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

Abstract

The application discloses a preparation method of a modified zinc-bromine flow battery carbon felt negative electrode and a carbon felt negative electrode prepared by the method, and belongs to the field of zinc-bromine flow batteries. The carbon felt is soaked in a mixed solution of cuprous sulfate in water and acetonitrile, then acetonitrile is gradually evaporated from the solution by heating, the cuprous sulfate gradually undergoes disproportionation reaction, and the elemental copper 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 elemental copper on the modified carbon felt is achieved. The elemental copper is relatively stable in chemical properties and has good affinity for zinc, and the loading of the elemental copper on the surface of the carbon felt can reduce the overpotential of zinc nucleation and increase the active sites on the surface of the carbon felt. In addition, there is a strong force between copper and zinc, which is conducive to the uniform deposition / detachment of zinc in the charging and discharging process, so that a more uniform zinc deposition layer is formed on the surface of the carbon felt, the 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, forming 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. After depositing tin, more anchor sites for zinc deposition are increased, 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:

[0007] (1) Vacuum drying the cleaned carbon felt to obtain carbon felt A;

[0008] (2) Adding cuprous sulfate to an organic nitrile and water mixture 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;

[0009] (3) Washing and vacuum drying carbon felt B to obtain the modified carbon felt negative electrode for zinc-bromine flow batteries.

[0010] Preferably, in step (1), the temperature of vacuum drying is 80-200°C, and the time is 5-20h.

[0011] 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 DEG C, and the time is 4-10 h.

[0012] Preferably, in step (3), the temperature of vacuum drying is 100-180 DEG C, and the time is 10-24 h.

[0013] The application further provides a modified zinc-bromine flow battery carbon felt negative electrode prepared by the above preparation method.

[0014] Compared with the prior art, the application has the following beneficial effects:

[0015] (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.

[0016] (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.

[0017] (3) The technical scheme provided by the present application, the copper element loaded on the surface of the carbon felt can be used as an efficient electrochemical reaction active site during the charging process, and its key role is to significantly reduce the activation energy barrier required for the reduction of zinc ions to nucleate and form an active site for electrochemical reaction on the surface of the carbon felt. The good zinc affinity of copper atoms can guide zinc to preferentially deposit on the active site formed by copper rather than the deposited zinc site, thereby effectively inhibiting the further development of zinc deposition unevenness during the charging process, achieving the inhibition of zinc dendrite growth, and effectively promoting and guiding the uniform deposition of zinc. Furthermore, this strong interaction between copper and zinc is not limited to the deposition stage, but extends throughout the charging and discharging cycle, and can bidirectionally promote the uniform deposition and stripping process of zinc. The synergistic effect of the zinc affinity of copper and the reduction of the zinc nucleation potential barrier directly leads to a significant optimization of the microstructure of the zinc deposition layer on the surface of the carbon felt, which becomes more uniform and dense. This optimized deposition layer structure can significantly inhibit the growth and spread of zinc dendrites. The effective inhibition of zinc dendrites not only eliminates the risk of short circuit caused by the penetration of the separator, but more importantly, it blocks the shuttle effect of bromine monomer from the positive electrode region to the negative electrode through the dendrite channel. Through this series of positive effects, the overall electrochemical performance of the zinc-bromine flow battery, including cycle stability, coulomb efficiency and safety, has been greatly improved.

[0018] (4) The technical scheme of the present application significantly improves the performance of the zinc-bromine flow battery by optimizing process parameters, such as the mass ratio of cuprous sulfate to carbon felt A, the molar ratio of organic nitrile to water, etc. The mass ratio of cuprous sulfate to carbon felt A plays a decisive role in the amount of copper element loaded on the carbon felt. The inventors found that when the mass ratio of cuprous sulfate to carbon felt A is too low, the amount of copper element loaded on the carbon felt is too small, which cannot effectively increase the active sites for zinc deposition; when the mass ratio is too large, the amount of copper element loaded on the carbon felt is too large, which can block the pore structure of the carbon felt, affect the transport of the electrolyte inside the carbon felt, and reduce the available space for zinc deposition. A proper mass ratio of cuprous sulfate to carbon felt A can introduce enough copper element active sites for zinc deposition on the carbon felt, while avoiding the blockage of the pore structure of the carbon felt by copper element. The inventors also found that the molar ratio of organic nitrile to water has an effect on 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 taken away during the evaporation of organic nitrile, which will significantly inhibit the disproportionation reaction of cuprous sulfate, which is not conducive to the loading of copper element on the carbon felt; when the molar ratio of organic nitrile to water is too low, the organic nitrile will be quickly evaporated, which cannot inhibit the disproportionation reaction of cuprous sulfate, and the disproportionation reaction will occur quickly, forming a large amount of copper element which cannot be loaded on the carbon felt in time. A proper molar ratio of organic nitrile to water is conducive to the controllable disproportionation reaction of cuprous sulfate, while ensuring the loading of copper element particles on the carbon felt.

[0019] (5) The present application significantly improves the comprehensive electrochemical performance of the zinc-bromine flow battery by regulating the cuprous sulfate disproportionation reaction and loading copper elemental particles on the carbon felt. Specifically, when the battery is at a current density of 60 mA / cm² and the charging area specific capacity is set to 40 mAh / cm², the zinc-bromine flow battery using the copper elemental modified carbon felt prepared by the technical solution as the negative electrode exhibits excellent performance indicators: the coulombic efficiency can be as high as 94.1%~96.2%, the voltage efficiency reaches 83.2%~86.7%, and the energy efficiency realized is in the range of 78.3%~83.4%. It is particularly worth noting that the zinc-bromine flow battery assembled with the copper elemental modified carbon felt prepared in Example 1 as the negative electrode has an energy efficiency and coulombic efficiency retention rate of 96.2% and 97.2% respectively after 1500 weeks of charge-discharge cycle test, which powerfully proves that the modified negative electrode material endows the battery with excellent long-term cycle stability. It can be seen that the copper elemental modified carbon felt negative electrode prepared by the present application not only has excellent chemical stability and electrochemical stability, but also significantly improves the efficiency indicators and cycle life of the zinc-bromine flow battery, lays a solid foundation for the popularization of the zinc-bromine flow battery in practical application fields such as large-scale energy storage, and has broad commercial application prospects. This technical breakthrough enables the zinc-bromine flow battery to have better electrochemical performance and longer service life when moving towards practical application. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The constant current charge-discharge curve graph for the electrochemical performance test of the zinc-bromine flow battery using the copper elemental modified carbon felt prepared by Example 1 of the present application and the carbon felt of Comparative Example 1 as the negative electrode, respectively;

[0021] Figure 2 The cycle curve graph for the electrochemical performance test of the zinc-bromine flow battery using the copper elemental modified carbon felt prepared by Example 1 of the present application as the negative electrode;

[0022] Figure 3 The cycle curve graph for the electrochemical performance test of the zinc-bromine flow battery using the carbon felt of Comparative Example 1 as the negative electrode;

[0023] Figure 4 The X-ray diffraction (XRD) graph of the copper elemental modified carbon felt prepared by Example 1 of the present application and the unmodified carbon felt;

[0024] Figure 5 The scanning electron microscope (SEM) graph of the copper elemental modified carbon felt prepared by Example 1 of the present application;

[0025] Figure 6 The scanning electron microscope (SEM) graph of the carbon felt of Comparative Example 1 of the present application;

[0026] Figure 7An electron map collected when energy dispersive X-ray spectroscopy analysis was performed on the elemental copper modified carbon felt prepared in Embodiment 1 of the present application;

[0027] Figure 8 For Figure 7 The selected area energy dispersive X-ray spectrogram (EDS). DETAILED DESCRIPTION

[0028] In order to make the present application more apparent and easy to understand, the technical solutions of the present application are further described and explained below by means of embodiments in conjunction with the accompanying drawings, but are not used to limit the protection scope of the present application.

[0029] The cuprous sulfate used in the embodiments of the present application was purchased from Gaide Chemical Network; other medicines and reagents were purchased from Aladdin Network or National Medicine Reagent Network. Embodiment 1

[0030] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven and dried at 130℃ for 13h to obtain carbon felt A. The mass ratio of cuprous sulfate to the carbon felt A obtained after drying was controlled to be 5:1, the molar ratio of cuprous sulfate to acetonitrile was 1:7, the cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 6:10 and stirred for 1.75h to obtain a cuprous sulfate solution. The carbon felt A was soaked in the cuprous sulfate solution and heated at 90℃ for 7h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140℃ for 17h to obtain a modified zinc-bromine flow battery carbon felt negative electrode. Embodiment 2

[0031] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven and dried at 125℃ for 14h to obtain carbon felt A. The mass ratio of cuprous sulfate to the carbon felt A obtained after drying was controlled to be 4:1, the molar ratio of cuprous sulfate to acetonitrile was 1:6, the cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 7:10 and stirred for 2h to obtain a cuprous sulfate solution. The carbon felt A was soaked in the cuprous sulfate solution and heated at 85℃ for 8h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 135℃ for 18h to obtain a modified zinc-bromine flow battery carbon felt negative electrode. Embodiment 3

[0032] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 135°C for 12h to obtain carbon felt A. The mass ratio of cuprous sulfate to the carbon felt A obtained after drying was controlled to be 6:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:8. The cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 6:10 and stirred for 1.5h to obtain a cuprous sulfate solution. The carbon felt A was immersed in the cuprous sulfate solution and heated at 95°C for 6h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 145°C for 16h to obtain a modified zinc-bromine flow battery carbon felt negative electrode. Example 4

[0033] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 100°C for 17h to obtain carbon felt A. The mass ratio of cuprous sulfate to the carbon felt A obtained after drying was controlled to be 2:1, and the molar ratio of cuprous sulfate to propionitrile was 1:5. The cuprous sulfate was added to a mixed solution of propionitrile and water with a molar ratio of 4:10 and stirred for 1h to obtain a cuprous sulfate solution. The carbon felt A was immersed in the cuprous sulfate solution and heated at 100°C for 5h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 120°C for 21h to obtain a modified zinc-bromine flow battery carbon felt negative electrode. Example 5

[0034] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 160°C for 9h to obtain carbon felt A. The mass ratio of cuprous sulfate to the carbon felt A obtained after drying was controlled to be 8:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:9. The cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 8:10 and stirred for 2.5h to obtain a cuprous sulfate solution. The carbon felt A was immersed in the cuprous sulfate solution and heated at 80°C for 9h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 160°C for 13h to obtain a modified zinc-bromine flow battery carbon felt negative electrode. Example 6

[0035] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 200°C for 5h to obtain carbon felt A. The mass ratio of cuprous sulfate to the carbon felt A obtained after drying was controlled to be 10:1, and the molar ratio of cuprous sulfate to butyronitrile was 1:6. The cuprous sulfate was added to a mixed solution of butyronitrile and water with a molar ratio of 2:10 and stirred for 3h to obtain a cuprous sulfate solution. The carbon felt A was immersed in the cuprous sulfate solution and heated at 110°C for 4h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 180°C for 10h to obtain a modified zinc-bromine flow battery carbon felt negative electrode. Example 7

[0036] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven and dried at 80°C for 20h to obtain carbon felt A. The mass ratio of cuprous sulfate to the dried carbon felt A obtained was controlled to be 1:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:7. The cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 10:10 and stirred for 0.5h to obtain a cuprous sulfate solution. The carbon felt A was soaked in the cuprous sulfate solution and heated at 70°C for 10h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with deionized water and ethanol, and the washed carbon felt was vacuum dried at 100°C for 24h to obtain a modified zinc-bromine flow battery carbon felt negative electrode.

[0037] Cuprous sulfate is unstable and will undergo disproportionation reaction when dissolved in water to form copper and copper sulfate. 1 mol of cuprous ions can be complexed by 2-4 mol of acetonitrile. When there is enough acetonitrile and other organic nitriles in the aqueous solution, the cuprous ions ionized from the cuprous sulfate are all complexed by the acetonitrile and other organic nitriles, and the disproportionation reaction is inhibited, and the cuprous sulfate will exist stably in the mixed solution. The carbon felt is soaked in the cuprous sulfate in the mixed solution of water and acetonitrile, and after heating, the acetonitrile in the mixed solution evaporates from the solution, and the amount of acetonitrile in the solution gradually decreases, and the amount of cuprous ions remains unchanged. When the amount of acetonitrile decreases to more than half of the molar number of cuprous ions in the solution, the complexed cuprous ions begin to dissociate, and the cuprous sulfate gradually begins to undergo disproportionation reaction, and the copper generated by the disproportionation reaction will be deposited on the surface of the carbon felt, thereby achieving the purpose of loading modified carbon felt with copper single element.

[0038] The method process and required equipment are relatively simple, the implementation process does not require high-temperature heating, and over-oxidation of the carbon felt can be avoided, so that the surface of the carbon felt contains more oxygen-containing functional groups, and the conductivity and strength of the carbon felt are reduced. Copper has good affinity for zinc, and when loaded on the surface of the carbon felt, the overpotential of zinc nucleation can be reduced, and the active sites on the surface of the carbon felt can be increased. During the charging process, due to the good affinity of copper atoms for zinc, zinc is preferentially deposited on the active sites formed by copper rather than the deposited zinc sites, thereby effectively inhibiting the further development of the uneven deposition of zinc during the charging process, achieving the inhibition of zinc dendrite growth, and effectively promoting and guiding the uniform deposition of zinc. Copper is relatively stable in chemical properties and is not easy to react with acid. This can avoid the reaction between copper loaded on the surface of the carbon felt and acidic substances in the electrolyte during the charging and discharging process of the zinc-bromine flow battery, causing the active sites to be ineffective. The electrical conductivity of copper is extremely high, and as an electrochemical reaction active site, it can quickly transfer electrons between the carbon felt and the zinc deposition layer, which is conducive to the rapid transfer of electrons during the zinc deposition / peeling process, reduces the interfacial charge transfer resistance, reduces polarization, and is conducive to accelerating the electrochemical reaction. In addition, copper has a strong force with zinc, which is conducive to the uniform deposition / peeling of zinc during the charging and discharging process, which is conducive to the formation of a more uniform zinc deposition layer on the surface of the carbon felt, reduces the formation of zinc dendrites, avoids the back-stabbing of the separator, causes the positive bromine element to shuttle, and improves the cycle life of the zinc-bromine flow battery.

[0039] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 130°C and dried for 13h to obtain carbon felt A. The carbon felt A was soaked in a mixed solution of acetonitrile and water with a molar ratio of 6:10 and heated at 90°C for 7h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140°C for 17h to obtain a modified zinc-bromine flow battery carbon felt negative electrode.

[0040] The difference from Example 1 is that Comparative Example 1 simply soaks the carbon felt in a mixed solution of acetonitrile and water and vacuum dries it, without loading copper single atoms on the carbon felt.

[0041] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 130°C and dried for 13h to obtain carbon felt A. The mass ratio of cuprous sulfate to the obtained carbon felt A after drying was controlled to be 20:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:7. The cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 6:10 and stirred for 1.75h to obtain a cuprous sulfate solution. The carbon felt A was soaked in the cuprous sulfate solution and heated at 90°C for 7h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140°C for 17h to obtain a modified zinc-bromine flow battery carbon felt negative electrode.

[0042] The difference from Example 1 is that the mass ratio of cuprous sulfate to carbon felt A obtained after drying in Comparative Example 2 is 20:1, which is higher than the value of this process parameter in all examples.

[0043] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 130°C for 13h to obtain carbon felt A. The mass ratio of cuprous sulfate to carbon felt A obtained after drying was controlled to be 0.1:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:7. The cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 6:10 and stirred for 1.75h to obtain a cuprous sulfate solution. The carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140°C for 17h to obtain a modified zinc-bromine flow battery carbon felt negative electrode.

[0044] The difference from Example 1 is that the mass ratio of cuprous sulfate to carbon felt A obtained after drying in Comparative Example 3 is 0.1:1, which is lower than the value of this process parameter in all examples.

[0045] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 130°C for 13h to obtain carbon felt A. The mass ratio of cuprous sulfate to carbon felt A obtained after drying was controlled to be 5:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:7. The cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 25:10 and stirred for 1.75h to obtain a cuprous sulfate solution. The carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140°C for 17h to obtain a modified zinc-bromine flow battery carbon felt negative electrode.

[0046] 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 value of this process parameter in all examples.

[0047] The carbon felt was washed to remove impurities on the surface of the carbon felt, and the washed carbon felt was placed in a vacuum oven at 130°C for 13h to obtain carbon felt A. The mass ratio of cuprous sulfate to carbon felt A obtained after drying was controlled to be 5:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:7. The cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 1:10 and stirred for 1.75h to obtain a cuprous sulfate solution. The carbon felt A was immersed in the cuprous sulfate solution and heated at 90°C for 7h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140°C for 17h to obtain a modified zinc-bromine flow battery carbon felt negative electrode.

[0048] 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 value of this process parameter in all examples.

[0049] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven at 130 °C for 13 h to obtain carbon felt A. The mass ratio of cuprous sulfate to the carbon felt A obtained after drying was controlled to be 5:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:7. The cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 6:10 and stirred for 1.75 h to obtain a cuprous sulfate solution. The carbon felt A was immersed in the cuprous sulfate solution and heated at 90 °C for 7 h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140 °C for 17 h to obtain carbon felt C. The carbon felt C was placed in a muffle furnace under an air atmosphere, and heated to 650 °C at a rate of 3 °C / min and kept for 0.5 h, and then naturally cooled to room temperature to obtain a modified carbon felt negative electrode for zinc-bromine flow battery.

[0050] The difference from Example 1 is that, in Comparative Example 6, the carbon felt loaded with copper was kept in a muffle furnace at 650 °C for 0.5 h, and part of the copper loaded on the carbon felt was oxidized to copper oxide.

[0051] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven at 130 °C for 13 h to obtain carbon felt A. The mass ratio of cuprous sulfate to the carbon felt A obtained after drying was controlled to be 5:1, and the molar ratio of cuprous sulfate to acetonitrile was 1:7. The cuprous sulfate was added to a mixed solution of acetonitrile and water with a molar ratio of 6:10 and stirred for 1.75 h to obtain a cuprous sulfate solution. The carbon felt A was immersed in the cuprous sulfate solution and heated at 90 °C for 7 h, and then taken out to obtain carbon felt B. The obtained carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140 °C for 17 h to obtain carbon felt C. The carbon felt C was placed in a muffle furnace under an air atmosphere, and heated to 650 °C at a rate of 3 °C / min and kept for 10 h, and then naturally cooled to room temperature to obtain a modified carbon felt negative electrode for zinc-bromine flow battery.

[0052] The difference from Example 1 is that, in Comparative Example 7, the carbon felt loaded with copper was kept in a muffle furnace at 650 °C for 10 h, and the copper loaded on the carbon felt was oxidized to copper oxide.

[0053] The carbon felt was cleaned to remove impurities on the surface of the carbon felt, and the cleaned carbon felt was placed in a vacuum oven at 130 °C for 13 h to obtain carbon felt A. A platinum-coated titanium mesh was used as an anode material, and the carbon felt A was used as a cathode. A 100 ml of 20 mM InCl3 and 3 M KBr mixed aqueous solution was used as an electroplating solution, and the carbon felt A was electroplated at a current density of 30 mA / cm 2 The obtained carbon felt B was washed with water and ethanol, and the washed carbon felt was vacuum dried at 140 °C for 17 h to obtain a modified carbon felt negative electrode for zinc-bromine flow battery.

[0054] The difference from Example 1 is that Comparative Example 8 uses an electroplating process to load indium element on the carbon felt.

[0055] The zinc-bromine flow battery was assembled for electrochemical performance test. The zinc-bromine flow battery was prepared by using the carbon felt prepared in the examples and comparative examples as negative electrode, unmodified carbon felt as positive electrode, microporous filter membrane as separator, and the electrolyte of the positive and negative electrodes was composed 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 the positive and negative carbon felt electrodes was 3 cm x 3 cm.

[0056] The electrochemical performance of the zinc-bromine flow battery was tested by using the constant current charge and discharge mode. During the test process, the electrolyte flowed at 35 mL / min, and first charged at a current of 60 mA / cm 2 for 40 min (the charging area specific capacity was 40 mAh / cm²), and then discharged at the same current to a voltage of 0.6 V. According to the battery charge and discharge curve, the electrochemical performance indicators such as coulombic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) of the battery were calculated.

[0057] The electrochemical performance results of the first circle charge and discharge test of each material are shown in Table 1.

[0058] Table 1

[0059] Coulombic efficiency (CE) / % Voltage efficiency (CE) / % Energy efficiency (EE) / % Example 1 96.2 86.7 83.4 Example 2 95.5 85.1 81.3 Example 3 95.8 84.9 81.3 Example 4 94.9 84.1 79.8 Example 5 94.7 84.2 79.7 Example 6 94.2 83.3 78.5 Example 7 94.1 83.2 78.3 Comparative Example 1 85.5 78.8 67.4 Comparative Example 2 80.2 79.8 64.0 Comparative Example 3 86.3 79.2 68.3 Comparative Example 4 86.6 79.4 68.8 Comparative Example 5 86.8 79.0 68.6 Comparative Example 6 87.6 78.1 68.4 Comparative Example 7 86.7 76.7 66.5 Comparative Example 8 87.7 79.9 70.1

[0060] As can be seen from Table 1, the coulombic efficiency, voltage efficiency and energy efficiency of the zinc-bromine flow battery using the carbon felt prepared in Examples 1-7 as the negative electrode are all better than those of the zinc-bromine flow battery using the carbon felt prepared in Comparative Examples 1-8 as the negative electrode, which shows that the electrochemical performance of the carbon felt can be significantly improved after being modified by loading copper element on the surface of the carbon felt. Among all the examples, Example 1 developed by using the optimal process parameters shows the best comprehensive performance, and the three efficiency parameters all reach the highest level. With the gradual increase of the range of the process parameters used, the coulombic efficiency, voltage efficiency and energy efficiency of Examples 2-7 have 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 can show that the process parameters such as the mass ratio of cuprous sulfate to carbon felt A, the molar ratio of organic nitrile to water, the molar ratio of cuprous sulfate to organic nitrile, heating temperature and time need to be optimized and combined, so as to better realize the effect of the copper element loading modified carbon felt, thereby significantly improving the electrochemical performance of the zinc-bromine flow battery.

[0061] The greater coulombic efficiency indicates more discharge capacity under the same charge capacity. The coulombic efficiency of examples 1-7 is greater than 94%, while the coulombic efficiency of comparative examples 1-8 is not more than 88%. This indicates that the carbon felt modified by copper loading can reversibly release more charge, because the copper loaded on the surface of the carbon felt has good affinity for zinc, and the copper loaded on the surface of the carbon felt can reduce the overpotential of zinc nucleation and increase the active sites on the surface of the carbon felt. In addition, there is a strong force between copper and zinc, which is conducive to the uniform deposition / stripping of zinc during the charging and discharging process, which is conducive to the formation of a more uniform zinc deposition layer on the surface of the carbon felt and reduces the formation of zinc dendrites. The voltage efficiency is the ratio of the average discharge voltage to the average charge voltage, and is related to the polarization phenomenon during the charging and discharging process of the battery. The voltage efficiency of examples 1-7 is greater than 83%, while the voltage efficiency of comparative examples 1-8 is not more than 80%. This indicates that the zinc-bromine flow battery using the carbon felt of examples 1-7 as the negative electrode has lower polarization and smaller voltage loss. This is because the copper loaded on the surface of the carbon felt has extremely high electrical conductivity, which as an electrochemical reaction active site is conducive to the transfer of electrons during the zinc deposition / stripping process. The energy efficiency is an evaluation index of the electrical energy conversion efficiency of the battery during the charging and discharging process, and its value is the comprehensive effect of coulombic efficiency and voltage efficiency. The energy efficiency of examples 1-7 is greater than 78%, while the energy efficiency of comparative examples 1-8 is not more than 71%. Due to the comprehensive beneficial effects of the copper loaded on the surface of the carbon felt in reducing the overpotential of zinc nucleation, increasing the active sites on the surface of the carbon felt, and reducing polarization, the energy efficiency of the zinc-bromine flow battery is improved after the copper loading modification.

[0062] As can be seen from comparative example 1 and comparative example 1, the performance indicators of example 1 are much better than those of comparative example 1. This can indicate that simply soaking the carbon felt in a mixed solution of organic nitrile and water and vacuum drying without loading copper on the carbon felt cannot achieve the purpose of improving the electrochemical performance of the carbon felt.

[0063] As can be seen from comparative example 1 and comparative examples 2 and 3, the mass ratio of cuprous sulfate to carbon felt A plays a decisive role in the amount of copper loaded on the carbon felt. When the mass ratio of cuprous sulfate to carbon felt A is too small, the amount of copper loaded on the carbon felt is too small, which cannot effectively increase the active sites for zinc deposition; when the mass ratio of cuprous sulfate to carbon felt A is too large, the amount of copper loaded on the carbon felt is too large, which can block the pore structure of the carbon felt, affect the transport of the electrolyte inside the carbon felt, and reduce the available space for zinc deposition. A proper mass ratio of cuprous sulfate to carbon felt A can introduce enough copper active sites for zinc deposition on the carbon felt, while avoiding the blockage of the pore structure of the carbon felt by copper.

[0064] As can be seen from Comparative Example 1 and Comparative Examples 4 and 5, the molar ratio of organic nitrile to water has an effect on the process of the cuprous sulfate disproportionation reaction. When the molar ratio of organic nitrile to water is too high, a large amount of water is taken away during the evaporation of the organic nitrile, which significantly inhibits the cuprous sulfate disproportionation reaction, and is not conducive to the loading of copper single particles on the carbon felt; when the molar ratio of organic nitrile to water is too low, the cuprous sulfate disproportionation reaction cannot be inhibited, and the disproportionation reaction occurs rapidly, forming a large amount of copper single particles that cannot be loaded on the carbon felt. A suitable molar ratio of organic nitrile to water is conducive to the occurrence of the cuprous sulfate disproportionation reaction, while ensuring that the copper single particles are loaded on the carbon felt.

[0065] As can be seen from Comparative Example 1 and Comparative Examples 6 and 7, the substance loaded on the carbon felt in the technical solution of the present application is only copper single particles, and its performance index is far superior to that of Comparative Example 6 which loads a copper and copper oxide composite, and Comparative Example 7 which loads copper oxide. Compared with the copper and copper oxide composite and copper oxide, the copper single particles loaded on the carbon felt have higher electrical conductivity, can rapidly transport electrons between the carbon felt and the zinc deposition layer, are conducive to the rapid transfer of charges during the zinc deposition / peeling process, can effectively reduce the interface charge transfer resistance, and reduce polarization. In addition, the long-time high-temperature heat treatment of Comparative Example 7 in an air atmosphere causes the carbon felt to be excessively oxidized, and a large number of oxygen-containing functional groups are formed on the surface of the carbon felt, which reduces the electrical conductivity and strength of the carbon felt. This also makes the performance of Comparative Example 7 far lower than that of Example 1.

[0066] As can be seen from Comparative Example 1 and Comparative Example 8, the performance index of Example 1 is far superior to that of Comparative Example 8. In addition, after 500 cycles, the coulombic efficiency, voltage efficiency and energy efficiency of Comparative Example 8 are reduced to 67.3%, 69.2% and 46.6%, respectively. This is because the indium single particles loaded on the carbon felt have relatively active chemical properties, and are prone to chemical reactions with acidic substances in the electrolyte, causing the indium active sites on the carbon felt for zinc deposition to be ineffective.

[0067] Figure 1 The galvanostatic charge-discharge curves of the carbon felt loaded with copper single particles prepared by Example 1 of the present application and the carbon felt of Comparative Example 1, which were used as the negative electrode of a zinc-bromine flow battery, were tested for electrochemical performance. The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 simply immersed the carbon felt in a mixed solution of acetonitrile and water and vacuum dried it, without loading copper single particles on the carbon felt. During the electrochemical performance test, the electrolyte flowed at a rate of 35 mL / min, and the current density was 60 mA / cm 2current constant current charging for 40 min (the charging area specific capacity is 40 mAh / cm2), and then discharged to 0.6 V at the same current constant current. It can be seen from the figure that the copper element modified carbon felt negative electrode obtained in Example 1 is about 4 mAh / cm2 higher than that of Comparative Example 1 in the discharge area specific capacity index. 2 This makes the coulombic efficiency of the carbon felt obtained in Example 1 about 10% higher than that of Comparative Example 1. The charging platforms of the two are not much different, but the discharge voltage of the copper element modified carbon felt is about 160 mV higher than that of Comparative Example 1, which makes the voltage efficiency of the carbon felt obtained in Example 1 about 7.9% higher than that of Comparative Example 1. The comprehensive effect of coulombic efficiency and voltage efficiency makes the energy efficiency of the carbon felt obtained in Example 1 16% higher than that of Comparative Example 1. Through the above comparison, it can be shown that the copper loaded on the surface of the carbon felt has beneficial effects in reducing the overpotential of zinc nucleation, increasing the active site on the surface of the carbon felt, reducing polarization, etc., so that the coulombic efficiency, voltage efficiency and energy efficiency of the zinc-bromine flow battery after copper loading modification are improved.

[0068] Figure 2 and Figure 3 respectively, the copper element modified carbon felt prepared by Example 1 of the present application and the carbon felt of Comparative Example 1 were used as the negative electrode of the zinc-bromine flow battery, and the cycle curve diagram of the electrochemical performance test was obtained. It can be seen that after 1500 cycles, the coulombic efficiency and energy efficiency of the copper element modified carbon felt negative electrode obtained in Example 1 decayed little, and the energy efficiency and coulombic efficiency retention rates were as high as 96.2% and 97.2% respectively. The carbon felt negative electrode of Comparative Example 1 fluctuated greatly during the cycle process, and after only 140 cycles, the coulombic efficiency and energy efficiency were attenuated by nearly 30% and 20% respectively. The formation of zinc dendrites is closely related to the coulombic efficiency, energy efficiency and cycle retention rate of the zinc-bromine flow battery. The continuous growth of zinc dendrites will penetrate the diaphragm, cause short circuit phenomenon, and lead to the production of "dead" zinc, thereby significantly reducing the coulombic efficiency, energy efficiency, and adversely affecting the stability and life of the system. Therefore, through comparison, it can be shown that the copper element modified carbon felt prepared by the technical solution of the present application has good effect in inhibiting zinc dendrites.

[0069] Figure 4The XRD patterns of the copper element modified carbon felt prepared in Example 1 and the unmodified carbon felt. The modified carbon felt prepared in Example 1 can obviously observe the copper (111), (200) and (220) diffraction peaks at 43.2°, 50.7° and 74.4°, which indicates that Example 1 successfully loads copper element on the carbon felt. Further comparing the XRD patterns of the modified carbon felt prepared in Example 1 and the unmodified carbon felt can see that, in addition to the diffraction peaks of copper element, the other diffraction peaks of the two are basically the same. The results can indicate that the loading on the surface of the carbon felt in Example 1 is only copper element, and no cuprous oxide, copper oxide and other compounds are generated; the modification process does not damage the crystal structure of the carbon felt, and while achieving copper particle loading, the original crystal phase characteristics of the carbon felt are completely retained.

[0070] Figure 5 and Figure 6 are the SEM patterns of the copper element modified carbon felt prepared in Example 1 and the carbon felt of Comparative Example 1, respectively. By Figure 5 it can be obviously seen that the carbon fibers of the copper element modified carbon felt prepared in Example 1 have many nanoparticles. While Figure 6 , the carbon fibers of the carbon felt of Comparative Example 1 are relatively smooth, and no obvious particles are seen.

[0071] Figure 7 is the electron map collected when the energy dispersive X-ray spectrum analysis of the copper element modified carbon felt prepared in Example 1 is carried out, Figure 8 is Figure 7 is the selected area energy dispersive X-ray spectrum (EDS) in Figure 7 , Figure 8 and Figure 4 , the XRD pattern of the copper element modified carbon felt prepared in Example 1 can determine Figure 5 that the nanoparticles on the carbon fibers in are copper element. Thus it can be further indicated that copper element is loaded on the carbon felt by the technical solution of Example 1.

[0072] The above specific embodiments further illustrate the present application, but these illustrations should not be understood as limiting the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a modified carbon felt negative electrode for a zinc-bromine flow battery, characterized in that, Includes the following steps: (1) The cleaned carbon felt was vacuum dried to obtain carbon felt A; (2) Add cuprous sulfate to a mixed solution of organic nitric acid and water and stir to obtain a cuprous sulfate solution; immerse carbon felt A in the cuprous sulfate solution and heat to react to obtain carbon felt B; the mass ratio of cuprous sulfate to carbon felt A is 1 to 10:

1. (3) Wash and vacuum dry carbon felt B to obtain the modified zinc bromine flow battery carbon felt negative electrode; In step (1), the vacuum drying temperature is 80-200℃ and the time is 5-20h; in step (2), the organic nitrile is one of acetonitrile, propionitrile, and butyronitrile; the molar ratio of organic nitrile to water is 2-10:10; the stirring time is 0.5-3h; the molar ratio of cuprous sulfate to organic nitrile in the cuprous sulfate solution is 1:5-9; the heating reaction temperature is 70-110℃ and the time is 4-10h; in step (3), the vacuum drying temperature is 100-180℃ and the time is 10-24h.

2. A modified zinc-bromine flow battery carbon felt negative electrode, characterized in that, The modified zinc-bromine flow battery carbon felt anode is prepared by the preparation method described in claim 1. The carbon felt anode comprises a carbon felt matrix and copper elemental particles loaded on the carbon felt.

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