Polymer-assisted active enhancement and structure-regulated carbon-based fiber materials, preparation method and application thereof

Abstract

The application belongs to the technical field of battery materials, and particularly relates to a carbon-based fiber material with polymer-assisted activity enhancement and structure regulation, a preparation method and application. The preparation method comprises the following steps: step (1), carbon-based fiber material is sequentially subjected to cleaning, acid etching and calcination to obtain pretreated material with active sites on the surface; step (2), a polymer is dispersed in a solvent to form a uniform and stable polymer loading solution; step (3), the pretreated material is immersed in the polymer loading solution prepared in step (2) for impregnation to obtain a loaded primary product; and step (4), the loaded primary product obtained in step (3) is subjected to washing and drying, and then sequentially subjected to pre-oxidation and carbonization treatment in a tube furnace, and then cooled to room temperature to obtain the carbon-based fiber material with polymer-assisted activity enhancement and structure regulation. The carbon-based fiber material prepared by the application can realize heteroatom doping and has high conductivity and activity.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a polymer-assisted activity enhancement and structure regulation carbon-based fiber material, its preparation method, and its application. Background Technology

[0002] Flow batteries, with their advantages of independent capacity and power design, long cycle life, high safety, and environmental friendliness, have shown irreplaceable application prospects in areas such as grid peak shaving and valley filling, and renewable energy consumption, becoming a key direction for current energy storage technology research and development and industrialization. Electrodes, as the core site of electrochemical reactions in flow batteries, directly determine the battery's energy efficiency, power density, and cycle stability. Currently, in commercial applications and research, flow battery electrodes mainly use high-temperature treated carbon-based fiber materials (such as graphite felt, carbon felt, and carbon cloth). Although these materials possess good conductivity and chemical stability, their surface inertness after high-temperature treatment results in inherent defects such as a lack of active sites, insufficient electrocatalytic activity, poor hydrophilicity, and weak adsorption capacity for active substances in the electrolyte (such as vanadium ions and iron ions).

[0003] To address the aforementioned technical challenges, researchers have proposed modification strategies such as surface oxidation, elemental doping, metal / metal oxide loading, and carbon nanomaterial composites. For example, the electronic structure of carbon materials can be modulated by doping with non-metallic elements like nitrogen and sulfur, or catalytic components such as sulfurized polyacrylonitrile and lead nanoparticles can be loaded to enhance reaction kinetics. Alternatively, electrospinning combined with dopamine pretreatment can be used to prepare nanofiber catalytic layers, optimizing the electrode surface structure and interfacial properties. However, existing modification technologies still have many shortcomings: some modification methods (such as noble metal loading) significantly increase electrode costs, making large-scale application difficult; some modification processes are complex and lengthy, failing to meet the needs of continuous production and resulting in poor product quality stability; simultaneously, most modification technologies fail to simultaneously address multiple issues such as improving electrode catalytic activity, membrane protection, and mass transfer enhancement, leading to limited improvements in overall battery performance and making it difficult to meet the stringent requirements of large-scale energy storage scenarios.

[0004] As flow batteries develop towards lightweight and high power density, graphite felt with a thickness of ≤1.0 cm has gradually become a research hotspot. Its advantages, such as small size, light weight, and short mass transfer distance, can effectively reduce battery internal resistance and improve ion transport efficiency, making it suitable for miniaturized, portable energy storage devices and high-density energy storage applications. However, the use of graphite felt with a thickness of ≤1.0 cm also brings many manufacturing challenges: Firstly, its thinness leads to poor structural stability, making it prone to fiber embrittlement, delamination, and breakage during modification processes such as etching activation, high-temperature calcination, polymer loading, and carbonization, resulting in compromised electrode structural integrity. Secondly, graphite felt has relatively low porosity and significant surface inertness, making it difficult to form a uniform and stable modified layer on its surface using conventional modification processes. This hinders the simultaneous improvement of active sites and structural stability, further exacerbating the difficulty of electrode fabrication and limiting its large-scale application in flow batteries.

[0005] Chinese patent CN111354952B discloses a graphite felt composite electrode and its preparation method, which incorporates carboxylated carbon nanotubes. The polydopamine complex was dispersed in an organic dispersant to form a uniform and stable suspension. Then, graphite felt was immersed in the suspension, allowing carboxylated carbon nanotubes to be absorbed. Polydopamine composites are modified onto graphite felt, cleaned and dried, and then carbonized in a tube furnace to obtain the final product. However, high-quality carboxylated carbon nanotubes are expensive, which is not conducive to large-scale industrial production and cost control. At the same time, carbon nanotubes are prone to agglomeration in solvents, requiring complex methods such as ultrasonication, ball milling, and the addition of surfactants to achieve uniform dispersion. This makes it difficult to control in actual production, and batch stability is hard to guarantee. It also increases the length of the process chain and energy consumption.

[0006] Therefore, it is necessary to develop a carbon fiber electrode modification technology that is simple to process, cost-controllable, and highly adaptable to large-scale production, so as to achieve synergistic optimization of electrode catalytic activity, hydrophilicity, and structural stability, while solving derivative problems such as membrane damage and poor mass transfer. Summary of the Invention

[0007] The purpose of this invention is to provide a polymer-assisted carbon-based fiber material with enhanced activity and structure, as well as its preparation method and application. The method of this invention is simple, cost-controllable, and highly adaptable to large-scale production. It can simultaneously achieve synergistic optimization of electrode catalytic activity, hydrophilicity, and structural stability, while solving derivative problems such as membrane damage and poor mass transfer.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing polymer-assisted activity-enhanced and structure-regulated carbon-based fiber materials includes the following steps: Step (1), base electrode pretreatment: the carbon-based fiber material is sequentially cleaned, acid etched and calcined to obtain a pretreated material with active sites on the surface; Step (2), preparation of polymer loading solution: disperse the polymer in a solvent to form a homogeneous and stable polymer loading solution; Step (3), Loading treatment: Immerse the pretreated material in the polymer loading liquid prepared in step (2) and impregnate to obtain the loaded primary product; Step (4) Surface loading carbonization treatment: The primary loaded product obtained in step (3) is washed and dried, placed in a tube furnace for pre-oxidation and carbonization treatment in sequence, and then cooled to room temperature to obtain a carbon-based fiber material with polymer-assisted activity enhancement and structure regulation.

[0009] Preferably, the carbon-based fiber material in step (1) includes any one of carbon felt, graphite felt, carbon cloth or carbon paper.

[0010] Preferably, the carbon-based fiber material in step (1) is graphite felt with a thickness of ≤1.0cm.

[0011] Existing technologies for modifying graphite felt with a thickness of ≤1.0 cm often employ methods such as precious metal loading and complex nanomaterial composites. These methods not only use expensive modifying materials, significantly increasing industrial production costs and hindering cost control in large-scale production, but also result in poor structural stability of graphite felt with a thickness of ≤1.0 cm. This invention uses a polymer solution as the loading medium, selecting low-cost, easily dispersible conventional polymers. A uniform and stable loading liquid can be formed without complex dispersion methods. The process is simple and easy to operate, effectively reducing production costs and energy consumption. Simultaneously, the polymer solution can uniformly wet the surface and pores of graphite felt with a thickness of ≤1.0 cm. The loading process is gentle, avoiding damage to the structure of graphite felt with a thickness of ≤1.0 cm. Furthermore, subsequent pre-oxidation and carbonization treatments form a uniform and stable carbon layer on its surface, simultaneously increasing active sites, improving hydrophilicity, and enhancing structural stability.

[0012] Preferably, the polymer is one or more of polyvinylpyrrolidone, epoxy resin, polyvinyl alcohol, polyimide, and polyethyleneimine; the solvent is one or more of deionized water, ethanol, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetonitrile.

[0013] Preferably, the mass fraction of the polymer in the solvent is in the range of 3wt%-20wt%.

[0014] Preferably, the calcination conditions are as follows: under an air atmosphere, the air flow rate is controlled at 60-100 mL / min, the temperature is increased to 440-460℃ at a heating rate of 2-3℃ / min, and held for 1-3 hours. Then, the temperature is increased to 530-550℃ at the same heating rate and held for 1-3 hours. After calcination, the temperature is naturally cooled to room temperature.

[0015] Preferred pre-oxidation conditions are as follows: heating to 250-260℃ at a heating rate of 2-4℃ / min, holding at that temperature for 1-3 hours, maintaining an air atmosphere, and then naturally cooling to 80-90℃.

[0016] Preferably, the carbonization conditions are as follows: heating at a rate of 4-5℃ / min to 1000-1020℃ and holding for 1.0-1.1h; heating at a rate of 3-4℃ / min to 1100-1120℃ and holding for 0.5-0.6h; heating at a rate of 2-3℃ / min to 1180-1200℃ and holding for 0.4-0.5h.

[0017] This invention overcomes the limitations of existing carbon-based fiber material modification technologies by combining polymer solution impregnation with precisely controlled pretreatment calcination and surface loading carbonization processes. This constructs an integrated modification system of pretreatment-polymer loading-gradient pre-oxidation carbonization, achieving synergistic optimization of carbon-based fiber material performance and a dual reduction in production costs and process complexity. This invention precisely defines the specific conditions for each key process: the pretreatment stage employs a segmented calcination process under air atmosphere, using specific flow rates, heating rates, segmented temperatures, and holding times to efficiently introduce active sites onto the carbon-based fiber surface while avoiding damage to the material structure; the pre-oxidation stage uses specific heating rates and temperature ranges to ensure stable cross-linking of the polymer-loaded layer, laying the foundation for subsequent carbonization; the carbonization stage employs a three-gradient heating carbonization process, gradually increasing the temperature and precisely controlling the heating rates and holding times of each gradient to promote the full transformation of the polymer-loaded layer into a uniform and stable carbon layer, effectively regulating the development of the material's pore structure.

[0018] The preparation method yields a polymer-assisted activity-enhanced and structure-regulated carbon-based fiber material.

[0019] The polymer-assisted activity-enhanced and structure-regulated carbon-based fiber material prepared by the aforementioned method is used as an electrode material in flow batteries.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention is based on adjusting the rheological properties of a polymer solution to uniformly load the polymer onto the surface of carbon fibers treated at high temperature, and then obtaining a carbon fiber felt covered with a thin carbon layer through carbonization treatment, which is used as an electrode for flow batteries; at the same time, different polymers contain different types of atoms, and through the carbonization step, heteroatom doping can be achieved simultaneously, realizing a modified electrode with both high conductivity and activity.

[0021] 2. This invention uses a polymer solution as the loading medium, selecting a low-cost, easily dispersible conventional polymer. A uniform and stable loading liquid can be formed without complex dispersion methods. The process is simple and easy to operate, effectively reducing production costs and energy consumption. At the same time, the polymer solution can uniformly wet the surface and pores of the graphite felt. The loading process is gentle, which can avoid damage to the graphite felt structure. Furthermore, through subsequent pre-oxidation and carbonization treatments, a uniform and stable carbon layer can be formed on its surface, simultaneously increasing the number of active sites, improving hydrophilicity, and enhancing structural stability.

[0022] 3. This invention combines precisely controlled pretreatment calcination and surface-loaded carbonization processes with the synergistic effect of polymer loading. This significantly improves the BET specific surface area of ​​the material, increases the active sites for electrochemical reactions, and optimizes mass transfer channels. It also effectively enhances the energy efficiency and cycle stability of vanadium redox flow batteries. At the same time, the process is simple, cost-controllable, and highly adaptable to large-scale production. It is especially suitable for the modification of graphite felt with a thickness of ≤1.0cm, solving the technical problems of easy structural damage and limited activity improvement in the modification of graphite felt with a thickness of ≤1.0cm. Attached Figure Description

[0023] Figure 1 A comparison chart of BET data for graphite felt, carbon-based fiber material prepared in Example 1, and carbon-based fiber material prepared in Example 4.

[0024] Figure 2 The image shows a SEM image of the carbon-based fiber material prepared in Example 1.

[0025] Figure 3 The carbon-based fiber material prepared in Example 1 at 250 mA / cm 2 A comparison chart showing the battery energy efficiency at the beginning and the battery energy efficiency after replacing the separator and electrolyte after 300 cycles.

[0026] Figure 4 SEM images of the surfaces of graphite felt and carbon-based fiber materials prepared in Comparative Example 2 are shown. The left image is the SEM image of graphite felt, and the right image is the SEM image of carbon-based fiber materials prepared in Comparative Example 2. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 This embodiment provides a polymer-assisted activity enhancement and structure regulation carbon-based fiber material, the preparation method of which includes the following steps: (1) Base electrode pretreatment: The graphite felt was cut into 5cm×5cm×0.25cm (thickness 0.25cm), and completely immersed in deionized water solution. It was ultrasonically treated at 80kHz for 30min. After ultrasonic treatment, it was rinsed repeatedly with deionized water 3 times. The cleaned graphite felt was dried at 80℃ for 4h. The dried graphite felt was immersed in 1.0mol / L nitric acid solution and treated at 60℃ for 2h. It was rinsed with deionized water until neutral and dried at 80℃ again for 2h. The etched and activated graphite felt was placed in a tube furnace. Under air atmosphere conditions, the air flow rate was controlled at 80mL / min. The temperature was raised to 450℃ at a rate of 2-3℃ / min and held for 2h. Then, the temperature was raised to 550℃ at the same rate and held for 2h. After calcination, it was naturally cooled to room temperature to obtain pretreated graphite felt. (2) Preparation of polymer loading solution: PVP is dissolved in deionized water, the mass fraction of PVP aqueous solution is 7wt%, and the solution is stirred until it becomes transparent to obtain polymer loading solution; (3) Loading treatment: The pretreated graphite felt is immersed in the above polymer loading liquid and loaded at room temperature of 25°C. After immersion for 5 minutes, it is taken out and gently squeezed with clean filter paper to remove obvious liquid droplets on the surface. The felt is placed in a forced-air drying oven at 80°C for 3 hours and then taken out to obtain the loaded graphite felt. (4) Post-treatment: The loaded graphite felt was placed in a tube furnace, air was introduced, the gas flow rate was adjusted to 60 mL / min, the temperature was raised to 260℃ at a heating rate of 2℃ / min, and held for 2 hours. The air atmosphere was maintained, and the temperature was naturally cooled to 80℃. The atmosphere in the tube furnace was switched to nitrogen (purity ≥99.99%), and a trace amount of CO2 was introduced at the same time. The volume fraction of CO2 was controlled to be 4%, and the total gas flow rate was 100 mL / min. The temperature was raised to 1000℃ at a heating rate of 5℃ / min and held for 1 hour. The temperature was raised from 1000℃ to 1100℃ at a heating rate of 3℃ / min and held for 0.5 hours. The temperature was raised from 1100℃ to 1200℃ at a heating rate of 2℃ / min and held for 0.5 hours. After carbonization, the nitrogen atmosphere was maintained and the temperature was naturally cooled to room temperature to obtain a carbon-based fiber material with polymer-assisted activity enhancement and structure regulation.

[0029] The atomic fractions of the original graphite felt from Example 1 and the polymer-assisted activity-enhanced and structure-regulated carbon-based fiber material prepared in Example 1 were determined, and the results are shown in Table 1.

[0030] Table 1 Comparison of Atomic Fractions

[0031] And the specific surface area was measured, and the results are as follows: Figure 1 As shown, the carbon-based fiber material prepared in Example 1 has a significantly improved specific surface area compared to commercial graphite felt, with a BET specific surface area reaching 6.74 m². 2 / g. Figure 2 The image shows a SEM image of the carbon-based fiber material prepared in Example 1. The area outlined is the carbon shell layer left after the fiber detaches due to external force intervention, verifying that PVP forms a thin carbon layer on the fiber surface.

[0032] like Figure 3 As shown, the materials prepared in this embodiment are used to assemble an all-vanadium redox flow battery with a current of 250 mA / cm². 2 After 300 cycles, the battery separator and electrolyte were replaced, and the battery energy efficiency could be restored to 76.7%, indicating that the prepared carbon-based fiber material was used as the electrode of the flow battery, and the battery performance was improved.

[0033] Example 2 This embodiment provides a polymer-assisted activity enhancement and structure regulation carbon-based fiber material, the preparation method of which includes the following steps: (1) Base electrode pretreatment: The graphite felt was cut into 5cm×5cm×0.25cm (thickness 0.25cm), and completely immersed in deionized water solution. It was ultrasonically treated at 80kHz for 30min. After ultrasonic treatment, it was rinsed repeatedly with deionized water 3 times. The cleaned graphite felt was dried at 80℃ for 4h. The dried graphite felt was immersed in 1.0mol / L nitric acid solution and treated at 60℃ for 2h. It was rinsed with deionized water until neutral and dried at 80℃ again for 2h. The etched and activated graphite felt was placed in a tube furnace. Under air atmosphere conditions, the air flow rate was controlled at 80mL / min. The temperature was raised to 450℃ at a rate of 2-3℃ / min and held for 2h. Then, the temperature was raised to 550℃ at the same rate and held for 2h. After calcination, it was naturally cooled to room temperature to obtain pretreated graphite felt. (2) Preparation of polymer loading solution: PVA is dissolved in deionized water (PVA aqueous solution mass fraction is 5wt%) and stirred until the solution is transparent to obtain polymer loading solution; (3) Loading treatment: The pretreated graphite felt is immersed in the above polymer loading liquid and loaded at room temperature of 25°C. After immersion for 5 minutes, it is taken out and gently squeezed with clean filter paper to remove obvious liquid droplets on the surface. The felt is placed in a forced-air drying oven at 80°C for 3 hours and then taken out to obtain the loaded graphite felt. (4) Post-treatment: The loaded graphite felt was placed in a tube furnace, air was introduced, the gas flow rate was adjusted to 60 mL / min, the temperature was raised to 260℃ at a rate of 2℃ / min, held for 2h, and then cooled naturally to 80℃ while maintaining the air atmosphere; the atmosphere in the tube furnace was switched to nitrogen (purity ≥99.99%), and a trace amount of CO2 was introduced at the same time, the CO2 volume fraction was controlled to be 4%, and the total gas flow rate was 100 mL / min; the temperature was raised to 1000℃ at a rate of 5℃ / min and held for 1h; the temperature was raised from 1000℃ to 1100℃ at a rate of 3℃ / min and held for 0.5h after reaching the temperature; the temperature was raised from 1100℃ to 1200℃ at a rate of 2℃ / min and held for 0.5h after reaching the temperature. After carbonization, the nitrogen atmosphere was maintained and the material was naturally cooled to room temperature to obtain a carbon-based fiber material with polymer-assisted activity enhancement and structure regulation. This embodiment presents an all-vanadium redox flow battery with electrode assembly, achieving a speed of 250 mA / cm². 2 The energy efficiency is 72.4%. The battery performance of the polyvinyl alcohol-assisted electrode in this embodiment is good, but slightly inferior to that in Example 1. This is mainly because the conductivity of the polyvinyl alcohol carbonization in this embodiment is slightly inferior to that of polyvinylpyrrolidone.

[0034] Example 3 This embodiment provides a polymer-assisted activity enhancement and structure regulation carbon-based fiber material, the preparation method of which includes the following steps: (1) Base electrode pretreatment: The graphite felt was cut into 5cm×5cm×0.25cm (thickness 0.25cm), and completely immersed in deionized water solution. It was ultrasonically treated at 80kHz for 30min. After ultrasonic treatment, it was rinsed repeatedly with deionized water 3 times. The cleaned graphite felt was dried at 80℃ for 4h. The dried graphite felt was immersed in 1.0mol / L nitric acid solution and treated at 60℃ for 2h. It was rinsed with deionized water until neutral and dried at 80℃ again for 2h. The etched and activated graphite felt was placed in a tube furnace. Under air atmosphere conditions, the air flow rate was controlled at 80mL / min. The temperature was raised to 450℃ at a rate of 2℃ / min and held for 2h. Then, the temperature was raised to 550℃ at the same rate and held for 2h. After calcination, it was naturally cooled to room temperature to obtain pretreated graphite felt. (2) Preparation of polymer loading liquid: The waterborne epoxy resin and curing agent are mixed uniformly at a mass ratio of 100:140, stirred at room temperature to form a homogeneous and viscous liquid, and then diluted with 50% of the total mass of water to obtain the final epoxy resin polymer loading liquid. (3) Loading treatment: The pretreated graphite felt is immersed in the above polymer loading liquid and loaded at room temperature of 25°C. After immersion for 5 minutes, it is taken out and gently squeezed with clean filter paper to remove obvious liquid droplets on the surface. The felt is placed in a forced-air drying oven at 80°C for 3 hours and then taken out to obtain the loaded graphite felt. (4) Post-treatment: The loaded graphite felt was placed in a tube furnace, air was introduced, the gas flow rate was adjusted to 60 mL / min, the temperature was raised to 260℃ at a heating rate of 2℃ / min, and held for 2 hours. The air atmosphere was maintained, and the temperature was naturally cooled to 80℃. The atmosphere in the tube furnace was switched to nitrogen (purity ≥99.99%), and a trace amount of CO2 was introduced at the same time. The volume fraction of CO2 was controlled to be 4%, and the total gas flow rate was 100 mL / min. The temperature was raised to 1000℃ at a heating rate of 5℃ / min and held for 1 hour. The temperature was raised from 1000℃ to 1100℃ at a heating rate of 3℃ / min and held for 0.5 hours. The temperature was raised from 1100℃ to 1200℃ at a heating rate of 2℃ / min and held for 0.5 hours. After carbonization, the nitrogen atmosphere was maintained and the temperature was naturally cooled to room temperature to obtain a carbon-based fiber material with polymer-assisted activity enhancement and structure regulation.

[0035] The all-vanadium redox flow battery assembled from carbon-based fiber materials prepared in this embodiment achieves a speed of 250 mA / cm². 2 The energy efficiency is 70.6%.

[0036] Example 4 This embodiment provides a polymer-assisted activity enhancement and structure regulation carbon-based fiber material, the preparation method of which includes the following steps: (1) Base electrode pretreatment: The graphite felt was cut into 5cm×5cm×0.25cm (thickness 0.25cm), and completely immersed in deionized water solution. It was ultrasonically treated at 80kHz for 30min. After ultrasonic treatment, it was rinsed repeatedly with deionized water 3 times. The cleaned graphite felt was dried at 80℃ for 4h. The dried graphite felt was immersed in 1.0mol / L nitric acid solution and treated at 60℃ for 2h. It was rinsed with deionized water until neutral and dried at 80℃ again for 2h. The etched and activated graphite felt was placed in a tube furnace. Under air atmosphere conditions, the air flow rate was controlled at 80mL / min. The temperature was raised to 450℃ at a rate of 2-3℃ / min and held for 2h. Then, the temperature was raised to 550℃ at the same rate and held for 2h. After calcination, it was naturally cooled to room temperature to obtain pretreated graphite felt. (2) Preparation of polymer loading solution: Prepare an N,N-dimethylformamide solution containing 7wt% polyacrylonitrile and 1wt% polyvinylpyrrolidone, stir evenly, and prepare polymer loading solution; (3) Loading treatment: The pretreated graphite felt is immersed in the above polymer loading liquid and loaded at room temperature of 25°C. After immersion for 5 minutes, it is taken out and gently squeezed with clean filter paper to remove obvious liquid droplets on the surface. The felt is placed in a forced-air drying oven at 80°C for 3 hours and then taken out to obtain the loaded graphite felt. (4) Post-treatment: The loaded graphite felt was placed in a tube furnace, air was introduced, the gas flow rate was adjusted to 60 mL / min, the temperature was raised to 260℃ at a heating rate of 2℃ / min, and held for 2 hours. The air atmosphere was maintained, and the temperature was naturally cooled to 80℃. The atmosphere in the tube furnace was switched to nitrogen (purity ≥99.99%), and a trace amount of CO2 was introduced at the same time. The volume fraction of CO2 was controlled to be 4%, and the total gas flow rate was 100 mL / min. The temperature was raised to 1000℃ at a heating rate of 5℃ / min and held for 1 hour. The temperature was raised from 1000℃ to 1100℃ at a heating rate of 3℃ / min and held for 0.5 hours. The temperature was raised from 1100℃ to 1200℃ at a heating rate of 2℃ / min and held for 0.5 hours. After carbonization, the nitrogen atmosphere was maintained and the temperature was naturally cooled to room temperature to obtain a carbon-based fiber material with polymer-assisted activity enhancement and structure regulation.

[0037] In this embodiment, the electrode specific surface area reaches 10.42 μm. 2 / g, the all-vanadium redox flow battery assembled from the carbon-based fiber material prepared in this embodiment achieves 250mA / cm 2 The energy efficiency is 74.6%. After 300 cycles, the capacity can be restored to 73.9% after replacing the diaphragm and electrolyte.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that, except for the PVP mass fraction of 25wt% in step (2), all other conditions are the same as in Example 1.

[0039] The BET specific surface area of ​​the carbon-based fiber material prepared in this comparative example is 12.65 m². 2 / g.

[0040] This comparative example demonstrates a vanadium redox flow battery assembled from carbon-based fiber materials, achieving a current of 250 mA / cm². 2 The energy efficiency was 69.45%. The poor battery performance was mainly due to the excessive amount of polymer. After carbonization, the carbon layer blocked the original pores of the graphite felt. Although a larger specific surface area was obtained, the excessively thick carbon layer affected the conductivity of the graphite felt and blocked the electrolyte flow pores, which was detrimental to battery operation.

[0041] Comparative Example 2 The difference between this comparative example and Example 1 is that the carbonization temperature in step (4) is changed to 500℃; all other conditions are the same as in Example 1.

[0042] The material prepared in this comparative example exhibits excellent hydrophilicity, but the felt is slightly stiff. The poor morphology of the felt is mainly due to the insufficient carbonization temperature of the selected polymer. Although the surface contains many functional groups, which improves the hydrophilicity of the felt, the polymer does not completely form a carbon layer and exists in the form of coke, resulting in a poor morphology of the felt itself. Figure 4 As shown.

[0043] Comparative Example 3 The difference between this comparative example and Example 4 is as follows: Under air atmosphere conditions, the air flow rate is controlled at 80 mL / min, the temperature is increased to 450°C at a heating rate of 2°C / min, and held for 2 hours. Then, the temperature is increased to 550°C at the same heating rate and held for 2 hours. After calcination, the temperature is naturally cooled to room temperature to obtain the pretreated graphite felt. Alternatively, under air atmosphere conditions, the temperature is increased to 500°C at a heating rate of 5°C / min and held for 4 hours. After calcination, the temperature is naturally cooled to room temperature to obtain the pretreated graphite felt.

[0044] Comparative Example 4 The difference between this comparative example and Example 4 is as follows: Under air atmosphere conditions, the air flow rate is controlled at 80 mL / min, the temperature is increased to 450°C at a heating rate of 2°C / min, and held for 2 hours. Then, the temperature is increased to 550°C at the same heating rate and held for 2 hours. After calcination, the temperature is naturally cooled to room temperature to obtain pretreated graphite felt. The method is replaced by: Under air atmosphere conditions, the air flow rate is controlled at 80 mL / min, the temperature is increased to 450°C at a heating rate of 5°C / min, and held for 2 hours. Then, the temperature is increased to 550°C at the same heating rate and held for 2 hours. After calcination, the temperature is naturally cooled to room temperature to obtain pretreated graphite felt.

[0045] Comparative Example 5 The difference between this comparative example and Example 4 is as follows: Under air atmosphere conditions, the air flow rate is controlled at 80 mL / min, the temperature is increased to 450°C at a heating rate of 2°C / min, and held for 2 hours. Then, the temperature is increased to 550°C at the same heating rate and held for 2 hours. After calcination, the temperature is naturally cooled to room temperature to obtain pretreated graphite felt. The method is replaced by: Under air atmosphere conditions, the air flow rate is controlled at 80 mL / min, the temperature is increased to 450°C at a heating rate of 1°C / min, and held for 2 hours. Then, the temperature is increased to 550°C at the same heating rate and held for 2 hours. After calcination, the temperature is naturally cooled to room temperature to obtain pretreated graphite felt.

[0046] Comparative Example 6 The difference between this comparative example and Example 4 is as follows: Under air atmosphere conditions, the air flow rate is controlled at 80 mL / min, the temperature is increased to 450°C at a heating rate of 2°C / min, and held for 2 hours. Then, the temperature is increased to 550°C at the same heating rate and held for 2 hours. After calcination, the temperature is naturally cooled to room temperature to obtain pretreated graphite felt. The method is replaced by: Under air atmosphere conditions, the air flow rate is controlled at 80 mL / min, the temperature is increased to 450°C at a heating rate of 2°C / min, and held for 2 hours. Then, the temperature is increased to 500°C at the same heating rate and held for 2 hours. After calcination, the temperature is naturally cooled to room temperature to obtain pretreated graphite felt.

[0047] Comparative Example 7 The difference between this comparative example and Example 4 is as follows: In step (4), the temperature was increased to 1000℃ at a heating rate of 5℃ / min and held for 1h; the temperature was increased from 1000℃ to 1100℃ at a heating rate of 3℃ / min and held for 0.5h after reaching the temperature; the temperature was increased from 1100℃ to 1200℃ at a heating rate of 2℃ / min and held for 0.5h after reaching the temperature. Instead, the temperature was increased to 1100℃ at a heating rate of 5℃ / min and held for 2h for carbonization, and then naturally cooled to room temperature.

[0048] Comparative Example 8 The difference between this comparative example and Example 4 is as follows: In step (4), the temperature was increased to 1000℃ at a heating rate of 5℃ / min and held for 1h; the temperature was increased from 1000℃ to 1100℃ at a heating rate of 3℃ / min and held for 0.5h; the temperature was increased from 1100℃ to 1200℃ at a heating rate of 2℃ / min and held for 0.5h. Instead, the temperature was increased to 1100℃ at a heating rate of 5℃ / min and held for 1h; then increased from 1100℃ to 1200℃ at a heating rate of 3℃ / min and held for 1h. After carbonization, the temperature was kept in a nitrogen atmosphere and allowed to cool naturally to room temperature.

[0049] Comparative Example 9 The difference between this comparative example and Example 4 is as follows: In step (4), the temperature was increased to 1000℃ at a heating rate of 5℃ / min and held for 1 hour; the temperature was increased from 1000℃ to 1100℃ at a heating rate of 3℃ / min and held for 0.5 hours; the temperature was increased from 1100℃ to 1200℃ at a heating rate of 2℃ / min and held for 0.5 hours. Instead, the temperature was increased to 950℃ at a heating rate of 5℃ / min and held for 1 hour; the temperature was increased from 950℃ to 1150℃ at a heating rate of 3℃ / min and held for 0.5 hours; the temperature was increased from 1150℃ to 1200℃ at a heating rate of 2℃ / min and held for 0.5 hours. After carbonization, the nitrogen atmosphere was maintained and the temperature was naturally cooled to room temperature.

[0050] Comparative Example 10 The difference between this comparative example and Example 4 is as follows: In step (4), the temperature was increased to 1000℃ at a heating rate of 5℃ / min and held for 1 hour; the temperature was increased from 1000℃ to 1100℃ at a heating rate of 3℃ / min and held for 0.5 hours; the temperature was increased from 1100℃ to 1200℃ at a heating rate of 2℃ / min and held for 0.5 hours. Instead, the temperature was increased to 1000℃ at a heating rate of 5℃ / min and held for 0.8 hours; the temperature was increased from 1000℃ to 1100℃ at a heating rate of 3℃ / min and held for 0.7 hours; the temperature was increased from 1100℃ to 1200℃ at a heating rate of 2℃ / min and held for 0.5 hours. After carbonization, the nitrogen atmosphere was maintained and the temperature was naturally cooled to room temperature.

[0051] Performance testing The performance of the polymer-assisted activity-enhanced and structure-regulated carbon-based fiber material prepared in this invention was tested: (1) the BET specific surface area was tested; (2) a vanadium redox flow battery was assembled using the carbon-based fiber material, and a constant current was used for charging and discharging to measure the performance at 250 mA / cm². 2 Energy efficiency (EE, %) = Coulomb efficiency (CE, %) × Voltage efficiency (VE, %); (3) After 300 cycles, replace the diaphragm and electrolyte, and measure at 250 mA / cm 2 Reduce energy efficiency.

[0052] The test results are shown in Table 2.

[0053] Table 2 Performance Test Results

[0054] As shown in Table 1, the carbon-based fiber materials of Examples 1-4 have excellent comprehensive performance, especially Example 4, which has the best effect.

[0055] Comparative Examples 3-6 demonstrate that a specific pretreatment calcination process is necessary to achieve efficient activation of graphite felt and ensure the comprehensive performance of carbon-based fiber materials. This specific pretreatment calcination process effectively etches the surface of graphite felt, introduces active defects, and protects its structural integrity, laying a solid foundation for subsequent polymer loading and carbonization processes. Deviating from these specific process parameters, regardless of changes in heating rate, calcination temperature, or heat preservation method, will result in poor pore structure development and insufficient surface activity, leading to a significant decrease in the material's specific surface area, energy efficiency, and cycle stability, thus failing to meet the requirements for vanadium redox flow battery electrodes.

[0056] As shown in Comparative Examples 7-10, in the post-processing stage of carbon-based fiber materials, the three-gradient carbonization process under specific conditions can achieve optimized control of the carbon layer structure, ensuring that the material has sufficient active sites, perfect pore structure and excellent cycle stability; it can effectively avoid problems such as carbon layer collapse and loss of active sites, and achieve synergistic improvement of material specific surface area, catalytic activity and structural stability.

[0057] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a polymer-assisted activity-enhanced and structure-regulated carbon-based fiber material, characterized in that, Includes the following steps: Step (1), base electrode pretreatment: the carbon-based fiber material is sequentially cleaned, acid etched and calcined to obtain a pretreated material with active sites on the surface; Step (2), preparation of polymer loading solution: disperse the polymer in a solvent to form a homogeneous and stable polymer loading solution; Step (3), Loading treatment: Immerse the pretreated material in the polymer loading liquid prepared in step (2) and impregnate to obtain the loaded primary product; Step (4) Surface loading carbonization treatment: The primary loaded product obtained in step (3) is washed and dried, placed in a tube furnace for pre-oxidation and carbonization treatment in sequence, and then cooled to room temperature to obtain a carbon-based fiber material with polymer-assisted activity enhancement and structure regulation.

2. The method for preparing carbon-based fiber materials with polymer-assisted activity enhancement and structure regulation according to claim 1, characterized in that, The carbon-based fiber material in step (1) includes any one of carbon felt, graphite felt, carbon cloth or carbon paper.

3. The method for preparing carbon-based fiber materials with polymer-assisted activity enhancement and structure regulation according to claim 2, characterized in that, The carbon-based fiber material in step (1) is a graphite felt with a thickness of ≤1.0cm.

4. The method for preparing carbon-based fiber materials with polymer-assisted activity enhancement and structure regulation according to claim 1, characterized in that, The polymer is one or more of polyvinylpyrrolidone, epoxy resin, polyvinyl alcohol, polyimide, and polyethyleneimine; the solvent is one or more of deionized water, ethanol, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetonitrile.

5. The method for preparing carbon-based fiber materials with polymer-assisted activity enhancement and structure regulation according to claim 1, characterized in that, The polymer mass fraction in the solvent ranges from 3wt% to 20wt%.

6. The method for preparing carbon-based fiber materials with polymer-assisted activity enhancement and structure regulation according to claim 1, characterized in that, The calcination conditions are as follows: under an air atmosphere, the air flow rate is controlled at 60-100 mL / min, the temperature is increased to 440-460℃ at a heating rate of 2-3℃ / min, and held for 1-3 hours. Then, the temperature is increased to 530-550℃ at the same heating rate and held for 1-3 hours. After calcination, the temperature is allowed to cool naturally to room temperature.

7. The method for preparing carbon-based fiber materials with polymer-assisted activity enhancement and structure regulation according to claim 6, characterized in that, The pre-oxidation conditions are as follows: heat to 250-260℃ at a heating rate of 2-4℃ / min, hold at that temperature for 1-3 hours, maintain an air atmosphere, and then allow to cool naturally to 80-90℃.

8. The method for preparing carbon-based fiber materials with polymer-assisted activity enhancement and structure regulation according to claim 7, characterized in that, The carbonization conditions are as follows: heat to 1000-1020℃ at a heating rate of 4-5℃ / min and hold for 1.0-1.1h; continue heating to 1100-1120℃ at a heating rate of 3-4℃ / min and hold for 0.5-0.6h; continue heating to 1180-1200℃ at a heating rate of 2-3℃ / min and hold for 0.4-0.5h.

9. A polymer-assisted activity-enhanced and structure-regulated carbon-based fiber material prepared by any one of claims 1-8.

10. The application of a polymer-assisted activity-enhanced and structure-regulated carbon-based fiber material prepared by any one of claims 1-8 as an electrode material in a flow battery.

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