A modified carbon fiber felt electrode material for a flow battery and its preparation method

Abstract

The present invention discloses a modified carbon fiber felt electrode material for a flow battery and a preparation method thereof. The method includes the following steps: S1: Prepare the carbon fiber felt: Use a precursor to obtain the carbon fiber felt by low-temperature carbonization under the action of a catalyst; S2: Prepare the modified carbon fiber felt; S3: Prepare the electrode material by high-temperature carbonization. The surface of the carbon fiber felt electrode material prepared by the present invention is connected by a modifier in a Π-Π conjugate form. By modifying and decorating the carbon fiber felt, the specific surface area of the carbon fiber felt is enlarged, and it has a unique microstructure, significantly reducing the surface resistivity of the material, increasing stable electroactive sites to accelerate the electron transfer rate, and effectively improving the overall electrochemical performance of the carbon fiber felt as an electrode material for a flow battery.

Description

Technical Field

[0001] The invention relates to the technical field of liquid flow battery materials, and in particular to a modified carbon fiber felt electrode material for a liquid flow battery and a preparation method thereof. Background Art

[0002] As the fossil energy that social and economic development relies on is becoming increasingly depleted, and the environmental degradation caused by traditional energy utilization methods is becoming more and more serious, it is urgent to save fossil energy and conduct large-scale research and development of renewable energy. Renewable energy sources such as wind power and solar energy have random and intermittent non-steady-state characteristics when generating electricity, which cannot meet the scheduling needs of grid load and power generation balance. Strengthening the stability of renewable energy is an important prerequisite for large-scale wind and solar power generation. Liquid flow batteries have attracted widespread attention as a new type of energy storage system. They provide ideal energy storage characteristics: long cycle life, flexible design, high safety, and low maintenance cost. Liquid flow batteries can turn intermittent, unstable, and uncontrollable renewable energy into stable, controllable, and high-quality energy. Since the positive and negative half-cell reactions of the battery occur on inert electrodes, the electrochemical activity of the electrode material is crucial to the energy conversion of liquid flow batteries.

[0003] Since carbon fiber felt has super flexibility, excellent conductivity and high mechanical strength, it is widely used in the fields of electrochemistry and composite materials. At the same time, as a commonly used electrode material, it has broad application prospects in liquid flow batteries. However, due to the small specific surface area of carbon fiber felt itself, in order to solve this problem, in the prior art, a Chinese invention patent application with patent application number 201810342586.8 discloses a method for preparing graphite felt for liquid flow batteries, which uses pre-oxidized felt raw materials to avoid ablation caused by excessive local temperature and reduce production costs; selects pre-oxidized felt of specific specifications to improve the quality of the finished product; the finished product obtained by the invention method has high electrode porosity, large specific surface area and stable electrode quality. However, this method requires pre-oxidized silk felt in advance. Although it expands the specific surface area, the surface of the material cannot form an effective microstructure and lacks sufficient active sites, resulting in a large surface resistivity of the material, which cannot meet the high requirements of liquid flow batteries in practical applications. Summary of the invention

[0004] In view of the above-mentioned deficiencies, the object of the present invention is to provide a modified carbonaceous fiber felt electrode material for liquid flow batteries and a preparation method thereof. By rationally designing the formula and process, a precursor is carbonized at low temperature in the presence of a catalyst to obtain a carbonaceous fiber felt, which is then modified to form a carbonaceous fiber felt electrode material with a unique microstructure on the surface of the material.

[0005] Another object of the present invention is to provide a modified carbon fiber felt electrode material obtained by the above preparation method. Through the microscopic structure on the surface of the material, the active sites are significantly increased, the electron transfer rate is accelerated, the surface resistivity is significantly reduced, and the material has high conductivity and excellent electrochemical performance, which can better meet the high requirements of the electrode material for flow batteries.

[0006] The technical solution adopted by the present invention to achieve the above object is:

[0007] A preparation method of a modified carbon fiber felt electrode material for a flow battery, characterized in that a modified carbon fiber felt electrode material is obtained by a three-step impregnation-high temperature carbonization method, including the following steps:

[0008] S1: Prepare carbon fiber felt: Use a precursor to obtain a carbon fiber felt by low-temperature carbonization under the action of a catalyst;

[0009] S2: Prepare modified carbon fiber felt: Prepare modifier dispersion liquid 1, dispersion liquid 2 and KOH solution respectively. First immerse the carbon fiber felt in dispersion liquid 1, then slowly add dispersion liquid 2, take it out and dry it at 120°C for 5 h, and finally immerse it in KOH solution, take it out and dry it at 120°C for 5 h;

[0010] Among them, dispersion liquid 1 is a solution prepared from one of dextrin, polyvinyl alcohol, glass micro-powder and PDA, and its concentration is 3 mg / ml to 10 mg / ml;

[0011] Dispersion liquid 2 is a solution prepared from one of reduced graphene oxide, graphene, graphene oxide, expandable graphite and activated carbon fiber, and its concentration is 10 mg / ml to 18 mg / ml;

[0012] S3: High-temperature carbonization to prepare electrode material: Under the protection of an argon atmosphere, perform high-temperature carbonization to obtain a modified carbon fiber felt electrode material with multiple active sites and a unique microscopic structure, in which the surface of the carbon fiber felt is connected by the modifier in a Π-Π conjugate form.

[0013] The precursor in step S1 is one of pitch, lignin, ultra-high molecular weight polyethylene, polyacrylonitrile and cellulose; the catalyst is one of zinc oxide, copper oxide, nitrogen-doped carbon nanotubes, cerium oxide and cobalt tetroxide.

[0014] The catalyst in step S1 accounts for 2% to 10% of the mass of the precursor. The catalyst and the precursor are sequentially added to a solution of one of N,N-dimethylformamide, thionyl chloride, ethylene carbonate or dimethylacetamide, and impregnated for 2 to 3 h.

[0015] The impregnated precursor is dried and then placed in a tube furnace and calcined at 400 to 600°C for 2 h to obtain a carbon fiber felt.

[0016] In the step S1, the catalyst accounts for 5% - 7% of the mass of the precursor; the concentration of the dispersion liquid 1 is 5mg / ml - 7mg / ml; the concentration of the dispersion liquid 2 is 12mg / ml - 16mg / ml.

[0017] In the step S2, the concentration of the KOH solution is 2mg / ml - 10mg / ml. First, the carbon fiber felt is impregnated in the dispersion liquid 1 for 20 min, then the dispersion liquid 2 is added and impregnated for 20 - 40 min, and after drying, it is impregnated in the KOH solution for 15 - 30 min.

[0018] The concentration of the KOH solution is 3mg / ml - 7mg / ml.

[0019] In the step S3, the temperature for high-temperature carbonization of the modified carbon fiber felt in a tube furnace is 1100 - 1300 °C, and the burning time is 2 - 3 h.

[0020] A modified carbon fiber felt electrode material for a flow battery prepared by the foregoing method, the surface of which has a unique microstructure with multiple active sites formed by modifiers connected in a Π-Π conjugate form.

[0021] The modified carbon fiber felt electrode material for a flow battery provided by the present invention and its preparation method have the following beneficial effects:

[0022] 1. The present invention obtains a carbon fiber felt electrode material by low-temperature carbonization in the presence of a catalyst. Through the modification and decoration of the carbon fiber felt and the cooperation of a specific preparation process, a microstructure is formed on the surface of the carbon fiber felt electrode material, where the fibers have drawn textures, concave and convex points, local surface damage, local adhesion between multiple fibers, a large pore structure, and the modifiers are connected in a Π-Π conjugate form to form a microstructure with multiple active sites. Therefore, the specific surface area is enlarged, and stable electroactive sites are increased to accelerate the electron transfer rate, which can effectively improve the overall electrochemical performance of the carbon fiber felt as an electrode material for a flow battery.

[0023] 2. The present invention uses substances such as dextrin, polyvinyl alcohol, glass micro powder, and PDA to improve the stability of the modifier on the carbon fiber felt and prevent it from falling off during the current cycle and affecting the battery performance.

[0024] 3. The present invention further improves the porosity of the carbon fiber felt by using a KOH solution, increases the specific surface roughness of the carbon fiber felt, and enlarges the specific surface area of the carbon fiber felt;

[0025] 4. The preparation method of the modified carbon fiber felt electrode material with high conductivity for a flow battery provided by the present invention modifies the carbon fiber felt using carbon nanomaterials, expands the specific surface area of the carbon fiber felt, increases the active sites to accelerate the electron transfer rate, and improves the electrochemistry of using the carbon fiber felt as an electrode material in a flow battery.

[0026] 5. The present invention uses carbon nanomaterials such as graphene oxide, reduced graphene oxide, and graphene, and combines the preparation process to modify the fiber surface, thereby forming a unique microstructure on the surface and between the fibers of the material, having excellent conductivity, high electron transfer rate, and high specific surface area; that is, through the unique combination of carbon materials and carbon fiber felt, the disadvantages exposed when the carbon fiber felt is used as an electrode material can be significantly improved, and thus an ideal electrode material with high conductivity and multifunction for a flow battery can be prepared.

[0027] 6. The preparation method provided by the present invention has few steps and is simple to operate, shortening the time cost of the preparation process, and is easy to industrialize to meet the market demand.

[0028] The above is an overview of the technical solution of the invention. The following further describes the present invention in conjunction with specific embodiments. Brief Description of the Drawings

[0029] Figure 1 It is the surface SEM diagram of the modified carbon fiber felt material prepared in Example 1 of the present invention. Detailed Description of the Invention

[0030] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined purpose, the following details the specific embodiments of the present invention in conjunction with the accompanying drawings and preferred embodiments.

[0031] The preparation method of the modified carbon fiber felt electrode material for a flow battery provided by the embodiment of the present invention includes the following steps:

[0032] S1: Prepare the carbon fiber felt: Use the precursor to obtain the carbon fiber felt through low-temperature carbonization in the presence of a catalyst. Specifically:

[0033] First, impregnate the precursor and the catalyst simultaneously in any one of the solutions of N,N-dimethylformamide, thionyl chloride, ethylene carbonate, or dimethylacetamide for 2 - 3 h. Ultrasonic stirring can also be selected to promote the mixing of substances. Take out the impregnated precursor and dry it for later use, and put the dried precursor into a tube furnace and calcine it at 400 - 600 °C for 2 h to obtain the carbon fiber felt.

[0034] The precursor described above can be selected from one of pitch, lignin, ultra-high molecular weight polyethylene, polyacrylonitrile, and cellulose, and the catalyst can be selected from one of zinc oxide, copper oxide, nitrogen-doped carbon nanotubes, cerium oxide, and cobalt tetroxide. The catalyst accounts for 2% - 10% of the mass of the precursor, preferably 5% - 7%. The catalyst has the best effect at this ratio, which can not only play a good catalytic effect to promote the low-temperature carbonization of the precursor but also avoid wasting the catalyst.

[0035] S2: Preparation of modified carbon fiber felt by three-step impregnation method: Prepare modifier dispersion liquid 1, dispersion liquid 2, and KOH solution respectively. First, immerse the carbon fiber felt obtained after low-temperature carbonization in dispersion liquid 1 for 20 min to allow dispersion liquid 1 to infiltrate the carbon fiber felt, creating conditions for subsequent adhesion of dispersion liquid 2 to the carbon fiber felt. Then, slowly add dispersion liquid 2, and control the impregnation time within 20 - 40 min. Take out the impregnated carbon fiber felt and dry it at 120 °C for 5 h. Finally, immerse it in KOH solution for 15 - 30 min, take it out and dry it at 120 °C for 5 h.

[0036] The above-mentioned dispersion liquid 1 can be made from one of dextrin, polyvinyl alcohol, glass micro-powder, and PDA, and dispersion liquid 2 can be prepared from one of reduced graphene oxide, graphene, graphene oxide, expandable graphite, and activated carbon fiber.

[0037] Use an ethanol solution to disperse the above substances, and control the concentration of dispersion liquid 1 within the range of 3 mg / ml - 10 mg / ml, preferably 5 mg / ml - 7 mg / ml. The dispersion liquid 1 within this concentration range can well increase the adhesiveness of the carbon fiber felt.

[0038] Control the concentration of dispersion liquid 2 within the range of 10 mg / ml - 18 mg / ml, preferably 12 mg / ml - 16 mg / ml. The substances in dispersion liquid 2 within this range can not only adhere to the carbon fiber felt to expand its specific surface area and improve conductivity but also will not accumulate excessively in the gaps of the carbon fiber felt to reduce the electron transfer rate.

[0039] Among them, control the concentration of the KOH solution within the range of 2 mg / ml - 10 mg / ml, preferably 3 mg / ml - 7 mg / ml. The KOH solution within this concentration range can improve the porosity of the carbon fiber felt, increase the surface roughness of the carbon fiber felt, and at the same time will not excessively corrode and damage the structure of the carbon fiber felt.

[0040] S3: Preparation of modified carbon fiber felt electrode material by high-temperature carbonization method: Under the protection of an argon atmosphere, high-temperature carbonize the dried modified carbon fiber felt to obtain a modified and decorated carbon fiber felt electrode material.

[0041] The modified carbon fiber felt is subjected to high-temperature carbonization in a tube furnace, with the temperature controlled at 1100-1300 °C and the burning time controlled at 2-3 h.

[0042] The modified carbon fiber felt for a flow battery obtained by the above preparation method, as an electrode material for a flow battery, has a unique microstructure with multiple active sites formed by modifiers connected in a Π-Π conjugate form, enabling the material to have excellent electrochemical properties such as high conductivity and cycle stability.

[0043] Example 1

[0044] See Appendix Figure 1 , the modified carbon fiber felt electrode material for a flow battery and its preparation method provided by the embodiments of the present invention are specific applications based on the foregoing embodiments, and its preparation method includes the following steps:

[0045] S1: Prepare carbon fiber felt: Take 2 g of ultra-high molecular weight polyethylene and 100 mg of zinc oxide accounting for 5% of its mass, add them to 20 ml of thionyl chloride, impregnate for 2 h, take out the impregnated ultra-high molecular weight polyethylene, dry it at 120 °C for 5 h, and put it into a tube furnace to burn at 400 °C for 2 h to obtain carbon fiber felt.

[0046] S2: Prepare modifier dispersion liquid 1 and dispersion liquid 2 respectively. Take 175 mg of dextrin and disperse it in 25 ml of absolute ethanol, so the concentration of dispersion liquid 1 is 7 mg / ml. Take 350 mg of graphene oxide and disperse it in 25 ml of absolute ethanol, so the concentration of dispersion liquid 2 is 14 mg / ml.

[0047] First, immerse the carbon fiber felt in the dextrin dispersion liquid for 20 min, then slowly add the graphene oxide dispersion liquid, and the impregnation time is 40 min. Take it out and dry it at 120 °C for 5 h.

[0048] Immerse the dried modified carbon fiber felt in a 5 mg / ml KOH solution for 25 min, and dry it again at 120 °C for 5 h.

[0049] S3: Under the protection of an argon atmosphere, burn the dried carbon fiber felt in a tube furnace at 1300 °C for 2 h to obtain the modified carbon fiber felt electrode material.

[0050] Compared with the unmodified carbon fiber felt, the carbon fiber felt obtained in this example has significantly improved battery electrochemical performance. The resistivity of the modified carbon fiber felt is only 9.8×10 -4 Ω·cm, and the battery capacity retention rate is as high as 87% after cycling 100 times when assembled in a flow battery.

[0051] Example 2

[0052] The modified carbon fiber felt electrode material for a flow battery provided by an embodiment of the present invention and its preparation method, which is a specific application based on the foregoing Embodiment 1, and the preparation method includes the following steps:

[0053] S1: Prepare the carbon fiber felt: Take 2 g of pitch and 60 mg of copper oxide accounting for 3% of the mass of the pitch, add them to 20 ml of dimethylacetamide and impregnate for 2 h. After taking out, the impregnated pitch is dried at 120 °C for 5 h, and then put into a tubular furnace and calcined at 400 °C for 2 h to obtain the carbon fiber felt.

[0054] S2: Prepare modifier dispersion liquid 1 and dispersion liquid 2 respectively. Take 125 mg of PDA and disperse it in 25 ml of absolute ethanol, that is, the concentration of dispersion liquid 1 is 5 mg / ml. Take 300 mg of graphene and disperse it in 25 ml of absolute ethanol, that is, the concentration of dispersion liquid 2 is 12 mg / ml.

[0055] First, immerse the carbon fiber felt in the PDA dispersion liquid for 20 min, and then slowly add the graphene dispersion liquid, and the impregnation time is 30 min. Take out the carbon fiber felt and dry it at 120 °C for 5 h.

[0056] Immerse the above-mentioned dried modified carbon fiber felt in a 3 mg / ml KOH solution for 20 min, and dry it again at 120 °C for 5 h.

[0057] S3: Under the protection of an argon atmosphere, calcine the dried carbon fiber felt in a tubular furnace at 1200 °C for 2.5 h to obtain the modified carbon fiber felt electrode material.

[0058] Example 3

[0059] The modified carbon fiber felt electrode material for a flow battery provided by an embodiment of the present invention and its preparation method, which is a specific application based on the foregoing Embodiments 1-2, and the preparation method includes the following steps:

[0060] S1: Prepare the carbon fiber felt: Take 2 g of polyacrylonitrile and 40 mg of nitrogen-doped carbon nanotubes accounting for 2% of the mass of the polyacrylonitrile, add them to 20 ml of N,N-dimethylformamide and impregnate for 2 h. After taking out the impregnated polyacrylonitrile, dry it at 120 °C for 5 h, and then put it into a tubular furnace and calcine it at 400 °C for 2 h to obtain the carbon fiber felt.

[0061] S2: Prepare modifier dispersion liquid 1 and dispersion liquid 2 respectively. Take 75 mg of polyvinyl alcohol and disperse it in 25 ml of absolute ethanol, that is, the concentration of dispersion liquid 1 is 3 mg / ml. Take 250 mg of reduced graphene oxide and disperse it in 25 ml of absolute ethanol, that is, the concentration of dispersion liquid 2 is 10 mg / ml.

[0062] First, immerse the carbon fiber felt in the polyvinyl alcohol dispersion for 20 min, then slowly add the reduced graphene oxide dispersion, and the immersion time is 20 min. Take out the immersed carbon fiber felt and dry it at 120 °C for 5 h.

[0063] Immerse the above-mentioned dried modified carbon fiber felt in a 2 mg / ml KOH solution for 15 min, and dry it again at 120 °C for 5 h.

[0064] S3: Under the protection of an argon atmosphere, burn the dried carbon fiber felt in a tube furnace at 1100 °C for 3 h to obtain the modified carbon fiber felt electrode material.

[0065] Example 4

[0066] The modified carbon fiber felt electrode material for a flow battery and its preparation method provided by the embodiments of the present invention are specific applications based on the foregoing embodiments. The preparation method includes the following steps:

[0067] S1: Prepare carbon fiber felt: Take 2 g of ultra-high molecular weight polyethylene and 140 mg of cerium oxide accounting for 7% of its mass, add them to 20 ml of ethylene carbonate and immerse for 2 h. Take out the immersed ultra-high molecular weight polyethylene and dry it at 120 °C for 5 h, and then put it into a tube furnace and burn it at 400 °C for 2 h to obtain the carbon fiber felt.

[0068] S2: Prepare modifier dispersions 1 and 2 respectively. Take 225 mg of glass micro-powder and disperse it in 25 ml of absolute ethanol, so the concentration of dispersion 1 is 9 mg / ml. Take 400 mg of expandable graphite and disperse it in 25 ml of absolute ethanol, so the concentration of dispersion 2 is 16 mg / ml.

[0069] First, immerse the carbon fiber felt in the glass micro-powder dispersion for 20 min, then slowly add the expandable graphite dispersion, and the immersion time is 40 min. Take out and dry it at 120 °C for 5 h.

[0070] Immerse the above-mentioned dried modified carbon fiber felt in a 7 mg / ml KOH solution for 20 min, and dry it again at 120 °C for 5 h.

[0071] S3: Under the protection of an argon atmosphere, burn the dried carbon fiber felt in a tube furnace at 1100 °C for 3 h to obtain the modified carbon fiber felt electrode material.

[0072] Example 5

[0073] The modified carbon fiber felt electrode material for a flow battery and its preparation method provided by the embodiments of the present invention are specific applications based on the foregoing Embodiments 1-4. The preparation method includes the following steps:

[0074] S1: Preparation of carbon fiber felt: Take 2 g of polyacrylonitrile and 180 mg of cobalt tetroxide, which accounts for 9% of the mass of polyacrylonitrile, add them to 20 ml of thionyl chloride and impregnate for 2 h. Take out the impregnated polyacrylonitrile, dry it at 120 °C for 5 h, and then put it into a tube furnace and calcine at 400 °C for 2 h to obtain the carbon fiber felt.

[0075] S2: Prepare modifier dispersion liquid 1 and dispersion liquid 2 respectively. Take 125 mg of polyvinyl alcohol and disperse it in 25 ml of absolute ethanol, so the concentration of dispersion liquid 1 is 10 mg / ml. Take 450 mg of activated carbon fiber and disperse it in 25 ml of absolute ethanol, so the concentration of dispersion liquid 2 is 18 mg / ml.

[0076] First, immerse the carbon fiber felt in the polyvinyl alcohol dispersion liquid for 10 min, and then slowly add the activated carbon fiber dispersion liquid, with an immersion time of 30 min. Take it out and dry it at 120 °C for 5 h.

[0077] Immerse the modified and decorated carbon fiber felt after drying in a 9 mg / ml KOH solution for 30 min, and then dry it again at 120 °C for 5 h.

[0078] S3: Under the protection of an argon atmosphere, calcine the dried carbon fiber felt in a tube furnace at 1200 °C for 2.5 h to obtain the modified carbon fiber felt electrode material.

[0079] Example 6

[0080] The modified carbon fiber felt electrode material for a flow battery and its preparation method provided by the embodiment of the present invention are specific applications based on the foregoing embodiments 1-5, and its preparation method includes the following steps:

[0081] S1: Preparation of carbon fiber felt: Add 2 g of pitch and 200 mg of nitrogen-doped carbon nanotubes, which account for 10% of the pitch, to 20 ml of N,N-dimethylformamide and impregnate for 2 h. Take out the impregnated pitch, dry it at 120 °C for 7 h, and then put it into a tube furnace and calcine at 400 °C for 2 h to obtain the carbon fiber felt.

[0082] S2: Prepare modifier dispersion liquid 1 and dispersion liquid 2 respectively. Take 125 mg of polyvinyl alcohol and disperse it in 25 ml of absolute ethanol, so the concentration of dispersion liquid 1 is 5 mg / ml. Take 300 mg of reduced graphene oxide and disperse it in 25 ml of ethanol, so the concentration of dispersion liquid 2 is 12 mg / ml.

[0083] First, immerse the carbon fiber felt in the polyvinyl alcohol dispersion liquid for 20 min, and then slowly add the reduced graphene oxide dispersion liquid, with an immersion time of 30 min. Take out the carbon fiber felt and dry it at 120 °C for 5 h.

[0084] The dried modified carbon fiber felt described above was immersed in a 10 mg / ml KOH solution for 30 min and then dried again at 120 °C for 5 h.

[0085] S3: Under the protection of an argon atmosphere, the dried carbon fiber felt was calcined in a tube furnace at 1300 °C for 2 h to obtain a modified carbon fiber felt electrode material.

[0086] The performances of the modified carbon fiber felt electrode materials obtained in Examples 1-6 were tested respectively, and the results are shown in Table 1.

[0087] Table 1: Performance test results of the modified carbon fiber felt

[0088] Resistivity (Ω·cm) Flow battery capacity retention rate (100 cycles) Example 1 <![CDATA[9.8×10 -4 > 87％ Example 2 <![CDATA[1.1×10 -3 > 84％ Example 3 <![CDATA[3.1×10 -3 > 73％ Example 4 <![CDATA[1.9×10 -3 > 79％ Example 5 <![CDATA[2.8×10 -3 > 75％ Example 6 <![CDATA[2.6×10 -3 > 76％

[0089] As can be seen from Table 1, the modified carbon fiber felt electrode materials prepared in Examples 1-6 of the present invention all have a low surface resistivity and excellent electrochemical performances such as high conductivity and cycle stability.

[0090] The embodiments described above are only a part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts belong to the scope of protection of the present invention.

Claims

1. A preparation method of a modified carbon fiber felt electrode material for a flow battery, characterized in that It uses a three-step impregnation-high temperature carbonization method to obtain a modified carbon fiber felt electrode material, including the following steps: S1: Prepare the carbon fiber felt: Use the precursor to obtain the carbon fiber felt by low-temperature carbonization under the action of a catalyst; The catalyst accounts for 2%-10% of the mass of the precursor. The catalyst and the precursor are sequentially added to a solution of N,N-dimethylformamide, thionyl chloride, ethylene carbonate or dimethylacetamide, and impregnated for 2-3 h; the impregnated precursor is dried and then placed in a tube furnace and calcined at 400-600 °C for 2 h to obtain the carbon fiber felt; S2: Prepare the modified carbon fiber felt: Prepare modifier dispersion liquid 1, dispersion liquid 2 and KOH solution respectively. First impregnate the carbon fiber felt in dispersion liquid 1, then slowly add dispersion liquid 2, take it out and dry it at 120 °C for 5 h, and finally impregnate it in the KOH solution, take it out and dry it at 120 °C for 5 h; among them, dispersion liquid 1 is a solution prepared from one of dextrin, polyvinyl alcohol, glass micro powder and PDA, and its concentration is 3 mg / ml-10 mg / ml; dispersion liquid 2 is a solution prepared from one of reduced graphene oxide, graphene, graphene oxide, expandable graphite and activated carbon fiber, and its concentration is 10 mg / ml-18 mg / ml; The concentration of the KOH solution is 2 mg / ml-10 mg / ml. First impregnate the carbon fiber felt in dispersion liquid 1 for 20 min, then add dispersion liquid 2 and impregnate for 20-40 min, and after drying, impregnate it in the KOH solution for 15-30 min; S3: Preparation of electrode material by high-temperature carbonization: Under the protection of an argon atmosphere, high-temperature carbonization is carried out to obtain a modified carbon fiber felt electrode material with a unique microstructure having multiple active sites, where the surface is composed of modifiers connected in a conjugated form.

2. The preparation method according to claim 1, characterized in that, The precursor in step S1 is one of pitch, lignin, ultra-high molecular weight polyethylene, polyacrylonitrile and cellulose.

3. The preparation method according to claim 2, characterized in that, The catalyst in step S1 is one of zinc oxide, copper oxide, nitrogen-doped carbon nanotubes, cerium oxide and cobalt tetroxide.

4. The preparation method according to claim 3, characterized in that, In step S1, the catalyst accounts for 5%-7% of the mass of the precursor, the concentration of dispersion liquid 1 is 5 mg / ml-7 mg / ml; the concentration of dispersion liquid 2 is 12 mg / ml-16 mg / ml.

5. The preparation method according to claim 4, wherein, The concentration of the KOH solution is 3 mg / ml-7 mg / ml.

6. The preparation method according to claim 1, characterized in that In step S3, the temperature for high-temperature carbonization of the modified carbon fiber felt in a tube furnace is 1100-1300 °C, and the calcination time is 2-3 h.

7. A modified carbon fiber felt for a flow battery prepared by the preparation method according to any one of claims 1-6, characterized in that, Its surface has a unique microstructure with multiple active sites formed by the modifier connected in a conjugated form.

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