Bipolar plate with integrated flow channel, method for manufacturing the same and all-vanadium redox flow battery stack

Abstract

This invention discloses an integrated bipolar plate with flow channels, its preparation method, and a vanadium redox flow battery stack. The bipolar plate body comprises a carbon composite conductive structure. Electrolyte flow channels are integrally formed on both surfaces of the bipolar plate body using a die extrusion-hot roller forming process. The bipolar plate body is made of a conductive resin composite material, which comprises the following components by weight: 40 parts polypropylene, 30 parts conductive graphite, 20 parts conductive carbon black, 5 parts carbon nanotubes, and 5 parts carbon fiber; and auxiliary components: 3-5 parts toughening agent and 1-2 parts lubricant. This invention solves the problems of high cost, low efficiency, and large thickness in traditional graphite bipolar plate engraving processes, as well as the complex assembly and easy leakage of spliced ​​flow channels. It has advantages such as high production efficiency, high volumetric energy density of the stack, good reliability, and suitability for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery technology, specifically to an integrated bipolar plate with flow channels, its preparation method, and a vanadium redox flow battery stack. Background Technology

[0002] Bipolar plates are the core component of vanadium redox flow battery stacks, primarily responsible for conducting current, distributing electrolyte, and separating the positive and negative electrode chambers. Their performance directly affects the stack's energy efficiency, power density, and lifespan. Currently, commonly used bipolar plate flow channel structures in vanadium redox flow batteries are mainly divided into two categories: machined and discrete. Among them, the flow field engraved on graphite bipolar plates and the flow field spliced ​​between the guide frame and carbon paper flow channel plate are the most typical. However, both types of structures have significant technical defects and are difficult to meet the requirements of large-scale applications.

[0003] One type is the graphite bipolar plate engraved flow field structure: this structure forms the flow channel by mechanically engraving a block of graphite bipolar plates. Its core drawbacks are concentrated in three aspects: processing cost, production efficiency, and fuel cell performance. First, graphite is brittle and easily fractured, requiring high-precision CNC engraving equipment for flow channel engraving, resulting in extremely high equipment investment and material costs. Second, the engraving cycle for complex flow channels (such as serpentine or grid-shaped channels) can be several hours long, leading to extremely low production efficiency. Third, to avoid plate breakage during engraving, the initial thickness of the graphite bipolar plate usually needs to be greater than 5mm, resulting in a larger overall fuel cell thickness and a reduction in volumetric energy density of more than 20%. Simultaneously, the thicker plates themselves increase the resistance of the conductive path, and irregular morphologies such as burrs and missing corners are prone to appear at the edges of the engraved flow channels, further exacerbating electrolyte flow disturbance and local contact resistance, leading to a decrease in fuel cell output power.

[0004] Another type is the flow field structure that combines a guide frame and a carbon paper flow channel plate: the flow channel is formed by splicing a guide frame and a flow channel plate made of carbon paper. Although this structure reduces the processing difficulty of the bipolar plate to some extent, the assembly process requires precise alignment of the interface between the guide frame and the flow channel plate, making the assembly steps cumbersome; moreover, misalignment at the splice is prone to occur due to assembly errors, leading to internal problems of the fuel cell stack such as blockage of the electrolyte flow channel, reducing the reliability and service life of the fuel cell stack.

[0005] Carbon composite bipolar plates have become a preferred alternative to traditional graphite bipolar plates due to their advantages such as low cost, resistance to vanadium electrolyte corrosion, and adjustable conductivity. However, existing carbon composite bipolar plates mostly follow the "first form a flat plate, then combine the flow channel plate with the flow channel" approach, failing to address the aforementioned core defects. Therefore, developing a carbon composite bipolar plate with integrated flow channel and plate molding and its efficient preparation method is of great significance for improving the performance and reducing the cost of vanadium redox flow battery stacks. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an integrated bipolar plate with flow channels and its preparation method and a vanadium redox flow battery stack, so as to solve the problems of high cost, low efficiency and thick plate of graphite bipolar plate engraving flow field processing, cumbersome assembly of flow field splicing of flow guide frame and carbon paper flow channel plate, easy misalignment and leakage, and poor performance consistency caused by the separation of flow channel processing and plate forming of existing carbon composite bipolar plates.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0008] An integrated bipolar plate with flow channels includes a bipolar plate body with a carbon composite conductive structure; the two surfaces of the bipolar plate body are integrally formed with electrolyte flow channels by die extrusion-hot press roll forming process; the bipolar plate body is made of conductive resin composite material, and the conductive resin composite material includes the following components in parts by weight: 40 parts polypropylene, 30 parts conductive graphite, 20 parts conductive carbon black, 5 parts carbon nanotubes, 5 parts carbon fiber, and auxiliary components: 3-5 parts toughening agent and 1-2 parts lubricant.

[0009] Preferably, the carbon fiber is a short-cut carbon fiber with a length of 5-10 mm; the toughening agent is an ethylene-α-olefin copolymer; and the lubricant is a polypropylene wax with a melting point of 160-170℃ or a polyethylene wax with a melting point of 105-115℃.

[0010] Preferably, the volume resistivity of the bipolar plate body is ≤50 mΩ·cm, and within 1.5 mol / L V. 3+ / V 4+ After immersion in the electrolyte for 1000 hours, the change rate of volume resistivity is ≤5%; the mechanical tensile strength of the bipolar plate body is ≥30MPa.

[0011] Preferably, the total thickness of the bipolar plate body is 4mm; the electrolyte channel is a single-layer structure with a rectangular, trapezoidal or semi-circular cross-sectional shape, and the channel depth is 1.5mm, the channel width is 1-5mm, and the channel spacing is 2-8mm.

[0012] Preferably, the electrolyte flow channel is arranged in a serpentine, parallel straight, or grid pattern, and the turning radius of the serpentine electrolyte flow channel is 3-8 mm, while the intersection angle of the grid electrolyte flow channel is 90° or 60°.

[0013] The method for fabricating an integrated bipolar plate with a flow channel includes the following steps: S1. Conductive carbon material coating modification: 30 parts of conductive graphite, 20 parts of conductive carbon black and 5 parts of carbon nanotubes are added to a powder modification machine, preheated and dispersed, and then cooled to complete the coating modification of conductive powder. S2. Internal mixing and granulation: The modified conductive powder is added together with 40 parts of polypropylene, 5 parts of carbon fiber, 3-5 parts of toughening agent and 1-2 parts of lubricant into an internal mixer for internal mixing and granulation to obtain conductive resin particles. S3. Die extrusion and hot press roller flow channel forming: The conductive resin particles are added to the extruder and extruded through the die into a continuous plate-shaped blank. The blank is fed between two hot press rollers to imprint the electrolyte flow channel and flatten it to a total thickness of 4mm. S4. Multi-roll cooling and cutting: The billet with electrolyte flow channels is fed into a multi-roll cooling device to cool to room temperature, and then cut by a CNC cutting machine to obtain an integrated bipolar plate with flow channels.

[0014] Preferably, in step S1, the process of cooling down after preheating and dispersion is as follows: first, the temperature is raised to 80-100℃ for preheating and dispersion for 10-15 minutes, and then a cooling medium is introduced to cool down to below 40℃.

[0015] Preferably, in step S2, the conditions for internal mixing and granulation are: internal mixing at a temperature of 160-180℃ and a rotation speed of 30-50r / min for 15-20min, to obtain conductive resin particles with a diameter of 2-3mm and a length of 3-5mm.

[0016] Preferably, in step S3, the extruder is a single-screw extruder, and the barrel temperature is set as follows: 150-160℃ for the feeding section, 170-180℃ for the plasticizing section, 180-190℃ for the homogenizing section, 180-185℃ for the die temperature, and the screw speed is 30-50 r / min. The thickness of the plate-shaped blank extruded by the die is 4.4-4.8 mm; The temperature of the hot press roller is controlled at 160-170℃, the roller pressure is controlled at 8-12MPa, and the roller speed is controlled at 0.3-0.8m / min. The surface of the hot press roller is engraved with a punch structure that matches the electrolyte flow channel. The punch structure has a draft angle of 1°-3° to facilitate separation from the formed plate blank. The surface of the punch structure is chrome-plated, with a hardness ≥HRC50 and a surface roughness Ra≤0.4μm. The edges of the embossed electrolyte channels have a 5-10mm cutting gap. In step S4, the blank fed into the multi-roller cooling device is cooled to room temperature by 3-5 sets of gradient cooling rollers, and then cut into the set size by a CNC cutting machine along the reserved cutting gap.

[0017] A vanadium redox flow battery stack with integrated bipolar plates includes several stacked individual cells and end plate assemblies located on both sides of the individual cells. The end plate assembly includes, from the inside out, a current collector, an insulating plate, and an end plate. The end plate is provided with an inlet manifold and an outlet manifold, and the two end plates are tightened and fixed together by a pull rod and a nut threaded to the end of the pull rod. Each individual cell includes a proton exchange membrane, two electrodes attached to both sides of the proton exchange membrane, and two integrated bipolar plates with flow channels attached to the outside of the two electrodes, respectively. Adjacent stacked individual cells share one integrated bipolar plate with flow channels. The electrolyte inlet and electrolyte outlet of the electrolyte flow channel on the integrated bipolar plate with flow channels are connected to the inlet manifold and outlet manifold on one end plate.

[0018] Due to the adoption of the above technical solutions, the technical progress achieved by this invention is as follows.

[0019] This invention solves the problem of high cost and low efficiency in engraving flow fields: through the integrated forming process of die extrusion and hot press roller, the flow channel and the plate are formed simultaneously, eliminating the investment in high-precision equipment and lengthy processing cycle of graphite engraving, increasing production efficiency by more than 10 times, and the output per shift can reach more than 1,000 pieces; the total thickness of the bipolar plate is fixed at 4mm, which increases the volumetric energy density by more than 20% compared with traditional graphite bipolar plates (>5mm), while avoiding the problem of increased internal resistance caused by engraving, and increasing the output power of the fuel cell stack by 5-8%.

[0020] This invention avoids the defects of spliced ​​flow field assembly and reliability: the integrated molding structure eliminates the need for splicing steps of flow guide frame and flow channel plate, saves positioning tooling and assembly time, and improves assembly efficiency by more than 40%; there are no splicing gaps and assembly errors, completely solving the problems of flow channel blockage and electrolyte cross-contamination, extending the continuous operating life of the fuel cell stack to more than 10,000 hours, and significantly improving reliability.

[0021] This invention optimizes the performance and consistency of carbon composite materials: through raw material pretreatment and extrusion rolling processes, carbon fibers are oriented within the plate, increasing mechanical strength by more than 30%; the smoothness of the flow channel edge Ra≤0.8μm reduces electrolyte flow resistance by 15-20%, and the electrolyte distribution in the electrode reaction area is more uniform; the conductive additives work synergistically with the carbon matrix, stabilizing the volume resistivity below 50mΩ·cm, and exhibiting better conductivity uniformity than mechanically processed structures.

[0022] This invention is adapted to the needs of large-scale production: the forming roller punch structure can be quickly replaced to adapt to batch production with different flow channel layouts; the entire preparation process is continuous, the material utilization rate is increased to more than 95% (the utilization rate of traditional engraving process is only 60-70%), the overall production cost is reduced by more than 40%, and it has the value of large-scale promotion. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the integrated bipolar plate with flow channel of the present invention; Figure 2 This is a top view of the integrated bipolar plate with flow channel of the present invention; Figure 3 This is a bottom view of the integrated bipolar plate with flow channel of the present invention; Figure 4 For the present invention Figure 1 Schematic diagram of section AA in the diagram; Figure 5 This is a schematic diagram of the fabrication apparatus for the integrated bipolar plate with flow channel of the present invention; Figure 6 This is a schematic diagram of the structure of the all-vanadium redox flow battery stack with integrated bipolar plate with flow channel according to the present invention. Figure 7 This is a perspective view of the vanadium redox flow battery stack with integrated bipolar plate and flow channel of the present invention.

[0024] The components include: 1. Extruder, 2. Hot press roller, 3. Multi-roller cooling device, 4. CNC cutting machine, 100. Bipolar plate body, 101. Electrolyte flow channel, 200. Single cell, 201. Proton exchange membrane, 202. Electrode, 203. Integrated bipolar plate with flow channel, 300. Collector plate, 400. Insulating plate, 500. End plate, 501. Inlet manifold, 502. Outlet manifold, 600. Tie rod, 700. Nut, 800. Baffle. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] An integrated bipolar plate with flow channels, combined with Figures 1 to 4 As shown, it includes a bipolar plate body 100, and electrolyte channels 101 are respectively provided on the two surfaces of the bipolar plate body 100. The bipolar plate body 100 is a carbon composite conductive structure. The electrolyte channels 101 and the bipolar plate body 100 are integrally formed by die extrusion-hot press roller forming process.

[0027] The total thickness of the bipolar plate body 100 is 4mm. The electrolyte channel 101 is a single-layer structure with a rectangular, trapezoidal or semi-circular cross-sectional shape, a channel depth of 1.5mm, a channel width of 1-5mm, and a channel spacing of 2-8mm.

[0028] The electrolyte flow channel 101 is arranged in a serpentine, parallel straight, or grid pattern. The turning radius of the serpentine electrolyte flow channel 101 is 3-8 mm, and the intersection angle of the grid electrolyte flow channel 101 is 90° or 60°.

[0029] The bipolar plate body is made of conductive resin composite material, which includes the following components in parts by weight: 40 parts polypropylene, 30 parts conductive graphite, 20 parts conductive carbon black, 5 parts carbon nanotubes, 5 parts carbon fiber, and auxiliary components: 3-5 parts toughening agent and 1-2 parts lubricant.

[0030] Specifically, the carbon fiber is short-cut carbon fiber with a length of 5-10 mm; the toughening agent is an ethylene-α-olefin copolymer, which can improve the impact resistance of the bipolar plate and increase the elongation at break by more than 20%; the lubricant is polypropylene wax or polyethylene wax, with a melting point of 160-170℃ when polypropylene wax is used and 105-115℃ when polyethylene wax is used. These lubricants reduce the frictional resistance between the material and the equipment during processing and improve the smoothness of the flow channel formation.

[0031] The bipolar plate body 100 made from the above components has a volume resistivity ≤50mΩ·cm, and is within 1.5mol / L V. 3+ / V 4+ After immersion in electrolyte for 1000 hours, the volume resistivity change rate is ≤5%; the mechanical tensile strength is ≥30MPa. At the same time, a fixed total thickness of 4mm can be achieved, which is more than 20% thinner than traditional graphite bipolar plates (thickness >5mm).

[0032] To better illustrate the technical solution of the present invention, the following are several specific embodiments: Example A1

[0033] In this embodiment, the total thickness of the bipolar plate is 4 mm, the flow channel layout is serpentine, and the turning radius is 5 mm. The flow channel cross-section is rectangular, the flow channel depth is 1.5 mm, the flow channel width is 2 mm, and the flow channel spacing is 3 mm. The specific proportions of the conductive resin composite material are: 40 parts polypropylene, 30 parts conductive graphite, 20 parts conductive carbon black, 5 parts carbon nanotubes, 5 parts short-cut carbon fibers with a length of 6 mm, 4 parts ethylene-α-olefin copolymer (toughening agent), and 1.5 parts polypropylene wax (lubricant). The measured volume resistivity of this bipolar plate is 42 mΩ·cm, at 1.5 mol / L V. 3+ / V 4+ After immersion in the electrolyte for 1000 hours, the resistivity change rate was 3.2%, and the tensile strength was 35 MPa. Example A2

[0034] In this embodiment, the total thickness of the bipolar plate is 4 mm, and the flow channel layout adopts a parallel straight shape. The flow channel cross-section is semi-circular, the flow channel depth is 1.5 mm, the flow channel width is 4 mm, and the flow channel spacing is 6 mm. The specific ratio of the conductive resin composite material is: 40 parts polypropylene, 30 parts conductive graphite, 20 parts conductive carbon black, 5 parts carbon nanotubes, 5 parts short-cut carbon fibers with a length of 8 mm, 3 parts ethylene-α-olefin copolymer (toughening agent), and 2 parts polyethylene wax (lubricant). The measured volume resistivity of this bipolar plate is 38 mΩ·cm, at 1.5 mol / L V. 3+ / V 4+ After immersion in the electrolyte for 1000 hours, the resistivity change rate was 2.8%, and the tensile strength was 38 MPa. Example A3

[0035] In this embodiment, the total thickness of the bipolar plate is 4 mm, and the flow channel layout adopts a grid pattern with a cross angle of 90°. The flow channel cross-section is trapezoidal, with a flow channel depth of 1.5 mm, a top width of 3 mm, a bottom width of 1 mm, and a flow channel spacing (i.e., grid rib width) of 5 mm. The specific proportions of the conductive resin composite material are: 40 parts polypropylene, 30 parts conductive graphite, 20 parts conductive carbon black, 5 parts carbon nanotubes, 5 parts short-cut carbon fibers with a length of 10 mm, 5 parts ethylene-α-olefin copolymer (toughening agent), and 1 part polypropylene wax (lubricant). The measured volume resistivity of this bipolar plate is 45 mΩ·cm, at 1.5 mol / L V. 3+ / V 4+ After immersion in the electrolyte for 1000 hours, the resistivity change rate was 4.1%, and the tensile strength was 32 MPa.

[0036] The above embodiments demonstrate that, through the material formulation and structural design of the present invention, excellent conductivity, corrosion resistance and mechanical strength can be obtained while maintaining a thickness of 4mm, and it can be flexibly adapted to different flow channel layout requirements.

[0037] A method for fabricating an integrated bipolar plate with a flow channel, such as... Figure 5 As shown, it includes the following steps: S1. Conductive carbon material coating modification: 30 parts of conductive graphite, 20 parts of conductive carbon black, and 5 parts of carbon nanotubes are added to a powder modification machine. After preheating and dispersion, the conductive powder is cooled to complete the coating modification, thereby improving its compatibility and dispersibility with the resin matrix.

[0038] In this step, the process of preheating and dispersing followed by cooling is as follows: first, heat the temperature to 80-100℃ for preheating and dispersing for 10-15 minutes, and then introduce a cooling medium to cool the temperature down to below 40℃.

[0039] S2. Internal mixing and granulation: The modified conductive powder is added together with 40 parts of polypropylene, 5 parts of carbon fiber, 3-5 parts of toughening agent and 1-2 parts of lubricant into an internal mixer for internal mixing and granulation to obtain conductive resin particles.

[0040] In this step, the conditions for internal mixing and granulation in the internal mixer are: mixing at a temperature of 160-180℃ and a speed of 30-50r / min for 15-20 minutes, and obtaining conductive resin particles with a diameter of 2-3mm and a length of 3-5mm.

[0041] S3. Die extrusion and hot press roller flow channel forming: The conductive resin particles are added to the extruder 1 and extruded through the die into a continuous plate-shaped blank. The blank is fed between two hot press rollers 2 to imprint the electrolyte flow channel and flatten it to a total thickness of 4mm.

[0042] In this step, extruder 1 is a single-screw extruder, and the barrel temperature is set as follows: feed section 150-160℃, plasticizing section 170-180℃, homogenizing section 180-190℃, die temperature 180-185℃, and screw speed 30-50 r / min. The thickness of the sheet-like blank extruded from the die is 4.4-4.8 mm (10%-20% thicker than the total thickness of the finished product). The temperature of the hot press roller 2 is controlled at 160-170℃, the roller pressure is controlled at 8-12MPa, and the roller speed is controlled at 0.3-0.8m / min. The surface of the hot press roller 2 is engraved with a punch structure that matches the electrolyte flow channel (punch height 1.5mm, corresponding to the depth of a single-layer flow channel). The punch structure has a draft angle of 1°-3° to facilitate the separation of the plate blank from the punch after forming. The surface of the punch structure is chrome-plated, with a hardness ≥HRC50 and a surface roughness Ra≤0.4μm. The edges of the embossed electrolyte channels have a 5-10mm cutting gap.

[0043] In this step, the punch structure of the hot press roller 2 can be quickly changed according to the flow channel layout requirements, with a change time of ≤30min, and is suitable for batch production of different flow channels such as serpentine and parallel straight lines; the reserved cutting gap can effectively avoid damage to the flow channel edge during the cutting process and improve the finished product qualification rate.

[0044] S4. Multi-roll cooling and cutting: The billet with electrolyte flow channels is fed into the multi-roll cooling device 3 to cool to room temperature, and then cut by the CNC cutting machine 4 to obtain an integrated bipolar plate with flow channels.

[0045] In this step, the blank fed into the multi-roller cooling device 3 is cooled to room temperature by 3-5 sets of gradient cooling rollers, and then cut into the set size by the CNC cutting machine 4 along the reserved cutting gap.

[0046] To more clearly demonstrate the process window and feasibility of this preparation method, the following are several specific process examples: Example B1 (corresponding to the serpentine flow channel bipolar plate of Production Example A1) S1. Add 30 parts of conductive graphite, 20 parts of conductive carbon black, and 5 parts of carbon nanotubes to a powder modifier, heat it to 90°C for preheating and dispersion for 12 minutes, and then pass in circulating cooling water to cool it down to 35°C.

[0047] S2. Add all the modified conductive powder, 40 parts of polypropylene, 5 parts of short-cut carbon fibers with a length of 6 mm, 4 parts of ethylene α-olefin copolymer, and 1.5 parts of polypropylene wax into a mixer and mix at 170°C and 40 r / min for 18 minutes. Then granulate to obtain conductive resin particles with a diameter of about 2.5 mm and a length of about 4 mm.

[0048] S3. Add the above granules to a single-screw extruder. Set the barrel temperature as follows: feed section 155℃, plasticizing section 175℃, homogenizing section 185℃, die temperature 182℃, and screw speed 40 r / min. The extruded continuous plate-shaped preform is approximately 4.6 mm thick. Then feed it between a pair of hot press rollers with serpentine punches (1.5 mm high, draft angle 2°) engraved on their surfaces. Set the hot press roller temperature to 165℃, roller pressure to 10 MPa, and roller speed to 0.5 m / min. While flattening the preform to a total thickness of 4 mm, serpentine runners with a depth of 1.5 mm are imprinted, with an 8 mm shearing gap reserved around the runners.

[0049] S4: The formed continuous plate is fed into a four-roll cooling device (temperature gradient: 120℃→80℃→40℃→room temperature water cooling) for cooling and shaping. Finally, it is cut into standard size of 500mm×500mm along the reserved gap by a CNC cutting machine to obtain the finished bipolar plate.

[0050] Example B2 (corresponding to the parallel straight flow channel bipolar plate of Production Example A2) S1: Heat to 85℃ for 15 minutes to preheat and disperse, then cool to 30℃.

[0051] S2: Mixing conditions: Mix at 165℃ and 35 r / min for 20 minutes. The conductive resin particles are approximately 2.2 mm in diameter and 3.5 mm in length.

[0052] S3: Extruder settings: Feed section 150℃, Plasticizing section 170℃, Homogenizing section 180℃, Die temperature 180℃, Screw speed 35 r / min. Billet thickness 4.5mm. Hot press roller (punch is parallel and straight) temperature 160℃, roller pressure 9 MPa, roller speed 0.4 m / min. Pre-cutting clearance is 6mm.

[0053] S4: Three-roll cooling (120℃→80℃→room temperature air cooling), cutting size is 400mm×400mm.

[0054] Example B3 (corresponding to the mesh-shaped flow channel bipolar plate of Production Example A3) S1: Heat to 95℃ for 10 minutes to preheat and disperse, then cool to 38℃.

[0055] S2: Mixing conditions: Mix at 175℃ and 45 r / min for 16 minutes. The conductive resin particles are approximately 2.8 mm in diameter and 4.5 mm in length.

[0056] S3: Extruder settings: Feed section 160℃, Plasticizing section 178℃, Homogenizing section 188℃, Die temperature 184℃, Screw speed 45 r / min. Billet thickness 4.7mm. Hot press roller (punch with 90° grid pattern) temperature 168℃, roller pressure 11 MPa, roller speed 0.7 m / min. Pre-cutting clearance is 10mm.

[0057] S4: Five-roller cooling (120℃→100℃→80℃→50℃→room temperature water cooling), with a cutting size of 600mm×600mm.

[0058] The above process examples demonstrate that the preparation method of the present invention has clear process parameters and good operability, and can stably and continuously produce integrated bipolar plates with different flow channel layouts and qualified performance, thus verifying the practicality and reproducibility of the technical solution of the present invention.

[0059] A vanadium redox flow battery stack with an integrated bipolar plate and flow channel, such as Figures 6 to 7 As shown, it includes several stacked individual cells 200 and end plate assemblies located on both sides of the several individual cells 200.

[0060] The end plate assembly, from the inside out, includes a current collector 300, an insulating plate 400, and an end plate 500. The current collector 300 collects current output, the insulating plate 400 provides electrical isolation, and the end plate 500 provides mechanical support and clamping force. The end plate 500 is equipped with an inlet manifold 501 and an outlet manifold 502. The two end plates 500 are tightened and fixed together by a through-type tie rod 600 and a nut 700 threaded to the end of the tie rod 600, thereby providing uniform and sufficient sealing pressure for the entire fuel cell stack. Furthermore, a baffle 800 is sandwiched between the two end plates 500, which encloses several individual cells 200, the current collector 300, and the insulating plate 400, providing protection and fixation.

[0061] Each single cell 200 includes a proton exchange membrane 201, two electrodes 202, and two integrated bipolar plates 203 with flow channels. The two electrodes 202 are respectively attached to both sides of the proton exchange membrane 201; the two integrated bipolar plates 203 with flow channels are respectively attached to the outer sides of the two electrodes 202. Adjacent stacked single cells 200 share a single integrated bipolar plate 203. This shared structure avoids the duplication of the integrated bipolar plate 203, making the stack structure more compact.

[0062] The electrolyte channel 101 on the integrated bipolar plate 203 has an electrolyte inlet and an electrolyte outlet, which are connected to the inlet manifold 501 and outlet manifold 502 provided on one end plate 500.

[0063] Specifically, when all the integrated bipolar plates 203 with flow channels are stacked and aligned, their electrolyte inlets form a continuous inlet channel in the vertical direction, which connects to the main inlet pipe 501 on the end plate 500; the electrolyte outlet forms a continuous outlet channel, which connects to the main outlet pipe 502 on the end plate 500. In this way, the electrolyte enters from the main inlet pipe 501, is distributed through the inlet channel to the electrolyte flow channel 101 of the integrated bipolar plate 203 with flow channels, flows in the electrolyte flow channel 101 and undergoes an electrochemical reaction with the electrode 202, then collects in the outlet channel, and finally is discharged from the main outlet pipe 502, forming a complete electrolyte circulation loop.

Claims

1. An integrated bipolar plate with flow channels, characterized in that: The bipolar plate body (100) includes a carbon composite conductive structure; the two surfaces of the bipolar plate body are integrally formed by die extrusion-hot roller forming process and electrolyte channels (101) are provided; the bipolar plate body is made of conductive resin composite material, and the conductive resin composite material includes the following components in parts by weight: 40 parts of polypropylene, 30 parts of conductive graphite, 20 parts of conductive carbon black, 5 parts of carbon nanotubes, 5 parts of carbon fiber, and auxiliary components: 3-5 parts of toughening agent and 1-2 parts of lubricant.

2. The integrated bipolar plate with flow channel according to claim 1, characterized in that: The carbon fiber is a short-cut carbon fiber with a length of 5-10 mm; the toughening agent is an ethylene-α-olefin copolymer; and the lubricant is a polypropylene wax with a melting point of 160-170℃ or a polyethylene wax with a melting point of 105-115℃.

3. The integrated bipolar plate with flow channel according to claim 1, characterized in that: The volume resistivity of the bipolar plate body (100) is ≤50 mΩ·cm, and within 1.5 mol / L V. 3+ / V 4+ After immersion in the electrolyte for 1000 hours, the change rate of volume resistivity is ≤5%; the mechanical tensile strength of the bipolar plate body is ≥30MPa.

4. The integrated bipolar plate with flow channel according to claim 1, characterized in that: The total thickness of the bipolar plate body (100) is 4mm; the electrolyte channel (101) is a single-layer structure with a rectangular, trapezoidal or semi-circular cross-sectional shape, and the channel depth is 1.5mm, the channel width is 1-5mm, and the channel spacing is 2-8mm.

5. The integrated bipolar plate with flow channel according to claim 1, characterized in that: The electrolyte flow channel (101) is arranged in a serpentine, parallel straight or grid shape, and the turning radius of the serpentine electrolyte flow channel (101) is 3-8mm, and the intersection angle of the grid electrolyte flow channel (101) is 90° or 60°.

6. The method for preparing an integrated bipolar plate with flow channels as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Conductive carbon material coating modification: 30 parts of conductive graphite, 20 parts of conductive carbon black and 5 parts of carbon nanotubes are added to a powder modification machine, preheated and dispersed, and then cooled to complete the coating modification of conductive powder. S2. Internal mixing and granulation: The modified conductive powder is added together with 40 parts of polypropylene, 5 parts of carbon fiber, 3-5 parts of toughening agent and 1-2 parts of lubricant into an internal mixer for internal mixing and granulation to obtain conductive resin particles. S3. Die extrusion and hot press roller flow channel forming: The conductive resin particles are added to the extruder and extruded through the die into a continuous plate-shaped blank. The blank is fed between two hot press rollers to imprint the electrolyte flow channel and flatten it to a total thickness of 4mm. S4. Multi-roll cooling and cutting: The billet with electrolyte flow channels is fed into a multi-roll cooling device to cool to room temperature, and then cut by a CNC cutting machine to obtain an integrated bipolar plate with flow channels.

7. The method for preparing an integrated bipolar plate with flow channels according to claim 6, characterized in that: In step S1, the process of cooling down after preheating and dispersion is as follows: first, the temperature is raised to 80-100℃ for preheating and dispersion for 10-15 minutes, and then a cooling medium is introduced to cool down to below 40℃.

8. The method for preparing an integrated bipolar plate with flow channels according to claim 6, characterized in that: In step S2, the conditions for internal mixing and granulation are as follows: internal mixing at a temperature of 160-180℃ and a speed of 30-50r / min for 15-20min, to obtain conductive resin particles with a diameter of 2-3mm and a length of 3-5mm.

9. The method for preparing an integrated bipolar plate with flow channels according to claim 6, characterized in that: In step S3, the extruder is a single-screw extruder, and the barrel temperature is set as follows: 150-160℃ for the feeding section, 170-180℃ for the plasticizing section, 180-190℃ for the homogenizing section, 180-185℃ for the die temperature, and 30-50 r / min for the screw speed. The thickness of the plate-shaped blank extruded by the die is 4.4-4.8 mm; The temperature of the hot press roller is controlled at 160-170℃, the roller pressure is controlled at 8-12MPa, and the roller speed is controlled at 0.3-0.8m / min. The surface of the hot press roller is engraved with a punch structure that matches the electrolyte flow channel. The punch structure has a draft angle of 1°-3° to facilitate separation from the formed plate blank. The surface of the punch structure is chrome-plated, with a hardness ≥HRC50 and a surface roughness Ra≤0.4μm. The edges of the embossed electrolyte channels have a 5-10mm cutting gap. In step S4, the blank fed into the multi-roller cooling device is cooled to room temperature by 3-5 sets of gradient cooling rollers, and then cut into the set size by a CNC cutting machine along the reserved cutting gap.

10. A vanadium redox flow battery stack with an integrated bipolar plate and flow channel, comprising a plurality of stacked single cells (200) and end plate assemblies located on both sides of the plurality of single cells (200), the end plate assembly comprising, from the inside out, a current collector (300), an insulating plate (400) and an end plate (500); the end plate (500) is provided with an inlet manifold (501) and an outlet manifold (502), and the two end plates (500) are tightened and fixed together by a pull rod (600) and a nut (700) threaded to the end of the pull rod (600), characterized in that: The single cell (200) includes a proton exchange membrane (201), two electrodes (202) attached to both sides of the proton exchange membrane (201), and two integrated bipolar plates (203) with flow channels as described in any one of claims 1 to 5 respectively attached to the outside of the two electrodes (202). The single cells (200) stacked adjacently share a single integrated bipolar plate (203) with flow channels. The electrolyte inlet and electrolyte outlet of the electrolyte flow channel (101) on the integrated bipolar plate (203) with flow channels are connected to the inlet manifold (501) and outlet manifold (502) provided on an end plate (500).

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