Composite electrode with built-in collar flow guide, method of making and use in flow battery

Abstract

The application belongs to the technical field of liquid flow battery, and particularly relates to a composite electrode with built-in connecting-collar flow guide groove, a preparation method and application in a liquid flow battery. Firstly, a pin-type flow guide groove carbon felt electrode with connecting collars is designed, then a high-activity carbon-based catalytic layer with high electrochemical active area is prepared, and finally the composite electrode with built-in connecting-collar flow guide groove is obtained. The prepared composite electrode is applied to the liquid flow battery, the carbon-based catalytic layer is in contact with the diaphragm, the high-activity area is provided while the diaphragm is prevented from being damaged; the pin-type flow guide groove carbon felt electrode with connecting collars is in contact with the bipolar plate, the carbon felt electrode serves as a reaction site while effective mass transfer is ensured. The composite electrode structure design can provide efficient electrolyte transmission channels and abundant reaction active sites at the same time, and can protect the diaphragm, effectively improving the energy conversion efficiency and cycle stability of the liquid flow battery. The preparation process is simple in operation, low in cost, suitable for large-scale production, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of flow battery, and particularly relates to a composite electrode with built-in connecting guide grooves, a preparation method and application in a flow battery. BACKGROUND

[0002] A flow battery is a large-scale energy storage device, and its core principle is to realize the storage and release of electric energy through the redox reaction of active substances (such as vanadium ions, electroactive organic matter, iron ions, etc.) in electrolyte. The electrode, as a key component of the flow battery, needs to meet the following requirements:

[0003] (1) High reaction activity area to improve the reaction rate;

[0004] (2) Uniform electrolyte mass transfer distribution to reduce concentration polarization;

[0005] (3) Good corrosion resistance and long service life;

[0006] (4) Interface stability with the diaphragm to avoid electrolyte cross-contamination caused by electrode fiber piercing the diaphragm.

[0007] Traditional flow battery electrodes mostly use carbon felt or porous carbon cloth as the substrate, which provides a basis for the electrochemical redox reaction of active substances due to its high porosity and conductivity. However, as the flow battery develops towards high power density and long service life, the traditional carbon felt electrode gradually exposes the following problems:

[0008] (1) Insufficient mass transfer efficiency: the internal pores of carbon felt are disordered, and the flow of electrolyte in it is prone to form local stagnant zones, leading to uneven transport of reactants and "concentration polarization" under high current density; although carving flow channels on the graphite bipolar plate can alleviate the electrolyte mass transfer problem to some extent, the negative effects of increased processing cost, increased contact resistance and decreased mechanical strength are difficult to solve;

[0009] (2) Limited reaction area: the physical specific surface area of carbon felt is only 0.5~5m 2 / g, and the real active area for electrochemical reaction is much lower than its physical specific surface area; the low active area leads to large electrochemical polarization and ohmic polarization, affecting the energy conversion efficiency and power density of the battery; loading catalyst materials on the surface of carbon felt is the most common method to improve the activity of the electrode, but the interface bonding force between the catalyst and the carbon fiber is poor, which is easy to fall off under the continuous erosion of the electrolyte, causing local blockage of the battery pipeline, pollution of the electrolyte, etc.

[0010] (3) Diaphragm puncture risk: There are fibers in the carbon felt in the plane (x-y) direction and the vertical (z) direction, and the vertical fibers that are not completely covered are easy to penetrate the electrode and contact the diaphragm, and under the pressure of the battery operation or the electrolyte flushing, the diaphragm is punctured, the positive and negative electrolyte cross leakage is accelerated, and the battery life is greatly shortened.

[0011] Therefore, there is an urgent need for a new type of flow battery composite electrode material that takes into account mass transfer optimization, active reaction area and diaphragm protection. SUMMARY

[0012] The purpose of the present application is to provide a composite electrode with built-in continuous collar flow guide grooves, a preparation method and application in a flow battery. The prepared composite electrode is applied in a flow battery, which can take into account mass transfer optimization, active reaction area and diaphragm protection.

[0013] In order to achieve the above purpose, the present application provides the following technical scheme:

[0014] A preparation method of a composite electrode with built-in continuous collar flow guide grooves, comprising the following steps:

[0015] S1, using a carving machine to carve flow guide grooves on the carbon felt substrate to obtain a continuous collar interdigital flow guide groove carbon felt electrode;

[0016] S2, preparing a high-activity carbon-based catalytic layer;

[0017] S3, compounding the continuous collar interdigital flow guide groove carbon felt electrode and the high-activity carbon-based catalytic layer to obtain a composite electrode with built-in continuous collar flow guide grooves.

[0018] Preferably, the carbon felt substrate is polyacrylonitrile-based carbon felt, the thickness is 2.5mm, the porosity is 90%, the fiber diameter is about 10um, and the average pore size is about 80um.

[0019] Preferably, the width of the continuous collar in the flow guide groove is 2mm-15mm, and the width of the continuous collar changes from small to large along the electrolyte flow direction.

[0020] In some preferred embodiments, the width of the continuous collar in the flow guide groove is 4mm-6mm, 7mm-9mm, 10mm-12mm, and 13mm-15mm along the electrolyte flow direction.

[0021] Preferably, the width of the flow guide groove is 1mm-6mm, and the width of the carbon felt electrode between the two rows of flow guide grooves is 15mm-30mm.

[0022] By designing the width of the connecting collar in the flow guide groove, the permeability of the carbon felt electrode can be significantly improved, and the electrochemical performance and performance stability of the prepared flow battery can be improved. This is because the width of the connecting collar is changed from small to large along the flow direction of the electrolyte, which can form a trapezoidal support frame. It not only maintains the structural stability of the carved carbon felt, but also facilitates the assembly of the battery stack, avoids uneven mass transfer caused by carbon felt collapse, guides the directional flow of electrolyte, reduces local retention area, and improves mass transfer efficiency, thereby significantly reducing concentration polarization. High permeability reduces electrolyte transmission resistance, thereby improving active material utilization, and thus improving the coulomb efficiency of the battery and reducing the cycle decay.

[0023] By directly carving the flow guide groove in the carbon felt, the manufacturing cost, electrical conductivity and performance stability of the conventional flow channel bipolar plate are solved, and the mass transfer and charge transfer efficiency is significantly improved. This is because the built-in flow guide groove shortens the electrolyte transmission path from two sections of bipolar plate flow channel → carbon felt pore to one section of carbon felt flow channel → carbon felt pore. Compared with grooving on the bipolar plate, the contact resistance is reduced, and the mass transfer dead zone caused by the edge burr of the bipolar plate flow channel is avoided; At the same time, the carbon felt flow channel as the main transmission channel improves the effective utilization rate of electrolyte, and the increase of charge transfer efficiency drives the increase of voltage efficiency, so the power density is improved, and the bipolar plate does not need to be grooved, so the cost is greatly reduced.

[0024] Preferably, the high-activity carbon-based catalytic layer is obtained by activating a thin carbon layer material composed of only planar fibers.

[0025] 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.

[0026] Preferably, the thin carbon layer material is a transverse structure, that is, the orientation of the fibers or sheets in the material is in the x-y plane direction, and there is no vertical direction.

[0027] Preferably, the thickness of the thin carbon layer material is 0.1mm-1.5mm.

[0028] In some preferred embodiments, the thin carbon layer material can be self-made or purchased.

[0029] In some preferred embodiments, the thin carbon layer material can be polyacrylonitrile-based carbon paper with a thickness of 0.3mm, from Liaoning Jingu Carbon Material Co., Ltd.

[0030] In some preferred embodiments, the thin carbon layer material can be a self-made functionalized polyacrylonitrile-based carbon nanofiber membrane. The preparation method of the functionalized polyacrylonitrile-based carbon nanofiber membrane includes the following steps:

[0031] A1, spinning;

[0032] A2, pre-oxidation treatment;

[0033] A3, carbonization treatment, to obtain a functionalized polyacrylonitrile-based carbon nanofiber membrane.

[0034] Preferably, the specific preparation method of step A1 is to dissolve polyacrylonitrile (PAN) in N,N-dimethylformamide (DMF) to prepare an electrospinning precursor spinning solution, add a functional component to it, and perform electrospinning and collect the fibers on the surface of an aluminum foil.

[0035] Preferably, the relative molecular mass of the PAN is 90000-150000

[0036] Preferably, the mass fraction of PAN in the spinning solution is 15%-20%.

[0037] Preferably, the addition amount of the functional component is 0.01%-10% of the mass of the spinning solution.

[0038] Preferably, the functional component includes but is not limited to one or more of graphene oxide (GO), carbon nanotubes, and bismuth salts.

[0039] Preferably, the specific steps of electrospinning are to deliver the spinning solution into a syringe loaded with a stainless steel needle, perform electrospinning using high voltage, and use a high-speed rotating drum to wind, to obtain the functionalized polyacrylonitrile-based carbon nanofiber membrane.

[0040] Preferably, the voltage of the electrospinning is 15-20 kV, and the fiber collection distance is 10 cm-20 cm.

[0041] Preferably, the rotating speed of the drum winding is 100-200 r / min.

[0042] Preferably, the temperature in the inner cabin of the electrospinning is 20℃-50℃.

[0043] Preferably, the temperature in the electrospinning cabin is 30-40℃, and the humidity is 40-50 RH%.

[0044] Preferably, the diameter of the functionalized polyacrylonitrile-based carbon nanofiber membrane is 100 nm-2 μm, and the fiber layer thickness is 0.1 mm-1.5 mm.

[0045] Preferably, in step A2, the specific conditions of the pre-oxidation treatment are: the atmosphere is air, the temperature is raised to 250-320℃ at a rate of 1-5℃ / min, and the temperature is maintained for 0.5 h-4 h.

[0046] Preferably, in step A3, the specific conditions of the carbonization treatment are: the atmosphere is nitrogen, the temperature is raised to 900-1200℃ at a rate of 5-10℃ / min, and the temperature is maintained for 1-3 h.

[0047] By preparing PAN-based carbon nanofiber catalytic layer with full x-y plane orientation of fibers and no vertical direction, the electrochemical active area of the catalytic layer can be improved, while the breakage rate of the battery separator and the energy efficiency decay rate are reduced. 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, avoiding the puncture of the separator caused by the vertical fibers under the electrolyte flushing; at the same time, the high electrochemical active area and the introduced electrocatalytic nanomaterials can provide abundant electrochemical reaction sites, greatly improve the electrochemical reaction rate, reduce the polarization increase and energy efficiency decay caused by insufficient reaction activity, improve the power density of the battery, and prolong the cycle life of the battery.

[0048] Preferably, the activation process includes but is not limited to one or more of heat treatment, acid treatment, plasma treatment, and catalyst loading.

[0049] In some preferred embodiments, the activation process can be a combination of two or more processes, which can be acid treatment or heat treatment first, and then catalyst loading.

[0050] Preferably, the specific conditions of the heat treatment are: the atmosphere is air, the temperature is increased to 400-700℃ at a rate of 3-7℃ / min, the temperature is kept for 30min-2h, and the furnace is cooled to room temperature.

[0051] Preferably, the specific steps of the acid treatment are: the thin carbon layer material is added to a nitric acid solution, treated at 75-85℃ and 250-350r / min for 2-4h, taken out, washed with deionized water repeatedly until the filtrate is neutral, and vacuum dried.

[0052] Preferably, the volume fraction of the nitric acid solution is 60%-68%.

[0053] Preferably, the solid-liquid ratio of the thin carbon layer material and the nitric acid solution is 1g:(20-50)mL.

[0054] Preferably, the specific conditions of the vacuum drying are: the temperature is 55-65℃, the vacuum degree is 0.08-0.09MPa, and the time is 10-15h.

[0055] Preferably, the specific steps of the catalyst loading are: the thin carbon layer material is fully immersed in a catalyst solution, taken out, washed with ethanol for 2 times, and dried.

[0056] Preferably, the preparation method of the catalyst solution is: the catalyst is mixed with a solvent, and the catalyst solution is obtained.

[0057] Preferably, the solid-liquid ratio of the catalyst and the solvent is 1g:(15-25)mL.

[0058] Preferably, the catalyst is a metal-based nanoparticle or carbon nanomaterial catalyst such as graphene oxide, carbon nanotube, etc.

[0059] Preferably, the solvent is an ethanol aqueous solution with a volume fraction of 50%.

[0060] Preferably, the impregnation time is 30 min to 2 h.

[0061] Preferably, the loading amount of the catalyst is 0.1% to 20% of the total mass of the thin carbon layer material.

[0062] Preferably, the drying is performed at a temperature of 55 to 65 DEG C, a vacuum degree of 0.08 to 0.09 MPa, and for a time of 3 to 5 h.

[0063] Preferably, in the step S3, the compounding process includes, but is not limited to, one or more of hot pressing, bonding, and lamination.

[0064] Preferably, the hot pressing is performed at a temperature of 150 to 200 DEG C, a pressure of 3 to 5 MPa, and for a pressure maintaining time of 5 to 10 min.

[0065] Preferably, the bonding needs to use a bonding agent, including but not limited to any one of polytetrafluoroethylene and phenolic resin, and the carbon felt electrode is compounded and pressed after the bonding agent is coated on the surface of the carbon felt electrode.

[0066] By sequentially performing heat treatment, acid treatment, and / or catalyst loading on the thin carbon layer material, the electrochemical active area of the catalyst layer is improved, thereby greatly improving the electrochemical performance of the battery. Because the heat treatment can effectively improve the surface affinity of the carbon fiber, providing a uniform substrate for further activation; being conducive to electrolyte infiltration; the nitric acid etching forms nano grooves on the surface of the carbon-based catalyst layer, improving the specific surface area and introducing active functional groups such as carboxyl groups, not only improving the hydrophilicity and electrochemical activity, but also serving as an anchoring site for the subsequent catalyst nanoparticles, making the catalyst more uniformly dispersed and firmly combined, the carboxyl group forms a strong coordination bond with the metal catalyst, reducing the shedding rate, improving the high electrochemical activity and stability of the catalyst layer, significantly reducing the polarization overpotential, improving the voltage efficiency, and thereby improving the electrochemical performance and stability of the prepared battery.

[0067] The second aspect of the present application provides a composite electrode with built-in continuous collar guide grooves prepared by the preparation method of the composite electrode with built-in continuous collar guide grooves.

[0068] The third aspect of the present application provides the application of the composite electrode with built-in continuous collar guide grooves in a flow battery, wherein, when the flow battery is assembled, the high-activity carbon-based catalyst layer of the composite electrode with built-in continuous collar guide grooves is in contact with the separator, and the carbon felt electrode with the continuous collar interdigital guide groove is in contact with the bipolar plate.

[0069] By designing the function partition of the flow channel carbon felt and the transverse carbon-based catalytic layer (the carbon felt electrode is in contact with the bipolar plate, and the carbon-based catalytic layer is in contact with the separator), the structural adaptability of the composite electrode and the flow battery prepared can be improved, thereby improving the battery performance. This may be because the carbon felt side focuses on electrolyte transmission, and the catalytic layer side focuses on electrochemical reaction, the function partition avoids the mutual interference of mass transfer and reaction, and the composition and structure of the catalytic layer can be adjusted according to the type of the flow battery, and the overall thickness of the electrode is controllable, which is suitable for the assembly of high-power-density flow battery stacks.

[0070] Preferably, the flow battery includes but is not limited to any one of a full-vanadium flow battery, an iron-chromium flow battery, a water-based organic flow battery, a zinc-bromine flow battery, and a full-iron flow battery.

[0071] Preferably, the bipolar plate used in the flow battery does not contain a flow channel.

[0072] The overall structural diagram of the flow battery assembled by the composite electrode prepared by the present application is shown in Figure 1 .

[0073] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0074] 1. The present application provides a composite electrode with built-in continuous ridge flow channels. First, a carbon felt electrode with continuous ridge flow channels is designed, then a high-activity carbon-based catalytic layer with high electrochemical activity area is prepared, and finally a composite electrode with built-in continuous ridge flow channels is obtained by compounding. The composite electrode applied in the flow battery can provide efficient electrolyte transmission channels and abundant reaction active sites at the same time, and can also protect the separator, effectively improving the energy conversion efficiency and cycle stability of the flow battery. The preparation process of the present application is simple, low in cost, suitable for large-scale production, and has wide application prospect.

[0075] 2. The present application provides a composite carbon-based porous electrode material to overcome the shortcomings of the existing carbon felt electrode of the flow battery. By carving a continuous ridge flow channel in the carbon felt, the electrolyte mass transfer is optimized while the overall structure of the carbon felt electrode is maintained, and a high-activity transverse carbon-based catalytic layer is introduced on the side close to the separator. On the one hand, the reaction area lost due to the carving of the flow channel is compensated, and on the other hand, the transversely oriented carbon-based carrier protects the separator, ultimately improving the energy efficiency, power density and cycle life of the flow battery.

[0076] 3.The invention designs to carve to obtain the carbon felt electrode material with the inter-finger flow channel structure, the carbon felt built-in flow guide groove guides the electrolyte to flow along the groove, reduces the local retention area; the inter-finger structure helps to maintain the overall structure of the carbon felt, is convenient for assembling, and effectively solves the problem that the carbon felt electrode structure is loose and difficult to assemble caused by carving the flow guide groove on the carbon felt; the flow channel structure can provide a channel for electrolyte transmission, and solve the processing cost and stability problem of the bipolar plate with flow channel.

[0077] 4.The invention can significantly improve the permeability of the carbon felt electrode and the electrochemical performance and performance stability of the prepared liquid flow battery by designing the width of the inter-finger of the flow guide groove.

[0078] 5.The invention solves the problems of manufacturing cost, electrical conductivity and performance stability of the conventional flow channel bipolar plate by directly carving the flow guide groove in the carbon felt, and the mass transfer and charge transfer efficiency is significantly improved.

[0079] 6.The invention forms a macroscopic flow channel-microscopic pore double-scale mass transfer network by selecting a specific carbon felt matrix and designing a corresponding inter-finger flow channel, so that the flow guide groove carbon felt can maintain high permeability under high compression rate and improve the energy efficiency of the battery.

[0080] 7.The invention can effectively compensate for the loss of carbon felt fibers caused by carving the flow guide groove by designing a fiber full-x-y plane orientation, a horizontal carbon-based catalytic layer without vertical orientation, and contacting the separator, thereby improving the reaction area and electrocatalytic activity of the electrode; at the same time, the horizontal orientation of the carbon-based catalytic layer separator has outstanding protection effect, can tightly cover the vertical fibers in the carbon felt matrix, can effectively reduce the damage rate of the separator, and the service life of the battery is significantly prolonged.

[0081] 8.The invention has strong structure adaptability, the flow guide groove carbon felt and the horizontal carbon-based catalytic layer are designed as functional partitions (the carbon felt electrode contacts the bipolar plate, and the carbon-based catalytic layer contacts the separator), which avoids mutual interference, can adjust the composition and structure of the catalytic layer according to the type of the liquid flow battery, the overall thickness of the electrode is controllable, and is suitable for the assembly of high-power-density liquid flow battery stacks. BRIEF DESCRIPTION OF DRAWINGS

[0082] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description.

[0083] Figure 1 The overall structure diagram of the liquid flow battery assembled by the composite electrode with built-in inter-finger flow guide groove prepared by the present invention;

[0084] Figure 2 The plane schematic diagram of the inter-finger flow guide groove carbon felt electrode prepared by the embodiment 1 of the present invention;

[0085] Figure 3 The scanning electron microscope images of the high-activity carbon-based catalytic layer prepared in the application are shown in the following figures. Figure 3 (a) is prepared in Example 1, Figure 3 (b) is prepared in Example 3, Figure 3 (c) is prepared in Example 4. DETAILED DESCRIPTION

[0086] The technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0087] The raw materials used in the application are commercially available, and specifically:

[0088] The carbon felt matrix is a polyacrylonitrile-based carbon fiber 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, and is from Liaoning Jingu Carbon Material Co., Ltd.

[0089] The relative molecular mass of PAN is 85000, and is from Shanghai Maikelin Biochemical Technology Co., Ltd.

[0090] Graphene oxide is from Pioneer Nanometer.

[0091] Example 1

[0092] The embodiment provides a composite electrode with built-in continuous collar flow guide grooves, a preparation method thereof, and steps are as follows:

[0093] S1, a carving machine is used to carve flow guide grooves on the carbon felt matrix to obtain a finger-shaped flow guide groove carbon felt electrode with continuous collars;

[0094] S2, a high-activity carbon-based catalytic layer is prepared;

[0095] S3, the finger-shaped flow guide groove carbon felt electrode with continuous collars and the high-activity carbon-based catalytic layer are compounded, and a composite electrode with built-in continuous collar flow guide grooves is obtained.

[0096] The widths of the continuous collars in the flow guide grooves are 5 mm, 8 mm, 11 mm and 14 mm in sequence along the electrolyte flow direction.

[0097] The width of the flow guide groove is 4.07 mm, and the width of the carbon felt electrode between the two rows of flow guide grooves is 25 mm.

[0098] The plan view of the finger-shaped flow guide groove carbon felt electrode with continuous collars is shown in Figure 2 .

[0099] The high-activity carbon-based catalytic layer is obtained by activating a thin carbon layer material.

[0100] The thin carbon layer material is a functionalized polyacrylonitrile-based carbon nanofiber film, and the preparation method of the functionalized polyacrylonitrile-based carbon nanofiber film comprises the following steps:

[0101] A1, spinning;

[0102] A2, pre-oxidation treatment;

[0103] A3, carbonization treatment, to obtain a polyacrylonitrile-based carbon fiber catalytic layer electrode.

[0104] The specific preparation method of step A1 is to dissolve PAN in DMF to prepare an electrospinning precursor spinning solution, add a functional component to the spinning solution, perform electrospinning, and collect the fibers on the surface of an aluminum foil to obtain the functionalized polyacrylonitrile-based carbon nanofiber film.

[0105] The mass fraction of PAN in the spinning solution is 14%.

[0106] The functional component in the spinning solution is graphene oxide.

[0107] The addition amount of the functional component is 0.5% of the mass of the spinning solution.

[0108] The specific steps of electrospinning are as follows: the spinning solution is delivered to a syringe loaded with a stainless steel needle, electrospinning is performed using high voltage, and a high-speed rotating drum is used for winding, to obtain the functionalized polyacrylonitrile-based carbon nanofiber film.

[0109] The electrospinning voltage is set to 20kV, and the fiber collection distance is 15cm.

[0110] The temperature in the electrospinning cabin is 35℃, and the humidity is 45RH%.

[0111] The rotating speed of the drum winding is 150r / min.

[0112] The thickness of the functionalized polyacrylonitrile-based carbon nanofiber film is 0.2mm, and the fiber diameter is about 200nm.

[0113] In step A2, the specific conditions of the pre-oxidation treatment are as follows: the atmosphere is air, the temperature is raised to 280℃ at a rate of 3℃ / min, and the temperature is maintained for 1h.

[0114] In step A3, the specific conditions of the carbonization treatment are as follows: the atmosphere is nitrogen, the temperature is raised to 1000℃ at a rate of 8℃ / min, and the temperature is maintained for 1.5h.

[0115] The activation treatment process is heat treatment.

[0116] The specific conditions of the heat treatment are as follows: the atmosphere is air, the temperature is raised to 550℃ at a rate of 5℃ / min, the temperature is maintained for 1h, and the temperature is cooled to room temperature with the furnace.

[0117] In the step S3, the composite process is hot pressing.

[0118] The specific conditions of the hot pressing are: temperature is 180℃, pressure is 4MPa, and pressure maintaining time is 8min.

[0119] Example 2

[0120] The difference between this example and Example 1 is only that the widths of the continuous grooves in the flow guide groove are 6mm, 9mm, 12mm, and 15mm in sequence along the electrolyte flow direction.

[0121] Example 3

[0122] The difference between this example and Example 1 is only that the thin carbon layer material is polyacrylonitrile-based carbon cloth with a thickness of 0.3mm from Liaoning Jingu Carbon Material Co., Ltd.

[0123] The activation treatment process is acid treatment.

[0124] The specific steps of the acid treatment are: adding the carbon cloth into a nitric acid solution, treating at 80℃ and 300r / min for 3h, taking out, repeatedly washing the carbon cloth with deionized water until the filtrate is neutral, and vacuum drying.

[0125] The volume fraction of the nitric acid solution is 65%.

[0126] The solid-liquid ratio of the carbon cloth and the nitric acid solution is 1g:35mL.

[0127] The specific conditions of the vacuum drying are: temperature is 60℃, vacuum degree is 0.085MPa, and time is 12h.

[0128] Example 4

[0129] The difference between this example and Example 1 is only that the thin carbon layer material is polyacrylonitrile-based carbon paper with a thickness of 0.3mm from Liaoning Jingu Carbon Material Co., Ltd.

[0130] The activation treatment process is: first performing heat treatment, and then performing catalyst loading.

[0131] The specific conditions of the heat treatment are: under nitrogen atmosphere, increasing the temperature to 900℃ at a rate of 5℃ / min, passing in CO2, maintaining for 40min, then changing to pass in nitrogen, and cooling to room temperature with the furnace.

[0132] The specific steps of the catalyst loading are: fully immersing the heat-treated thin carbon layer material into a catalyst solution, taking out, washing with ethanol for 2 times, and drying.

[0133] The preparation method of the catalyst solution is: mixing the catalyst with a solvent, and obtaining.

[0134] The solid-liquid ratio of the catalyst and solvent is 1 g:20 mL.

[0135] The catalyst is Bi nanoparticle.

[0136] The solvent is 50% ethanol aqueous solution.

[0137] The impregnation time is 1 h.

[0138] The loading of Bi in the catalyst is 1.7% of the mass of carbon cloth.

[0139] The specific conditions of drying are: temperature is 60℃, vacuum degree is 0.085 MPa, and time is 4 h.

[0140] Comparative Example 1

[0141] The difference between this comparative example and Example 1 is only that the carbon felt electrode does not have the connecting collar, and only has the flow guide groove with a width of 4.07 mm, and the width of the carbon felt electrode between the two rows of flow guide grooves is 25 mm.

[0142] Comparative Example 2

[0143] The difference between this comparative example and Example 1 is only that the width of the connecting collar in the flow guide groove is uniform, and is 8 mm.

[0144] Comparative Example 3

[0145] The difference between this comparative example and Example 1 is only that the flow channel of the carbon felt electrode is a straight groove type, and the width is 4.07 mm, and the width of the carbon felt electrode between the two rows of straight groove types is 25 mm.

[0146] Comparative Example 4

[0147] The difference between this comparative example and Example 1 is only that the width of the connecting collar in the flow guide groove is 14 mm, 11 mm, 8 mm, and 5 mm in sequence along the flow direction of the electrolyte.

[0148] Performance Test

[0149] (1) Carbon felt electrode performance test

[0150] The permeability of the carbon felt without flow guide groove and the carbon felt with the interlinked interdigitated flow guide groove prepared in Example 1 were tested by using the FR-SI flow resistance instrument (permeability). 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 cut-off rotation speed was 1000 r / min; and the increasing rotation speed was 10 r / min. μ represents the liquid viscosity coefficient required when calculating the Darcy value, which was set to 0.00298 Pa.s during the test; L represents the sample size, which was set to 10 cm, with the length and width being equal; A represents the sample cross-sectional area, which was set to 4 cm 2 ; and the sample compression rate represents the sample compression rate during the test, which was set to 10%~70%. The formula was used for calculation: .

[0151] wherein, K represents the permeability, μm 2 (square microns); and the test results are shown in Table 1.

[0152] Table 1: Permeability test results under different compression rates

[0153]

[0154] As can be seen from Table 1, the carbon felt with the flow guide groove shows more excellent permeability, indicating that the transmission resistance of the electrolyte in the electrode is smaller, which helps to improve the mass transfer performance of the electrode, reduce the pump consumption, and improve the system efficiency.

[0155] The permeability of the carbon felt electrodes of Example 1-2 and Comparative Example 1-4 was tested under a fixed compression rate of 50%, and the results are shown in Table 2.

[0156] Table 2: Permeability test results of carbon felt electrodes

[0157]

[0158] As can be seen from Table 2, the permeability of Example 1 and Example 2 is higher, which provides excellent mass transfer channels while maintaining the structure. Comparative Example 1 has no interlinked structure, and the flow channel is completely through, so the fluid flow resistance is the smallest, and thus the permeability is the highest, but this sacrifices the mechanical strength and may affect the battery performance; Comparative Example 2 has equal-width interlinks, which destroys the gradient distribution of the flow field, easily produces flow dead zones and vortexes, increases the flow resistance, and thus reduces the permeability; Comparative Example 3 has a straight groove type flow channel, which has a long flow channel and no flow field disturbance caused by the interlinks, so the electrolyte is easy to short circuit and difficult to effectively force the electrolyte to penetrate into the carbon felt, thus the mass transfer effect is poor; Comparative Example 4 has an inverse gradient interlink, in which the interlink at the electrolyte inflow end is wide, and the interlink at the electrolyte outflow end is narrow, which is not conducive to the uniform distribution and smooth discharge of the electrolyte, and the flow resistance is greater than that of the positive gradient, so the permeability is lower.

[0159] (2) Carbon-based catalytic layer performance

[0160] With 2M sulfuric acid as electrolyte, carbon felt matrix and carbon-based catalytic layer prepared in Example 1 and Example 3-4 as working electrode respectively, saturated calomel electrode as reference electrode, platinum plate as counter electrode, cyclic voltammograms at different scan rates were tested under the voltage window of-0.1V~+0.1V (vs. SCE), and the electrochemical active area ECSA of the two groups of electrode materials was calculated by the following formula, and the results are shown in Table 3.

[0161]

[0162] Wherein: I, current density (mA·cm -2 ); v, scan rate (mV·s -1 ); Cs, specific capacitance, 0.035 mF·cm -2 ; A, electrode geometric area (m 2 ); m, electrode mass (g).

[0163] Table 3 Test results of electrochemical active area of carbon-based catalytic layer

[0164]

[0165] As can be seen from Table 3, the electrochemical active area of the carbon nanofiber catalytic layer prepared in Example 1 is high, and because the fiber diameter is nanoscale, it shows a large active specific surface area which is helpful for the electrochemical reaction process and reduces the polarization overpotential, which helps to improve the performance of the battery. Example 3 is a carbon cloth matrix only treated with acid, which can improve the specific surface area and functional groups of the electrode to some extent and improve the electrochemical active area of the electrode; the matrix of Example 4 is carbon paper, which is first heat treated to improve the surface hydrophilicity, and then loaded with Bi-based nanoparticles on the surface to improve the surface roughness of the electrode, which is beneficial to improve the electrochemical active area of the electrode.

[0166] The scanning electron microscope images of the high-activity carbon-based catalytic layer prepared in Example 1 and Example 3-4 are shown in Figure 3 .

[0167] 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 amount 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 by x-y-plane fibers in order; from Figure 3 (c) it can be seen that there are also planar curved carbon fibers in the carbon paper.

[0168] (3) Battery performance test

[0169] The integrated composite electrodes prepared in Example 1-Example 4 and Comparative Example 1-Comparative Example 4 were used to assemble full vanadium flow batteries as positive and negative electrode materials, wherein, when assembling the flow battery, the high-activity carbon-based catalytic layer of the composite electrode with the built-in connecting ridge flow channel was in contact with the separator, and the carbon felt electrode with the connecting ridge interdigital flow channel was in contact with the bipolar plate. The carbon felt matrix (polyacrylonitrile-based carbon fiber felt) was used as a control group 1 to assemble the battery, and the composite electrode prepared in Example 1 was used, the high-activity carbon-based catalytic layer of the composite electrode with the built-in connecting ridge flow channel was in contact with the bipolar plate, and the carbon felt electrode with the connecting ridge interdigital flow channel was in contact with the separator. The prepared battery was a control group 2. The performance of the battery was tested: mainly including charge-discharge test (battery efficiency), cycle stability test (single cycle attenuation rate) and battery polarization curve test (power density).

[0170] Battery assembly: the prepared electrode material was used as the positive and negative electrode of the battery, the electrode compression ratio was 25%, Nafion 212 proton exchange membrane was selected to isolate the positive and negative electrolyte, and the working area of the electrode was 3×3 cm 2 , the electrolyte was 1.65 MVO 2+ +3.0 MH2SO4 solution, the volume of the electrolyte used in the positive and negative electrodes was 20 mL and 10 mL respectively, the electrolyte flow rate was 30 mL·min -1 , the bipolar plate was a carbon composite bipolar plate without flow channel; the charge-discharge current density was 200 mA·cm -2 , and the cutoff voltage during the charge-discharge process was 1.75 V and 1.0 V respectively. The cycle stability test was carried out at a current density of 250 mA·cm-2.

[0171] The calculation formulas of the Coulombic Efficiency (CE), Energy Efficiency (EE) and Voltage Efficiency (VE) of the battery are as follows:

[0172]

[0173]

[0174]

[0175] Wherein: I d and I c are the discharge current and the charge current respectively, t is time, V d and V c are the discharge voltage and the charge voltage respectively.

[0176] The discharge polarization curves of the vanadium batteries assembled with WC-ECNFs and ECNFs as electrodes were respectively tested by constant current charging the batteries at different current densities until the voltage was less than 0.5 V. The peak power density can be obtained by taking the current density-voltage product of the polarization curve as the ordinate and the current density as the abscissa. The batteries of Example 1 and Example 2 were cycled at a current density of 250 mA·cm -2 The cycle stability of the batteries was investigated by comparing the attenuation rate of energy efficiency under long cycle.

[0177] The test results are shown in Table 4.

[0178] Table 4 Battery performance

[0179]

[0180] As shown in Table 4, the batteries prepared by combining the high-mass transfer carbon felt electrode and the high-activity carbon nanofiber catalyst layer in Example 1 and Example 2 have excellent electrochemical performance and high reaction rate and stability. The counterexample 1 has no continuous batten structure, although the permeability is high, but the structure is unstable, the electrode is deformed under long-term operation, the polarization increases, and the cycle stability is poor; the counterexample 2 has equal-width continuous battens, and the flow field distribution is relatively uneven, and the local concentration polarization is large; the counterexample 3 has a straight slot flow channel, and the mass transfer effect is the worst, and the concentration polarization is relatively large; the counterexample 4 has a reverse gradient flow field distribution, and the wide continuous batten at the inflow end hinders the initial distribution of the electrolyte, and the efficiency is lower than that of the positive gradient; the carbon cloth is used as the substrate and subjected to acid treatment in Example 3, which is used for the carbon-based catalyst layer, and the corresponding battery performance is high; the carbon paper is used as the substrate, and the heat treatment and Bi-based catalyst loading are adopted in Example 4, which can further improve the voltage efficiency of the battery. Since the Bi-based catalyst can improve the electrochemical activity of the negative vanadium ions while inhibiting hydrogen evolution, the cycle stability of the battery is also good. The control group 1 has poor mass transfer and small active area, and all the performances are the worst, and the attenuation is the fastest; the control group 2 is incorrectly assembled, the carbon felt pierces the separator, leading to short circuit, the catalyst layer interface fails, the reaction area suddenly decreases, the flow guide groove function is wasted, and the mass transfer deteriorates. Therefore, the composite electrode with the built-in continuous batten flow guide groove prepared by using the raw materials and the method described in the application can provide an efficient electrolyte transport channel and a large number of reaction active sites, and can protect the separator, which is assembled in the flow battery by a specific assembly method, and can effectively improve the energy conversion efficiency and cycle stability of the flow battery.

[0181] The above is the preferred embodiment of the application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the application, a number of improvements and refinements can be made, which should be considered as the protection scope of the application.

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; the carbon felt substrate is a polyacrylonitrile-based carbon felt with a thickness of 2.5 mm, a porosity of 90%, a fiber diameter of 10 μm, and an average pore size of 80 μm. 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 width of the connecting joint in the flow channel is 4mm~6mm, 7mm~9mm, 10mm~12mm, and 13mm~15mm respectively along the electrolyte flow direction; the width of the flow channel is 1mm~6mm, and the width of the carbon felt electrode between the two rows of flow channels is 15mm~30mm. The highly active carbon-based catalytic layer is obtained by activating a thin carbon layer material composed only of planar fibers. The thin carbon layer material is a functionalized polyacrylonitrile-based carbon nanofiber membrane, and the preparation method includes: A1. Spinning: PAN is dissolved in DMF to prepare an electrospinning precursor spinning solution. Functional components are added to the solution, electrospinning is performed, and the fibers are collected on the surface of aluminum foil to obtain the product. The functional components include one or more of graphene oxide, carbon nanotubes, and bismuth salts. A2. Pre-oxidation treatment: The atmosphere is air, and the temperature is increased to 250~320℃ at a rate of 1~5℃ / min, and held for 0.5h~4h. A3. Carbonization treatment: The atmosphere is nitrogen, and the temperature is raised to 900~1200℃ at 5~10℃ / min and kept at the temperature for 1~3h to obtain a functionalized polyacrylonitrile-based carbon nanofiber membrane with a diameter of 100nm~2μm and a fiber layer thickness of 0.1mm~1.5mm. Activation processes include one or more of the following: heat treatment, acid treatment, plasma treatment, and catalyst loading. Heat treatment: The atmosphere is air, the temperature is increased to 400~700℃ at 3~7℃ / min, held for 30min~2h, and then cooled to room temperature in the furnace; Acid treatment: Add the thin carbon layer material to a nitric acid solution and 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. Then, vacuum dry it. Catalyst loading: Immerse the thin carbon layer material fully in the catalyst solution, remove it, wash it twice with ethanol, and dry it.

2. The method for preparing the composite electrode with built-in connecting groove according to claim 1, characterized in that, 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 spinning solution mass; 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℃.

3. The method for preparing the composite electrode with built-in connecting groove according to claim 2, characterized in that, 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 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 solvent is a 50% (v / v) aqueous solution of ethanol; 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 one or more of hot pressing and bonding. 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 any one of polytetrafluoroethylene or phenolic resin. The adhesive is applied to the surface of the carbon felt electrode and then laminated.

4. 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 3.

5. The application of the composite electrode with built-in connecting groove as described in claim 4 in a flow battery.

6. The application of the composite electrode with built-in connecting channel as described in claim 5 in a flow battery, 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.

Images