An oxygen-rich 3D covalent organic framework@carbon nanotube composite material, a preparation method and application thereof

Abstract

The application belongs to the field of energy storage / photovoltaic conversion, and relates to an oxygen-rich 3D covalent organic framework@carbon nanotube composite material and a preparation method and application thereof. The preparation method of the oxygen-rich 3D covalent organic framework@carbon nanotube composite material comprises the following steps: S1. carbon nanotube pretreatment: linking carboxyl and amino groups to carbon nanotubes to obtain modified carbon nanotubes; S2. interface self-assembly: dispersing the modified carbon nanotubes in water to form an aqueous phase, dispersing a tetrahedral monomer and an oxygen-containing diamine monomer in an organic solvent to form an oil phase, mixing the aqueous phase and the oil phase, and then performing in-situ growth-interface crosslinking reaction on the obtained Pickering emulsion, and then filtering, washing and drying the obtained reaction product to obtain the oxygen-rich 3D covalent organic framework@carbon nanotube composite material. The oxygen-rich 3D covalent organic framework@carbon nanotube composite material obtained by the above method has good conductivity and is conducive to improving the cycle capacity retention rate of a battery.

Description

Technical Field

[0001] This invention belongs to the field of energy storage / photovoltaic conversion, specifically relating to an oxygen-rich 3D covalent organic framework@carbon nanotube composite material, its preparation method, and its application. Background Technology

[0002] In the field of energy storage and photoelectric conversion materials, covalent organic frameworks (COFs) have shown great potential in catalysis, gas adsorption, and energy storage due to their highly ordered pore structure and abundant active sites. Currently, researchers mainly explore applications using two-dimensional layered COF materials (2DCOFs). These materials are typically constructed through dynamic covalent bonds such as imine bonds and borate ester bonds, forming a layered stacked structure.

[0003] Although these 2D COFs possess high specific surface area and well-defined pores, significant limitations have been observed in practical electrochemical applications. First, due to π-π stacking, the COF layers are tightly packed, burying approximately 40%–60% of the theoretical active sites. This hinders electrolyte wetting and limits the exposure and utilization of active sites. Second, this two-dimensional structure is prone to interlayer slip during electrochemical processes, further reducing the accessibility of active sites and leading to structural collapse during long-term electrochemical cycling, resulting in performance degradation. Studies show that the electrochemical active area of ​​traditional 2D COF materials is typically only 30%–50% of the theoretical value. Furthermore, most of these organic framework materials are composed of organic units linked by covalent bonds, and are themselves semiconductors or insulators with low electron mobility, generally exhibiting poor conductivity and lithium-ion conduction performance. This makes it difficult to meet the requirements for efficient charge transport, significantly reducing cycle capacity retention when applied to batteries, severely limiting their effectiveness in electrochemical applications.

[0004] Existing technologies have recognized that introducing carbon nanotubes (CNTs) into COF materials can improve conductivity, but the resulting conductive networks have significant drawbacks. Firstly, current techniques typically employ physical mixing methods to introduce CNTs, which leads to uneven CNT distribution and the formation of conductive "islands." Secondly, the interface between COF and CNTs is insufficient, resulting in high interfacial resistance (typically >50 Ω·cm). 2Electrochemical impedance spectroscopy (EIS) shows that the charge transfer resistance of existing COF / CNT composites is an order of magnitude higher than the ideal value. Secondly, most existing COF / CNT composites employ basic imine or borate ester-bonded COF structures, lacking functionalization designs for specific electrochemical reactions. Taking the oxygen reduction reaction as an example, unmodified COF materials have insufficient catalytic active site density and lack suitable electronic structures to optimize the adsorption energy of oxygen intermediates. This directly leads to low intrinsic catalytic activity, typically requiring noble metal doping to meet practical requirements. The main reasons for this deficiency are: on the one hand, existing synthesis methods struggle to introduce active functional groups while maintaining COF crystallinity; on the other hand, conventional post-modification methods easily disrupt the COF framework structure, leading to decreased porosity. Studies show that these technical deficiencies are mutually reinforcing: the two-dimensional structure results in insufficient active sites, which in turn leads to insufficient catalytic activity in electrochemical processes. This deficiency forces researchers to increase the noble metal loading, which further deteriorates the uniformity of the conductive network; while stringent synthesis conditions limit the designability of the material structure, making functionalization difficult to implement. This technical dilemma makes it difficult to balance performance and cost in existing COF composite materials, which seriously hinders their practical application.

[0005] For example, CN117568861A discloses a method of combining COF and CNT to obtain COF / CNT composite materials through physical mixing or in-situ polymerization, utilizing the conductive network of CNTs to partially alleviate the insulation problem of COF. However, this COF / CNT composite material still has significant limitations: (1) Structural limitations: the interlayer π-π stacking of 2D-COF leads to the burial of active sites, and the rigid layered structure easily hinders electrolyte mass transfer; (2) Insufficient interfacial contact: the physical mixing method makes it difficult to achieve molecular-level coupling between COF and CNT, resulting in low interfacial charge transport efficiency; (3) Functional limitations: traditional COFs lack oxygen-rich functional group design, resulting in insufficient catalytic activity for key electrochemical processes such as oxygen reduction reaction (ORR). More seriously, during electrochemical cycling, this imperfect conductive network is prone to local breakage, leading to rapid performance degradation and reduced cycle capacity retention. Summary of the Invention

[0006] The primary objective of this invention is to overcome the shortcomings of existing methods in producing covalent organic framework@carbon nanotube composite materials with poor conductivity and poor battery cycle capacity retention. Instead, this invention provides a novel method for preparing oxygen-enriched 3D covalent organic framework@carbon nanotube composite materials. The oxygen-enriched 3D covalent organic framework@carbon nanotube composite materials obtained by this method exhibit good conductivity and are beneficial for improving battery cycle capacity retention.

[0007] The second objective of this invention is to provide an oxygen-rich 3D covalent organic framework@carbon nanotube composite material prepared by the above method.

[0008] A third objective of this invention is to provide the application of the above-mentioned oxygen-rich 3D covalent organic framework@carbon nanotube composite material in battery cathode materials.

[0009] The preparation method of the oxygen-rich 3D covalent organic framework@carbon nanotube composite material provided by the present invention includes the following steps:

[0010] S1. Carbon nanotube pretreatment: Carboxyl and amino groups are bonded to carbon nanotubes to obtain modified carbon nanotubes;

[0011] S2. Interface self-assembly: Modified carbon nanotubes are dispersed in water to form an aqueous phase, and tetrahedral monomers and oxygen-containing diamine monomers are dispersed in an organic solvent to form an oil phase. The aqueous and oil phases are mixed, and the resulting Pickering emulsion is subjected to an in-situ growth-interfacial crosslinking reaction. The resulting reaction product is then filtered, washed, and dried to obtain an oxygen-rich 3D covalent organic framework@carbon nanotube composite material.

[0012] The key to this invention lies in simultaneously modifying nanotubes with carboxyl and amino groups, and forming a carbon nanotube framework (COF) through in-situ growth and interfacial crosslinking reactions using tetrahedral monomers and oxygen-containing diamine monomers. This allows for the construction of an oxygen-rich 3D covalent organic framework@carbon nanotube composite material with a three-dimensional interpenetrating network structure, thereby improving conductivity and cycle capacity retention in lithium-ion batteries. The reason for this is speculated to be twofold: First, the carboxyl and amino groups on the surface of carbon nanotubes can undergo dehydration condensation reactions to form carbon nanotube bonds. The tetrahedral monomers and oxygen-containing diamine monomers can form an oxygen-rich COF framework through dynamic covalent reactions. Simultaneously, the carboxyl groups on the surface of carbon nanotubes can react with the active groups of the oxygen-containing diamine monomers, such as hydroxyl groups, to bond the carbon nanotube bonds to the oxygen-rich COF framework, thus forming an oxygen-rich 3D covalent organic framework@carbon nanotube composite material with an interpenetrating network structure. Second, using the tetrahedral monomers and oxygen-containing diamine monomers as COF synthesis monomers allows for the use of Pickering emulsions. Templates are used to stabilize the oil-water interface by utilizing the amphiphilic properties of modified carbon nanotubes (modified hydrophobically / hydrophilically). COFs are then assembled on the surface of emulsion droplets to form a three-dimensional continuous conductive network. The resulting oxygen-rich 3D covalent organic framework@carbon nanotube composite material possesses a three-dimensional interpenetrating network structure. The open three-dimensional channels increase the exposure of active sites from 30-50% in traditional materials to 85-95%, improving the utilization rate of active sites by 2-3 times. This increases electrolyte permeability by over 80%. The formation of the interpenetrating network structure significantly enhances structural stability, allowing the material to retain over 92% of its initial capacity after 10,000 charge-discharge cycles, far superior to the 65-70% of 2D COF materials. Tetrahedral monomers and oxygen-containing diamine monomers are used as COF synthesis monomers, assembled on the surface of emulsion droplets using a Pickering emulsion template. Modified carbon nanotubes act as interface stabilizers, guiding the COF monomers to undergo imide condensation and interfacial condensation reactions along the droplet surface to form 3D-OCOF (structure as shown). Figure 1 As shown in the figure, the upper figure is a schematic diagram of the topological framework of 3D-OCOF, and the lower figure is a schematic diagram of the structure of 3D-OCOF. The obtained 3D-OCOF has a hierarchical pore structure consisting of main channels with a pore size distribution of 1.2 nm to 2.8 nm and micropores with a pore size distribution of 0.5 nm to 0.8 nm. Each unit in the framework contains 2.5 to 3.5 hydroxyl / carbonyl functional groups, and the specific surface area reaches 1200 to 1800 m². 2 / g, this special porous structure can increase the lithium-ion diffusion coefficient to 2.3×10 -9The COF is above cm² / s, an order of magnitude higher than that of traditional materials. COF is synthesized using tetrahedral monomers and oxygen-containing diamine monomers. The introduction of oxygen-rich functional groups in tetrahedral monomers and oxygen-containing diamines can enhance catalytic activity. Hydroxyl / carbonyl functional groups can significantly reduce the oxygen reduction overpotential, and the oxygen-rich environment can significantly improve the selectivity of electron transfer pathways, effectively suppressing side reactions. The oxygen-containing groups in the oxygen-containing diamine monomers can form a stable bilayer structure with the electrolyte, enhancing interfacial stability and significantly reducing interfacial impedance. These changes are all beneficial to improving the battery's cycle capacity retention rate. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of 3D-OCOF in the oxygen-rich 3D covalent organic framework@carbon nanotube composite material obtained by the method provided in this invention;

[0014] Figure 2 This is a scanning electron microscope (SEM) image of the oxygen-enriched 3D covalent organic framework@carbon nanotube composite material obtained in Example 1. Detailed Implementation

[0015] The preparation method of the oxygen-enriched 3D covalent organic framework@carbon nanotube composite material provided by this invention includes the following steps: S1. Carbon nanotube pretreatment: Carboxyl and amino groups are bonded to carbon nanotubes to obtain modified carbon nanotubes; S2. Interface self-assembly: Modified carbon nanotubes are dispersed in water to form an aqueous phase, tetrahedral monomers and oxygen-containing diamine monomers are dispersed in an organic solvent to form an oil phase, the aqueous phase and oil phase are mixed, and the resulting Pickering emulsion is subjected to an in-situ growth-interfacial crosslinking reaction. The resulting reaction product is then filtered, washed, and dried to obtain the oxygen-enriched 3D covalent organic framework@carbon nanotube composite material. Using the above method to prepare the oxygen-enriched 3D covalent organic framework@carbon nanotube composite material, the modified carbon nanotubes can act as an interface stabilizer, and the COF forming monomers can undergo imine bond condensation and interfacial condensation reactions on the surface of the emulsion droplets using the Pickering emulsion template, thereby simultaneously constructing a 3D-COF framework and COF-CNT covalent connections.

[0016] In this invention, the diameter of the carbon nanotube is preferably 10nm to 20nm, such as 10nm, 12nm, 14nm, 16nm, 18nm, 20nm or any value between them; the length is preferably 5μm to 15μm, such as 5μm, 8μm, 10μm, 12μm, 15μm or any value between them.

[0017] In this invention, the content of carboxyl groups in the modified carbon nanotubes is preferably 1.5 to 3.0 mmol / g, such as 1.5 mmol / g, 1.8 mmol / g, 2.1 mmol / g, 2.4 mmol / g, 2.7 mmol / g, 3.0 mmol / g, or any value between them; the density of amino groups is preferably 0.4 to 1.4 mmol / g, such as 0.4 mmol / g, 0.6 mmol / g, 0.8 mmol / g, 1.0 mmol / g, 1.2 mmol / g, 1.4 mmol / g, or any value between them.

[0018] In this invention, in step S1, the modified carbon nanotubes are preferably prepared by the following method: carbon nanotubes are ultrasonically treated in an acid solution to bond carboxyl groups to the surface of the carbon nanotubes; the resulting carboxyl-based carbon nanotubes are then coupled with an aminosilane coupling agent to bond amino groups to the surface of the carboxyl-based carbon nanotubes. The resulting product is the modified carbon nanotube. The acid solution is preferably a mixture of sulfuric acid and nitric acid. The molar ratio of sulfuric acid to nitric acid in the mixture is preferably (2–4):1, such as 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, or any value between them. The aminosilane coupling agent preferably contains both amino and alkoxy groups, and can be selected from at least one of 3-aminopropyltriethoxysilane (APTES), N-aminoethyl-γ-aminopropyltrimethoxysilane (KH-792), and N-phenyl-γ-aminopropyltrimethoxysilane (KH-370). The aminosilane coupling agent can generate silanol (Si-OH) through hydrolysis, which then undergoes a condensation reaction with oxygen-containing groups (such as carboxyl groups, hydroxyl groups, etc.) on the surface of carbon nanotubes to form a stable covalent bond (Si-OC), thereby grafting the amino group (-NH2) onto the surface of the carbon nanotubes.

[0019] In this invention, in step S1, the conditions for ultrasonic treatment preferably include a temperature of 20℃ to 45℃, such as 20℃, 22℃, 25℃, 28℃, 30℃, 32℃, 35℃, 38℃, 40℃, 42℃, 45℃ or any value between them; and a time of 1h to 5h, such as 1h, 2h, 3h, 4h, 5h or any value between them.

[0020] In this invention, in step S1, the coupling reaction conditions preferably include a temperature of 70°C to 90°C, such as 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, or any value between them; and a time of 10h to 15h, such as 10h, 11h, 12h, 13h, 14h, 15h, or any value between them.

[0021] In this invention, in step S2, the weight ratio of the modified carbon nanotubes in the aqueous phase to the total weight of the tetrahedral monomers and oxydiamine monomers in the oil phase is preferably 100:(1-100), such as 100:1, 100:5, 100:10, 100:15, 100:20, 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90, 100:100, or any value between them. The molar ratio of the tetrahedral monomers to the oxydiamine monomers is preferably (0.4-0.6):1, such as 0.4:1, 0.42:1, 0.45:1, 0.48:1, 0.5:1, 0.52:1, 0.55:1, 0.58:1, 0.6:1, or any value between them.

[0022] In this invention, in step S2, the tetrahedral monomer may include at least one of tetra(4-formylphenyl)methane, tetra(4-formylphenyl)silane, and 1,2,4,5-tetra(4-formylphenyl)benzene. The oxydiamine monomer must simultaneously contain an amino group and a hydroxyl group and / or a hydroxyl precursor, wherein the hydroxyl precursor refers to a group that can be converted into a hydroxyl group under in-situ growth-interfacial crosslinking reaction conditions. Examples of the oxydiamine monomer include at least one of 2,5-diaminophenyl-1,4-diphenol, 2,5-methoxy-terephthalic acid dihydrazide, 2,5-disulfonic acid p-phenylenediamine, and 2,5-diethoxyphenyl-1,4-di(formylhydrazide).

[0023] In this invention, in step S2, the conditions for the in-situ growth-interface crosslinking reaction preferably include a temperature of 70℃ to 90℃, such as 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, or any value between them; and a time of 10h to 72h, such as 10h, 15h, 18h, 20h, 24h, 28h, 32h, 36h, 48h, 72h, or any value between them. The inventors of this invention have discovered that when the in-situ growth-interface crosslinking reaction time is controlled within 10h to 72h, the pore size distribution of the oxygen-rich 3D covalent organic framework@carbon nanotube composite material can be narrowed, and its stability improved. When the in-situ growth-interface crosslinking reaction time exceeds 72h, the material's cycle life will decrease due to partial framework collapse. Therefore, controlling the in-situ growth-interface crosslinking reaction time within 10h to 72h is more beneficial for improving battery cycle life.

[0024] In this invention, the in-situ growth-interfacial crosslinking reaction is preferably carried out in the presence of an acid catalyst. The acid catalyst can be a strong acid or a weak acid, preferably a weak acid. Examples of strong acids include concentrated sulfuric acid and trifluoroacetic acid. Using a strong acid as a catalyst not only corrodes the reaction equipment, increasing production costs (equipment investment increases by approximately 35%), but also generates a large amount of acidic waste liquid during post-processing, increasing treatment costs. More importantly, because the COF growth mechanism relies excessively on acid-catalyzed dynamic covalent chemistry and lacks precise control over the nucleation-growth process under mild conditions, strong acid conditions can also affect the orderly growth of COF and cause partial degradation, increasing batch-to-batch variability (performance fluctuations between batches can reach ±15%). Examples of weak acid catalysts include at least one of p-toluenesulfonic acid, acetic acid, scandium trifluoromethanesulfonate, and trifluoroacetic acid. When a weak acid is used as a catalyst, it not only promotes the orderly growth of COF and gives the battery better cycle capacity retention, but also makes the reaction conditions milder, reduces equipment corrosion, and has high atom economy, with raw material utilization exceeding 85% and waste reduction exceeding 70%. Furthermore, the dosage of the weak acid catalyst should be such that its concentration in the system is 0.01–0.1 mol / L (e.g., 0.01, 0.02, 0.04, 0.06, 0.08, 0.1 mol / L or any value between them).

[0025] In this invention, the in-situ growth-interfacial crosslinking reaction is preferably carried out in the presence of trace amounts of water. This provides controllable hydrolytic groups, promoting interfacial bonding because water molecules regulate the hydrolysis rate and enhance the strength of interfacial chemical bonds. The amount of water used is preferably 0.2–1 vol.%, such as 0.2 vol.%, 0.4 vol.%, 0.6 vol.%, 0.8 vol.%, 1 vol.%, or any value between these values.

[0026] In this invention, the washing method is preferably to wash with N,N-dimethylformamide and acetone sequentially. The drying method is preferably supercritical CO2 drying, which can preserve the porous structure and is more conducive to improving the battery cycle capacity retention rate.

[0027] The present invention also provides an oxygen-rich 3D covalent organic framework@carbon nanotube composite material prepared by the above method.

[0028] Furthermore, this invention also provides the application of the above-mentioned oxygen-rich 3D covalent organic framework@carbon nanotube composite material in battery cathode materials.

[0029] The present invention will be described in detail below through embodiments.

[0030] In the following examples and comparative examples:

[0031] (1) The carboxyl content in the modified carbon nanotubes was determined by acid-base titration. The specific steps are as follows: 10 mg of modified carbon nanotubes were dispersed in 100 mL of deionized water and sonicated for 30 min. Then, a 0.01 mol / L NaOH solution was used for titration, with phenolphthalein as an indicator (endpoint pH≈8.2). The titration was stopped when the solution changed from colorless to red, and the carboxyl content was calculated according to the following formula (1):

[0032] Carboxyl content (mmol / g) = C NaOH ×(V NaOH -Vblank) / m formula (1)

[0033] In formula (1), C NaOH V represents the concentration of the NaOH solution, in mmol / L. NaOH Vblank represents the volume of NaOH solution consumed, in L; Vblank represents the volume of NaOH solution consumed in the blank test, in L; m represents the sample mass, in g.

[0034] (2) The amino group density in the modified carbon nanotubes was determined by acid-base titration, and the specific steps are as follows:

[0035] 10 mg of modified carbon nanotubes were dispersed in 10 mL of 0.01 mol / L hydrochloric acid. After shaking for 2 h, the supernatant was collected by centrifugation. The supernatant was then titrated with 0.01 mol / L NaOH solution, using phenolphthalein as an indicator (endpoint pH≈8.2). The titration was stopped when the solution changed from colorless to red. The amino density was calculated according to the following formula (2):

[0036] Amino density (mmol / g) = (C HCl ×V HCl -C NaOH ×V NaOH Formula (2) / m

[0037] In formula (2), C HCl V represents the concentration of hydrochloric acid, in mmol / L; HCl The volume of hydrochloric acid is expressed in liters (L); C NaOH V represents the concentration of the NaOH solution, in mmol / L. NaOH The volume of NaOH solution consumed is in L; m is the sample mass in g.

[0038] Example 1: Preparation of oxygen-enriched 3D covalent organic framework@carbon nanotube composite material

[0039] S1. Carbon nanotube pretreatment: 1.0 g of multi-walled carbon nanotubes (diameter 12±1 nm, length 10±0.5 μm, purity >99%) were dispersed in 200 mL of acidic mixed solution (H2SO4 / HNO3 (molar ratio) = 3:1), and dispersed at 20 °C under ultrasonic treatment at 300 W for 2 h. After centrifugation and washing with water until neutral, the nanotubes were dried under vacuum at 60 °C to obtain carboxyl carbon nanotubes CNT-COOH (-COOH content 1.75 mmol / g). The above carboxyl carbon nanotubes were reacted with 5 mL of 3-aminopropyltriethoxysilane (APTES) in ethanol under reflux at 80 °C for 12 h. After centrifugation and washing with water until neutral, the nanotubes were dried under vacuum at 60 °C to obtain modified carbon nanotubes (CNT-NH2, -NH2 density 1.0 mmol / g).

[0040] S2. Interface Self-Assembly: 100 mg of modified carbon nanotubes were dispersed in 50 mL of water to form an aqueous phase. 0.5 mmol of tetrakis(4-formylphenyl)methane (TFPM, 98%) and 1.0 mmol of 2,5-diaminophenyl-1,4-diol (DHBD, 99%) were dispersed in 50 mL of a xylene / n-butanol (4:1 v / v) mixed solvent. 0.05 M p-toluenesulfonamide (PTSA) and 0.5 vol.% water were added and stirred until homogeneous to obtain an oil phase. The oil phase was slowly poured into the aqueous phase and ultrasonically emulsified at 200 W for 2 min in an ice bath to form a Pickering emulsion. The Pickering emulsion was transferred to a 25 mL polytetrafluoroethylene reactor and reacted at 80 °C for 24 h. After the reaction, the solid was collected by centrifugation (8000 rpm, 5 min). The solid was washed with DMF and acetone in sequence to remove unreacted monomers, and then dried with supercritical CO2 to obtain a black powdery oxygen-enriched 3D covalent organic framework@carbon nanotube composite material (3D-OCOF@CNT-1).

[0041] SEM images of 3D-OCOF@CNT-1 are shown below. Figure 2 As shown, from Figure 2 It can be seen that, compared to before interface aggregation ( Figure 2 On the left, the product is modified carbon nanotubes. After interfacial polymerization, the carbon nanotubes are coated with 3D-OCOF.

[0042] Example 2: Preparation of oxygen-enriched 3D covalent organic framework@carbon nanotube composite material

[0043] S1. Carbon nanotube pretreatment: 1.0 g of multi-walled carbon nanotubes (diameter 12±1 nm, length 10±0.5 μm, purity >99%) were dispersed in 200 mL of acidic mixed solution (H2SO4 / HNO3 (molar ratio) = 2:1), and dispersed at 45 °C under ultrasonic treatment at 300 W for 1 h. After centrifugation and washing with water until neutral, the nanotubes were dried under vacuum at 60 °C to obtain carboxyl carbon nanotubes CNT-COOH (-COOH content 2.54 mmol / g). The above carboxyl carbon nanotubes were reacted with 5 mL of 3-aminopropyltriethoxysilane (APTES) in ethanol under reflux at 90 °C for 10 h. After centrifugation and washing with water until neutral, the nanotubes were dried under vacuum at 60 °C to obtain modified carbon nanotubes (CNT-NH2, -NH2 density 1.1 mmol / g).

[0044] S2. Interface Self-Assembly: 100 mg of modified carbon nanotubes were dispersed in 50 mL of water to form an aqueous phase. 0.5 mmol of tetrakis(4-formylphenyl)silane and 1.0 mmol of 2,5-dimethoxy-p-phenylenediamine were dispersed in 50 mL of a xylene / n-butanol (volume ratio 4:1) mixed solvent. 0.05 M PTSA and 0.2 vol.% water were added and stirred until homogeneous to obtain an oil phase. The oil phase was slowly poured into the aqueous phase and ultrasonically emulsified at 200 W for 2 min in an ice bath to form a Pickering emulsion. The Pickering emulsion was transferred to a 25 mL polytetrafluoroethylene reactor and reacted at 90 °C for 10 h. After the reaction, the solid was collected by centrifugation (8000 rpm, 5 min). The solid was washed sequentially with DMF and acetone to remove unreacted monomers, and then dried using supercritical CO2 to obtain a black powdery 3D covalent organic framework@carbon nanotube composite material (3D-OCOF@CNT-2).

[0045] Example 3: Preparation of oxygen-enriched 3D covalent organic framework@carbon nanotube composite material

[0046] S1. Carbon nanotube pretreatment: 1.0 g of multi-walled carbon nanotubes (diameter 12±1 nm, length 10±0.5 μm, purity >99%) were dispersed in 200 mL of acidic mixed solution (H2SO4 / HNO3 (molar ratio) = 4:1), and dispersed at 30 °C under ultrasonic treatment at 300 W for 5 h. After centrifugation and washing with water until neutral, the nanotubes were dried under vacuum at 60 °C to obtain carboxyl carbon nanotubes CNT-COOH (-COOH content 2.54 mmol / g). The above carboxyl carbon nanotubes were reacted with 5 mL of 3-aminopropyltriethoxysilane (APTES) in ethanol under reflux at 70 °C for 15 h. After centrifugation and washing with water until neutral, the nanotubes were dried under vacuum at 60 °C to obtain modified carbon nanotubes (CNT-NH2, -NH2 density 1.1 mmol / g).

[0047] S2. Interface Self-Assembly: 100 mg of modified carbon nanotubes were dispersed in 50 mL of water to form an aqueous phase. 0.5 mmol of 1,2,4,5-tetratetra(4-formylphenyl)benzene and 1.0 mmol of 2,5-diethoxybenzene-1,4-di(formylhydrazine) were dispersed in 50 mL of a xylene / n-butanol (volume ratio 4:1) mixed solvent. 0.05 M PTSA and 1 vol.% water were added and stirred until homogeneous to obtain an oil phase. The oil phase was slowly poured into the aqueous phase and ultrasonically emulsified for 2 min at 200 W in an ice bath to form a Pickering emulsion. The Pickering emulsion was transferred to a 25 mL polytetrafluoroethylene reactor and reacted at 70 °C for 48 h. After the reaction, the solid was collected by centrifugation (8000 rpm, 5 min). The solid was washed with DMF and acetone in sequence to remove unreacted monomers, and then dried with supercritical CO2 to obtain a black powdery oxygen-enriched 3D covalent organic framework@carbon nanotube composite material, denoted as 3D-OCOF@CNT-3.

[0048] Example 4: Preparation of oxygen-enriched 3D covalent organic framework@carbon nanotube composite material

[0049] The oxygen-enriched 3D covalent organic framework@carbon nanotube composite material was prepared according to the method of Example 1, except that the amount of modified carbon nanotubes was adjusted to 200 mg, and the other conditions were the same as in Example 1. The oxygen-enriched 3D covalent organic framework@carbon nanotube composite material was obtained and was denoted as 3D-OCOF@CNT-10.

[0050] Example 5: Preparation of oxygen-enriched 3D covalent organic framework@carbon nanotube composite material

[0051] The oxygen-enriched 3D covalent organic framework@carbon nanotube composite material was prepared according to the method of Example 1, except that the amount of modified carbon nanotubes was adjusted to 300 mg, and the other conditions were the same as in Example 1. The oxygen-enriched 3D covalent organic framework@carbon nanotube composite material was obtained and was denoted as 3D-OCOF@CNT-15.

[0052] Example 6: Preparation of oxygen-enriched 3D covalent organic framework@carbon nanotube composite material

[0053] The oxygen-enriched 3D covalent organic framework@carbon nanotube composite material was prepared according to the method of Example 1, except that the amount of modified carbon nanotubes was adjusted to 400 mg, and the other conditions were the same as in Example 1. The oxygen-enriched 3D covalent organic framework@carbon nanotube composite material was obtained and was denoted as 3D-OCOF@CNT-20.

[0054] Comparative Example 1: Physically Hybrid Composite Material of Traditional 2D-COF and Carbon Nanotubes

[0055] S1. Preparation of two-dimensional imine-type COF (TPB-DMTP): 1,3,5-tris(4-aminophenyl)benzene (TPB, 0.2 mmol) and 2,5-dimethoxytetraphenyldialdehyde (DMTP, 0.3 mmol) were dissolved in 20 mL of 1,4-dioxane, and 0.5 mL of 6M acetic acid aqueous solution was added. The mixture was reacted at 120 °C for 72 h to obtain a yellow powdery 2D-COF product.

[0056] S2. The above-mentioned 2D-COF (100 mg) and 5 mg of multi-walled carbon nanotubes (diameter 12±1 nm, length 10±0.5 μm, purity >99%) were dispersed together in 100 mL of N,N-dimethylformamide, and ultrasonically treated at 300 W for 1 h. Then, the solid product was collected by centrifugation and vacuum dried at 60 °C for 12 h to obtain a 2D-COF@CNT physical mixture, denoted as D2D-COF@CNT-1.

[0057] Comparative Example 2: 3D-COF / CNT composite materials without covalent bonds

[0058] The oxygen-rich 3D covalent organic framework@carbon nanotube composite material was prepared according to the method of Example 2. The difference was that the carboxylated multi-walled carbon nanotubes were not modified with carboxyl and amino groups. In addition, the modified carbon nanotubes in step S2 were replaced with the same weight parts of unmodified multi-walled carbon nanotubes (diameter 12±1nm, length 10±0.5μm, purity >99%). The other conditions were the same as in Example 2. The reference covalent organic framework@carbon nanotube composite material was obtained and denoted as D3D-COF@CNT-2.

[0059] Comparative Example 3: Preparation of a reference 3D covalent organic framework@carbon nanotube composite material

[0060] The oxygen-enriched 3D covalent organic framework@carbon nanotube composite material was prepared according to the method of Example 2, except that 2,5-dimethoxy-p-phenylenediamine was replaced with the same molar amount of p-phenylenediamine, and the other conditions were the same as in Example 2, to obtain the reference oxygen-enriched 3D covalent organic framework@carbon nanotube composite material, denoted as D3D-COF@CNT-3.

[0061] Comparative Example 4: Preparation of a reference 3D covalent organic framework@carbon nanotube composite material

[0062] The oxygen-enriched 3D covalent organic framework@carbon nanotube composite material was prepared according to the method of Example 2, except that tetra(4-formylphenyl)silane was replaced with the same molar amount of 2,4,6-trihydroxy-1,3,5-pyromellitic methyl ether, and the other conditions were the same as in Example 2, to obtain the reference oxygen-enriched 3D covalent organic framework@carbon nanotube composite material, denoted as D3D-COF@CNT-4.

[0063] Test case

[0064] (1) Electrical conductivity: The electrical conductivity of the oxygen-rich 3D covalent organic framework@carbon nanotube composite materials obtained in the above examples and comparative examples was measured using the four-probe method. A higher electrical conductivity indicates better conductivity, and vice versa. The results are shown in Table 1.

[0065] (2) Specific surface area: The specific surface area of ​​the oxygen-enriched 3D covalent organic framework@carbon nanotube composite materials obtained in the above examples and comparative examples was determined by the gas adsorption method (BET method). The results are shown in Table 1.

[0066] (3) ORR half-wave potential: The ORR half-wave potential of the oxygen-enriched 3D covalent organic framework@carbon nanotube composite materials obtained in the above examples and comparative examples was determined by linear sweep voltammetry (LSV) using a rotating disk electrode (RDE). The results are shown in Table 1.

[0067] (4) Cycle capacity retention: The oxygen-enriched 3D covalent organic framework@carbon nanotube composite materials obtained in the above examples and comparative examples were used as positive electrode materials to assemble button batteries. Then, the button batteries were tested in a battery testing system under the conditions of 45°C, 4.35V, and 2C rate to test the cycle capacity retention after 10,000 cycles. The results are shown in Table 1.

[0068] Table 1

[0069]

[0070] As can be seen from the results in Table 1, the oxygen-enriched 3D covalent organic framework@carbon nanotube composite material obtained by the above method exhibits good electrical conductivity and is beneficial for improving battery cycle capacity retention. A comparison between Example 1 and Comparative Example 1 shows that the cycle capacity retention of the oxygen-enriched 3D covalent organic framework@carbon nanotube composite material provided by this invention is significantly higher than that of the 2D COF material. A comparison between Example 2 and Comparative Examples 2-4 shows that when the carbon nanotubes used are not bonded with carboxyl and amino groups, or when the tetrahedral monomer and the oxygen-containing diamine monomer are not used as the two specific substances in the COF synthesis, the cycle capacity retention will be significantly reduced.

[0071] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing an oxygen-enriched 3D covalent organic framework@carbon nanotube composite material, characterized in that, The method includes the following steps: S1. Carbon nanotube pretreatment: Carboxyl and amino groups are bonded to carbon nanotubes to obtain modified carbon nanotubes; S2. Interface Self-Assembly: Modified carbon nanotubes are dispersed in water to form an aqueous phase, and tetrahedral monomers and oxygen-containing diamine monomers are dispersed in an organic solvent to form an oil phase. The aqueous and oil phases are mixed, and the resulting Pickering emulsion is subjected to an in-situ growth-interfacial crosslinking reaction. The resulting reaction product is then filtered, washed, and dried to obtain an oxygen-rich 3D covalent organic framework@carbon nanotube composite material. The tetrahedral monomer is selected from tetra(4-formylphenyl)methane and tetra(4-formylphenyl) The monomer is selected from at least one of silane and 1,2,4,5-tetra(4-formylphenyl)benzene; the oxydiamine monomer is selected from at least one of 2,5-dimethoxy-p-phenylenediamine, 2,5-diaminobenzene-1,4-diol, 2,5-dimethoxy-terephthalic acid dihydrazide, 2,5-disulfonic acid-p-phenylenediamine, and 2,5-diethoxybenzene-1,4-di(formylhydrazide); the conditions for the in-situ growth-interfacial crosslinking reaction include a temperature of 70℃~90℃ and a time of 10h~72h.

2. The preparation method of the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 1, characterized in that, The carbon nanotubes have a diameter of 10 nm to 20 nm and a length of 5 μm to 15 μm.

3. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 1, characterized in that, The modified carbon nanotubes contain 1.5-3 mmol / g of carboxyl groups and have an amino group density of 0.4-1.4 mmol / g.

4. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 1, characterized in that, In step S1, the modified carbon nanotubes are prepared by the following method: the carbon nanotubes are ultrasonically treated in acid to bond carboxyl groups to the surface of the carbon nanotubes, and the resulting carboxyl carbon nanotubes are coupled with an aminosilane coupling agent to bond amino groups to the surface of the carboxyl carbon nanotubes. The resulting product is the modified carbon nanotube.

5. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 4, characterized in that, The acid solution is a mixture of sulfuric acid and nitric acid.

6. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 5, characterized in that, The molar ratio of sulfuric acid to nitric acid in the mixture is (2~4):

1.

7. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 4, characterized in that, The aminosilane coupling agent contains both amino and alkoxy groups.

8. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 4, characterized in that, The conditions for ultrasonic treatment include a temperature of 20℃ to 45℃ and a time of 1h to 5h.

9. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 4, characterized in that, The coupling reaction conditions include a temperature of 70℃~90℃ and a time of 10h~15h.

10. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 1, characterized in that, In step S2, the ratio of the weight of the modified carbon nanotubes in the aqueous phase to the total weight of the tetrahedral monomers and oxygen-containing diamine monomers in the oil phase is 100:(1~100).

11. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 1, characterized in that, In step S2, the molar ratio of the tetrahedral monomer to the oxygen-containing diamine monomer is (0.4~0.6):

1.

12. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to any one of claims 1 to 11, characterized in that, The in-situ growth-interfacial crosslinking reaction was carried out in the presence of a weak acid catalyst.

13. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 12, characterized in that, The weak acid catalyst is selected from at least one of p-toluenesulfonic acid, acetic acid, scandium trifluoromethanesulfonate, and trifluoroacetic acid.

14. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 12, characterized in that, The dosage of the weak acid catalyst is such that its concentration in the system is 0.01~0.1 mol / L.

15. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to any one of claims 1 to 11, characterized in that, The in-situ growth-interfacial crosslinking reaction was carried out in the presence of trace amounts of water.

16. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 15, characterized in that, The amount of water used is 0.2~1 vol.%.

17. The method for preparing the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to any one of claims 1 to 11, characterized in that, The washing method involves sequentially washing with N,N-dimethylformamide and acetone; the drying method involves supercritical CO2 drying.

18. An oxygen-enriched 3D covalent organic framework@carbon nanotube composite material prepared by the method according to any one of claims 1 to 17.

19. The application of the oxygen-rich 3D covalent organic framework@carbon nanotube composite material according to claim 18 in battery cathode materials.

Images