Composite electrode with built-in lappet-connected diversion trench, preparation method and application of composite electrode in flow battery

Abstract

The invention belongs to the technical field of flow batteries, and particularly relates to a composite electrode with a built-in lappet-connected diversion trench, a preparation method and application of the composite electrode in a flow battery. Firstly, an interdigitated diversion trench carbon felt electrode with a lappet is designed, then a high-activity carbon-based catalyst layer with a high electrochemical active area is prepared, and finally, the composite electrode with the built-in lappet diversion trench is obtained through compounding. The prepared composite electrode is applied to a flow battery, and a carbon-based catalyst layer is contacted with a diaphragm, so that the diaphragm is prevented from being damaged while a high-activity area is provided; the interdigitated diversion trench carbon felt electrode with the lappets is in contact with the bipolar plate, and the carbon felt electrode serves as a reaction place and ensures effective mass transfer at the same time. According to the structural design of the composite electrode, an efficient electrolyte transmission channel and rich reaction active sites can be provided at the same time, the diaphragm can be protected, and the energy conversion efficiency and the cycling stability of the flow battery are effectively improved. The preparation process is simple to operate, low in cost and suitable for large-scale production, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, specifically relating to a composite electrode with built-in connecting channel, its preparation method, and its application in flow batteries. Background Technology

[0002] A flow battery is a large-scale energy storage device. Its core principle is to store and release electrical energy through the redox reactions of active substances (such as vanadium ions, electroactive organic compounds, and iron ions) in the electrolyte. As a key component of a flow battery, the electrodes must simultaneously meet the following requirements: (1) High reactive surface area to increase reaction rate; (2) Uniform electrolyte mass transfer distribution to reduce concentration polarization; (3) Good corrosion resistance and long service life; (4) Interface stability with the diaphragm, to avoid cross-contamination of electrolyte due to electrode fibers piercing the diaphragm.

[0003] Traditional flow battery electrodes often use carbon felt or porous carbon cloth as the substrate, whose high porosity and conductivity provide the basis for the electrochemical redox reactions of the active materials. However, as flow batteries develop towards higher power density and longer lifespan, traditional carbon felt electrodes are gradually revealing the following problems: (1) Insufficient mass transfer efficiency: The internal channels of carbon felt are disordered, and the flow of electrolyte in it is prone to form local stagnation zones, resulting in uneven transport of reactants. Under high current density, "concentration polarization" is likely to occur. Although engraving flow channels on graphite bipolar plates can alleviate the electrolyte mass transfer problem to a certain extent, the negative impacts of increased processing costs, increased contact resistance and decreased mechanical strength are difficult to solve. (2) Limited reaction area: The physical specific surface area of ​​carbon felt is only 0.5~5m². 2 / g, the actual active area used for electrochemical reactions is far lower than its physical specific surface area; the lower active area will lead to greater electrochemical polarization and ohmic polarization, affecting the energy conversion efficiency and power density of the battery; loading catalytic materials on the carbon felt surface is the most common method to improve electrode activity, but the interfacial bonding force between the catalyst and carbon fiber is poor, and it is easy to fall off under the continuous flushing of the electrolyte, causing risks such as local blockage of battery pipelines and contamination of electrolyte; (3) Risk of puncture to the separator: There are fibers in the planar (xy) direction and vertical (z) direction in the carbon felt. The vertical fibers that are not fully covered can easily penetrate the electrode and come into contact with the separator. Under the battery operating pressure or electrolyte flushing, the separator will be punctured, accelerating the cross-leakage of positive and negative electrolytes and significantly shortening the battery life.

[0004] Therefore, there is an urgent need for a novel composite electrode material for flow batteries that takes into account mass transfer optimization, active reaction area, and membrane protection. Summary of the Invention

[0005] The purpose of this invention is to provide a composite electrode with a built-in connecting channel, a preparation method, and its application in a flow battery. The composite electrode prepared and applied in a flow battery can simultaneously optimize mass transfer, increase the active reaction area, and protect the membrane.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a composite electrode with a built-in connecting groove includes the following steps: S1. A flow guide groove is engraved on the carbon felt substrate using a carving machine to obtain a carbon felt electrode with a connecting finger-shaped flow guide groove. S2. Preparation of a highly active carbon-based catalytic layer; S3. Combine the interlocking finger-shaped flow guide groove carbon felt electrode with a high-activity carbon-based catalyst layer to obtain a composite electrode with an internal interlocking flow guide groove.

[0007] Preferably, the carbon felt matrix is ​​a polyacrylonitrile-based carbon felt with a thickness of 2.5 mm, a porosity of 90%, a fiber diameter of about 10 μm, and an average pore size of about 80 μm.

[0008] Preferably, the width of the connecting flap in the flow channel is 2mm to 15mm, and the width of the connecting flap changes from small to large along the electrolyte flow direction.

[0009] In some preferred embodiments, the width of the connecting flap in the guide groove is 4mm~6mm, 7mm~9mm, 10mm~12mm, and 13mm~15mm respectively along the electrolyte flow direction.

[0010] Preferably, the width of the guide groove is 1mm to 6mm, and the width of the carbon felt electrode between the two rows of guide grooves is 15mm to 30mm.

[0011] By designing the width of the connector in the flow channel, the permeability of the carbon felt electrode can be significantly improved, while simultaneously enhancing the electrochemical performance and stability of the fabricated flow battery. This is because setting the connector width to vary from small to large along the electrolyte flow direction forms a trapezoidal support frame. This maintains the structural stability of the carbon felt after carving, facilitating battery stack assembly, while also preventing mass transfer unevenness caused by loose carbon felt. It guides the electrolyte flow in a directional manner, reduces local stagnation areas, improves mass transfer efficiency, and thus significantly reduces concentration polarization. High permeability reduces electrolyte transport resistance, thereby improving the utilization rate of active materials, which in turn improves the battery's coulombic efficiency and reduces cycle degradation.

[0012] By directly engraving the flow channels within the carbon felt, the manufacturing cost, conductivity, and performance stability issues of conventional bipolar plates are resolved, resulting in a significant improvement in mass and charge transfer efficiency. This is because the built-in flow channels shorten the electrolyte transport path from a two-stage process of bipolar plate channel → carbon felt pores to an integrated process of carbon felt channel → carbon felt pores. Compared to engraving grooves on the bipolar plate, this reduces contact resistance and avoids mass transfer dead zones caused by burrs at the edges of the bipolar plate channel. Simultaneously, the carbon felt channel, as the main transport channel, improves the effective utilization rate of the electrolyte. The increased charge transfer efficiency leads to higher voltage efficiency and higher power density. Furthermore, the bipolar plate does not require engraving, significantly reducing costs.

[0013] Preferably, the highly active carbon-based catalyst layer is obtained by activating a thin carbon layer material composed only of planar fibers.

[0014] Preferably, the thin carbon layer material includes, but is not limited to, one or more of carbon paper, carbon cloth, carbon felt, carbon nanofiber membrane, and graphene paper.

[0015] Preferably, the thin carbon layer material has a transverse structure, that is, the orientation of the fibers or sheets in the material is in the xy plane direction, and there is no vertical direction.

[0016] Preferably, the thickness of the thin carbon layer material is 0.1 mm to 1.5 mm.

[0017] In some preferred embodiments, the thin carbon layer material can be either homemade or purchased.

[0018] In some preferred embodiments, the thin carbon layer material may be polyacrylonitrile-based carbon paper with a thickness of 0.3 mm, sourced from Liaoning Jingu Carbon Materials Co., Ltd.

[0019] In some preferred embodiments, the thin carbon layer material may be a self-made functionalized polyacrylonitrile-based carbon nanofiber membrane, and the preparation method of the functionalized polyacrylonitrile-based carbon nanofiber membrane includes the following steps: A1. Spinning; A2. Pre-oxidation treatment; A3. Carbonization treatment yields functionalized polyacrylonitrile-based carbon nanofiber membranes.

[0020] Preferably, the specific preparation method of step A1 is as follows: dissolve polyacrylonitrile (PAN) in N,N-dimethylformamide (DMF) to prepare an electrospinning precursor spinning solution, add functional components to it, perform electrospinning, and collect the fibers onto the surface of aluminum foil to obtain the product.

[0021] Preferably, the relative molecular mass of the PAN is 90,000 to 150,000. Preferably, the mass fraction of PAN in the spinning solution is 15% to 20%.

[0022] Preferably, the amount of the functional component added is 0.01% to 10% of the mass of the spinning solution.

[0023] Preferably, the functional components include, but are not limited to, one or more of graphene oxide (GO), carbon nanotubes, and bismuth salts.

[0024] Preferably, the specific steps of the electrospinning are as follows: the spinning solution is delivered into a syringe containing a stainless steel needle, electrospinning is performed using high voltage, and the solution is wound using a high-speed rotating roller to obtain the desired product.

[0025] Preferably, the electrospinning voltage is 15~20kV and the take-up distance is 10cm~20cm.

[0026] Preferably, the rotational speed of the roller winding is 100~200 r / min.

[0027] Preferably, the temperature of the electrospinning chamber is 20℃~50℃.

[0028] Preferably, the temperature inside the electrospinning chamber is 30~40℃ and the humidity is 40~50RH.

[0029] Preferably, the functionalized polyacrylonitrile-based carbon nanofiber membrane has a diameter of 100 nm to 2 μm and a fiber layer thickness of 0.1 mm to 1.5 mm.

[0030] Preferably, in step A2, the specific conditions for the pre-oxidation treatment are: the atmosphere is air, the temperature is increased to 250~320℃ at a rate of 1~5℃ / min, and the temperature is maintained for 0.5h~4h.

[0031] Preferably, in step A3, the specific conditions for carbonization treatment are: nitrogen atmosphere, heating to 900-1200℃ at 5-10℃ / min, and holding at that temperature for 1-3 hours.

[0032] By preparing a PAN-based carbon nanofiber catalytic layer with fibers oriented in the entire xy plane and without any perpendicular orientation, the electrochemical active area of ​​the catalytic layer can be increased, while reducing the battery separator breakage rate and energy efficiency degradation rate. This is because the transverse fibers tightly cover the vertical fibers of the carbon felt, forming a physical barrier between the separator and the carbon felt, preventing the separator from being punctured by the vertical fibers under electrolyte scouring; at the same time, the high electrochemical active area and the introduced electrocatalytic nanomaterials provide abundant electrochemical reaction sites, greatly improving the electrochemical reaction rate, reducing the increase in polarization and energy efficiency degradation caused by insufficient reaction activity, increasing the battery power density, and extending the battery cycle life.

[0033] Preferably, the activation process includes, but is not limited to, one or more of the following: heat treatment, acid treatment, plasma treatment, and catalyst loading.

[0034] In some preferred embodiments, the activation treatment may be a combination of two or more processes, such as acid treatment or heat treatment followed by catalyst loading.

[0035] Preferably, the specific conditions for the heat treatment are: the atmosphere is air, the temperature is increased to 400-700°C at a rate of 3-7°C / min, the temperature is held for 30 min-2 h, and then cooled to room temperature in the furnace.

[0036] Preferably, the specific steps of the acid treatment are as follows: add the thin carbon layer material to a nitric acid solution, treat it at 75~85℃ and 250-350r / min for 2~4h, take it out and wash the carbon cloth repeatedly with deionized water until the filtrate is neutral, and then vacuum dry it.

[0037] Preferably, the volume fraction of the nitric acid solution is 60% to 68%.

[0038] Preferably, the solid-liquid ratio of the thin carbon layer material to the nitric acid solution is 1g:(20~50)mL.

[0039] Preferably, the specific conditions for vacuum drying are: temperature of 55~65℃, vacuum degree of 0.08~0.09MPa, and time of 10~15h.

[0040] Preferably, the specific steps for catalyst loading are as follows: fully immerse the thin carbon layer material in the catalyst solution, remove it, wash it twice with ethanol, and dry it.

[0041] Preferably, the catalyst solution is prepared by mixing the catalyst with a solvent.

[0042] Preferably, the solid-liquid ratio of the catalyst to the solvent is 1 g: (15~25) mL.

[0043] Preferably, the catalyst is a metal-based nanoparticle catalyst such as Bi, Ti, Sb, Pb, Mn, Nb, or a carbon nanomaterial catalyst such as graphene oxide or carbon nanotubes.

[0044] Preferably, the solvent is an aqueous solution of ethanol with a volume fraction of 50%.

[0045] Preferably, the immersion time is 30 min to 2 h.

[0046] Preferably, the catalyst loading is 0.1%-20% of the total mass of the thin carbon layer material.

[0047] Preferably, the specific drying conditions are: temperature of 55~65℃, vacuum degree of 0.08~0.09MPa, and time of 3~5h.

[0048] Preferably, in step S3, the composite process includes, but is not limited to, one or more of hot pressing, bonding, and lamination.

[0049] Preferably, the specific conditions for hot pressing are: temperature of 150~200℃, pressure of 3~5MPa, and holding time of 5~10min.

[0050] Preferably, the bonding requires the use of an adhesive, including but not limited to any one of polytetrafluoroethylene and phenolic resin, which can be applied to the surface of the carbon felt electrode and then laminated.

[0051] By sequentially subjecting the thin carbon layer material to heat treatment, acid treatment, and / or catalyst loading, the electrochemical active area of ​​the catalyst layer was increased, thereby significantly improving the electrochemical performance of the battery. Heat treatment effectively enhances the surface affinity of the carbon fibers, providing a uniform substrate for further activation and facilitating electrolyte wetting. Nitric acid etching forms nanogrooves on the surface of the carbon-based catalyst layer, increasing the specific surface area and introducing active functional groups such as carboxyl groups. This not only improves hydrophilicity and electrochemical activity but also serves as anchoring points for subsequent catalyst nanoparticles, resulting in more uniform catalyst dispersion and stronger bonding. The carboxyl groups form strong coordination bonds with the metal catalyst, reducing the shedding rate and enhancing the high electrochemical activity and stability of the catalyst layer. This significantly reduces polarization overpotential and improves voltage efficiency, thereby enhancing the electrochemical performance and stability of the prepared battery.

[0052] The second aspect of the present invention provides a method for preparing the composite electrode with the built-in connecting flow channel, resulting in a composite electrode with the built-in connecting flow channel.

[0053] A third aspect of the present invention provides the application of the composite electrode with built-in connecting groove in a flow battery, wherein, when assembling the flow battery, the highly active carbon-based catalyst layer of the composite electrode with built-in connecting groove is in contact with the separator, and the connecting finger-shaped carbon felt electrode with connecting groove is in contact with the bipolar plate.

[0054] By designing functional zones for the flow channel carbon felt and the transverse carbon-based catalyst layer (the carbon felt electrode contacts the bipolar plate, and the carbon-based catalyst layer contacts the separator), the structural compatibility of the prepared composite electrode with the flow battery can be improved, thereby enhancing battery performance. This is likely because the carbon felt side focuses on electrolyte transport, while the catalyst layer side focuses on electrochemical reactions. The functional zoning avoids mutual interference between mass transfer and reaction. Furthermore, the composition and structure of the catalyst layer can be adjusted according to the type of flow battery, and the overall electrode thickness is controllable, making it suitable for assembling high-power-density flow battery stacks.

[0055] Preferably, the flow battery includes, but is not limited to, any one of vanadium redox flow batteries, iron-chromium flow batteries, aqueous organic flow batteries, zinc-bromine flow batteries, and all-iron flow batteries.

[0056] Preferably, the bipolar plates used in the flow battery do not contain flow channels.

[0057] The overall structural diagram of the flow battery assembled with the composite electrode prepared according to the present invention is shown below. Figure 1 .

[0058] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention provides a composite electrode with an internal connecting channel. First, a carbon felt electrode with an interlocking finger-shaped channel is designed. Then, a highly active carbon-based catalyst layer with a high electrochemical active area is prepared. Finally, these are combined to obtain the composite electrode with the internal connecting channel. When applied to flow batteries, this composite electrode can simultaneously provide efficient electrolyte transport channels and abundant reactive sites, while also protecting the separator, effectively improving the energy conversion efficiency and cycle stability of the flow battery. The preparation process of this invention is simple and low-cost, suitable for large-scale production, and has broad application prospects.

[0059] 2. This invention addresses the shortcomings of existing carbon felt electrodes for flow batteries by providing a composite carbon-based porous electrode material. By carving interlocking finger-shaped flow channels in the carbon felt to optimize electrolyte mass transfer while maintaining the overall structure of the carbon felt electrode, a highly active transverse carbon-based catalytic layer is introduced near the separator. This compensates for the reaction area lost due to the carving of the flow channels and protects the separator through the transversely oriented carbon-based support, ultimately improving the energy efficiency, power density, and cycle life of the flow battery.

[0060] 3. This invention designs and carves a carbon felt electrode material with a ferrule-like flow channel structure. The carbon felt has built-in flow guide grooves that guide the electrolyte to flow directionally along the channels, reducing local stagnation areas. The ferrule structure helps maintain the overall structure of the carbon felt and facilitates assembly. At the same time, it effectively solves the problem of loose carbon felt electrode structure and difficulty in assembly caused by carving flow guide grooves on the carbon felt. The flow channel structure can provide a channel for electrolyte transmission, solving the processing cost and stability problems caused by bipolar plates with flow channels.

[0061] 4. By designing the width of the connecting flange in the flow channel, this invention can significantly improve the permeability of the carbon felt electrode while enhancing the electrochemical performance and stability of the prepared flow battery.

[0062] 5. This invention solves the problems of manufacturing cost, conductivity and performance stability of conventional flow channel bipolar plates by directly engraving the flow channel inside the carbon felt, and significantly improves the mass transfer and charge transfer efficiency.

[0063] 6. This invention selects a specific carbon felt matrix and designs corresponding interdigitated flow channels to form a dual-scale mass transfer network of macro-flow channels and micro-pores, which enables the carbon felt in the flow channel to maintain high permeability under high compression ratio and improve battery energy efficiency.

[0064] 7. This invention, by designing a transverse carbon-based catalyst layer with fibers oriented in the xy plane and without any vertical direction, and contacting it with the separator, can effectively compensate for the loss of carbon felt fibers caused by the engraving of the flow channel, and improve the reaction area and electrocatalytic activity of the electrode; at the same time, the transversely oriented carbon-based catalyst layer has an outstanding separator protection effect, which can tightly cover the vertical fibers in the carbon felt substrate, effectively reduce the separator breakage rate, and significantly extend the battery life.

[0065] 8. The present invention has strong structural adaptability. The functional partition design of the flow channel carbon felt and the transverse carbon-based catalyst layer (the carbon felt electrode is in contact with the bipolar plate, and the carbon-based catalyst layer is in contact with the membrane) avoids mutual interference. The composition and structure of the catalyst layer can be adjusted according to the type of flow battery. The overall thickness of the electrode is controllable and it is suitable for the assembly of high power density flow battery stacks. Attached Figure Description

[0066] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0067] Figure 1 This is an overall structural diagram of a flow battery assembled with a composite electrode featuring a built-in connecting groove, as prepared in this invention. Figure 2 This is a planar schematic diagram of the interlocking finger-type flow channel carbon felt electrode prepared according to Embodiment 1 of the present invention; Figure 3 This is a scanning electron microscope image of the highly active carbon-based catalyst layer prepared in this invention; wherein... Figure 3 (a) Prepared in Example 1, Figure 3 (b) was prepared for Comparative Example 5. Figure 3 (c) is prepared for Comparative Example 6. Detailed Implementation

[0068] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0069] All raw materials used in this invention are commercially available, specifically: The carbon felt matrix is ​​polyacrylonitrile-based carbon fiber felt with a thickness of 2.5 mm, a porosity of 90%, a fiber diameter of approximately 10 μm, and an average pore size of approximately 80 μm. It is sourced from Liaoning Jingu Carbon Materials Co., Ltd.

[0070] PAN has a relative molecular mass of 85,000 and is sourced from Shanghai Maclean Biotechnology Co., Ltd.

[0071] Graphene oxide, from Pioneer Nano.

[0072] Example 1 This embodiment provides a composite electrode with a built-in connecting groove, and its preparation method includes the following steps: S1. A flow guide groove is engraved on the carbon felt substrate using a carving machine to obtain a carbon felt electrode with a connecting finger-shaped flow guide groove. S2. Preparation of a highly active carbon-based catalytic layer; S3. Combine the interlocking finger-shaped flow guide groove carbon felt electrode with a high-activity carbon-based catalyst layer to obtain a composite electrode with an internal interlocking flow guide groove.

[0073] The widths of the connecting flaps in the flow channel are 5mm, 8mm, 11mm, and 14mm respectively along the electrolyte flow direction.

[0074] The width of the guide groove is 4.07 mm, and the width of the carbon felt electrode between the two rows of guide grooves is 25 mm.

[0075] A plan view of the interlocking finger-type flow guide groove carbon felt electrode is shown below. Figure 2 .

[0076] The highly active carbon-based catalytic layer is obtained by activating a thin carbon layer material.

[0077] The thin carbon layer material is a functionalized polyacrylonitrile-based carbon nanofiber membrane, and the preparation method of the functionalized polyacrylonitrile-based carbon nanofiber membrane includes the following steps: A1. Spinning; A2. Pre-oxidation treatment; A3. Carbonization treatment yields a polyacrylonitrile-based carbon fiber catalytic layer electrode.

[0078] The specific preparation method of step A1 is as follows: PAN is dissolved in DMF to prepare an electrospinning precursor spinning solution, functional components are added to it, electrospinning is performed, and the fibers are collected on the surface of aluminum foil to obtain the product.

[0079] The mass fraction of PAN in the spinning solution is 14%.

[0080] The functional component in the spinning solution is graphene oxide.

[0081] The amount of the functional component added is 0.5% of the mass of the spinning solution.

[0082] The specific steps of the electrospinning are as follows: the spinning solution is delivered into a syringe containing a stainless steel needle, electrospinning is performed using high voltage, and the solution is wound using a high-speed rotating roller to obtain the desired product.

[0083] The electrospinning voltage is set to 20kV and the take-up distance is 15cm.

[0084] The temperature inside the electrospinning chamber is 35°C and the humidity is 45%RH.

[0085] The rotational speed of the roller winding is 150 r / min.

[0086] The functionalized polyacrylonitrile-based carbon nanofiber membrane has a thickness of 0.2 mm and a fiber diameter of approximately 200 nm.

[0087] In step A2, the specific conditions for the pre-oxidation treatment are: the atmosphere is air, the temperature is increased to 280℃ at 3℃ / min, and the temperature is maintained for 1 hour.

[0088] In step A3, the specific conditions for carbonization are as follows: the atmosphere is nitrogen, the temperature is increased to 1000℃ at 8℃ / min, and the temperature is maintained for 1.5h.

[0089] The activation process is a heat treatment.

[0090] The specific conditions for the heat treatment are as follows: the atmosphere is air, the temperature is increased to 550°C at a rate of 5°C / min, held at that temperature for 1 hour, and then cooled to room temperature in the furnace.

[0091] In step S3, the composite process is hot pressing.

[0092] The specific conditions for hot pressing are: temperature 180℃, pressure 4MPa, and holding time 8min.

[0093] Example 2 The only difference between this embodiment and Embodiment 1 is that the width of the connecting flap in the flow channel is 6mm, 9mm, 12mm, and 15mm respectively along the electrolyte flow direction.

[0094] Example 3 The only difference between this comparative example and Example 1 is that the thin carbon layer material is polyacrylonitrile-based carbon cloth with a thickness of 0.3 mm, which comes from Liaoning Jingu Carbon Materials Co., Ltd.

[0095] The activation process is an acid treatment.

[0096] The specific steps of the acid treatment are as follows: add carbon cloth to nitric acid solution, treat at 80℃ and 300r / min for 3h, take it out and wash the carbon cloth repeatedly with deionized water until the filtrate is neutral, and then vacuum dry it.

[0097] The volume fraction of the nitric acid solution is 65%.

[0098] The solid-liquid ratio of the carbon cloth and nitric acid solution is 1g:35mL.

[0099] The specific conditions for vacuum drying are: temperature 60℃, vacuum degree 0.085MPa, and time 12h.

[0100] Example 4 The only difference between this comparative example and Example 1 is that the thin carbon layer material is polyacrylonitrile-based carbon paper with a thickness of 0.3 mm, which comes from Liaoning Jingu Carbon Materials Co., Ltd.

[0101] The activation process is as follows: first, heat treatment is performed, and then catalyst loading is performed.

[0102] The specific conditions for the heat treatment are as follows: under a nitrogen atmosphere, the temperature is increased to 900°C at a rate of 5°C / min, CO2 is introduced, and the temperature is maintained for 40 minutes. Then, nitrogen is introduced, and the furnace is cooled to room temperature.

[0103] The specific steps for catalyst loading are as follows: fully immerse the heat-treated thin carbon layer material in the catalyst solution, remove it, wash it twice with ethanol, and dry it.

[0104] The catalyst solution is prepared by mixing the catalyst with a solvent.

[0105] The solid-liquid ratio of the catalyst and solvent is 1g:20mL.

[0106] The catalyst is Bi nanoparticles.

[0107] The solvent is an aqueous solution of ethanol with a volume fraction of 50%.

[0108] The soaking time is 1 hour.

[0109] The catalyst has a Bi loading of 1.7% of the carbon cloth mass.

[0110] The specific drying conditions are: temperature 60℃, vacuum degree 0.085MPa, and time 4h.

[0111] Comparative Example 1 The only difference between this comparative example and Example 1 is that the carbon felt electrode does not have a connecting flap, but only a guide groove with a width of 4.07 mm, and the width of the carbon felt electrode between the two rows of guide grooves is 25 mm.

[0112] Comparative Example 2 The only difference between this comparative example and Example 1 is that the width of the connecting flaps in the guide groove is uniform, all being 8mm.

[0113] Comparative Example 3 The only difference between this comparative example and Example 1 is that the flow channel of the carbon felt electrode is a straight groove type with a width of 4.07 mm, and the width of the carbon felt electrode between the two rows of straight grooves is 25 mm.

[0114] Comparative Example 4 The only difference between this comparative example and Example 1 is that the width of the connecting flap in the flow channel is 14mm, 11mm, 8mm, and 5mm respectively along the electrolyte flow direction.

[0115] Performance testing (1) Performance testing of carbon felt electrode The permeability of a conventional carbon felt electrode without flow channels and the carbon felt electrode with interlocking finger-shaped flow channels prepared in Example 1 were tested using an FR-SI flow resistance meter (permeability test). The target pressure was set to 0.45 MPa; the preset rotation speed was 0 r / min; the initial rotation speed was 300 r / min; the cutoff rotation speed was 1000 r / min; and the increase in rotation speed was 10 r / min. μ represents the liquid viscosity coefficient required to calculate the Darcy value from the measured data, and was set to 0.00298 Pa·s during the test; L represents the sample size, with length and width equal, fixed at 10 cm; A represents the sample cross-sectional area, set to 4 cm². 2 Sample compression ratio represents the compression rate of the sample during the test, and is set to 10%~70%. It is calculated using the following formula: .

[0116] Where K represents permeability, in μm 2 (square micrometers); test results are shown in Table 1.

[0117] Table 1. Permeability test results under different compression ratios

[0118] As shown in Table 1, the carbon felt with flow channels exhibits superior permeability, indicating that the electrolyte has less resistance to transport in the electrode, which helps to improve the mass transfer performance of the electrode, reduce pump consumption, and improve system efficiency.

[0119] With a fixed compression rate of 50%, the permeability of carbon felt electrodes in Examples 1-2 and Comparative Examples 1-4 was tested, and the results are shown in Table 2.

[0120] Table 2. Results of carbon felt electrode permeability test

[0121] As shown in Table 2, Examples 1 and 2 exhibit high permeability, providing excellent mass transfer channels while maintaining the structure. Comparative Example 1, with its seamless structure and fully unobstructed flow channel, exhibits the lowest fluid flow resistance and thus the highest permeability. However, this sacrifices mechanical strength and may affect battery performance. Comparative Example 2, with its uniform-width joint, disrupts the gradient distribution of the flow field, easily generating dead zones and eddies, increasing flow resistance and leading to a decrease in permeability. Comparative Example 3, with its straight-groove flow channel, has a long channel length and lacks the flow field disturbance caused by the joint, making it easy for the electrolyte to short-circuit and difficult to effectively force the electrolyte to penetrate into the carbon felt, resulting in poor mass transfer. Comparative Example 4, with its reverse gradient joint, has a wide joint at the electrolyte inlet and a narrow joint at the outlet, which is not conducive to uniform electrolyte distribution and smooth discharge. The flow resistance is greater than that of the forward gradient, hence the lower permeability.

[0122] (2) Performance of carbon-based catalyst layer Using 2M sulfuric acid as the electrolyte, the carbon felt substrate and the carbon-based catalyst layer prepared in Examples 1-2 and Comparative Examples 5-6 were used as working electrodes, respectively. The saturated calomel electrode was used as the reference electrode and the platinum sheet was used as the counter electrode. Cyclic voltammetry curves at different scan rates were tested within a voltage window of -0.1V to +0.1V (vs. SCE). The electrochemical active area (ECSA) of the two electrode materials was calculated using the following formula. The results are shown in Table 3.

[0123]

[0124] Where: I, current density (mA·cm) -2 v, scan rate (mV·s) -1 Cs, specific capacitance, 0.035 mF·cm -2 A, Electrode geometric area (m²) 2 ); m, electrode mass (g).

[0125] Table 3 Results of electrochemical active area test of carbon-based catalyst layer

[0126] As shown in Table 3, the carbon nanofiber catalyst layer prepared in Example 1 has a high electrochemical active area. Because its fiber diameter is at the nanometer level, it exhibits a large active specific surface area, which is beneficial to the electrochemical reaction process, reduces polarization overpotential, and helps improve battery performance. Example 3 uses a carbon cloth substrate that has only undergone acid treatment, which can increase the electrode's specific surface area and functional groups to a certain extent, thereby enhancing the electrode's electrochemical active area. Example 4 uses carbon paper as the substrate, which is first heat-treated to improve surface hydrophilicity, and then Bi-based nanoparticles are loaded onto the surface to increase the electrode's surface roughness, which is beneficial for improving the electrode's electrochemical active area.

[0127] Scanning electron microscope (SEM) images of the highly active carbon-based catalyst layers prepared in Examples 1 and 3-4 are shown below. Figure 3 .

[0128] from Figure 3 (a) It can be seen that the carbon nanofiber catalytic layer does not contain vertical fibers, the fiber diameter is about 200 nm, and after activation treatment, the surface has a certain number of active functional groups, which can provide abundant electrochemical reaction active sites and effectively improve the electrochemical reaction activity of the electrode. From Figure 3 (b) It can be seen that the activated carbon cloth is woven from xy-planar fibers in an orderly manner; from Figure 3 (c) It can be seen that carbon fibers with near-planar curves also exist in carbon paper.

[0129] (3) Battery performance test Vanadium redox flow batteries were assembled using integrated composite electrodes prepared in Examples 1-2 and Comparative Examples 1-6 as positive and negative electrode materials. During assembly, the highly active carbon-based catalyst layer of the composite electrode with built-in connecting channels contacted the separator, while the carbon felt electrode with connecting channels and finger-shaped channels contacted the bipolar plate. A carbon felt matrix (polyacrylonitrile-based carbon fiber felt) was used as control group 1 for battery assembly. Simultaneously, the composite electrode prepared in Example 1, with its highly active carbon-based catalyst layer in contact with the bipolar plate and the carbon felt electrode with connecting channels and finger-shaped channels in contact with the separator, was used as control group 2. Battery performance was tested, primarily including charge-discharge tests (battery efficiency), cycle stability tests (single-cycle decay rate), and battery polarization curve tests (power density).

[0130] Battery Assembly: The prepared electrode materials were used as the positive and negative electrodes to assemble the battery. The electrode compression ratio was 25%. A Nafion 212 proton exchange membrane was used to isolate the positive and negative electrolytes. The working area of ​​the electrodes used was 3×3 cm². 2 The electrolyte is 1.65 MVO. 2+ The electrolyte solution used was 3.0 M H₂SO₄, with volumes of 20 mL for the positive electrode and 10 mL for the negative electrode. The electrolyte flow rate was 30 mL / min. -1 The bipolar plate is a carbon composite bipolar plate without flow channels; the charge / discharge current density is 200 mA·cm⁻¹. -2 The cutoff voltages during charging and discharging are 1.75V and 1.0V, respectively. Cyclic stability tests were conducted at a current density of 250mA·cm⁻².

[0131] The formulas for calculating the coulombic efficiency (CE), energy efficiency (EE), and voltage efficiency (VE) of a battery are as follows:

[0132]

[0133]

[0134] in: I d and I c represents the discharge current and the charging current, respectively. t For time, V d and V c represents the discharge voltage and the charging voltage, respectively.

[0135] By constantly charging the battery at different current densities until the voltage is less than 0.5V, the discharge polarization curves of vanadium batteries assembled with WC-ECNFs and ECNFs as electrodes were obtained. The peak power density can be calculated by plotting the current density-voltage product of the polarization curves on the ordinate and the current density on the abscissa. At 250 mA·cm⁻¹ -2 The battery's cycle stability was assessed by comparing the rate of energy efficiency degradation under long-term cycling after 1000 cycles at the current density.

[0136] The test results are shown in Table 4.

[0137] Table 4 Battery Performance

[0138] As shown in Table 4, Examples 1 and 2, which use a composite of high-mass-transfer carbon felt electrode and highly active carbon nanofiber catalyst layer, produce batteries with excellent electrochemical performance, high reaction rate, and high stability. Comparative Example 1, lacking a connecting structure, has high permeability but unstable structure, leading to electrode deformation, increased polarization, and poor cycle stability over long-term operation. Comparative Example 2, with its uniformly wide connecting structure, exhibits relatively uneven flow field distribution and significant local concentration polarization. Comparative Example 3, with its straight-groove flow channel, shows the worst mass transfer effect and relatively large concentration polarization. Comparative Example 4 suffers from poor reverse gradient flow field distribution; the wide connecting structure at the inlet hinders the initial distribution of the electrolyte, resulting in lower efficiency than the forward gradient. Example 3, using carbon cloth as the substrate and acid-treated for the carbon-based catalyst layer, exhibits high battery performance. Example 4, using carbon paper as the substrate and employing heat treatment and Bi-based catalyst loading, further improves the battery's voltage efficiency. Since the Bi-based catalyst can enhance the electrochemical activity of vanadium ions at the negative electrode while inhibiting hydrogen evolution, the battery also demonstrates good cycle stability. Control group 1 exhibited poor mass transfer, a small active area, and the worst overall performance, with the fastest degradation. Control group 2 was incorrectly assembled, with the carbon felt piercing the separator, leading to a short circuit, catalytic layer interface failure, a sharp reduction in reaction area, and the failure of the flow channel function, resulting in deteriorated mass transfer. Therefore, the composite electrode with built-in connecting flow channels, which can be prepared using the raw materials and methods described in this application, can simultaneously provide efficient electrolyte transport channels and abundant reactive sites, while protecting the separator. When assembled into a flow battery using a specific assembly method, it can effectively improve the energy conversion efficiency and cycle stability of the flow battery.

[0139] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a composite electrode with a built-in connecting groove, characterized in that, Includes the following steps: S1. A flow guide groove is engraved on the carbon felt substrate using a carving machine to obtain a carbon felt electrode with a connecting finger-shaped flow guide groove. S2. Preparation of a highly active carbon-based catalytic layer; S3. Combine the interlocking finger-shaped flow guide groove carbon felt electrode with a high-activity carbon-based catalyst layer to obtain a composite electrode with an internal interlocking flow guide groove. The carbon felt matrix is ​​a polyacrylonitrile-based carbon felt with a thickness of 2.5 mm, a porosity of 90%, a fiber diameter of approximately 10 μm, and an average pore size of approximately 80 μm. The width of the connecting flap in the flow channel is 2mm to 15mm, and the width of the connecting flap changes from small to large along the direction of electrolyte flow.

2. The method for preparing the composite electrode with built-in connecting groove according to claim 1, characterized in that, The width of the connecting flap in the flow channel is 4mm~6mm, 7mm~9mm, 10mm~12mm, and 13mm~15mm respectively along the electrolyte flow direction.

3. The method for preparing the composite electrode with built-in connecting groove according to claim 1, characterized in that, The width of the guide groove is 1mm to 6mm, and the width of the carbon felt electrode between the two rows of guide grooves is 15mm to 30mm.

4. The method for preparing the composite electrode with built-in connecting groove according to claim 1, characterized in that, The highly active carbon-based catalytic layer is obtained by activating a thin carbon layer material consisting only of planar fibers.

5. The method for preparing the composite electrode with built-in connecting groove according to claim 4, characterized in that, The thin carbon layer material includes, but is not limited to, one or more of the following: carbon paper, carbon cloth, carbon felt, carbon nanofiber membrane, and graphene paper with a planar structure.

6. The method for preparing the composite electrode with built-in connecting groove according to claim 5, characterized in that, The thin carbon layer material is a functionalized polyacrylonitrile-based carbon nanofiber membrane, and the preparation method of the functionalized polyacrylonitrile-based carbon nanofiber membrane includes the following steps: A1. Spinning; A2. Pre-oxidation treatment; A3. Carbonization treatment to obtain functionalized polyacrylonitrile-based carbon nanofiber membrane; The specific preparation method of step A1 is as follows: PAN is dissolved in DMF to prepare an electrospinning precursor spinning solution, functional components are added to it, electrospinning is performed and the fibers are collected on the surface of aluminum foil to obtain the product. The relative molecular mass of the PAN is 90,000 to 150,000; The mass fraction of PAN in the spinning solution is 15%~20%; The amount of the functional component added is 0.01% to 10% of the mass of the spinning solution; The functional components include one or more of graphene oxide, carbon nanotubes, and bismuth salts. The specific steps of the electrospinning are as follows: the spinning solution is delivered into a syringe containing a stainless steel needle, electrospinning is performed using high voltage, and the solution is wound using a high-speed rotating roller to obtain the desired product. The electrospinning voltage is 15~20kV, and the take-up distance is 10cm~20cm; The rotational speed of the roller winding is 100~200 r / min; The temperature of the electrospinning chamber is 20℃~50℃; The temperature inside the electrospinning chamber is 30~40℃, and the humidity is 40~50%RH%. The functionalized polyacrylonitrile-based carbon nanofiber membrane has a diameter of 100 nm to 2 μm and a fiber layer thickness of 0.1 mm to 1.5 mm. In step A2, the specific conditions for the pre-oxidation treatment are: the atmosphere is air, the temperature is increased to 250~320℃ at a rate of 1~5℃ / min, and the temperature is maintained for 0.5h~4h; In step A3, the specific conditions for carbonization are as follows: the atmosphere is nitrogen, the temperature is increased to 900-1200℃ at a rate of 5-10℃ / min, and the temperature is maintained for 1-3 hours.

7. The method for preparing the composite electrode with built-in connecting groove according to claim 6, characterized in that, The activation process includes, but is not limited to, one or more of the following: heat treatment, acid treatment, plasma treatment, and catalyst loading. The specific conditions for the heat treatment are as follows: the atmosphere is air, the temperature is increased to 400-700℃ at a rate of 3-7℃ / min, the temperature is held for 30min-2h, and then cooled to room temperature in the furnace. The specific steps of the acid treatment are as follows: add the thin carbon layer material to a nitric acid solution, treat it at 75~85℃ and 250-350r / min for 2~4h, take it out and wash the carbon cloth repeatedly with deionized water until the filtrate is neutral, and then vacuum dry it. The volume fraction of the nitric acid solution is 60%~68%; The solid-liquid ratio of the thin carbon layer material to the nitric acid solution is 1 g: (20~50) mL; The specific conditions for vacuum drying are: temperature 55~65℃, vacuum degree 0.08~0.09MPa, and time 10~15h; The specific steps for catalyst loading are as follows: fully immerse the thin carbon layer material in the catalyst solution, remove it, wash it twice with ethanol, and dry it. The catalyst solution is prepared by mixing the catalyst with a solvent. The solid-liquid ratio of the catalyst and solvent is 1g:(15~25)mL; The catalyst is a metal-based nanoparticle catalyst such as Bi, Ti, Sb, Pb, Mn, Nb or a carbon nanomaterial catalyst such as graphene oxide or carbon nanotubes. The solvent is a 50% (v / v) aqueous solution of ethanol; The soaking time is 30 minutes to 2 hours; The catalyst loading is 0.1%-20% of the total mass of the thin carbon layer material; The specific drying conditions are: temperature 55~65℃, vacuum degree 0.08~0.09MPa, and time 3~5h; In step S3, the composite process includes, but is not limited to, one or more of hot pressing, bonding, and lamination. The specific conditions for hot pressing are: temperature 150~200℃, pressure 3~5MPa, and holding time 5~10min; The bonding process requires the use of an adhesive, including but not limited to polytetrafluoroethylene and phenolic resin. The adhesive is applied to the surface of the carbon felt electrode and then laminated.

8. The composite electrode with built-in connecting groove prepared by the method of preparing the composite electrode with built-in connecting groove according to any one of claims 1 to 7.

9. The application of the composite electrode with built-in connecting groove as described in claim 8 in a flow battery.

10. The application of the composite electrode with built-in connecting groove in a flow battery according to claim 9, characterized in that, When assembling a flow battery, the highly active carbon-based catalyst layer of the composite electrode with built-in connecting grooves contacts the membrane, and the connecting finger-shaped carbon felt electrode contacts the bipolar plate.

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