A bipolar plate for a vanadium redox flow battery and a method of making the same

Abstract

This invention provides a bipolar plate for a vanadium redox flow battery and its preparation method. The preparation method of the bipolar plate includes the following steps: Step 1: Weigh the components according to the following weight ratio: 70-90 parts graphite worms; 10-30 parts resin; resin particle size < graphite worm pore size; Step 2: Heat and mix the components to a temperature 20°C above the resin melting temperature. Spray the graphite worms and resin sequentially or simultaneously into a mixing device. The resin adheres to the surface of the worm fibers upon contact with the graphite worms, thus preparing a mixture; Step 3: Form the bipolar plate. This invention optimizes the selection and dosage of resin and graphite worms, and employs specific mixing equipment and processes to ensure a good mixing state between the resin and graphite worms, effectively improving the conductivity of the bipolar plate and reducing the loss rate of raw materials, fundamentally saving costs. This is of great significance for the large-scale production of vanadium redox flow battery bipolar plates.

Description

Technical Field

[0001] This invention relates to vanadium redox flow battery technology, and more particularly to a bipolar plate for a vanadium redox flow battery and its preparation method. Background Technology

[0002] Vanadium redox flow batteries are a new type of high-capacity energy storage battery with advantages such as high energy conversion efficiency, safe operation, independently designable power and capacity, long service life, and environmental friendliness. They can supplement grid peak-shaving energy storage devices, effectively improving the acceptance of renewable energy generation and energy utilization efficiency, and have broad application prospects in areas such as new energy integration and smart grid construction. The electrolyte in vanadium batteries is acidic, requiring bipolar plates to have good corrosion resistance. Graphite bipolar plates have good electrical conductivity, and their corrosion resistance can be improved by adding corrosion-resistant materials and improving the manufacturing process, but their mechanical properties are poor. To improve their mechanical properties, their thickness is generally increased, which makes their manufacturing cost relatively high. The main obstacle to the large-scale production of bipolar plates for vanadium redox flow batteries is the high cost of raw materials in the initial investment. As one of the key components of vanadium redox flow batteries, bipolar plates play a role in connecting the positive and negative electrodes of different single cells and conducting current. They have a significant impact on the cost and energy efficiency of vanadium redox flow battery energy storage systems and require good conductivity, oxidation resistance, acid corrosion resistance and mechanical strength.

[0003] Currently, bipolar plates are mainly divided into two categories: graphite bipolar plates and metal alloy bipolar plates. Graphite bipolar plates dominate the fuel cell market due to their excellent chemical stability and low price. They are primarily made by heating and pressing graphite with resin and other binders, with the binder resin accounting for about 25% of the total weight, indicating a very broad market potential. With the trend towards lighter fuel cells, higher requirements are being placed on bipolar plate production. Currently, the thickness of bipolar plates has been reduced to below 1 mm, thus demanding higher bonding strength and mechanical properties from the resin binder. Graphite, as the main guarantee of the bipolar plate's conductivity, is also a major contributor to its cost. Therefore, reducing graphite utilization loss and ensuring full utilization of graphite's inherent properties are equally important.

[0004] Currently, domestically produced graphite bipolar plates are mainly made by uniformly mixing one or more solid resin powders with different graphite powders, followed by roll pressing or hot molding. The resin powder, primarily thermoplastic resin, mainly serves to bind the graphite and increase the mechanical strength of the bipolar plate. However, due to the uneven mixing of the two powders, the flow channel dimensional accuracy of the graphite bipolar plate is low, local gaps are large, the mechanical strength is not ideal, and the defect rate is high.

[0005] Currently, most of the materials used in the molding of bipolar plates include resin and expanded graphite. The large amount of these two materials is also the main factor in the increase in the cost of bipolar plates. Although some literature mentions the screening and modification process of resin and expanded graphite before use, it can often only ensure a good material state before mixing. After mixing with mixing equipment, the aspect ratio of expanded graphite is destroyed, and the mixing effect of resin and expanded graphite is difficult to guarantee.

[0006] Currently available methods for mixing resin and graphite in bipolar plate components mainly include using high-speed mixers and air-jet mixers to mix multiple materials. High-speed mixers offer a simple and rapid mixing process, allowing for large-scale material mixing. However, they cause significant damage to expanded graphite during mixing, making it difficult to guarantee the aspect ratio of the expanded graphite in the mixed material. A low aspect ratio of expanded graphite leads to substandard tensile and flexural strength in the blended product. Air-jet mixers can achieve rapid and uniform mixing of materials within a full volume, but they cannot screen and remove irregular expanded graphite during the mixing process. This results in uneven expanded graphite particle size, irregular shapes, and sharp edges after mixing. After molding and rolling, the bipolar plates may have defects with large local voids, severely affecting the density uniformity and airtightness of the bipolar plates, and consequently impacting their mechanical properties and electrical conductivity. Summary of the Invention

[0007] The purpose of this invention is to address the problems of low adhesion and uneven mixing leading to unsatisfactory conductivity of bipolar plates for vanadium redox flow batteries prepared by traditional electrostatic adsorption methods. This invention proposes a method for preparing vanadium redox flow battery bipolar plates. By optimizing the selection and dosage of resin and graphite worms, and employing specific mixing equipment and processes, this method ensures a good mixing state between the resin and graphite worms, effectively improving the conductivity of the bipolar plate and reducing raw material loss, thus fundamentally saving costs. This method is of great significance for the large-scale production of vanadium redox flow battery bipolar plates.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing a bipolar plate for an all-vanadium redox flow battery, comprising the following steps:

[0009] Step 1: Weigh each component according to the following weight ratio:

[0010] 70-90 samples of graphite worms;

[0011] 10-30 parts of resin;

[0012] Resin particle size < graphite worm pore size

[0013] Step 2: Heat and mix

[0014] Each component is heated to more than 20°C above the resin melting temperature, and the resin is in the form of droplets. Graphite worms and resin are sprayed into the mixing equipment sequentially or simultaneously. The resin adheres to the surface of the graphite worm fibers the moment it comes into contact with the graphite worms, forming a strong adhesive force that does not fall off over time, thus preparing the mixture.

[0015] Step 3: Bipolar plate forming.

[0016] Furthermore, the preferred amount of graphite worms is 80-90 parts; and the amount of resin is 10-20 parts.

[0017] Furthermore, in step 1, the resin particle size is smaller than the graphite worm pore size, which ensures that the resin (e.g., PVDF) enters the graphite worm micropores under the action of wind, forming a uniform distribution of the two substances.

[0018] Further, the graphite worm pore size in step 1 is ≥20 μm, and the resin particle size is <20 μm. Preferably, the graphite worm pore size is 20–60 μm.

[0019] Furthermore, the graphite worm is made from expandable graphite.

[0020] Furthermore, the expandable graphite modification method includes the following steps: placing expandable graphite in a high-temperature expansion furnace, setting the temperature to 500-850℃, the expansion reaction time to 10-15s, the volume expansion ratio of the expandable graphite to 150-300, changing from sheet-like to worm-like, thereby making the structure loose, porous and curved, increasing the surface area, increasing the surface energy, and enhancing the adsorption capacity. The worm-like graphite can interlock with each other, thus increasing its softness, resilience and plasticity.

[0021] Furthermore, the pore size of the graphite worm is related to the mesh size of its precursor, expandable graphite. For example, to maintain the micropore size of the graphite worm surface >20µm, the mesh size of the raw material expandable graphite is 150-250.

[0022] Expanded graphite (EG) is a loose, porous, worm-like material obtained from natural graphite flakes through intercalation, washing, drying, and high-temperature expansion. Besides possessing the excellent properties of natural graphite, such as resistance to cold and heat, corrosion resistance, and self-lubrication, EG also exhibits properties not found in natural graphite, including softness, compression resilience, adsorption, environmental compatibility, biocompatibility, and radiation resistance. Before modification, expanded graphite needs to be screened based on mesh size.

[0023] The specific operation is as follows: The expandable graphite used for modification is sieved to ensure that its mesh size is between 150 and 250 mesh. Expandable graphite in this mesh size range is different from conventional 50, 80, and 100 mesh expandable graphite. Although smaller mesh sizes expand more easily and have a larger expansion ratio, this characteristic makes it difficult to precisely control the microscopic expansion of the expanded graphite surface. Expandable graphite with conventional mesh sizes has a large overall length-to-diameter ratio, making it difficult to ensure the uniformity of the overall expansion ratio during the expansion process. This also results in the micropore size of the graphite worms obtained from the modified expandable graphite not meeting the requirements, affecting the subsequent bonding ratio between the graphite worms and the resin. Expandable graphite with a mesh size range of 150 to 250 mesh (optimal mesh size = 180 mesh), and the micropore size of the modified graphite worms maintained between 20 and 60 μm (optimal pore size = 30 μm), corresponds to the particle size state of PVDF after high temperature, which can effectively ensure the bonding ratio between the two.

[0024] Furthermore, the resin is selected from one or more of PTFE, PVDF, PE, FEP, and PFA. PTFE, PVDF, PE, FEP, and PFA exhibit high resistance to almost all organic and inorganic compounds, whether acidic or alkaline. These materials demonstrate generally durable resistance to acids, alkalis, and chlorides, while also exhibiting excellent resistance to mechanical damage in terms of abrasion resistance, impact resistance, and toughness, playing a crucial role in improving the hermeticity of bipolar plates.

[0025] Furthermore, the resin is a modified resin, which is prepared by the following method: placing the granular resin into a horizontal sand mill, setting the mill linear speed to 8-15 m / s (optimal linear speed = 10 m / s), the filling rate to 70-80%, and the reaction time to 10-25 min, to obtain resin powder with a particle size range of <20 μm.

[0026] Furthermore, the mixing device is a cyclone dust collector. The mixing mechanism of the cyclone dust collector is to rotate the material-containing airflow, using centrifugal force to separate the material from the airflow and collect it on the wall of the collector, and then using gravity to allow the material to fall into the ash hopper. This invention aims to achieve the desired mixing effect by controlling the order and proportion of the addition of graphite worms and resin.

[0027] Furthermore, the heating and mixing process is as follows:

[0028] S1 sets the airflow velocity at the inlet of the cyclone dust collector to 12-20 m / s, with the optimal inlet airflow velocity being 18 m / s. This airflow velocity ensures that materials (resin) with a particle size of 15-30 μm will not be discharged from the exhaust pipe along with the high-temperature airflow. It can also remove graphite worms with insufficient expansion ratio and morphological damage, thereby further improving the mixing effect and the uniformity of bipolar plate rolling and molding.

[0029] S2 sets the pressure of the cyclone dust collector to 500-2000Pa, with the optimal pressure being 1200Pa. This pressure ensures that the shape of the graphite worms remains unchanged, effectively preventing the graphite worms from breaking, becoming irregular in shape, or developing sharp edges during material mixing. This does not affect the subsequent mixing effect and reduces the local space gap between the bipolar plates.

[0030] S3 sets the airflow temperature of the cyclone dust collector to 140-180℃, with the optimal temperature being 160℃. At this temperature, the resin (one or more of PTFE, PVDF, PE, FEP, and PFA) softens and becomes a molten droplet bonded state. This state is beneficial for strengthening the binding between the resin and graphite worms, so that the uniformly mixed resin and graphite worms maintain a good binding state during material transfer and long-term storage, thus improving the mixing effect of the resin and graphite worms.

[0031] In S4, the material addition order is to add graphite worms first, followed by resin. First, graphite worms are added through the feed inlet 1 of the cyclone dust collector. After adding the graphite worms for 15-25 seconds, observe whether there are any small, broken, or irregularly shaped graphite worms at the air outlet 2. If so, continue adding graphite worms through the feed inlet 1 of the cyclone dust collector, and at the same time, turn on the vibration device 3. After vibrating and mixing for 15-20 seconds, the material is discharged through the discharge outlet 4 and collected uniformly by the collection ash hopper 5. Ultimately, this achieves the effect of uniform material mixing without damaging the shape of the graphite worms.

[0032] Furthermore, step 3, the bipolar plate forming, includes loading the mixture into a mold and hot pressing it into shape.

[0033] Furthermore, the molding pressure of the hot pressing is 20-40 MPa, the molding temperature is 140-180℃, and the curing time is 25-40 min.

[0034] Another objective of this invention is to disclose a bipolar plate for an all-vanadium redox flow battery, which is prepared using the method described above.

[0035] Furthermore, the thickness of the bipolar plate in the vanadium redox flow battery is 0.85–0.9 mm, and the density is 1.75–1.95 g / cm³. 3 Flexural strength = 45~68MPa, electrical conductivity = 280~350s / cm.

[0036] This invention relates to a vanadium redox flow battery bipolar plate and its preparation method. Through material screening and modification, material addition methods, and the final material mixing method, it effectively improves the material mixing effect and enhances the performance of the vanadium redox flow battery bipolar plate. Specifically, compared with existing technologies, it has the following advantages:

[0037] 1) Decreasing manufacturing costs of bipolar plates

[0038] Compared with traditional processes, the resin particles used in this invention are smaller, making it easier to mix evenly with graphite worms, and requiring less resin, reducing resin usage by 5% to 8% compared to traditional processes; at the same time, thanks to the optimization of mixing technology parameters, the loss of graphite worms during the mixing process is reduced, and the cost of using graphite worms is reduced by about 3%.

[0039] 2) The conductivity of the bipolar plates is significantly improved, resulting in an increase in the efficiency of the all-vanadium redox flow battery.

[0040] Thanks to the preservation of the graphite worm morphology during the mixing process, the bipolar plate better maintains the good conductivity of graphite itself, that is, it has a lower contact resistance with the electrode, which reduces the ohmic internal resistance of the vanadium redox flow battery, improves the energy efficiency of the flow battery, and enhances the performance of the vanadium redox flow battery, with the corresponding stack performance increasing by about 4%.

[0041] 3) The materials are mixed evenly, improving the acid corrosion resistance of the bipolar plates and reducing maintenance costs.

[0042] With the improvement of material mixing uniformity, the graphite worms and small-particle resin are more well combined and distributed, the local gaps in the bipolar plate itself are improved, the overall uniformity is improved, the density and mechanical strength are strengthened, the overall acid corrosion resistance is improved, the service life of the bipolar plate stack is increased, and the later maintenance cost is reduced by about 3%.

[0043] In summary, addressing the challenges in the traditional preparation process of bipolar plates for vanadium redox flow batteries, this invention optimizes the selection and dosage of resin and graphite worms, utilizes specific mixing equipment and processes to ensure a good mixing state between the resin and graphite worms, effectively improves the conductivity of the bipolar plate, reduces the loss rate of both materials, and fundamentally saves costs. This is of great significance for the large-scale production of bipolar plates for vanadium redox flow batteries. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of the cyclone dust collector. Detailed Implementation

[0045] The present invention will be further described below with reference to the embodiments:

[0046] Example 1

[0047] This embodiment discloses a method for preparing a bipolar plate for an all-vanadium redox flow battery, including the following steps:

[0048] Step 1: Weigh each component according to the following weight ratio:

[0049] 80 samples of graphite worms;

[0050] 20 parts of resin (PVDF - polyvinylidene fluoride);

[0051] The graphite worms have a mesh size of 150, a surface pore size of 20 μm, and a resin particle size of 15 μm.

[0052] Step 2: Heat and mix

[0053] 1) Set the airflow velocity at the inlet of the cyclone dust collector to 12m / s. This airflow velocity can ensure that the material will not be discharged from the exhaust pipe along with the high-temperature airflow. At the same time, it can also remove graphite worms with insufficient expansion ratio and morphological damage, thereby further improving the mixing effect and the uniformity of bipolar plate rolling and molding.

[0054] 2) Set the pressure of the cyclone dust collector to 500Pa. Under this pressure, the shape of the expanded graphite itself can be guaranteed not to change. This can effectively prevent the expanded graphite from breaking, becoming irregular in shape, or having sharp edges during the material mixing process, without affecting the subsequent mixing effect and reducing the local space gap of the bipolar plate.

[0055] 3) Set the airflow temperature of the cyclone dust collector to 120℃. At this temperature, the resin softens and becomes a molten droplet bond. This state is conducive to strengthening the bonding between the resin and expanded graphite, so that the resin and expanded graphite, after being mixed evenly, still maintain a good bond during material transfer and long-term storage, thus improving the mixing effect of the resin and expanded graphite.

[0056] 4) The material addition order is to add graphite worms first. First, add graphite worms through the feed port 1 of the cyclone dust collector. After adding graphite worms for 15 seconds, observe whether there are small, broken, and irregularly shaped expanded graphite particles at the air outlet 2. If so, start continuously feeding graphite worms and add resin at the same time. At the same time, turn on the vibration device 3 and vibrate and mix for 15 seconds. Then, discharge through the discharge port 4 and collect it uniformly by the collection ash hopper 5. In the end, the effect of uniform material mixing without damaging the expanded graphite is achieved.

[0057] Step 3: Bipolar plate forming

[0058] The mixture was placed into a mold and hot-pressed at a molding pressure of 20 MPa, a molding temperature of 140°C, and a curing time of 40 min. The prepared vanadium redox flow battery bipolar plates are shown in Table 1. Unless otherwise specified, all percentages in this invention are by mass.

[0059] Table 1 Comparison of bipolar plate performance

[0060] performance Example 1 Compare with Example 1 Resin dosage 20％ 20％ <![CDATA[Bipolar plate density g / cm 3 > 1.8 1.77 Flexural strength (MPa) 55 49 Conductivity s / cm 298 279

[0061] This embodiment 1 uses a higher mixing temperature, which better ensures the melting state of the resin and increases the mixing strength of the resin and graphite. Compared with control example 1, the density of the present invention is higher.

[0062] Comparative Example 1: It is basically the same as Example 1, except that the airflow velocity at the air inlet is 15m / s, the mixing pressure is 1000Pa, the mixing temperature is 25℃, it is loaded into the molding mold, the molding pressure is 20MPa, the molding temperature is 160℃, and the curing time is 40min.

[0063] Example 2

[0064] This embodiment discloses a method for preparing a bipolar plate for a vanadium redox flow battery, which is basically the same as that in Example 1, except that the expanded graphite content is 85%, the resin content is 15%, the expanded graphite mesh size is 180 mesh, the micropore size of the graphite worm surface is 25 μm, the resin particle size is 18 μm, the airflow velocity at the air inlet is 18 m / s, the mixing pressure is 1200 Pa, the mixing temperature is 150 °C, and the molding process involves hot pressing at a molding pressure of 45 MPa, a molding temperature of 180 °C, and a curing time of 60 min. The prepared vanadium redox flow battery bipolar plates are shown in Table 2.

[0065] Table 2 Comparison of Bipolar Plate Performance

[0066] performance Example 2 Compare with Example 2 Resin dosage 15％ 15％ <![CDATA[Bipolar plate density g / cm 3 > 1.92 1.89 Flexural strength MPa 61 57 Conductivity s / cm 290 300

[0067] In this embodiment, a vibrating device is used during the mixing process, which can reduce the amount of resin loss during material mixing and discharge. Compared with Comparative Example 2, the overall bending strength and density of the bipolar plate are improved.

[0068] Comparative Example 2: It is basically the same as Example 2, except that there is no vibration process during the mixing process of the cyclone dust collector.

[0069] Example 3

[0070] This embodiment discloses a method for preparing a bipolar plate for a vanadium redox flow battery, which is basically the same as that in Example 1, except that the expanded graphite content is 90%, the resin content is 10%, the expanded graphite mesh size is 200 mesh, the micropore size of the graphite worm surface is 30 μm, the resin particle size is 21 μm, the airflow velocity at the air inlet is 12 m / s, the mixing pressure is 800 Pa, the mixing temperature is 120 °C, the molding is hot-pressed under a mold with a molding pressure of 30 MPa, a molding temperature of 190 °C, and a curing time of 40 min. The prepared vanadium redox flow battery bipolar plates are shown in Table 3.

[0071] Table 3 Comparison of Bipolar Plate Performance

[0072] performance Example 3 Compare with Example 3 Resin dosage 10％ 10％ <![CDATA[Bipolar plate density g / cm 3 > 1.74 1.68 Flexural strength (MPa) 38 31 Conductivity s / cm 320 335

[0073] Compared with Comparative Example 3, the expandable graphite in this embodiment has a larger mesh size, better uniformity of micropore size on the surface of graphite worms, better bonding effect between graphite and resin, and reduced separation of resin and graphite during the transfer of mixed materials.

[0074] Comparative Example 3: It is basically the same as Example 3, except that expandable graphite with a mesh size of less than 100 is used.

[0075] Example 4

[0076] This embodiment discloses a method for preparing a bipolar plate for a vanadium redox flow battery, which is basically the same as that in Example 1, except that the expanded graphite content is 82%, the resin content is 18%, the expanded graphite mesh size is 220 mesh, the micropore size of the graphite worm surface is 36 μm, the resin particle size is 15 μm, the airflow velocity at the air inlet is 12 m / s, the mixing pressure is 500 Pa, the mixing temperature is 180 °C, the molding is hot-pressed, the molding pressure is 30 MPa, the molding temperature is 140 °C, and the curing time is 40 min; the prepared vanadium redox flow battery bipolar plate is shown in Table 4.

[0077] Table 4 Comparison of Bipolar Plate Performance

[0078] performance Example 4 Compare with Example 4 Resin dosage 18％ 18％ <![CDATA[Bipolar plate density g / cm 3 > 1.8 1.75 Flexural strength (MPa) 57 52 Conductivity s / cm 265 255

[0079] Compared with Comparative Example 4, this embodiment uses a cyclone dust collector to mix graphite and resin, and the overall mixing effect is better than that of the ball mold mixing method. The overall performance of the bipolar plate in Example 4 is improved compared with Comparative Example 4.

[0080] Comparative Example 4: It is basically the same as Example 4, except that ball milling is used to mix graphite and resin.

[0081] Example 5

[0082] This embodiment discloses a method for preparing a bipolar plate for a vanadium redox flow battery, which is basically the same as that in Example 1, except that the expanded graphite content is 85%, the resin content is 15%, the expanded graphite mesh size is 250 mesh, the micropore size of the graphite worm surface is 50 μm, the resin particle size is 21 μm, the airflow velocity at the air inlet is 15 m / s, the mixing pressure is 1000 Pa, the mixing temperature is 150 °C, the material is loaded into a molding die, the molding pressure is 30 MPa, the molding temperature is 150 °C, and the curing time is 30 min. The prepared vanadium redox flow battery bipolar plates are shown in Table 5.

[0083] Table 5 Comparison of bipolar plate performance

[0084] performance Example 5 Compare with Example 5 Resin dosage 15％ 15％ <![CDATA[Bipolar plate density g / cm 3 > 1.67 1.65 Flexural strength MPa 43 40 Conductivity s / cm 285 291

[0085] This embodiment uses a resin with a smaller particle size, and the resin particle size is much smaller than the micropore size on the surface of graphite worms. In contrast, the resin particle size in Control Example 5 is larger than the micropore size on the surface of graphite worms. Under the same bipolar plate formulation, Example 5 has better compactness, mechanical strength, and density than Control Example 5.

[0086] Comparative Example 5: Basically the same as Example 5, except that the resin particle size is 65 μm.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a bipolar plate for an all-vanadium redox flow battery, characterized in that, Includes the following steps: Step 1: Weigh each component according to the following weight ratio: 70-90 portions of graphite worms; 10-30 parts resin; Resin particle size < graphite worm pore size; Step 2: Heat and mix Each component is heated to 20°C above the resin melting temperature. Graphite worms and resin are sprayed into the mixing equipment sequentially or simultaneously. The resin adheres to the surface of the graphite worm fibers the moment it comes into contact with the graphite worms, thus preparing the mixture. Step 3: Bipolar plate forming; The mixing device is a cyclone dust collector; The heating and mixing process in step 2 is as follows: S1 sets the airflow velocity at the inlet of the cyclone dust collector to be 12~20m / s; S2 sets the pressure of the cyclone dust collector to 500~2000Pa; S3 sets the airflow temperature of the cyclone dust collector to 120~180℃; S4 First, graphite worms are added through the feed inlet of the cyclone dust collector. After 15-25 seconds, observe whether there are any small, broken, or irregularly shaped graphite worms at the air outlet. If so, start adding graphite worms through the feed inlet of the cyclone dust collector and turn on the vibration device at the same time. After vibrating and mixing for 15-20 seconds, the material is discharged through the discharge outlet and collected uniformly by the ash collection hopper.

2. The method for preparing the bipolar plate of the all-vanadium redox flow battery according to claim 1, characterized in that, The graphite worms described in step 1 have a pore size ≥ 20 μm and a resin particle size < 20 μm.

3. The method for preparing the bipolar plate of the all-vanadium redox flow battery according to claim 1, characterized in that, The graphite worms are modified from expandable graphite. The method for modifying expandable graphite includes the following steps: placing expandable graphite in a high-temperature expansion furnace, setting the temperature to 500~850℃, the expansion reaction time to 10~15s, and the volume expansion ratio of expandable graphite to 150~300.

4. The method for preparing the bipolar plate of the all-vanadium redox flow battery according to claim 3, characterized in that, The number of graphite worms is 150-250.

5. The method for preparing the bipolar plate of the all-vanadium redox flow battery according to claim 1, characterized in that, The resin is selected from one or more of PTFE, PVDF, PE, FEP and PFA.

6. The method for preparing the bipolar plate of the all-vanadium redox flow battery according to claim 1, characterized in that, Step 3, the bipolar plate forming, includes loading the mixture into a mold and hot pressing it into shape.

7. The method for preparing the bipolar plate of the all-vanadium redox flow battery according to claim 6, characterized in that, The molding pressure of the hot pressing is 20~35MPa, the molding temperature is 140~160℃, and the curing time is 25~40min.

8. A bipolar plate for an all-vanadium redox flow battery, characterized in that, It is prepared using the method for preparing the all-vanadium redox flow battery bipolar plate according to any one of claims 1-7.

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