All-vanadium redox flow battery carbon felt based on W-CCN and preparation method and application thereof

Abstract

The invention discloses an all-vanadium redox flow battery carbon felt based on W-CCN and a preparation method and application thereof, and belongs to the technical field of electrochemical energy storage, and the method comprises the following steps: mixing and dissolving urea and ammonium metatungstate in deionized water, heating in a water bath, stirring, evaporating to dryness, mixing with lithium chloride, uniformly grinding, sequentially roasting, cooling to room temperature, washing, and drying to obtain the all-vanadium redox flow battery carbon felt based on W-CCN. The W-CCN composite material is obtained; the W-CCN composite material is prepared into a W-CCN solution; and soaking the carbon felt in the W-CCN solution, and carrying out vacuum drying to obtain the W-CCN-based all-vanadium redox flow battery carbon felt. W-CCN is loaded on the carbon felt, and tungsten is used as an efficient catalytic center to accelerate positive and negative electrode electron transfer, so that the activation energy is reduced, and side reactions are reduced; the W-CCN nanostructure increases the electrochemical active surface area, more active sites are exposed, and the utilization rate of the electrolyte is improved; the nitrogen functional group improves the hydrophilicity of the carbon felt, ensures full permeation of electrolyte and reduces ion transmission ohmic polarization; and the W-N bond slows down electrochemical corrosion and oxidation of the carbon felt, improves the electrode durability and prolongs the cycle life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a carbon felt for an all-vanadium redox flow battery based on W-CCN, its preparation method, and its application. Background Technology

[0002] With the increasing prominence of clean energy, the demand for energy storage technologies is becoming more diversified. Flow batteries, as a highly efficient and sustainable medium- to long-term energy storage technology, have attracted significant attention. Vanadium redox flow batteries (VRFBs) have become an important candidate technology for large-scale energy storage due to their advantages such as storing active materials in a liquid electrolyte, independently designable power and capacity, and long cycle life, showing broad application prospects in smart grids, renewable energy grid integration, and distributed generation. However, their commercialization process is still constrained by low energy conversion efficiency and difficulties in increasing power density.

[0003] The core root cause of low energy efficiency lies in various polarization losses within the battery, among which electrochemical polarization is a key factor. The electrochemical reactions in vanadium redox flow batteries primarily occur on the carbon felt electrode surfaces of both the positive and negative electrodes. Currently, commercially available vanadium redox flow batteries commonly use heat-treated carbon felt or graphite felt as electrodes. Although the heat treatment process can introduce oxygen-containing functional groups to some extent, improving wettability and electrochemical activity, the intrinsic catalytic activity of carbon materials for the vanadium ion couple remains very low, leading to serious consequences. For example, high activation overpotential: positive electrode (VO 2+ / VO2 + ) and negative electrode (V 3+ / V 2+The slow electron transfer process and high activation energy of the main reaction increase the probability of side reactions. To drive the slow electrode reactions, an additional voltage much higher than the theoretical equilibrium potential must be applied, which manifests as an increase in charging voltage during charging and a decrease in discharging voltage during discharging. Significant voltage polarization and energy loss: The aforementioned overpotential directly translates into huge voltage polarization, significantly reducing the battery's voltage efficiency. A large amount of electrical energy is dissipated as heat, resulting in unsatisfactory energy efficiency of the entire system. Power density limitation: The slow reaction kinetics limit the battery's ability to operate at high current densities because polarization intensifies dramatically at high rates, forcing the battery to operate only at lower current densities, thus restricting the improvement of its power density. Chinese patent application CN114156493A proposes a method to improve the conductivity and activity of carbon felt by combining sulfuric acid activation with acetylene black impregnation. While this improves conductivity, its effect on reaction kinetics is limited. Chinese patent application CN115472849A introduces elemental Bi on the surface of the carbon felt to enhance the negative electrode reaction activity, but this process is complex, lacks stability, and has limited catalytic effect on the positive electrode. To overcome the shortcomings of insufficient catalytic activity in carbon felt electrodes, some studies have attempted to modify the electrodes. These modifications mainly include: modification with noble metals and their oxides, such as using platinum, iridium, ruthenium, and other noble metal nanoparticles or their oxides as catalysts. Although these materials possess high catalytic activity, their high cost and resource scarcity severely hinder their application in large-scale energy storage. Furthermore, their long-term stability in highly acidic and oxidizing working environments also faces challenges.

[0004] Therefore, developing a novel electrode material that combines high intrinsic catalytic activity, excellent electronic conductivity, outstanding chemical stability, and low cost has become an urgent need and an important research direction for advancing vanadium redox flow battery technology. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a carbon felt for a vanadium redox flow battery based on W-CCN, its preparation method and application, so as to solve the technical problems of low catalytic activity, slow reaction kinetics, poor stability and complex modification process of existing carbon felt electrodes for vanadium redox flow batteries.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN, comprising: Urea and ammonium metatungstate were mixed and dissolved in deionized water, and then heated and stirred in a water bath to evaporate to dryness to obtain a precursor mixture. The precursor mixture was mixed with lithium chloride and ground evenly, and then calcined, cooled to room temperature, washed and dried to obtain a W-CCN composite material. The W-CCN composite material was dissolved in deionized water to prepare a W-CCN solution. The carbon felt was immersed in the W-CCN solution, and the immersed carbon felt was dried under vacuum to obtain a W-CCN-based vanadium redox flow battery carbon felt.

[0007] Preferably, the water bath heating temperature is 80-85℃.

[0008] Preferably, the calcination conditions include: heating to 560-600℃ at a heating rate of 2-5℃ / min, and holding at that temperature for 2-4 hours.

[0009] Preferably, the washing conditions include: washing with hot deionized water at 60-80°C until no chloride ions are present.

[0010] Preferably, the drying conditions include drying overnight at 60-80°C.

[0011] Preferably, the concentration of the W-CCN solution is 5-25 mg / mL.

[0012] Preferably, the carbon felt is soaked in the W-CCN solution for 30-60 minutes.

[0013] Preferably, the vacuum drying temperature is 60-80℃ and the vacuum drying time is 6-10h.

[0014] This invention discloses a carbon felt for a vanadium redox flow battery based on W-CCN, which is prepared using the above-described method for preparing carbon felt for a vanadium redox flow battery based on W-CCN.

[0015] This invention discloses the application of W-CCN-based carbon felt for vanadium redox flow batteries in the preparation of vanadium redox flow batteries, with a coulombic efficiency of 95.0%-96.8%, an energy efficiency of 80.56%-84.02%, and a voltage efficiency of 84.8%-86.8%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN. By loading tungsten-doped graphitic carbon nitride (W-CCN) onto the carbon felt, the tungsten-doped graphitic carbon nitride composite material is applied to the electrode field of all-vanadium redox flow batteries. Tungsten in W-CCN serves as a highly efficient catalytic center, which can significantly accelerate the reaction of the cathode (VO2+). 2+ / VO2 +) and negative electrode (V 3+ / V 2+ This method utilizes electron transfer processes to effectively reduce overpotential and improve battery voltage and energy efficiency. Simultaneously, the graphitic carbon nitride substrate in W-CCN exhibits stable chemical properties, and the strong WN bonds formed between the substrate and tungsten effectively prevent the dissolution and loss of active components during cycling. It also protects the carbon felt substrate, mitigating electrochemical corrosion and oxidation, and significantly enhancing electrode durability and battery cycle life. This method offers complete process steps and is easy to operate, providing a basic framework for subsequent parameter optimization.

[0017] Furthermore, the water bath heating temperature is 80-85℃. This temperature range ensures that urea and ammonium metatungstate are fully dissolved and mixed in deionized water, maintaining a stable reaction environment during the stirring evaporation process. At this temperature, the water gradually evaporates, allowing the reactants to mix uniformly and form a precursor mixture. This provides a uniform precursor foundation for the nucleation and growth of W-CCN during the subsequent high-temperature calcination process. The suitable evaporation temperature avoids low evaporation efficiency due to excessively low temperatures and prevents localized uneven reactions that may occur due to excessively high temperatures.

[0018] Furthermore, the calcination conditions are as follows: heating to 560-600℃ at a heating rate of 2-5℃ / min, and holding at this temperature for 2-4 hours. This calcination process is a key step in the synthesis of tungsten-doped graphitic carbon nitride, ensuring the acquisition of W-CCN composite materials with highly efficient catalytic activity and a stable WN bond structure. A moderate heating rate avoids structural defects in the product caused by drastic temperature changes, ensuring sufficient decomposition and rearrangement of the precursor during the heating process; the calcination temperature range of 560-600℃ allows graphitic carbon nitride to smoothly form a layered structure, while simultaneously promoting the doping of tungsten atoms into the carbon nitride framework through WN chemical bonds; the 2-4 hour holding time ensures the full progress of the reaction, resulting in W-CCN products with good crystallinity and uniform distribution of active sites.

[0019] Furthermore, the washing conditions involved washing with hot deionized water at 60-80℃ until no chloride ions were present, followed by drying overnight at 60-80℃. The calcined product contained soluble salts such as lithium chloride; washing with hot deionized water effectively removed chloride ions. The product was then tested with 0.1 mol / L silver nitrate solution until no white precipitate was found, ensuring the purity of the W-CCN composite powder and preventing residual impurities from adversely affecting subsequent electrode performance. The drying temperature of 60-80℃ was moderate and effective in removing moisture without damaging the structure of W-CCN or the stability of the WN bonds. This purification process ensured the purity and structural integrity of the W-CCN composite material, providing high-quality active material for carbon felt loading.

[0020] Furthermore, the concentration of the W-CCN solution was 5-25 mg / mL. Performance data from Examples 1-4 show that as the W-CCN solution concentration gradually increased from 5 mg / mL (Example 1) to 20 mg / mL (Example 4), the coulombic efficiency of the battery increased from 95.0% to 96.4%, the voltage efficiency from 84.8% to 86.8%, and the energy efficiency from 80.56% to 83.68%, exhibiting a continuous upward trend. However, when the concentration was further increased to 25 mg / mL (Example 5), the efficiency decreased slightly (coulombic efficiency 96.1%, energy efficiency 83.03%). This indicates that the concentration range of 5-25 mg / mL covers the range from low concentration to slightly above the optimal concentration, with approximately 20 mg / mL being the preferred concentration. Within this range, W-CCN can form a suitable and uniform load on the carbon felt surface, ensuring sufficient catalytic active sites while avoiding the problem of W-CCN clogging the micropores and mesopores on the carbon felt surface and reducing the effective reaction area due to excessively high concentrations.

[0021] Furthermore, the carbon felt was immersed in the W-CCN solution for 30-60 minutes. Performance data from Examples 4, 6, and 7 show that at the same concentration (20 mg / mL), as the immersion time increased from 30 minutes (Example 4) to 45 minutes (Example 6), and then to 60 minutes (Example 7), the coulombic efficiency of the battery increased from 96.4% to 96.8%, and the energy efficiency increased from 83.68% to 84.02%, exhibiting a continuous upward trend. This is because during immersion, W-CCN molecules initially adsorb rapidly onto the outer surface of the carbon felt and at the macropore inlets, resulting in limited catalytic active sites. As the immersion time increased to 60 minutes, the concentration gradient-driven diffusion effect allowed W-CCN molecules sufficient time to diffuse from the bulk solution into the internal pores and deeper surfaces of the carbon felt, significantly increasing the number of catalytic active sites and thus improving the electrochemical performance of the battery. The 30-60 minute range ensured sufficient penetration and adhesion of W-CCN.

[0022] Furthermore, the vacuum drying temperature was 60-80℃, and the time was 6-10h. Performance data from Examples 7-11 show that when the concentration (20mg / mL) and soaking time (60min) were fixed, changing the drying temperature (60-80℃) and drying time (6-10h) resulted in minimal changes in various efficiency indicators: energy efficiency fluctuated between 83.66% and 84.02%, coulombic efficiency remained stable at 96.6%-96.8%, and voltage efficiency remained stable at 86.6%-86.8%. This indicates that the preparation method has high tolerance for subsequent drying processes; the temperature range of 60-80℃ and the time range of 6-10h can effectively remove the solvent and allow W-CCN to firmly adhere to the carbon felt surface without damaging the already formed active site structure, demonstrating the stability and operability of the process.

[0023] This invention discloses a W-CCN-based carbon felt for an all-vanadium redox flow battery, in which W-CCN composite material with a WN bond structure is successfully loaded onto the carbon felt surface. On one hand, the tungsten in W-CCN acts as a highly efficient catalytic center, accelerating the electron transfer process between the positive and negative electrodes, reducing the activation energy of the main reaction, and minimizing side reactions. On the other hand, W-CCN is rich in nitrogen functional groups and possesses excellent hydrophilicity, significantly improving the wettability of the carbon felt to the vanadium electrolyte, ensuring sufficient electrolyte penetration into the electrode's internal pores, and reducing ohmic polarization of ion transport. Simultaneously, the nanostructure of W-CCN significantly increases the electrochemically active surface area of ​​the carbon felt, exposing more active sites and improving the utilization rate of active materials. Furthermore, the graphitic carbon nitride substrate is chemically stable, and the strong chemical bond between it and tungsten effectively prevents the dissolution and loss of active components, while also protecting the carbon felt substrate and mitigating electrochemical corrosion and oxidation. This product integrates high-efficiency catalysis, excellent hydrophilicity, and high stability, making it an ideal electrode material for all-vanadium redox flow batteries.

[0024] This invention discloses the application of W-CCN-based carbon felt for vanadium redox flow batteries in their fabrication. Performance test results from Examples 1-11 show that the vanadium redox flow batteries assembled using the W-CCN-modified carbon felt of this invention achieve a coulombic efficiency of 95.0%-96.8%, a voltage efficiency of 84.8%-86.8%, and an energy efficiency of 80.56%-84.02%, all superior to the 93.8%, 83.7%, and 78.51% of Comparative Example 1 (unmodified carbon felt). This is because the W-CCN on the carbon felt of this invention exerts multiple synergistic effects: the tungsten catalytic center accelerates electron transfer, reduces overpotential, and improves voltage and energy efficiency; the hydrophilicity of W-CCN and the increased active surface area improve electrolyte utilization and the number of reactive sites, further enhancing efficiency; the stable WN bonds and the protective effect of the carbon nitride substrate reduce side reactions and loss of active components, maintaining high coulombic efficiency. This battery combines high efficiency and high stability, making it suitable for large-scale energy storage applications such as smart grids, renewable energy grid integration, and distributed generation. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0027] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0028] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0029] In this invention, unless otherwise specified, the numerical range "a~b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" indicates that the text already includes real numbers between "6~22", and "6~22" is simply an abbreviation for these numerical combinations.

[0030] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0031] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0032] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0033] This invention provides a method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN, comprising the following steps: 1) Synthesis of W-CCN composite material 100g of urea and 6g of ammonium metatungstate were dissolved and mixed in 200ml of deionized water, and then heated and stirred in a water bath at 80-85℃ until the mixture was evaporated to dryness, yielding a precursor mixture. The precursor mixture was then thoroughly ground with 60g of lithium chloride and placed in a covered alumina crucible. The mixture was then calcined in a muffle furnace at a programmed temperature of 2-5℃ / min to 560-600℃ for 2-4 hours, followed by natural cooling to room temperature. Finally, the cooled sintered block was washed repeatedly with 70℃ hot deionized water until no chloride ions were found (the filtrate was tested with 0.1mol / L silver nitrate solution and no white precipitate was observed). The resulting solid was then dried overnight in an oven at 60-80℃ to obtain a yellow W-CCN composite powder, which was stored in a desiccator.

[0034] 2) Preparation of carbon felt for all-vanadium redox flow batteries based on W-CCN A certain mass of W-CCN composite material powder was weighed and dissolved in deionized water to form W-CCN solutions of different concentrations. 20 ml of each solution was taken, and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 30-60 minutes. The immersed carbon felt was then placed in a vacuum drying oven and dried at 60-80℃ for 6-10 hours to obtain the W-CCN-based vanadium redox flow battery carbon felt.

[0035] This invention supports W-CCN composite material on carbon felt. The tungsten in the W-CCN composite material serves as a highly efficient catalytic center, which can significantly accelerate the cathode (VO2+) process. 2+ / VO2 + ) and negative electrode (V 3+ / V 2+ The electron transfer process of the W-CCN composite material effectively reduces overpotential and improves the voltage and energy efficiency of the vanadium redox flow battery. The strong acidity and oxidizing environment of the vanadium redox flow battery pose a severe challenge to the electrode materials. The graphitic carbon nitride substrate in the W-CCN composite material is chemically stable, and the strong WN bonds formed between it and tungsten effectively prevent the dissolution and loss of active components during cycling. Simultaneously, it also protects the carbon felt substrate, slowing down its electrochemical corrosion and oxidation, significantly improving electrode durability and battery cycle life, enhancing the chemical and structural stability of the electrode, and extending cycle life. The carbon felt surface is hydrophobic, resulting in poor wettability to aqueous electrolytes and increasing ion transport resistance. The W-CCN composite material optimizes the electrode interface properties and promotes ion mass transfer. Due to its high nitrogen functional group content, it has good hydrophilicity. After loading with the W-CCN composite material, the wettability of the carbon felt to the vanadium electrolyte is significantly improved, ensuring that the electrolyte can fully penetrate into the internal pores of the electrode and effectively reducing ohmic polarization of ion transport. Significantly increasing the electrochemical active surface area of ​​the carbon felt exposes more active sites, providing a greater number of sites for the redox reactions of vanadium ions. This improves the utilization rate of the active material, significantly enhancing capacity utilization and slowing down long-term capacity decay. During battery operation, especially on the positive electrode side, higher potentials can lead to side reactions such as oxygen evolution on the carbon felt surface, consuming charge and reducing coulombic efficiency. Excellent catalytic activity ensures efficient and reversible conversion of vanadium ions during charge and discharge, reducing the occurrence of side reactions and contributing to improved battery coulombic efficiency and operational stability.

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The components of the embodiments of the present invention described and shown herein can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0037] Example 1 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: 100g of urea and 6g of ammonium metatungstate were dissolved and mixed in 200ml of deionized water, and then heated and stirred in an 80℃ water bath until dry to obtain a precursor mixture. The precursor mixture was then thoroughly ground with 60g of lithium chloride and placed in a covered alumina crucible. The mixture was then heated in a muffle furnace to 580℃ at a rate of 3℃ / min and calcined for 3 hours, followed by natural cooling to room temperature. Finally, the cooled sintered block was washed repeatedly with 70℃ hot deionized water until no chloride ions were found (the filtrate showed no white precipitate when tested with 0.1mol / L silver nitrate solution). The resulting solid was then dried overnight in an 80℃ oven to obtain yellow W-CCN composite powder, which was stored in a desiccator.

[0038] The prepared W-CCN composite powder was prepared into a 5 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 30 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 70 °C for 8 h to finally obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0039] Example 2 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: The preparation process of W-CCN composite powder is the same as in Example 1.

[0040] The prepared W-CCN composite powder was prepared into a 10 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 30 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 70 °C for 8 h to finally obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0041] Example 3 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: The preparation process of W-CCN composite powder is the same as in Example 1.

[0042] The prepared W-CCN composite powder was formulated into a 15 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 30 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 70 °C for 8 h to obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0043] Example 4 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: The preparation process of W-CCN composite powder is the same as in Example 1.

[0044] The prepared W-CCN composite powder was formulated into a 20 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 30 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 70 °C for 8 h to obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0045] Example 5 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: The preparation process of W-CCN composite powder is the same as in Example 1.

[0046] The prepared W-CCN composite powder was formulated into a 25 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 30 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 70 °C for 8 h to finally obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0047] Example 6 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: The preparation process of W-CCN composite powder is the same as in Example 1.

[0048] The prepared W-CCN composite powder was formulated into a 20 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 45 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 70 °C for 8 h to obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0049] Example 7 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: The preparation process of W-CCN composite powder is the same as in Example 1.

[0050] The prepared W-CCN composite powder was prepared into a 20 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 60 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 70 °C for 8 h to finally obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0051] Example 8 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: The preparation process of W-CCN composite powder is the same as in Example 1.

[0052] The prepared W-CCN composite powder was formulated into a 20 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 60 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 60 °C for 8 h to obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0053] Example 9 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: The preparation process of W-CCN composite powder is the same as in Example 1.

[0054] The prepared W-CCN composite powder was formulated into a 20 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 60 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 80 °C for 8 h to finally obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0055] Example 10 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: 100g of urea and 6g of ammonium metatungstate were dissolved and mixed in 200ml of deionized water, and then heated and stirred in an 83℃ water bath until dry to obtain a precursor mixture. The precursor mixture was then thoroughly ground with 60g of lithium chloride and placed in a covered alumina crucible. The mixture was then heated in a muffle furnace to 560℃ at a programmed rate of 2℃ / min and calcined for 2 hours, followed by natural cooling to room temperature. Finally, the cooled sintered block was washed repeatedly with 70℃ hot deionized water until no chloride ions were found (the filtrate showed no white precipitate when tested with 0.1mol / L silver nitrate solution). The resulting solid was then dried overnight in a 60℃ oven to obtain yellow W-CCN composite powder, which was stored in a desiccator.

[0056] The prepared W-CCN composite powder was formulated into a 20 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 60 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 70 °C for 6 h to obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0057] Example 11 The preparation of a carbon felt for an all-vanadium redox flow battery based on W-CCN includes: 100g of urea and 6g of ammonium metatungstate were dissolved and mixed in 200ml of deionized water, and then heated and stirred in an 85℃ water bath until dry to obtain a precursor mixture. The precursor mixture was then thoroughly ground with 60g of lithium chloride and placed in a covered alumina crucible. The mixture was then heated in a muffle furnace to 600℃ at a programmed rate of 5℃ / min and calcined for 4 hours, followed by natural cooling to room temperature. Finally, the cooled sintered block was washed repeatedly with 70℃ hot deionized water until no chloride ions were found (the filtrate showed no white precipitate when tested with 0.1mol / L silver nitrate solution). The resulting solid was then dried overnight in a 70℃ oven to obtain yellow W-CCN composite powder, which was stored in a desiccator.

[0058] The prepared W-CCN composite powder was formulated into a 20 mg / ml solution. 20 ml of this solution was taken and a carbon felt measuring 3 cm × 3 cm and 3 mm in thickness was immersed in the solution for 60 min. The immersed carbon felt was then placed in a vacuum drying oven and dried at 70 °C for 10 h to finally obtain the carbon felt for the W-CCN-based all-vanadium redox flow battery.

[0059] Comparative Example 1 Unmodified carbon felt was used.

[0060] The carbon felt vanadium redox flow battery assembled in Examples 1-11 and Comparative Example 1 were subjected to vanadium redox flow battery performance tests. The experimental conditions were: commercially available carbon felt electrodes, Nafion membrane with a thickness of 50 μm and a size of 3.5 cm × 3.5 cm, and a charge / discharge current density of 80 mA / cm². 2 The charging time was 6 hours, the discharge cutoff voltage was 1.0V, the positive and negative electrolytes were both 100mL, the test environment temperature was room temperature, and the battery performance in the examples and comparative examples was tested under the same conditions. The test results are shown in Table 2.

[0061] Table 1 Comparison of parameters in Examples 1-11 and Comparative Example 1

[0062] Table 2 Comparison of performance test results of vanadium redox flow batteries assembled with carbon felt in Examples 1-11 and Comparative Example 1

[0063] Table 1 compares the parameters in Examples 1-11 and Comparative Example 1; Table 2 compares the performance test results of the vanadium redox flow batteries assembled with carbon felt prepared in Examples 1-11 and Comparative Example 1. As shown in the tables, the coulombic efficiency of the vanadium redox flow battery is 95.0%-96.8%; the energy efficiency is 80.56%-84.02%; and the voltage efficiency is 84.8%-86.8%. By loading W-CCN onto the carbon felt, the cathode (VO2+) can be greatly accelerated. 2+ / VO2 + ) and negative electrode (V 3+ / V 2+ The electron transfer process of the carbon felt lowers the activation energy of the main reaction and reduces the occurrence of side reactions. On the other hand, it significantly increases the electrochemical active surface area of ​​the carbon felt, exposing more active sites and thus improving the utilization rate of the electrolyte. It also significantly improves the wettability of the carbon felt to the vanadium electrolyte, ensuring that the electrolyte can fully penetrate into the internal pores of the electrode, effectively reducing ohmic polarization of ion transport, and significantly improving electrode durability and battery cycle life.

[0064] Comparing Examples 1-5 with Comparative Example 1, the electrochemical performance data measured when W-CCN solutions of different concentrations were applied to the carbon felt electrode of a vanadium redox flow battery were all superior to those measured using an unmodified carbon felt electrode. Table 2 clearly shows that W-CCN, on the one hand, accelerates the reaction of the positive electrode (VO2+)... 2+ / VO2 + ) and negative electrode (V 3+ / V 2+The electron transfer process effectively reduces overpotential, lowers the activation energy of the main reaction, and reduces the occurrence of side reactions, thereby improving the voltage efficiency and energy efficiency of the vanadium redox flow battery. On the other hand, the graphitic carbon nitride substrate in W-CCN is chemically stable, and the strong chemical bonds formed with tungsten (such as WN bonds) effectively prevent the dissolution and loss of active components during cycling, thus protecting the carbon felt substrate, slowing down its electrochemical corrosion and oxidation, significantly improving electrode durability and battery cycle life, enhancing the chemical and structural stability of the electrode, and extending cycle life. Furthermore, loading W-CCN onto the carbon felt surface optimizes the electrode interface properties and promotes ion mass transfer. Due to its rich nitrogen functional groups and good hydrophilicity, the wettability of the carbon felt to the vanadium electrolyte is significantly improved, ensuring that the electrolyte can fully penetrate into the internal pores of the electrode, effectively reducing ohmic polarization of ion transport, thereby improving the electrochemical performance of the vanadium redox flow battery. Furthermore, loading W-CCN onto the carbon felt significantly increases the electrochemical active surface area of ​​the carbon felt, exposing more active sites on the carbon felt electrode. This provides a greater number of active sites for the redox reaction of vanadium ions, improving the utilization rate of the active material, significantly increasing capacity utilization, and slowing down long-term capacity decay, thereby improving the battery's coulombic efficiency, voltage efficiency, and energy efficiency. Finally, when W-CCN is loaded onto the carbon felt, its excellent catalytic activity ensures the efficient and reversible conversion of vanadium ions during charge and discharge, reducing the occurrence of side reactions, thus improving the battery's coulombic efficiency and operational stability.

[0065] Compared with Examples 1-5, Example 4 exhibits relatively superior overall electrochemical performance, demonstrating that increasing the concentration of W-CCN solution significantly improves the coulombic efficiency, voltage efficiency, and energy efficiency of the vanadium redox flow battery. This indicates that different concentrations of W-CCN solution have a profound impact on the performance of the fabricated carbon felt electrode. Table 2 clearly shows that increasing the concentration of W-CCN solution improves the electrochemical performance of the vanadium redox flow battery. However, when the concentration of W-CCN solution is too high, the coulombic efficiency, voltage efficiency, and energy efficiency decrease. This is mainly because when the concentration of W-CCN solution is too high, W-CCN blocks the micropores and mesopores on the carbon felt surface, reducing the effective reaction area. The electrolyte cannot enter the blocked pores, thus reducing the actual area participating in the reaction.

[0066] Comparing Examples 4 and 6-7, Example 7 exhibits relatively superior overall electrochemical performance, demonstrating that increasing the immersion time of the carbon felt electrode significantly improves the coulombic efficiency, voltage efficiency, and energy efficiency of the vanadium redox flow battery. This indicates that the immersion time of the carbon felt electrode in the W-CCN solution has a profound impact on the performance of the fabricated carbon felt electrode. Table 2 clearly shows that extending the immersion time of the carbon felt electrode in the W-CCN solution can improve the electrochemical performance of the vanadium redox flow battery. This is mainly because, during the carbon felt immersion process, W-CCN molecules are initially rapidly adsorbed onto the outer surface of the carbon felt electrode, which is most easily accessible, and at the entrances of some macropores. At this stage, the adsorption amount is small, the coverage is uneven, and only isolated spots are formed, limiting the catalytic active sites. As the immersion time increases, the concentration gradient-driven diffusion continues, giving W-CCN molecules sufficient time to diffuse from the bulk solution into the internal pores of the carbon felt, deeper surfaces, and previously uncovered areas, increasing the number of catalytic active sites and thus improving the electrochemical performance of the vanadium redox flow battery.

[0067] Comparing Examples 7-11, the electrochemical performance data did not change significantly, proving that the drying temperature and drying time of the carbon felt electrode have little effect on the active sites and reaction area on the carbon felt electrode.

[0068] In summary, this invention provides a W-CCN-based carbon felt for an all-vanadium redox flow battery, its preparation method, and its application. This method loads W-CCN onto the carbon felt, which can significantly accelerate the cathode (VO2+) process. 2+ / VO2 + ) and negative electrode (V 3+ / V 2+ The electron transfer process reduces the activation energy of the main reaction and decreases the occurrence of side reactions. On the other hand, it significantly increases the electrochemical active surface area of ​​the carbon felt, exposing more active sites and thus improving the utilization rate of the electrolyte. It also significantly improves the wettability of the carbon felt to the vanadium electrolyte, ensuring that the electrolyte can fully penetrate into the internal pores of the electrode and effectively reduce the ohmic polarization of ion transport. In addition, it can slow down the electrochemical corrosion and oxidation of the carbon felt, thereby significantly improving the durability of the electrode and the cycle life of the battery.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN, characterized in that, include: Urea and ammonium metatungstate were mixed and dissolved in deionized water, and then evaporated to dryness by heating and stirring in a water bath to obtain a precursor mixture. The precursor mixture was mixed and ground evenly with lithium chloride, and then calcined, cooled to room temperature, washed and dried to obtain a W-CCN composite material. The W-CCN composite material was dissolved in deionized water to prepare a W-CCN solution. The carbon felt was immersed in the W-CCN solution, and the immersed carbon felt was vacuum dried to obtain a W-CCN-based carbon felt for an all-vanadium redox flow battery.

2. The method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN according to claim 1, characterized in that, The water bath heating temperature is 80-85℃.

3. The method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN according to claim 1, characterized in that, The calcination conditions include: heating to 560-600℃ at a heating rate of 2-5℃ / min, and holding at that temperature for 2-4 hours.

4. The method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN according to claim 1, characterized in that, The washing conditions include: washing with hot deionized water at 60-80℃ until there are no chloride ions.

5. The method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN according to claim 1, characterized in that, The drying conditions include drying overnight at 60-80°C.

6. The method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN according to claim 1, characterized in that, The concentration of the W-CCN solution is 5-25 mg / mL.

7. The method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN according to claim 1, characterized in that, The carbon felt is soaked in W-CCN solution for 30-60 minutes.

8. The method for preparing carbon felt for an all-vanadium redox flow battery based on W-CCN according to claim 1, characterized in that, The vacuum drying temperature is 60-80℃, and the vacuum drying time is 6-10h.

9. A carbon felt for an all-vanadium redox flow battery based on W-CCN, characterized in that, The carbon felt for a vanadium redox flow battery based on W-CCN was prepared using any one of claims 1-8.

10. The application of the W-CCN-based carbon felt for all-vanadium redox flow batteries as described in claim 9 in the preparation of all-vanadium redox flow batteries, characterized in that, The vanadium redox flow battery has a coulombic efficiency of 95.0%-96.8%, an energy efficiency of 80.56%-84.02%, and a voltage efficiency of 84.8%-86.8%.

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