Composite bipolar plate having a three-dimensional conductive network and method of making same

Abstract

The application relates to the technical field of liquid flow batteries, and discloses a composite bipolar plate with a three-dimensional conductive network and a preparation method thereof, wherein polymethyl methacrylate is used as a matrix, modified graphite felt and modified carbon material are used as conductive fillers to form a three-dimensional conductive network, and the conductive performance and mechanical performance of the composite bipolar plate are improved; the surface of the modified carbon material is adsorbed with modified polymers, the tail end of the polymer is grafted with a long chain of polymethyl methacrylate, meanwhile, a shell layer of polymethyl methacrylate is prepared on the surface of the modified graphite felt fiber, and the shell layer and the polymethyl methacrylate matrix have good compatibility; the integrity of the conductive path of the graphite felt fiber is reserved, defects at the interface between the matrix and the graphite felt fiber are reduced, the modified carbon material is better dispersed and overlapped on the surface of the graphite felt fiber, a more complete conductive network is formed, the conductive performance of the bipolar plate is improved, and the voltage efficiency and energy efficiency of the liquid flow battery are enhanced.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, specifically to a composite bipolar plate with a three-dimensional conductive network and its preparation method. Background Technology

[0002] When a flow battery is operating, the electrolyte flows through the stack via a pump and piping, where the transfer and storage of electrons between the positive and negative electrode active materials completes, realizing the interconversion of chemical energy and electrical energy. Therefore, the stack plays a crucial role in the output power. The bipolar plate, as one of the key materials in the stack, serves to isolate the positive and negative electrode electrolytes and transport electrons. Its own impedance is one of the main factors affecting the ohmic polarization of the flow battery. When the impedance is too high, on the one hand, it occupies more of the circuit voltage division, increasing the charging overpotential and reducing the charging capacity; on the other hand, the impedance causes electrical energy to be converted into internal heat dissipation, resulting in insufficient energy efficiency. Therefore, an ideal bipolar plate needs to have good conductivity and corrosion resistance, while also possessing sufficient strength and toughness to prevent damage during stack assembly.

[0003] Existing commercial bipolar plates are mainly divided into three categories: metal bipolar plates, graphite bipolar plates, and carbon-plastic composite bipolar plates. Metal bipolar plates have superior conductivity and mechanical properties, but they are prone to electrochemical corrosion when in contact with some strong acid or strong alkali electrolytes. Surface treatment is one of the effective measures to improve corrosion resistance; however, the treatment process affects surface conductivity and increases costs. Compared with metal bipolar plates, graphite bipolar plates not only have good conductivity but also resist electrochemical corrosion, making them the bipolar plates used in most kilowatt-class fuel cell stacks. However, their strength is relatively low, the processing technology is complex, and they are prone to brittleness during transportation and stacking, which limits the further development of graphite bipolar plates. Carbon-plastic composite bipolar plates combine the high conductivity and corrosion resistance of graphite with the high mechanical properties and ease of processing of resin. However, compared with the former two, their conductivity is still at a relatively low level. Further improving their conductivity usually requires increasing the content of conductive carbon material, which leads to a low resin content and insufficient adhesion and strength. Therefore, how to form specific conductive pathways with low carbon content, thereby improving conductivity while reducing the impact on mechanical properties, has become an urgent problem and challenge in the field of bipolar plates. Summary of the Invention

[0004] To address the shortcomings of the prior art, this invention provides a composite bipolar plate with a three-dimensional conductive network and its preparation method. The method prepares a bipolar plate with a composite conductive network of modified carbon material / graphite felt / polymethyl methacrylate, achieving both high conductivity and high mechanical strength at a low carbon material content.

[0005] The present invention adopts the following technical solution:

[0006] In a first aspect, a method for preparing a composite bipolar plate with a three-dimensional conductive network is disclosed, comprising the following steps:

[0007] Step S1: Add the catalyst, bromine-containing monomer, and vinyl monomer to anhydrous dichloromethane, introduce ethylene gas, and carry out reaction a. After the reaction is completed, perform post-treatment to obtain a macromolecular initiator. Add the macromolecular initiator, methyl methacrylate monomer, cuprous bromide, pentamethyldiethylenetriamine, graphite, and carbon nanotubes to anhydrous toluene under nitrogen protection to carry out reaction b. After the reaction is completed, pour the reaction product into a stirred tank and disperse it by ball milling to obtain a mixed slurry. Then, dry it by rotary evaporation to obtain the modified carbon material.

[0008] The modified carbon material has a modified polymer on its surface, which prevents the carbon material from agglomerating while increasing the compatibility between the carbon material and the polymethyl methacrylate matrix, so that the carbon material can be uniformly dispersed in the matrix.

[0009] Step S2: Immerse the graphite felt in N-methylpyrrolidone, add the initiator and methyl methacrylate monomer, mix well, and carry out the reaction. After the reaction is completed, rinse the graphite felt with N-methylpyrrolidone and then freeze-dry it to obtain the modified graphite felt.

[0010] Its surface has a polymethyl methacrylate shell, which enhances the compatibility between the graphite felt and the bipolar plate substrate. In addition, freeze drying can preserve the three-dimensional conductive network of the graphite felt more completely.

[0011] Step S3: Add methyl methacrylate monomer and initiator to a beaker for reaction, then add modified carbon material and stir to obtain a mixed prepolymer liquid; pour the mixed prepolymer liquid onto the surface of the modified graphite felt and hot-press for the first time to obtain a conductive layer; then cover the upper and lower surfaces of the conductive layer with carbon paper and hot-press for the second time to obtain a composite bipolar plate with a three-dimensional conductive network.

[0012] The mixed prepolymer has a low viscosity, which allows it to be injected more evenly into the gaps in the graphite felt, providing a bipolar plate skeleton and enhancing the mechanical properties of the bipolar plate.

[0013] In one implementation, in step S1:

[0014] The mass ratio of the catalyst, bromine-containing monomer, vinyl monomer, and anhydrous dichloromethane is 0.25:(1~2):(1~2):(20~40);

[0015] The catalyst is one of palladium diimide and nickel diimide;

[0016] The bromine-containing monomer is one of 2-(2-bromoisobutyryloxy)ethyl methacrylate and 2-(2-bromoisobutyryloxy)ethyl acrylate;

[0017] The vinyl monomer is one of 2-vinylnaphthalene, 1-naphthyl 2-acrylate, methyl 9-anthracene acrylate, and methyl 9-anthracene methacrylate.

[0018] The monomer contains large π-bond units, which can form π-π non-covalent forces with graphite and carbon nanotubes, thus modifying carbon materials in situ.

[0019] In one implementation, in step S1:

[0020] The mass ratio of the macromolecular initiator, methyl methacrylate monomer, cuprous bromide, pentamethyldiethylenetriamine, anhydrous toluene, graphite and carbon nanotubes is 30:(200~700):1:(2~4):(200~300):(1~4):(1~4);

[0021] The temperature of reaction b is 80℃, and the time is 4~12h.

[0022] In one implementation, in step S1:

[0023] The ball milling dispersion is carried out using a high-speed disperser. Zirconia beads are placed in the stirring tank, the dispersion disc rotates at 2500~3000 rpm, and the time is 12~24h.

[0024] The rotary evaporation drying process is carried out at a rotation speed of 15-30 rpm, a rotary evaporation temperature of 70°C, and a vacuum degree of 0.1 MPa.

[0025] In one implementation, in step S2:

[0026] The mass ratio of the graphite felt, N-methylpyrrolidone, initiator and methyl methacrylate monomer is 15:(80~120):(0.5~1):10;

[0027] The reaction was carried out at a temperature of 80°C for 1.5 hours.

[0028] The polymethyl methacrylate shell structure formed on the surface of graphite felt fibers has good compatibility with the polymethyl methacrylate matrix. This not only preserves the integrity of the conductive pathways of the graphite felt fibers, but also ensures that the modified carbon materials can be well dispersed and overlapped on the fiber surface, forming a more complete conductive network and promoting the improvement of the conductivity of the bipolar plate.

[0029] The initiator is one of azobisisobutyronitrile and benzoyl peroxide;

[0030] The polymerization of methyl methacrylate monomers on the surface of graphite felt fibers is initiated to form a polymethyl methacrylate coating layer.

[0031] In one implementation, in step S2:

[0032] The freeze-drying temperature is -60℃, and the drying time is 12~24h.

[0033] In one implementation, in step S3:

[0034] The mass ratio of the methyl methacrylate monomer, initiator, and modified carbon material is 30:0.75:(0.15~3);

[0035] The reaction was carried out at a temperature of 75°C for 30-50 minutes.

[0036] The stirring time is 10 minutes;

[0037] The temperature of the first hot pressing is 120~150℃, the pressure is 3~6MPa, and the time is 20~60min;

[0038] The second hot pressing was performed at a temperature of 160°C, a pressure of 5 MPa, and a time of 20 minutes.

[0039] By controlling the viscosity change characteristics of the prepolymer during the synthesis of polymethyl methacrylate, and combining it with modified carbon materials at a low viscosity before the prepolymer synthesis enters the auto-acceleration stage, the dispersibility of the modified carbon materials is improved, while they can be well injected into the gaps of the graphite felt to form a complete mechanical skeleton and improve the mechanical properties of the bipolar plate.

[0040] Using polymethyl methacrylate thermoplastic material as the matrix, the prepared bipolar plate can be repaired by hot pressing after breakage, while maintaining good conductivity and mechanical properties.

[0041] In one implementation, in step S3:

[0042] The modified graphite felt has a thickness of 2-6 mm, and the carbon paper has a thickness of 0.05-0.2 mm.

[0043] Secondly, a composite bipolar plate with a three-dimensional conductive network is disclosed, which is prepared by the above-mentioned method for preparing a composite bipolar plate with a three-dimensional conductive network.

[0044] Preferably, the thickness of the composite bipolar plate is 0.6~1mm.

[0045] In summary, the present invention has the following beneficial effects:

[0046] 1. The modified carbon material obtained in this invention has a modified polymer adsorbed on its surface, and the polymer ends are grafted with long polymethyl methacrylate chains. At the same time, a polymethyl methacrylate shell is prepared on the surface of the modified graphite felt fiber. Both have good compatibility with the polymethyl methacrylate matrix. This not only preserves the integrity of the conductive pathway of the graphite felt fiber, but also reduces defects at the interface between the matrix and the graphite felt fiber. This promotes better dispersion and bonding of the modified carbon material on the surface of the graphite felt fiber, forming a more complete conductive network and improving the conductivity of the bipolar plate.

[0047] 2. This invention can control the viscosity change characteristics of the prepolymer during the synthesis of polymethyl methacrylate. Before the prepolymer synthesis enters the automatic acceleration stage, when the viscosity is low, it can be combined with modified carbon materials. This improves the dispersibility of the modified carbon materials and allows them to be well injected into the gaps of the graphite felt to form a complete mechanical skeleton, thereby improving the mechanical properties of the bipolar plate.

[0048] 3. The present invention uses polymethyl methacrylate thermoplastic material as the matrix. The bipolar plate prepared by it can be repaired by hot pressing after breakage, while maintaining good conductivity and mechanical properties. Attached Figure Description

[0049] Figure 1 This is a physical image of the composite bipolar plate prepared in Example 1 of this invention;

[0050] Figure 2 This is a comparison diagram of the resistivity of bipolar plates obtained from embodiments and comparative examples of the present invention;

[0051] Figure 3 These are SEM cross-sectional images of the composite bipolar plates prepared in Example 1 and Comparative Example 2 of this invention;

[0052] Figure 4 It is the tensile strength of the composite bipolar plate prepared by this invention. Detailed Implementation

[0053] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0054] Example 1: The following technical solution is adopted.

[0055] Step S1: Add 0.25g palladium diimide, 1g ethyl 2-(2-bromoisobutyryloxy)methacrylate, and 1.5g... 1-Naphthyl 2-acrylate was added to 30g of anhydrous dichloromethane, ethylene gas was introduced, the pressure was adjusted to 0.1MPa, and the reaction was carried out at 25℃ for 24h. After the reaction was completed, the reactants were dissolved and precipitated, and the precipitate was dried to obtain a macromolecular initiator. 1.5g of macromolecular initiator, 600g of methyl methacrylate monomer, 0.05g of cuprous bromide, 0.15g of pentamethyldiethylenetriamine, 0.05g of graphite, and 0.05g of carbon nanotubes were added to 200g of anhydrous toluene under nitrogen protection and reacted at 80℃ for 8h. After the reaction was completed, the reaction product was poured into a stirred tank and ball-milled for 12h using a high-speed disperser at a speed of 3000rpm to obtain a mixed slurry. Subsequently, it was dried by rotary evaporation at 70℃ under a vacuum of 0.1MPa and a speed of 20rpm to obtain a modified carbon material.

[0056] Step S2: Immerse 15g of graphite felt with a thickness of 4mm in 80g of N-methylpyrrolidone, add 0.75g of benzoyl peroxide and 10g of methyl methacrylate monomer, mix well, react at 80℃ for 1.5h, after which the graphite felt is washed with N-methylpyrrolidone, and then freeze-dried at -60℃ for 16h to obtain modified graphite felt;

[0057] Step S3: Add 30g of methyl methacrylate monomer and 0.75g of benzoyl peroxide to a beaker and react at 75℃ for 30min. Then add 0.15g of modified carbon material and stir for 10min to obtain a mixed prepolymer solution. Pour the mixed prepolymer solution onto the surface of the modified graphite felt and hot-press at 150℃ and 5MPa for 20min to obtain a conductive layer. Then cover the upper and lower surfaces of the conductive layer with 0.1mm thick carbon paper and hot-press at 160℃ and 5MPa for 20min to obtain a composite bipolar plate with a three-dimensional conductive network.

[0058] Example 2: The following technical solution is adopted.

[0059] Step S1: Add 0.25g palladium diimide, 2g 2-(2-bromoisobutoxy)ethyl acrylate, and 2g methyl 9-anthracene acrylate to 20g anhydrous dichloromethane, introduce ethylene gas, adjust the pressure to 0.1MPa, and react at 25℃ for 24h. After the reaction, dissolve and precipitate the reactants, and dry the precipitate to obtain a macromolecular initiator. Add 1.5g macromolecular initiator, 200g methyl methacrylate monomer, 0.05g cuprous bromide, 0.1g pentamethyldiethylenetriamine, 0.1g graphite, and 0.1g carbon nanotubes to 300g anhydrous toluene under nitrogen protection, and react at 80℃ for 12h. After the reaction, pour the reaction product into a stirred tank and ball mill it for 24h using a high-speed disperser at a speed of 2500rpm to obtain a mixed slurry. Then, dry it by rotary evaporation at 70℃ under a vacuum of 0.1MPa and a speed of 15rpm to obtain the modified carbon material.

[0060] Step S2: Immerse 15g of graphite felt with a thickness of 4mm in 100g of N-methylpyrrolidone, add 0.5g of benzoyl peroxide and 10g of methyl methacrylate monomer, mix well, react at 80℃ for 1.5h, after which the graphite felt is washed with N-methylpyrrolidone, and then freeze-dried at -60℃ for 18h to obtain modified graphite felt;

[0061] Step S3: Add 30g of methyl methacrylate monomer and 0.75g of benzoyl peroxide to a beaker and react at 75℃ for 40min. Then add 0.3g of modified carbon material and stir for 10min to obtain a mixed prepolymer solution. Pour the mixed prepolymer solution onto the surface of the modified graphite felt and hot-press at 120℃ and 6MPa for 40min to obtain a conductive layer. Then cover the upper and lower surfaces of the conductive layer with 0.1mm thick carbon paper and hot-press at 160℃ and 5MPa for 20min to obtain a composite bipolar plate with a three-dimensional conductive network.

[0062] Example 3: The following technical solution is adopted.

[0063] Step S1: Add 0.25g nickel diimide, 1.5g ethyl 2-(2-bromoisobutyryloxy) methacrylate, and 2g anthracene methyl acrylate to 40g anhydrous dichloromethane. Purge with ethylene gas, adjust the pressure to 0.5MPa, and react at 25℃ for 24h. After the reaction, dissolve and precipitate the reactants. Dry the precipitate to obtain a macromolecular initiator. Add 1.5g macromolecular initiator, 700g methyl methacrylate monomer, and 0.05g... Cuprous bromide, 0.2 g pentamethyldiethylenetriamine, 0.2 g graphite, and 0.05 g carbon nanotubes were added to 250 g anhydrous toluene under nitrogen protection and reacted at 80 °C for 12 h. After the reaction was completed, the product was poured into a stirred tank and ball-milled for 16 h using a high-speed disperser at a speed of 2800 rpm to obtain a mixed slurry. The slurry was then dried by rotary evaporation at 70 °C under a vacuum of 0.1 MPa and a speed of 30 rpm to obtain the modified carbon material.

[0064] Step S2: Immerse 15g of graphite felt with a thickness of 6mm in 120g of N-methylpyrrolidone, add 1g of benzoyl peroxide and 10g of methyl methacrylate monomer, mix well, react at 80℃ for 1.5h, after which the graphite felt is washed with N-methylpyrrolidone, and then freeze-dried at -60℃ for 24h to obtain modified graphite felt;

[0065] Step S3: Add 30g of methyl methacrylate monomer and 0.75g of benzoyl peroxide to a beaker and react at 75℃ for 50min. Then add 0.6g of modified carbon material and stir for 10min to obtain a mixed prepolymer solution. Pour the mixed prepolymer solution onto the surface of the modified graphite felt and hot-press at 140℃ and 3MPa for 50min to obtain a conductive layer. Then cover the upper and lower surfaces of the conductive layer with 0.05mm thick carbon paper and hot-press at 160℃ and 5MPa for 20min to obtain a composite bipolar plate with a three-dimensional conductive network.

[0066] Example 4: The following technical solution is adopted.

[0067] Step S1: Add 0.25g nickel diimide, 1.5g 2-(2-bromoisobutyryloxy)ethyl methacrylate, and 1g... 2-Vinylnaphthalene was added to 40g of anhydrous dichloromethane, ethylene gas was introduced, the pressure was adjusted to 0.5MPa, and the reaction was carried out at 25℃ for 24h. After the reaction was completed, the reactants were dissolved and precipitated, and the precipitate was dried to obtain a macromolecular initiator. 1.5g of macromolecular initiator, 500g of methyl methacrylate monomer, 0.05g of cuprous bromide, 0.15g of pentamethyldiethylenetriamine, 0.05g of graphite, and 0.2g of carbon nanotubes were added to 200g of anhydrous toluene under nitrogen protection and reacted at 80℃ for 4h. After the reaction was completed, the reaction product was poured into a stirred tank and ball-milled for 20h using a high-speed disperser at a speed of 2600rpm to obtain a mixed slurry. Subsequently, it was dried by rotary evaporation at 70℃ under a vacuum of 0.1MPa and a speed of 20rpm to obtain a modified carbon material.

[0068] Step S2: Immerse 15g of graphite felt with a thickness of 2mm in 120g of N-methylpyrrolidone, add 0.75g of azobisisobutyronitrile and 10g of methyl methacrylate monomer, mix well, react at 80℃ for 1.5h, after which the graphite felt is washed with N-methylpyrrolidone, and then freeze-dried at -60℃ for 24h to obtain modified graphite felt;

[0069] Step S3: Add 30g of methyl methacrylate monomer and 0.75g of azobisisobutyronitrile to a beaker and react at 75℃ for 50min. Then add 1.5g of modified carbon material and stir for 10min to obtain a mixed prepolymer solution. Pour the mixed prepolymer solution onto the surface of the modified graphite felt and hot-press at 150℃ and 5MPa for 60min to obtain a conductive layer. Then cover the upper and lower surfaces of the conductive layer with 0.2mm thick carbon paper and hot-press at 160℃ and 5MPa for 20min to obtain a composite bipolar plate with a three-dimensional conductive network.

[0070] Example 5: The following technical solution is adopted.

[0071] Step S1: Add 0.25g palladium diimide, 1g ethyl 2-(2-bromoisobutyryloxy)methacrylate, and 1.5g... 1-Naphthyl 2-acrylate was added to 40g of anhydrous dichloromethane, ethylene gas was introduced, the pressure was adjusted to 0.1MPa, and the reaction was carried out at 25℃ for 24h. After the reaction was completed, the reactants were dissolved and precipitated, and the precipitate was dried to obtain a macromolecular initiator. 1.5g of macromolecular initiator, 600g of methyl methacrylate monomer, 0.05g of cuprous bromide, 0.15g of pentamethyldiethylenetriamine, 0.15g of graphite, and 0.05g of carbon nanotubes were added to 200g of anhydrous toluene under nitrogen protection and reacted at 80℃ for 8h. After the reaction was completed, the reaction product was poured into a stirred tank and ball-milled for 12h using a high-speed disperser at a speed of 3000rpm to obtain a mixed slurry. Subsequently, it was dried by rotary evaporation at 70℃ under a vacuum of 0.1MPa and a speed of 25rpm to obtain a modified carbon material.

[0072] Step S2: Immerse 15g of graphite felt with a thickness of 4mm in 80g of N-methylpyrrolidone, add 0.75g of benzoyl peroxide and 10g of methyl methacrylate monomer, mix well, react at 80℃ for 1.5h, after which the graphite felt is washed with N-methylpyrrolidone, and then freeze-dried at -60℃ for 12h to obtain modified graphite felt;

[0073] Step S3: Add 30g of methyl methacrylate monomer and 0.75g of benzoyl peroxide to a beaker and react at 75°C for 50min. Then add 3g of modified carbon material and stir for 10min to obtain a mixed prepolymer solution. Pour the mixed prepolymer solution onto the surface of the modified graphite felt and hot-press at 150°C and 5MPa for 60min to obtain a conductive layer. Then cover the upper and lower surfaces of the conductive layer with 0.1mm thick carbon paper and hot-press at 160°C and 5MPa for 20min to obtain a composite bipolar plate with a three-dimensional conductive network.

[0074] Comparative Example 1: The following technical solution is adopted.

[0075] Compared with Example 1, the difference is that in step S1, 0.05g of graphite, 0.05g of carbon nanotubes and 200g of anhydrous toluene are poured into a stirred tank and ball-milled for 12h using a high-speed disperser to obtain a mixed slurry, wherein the dispersion disc speed is 3000rpm, and then dried by rotary evaporation at 70°C with a vacuum degree of 0.1MPa and a speed of 20rpm to obtain the modified carbon material.

[0076] Comparative Example 2: The following technical solution is adopted.

[0077] The difference from Example 1 is that the graphite felt was not modified in step S2.

[0078] Comparative Example 3: The following technical solution is adopted.

[0079] Compared with Example 1, the difference is that in step S3, the methyl methacrylate monomer was not pre-reacted at 75°C for 30 minutes, but directly subjected to the first hot pressing. The hot pressing temperature was 150°C, the pressure was 5 MPa, and the hot pressing time was 60 minutes.

[0080] Comparative Example 4: The following technical solution is adopted.

[0081] Compared with Example 1, the difference is that the bipolar plate prepared in Example 1 is broken and then re-prepared by hot pressing to form a composite bipolar plate. The hot pressing temperature is 160°C, the pressure is 5MPa, and the hot pressing time is 20min.

[0082] Comparative Example 5: The following technical solution is adopted.

[0083] Commercial carbon-plastic bipolar plates are used.

[0084] The bipolar plates obtained in Examples 1-5 and Comparative Examples 1-5 were assembled into a battery stack, and vanadium electrolyte was introduced. Battery performance was tested under the same test conditions, and the coulombic efficiency, voltage efficiency, and energy efficiency of the battery were recorded. The test results are shown in Table 1.

[0085] Table 1 Battery Performance Test Table

[0086]

[0087] like Figure 1 As shown, the composite bipolar plate prepared in Example 1 has a lateral dimension of approximately 150mm × 115mm and a thickness of 0.806mm. Figure 2 As shown in Table 1, compared to Comparative Example 1, Examples 1-5 exhibit higher voltage efficiency, energy efficiency, and lower resistivity. This is because the modified carbon materials in Examples 1-5 have modified polymers adsorbed on their surface, with polymethyl methacrylate (PMMA) long chains grafted onto the polymer ends. These polymers have good compatibility with the PMMA matrix, promoting better dispersion of the modified carbon materials within the matrix and forming a more complete conductive network. This enhances the conductivity of the bipolar plate, thereby improving the voltage and energy efficiency of the flow battery. Compared to Comparative Example 2, Examples 1-5 also exhibit higher voltage and energy efficiency. This is because a PMMA shell is prepared on the surface of the modified graphite felt fiber, which has good compatibility with the PMMA matrix. This reduces defects at the interface between the matrix and the graphite felt fiber, ensuring that the modified carbon material can be well dispersed and bonded to the graphite felt fiber surface, promoting improved conductivity of the bipolar plate, and thus enhancing the voltage and energy efficiency of the flow battery. Figure 3As shown, in Example 1, the graphite felt fiber surface is covered with a complete polymethyl methacrylate matrix, while in Comparative Example 2, because the graphite felt was not modified with polymethyl methacrylate, defects exist between the graphite felt fibers. In Comparative Example 3, because no pre-reaction was performed, the prepolymer solution did not have a certain viscosity, and therefore could not be hot-pressed to form a bipolar plate with a certain mechanical strength. This indicates that by controlling the viscosity of the prepolymer solution during the reaction process, polymethyl methacrylate can be infused into the interior of the graphite felt fibers to form a complete mechanical skeleton, thereby improving the mechanical properties of the bipolar plate. Comparative Example 4 is a composite bipolar plate obtained by re-hot-pressing repair after the composite bipolar plate prepared in Example 1 was broken. Figure 2 and Figure 4 As shown, after hot-pressing repair, the resistivity and tensile strength of Comparative Example 4 are similar to those of Example 1, indicating that the prepared bipolar plate can be repaired by hot pressing after fracture, while maintaining good conductivity and mechanical properties. Therefore, the voltage efficiency and energy efficiency of the flow battery are similar. Compared with the commercial carbon-plastic bipolar plate of Comparative Example 5, Examples 1-5 all showed higher flow battery performance, proving that the modified carbon material / graphite felt / polymethyl methacrylate composite bipolar plate with a three-dimensional conductive network not only has higher conductivity but also increased tensile strength, further improving the performance of the flow battery.

[0088] From the above detailed description of the embodiments of the present invention, it can be understood that the present invention provides a composite bipolar plate with a three-dimensional conductive network and its preparation method. The thermoplastic polymethyl methacrylate (PMMA) is used as the matrix, graphite felt is used as the three-dimensional conductive main network, and modified carbon material is used as the conductive secondary network to provide more conductive pathways for the graphite felt. Through in-situ modification of carbon material and graphite felt, PMMA can better enter the gaps in graphite felt to form a mechanical skeleton, while enhancing the dispersion of modified carbon material in PMMA matrix. This improves both the conductivity and mechanical properties of the composite bipolar plate, thereby increasing the voltage efficiency and energy efficiency of the flow battery.

[0089] Although the present invention has been preferably disclosed above, it is not intended to limit the present invention. Any person skilled in the art may make appropriate modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope defined in the claims.

Claims

1. A method of making a composite bipolar plate having a three-dimensional electrically conductive network, characterized by, Includes the following steps: Step S1: Add the catalyst, bromine-containing monomer, and vinyl monomer to anhydrous dichloromethane, introduce ethylene gas, and carry out reaction a. After the reaction is completed, perform post-treatment to obtain a macromolecular initiator. Add the macromolecular initiator, methyl methacrylate monomer, cuprous bromide, pentamethyldiethylenetriamine, graphite, and carbon nanotubes to anhydrous toluene under nitrogen protection to carry out reaction b. After the reaction is completed, pour the reaction product into a stirred tank and disperse it by ball milling to obtain a mixed slurry. Then, dry it by rotary evaporation to obtain the modified carbon material. Step S2: Immerse the graphite felt in N-methylpyrrolidone, add the initiator and methyl methacrylate monomer, mix well, and carry out the reaction. After the reaction is completed, rinse the graphite felt with N-methylpyrrolidone and then freeze-dry it to obtain the modified graphite felt. Step S3: Add methyl methacrylate monomer and initiator to a beaker for reaction, then add modified carbon material and stir to obtain a mixed prepolymer liquid; pour the mixed prepolymer liquid onto the surface of the modified graphite felt and hot-press for the first time to obtain a conductive layer; Carbon paper was then covered on the upper and lower surfaces of the conductive layer, followed by a second hot pressing to obtain a composite bipolar plate with a three-dimensional conductive network.

2. The production method according to claim 1, wherein In step S1: The mass ratio of the catalyst, bromine-containing monomer, vinyl monomer, and anhydrous dichloromethane is 0.25:(1~2):(1~2):(20~40); The catalyst is one of palladium diimide and nickel diimide; The bromine-containing monomer is one of 2-(2-bromoisobutyryloxy)ethyl methacrylate and 2-(2-bromoisobutyryloxy)ethyl acrylate; The vinyl monomer is one of 2-vinylnaphthalene, 1-naphthyl 2-acrylate, methyl 9-anthracene acrylate, and methyl 9-anthracene methacrylate.

3. The production method according to claim 1, wherein In step S1: The mass ratio of the macromolecular initiator, methyl methacrylate monomer, cuprous bromide, pentamethyldiethylenetriamine, anhydrous toluene, graphite and carbon nanotubes is 30:(200~700):1:(2~4):(200~300):(1~4):(1~4); The temperature of reaction b is 80℃, and the time is 4~12h.

4. The production method according to claim 1, wherein In step S1: The ball milling dispersion is carried out using a high-speed disperser. Zirconia beads are placed in the stirring tank, the dispersion disc rotates at 2500~3000 rpm, and the time is 12~24h. The rotary evaporation drying process is carried out at a rotation speed of 15-30 rpm, a rotary evaporation temperature of 70°C, and a vacuum degree of 0.1 MPa.

5. The production method according to claim 1, wherein In step S2: The mass ratio of the graphite felt, N-methylpyrrolidone, initiator and methyl methacrylate monomer is 15:(80~120):(0.5~1):10; The reaction was carried out at a temperature of 80°C for 1.5 hours. The initiator is one of azobisisobutyronitrile (AIBN) and benzoyl peroxide.

6. The production method according to claim 1, wherein In step S2: The freeze-drying temperature is -60℃, and the drying time is 12~24h.

7. The production method according to claim 1, wherein In step S3: The mass ratio of the methyl methacrylate monomer, initiator, and modified carbon material is 30:0.75:(0.15~3); The reaction was carried out at a temperature of 75°C for 30-50 minutes. The stirring time is 10 minutes; The temperature of the first hot pressing is 120~150℃, the pressure is 3~6MPa, and the time is 20~60min; The second hot pressing was performed at a temperature of 160°C, a pressure of 5 MPa, and a time of 20 minutes.

8. The production method according to claim 1, wherein In step S3: The modified graphite felt has a thickness of 2-6 mm, and the carbon paper has a thickness of 0.05-0.2 mm.

9. A composite bipolar plate having a three-dimensional conductive network, characterized by, It is prepared by the preparation method described in any one of claims 1 to 8.

10. The composite bipolar plate of claim 9, wherein The thickness of the composite bipolar plate is 0.6~1mm.

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