Phenolic resin microsphere-based porous carbon conductive composite material and preparation method thereof

Abstract

The invention discloses a phenolic resin microsphere-based porous carbon conductive composite material and a preparation method thereof, and belongs to the technical field of conductive materials. Phenolic resin microspheres with specific molecular weight and hydroxymethyl content are used as carbon precursors, nitrogen-doped carbon nanofibers are introduced to construct a continuous conductive network, a metal-ligand self-assembled mesoporous template agent is adopted to form ordered multilevel channels, and a skeleton structure is enhanced by virtue of a boric acid ester crosslinking aid. The preparation method comprises the steps of potential regulation and control dispersion of precursor slurry, alkaline steam aging forming and gradient pyrolysis carbonization in an inert atmosphere. The method avoids the use of strong corrosive reagents, and the process is environment-friendly. The obtained composite material has high specific surface area, excellent conductivity and good mechanical strength, effectively solves the technical problems that a traditional porous carbon material is disordered in pore structure, insufficient in conductivity and weak in mechanical property and is difficult to synergistically optimize, and has wide application prospects in the fields of supercapacitor electrodes, silicon-carbon negative electrodes and the like.

Description

Technical Field

[0001] This invention belongs to the field of conductive materials technology, specifically relating to a phenolic resin microsphere-based porous carbon conductive composite material and its preparation method. Background Technology

[0002] Phenolic resin-based porous carbon is widely used in supercapacitor electrodes and silicon-carbon anodes due to its advantages such as readily available raw materials, high carbon yield, and tunable structure. However, traditional preparation methods mostly rely on physical or chemical activation. The former has low activation efficiency, while the latter causes equipment damage and environmental pollution due to the use of highly corrosive reagents, and the resulting material has a randomly distributed pore structure with limited conductivity. To improve conductivity, carbon nanotubes or graphene are often introduced as conductivity-enhancing phases. However, these nanomaterials have poor dispersion in phenolic resin matrices, are prone to agglomeration, and have weak interfacial bonding with the matrix, resulting in discontinuous conductive pathways and limited overall conductivity improvement.

[0003] Patent application CN110444411A discloses a conductive organic polymer-encapsulated phenolic resin-based porous carbon composite material. This method involves in-situ polymerization of the conductive organic polymer on the surface of the phenolic resin-based porous carbon to construct a core-shell structure, thereby improving the material's specific capacity and cycle stability. However, in this technical solution, the conductive polymer only coats the outer surface of the porous carbon, making it difficult to penetrate deep into the pores to form a three-dimensional continuous conductive network, resulting in limited improvement in bulk conductivity. Furthermore, the organic polymer is prone to swelling and degradation during long-term electrochemical cycling, affecting the material's structural stability and service life. In addition, its preparation process requires microwave hydrothermal reaction, which is demanding and unsuitable for large-scale production. Patent application CN103215693A discloses graphene oxide-modified phenolic resin-based ultrafine porous carbon fibers and their preparation method. This method involves blending graphene oxide with phenolic resin, followed by electrospinning, curing, and carbonization to obtain composite carbon fibers with a microporous structure, aiming to improve the material's flexibility and conductivity. However, although the graphene oxide in the phenolic resin matrix is ​​ultrasonically dispersed in this method, it is still difficult to completely avoid layer stacking and local agglomeration, resulting in an uneven conductive network. Moreover, the oxygen-containing functional groups remaining after carbonization may introduce structural defects, which may reduce carrier mobility. In addition, single activation or porosimetry strategies usually result in the pore size distribution being concentrated in the micropore or mesopore region, making it difficult to simultaneously achieve synergistic optimization of high specific surface area and efficient ion transport capability.

[0004] In summary, existing technologies still have room for improvement in balancing pore structure order, conductivity enhancement, and overall material mechanical integrity. There is an urgent need to prepare a multifunctional conductive carbon material that combines high conductivity, high specific surface area, and excellent ion transport capabilities. Summary of the Invention

[0005] One of the objectives of this invention is to provide a phenolic resin microsphere-based porous carbon conductive composite material, which solves the problems of disordered pore structure, insufficient conductivity and weak mechanical strength in the prior art, which are difficult to optimize in a coordinated manner.

[0006] The second objective of this invention is to provide a method for preparing a phenolic resin microsphere-based porous carbon conductive composite material, which is used to prepare the above-mentioned phenolic resin microsphere-based porous carbon conductive composite material.

[0007] The objective of this invention can be achieved through the following technical solutions: In a first aspect, a phenolic resin microsphere-based porous carbon conductive composite material comprises, by mass parts: 100 parts of phenolic resin microsphere precursor, 3-8 parts of nitrogen-doped carbon nanofibers, 5-12 parts of metal-ligand self-assembly mesoporous template agent, and 1-4 parts of borate ester crosslinking aid; the composite material is a carbonized product obtained by pyrolysis reaction of the above components after mixing and molding, under an inert protective gas atmosphere. The phenolic resin microsphere precursor is formed by the condensation polymerization of phenol and formaldehyde under the action of an alkaline catalyst, with a weight-average molecular weight of 3000–3500 and a hydroxymethyl content of 15%–20%. The nitrogen-doped carbon nanofibers are prepared by electrospinning combined with ammonia heat treatment. They have a diameter of 80–150 nm, and their surface includes pyridine and graphitic nitrogen functional groups with an aspect ratio greater than 150. The metal-ligand self-assembled mesoporous template agent is formed by the self-assembly of transition metal ions and nitrogen-containing aromatic carboxylic acid ligands in a water-alcohol mixed solvent. The crystal size is 300–500 nm and the channels are arranged in a hexagonal order. The borate ester crosslinking aid is a dynamic covalent network precursor formed by the in-situ condensation of arylboronic acid and polyol. During pyrolysis, it decomposes to generate boron doping sites and stabilizes the porous framework structure.

[0008] This application uses phenolic resin microspheres with controllable hydroxymethyl content as carbon precursors to ensure high carbonization yield and a rigid framework. High aspect ratio nitrogen-doped carbon nanofibers are introduced, whose surface nitrogen functional groups enhance interfacial bonding with the resin and construct a pervasive conductive network. After pyrolysis, the organic portion of the metal-ligand self-assembly template agent carbonizes to form ordered mesoporous carbon walls, while metal ions are reduced to nanoparticles and catalyze the graphitization of surrounding carbon. Finally, acid washing leaves through-holes, collectively constructing a conductive hierarchical porous system. The borate ester crosslinking agent plays a dynamic covalent role during the curing and pyrolysis stages, enhancing the gel network strength in the early stages and decomposing in the later stages to achieve boron doping and release gas to assist in pore formation, thereby simultaneously optimizing the material's conductivity, porosity, and structural stability.

[0009] Furthermore, the preparation of the nitrogen-doped carbon nanofibers includes the following steps: dissolving polyacrylonitrile and polyvinylpyrrolidone in N,N-dimethylformamide, forming a nanofiber film by electrospinning, then pre-oxidizing at 260–280°C for 2–3 hours in an inert atmosphere, and then carbonizing at 800–900°C for 1–2 hours in an ammonia atmosphere to obtain conductive nanofibers with nitrogen-rich functional groups on the surface.

[0010] Electrospinning is used to prepare PAN / PVP hybrid fibers, and pre-oxidation is used to form a stable trapezoidal structure to prevent melting during carbonization. High-temperature ammonia treatment introduces pyridine nitrogen and graphitic nitrogen into the carbon skeleton, improving conductivity and surface chemical activity.

[0011] Furthermore, the transition metal ion in the metal-ligand self-assembled mesoporous template agent is selected from at least one of cobalt ions, zinc ions, or iron ions, and the nitrogen-containing aromatic carboxylic acid ligand is at least one of 2-methylimidazole, terephthalic acid, or trimesic acid.

[0012] Transition metal ions and nitrogen-containing / carboxylic acid ligands form ordered mesoscopic structures through coordination self-assembly. After pyrolysis, the organic ligands carbonize to form pore walls, and the metal ions are reduced to nanoparticles and catalyze graphitization to form ordered mesopores.

[0013] Furthermore, the borate ester crosslinking aid is prepared by reacting phenylboronic acid and pentaerythritol in ethanol at 60–80°C for 1–2 hours in a molar ratio of (1.8–2.2):1, and its molecular structure includes multiple hydrolyzable borate ester bonds.

[0014] Phenylboronic acid forms dynamic borate ester bonds with polyols, which can enhance crosslinking through hydrolysis-recombination during the wet gelation stage; during pyrolysis, the borate ester decomposes, and boron atoms are doped into the carbon framework, improving the conductivity of carbon materials and stabilizing the pore structure.

[0015] Furthermore, in the preparation of the phenolic resin microsphere precursor, the molar ratio of phenol to formaldehyde is 1:(1.2-1.8), the alkaline catalyst is sodium hydroxide or ammonia, the reaction temperature is 75–85℃, and the reaction time is 3–5 hours.

[0016] Controlling the phenol / formaldehyde molar ratio and the type of alkaline catalyst can regulate the resin molecular weight and hydroxymethyl content, affecting the subsequent crosslinking density and carbonization yield; a higher formaldehyde ratio is conducive to the formation of more hydroxymethyl groups, thereby improving the crosslinking ability.

[0017] Secondly, a method for preparing a phenolic resin microsphere-based porous carbon conductive composite material includes the following steps: S1. Preparation of precursor slurry: Dissolve phenolic resin microsphere precursor in a polar organic solvent, add nitrogen-doped carbon nanofibers, and disperse evenly under ultrasonic power of 250–350W and shear rate of 1800–2200rpm. Then add metal-ligand self-assembled mesoporous template agent and borate ester crosslinking aid, and continue stirring until a homogeneous slurry is formed. S2. Molding and aging of wet gel: The slurry is injected into a mold and allowed to stand and cure for 12–24 hours under conditions of relative humidity of 60%–80% and temperature of 40–60℃ to form a three-dimensional network structure wet gel; then it is placed in an alkaline steam environment for post-crosslinking aging for 10–14 hours to fully reconstruct the borate ester bonds and enhance the rigidity of the skeleton. S3. Gradient pyrolysis carbonization: The aged wet gel is placed in a tube furnace and pyrolyzed in an inert protective gas atmosphere using a multi-stage heating program. The first stage is heated to 100–150℃ and held for 2–4 hours, the second stage is heated to 300–400℃ and held for 1–2 hours, and the final stage is heated to 700–900℃ and held for 2–3 hours, finally obtaining a phenolic resin microsphere-based porous carbon conductive composite material. S4. Post-treatment: The pyrolysis product is washed with hydrochloric acid or nitric acid solution with a concentration of 0.4–0.6 mol / L to remove residual metal particles, and then washed alternately with deionized water and ethanol, and vacuum dried at 80–90℃ for 10–14 hours to obtain phenolic resin microsphere-based porous carbon conductive composite material.

[0018] Throughout the preparation process, the order of addition of each component, the material ratio, the heat treatment temperature range, and the atmosphere control were all strictly limited. For example, nitrogen-doped carbon nanofibers must be added after the phenolic resin microsphere precursor is completely dissolved, and single-fiber dispersion is achieved under the synergistic effect of ultrasound and high-speed shearing; the metal-ligand self-assembled mesoporous template agent must be introduced after the nitrogen-doped carbon nanofibers are uniformly dispersed to avoid agglomeration caused by adsorption of nanofibers on the crystal surface; the borate ester crosslinking aid must be added after the template agent is dispersed to ensure that it is in full contact with the hydroxyl groups of the phenolic resin and undergoes a dynamic exchange reaction; the aging of the wet gel must be carried out in an alkaline vapor environment to promote the reconstruction of borate ester bonds and network densification; in the gradient pyrolysis program, the holding time and gas flow rate of each heating stage must be precisely matched to ensure that the orderly decomposition of the template agent, the in-situ reduction of metal ions, and the graphitization of the carbon skeleton proceed simultaneously. Furthermore, the molar ratio of transition metal ions to ligands in metal-ligand self-assembled mesoporous templates determines the size and distribution density of metal nanoparticles after pyrolysis. If the proportion of cobalt ions is too high, excessive catalysis will lead to uneven local graphitization; if there is an excess of ligands, too much residual carbon will block the pores.

[0019] The prepared phenolic resin microsphere-based porous carbon conductive composite material consists of a triple network: first, a spherical carbon matrix formed by the pyrolysis of phenolic resin; second, a continuous conductive pathway formed by nitrogen-doped carbon nanofibers running through it; and third, a mesoporous support framework formed by metal / carbon composite nanoparticles embedded in the pore walls after the pyrolysis of the metal-ligand template agent. Due to the high interfacial bonding strength caused by the hydrogen bond between the pyridine nitrogen on the surface of the nitrogen-doped carbon nanofibers and the hydroxymethyl group of the phenolic resin, and the π–π stacking of its graphitic nitrogen with the carbon matrix, the interfacial bonding strength is high. At the same time, the boron atoms generated by the pyrolysis of the borate ester crosslinking aid replace the carbon atoms in the graphite layer to form B–C bonds, which synergistically construct a pn co-doped electronic structure with the nitrogen doping sites, resulting in a highly continuous carrier migration path.

[0020] Furthermore, the polar organic solvent mentioned in step S1 is selected from at least one of ethanol, acetone, or N-methylpyrrolidone, and its amount is 1.8–2.2 times the mass of the phenolic resin microsphere precursor. Polar solvents (such as NMP) can fully dissolve phenolic resin and disperse nanofibers. The amount used affects the viscosity and formability of the slurry; too much will lead to difficulties in curing, while too little will result in uneven dispersion.

[0021] Furthermore, the alkaline vapor mentioned in step S2 is generated by the volatilization of ammonia or ammonium bicarbonate solution, with an ambient pH of 9.5–10.5. Alkaline vapor (such as ammonia) promotes the dynamic recombination of borate ester bonds, enhancing the strength of the gel network; simultaneously, alkaline conditions may catalyze further condensation of the phenolic resin, improving the rigidity of the framework.

[0022] Furthermore, the inert protective gas in step S3 is nitrogen or argon, with a flow rate of 90–110 mL / min, and 1.8–2.2 °C / min, 1.3–1.7 °C / min, and 0.8–1.2 °C / min for the first, second, and final stages, respectively. Segmented heating ensures the orderly evaporation of the solvent, thermal condensation of the precursor, decomposition of the template agent, and carbonization processes, preventing violent decomposition that could lead to pore collapse; the inert gas prevents oxidation and maintains the integrity of the carbon structure.

[0023] Furthermore, the nitrogen-doped carbon nanofibers have a Zeta potential of -35 to -30 mV in the slurry, while the phenolic resin precursor solution has a Zeta potential of +20 to +25 mV. The nanofibers and the resin solution have opposite Zeta potentials, which promote uniform dispersion and tight interfacial bonding through electrostatic attraction, preventing fiber aggregation.

[0024] Furthermore, during the pyrolysis process, the micropores formed by the carbonization of the metal-ligand self-assembled mesoporous template agent are interconnected with the mesopores formed by the catalytic graphitization of the metal particles, constructing a three-level pore system of micropores-mesopores-macropores. Ligand carbonization generates microporous carbon, while the surrounding carbon is catalyzed by the metal particles and may be removed by acid washing, leaving mesopores / macropores, forming a multi-level pore system that enhances mass transfer and electrical conductivity pathways.

[0025] Furthermore, the gaseous byproducts generated during the decomposition of the borate ester crosslinking aid during pyrolysis participate in pore formation, optimizing pore connectivity. The small molecule gases (such as alcohols and water vapor) generated by the pyrolysis of borate esters form escape channels in the carbon skeleton, increasing pore connectivity and optimizing the pore structure.

[0026] In the technical solution described in this invention, all operational steps, material ratios, and process parameters are essential technical features for achieving the technical effect, and none can be omitted. If the metal-ligand self-assembly mesoporous template agent is omitted and traditional ZIF-8 is used, the skeleton shrinkage rate exceeds 40% during pyrolysis above 700℃, and the mesopores collapse; if nitrogen-doped carbon nanofibers are added directly without Zeta potential regulation, sedimentation will occur due to the similarity of surface charge with the resin, and the conductive network will be interrupted; if the borate ester crosslinking aid is not added before curing, the precursor will have insufficient mechanical strength and crack during drying; if the temperature of the first stage of gradient pyrolysis is higher than 150℃, the solvent will evaporate violently, resulting in a loose gel structure; if the temperature of the last stage is lower than 700℃, the degree of graphitization will be insufficient, and the electrical conductivity will decrease significantly. Therefore, this invention achieves simultaneous optimization of pore structure order, electrical continuity and mechanical integrity through the synergistic control of metal-ligand template agent design, nanofiber surface functionalization, dynamic crosslinking of borate esters and multi-stage pyrolysis process, thus solving the technical contradictions in the prior art of strong activation corrosion, disordered pores, poor dispersion of conductive phase and template collapse.

[0027] The beneficial effects of this invention are: (1) This invention uses 100 parts of phenolic resin microsphere precursor as the carbon matrix core, combined with 3-8 parts of nitrogen-doped carbon nanofibers, 5-12 parts of metal-ligand self-assembled mesoporous template agent and 1-4 parts of borate ester crosslinking aid. The components are highly compatible and functionally complementary, forming a highly efficient and synergistic composite system. Among them, the weight-average molecular weight of the phenolic resin microsphere precursor is controlled at 3000-3500 and the hydroxymethyl content is 15%-20%, which can not only ensure the solubility in polar solvents to adapt to the preparation of slurry, but also provide sufficient active sites for subsequent crosslinking reactions, laying the foundation for the formation of a stable carbon skeleton in the composite material.

[0028] (2) The metal-ligand self-assembled mesoporous template agent introduced in this invention replaces traditional MOF materials and chemical activators, completely avoiding the use of highly corrosive reagents and taking into account the environmental friendliness and safety of the preparation process. The template agent is formed by the self-assembly of at least one transition metal ion from cobalt ions, zinc ions, and iron ions with at least one nitrogen-containing aromatic carboxylic acid ligand from 2-methylimidazole, terephthalic acid, and trimesic acid in a water-alcohol mixed solvent. The crystal size is 300–500 nm and the pores are arranged in a hexagonal order. During the pyrolysis process, the ligands carbonize to form micropores, and the metal particles catalyze graphitization to form mesopores. At the same time, the metal nanoparticles generated in situ can effectively inhibit the collapse of the pores. With the pre-set ordered pores, a three-level pore structure of micropores-mesopores-macropores is finally constructed, which takes into account the high specific surface area and efficient ion transport capability of the material.

[0029] (3) The 3–8 parts of nitrogen-doped carbon nanofibers introduced in this invention further optimize the conductivity of the material. The nanofibers are prepared by electrospinning combined with ammonia heat treatment, with a diameter of 80–150 nm. The surface is rich in pyridine and graphitic nitrogen functional groups with an aspect ratio greater than 150. Due to the strong interfacial interaction between the surface nitrogen functional groups and the phenolic resin matrix, they can be uniformly dispersed in the matrix without agglomeration, quickly constructing a continuous conductive path and significantly improving the overall conductivity of the material. At the same time, 1–4 parts of borate ester crosslinking aid play multiple synergistic roles. The molecular structure of this aid contains multiple hydrolyzable borate ester bonds, forming a dynamic covalent network in the precursor stage to enhance the mechanical integrity of the material and avoid skeleton damage during molding and pyrolysis. In the carbonization stage, it decomposes to generate boron doping sites, forming a synergistic effect with nitrogen doping, effectively regulating the electronic structure of the material, improving carrier concentration and migration efficiency, and achieving simultaneous optimization of conductivity and mechanical strength.

[0030] (4) The overall preparation process of this invention does not require strong acid or strong alkali activation treatment. Through pyrolysis under an inert protective gas atmosphere and subsequent post-treatment, the pore structure and conductive network constructed by each component can be precisely preserved. Moreover, the material structure and properties can be precisely controlled by adjusting the distribution ratio and structural parameters of each component. The phenolic resin microsphere-based porous carbon conductive composite material has high specific surface area, excellent conductivity, stable and ordered pore structure and good mechanical properties. It can be widely used in supercapacitor electrodes, silicon-carbon anodes and other fields. It effectively solves the technical bottleneck of disordered pore structure, insufficient conductivity and weak mechanical strength in the prior art, which are difficult to optimize in a coordinated manner. It has significant technical innovation and industrial application value. Attached Figure Description

[0031] The invention will now be further described with reference to the accompanying drawings.

[0032] Figure 1 The image shows a scanning electron microscope (SEM) image of the phenolic resin microsphere-based porous carbon conductive composite material prepared in Example 1. The scale bar is 1 μm. Figure 2 The image shows a scanning electron microscope (SEM) image of the phenolic resin microsphere-based porous carbon conductive composite material prepared in Example 1. The scale bar is 10 μm. Detailed Implementation

[0033] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0034] Example 1 This embodiment provides a phenolic resin microsphere-based porous carbon conductive composite material, which is prepared through the following steps: S1. Preparation of the precursor slurry: 100 parts of phenolic resin microsphere precursor (prepared by reacting phenol and formaldehyde at a molar ratio of 1:1.5 in ammonia water at 80℃ for 4 hours, with a weight-average molecular weight of 3200 and a hydroxymethyl content of 18%) were added to a three-necked flask, along with 200 parts of anhydrous ethanol. The mixture was stirred in a 60℃ water bath until completely dissolved, forming a transparent solution. Subsequently, 5 parts of nitrogen-doped carbon nanofibers (diameter 120nm, aspect ratio >150, surface Zeta potential -32mV) were added. The mixture was ultrasonically treated at 300W for 30 minutes while being sheared and stirred at 2000rpm for 1 hour to ensure uniform dispersion of the fibers in a single strand state. Then, 8 parts of metal-ligand self-assembled mesoporous template agent (made from Co...) were added. 2+ It was self-assembled with 2-methylimidazole in a water-ethanol mixed solvent, with a crystal size of 350 nm and hexagonal ordered channels. Stirring was continued for 30 minutes. Finally, 2.5 parts of borate ester crosslinking aid (prepared by reacting phenylboronic acid and pentaerythritol in ethanol at 70 °C for 1.5 hours at a molar ratio of 2.0:1) were added, and the mixture was stirred for 1 hour to obtain a homogeneous slurry.

[0035] S2. Molding and aging of wet gel: The above slurry is injected into a polytetrafluoroethylene mold and placed in a constant temperature and humidity chamber. It is allowed to stand and cure for 18 hours at a relative humidity of 70% and a temperature of 50°C to form a three-dimensional network wet gel. Then the mold is transferred to a sealed container containing saturated ammonia vapor and aged at 40°C for 12 hours to allow the borate ester bonds to undergo dynamic exchange and enhance the rigidity of the skeleton.

[0036] S3. Gradient pyrolysis carbonization: The aged wet gel is placed in a tube furnace, and high-purity nitrogen gas is introduced (flow rate 100 mL / min). The temperature is increased to 120°C at 2°C / min and held for 3 hours to complete solvent evaporation and hydroxymethyl condensation. Then, the temperature is increased to 350°C at 1.5°C / min and held for 1.5 hours to partially decompose the metal-ligand template agent, Co... 2+ It is reduced to Co nanoparticles; finally, the temperature is increased to 800℃ at 1℃ / min and held for 2.5 hours to complete deep carbonization and graphitization, resulting in black block carbon material.

[0037] S4. Post-treatment: The pyrolysis product was immersed in 0.5 mol / L hydrochloric acid solution and stirred at room temperature for 6 hours to dissolve residual Co particles; then washed with deionized water until neutral, and replaced three times with anhydrous ethanol; finally, it was vacuum dried at 80℃ for 12 hours to obtain phenolic resin microsphere-based porous carbon conductive composite material; scanning electron microscope images are shown below. Figure 1 (Scale bar is 1μm) and Figure 2 (Scale bar is 10μm) As shown.

[0038] Example 2 The difference between this embodiment and Example 1 is that the amount of nitrogen-doped carbon nanofibers added is 3 parts, while the other raw materials and preparation process remain the same as in Example 1.

[0039] Example 3 The difference between this embodiment and Example 1 is that the amount of nitrogen-doped carbon nanofibers added is 8 parts, while the other raw materials and preparation process remain the same as in Example 1.

[0040] Example 4 The difference between this embodiment and Example 1 is that the amount of metal-ligand self-assembled mesoporous template agent added is 5 parts, while the remaining raw materials and preparation process are the same as in Example 1.

[0041] Example 5 The difference between this embodiment and Example 1 is that the amount of metal-ligand self-assembled mesoporous template agent added is 12 parts, while the remaining raw materials and preparation process are the same as in Example 1.

[0042] Example 6 The difference between this embodiment and Example 1 is that the amount of borate ester crosslinking aid added is 1 part, while the remaining raw materials and preparation process are the same as in Example 1.

[0043] Example 7 The difference between this embodiment and Example 1 is that the amount of borate ester crosslinking aid added is 4 parts, while the remaining raw materials and preparation process are the same as in Example 1.

[0044] Example 8 The difference between this embodiment and Example 1 is that the final pyrolysis temperature in step S3 is 700°C, while the remaining raw materials and preparation process are the same as in Example 1.

[0045] Example 9 The difference between this embodiment and Example 1 is that the final pyrolysis temperature in step S3 is 900°C, while the remaining raw materials and preparation process are the same as in Example 1.

[0046] Example 10 The difference between this embodiment and Embodiment 1 is that the metal-ligand self-assembly mesoporous template agent used is Zn. 2+ The raw materials and preparation process are the same as in Example 1, except for the terephthalic acid ligand system.

[0047] Example 11 The difference between this embodiment and Example 1 is that the diameter of the nitrogen-doped carbon nanofibers is 80 nm, while the other raw materials and preparation process remain the same as in Example 1.

[0048] Comparative Example 1 The difference between this comparative example and Example 1 is that the metal-ligand self-assembled mesoporous template agent is not used, but an equal mass of ZIF-8 is used instead. The other raw materials and preparation process are the same as in Example 1.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that the nitrogen-doped carbon nanofibers were added directly to the slurry without Zeta potential modulation, while the other raw materials and preparation process remained the same as in Example 1.

[0050] Comparative Example 3 The difference between this comparative example and Example 1 is that the alkaline vapor aging in step S2 is omitted, and only conventional curing is performed. The other raw materials and preparation process are the same as in Example 1.

[0051] Comparative Example 4 The difference between this comparative example and Example 1 is that in step S3, the temperature is raised to 800°C in one step (heating rate 5°C / min) without gradient holding, while the other raw materials and preparation process remain the same as in Example 1.

[0052] Comparative Example 5 The difference between this comparative example and Example 1 is that no borate ester crosslinking aid is added, while the other raw materials and preparation process remain the same as in Example 1.

[0053] Comparative Example 6 The difference between this comparative example and Example 1 is that undoped carbon nanofibers were used instead of nitrogen-doped carbon nanofibers, while the other raw materials and preparation process remained the same as in Example 1.

[0054] Comparative Example 7 The difference between this comparative example and Example 1 is that the pyrolysis temperature at the end of step S3 is 600°C, while the other raw materials and preparation process remain the same as in Example 1.

[0055] Performance testing 1. Volumetric conductivity test: A four-probe conductivity meter was used. The sample size was Φ10mm×3mm. Five different points were tested on each sample, and the average value was taken as the final volumetric conductivity.

[0056] 2. Pore structure parameter testing: The liquid nitrogen adsorption-desorption method (BET method) was used with a specific surface area and porosity analyzer. Before testing, the samples were degassed in vacuum at 120℃ for 12h. The specific surface area (SSA) was calculated using the BET model. The pore size distribution and pore volume of mesopores (2-50nm) were calculated, and the pore volume of micropores (<2nm) was calculated. The total pore volume was the single-point adsorption pore volume (P / P0=0.99).

[0057] 3. Compressive strength test: According to GB / T 1431-2019 "Method for Determination of Compressive Strength of Carbon Materials", a universal testing machine was used. The sample size was Φ10mm×10mm, the loading rate was 1mm / min, and 3 parallel samples were tested in each group. The average value was taken.

[0058] 4. Electrochemical performance testing: The electrochemical performance was tested using a three-electrode system on an electrochemical workstation. The working electrode was a composite material electrode (active material mass loading 1.5 mg / cm³). 2 The counter electrode was a platinum sheet, the reference electrode was a saturated calomel electrode (SCE), and the electrolyte was a 6 mol / L KOH aqueous solution. Cyclic voltammetry (CV, scan rate 5-100 mV / s) and constant current charge-discharge curves (GCD, current density 0.5-10 A / g) were tested, and the specific capacitance was calculated (based on the mass of the active material). Cyclic stability was tested by cycling 5000 times at a current density of 5 A / g, and the specific capacitance retention rate after cycling was recorded.

[0059] The results are shown in Table 1: Table 1

[0060] As shown in Table 1, Examples 1-7 demonstrate that when the amount of nitrogen-doped carbon nanofiber added is 3-8 parts, the volumetric conductivity and specific capacitance gradually increase with increasing addition amount, but excessive addition (8 parts) slightly reduces the specific surface area (fiber agglomeration occupies pores); when the amount of metal-ligand template agent added is 5-12 parts, the specific surface area and pore volume increase with increasing amount, but excessive addition weakens the mechanical strength (excessive template agent ratio leads to a decrease in the carbon skeleton ratio); when the amount of borate ester crosslinking aid added is 1-4 parts, the mechanical strength and cycle stability are significantly improved, insufficient addition results in insufficient crosslinking density, and excessive addition has no significant benefit to the pore structure. Among them, the ratio in Example 1 (5 parts nitrogen-doped fiber, 8 parts template agent, 2.5 parts borate ester) achieves the optimal balance of various properties.

[0061] Examples 8-9 and Comparative Example 7 show that the final pyrolysis temperature should be controlled between 700-900℃. If the temperature is too low (600℃), the graphitization degree is insufficient, resulting in low conductivity and specific capacitance; if the temperature is too high (900℃), the channels collapse slightly, leading to a slight decrease in specific surface area and pore volume. Example 11 demonstrates that reducing the diameter of nitrogen-doped carbon nanofibers (80nm) can improve dispersibility and further optimize electrical conductivity and mass transfer performance.

[0062] Compared with the comparative examples, this invention exhibits significant performance advantages through the synergistic design of components and processes: ① Comparative Example 1 uses ZIF-8 instead of the self-assembling template agent, resulting in a significant decrease in specific surface area, pore volume, and mechanical strength due to excessively high skeleton shrinkage rate (>40%) during pyrolysis; ② Comparative Example 2 does not regulate the Zeta potential, leading to the agglomeration of nitrogen-doped fibers and interruption of the conductive network, with volumetric conductivity only 1 / 4 of that in Example 1 and a significant reduction in specific capacitance; ③ Comparative Example 3 omits alkaline steam aging, resulting in insufficient reconstruction of borate ester bonds and compressive strength less than 60% of that in Example 1; ④ Comparative Example 4 undergoes one-step pyrolysis, leading to destruction of the pore structure and comprehensive deterioration of all properties; ⑤ Comparative Example 5 lacks a borate ester crosslinking agent, resulting in extremely poor mechanical strength and decreased cycle stability; ⑥ Comparative Example 6 lacks nitrogen doping modification, resulting in discontinuous conductive pathways and a significant decrease in conductivity and specific capacitance.

[0063] The composite materials in Examples 1-11 exhibit significantly better volume conductivity, BET specific surface area, compressive strength, 0.5 A / g specific capacitance, and retention rate after 5000 cycles than their respective comparative examples, fully meeting the requirements for use as electrodes in supercapacitors and medium-to-high performance electromagnetic shielding materials.

[0064] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A phenolic resin microsphere-based porous carbon conductive composite material, characterized in that, The composite material comprises the following components by mass: 100 parts of phenolic resin microsphere precursor, 3–8 parts of nitrogen-doped carbon nanofibers, 5–12 parts of metal-ligand self-assembled mesoporous template agent, and 1–4 parts of borate ester crosslinking aid; the composite material is a carbonized product obtained by pyrolysis reaction of the above components after mixing and molding, under an inert protective gas atmosphere. The phenolic resin microsphere precursor is formed by the condensation polymerization of phenol and formaldehyde under the action of an alkaline catalyst, with a weight-average molecular weight of 3000–3500 and a hydroxymethyl content of 15%–20%. The nitrogen-doped carbon nanofibers are prepared by electrospinning combined with ammonia heat treatment. They have a diameter of 80–150 nm, and their surface includes pyridine and graphitic nitrogen functional groups with an aspect ratio greater than 150. The metal-ligand self-assembled mesoporous template agent is formed by the self-assembly of transition metal ions and nitrogen-containing aromatic carboxylic acid ligands in a water-alcohol mixed solvent. The crystal size is 300–500 nm and the channels are arranged in a hexagonal order. The borate ester crosslinking aid is a dynamic covalent network precursor formed by the in-situ condensation of arylboronic acid and polyol. During pyrolysis, it decomposes to generate boron doping sites and stabilizes the porous framework structure.

2. The phenolic resin microsphere-based porous carbon conductive composite material according to claim 1, characterized in that, The preparation of the nitrogen-doped carbon nanofibers includes the following steps: dissolving polyacrylonitrile and polyvinylpyrrolidone in N,N-dimethylformamide, forming a nanofiber membrane by electrospinning, then pre-oxidizing at 260–280°C for 2–3 hours in an inert atmosphere, and then carbonizing at 800–900°C for 1–2 hours in an ammonia atmosphere to obtain conductive nanofibers with nitrogen-rich functional groups on the surface.

3. The phenolic resin microsphere-based porous carbon conductive composite material according to claim 1, characterized in that, The transition metal ion in the metal-ligand self-assembled mesoporous template agent is selected from at least one of cobalt ions, zinc ions, or iron ions, and the nitrogen-containing aromatic carboxylic acid ligand is at least one of 2-methylimidazole, terephthalic acid, or trimesic acid.

4. The phenolic resin microsphere-based porous carbon conductive composite material according to claim 1, characterized in that, The borate ester crosslinking aid is prepared by reacting phenylboronic acid and pentaerythritol in ethanol at 60–80 °C for 1–2 hours in a molar ratio of (1.8–2.2):1, and its molecular structure includes multiple hydrolyzable borate ester bonds.

5. The phenolic resin microsphere-based porous carbon conductive composite material according to claim 1, characterized in that, In the preparation of the phenolic resin microsphere precursor, the molar ratio of phenol to formaldehyde is 1:(1.2-1.8), the alkaline catalyst is sodium hydroxide or ammonia, the reaction temperature is 75–85℃, and the reaction time is 3–5 hours.

6. A method for preparing a phenolic resin microsphere-based porous carbon conductive composite material, characterized in that, The preparation of the phenolic resin microsphere-based porous carbon conductive composite material according to any one of claims 1–5 includes the following steps: S1. Preparation of precursor slurry: Dissolve phenolic resin microsphere precursor in a polar organic solvent, add nitrogen-doped carbon nanofibers, and disperse evenly under ultrasonic power of 250–350W and shear rate of 1800–2200rpm. Then add metal-ligand self-assembled mesoporous template agent and borate ester crosslinking aid, and continue stirring until a homogeneous slurry is formed. S2. Molding and aging of wet gel: The slurry is injected into a mold and allowed to stand and cure for 12–24 hours under conditions of relative humidity of 60%–80% and temperature of 40–60℃ to form a three-dimensional network structure wet gel; then it is placed in an alkaline steam environment for post-crosslinking aging for 10–14 hours to fully reconstruct the borate ester bonds and enhance the rigidity of the skeleton. S3. Gradient pyrolysis carbonization: The aged wet gel is placed in a tube furnace and pyrolyzed in an inert protective gas atmosphere using a multi-stage heating program. The first stage is heated to 100–150℃ and held for 2–4 hours, the second stage is heated to 300–400℃ and held for 1–2 hours, and the final stage is heated to 700–900℃ and held for 2–3 hours, finally obtaining a phenolic resin microsphere-based porous carbon conductive composite material.

7. The method for preparing a phenolic resin microsphere-based porous carbon conductive composite material according to claim 6, characterized in that, After obtaining the phenolic resin microsphere-based porous carbon conductive composite material, a post-processing step is also included: the pyrolysis product is washed with hydrochloric acid or nitric acid solution with a concentration of 0.4–0.6 mol / L to remove residual metal particles, and then washed alternately with deionized water and ethanol, and vacuum dried at 80–90℃ for 10–14 hours.

8. The method for preparing a phenolic resin microsphere-based porous carbon conductive composite material according to claim 6, characterized in that, The polar organic solvent in step S1 is selected from at least one of ethanol, acetone or N-methylpyrrolidone, and the amount used is 1.8–2.2 times the mass of the phenolic resin microsphere precursor; the alkaline vapor in step S2 is generated by the volatilization of ammonia or ammonium bicarbonate solution, and the ambient pH is 9.5–10.

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9. The method for preparing a phenolic resin microsphere-based porous carbon conductive composite material according to claim 6, characterized in that, The inert protective gas mentioned in step S3 is nitrogen or argon, with a gas flow rate of 90–110 mL / min, and the heating rates of the first, second, and final stages are 1.8–2.2 °C / min, 1.3–1.7 °C / min, and 0.8–1.2 °C / min, respectively.

10. The method for preparing a phenolic resin microsphere-based porous carbon conductive composite material according to claim 6, characterized in that, The zeta potential of the nitrogen-doped carbon nanofibers in the slurry is -35–-30mV, and the zeta potential of the phenolic resin microsphere precursor solution is +20–+25mV.

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