A method of making a bipolar plate with flow channels for a flow battery

Abstract

The application relates to the field of liquid flow battery manufacturing, in particular to a preparation method of a bipolar plate with a flow channel for a liquid flow battery. The specific steps are as follows: (1) after mixing nano graphite and carbon nanotubes with a dispersing agent, a coupling agent is added to perform surface treatment, so that a two-component nano conductive agent is obtained; (2) the two-component nano conductive agent is mixed with a high polymer resin in a high mixer, and then granulation is performed through a screw extruder, so that a two-component nano conductive agent / high polymer resin composite conductive master batch is obtained; (3) the composite conductive master batch is extruded into a conductive sheet through an extruder; (4) the two-component nano conductive agent is made into profile material with a flow field through a hydraulic machine; and (5) the profile material with the flow field is respectively arranged on the two sides of the conductive sheet and is put into a mold to be integrated and shaped through a hot press, so that the bipolar plate with the flow channel for the liquid flow battery is obtained. The bipolar plate for the liquid flow battery is prepared, the amount of the conductive filler is reduced, the welding performance of the material is improved while the conductivity is improved.

Description

Technical Field

[0001] This invention relates to the field of flow battery manufacturing, specifically to a method for preparing a flow battery with a bipolar plate having a flow channel. Background Technology

[0002] In today's world, energy is a vital material foundation for human survival and development, and a crucial factor in promoting economic growth. With the rapid development of the national economy, the demand for energy is increasing daily. The depletion of traditional fossil fuels has led to severe environmental pollution, making the development of renewable energy an essential approach. The integration of renewable energy into the grid and the peak-shaving and frequency regulation of large power grids both rely heavily on advanced energy storage technologies. Flow batteries can not only ensure the storage of intermittent energy sources such as solar, wind, and tidal power, but also shift electricity from off-peak to peak demand periods, thereby maintaining a stable balance in electricity consumption and enhancing grid stability.

[0003] Flow batteries offer higher energy capacity compared to capacitors and solid-state batteries. The energy is stored in an electrolyte solution containing active materials, which is housed in a reservoir and circulated into the battery chamber via a pump. During charging and discharging, the flowing electrolyte transports the electrolyte solution to the battery chamber, where an electrochemical reaction occurs, converting chemical energy into electrical energy. This unique structure is ideal for large-scale energy storage needs, as the electrolyte concentration can be adjusted according to the required energy level.

[0004] The technological challenges facing bipolar plates in existing vanadium redox flow batteries lie in simultaneously meeting the application of stack welding processes and the trend towards flow-through structures to adapt to the needs of battery stack technology development. Currently, the all-vanadium route is the most mature and is the main route promoted in my country, having reached the early stages of commercialization. However, all-vanadium redox flow batteries are not without their flaws. The main factor restricting their development remains their high cost. Ensuring the reliability of the system during long-term operation and reducing system costs are urgent issues that need to be addressed. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention aims to propose a method for preparing a bipolar plate with a flow channel for flow batteries, which addresses the technological development and challenges faced by bipolar plates in existing flow battery stacks. This method needs to simultaneously meet the application of stack welding processes and the trend of flow-through structures, in order to adapt to the needs of battery stack technology development.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing a bipolar plate with flow channels for a flow battery includes the following steps: (1) mixing nano-graphite and carbon nanotubes with a dispersant, adding a coupling agent for surface treatment to obtain a two-component nano-conductive agent; (2) mixing the two-component nano-conductive agent with a polymer resin in a high-speed mixer, and then granulating it through a screw extruder to obtain a two-component nano-conductive agent / polymer resin composite conductive masterbatch; (3) extruding the composite conductive masterbatch into a conductive sheet through an extruder; (4) taking the two-component nano-conductive agent and forming it into a profile with a flow field through a hydraulic press; (5) placing the profile with the flow field on both sides of the conductive sheet and placing it into a mold and pressing it into an integral shape through a hot press.

[0008] The method for preparing a flow battery with a bipolar plate with a flow channel, wherein the content of the two-component nano-conductive agent in the composite conductive masterbatch is 10wt% to 50wt%, and the content of the polymer resin is 50wt% to 90wt%.

[0009] The method for preparing a flow battery with a bipolar plate with a flow channel includes a two-component nano-conductive agent comprising nano-graphite, carbon nanotubes, a dispersant, and a coupling agent. The weight ratio of nano-graphite to carbon nanotubes is 1:1 to 1:9. The dispersant accounts for 0.1% to 10% of the mass of the conductive agent, and the coupling agent accounts for 0.1% to 3% of the mass of the conductive agent.

[0010] The method for preparing a flow battery with a bipolar plate with flow channels uses graphite nanoparticles with a particle size of 1μm to 50μm, a carbon content of 90wt% to 99.9wt%, and a moisture content of <0.5wt%; the carbon nanotubes are single-walled or multi-walled carbon nanotubes with a purity of >98wt% and a diameter of 0.4 to 100nm.

[0011] The method for preparing a flow battery with a bipolar plate having a flow channel uses a polymer resin that is one or a mixture of two or more of the following: polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polypropylene, polyethylene, ABS, chlorinated polyethylene, epoxy resin, phenolic resin, and vinyl resin.

[0012] The specific steps of the fabrication method for the flow battery with a bipolar plate having a flow channel are as follows:

[0013] (1) Nanographite and carbon nanotubes are mixed with 0.1% to 10% of dispersant by weight of conductive agent at a weight ratio of 1:1 to 1:9, and then 0.1% to 3% of coupling agent by weight of conductive agent is added for surface treatment to obtain a two-component nano-conductive agent; N-methylpyrrolidone is used as the dispersant, and silane or titanate coupling agent is used as the coupling agent.

[0014] (2) Mix the two-component nano-conductive agent, which accounts for 10% to 50% of the total mass of the composite conductive masterbatch, with the polymer resin, which accounts for 50% to 90% of the total mass of the composite conductive masterbatch, in a high-speed mixer at a speed of 1000 to 1500 rpm, and then granulate it through a screw extruder to obtain the two-component nano-conductive agent / polymer resin composite conductive masterbatch. The composite conductive masterbatch has 350 to 600 particles / 10g and the particle size is uniform.

[0015] (3) Extruding the composite conductive masterbatch into conductive sheets using a screw extruder;

[0016] (4) Take the two-component nano-conductive agent and mold it into a profile with a flow field. The molding pressure is 5MPa to 100MPa and the molding time is 10 to 30min.

[0017] (5) The profile with the flow field is placed on both sides of the conductive sheet and put into the mold. It is pressed into a whole shape by a hot press. The forming pressure is 5MPa~100MPa, the forming temperature is 150~200℃, and the forming time is 5~30min.

[0018] The method for preparing a flow battery with a bipolar plate having flow channels involves a conductive sheet with a thickness of 0.2–2 mm, a profile with a flow field placed on both sides of the conductive sheet, the width of the flow channel being 0.5–5 mm, the depth being 0.2–2.5 mm, the width of the ridge being 0.5–10 mm, and two or more types of turbulence grooves being provided along the fluid flow direction, with the spacing between adjacent turbulence grooves being 2–12 mm.

[0019] The aforementioned method for preparing a flow battery with a bipolar plate having a flow channel involves placing the ridges of the flow channel on the outer surfaces of both sides of the conductive sheet, with the height being the depth of the flow channel.

[0020] The method for preparing a flow battery with a bipolar plate having a flow channel has a flow field shape that is one of an interdigitated flow field, a single serpentine flow field, or two or more serpentine flow fields.

[0021] In the aforementioned method for preparing a flow battery with a bipolar plate having flow channels, the external release agent used during molding is an ethanol solution of phenolic resin or WEICON PTFE.

[0022] The design concept of this invention is:

[0023] This invention uses a two-component nano-conductive agent to form a profile with a flow field through a hydraulic mechanism, ensuring the conductivity of the flow field. The ridge protrusion structure in the flow field improves mass transfer while reducing the contact resistance between the agent and the electrode. This ridge protrusion structure is beneficial for reducing the electrode thickness and reducing physical internal resistance. At the same time, the composite molding process with conductive sheet increases the feasibility of processing and improves processing efficiency.

[0024] The advantages and beneficial effects of this invention are:

[0025] 1. The bipolar plate provided by this invention reduces the amount of conductive filler, improves conductivity and welding performance of the material, solves the problem of battery stack sealing performance, and improves system safety.

[0026] 2. This invention eliminates or reduces liquid phase mass transfer resistance by increasing the flow channel structure, which improves the power density of the fuel cell stack and reduces battery cost, thus improving economic efficiency.

[0027] 3. The process route of this invention is simple, has no special requirements for equipment, is economical, and can be mass-produced.

[0028] 4. A battery assembled using the bipolar plate of this invention is tested at a current density of 160 mA / cm². 2 The battery charge / discharge performance parameters are as follows: coulombic efficiency 96-98%, voltage efficiency 83-85%, and energy efficiency 81-83%. Attached Figure Description

[0029] Figure 1 This is a front view of a flow battery with a bipolar plate with flow channels, as described in Example 1.

[0030] Figure 2 This is a side view of a flow battery with a bipolar plate with flow channels, as described in Example 1.

[0031] Figure 3 This is a front view of a flow battery with a bipolar plate with flow channels, as described in Example 2.

[0032] Figure 4 This is a side view of a flow battery with a bipolar plate with flow channels, as shown in Example 2.

[0033] Figure 5 This is a front view of a flow battery with a bipolar plate with flow channels, as described in Example 3.

[0034] Figure 6 This is a side view of a flow battery with a bipolar plate with flow channels, as described in Example 3.

[0035] Figure 7 This is a front view of a flow battery with a bipolar plate with flow channels, as described in Example 4.

[0036] Figure 8 This is a side view of a flow battery with a bipolar plate with flow channels, as described in Example 4.

[0037] In the figure, 1 is a conductive sheet, 2 is a profile with a flow field, 3 is a flow channel, 4 is a turbulence groove, and 5 is a ridge. Detailed Implementation

[0038] In the specific implementation process, the preparation method of the flow battery bipolar plate with flow channel of the present invention includes the following steps: (1) After mixing nano-graphite and carbon nanotubes with a dispersant, a coupling agent is added for surface treatment to obtain a two-component nano-conductive agent; (2) The two-component nano-conductive agent and polymer resin are mixed in a high-speed mixer and then granulated by a screw extruder to obtain a two-component nano-conductive agent / polymer resin composite conductive masterbatch; (3) The composite conductive masterbatch is extruded into a conductive sheet by an extruder; (4) The two-component nano-conductive agent is taken and formed into a profile with flow field by a hydraulic press; (5) The profile with flow field is placed on both sides of the conductive sheet and placed into a mold and pressed into an integral shape by a hot press to obtain a flow battery bipolar plate with flow channel.

[0039] In the composite conductive masterbatch of this invention, the content of the two-component nano-conductive agent is 10wt% to 50wt%, and the content of the polymer resin is 50wt% to 90wt%. The two-component nano-conductive agent includes nano-graphite, carbon nanotubes, a dispersant, and a coupling agent. The weight ratio of nano-graphite to carbon nanotubes is 1:1 to 1:9. The dispersant accounts for 0.1% to 10% of the conductive agent by mass, and the coupling agent accounts for 0.1% to 3% of the conductive agent by mass. The nano-graphite has a particle size of 1μm to 50μm, preferably 1μm to 10μm; a carbon content of 90wt% to 99.9wt%, and a moisture content of <0.5wt%. The carbon nanotubes are single-walled or multi-walled carbon nanotubes with a purity >98wt% and a diameter of 0.4 to 100nm, preferably 0.4 to 20nm. The polymer resin can be one or a mixture of two or more of the following: polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polypropylene, polyethylene, ABS, chlorinated polyethylene, epoxy resin, phenolic resin, and vinyl resin.

[0040] In this invention, the conductive sheet has a thickness of 0.2–2 mm; a profile with a flow field is placed on both sides of the conductive sheet, with a flow channel width of 0.5–5 mm, a depth of 0.2–2.5 mm, and a ridge width of 0.5–10 mm. The ridge of the flow channel is placed above the outer surfaces of both sides of the conductive sheet, and its height is equal to the flow channel depth. Two or more types of turbulence grooves are provided along the fluid flow direction, with a spacing of 2–12 mm between adjacent turbulence grooves. The function of the turbulence grooves is to make the gradient change of the fluid more uniform when diffusing horizontally and more uniform when diffusing vertically. The shape of the flow field is one of a cross-shaped flow field, a single serpentine flow field, or two or more serpentine flow fields.

[0041] The present invention will now be described in detail through examples.

[0042] Example 1

[0043] Nano-graphite and single-walled carbon nanotubes were mixed at a weight ratio of 1:4 with 10% N-methylpyrrolidone (NMP) dispersant (by weight of the conductive agent). Then, 3% titanate coupling agent (by weight of the conductive agent) was added for surface treatment to obtain a two-component nano-conductive agent. 30% of the two-component nano-conductive agent (by weight of the composite conductive masterbatch) was mixed with 70% polyethylene (PE) (by weight of the composite conductive masterbatch) in a high-speed mixer at 1500 rpm. The mixture was then granulated using a screw extruder to obtain a two-component nano-conductive agent / polymer resin composite conductive masterbatch. The composite conductive masterbatch had a density of 500 granules / 10g and uniform particle size. The composite conductive masterbatch was extruded into conductive sheets using a screw extruder. Finally, the two-component nano-conductive agent was compression molded (using WEICON PTFE dry lubricant spray from Germany as the external release agent). PTFE is pressed into a profile with a cross-flow field shape. The width of the flow channel 3 is 2 mm, the depth is 1.5 mm, the width of the ridge 5 is 5 mm, and five turbulence grooves 4 are provided along the fluid flow direction, with a spacing of 7 mm between adjacent turbulence grooves 4. The molding pressure is 50 MPa, and the molding time is 30 min. The profile 2 with the flow field is placed on both sides of the conductive sheet 1 and placed into a mold, then pressed into a single piece using a hot press. The molding pressure is 30 MPa, the molding temperature is 160℃, and the molding time is 20 min. This yields a bipolar plate with flow channels for a flow battery. See [link to relevant documentation]. Figures 1-2 .

[0044] A battery was assembled using this bipolar plate at a current density of 160 mA / cm². 2 The battery charge / discharge performance parameters are as follows: coulombic efficiency 96.5%, voltage efficiency 84.1%, and energy efficiency 81.2%.

[0045] Example 2

[0046] Nano-graphite and single-walled carbon nanotubes were mixed at a weight ratio of 1:3 with 8% N-methylpyrrolidone (NMP) dispersant (by weight of the conductive agent). Then, 1% titanate coupling agent (by weight of the conductive agent) was added for surface treatment to obtain a two-component nano-conductive agent. 40% of the two-component nano-conductive agent (by weight of the composite conductive masterbatch) was mixed with 60% polypropylene (PP) (by weight of the composite conductive masterbatch) in a high-speed mixer at 1000 rpm. The mixture was then granulated using a screw extruder to obtain a two-component nano-conductive agent / polymer resin composite conductive masterbatch with a density of 400 granules / 10g and uniform particle size. The composite conductive masterbatch was extruded into conductive sheets using a screw extruder. Finally, the two-component nano-conductive agent was compression molded (using WEICON PTFE dry lubricant spray from Germany as the external release agent). PTFE is pressed into a profile with a single serpentine flow field. The width of the flow channel 3 is 1.5 mm, the depth is 1 mm, the width of the ridge 5 is 4 mm, and five turbulence grooves 4 are provided along the fluid flow direction, with a spacing of 5.5 mm between adjacent turbulence grooves 4. The molding pressure is 40 MPa, and the molding time is 20 min. The profile 2 with the flow field is placed on both sides of the conductive sheet 1 and placed into a mold, then pressed into a single piece using a hot press. The molding pressure is 25 MPa, the molding temperature is 180℃, and the molding time is 30 min. This yields a bipolar plate with flow channels for a flow battery. See [link to relevant documentation]. Figures 3-4 .

[0047] A battery was assembled using this bipolar plate at a current density of 160 mA / cm². 2 The battery charge / discharge performance parameters are as follows: coulombic efficiency 97.2%, voltage efficiency 84.0%, and energy efficiency 81.6%.

[0048] Example 3

[0049] Nano-graphite and multi-walled carbon nanotubes were mixed at a weight ratio of 1:2 with 5% N-methylpyrrolidone (NMP) dispersant (by weight of the conductive agent). Then, 2% titanate coupling agent (by weight of the conductive agent) was added for surface treatment to obtain a two-component nano-conductive agent. 25% of the two-component nano-conductive agent (by weight of the composite conductive masterbatch) was mixed with 75% polyvinylidene fluoride (PVDF) (by weight of the composite conductive masterbatch) in a high-speed mixer at 1200 rpm, and then granulated using a screw extruder to obtain a two-component nano-conductive agent / polymer resin composite conductive masterbatch. The particle size is 380 particles / 10g, and the particle size is uniform. The composite conductive masterbatch is extruded into conductive sheets using a screw extruder. A two-component nano-conductive agent is molded (the external release agent used is an ethanol solution of phenolic resin, with a phenolic resin concentration of 20-30 wt%), and pressed into a profile with a multi-serpentine flow field. The width of the flow channel 3 is 1 mm, the depth is 2 mm, the width of the ridge 5 is 8 mm, and 5 turbulence grooves 4 are provided along the fluid flow direction, with a spacing of 9 mm between adjacent turbulence grooves 4. The molding pressure is 40 MPa, and the molding time is 25 min. The profile 2 with the flow field is placed on both sides of the conductive sheet 1 and placed into a mold, and then pressed into an integral shape using a hot press. The molding pressure is 50 MPa, the molding temperature is 200℃, and the molding time is 30 min. A flow channel bipolar plate for a flow battery is obtained. Figures 5-6 .

[0050] A battery was assembled using this bipolar plate at a current density of 160 mA / cm². 2 The battery charge / discharge performance parameters are: coulombic efficiency 97.0%, voltage efficiency 83.5%, and energy efficiency 81.0%.

[0051] Example 4

[0052] Nano-graphite and multi-walled carbon nanotubes were mixed at a weight ratio of 1:1 with 3% N-methylpyrrolidone (NMP) dispersant (by weight of the conductive agent). Then, 2% silane coupling agent (by weight of the conductive agent) was added for surface treatment to obtain a two-component nano-conductive agent. 35% of the two-component nano-conductive agent (by weight of the composite conductive masterbatch) was mixed with 65% polyethylene (PE) (by weight of the composite conductive masterbatch) in a high-speed mixer at 1300 rpm. The mixture was then granulated using a screw extruder to obtain a two-component nano-conductive agent / polymer resin composite conductive masterbatch. The composite conductive masterbatch had a composition of 5... 50 particles / 10g, with uniform particle size; the composite conductive masterbatch is extruded into conductive sheets using a screw extruder; a two-component nano-conductive agent is molded (the external release agent used is an ethanol solution of phenolic resin, with a phenolic resin concentration of 20-30 wt%), and pressed into a profile with a single serpentine flow field. The width of the flow channel 3 is 5 mm, the depth is 1 mm, the width of the ridge 5 is 7 mm, and 5 turbulence grooves 4 are provided along the fluid flow direction, with a spacing of 12 mm between adjacent turbulence grooves 4; the molding pressure is 60 MPa, and the molding time is 30 min. The profile 2 with the flow field is placed on both sides of the conductive sheet 1 and placed into a mold, and pressed into an integral shape using a hot press. The molding pressure is 20 MPa, the molding temperature is 160℃, and the molding time is 20 min; a bipolar plate with flow channels for a flow battery is obtained, see Figures 7-8 .

[0053] A battery was assembled using this bipolar plate at a current density of 160 mA / cm². 2 The battery charge / discharge performance parameters are as follows: coulombic efficiency 97.3%, voltage efficiency 84.3%, and energy efficiency 82.0%.

[0054] The results of the embodiments show that the present invention reduces the amount of conductive filler, improves conductivity while enhancing the weldability of the material, and eliminates or reduces liquid phase mass transfer resistance by increasing the flow channel structure, thereby increasing the power density of the fuel cell stack and reducing battery costs, thus improving economic efficiency. The process route of the present invention is simple, requires no special equipment, is economical, and can be mass-produced.

Claims

1. A method for preparing a flow battery with a bipolar plate having a flow channel, characterized in that, The specific steps are as follows: (1) Nanographite and carbon nanotubes are mixed with 0.1% to 10% of dispersant by weight of conductive agent at a weight ratio of 1:1 to 1:9, and then 0.1% to 3% of coupling agent by weight of conductive agent is added for surface treatment to obtain a two-component nanoconductive agent; N-methylpyrrolidone is used as the dispersant, and silane or titanate coupling agent is used as the coupling agent. (2) Mix the two-component nano-conductive agent, which accounts for 10% to 35% of the total mass of the composite conductive masterbatch, with the polymer resin, which accounts for 65% to 90% of the total mass of the composite conductive masterbatch, in a high-speed mixer at a speed of 1000 to 1500 rpm, and then granulate it through a screw extruder to obtain the two-component nano-conductive agent / polymer resin composite conductive masterbatch. The composite conductive masterbatch has 350 to 600 particles / 10g and the particle size is uniform. (3) The composite conductive masterbatch is extruded into conductive sheets using a screw extruder; (4) Take the two-component nano-conductive agent and mold it into a profile with a flow field. The molding pressure is 5MPa~100MPa and the molding time is 10~30min. (5) Place the profile with flow field on both sides of the conductive sheet and put it into the mold. Press it into a whole shape by hot press. The forming pressure is 5MPa~100MPa, the forming temperature is 150~200℃, and the forming time is 5~30min. The polymer resin is one or more of the following: polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polypropylene, polyethylene, ABS, chlorinated polyethylene, epoxy resin, phenolic resin, and vinyl resin. The conductive sheet has a thickness of 0.2~2mm. A profile with a flow field is placed on both sides of the conductive sheet. The width of the flow channel is 0.5~5mm, the depth is 0.2~2.5mm, and the width of the ridge is 0.5~10mm. Two or more types of turbulence grooves are provided along the fluid flow direction. The spacing between adjacent turbulence grooves is 2~12mm. The turbulence grooves make the gradient change of the fluid more uniform when it diffuses in the horizontal direction and more uniform when it diffuses in the vertical direction. The ridge of the flow channel is placed on the outer surface of both sides of the conductive sheet, and the height is the depth of the flow channel. The nano-graphite has a particle size of 1μm~50μm, a carbon content of 90wt%~99.9wt%, and a moisture content of <0.5wt%; the carbon nanotubes are single-walled or multi-walled carbon nanotubes with a purity of >98wt% and a diameter of 0.4~100nm. The shape of the flow field is one of the following: cross-toe flow field, single serpentine flow field, and two or more serpentine flow fields; During compression molding, the external release agent used is an ethanol solution of phenolic resin or WEICON PTFE; A profile with a flow field is formed by using a two-component nano-conductive agent through a hydraulic mechanism to ensure the conductivity of the flow field. The ridge protrusion structure in the flow field improves mass transfer and reduces the contact resistance between the electrode and the electrode. This ridge protrusion structure is conducive to reducing the electrode thickness and reducing the physical internal resistance.

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