A method for regenerating a vanadium cell waste graphite felt electrode

Abstract

The application relates to the technical field of electrodes of all-vanadium redox flow batteries, and discloses a vanadium battery waste graphite felt electrode regeneration method, which comprises the following steps: immersing a waste graphite felt electrode in a pretreatment liquid, performing ultrasonic treatment, centrifugally throwing out water, and obtaining a pretreated graphite felt electrode; adding urea solution and boric acid solution in sequence, making the graphite felt electrode completely immerse in the solution, then slowly adding a strong alkali solution and an alcohol solution, heating and stirring, vacuum drying, obtaining a precursor graphite felt electrode, heat treatment, cleaning, freeze-drying, and obtaining a regenerated graphite felt electrode. Through the cleaning-activation regeneration process, impurities in the waste graphite felt electrode can be effectively removed, the activity of the graphite felt can be effectively improved, the catalytic performance of the graphite felt can be improved, and the efficiency of the battery can be improved.

Description

Technical Field

[0001] This application relates to the field of vanadium redox flow battery electrode technology, and in particular to a method for regenerating waste graphite felt electrodes from vanadium batteries. Background Technology

[0002] Vanadium redox flow batteries (vanadium batteries) convert electrical energy into chemical energy through redox reactions of vanadium ions in different valence states in the positive and negative electrode electrolytes. Electrodes are the core components of vanadium redox flow batteries, providing a site for redox reactions of the positive and negative electrode energy storage active materials (vanadium ions in different valence states). The requirements for electrodes in vanadium redox flow batteries are: (1) high catalytic activity to reduce the internal resistance and activation polarization of the battery, and improve the energy efficiency and voltage efficiency of the battery; (2) high conductivity to accelerate the electron transport rate in the redox reaction, and improve the energy efficiency and voltage efficiency of the battery; (3) excellent physical and chemical stability to ensure long-term stable operation of the battery; and (4) low price to facilitate large-scale commercialization.

[0003] The commonly used electrode is the graphite felt electrode. However, after long-term use, the catalytic activity of the graphite felt electrode will gradually decrease, which directly leads to a decline in battery performance. Summary of the Invention

[0004] The purpose of this application is to provide a method for regenerating waste graphite felt electrodes for vanadium batteries. By activating the fiber structure of the waste graphite felt electrodes, the active area of ​​the electrodes is increased. By modifying the functional groups of the graphite felt electrode fibers, their conductivity and material interaction with the electrolyte are improved, thereby increasing the reaction rate of the redox reaction in the battery and thus improving the battery efficiency.

[0005] To achieve the above objectives, this application provides the following technical solution:

[0006] This application provides a method for regenerating waste graphite felt electrodes from vanadium batteries, including the following steps:

[0007] Step S1: Immerse the waste graphite felt electrode in the pretreatment solution, sonicate it, remove it after the treatment, centrifuge to remove water, and obtain the pretreated graphite felt electrode.

[0008] Step S2: Place the pretreated graphite felt electrode in a reactor, add urea solution and boric acid solution in sequence to completely immerse the graphite felt electrode, then slowly add strong alkali solution and alcohol solution, heat and stir to react for a period of time, remove the graphite felt electrode, vacuum dry it to obtain the precursor graphite felt electrode.

[0009] Step S3: The precursor graphite felt electrode is placed in an atmosphere furnace for heat treatment. After the heat treatment is completed, the graphite felt electrode is taken out, cleaned, and freeze-dried to obtain a regenerated graphite felt electrode.

[0010] In one implementation, in step S1:

[0011] The pretreatment solution is obtained by dispersing calcium hydroxide, ammonium salt and water in a mass ratio of 1:(0.7~1):100; wherein the ammonium salt is one of ammonium chloride, ammonium formate and ammonium acetate.

[0012] Calcium ions can effectively remove residual sulfate ions from waste graphite felt electrodes, while ammonium ions and hydroxide ions can effectively remove residual vanadium ions and other metal ions from waste graphite felt electrodes, reducing the adverse effects of regenerated waste graphite felt electrodes on battery performance.

[0013] In one implementation, in step S1:

[0014] The ultrasonic treatment has a power of 100~300W, a frequency of 40kHz, a temperature of 30~50℃, and a time of 2~4h.

[0015] The centrifugation speed for removing water is 1000~3000 rpm, and the time is 3~5 minutes.

[0016] This removes most of the moisture and sediment, making it easier for subsequent liquid impregnation operations.

[0017] In one implementation, in step S2:

[0018] The volume ratio of the urea solution, boric acid solution, strong alkali solution and alcohol solution is 1:(4~6):(5~8):(1~3).

[0019] The addition of a strong alkali solution makes the solution alkaline. Under alkaline conditions, boric acid transforms from an electrically neutral planar triangular structure (B(OH)3) into a negatively charged tetrahedral borate ion (B(OH)4). - It can coordinate with alcohols to form complexes.

[0020] In one implementation method

[0021] The concentration of the urea solution is 1~2 mol / L;

[0022] The concentration of the boric acid solution is 0.5~1 mol / L;

[0023] The strong alkaline solution is either sodium hydroxide solution or potassium hydroxide solution, with a concentration of 2~4 mol / L.

[0024] The addition of urea can not only generate carbon dioxide to further remove residual calcium ions, but also provide nitrogen-doped nitrogen sources and ammonium ions for the recycling of waste graphite felt.

[0025] In one implementation method

[0026] The alcohol solution is one of the following: 1,2-propanediol solution, 1,3-butanediol solution, 2-ethyl-1,3-hexanediol solution, 2-butyl-2-ethyl-1,3-propanediol solution, fructose solution, and sucrose solution, with a concentration of 0.6~1.2 mol / L.

[0027] Diols in alcohol solutions can form stable complexes with boric acid under alkaline conditions and be loaded in situ onto the surface of graphite felt fibers. After subsequent treatment, the activity of graphite felt fibers can be effectively improved.

[0028] In one implementation, in step S2:

[0029] The heating and stirring reaction is carried out at a temperature of 60~90℃ for a time of 0.5~2h.

[0030] The vacuum drying temperature is 70~90℃, and the time is 4~6h.

[0031] In one implementation, in step S3:

[0032] The heat treatment method is as follows: the precursor graphite felt electrode is heated to 150~250℃ at a heating rate of 5℃ / min under a protective gas atmosphere, held for 0.5h, and then heated to 700~900℃ at a heating rate of 5℃ / min, held for 1~3h.

[0033] A two-step heat treatment process is employed. Holding at 150-250℃ for 0.5 hours facilitates the more robust loading of the complexes formed by alcohols and boric acid onto the graphite felt fibers. Simultaneously, excess urea is decomposed, and the resulting ammonia is adsorbed onto the graphite felt, which is beneficial for subsequent nitrogen doping. Holding at 700-900℃ for 1-3 hours removes most of the oxygen-containing groups, while nitrogen and boron doping effectively enhances the activity of the graphite felt fibers. Furthermore, excess alkali and ammonia can perform a minor etching on the surface of the graphite felt fibers, leading to more exposed active sites after subsequent cleaning.

[0034] In one embodiment, the protective gas is either nitrogen or argon.

[0035] In one implementation, in step S3:

[0036] The cleaning method is as follows: place the graphite felt electrode in water at 60~80℃, shake for 5 minutes, take it out and spin dry, then place it in another portion of water at 60~80℃, shake for 5 minutes, and take it out.

[0037] The freeze-drying temperature is -40~-60℃, and the time is 6~8h.

[0038] The beneficial effects of this application are:

[0039] 1. This application utilizes a cleaning-activation regeneration process to effectively remove impurities from spent graphite felt electrodes and significantly improve their activity and catalytic performance. Furthermore, the recycling of replaced spent graphite felt electrodes not only reduces the overall lifespan cost of vanadium redox flow batteries but also minimizes resource waste.

[0040] 2. This application utilizes boric acid under alkaline conditions to transform the electrically neutral planar triangular structure (B(OH)3) into the negatively charged tetrahedral borate ion (B(OH)4). - The boron-containing complex, which can coordinate with alcohols to form a complex, can be loaded in situ onto the surface of graphite felt fibers. After subsequent treatment, the activity of graphite felt fibers can be effectively improved.

[0041] 3. This application employs a two-step heat treatment method. The initial low-temperature treatment facilitates the more robust loading of the complexes formed by alcohols and boric acid onto the graphite felt fibers, while simultaneously decomposing excess urea. The resulting ammonia is adsorbed onto the graphite felt, which is beneficial for subsequent nitrogen doping. The further high-temperature treatment removes most of the oxygen-containing groups, and the nitrogen and boron doping effectively enhances the activity of the graphite felt fibers. In addition, excess alkali and ammonia can perform micro-etching on the surface of the graphite felt fibers, and subsequent cleaning allows the graphite felt fibers to form more exposed active sites. Attached Figure Description

[0042] Figure 1 This application discloses a method for regenerating waste graphite felt electrodes from vanadium batteries;

[0043] Figure 2 SEM image of the regenerated graphite felt electrode obtained in Example 1. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0045] like Figure 1 As shown, a method for regenerating waste graphite felt electrodes from vanadium batteries includes the following steps:

[0046] Step S1: Immerse the waste graphite felt electrode in the pretreatment solution, and ultrasonically treat it for 2-4 hours with a power of 100-300W, a frequency of 40kHz, and a temperature of 30-50℃. After treatment, remove the electrode and centrifuge it at 1000-3000rpm for 3-5 minutes to remove water, thus obtaining the pretreated graphite felt electrode. The pretreatment solution is composed of calcium hydroxide, ammonium salt, and water dispersed in a mass ratio of 1:(0.7-1):100. The ammonium salt is one of ammonium chloride, ammonium formate, and ammonium acetate.

[0047] Step S2: Place the pretreated graphite felt electrode in a reactor, and successively add a 1-2 mol / L urea solution and a 0.5-1 mol / L boric acid solution to completely immerse the graphite felt electrode. Then, slowly add a 2-4 mol / L strong alkali solution and a 0.6-1.2 mol / L alcohol solution. Heat and stir the reaction at 60-90℃ for 0.5-2 hours. Remove the graphite felt electrode and vacuum dry it at 70-90℃ for 4-6 hours to obtain the precursor graphite felt electrode. The volume ratio of the urea solution, boric acid solution, strong alkali solution, and alcohol solution is 1:(4-6):(5-8):(1-3). The strong alkali solution is either sodium hydroxide solution or potassium hydroxide solution. The alcohol solution is either 1,2-propanediol solution, 1,3-butanediol solution, 2-ethyl-1,3-hexanediol solution, 2-butyl-2-ethyl-1,3-propanediol solution, fructose solution, or sucrose solution.

[0048] Step S3: Place the precursor graphite felt electrode in an atmosphere furnace under a protective gas atmosphere. First, heat it to 150~250℃ at a heating rate of 5℃ / min and hold for 0.5h. Then, heat it to 700~900℃ at a heating rate of 5℃ / min and hold for 1~3h. After the heating is complete, remove the graphite felt electrode and place it in water at 60~80℃. Shake for 5min, remove and spin dry. Then place it in another portion of water at 60~80℃ and shake for 5min. Remove and clean it. Freeze-dry at -40~-60℃ for 6~8h to obtain a regenerated graphite felt electrode. The protective gas is either nitrogen or argon.

[0049] Example 1: The following scheme is adopted.

[0050] Step S1: Immerse the waste graphite felt electrode in a pretreatment solution prepared by dispersing calcium hydroxide, ammonium chloride and water in a mass ratio of 1:0.7:100. Set the power to 100W, the frequency to 40kHz and the temperature to 30℃ for ultrasonic treatment for 2h. After the treatment, take it out and centrifuge at 1000rpm for 3min to remove the water, and obtain the pretreated graphite felt electrode.

[0051] Step S2: Place the pretreated graphite felt electrode in a reactor, and add 1 mol / L urea solution and 0.5 mol / L boric acid solution successively to completely immerse the graphite felt electrode. Then, slowly add 2 mol / L sodium hydroxide solution and 0.6 mol / L 1,2-propanediol solution. Heat and stir the reaction at 60°C for 0.5 h. Remove the graphite felt electrode and vacuum dry it at 70°C for 4 h to obtain the precursor graphite felt electrode. The volume ratio of urea solution, boric acid solution, strong alkali solution and alcohol solution is 1:4:5:1.

[0052] Step S3: Place the precursor graphite felt electrode in an atmosphere furnace under a nitrogen atmosphere, first heat it to 150℃ at a heating rate of 5℃ / min, hold it at that temperature for 0.5h, then heat it to 800℃ at a heating rate of 5℃ / min, hold it at that temperature for 2h. After that, take out the graphite felt electrode, place it in 60℃ water, shake it for 5min, take it out and spin it dry, then place it in another portion of 60℃ water, shake it for 5min, take it out and clean it, freeze dry it at -40℃ for 6h to obtain the regenerated graphite felt electrode.

[0053] like Figure 2 As shown, the surface of the graphite felt electrode fiber obtained in this embodiment is rough, and there is a material loaded on the surface. This indicates that the regeneration method of this application increases the defects on the surface of the graphite felt fiber, thereby increasing the specific surface area and reactive sites. At the same time, the presence of carbon material loaded on it further enhances the reactivity of the graphite felt electrode.

[0054] Example 2: The following scheme is adopted.

[0055] Step S1: Immerse the waste graphite felt electrode in a pretreatment solution prepared by dispersing calcium hydroxide, ammonium formate and water in a mass ratio of 1:1:100. Set the power to 300W, the frequency to 40kHz, and the temperature to 50℃ for ultrasonic treatment for 4 hours. After the treatment, take it out and centrifuge it at 3000rpm for 5 minutes to remove the water, and obtain the pretreated graphite felt electrode.

[0056] Step S2: Place the pretreated graphite felt electrode in a reactor, and add urea solution with a concentration of 2 mol / L and boric acid solution with a concentration of 1 mol / L successively to completely immerse the graphite felt electrode. Then, slowly add potassium hydroxide solution with a concentration of 4 mol / L and 1,3-butanediol solution with a concentration of 1.2 mol / L. Heat and stir the reaction at 90°C for 2 hours. Remove the graphite felt electrode and vacuum dry it at 90°C for 6 hours to obtain the precursor graphite felt electrode. The volume ratio of urea solution, boric acid solution, strong alkali solution and alcohol solution is 1:6:8:3.

[0057] Step S3: Place the precursor graphite felt electrode in an atmosphere furnace under an argon atmosphere, first heat it to 250℃ at a heating rate of 5℃ / min, hold it at that temperature for 0.5h, then heat it to 900℃ at a heating rate of 5℃ / min, hold it at that temperature for 3h. After that, take out the graphite felt electrode, place it in 80℃ water, shake it for 5min, take it out and spin it dry, then place it in another portion of 80℃ water, shake it for 5min, take it out and clean it, freeze dry it at -60℃ for 8h to obtain the regenerated graphite felt electrode.

[0058] Example 3: The following scheme is adopted.

[0059] Step S1: Immerse the waste graphite felt electrode in a pretreatment solution prepared by dispersing calcium hydroxide, ammonium acetate and water in a mass ratio of 1:0.8:100. Set the power to 200W, the frequency to 40kHz and the temperature to 40℃ for ultrasonic treatment for 3h. After the treatment, take it out and centrifuge at 2000rpm for 4min to remove the water, and obtain the pretreated graphite felt electrode.

[0060] Step S2: Place the pretreated graphite felt electrode in a reactor, and add 1.5 mol / L urea solution and 0.8 mol / L boric acid solution successively to completely immerse the graphite felt electrode. Then, slowly add 3 mol / L potassium hydroxide solution and 0.8 mol / L 2-ethyl-1,3-hexanediol solution. Heat and stir at 80°C for 1 hour. Remove the graphite felt electrode and vacuum dry at 80°C for 5 hours to obtain the precursor graphite felt electrode. The volume ratio of urea solution, boric acid solution, strong alkali solution and alcohol solution is 1:5:6:2.

[0061] Step S3: Place the precursor graphite felt electrode in an atmosphere furnace under an argon atmosphere, first heat it to 200℃ at a heating rate of 5℃ / min, hold it at that temperature for 0.5h, then heat it to 800℃ at a heating rate of 5℃ / min, hold it at that temperature for 2h. After that, take out the graphite felt electrode, place it in 70℃ water, shake it for 5min, take it out and spin it dry, then place it in another 70℃ water, shake it for 5min, take it out and clean it, freeze dry it at -50℃ for 7h to obtain the regenerated graphite felt electrode.

[0062] Example 4: The following scheme is adopted.

[0063] Step S1: Immerse the waste graphite felt electrode in a pretreatment solution prepared by dispersing calcium hydroxide, ammonium chloride and water in a mass ratio of 1:0.9:100. Set the power to 150W, the frequency to 40kHz and the temperature to 40℃ for ultrasonic treatment for 4 hours. After the treatment, take it out and centrifuge at 3000rpm for 5 minutes to remove the water, and obtain the pretreated graphite felt electrode.

[0064] Step S2: Place the pretreated graphite felt electrode in a reactor, and add 1.8 mol / L urea solution and 0.9 mol / L boric acid solution successively to completely immerse the graphite felt electrode. Then, slowly add 4 mol / L potassium hydroxide solution and 1 mol / L 2-butyl-2-ethyl-1,3-propanediol solution. Heat and stir the reaction at 70°C for 1.5 h. Remove the graphite felt electrode and vacuum dry it at 80°C for 6 h to obtain the precursor graphite felt electrode. The volume ratio of urea solution, boric acid solution, strong alkali solution and alcohol solution is 1:4:7:2.

[0065] Step S3: Place the precursor graphite felt electrode in an atmosphere furnace under an argon atmosphere, first heat it to 250℃ at a heating rate of 5℃ / min, hold it at that temperature for 0.5h, then heat it to 800℃ at a heating rate of 5℃ / min, hold it at that temperature for 2h. After that, take out the graphite felt electrode, place it in 70℃ water, shake it for 5min, take it out and spin it dry, then place it in another portion of 70℃ water, shake it for 5min, take it out and clean it, freeze dry it at -60℃ for 8h to obtain the regenerated graphite felt electrode.

[0066] Example 5: The following scheme is adopted.

[0067] Step S1: Immerse the waste graphite felt electrode in a pretreatment solution prepared by dispersing calcium hydroxide, ammonium acetate and water in a mass ratio of 1:0.9:100. Set the power to 300W, the frequency to 40kHz and the temperature to 50℃ for ultrasonic treatment for 2h. After the treatment, take it out and centrifuge at 3000rpm for 3min to remove water, and obtain the pretreated graphite felt electrode.

[0068] Step S2: Place the pretreated graphite felt electrode in a reactor, and add 1 mol / L urea solution and 0.5 mol / L boric acid solution successively to completely immerse the graphite felt electrode. Then, slowly add 2 mol / L potassium hydroxide solution and 1.2 mol / L fructose solution. Heat and stir the reaction at 90°C for 0.5 h. Remove the graphite felt electrode and vacuum dry it at 90°C for 4 h to obtain the precursor graphite felt electrode. The volume ratio of urea solution, boric acid solution, strong alkali solution and alcohol solution is 1:5:7:2.

[0069] Step S3: Place the precursor graphite felt electrode in an atmosphere furnace under a nitrogen atmosphere, first heat it to 250℃ at a heating rate of 5℃ / min, hold it at that temperature for 0.5h, then heat it to 700℃ at a heating rate of 5℃ / min, hold it at that temperature for 1h. After that, take out the graphite felt electrode, place it in 60℃ water, shake it for 5min, take it out and spin it dry, then place it in another portion of 60℃ water, shake it for 5min, take it out and clean it, freeze dry it at -40℃ for 6h to obtain the regenerated graphite felt electrode.

[0070] Example 6: The following scheme is adopted.

[0071] Step S1: Immerse the waste graphite felt electrode in a pretreatment solution prepared by dispersing calcium hydroxide, ammonium chloride and water in a mass ratio of 1:0.7:100. Set the power to 300W, the frequency to 40kHz and the temperature to 50℃ for ultrasonic treatment for 4h. After the treatment, take it out and centrifuge at 3000rpm for 5min to remove the water, and obtain the pretreated graphite felt electrode.

[0072] Step S2: Place the pretreated graphite felt electrode in a reactor, and add 2 mol / L urea solution and 1 mol / L boric acid solution successively to completely immerse the graphite felt electrode. Then, slowly add 4 mol / L potassium hydroxide solution and 0.6 mol / L sucrose solution. Heat and stir the reaction at 60°C for 0.5 h. Remove the graphite felt electrode and vacuum dry it at 70°C for 4 h to obtain the precursor graphite felt electrode. The volume ratio of urea solution, boric acid solution, strong alkali solution and alcohol solution is 1:6:8:3.

[0073] Step S3: Place the precursor graphite felt electrode in an atmosphere furnace under an argon atmosphere, first heat it to 250℃ at a heating rate of 5℃ / min, hold it at that temperature for 0.5h, then heat it to 900℃ at a heating rate of 5℃ / min, hold it at that temperature for 3h. After that, take out the graphite felt electrode, place it in 80℃ water, shake it for 5min, take it out and spin it dry, then place it in another portion of 80℃ water, shake it for 5min, take it out and clean it, freeze dry it at -60℃ for 8h to obtain the regenerated graphite felt electrode.

[0074] Comparative Example 1: Waste graphite felt electrode.

[0075] Comparative Example 2: The difference between this comparative example and Example 1 is that the waste graphite felt is directly washed with water in step S1.

[0076] Comparative Example 3: The difference between this comparative example and Example 1 is that urea solution is not added in step S2.

[0077] Comparative Example 4: The difference between this comparative example and Example 1 is that boric acid solution is not added in step S2.

[0078] Comparative Example 5: The difference between this comparative example and Example 1 is that no alcohol solution is added in step S2.

[0079] Comparative Example 6: The difference between this comparative example and Example 1 is that the heat treatment method in step S3 is to directly heat to 800°C at a heating rate of 5°C / min and hold for 2 hours.

[0080] Graphite felt specific surface area test: The graphite felts obtained in Examples 1-6 and Comparative Examples 1-6 were tested using the BET specific surface area test method.

[0081] Battery efficiency test: Vanadium redox flow batteries were assembled using graphite felt electrodes obtained in Examples 1-6 and Comparative Examples 1-6, and charged and discharged under the same operating conditions to test the coulombic efficiency, energy efficiency, and voltage efficiency of the batteries.

[0082] The test results are shown in Table 1:

[0083] Table 1 Summary of Test Results

[0084]

[0085] As shown in Table 1, the specific surface area, coulombic efficiency, energy efficiency, and voltage efficiency of the graphite felt electrodes in Examples 1-6 are significantly higher than those in Comparative Example 1, indicating that the method of this application can effectively regenerate waste graphite felt electrodes from vanadium batteries. A comparison between Example 1 and Comparative Example 2 shows that calcium ions in the pretreatment solution of step S1 can effectively remove residual sulfate ions from the waste graphite felt electrodes, while ammonium ions and hydroxide ions can effectively remove residual vanadium ions and other metal ions, reducing the adverse effects of the regenerated waste graphite felt electrodes on battery performance. Furthermore, a comparison between Example 1 and Comparative Examples 3-5 shows that urea, boric acid, and alcohols all have a significant impact on the performance of the regenerated waste graphite felt electrodes. This is mainly because boric acid, under alkaline conditions, transforms from an electrically neutral planar triangular structure (B(OH)3) into a negatively charged tetrahedral borate ion (B(OH)4). - The boron-containing complex, which can coordinate with alcohols to form complexes, is used to load boron-containing complexes in situ onto the surface of graphite felt fibers. Subsequent treatment effectively improves the activity of the graphite felt fibers. Urea not only generates carbon dioxide to further remove residual calcium ions, but also provides nitrogen sources and ammonium ions for recycling waste graphite felt. Finally, comparing Example 1 and Comparative Example 6, it can be seen that although their initial efficiencies are comparable, the voltage efficiency of the graphite felt electrode obtained in Comparative Example 6 without initial low-temperature heat treatment decays more rapidly with long-term battery operation. This is mainly because the initial low-temperature treatment facilitates a more robust loading of the complexes formed by alcohols and boric acid onto the graphite felt fibers, while also decomposing excess urea, with the resulting ammonia adsorbed onto the graphite felt, which is beneficial for subsequent nitrogen doping. Further high-temperature treatment removes most of the oxygen-containing groups, and nitrogen and boron doping effectively improves the activity of the graphite felt fibers. Furthermore, excess alkali and ammonia can perform micro-etching on the surface of the graphite felt fibers, and subsequent cleaning allows for the formation of more exposed active sites.

[0086] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for regenerating waste graphite felt electrodes from vanadium batteries, characterized in that, Includes the following steps: Step S1: Immerse the waste graphite felt electrode in the pretreatment solution, sonicate it, remove it after the procedure, centrifuge to remove water, and obtain the pretreated graphite felt electrode; the pretreatment solution is obtained by dispersing calcium hydroxide, ammonium salt and water in a mass ratio of 1:(0.7~1):100; wherein the ammonium salt is one of ammonium chloride, ammonium formate and ammonium acetate. Step S2: Place the pretreated graphite felt electrode in a reactor, and add urea solution with a concentration of 1~2 mol / L and boric acid solution with a concentration of 0.5~1 mol / L successively to completely immerse the graphite felt electrode. Then, slowly add strong alkali solution with a concentration of 2~4 mol / L and alcohol solution with a concentration of 0.6~1.2 mol / L. The volume ratio of the urea solution, boric acid solution, strong alkali solution and alcohol solution is 1:(4~6):(5~8):(1~3). After heating and stirring for a period of time, remove the graphite felt electrode and vacuum dry it to obtain the precursor graphite felt electrode. Step S3: The precursor graphite felt electrode is placed in an atmosphere furnace for heat treatment. After the heat treatment is completed, the graphite felt electrode is taken out, cleaned, and freeze-dried to obtain a regenerated graphite felt electrode. The heat treatment method is as follows: the precursor graphite felt electrode is heated to 150~250℃ at a heating rate of 5℃ / min under a protective gas atmosphere and held for 0.5h, and then heated to 700~900℃ at a heating rate of 5℃ / min and held for 1~3h.

2. The regeneration method as described in claim 1, characterized in that, In step S1: The ultrasonic treatment has a power of 100~300W, a frequency of 40kHz, a temperature of 30~50℃, and a time of 2~4h. The centrifugation speed for removing water is 1000~3000 rpm, and the time is 3~5 minutes.

3. The regeneration method as described in claim 1, characterized in that, The strong alkaline solution is either sodium hydroxide solution or potassium hydroxide solution.

4. The regeneration method as described in claim 1, characterized in that, The alcohol solution is one of 1,2-propanediol solution, 1,3-butanediol solution, 2-ethyl-1,3-hexanediol solution, and 2-butyl-2-ethyl-1,3-propanediol solution.

5. The regeneration method as described in claim 1, characterized in that, In step S2: The heating and stirring reaction is carried out at a temperature of 60~90℃ for a time of 0.5~2h. The vacuum drying temperature is 70~90℃, and the time is 4~6h.

6. The regeneration method as described in claim 1, characterized in that, The protective gas is either nitrogen or argon.

7. The regeneration method as described in claim 1, characterized in that, In step S3: The cleaning method is as follows: place the graphite felt electrode in water at 60~80℃, shake for 5 minutes, take it out and spin dry, then place it in another portion of water at 60~80℃, shake for 5 minutes, and take it out. The freeze-drying temperature is -40~-60℃, and the time is 6~8h.

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