A method for producing graphene aerogel using composite bipolar plates from spent flow batteries.

Abstract

This invention relates to a method for producing graphene aerogel using composite bipolar plates from spent flow batteries, belonging to the field of graphene aerogel preparation technology. This invention utilizes the instantaneous high-temperature environment of flash Joule heat treatment to achieve carbonization of the composite bipolar plate and fixation of the carbon skeleton. Combined with the thermal stress generated by the instantaneous temperature rise, the spent composite bipolar plates from flow batteries are transformed into graphene aerogel material. Through acid washing or alternating acid-water solution immersion treatment, metal particles adsorbed during flow battery operation and formed after Joule heat treatment can be effectively removed. After natural drying, high-value graphene aerogel is obtained. This invention can replace graphene products prepared from natural graphite, reducing the production cost of graphene aerogel, while simultaneously solving the pollution and carbon emissions caused by the traditional method of treating spent composite bipolar plates—incineration—achieving the goal of turning waste into treasure.

Description

Technical Field

[0001] This invention relates to the field of graphene aerogel preparation technology, and in particular to a method for producing graphene aerogel using composite bipolar plates from waste flow batteries. Background Technology

[0002] With the rapid development of renewable energy, the demand for long-term energy storage technology in new power systems is increasing. Flow batteries, due to their high safety and long lifespan, have become one of the preferred technologies for long-term energy storage. Bipolar plates, as the core component of flow battery stacks, connect multiple individual cells in series / parallel to provide capacities ranging from kilowatts to megawatts, and play a crucial role in the efficiency, cycle life, and cycle stability of the entire energy storage system.

[0003] Based on the different raw materials used in their manufacture, bipolar plates can be divided into three main categories: metal plates, graphite plates, and composite plates. Currently, the most common composite plate—the carbon-plastic composite bipolar plate—has become the mainstream choice for high-power flow battery stacks due to its advantages of lightweight, high strength, and low cost. Carbon-plastic composite bipolar plates are typically made by mixing conductive carbon materials and thermoplastic resins, and the finished material is obtained through injection molding or compression molding. It is estimated that approximately 100,000 square meters of bipolar plates are needed for every 100MW of vanadium redox flow battery produced. In the future, with the implementation of global flow battery energy storage projects, the market stock of bipolar plates will continue to increase. However, due to improper handling during transportation or stack installation, or after a certain service period, due to aging, corrosion, or performance degradation of the plates, a large number of waste composite bipolar plates will be generated. Waste composite bipolar plates contain a high proportion of carbon materials and a certain amount of metallic impurities, such as vanadium, zinc, and iron. If they are directly discarded or piled up, it will not only waste resources but also cause environmental problems.

[0004] Currently, there are few technologies for the resource utilization of waste composite bipolar plates. The industry primarily uses direct incineration to treat retired waste bipolar plates, but this process generates a large amount of carbon dioxide. Chinese patent document CN118156533A discloses a method for recycling carbon-plastic composite bipolar plates. The method involves treating waste composite bipolar plates with an acid solution via ultrasonic treatment, followed by sanding or milling to pulverize them. The pulverized bipolar plates are then mixed with a lubricant and extruded and calendered to produce new bipolar plates. This method can achieve material recycling to some extent, but it has the following problems. First, this method is complex, involving multiple processes such as ultrasonication, machining, and pulverization, resulting in a lengthy process. Second, to remove metal ions adsorbed on the surface during the flow battery's cycle, this method requires removing 0.08–0.1 mm of bipolar plate material from both sides, leading to waste of bipolar plate raw materials. Furthermore, repeated hot-melt processing causes aging of the resin matrix, significantly impacting the cycle stability of the bipolar plates. Finally, ultrasonic treatment, milling, and calendering extrusion consume substantial amounts of electrical energy, making it difficult to meet the economic requirements for commercial applications. Therefore, existing technologies primarily focus on the reshaping of waste composite bipolar plates, lacking an effective way to achieve low-cost and high-value transformation of composite bipolar plates. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing graphene aerogel using composite bipolar plates from spent flow batteries. This method requires only simple surface cleaning, followed by a one-step flash Joule heat treatment to convert the spent composite bipolar plates from flow batteries into high-value graphene aerogel material. Then, acid immersion is used to remove metal particles adsorbed during flow battery operation and formed after heat treatment, thus achieving a closed-loop "waste-product" cycle.

[0006] To achieve this objective, the technical solution of the present invention is as follows:

[0007] A method for producing graphene aerogel using composite bipolar plates from spent flow batteries, characterized by comprising the following steps:

[0008] (1) The cleaned waste flow battery is placed in a flash Joule heating device with composite bipolar plates. Under the protection of low-pressure inert gas, it is pulsed to obtain graphene aerogel material. The pulse treatment is as follows: the discharge voltage of the flash Joule heating device is set to 170-200V, the short pulse discharge time is 10-100ms, and it is naturally cooled to room temperature. Then the long pulse discharge time is 1-3s, and it is naturally cooled to room temperature again.

[0009] (2) The graphene aerogel material is soaked, washed with water, and dried naturally to obtain graphene aerogel produced using composite bipolar plates from waste flow batteries.

[0010] Preferably, the composite bipolar plate for the waste flow battery is used in one of the following fields: vanadium redox flow battery, zinc-bromine flow battery, iron-chromium flow battery, zinc-iron flow battery, sulfur-iron flow battery, or organic flow battery.

[0011] Preferably, the composite bipolar plate for waste flow batteries refers to a type of material that is disassembled from retired flow battery stacks that have reached their service life, or that has undergone chemical or electrochemical corrosion due to prolonged use, or has aged due to imperfect manufacturing processes, or has broken and been scrapped during stack disassembly, transportation, or improper operation, or is leftover material after cutting.

[0012] Preferably, in step (1), the inert gas is one of nitrogen, argon, or helium; and the low pressure is 4-8 kPa.

[0013] Preferably, in step (2), the soaking treatment is to alternately soak in acid solution and aqueous solution or soak in acid solution for a long time.

[0014] Preferably, the acid solution is a sulfuric acid solution or a hydrochloric acid solution.

[0015] Preferably, the acid solution contains H + The mass concentration is 3-4 g / L.

[0016] Preferably, the alternating immersion in the acid solution and aqueous solution involves immersing the patient in the acid solution and aqueous solution sequentially, repeating this process 2 to 4 times.

[0017] Preferably, the acid solution soaking time is 1 to 3 hours.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) This invention is based on the self-connected conductive network of waste composite bipolar plates (conductivity ≥ 6.67 S / cm) and the extremely rapid heating and peak temperature of flash Joule heating technology (heating the material to a high temperature of over 2500℃ within milliseconds), so that the current is uniformly distributed along the carbon conductive network and concentrated at the micro-contact points, thereby achieving controllable energy input and causing the carbonization products of the polymer and carbon materials to undergo instantaneous rearrangement and graphitization. Compared with the traditional graphene aerogel preparation process, the entire conversion process of this invention is completed in seconds, without the need for complex processes such as traditional chemical vapor deposition or hydrothermal synthesis (which take several hours to tens of hours), and also avoids the use of complex templates, thus achieving efficient and low-cost preparation of graphene aerogels.

[0020] (2) This invention achieves instantaneous solid-phase transformation of non-carbon-forming polymer-based waste composite bipolar plates through two high-pressure pulse treatments. The first short-pulse treatment ensures that the material as a whole is rapidly heated to above 1400°C before macroscopic melting, deformation, or collapse occurs. Simultaneously, the local thermonuclear effect generated by conductive fillers such as carbon black inside the composite bipolar plate induces efficient and uniform graphitization of non-carbon-forming polymers such as polypropylene. In the second long-pulse treatment, after obtaining sufficient heat energy, the atomic vibrations of the graphitized sheets intensify, and thermal expansion occurs between the sheets, leading to volume expansion of the composite material and the construction of a graphene aerogel structure with a specific surface area of ​​200–600 m². 2 / g.

[0021] (3) In this invention, the graphene aerogel material is immersed in an acid solution to dissolve the metal particles that are adsorbed by the operation of the flow battery and formed after heat treatment. The concentration gradient inside and outside the pores is increased by water washing, thereby improving the desorption efficiency of the metal particles in the porous graphene aerogel material and realizing the deep cleaning and regeneration of the material's pore structure.

[0022] (4) The graphene aerogel prepared by this invention is a continuous three-dimensional network formed by graphene sheets through π-π stacking and covalent bonding. Scanning electron microscopy reveals that the graphene sheets are tightly bonded together without obvious structural defects, thus effectively resisting capillary forces during natural drying and preventing the structural collapse of the graphene aerogel during natural drying. Therefore, high-performance graphene aerogels can be obtained through conventional drying without relying on freeze-drying or supercritical drying techniques, significantly reducing the energy consumption and cost of graphene aerogel preparation.

[0023] (5) This invention transforms waste composite bipolar plates from flow batteries into graphene aerogel material in one step using flash Joule heating technology. This not only avoids the pollution and carbon emissions caused by the traditional treatment method of waste bipolar plates—incineration—but also proposes a low-cost graphene aerogel preparation process. Compared with the traditional pyrolysis method, this invention reduces the energy consumption cost of graphene aerogel production by 8.28 to 1525.50 times, and the prepared porous graphene aerogel material has good electrical conductivity, >2600 S / m, which is more than 10.5 times that of the conventional pyrolysis process, truly realizing "turning waste into treasure". Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of the graphene aerogel obtained after Joule heat treatment in Example 2.

[0025] Figure 2The images shown are scanning electron microscope (SEM) images of the porous graphene aerogel surface before and after alternating acid solution-water solution immersion in Example 1; where A is the SEM image of the porous graphene aerogel surface before immersion, and B is the SEM image of the porous graphene aerogel surface after immersion.

[0026] Figure 3 The nitrogen adsorption-desorption isotherm of the graphene aerogel prepared in Example 1. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0028] In addition, the experimental methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available products unless otherwise specified.

[0029] The flash Joule heating device used in this invention is a Joule flash heating device manufactured by Shenzhen Zhongke Jingyan Technology Co., Ltd. The basic parameters of the device include: power 1800W, temperature measurement value 1000~10000K, and heating rate ≥1000K / ms.

[0030] This invention was supported by the Natural Science Foundation of Shandong Province, project approval number ZR2023QB180. Example 1

[0031] (1) The thermogravimetric analysis (TGA) of the recycled waste flow battery composite bipolar plates was performed according to GB / T13021-2023 to determine that the thermoplastic polymer content was 50%. The waste composite bipolar plates were repeatedly cleaned with anhydrous ethanol and deionized water to remove surface impurities. The bipolar plates were then dried in a 60°C oven for 12 hours. The bipolar plate samples were placed in a quartz tube, and the quartz tube containing the samples was placed in a vacuum reaction chamber. The graphite rod and the samples were fixed on the Joule flash heating device by copper electrodes. Nitrogen gas was introduced into the tube, and the gas pressure inside the tube was stabilized at 6 kPa by adjusting the inlet valve and the exhaust valve to maintain a low-pressure environment during the reaction process. Pulse processing was performed, and the discharge voltage was set to 170 V and the discharge time was set to 50 ms. After cooling to room temperature, a second discharge was performed with a discharge time of 3 s. After the discharge was completed, the vacuum pump was turned off and the inlet valve was opened. After the pressure was restored and the quartz tube cooled to room temperature, the quartz tube was removed to obtain graphene aerogel material.

[0032] (2) Take out the graphene aerogel material and soak it in a 14.7% sulfuric acid solution (H2O). +After soaking in an aqueous solution with a mass concentration of 3 g / L for 20 minutes, the graphene aerogel material was removed and then soaked in the aqueous solution for 8 minutes. This process was repeated 4 times. The graphene aerogel material was then soaked in a deionized aqueous solution for 10 minutes, and the water was changed. This process was repeated 3 times until the pH of the aqueous solution was neutral. Excess water on the surface of the graphene aerogel material was wiped off, and the material was allowed to air dry at room temperature for 48 hours to obtain the graphene aerogel. Example 2

[0033] (1) The thermogravimetric analysis (TGA) of the recycled waste flow battery composite bipolar plate was performed according to GB / T13021-2023 to determine that its thermoplastic polymer content was 20%. The waste composite bipolar plate was repeatedly cleaned with anhydrous ethanol and deionized water to remove surface impurities. After drying the bipolar plate in an 80℃ forced-air oven for 6 hours, it was taken out. The bipolar plate sample was placed in a quartz tube, and the quartz tube containing the sample was placed in a vacuum reaction chamber. The graphite rod and the sample were fixed on the Joule flash heating device by copper electrodes. Helium gas was introduced into the tube, and the gas pressure in the tube was stabilized at 8KPa by adjusting the inlet valve and the exhaust valve to maintain a low-pressure environment during the reaction process. The discharge voltage was set to 200V and the discharge time was set to 10ms. After cooling to room temperature, a second discharge was performed with a discharge time of 1s. After the discharge was completed, the vacuum pump was turned off and the inlet valve was opened. After the pressure was restored and the quartz tube cooled to room temperature, the quartz tube was taken out to obtain graphene aerogel material.

[0034] (2) Take out the graphene aerogel material and soak it in a 11.41% hydrochloric acid solution (H2O). + The graphene aerogel material was soaked in an aqueous solution (with a mass concentration of 3.5 g / L) for 10 minutes and then removed. The graphene aerogel material was then soaked in the aqueous solution for 10 minutes and removed. This process was repeated twice. The graphene aerogel material was then soaked in a deionized aqueous solution for 10 minutes and the water was changed. This process was repeated twice. The pH of the aqueous solution was then adjusted to neutral. Excess water on the surface of the graphene aerogel material was wiped off, and the material was allowed to air dry at room temperature for 48 hours to obtain the graphene aerogel. Example 3

[0035] (1) The thermogravimetric analysis (TGA) of the recycled waste flow battery composite bipolar plate was performed according to GB / T13021-2023 to determine that its thermoplastic polymer content was 70%. The waste composite bipolar plate was repeatedly cleaned with anhydrous ethanol and deionized water to remove surface impurities. After drying the bipolar plate in a 70°C oven for 8 hours, it was taken out. The bipolar plate sample was placed in a quartz tube, and the quartz tube containing the sample was placed in a vacuum reaction chamber. The graphite rod and the sample were fixed on the Joule flash heating device by copper electrodes. Argon gas was introduced into the tube, and the gas pressure in the tube was stabilized at 4 kPa by adjusting the inlet valve and the exhaust valve to maintain a low-pressure environment during the reaction process. The discharge voltage was set to 190 V and the discharge time was set to 100 ms. After cooling to room temperature, a second discharge was performed with a discharge time of 2 s. After the discharge was completed, the vacuum pump was turned off and the inlet valve was opened. After the pressure was restored and the quartz tube cooled to room temperature, the quartz tube was taken out to obtain graphene aerogel material.

[0036] (2) Take out the graphene aerogel material and soak it in a 19.6% sulfuric acid solution (H2O). + The graphene aerogel material was soaked in a solution with a mass concentration of 4 g / L for 1 hour, then removed and soaked in a deionized aqueous solution for 20 minutes. The water was changed after soaking, and the process was repeated twice until the pH of the aqueous solution was neutral. Excess water on the surface of the graphene aerogel material was wiped off, and the material was allowed to dry naturally at room temperature for 36 hours to obtain the graphene aerogel. Example 4

[0037] (1) The thermogravimetric analysis (TGA) of the recycled waste flow battery composite bipolar plate was performed according to GB / T13021-2023 to determine that its thermoplastic polymer content was 50%. The waste composite bipolar plate was repeatedly cleaned with anhydrous ethanol and deionized water to remove surface impurities. After drying the bipolar plate in a 60℃ forced-air oven for 12 hours, it was taken out. The bipolar plate sample was placed in a quartz tube, and the quartz tube containing the sample was placed in a vacuum reaction chamber. The graphite rod and the sample were fixed on the Joule flash heating device by copper electrodes. Nitrogen gas was introduced into the tube, and the gas pressure in the tube was stabilized at 6KPa by adjusting the inlet valve and the exhaust valve to maintain a low-pressure environment during the reaction process. The discharge voltage was set to 180V and the discharge time was set to 50ms. After cooling to room temperature, a second discharge was performed with a discharge time of 3s. After the discharge was completed, the vacuum pump was turned off and the inlet valve was opened. After the pressure was restored and the quartz tube cooled to room temperature, the quartz tube was taken out to obtain graphene aerogel material.

[0038] (2) Take out the graphene aerogel material and soak it in a 10.52% hydrochloric acid solution (H2O). +The graphene aerogel material was soaked in a solution with a mass concentration of 3.2 g / L for 3 hours, then removed and soaked in a deionized water solution for 30 minutes. The water was changed after soaking, and the process was repeated 4 times until the pH of the solution was neutral. Excess water on the surface of the graphene aerogel material was wiped off, and the material was allowed to dry naturally at room temperature for 48 hours to obtain the graphene aerogel. Comparative Example 1

[0039] (1) 5g of high-purity flake graphite was weighed and graphene oxide powder was prepared using the modified Hummers method. First, 600mL of concentrated sulfuric acid and 67mL of phosphoric acid were placed in a 2000mL three-necked flask and mixed evenly under ice bath conditions. Then, 5g of high-purity flake graphene was added to the three-necked flask. After that, 10.8g of potassium permanganate powder was slowly added, and the temperature was controlled not to exceed 35℃. After adding potassium permanganate, the three-necked flask was transferred to a constant temperature water bath. The water bath temperature was set to 50℃, the stirring speed was 400rpm, and the mixture was stirred for 12h. After the reaction was complete and cooled to room temperature, the solution in the three-necked flask was slowly poured into 240 mL of 3% hydrogen peroxide solution. After natural sedimentation, the supernatant was removed, and 1500 mL of deionized water was added. The mixture was stirred thoroughly and allowed to settle naturally. This process was repeated 3–5 times. The lower turbidity was then poured into a dialysis bag for dialyzing, with the deionized water being replaced as needed based on the pH value of the aqueous solution until the pH of the deionized water reached neutral. Finally, the solution was vacuum dried at 60 °C for 12 h to obtain a brownish-yellow graphene oxide powder.

[0040] (2) Dissolve graphene oxide powder in deionized water to prepare an aqueous solution of graphene oxide with a concentration of 8 mg / mL. Mix 10 mL of the 8 mg / mL aqueous solution of graphene oxide and 1.6 mL of the 50 mg / mL aqueous solution of sodium dodecyl sulfate with mechanical stirring at a speed of 1200 rpm for 10 min to obtain wet foam of graphene oxide;

[0041] (2) Immediately place the beaker containing wet graphene oxide foam into a liquid helium tank and freeze for 5 minutes. Place the frozen beaker in a freeze dryer and dry for 30 hours. After all the internal ice crystals have sublimated, remove the dry graphene oxide foam. Place the dry graphene oxide foam in a tube furnace under helium atmosphere protection and pyrolyze at 1400℃ for 4 hours to remove most of the oxygen-containing functional groups on the surface of the dry graphene oxide foam, obtaining the reduced graphene aerogel. Comparative Example 2

[0042] (1) The thermogravimetric analysis of the recycled waste flow battery composite bipolar plates was carried out in accordance with GB / T13021-2023 to determine that the thermoplastic polymer content was 50%. The waste composite bipolar plates were repeatedly cleaned with anhydrous ethanol and deionized water to remove surface impurities. After that, the bipolar plates were dried in a 60°C forced-air oven for 12 hours and then taken out.

[0043] (2) Place the bipolar plate in the microwave pyrolysis furnace, continuously introduce nitrogen gas at a flow rate of 1L / min, set the power to 1000W, turn on the microwave reactor, and take out the product after reacting for 1 hour. Comparative Example 3

[0044] (1) The thermogravimetric analysis of the recycled waste flow battery composite bipolar plates was carried out in accordance with GB / T13021-2023 to determine that the thermoplastic polymer content was 70%. The waste composite bipolar plates were repeatedly cleaned with anhydrous ethanol and deionized water to remove surface impurities. After that, the bipolar plates were dried in a 70°C forced-air oven for 8 hours and then taken out.

[0045] (2) Place the bipolar plate sample in a quartz tube, and place the quartz tube containing the sample into a vacuum reaction chamber. Fix the graphite rod and sample to the Joule flash heating device using copper electrodes. Introduce argon gas into the tube and stabilize the gas pressure inside the tube at 4 kPa by adjusting the inlet valve and the exhaust valve to maintain a low-pressure environment during the reaction process. Set the discharge voltage to 190 V and the discharge time to 100 ms. After cooling to room temperature, turn off the vacuum pump and open the inlet valve. After the pressure recovers and the quartz tube cools to room temperature, remove the quartz tube to obtain the product. Comparative Example 4

[0046] (1) The thermogravimetric analysis of the recycled waste flow battery composite bipolar plates was carried out in accordance with GB / T13021-2023 to determine that the thermoplastic polymer content was 70%. The waste composite bipolar plates were repeatedly cleaned with anhydrous ethanol and deionized water to remove surface impurities. After that, the bipolar plates were dried in a 70°C forced-air oven for 8 hours and then taken out.

[0047] (2) Place the bipolar plate sample in a quartz tube, and place the quartz tube containing the sample into a vacuum reaction chamber. Fix the graphite rod and sample to the Joule flash heating device using copper electrodes. Introduce argon gas into the tube and stabilize the gas pressure inside the tube at 4 kPa by adjusting the inlet valve and the exhaust valve to maintain a low-pressure environment during the reaction process. Set the discharge voltage to 190 V and the discharge time to 2 s. After cooling to room temperature, turn off the vacuum pump and open the inlet valve. After the pressure recovers and the quartz tube cools to room temperature, remove the quartz tube to obtain the product.

[0048] Table 1. Performance and energy consumption results of graphene aerogels prepared in Examples 1-4 and Comparative Examples 1-4.

[0049] <![CDATA[Surface area, m 2 / g]]> Energy consumption, J Electrical conductivity, S / m Example 1 201.8 282060 2657 Example 2 526.2 387840 4123 Example 3 369.7 42450 3849 Example 4 201.8 157853 2657 Comparative Example 1 241.3 64800000 252 Comparative Example 2 11.9 3600000 21 Comparative Example 3 14.7 2022 43 Comparative Example 4 124.1 40432 18.2

[0050] As shown in Table 1, the graphene aerogels prepared using flash Joule heating technology (Examples 1-4) consumed 167 to 1526 times less energy than the tube furnace method in Comparative Example 1. This is mainly due to two factors: First, flash Joule heating can generate ultra-high temperatures above 2000℃ within milliseconds, achieving instantaneous and efficient energy utilization; second, the composite bipolar plate itself has good electrical conductivity (≥6.67 S / cm) and extremely low resistance, thus significantly reducing energy consumption. In contrast, the tube furnace method has a slow heating rate (10-30℃ / min), takes a long time to reach 1400℃, and requires long-term heat preservation to ensure sufficient removal of oxygen-containing functional groups, resulting in higher total energy consumption. As shown in Comparative Example 2, due to the slow heating rate of microwave heating, it is impossible to reach high temperatures above 1400℃ in a short time, causing the non-carbon-forming polymers in the composite bipolar plate to almost completely decompose into small molecule volatiles, ultimately resulting in a disordered carbon slag structure, and a significant reduction in the specific surface area and electrical conductivity of the material.

[0051] During long-term operation of flow batteries, metal ions such as vanadium, iron, and zinc adsorb onto the surface and internal pores of the bipolar plates. These ions are difficult to remove completely through conventional cleaning. In flash Joule heat treatment, the bipolar plates are transformed into graphene aerogels, while the adsorbed metal ions are reduced to metal particles at high temperatures. Subsequently, these immobilized metal particles are dissolved and removed through prolonged immersion in acid solution or alternating immersion in acid / aqueous solution (Examples 1 and 4). Extraction of these acid wash solutions allows for the efficient recovery of valuable metals, which can then be reused in the production of new electrolytes or for other industrial applications, thus closing the battery material recycling loop and reducing dependence on primary mineral resources. Simultaneously, the removal of metal particles effectively improves the purity and chemical stability of the graphene aerogel, enhancing its subsequent performance in adsorption and catalysis applications.

[0052] This invention transforms waste composite bipolar plates into graphene aerogels. Thanks to the energy input from two flash Joule heating processes, the transformation from composite bipolar plates to graphite blocks and then to graphene aerogels is completed in steps. The first short-pulse treatment ensures that the material is rapidly heated to above 1400°C before macroscopic melting, deformation, or collapse occurs. Simultaneously, the localized thermonuclear effect generated by conductive fillers such as carbon black inside the composite bipolar plate induces efficient and uniform graphitization of non-carbon-forming polymers such as polypropylene. In the second long-pulse treatment, the graphitized sheets, after receiving sufficient heat energy, experience intensified atomic vibrations, resulting in thermal expansion between the sheets. This causes the composite material to expand in volume, thus constructing the graphene aerogel structure. If only a single short-pulse treatment is used, the product is only amorphous graphite blocks (Comparative Example 3), while a single long-pulse treatment results in graphene powder due to framework destruction (Comparative Example 4). Only through the synergy of both methods can a structurally complete graphene aerogel with high conductivity and high specific surface area be obtained.

[0053] Figure 1 This is a scanning electron microscope (SEM) image of the graphene aerogel obtained in Example 2 after Joule heat treatment. Figure 1 It can be seen that flash Joule heating technology can transform waste composite bipolar plates into high-value graphene aerogel materials with rich porosity in a short time. This is because waste composite bipolar plates used in flow batteries are composed of thermoplastic resins such as polypropylene, polyethylene, and polyvinyl chloride, and carbon materials such as carbon black and graphite powder. The carbon materials inside the bipolar plates have formed a continuous permeation network (conductivity ≥ 6.67 S / cm). In the first short-pulse processing step, thanks to the ultra-high temperature environment provided by flash Joule heating, the non-carbon-forming polymers rearrange to form a more thermodynamically stable graphene lattice structure before forming volatile small molecules. In the second long-pulse processing step, the graphitized carbon skeleton is uniformly heated. The graphite sheets repel each other under thermal action, forming a huge expansion force that can expand the dense precursor to form a porous aerogel structure. After the current is turned off, the temperature drops sharply. This rapid cooling inhibits the accumulation of graphene sheets, realizing the transformation from graphene framework to graphene aerogel.

[0054] Figure 2 These are scanning electron microscope (SEM) images of the porous graphene aerogel surface in Example 1 before and after alternating acid-water solution immersion. Figure 2 As can be seen from the comparison of scanning electron microscopy images, after alternating immersion treatment with 20% sulfuric acid solution and aqueous solution, the metal particles adsorbed inside the graphene aerogel material have been removed, proving that this method can effectively remove the metal particles adsorbed inside the graphene.

[0055] Figure 3The nitrogen adsorption-desorption isotherm of the graphene aerogel prepared in Example 1 confirms the porous structure of the graphene aerogel after Joule heat treatment. The specific surface area of ​​this graphene aerogel is calculated to be 201.8 m² using the Brunner-Emmet-Teller model. 2 ·g -1 .

Claims

1. A method for producing graphene aerogel using composite bipolar plates from spent flow batteries, characterized in that, Includes the following steps: (1) The cleaned waste flow battery with composite bipolar plate is placed in a flash Joule heating device. Under low-pressure inert gas protection, after pulse treatment, a crude graphene aerogel is obtained. The pulse treatment is as follows: the discharge voltage of the flash Joule heating device is set to 170-200V, the short pulse discharge time is 10-100ms, and it is naturally cooled to room temperature. Then, the long pulse discharge time is 1-3s, and it is naturally cooled to room temperature again. (2) The crude graphene aerogel was soaked, washed with water, and dried naturally to obtain graphene aerogel.

2. The method for producing graphene aerogel using composite bipolar plates from spent flow batteries according to claim 1, characterized in that, The composite bipolar plate for the waste flow battery is used in one of the following fields: vanadium redox flow battery, zinc-bromine flow battery, iron-chromium flow battery, zinc-iron flow battery, sulfur-iron flow battery, and organic flow battery.

3. The method for producing graphene aerogel using composite bipolar plates from spent flow batteries according to claim 2, characterized in that, The composite bipolar plates used in waste flow batteries refer to those dismantled from retired flow battery stacks that have reached their service life, or those that have undergone chemical or electrochemical corrosion due to prolonged use, or have aged due to imperfect manufacturing processes, or have broken and been scrapped during stack dismantling, transportation, or improper operation, or those that are leftover scrap after cutting.

4. The method for producing graphene aerogel using composite bipolar plates from spent flow batteries according to claim 1, characterized in that, In step (1), the inert gas is one of nitrogen, argon, or helium; the low pressure is 4-8 kPa.

5. The method for producing graphene aerogel using composite bipolar plates from spent flow batteries according to claim 1, characterized in that, In step (2), the soaking treatment is to alternately soak in acid solution and aqueous solution or soak in acid solution for a long time.

6. The method for producing graphene aerogel using composite bipolar plates from spent flow batteries according to claim 5, characterized in that, The acid solution is either sulfuric acid solution or hydrochloric acid solution.

7. The method for producing graphene aerogel using composite bipolar plates from spent flow batteries according to claim 6, characterized in that, H in acid solution + The mass concentration is 3-4 g / L.

8. The method for producing graphene aerogel using composite bipolar plates from spent flow batteries according to claim 6, characterized in that, The acid solution and aqueous solution are alternately soaked in the acid solution and aqueous solution, and this is repeated 2 to 4 times.

9. The method for producing graphene aerogel using composite bipolar plates from spent flow batteries according to claim 6, characterized in that, Soaking in acid solution for a long time means soaking in the acid solution for 1 to 3 hours.

Images