Composite electrode and preparation method

Abstract

The invention relates to the technical field of electrode materials, and particularly provides a composite electrode and a preparation method. The preparation method of the composite electrode comprises the following steps: providing at least two layers of carbon paper substrates, carbon cloth substrates and two layers of carbon fiber needled felts; stacking at least two layers of carbon paper base materials and carbon cloth base materials along the thickness direction to obtain a carbon fiber composite base material; wherein the carbon cloth base material is positioned between the at least two layers of carbon paper base materials; performing needling compounding on the carbon fiber composite base material by using two layers of carbon fiber needled felts to obtain a composite electrode; wherein the two layers of carbon fiber needled felts are respectively formed on the upper surface and the lower surface of the carbon fiber composite base material. The composite electrode and the preparation method provided by the invention are used for reducing the thickness of the electrode material for the all-vanadium redox flow battery and improving the thickness uniformity and the quality stability of the electrode material.

Description

Technical Field

[0001] The present disclosure relates to the technical field of electrode materials, and in particular to a composite electrode and a preparation method thereof. Background Art

[0002] Vanadium Redox Flow Battery (VRFB) is a redox battery with vanadium as the active material in a circulating liquid state. As one of the key materials of vanadium redox flow battery, the electrode material itself does not directly participate in the reaction, but provides a reaction site for the redox reaction during the charging and discharging process, and provides a channel for the transmission of internal active substances. The performance of the electrode material directly affects the electrochemical reaction rate, battery internal resistance and electrolyte transmission process.

[0003] In the related technology, the electrode material of all-vanadium liquid flow battery is mainly carbon felt or graphitized felt, which is thick, resulting in large internal resistance of the battery and is not conducive to electrolyte transmission. Carbon paper and carbon cloth have gradually attracted attention in the industry due to their flexible thickness design. However, since carbon cloth is too soft, the electrode is prone to collapse during the battery assembly process, resulting in unstable battery performance; the brittleness of carbon paper itself leads to poor battery compression resilience, and its high volume density also leads to large mass transfer losses in the battery. Summary of the invention

[0004] The present disclosure is proposed in view of the above problems. The present disclosure provides a composite electrode and a preparation method, which reduces the thickness of the electrode material for all-vanadium liquid flow battery and improves its thickness uniformity and quality stability.

[0005] According to one aspect of the present disclosure, there is provided a method for preparing a composite electrode, comprising:

[0006] Providing at least two layers of carbon paper substrate, carbon cloth substrate and two layers of carbon fiber needle felt;

[0007] Stacking at least two layers of the carbon paper substrate and the carbon cloth substrate in a thickness direction to obtain a carbon fiber composite substrate; wherein the carbon cloth substrate is located between the at least two layers of the carbon paper substrate;

[0008] The carbon fiber composite substrate is needle-punched and composited using two layers of the carbon fiber needle-punched felt to obtain a composite electrode; wherein the two layers of the carbon fiber needle-punched felt are respectively formed on the upper surface and the lower surface of the carbon fiber composite substrate.

[0009] According to another aspect of the present disclosure, a composite electrode is provided, comprising a carbon fiber composite substrate and two layers of carbon fiber needle felt respectively formed on the upper surface and the lower surface of the carbon fiber composite substrate, wherein the carbon fiber composite substrate comprises at least two layers of a carbon paper substrate and a carbon cloth substrate stacked along a thickness direction, and the carbon cloth substrate is located between the at least two layers of the carbon paper substrate.

[0010] According to yet another aspect of the present disclosure, a battery is provided, comprising the above composite electrode.

[0011] In one or more technical solutions provided in the embodiments of the present disclosure, first, at least two layers of carbon paper substrate, carbon cloth substrate and two layers of carbon fiber needle felt are provided; at least two layers of carbon paper substrate and carbon cloth substrate are stacked in the thickness direction to obtain a carbon fiber composite substrate; wherein the carbon cloth substrate is located between at least two layers of carbon paper substrate. Since the carbon cloth substrate is located between two layers of carbon paper substrate during the battery assembly process, the carbon paper substrate can provide support for the carbon cloth substrate, improving the problem that the carbon cloth substrate is prone to collapse due to being too soft; at the same time, the carbon cloth substrate can improve the brittleness of the carbon paper substrate, improve the battery compression resilience, and improve the stability of the battery performance, thereby ensuring that the electrode material has both the wide working potential range, good chemical and mechanical stability and good conductivity of the carbon cloth substrate under electrochemical reaction conditions, and the high energy density per unit volume and excellent electrochemical performance of the carbon paper substrate. Then, the carbon fiber composite substrate is needle-punched and composited with two layers of carbon fiber needle felt to obtain a composite electrode. The composite electrode has a thin thickness and can ensure uniform thickness. The layers are tightly combined without stratification, avoiding defects such as interlayer depression or bulging, and improving its thickness uniformity and quality stability. At the same time, the two layers of carbon fiber needle felt are formed on the upper and lower surfaces of the carbon fiber composite substrate respectively, which can protect the carbon paper substrate on the upper and lower surfaces of the carbon fiber composite substrate and reduce the possibility of damage to the carbon paper substrate during battery assembly due to its high brittleness. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and other purposes, features and advantages of the present disclosure will become more apparent by describing the embodiments of the present disclosure in more detail in conjunction with the accompanying drawings. The accompanying drawings are used to provide a further understanding of the embodiments of the present disclosure and constitute a part of the specification. Together with the embodiments of the present disclosure, they are used to explain the present disclosure and do not constitute a limitation of the present disclosure. In the accompanying drawings, the same reference numerals generally represent the same components or steps.

[0013] Figure 1 A schematic diagram showing a process of preparing a composite electrode according to an embodiment of the present disclosure;

[0014] Figure 2 The schematic diagram of the structure of the composite electrode according to the embodiment of the present invention is shown.

[0015] Reference numerals:

[0016] 210-carbon fiber needle felt, 220-carbon fiber composite substrate, 221-carbon paper substrate, 222-carbon cloth substrate. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present disclosure more obvious, the exemplary embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments of the present disclosure, and it should be understood that the present disclosure is not limited to the exemplary embodiments described here.

[0018] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0019] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present disclosure, "multiple" means two or more, unless otherwise clearly and specifically defined. "Several" means one or more, unless otherwise clearly and specifically defined.

[0020] In the description of the present disclosure, it is necessary to understand that the directions or positional relationships indicated by the terms "upper", "lower", "front", "back", "left", "right", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present disclosure.

[0021] In the description of the present disclosure, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances.

[0022] It should be noted that, in the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the present disclosure should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0023] In the present invention, "at least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, the combination of a and b, the combination of a and c, the combination of b and c, or the combination of a, b and c, where a, b, c can be single or multiple.

[0024] The all-vanadium liquid flow battery is a rechargeable liquid flow battery that uses the change in the valence of vanadium ions to achieve the conversion between electrical energy and chemical energy. The advantages of the all-vanadium liquid flow battery include: First, it can be charged and discharged an unlimited number of times, and the energy and power are independent. The energy capacity (total energy) of the battery can be changed without affecting its power (energy per second). Second, it has a long life and is scalable. It can break through the limitations of lithium-ion batteries in the energy storage time in the power system and be used for long-term energy storage. It has a certain development space in the power system. Third, it is relatively less affected by the environment. On the one hand, vanadium is abundant, and on the other hand, the electrolyte can be recycled and reused.

[0025] All-vanadium liquid flow battery has become one of the preferred technologies in the fields of renewable energy storage, grid peak regulation, backup power supply, etc. due to its high safety, long life and low pollution. Vanadium battery realizes the reciprocating conversion of chemical energy to electrical energy through the change of vanadium ion valence, thereby storing and releasing the electricity generated by wind or solar energy. The industry figuratively calls it "power bank". All-vanadium liquid flow battery is the only battery with a single active substance in liquid flow battery. It stores electrical energy in sulfuric acid electrolyte with vanadium ions of different valence states in the form of chemical energy. The electrolyte is pressed into the battery stack by an external pump, and circulates through the closed loop of different liquid storage tanks and half-cells under the action of mechanical power. Proton exchange membrane is used as a diaphragm in the battery pack, and the electrolyte solution flows parallel to the electrode surface and an electrochemical reaction occurs. The chemical energy stored in the solution is converted into electrical energy by collecting and conducting current through the double electrode plate. This reaction process is reversible, allowing vanadium batteries to successfully complete the process of charging, discharging and recharging.

[0026] The all-vanadium liquid flow battery system consists of a power unit (cell stack), an energy unit (electrolyte and electrolyte storage tank), an electrolyte delivery unit (pipelines, valves, pumps, sensors and other auxiliary components) and a battery management system. The cell stack is composed of ion exchange membranes, electrode materials, bipolar plates, electrode frames, seals and other materials.

[0027] As one of the key core materials of all-vanadium liquid flow batteries, electrode materials do not directly participate in the reaction as reactants in all-vanadium liquid flow batteries, but only provide a reaction site for the redox reaction during the charging and discharging process, and provide a channel for the transmission of internal active substances. The performance requirements of electrode materials mainly include: high specific surface area, appropriate porosity and surface activity, high conductivity, good mechanical properties, corrosion resistance, stable charging and discharging process, low price of electrode materials, extensive resources, and long service life.

[0028] The performance of electrode materials directly affects the electrochemical reaction rate, battery internal resistance and electrolyte transport process. Therefore, structural design and surface property modification of electrode materials are of great significance for improving battery power density, operating efficiency and service life, and reducing system costs.

[0029] Carbon-based electrodes have the advantages of low cost, good flexibility, light weight, and easy doping and surface modification, making them widely used in various energy storage devices. Existing flow battery electrode materials are relatively thick, resulting in large mass transfer resistance and reduced redox rate, which affects the power density and electrochemical performance of the battery.

[0030] At present, carbon felt is still the main material for VRFB electrodes. Reducing the thickness of carbon felt or using thinner and more ordered electrode materials such as carbon cloth is the focus of researchers. How to ensure sufficient mass transfer of electrolyte and sufficient specific surface area of ​​electrodes while reducing the ohmic polarization of the battery is a problem that needs to be solved in practical applications of future electrode materials. The development of thin electrodes with higher surface area and smaller thickness for all-vanadium liquid flow batteries will help reduce the physical space of the battery stack, enhance electrochemical performance, and also help reduce the total cost of the battery stack.

[0031] In the related technology, the mainstream preparation process of electrode materials is the needle punching process. The thickness of the carbon felt or graphite felt produced by the needle punching process is relatively large, and the thickness uniformity and quality stability of the product with a thickness less than 1mm are difficult to guarantee. The thickness of the finished felt is generally not less than 1mm, which leads to a large internal resistance of the battery and is not conducive to the transmission of the electrolyte.

[0032] At the same time, carbon paper and carbon cloth have gradually attracted attention in the industry due to their flexible thickness design. Among thin electrode materials, carbon cloth electrodes have a wide working potential range, good chemical and mechanical stability, and good conductivity under electrochemical reaction conditions, but they are too soft and prone to collapse during battery assembly, resulting in unstable battery performance; carbon paper electrodes have a high energy density per unit volume and excellent electrochemical performance, but their high brittleness leads to poor battery compression resilience.

[0033] In view of the above problems, the embodiments of the present disclosure provide a composite electrode and a preparation method, which solves the problem of poor hydrophilicity and conductivity of the electrodes of the prior art all-vanadium redox flow battery. The conductivity and hydrophilicity of the vanadium battery are improved, thereby reducing the resistivity of the electrode. It should be understood that the composite electrode can be applied to all-vanadium redox flow batteries.

[0034] Figure 1 The schematic diagram of the process of preparing the composite electrode of the present disclosure is shown as follows: Figure 1 As shown, the method for preparing the composite electrode of the embodiment of the present disclosure includes:

[0035] S101, providing at least two layers of carbon paper substrate, a carbon cloth substrate and two layers of carbon fiber needle felt;

[0036] S102, stacking at least two layers of carbon paper substrate and carbon cloth substrate in a thickness direction to obtain a carbon fiber composite substrate; wherein the carbon cloth substrate is located between the at least two layers of carbon paper substrate;

[0037] S103, using two layers of carbon fiber needle punched felt to perform needle punching composite on the carbon fiber composite substrate to obtain a composite electrode; wherein the two layers of carbon fiber needle punched felt are respectively formed on the upper surface and the lower surface of the carbon fiber composite substrate.

[0038] Specifically, at least two layers of carbon paper substrate, carbon cloth substrate and two layers of carbon fiber needle felt are prepared. Here, the thickness of the carbon paper substrate is 0.1mm-0.2mm, the thickness of the carbon cloth substrate is 0.3mm-0.4mm, and the thickness of the carbon fiber needle felt is 0.02-0.05mm. These materials are relatively thin, which can significantly reduce the surface resistance and charge transfer distance, increase the redox reactivity of the active material and the power density of the all-vanadium redox flow battery.

[0039] Preferably, the thickness of the carbon paper substrate is 0.15 mm to 0.18 mm. The carbon paper can be prepared by continuous production equipment through wet papermaking, resin coating, hot pressing curing, low temperature carbonization, and high temperature graphitization. The weight of the carbon paper is 50 g / m 2 -60g / m 2 , thickness is 0.15mm-0.18mm.

[0040] The embodiment of the present disclosure can design the thickness of the electrode material by the number of layers of the carbon paper substrate. It should be understood that the fewer the number of layers of the carbon paper substrate, the thinner the prepared composite electrode.

[0041] Taking the carbon paper substrate as two layers as an example, a layer of carbon paper substrate, a layer of carbon cloth substrate and a layer of carbon paper substrate are stacked in the thickness direction in sequence to obtain a carbon fiber composite substrate. Among them, during the battery assembly process, the carbon cloth substrate is located between the two layers of carbon paper substrate, and the carbon paper substrate can provide support for the carbon cloth substrate, improving the problem that the carbon cloth substrate is prone to collapse due to its excessive softness; at the same time, the carbon cloth substrate can improve the brittleness of the carbon paper substrate, improve the battery compression resilience, and improve the stability of battery performance, thereby ensuring that the electrode material has both the wide working potential range, good chemical and mechanical stability and good conductivity of the carbon cloth substrate under electrochemical reaction conditions, and the high energy density per unit volume and excellent electrochemical performance of the carbon paper substrate.

[0042] After obtaining the carbon fiber composite substrate, a layer of carbon fiber needle felt is laid on the upper and lower surfaces of the carbon fiber composite substrate respectively, and the carbon paper substrate and the carbon cloth substrate are needle-punched and composited by a needle-punched composite machine. The long fibers of the carbon fiber needle felt penetrate the substrate longitudinally and reciprocatingly to achieve the effect of combining the layers of the composite substrate without stratification, thereby obtaining a composite electrode, avoiding defects such as depressions or bulges between layers, so that the composite electrode has a thinner thickness while improving its thickness uniformity and quality stability. Here, the process conditions of needle-punching composite include: needle depth of 2mm, frequency of 50HZ. After needle-punching composite, the thickness of the obtained composite electrode is 0.5mm-0.8mm.

[0043] At the same time, since the carbon paper substrate on the upper and lower surfaces of the carbon fiber composite substrate is highly brittle, when two layers of carbon fiber needle felt are respectively formed on the upper and lower surfaces of the carbon fiber composite substrate, the carbon paper substrate can be protected and the possibility of damage to the carbon paper substrate during battery assembly can be reduced.

[0044] In the preparation method of the composite electrode provided by the embodiment of the present disclosure, first, at least two layers of carbon paper substrate, carbon cloth substrate and two layers of carbon fiber needle felt are provided; at least two layers of carbon paper substrate and carbon cloth substrate are stacked in the thickness direction to obtain a carbon fiber composite substrate; wherein the carbon cloth substrate is located between at least two layers of carbon paper substrate. Since the carbon cloth substrate is located between two layers of carbon paper substrate during the battery assembly process, the carbon paper substrate can provide support for the carbon cloth substrate, improving the problem that the carbon cloth substrate is prone to collapse due to being too soft; at the same time, the carbon cloth substrate can improve the brittleness of the carbon paper substrate, improve the battery compression resilience, and improve the stability of the battery performance, thereby ensuring that the electrode material has both the wide working potential range, good chemical and mechanical stability and good conductivity of the carbon cloth substrate under electrochemical reaction conditions, and the high energy density per unit volume and excellent electrochemical performance of the carbon paper substrate. Then, the carbon fiber composite substrate is needle-punched and composited with two layers of carbon fiber needle felt to obtain a composite electrode. The composite electrode has a thin thickness and can ensure uniform thickness. The layers are tightly combined without stratification, avoiding defects such as interlayer depression or bulging, and improving its thickness uniformity and quality stability. At the same time, the two layers of carbon fiber needle felt are formed on the upper and lower surfaces of the carbon fiber composite substrate respectively, which can protect the carbon paper substrate on the upper and lower surfaces of the carbon fiber composite substrate and reduce the possibility of damage to the carbon paper substrate during battery assembly due to its high brittleness.

[0045] In one achievable manner, before stacking at least two layers of carbon paper substrate and carbon cloth substrate in a thickness direction to obtain a carbon fiber composite substrate, the method for preparing the composite electrode further comprises:

[0046] Each layer of carbon paper substrate is nitrogen-doped using a nitrogen precursor.

[0047] Specifically, in order to further improve the electrochemical properties of electrode materials, it is necessary to perform surface modification on electrode materials. Carbon nanofiber is a carbon fiber with a diameter at the nanometer scale, which is usually curled up by a graphite sheet structure formed by sp2 hybridization of carbon atoms, and has a unique one-dimensional nanostructure and excellent physical and chemical properties. Carbon nanofiber has high conductivity, thermal stability and specific surface area. Modifying carbon nanofiber (CarbonNanofiber, CNF) on the surface of electrode materials can effectively improve the overall conductivity, thermal stability and specific surface area of ​​electrode materials such as carbon felt, while improving its hydrophilicity and surface resistance. At the same time, the hollow structure of carbon nanofiber can also provide more active sites for vanadium ion reaction.

[0048] In the related art, carbon nanofibers are modified onto carbon cloth by a method of coating with an adhesive material or a chemical vapor deposition (CVD) modification method, but the performance of such activated modifications is unstable. For example: in the coating process, the use of conventional adhesives may promote the shedding of carbon nanofibers on the surface of the carbon cloth after the VRFB cycle test. Another example: carbon nanofibers deposited on the surface of the carbon cloth by the chemical vapor deposition method may also fall off during the assembly process. Although the shedding of carbon nanofibers is less than that of the adhesive material coating method, the chemical vapor deposition method is expensive and time-consuming, which is not conducive to industrial production. The shedding of carbon nanofibers will reduce the electrochemically active surface area of ​​the carbon cloth electrode and weaken the connectivity of the carbon cloth. The interface resistance between the adhesive, carbon cloth and carbon nanofibers may also increase the overpotential and reduce the performance of the flow battery.

[0049] Based on this, the embodiment of the present disclosure adopts a post-synthesis method to react a pre-synthesized carbon material with a nitrogen precursor to prepare a nitrogen-doped carbon paper substrate, and uniformly generates nitrogen-doped carbon nanofibers on the surface of the carbon paper substrate. Specifically, it is a microwave-assisted post-synthesis nitrogen-doped carbon material preparation method, which is a method for synthesizing nitrogen-doped carbon materials using microwave heating technology, and has the advantages of simple operation, short reaction time and environmental friendliness.

[0050] Here, the nitrogen precursor may include, but is not limited to, one of ammonia water, urea, and melamine.

[0051] Exemplarily, the nitrogen doping treatment may be a microwave nitrogen doping treatment, and the process conditions of the microwave nitrogen doping treatment may include: a microwave treatment temperature of 700° C.-800° C., and a reaction time of 1 h-3 h.

[0052] The disclosed embodiment can process the carbon paper substrate under microwave conditions under the action of a nitrogen precursor, so that carbon nanofibers are generated on the surface of the carbon paper substrate. When performing nitrogen doping treatment, a microwave reactor is used to directly act on the carbon paper substrate using the high-frequency electromagnetic field of microwaves, so that its molecules and ions produce violent thermal motion under the action of microwaves, thereby rapidly heating up and initiating chemical reactions. In this process, microwave heating directly transfers energy to the material through the interaction between microwaves and polar molecules inside the material, achieving internal heating and avoiding heat conduction losses in traditional heating methods. Due to the different absorption capacities of different substances for microwaves, microwave heating is selective and can achieve efficient heating of specific substances (nitrogen precursors in the disclosed embodiment) while reducing heating of the surrounding environment. Microwave pyrolysis can heat ammonia water to the required temperature in a very short time to achieve rapid reaction. At the same time, the penetration of microwaves makes the heating process more uniform, avoiding the problem of local overheating or cold spots, thereby achieving rapid and uniform heating.

[0053] Microwave energy causes the vibration of water molecules in nitrogen precursors such as ammonia water to intensify, generating more heat energy, which helps ammonia water to pyrolyze faster into carbon and nitrogen oxides or nitrogen organic complexes, such as ammonia (NH3), water (H2O), carbon dioxide (CO2), and a small amount of nitric oxide (NO) and nitrogen dioxide (NO2). The uniformity of microwave heating helps to achieve uniform nitrogen doping on the surface of the carbon paper substrate. Microwaves can quickly and uniformly heat the entire reaction system. Therefore, the embodiments of the present disclosure can better control the distribution of nitrogen doping through microwave nitrogen doping treatment.

[0054] At the same time, the embodiment of the present disclosure can better control the amount of nitrogen doping by controlling the concentration of the nitrogen precursor. Exemplarily, in the method for preparing the composite electrode provided by the embodiment of the present disclosure, the reaction concentration of the nitrogen precursor is 10%-15%. Preferably, the reaction concentration of the nitrogen precursor is 12%. Here, although nitrogen doping can improve the activity of the electrode, when the reaction concentration of the nitrogen precursor is too high, it may cause too many active sites to form on the surface of the carbon paper substrate, which in turn reduces the electrochemical activity.

[0055] It can be seen that when the carbon paper substrate is subjected to nitrogen doping surface modification in the embodiment of the present disclosure, the nitrogen doping degree and structure controllability are high. The nitrogen type in the nitrogen-doped carbon material described in the embodiment of the present disclosure is graphitic nitrogen, and the nitrogen content can reach 10%.

[0056] Based on this, the embodiments of the present disclosure can nitrogen-dope carbon nanofibers on the surface of a carbon paper substrate. The nitrogen-doped carbon nanofibers are carbon catalysts for active sites of the redox reaction of vanadium ions. When connected to an electrode, the nitrogen-doped carbon nanofibers play the role of connecting each fiber of the carbon paper substrate, and through this connection, the number of active sites for promoting the redox reaction of vanadium ions is increased.

[0057] In one achievable manner, before nitrogen doping the carbon paper substrate with a nitrogen precursor, the method for preparing the composite electrode further comprises:

[0058] The carbon paper substrate is laser punched.

[0059] Specifically, carbon paper substrates have low porosity and high bulk density, which limits their mass transfer. In addition, existing electrode felts have few activation sites, unstable activation effects, and the activation durability needs to be improved.

[0060] The disclosed embodiment can perform laser drilling on the carbon paper substrate to create pores on the carbon paper substrate to improve the transmission of active substances in the thickness direction of the composite electrode, further improve the peak power density of the flow battery, and increase the discharge capacity of the battery. At the same time, the pores can also increase the specific surface area of ​​the carbon paper substrate and increase the reactive active sites.

[0061] Here, the laser drilling process may include carbon dioxide (CO2) laser drilling process and ultraviolet (UV) laser drilling process. The pore size of the carbon paper substrate after the laser drilling process is 0.2mm-0.5mm, and the pore spacing is 3mm-8mm. Preferably, the pore size of the carbon paper substrate after the laser drilling process is 0.3mm-0.4mm, and the pore spacing is 4mm-6mm.

[0062] The disclosed embodiments can achieve uniform distribution of pores on the carbon paper substrate by controlling the pore diameter and the pore spacing, thereby avoiding the situation where large defects in the carbon paper substrate, poor conductivity, fewer reactive sites, and no obvious improvement in specific surface area are caused by larger pore diameters and smaller pore spacing, and at the same time avoiding the situation where no obvious improvement in mass transfer effect of the carbon paper substrate is caused by smaller pore diameters and larger pore spacing.

[0063] Since the carbon paper substrate is laser-punched in the embodiment of the present disclosure, the carbon paper substrate has a larger specific surface area, and the carbon paper substrate itself has a smaller porosity (compared to the carbon cloth substrate and the carbon fiber needle felt). When the composite electrode is assembled and used, the carbon paper with a larger surface area and smaller porosity is close to the membrane side; the carbon cloth substrate with a larger porosity and smaller mass transfer resistance is close to the flow field side. This structure enhances the diffusion of active substances and convection under the ribs, avoids the loss of reactive surface area, and improves the utilization rate of the electrode.

[0064] The principle involved is: when the electrolyte undergoes an electrochemical reaction on the carbon fiber surface of the porous electrode, the reaction ion mass transfer is carried out through collision or adsorption. Therefore, the electrode needs to have a large number of active sites as collision sites and adsorption sites to reduce the reaction overpotential in the electrode.

[0065] At the microscopic scale, the pore structure of the battery can be regulated from macropores to micropores through physical or chemical treatment methods. By stacking multiple layers of electrodes with different porosities, the electrode specific surface area can be increased, achieving synergistic optimization between improving the transport of active substances in the electrolyte and promoting electrochemical reactions.

[0066] In the method of the embodiment of the present disclosure, the composite electrode is arranged in the order of carbon fiber needle felt, carbon paper substrate, carbon cloth substrate, carbon paper substrate and carbon fiber needle felt in the thickness direction, and the pore distribution of the composite electrode is a three-level distribution of macropores (carbon fiber needle felt), mesopores (carbon paper substrate after laser punching) to micropores (carbon cloth substrate). The specific surface area of ​​the composite electrode is increased through the three-level pore distribution, thereby achieving synergistic optimization between improving the transmission of active substances in the electrolyte and promoting electrochemical reactions.

[0067] In one achievable manner, before stacking at least two layers of carbon paper substrate and carbon cloth substrate in a thickness direction to obtain a carbon fiber composite substrate, the method for preparing the composite electrode further comprises:

[0068] The surface of the carbon cloth substrate is plasma treated.

[0069] Specifically, in order to increase the specific surface area of ​​the carbon cloth substrate while ensuring that it has a small porosity, the embodiment of the present disclosure performs plasma treatment on the carbon cloth substrate, with the aim of forming defects such as stripes and grooves on the surface of the carbon fibers on the surface of the carbon cloth substrate, thereby increasing the reaction specific surface area and improving the surface activity and water wettability of the carbon cloth.

[0070] The principle of plasma treatment is to directly contact the oxidizing medium (such as oxygen, air gas) with the carbon fiber surface, so that the unsaturated carbon in the carbon fiber is oxidized, and then oxygen-containing functional groups such as hydroxyl (-OH), carbonyl (-C=O) and carboxyl (-COOH) are introduced into the carbon fiber structure. Due to the consumption of unsaturated carbon, holes may also be formed on the carbon fiber surface, further increasing the specific surface area of ​​the carbon cloth substrate.

[0071] Illustratively, the embodiments of the present disclosure may use a continuous plasma treatment test furnace to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10-20 mm / s.

[0072] On the basis of the above embodiments, the embodiments of the present disclosure also provide a composite electrode, which is prepared using the above-mentioned composite electrode preparation method. The composite electrode includes a carbon fiber composite substrate and two layers of carbon fiber needle felt formed on the upper surface and lower surface of the carbon fiber composite substrate, respectively. The carbon fiber composite substrate includes at least two layers of carbon paper substrate and carbon cloth substrate stacked along the thickness direction, and the carbon cloth substrate is located between the at least two layers of carbon paper substrate.

[0073] Specifically, Figure 2 The structure diagram of the composite electrode according to the embodiment of the present invention is shown in FIG. Figure 2 As shown, the composite electrode of the embodiment of the present invention includes a carbon fiber composite substrate 220 and two layers of carbon fiber needle felt 210 respectively formed on the upper surface and the lower surface of the carbon fiber composite substrate 220. Taking the carbon paper substrate as an example with two layers, the carbon fiber composite substrate 220 includes at least two layers of carbon paper substrate 221 and carbon cloth substrate 222 stacked in the thickness direction, and the carbon cloth substrate 222 is located between the at least two layers of carbon paper substrate 221.

[0074] On the basis of the above-mentioned embodiment, the embodiment of the present disclosure further provides a battery, which includes the above-mentioned composite electrode.

[0075] In order to verify the effect of the composite electrode provided by the embodiment of the present disclosure, the embodiment of the present disclosure is demonstrated by comparing the embodiment with the comparative example.

[0076] Embodiment 1

[0077] The method for preparing the composite electrode provided in the first embodiment of the present disclosure comprises the following steps:

[0078] (1) Preparation of carbon paper substrate

[0079] The carbon paper substrate provided in the embodiment of the present disclosure is a self-made product of Shandong Renfeng Special Materials Co., Ltd., which is prepared by wet papermaking, resin coating, hot pressing curing, low-temperature carbonization, and high-temperature graphitization. The weight of the carbon paper substrate is 50g / m 2 , thickness is 165μm.

[0080] (2) Laser drilling of carbon paper substrate

[0081] The carbon paper substrate prepared in step (1) is subjected to laser drilling treatment, using a carbon dioxide laser drilling device to make regular holes in the carbon paper substrate, wherein the pore diameter of the carbon paper substrate is 0.3 mm and the pore spacing is 5 mm.

[0082] (3) Nitrogen-doped carbon nanofibers on the surface of carbon paper substrate

[0083] A microwave reactor was used, ammonia water was used as a nitrogen precursor, and a one-step heat treatment was performed under microwave heating conditions to grow carbon nanofibers on the surface of a carbon paper substrate, wherein the microwave heating temperature was 700°C, the reaction time was 2h, and the reaction concentration of the nitrogen precursor was 12%.

[0084] (4) Plasma treatment of carbon cloth substrate

[0085] A continuous plasma treatment test furnace was used to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10 mm / s.

[0086] (5) Needle punching composite of carbon paper substrate and carbon cloth substrate

[0087] The carbon paper substrate of step (3) and the carbon cloth substrate of step (4) are compositely stacked with the carbon fiber needle felt, with a total of 5 layers, wherein the carbon cloth substrate has 1 layer, and the carbon paper substrate and the carbon fiber needle felt have 2 layers each, wherein the middle layer is a layer of carbon cloth substrate, and the two layers of carbon paper substrate are respectively located on the upper and lower surfaces of both sides of the carbon cloth substrate, and the two outermost surfaces are each a layer of carbon fiber needle felt.

[0088] The carbon paper substrate and the carbon cloth substrate are needle-punched and compounded by using a needle-punched composite machine. The long fibers of the carbon fiber needle-punched felt penetrate the composite substrate longitudinally and reciprocatingly to achieve the effect of combining the composite substrate layers without stratification, thereby obtaining a composite electrode. The needle-punching parameters are 2mm in depth and 50HZ in frequency.

[0089] Embodiment 2

[0090] The preparation method of the composite electrode provided in the second embodiment of the present disclosure comprises the following steps:

[0091] (1) Preparation of carbon paper substrate

[0092] The carbon paper substrate provided in the embodiment of the present disclosure is a self-made product of Shandong Renfeng Special Materials Co., Ltd., which is prepared by wet papermaking, resin coating, hot pressing curing, low-temperature carbonization, and high-temperature graphitization. The weight of the carbon paper substrate is 60g / m 2 , thickness is 183μm.

[0093] (2) Laser drilling of carbon paper substrate

[0094] The carbon paper substrate prepared in step (1) is subjected to laser drilling treatment, using a carbon dioxide laser drilling device to make regular holes in the carbon paper substrate, wherein the pore diameter of the carbon paper substrate is 0.3 mm and the pore spacing is 5 mm.

[0095] (3) Nitrogen-doped carbon nanofibers on the surface of carbon paper substrate

[0096] A microwave reactor was used, ammonia water was used as a nitrogen precursor, and a one-step heat treatment was performed under microwave heating conditions to grow carbon nanofibers on the surface of a carbon paper substrate, wherein the microwave heating temperature was 700°C and the reaction time was 2h.

[0097] (4) Plasma treatment of carbon cloth substrate

[0098] A continuous plasma treatment test furnace was used to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10 mm / s.

[0099] (5) Needle punching composite of carbon paper substrate and carbon cloth substrate

[0100] The carbon paper substrate of step (3) and the carbon cloth substrate of step (4) are compositely stacked with the carbon fiber needle felt, with a total of 5 layers, wherein the carbon cloth substrate has 1 layer, and the carbon paper substrate and the carbon fiber needle felt have 2 layers each, wherein the middle layer is a layer of carbon cloth substrate, and the two layers of carbon paper substrate are respectively located on the upper and lower surfaces of both sides of the carbon cloth substrate, and the two outermost surfaces are each a layer of carbon fiber needle felt.

[0101] The carbon paper substrate and the carbon cloth substrate are needle-punched and compounded by using a needle-punched composite machine. The long fibers of the carbon fiber needle-punched felt penetrate the composite substrate longitudinally and reciprocatingly to achieve the effect of combining the composite substrate layers without stratification, thereby obtaining a composite electrode. The needle-punching parameters are 2mm in depth and 50HZ in frequency.

[0102] Embodiment 3

[0103] The method for preparing the composite electrode provided in the third embodiment of the present disclosure comprises the following steps:

[0104] (1) Preparation of carbon paper substrate

[0105] The carbon paper substrate provided in the embodiment of the present disclosure is a self-made product of Shandong Renfeng Special Materials Co., Ltd., which is prepared by wet papermaking, resin coating, hot pressing curing, low-temperature carbonization, and high-temperature graphitization. The weight of the carbon paper substrate is 50g / m 2 , thickness is 165μm.

[0106] (2) Laser drilling of carbon paper substrate

[0107] The carbon paper substrate prepared in step (1) is subjected to laser drilling treatment, using a carbon dioxide laser drilling device to make regular holes in the carbon paper substrate, wherein the pore diameter of the carbon paper substrate is 0.2 mm and the pore spacing is 3 mm.

[0108] (3) Nitrogen-doped carbon nanofibers on the surface of carbon paper substrate

[0109] A microwave reactor was used, ammonia water was used as a nitrogen precursor, and a one-step heat treatment was performed under microwave heating conditions to grow carbon nanofibers on the surface of a carbon paper substrate, wherein the microwave heating temperature was 700°C and the reaction time was 2h.

[0110] (4) Plasma treatment of carbon cloth substrate

[0111] A continuous plasma treatment test furnace was used to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10 mm / s.

[0112] (5) Needle punching composite of carbon paper substrate and carbon cloth substrate

[0113] The carbon paper substrate of step (3) and the carbon cloth substrate of step (4) are compositely stacked with the carbon fiber needle felt, with a total of 5 layers, wherein the carbon cloth substrate has 1 layer, and the carbon paper substrate and the carbon fiber needle felt have 2 layers each, wherein the middle layer is a layer of carbon cloth substrate, and the two layers of carbon paper substrate are respectively located on the upper and lower surfaces of both sides of the carbon cloth substrate, and the two outermost surfaces are each a layer of carbon fiber needle felt.

[0114] The carbon paper substrate and the carbon cloth substrate are needle-punched and compounded by using a needle-punched composite machine. The long fibers of the carbon fiber needle-punched felt penetrate the composite substrate longitudinally and reciprocatingly to achieve the effect of combining the composite substrate layers without stratification, thereby obtaining a composite electrode. The needle-punching parameters are 2mm in depth and 50HZ in frequency.

[0115] Embodiment 4

[0116] The preparation method of the composite electrode provided in the fourth embodiment of the present disclosure comprises the following steps:

[0117] (1) Preparation of carbon paper substrate

[0118] The carbon paper substrate provided in the embodiment of the present disclosure is a self-made product of Shandong Renfeng Special Materials Co., Ltd., which is prepared by wet papermaking, resin coating, hot pressing curing, low-temperature carbonization, and high-temperature graphitization. The weight of the carbon paper substrate is 50g / m 2 , thickness is 165μm.

[0119] (2) Laser drilling of carbon paper substrate

[0120] The carbon paper substrate prepared in step (1) is subjected to laser drilling treatment, using a carbon dioxide laser drilling device to make regular holes in the carbon paper substrate, wherein the pore diameter of the carbon paper substrate is 0.5 mm and the pore spacing is 8 mm.

[0121] (3) Nitrogen-doped carbon nanofibers on the surface of carbon paper substrate

[0122] A microwave reactor was used, ammonia water was used as a nitrogen precursor, and a one-step heat treatment was performed under microwave heating conditions to grow carbon nanofibers on the surface of a carbon paper substrate, wherein the microwave heating temperature was 700°C and the reaction time was 2h.

[0123] (4) Plasma treatment of carbon cloth substrate

[0124] A continuous plasma treatment test furnace was used to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10 mm / s.

[0125] (5) Needle punching composite of carbon paper substrate and carbon cloth substrate

[0126] The carbon paper substrate of step (3) and the carbon cloth substrate of step (4) are compositely stacked with the carbon fiber needle felt, with a total of 5 layers, wherein the carbon cloth substrate has 1 layer, and the carbon paper substrate and the carbon fiber needle felt have 2 layers each, wherein the middle layer is a layer of carbon cloth substrate, and the two layers of carbon paper substrate are respectively located on the upper and lower surfaces of both sides of the carbon cloth substrate, and the two outermost surfaces are each a layer of carbon fiber needle felt.

[0127] The carbon paper substrate and the carbon cloth substrate are needle-punched and compounded by using a needle-punched composite machine. The long fibers of the carbon fiber needle-punched felt penetrate the composite substrate longitudinally and reciprocatingly to achieve the effect of combining the composite substrate layers without stratification, thereby obtaining a composite electrode. The needle-punching parameters are 2mm in depth and 50HZ in frequency.

[0128] Embodiment 5

[0129] The method for preparing the composite electrode provided in the fifth embodiment of the present disclosure comprises the following steps:

[0130] (1) Preparation of carbon paper substrate

[0131] The carbon paper substrate provided in the embodiment of the present disclosure is a self-made product of Shandong Renfeng Special Materials Co., Ltd., which is prepared by wet papermaking, resin coating, hot pressing curing, low-temperature carbonization, and high-temperature graphitization. The weight of the carbon paper substrate is 50g / m 2 , thickness is 165μm.

[0132] (2) Laser drilling of carbon paper substrate

[0133] The carbon paper substrate prepared in step (1) is subjected to laser drilling treatment, using a carbon dioxide laser drilling device to make regular holes in the carbon paper substrate, wherein the pore diameter of the carbon paper substrate is 0.3 mm and the pore spacing is 5 mm.

[0134] (3) Nitrogen-doped carbon nanofibers on the surface of carbon paper substrate

[0135] A microwave reactor was used, ammonia water was used as a nitrogen precursor, and a one-step heat treatment was performed under microwave heating conditions to grow carbon nanofibers on the surface of a carbon paper substrate, wherein the microwave heating temperature was 700°C, the reaction time was 2h, and the reaction concentration of the nitrogen precursor was 10%.

[0136] (4) Plasma treatment of carbon cloth substrate

[0137] A continuous plasma treatment test furnace was used to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10 mm / s.

[0138] (5) Needle punching composite of carbon paper substrate and carbon cloth substrate

[0139] The carbon paper substrate of step (3) and the carbon cloth substrate of step (4) are compositely stacked with the carbon fiber needle felt, with a total of 5 layers, wherein the carbon cloth substrate has 1 layer, and the carbon paper substrate and the carbon fiber needle felt have 2 layers each, wherein the middle layer is a layer of carbon cloth substrate, and the two layers of carbon paper substrate are respectively located on the upper and lower surfaces of both sides of the carbon cloth substrate, and the two outermost surfaces are each a layer of carbon fiber needle felt.

[0140] The carbon paper substrate and the carbon cloth substrate are needle-punched and compounded by using a needle-punched composite machine. The long fibers of the carbon fiber needle-punched felt penetrate the composite substrate longitudinally and reciprocatingly to achieve the effect of combining the composite substrate layers without stratification, thereby obtaining a composite electrode. The needle-punching parameters are 2mm in depth and 50HZ in frequency.

[0141] Embodiment 6

[0142] The method for preparing the composite electrode provided in the sixth embodiment of the present disclosure comprises the following steps:

[0143] (1) Preparation of carbon paper substrate

[0144] The carbon paper substrate provided in the embodiment of the present disclosure is a self-made product of Shandong Renfeng Special Materials Co., Ltd., which is prepared by wet papermaking, resin coating, hot pressing curing, low-temperature carbonization, and high-temperature graphitization. The weight of the carbon paper substrate is 50g / m 2 , thickness is 165μm.

[0145] (2) Laser drilling of carbon paper substrate

[0146] The carbon paper substrate prepared in step (1) is subjected to laser drilling treatment, using a carbon dioxide laser drilling device to make regular holes in the carbon paper substrate, wherein the pore diameter of the carbon paper substrate is 0.3 mm and the pore spacing is 5 mm.

[0147] (3) Nitrogen-doped carbon nanofibers on the surface of carbon paper substrate

[0148] A microwave reactor was used, ammonia water was used as a nitrogen precursor, and a one-step heat treatment was performed under microwave heating conditions to grow carbon nanofibers on the surface of a carbon paper substrate, wherein the microwave heating temperature was 700°C, the reaction time was 2h, and the reaction concentration of the nitrogen precursor was 15%.

[0149] (4) Plasma treatment of carbon cloth substrate

[0150] A continuous plasma treatment test furnace was used to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10 mm / s.

[0151] (5) Needle punching composite of carbon paper substrate and carbon cloth substrate

[0152] The carbon paper substrate of step (3) and the carbon cloth substrate of step (4) are compositely stacked with the carbon fiber needle felt, with a total of 5 layers, wherein the carbon cloth substrate has 1 layer, and the carbon paper substrate and the carbon fiber needle felt have 2 layers each, wherein the middle layer is a layer of carbon cloth substrate, and the two layers of carbon paper substrate are respectively located on the upper and lower surfaces of both sides of the carbon cloth substrate, and the two outermost surfaces are each a layer of carbon fiber needle felt.

[0153] The carbon paper substrate and the carbon cloth substrate are needle-punched and compounded by using a needle-punched composite machine. The long fibers of the carbon fiber needle-punched felt penetrate the composite substrate longitudinally and reciprocatingly to achieve the effect of combining the composite substrate layers without stratification, thereby obtaining a composite electrode. The needle-punching parameters are 2mm in depth and 50HZ in frequency.

[0154] Comparative Example 1

[0155] The preparation method of the composite electrode provided in Comparative Example 1 of the present disclosure comprises the following steps:

[0156] (1) Preparation of carbon paper substrate

[0157] The carbon paper substrate provided in the embodiment of the present disclosure is a self-made product of Shandong Renfeng Special Materials Co., Ltd., which is prepared by wet papermaking, resin coating, hot pressing curing, low-temperature carbonization, and high-temperature graphitization. The weight of the carbon paper substrate is 50g / m 2 , thickness is 165μm.

[0158] (2) Laser drilling of carbon paper substrate

[0159] The carbon paper substrate prepared in step (1) is subjected to laser drilling treatment, using a carbon dioxide laser drilling device to make regular holes in the carbon paper substrate, wherein the pore diameter of the carbon paper substrate is 0.3 mm and the pore spacing is 5 mm.

[0160] (3) Plasma treatment of carbon cloth substrate

[0161] A continuous plasma treatment test furnace was used to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10 mm / s.

[0162] (4) Needle punching composite of carbon paper substrate and carbon cloth substrate

[0163] The carbon paper substrate of step (2) and the carbon cloth substrate of step (3) are compositely stacked with the carbon fiber needle felt, with a total of 5 layers, wherein the carbon cloth substrate has 1 layer, and the carbon paper substrate and the carbon fiber needle felt have 2 layers each, wherein the middle layer is a layer of carbon cloth substrate, and the two layers of carbon paper substrate are respectively located on the upper and lower surfaces of both sides of the carbon cloth substrate, and the two outermost surfaces are each a layer of carbon fiber needle felt.

[0164] The carbon paper substrate and the carbon cloth substrate are needle-punched and compounded by using a needle-punched composite machine. The long fibers of the carbon fiber needle-punched felt penetrate the composite substrate longitudinally and reciprocatingly to achieve the effect of combining the composite substrate layers without stratification, thereby obtaining a composite electrode. The needle-punching parameters are 2mm in depth and 50HZ in frequency.

[0165] Comparative Example 2

[0166] The preparation method of the composite electrode provided in Comparative Example 2 of the present disclosure comprises the following steps:

[0167] (1) Preparation of carbon paper substrate

[0168] The carbon paper substrate provided in the embodiment of the present disclosure is a self-made product of Shandong Renfeng Special Materials Co., Ltd., which is prepared by wet papermaking, resin coating, hot pressing curing, low-temperature carbonization, and high-temperature graphitization. The weight of the carbon paper substrate is 50g / m 2 , thickness is 165μm.

[0169] (2) Nitrogen-doped carbon nanofibers on the surface of carbon paper substrate

[0170] A microwave reactor was used, ammonia water was used as a nitrogen precursor, and a one-step heat treatment was performed under microwave heating conditions to grow carbon nanofibers on the surface of a carbon paper substrate, wherein the microwave heating temperature was 700°C and the reaction time was 2h.

[0171] (3) Plasma treatment of carbon cloth substrate

[0172] A continuous plasma treatment test furnace was used to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10 mm / s.

[0173] (4) Needle punching composite of carbon paper substrate and carbon cloth substrate

[0174] The carbon paper substrate of step (2) and the carbon cloth substrate of step (3) are compositely stacked with the carbon fiber needle felt, with a total of 5 layers, wherein the carbon cloth substrate has 1 layer, and the carbon paper substrate and the carbon fiber needle felt have 2 layers each, wherein the middle layer is a layer of carbon cloth substrate, and the two layers of carbon paper substrate are respectively located on the upper and lower surfaces of both sides of the carbon cloth substrate, and the two outermost surfaces are each a layer of carbon fiber needle felt.

[0175] The carbon paper substrate and the carbon cloth substrate are needle-punched and compounded by using a needle-punched composite machine. The long fibers of the carbon fiber needle-punched felt penetrate the composite substrate longitudinally and reciprocatingly to achieve the effect of combining the composite substrate layers without stratification, thereby obtaining a composite electrode. The needle-punching parameters are 2mm in depth and 50HZ in frequency.

[0176] Comparative Example 3

[0177] The preparation method of the composite electrode provided in Comparative Example 3 of the present disclosure comprises the following steps:

[0178] (1) Preparation of carbon paper substrate

[0179] The carbon paper substrate provided in the embodiment of the present disclosure is a self-made product of Shandong Renfeng Special Materials Co., Ltd., which is prepared by wet papermaking, resin coating, hot pressing curing, low-temperature carbonization, and high-temperature graphitization. The weight of the carbon paper substrate is 50g / m 2 , thickness is 165μm.

[0180] (2) Laser drilling of carbon paper substrate

[0181] The carbon paper substrate prepared in step (1) is subjected to laser drilling treatment, using a carbon dioxide laser drilling device to make regular holes in the carbon paper substrate, wherein the pore diameter of the carbon paper substrate is 0.3 mm and the pore spacing is 5 mm.

[0182] (3) Nitrogen-doped carbon nanofibers on the surface of carbon paper substrate

[0183] A microwave reactor was used, ammonia water was used as a nitrogen precursor, and a one-step heat treatment was performed under microwave heating conditions to grow carbon nanofibers on the surface of a carbon paper substrate, wherein the microwave heating temperature was 700°C and the reaction time was 2h.

[0184] (4) Plasma treatment of carbon cloth substrate

[0185] A continuous plasma treatment test furnace was used to perform atmospheric pressure plasma treatment on the surface of the carbon cloth substrate at a treatment speed of 10 mm / s.

[0186] When assembling the electrode, the carbon paper substrate and the carbon cloth substrate are stacked in sequence, with a total of 3 layers, wherein the carbon cloth substrate has 1 layer and the carbon paper substrate has 2 layers, wherein the carbon paper substrate is close to the membrane side and the carbon cloth substrate is close to the electrode plate side, that is, the middle layer is a single layer of carbon cloth substrate, and the two layers of carbon paper substrate are respectively located on the upper surface and the lower surface of the carbon cloth substrate.

[0187] The present disclosure tests the relevant data of the composite electrodes prepared in the examples and comparative examples. The test method is as follows:

[0188] Thickness: Use a fabric thickness gauge to test the thickness of the electrode without pressure, unit: mm.

[0189] Vertical resistivity: The resistivity of the electrode in the vertical direction under 1MPa pressure is tested using a powder resistivity tester. Unit: mΩ·cm 2 .

[0190] Tensile strength: The tensile strength of the electrode is tested using a universal testing machine, unit: MPa.

[0191] Porosity: Use a true density tester to test the porosity of the electrode, unit: %.

[0192] Coulomb efficiency, energy efficiency, and voltage efficiency tests: Prepare proton membranes, plates, electrodes, peristaltic pumps, vanadium electrolytes, etc. in advance, and use an electrochemical workstation to perform charge and discharge cycle tests on the electrodes. The test temperature is 50°C and the current density is 120 mA / cm 2 .

[0193] The test results of the embodiments of the present disclosure and the comparative examples are shown in the following table:

[0194]

[0195] As can be seen from the above table, by comparing the data of the embodiment and the comparative example, it can be found that the composite electrode prepared by the method of the embodiment of the present disclosure has a thickness of less than 0.78 mm and a vertical resistivity of less than 31 mΩ·cm 2 , Coulomb efficiency is greater than 94.25%, energy efficiency is greater than 80.75%, and voltage efficiency is greater than 81.68%.

[0196] By comparing Examples 1 to 6 and Comparative Examples 1 to 3, it can be seen that the electrochemical performance (including coulomb efficiency, energy efficiency and voltage efficiency) of the composite electrode obtained in Examples 1 to 4 is better than the composite electrode obtained in Comparative Example 1 where the carbon paper substrate is not subjected to nitrogen doping treatment, and is also better than the composite electrode obtained in Comparative Example 2 where the carbon paper substrate is not subjected to laser drilling treatment, and is also better than the composite electrode obtained in Comparative Example 3 where the carbon paper substrate and the carbon cloth substrate are stacked and placed in sequence during electrode assembly. The composite electrode in Comparative Example 3 has a large vertical resistivity and a small porosity, a small specific surface area, and a small number of active sites for promoting the redox reaction of vanadium ions.

[0197] Additionally, as used herein, "or" used in a list of items beginning with "at least one" indicates a separate list, so that, for example, a list of "at least one of A, B, or C" means A or B or C, or AB or AC or BC, or ABC (i.e., A and B and C). Furthermore, the word "exemplary" does not mean that the example described is preferred or better than other examples.

[0198] It should also be noted that in the system and method of the present disclosure, each component or each step can be decomposed and / or recombined. Such decomposition and / or recombination should be regarded as equivalent solutions of the present disclosure.

[0199] Various changes, substitutions, and modifications of the techniques described herein may be made without departing from the teachings defined by the appended claims. Furthermore, the scope of the claims of the present disclosure is not limited to the specific aspects of the processes, machines, manufactures, compositions of events, means, methods, and actions described above. Currently existing or later to be developed processes, machines, manufactures, compositions of events, means, methods, or actions that perform substantially the same functions or achieve substantially the same results as the corresponding aspects described herein may be utilized. Thus, the appended claims include such processes, machines, manufactures, compositions of events, means, methods, or actions within their scope.

[0200] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present disclosure. Therefore, the present disclosure is not intended to be limited to the aspects shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

[0201] The above description has been given for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present disclosure to the forms disclosed herein. Although multiple example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations thereof.

Claims

1. A method for preparing a composite electrode, characterized in that: include: Providing at least two layers of carbon paper substrate, carbon cloth substrate and two layers of carbon fiber needle felt; Stacking at least two layers of the carbon paper substrate and the carbon cloth substrate in a thickness direction to obtain a carbon fiber composite substrate; wherein the carbon cloth substrate is located between the at least two layers of the carbon paper substrate; The carbon fiber composite substrate is needle-punched and composited using two layers of the carbon fiber needle-punched felt to obtain a composite electrode; wherein the two layers of the carbon fiber needle-punched felt are respectively formed on the upper surface and the lower surface of the carbon fiber composite substrate.

2. The method for preparing a composite electrode according to claim 1, characterized in that: Before stacking at least two layers of the carbon paper substrate and the carbon cloth substrate in a thickness direction to obtain a carbon fiber composite substrate, the method further comprises: Each layer of the carbon paper substrate is subjected to nitrogen doping treatment using a nitrogen precursor.

3. The method for preparing a composite electrode according to claim 2, characterized in that: The reaction concentration of the nitrogen precursor is 10%-15%.

4. The method for preparing a composite electrode according to claim 2, characterized in that: The nitrogen doping treatment is a microwave nitrogen doping treatment, and the process conditions of the microwave nitrogen doping treatment include: a microwave treatment temperature of 700° C.-800° C., and a reaction time of 1 h-3 h.

5. The method for preparing a composite electrode according to claim 2, characterized in that: Before performing nitrogen doping treatment on each layer of the carbon paper substrate using a nitrogen precursor, the method further comprises: The carbon paper substrate is subjected to laser drilling treatment.

6. The method for preparing a composite electrode according to claim 5, characterized in that: The pore size of the carbon paper substrate after laser drilling is 0.2mm-0.5mm, and the pore spacing is 3mm-8mm.

7. The method for preparing a composite electrode according to any one of claims 1 to 6, characterized in that: Before stacking at least two layers of the carbon paper substrate and the carbon cloth substrate in a thickness direction to obtain a carbon fiber composite substrate, the method further comprises: The surface of the carbon cloth substrate is subjected to plasma treatment.

8. The method for preparing a composite electrode according to any one of claims 1 to 6, characterized in that: The process conditions of the needle punching composite include: needle depth of 2 mm and frequency of 50 Hz.

9. A composite electrode, characterized in that: The composite electrode is prepared using the composite electrode preparation method described in any one of claims 1 to 8, and the composite electrode includes a carbon fiber composite substrate and two layers of carbon fiber needle felt formed on the upper surface and lower surface of the carbon fiber composite substrate, respectively. The carbon fiber composite substrate includes at least two layers of carbon paper substrate and carbon cloth substrate stacked along the thickness direction, and the carbon cloth substrate is located between at least two layers of the carbon paper substrate.

10. A battery, characterized in that: The battery comprises the composite electrode according to claim 9.

Images