Preparation method of modified zinc-bromine flow battery carbon felt negative electrode and carbon felt negative electrode prepared by method

Abstract

The invention discloses a preparation method of a modified zinc-bromine flow battery carbon felt negative electrode and the carbon felt negative electrode prepared by the method, and belongs to the field of zinc-bromine flow batteries. According to the method, after the carbon felt is soaked in a mixed solution of cuprous sulfate, water and acetonitrile, the acetonitrile is gradually evaporated from the solution through heating, the cuprous sulfate is gradually subjected to disproportionation reaction, and the copper elementary substance generated by the disproportionation reaction of the cuprous sulfate is deposited on the surface of the carbon felt, so that the purpose of loading the modified carbon felt with the copper elementary substance is achieved. The copper elementary substance is relatively stable in chemical property and has good zinc affinity, and the copper elementary substance is loaded on the surface of the carbon felt, so that the overpotential of zinc nucleation can be reduced, and reaction active sites on the surface of the carbon felt are increased. Besides, relatively strong acting force exists between copper and zinc, so that uniform deposition / stripping of zinc in the charging and discharging process is facilitated, a more uniform zinc deposition layer is formed on the surface of the carbon felt, formation of zinc dendrites is reduced, and the electrochemical performance of the zinc-bromine flow battery is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of zinc-bromine flow batteries, and particularly relates to a preparation method of a modified carbon felt negative electrode of a zinc-bromine flow battery and a carbon felt negative electrode prepared by the method. BACKGROUND

[0002] To meet the demand for sustainable growth of energy for economic and social development, it is necessary to vigorously develop renewable energy such as wind energy, solar energy and tidal energy. However, these renewable energy sources are easily limited by geographical environmental changes, and have problems such as intermittency and volatility. This makes it possible for renewable energy power generation to directly connect to the grid to damage the stability of the power system. Therefore, the development of renewable energy has greatly promoted the demand for high safety, low cost, long life and environmentally friendly electrochemical energy storage technology.

[0003] Among numerous electrochemical energy storage technologies, zinc-bromine flow batteries are considered as the most promising large-scale long-time energy storage technology in the future due to their low cost, high energy density, high safety and long life. However, during the charging and discharging process, zinc-bromine flow battery negative electrode is easy to form zinc dendrites. With the continuous growth of zinc dendrites, the diaphragm will be pierced, causing the mixing of positive and negative electrolytes, causing serious self-discharge of zinc-bromine flow battery. Electrode material, as the main place of electrochemical reaction of zinc-bromine flow battery, although does not directly participate in the redox reaction, plays an important role in loading deposited zinc, and the physical and chemical properties of its surface greatly affect the zinc deposition process. Carbon felt becomes the preferred electrode material of zinc-bromine flow battery due to its low price, large porosity and good chemical stability, but its electrochemical activity cannot fully meet the requirements of zinc-bromine flow battery, so it is particularly important to modify the surface of carbon felt.

[0004] A layer of metal or oxide is loaded on the surface of carbon felt to increase the active sites of zinc deposition, thereby reducing the local zinc deposition rate, forming a more uniform and dense zinc deposition structure, and ultimately achieving the purpose of inhibiting the formation of negative zinc dendrites. The Chinese patent document with publication number CN117832517A discloses a method of loading nickel, tin, cobalt and other metal oxides on the surface of carbon felt using a high-temperature sintering process. After modification, the active sites on the surface of carbon felt are increased, thereby improving the performance of the battery. However, this method requires high-temperature sintering to decompose the metal salt into the corresponding metal oxide, which can cause excessive oxidation of the carbon felt and form too many oxygen-containing functional groups on the surface of the carbon felt, thereby reducing the conductivity and strength of the carbon felt. In addition, the conductivity of metal oxide is low, which is not conducive to the rapid transfer of electrons between the carbon felt and the zinc deposition layer, and is not conducive to the transfer of electrons during the zinc deposition / peeling process, increasing the interface charge transfer resistance. The Chinese patent document with publication number CN117039019A discloses a method of depositing tin on the surface of carbon felt using an electrodeposition process. The deposition of tin increases more anchor sites for zinc deposition, thereby improving the electrochemical performance of the battery. However, the deposited tin has strong chemical reactivity and is easily reacted with acidic substances in the electrolyte during the charging and discharging process of the battery, causing the active sites to be ineffective. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing a modified carbon felt negative electrode for zinc-bromine flow batteries, which can solve the problems of excessive oxidation of carbon felt and low conductivity of oxide affecting electron transfer during zinc deposition / peeling caused by loading oxide on the surface of carbon felt in the prior art, and solve the problem of reaction between loaded metal active sites and acidic substances in the electrolyte, causing tin active sites for zinc deposition to be ineffective. The method is a simple liquid deposition process suitable for large-scale production.

[0006] To solve the above technical problems, the present application provides a method for preparing a modified carbon felt negative electrode for zinc-bromine flow batteries, which comprises the following steps: (1) vacuum drying the cleaned carbon felt to obtain carbon felt A; (2) adding cuprous sulfate to a mixed solution of organic nitrile and water and stirring to obtain a cuprous sulfate solution; soaking carbon felt A in the cuprous sulfate solution and heating to react to obtain carbon felt B; the mass ratio of cuprous sulfate to carbon felt A is 1-10:1; (3) washing and vacuum drying carbon felt B to obtain the modified carbon felt negative electrode for zinc-bromine flow batteries.

[0007] Preferably, in step (1), the temperature of vacuum drying is 80-200°C, and the time is 5-20h.

[0008] Preferably, in step (2), the organic nitrile is one of acetonitrile, propionitrile, and butyronitrile; the molar ratio of the organic nitrile to water is 2-10:10; the stirring time is 0.5-3 h; the molar ratio of cuprous sulfate to the organic nitrile in the cuprous sulfate solution is 1:5-9; the heating reaction temperature is 70-110℃, and the time is 4-10 h.

[0009] Preferably, in step (3), the temperature of vacuum drying is 100-180℃, and the time is 10-24 h.

[0010] The application also provides a modified zinc-bromine flow battery carbon felt negative electrode prepared by the above preparation method; the carbon felt negative electrode comprises a carbon felt matrix and copper single particle loaded on the carbon felt.

[0011] Compared with the prior art, the application has the following beneficial effects: (1) The application provides a preparation method of a modified zinc-bromine flow battery carbon felt negative electrode, which loads copper single particles on the surface of the carbon felt negative electrode by regulating the disproportionation reaction of cuprous sulfate. Since cuprous sulfate is unstable and will undergo a disproportionation reaction when dissolved in water to form copper and copper sulfate, the disproportionation reaction is inhibited when the aqueous solution contains an organic nitrile, and cuprous sulfate will exist stably. After the carbon felt is soaked in a mixed solution of cuprous sulfate, water, and organic nitrile, the organic nitrile is evaporated from the solution by heating, and the cuprous sulfate gradually starts to undergo a disproportionation reaction. The copper single particles generated by the disproportionation reaction of cuprous sulfate will deposit on the surface of the carbon felt, thereby achieving the purpose of loading copper single particles on the modified carbon felt. The method has simple process steps, low equipment requirements, and does not require high-temperature heating in the implementation process, which can avoid excessive oxidation of the carbon felt to increase the oxygen-containing functional groups on the surface of the carbon felt, thereby maximizing the inherent conductivity and mechanical strength of the carbon felt.

[0012] (2) The technical solution provided by the application loads copper single particles on the surface of the carbon felt, which are chemically stable and difficult to react with zinc bromide solutes, complexing agents, and acids in the electrolyte, effectively avoiding the problem of invalidation of zinc deposition active sites caused by reactions during the charging and discharging process, and providing a basis for long-life operation of the battery. At the same time, the copper single particles have excellent conductivity. During the charging and discharging process, the copper single particles loaded on the carbon felt can act as active sites for zinc deposition, rapidly transfer electrons between the carbon felt and the zinc deposition layer, promote the rapid transfer of electrons during the zinc deposition / peeling process, significantly reduce the interfacial charge transfer resistance, reduce polarization, and thus promote the efficient progress of electrochemical reactions.

[0013] (3) The technical solution provided by this invention involves loading elemental copper onto the surface of a carbon felt. During charging, the copper particles loaded on the carbon felt surface can serve as highly efficient electrochemical reaction active sites. Their key function is to significantly reduce the activation energy barrier required for zinc ion reduction and nucleation, and to form active sites for electrochemical reactions on the carbon felt surface. The excellent zinc affinity of copper atoms can guide zinc to preferentially deposit at the active sites formed by copper rather than at already deposited zinc sites, thereby effectively suppressing the further development of uneven zinc deposition during charging, inhibiting zinc dendrite growth, and effectively promoting and guiding uniform zinc deposition. Furthermore, this strong interaction between copper and zinc is not limited to the deposition stage but extends throughout the entire charge-discharge cycle, bidirectionally promoting the uniform deposition and stripping of zinc. The synergistic effect of copper's zinc affinity and the reduction of the zinc nucleation barrier directly leads to a significant optimization of the microstructure of the zinc deposition layer on the carbon felt surface, making it more uniform and dense. This optimized deposition layer structure can significantly inhibit the growth and propagation of zinc dendrites. The effective suppression of zinc dendrites not only eliminates the risk of short circuits caused by them piercing the separator, but more importantly, it blocks the shuttle effect of elemental bromine in the positive electrode region through dendrite channels to the negative electrode. Through this series of positive effects, the overall electrochemical performance of the zinc-bromine flow battery, including cycle stability, coulombic efficiency, and safety, has been significantly improved.

[0014] (4) The technical solution of this invention significantly improves the performance of zinc-bromine flow batteries by optimizing process parameters. For example, the mass ratio of cuprous sulfate to carbon felt A and the molar ratio of organic nitriles to water. The mass ratio of cuprous sulfate to carbon felt A plays a decisive role in the amount of copper loaded on the carbon felt. The inventors found that when the mass ratio of cuprous sulfate to carbon felt A is too small, there are fewer copper particles loaded on the carbon felt, which cannot effectively increase the active sites for zinc deposition; when it is too large, there are more copper particles loaded on the carbon felt, which will block the pore structure of the carbon felt, affect the transport of electrolyte inside the carbon felt, and reduce the available space for zinc deposition. An appropriate mass ratio of cuprous sulfate to carbon felt A can introduce enough copper zinc deposition active sites on the carbon felt, while avoiding the copper blocking the pore structure of the carbon felt. The inventors also found that the molar ratio of organic nitriles to water affects the disproportionation reaction of cuprous sulfate. When the molar ratio of organic nitrile to water is too high, the evaporation of the organic nitrile will carry away a large amount of water, significantly inhibiting the disproportionation reaction of cuprous sulfate and hindering the loading of elemental copper onto the carbon felt. Conversely, when the molar ratio is too low, the organic nitrile will evaporate rapidly, failing to inhibit the disproportionation reaction of cuprous sulfate, and the reaction will occur quickly, leaving insufficient time for the large amount of elemental copper to be loaded onto the carbon felt. A suitable molar ratio of organic nitrile to water is beneficial for the controllable conduct of the cuprous sulfate disproportionation reaction while ensuring that elemental copper particles are loaded onto the carbon felt.

[0015] (5) This invention significantly improves the overall electrochemical performance of zinc-bromine flow batteries by loading copper elemental particles onto carbon felt through regulating the disproportionation reaction of cuprous sulfate. Specifically, when the battery is at a current density of 60 mA / cm² and the specific capacity of the charging area is set to 40 mAh / cm², the zinc-bromine flow battery using the copper-modified carbon felt prepared in this technical solution as the negative electrode exhibits excellent performance indicators: the coulombic efficiency can reach 94.1% to 96.2%, the voltage efficiency reaches 83.2% to 86.7%, and the energy efficiency is in the range of 78.3% to 83.4%. Of particular note is that the zinc-bromine flow battery assembled with the copper-modified carbon felt negative electrode prepared in Example 1, after a charge-discharge cycle test of up to 1500 cycles, retains an energy efficiency and coulombic efficiency of up to 96.2% and 97.2%, respectively. This result strongly proves that the modified negative electrode material endows the battery with excellent long-term cycle stability. As can be seen, the copper-modified carbon felt anode prepared in this invention not only possesses excellent chemical and electrochemical stability, but also significantly improves the efficiency and cycle life of zinc-bromine flow batteries. This lays a solid foundation for the promotion of zinc-bromine flow batteries in practical applications such as large-scale energy storage, and has broad commercial application prospects. This technological breakthrough enables zinc-bromine flow batteries to possess superior electrochemical performance and a longer service life when moving towards practical applications. Attached Figure Description

[0016] Figure 1 The constant current charge-discharge curves are used to test the electrochemical performance of the copper-modified carbon felt prepared in Example 1 of this invention and the carbon felt in Comparative Example 1, respectively, as the negative electrodes of the zinc-bromine flow battery. Figure 2 Cyclic curves for electrochemical performance testing of the copper-modified carbon felt prepared in Example 1 of this invention as the negative electrode of a zinc-bromine flow battery. Figure 3 Cyclic curves for electrochemical performance testing using carbon felt as the negative electrode of a zinc-bromine flow battery (Comparative Example 1). Figure 4 X-ray diffraction (XRD) patterns of copper-modified carbon felt and unmodified carbon felt prepared in Example 1 of this invention; Figure 5 This is a scanning electron microscope (SEM) image of the copper-modified carbon felt prepared in Example 1 of the present invention. Figure 6 This is a scanning electron microscope (SEM) image of carbon felt, Comparative Example 1 of the present invention; Figure 7 This is an electron image collected during energy-dispersive X-ray spectroscopy analysis of the copper-modified carbon felt prepared in Example 1 of this invention; Figure 8 for Figure 7Energy dispersive X-ray spectra (EDS) of selected regions. Detailed Implementation

[0017] To make the present invention more apparent and understandable, the technical solution of the present invention will be further described and illustrated below through embodiments and in conjunction with the accompanying drawings, but this is not intended to limit the scope of protection of the present invention.

[0018] The cuprous sulfate used in this embodiment of the invention was purchased from Gaide Chemicals website; other medicines and reagents were purchased from Aladdin website or Sinopharm Reagents website. Example 1

[0019] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 130°C for 13 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 5:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:7. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 6:10 and stirred for 1.75 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7 hours, then removed to obtain carbon felt B. Carbon felt B was washed with water and ethanol, and the washed carbon felt was then vacuum-dried at 140°C for 17 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode. Example 2

[0020] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 125°C for 14 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 4:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:6. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 7:10 and stirred for 2 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 85°C for 8 hours, then removed to obtain carbon felt B. Carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was then vacuum-dried at 135°C for 18 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode. Example 3

[0021] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 135°C for 12 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 6:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:8. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 6:10 and stirred for 1.5 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 95°C for 6 hours, then removed to obtain carbon felt B. Carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was then vacuum-dried at 145°C for 16 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode. Example 4

[0022] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 100°C for 17 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 2:1, and the molar ratio of cuprous sulfate to propionitrile was controlled at 1:5. Cuprous sulfate was added to a mixed solution of propionitrile and water at a molar ratio of 4:10 and stirred for 1 hour to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 100°C for 5 hours, then removed to obtain carbon felt B. Carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was then vacuum-dried at 120°C for 21 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode. Example 5

[0023] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 160°C for 9 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 8:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:9. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 8:10 and stirred for 2.5 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 80°C for 9 hours, then removed to obtain carbon felt B. Carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was then vacuum-dried at 160°C for 13 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode. Example 6

[0024] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 200°C for 5 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 10:1, and the molar ratio of cuprous sulfate to nitrile was controlled at 1:6. Cuprous sulfate was added to a mixed solution of nitrile and water at a molar ratio of 2:10 and stirred for 3 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 110°C for 4 hours, then removed to obtain carbon felt B. Carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was then vacuum-dried at 180°C for 10 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode. Example 7

[0025] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 80°C for 20 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 1:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:7. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 10:10 and stirred for 0.5 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 70°C for 10 hours, then removed to obtain carbon felt B. Carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was then vacuum-dried at 100°C for 24 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode.

[0026] Cuprous sulfate is unstable and undergoes a disproportionation reaction when dissolved in water, forming copper and copper sulfate. 1 mol of cuprous ions can be complexed by 2–4 mol of acetonitrile. When the aqueous solution contains a sufficient amount of organic nitriles such as acetonitrile, the cuprous ions formed by the ionization of cuprous sulfate are completely complexed by these organic nitriles, inhibiting the disproportionation reaction, and the cuprous sulfate remains stable in the mixed solution. When carbon felt is immersed in a mixed solution of cuprous sulfate in water and acetonitrile, and then heated, the acetonitrile in the mixed solution evaporates, gradually decreasing the amount of acetonitrile in the solution, while the amount of cuprous ions initially remains constant. When the amount of acetonitrile decreases to more than half the molar number of cuprous ions in the solution, the complexed cuprous ions begin to dissociate, and the cuprous sulfate gradually begins to undergo a disproportionation reaction. The copper generated through this disproportionation reaction deposits on the surface of the carbon felt, thus achieving the purpose of copper-loaded modification of the carbon felt.

[0027] This method involves a relatively simple process and requires minimal equipment. The implementation does not require high-temperature heating, thus avoiding excessive oxidation of the carbon felt, which increases the number of oxygen-containing functional groups on the carbon felt surface, reducing its conductivity and strength. Copper has excellent zinc affinity; when loaded onto the carbon felt surface, it reduces the overpotential for zinc nucleation and increases the number of reactive sites on the carbon felt surface. During charging, due to the excellent zinc affinity of copper atoms, zinc is preferentially deposited at the active sites formed by copper rather than at already deposited zinc sites, effectively suppressing the further development of uneven zinc deposition during charging, inhibiting zinc dendrite growth, and effectively promoting and guiding uniform zinc deposition. Copper is chemically relatively stable and does not readily react with acids. This avoids the reaction between copper loaded on the carbon felt surface and acidic substances in the electrolyte during the charging and discharging of the zinc-bromine flow battery, preventing the active sites from becoming ineffective. Copper has extremely high conductivity; as an active site for electrochemical reactions, it can rapidly transfer electrons between the carbon felt and the zinc deposition layer, facilitating rapid electron transfer during zinc deposition / stripping, reducing interfacial charge transfer resistance, lowering polarization, and accelerating the electrochemical reaction. In addition, the strong interaction between copper and zinc is beneficial to the uniform deposition / stripping of zinc during charging and discharging. This helps to form a more uniform zinc deposition layer on the carbon felt surface, reduces the formation of zinc dendrites, avoids back puncture of the separator, prevents the shuttle of elemental bromine in the positive electrode, and improves the cycle life of the zinc-bromine flow battery. Comparative Example 1

[0028] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 130°C for 13 hours to obtain carbon felt A. Carbon felt A was then immersed in a mixed solution of acetonitrile and water at a molar ratio of 6:10 and heated at 90°C for 7 hours. Afterward, it was removed to obtain carbon felt B. Carbon felt B was washed with water and ethanol, and then vacuum-dried at 140°C for 17 hours to obtain the modified zinc-bromine flow battery carbon felt anode.

[0029] The difference from Example 1 is that in Comparative Example 1, the carbon felt was simply soaked in a mixture of acetonitrile and water and then vacuum dried, without loading elemental copper onto the carbon felt. Comparative Example 2

[0030] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 130°C for 13 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 20:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:7. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 6:10 and stirred for 1.75 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7 hours, then removed to obtain carbon felt B. Carbon felt B was washed with water and ethanol, and the washed carbon felt was then vacuum-dried at 140°C for 17 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode.

[0031] The difference from Example 1 is that the mass ratio of cuprous sulfate to dried carbon felt A in Comparative Example 2 is 20:1, which is higher than the process parameter value in all examples. Comparative Example 3

[0032] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 130°C for 13 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 0.1:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:7. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 6:10 and stirred for 1.75 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7 hours, then removed to obtain carbon felt B. Carbon felt B was washed with water and ethanol, and the washed carbon felt was then vacuum-dried at 140°C for 17 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode.

[0033] The difference from Example 1 is that the mass ratio of cuprous sulfate to dried carbon felt A in Comparative Example 3 is 0.1:1, which is lower than the process parameter value in all examples. Comparative Example 4

[0034] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 130°C for 13 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 5:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:7. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 25:10 and stirred for 1.75 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7 hours, then removed to obtain carbon felt B. Carbon felt B was washed with water and ethanol, and the washed carbon felt was then vacuum-dried at 140°C for 17 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode.

[0035] The difference from Example 1 is that the molar ratio of acetonitrile to water in Comparative Example 4 is 25:10, which is higher than the process parameter value in all examples. Comparative Example 5

[0036] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 130°C for 13 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 5:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:7. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 1:10 and stirred for 1.75 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7 hours, then removed to obtain carbon felt B. Carbon felt B was washed with water and ethanol, and the washed carbon felt was then vacuum-dried at 140°C for 17 hours to obtain the modified zinc-bromine flow battery carbon felt negative electrode.

[0037] The difference from Example 1 is that the molar ratio of acetonitrile to water in Comparative Example 5 is 1:10, which is lower than the process parameter value in all examples. Comparative Example 6

[0038] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 130°C for 13 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 5:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:7. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 6:10 and stirred for 1.75 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7 hours, then removed to obtain carbon felt B. Carbon felt B was washed with water and ethanol, and then vacuum-dried at 140°C for 17 hours to obtain carbon felt C. Carbon felt C was placed in a muffle furnace under air atmosphere and heated to 650°C at a rate of 3°C / min, and held at that temperature for 0.5 hours. After the holding period, the muffle furnace was allowed to cool naturally to room temperature to obtain the modified zinc-bromine flow battery carbon felt negative electrode.

[0039] The difference from Example 1 is that in Comparative Example 6, the copper-loaded carbon felt was kept at 650°C for 0.5 hours in a muffle furnace to oxidize part of the copper loaded on the carbon felt into copper oxide. Comparative Example 7

[0040] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 130°C for 13 hours to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A was controlled at 5:1, and the molar ratio of cuprous sulfate to acetonitrile was controlled at 1:7. Cuprous sulfate was added to a mixed solution of acetonitrile and water at a molar ratio of 6:10 and stirred for 1.75 hours to obtain a cuprous sulfate solution. Carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7 hours, then removed to obtain carbon felt B. Carbon felt B was washed with water and ethanol, and then vacuum-dried at 140°C for 17 hours to obtain carbon felt C. Carbon felt C was placed in a muffle furnace under air atmosphere and heated to 650°C at a rate of 3°C / min, and held at that temperature for 10 hours. After the holding period, the muffle furnace was allowed to cool naturally to room temperature to obtain the modified zinc-bromine flow battery carbon felt negative electrode.

[0041] The difference from Example 1 is that in Comparative Example 7, the copper-loaded carbon felt was kept at 650°C for 10 hours in a muffle furnace to oxidize the copper loaded on the carbon felt into copper oxide. Comparative Example 8

[0042] The carbon felt was cleaned to remove impurities from its surface. The cleaned carbon felt was then dried in a vacuum oven at 130°C for 13 hours to obtain carbon felt A. A platinum-titanium plated mesh was used as the anode material, carbon felt A as the cathode, and 100 ml of a mixed aqueous solution of 20 mM InCl3 and 3 M KBr was used as the electroplating solution. The electroplating was carried out at 30 mA / cm². 2 Carbon felt A was electroplated at a current density of 10 min. The electroplated carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140℃ for 17 h to obtain the modified zinc-bromine flow battery carbon felt negative electrode.

[0043] The difference from Example 1 is that Comparative Example 8 uses an electroplating process to load elemental indium onto a carbon felt.

[0044] Electrochemical performance tests were conducted on a zinc-bromine flow battery assembled from the samples prepared in the examples and comparative examples. The battery used carbon felt as the negative electrode, unmodified carbon felt as the positive electrode, and a microporous membrane as the separator. The electrolytes for both the positive and negative electrodes consisted of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 M tetramethylammonium bromide, and 0.2 M tetrabutylammonium bromide. The effective area of ​​both the positive and negative carbon felt electrodes was 3 cm × 3 cm.

[0045] The electrochemical performance of the zinc-bromine flow battery was tested using a constant current charge-discharge mode. During the test, the electrolyte flowed at 35 mL / min, initially at 60 mA / cm². 2The battery was charged at a constant current for 40 minutes (charged area specific capacity of 40 mAh / cm²), and then discharged at the same constant current until the voltage reached 0.6V. Based on the battery charge-discharge curves, the electrochemical performance indicators such as coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were calculated.

[0046] The electrochemical performance results of each material in the first charge-discharge test are shown in Table 1.

[0047]

[0048] As shown in Table 1, the coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine flow battery using the carbon felt obtained in Examples 1-7 as the negative electrode are all superior to those of the zinc-bromine flow battery using the carbon felt obtained in Comparative Examples 1-8 as the negative electrode. This indicates that the electrochemical performance of the carbon felt can be significantly improved by loading copper onto its surface. Among all the examples, Example 1, carried out with the optimal process parameters, exhibits the best overall performance, with all three efficiency parameters reaching the highest level. As the range of process parameters gradually increases, the three key indicators of coulombic efficiency, voltage efficiency, and energy efficiency in Examples 2-7 show a decreasing trend. The coulombic efficiency, voltage efficiency, and energy efficiency of Example 1 are 96.2%, 86.7%, and 83.4%, respectively; while the coulombic efficiency, voltage efficiency, and energy efficiency of Example 7 are 94.1%, 83.2%, and 78.3%, respectively. This suggests that optimizing the combination of various process parameters, such as the mass ratio of cuprous sulfate to carbon felt A, the molar ratio of organic nitriles to water, the molar ratio of cuprous sulfate to organic nitriles, heating temperature, and time, is necessary to better achieve the effect of copper-loaded modified carbon felt, thereby significantly improving the electrochemical performance of zinc-bromine flow batteries.

[0049] With the same charging capacity, a higher coulombic efficiency indicates a greater discharging capacity. The coulombic efficiencies of Examples 1-7 are greater than 94%, while those of Comparative Examples 1-8 do not exceed 88%. This indicates that the carbon felt modified with copper loading can reversibly release more charge. This is because the copper loaded on the carbon felt surface has good zinc affinity, which can reduce the overpotential for zinc nucleation and increase the reactive sites on the carbon felt surface. In addition, there is a strong interaction between copper and zinc, which is beneficial to the uniform deposition / stripping of zinc during charging and discharging. This is conducive to the formation of a more uniform zinc deposition layer on the carbon felt surface and reduces the formation of zinc dendrites. Voltage efficiency is the ratio of average discharge voltage to average charging voltage and is related to the polarization phenomenon during battery charging and discharging. The voltage efficiency of Examples 1-7 is greater than 83%, while that of Comparative Examples 1-8 does not exceed 80%. This indicates that the zinc-bromine flow battery using the carbon felt obtained in Examples 1-7 as the negative electrode has lower polarization and less voltage loss. This is because the copper loaded on the carbon felt surface has extremely high electrical conductivity, which, as an active site for electrochemical reactions, facilitates electron transfer during zinc deposition / stripping. Energy efficiency is an evaluation index of the energy conversion efficiency of a battery during charge and discharge; its value is a combination of coulombic efficiency and voltage efficiency. Examples 1-7 have energy efficiencies greater than 78%, while Comparative Examples 1-8 have energy efficiencies not exceeding 71%. Due to the combined beneficial effects of copper loaded on the carbon felt surface in reducing the overpotential for zinc nucleation, increasing the reactive sites on the carbon felt surface, and reducing polarization, the energy efficiency of the zinc-bromine flow battery is improved after copper loading modification.

[0050] Comparing Example 1 and Comparative Example 1, it can be seen that the performance indicators of Example 1 are far superior to those of Comparative Example 1. This demonstrates that simply immersing the carbon felt in a mixed solution of organic nitric acid and water and then vacuum drying it, without loading elemental copper onto the carbon felt, cannot achieve the goal of improving the electrochemical performance of the carbon felt.

[0051] Comparing Example 1 with Comparative Examples 2 and 3, it can be seen that the mass ratio of cuprous sulfate to carbon felt A plays a decisive role in the amount of elemental copper loaded on the carbon felt. When the mass ratio of cuprous sulfate to carbon felt A is too small, there are fewer elemental copper particles loaded on the carbon felt, which cannot effectively increase the active sites for zinc deposition; when it is too large, there are more elemental copper particles loaded on the carbon felt, which will block the porous structure of the carbon felt, affecting the transport of electrolyte within the carbon felt and reducing the available space for zinc deposition. An appropriate mass ratio of cuprous sulfate to carbon felt A can introduce a sufficient number of elemental copper zinc deposition active sites on the carbon felt, while avoiding the blockage of the porous structure by elemental copper.

[0052] Comparing Example 1 with Comparative Examples 4 and 5, it can be seen that the molar ratio of organic nitrile to water affects the disproportionation reaction of cuprous sulfate. When the molar ratio of organic nitrile to water is too high, a large amount of water will be carried away during the evaporation of the organic nitrile, significantly inhibiting the disproportionation reaction of cuprous sulfate and hindering the loading of elemental copper onto the carbon felt. When the molar ratio of organic nitrile to water is too low, the disproportionation reaction of cuprous sulfate cannot be inhibited, and the disproportionation reaction will occur rapidly, leaving insufficient time for the large amount of elemental copper to be loaded onto the carbon felt. A suitable molar ratio of organic nitrile to water is beneficial to the occurrence of the disproportionation reaction of cuprous sulfate while ensuring that elemental copper particles are loaded onto the carbon felt.

[0053] In Comparative Example 6, when held at 650°C for 0.5 hours in air, some elemental copper loaded on the carbon felt was oxidized to copper oxide, resulting in a copper-copper oxide composite. In Comparative Example 7, when held at 650°C for 10 hours in air, the elemental copper loaded on the carbon felt was oxidized to copper oxide, resulting in a copper oxide composite. Comparing Example 1 with Comparative Examples 6 and 7, it can be seen that the material loaded on the carbon felt in this invention consists only of elemental copper particles, and its performance indicators are far superior to those of Comparative Example 6, which loads copper and copper oxide composites, and Comparative Example 7, which loads copper oxide. Compared to copper and copper oxide composites and copper oxide, elemental copper loaded on the carbon felt has higher conductivity, allowing for rapid electron transfer between the carbon felt and the zinc deposition layer. This facilitates rapid charge transfer during zinc deposition / stripping, effectively reducing interfacial charge transfer resistance and polarization. Furthermore, the prolonged high-temperature heat treatment in Comparative Example 7 under air conditions caused excessive oxidation of the carbon felt, resulting in excessive oxygen-containing functional groups on the carbon felt surface, which reduced the conductivity and strength of the carbon felt. This also resulted in Comparative Example 7 having significantly lower performance than Example 1.

[0054] Comparing Example 1 and Comparative Example 8, it can be seen that the performance indicators of Example 1 are far superior to those of Comparative Example 8. Furthermore, in long-cycle testing of Comparative Example 8, after only 500 cycles, its coulombic efficiency, voltage efficiency, and energy efficiency decreased to 67.3%, 69.2%, and 46.6%, respectively. This is because the indium element supported on the carbon felt is chemically reactive and easily reacts with acidic substances in the electrolyte, causing the indium active sites deposited on the zinc on the carbon felt to become ineffective.

[0055] Figure 1 The constant current charge-discharge curves are shown for electrochemical performance testing of the copper-modified carbon felt prepared in Example 1 and the carbon felt in Comparative Example 1, respectively, as the negative electrodes of a zinc-bromine flow battery. The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, the carbon felt was simply immersed in a mixture of acetonitrile and water and then vacuum dried; no copper was loaded onto the carbon felt. During the electrochemical performance testing, the electrolyte flowed at 35 mL / min, and the current was 60 mA / cm². 2The electrode was charged with a constant current for 40 minutes (charging area specific capacity of 40 mAh / cm²), and then discharged with the same constant current until the voltage reached 0.6V. As shown in the figure, the copper-modified carbon felt anode obtained in Example 1 has a discharge area specific capacity approximately 4 mAh / cm² higher than that of Comparative Example 1. 2 This results in the carbon felt obtained in Example 1 having a coulombic efficiency approximately 10% higher than that in Comparative Example 1. While the charging plateaus of the two are similar, the negative electrode discharge voltage of the copper-modified carbon felt is approximately 160 mV higher than that of Comparative Example 1, leading to a voltage efficiency approximately 7.9% higher for the carbon felt obtained in Example 1 compared to Comparative Example 1. The combined effect of coulombic and voltage efficiencies results in an energy efficiency 16% higher for the carbon felt obtained in Example 1 than that of Comparative Example 1. The above comparison demonstrates that copper loaded on the surface of the carbon felt plays a beneficial role in reducing the overpotential for zinc nucleation, increasing the reactive sites on the carbon felt surface, and reducing polarization, thereby improving the coulombic, voltage, and energy efficiencies of the zinc-bromine flow battery after copper loading modification.

[0056] Figure 2 and Figure 3 Cyclic performance curves of the copper-modified carbon felt prepared in Example 1 and the carbon felt in Comparative Example 1, respectively, as negative electrodes in a zinc-bromine flow battery, were obtained. It can be seen that the copper-modified carbon felt negative electrode obtained in Example 1 exhibits minimal decay in coulombic efficiency and energy efficiency after 1500 cycles, maintaining energy efficiency and coulombic efficiency at 96.2% and 97.2%, respectively. In contrast, the carbon felt negative electrode in Comparative Example 1 shows significant fluctuations during cycling; after only 140 cycles, coulombic efficiency and energy efficiency decreased by nearly 30% and 20%, respectively. The formation of zinc dendrites is closely related to the coulombic efficiency, energy efficiency, and cycle retention of the zinc-bromine flow battery. The continuous growth of zinc dendrites can penetrate the separator, causing short circuits and leading to the formation of "dead" zinc, thus significantly reducing coulombic efficiency and energy efficiency, and adversely affecting the system's stability and lifespan. Therefore, this comparison demonstrates that the copper-modified carbon felt prepared using the technical solution of this invention has a very good effect on suppressing zinc dendrites.

[0057] Figure 4The X-ray diffraction (XRD) patterns of the copper-modified carbon felt and the unmodified carbon felt prepared in Example 1 of this invention are shown. The modified carbon felt obtained in Example 1 clearly shows the (111), (200), and (220) diffraction peaks of copper at 43.2°, 50.7°, and 74.4°, indicating that copper was successfully loaded onto the carbon felt in Example 1. Further comparison of the XRD patterns of the modified and unmodified carbon felt prepared in Example 1 shows that, apart from the diffraction peaks of copper, the other diffraction peaks are basically the same. This result indicates that the modification process in Example 1 only loaded copper onto the surface of the carbon felt, without generating compounds such as cuprous oxide or copper oxide; the modification process did not damage the crystal structure of the carbon felt, and while achieving copper particle loading, it completely preserved the original crystal phase characteristics of the carbon felt.

[0058] Figure 5 and Figure 6 The images shown are scanning electron microscope (SEM) images of the copper-modified carbon felt prepared in Example 1 of this invention and the carbon felt in Comparative Example 1, respectively. Figure 5 It can be clearly seen that the carbon fibers of the copper-modified carbon felt prepared in Example 1 contain many nanoparticles. Figure 6 In the comparison example 1, the carbon fibers of the carbon felt were relatively smooth, and no large number of obvious particles were observed.

[0059] Figure 7 This is an electron image collected during energy-dispersive X-ray spectroscopy analysis of the copper-modified carbon felt prepared in Example 1 of this invention. Figure 8 for Figure 7 The selected region was analyzed using energy-dispersive X-ray spectroscopy (EDS). Besides carbon and oxygen signals, a significant copper signal was observed in the spectrum. Combined with... Figure 7 , Figure 8 and Figure 4 The X-ray diffraction (XRD) pattern of the copper-modified carbon felt prepared in Example 1 can determine... Figure 5 The nanoparticles on the carbon fiber are elemental copper. This further illustrates that elemental copper was loaded onto the carbon felt using the technical solution of Example 1.

[0060] The specific embodiments described above provide a further detailed explanation of the present invention; however, these descriptions should not be construed as limiting the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of preparing a modified zinc-bromine flow battery carbon felt negative electrode, characterized in that, The method comprises the following steps: (1) vacuum drying the cleaned carbon felt to obtain carbon felt A; (2) adding cuprous sulfate into a mixed solution of organic nitrile and water and stirring to obtain a cuprous sulfate solution; soaking the carbon felt A in the cuprous sulfate solution and heating to react, to obtain carbon felt B; the mass ratio of the cuprous sulfate to the carbon felt A is 1-10:1; (3) washing and vacuum drying the carbon felt B to obtain the modified carbon felt negative electrode for zinc-bromine flow battery; In the step (2), the organic nitrile is one of acetonitrile, propionitrile and butyronitrile; the molar ratio of the organic nitrile to water is 2-10:10; the stirring time is 0.5-3 h; the molar ratio of the cuprous sulfate to the organic nitrile in the cuprous sulfate solution is 1:5-9; the heating reaction temperature is 70-110 ℃, and the time is 4-10 h.

2. The method of making a modified zinc-bromine flow battery carbon felt negative electrode according to claim 1, wherein, In the step (1), the temperature for vacuum drying is 80-200 ℃, and the time is 5-20 h.

3. The method of making a modified zinc-bromine flow battery carbon felt negative electrode of claim 1, wherein, In the step (3), the temperature for vacuum drying is 100-180 ℃, and the time is 10-24 h.

4. A modified zinc-bromine flow battery carbon felt negative electrode, characterized by, The modified carbon felt negative electrode for zinc-bromine flow battery is prepared by the method according to any one of claims 1-3, and the carbon felt negative electrode comprises a carbon felt matrix and copper single particle loaded on the carbon felt.

Images