A kind of liquid flow battery composite bipolar plate and its molecular migration control preparation method

Abstract

The application belongs to the field of redox flow batteries, and provides a liquid flow battery composite bipolar plate and a molecular migration control preparation method thereof. The method comprises the following steps: (1) mixing phenolic resin, a curing agent, carbon-based conductive fillers and a replacement migration agent to obtain a composite material; the replacement migration agent is a long-chain alkyl primary amide; the content of the replacement migration agent in the composite material is 2 wt.%-3 wt.%; (2) placing the composite material in a mold, heating to 150-160 DEG C and hot-pressing at 15-30 MPa at the temperature to form a molding blank, cooling to room temperature, demolding to obtain the molding blank; (3) aging the molding blank at 20-40 DEG C to allow the replacement migration agent to fully migrate to the surface of the molding blank, then washing the replacement migration agent on the surface of the molding blank, and drying to obtain the liquid flow battery composite bipolar plate. The application can realize the preparation of the composite bipolar plate without post-processing and improve the performance of the composite bipolar plate.

Description

Technical Field

[0001] This invention belongs to the field of redox flow batteries and relates to a composite bipolar plate for flow batteries and its molecular migration regulation preparation method. Background Technology

[0002] Flow batteries are energy storage devices that dissolve active materials in a liquid electrolyte and convert electrical energy into chemical energy through an external storage tank, an electrolyte circulation system, and an electrochemical reactor. Compared with traditional secondary batteries, flow batteries have advantages such as independently designable capacity and power, high intrinsic safety, long cycle life, and easy scalability. They have significant application value in areas such as renewable energy grid connection, grid peak shaving and frequency regulation, medium- and long-term energy storage, and backup power.

[0003] Vanadium redox flow batteries are among the most thoroughly researched and maturely engineered flow battery systems. Both their positive and negative electrode electrolytes use vanadium ions in different valence states as active materials, reducing the risk of irreversible failure due to cross-contamination. They also feature deep charge / discharge capability, electrolyte recyclability, and ease of maintenance. As flow batteries develop towards higher power density, longer lifespan, and lower cost, performance optimization of key components such as bipolar plates, electrodes, and ion exchange membranes becomes particularly important.

[0004] Bipolar plates are typically located between adjacent single cells, serving multiple functions including electron conduction, electrolyte isolation, mechanical support, and flow field construction. Bipolar plates need to simultaneously possess high bulk conductivity and surface conductivity, good acid corrosion resistance, sufficient mechanical strength, dimensional stability, and machinability. Currently, graphite-based or carbon-based conductive composite material bipolar plates are attracting significant attention due to their lower cost, ease of hot-pressing, and suitability for mass production.

[0005] Existing composite bipolar plates are typically manufactured by hot pressing conductive carbon fillers with a thermosetting resin matrix. During the hot pressing process, the resin matrix experiences viscosity reduction and flow under high temperature and pressure. Under applied pressure, it migrates into the pores and surface areas between the conductive fillers, easily accumulating at the mold interface or on the bipolar plate surface, forming a continuous or semi-continuous resin-rich layer. Since the conductivity of resin is much lower than that of conductive fillers such as expanded graphite and carbon black, this resin-rich layer can obscure the conductive pathways on the bipolar plate surface, increasing interfacial contact resistance and area resistivity, thereby reducing the voltage efficiency and energy efficiency of the flow battery.

[0006] To address the issue of resin-rich layers, existing technologies often employ post-processing methods such as mechanical grinding, plasma etching, chemical etching, or secondary pressing to remove or destroy the resin on the surface of the bipolar plate. However, mechanical grinding easily causes thickness loss and surface structure damage, plasma or chemical treatments have high requirements for equipment and process windows, and secondary pressing may introduce new interface defects. These methods are passive treatments performed after the formation of the resin-rich layer, making it difficult to control the migration behavior of the resin matrix from the molding stage. Post-processing inevitably has an adverse effect on the performance of the bipolar plate. Therefore, if a method for preparing composite bipolar plates could be provided that can actively control the migration behavior of the resin matrix and the surface structure of the bipolar plate during hot pressing, thereby avoiding the problems caused by post-processing to some extent, it would have a positive impact on improving the performance of composite bipolar plates. Summary of the Invention

[0007] To address the problem that existing technologies form a resin-rich layer during the fabrication of composite bipolar plates for flow batteries, requiring specialized post-processing to remove the resin-rich layer, but this post-processing inevitably has an adverse effect on the performance of the bipolar plate, and some post-processing methods are also limited by equipment and narrow process windows, this invention provides a composite bipolar plate for flow batteries and a method for preparing it by regulating molecular migration, so as to achieve the preparation of composite bipolar plates without post-processing and improve the performance of composite bipolar plates.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a flow battery composite bipolar plate with controlled molecular migration includes the following steps:

[0010] (1) Phenolic resin, curing agent, carbon-based conductive filler and alternative migration agent are thoroughly mixed to obtain a composite material; the alternative migration agent is a long-chain alkyl primary amide; in the composite material, the content of the alternative migration agent is 2 wt.%~3 wt.%, and the mass ratio of the sum of the mass of phenolic resin and curing agent to the mass ratio of the mass of carbon-based conductive filler is (40~10):(60~90).

[0011] (2) Place the composite material in the mold, heat it to 150~160 ℃ and hot press it at 15~30 MPa at the same temperature, cool it to room temperature, demold it, and obtain the molded blank.

[0012] (3) The molded blank is aged at 20~40 ℃ to allow the substitute migration agent to fully migrate to the surface of the molded blank. Then, the substitute migration agent on the surface of the molded blank is washed away and dried to obtain the flow battery composite bipolar plate.

[0013] In step (1) of the above preparation method, the long-chain alkyl primary amide has low surface energy and strong surface migration ability. During hot pressing, the long-chain alkyl primary amide migrates to the surface of the molded preform before the phenolic resin and occupies the surface position of the molded preform, thus competing with the surface enrichment behavior of the phenolic resin and limiting the surface enrichment of the phenolic resin to a certain extent. Feasible long-chain alkyl primary amides include at least one of erucamide, oleamide, and stearamide.

[0014] In the above preparation method, step (1) involves adding polyethylene glycol (PEG) during the preparation of the composite material. PEG forms hydrogen bonds or other intermolecular interactions with phenolic resin through hydroxyl, ether oxygen, and other groups, constructing an in-situ fixed network, inhibiting the free migration of phenolic resin segments, and enhancing the cohesive force within the phenolic resin matrix and the bonding strength at the phenolic resin-carbon-based conductive filler interface. Furthermore, the molecular weight and dosage of PEG affect the performance of the composite bipolar plate. For example, if the molecular weight or dosage of PEG is too low, the segment bridging ability is insufficient; if the molecular weight or dosage of PEG is too high, it may cause problems such as decreased dispersibility and increased swelling of the composite bipolar plate in an aqueous medium. The content of PEG in the composite material is 1 wt.% to 3 wt.%. The number-average molecular weight of PEG is 7000 to 8000.

[0015] In step (1) of the above-mentioned composite bipolar plate preparation method, the carbon-based conductive filler consists of a main filler and an auxiliary filler. The main filler accounts for 80 wt.%~95 wt.% of the carbon-based conductive filler, and the auxiliary filler accounts for 5 wt.%~20 wt.% of the carbon-based conductive filler. The main filler is at least one of two-dimensional or three-dimensional carbon-based conductive fillers, and the auxiliary filler is at least one of one-dimensional or zero-dimensional carbon-based conductive fillers. The main filler is used to form the main conductive framework, and the auxiliary filler is used to fill the gaps between the main fillers to reinforce the conductive path. Feasible main fillers include at least one of expanded graphite, flake graphite, and spherical graphite, and auxiliary fillers include at least one of conductive carbon black, carbon nanotubes, and chopped carbon fibers.

[0016] In step (1) of the above-mentioned composite bipolar plate preparation method, the mass ratio of the curing agent to the phenolic resin is (7~9):100.

[0017] In the above-mentioned method for preparing composite bipolar plates, the phenolic resin is a linear thermoplastic phenolic resin, and the curing agent is hexamethylenetetramine.

[0018] In step (1) of the above-mentioned composite bipolar plate preparation method, the mixing method used in preparing the composite material can be any existing technology. For example, ball milling, mechanical stirring, high-speed shearing, or ultrasonic dispersion can be used for mixing; preferably, a planetary ball mill is used at 100~400 r·min -1 Dispersion and mixing are carried out using grinding balls under certain rotational speed conditions.

[0019] In step (2) of the above-mentioned composite bipolar plate preparation method, the mold can be any mold used in the prior art for preparing composite bipolar plates. For example, an aluminum alloy mold can be used.

[0020] In step (2) of the above-mentioned composite bipolar plate preparation method, the hot pressing time is controlled to be 15~25 min.

[0021] In step (3) of the above-mentioned composite bipolar plate preparation method, aging refers to placing the molded blank in an environment of 20~40 ℃ for a period of time to allow the substitute migration agent to fully migrate to the surface of the molded blank. The aging time is usually controlled to be 60~360 min, and further, the aging time can be controlled to be 60~240 min.

[0022] In step (3) of the above-mentioned composite bipolar plate preparation method, when washing away the substitute migration agent on the surface of the molded blank, hot alcohol solvents, such as methanol or ethanol at 50~60 ℃, can be used for cleaning, or methanol aqueous solution or ethanol aqueous solution at 50~60 ℃ can be used for cleaning.

[0023] The present invention also provides a flow battery composite bipolar plate prepared by the above method.

[0024] The main technical principles of this invention are as follows:

[0025] 1. This invention regulates the surface and interface structure of a composite bipolar plate through a molecular migration control strategy. Fundamentally, it uses low-surface-energy migratory molecules as substitute migratory agents. Leveraging their lower surface energy and preferential migration relative to phenolic resin, these molecules occupy the surface region of the preform before resin accumulation, effectively inhibiting excessive resin accumulation on the composite bipolar plate surface. Furthermore, polyethylene glycol is introduced as an in-situ fixative in addition to the substitute migratory agent, constructing a synergistic system of surface substitution migration and internal in-situ fixation. While using the substitute migratory agent to suppress excessive resin accumulation on the composite bipolar plate surface, polyethylene glycol with an appropriate molecular chain length forms a hydrogen bond network with the resin, further inhibiting resin migration to the surface and enhancing the cohesion within the resin matrix and the bonding strength at the resin-carbon-based conductive filler interface.

[0026] 2. More specifically: (1) During the hot pressing process, the alternative migration agent preferentially migrates to the free surface by relying on the difference in surface energy and thermally driven diffusion, competing with the surface enrichment of the resin, changing the formation mechanism of the composite bipolar plate surface layer, and transforming the dense insulating layer originally formed by the resin into a removable alternative migration agent surface layer. By removing the alternative migration agent located on the surface layer by solvent washing, the conductive network can be effectively exposed, thereby improving the surface conductivity of the composite bipolar plate. At the same time, the introduction of the alternative migration agent also reduces the surface roughness of the composite bipolar plate and increases its surface smoothness and uniformity, which is beneficial to reducing the surface contact resistance.

[0027] (2) Polyethylene glycol forms a hydrogen bond network with the resin, which on the one hand restricts the free movement and large-scale migration of the resin chain segments, restricts the resin migration to the surface, and enhances the cohesion inside the resin matrix. On the other hand, under the dual constraints of the resin network and the hydrogen bond network, it can improve the coating and bonding stability of the carbon-based conductive filler, and improve the spatial distribution stability of the carbon-based conductive filler and the uniformity of the conductive network structure.

[0028] (3) The introduction of alternative migration agents alters the enrichment behavior of surface components during hot pressing, weakening the continuous coverage of the resin-rich layer on the surface. This facilitates more complete exposure of carbon-based conductive fillers and other polar components on the surface, thereby changing the surface chemical properties of the composite bipolar plate. While improving the internal structural stability, polyethylene glycol also regulates the distribution of polar groups in the resin matrix, indirectly affecting the surface properties of the composite bipolar plate and enhancing the affinity of the surface layer for polar liquid media. The combined effect of these two aspects also improves the surface wettability of the composite bipolar plate.

[0029] This invention actively intervenes in the resin migration path, distribution state, and internal rearrangement behavior by replacing the migration agent and the synergistic effect of polyethylene glycol, achieving multi-scale structural control from the interface to the bulk phase. This reduces the interfacial resistance and surface roughness of the composite bipolar plate, while improving its mechanical stability and surface wettability.

[0030] 3. Building upon points 1 and 2, and through rational process design and effective matching of multiple process parameters, the overall performance of the composite bipolar plate was significantly improved. Firstly, by controlling the amount of the substitute migration agent, the mild time of hot pressing, and aging conditions, the migration behavior and distribution of the substitute migration agent, the migration and cross-linking behavior of the resin, the construction of the conductive network, and the bonding between the conductive network and resin groups were comprehensively regulated. Secondly, by controlling the polyethylene glycol molecular chain length and the amount of polyethylene glycol, the migration behavior of the resin was further regulated, and the internal cohesion of the resin matrix was strengthened, improving the interfacial bonding between the resin matrix and the carbon-based conductive filler. Thirdly, through the above process controls, the interfacial wettability and surface morphology of the composite bipolar plate were also improved. Ultimately, without requiring post-processing, the overall performance of the composite bipolar plate, including conductivity, mechanical properties, surface wettability, surface smoothness, and corrosion resistance, was enhanced.

[0031] Compared with the prior art, the technical solution of the present invention can produce the following beneficial technical effects:

[0032] 1. This invention provides a method for preparing a composite bipolar plate with actively controllable resin migration. The method involves thoroughly mixing phenolic resin, a curing agent, a carbon-based conductive filler, and a substitute migration agent to form a composite mixture, which is then hot-pressed at 150-160 °C and 15-30 MPa. After cooling to room temperature and demolding, the mixture is aged at 20-40 °C. The aging process involves cleaning to remove the substitute migration agent from the surface of the molded preform, followed by drying to obtain the flow battery composite bipolar plate. This invention uses low surface energy migratory molecules as substitute migration agents. Utilizing their low surface energy and preferential migration characteristics, the process conditions are controlled to ensure that the substitute migration agent occupies the surface area of ​​the molded preform before resin enrichment, effectively inhibiting excessive resin enrichment on the surface of the composite bipolar plate. Furthermore, polyethylene glycol is introduced as an in-situ fixative, constructing a synergistic system of surface substitution migration and internal in-situ fixation. While utilizing alternative migration agents to suppress excessive resin accumulation on the surface of composite bipolar plates, the invention also leverages polyethylene glycol to form a hydrogen bond network with the resin, further inhibiting resin migration to the surface and enhancing the cohesion within the resin matrix and the bonding strength at the resin-carbon-based conductive filler interface. This method actively regulates resin migration behavior during the bipolar plate molding process and post-molding aging, fundamentally reducing resin accumulation on the surface. This avoids damage to the bipolar plate surface caused by traditional post-processing methods such as mechanical grinding or chemical etching, and also solves the problem of some post-processing methods being limited by equipment and narrow process windows.

[0033] 2. The method of this invention, through the synergistic effect of a replacement migration agent and polyethylene glycol, actively intervenes in the resin migration path, distribution state, and internal rearrangement behavior, achieving multi-scale structural control from the interface to the bulk phase. This reduces the interfacial resistance and surface roughness of the composite bipolar plate while improving its mechanical stability and surface wettability. Experimental results show that the resistivity of the composite bipolar plate sample prepared by the method of this invention can be as low as 0.075 Ω, and the conductivity can be reduced from approximately 50 S·cm. -1 Increased to approximately 143 S·cm -1 The bending strength can be increased from approximately 23.7 MPa to approximately 31.2 MPa. Furthermore, the surface wettability and corrosion resistance of the composite bipolar plate prepared by the above method of the present invention are improved to a certain extent. The surface water contact angle is reduced from approximately 112° to approximately 78°. In polarization testing, the corrosion potential shifts positively and the corrosion current density decreases, which is beneficial for the uniform spread of the electrolyte at the interface between the composite bipolar plate and the electrode, thereby improving the operational stability of the fuel cell stack.

[0034] 3. The process flow of the method described in this invention is compatible with the hot pressing molding process for the preparation of existing composite bipolar plates. It only requires the introduction of alternative migration agents or further introduction of polyethylene glycol during the mixing of phenolic resin and carbon-based conductive filler, and the addition of aging and cleaning steps to achieve the preparation of high-quality composite bipolar plates. No post-processing is required, which is suitable for the mass production of composite bipolar plates for flow batteries and also provides a new approach to suppressing the formation of resin-rich layers. Attached Figure Description

[0035] Figure 1 These are SEM images of the near-surface cross-sections of the aged preforms and composite bipolar plates prepared in Example 1 and Comparative Example 1.

[0036] Figure 2 These are AFM images of the composite bipolar plates prepared in Example 1 and Comparative Example 1.

[0037] Figure 3 These are the infrared spectra of the aged molded blanks prepared in Example 1 and Comparative Example 1.

[0038] Figure 4 The images show the ASR test results of the aged preforms and composite bipolar plates prepared in Example 1 and Comparative Example 1.

[0039] Figure 5 These are images showing the cross-sectional morphology and compositional analysis results of samples after aging for different times.

[0040] Figure 6 This is a graph showing the resistance test results of composite bipolar plates prepared with different erucamide contents in Example 5.

[0041] Figure 7This is a graph showing the resistance test results of composite bipolar plates prepared at different hot-pressing temperatures in Example 6.

[0042] Figure 8 This is a graph showing the resistance test results of the composite bipolar plates prepared by different hot pressing times in Example 7.

[0043] Figure 9 This is a graph showing the bending strength test results of composite bipolar plates prepared with different polyethylene glycol 8000 contents in Example 8.

[0044] Figure 10 This is a graph showing the swelling rate test results of composite bipolar plates prepared with different polyethylene glycol 8000 contents in Example 8.

[0045] Figure 11 This is a graph showing the bending strength test results of composite bipolar plates prepared with polyethylene glycol of different molecular weights in Example 8.

[0046] Figure 12 This is a graph showing the swelling rate test results of composite bipolar plates prepared with polyethylene glycol of different molecular weights in Example 8.

[0047] Figure 13 The graph shows the bending strength test results of the composite bipolar plates prepared in Example 9 and Comparative Example 1.

[0048] Figure 14 The graph shows the surface wettability test results of the composite bipolar plates prepared in Example 9 and Comparative Example 1.

[0049] Figure 15 The resistivity test results are shown in the graphs for the composite bipolar plates prepared in Example 9 and Comparative Example 1.

[0050] Figure 16 The graph shows the corrosion resistance test results of the composite bipolar plates prepared in Example 9 and Comparative Example 1.

[0051] Figure 17 Figures (a) to (c) are photographs of the vanadium redox flow battery test platform, the vanadium redox flow battery, and the composite bipolar plate, respectively.

[0052] Figure 18 Figures (a) to (c) show the coulombic efficiency, energy efficiency, and voltage efficiency of the composite bipolar plates prepared in Example 9 and Comparative Example 1 under different currents. Detailed Implementation

[0053] The following examples further illustrate the composite bipolar plate for flow batteries and its molecular migration regulation preparation method according to the present invention. It should be noted that the following examples are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0054] In the following examples and comparative examples, the phenolic resin used was a linear thermoplastic phenolic resin, brand name PF2123, purchased from Henan Bolun Materials Co., Ltd. This phenolic resin was premixed with hexamethylenetetramine as a curing agent at the time of manufacture, and the mass ratio of curing agent to phenolic resin was 7:100; the expanded graphite had a purity of 99.8% and a size of 20 mesh (D). 50 The conductive carbon black (approximately 600-800 μm) was purchased from Anhui Zesheng Technology Co., Ltd.; the conductive carbon black was of battery grade, brand name TimcalSuper P LI, and purchased from Shanghai Baika Chemical Technology Co., Ltd. All other reagents were standard reagents in the field and readily available.

[0055] Example 1

[0056] In this embodiment, erucamide is used as an alternative migration agent to provide a method for preparing a flow battery composite bipolar plate with molecular migration regulation. The steps are as follows:

[0057] (1) Phenolic resin (premixed with hexamethylenetetramine curing agent, with a mass ratio of curing agent to phenolic resin of 7:100), carbon-based conductive filler, and erucamide are added to a planetary ball mill, along with grinding balls of different particle sizes (1~3 mm), and the mixture is milled at 300 r·min. -1 The mixture was ball-milled at a certain speed until all components were fully mixed to obtain a composite material. The carbon-based conductive filler was composed of expanded graphite and conductive carbon black in a mass ratio of 80:20. In the composite material, the mass ratio of the sum of the masses of phenolic resin and curing agent to the mass ratio of the carbon-based conductive carbon filler was 40:60, and the content of erucamide was 2 wt.%.

[0058] (2) Place the composite material in an aluminum alloy mold, then place it on a flat vulcanizing machine, heat it to 150 ℃ and hot press it at 150 ℃ and 20 MPa for 15 min, cool it to room temperature, demold it, and obtain the molded blank.

[0059] (3) The molded preform is aged at room temperature (25 °C) for 240 min, and then the aged preform is cleaned with ethanol at 50 °C to remove the erucamide on the surface and expose the near-surface conductive network. Then it is dried at 60 °C to obtain a composite bipolar plate with a size of 8 cm × 6 cm × 1 mm.

[0060] Comparative Example 1

[0061] The operation of this comparative example is basically the same as that of Example 1, except that: in step (1), erucamide is not added when preparing the composite material.

[0062] Example 2

[0063] In this embodiment, the surface morphology and surface chemical composition of the aged preforms and composite bipolar plates prepared in Example 1 and Comparative Example 1 are characterized.

[0064] 1. Surface morphology

[0065] The microstructure of the near-surface cross-sections of the aged preforms and composite bipolar plates prepared in Example 1 and Comparative Example 1 was observed using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown. Figure 1 Figures (a) and (b) are SEM images of the near-surface cross-section of the aged preform and the composite bipolar plate prepared in Example 1. Figure 1 Figures (c) and (d) are SEM images of the near-surface cross-section of the aged preform and the composite bipolar plate prepared in Example 1. Figure 1 It can be seen that the aged molded preforms prepared in Example 1 and Comparative Example 1 both exhibit certain surface coverage characteristics. Relatively speaking, the coverage layer of Comparative Example 1 is denser. After ethanol cleaning, the surface coverage layer in Example 1 can be effectively removed, the thickness of the coverage layer becomes thinner, and the sample surface changes from the original continuous coverage state to a morphology with obvious exposure of the internal conductive phase. In the near-surface region after cleaning, the distribution boundary of the conductive filler is clearer, and the surface structure is more uniform, indicating that ethanol cleaning selectively removes the erucamide layer that migrated to the surface. In contrast, the surface coverage layer in Comparative Example 1 remains basically unchanged. It can be seen that the introduction of erucamide changes the migration and enrichment mode of surface components during hot pressing, transforming the originally difficult-to-remove resin-rich layer into a solvent-removable surface coverage layer, thereby creating conditions for the exposure of conductive pathways and the reduction of interfacial resistance.

[0066] Atomic force microscopy (AFM) was performed on the composite bipolar plates prepared in Example 1 and Comparative Example 1 to observe the differences in their surface structures at the nanoscale. The results are as follows: Figure 2 As shown. Figure 2 Figure (a) is the AFM image of the composite bipolar plate prepared in Example 1. Figure 2 Figure (b) is the AFM image of the composite bipolar plate prepared in Example 1. Figure 2It can be seen that the composite bipolar plate prepared in Comparative Example 1 exhibits obvious peak-valley undulations on its surface, with uneven surface morphology in local areas, indicating strong non-uniformity in the distribution of surface components. This is consistent with the surface enrichment phenomenon observed by SEM. In contrast, the surface morphology of the composite bipolar plate prepared in Example 1 is significantly smoother, with a significantly reduced surface undulation amplitude within the same scanning range, and a decrease in the number of local protrusions and valleys, indicating that the surface structure uniformity has been effectively improved. Quantitative analysis based on AFM test results shows that the surface roughness of the composite bipolar plate prepared in Comparative Example 1 is 64.7 nm, while that of the composite bipolar plate prepared in Example 1 is 31.6 nm. This indicates that the removable layer formed after erucic acid amide migrates to the surface during hot pressing effectively inhibits the excessive enrichment of phenolic resin on the surface and promotes the re-uniform manifestation of conductive filler and resin matrix in the surface area after cleaning, resulting in improved surface smoothness and reduced roughness of the composite bipolar plate.

[0067] 2. Surface chemical composition

[0068] The infrared spectra of the aged molded preforms prepared in Example 1 and Comparative Example 1 were tested, and the results are as follows: Figure 3 As shown. By Figure 3 It can be seen that the aged preform prepared in Comparative Example 1 did not show characteristic absorption signals of fatty amides on its surface, and its surface chemical composition mainly originated from the phenolic resin matrix and the conductive filler itself. In contrast, the aged preform prepared in Example 1 showed absorption signals at approximately 1020 cm⁻¹. -1 Significant fatty amide characteristic absorption was observed nearby, indicating that erucamide underwent significant migration during hot pressing and formed a detectable enrichment layer on the sample surface.

[0069] Example 3

[0070] In this embodiment, the area resistivity (ASR) of the aged preforms and composite bipolar plates prepared in Example 1 and Comparative Example 1 is characterized.

[0071] ASR (Automatic Resistor Resistance) was measured using a sandwich resistance test method. During the test, the sample was placed between two carbon felts and clamped with a copper plate as the outer electrode. The copper plate, carbon felt, and sample formed a sandwich structure, and the measurement was performed under a certain pressure to simulate the pressure conditions during actual fuel cell stack assembly. Specifically, firstly, carbon felts and copper plates of corresponding areas were prepared based on the sample surface area (A). To eliminate the influence of the resistance of the test system itself, before the formal measurement, the sample was not placed; only the two layers of carbon felt were clamped between the copper plate electrodes, and the blank resistance of the system was measured under the same pressure, denoted as R0. Subsequently, the sample was placed between the two layers of carbon felts, and the test was performed again under the same pressure conditions to obtain the total resistance, including the sample's bulk resistance and the interface contact resistance, denoted as R1. By calculating the difference between the two measurement results, the actual resistance of the sample in the test structure could be obtained. Where R is the equivalent resistance of the sample in the test structure, and combined with the effective test area A of the sample, the ASR of the sample can be calculated: .

[0072] The ASR test results of the aged preforms and composite bipolar plates prepared in Example 1 and Comparative Example 1 are as follows: Figure 4 As shown. Figure 4 In the image, "before cleaning" represents the aged preform, and "after cleaning" represents the preform. (The image is composed of...) Figure 4 It can be seen that the ASR of the aged preform prepared in Comparative Example 1 is approximately 500 mΩ·cm. 2 It exhibits a high interfacial resistance level; after cleaning with ethanol, its ASR decreases to approximately 480 mΩ·cm. 2 The variation was relatively small. This is mainly because a relatively stable resin-rich layer formed on the sample surface during the hot pressing process in Comparative Example 1. This layer was difficult to remove effectively under ethanol cleaning conditions, resulting in the surface conductive filler still being continuously covered by the insulating phase. In contrast, the ASR of the aged molded preform prepared in Example 1 was approximately 320 mΩ·cm. 2 This indicates that, even without ethanol cleaning, the introduction of erucamide had a positive impact on the sample surface structure and improved the surface conductivity to some extent; after ethanol cleaning, its ASR decreased to approximately 140 mΩ·cm. 2 The decrease of more than 50% indicates that the erucamide coating can be effectively cleaned and removed, thereby exposing more internal conductive fillers and effectively optimizing the interfacial conductivity of the composite bipolar plate.

[0073] Example 4

[0074] In this embodiment, the effect of aging time on erucamide migration was investigated.

[0075] (1) Phenolic resin (premixed with hexamethylenetetramine curing agent, with a mass ratio of curing agent to phenolic resin of 7:100), carbon-based conductive filler, and erucamide are added to a planetary ball mill, along with grinding balls of different particle sizes (1~3 mm), and the mixture is milled at 300 r·min. -1 The mixture was ball-milled at a certain speed until all components were fully mixed to obtain a composite material. The carbon-based conductive filler was composed of expanded graphite and conductive carbon black in a mass ratio of 80:20. In the composite material, the mass ratio of the sum of the masses of phenolic resin and curing agent to the mass ratio of the carbon-based conductive carbon filler was 40:60, and the content of erucamide was 2 wt.%.

[0076] (2) Place the composite material in an aluminum alloy mold, then place it on a flat vulcanizing machine, heat it to 150 ℃ and hot press it at 150 ℃ and 20 MPa for 15 min, cool it to room temperature, demold it, and obtain the molded blank.

[0077] (3) The molded preform was aged at room temperature (25 °C). During the aging process, the preform was removed at 5 min, 15 min, 30 min, 60 min, 240 min and 480 min. After cleaning the surface erucamide with ethanol, it was returned to the aging environment for further aging. This operation ensured that the erucamide detected after each aging interval came from newly migrated erucamide from the interior, rather than residual surface deposits, thus clearly assessing the effect of time on the redistribution process of erucamide.

[0078] Cross-sectional morphology and composition analysis were performed on samples after aging for different times. The results are as follows: Figure 5 As shown. By Figure 5It can be seen that when the aging time is 15 min, only a small amount of erucamide migrates from the matrix to the near-surface region inside the sample. At this time, the characteristic signal (N element signal) related to erucamide has appeared in the cross-section, but the overall enrichment degree is low. When the aging time is 60 min, the migration of erucamide molecules is further enhanced, and the internal erucamide continues to diffuse to the surface and undergoes more obvious enrichment in the near-surface region, so the erucamide content detected in the cross-section reaches a high level. This indicates that within this time range, there is still sufficient migration driving force and erucamide reserves available for migration inside the sample, so the migration process is the most active. As the aging time is further extended, the amount of erucamide that can migrate inside the sample gradually decreases, and the amount of new migration is significantly lower than in the early stage, resulting in the erucamide signal detected in the cross-section no longer continuously increasing. When the aging time is 240~480 min, the reserves of erucamide that can migrate inside the sample gradually approach depletion, the migration process tends to weaken, and the erucamide signal detectable in the cross-section decreases. This indicates that erucamide migration is not infinite but is limited by initial reserves and diffusion kinetics, with an optimal aging time range.

[0079] Example 5

[0080] In this embodiment, the effect of erucamide content on the resistance of composite bipolar plates was investigated. The operation was basically the same as in Example 1, except that: in step (1), a total of 5 experimental groups were designed, and the content of erucamide in the composite material of each experimental group was 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, and 5 wt.%.

[0081] The resistance of the prepared composite bipolar plate sample (8 cm × 6 cm × 1 mm) was measured using a resistance meter with an accuracy of 0.001 Ω. During the test, the composite bipolar plate was placed between the electrode holders of the meter, and the electrodes were held in place to ensure stable contact with the surface of the composite bipolar plate. The resistance value was then measured, and the results are as follows. Figure 6 As stated above. By Figure 6 It is known that when the content of erucic acid amide in the composite material is 2 wt.%~3 wt.%, the resistance of the composite bipolar plate is relatively low. Decreasing or increasing the content of erucic acid amide on this basis is not conducive to reducing the resistance of the composite bipolar plate. This indicates that a higher erucic acid amide content is not necessarily more beneficial; excessive addition may actually weaken its positive regulatory effect. This may be because erucic acid amide itself is a non-conductive organic molecule. In appropriate amounts, it can improve the surface structure through preferential migration. However, when the content is too high, some erucic acid amide may not exist solely as a surface migration layer, but rather blend with the phenolic resin inside the molded preform or locally accumulate, even forming a thicker non-conductive aggregate region. This increases the interfacial impedance during electron transport, leading to an increase in resistance.

[0082] Example 6

[0083] In this embodiment, the effect of hot pressing temperature on the resistance of composite bipolar plates was investigated. The operation was basically the same as in Example 1, except that: in step (2), a total of 6 experimental groups were designed, and the hot pressing temperatures used in each experimental group were 130, 140, 150, 160, 170 and 180 ℃ respectively.

[0084] The resistance of the prepared composite bipolar plate sample (8 cm × 6 cm × 1 mm) was measured using a resistance meter, and the results are as follows: Figure 7 As shown. By Figure 7 It is known that when the hot-pressing temperature is 150~160 ℃, the resistance of the composite bipolar plate is relatively low. Lowering or raising the hot-pressing temperature further hinders the reduction of the composite bipolar plate's resistance. This may be because, at lower hot-pressing temperatures, the migration driving force of erucic acid amide is insufficient, limiting its enrichment process on the surface and making it difficult to fully replace the migration and aggregation behavior of phenolic resin on the surface, resulting in a relatively thick insulating covering layer near the surface. When the hot-pressing temperature is too high, it accelerates the softening and flow of phenolic resin, while simultaneously enhancing the migration of both erucic acid amide and phenolic resin, leading to their co-accumulation near the surface, forming a relatively thick covering layer and weakening the effective exposure of the conductive filler on the surface. Simultaneously, high temperatures accelerate the cross-linking and curing reaction of phenolic resin, hindering the optimization of the conductive filler distribution and limiting the perfection of the conductive pathway. Furthermore, high temperatures may also cause localized aggregation of erucic acid amide at high temperatures, forming a non-conductive phase enrichment region and increasing the interfacial impedance in the electron transport path.

[0085] Example 7

[0086] In this embodiment, the effect of hot pressing time on the resistance of composite bipolar plates was investigated. The operation was basically the same as in Example 1, except that: in step (2), a total of 5 experimental groups were designed, and the hot pressing time used in each experimental group was 5, 10, 15, 20 and 25 min respectively.

[0087] The resistance of the prepared composite bipolar plate sample (8 cm × 6 cm × 1 mm) was measured using a resistance meter, and the results are as follows: Figure 8 As shown. By Figure 8 It can be seen that when the hot pressing time is 15~20 min, the resistance of the composite bipolar plate is relatively low. If the hot pressing time is shortened or extended on this basis, it will not be conducive to reducing the resistance of the composite bipolar plate.

[0088] Example 8

[0089] In this embodiment, the effect of introducing polyethylene glycol on the performance of composite bipolar plates was investigated.

[0090] 1. Preparation method

[0091] (1) Phenolic resin (premixed with hexamethylenetetramine curing agent, with a mass ratio of curing agent to phenolic resin of 7:100), carbon-based conductive filler, and polyethylene glycol (PEG 8000) with a molecular weight of 8000 are added to a planetary ball mill, along with grinding balls of different particle sizes (1~3 mm), and the mixture is milled at 300 r·min. -1 The mixture is ball-milled at a certain speed until all components are fully mixed to obtain a composite material. The carbon-based conductive filler is composed of expanded graphite and conductive carbon black in a mass ratio of 4:1. In the composite material, the mass ratio of the sum of the masses of phenolic resin and curing agent to the mass of carbon-based conductive carbon filler is 30:70, and the content of PEG 8000 is 3 wt.%.

[0092] (2) Place the composite material in an aluminum alloy mold, heat it to 150 ℃ and hot press it at 150 ℃ and 20 MPa for 15 min, cool it to room temperature, demold it, and obtain the molded blank.

[0093] (3) The molded preform is aged at room temperature for 240 min, and then the aged preform is cleaned with ethanol at 50 °C to remove the erucamide on the surface and expose the near-surface conductive network. Then it is dried at 60 °C to obtain the composite bipolar plate.

[0094] 2. Following the preparation method in step 1, six experimental groups were designed, with PEG 8000 content of 0 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, and 5 wt.% in each group. The bending strength and swelling rate of the prepared composite bipolar plates were tested.

[0095] Bending strength was tested using a WDW-1010 testing machine via a three-point bending test. First, the sample was processed into a standard specimen meeting the testing requirements, ensuring a flat surface, uniform thickness, and intact edges. The specimen was then placed horizontally between two support points with a span of 20 mm. A loading head was applied at a rate of 5 mm / min. -1 A continuous load is applied to the middle of the specimen at a certain rate until the specimen undergoes significant deformation or fracture. During the test, the instrument automatically records the relationship between load and displacement changes, and obtains the bending strength accordingly. Three measurements are taken, and the average value is used as the result of the sample's bending strength. The results are as follows: Figure 9As shown, without PEG, the flexural strength of the composite bipolar plate was 20.7 MPa. When the PEG content increased to 1 wt.%, 2 wt.%, and 3 wt.%, the flexural strength of the composite bipolar plate increased to approximately 23 MPa, 26 MPa, and 30 MPa, respectively, showing a significant upward trend. This indicates that within this range, the introduction of PEG can effectively improve the mechanical properties of the composite bipolar plate. When the PEG content further increased to 4 wt.% and 5 wt.%, the flexural strength of the composite bipolar plate was 31 MPa and 31.5 MPa, respectively. Although the upward trend continued, the increase was significantly reduced, indicating that the promoting effect of PEG on the mechanical properties of the composite bipolar plate had reached saturation.

[0096] To evaluate the water absorption capacity and dimensional stability of the composite bipolar plate in the operating environment of a flow battery, the swelling rate was determined by a gravimetric method. First, the sample was dried in a drying oven until its mass was constant, cooled to room temperature, and its initial mass was recorded as m0. Next, the dried sample was completely immersed in deionized water for 7 days. After immersion, the sample was removed, and the surface moisture was quickly and gently absorbed with filter paper or a soft cloth. Its mass was immediately recorded as m1. The swelling rate was calculated using (m1-m0) / m0 × 100%, and the results are as follows: Figure 10 As shown, the swelling rate of the composite bipolar plate continuously increases with the increase of PEG content. Considering the combined effects of PEG on the mechanical and swelling properties of the composite bipolar plate, the PEG content in the composite material was determined to be 2 wt.%~3 wt.%.

[0097] 3. Following the preparation method in step 1, three experimental groups were designed, using PEG6000, PEG8000, and PEG10000 in each group, respectively. The flexural strength and swelling rate of the prepared composite bipolar plates were tested, and the results are as follows: Figures 11-12 As shown, from a comprehensive performance perspective, PEG 8000 exhibits a good balance between mechanical reinforcement and swelling control.

[0098] Example 9

[0099] In this embodiment, erucamide is used as a substitute migration agent and PEG 8000 is introduced to provide a method for preparing a flow battery composite bipolar plate with molecular migration regulation. The steps are as follows:

[0100] (1) Phenolic resin (which is premixed with hexamethylenetetramine curing agent, with a mass ratio of curing agent to phenolic resin of 7:100), carbon-based conductive filler, erucamide and PEG 8000 are added to a planetary ball mill, along with grinding balls of different particle sizes (1~3 mm), and the mixture is milled at 300 r·min. -1The mixture is ball-milled at a certain speed until all components are fully mixed to obtain a composite material. The carbon-based conductive filler is composed of expanded graphite and conductive carbon black in a mass ratio of 80:20. In the composite material, the mass ratio of the sum of the masses of phenolic resin and curing agent to the mass ratio of the carbon-based conductive carbon filler is 40:60, the content of erucamide is 2 wt.%, and the content of PEG 8000 is 3 wt.%.

[0101] (2) Place the composite material in an aluminum alloy mold, then place it on a flat vulcanizing machine, heat it to 150 ℃ and hot press it at 150 ℃ and 20 MPa for 15 min, cool it to room temperature, demold it, and obtain the molded blank.

[0102] (3) The molded preform is aged at room temperature (25 °C) for 240 min, and then the aged preform is cleaned with ethanol at 50 °C to remove the erucamide on the surface and expose the near-surface conductive network. Then it is dried at 60 °C to obtain a composite bipolar plate with a size of 8 cm × 6 cm × 1 mm.

[0103] Example 10

[0104] In this embodiment, the mechanical properties, surface wettability, electrical conductivity and corrosion resistance of the composite bipolar plates prepared in Example 9 and Comparative Example 1 were tested.

[0105] 1. Mechanical properties

[0106] The bending strength of the composite bipolar plates prepared in Example 9 and Comparative Example 1 was tested, and the results are as follows: Figure 13 As shown, the composite bipolar plate prepared in Comparative Example 1 has a flexural strength of 20.7 MPa, while the composite bipolar plate prepared in Example 10 has a full strength of 32.3 MPa, representing an increase of 60%. Furthermore, compared to the composite bipolar plate prepared in Example 8 under the same PEG addition conditions (flexural strength approximately 30 MPa), the composite bipolar plate prepared in Example 9 exhibits improved flexural strength. This demonstrates that adding erucamide to the PEG substrate does not lead to a decrease in mechanical properties.

[0107] 2. Surface wettability

[0108] The contact angle (CA) was used as an indicator to evaluate surface wettability. The surface wettability of the composite bipolar plates prepared in Example 9 and Comparative Example 1 was tested. Specifically, under conditions of 25 °C and 40% relative humidity, 5 μL of deionized water droplets were added to the test platform, and the CA values ​​were obtained using an optical contact angle meter. All CA data were the average of at least three independent measurements. The results are shown below. Figure 14As shown, the CA values ​​of the composite bipolar plates prepared in Comparative Example 1 and Example 9 are 112° and 78°, respectively, indicating that the surface of the composite bipolar plate in Example 9 changes from a relatively hydrophobic state to a relatively hydrophilic state, and its surface wettability is effectively improved. This may be due to: First, the surface migration of erucamide changes the enrichment behavior of surface components during hot pressing, weakening the continuous coverage of the original resin-rich layer on the surface, allowing conductive fillers and other polar components to be more fully exposed in the surface area, thus changing the surface chemical properties; Second, the introduction of PEG, while improving the internal structural stability, may also indirectly affect the surface properties by adjusting the distribution of polar groups in the resin matrix, thereby enhancing the affinity of the surface layer for polar liquid media. Better surface wettability is beneficial for the electrolyte to form a more uniform and stable liquid film at the interface between the composite bipolar plate and the electrode, promoting the uniformity of ion transport and interfacial reactions, and reducing the mass transfer limitation caused by insufficient wetting in local areas. Especially during long-term cyclic operation, good surface wettability helps maintain the stability of electrolyte distribution in the flow channel and reduces the adverse effects of local drying or uneven flow on the performance of flow batteries.

[0109] 3. Conductivity test

[0110] The resistivity of the composite bipolar plates prepared in Example 9 and Comparative Example 1 was measured using a four-probe resistance meter, and the conductivity was calculated accordingly. The results are as follows: Figure 15 As shown. The composite bipolar plate prepared in Comparative Example 1 has a conductivity of 50 S·cm. -1 The composite bipolar plate prepared in Example 9 has an electrical conductivity of 143 S·cm. -1 The conductivity was significantly improved. This indicates that the synergistic effect of erucamide surface migration regulation and PEG in-situ fixation effectively improved the construction state of the conductive network inside the composite bipolar plate and the interfacial electron transport capability, significantly enhancing the overall conductivity. This invention's improvement in the conductivity of the composite bipolar plate is of great significance for maintaining efficient electron transport in flow batteries under actual operating conditions, and is beneficial for reducing energy loss during flow battery operation, improving battery output performance and operational stability.

[0111] 4. Corrosion resistance

[0112] The corrosion resistance of the composite bipolar plates prepared in Example 9 and Comparative Example 1 was tested using an electrochemical workstation. A three-electrode system was employed, with the composite bipolar plate as the working electrode, a platinum sheet as the counter electrode, and an Ag / AgCl electrode as the reference electrode, using sodium chloride solution as the electrolyte. The composite bipolar plates were cut into samples of the same size, cleaned, and dried, exposing only a fixed area as the effective working region. After immersing the samples in the electrolyte, they were allowed to stand until the open-circuit potential stabilized before potentiodynamic polarization testing. The corrosion potential and corrosion current density were obtained using the Tafel extrapolation method. At least three parallel experiments were performed for each sample group, and the average value was taken. The results are shown below. Figure 16 As shown.

[0113] Depend on Figure 16 It can be seen that, compared with Comparative Example 1, the corrosion potential of the composite bipolar plate prepared in Example 9 shows a certain positive shift trend, and the corrosion current density decreases, indicating that its self-corrosion tendency in the corrosive medium is weakened, the corrosion reaction kinetics are suppressed, and it exhibits better electrochemical corrosion stability. This may be due to the dual optimization of the surface structure and internal interface state of the composite bipolar plate. The surface migration regulation of erucic acid amide weakens the uneven coverage of the resin-rich surface layer, making the surface composition more uniform, reducing local defects and easily corroded sites. The in-situ fixation of PEG enhances the internal structural stability of the resin matrix and the bonding strength of the conductive filler / resin matrix interface, reducing the possibility of corrosive medium penetrating and spreading along the interface, thereby improving the overall resistance to electrochemical corrosion.

[0114] Example 11

[0115] In this embodiment, a single cell was assembled using the composite bipolar plates prepared in Example 9 and Comparative Example 1, and the assembled single cell was subjected to cyclic charge-discharge tests to evaluate the coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) at different current densities.

[0116] A vanadium redox flow battery (VRFB) test platform was built to test the electrochemical performance of the composite bipolar plate. For example... Figure 17 As shown, the experimental platform mainly consists of a single vanadium redox flow battery (VRFB), an electrolyte storage system, a circulation pipeline system, and a charge / discharge tester. Its overall structure can simulate the electrolyte circulation, ion transport, and current output processes of a VRFB during actual operation. To facilitate electrode clamping for the charge / discharge tester and battery assembly, the composite bipolar plate has been fabricated... Figure 17 The structure shown in Figure (c).

[0117] A single cell is assembled from components such as end plates, composite bipolar plates, electrodes, ion exchange membranes, and sealing gaskets. The composite bipolar plates are installed within the battery structure, forming a complete electrochemical reaction unit together with the carbon felt electrodes and ion exchange membranes. The electrolyte storage system consists of positive and negative electrode storage tanks, used to store the positive and negative electrode electrolytes, respectively. The storage tanks are connected to the single cell via corrosion-resistant piping, forming a complete electrolyte circulation loop. The circulation piping system mainly includes inlet pipes, connectors, valves, and a pump, and its function is to achieve continuous transport of the positive and negative electrode electrolytes between the storage tanks and the single cell. The piping material is resistant to corrosion from vanadium redox flow battery electrolytes. A charge-discharge tester is used for constant current charge-discharge testing and performance data acquisition of the single cell. The electrodes of the charge-discharge tester are connected to the composite bipolar plate electrodes of the single cell, and can record parameters such as voltage, current, capacity, and efficiency in real time during the charge-discharge process.

[0118] At a constant electrolyte flow rate of 70 mL·min -1 Single cells were operated under constant room temperature (25 °C) and fixed VRFB electrolyte (purchased from Dalian Borong High-Tech Materials Co., Ltd.) conditions, and programmed constant current charge-discharge tests were performed using a charge-discharge tester. The test was conducted at 100 mA·cm⁻¹. -2 As the initial current density, then at 50 mA·cm -2 The current density is gradually increased by gradient, and three charge-discharge cycles are performed continuously under each current density condition to reduce random errors and improve the representativeness and reliability of the test results.

[0119] Figure 18 Figure (a) shows the coulombic efficiency of the composite bipolar plates prepared in Example 9 and Comparative Example 1 under different currents. Figure 18 Figure (b) shows the energy efficiency of the composite bipolar plates prepared in Example 9 and Comparative Example 1 under different currents. Figure 18 Figure (c) shows the voltage efficiency of the composite bipolar plates prepared in Example 9 and Comparative Example 1 at different currents. In terms of coulombic efficiency, both groups of samples maintained a high level throughout the entire test current density range, with coulombic efficiencies between 95% and 97%, showing minimal fluctuation with changes in current density. This indicates that the composite bipolar plates prepared by the method of this invention did not significantly affect the intrinsic Faraday efficiency of the electrolyte system; their performance improvement mainly stemmed not from changes in charge utilization, but rather from improvements in the internal transport process and polarization behavior of the battery. In terms of voltage efficiency (VE), at 100 mA·cm⁻¹... -2 Under the conditions, the single cells prepared based on the composite bipolar plates prepared in Example 9 and Comparative Example 1 have VE values ​​of 87% and 85%, respectively, which are quite close; when the current density is increased to 300 mA·cm -2At that time, the single cells prepared based on the composite bipolar plates prepared in Example 9 and Comparative Example 1 had voltage efficiency (VE) of 67% and 60%, respectively, with the difference between the two widening to 7%. This indicates that the composite bipolar plate prepared in Example 9 can effectively reduce the internal voltage loss of the battery over a wider current density range, especially showing a more significant advantage at high current densities. The trend of energy efficiency (EE) is basically consistent with that of voltage efficiency, but it better reflects the overall impact of the composite bipolar plate on the performance of the single cell at 100 mA·cm⁻¹. -2 Under the conditions, the single cells prepared based on the composite bipolar plates prepared in Example 9 and Comparative Example 1 had EE values ​​of 84% and 82%, respectively, which were quite close; when the current density was increased to 300 mA·cm -2 At that time, the EE of the single cells prepared based on the composite bipolar plates prepared in Example 9 and Comparative Example 1 were 65% and 58%, respectively, with a difference of 7%. Since EE is essentially the product of CE and VE, and the difference in CE is small, the improvement in EE of the single cells prepared based on the composite bipolar plates prepared in Example 9 and Comparative Example 1 mainly comes from the improvement in VE.

[0120] Example 12

[0121] In this embodiment, oleamide is used as a substitute migration agent and PEG 8000 is introduced to provide a method for preparing a flow battery composite bipolar plate with molecular migration regulation. The steps are as follows:

[0122] (1) Phenolic resin (premixed with hexamethylenetetramine curing agent, with a mass ratio of curing agent to phenolic resin of 7:100), carbon-based conductive filler, oleamide and PEG 8000 are added to a planetary ball mill, along with grinding balls of different particle sizes (1~3 mm), and the mixture is milled at 300 r·min. -1 The mixture was ball-milled at a certain speed until all components were fully mixed to obtain a composite material. The carbon-based conductive filler was composed of flake graphite (20 mesh size) and conductive carbon black in a mass ratio of 90:10. In the composite material, the mass ratio of the sum of the masses of phenolic resin and curing agent to the mass ratio of the carbon-based conductive carbon filler was 40:60, the content of oleamide was 2 wt.%, and the content of PEG8000 was 3 wt.%.

[0123] (2) Place the composite material in an aluminum alloy mold, then place it on a flat vulcanizing machine, heat it to 150 ℃ and hot press it at 150 ℃ and 20 MPa for 15 min, cool it to room temperature, demold it, and obtain the molded blank.

[0124] (3) The molded preform is aged at room temperature (25 °C) for 240 min, and then the aged preform is cleaned with ethanol at 50 °C to remove the oleamide on the surface and expose the near-surface conductive network. Then it is dried at 60 °C to obtain a composite bipolar plate with a size of 8 cm × 6 cm × 1 mm.

[0125] Example 13

[0126] In this embodiment, stearamide is used as a substitute migration agent and PEG 8000 is introduced to provide a method for preparing a flow battery composite bipolar plate with molecular migration regulation. The steps are as follows:

[0127] (1) Phenolic resin (premixed with hexamethylenetetramine curing agent, with a mass ratio of curing agent to phenolic resin of 7:100), carbon-based conductive filler, stearamide and PEG 8000 are added to a planetary ball mill, along with grinding balls of different particle sizes (1~3 mm), and the mixture is milled at 300 r·min. -1 The mixture was ball-milled at a certain speed until all components were fully mixed to obtain a composite material. The carbon-based conductive filler was composed of expanded graphite, conductive carbon black, and chopped carbon fibers (monofilament diameter 7 μm, cut length 3 mm) in a mass ratio of 91:5.5:3.5. In the composite material, the mass ratio of the sum of the masses of phenolic resin and curing agent to the mass ratio of carbon-based conductive carbon filler was 20:80, the content of stearamide was 2 wt.%, and the content of PEG 8000 was 3 wt.%.

[0128] (2) Place the composite material in an aluminum alloy mold, then place it on a flat vulcanizing machine, heat it to 150 ℃ and hot press it at 150 ℃ and 20 MPa for 15 min, cool it to room temperature, demold it, and obtain the molded blank.

[0129] (3) The molded preform is aged at room temperature (25 °C) for 240 min, and then the aged preform is cleaned with ethanol at 55 °C to remove the stearamide on the surface and expose the near-surface conductive network. Then it is dried at 60 °C to obtain a composite bipolar plate with a size of 8 cm × 6 cm × 1 mm.

[0130] Example 14

[0131] In this embodiment, erucamide is used as a substitute migration agent and PEG 8000 is introduced to provide a method for preparing a flow battery composite bipolar plate with molecular migration regulation. The steps are as follows:

[0132] (1) Phenolic resin (which is premixed with hexamethylenetetramine curing agent, with a mass ratio of curing agent to phenolic resin of 7:100), carbon-based conductive filler, erucamide and PEG 8000 are added to a planetary ball mill, along with grinding balls of different particle sizes (1~3 mm), and the mixture is milled at 300 r·min.-1 The mixture was ball-milled at a certain speed until all components were fully mixed to obtain a composite material. The carbon-based conductive filler was composed of flake graphite (20 mesh size) and chopped carbon fibers (7 μm monofilament diameter, 3 mm cut length) in a mass ratio of 95:5. In the composite material, the mass ratio of the sum of the masses of phenolic resin and curing agent to the mass of carbon-based conductive carbon filler was 10:90, the content of erucamide was 2 wt.%, and the content of PEG 8000 was 3 wt.%.

[0133] (2) Place the composite material in an aluminum alloy mold, then place it on a flat vulcanizing machine, heat it to 150 ℃ and hot press it at 150 ℃ and 20 MPa for 15 min, cool it to room temperature, demold it, and obtain the molded blank.

[0134] (3) The molded preform is aged at room temperature (25 °C) for 240 min, and then the aged preform is cleaned with ethanol at 50 °C to remove the erucamide on the surface and expose the near-surface conductive network. Then it is dried at 60 °C to obtain a composite bipolar plate with a size of 8 cm × 6 cm × 1 mm.

Claims

1. A method for preparing a composite bipolar plate for a flow battery with controlled molecular migration, characterized in that, Includes the following steps: (1) Phenolic resin, curing agent, carbon-based conductive filler and alternative migration agent are thoroughly mixed to obtain a composite material; the alternative migration agent is a long-chain alkyl primary amide; in the composite material, the content of the alternative migration agent is 2 wt.%~3 wt.%, and the mass ratio of the sum of the mass of phenolic resin and curing agent to the mass ratio of the mass of carbon-based conductive filler is (40~10):(60~90). (2) Place the composite material in the mold, heat it to 150~160 ℃ and hot press it at 15~30 MPa at the same temperature, cool it to room temperature, demold it, and obtain the molded blank. (3) The molded blank is aged at 20~40 ℃ to allow the substitute migration agent to fully migrate to the surface of the molded blank. Then, the substitute migration agent on the surface of the molded blank is washed away and dried to obtain the flow battery composite bipolar plate.

2. The method for preparing a flow battery composite bipolar plate according to claim 1, characterized in that, The long-chain alkyl primary amides include at least one of erucamide, oleamide, and stearamide.

3. The method for preparing a flow battery composite bipolar plate according to claim 1, characterized in that, In step (1), polyethylene glycol was added during the preparation of the composite material. The content of polyethylene glycol in the composite material was 1 wt.% to 3 wt.%.

4. The method for preparing a flow battery composite bipolar plate according to claim 3, characterized in that, The number average molecular weight of the polyethylene glycol is 7000-8000.

5. The method for preparing a flow battery composite bipolar plate according to claim 1, characterized in that, The carbon-based conductive filler consists of a main filler and an auxiliary filler. The main filler accounts for 80 wt.% to 95 wt.% of the carbon-based conductive filler, and the auxiliary filler accounts for 5 wt.% to 20 wt.% of the carbon-based conductive filler. The main filler is at least one of two-dimensional or three-dimensional carbon-based conductive fillers, and the auxiliary filler is at least one of one-dimensional or zero-dimensional carbon-based conductive fillers.

6. The method for preparing a flow battery composite bipolar plate according to claim 5, characterized in that, The main filler includes at least one of expanded graphite, flake graphite, and spherical graphite, and the auxiliary filler includes at least one of conductive carbon black, carbon nanotubes, and chopped carbon fibers.

7. The method for preparing a flow battery composite bipolar plate according to any one of claims 1 to 6, characterized in that, In step (3), the aging time is controlled to be 60~360 min.

8. The method for preparing a flow battery composite bipolar plate according to any one of claims 1 to 6, characterized in that, Step (2) Control the hot pressing time to 15~25 min during hot pressing.

9. The method for preparing a flow battery composite bipolar plate according to any one of claims 1 to 6, characterized in that, The mass ratio of the curing agent to the phenolic resin is (7~9):

100.

10. A flow battery composite bipolar plate prepared by the method of any one of claims 1 to 9.

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