A zinc-bromine flow battery and a method of making the same

Abstract

This invention provides a zinc-bromine flow battery and its preparation method, relating to the field of zinc-bromine flow battery technology. The invention involves impregnating and calcining a carbon felt with a first precursor solution containing tin chloride, ferric nitrate, and sodium citrate to obtain a SnO2-Fe@carbon felt positive electrode composite material with high catalytic activity. After impregnating the carbon felt with a second precursor solution containing copper acetate, it is reacted with ascorbic acid to obtain a Cu@carbon felt negative electrode composite material with high zinc affinity. The zinc-bromine flow battery is then assembled. This invention, through the SnO2-Fe / Cu bifunctional composite electrode design, effectively solves the problems of kinetic lag in the positive electrode reaction, bromine shuttle, and zinc dendrite extension piercing the ion exchange membrane in zinc-bromine flow batteries, synergistically optimizing the electrochemical performance, cycle life, and cost-effectiveness of the zinc-bromine flow battery.

Description

Technical Field

[0001] This invention relates to the field of zinc-bromine flow battery technology, and in particular to a zinc-bromine flow battery and its preparation method. Background Technology

[0002] With the development and progress of human society, our demand for energy is increasing, and the relationship between humans and energy is becoming increasingly close. Energy has become a necessity for our daily work and life. Currently, my country's reliance on traditional energy sources is no longer sufficient to meet the enormous energy demands and environmental protection requirements brought about by social development, and the existing traditional energy system faces significant challenges. Therefore, zinc, with its high energy density and relatively low cost, is considered to have good feasibility and operability in large-scale energy storage systems, while flow batteries also have a promising future in the field of energy storage technology. Consequently, in recent years, zinc-bromine redox flow batteries, combining these two advantages, have gradually gained attention and importance. Compared with lead-acid batteries, zinc-bromine flow batteries have higher energy and power densities, are more efficient and cleaner, and have a relatively higher price advantage compared to other flow batteries.

[0003] However, the technical problems of zinc-bromine flow batteries can be summarized in the following three aspects: (1) Bromine has strong corrosive and oxidizing properties, which will cause certain damage to battery components. (2) The strong volatility and diffusion of bromine will reduce the safety and life of the battery: the volatility of bromine leads to a reduction in the active material of the battery, reducing the efficiency, capacity and cycle life of the battery; and when bromine diffuses to the negative electrode, it is easy to react chemically with the active material of the negative electrode, thereby causing the battery to self-discharge and reduce the battery efficiency. (3) Br2 / Br - The slow kinetics of redox couples lead to greater battery polarization, lower battery power density, and consequently, increased battery cost.

[0004] Furthermore, due to Br2 / Br - Redox couples are commonly used as positive electrode couples in flow batteries due to their high potential, high solubility, abundant sources, and low cost. The use of Br₂ / Br₂ redox couples... -As an active electrode pair, zinc-bromine flow batteries face a series of problems, such as relatively low activity and strong corrosivity. Furthermore, zinc dendrites form during charging: during charging, the zinc anode undergoes nucleation and growth evolution. When the deposited zinc layer reaches a certain thickness, the zinc deposition transforms from dense two-dimensional layered growth to three-dimensional dendritic growth. If zinc dendrites are not suppressed, especially during deep charging, and without effective interface control, the disordered growth of zinc dendrites will continue to extend and pierce the ion exchange membrane, causing direct connection between the positive and negative electrodes, leading to an internal short circuit and irreversible battery failure. Therefore, there is an urgent need to develop a method that can induce uniform zinc deposition and possess excellent affinity between the zinc layer and the substrate, thereby completely avoiding battery failure caused by physical penetration of zinc dendrites.

[0005] Chinese patent document CN109786761A discloses a cathode material for zinc-bromine flow batteries, its preparation, and its application. The core of the patent lies in a one-step sintering method, where an organic compound of sulfur, titanium, and carbon is sintered at high temperature under an inert gas atmosphere to form carbon-coated titanium disulfide nanoparticles. This patent uses carbon-coated metallic titanium disulfide (TiS2@C) as the cathode catalyst material; however, its catalytic activity is limited by the inherent properties of TiS2. TiS2 is easily oxidized in the highly oxidizing ZnBr2 electrolyte, leading to surface structure damage and the failure of catalytic active sites. Furthermore, in practical applications, the carbon coating layer may crack during long-term cycling due to electrolyte penetration or mechanical stress, exposing uncoated TiS2 and accelerating material degradation. While TiS2@C reduces bromine (Br2) formation, the bromine permeability has not been clearly tested; the carbon coating layer may not completely prevent the physical diffusion of Br2, especially during long-term cycling, where material aging may lead to increased permeability.

[0006] Chinese patent document CN119742379A discloses a method for modifying a carbon felt electrode in a zinc-bromine flow battery and the zinc-bromine flow battery itself. Metal nanoparticles are introduced onto the surface of the carbon felt as Br... - / Br2 reaction active sites, lower the activation energy of redox reactions, and increase Br - The efficiency of oxidation to Br2. Among these, metal nanoparticles serve as nucleation sites, guiding Zn... 2+ Uniform deposition inhibits dendrite formation and prevents short circuits caused by piercing the diaphragm. However, if the modified electrode does not form uniform zinc-loving sites, dendrite growth may still occur due to excessively high local current density, which could pierce the diaphragm and cause a short circuit. Summary of the Invention

[0007] To address the technical problems existing in the prior art, this invention provides a zinc-bromine flow battery and its preparation method. Through the design of a SnO2-Fe / Cu bifunctional composite electrode, the invention effectively solves the problems of sluggish positive electrode reaction kinetics, bromine shuttle, and zinc dendrite extension piercing the ion exchange membrane at the negative electrode in zinc-bromine flow batteries. This synergistically optimizes the electrochemical performance, cycle life, and cost-effectiveness of the zinc-bromine flow battery.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a zinc-bromine flow battery includes the following steps: Step S01: Dissolve tin chloride, ferric nitrate, and sodium citrate in deionized water to obtain a first precursor solution; place the washed and activated carbon felt in the first precursor solution, ultrasonically impregnate it, remove the carbon felt and dry it, place it in a protective atmosphere, and perform gradient heating calcination to obtain SnO2-Fe@carbon felt cathode composite material. Step S02: Dissolve copper acetate in deionized water to obtain a second precursor solution; immerse the washed and activated carbon felt in the second precursor solution, and then heat it to 40-80℃ in an inert atmosphere, and add ascorbic acid solution dropwise while keeping it warm; after the ascorbic acid solution is added, keep it warm for reaction; then treat it with ultrasound and freeze dry to obtain Cu@carbon felt anode composite material.

[0009] Step S03: Using SnO2-Fe@carbon felt positive electrode composite material as positive electrode and Cu@carbon felt negative electrode composite material as negative electrode, a zinc-bromine flow battery is assembled.

[0010] Preferably, in step S01, the mass ratio of tin chloride to ferric nitrate in the first precursor solution is 7:1-5; The mass of sodium citrate added is 0.1-1% of the total mass of tin chloride and ferric nitrate.

[0011] Preferably, in step S01, the concentration of ferric nitrate in the first precursor solution is 0.01-0.07 mol / L; The volume of the first precursor solution should be controlled to be 2-5 times the volume of the washed and activated carbon felt.

[0012] Preferably, in step S01, the ultrasonic impregnation time is 0.1-1 h; Gradient heating calcination involves first heating to a calcination temperature of 450-550℃ and holding the temperature for 1-6 hours; then continuing to heat to 600-700℃ and holding the temperature for 1-6 hours.

[0013] Preferably, in step S02, the concentration of copper acetate in the second precursor solution is 0.05-0.1 mol / L; The concentration of ascorbic acid in the ascorbic acid solution is 0.28-0.56 mol / L.

[0014] Preferably, in step S02, the volume of the second precursor solution is controlled to be 2-5 times the volume of the washed and activated carbon felt.

[0015] Preferably, in step S02, the heat preservation reaction time is 0.3-0.7 h; the ultrasonic treatment time is 0.3-0.7 h.

[0016] Preferably, in step S03, the electrolyte used in the zinc-bromine flow battery is composed of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 mol / L tetramethylammonium bromide and 0.2 mol / L tetrabutylammonium bromide.

[0017] Furthermore, the washed and activated carbon felt is prepared by the following method: the carbon felt is treated sequentially with anhydrous ethanol, hydrochloric acid solution, and sodium hydroxide solution, and then dried.

[0018] Specifically, the carbon felt is immersed in anhydrous ethanol, ultrasonically treated, and then washed with water; then it is placed in hydrochloric acid solution, etched at 45-50℃, and washed with water until neutral; then it is placed in sodium hydroxide solution, soaked at 65-70℃, washed with water until neutral, and dried to obtain the washed and activated carbon felt.

[0019] A zinc-bromine flow battery is prepared using the aforementioned method.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the preparation of the zinc-bromine flow battery of the present invention, the SnO2-Fe@carbon felt cathode composite material with high catalytic activity is used: significantly improving the Br2 / Br... - Reaction kinetics, limiting bromine shuttle. The role of SnO2 sites: Oxygen vacancies and a specific electronic structure on the SnO2 surface can effectively adsorb bromine species and lower the activation energy of the reaction. The role of Fe sites: Fe has abundant variable valence states (e.g., Fe2+). 2+ / Fe 3+ SnO2 can provide a large number of active sites to participate in the redox reaction of bromine, and can further optimize the electronic structure of SnO2, thereby improving the adsorption energy of Br2. The heterojunction structure formed by SnO2 and Fe can optimize the electron configuration on the material surface and significantly accelerate the adsorption of Br2. -The conversion rate of Br2 is improved, thereby enhancing the battery's power and energy efficiency. Suppressing the bromine shuttle effect and improving rate performance and energy efficiency are achieved through physical confinement: SnO2-Fe particles adhere to the three-dimensional porous framework of the carbon felt, filling some pores and physically preventing large bromine molecules from moving freely. Chemical adsorption: The polarity of the SnO2 surface provides a strong affinity for Br2 and polybrominates. Simultaneously, the Fe active sites can anchor free bromine to the surface and pores of the positive electrode carbon felt by forming weak chemical bonds with bromine (such as Fe-Br). Furthermore, the excellent adsorption and enrichment capacity of the SnO2-Fe composite material for bromine allows the originally adsorbed and fixed bromine to rapidly gain electrons nearby during discharge, converting back into bromide ions and dissolving back into the electrolyte. This significantly accelerates the kinetics of the bromine redox reaction, enabling the battery to maintain stable capacity and low electrochemical polarization even at high current densities.

[0021] 2. In the fabrication of the zinc-bromine flow battery of the present invention, a Cu@carbon felt anode composite material with high zinc affinity is used: Cu atoms are loaded on the anode; uniform zinc deposition is achieved, suppressing dendrite growth and self-discharge. The Cu nanoparticles, due to their strong zinc affinity, can rapidly capture Zn. 2+ It provides abundant and uniform nucleation sites, significantly reduces nucleation overpotential, and induces two-dimensional uniform deposition of zinc on the carbon felt surface, avoiding localized protrusions. Its excellent conductivity can homogenize the local electric field of the carbon felt, prevent electric field concentration, and accelerate Zn deposition. 2+ The gain / loss electron kinetics reduce charge / discharge polarization voltage and improve energy efficiency. During deposition, Cu nanoparticles can form a CuZn alloy layer (such as CuZn5) in situ with the pre-deposited zinc, further enhancing zinc affinity, guiding dense parallel growth of zinc, and completely blocking vertical dendrite extension. This structure ensures a dense and well-adhesive deposition layer, reducing the formation of "dead zinc," and significantly reducing the risk of self-discharge and short circuits. Cu nanoparticles increase the overpotential of the hydrogen evolution reaction at the negative electrode, suppress side reactions in aqueous electrolytes, and reduce the ineffective consumption of active zinc; they also delay the diffusion of free bromine and polybrominates from the positive electrode to the negative electrode, avoiding chemical self-discharge. Specific Cu substrates can also induce ideal crystal orientation in the zinc deposition layer, further improving the long-term cycle stability and reversibility of the negative electrode, providing key negative electrode material support for high-performance zinc-bromine flow batteries.

[0022] 3. The zinc-bromine flow battery of the present invention, through a paired design using a SnO2-Fe@carbon felt positive electrode composite material with high catalytic activity as the positive electrode and a Cu@carbon felt negative electrode composite material with high zinc affinity as the negative electrode, forms a bipolar interface synergistic mechanism: one side of the positive electrode utilizes the polar interface provided by the SnO2-based framework and Fe doping, which is bromine-resistant, conductive, and has Lewis acidity, to achieve chemical anchoring and confinement of polybrominates, and interacts with Br2 / Br -The catalytic acceleration of redox kinetics suppresses bromine shuttle and its disturbance to the negative electrode interface. On the negative electrode side, Cu's high zinc affinity lowers the Zn nucleation barrier and increases the nucleation site density, inducing uniform two-dimensional zinc deposition while suppressing dendrite tip growth and dead zinc formation. After coupling, the suppression of shuttle by the positive electrode provides a more stable chemical boundary for the negative electrode, allowing the zinc affinity-induced effect of Cu to be sustained. The control of deposition morphology and dead zinc by the negative electrode reduces local current distortion and active material consumption in the zinc-bromine flow battery system, alleviates the positive electrode polarization effect, and thus forms a positive cycle of reduced bromine shuttle, reduced polarization, and reduced dendrites and dead zinc, achieving high voltage efficiency, coulombic efficiency, and long-term cycle stability.

[0023] 4. The zinc-bromine flow battery of the present invention effectively achieves comprehensive performance optimization and breaks through technical bottlenecks: (1) Electrochemical performance: The improvement of positive electrode reaction kinetics and the uniformity of negative electrode zinc deposition can improve the energy efficiency of the battery and reduce polarization. (2) Cycle life synergy: The suppression of positive electrode bromine shuttle effect and the suppression of negative electrode zinc dendrite can significantly extend the cycle life of the battery. (3) Cost-effectiveness synergy: The loading process of SnO2-Fe / Cu composite material has the characteristics of low cost and large scale, which can reduce the manufacturing cost of the battery.

[0024] 5. In the preparation of the zinc-bromine flow battery of the present invention, copper is selected as the loading metal for the negative electrode carbon felt. Copper, with its excellent zinc affinity and conductivity, is an ideal choice for modifying the negative electrode of the zinc-bromine battery. In terms of nucleation kinetics, Cu has a very strong adsorption energy for zinc atoms, providing an extremely low nucleation overpotential, inducing uniform anchoring and deposition of zinc ions, and suppressing dendrite growth at its source. In contrast, although Bi, In, and Sb have zinc affinity, the alloys formed with zinc are accompanied by significant volume expansion, easily leading to the pulverization and shedding of the active material after long-term cycling; while Co and Ni have a much weaker affinity for zinc than Cu, with high nucleation overpotentials, making them more prone to inducing local protrusions and dendrites. In terms of conductivity, Cu, as an excellent conductor in the industry, can significantly reduce the internal resistance of the negative electrode, avoiding local overheating and electric field concentration. Conversely, the conductivity of Bi, In, and Sb is only about 1 / 50th that of Cu; if used as a coating, they would become stumbling blocks to electron conduction, significantly increasing battery polarization. In summary, Cu has overwhelming advantages in inducing uniform deposition, ensuring electron transport, and suppressing side reactions.

[0025] 6. The zinc-bromine flow battery of the present invention improves the overall electrochemical performance of the zinc-bromine flow battery by reacting tin chloride with ferric nitrate and then performing gradient calcination to generate SnO2-Fe@carbon felt, followed by the reaction of copper acetate and ascorbic acid to form Cu@carbon felt. Specifically, when the battery operates at 60 mA / cm², 2 At the given current density, the specific capacity of the charging area is set to 40mAh / cm². 2Zinc-bromine flow batteries using SnO2-Fe@carbon felt and Cu@carbon felt as positive and negative electrodes prepared according to this technical solution exhibit excellent performance indicators: coulombic efficiency reaches 99.1%-96.7%, voltage efficiency reaches 86.2%-83.5%, and the resulting energy efficiency is in the range of 84.1%-81.1%. Of particular note is that the zinc-bromine flow battery assembled with the SnO2-Fe@carbon felt and Cu@carbon felt positive and negative electrodes prepared in Example 1, after a 1000-cycle charge-discharge test, maintained an energy efficiency and coulombic efficiency retention rate of approximately 84% and 97%, respectively. This result strongly demonstrates that the modified positive and negative electrode materials endow the battery with excellent long-term cycle stability. It is evident that the SnO2-Fe@carbon felt positive electrode prepared in this invention optimizes the battery's energy efficiency and cycle life by improving bromine reaction kinetics and suppressing the shuttle effect; the Cu@carbon felt negative electrode improves the cycle capacity retention rate by improving zinc deposition uniformity and suppressing dendrites. Both technologies have achieved key performance breakthroughs by addressing the core pain points of traditional carbon felt electrodes, laying the foundation for the commercial application of zinc-bromine flow batteries. Attached Figure Description

[0026] Figure 1 The constant current charge-discharge curves are used to test the electrochemical performance of the zinc-bromine flow battery of Example 1 and the zinc-bromine flow battery of Comparative Example 1.

[0027] Figure 2 Cyclic curves are used to test the electrochemical performance of the zinc-bromine flow battery in Example 1.

[0028] Figure 3 Cyclic curves for testing the electrochemical performance of the zinc-bromine flow battery in Comparative Example 1.

[0029] Figure 4 The images show the X-ray diffraction (XRD) patterns of the SnO2-Fe@carbon felt positive electrode composite material, Cu@carbon felt negative electrode composite material, and blank carbon felt prepared in Example 1.

[0030] Figure 5 The image shows a scanning electron microscope (SEM) image of the SnO2-Fe@carbon felt cathode composite material prepared in Example 1.

[0031] Figure 6 The image shows a scanning electron microscope (SEM) image of the Cu@carbon felt anode composite material prepared in Example 1.

[0032] Figure 7 The image shows a scanning electron microscope (SEM) image of the ascorbic acid@carbon felt anode composite material prepared in Comparative Example 1. Detailed Implementation

[0033] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] This invention provides a method for preparing a zinc-bromine flow battery, comprising the following steps: Step S01: Dissolve tin chloride, ferric nitrate, and sodium citrate in deionized water to obtain a first precursor solution; place the washed and activated carbon felt in the first precursor solution, ultrasonically impregnate it, remove the carbon felt, vacuum dry it, and place it in a protective atmosphere for gradient heating calcination to obtain a SnO2-Fe@carbon felt cathode composite material with high catalytic activity. Step S02: Dissolve copper acetate in deionized water to obtain a second precursor solution; immerse the washed and activated carbon felt in the second precursor solution, and then heat it to 40-80℃ in an inert atmosphere, while keeping it at the temperature and adding ascorbic acid solution dropwise; after the ascorbic acid solution is added, keep it at the temperature for reaction; then treat it with ultrasound and freeze dry to obtain Cu@carbon felt anode composite material with high zinc affinity.

[0036] Step S03: Using SnO2-Fe@carbon felt positive electrode composite material as positive electrode and Cu@carbon felt negative electrode composite material as negative electrode, a zinc-bromine flow battery is assembled.

[0037] Preferably, in step S01, the mass ratio of tin chloride to ferric nitrate in the first precursor solution is 7:1-5; the added mass of sodium citrate is 0.1-1% (preferably 0.3-0.7%) of the total mass of tin chloride and ferric nitrate.

[0038] Preferably, in step S01, the concentration of ferric nitrate in the first precursor solution is 0.01-0.07 mol / L.

[0039] Preferably, in step S01, the volume of the first precursor solution is controlled to be 2-5 times the volume of the washed and activated carbon felt.

[0040] Preferably, in step S01, the ultrasonic impregnation time is 0.1-1h.

[0041] Preferably, in step S01, the vacuum drying temperature is 60-90℃, and the vacuum drying time is 5-10 hours. Preferably, in step S01, the protective atmosphere is one of the following: nitrogen, argon, helium, hydrogen-nitrogen mixture, or argon-hydrogen mixture.

[0042] Furthermore, in step S01, the gradient heating calcination method is as follows: first, heat to a calcination temperature of 450-550℃ and hold for calcination for 1-6 hours; then continue to heat to 600-700℃ and hold for calcination for 1-6 hours.

[0043] Preferably, in step S01, the heating rate of the gradient heating calcination is 1-8℃ / min (preferably 1-5℃ / min).

[0044] Preferably, in step S02, the concentration of copper acetate in the second precursor solution is 0.05-0.1 mol / L; and the concentration of ascorbic acid in the ascorbic acid solution is 0.28-0.56 mol / L.

[0045] Preferably, in step S02, the volume of the second precursor solution is controlled to be 2-5 times the volume of the washed and activated carbon felt.

[0046] Preferably, in step S02, the mass ratio of copper acetate in the second precursor solution to ascorbic acid in the ascorbic acid solution is controlled to be 1:3-7.

[0047] Preferably, in step S02, the inert atmosphere is one of the following: nitrogen, argon, helium, or neon.

[0048] Preferably, in step S02, the heat preservation reaction time is 0.3-0.7 h.

[0049] Preferably, in step S02, the ultrasonic treatment time is 0.3-0.7 h. In this process, the purpose of ultrasonic treatment is to use ultrasound to eliminate the mass transfer of precursor ions from the three-dimensional pores of the carbon felt to the fiber interior, thereby achieving uniform anchoring of Cu on the entire cross section of the carbon felt and the fiber surface, thus avoiding localized enrichment of Cu or the formation of non-firmly attached particles, and providing a structural basis for obtaining Cu@carbon felt anodes with high zinc affinity and high cycle stability.

[0050] Preferably, in step S02, the freeze-drying temperature is -40°C to -10°C, and the freeze-drying time is 2-10 hours.

[0051] Preferably, in step S03, the electrolyte used for the positive and negative electrodes consists of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 mol / L tetramethylammonium bromide and 0.2 mol / L tetrabutylammonium bromide.

[0052] Further, in step S01 or step S02, the washed and activated carbon felt is prepared by the following method: immersing the carbon felt in anhydrous ethanol, ultrasonically treating it, and then washing it with water; then placing it in hydrochloric acid solution, etching it at 45-50℃, and then washing it with water until neutral; then placing it in sodium hydroxide solution, soaking it at 65-70℃, washing it with water until neutral, and drying it to obtain the washed and activated carbon felt.

[0053] Preferably, the volume ratio of carbon felt to anhydrous ethanol is 1:2-5; the volume ratio of carbon felt to hydrochloric acid solution is 1:2-5; and the volume ratio of carbon felt to sodium hydroxide solution is 1:2-5.

[0054] Preferably, the concentration of the hydrochloric acid solution is 2.5-3 mol / L; the concentration of the sodium hydroxide solution is 2.5-3 mol / L.

[0055] Preferably, the etching time at 45-50℃ is 2.5-3.5h; and the immersion time at 65-70℃ is 0.3-1h.

[0056] The present invention also provides a zinc-bromine flow battery prepared by the aforementioned method.

[0057] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below in conjunction with some specific embodiments.

[0058] The washed and activated carbon felt used in subsequent embodiments and comparative examples were specifically treated as follows: The carbon felt was cut into 3cm × 3cm pieces and completely immersed in 2.5 times its volume of anhydrous ethanol solution, and ultrasonically treated for 0.5h. Then, it was ultrasonically cleaned three times with deionized water (0.5h each time) to remove residual organic solvents. The cleaned carbon felt was then immersed in 2.5 times its volume of hydrochloric acid solution (3mol / L) and etched at 50℃ for 3h. It was then rinsed with deionized water until neutral and dried to obtain the etched carbon felt. The etched carbon felt was then immersed in 2.5 times its volume of sodium hydroxide solution (3mol / L) and soaked at 70℃ for 0.5h. It was then rinsed with deionized water until neutral and placed in a vacuum drying oven at 100℃ for 24h to obtain washed and activated carbon felt, which was then stored for later use.

[0059] Example 1 This embodiment provides a method for preparing a zinc-bromine flow battery, the specific steps of which are as follows: (1) Preparation of cathode composite material: The mass ratio of tin chloride to ferric nitrate is 7:4, and the mass of sodium citrate is 0.5% of the total mass of tin chloride and ferric nitrate as a complexing agent. Tin chloride, ferric nitrate and sodium citrate are dissolved in deionized water, and the concentration of ferric nitrate is 0.05mol / L to prevent the hydrolysis and precipitation of metal ions, to obtain the first precursor solution. The washed and activated carbon felt is placed in the first precursor solution, and the volume of the first precursor solution is controlled to be 4 times the volume of the carbon felt. After ultrasonic impregnation for 0.5h, it is vacuum dried at 80℃ for 8h. Then it is placed in a hydrogen-nitrogen mixed atmosphere (the volume ratio of hydrogen to nitrogen is 8:92) for gradient heating calcination: the temperature is raised to 500℃ at a heating rate of 3℃ / min and kept at the temperature for 2h for reduction. The temperature is further raised to 650℃ at a heating rate of 3℃ / min and kept at the temperature for 3h for crystallization. It is then naturally cooled to room temperature to obtain SnO2-Fe@carbon felt cathode composite material with high catalytic activity.

[0060] (2) Preparation of negative electrode composite material: Copper acetate was dissolved in deionized water to obtain a second precursor solution with a copper acetate concentration of 0.1 mol / L; the washed and activated carbon felt was placed in the second precursor solution, and the volume of the second precursor solution was controlled to be 5 times the volume of the carbon felt. After impregnation at room temperature, the solution was heated to 60°C in a water bath under an argon atmosphere. Ascorbic acid solution with a concentration of 0.56 mol / L was added dropwise at a rate of 5 mL / min, and the mass ratio of copper acetate in the second precursor solution to ascorbic acid in the ascorbic acid solution was controlled to be 1:5. After the addition was completed, the mixture was kept warm and stirred for 0.5 h. After ultrasonic treatment for 0.5 h, the solid was taken out and the freeze-drying temperature was controlled to be -20°C. The mixture was freeze-dried for 8 h to obtain Cu@carbon felt negative electrode composite material with high zinc affinity.

[0061] (3) Assemble the zinc-bromine flow battery: Lay the negative electrode aluminum alloy end plate flat on the table, insert the four positioning rods into the four corners respectively, and place the Teflon insulating sheet, gold-plated copper current collector, fluororubber sealing ring along the positioning rods in sequence, and then place the graphite plate with flow channel (the flow channel area is 3cm×3cm), which is the negative electrode plate. Place the EPDM rubber sealing sheet on the graphite plate with flow channel, and then place the Cu@carbon felt negative electrode composite material to ensure that it completely covers the flow channel area and does not exceed the edge.

[0062] The pre-treated microporous membrane is then smoothly laid over the negative electrode carbon felt, ensuring no wrinkles or displacement. Next, an EPDM rubber sealing sheet, a SnO2-Fe@carbon felt positive electrode composite material, and the separator are placed sequentially on the microporous membrane. Then, a graphite plate with flow channels (positive electrode plate), a gold-plated copper current collector, a Teflon insulating sheet, a fluororubber sealing ring, and a positive electrode aluminum alloy end plate are placed sequentially. Finally, the connections are tightened with bolts, and electrolyte is added to the positive and negative electrode areas to produce a zinc-bromine flow battery.

[0063] The electrolyte consists of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 mol / L tetramethylammonium bromide and 0.2 mol / L tetrabutylammonium bromide.

[0064] This embodiment also provides a zinc-bromine flow battery prepared using the aforementioned method.

[0065] Example 2 This embodiment provides a method for preparing a zinc-bromine flow battery, the specific steps of which are as follows: (1) Preparation of cathode composite material: The mass ratio of tin chloride to ferric nitrate is 7:1, and the mass of sodium citrate is 0.3% of the total mass of tin chloride and ferric nitrate as a complexing agent. Tin chloride, ferric nitrate and sodium citrate are dissolved in deionized water, and the concentration of ferric nitrate is 0.012 mol / L to prevent the hydrolysis and precipitation of metal ions, to obtain the first precursor solution. The washed and activated carbon felt is placed in the first precursor solution, and the volume of the first precursor solution is controlled to be twice the volume of the carbon felt. After ultrasonic impregnation for 0.1 h, it is vacuum dried at 70 °C for 9 h. Then it is placed in a hydrogen-nitrogen mixed atmosphere (the volume ratio of hydrogen to nitrogen is 8:92) for gradient heating calcination: the temperature is raised to 450 °C at a heating rate of 2 °C / min and kept at the temperature for 1 h for reduction. The temperature is further raised to 600 °C at a heating rate of 2 °C / min and kept at the temperature for 2 h for crystallization. It is then naturally cooled to room temperature to obtain SnO2-Fe@carbon felt cathode composite material with high catalytic activity.

[0066] (2) Preparation of negative electrode composite material: Copper acetate was dissolved in deionized water to obtain a second precursor solution with a copper acetate concentration of 0.1 mol / L; the washed and activated carbon felt was placed in the second precursor solution, and the volume of the second precursor solution was controlled to be 5 times the volume of the carbon felt. After impregnation at room temperature, the solution was heated to 80°C in a water bath under a helium atmosphere. Ascorbic acid solution with a concentration of 0.34 mol / L was added dropwise at a rate of 5 mL / min, and the mass ratio of copper acetate in the second precursor solution to ascorbic acid in the ascorbic acid solution was controlled to be 1:3. After the addition was completed, the mixture was kept warm and stirred for 0.7 h. After ultrasonic treatment for 0.3 h, the solid was taken out and the freeze-drying temperature was controlled to be -35°C. The mixture was freeze-dried for 6 h to obtain Cu@carbon felt negative electrode composite material with high zinc affinity.

[0067] (3) Assemble the zinc-bromine flow battery: Lay the negative electrode aluminum alloy end plate flat on the table, insert the four positioning rods into the four corners respectively, and place the Teflon insulating sheet, gold-plated copper current collector, fluororubber sealing ring along the positioning rods in sequence, and then place the graphite plate with flow channel (the flow channel area is 3cm×3cm), which is the negative electrode plate. Place the EPDM rubber sealing sheet on the graphite plate with flow channel, and then place the Cu@carbon felt negative electrode composite material to ensure that it completely covers the flow channel area and does not exceed the edge.

[0068] The pre-treated microporous membrane is then smoothly laid over the negative electrode carbon felt, ensuring no wrinkles or displacement. Next, an EPDM rubber sealing sheet, a SnO2-Fe@carbon felt positive electrode composite material, and the separator are placed sequentially on the microporous membrane. Then, a graphite plate with flow channels (positive electrode plate), a gold-plated copper current collector, a Teflon insulating sheet, a fluororubber sealing ring, and a positive electrode aluminum alloy end plate are placed sequentially. Finally, the connections are tightened with bolts, and electrolyte is added to the positive and negative electrode areas to produce a zinc-bromine flow battery.

[0069] The electrolyte consists of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 mol / L tetramethylammonium bromide and 0.2 mol / L tetrabutylammonium bromide.

[0070] This embodiment also provides a zinc-bromine flow battery prepared using the aforementioned method.

[0071] Example 3 This embodiment provides a method for preparing a zinc-bromine flow battery, the specific steps of which are as follows: (1) Preparation of cathode composite material: The mass ratio of tin chloride to ferric nitrate is 7:2, and the mass of sodium citrate is 0.4% of the total mass of tin chloride and ferric nitrate as a complexing agent. Tin chloride, ferric nitrate and sodium citrate are dissolved in deionized water, and the concentration of ferric nitrate is 0.025mol / L to prevent the hydrolysis and precipitation of metal ions, to obtain the first precursor solution. The washed and activated carbon felt is placed in the first precursor solution, and the volume of the first precursor solution is controlled to be 2.5 times the volume of the carbon felt. After ultrasonic impregnation for 0.2h, it is vacuum dried at 60℃ for 10h. Then it is placed in an argon atmosphere for gradient heating calcination: the temperature is raised to 480℃ at a heating rate of 4℃ / min and kept at the temperature for 3h for reduction. The temperature is further raised to 630℃ at a heating rate of 4℃ / min and kept at the temperature for 4h for crystallization. It is then naturally cooled to room temperature to obtain SnO2-Fe@carbon felt cathode composite material with high catalytic activity.

[0072] (2) Preparation of negative electrode composite material: Copper acetate was dissolved in deionized water to obtain a second precursor solution with a copper acetate concentration of 0.1 mol / L; the washed and activated carbon felt was placed in the second precursor solution, and the volume of the second precursor solution was controlled to be 3.5 times the volume of the carbon felt. After impregnation at room temperature, the solution was heated to 70°C in a water bath under a nitrogen atmosphere, and an ascorbic acid solution with a concentration of 0.46 mol / L was added dropwise at a rate of 5 mL / min. The mass ratio of copper acetate in the second precursor solution to ascorbic acid in the ascorbic acid solution was controlled to be 1:4. After the addition was completed, the mixture was kept warm and stirred for 0.6 h. After ultrasonic treatment for 0.4 h, the solid was taken out, and the freeze-drying temperature was controlled to be -10°C. The mixture was freeze-dried for 10 h to obtain Cu@carbon felt negative electrode composite material with high zinc affinity.

[0073] (3) Assemble the zinc-bromine flow battery: Lay the negative electrode aluminum alloy end plate flat on the table, insert the four positioning rods into the four corners respectively, and place the Teflon insulating sheet, gold-plated copper current collector, fluororubber sealing ring along the positioning rods in sequence, and then place the graphite plate with flow channel (the flow channel area is 3cm×3cm), which is the negative electrode plate. Place the EPDM rubber sealing sheet on the graphite plate with flow channel, and then place the Cu@carbon felt negative electrode composite material to ensure that it completely covers the flow channel area and does not exceed the edge.

[0074] The pre-treated microporous membrane is then smoothly laid over the negative electrode carbon felt, ensuring no wrinkles or displacement. Next, an EPDM rubber sealing sheet, a SnO2-Fe@carbon felt positive electrode composite material, and the separator are placed sequentially on the microporous membrane. Then, a graphite plate with flow channels (positive electrode plate), a gold-plated copper current collector, a Teflon insulating sheet, a fluororubber sealing ring, and a positive electrode aluminum alloy end plate are placed sequentially. Finally, the connections are tightened with bolts, and electrolyte is added to the positive and negative electrode areas to produce a zinc-bromine flow battery.

[0075] The electrolyte consists of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 mol / L tetramethylammonium bromide and 0.2 mol / L tetrabutylammonium bromide.

[0076] This embodiment also provides a zinc-bromine flow battery prepared using the aforementioned method.

[0077] Example 4 This embodiment provides a method for preparing a zinc-bromine flow battery, the specific steps of which are as follows: (1) Preparation of cathode composite material: The mass ratio of tin chloride to ferric nitrate is 7:3, and the mass of sodium citrate is 0.6% of the total mass of tin chloride and ferric nitrate as a complexing agent. Tin chloride, ferric nitrate and sodium citrate are dissolved in deionized water, and the concentration of ferric nitrate is 0.037mol / L to prevent the hydrolysis and precipitation of metal ions, so as to obtain the first precursor solution. The washed and activated carbon felt is placed in the first precursor solution, and the volume of the first precursor solution is controlled to be 3.5 times the volume of the carbon felt. After ultrasonic impregnation for 0.3h, it is vacuum dried at 70℃ for 9h. Then it is placed in a nitrogen atmosphere for gradient heating calcination: the temperature is raised to 520℃ at a heating rate of 1℃ / min and kept at the temperature for 4h for reduction. The temperature is further raised to 680℃ at a heating rate of 1℃ / min and kept at the temperature for 5h for crystallization. It is then naturally cooled to room temperature to obtain SnO2-Fe@carbon felt cathode composite material with high catalytic activity.

[0078] (2) Preparation of negative electrode composite material: Copper acetate was dissolved in deionized water to obtain a second precursor solution with a copper acetate concentration of 0.05 mol / L; the washed and activated carbon felt was placed in the second precursor solution, and the volume of the second precursor solution was controlled to be 3.5 times the volume of the carbon felt. After impregnation at room temperature, the solution was heated to 40°C in a water bath under an argon atmosphere. Ascorbic acid solution with a concentration of 0.39 mol / L was added dropwise at a rate of 5 mL / min, and the mass ratio of copper acetate in the second precursor solution to ascorbic acid in the ascorbic acid solution was controlled to be 1:7. After the addition was completed, the mixture was kept warm and stirred for 0.3 h. After ultrasonic treatment for 0.7 h, the solid was taken out and the freeze-drying temperature was controlled to be -30°C. The mixture was freeze-dried for 9 h to obtain Cu@carbon felt negative electrode composite material with high zinc affinity.

[0079] (3) Assemble the zinc-bromine flow battery: Lay the negative electrode aluminum alloy end plate flat on the table, insert the four positioning rods into the four corners respectively, and place the Teflon insulating sheet, gold-plated copper current collector, fluororubber sealing ring along the positioning rods in sequence, and then place the graphite plate with flow channel (the flow channel area is 3cm×3cm), which is the negative electrode plate. Place the EPDM rubber sealing sheet on the graphite plate with flow channel, and then place the Cu@carbon felt negative electrode composite material to ensure that it completely covers the flow channel area and does not exceed the edge.

[0080] The pre-treated microporous membrane is then smoothly laid over the negative electrode carbon felt, ensuring no wrinkles or displacement. Next, an EPDM rubber sealing sheet, a SnO2-Fe@carbon felt positive electrode composite material, and the separator are placed sequentially on the microporous membrane. Then, a graphite plate with flow channels (positive electrode plate), a gold-plated copper current collector, a Teflon insulating sheet, a fluororubber sealing ring, and a positive electrode aluminum alloy end plate are placed sequentially. Finally, the connections are tightened with bolts, and electrolyte is added to the positive and negative electrode areas to produce a zinc-bromine flow battery.

[0081] The electrolyte consists of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 mol / L tetramethylammonium bromide and 0.2 mol / L tetrabutylammonium bromide.

[0082] This embodiment also provides a zinc-bromine flow battery prepared using the aforementioned method.

[0083] Example 5 This embodiment provides a method for preparing a zinc-bromine flow battery, the specific steps of which are as follows: (1) Preparation of cathode composite material: The mass ratio of tin chloride to ferric nitrate is 7:5, and the mass of sodium citrate is 0.7% of the total mass of tin chloride and ferric nitrate as a complexing agent. Tin chloride, ferric nitrate and sodium citrate are dissolved in deionized water, and the concentration of ferric nitrate is 0.062 mol / L to prevent the hydrolysis and precipitation of metal ions, to obtain the first precursor solution. The washed and activated carbon felt is placed in the first precursor solution, and the volume of the first precursor solution is controlled to be 5 times the volume of the carbon felt. After ultrasonic impregnation for 0.7 h, it is vacuum dried at 90 °C for 6 h. Then it is placed in a helium atmosphere for gradient heating calcination: the temperature is raised to 550 °C at a heating rate of 5 °C / min and kept at the temperature for 5 h. The temperature is further raised to 700 °C at a heating rate of 5 °C / min and kept at the temperature for 1 h for crystallization. It is then naturally cooled to room temperature to obtain SnO2-Fe@carbon felt cathode composite material with high catalytic activity.

[0084] (2) Preparation of negative electrode composite material: Copper acetate was dissolved in deionized water to obtain a second precursor solution with a copper acetate concentration of 0.05 mol / L; the washed and activated carbon felt was placed in the second precursor solution, and the volume of the second precursor solution was controlled to be 3 times the volume of the carbon felt. After impregnation at room temperature, the solution was heated to 50°C in a water bath under a nitrogen atmosphere, and an ascorbic acid solution with a concentration of 0.34 mol / L was added dropwise at a rate of 5 mL / min. The mass ratio of copper acetate in the second precursor solution to ascorbic acid in the ascorbic acid solution was controlled to be 1:6. After the addition was completed, the mixture was kept warm and stirred for 0.4 h. After ultrasonic treatment for 0.6 h, the solid was taken out, and the freeze-drying temperature was controlled to be -40°C. The mixture was freeze-dried for 7 h to obtain Cu@carbon felt negative electrode composite material with high zinc affinity.

[0085] (3) Assemble the zinc-bromine flow battery: Lay the negative electrode aluminum alloy end plate flat on the table, insert the four positioning rods into the four corners respectively, and place the Teflon insulating sheet, gold-plated copper current collector, fluororubber sealing ring along the positioning rods in sequence, and then place the graphite plate with flow channel (the flow channel area is 3cm×3cm), which is the negative electrode plate. Place the EPDM rubber sealing sheet on the graphite plate with flow channel, and then place the Cu@carbon felt negative electrode composite material to ensure that it completely covers the flow channel area and does not exceed the edge.

[0086] The pre-treated microporous membrane is then smoothly laid over the negative electrode carbon felt, ensuring no wrinkles or displacement. Next, an EPDM rubber sealing sheet, a SnO2-Fe@carbon felt positive electrode composite material, and the separator are placed sequentially on the microporous membrane. Then, a graphite plate with flow channels (positive electrode plate), a gold-plated copper current collector, a Teflon insulating sheet, a fluororubber sealing ring, and a positive electrode aluminum alloy end plate are placed sequentially. Finally, the connections are tightened with bolts, and electrolyte is added to the positive and negative electrode areas to produce a zinc-bromine flow battery.

[0087] The electrolyte consists of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 mol / L tetramethylammonium bromide and 0.2 mol / L tetrabutylammonium bromide.

[0088] This embodiment also provides a zinc-bromine flow battery prepared using the aforementioned method.

[0089] Comparative Example 1 This comparative example adopts the technical solution of Example 1, the difference being that the addition of copper acetate is omitted in step (2), and the specific operation of step (2) is adjusted accordingly: Ascorbic acid was dissolved in deionized water to obtain an ascorbic acid solution with a concentration of 0.56 mol / L. The washed and activated carbon felt was placed in the ascorbic acid solution, and the volume of the ascorbic acid solution was controlled to be 5 times the volume of the carbon felt. After impregnation at room temperature, the solution was heated to 60°C in a water bath under an argon atmosphere and stirred for 0.5 h. After ultrasonic treatment for 0.5 h, the solid was removed and freeze-dried at -20°C for 8 h to obtain the ascorbic acid@carbon felt anode composite material.

[0090] All other processes and parameters are the same as in Example 1.

[0091] Comparative Example 2 This comparative example uses the technical solution of Example 1, except that the addition of tin chloride is omitted in step (1) to obtain the iron compound@carbon felt cathode composite material. Other processes and parameters are the same as in Example 1.

[0092] Electrochemical performance tests were conducted on the zinc-bromine flow batteries of each embodiment and comparative example, using a constant current charge-discharge mode. Specifically, during the test, the positive and negative electrolytes were controlled to flow at 35 mL / min, initially at 60 mA / cm². 2 Constant current charging for 40 minutes (charge area specific capacity of 40mAh / cm²) 2 The battery was then discharged at a constant current until the voltage reached 0.6V. Based on the battery charge-discharge curves, the coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were calculated. The results of the second charge-discharge test for each battery are shown in the table below:

[0093] As can be seen from the table above, the coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine flow batteries using SnO2-Fe@carbon felt positive electrode composite material and Cu@carbon felt negative electrode composite material in Examples 1-5 are all better than those using the zinc-bromine flow batteries using positive and negative electrode carbon felt obtained in Comparative Example 1. This indicates that by loading SnO2-Fe onto the surface of the positive electrode carbon felt and loading Cu onto the negative electrode carbon felt, the electrochemical performance of the carbon felt can be significantly improved through positive and negative stage modification.

[0094] Of all the embodiments, Example 1, carried out with optimal process parameters, exhibited excellent overall performance, with all three efficiency parameters reaching the highest levels. With changes in the process parameters used, the three key indicators—coulombic efficiency, voltage efficiency, and energy efficiency—of Examples 2-5 all showed a decreasing trend. The coulombic efficiency, voltage efficiency, and energy efficiency of Example 1 were 97.6%, 86.2%, and 84.1%, respectively; while those of Example 5 were 96.7%, 83.8%, and 81.1%, respectively. This demonstrates that optimizing the combination of various process parameters, such as the molar ratio of tin chloride to ferric nitrate, the mass ratio of copper acetate to ascorbic acid, the vacuum drying temperature, the calcination temperature and atmosphere, and the heating temperature and time, is necessary to better achieve the effect of SnO2-Fe loading on the positive electrode and Cu elemental carbon felt loading on the negative electrode, thereby significantly improving the electrochemical performance of the zinc-bromine flow battery.

[0095] With the same charging capacity, a higher coulombic efficiency indicates a greater discharge capacity. The coulombic efficiencies of Examples 1-5 are all no less than 96.7%, while the coulombic efficiency of Comparative Example 1 is no more than 96%. This indicates that carbon felt modified with elemental Cu on the negative electrode after loading SnO2-Fe on the positive electrode can reversibly release more charge. Analysis shows that the difference in coulombic efficiency between Example 1 and Comparative Example 1 mainly comes from whether the negative electrode interface has a metal Cu layer with strong zinc affinity: Cu@carbon felt significantly inhibits dendrite derivation and dead zinc formation by reducing the Zn nucleation overpotential, increasing the nucleation density, and inducing two-dimensional uniform zinc deposition. At the same time, the denser and flatter Zn deposition morphology reduces the effective reaction area of ​​the negative electrode and weakens the redox consumption of shuttle to the polybrominated compounds on the negative electrode surface. Therefore, it exhibits a higher coulombic efficiency under the same operating conditions. In contrast, the ascorbic acid@carbon felt of Comparative Example 1 lacks this zinc-affinity metal interface, and zinc still mainly grows locally at high overpotential, resulting in more severe dead zinc and roughening, and a correspondingly lower coulombic efficiency.

[0096] Voltage efficiency is the ratio of average discharge voltage to average charge voltage, and it is related to the polarization phenomenon during battery charging and discharging. The voltage efficiency of Examples 1-5 is greater than 83.5%, while the voltage efficiency of Comparative Examples 1-2 is less than 75%. This indicates that the zinc-bromine flow battery using the carbon cathode loaded with SnO2-Fe and the anode loaded with Cu-modified carbon felt obtained in Examples 1-5 has lower polarization. The lattice defects of SnO2 synergize with the active sites of Fe single atoms. Fe single atoms can optimize the electronic structure of SnO2, providing more physical adsorption sites for Br2, reducing Br2 diffusion to the anode, and increasing Br2 adsorption capacity. - The reduction reaction interface increases the reaction rate, while also reducing the Br2 / Br2 ratio. - The activation energy of the reaction increases the reaction rate constant and decreases the Br2 / Br ratio.- The redox overpotential is reduced, thereby minimizing voltage loss due to activation polarization. Furthermore, electron transfer during zinc deposition / stripping benefits from the highly conductive copper active sites on the carbon felt surface.

[0097] Energy efficiency is an evaluation index of the energy conversion efficiency of a battery during charging and discharging. Its value is a combination of coulombic efficiency and voltage efficiency. Examples 1-5 have an energy efficiency greater than 81.1%, while Comparative Examples 1-2 have an energy efficiency not exceeding 72%. The positive electrode carbon felt-supported SnO2-Fe composite material can improve the energy efficiency of the zinc-bromine flow battery through multiple mechanisms, including synergistic enhancement of reaction kinetics, suppression of the bromine shuttle effect, and optimization of the electrode structure. The copper loading modification of the negative electrode significantly reduces the nucleation overpotential of zinc and provides abundant reactive sites, while effectively reducing battery polarization. The combined effect of these factors ultimately leads to the improvement in the energy efficiency of the zinc-bromine flow battery.

[0098] Comparing Example 1 and Comparative Example 1, it can be seen that the advantages of the positive electrode are: SnO2-Fe can still effectively improve the positive electrode reaction kinetics; the main role of ascorbic acid is to introduce oxygen-containing functional groups (-OH, -COOH), which will affect electron conduction to a certain extent, increase interfacial impedance and reaction energy barrier, leading to intensified polarization and significantly reducing voltage and energy efficiency. Its ability to guide zinc ions is limited, easily causing concentration polarization, resulting in rapid voltage decay. Once the guidance is lost, zinc dendrites will grow uncontrollably, which may not only pierce the separator and cause a short circuit, but the "dead zinc" formed by its shedding will also reduce coulombic efficiency and cycle life.

[0099] Comparing Example 1 and Comparative Example 2, it can be seen that the negative electrode has the following advantages: Cu can still effectively guide the uniform precipitation of zinc in the negative electrode and the loading of Fe species on the carbon fiber surface. However, Fe2O3 has extremely low intrinsic conductivity. When it is attached to the carbon fiber surface in the form of discrete particles, electron transport needs to cross a large number of particle boundaries, which constitutes a significant polarization bottleneck. Moreover, this phase contains Fe in the bromine-containing electrolyte. 3+ The risk of slow dissolution leads to a decline in catalytic activity, resulting in fewer and fewer adsorption sites and a lack of Sn. 4+ Site pair Br - The chemical confinement of the positive electrode leads to a sharp increase in polarization and severe self-discharge.

[0100] Figure 1 The constant current charge-discharge curves are for electrochemical performance testing of the zinc-bromine flow battery of Example 1 and the zinc-bromine flow battery of Comparative Example 1. The difference between Comparative Example 1 and Example 1 is that the negative electrode uses an ascorbic acid@carbon felt composite material. During the electrochemical performance testing, the electrolyte flowed at 35 mL / min, and the current was 60 mA / cm². 2 Constant current charging for 40 minutes (charge area specific capacity of 40mAh / cm²) 2Then, it is discharged at a constant current until the voltage reaches 0.6V. As can be seen from the figure, in terms of discharge area specific capacity, the SnO2-Fe@carbon felt positive electrode and Cu@carbon felt negative electrode obtained in Example 1 are about 7 mAh / cm² higher than those in Comparative Example 1. 2 This results in the carbon felt obtained in Example 1 having a coulombic efficiency approximately 2.3% higher than that in Comparative Example 1. While the charging plateaus of the two are not significantly different, the discharge voltages at the positive and negative electrodes of the SnO2-Fe@carbon felt and Cu@carbon felt are approximately 200mV higher than those in Comparative Example 1, resulting in a voltage efficiency approximately 12% higher for the carbon felt obtained in Example 1 compared to Comparative Example 1. The combined effect of coulombic and voltage efficiency makes the energy efficiency of the carbon felt obtained in Example 1 approximately 14% higher than that in Comparative Example 1. The above comparison demonstrates that the voltage plateau of Example 1 is more stable: during charging and discharging, voltage fluctuations are smaller, especially in the high-capacity range (30mAh / cm³). 2 Afterwards, the voltage drop rate was much slower than in Comparative Example 1. Comparative Example 1 exhibited a faster voltage plateau decay: after a slight increase in capacity, the voltage dropped rapidly, and polarization was significantly greater. Essentially, the loaded SnO2-Fe and Cu act as catalysts, reducing the overpotential of the electrode reactions. Positive electrode: SnO2-Fe catalyzes the reduction (discharge) of Br2 and the oxidation (charging) of Br-, accelerating bromine adsorption / desorption, reducing side reactions such as bromine shuttle, and lowering reaction resistance. Negative electrode: Cu optimizes zinc deposition, reduces the tendency for zinc dendrite growth, decreases the hydrogen evolution overpotential, and improves the uniformity and efficiency of the zinc reaction. Furthermore, the SnO2-Fe on the surface of the positive electrode carbon felt and the Cu on the surface of the negative electrode carbon felt provide Br2 oxidation active sites, reducing the overpotential for zinc nucleation, increasing the reactive sites on the carbon felt surface, and reducing polarization, among other beneficial effects. This results in improved coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine flow battery after SnO2-Fe and Cu loading modification.

[0101] Figure 2 and Figure 3 The figures show the cycle curves for the electrochemical performance tests of the zinc-bromine flow batteries in Example 1 and Comparative Example 1, respectively. It can be seen that the SnO2-Fe@carbon felt positive electrode and Cu@carbon felt negative electrode obtained in Example 1 showed minimal decay in coulombic efficiency and energy efficiency after 1000 cycles, with energy efficiency and coulombic efficiency retention rates as high as approximately 84% and 97%, respectively. In contrast, the carbon felt positive and negative electrodes of Comparative Example 1 fluctuated significantly during cycling; after only 110 cycles, the coulombic efficiency and energy efficiency decreased by nearly 5% and 12%, respectively. Figure 2As can be seen, Cu-modified carbon felt can provide uniform nucleation sites for zinc deposition, reducing the formation of zinc dendrites and zinc dead zones, thereby significantly improving coulombic efficiency and cycling stability. This is the core reason why there is almost no degradation after 1000 cycles. Reducing interfacial impedance, Cu's excellent conductivity can improve charge transfer at the negative electrode interface and reduce polarization losses during charge and discharge, thus ensuring that energy efficiency remains stable at a high level for a long time. And from... Figure 3 In contrast, ascorbic acid, as an organic modifier, suffers from poor stability and rapid efficiency decay. It is prone to decomposition or desorption in the battery's charging and discharging environment, leading to a gradual loss of the negative electrode interface modification effect and a decrease in the reversibility of zinc deposition / dissolution. Consequently, both coulombic efficiency and energy efficiency continuously decline. Furthermore, ascorbic acid exhibits significant polarization loss; its conductivity is far inferior to that of metallic Cu, increasing the charge transfer impedance at the negative electrode interface and resulting in greater energy loss during charging and discharging. Therefore, its initial energy efficiency is significantly lower than that of the Cu-modified system, and with further cycling, the impedance increases, leading to a continuous decline in efficiency. This comparison demonstrates that the SnO2-Fe@carbon felt for the positive electrode and the Cu@carbon felt for the negative electrode prepared using the technical solution of this invention have excellent effects in suppressing bromine volatilization and permeation, as well as inhibiting zinc dendrite formation.

[0102] Figure 4 X-ray diffraction (XRD) patterns of the SnO2-Fe@carbon felt cathode composite material, Cu@carbon felt anode composite material, and blank carbon felt (i.e., washed and activated carbon felt) prepared in Example 1. The modified carbon felt for the cathode obtained in Example 1... Figure 4 Diffraction peaks of SnO2 and Fe were clearly observed in the XRD patterns. SnO2 diffraction peaks were clearly observed at 33.9° and 37.9°, while Fe diffraction peaks were clearly observed at 44.7°, 65.0°, and 82.3°. Copper diffraction peaks were clearly observed at 43.2°, 50.4°, and 74.1° in the modified carbon felt for the negative electrode. This indicates that Example 1 successfully loaded SnO2 and Fe onto the positive electrode carbon felt, and successfully loaded Cu onto the negative electrode carbon felt. Further comparison of the XRD patterns of the modified carbon felt and the blank carbon felt prepared in Example 1 shows that, apart from the diffraction peaks of SnO2, Fe, and Cu, the other diffraction peaks are basically consistent. Therefore, the positive and negative electrode modification process of this invention did not damage the carbon felt crystal structure, and while achieving copper particle loading, it completely preserved the original crystal phase characteristics of the carbon felt.

[0103] Figure 5 , Figure 6 and Figure 7 The images shown are scanning electron microscope (SEM) images of the SnO2-Fe@carbon felt positive electrode composite material, Cu@carbon felt negative electrode composite material, and ascorbic acid@carbon felt negative electrode composite material prepared in Example 1 of this invention. Figure 5 , Figure 6 and Figure 7It is evident that the carbon felt of the positive electrode composite material prepared in Example 1 is loaded with SnO2 and Fe, while the carbon fibers of the negative electrode composite material are loaded with Cu nanoparticles. Figure 7 In Comparative Example 1, the carbon fibers of the ascorbic acid@carbon felt anode composite material were relatively smooth, and no large number of obvious particles were observed.

[0104] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0105] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a zinc-bromine flow battery, characterized in that, Includes the following steps: Step S01: Dissolve tin chloride, ferric nitrate, and sodium citrate in deionized water to obtain a first precursor solution; place the washed and activated carbon felt in the first precursor solution, ultrasonically impregnate it, remove the carbon felt and dry it, place it in a protective atmosphere, and perform gradient heating calcination to obtain SnO2-Fe@carbon felt cathode composite material. Step S02: Dissolve copper acetate in deionized water to obtain a second precursor solution; immerse the washed and activated carbon felt in the second precursor solution, and then heat it to 40-80℃ in an inert atmosphere, while keeping it at the temperature and adding ascorbic acid solution dropwise; after the ascorbic acid solution is added, keep it at the temperature for reaction; then treat it with ultrasound and freeze dry to obtain Cu@carbon felt anode composite material; Step S03: Using SnO2-Fe@carbon felt positive electrode composite material as positive electrode and Cu@carbon felt negative electrode composite material as negative electrode, a zinc-bromine flow battery is assembled.

2. The method for preparing a zinc-bromine flow battery according to claim 1, characterized in that, In step S01, the mass ratio of tin chloride to ferric nitrate in the first precursor solution is 7:1-5. The mass of sodium citrate added is 0.1-1% of the total mass of tin chloride and ferric nitrate.

3. The method for preparing a zinc-bromine flow battery according to claim 1, characterized in that, In step S01, the concentration of ferric nitrate in the first precursor solution is 0.01-0.07 mol / L; The volume of the first precursor solution should be controlled to be 2-5 times the volume of the washed and activated carbon felt.

4. The method for preparing a zinc-bromine flow battery according to claim 1, characterized in that, In step S01, the ultrasonic impregnation time is 0.1-1 h; Gradient heating calcination involves first heating to a calcination temperature of 450-550℃ and holding the temperature for 1-6 hours; then continuing to heat to 600-700℃ and holding the temperature for 1-6 hours.

5. The method for preparing a zinc-bromine flow battery according to claim 1, characterized in that, In step S02, the concentration of copper acetate in the second precursor solution is 0.05-0.1 mol / L; The concentration of ascorbic acid in the ascorbic acid solution is 0.28-0.56 mol / L.

6. The method for preparing a zinc-bromine flow battery according to claim 1, characterized in that, In step S02, the volume of the second precursor solution is controlled to be 2-5 times the volume of the washed and activated carbon felt. The mass ratio of copper acetate in the second precursor solution to ascorbic acid in the ascorbic acid solution is controlled to be 1:3-7.

7. The method for preparing a zinc-bromine flow battery according to claim 1, characterized in that, In step S02, the heat preservation reaction time is 0.3-0.7 h; the ultrasonic treatment time is 0.3-0.7 h.

8. The method for preparing a zinc-bromine flow battery according to claim 1, characterized in that, In step S03, the electrolyte used in the zinc-bromine flow battery is composed of 2 mol / L zinc bromide, 3 mol / L potassium chloride, 0.2 mol / L tetramethylammonium bromide and 0.2 mol / L tetrabutylammonium bromide.

9. The method for preparing a zinc-bromine flow battery according to claim 1, characterized in that, The washed and activated carbon felt is prepared by the following method: the carbon felt is treated sequentially with anhydrous ethanol, hydrochloric acid solution, and sodium hydroxide solution, and then dried.

10. A zinc-bromine flow battery, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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