilled water, change the distilled water every six hours, dialyze for a total of 24 hours, centrifuge the dialysate, freeze the supernatant at low temperature, freeze-dry in a freeze dryer for 12 hours, grind, and obtain carbon quantum dots. Step A5: Add p-phenylenediamine, dialdehyde pyridylthiophene anthracene, carbon quantum dots, and N,N-dimethylformamide to a weighing bottle, sonicate for 20-30 min, add acetic acid aqueous solution and sonicate for 10 min, transfer to a reaction tube, freeze and thaw three times under liquid nitrogen vacuum, react at 120℃ for 24 h, react at 130℃ for 24 h, react at 140℃ for 48 h, cool, centrifuge to collect the precipitate, wash with acetone 5-7 times, freeze-dry for 12 h, grind to obtain thiophene pyridyl anthracene COFs-supported carbon quantum dots.

[0008] In a preferred embodiment of the present invention, the ratio of 9,10-dibromoanthracene, 5-bromothiophene-2-boronic acid, anhydrous sodium carbonate, tetra(triphenylphosphine)palladium and N,N-dimethylformamide in step A1 is 1-2 mmol: 2.5-5 mmol: 3-6 mmol: 0.05-0.1 mmol: 45-90 mL.

[0009] In a preferred embodiment of the present invention, the volume ratio of petroleum ether to dichloromethane in the petroleum ether / dichloromethane mixed solvent in step A1 is 1:1.

[0010] In a preferred embodiment of the present invention, the ratio of dibromothienylanthracene, 2-bromopyridine-5-boronic acid, anhydrous sodium carbonate, tetra(triphenylphosphine)palladium and N,N-dimethylformamide in step A2 is 1-2 mmol: 2.5-5 mmol: 3-6 mmol: 0.05-0.1 mmol: 45-90 mL.

[0011] In a preferred embodiment of the present invention, the volume ratio of petroleum ether to dichloromethane in the petroleum ether / dichloromethane mixed solvent in step A2 is 1:1.

[0012] In a preferred embodiment of the present invention, the ratio of the amounts of dibromopyridylthiophene anthracene, 3,5-dicarboxyphenylboronic acid, 1,4-dioxane, N,N-dimethylformamide, potassium carbonate aqueous solution, and tetrakis(triphenylphosphine)palladium in step A3 is 1-2 mmol: 2.5-5 mmol: 37.5-75 mL: 12.5-25 mL: 10-20 mL: 0.15-0.3 mmol.

[0013] In a preferred embodiment of the present invention, the molar concentration of the potassium carbonate aqueous solution in step A3 is 2 mol / L.

[0014] In a preferred embodiment of the present invention, the ratio of chitosan, aqueous acetic acid solution, cellulase, anhydrous citric acid, deionized water and sodium dodecyl sulfate in step A4 is 1-2g: 100-200mL: 0.5-1g: 0.5-1g: 10-20mL: 0.1-0.2g.

[0015] In a preferred embodiment of the present invention, the mass fraction of the acetic acid aqueous solution in step A4 is 1%.

[0016] In a preferred embodiment of the present invention, the molar concentration of the sodium hydroxide aqueous solution in step A4 is 0.1 mol / L.

[0017] In a preferred embodiment of the present invention, the ratio of p-phenylenediamine, dialdehyde pyridylthiophene anthracene, carbon quantum dots, N,N-dimethylformamide and aqueous acetic acid in step A5 is 0.219-0.438 mmol: 0.066-0.132 mmol: 20-40 mg: 5-10 mL: 0.3-0.6 mL.

[0018] In a preferred embodiment of the present invention, the molar concentration of the acetic acid aqueous solution in step A5 is 8 mol / L.

[0019] Secondly, a method for preparing a multi-element doped modified carbon-based composite material includes the following steps: Step 1: Weigh 20-30 parts by weight of thiophenepyridine anthracene COFs-supported carbon quantum dots and 5-10 parts by weight of multi-walled carbon nanotubes, and set aside; the multi-walled carbon nanotubes have a diameter of 10-30 nm and a length of 1-2 μm. Step 2: Thiophenepyridine anthracene COFs-loaded carbon quantum dots and multi-walled carbon nanotubes are mixed to obtain multi-element doped modified carbon-based composite materials.

[0020] The beneficial effects of this invention are: This invention discloses a multi-element doped modified carbon-based composite material. Carbon quantum dots are obtained by carbonizing chitosan with citric acid. Dialdehyde pyridylthiophene anthracene is synthesized and reacted with p-phenylenediamine to obtain thiophene pyridyl anthracene COFs. Carbon quantum dots are then doped into the thiophene pyridyl anthracene COFs to obtain thiophene pyridyl anthracene COFs loaded with carbon quantum dots, which enhances the sodium storage performance and thus improves the cycle stability and rate capacity of sodium-ion batteries.

[0021] A multi-element doped modified carbon-based composite material was prepared. 9,10-Dibromoanthracene reacted with 5-bromothiophene-2-boric acid to obtain dibromothiophene anthracene. Dibromothiophene anthracene reacted with 2-bromopyridin-5-boric acid to obtain dibromopyridinylthiophene anthracene. Dibromopyridinylthiophene anthracene reacted with 3,5-dicarboxyphenylboric acid to generate dialdehydepyridinylthiophene anthracene. Chitosan was enzymatically hydrolyzed by cellulase and carbonized with citric acid under high pressure and hydrothermal conditions to form carbon quantum dots. The amino group in p-phenylenediamine reacted with the aldehyde group in dialdehydepyridinylthiophene anthracene to generate thiophenepyridinyl anthracene COFs. Carbon quantum dots were then incorporated into the thiophenepyridinyl anthracene COFs to obtain thiophenepyridinyl anthracene COFs loaded with carbon quantum dots. The sulfur atom of thiophene forms p-π conjugation with the π-electron system of the anthracene ring, enhancing the electron-donating ability of the material and promoting the adsorption of sodium ions on the electrode surface. The CS bond of thiophene has rotational freedom and can absorb the volume of COFs during charge and discharge. The expansion of the pyridine group extends the cycle life. The planar structure of the pyridine group forms π-π stacked channels with the anthracene ring, providing a directional transport channel for sodium ions. The aromaticity of the thiophene and pyridine groups endows COFs with good chemical stability and resistance to electrolyte corrosion. The hollow structure of the thiophene-pyridine-anthracite COFs loaded with carbon quantum dots can shorten the transport path of sodium ions, effectively improving the transport rate and storage capacity of sodium ions, thereby improving the discharge specific capacity and cycle stability of the electrode material. The doping of carbon quantum dots can effectively improve the conductivity of COFs, thereby accelerating the electron transport rate. The high specific surface area increases the contact area between the electrode and the electrolyte, promotes the adsorption / desorption of sodium ions, and improves the specific capacity. The presence of elements such as S and N can not only optimize the electronic structure and electrochemical properties of the material, but also improve the conductivity and sodium storage capacity of the material, thereby improving the cycle stability and rate capacity of the negative electrode material, thus improving the cycle performance and sodium storage efficiency of sodium-ion batteries. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1:

[0024] This embodiment describes a method for preparing a multi-element doped modified carbon-based composite material, including the following steps: Step A1: 1 mmol of 9,10-dibromoanthracene, 2.5 mmol of 5-bromothiophene-2-boric acid, 3 mmol of anhydrous sodium carbonate, 0.05 mmol of tetrakis(triphenylphosphine)palladium and 45 mL of N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 10 min. The reaction was carried out at 100 °C for 8 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromothiophene anthracene. Step A2: 1 mmol dibromothiophene anthracene, 2.5 mmol 2-bromopyridine-5-boric acid, 3 mmol anhydrous sodium carbonate, 0.05 mmol tetra(triphenylphosphine)palladium, and 45 mL N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer, and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 10 min. The reaction was carried out at 100 °C for 12 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromopyridinethiophene anthracene. Step A3: 1 mmol of dibromopyridylthiophene anthracene, 2.5 mmol of 3,5-dicarboxyphenylboronic acid, 37.5 mL of 1,4-dioxane and 12.5 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and thermometer. The mixture was stirred for 5 min, and 10 mL of 2 mol / L potassium carbonate aqueous solution was added dropwise. The mixture was purged with nitrogen three times. 0.15 mmol of tetra(triphenylphosphine)palladium was added and stirred for 5 min. The mixture was stirred at 100 °C for 24 h. The mixture was filtered, and the residue was washed with ethyl acetate to obtain dialdehydepyridylthiophene anthracene. Step A4: Add 1g chitosan, 100mL of 1% acetic acid aqueous solution and 0.5g cellulase to a three-necked flask equipped with a thermometer and stirrer. Stir for 5min and enzymatically hydrolyze at 50℃ for 4h. Adjust the pH to 5 with 0.1mol / L sodium hydroxide aqueous solution. Centrifuge. Add the supernatant, 0.5g anhydrous citric acid and 10mL deionized water to a beaker. Add 0.1g sodium dodecyl sulfate and sonicate for 30min. Transfer to a high-pressure reactor. Purge with nitrogen three times. React at 120℃ for 2h, 160℃ for 2h, and 180℃ for 4h. Cool and transfer through a filter membrane to a dialysis bag. Place in distilled water and change the distilled water every six hours for a total of 24h. Centrifuge the dialysate. Freeze the supernatant at low temperature and freeze it in a freeze dryer for 12h. Grind to obtain carbon quantum dots. Step A5: Add 0.219 mmol p-phenylenediamine, 0.066 mmol dialdehyde pyridylthiophene anthracene, 20 mg carbon quantum dots and 5 mL N,N-dimethylformamide to a weighing bottle, sonicate for 20 min, add 0.3 mL 8 mol / L acetic acid aqueous solution, sonicate for 10 min, transfer to a reaction tube, freeze-thaw three times under liquid nitrogen vacuum, react at 120 °C for 24 h, react at 130 °C for 24 h, react at 140 °C for 48 h, cool, centrifuge to collect the precipitate, wash five times with acetone, freeze-dry for 12 h, grind to obtain thiophene pyridyl anthracene COFs supported carbon quantum dots; Step A6: Weigh 20 parts by weight of thiophenepyridine anthracene COFs-supported carbon quantum dots and 5 parts by weight of multi-walled carbon nanotubes for later use; the diameter of the multi-walled carbon nanotubes is 10-30 nm and the length is 1-2 μm. Step A7: Mix thiophenepyridine anthracene COFs-loaded carbon quantum dots and multi-walled carbon nanotubes to obtain a multi-element doped modified carbon-based composite material.

[0025] Example 2:

[0026] This embodiment describes a method for preparing a multi-element doped modified carbon-based composite material, including the following steps: Step A1: 1.5 mmol of 9,10-dibromoanthracene, 3.75 mmol of 5-bromothiophene-2-boric acid, 4.5 mmol of anhydrous sodium carbonate, 0.075 mmol of tetrakis(triphenylphosphine)palladium, and 67.5 mL of N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer, and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 15 min. The reaction was carried out at 100 °C for 9 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromothiophene anthracene. Step A2: 1.5 mmol dibromothiophene anthracene, 3.75 mmol 2-bromopyridine-5-boric acid, 4.5 mmol anhydrous sodium carbonate, 0.075 mmol tetra(triphenylphosphine)palladium, and 67.5 mL N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer, and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 15 min. The reaction was carried out at 100 °C for 12 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromopyridinethiophene anthracene. Step A3: 1.5 mmol of dibromopyridylthiophene anthracene, 3.75 mmol of 3,5-dicarboxyphenylboronic acid, 56.25 mL of 1,4-dioxane and 18.75 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and thermometer. The mixture was stirred for 7 min, and 15 mL of 2 mol / L potassium carbonate aqueous solution was added dropwise. The mixture was purged with nitrogen three times. 0.225 mmol of tetra(triphenylphosphine)palladium was added and stirred for 7 min. The mixture was stirred at 100 °C for 24 h. The mixture was filtered, and the residue was washed with ethyl acetate to obtain dialdehydepyridylthiophene anthracene. Step A4: Add 1.5g chitosan, 150mL of 1% acetic acid aqueous solution, and 0.75g cellulase to a three-necked flask equipped with a thermometer and stirrer. Stir for 7 minutes and enzymatically hydrolyze at 50℃ for 4 hours. Adjust the pH to 5 with 0.1mol / L sodium hydroxide aqueous solution. Centrifuge. Add the supernatant, 0.75g anhydrous citric acid, and 15mL deionized water to a beaker. Add 0.15g sodium dodecyl sulfate and sonicate for 30 minutes. Transfer to a high-pressure reactor. Purge with nitrogen three times. React at 120℃ for 2 hours, 160℃ for 2 hours, and 180℃ for 4 hours. Cool and transfer through a filter membrane to a dialysis bag. Place the bag in distilled water and change the distilled water every six hours for a total of 24 hours. Centrifuge the dialysate. Freeze the supernatant at low temperature and freeze it in a freeze dryer for 12 hours. Grind to obtain carbon quantum dots. Step A5: 0.3285 mmol p-phenylenediamine, 0.099 mmol dialdehyde pyridylthiophene anthracene, 30 mg carbon quantum dots and 7.5 mL N,N-dimethylformamide were added to a weighing bottle and sonicated for 25 min. Then, 0.45 mL of 8 mol / L acetic acid aqueous solution was added and sonicated for 10 min. The mixture was transferred to a reaction tube and subjected to three freeze-thaw cycles under liquid nitrogen. The reaction was carried out at 120 °C for 24 h, at 130 °C for 24 h, and at 140 °C for 48 h. After cooling, the precipitate was collected by centrifugation, washed 6 times with acetone, freeze-dried for 12 h, and ground to obtain thiophene pyridyl anthracene COFs-supported carbon quantum dots. Step A6: Weigh 25 parts by weight of thiophenepyridine anthracene COFs-supported carbon quantum dots and 7.5 parts by weight of multi-walled carbon nanotubes for later use; the multi-walled carbon nanotubes have a diameter of 10-30 nm and a length of 1-2 μm. Step A7: Mix thiophenepyridine anthracene COFs-loaded carbon quantum dots and multi-walled carbon nanotubes to obtain a multi-element doped modified carbon-based composite material.

[0027] Example 3:

[0028] This embodiment describes a method for preparing a multi-element doped modified carbon-based composite material, including the following steps: Step A1: 2 mmol of 9,10-dibromoanthracene, 5 mmol of 5-bromothiophene-2-boric acid, 6 mmol of anhydrous sodium carbonate, 0.1 mmol of tetrakis(triphenylphosphine)palladium and 90 mL of N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 20 min. The reaction was carried out at 100 °C for 10 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromothiophene anthracene. Step A2: 2 mmol of dibromothiophene anthracene, 5 mmol of 2-bromopyridine-5-boric acid, 6 mmol of anhydrous sodium carbonate, 0.1 mmol of tetrakis(triphenylphosphine)palladium and 90 mL of N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 20 min. The reaction was carried out at 100 °C for 12 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromopyridinethiophene anthracene. Step A3: 2 mmol of dibromopyridylthiophene anthracene, 5 mmol of 3,5-dicarboxyphenylboronic acid, 75 mL of 1,4-dioxane and 25 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred for 10 min, and 20 mL of 2 mol / L potassium carbonate aqueous solution was added dropwise. The mixture was purged with nitrogen three times. 0.3 mmol of tetrakis(triphenylphosphine)palladium was added and stirred for 10 min. The mixture was stirred at 100 °C for 24 h. The mixture was filtered, and the residue was washed with ethyl acetate to obtain dialdehydepyridylthiophene anthracene. Step A4: Add 2g chitosan, 200mL of 1% acetic acid aqueous solution and 1g cellulase to a three-necked flask equipped with a thermometer and stirrer. Stir for 10min and enzymatically hydrolyze at 50℃ for 4h. Adjust the pH to 5 with 0.1mol / L sodium hydroxide aqueous solution. Centrifuge. Add the supernatant, 1g anhydrous citric acid and 20mL deionized water to a beaker. Add 0.2g sodium dodecyl sulfate and sonicate for 30min. Transfer to a high-pressure reactor. Purge with nitrogen three times. React at 120℃ for 2h, 160℃ for 2h, and 180℃ for 4h. Cool and transfer through a filter membrane to a dialysis bag. Place in distilled water and change the distilled water every six hours for a total of 24h. Centrifuge the dialysate. Freeze the supernatant at low temperature and freeze-dry in a freeze dryer for 12h. Grind to obtain carbon quantum dots. Step A5: Add 0.438 mmol of p-phenylenediamine, 0.132 mmol of dialdehyde pyridylthiophene anthracene, 40 mg of carbon quantum dots and 10 mL of N,N-dimethylformamide to a weighing bottle, sonicate for 30 min, add 0.6 mL of 8 mol / L acetic acid aqueous solution, sonicate for 10 min, transfer to a reaction tube, freeze-thaw three times under liquid nitrogen vacuum, react at 120 °C for 24 h, react at 130 °C for 24 h, react at 140 °C for 48 h, cool, centrifuge to collect the precipitate, wash with acetone 7 times, freeze-dry for 12 h, grind to obtain thiophene pyridyl anthracene COFs supported carbon quantum dots; Step A6: Weigh out 30 parts by weight of thiophenepyridine anthracene COFs-loaded carbon quantum dots and 10 parts by weight of multi-walled carbon nanotubes for later use; the diameter of the multi-walled carbon nanotubes is 10-30 nm and the length is 1-2 μm. Step A7: Mix thiophenepyridine anthracene COFs-loaded carbon quantum dots and multi-walled carbon nanotubes to obtain a multi-element doped modified carbon-based composite material.

[0029] Comparative Example 1: This comparative example illustrates a method for preparing a multi-element doped modified carbon-based composite material, comprising the following steps: Step A1: 2 mmol of 9,10-dibromoanthracene, 5 mmol of 5-bromothiophene-2-boric acid, 6 mmol of anhydrous sodium carbonate, 0.1 mmol of tetrakis(triphenylphosphine)palladium and 90 mL of N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 20 min. The reaction was carried out at 100 °C for 10 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromothiophene anthracene. Step A2: 2 mmol of dibromothiophene anthracene, 5 mmol of 3,5-dicarboxyphenylboronic acid, 75 mL of 1,4-dioxane and 25 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred for 10 min, and 20 mL of 2 mol / L potassium carbonate aqueous solution was added dropwise. The mixture was purged with nitrogen three times. 0.3 mmol of tetrakis(triphenylphosphine)palladium was added and stirred for 10 min. The mixture was stirred at 100 °C for 24 h. The mixture was filtered, and the residue was washed with ethyl acetate to obtain dialdehyde thiophene anthracene. Step A3: Add 2g chitosan, 200mL of 1% acetic acid aqueous solution and 1g cellulase to a three-necked flask equipped with a thermometer and stirrer. Stir for 10min and enzymatically hydrolyze at 50℃ for 4h. Adjust the pH to 5 with 0.1mol / L sodium hydroxide aqueous solution. Centrifuge. Add the supernatant, 1g anhydrous citric acid and 20mL deionized water to a beaker. Add 0.2g sodium dodecyl sulfate and sonicate for 30min. Transfer to a high-pressure reactor. Purge with nitrogen three times. React at 120℃ for 2h, 160℃ for 2h, and 180℃ for 4h. Cool and transfer through a filter membrane to a dialysis bag. Place in distilled water and change the distilled water every six hours for a total of 24h. Centrifuge the dialysate. Freeze the supernatant at low temperature and freeze it in a freeze dryer for 12h. Grind to obtain carbon quantum dots. Step A4: Add 0.438 mmol p-phenylenediamine, 0.132 mmol dialdehyde thiophene anthracene, 40 mg carbon quantum dots and 10 mL N,N-dimethylformamide to a weighing bottle, sonicate for 30 min, add 0.6 mL 8 mol / L acetic acid aqueous solution, sonicate for 10 min, transfer to a reaction tube, freeze-thaw three times under liquid nitrogen vacuum, react at 120 °C for 24 h, react at 130 °C for 24 h, react at 140 °C for 48 h, cool, centrifuge to collect the precipitate, wash with acetone 7 times, freeze-dry for 12 h, grind to obtain thiophene anthracene COFs-loaded carbon quantum dots; Step A5: Weigh out 30 parts by weight of thienyl anthracene COFs-supported carbon quantum dots and 10 parts by weight of multi-walled carbon nanotubes for later use; the diameter of the multi-walled carbon nanotubes is 10-30 nm and the length is 1-2 μm. Step A6: Mix thiophene anthracene-based COFs-loaded carbon quantum dots and multi-walled carbon nanotubes to obtain a multi-element doped modified carbon-based composite material.

[0030] Comparative Example 2: This comparative example illustrates a method for preparing a multi-element doped modified carbon-based composite material, comprising the following steps: Step A1: 2 mmol of 9,10-dibromoanthracene, 5 mmol of 5-bromopyridine-2-boric acid, 6 mmol of anhydrous sodium carbonate, 0.1 mmol of tetrakis(triphenylphosphine)palladium and 90 mL of N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 20 min. The reaction was carried out at 100 °C for 10 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromopyridine anthracene. Step A2: 2 mmol of dibromopyridinyl anthracene, 5 mmol of 3,5-dicarboxyphenylboronic acid, 75 mL of 1,4-dioxane and 25 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred for 10 min, and 20 mL of 2 mol / L potassium carbonate aqueous solution was added dropwise. The mixture was purged with nitrogen three times. 0.3 mmol of tetrakis(triphenylphosphine)palladium was added and stirred for 10 min. The mixture was stirred at 100 °C for 24 h. The mixture was filtered, and the residue was washed with ethyl acetate to obtain dialdehydepyridinyl anthracene. Step A3: Add 2g chitosan, 200mL of 1% acetic acid aqueous solution and 1g cellulase to a three-necked flask equipped with a thermometer and stirrer. Stir for 10min and enzymatically hydrolyze at 50℃ for 4h. Adjust the pH to 5 with 0.1mol / L sodium hydroxide aqueous solution. Centrifuge. Add the supernatant, 1g anhydrous citric acid and 20mL deionized water to a beaker. Add 0.2g sodium dodecyl sulfate and sonicate for 30min. Transfer to a high-pressure reactor. Purge with nitrogen three times. React at 120℃ for 2h, 160℃ for 2h, and 180℃ for 4h. Cool and transfer through a filter membrane to a dialysis bag. Place in distilled water and change the distilled water every six hours for a total of 24h. Centrifuge the dialysate. Freeze the supernatant at low temperature and freeze it in a freeze dryer for 12h. Grind to obtain carbon quantum dots. Step A4: Add 0.438 mmol p-phenylenediamine, 0.132 mmol dialdehyde pyridine anthracene, 40 mg carbon quantum dots and 10 mL N,N-dimethylformamide to a weighing bottle, sonicate for 30 min, add 0.6 mL 8 mol / L acetic acid aqueous solution, sonicate for 10 min, transfer to a reaction tube, freeze-thaw three times under liquid nitrogen vacuum, react at 120 °C for 24 h, react at 130 °C for 24 h, react at 140 °C for 48 h, cool, centrifuge to collect the precipitate, wash with acetone 7 times, freeze-dry for 12 h, grind to obtain pyridine anthracene COFs supported carbon quantum dots; Step A5: Weigh out 30 parts by weight of pyridine anthraquinone COFs-loaded carbon quantum dots and 10 parts by weight of multi-walled carbon nanotubes for later use; the diameter of the multi-walled carbon nanotubes is 10-30 nm and the length is 1-2 μm. Step A6: Mix pyridine anthracene COFs-loaded carbon quantum dots and multi-walled carbon nanotubes to obtain a multi-element doped modified carbon-based composite material.

[0031] Comparative Example 3: This comparative example illustrates a method for preparing a multi-element doped modified carbon-based composite material, comprising the following steps: Step A1: 2 mmol of 9,10-dibromoanthracene, 5 mmol of 5-bromothiophene-2-boric acid, 6 mmol of anhydrous sodium carbonate, 0.1 mmol of tetrakis(triphenylphosphine)palladium and 90 mL of N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 20 min. The reaction was carried out at 100 °C for 10 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromothiophene anthracene. Step A2: 2 mmol of dibromothiophene anthracene, 5 mmol of 2-bromopyridine-5-boric acid, 6 mmol of anhydrous sodium carbonate, 0.1 mmol of tetrakis(triphenylphosphine)palladium and 90 mL of N,N-dimethylformamide were added to a four-necked flask equipped with a thermometer, stirrer and reflux condenser. Nitrogen gas was introduced for protection, and the mixture was stirred for 20 min. The reaction was carried out at 100 °C for 12 h. After cooling, the mixture was extracted three times with ethyl acetate. The organic phases were combined and washed five times with saturated brine. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was evaporated to dryness under reduced pressure. The solution was purified by silica gel column chromatography using a petroleum ether / dichloromethane mixed solvent (petroleum ether to dichloromethane volume ratio of 1:1) as the eluent to obtain dibromopyridinethiophene anthracene. Step A3: 2 mmol of dibromopyridylthiophene anthracene, 5 mmol of 3,5-dicarboxyphenylboronic acid, 75 mL of 1,4-dioxane and 25 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer and a thermometer. The mixture was stirred for 10 min, and 20 mL of 2 mol / L potassium carbonate aqueous solution was added dropwise. The mixture was purged with nitrogen three times. 0.3 mmol of tetrakis(triphenylphosphine)palladium was added and stirred for 10 min. The mixture was stirred at 100 °C for 24 h. The mixture was filtered, and the residue was washed with ethyl acetate to obtain dialdehydepyridylthiophene anthracene. Step A4: Add 0.438 mmol of p-phenylenediamine, 0.132 mmol of dialdehyde pyridylthiophene anthracene, and 10 mL of N,N-dimethylformamide to a weighing bottle, sonicate for 30 min, add 0.6 mL of 8 mol / L acetic acid aqueous solution, sonicate for 10 min, transfer to a reaction tube, freeze-thaw three times under liquid nitrogen vacuum, react at 120 °C for 24 h, react at 130 °C for 24 h, react at 140 °C for 48 h, cool, centrifuge to collect the precipitate, wash with acetone 7 times, freeze-dry for 12 h, grind to obtain thiophene pyridyl anthracene COFs; Step A5: Weigh out 30 parts by weight of thiophenepyridine anthracene COFs and 10 parts by weight of multi-walled carbon nanotubes for later use; the diameter of the multi-walled carbon nanotubes is 10-30 nm and the length is 1-2 μm. Step A6: Mix thiophenepyridine anthracene COFs-loaded carbon quantum dots and multi-walled carbon nanotubes to obtain a multi-element doped modified carbon-based composite material.

[0032] Performance testing: The carbon-based composite materials of Examples 1-3 and Comparative Examples 1-3, carboxymethyl cellulose, and acetylene black were mixed in a mass ratio of 7:2:1. Deionized water was added and the mixture was ground into a slurry. The slurry was then evenly coated onto copper foil using a scraper, with an electrode surface loading of 1 mg / cm². 2 The copper foil was placed in a drying oven and vacuum dried at 80°C for 12 hours. The electrode sheet was then cut into Φ14mm specifications. A half-cell was obtained by using a Φ16mm sodium sheet as the counter electrode, glass fiber as the separator, and 1mol / L sodium perchlorate solution (a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) as the electrolyte and assembling the cells using a CR2016 coin cell casing. Cyclic performance tests were conducted on the half-cells of Examples 1-3 and Comparative Examples 1-3 at a current density of 1 A / g, with 100 cycles per cell. Rate performance tests were conducted on the half-cells of Examples 1-3 and Comparative Examples 1-3 at current densities of 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, and 5 A / g.

[0033] Referring to the table above, based on the comparison between Examples 1-3 and Comparative Examples 1-3, it can be seen that the carbon-based composite material prepared by adding thiophenepyridine anthracene COFs to support carbon quantum dots has good cycling performance and rate performance. Based on the comparison between Example 3 and Comparative Example 1, it can be seen that the discharge specific capacity of the carbon-based composite material prepared by adding thiophenepyridine anthracene COFs loaded with carbon quantum dots after 100 cycles is higher than that of the carbon-based composite material prepared by adding thiophenepyridine anthracene COFs loaded with carbon quantum dots after 100 cycles. This indicates that adding thiophenepyridine anthracene COFs loaded with carbon quantum dots can improve the cycling performance of carbon-based composite materials. Based on the comparison between Example 3 and Comparative Example 2, it can be seen that the discharge specific capacity of the carbon-based composite material prepared by adding thiophenepyridine anthracene COFs loaded with carbon quantum dots after 100 cycles is higher than that of the carbon-based composite material prepared by adding pyridine anthracene COFs loaded with carbon quantum dots after 100 cycles. This indicates that adding thiophenepyridine anthracene COFs loaded with carbon quantum dots can improve the cycling performance of carbon-based composite materials. Based on the comparison between Example 3 and Comparative Example 3, it can be seen that the discharge specific capacity of the carbon-based composite material prepared by adding thiophenepyridine anthracene COFs to support carbon quantum dots is higher than that of the carbon-based composite material prepared by adding thiophenepyridine anthracene COFs to support carbon quantum dots after 100 cycles. This indicates that adding thiophenepyridine anthracene COFs to support carbon quantum dots can improve the cycling performance of carbon-based composite materials.

[0034] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0035] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. A multi-element doped modified carbon-based composite material, characterized in that, Includes the following components by weight: Thiophenepyridine anthracene COFs supported on 20-30 parts of carbon quantum dots and 5-10 parts of multi-walled carbon nanotubes; The thiophenepyridine anthracene COFs-loaded carbon quantum dots are prepared by the following steps: Step A1: 9,10-dibromoanthracene, 5-bromothiophene-2-boronic acid, anhydrous sodium carbonate, tetrakis(triphenylphosphine)palladium and N,N-dimethylformamide are stirred and reacted to obtain dibromothiophene anthracene; Step A2: Dibromothiophene anthracene, 2-bromopyridin-5-boronic acid, anhydrous sodium carbonate, tetrakis(triphenylphosphine)palladium and N,N-dimethylformamide are stirred and reacted to obtain dibromopyridinylthiophene anthracene; Step A3: Dibromopyridylthiophene anthracene, 3,5-dicarboxyphenylboronic acid, 1,4-dioxane and N,N-dimethylformamide are stirred, potassium carbonate aqueous solution is added, tetrakis(triphenylphosphine)palladium is added and stirred to react, and dialdehydepyridylthiophene anthracene is obtained. Step A4: Stir chitosan, aqueous acetic acid solution and cellulase to enzymatically hydrolyze the mixture, and then sonicate it with anhydrous citric acid, deionized water and sodium dodecyl sulfate to react and obtain carbon quantum dots; Step A5: Sonicate p-phenylenediamine, dialdehyde pyridylthiophene anthracene, carbon quantum dots and N,N-dimethylformamide, add aqueous acetic acid solution and sonicate to react, to obtain thiophene pyridyl anthracene COFs supported carbon quantum dots.

2. The multi-element doped modified carbon-based composite material according to claim 1, characterized in that, The ratio of 9,10-dibromoanthracene, 5-bromothiophene-2-boronic acid, anhydrous sodium carbonate, tetra(triphenylphosphine)palladium, and N,N-dimethylformamide in step A1 is 1-2 mmol: 2.5-5 mmol: 3-6 mmol: 0.05-0.1 mmol: 45-90 mL.

3. The multi-element doped modified carbon-based composite material according to claim 1, characterized in that, The ratio of dibromothienylanthracene, 2-bromopyridine-5-boronic acid, anhydrous sodium carbonate, tetra(triphenylphosphine)palladium, and N,N-dimethylformamide in step A2 is 1-2 mmol: 2.5-5 mmol: 3-6 mmol: 0.05-0.1 mmol: 45-90 mL.

4. The multi-element doped modified carbon-based composite material according to claim 1, characterized in that, The ratio of dibromopyridylthiophene anthracene, 3,5-dicarboxyphenylboronic acid, 1,4-dioxane, N,N-dimethylformamide, potassium carbonate aqueous solution, and tetra(triphenylphosphine)palladium in step A3 is 1-2 mmol: 2.5-5 mmol: 37.5-75 mL: 12.5-25 mL: 10-20 mL: 0.15-0.3 mmol.

5. The multi-element doped modified carbon-based composite material according to claim 1, characterized in that, The molar concentration of the potassium carbonate aqueous solution mentioned in step A3 is 2 mol / L.

6. The multi-element doped modified carbon-based composite material according to claim 1, characterized in that, The ratio of chitosan, acetic acid aqueous solution, cellulase, anhydrous citric acid, deionized water and sodium dodecyl sulfate in step A4 is 1-2g: 100-200mL: 0.5-1g: 0.5-1g: 10-20mL: 0.1-0.2g.

7. The multi-element doped modified carbon-based composite material according to claim 1, characterized in that, The acetic acid aqueous solution in step A4 has a mass fraction of 1%.

8. The multi-element doped modified carbon-based composite material according to claim 1, characterized in that, The ratio of p-phenylenediamine, dialdehyde pyridylthiophene anthracene, carbon quantum dots, N,N-dimethylformamide, and aqueous acetic acid in step A5 is 0.219-0.438 mmol : 0.066-0.132 mmol : 20-40 mg : 5-10 mL : 0.3-0.6 mL.

9. The multi-element doped modified carbon-based composite material according to claim 1, characterized in that, The molar concentration of the acetic acid aqueous solution in step A5 is 8 mol / L.

10. A method for preparing a multi-element doped modified carbon-based composite material, characterized in that, The method for preparing the multi-element doped modified carbon-based composite material as described in any one of claims 1-9 includes the following steps: Step 1: Weigh 20-30 parts by weight of thiophenepyridine anthracene COFs-supported carbon quantum dots and 5-10 parts by weight of multi-walled carbon nanotubes, and set aside; the multi-walled carbon nanotubes have a diameter of 10-30 nm and a length of 1-2 μm. Step 2: Thiophenepyridine anthracene COFs-loaded carbon quantum dots and multi-walled carbon nanotubes are mixed to obtain multi-element doped modified carbon-based composite materials.

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