Flexible graphite bipolar plate of flow battery and preparation method of flexible graphite bipolar plate

Abstract

The invention relates to the field of fuel cells, and discloses a preparation method of a flexible graphite bipolar plate of a flow battery, which comprises the following steps: mixing worm graphite powder with different particle sizes in a three-dimensional mixer to obtain mixed powder; the mixed powder is put into a mold with a vibration device, a prefabricated blank is prepared through a vibration compression molding technology, and pores are formed in the prefabricated blank; putting the prefabricated blank into a resin solution, and carrying out impregnation reinforcement to obtain a primary plate body; and sequentially cleaning, curing and drying the primary plate body to prepare the flexible graphite bipolar plate of the flow battery and the flexible graphite bipolar plate of the flow battery. The density of the bipolar plate substrate and the density of the ridge are kept consistent, so that the conductive and mechanical properties of the flexible graphite bipolar plate are improved, meanwhile, the production mode is simple, the density difference between products is small, the yield of the products is high, the waste plate rate is reduced, and the overall production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, specifically to a flexible graphite bipolar plate for a flow battery and its preparation method. Background Technology

[0002] As a crucial component of flow batteries, bipolar plates possess low resistivity and low contact resistance with the electrode materials. Flow battery bipolar plates typically employ a flow-field-free structure, where the electrolyte flows directly through the entire porous electrode, resulting in a relatively long flow distance within the porous electrode. To achieve lower voltage drop losses and reduce the internal resistance of the flow battery, flow field structures are introduced on both sides of the bipolar plates. This reduces the flow distance of the electrolyte within the porous electrode and the voltage drop losses, thereby improving the performance of the flow battery.

[0003] Currently, there are two main methods for preparing graphite bipolar plates for flow batteries with flow channels. One method involves mechanically carving and shaping hard graphite. This process typically involves mixing carbon powder or graphite powder with a graphitizable resin, subjecting it to high temperature and pressure for graphitization, then impregnating and sealing the graphite plate, and finally machining the required flow channels on its surface using a CNC machine tool. The other method is hot pressing. This involves mixing, granulating, crushing, and sieving graphite powder, conductive carbon materials, resin, coupling agents, and lubricants, followed by hot pressing in a mold with a flow channel design. Examples include a molding method for composite graphite bipolar plates (CN 118977434 A) and a method for preparing composite material bipolar plates for vanadium redox flow batteries (CN 118800924 A).

[0004] However, the above methods all have defects in the production of fluid flow bipolar plates with flow channels. The main reason is that the density of resin and graphite materials are highly correlated. During the mixing process, the resin and graphite materials in the composite powder are easily separated into layers. The material distribution in the final bipolar plate is not uniform. Since the flow channels on the bipolar plate are uniformly distributed in the bipolar plate, the conductivity of different flow channels is not the same, which affects the overall conductivity of the plate. At the same time, the uneven distribution of resin will also make some parts of the bipolar plate more "brittle", resulting in a corresponding decrease in the mechanical properties of the plate. Summary of the Invention

[0005] The purpose of this invention is to provide a flexible graphite bipolar plate for flow batteries and its preparation method, so as to solve the technical problem that it is difficult to obtain a relatively homogeneous flexible graphite bipolar plate with flow channels through a relatively simple method in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution: This invention provides a method for preparing a flexible graphite bipolar plate for a flow battery, comprising the following steps: S100. Mix worm graphite powder of different particle sizes in a three-dimensional mixer to obtain mixed powder; S200. The mixed powder is placed into a mold with a vibration device, and the mixed powder is made to flow in the mold until it is evenly distributed through a vibration molding process. The mixed powder interlocks with each other during the flow and forms a network structure to obtain a preform containing pores. S300. The preform is placed into a resin solution for impregnation and strengthening. The resin solution fills the pores to obtain a primary plate. S400: The primary plate is sequentially cleaned, cured, and dried to obtain a flexible graphite bipolar plate for a flow battery.

[0007] In a preferred embodiment of the present invention, in step S100, the particle size range of the worm graphite powder is selected from 30-80 mesh and 200-300 mesh. Mixing time is 30-60 minutes.

[0008] In a preferred embodiment of the present invention, in step S200, the vibration molding process satisfies the following conditions: The vibration frequency range is 0~50Hz, the molding pressure is 30~50MPa, the holding time is 30~60 seconds, and the vacuum degree is less than 10mbar.

[0009] In a preferred embodiment of the present invention, in step S200, the thickness of the preform is 4-6 mm, the base thickness is 1 mm, and the density of the preform is 0.8-1.3 g / cm³. 3 .

[0010] In a preferred embodiment of the present invention, in step S300, the resin solution is any one or more of phenolic resin or epoxy resin. The impregnation strengthening time is 30-60 minutes.

[0011] As a preferred embodiment of the present invention, in step S400, the cleaning is to clean the resin solution on the surface of the primary plate to prevent the resin material from completely coating the surface of the graphite material.

[0012] In a preferred embodiment of the present invention, in step S400, the curing process satisfies the following conditions: The curing temperature is 80℃, and the curing time is 30~60min.

[0013] In a preferred embodiment of the present invention, in step S400, the drying process satisfies the following conditions: The drying temperature is 60℃ and the drying time is 60~120min.

[0014] The present invention provides a flexible graphite bipolar plate for flow batteries, comprising a plate body, an inverted U-shaped ridge structure inserted on the plate body, the ridge structure having flow channels, and a substrate at the bottom of the plate body, the flow channels being disposed on the substrate.

[0015] In a preferred embodiment of the present invention, the bipolar plate has a conductivity of 409.6~447.8 S / cm, a flexural strength of 42.3~51.5 MPa, and an air permeability of 1.9×10⁻⁶. -9 ~5.2×10 -8 cm 3 / cm 2 ·s.

[0016] Compared with the prior art, the present invention has the following advantages: This invention changes the manufacturing process of flexible graphite bipolar plates. By mixing worm graphite powder of different particle sizes through a three-dimensional mixing mechanism, a preform with uniform density is prepared by vibration and vacuum molding. The worm graphite powder of different particle sizes interlocks with each other to form a network structure during the molding process, which provides pores for resin impregnation. During the impregnation process, the resin can be impregnated uniformly, and the density of the substrate and the ridges can be kept consistent, thereby improving the electrical conductivity and mechanical properties of the flexible graphite bipolar plate. The process disclosed in this invention, which combines vacuum vibration molding with resin impregnation reinforcement, makes it easy to control the density of the board, minimizes the density difference between products, results in a high yield, reduces the scrap rate, and improves overall production efficiency. The bipolar plate provided by this invention improves the homogeneity of graphite and resin distribution in the bipolar plate, and the density of the substrate and the ridge can be kept consistent, thereby enabling the graphite bipolar plate to obtain good electrical conductivity and mechanical properties. Attached Figure Description

[0017] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0018] Figure 1 A schematic flowchart illustrating the preparation method of the flexible graphite bipolar plate for a flow battery provided by the present invention; Figure 2 This invention provides a structural schematic diagram of a flexible graphite bipolar plate for a flow battery. Figure 3A schematic diagram of the structure of the dynamic modulation vacuum vibration compaction system is provided for this invention; Figure 4 Provided for the present invention Figure 3 A schematic diagram of the internal structure of the double-layer mold in the embodiment shown.

[0019] The labels in the diagram represent the following: 1-Plate body; 2-Ridge structure; 3-Flow channel; 4-Base; 5-Vibration table; 6-Dynamic vacuum modulation system; 7-Double-layer mold; 8-Inner cavity; 9-Connecting through hole; 10-Vacuum modulation cavity; 601-Vacuum pump; 602-Inlet pump; 603-High-speed switching valve; 604-Vacuum line; 605-Micro-inlet valve; 606-Inlet line; 701 - First housing; 702 - Second housing. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, this invention provides a method for preparing a flexible graphite bipolar plate for a flow battery, comprising the following steps: S100. Mix worm graphite powder of different particle sizes in a three-dimensional mixer to obtain mixed powder; S200. The mixed powder is placed into a mold with a vibration device. Through vibration molding process, the mixed powder flows in the mold until it is evenly distributed. During the flow, the mixed powder interlocks with each other and forms a network structure to obtain a preform containing pores. S300. The preform is placed into the resin solution for impregnation and strengthening. The resin solution fills into the pores to obtain the primary plate. S400: The primary plate is sequentially cleaned, cured, and dried to obtain a flexible graphite bipolar plate for flow batteries.

[0022] The density uniformity of the preform of flexible graphite bipolar plate has a significant impact on the conductivity and mechanical properties of the final bipolar plate product. The purpose of this invention is to prepare a preform with uniform density by changing the manufacturing process of flexible graphite bipolar plate, and finally obtain a flexible graphite bipolar plate with good conductivity and mechanical properties to meet the requirements of flow battery use.

[0023] In step S100, the particle size of the worm graphite powder can be selected within a preferred range. The difference in particle size is to enable them to interlock during vibration molding, thereby forming a network structure. This network structure is strongly correlated with the difference in particle size of the worm graphite powder. Preferably, the particle sizes of the worm graphite powder are 30-80 mesh and 200-300 mesh.

[0024] In step S100, the mixing time of the worm graphite powder in the three-dimensional mixer can be arbitrarily selected. Preferably, the worm graphite powder is mixed in the three-dimensional mixer for 30 to 60 minutes so that the worm graphite powders of different particle sizes can be mixed as evenly as possible, which facilitates the flow during the subsequent molding process.

[0025] In step S200, the vibration molding process is carried out in a vacuum environment.

[0026] Vibration molding is a manufacturing process that combines vibration energy with molding. The vibration frequency range is 0~50Hz, the molding pressure is 30~50MPa, the holding pressure is 30~60 seconds, the vacuum degree is less than 10mbar, the thickness of the graphite bipolar plate preform is 4~6mm, the substrate is 1mm, and the preform density is 0.8~1.3g / cm³. 3 .

[0027] In step S300, the impregnation process needs to be carried out in a vacuum environment to reduce the generation of air bubbles and to allow the resin solution to quickly fill the pores of the network structure.

[0028] The resin solution can be selected within any range, but the principle is that it should have a low viscosity, close to that of water. Specifically, the resin solution is one or both of phenolic resin and epoxy resin. Both phenolic resin and epoxy resin have low viscosity, which allows them to quickly penetrate into the three-dimensional network structure composed of graphite materials without damaging the structure. At the same time, they can reduce the generation of bubbles, resulting in a more uniform density of the bipolar plate.

[0029] The impregnation time of the resin solution can be selected within a wide range, and the time is limited by the temperature and the size of the bipolar plate. Preferably, the impregnation time can be 30 to 60 minutes.

[0030] In step S400, cleaning involves washing the resin solution off the surface of the primary plate to prevent the resin material from completely coating the surface of the graphite material, which would cause uneven surface density. After cleaning, the primary plate is cured at 80°C for 30-60 minutes and then dried at 60°C for 60-120 minutes to obtain the final product.

[0031] This invention relates to the field of flow battery technology, and more particularly to a method for preparing a flexible graphite bipolar plate for flow batteries. The method involves mixing worm-shaped graphite powders of different particle sizes using a three-dimensional mixing mechanism, and then preparing a preform with uniform density using vibration and vacuum molding processes. The compressed worm-shaped graphite powders form a network connection structure, effectively improving conductivity. Simultaneously, the porous flexible graphite bipolar plate preform facilitates resin impregnation, enhancing mechanical properties.

[0032] The three-dimensional mixing mechanism can be selected within a preferred range. In the preparation process of this invention, the SBH series is selected, specifically SBH~10, which belongs to small three-dimensional mixers and is suitable for small-scale material mixing.

[0033] In actual production, the SYH series can also be used to meet the requirements of large-scale production.

[0034] Molds with vibration devices are common in the market. This invention uses a powder compact mold, which includes an upper mold base, a gear transmission system (rack + gear), a lower mold base and a push rod. The vibration device is supported by the base to achieve material mixing during the compaction process.

[0035] like Figure 2 As shown, the present invention further provides a flexible graphite bipolar plate for a flow battery. The bipolar plate includes a plate body 1, an inverted U-shaped ridge structure 2 inserted on the plate body 1, a flow channel 3 disposed inside the ridge structure 2, and a substrate 4 disposed at the bottom of the plate body 1, with the flow channel 3 disposed on the substrate 4.

[0036] The flow channels 3 are located on both sides of the bipolar plate. The density uniformity of the flow channels 3 has a significant impact on the conductivity and mechanical properties of the final bipolar plate product. Unlike existing bipolar plates, the bipolar plate provided by this invention has a uniform density, which makes the density of the substrate and the ridge consistent, thereby obtaining a flexible graphite bipolar plate with good conductivity and mechanical properties, meeting the requirements for use in flow batteries, and improving the conductivity of the flexible graphite bipolar plate.

[0037] The thickness of plate 1 is 4~6mm, and the thickness of base 4 is 1mm.

[0038] The following examples and comparative examples illustrate the points: Example 1: Step 1: Mix 30-80 mesh and 200-300 mesh worm graphite powder in a 1:1 ratio in a 3D mixer of model SBH-10.

[0039] Step 2: Pour the mixed worm graphite powder into a powder compact mold for vacuum molding to prepare a flexible graphite bipolar plate preform. The vibration frequency is 20Hz, the molding pressure is 30~50MPa, the holding pressure is 30 seconds, the vacuum degree is less than 10mbar, the thickness of the flexible graphite bipolar plate preform is 4mm, and the bulk density is 1.0g / cm³. 3 .

[0040] Step 3: Resin impregnation strengthening is performed on the flexible graphite bipolar plate preform. After impregnation for 30 minutes, the primary plate is removed.

[0041] Step 4: Clean the resin of the primary plate. After cleaning, cure at 80°C for 30 minutes and dry at 50°C for 60 minutes to obtain Example 1.

[0042] Example 2: Step 1 is the same as in Example 1, except that: The vibration frequency in step 2 is 40Hz, the molding pressure is 30~50MPa, the holding time is 60 seconds, the vacuum degree is less than 10mbar, the thickness of the graphite bipolar plate preform is 6mm, and the bulk density is 1.0g / cm³. 3 .

[0043] Step 3: Soaking time is 50 minutes.

[0044] Step 4: Curing at 80°C for 50 minutes and drying at 50°C for 100 minutes to obtain Example 2.

[0045] Example 3: The vibration frequency in step 2 is 40Hz, the molding pressure is 30~50MPa, the holding pressure is 60 seconds, the vacuum degree is less than 10mbar, the thickness of the graphite bipolar plate preform is 6mm, and the bulk density is 0.8g / cm³. 3 .

[0046] Step 3: Soaking time is 40 minutes.

[0047] Step 4 involves curing at 80°C for 50 minutes and drying at 50°C for 100 minutes to obtain Example 3.

[0048] Comparative Example 1: Step 1: Mix 30-80 mesh and 200-300 mesh worm graphite powder in a 1:1 ratio in a 3D mixer of model SBH-10.

[0049] Step 2: Pour the mixed worm graphite powder into a mold for vacuum molding to prepare a flexible graphite bipolar plate preform. The molding pressure is 50 MPa, the holding pressure is 60 seconds, the vacuum degree is less than 10 mbar, and the thickness of the graphite bipolar plate preform is 6 mm.

[0050] Step 3: The flexible graphite bipolar plate preform is reinforced by resin impregnation. After impregnation for 40 minutes, the graphite bipolar plate is removed.

[0051] Step 4: Clean the resin on the surface of the graphite bipolar plate, cure it at 80℃ for 50 minutes, and dry it at 50℃ for 100 minutes to obtain the flexible graphite bipolar plate product.

[0052] Comparative Example 2: Step 1: Mix 30-80 mesh and 200-300 mesh worm graphite powder and resin in a 1:1 ratio in a three-dimensional mixer of model SBH-10. The resin mass percentage is 35%, and resin-coated graphite-based composite powder is obtained. Step 2: The graphite-based composite powder is hot-pressed in a mold at a pressure of 30 MPa and a curing temperature of 200℃ for 30 minutes to obtain a product with a thickness of 6 mm and a density of 1.8 g / cm³. 3 Graphite bipolar plates.

[0053] The main difference between Comparative Example 1 and Example 3 is that vibration was not used in step 2.

[0054] The main difference between Comparative Example 2 and the Example is that the graphite powder was premixed with the resin instead of being impregnated.

[0055] The graphite bipolar plates prepared in the examples and comparative examples were tested, and the test results are shown in Table 1.

[0056] Table 1 Conductivity (S / cm) Flexural strength (MPa) <![CDATA[Air permeability (cm 3 / cm 2 ·s)]]> <![CDATA[Preform density g / cm 3 > Example 1 447.8 46.8 <![CDATA[5.2×10 -8 ]]> 1.0 Example 2 438.5 42.3 <![CDATA[1.5×10 -8 ]]> 1.0 Example 3 409.6 51.5 <![CDATA[1.9×10 -9 ]]> 0.8 Comparative Example 1 183.5 30.6 <![CDATA[8.7×10 -7 ]]> / Comparative Example 2 125.7 35.2 <![CDATA[2.3×10 -7 ]]> 1.8 Table 1 shows the performance test results of graphite bipolar plates. As can be seen from the comparison between the examples and the comparative examples, the flexible graphite bipolar plates prepared by the combination of vacuum vibration molding and resin impregnation reinforcement process are superior to those prepared by non-vibration molding or hot pressing in terms of both conductivity and mechanical properties.

[0057] As shown in the examples, the density of the flexible graphite bipolar plate preform is between 0.8 and 1.3 g / cm³. 3 Within a certain range, the higher the density, the better the conductivity of the bipolar plate, but the lower the mechanical properties. This is mainly due to the increased proportion of flexible graphite and the decreased resin content, which also reduces air permeability.

[0058] As can be seen from the comparative examples, the overall performance of the flexible graphite bipolar plate prepared by direct molding process (Comparative Example 2) is much lower than that of the flexible graphite bipolar plate prepared by a combination of vibration molding and resin impregnation reinforcement process (Comparative Example 2). The main reason is that the density difference between the base and the ridge of the flexible graphite bipolar plate preform is large during the molding process of Comparative Example 2. The bending strength of Comparative Example 2 is higher than that of Comparative Example 1. The main reason is that the resin content is higher and the resin is aggregated together, which improves the overall mechanical properties of the plate, but has the opposite effect on the mechanical properties of the electrode side.

[0059] The flexible graphite bipolar plate for flow batteries and its preparation method described in this embodiment have the following advantages: (1) Flexible graphite bipolar plate preforms are prepared by vibration molding process. Auxiliary vibration is applied during the molding process to help expel air and reduce defects such as bubbles and pores, so that the product density is between 0.8 and 1.3 g / cm³. 3 Within the specified range, improve product density; (2) Vibration energy is used to promote the flow and uniform distribution of materials in the mold, so that the density of the base and the ridge are consistent; (3) The worm graphite powders with different particle sizes interlock and form a network structure during the molding process, which improves the conductivity of the flexible graphite bipolar plate.

[0060] (4) The flexible graphite preform is strengthened by resin impregnation, which improves the mechanical properties of the flexible graphite bipolar plate.

[0061] Therefore, by adopting the graphite bipolar plate preparation method for flow batteries provided by this invention, graphite bipolar plates with good conductivity and mechanical properties can be obtained, the density is easy to control, the density difference between products is small, the product yield is high, the scrap rate is reduced, and the overall production efficiency is improved.

[0062] In the method disclosed in this invention, a mold with a vibration device is used for vacuum molding to promote the flow and uniform distribution of materials in the mold, so that worm graphite powders with different particle sizes interlock and form a network structure during the molding process.

[0063] However, in the actual production process, worm graphite powder with different particle sizes is prone to "bridging" during the flow process, which leads to air bubbles in the graphite and reduces the fluidity of the powder. It is necessary to vibrate for a long time and a large amplitude to reduce the impact of air bubbles on the graphite plate molding process, and the overall processing efficiency of the molding process becomes lower.

[0064] To solve this problem, such as Figures 3 to 4As shown, the present invention further provides a dynamic modulation vacuum vibration compaction system for vibration molding process, including an electromagnetic or servo hydraulic high-frequency vibration table 5, a dynamic vacuum modulation system 6, and an integrated control system. The high-frequency vibration table 5 is provided with a double-layer mold 7, and the double-layer mold 7 is provided with an inner cavity 8. The inner cavity 8 is used to contain worm graphite powder. The outer shell of the double-layer mold 7 and the inner cavity 8 form a vacuum modulation cavity 10. The inner cavity 8 is connected to the vacuum modulation cavity 10 through a connecting through hole 9.

[0065] The dynamic vacuum modulation system 6 includes a vacuum pump 601 and an air intake pump 602. The vacuum modulation cavity 10 is connected to a vacuum pipeline 604 via a high-speed switching valve 603. The vacuum pipeline 604 is connected to the vacuum pump 601. The inner cavity 8 is connected to an air intake pipeline 606 via a micro air intake valve 605. The air intake pipeline is connected to the air intake pump 602.

[0066] The vacuum pump 601 is used to extract air from the vacuum modulation chamber 10, thereby providing a stable vacuum environment.

[0067] The high-speed switching valve 603 is a piezoelectric or high-speed solenoid valve, installed between the vacuum line 604 and the double-layer mold 7.

[0068] The air intake pump 602 is used to inject a precisely controllable trace amount of gas into the inner cavity 8 through the trace intake valve 605. The inner cavity 8 is connected to the dynamic vacuum modulation system 6.

[0069] Inert gases can be used for trace amounts of gas.

[0070] The integrated control system includes a controller and sensors. The controller is a PCL controller, etc., and is communicatively connected to the vacuum pump 601, high-speed switching valve 603, micro-inlet valve 605, and sensors. The sensors are installed in the vacuum modulation chamber 10 to monitor the vacuum level, vibration acceleration, temperature, etc. in the vacuum modulation chamber 10 in real time.

[0071] The controller is used to synchronously coordinate the opening and closing sequence of the high-speed switching valve 603 and the micro-inlet valve 605 according to the set program and the data reflected by the sensor, so as to ensure that the vibration waveform (frequency, amplitude) and the vacuum modulation waveform (phase, amplitude, frequency) are precisely synchronized or form a specific phase difference, so that the vacuum degree (from 90mbar to 10mbar) in the mold cavity can be controlled and periodically fluctuated within the frequency range of 0-50Hz.

[0072] The working principle of the dynamic modulation vacuum vibration compaction system is as follows: 1. Load the well-mixed worm graphite powder into the mold cavity, seal the system, and apply a pressure of 30~50MPa; 2. Start the vacuum pump and evacuate the vacuum modulation chamber inside the mold to a basic high vacuum (e.g., 10 mbar) to remove most of the free gas. Hold the pressure for 30-60 seconds. 3. Start the high-frequency vibration table and compact the worm graphite powder with a variable frequency (e.g., 0-50Hz) and amplitude; At the same time, the dynamic vacuum modulation system begins to operate: "Exhalation" phase (reducing vacuum): The controller briefly closes the high-speed switching valve and instantly opens the micro-inlet valve, allowing a small amount of gas to be injected into the mold cavity. The pressure inside the cavity rises rapidly from 10 mbar to 90 mbar. This instantaneous pressure increase causes the remaining bubbles to expand rapidly due to the decrease in external pressure. The bubble walls become thinner, the bridging state is broken, and they become interconnected. "Inhalation" phase (restoring high vacuum): The controller quickly closes the inlet valve and opens the high-speed switching valve. The vacuum pump rapidly and violently extracts the injected gas along with the gas inside the expanded bubble, causing a sudden drop in pressure from 90 mbar back to 10 mbar. This process generates strong suction shear force and pressure difference, which on the one hand extracts the gas from the connected gas channel, and on the other hand, the bubble bursts during violent contraction.

[0073] Throughout the process, vibration continues, promoting the rearrangement of powder particles and providing channels for the movement and overflow of bubbles.

[0074] Furthermore, in the actual production process, the above-mentioned "exhalation-inhalation" cycle can be repeated, thereby performing "lung-like cleaning" on the inside of the powder. After the process is completed, a green body with a high degree of homogeneity is obtained.

[0075] The dynamic modulation vacuum vibration compaction system provided by this invention utilizes the drastic changes in vacuum to apply alternating expansion-compression stress to the air bubbles between and inside the worm graphite powder particles, causing them to break, merge, and be extracted through the powder gaps, preventing powder "bridging." Alternating shear force is applied to help the bubble walls break, ensuring the effective execution of the vacuum vibration molding process and improving the homogeneity of the flexible graphite preform.

[0076] Traditional static seals are prone to failure under high-frequency vibration. The following provides a dynamic sealing structure for vibration: The double-layer mold 7 includes a first shell 701 and a second shell 702. The second shell 702 is wrapped around the outside of the first shell 701. A molding system (not shown in the figure) is provided on the second shell 702. The vibration table 5 can drive the entire first shell 701 and the second shell 702 to vibrate together.

[0077] The inner cavity 8 is disposed within the first housing 701, and the vacuum modulation cavity 10 is disposed between the first housing 701 and the second housing 702. Both the first housing 701 and the second housing 702 can be opened and are sealed by a combination of high-performance rubber O-rings and labyrinth seals to ensure that the inner cavity 8 and the vacuum modulation cavity 10 maintain good airtightness under high-frequency vibration.

[0078] The micro-intake valve 605 is disposed on the first housing 701, and the high-speed switching valve 603 is disposed on the second housing 702.

[0079] The vacuum line 604 and the air inlet line 606 are flexible metal corrugated pipes, or both the ends of the vacuum line 604 and the air inlet line 606 are provided with flexible metal corrugated pipes.

[0080] Flexible metal bellows are resistant to vibration, allowing for minute displacements while maintaining a seal, ensuring good airtightness even under high-frequency vibration.

[0081] The intense pumping of air by the vacuum pump may carry away fine powder. To prevent powder from escaping and causing contamination, a precision metal sintered filter (which can be backflushed and cleaned) is installed at the interface between the connecting hole 9 and the vacuum line 604 to block powder but allow gas to pass through.

[0082] The embodiments provided by this invention are devices that combine vacuum and vibration. This device uses the kinetic energy generated by vibration to dynamically change the vacuum level inside the mold, causing the vacuum level inside the mold to change at a high frequency, accelerating the expansion, rupture and extrusion of bubbles inside the powder. At the same time, the dynamic vacuum directly acts on the bubbles themselves. The two work together to greatly improve the degassing efficiency, and are expected to significantly shorten the production cycle of the traditional long-term vibration degassing and compaction process, and improve the homogeneity of graphite ligands.

[0083] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A method of making a flexible graphite bipolar plate for a flow battery, the method comprising: The method comprises the following steps: S100, mixing worm graphite powder with different particle sizes in a three-dimensional mixer to obtain a mixed powder; S200, placing the mixed powder into a mold with a vibration device, and using a vibration molding process to make the mixed powder flow in the mold until it is uniformly distributed, the mixed powder bites each other during the flow process, and a network structure is formed to obtain a preform, the preform contains pores; S300, placing the preform into a resin solution for impregnation reinforcement, and the resin solution fills into the pores to obtain a primary plate body; S400, sequentially cleaning, curing and drying the primary plate body to obtain a flexible graphite bipolar plate for flow batteries.

2. The method of claim 1, wherein the method further comprises: In the step S100, the particle size of the worm graphite powder ranges from 30 to 80 mesh and 200 to 300 mesh. The mixing time is 30 to 60 minutes.

3. The method of claim 1, wherein the method further comprises: In the step S200, the vibration molding process satisfies the following conditions: The vibration frequency ranges from 0 to 50 Hz, the molding pressure is 30 to 50 MPa, the pressure holding time is 30 to 60 seconds, and the vacuum degree is less than 10 mbar.

4. The method of claim 3, wherein the graphite bipolar plate is flexible. In the step S200, the thickness of the green body is 4-6 mm, the thickness of the substrate is 1 mm, and the density of the green body is 0.8-1.3 g / cm 3 .

5. The method of claim 1, wherein the method further comprises: In the step S300, the resin solution is any one or more of phenolic resin or epoxy resin. The impregnation reinforcement time is 30 to 60 minutes.

6. The method of claim 1, wherein the method further comprises: In the step S400, the cleaning is to clean the resin solution on the surface of the primary plate body to prevent the resin material from completely wrapping the surface of the graphite material.

7. The method of claim 1, wherein the method further comprises: In the step S400, the curing satisfies the following conditions: The curing temperature is 80℃, and the curing time is 30 to 60 minutes.

8. The method of claim 1, wherein the method further comprises: In the step S400, the drying satisfies the following conditions: The drying temperature is 60℃, and the drying time is 60 to 120 minutes.

9. A flexible graphite bipolar plate for a flow battery prepared according to the method of any one of claims 1-8, wherein, The plate body (1) is provided with an inverted U-shaped ridge structure (2), the ridge structure (2) is provided with a flow channel (3), the bottom of the plate body (1) is provided with a base (4), and the flow channel (3) is arranged on the base (4).

10. A flexible graphite bipolar plate for a flow battery according to claim 9, wherein, The conductivity of the bipolar plate is 409.6~447.8S / cm, the bending strength is 42.3~51.5MPa, the air permeability is 1.9×10 -9 ~5.2×10 - 8 cm 3 / cm 2 ·s.

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