Preparation method and application of zinc-bromine flow battery positive electrode material

Abstract

The application provides a preparation method and application of a zinc-bromine flow battery positive electrode material, and belongs to the technical field of flow batteries.The tin source, bismuth source and solvent are subjected to first wet ball milling, the obtained mixture is subjected to second wet ball milling with a saccharide carbon source, the product is transferred into a mixed system of a polymer surfactant and a polar solvent, and is subjected to stirring reaction and solvothermal reaction in sequence; the product after reaction is subjected to argon temperature calcination and ammonia argon mixed gas nitrogenation, the product is completely mixed with a bromine source, a polar organic solvent and hard carbon, and after reaction in a closed container, a nitrogen-doped carbon tin / stannic bismuth heterojunction with hard carbon coating, namely a zinc-bromine flow battery positive electrode material, is obtained.The zinc-bromine flow battery positive electrode material prepared by the preparation method has the advantages that the bromine concentration in an electrochemical reaction system is stable, the bromine redox reaction rate is improved, the volume expansion of the positive electrode material and bromine shuttling can be avoided, and therefore the energy efficiency and cycle stability of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of zinc-bromine flow battery technology, and in particular to a method for preparing and applying a zinc-bromine flow battery cathode material. Background Technology

[0002] In zinc-bromine flow batteries, the redox reaction rate of bromine at the positive electrode is slow, and the oxidation of bromine generates polymerized bromide ions, which cause volume expansion of the electrode material and complicate the reaction process, resulting in battery capacity loss. Furthermore, bromine in the electrolyte not only reacts directly with the zinc negative electrode, causing localized corrosion, but it can also penetrate the separator, leading to battery self-discharge or even short circuits. To address these technical problems, existing technologies for optimizing the positive electrode material mainly focus on coating processes and surface modification. However, both methods generally suffer from uneven coating or modification layers, poor interfacial stability of the coating or modification layers, and the inability to effectively suppress bromide ion shuttle, directly limiting the electrochemical performance, energy efficiency, and cycle stability of the zinc-bromine flow battery positive electrode.

[0003] Chinese patent document CN120600840A discloses a positive electrode material for zinc-bromine flow batteries, its preparation method, and its application. The method involves crushing and sieving an activated carbon source, adding it to an aqueous dispersion of graphene oxide, stirring, centrifuging, removing the supernatant, drying, mixing with an activator, and activating under an inert atmosphere to obtain a graphene / activated carbon composite material. This composite material is then attached to a carbon-plastic bipolar plate to obtain the positive electrode material for zinc-bromine flow batteries. However, SEM images of the material obtained by this method show a significant stacking effect in the composite material after the addition of graphene, which hinders the Br₂ process. - Meanwhile, the van der Waals forces between the composite layers of the material are weak, making it prone to swelling and peeling when immersed in bromine electrolyte, which leads to the shedding of the coating layer on the surface of the current collector and causes the electrochemical performance of the electrode to degrade.

[0004] Chinese patent document CN120834221A discloses a composite membrane material for flow batteries and its preparation method. The method involves spraying a ZIF-8 metal-organic framework solution onto the positive electrode side of a microporous membrane, followed by drying to obtain the composite membrane material. The microporous structure of the material obtained by this method allows small-sized ions to pass through. While it can suppress bromide ion shuttle to some extent, it directly blocks Br2 and Br3. - The penetration of bromine species on the positive electrode side will restrict mass transfer, resulting in incomplete positive electrode reaction and a rapid decrease in energy efficiency with cycling. Summary of the Invention

[0005] To address the technical problems existing in the prior art, this invention provides a method for preparing and applying a cathode material for a zinc-bromine flow battery. A heterojunction precursor is obtained through two wet ball milling processes and a chemical precipitation process induced by a polymeric surfactant. A nitrogen-doped tin carbide / bismuth stannate heterojunction obtained by medium-temperature calcination and ammonia-argon mixed gas nitriding is then mixed with a bromine source and hard carbon to obtain a hard carbon-supported nitrogen-doped tin carbide / bismuth stannate heterojunction composite material. The aforementioned technical methods work together synergistically to effectively solve the problems of slow bromine oxidation kinetics, volume expansion due to polybromine ion generation, and bromine shuttle effect in existing cathode materials, which lead to decreased electrochemical performance. This method achieves stable bromine concentration in the electrochemical reaction system, increases the redox reaction rate of bromine, and avoids volume expansion and bromine shuttle in the cathode material, thereby improving the energy efficiency and cycle stability of the battery.

[0006] 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 cathode material includes the following steps: Step S01: The tin source, bismuth source and polar solvent are subjected to a first wet ball milling to obtain a mixture; the mixture is then subjected to a second wet ball milling with a sugar carbon source to obtain system A; Step S02: Mix the polymeric surfactant with a polar organic solvent to obtain system B; Step S03: Add system A to system B, stir and react at 70-80℃, transfer to a sealed container, and after solvothermal reaction at 140-180℃, separate and collect the solid. The solid is washed and dried to obtain the precursor. Step S04: The precursor is heated to 600-750℃ in an argon atmosphere, kept at the temperature, and nitrided by introducing a mixed atmosphere of ammonia and argon to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction. Step S05: After mixing the nitrogen-doped tin carbide / bismuth stannate heterojunction with a bromine source and a polar organic solvent, hard carbon is added, and the mixture is transferred to a sealed container. After a sealed reaction at 140-180℃, the solids are separated and collected. The solids are then washed and dried to obtain the zinc-bromine flow battery cathode material.

[0007] Preferably, in step S01, the tin source is one of tin dioxide, tin tetrachloride, and tin acetate; The bismuth source is one of bismuth oxide, bismuth trichloride, or bismuth hydroxide; The carbohydrate carbon source is one of glucose, sucrose, or soluble starch; The polar solvent is deionized water or ethanol.

[0008] Preferably, in step S01, the molar ratio of tin source, bismuth source, and sugar-based carbon source is 1:0.65-0.7:0.33-0.4; The concentration of the tin source in the polar solvent is 0.5-1 mol / L.

[0009] Preferably, in step S01, the vibration frequency of the first wet ball mill is 1500-2500 r / min, and the time of the first wet ball mill is 20-30 min; the vibration frequency of the second wet ball mill is 700-950 r / min, and the time of the second wet ball mill is 9-16 h.

[0010] Preferably, in step S02, the polymeric surfactant is one of PVP-K90 and PEG-2000; The polar organic solvent is ethanol or ethylene glycol; The concentration of polymeric surfactants in polar organic solvents is 0.625-4 g / L.

[0011] Preferably, in step S03, the concentration of the tin source in system A within the polar organic solvent in system B is 0.125-0.2 mmol / mL; The stirring reaction time is 1-2 hours; the solvothermal reaction time is 10-16 hours.

[0012] Preferably, in step S04, the heating rate to 600-750℃ is 5-10℃ / min; The nitriding process is carried out under heat and in a mixed atmosphere of ammonia and argon for 2-4 hours. In a mixed atmosphere of ammonia and argon, the volume percentage of ammonia is 3-8%.

[0013] Preferably, in step S05, the bromine source is sodium bromide or potassium bromide; The polar organic solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; The concentration of nitrogen-doped tin carbide / bismuth stannate heterojunction in polar organic solvent is 0.033-0.05 g / mL; the concentration of bromine source in polar organic solvent is 0.0165-0.05 mol / L; and the mass ratio of hard carbon to bromine source is 1-2:1.

[0014] Preferably, in step S05, the time for the sealed reaction at 140-180°C is 12-18 hours.

[0015] A zinc-bromine flow battery, wherein the zinc-bromine flow battery positive electrode material prepared by the aforementioned method is used as the positive electrode of the zinc-bromine flow battery.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The method for preparing the zinc-bromine flow battery cathode material of the present invention yields a composite material with multiple synergistic advantages: the high conductivity of tin carbide synergistically combines with the oxygen vacancy catalytic sites of bismuth stannate, significantly reducing Br₂ levels. - The activation energy of the oxidation reaction improves the reaction kinetic efficiency; the closed-pore energy of hard carbon enriches Br. - It also shortens the mass transfer distance and can alleviate Br - Converted to Br3 - The volume expansion traps polybrominated species and inhibits bromine shuttle to reduce self-discharge; the addition of sodium bromide forms a stable complex structure with bismuth stannate, continuously participates in the reaction and ensures the stability of bromine concentration in the electrochemical reaction system, thus enabling the composite material to exhibit excellent energy efficiency.

[0017] 2. In the preparation of the zinc-bromine flow battery cathode material of the present invention, the precursor of the tin carbide / bismuth stannate heterojunction is prepared by a process of two wet ball milling, chemical precipitation (stirring reaction) and solvothermal reaction. Specifically, the first wet ball milling can form a stable bismuth stannate crystal structure, and the second wet ball milling can promote the reaction of unreacted tin source and sugar carbon source to generate tin carbide. The two wet ball milling processes can form bismuth stannate and tin carbide monomers with high purity, providing independent dispersion units for the uniform connection of the heterojunction. The chemical precipitation process of stirring reaction can provide a mild reaction environment for the ball-milled and dispersed materials. Then, the solvothermal reaction accelerates the formation of bismuth stannate and tin carbide seed crystals. The long-chain structure of the polymer surfactant can kinetically connect with the bismuth stannate and tin carbide materials, providing sufficient kinetic conditions for the uniform growth of the heterojunction and avoiding the formation of agglomerates between the materials themselves. This effectively controls the uniform growth of the heterojunction and finally obtains a material with uniform and continuous active sites.

[0018] Tin carbide, as a metallic conductive material, can rapidly transport Br to the surface of the electrode material, synergistically with nitrogen doping to prevent charge accumulation at active sites. Bismuth stannate, with its vacancy-type structure, provides adsorption sites for Br. The Bi-O bond forms a Bi-O-Br complex, anchoring Br in the heterojunction structure and preventing Br from diffusing to the negative electrode through the electrolyte. Furthermore, the complex structure is reversible, allowing for stable Br complexation and release during cycling, thereby improving the cycle performance of the zinc-bromine flow battery.

[0019] 3. In the preparation of the zinc-bromine flow battery cathode material of the present invention, a nitrogen-doped tin carbide / bismuth stannate heterojunction is obtained through an argon-heated calcination process and an ammonia-argon mixed-gas heat-preserving nitriding process. This process enables nitrogen doping modification while ensuring the integrity of the heterostructure crystal structure. The argon-heated calcination process ensures the formation of the metallic conductive structure of SnC and the pyrochlore structure of Bi2Sn2O7, preventing the precursor from being oxidized or reduced during crystal formation. The ammonia-argon mixed-gas heat-preserving nitriding process forms strongly electronegative Bi-N bonds, while the complexation in bismuth stannate is a Bi-ON bond, forming a double barrier. Nitrogen doping can change the band structure of the interface, forming local micro-conductive regions, accelerating the efficient transport of electrons from the material surface to the oxygen vacancies in bismuth stannate, alleviating interfacial polarization caused by charge accumulation, thereby improving the electrochemical performance of the zinc-bromine flow battery.

[0020] 4. In the preparation of the zinc-bromine flow battery cathode material of the present invention, a bromine source is added during the heterojunction coating stage to improve energy efficiency. The addition of hard carbon material not only electrostatically attracts Br, but also alleviates the effects of Br... - Transformation into Br3 - The resulting volume expansion contributes to improved electrochemical performance of the zinc-bromine flow battery. Simultaneously, the addition of a bromine source during the reaction promotes the formation of Bi-O-Br bonds between Br and calcined oxygen-containing functional groups, enabling continuous absorption and release of Br during cycling. - Ensure that Br in the electrolyte - The concentration is stable; furthermore, the addition of hard carbon materials can coat heterojunction materials, and the turbulent pore structure of hard carbon materials generates capillary tension during the electrochemical reaction stage, Br - High concentration regions are formed within the pores through electrostatic adsorption and capillary condensation, thereby increasing the adsorption concentration of Br. The closed-pore nanocage structure restricts the spatial range of expansion, so that volume changes only occur within the pores. Dynamically, this avoids the accumulation and transmission of expansion stress, maintains structural integrity, and improves electrochemical performance.

[0021] 5. Using the zinc-bromine flow battery cathode material prepared according to this invention, a zinc-bromine flow battery was assembled and its electrochemical performance was tested at 30 mA / cm². 2 After 200 cycles at the current density, the coulombic efficiency is 90.8-92.8%, the voltage efficiency is 87.9-89.5%, and the energy efficiency is 81.4-82.8%. These data indicate that the zinc-bromine flow battery cathode material (hard carbon-coated nitrogen-doped tin carbide / bismuth stannate heterojunction) prepared in this invention exhibits excellent electrochemical performance in zinc-bromine flow batteries. Attached Figure Description

[0022] Figure 1The images show the SEM spectra of the zinc-bromine flow battery cathode materials prepared in Examples 1 and Comparative Examples 1-3, respectively. In the images, (a)-(d) are the SEM spectra of the zinc-bromine flow battery cathode materials prepared in Examples 1, Comparative Examples 1, Comparative Examples 2 and Comparative Examples 3, respectively.

[0023] Figure 2 The XRD patterns are of the zinc-bromine flow battery cathode materials prepared in Example 1 and Comparative Example 1.

[0024] Figure 3 XPS spectrum of the zinc-bromine flow battery cathode material prepared in Example 1.

[0025] Figure 4 The image shows the TEM spectrum of the zinc-bromine flow battery cathode material prepared in Example 1.

[0026] Figure 5 The zinc-bromine flow battery cathode material prepared in Example 1 operates at 30 mA / cm². 2 The energy efficiency curve after 200 cycles at current density. Detailed Implementation

[0027] 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.

[0028] 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.

[0029] This invention provides a method for preparing a positive electrode material for a zinc-bromine flow battery, comprising the following steps: Step S01: Tin source, bismuth source and polar solvent are subjected to a first wet ball milling to obtain a mixture; the mixture is then subjected to a second wet ball milling with a sugar carbon source to obtain system A; Step S02: Mix the polymeric surfactant with a polar organic solvent to obtain system B; Step S03: Add system A to system B, stir and react at 70-80℃, transfer to a sealed container, and after solvothermal reaction at 140-180℃, separate and collect the solid. The solid is washed and dried to obtain the precursor of tin carbide / bismuth stannate heterojunction. Step S04: The precursor is heated to a calcination temperature of 600-750℃ in an argon atmosphere, held at the temperature, and nitrided by introducing a mixed atmosphere of ammonia and argon to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction. Step S05: After mixing the nitrogen-doped tin carbide / bismuth stannate heterojunction with a bromine source and a polar organic solvent, hard carbon is added, and the mixture is transferred to a sealed container. After a sealed reaction at 140-180℃, the solid is separated and collected. The solid is then washed and dried to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction coated with hard carbon, which is the positive electrode material for zinc-bromine flow batteries.

[0030] In this embodiment of the invention, step S01 employs a first wet ball milling process to form a stable bismuth stannate crystal structure, followed by a second wet ball milling process to promote the reaction of unreacted tin source with sugar-based carbon source to generate tin carbide precursors. The combined effect of two wet ball milling processes forms high-purity bismuth stannate and tin carbide precursors, providing independent dispersion units for the uniform connection of the heterojunction. The chemical precipitation process with stirring in step S03 provides a mild reaction environment for the ball-milled and dispersed materials. A closed solvothermal reaction further accelerates the formation of bismuth stannate and tin carbide seed crystals. Furthermore, the long-chain structure of the polymeric surfactant added in step S02 kinetically allows it to connect with the bismuth stannate and tin carbide materials, providing sufficient kinetic conditions for the uniform growth of the heterojunction and preventing the formation of agglomerates between the materials themselves. This effectively controls the uniform growth of the heterojunction, ultimately resulting in a material with uniform and continuous active sites. Then, through the argon calcination and ammonia-argon mixed gas nitriding process in step S04, nitrogen doping modification is achieved while ensuring the integrity of the heterojunction's crystal structure, resulting in a nitrogen-doped tin carbide / bismuth stannate heterojunction. Then, in step S05, a bromine source and hard carbon are introduced. The addition of the bromine source improves energy efficiency, while the addition of hard carbon material electrostatically attracts Br and alleviates the effects of Br. - Transformation into Br3 - The resulting volume expansion, in turn, enhances the electrochemical performance of zinc-bromine flow batteries. The aforementioned techniques work together synergistically to effectively address the problems in existing technologies where the cathode material's volume expansion due to slow bromine oxidation kinetics, the formation of polybromine ions, and the bromine shuttle effect lead to a decline in electrochemical performance. This achieves stable bromine concentration in the electrochemical reaction system, increases the redox reaction rate of bromine, and avoids cathode material volume expansion and bromine shuttle, thereby improving the battery's energy efficiency and cycle stability.

[0031] Preferably, in step S01, the tin source is one of tin dioxide, tin tetrachloride, and tin acetate; the bismuth source is one of bismuth oxide, bismuth trichloride, and bismuth hydroxide; the polar solvent is deionized water or ethanol; the carbohydrate carbon source is one of glucose, sucrose, and soluble starch; the molar ratio of the tin source, bismuth source, and carbohydrate carbon source is 1:0.65-0.7:0.33-0.4; and the concentration of the tin source in the polar solvent is 0.5-1 mol / L.

[0032] Preferably, in step S01, the vibration frequency of the first wet ball mill is 1500-2500 r / min; the time of the first wet ball mill is 20-30 min; the vibration frequency of the second wet ball mill is 700-950 r / min; and the time of the second wet ball mill is 9-16 h.

[0033] Preferably, in step S02, the polymeric surfactant is one of PVP-K90 and PEG-2000; the polar organic solvent is ethanol or ethylene glycol; and the concentration of the polymeric surfactant in the polar organic solvent is 0.625-4 g / L.

[0034] Preferably, in step S03, the concentration of the tin source in system A in the polar organic solvent in system B is 0.125-0.2 mmol / mL.

[0035] Preferably, in step S03, the stirring reaction time is 1-2 hours; the solvothermal reaction time is 10-16 hours; the drying temperature is 80-100°C; and the drying time is 4-8 hours.

[0036] Preferably, in step S04, the heating rate to 600-750℃ is 5-10℃ / min; the nitriding treatment time is 2-4h; and in the mixed atmosphere of ammonia and argon, the volume percentage of ammonia is 3-8%.

[0037] Preferably, in step S05, the bromine source is sodium bromide or potassium bromide; the polar organic solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; the concentration of the nitrogen-doped tin carbide / bismuth stannate heterojunction in the polar organic solvent is 0.033-0.05 g / mL; the concentration of the bromine source in the polar organic solvent is 0.0165-0.05 mol / L; and the mass ratio of hard carbon to bromine source is 1-2:1.

[0038] Preferably, in step S05, the sealed reaction time is 12-18 hours; the drying temperature is 140-160°C; and the drying time is 10-16 hours.

[0039] Preferably, in step S05, the specific surface area of ​​the hard carbon is less than 10 m². 2 / g.

[0040] This invention also provides a zinc-bromine flow battery, wherein the zinc-bromine flow battery positive electrode material prepared by the aforementioned method is used as the positive electrode of the zinc-bromine flow battery.

[0041] 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.

[0042] Example 1 This embodiment provides a method for preparing a positive electrode material for a zinc-bromine flow battery, the specific steps of which are as follows: (1) Mix 10 mmol tin dioxide, 6.5 mmol bismuth oxide and 20 mL ethanol, and mill them in a high-energy vibratory ball mill (MH100) at 2000 r / min for 30 min. Mix the resulting mixture with 3.5 mmol soluble starch and mill it in a three-dimensional vibratory planetary ball mill (MSK-SFM-3-Ⅱ) at 750 r / min for 12 h to form system A; (2) Mix 0.1g of PVP-K90 with 50mL of ethylene glycol to form system B; (3) Add all of system A to system B and stir at 80°C for 2 hours. Then transfer to a sealed container and react at 180°C for 16 hours. Separate and collect the solid. After washing, dry the solid at 100°C for 5 hours to obtain the precursor of tin carbide / bismuth stannate heterojunction. (4) The precursor is placed in a tube furnace and heated to 700°C at 5°C / min under an argon protective atmosphere. The temperature is maintained and 5% ammonia is immediately introduced to form a mixture of ammonia and argon. Nitrogenation is carried out for 3 hours to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction. (5) 2g of nitrogen-doped tin carbide / bismuth stannate heterojunction was mixed with 1mmol sodium bromide and 50mL N,N-dimethylformamide, and then 0.205g of hard carbon was added. The mixture was transferred to a sealed container and reacted at 160℃ for 18h. The solid was separated and collected. After washing, the solid was dried at 150℃ for 12h to obtain nitrogen-doped tin carbide / bismuth stannate heterojunction coated with hard carbon, which is the positive electrode material of zinc bromine flow battery.

[0043] Example 2 This embodiment provides a method for preparing a positive electrode material for a zinc-bromine flow battery, the specific steps of which are as follows: (1) Mix 10 mmol tin tetrachloride, 6.5 mmol bismuth trichloride and 20 mL deionized water, and mill the mixture in a high-energy vibratory ball mill (MH100) at 2500 r / min for 20 min. Mix the resulting mixture with 3.3 mmol glucose and mill it in a three-dimensional vibratory planetary ball mill (MSK-SFM-3-Ⅱ) at 700 r / min for 16 h to form system A. (2) Mix 0.2g of PEG-2000 with 50mL of ethanol to form system B; (3) Add all of system A to system B and stir at 70°C for 1 hour. Then transfer to a sealed container and react at 140°C for 16 hours. Separate and collect the solid. After washing, dry the solid at 80°C for 8 hours to obtain the precursor of tin carbide / bismuth stannate heterojunction. (4) The precursor is placed in a tube furnace and heated to 600°C at 10°C / min under an argon protective atmosphere. The temperature is maintained and 8% ammonia is immediately introduced to form a mixture of ammonia and argon. The mixture is then kept at the temperature for 2 hours to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction. (5) 2g of nitrogen-doped tin carbide / bismuth stannate heterojunction was mixed with 1.5mmol potassium bromide and 40mL N-methylpyrrolidone, and then 0.178g of hard carbon was added. The mixture was transferred to a sealed container and reacted at 180°C for 12h. The solid was separated and collected. After washing, the solid was dried at 160°C for 16h to obtain nitrogen-doped tin carbide / bismuth stannate heterojunction with hard carbon coating, which is the positive electrode material of zinc bromine flow battery.

[0044] Example 3 This embodiment provides a method for preparing a positive electrode material for a zinc-bromine flow battery, the specific steps of which are as follows: (1) Mix 10 mmol tin acetate, 6.8 mmol bismuth hydroxide and 10 mL ethanol, and mill the mixture in a high-energy vibratory ball mill (MH100) at 2500 r / min for 25 min. Mix the resulting mixture with 4 mmol sucrose and mill it in a three-dimensional vibratory planetary ball mill (MSK-SFM-3-Ⅱ) at 950 r / min for 9 h to form system A. (2) Mix 0.05g of PVP-K90 with 80mL of ethylene glycol to form system B; (3) Add all of system A to system B and stir at 75°C for 2 hours. Then transfer to a sealed container and react at 180°C for 10 hours. Separate and collect the solid. After washing, dry the solid at 90°C for 4 hours to obtain the precursor of tin carbide / bismuth stannate heterojunction. (4) The precursor is placed in a tube furnace and heated to 650°C at 6°C / min under an argon protective atmosphere. The temperature is maintained and 3% ammonia is immediately introduced to form a mixture of ammonia and argon. The mixture is then nitrided for 4 hours to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction. (5) 2g of nitrogen-doped tin carbide / bismuth stannate heterojunction was mixed with 2mmol sodium bromide and 50mL N,N-dimethylacetamide, and then 0.308g of hard carbon was added. The mixture was transferred to a sealed container and reacted at 140°C for 18h. The solid was separated and collected. After washing, the solid was dried at 140°C for 10h to obtain nitrogen-doped tin carbide / bismuth stannate heterojunction with hard carbon coating, which is the positive electrode material of zinc bromine flow battery.

[0045] Example 4 This embodiment provides a method for preparing a positive electrode material for a zinc-bromine flow battery, the specific steps of which are as follows: (1) Mix 10 mmol tin dioxide, 6.9 mmol bismuth trichloride and 15 mL deionized water, and mill the mixture in a high-energy vibratory ball mill (MH100) at 1500 r / min for 30 min. Mix the resulting mixture with 3.7 mmol glucose and mill it in a three-dimensional vibratory planetary ball mill (MSK-SFM-3-Ⅱ) at 900 r / min for 14 h to form system A. (2) Mix 0.15g PEG-2000 with 70mL ethanol to form system B; (3) Add all of system A to system B and stir at 70°C for 2 hours. Then transfer to a sealed container and react at 160°C for 14 hours. Separate and collect the solid. After washing, dry the solid at 100°C for 8 hours to obtain the precursor of tin carbide / bismuth stannate heterojunction. (4) The precursor is placed in a tube furnace and heated to 750°C at 8°C / min under an argon protective atmosphere. The temperature is maintained and 4% ammonia is immediately introduced to form a mixture of ammonia and argon. The mixture is then kept at the temperature for 2 hours to nitrid, resulting in a nitrogen-doped tin carbide / bismuth stannate heterojunction. (5) 2g of nitrogen-doped tin carbide / bismuth stannate heterojunction was mixed with 1.5mmol sodium bromide and 60mL N-methylpyrrolidone, and then 0.308g of hard carbon was added. The mixture was transferred to a sealed container and reacted at 150°C for 14h. The solid was separated and collected. After washing, the solid was dried at 150°C for 16h to obtain nitrogen-doped tin carbide / bismuth stannate heterojunction with hard carbon coating, which is the positive electrode material of zinc bromine flow battery.

[0046] Example 5 This embodiment provides a method for preparing a positive electrode material for a zinc-bromine flow battery, the specific steps of which are as follows: (1) Mix 10 mmol tin acetate, 6.6 mmol bismuth oxide and 20 mL deionized water, and mill the mixture in a high-energy vibratory ball mill (MH100) at 2000 r / min for 20 min. Mix the resulting mixture with 3.5 mmol sucrose and mill the mixture in a three-dimensional vibratory planetary ball mill (MSK-SFM-3-Ⅱ) at 800 r / min for 10 h to form system A; (2) Mix 0.2g of PEG-2000 with 80mL of ethylene glycol to form system B; (3) Add all of system A to system B and stir at 80°C for 1 hour. Then transfer to a sealed container and react at 180°C for 10 hours. Separate and collect the solid. After washing, dry the solid at 80°C for 4 hours to obtain the precursor of tin carbide / bismuth stannate heterojunction. (4) The precursor is placed in a tube furnace and heated to 600°C at 7°C / min under an argon protective atmosphere. The temperature is maintained and 6% ammonia is immediately introduced to form a mixture of ammonia and argon. Nitriding is carried out for 4 hours to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction. (5) 2g of nitrogen-doped tin carbide / bismuth stannate heterojunction was mixed with 2mmol of potassium bromide and 40mL of N,N-dimethylacetamide, and then 0.476g of hard carbon was added. The mixture was transferred to a sealed container and reacted at 160°C for 12h. The solid was separated and collected. After washing, the solid was dried at 160°C for 12h to obtain nitrogen-doped tin carbide / bismuth stannate heterojunction with hard carbon coating, which is the positive electrode material of zinc bromine flow battery.

[0047] Example 6 This embodiment provides a method for preparing a positive electrode material for a zinc-bromine flow battery, the specific steps of which are as follows: (1) Mix 10 mmol tin tetrachloride, 6.7 mmol bismuth hydroxide and 15 mL ethanol, and mill the mixture in a high-energy vibrating ball mill (MH100) at 1500 r / min for 20 min. Mix the resulting mixture with 3.9 mmol soluble starch and mill the mixture in a three-dimensional vibrating planetary ball mill (MSK-SFM-3-Ⅱ) at 850 r / min for 12 h to form system A. (2) Mix 0.05g of PVP-K90 with 50mL of ethylene glycol to form system B; (3) Add all of system A to system B and stir at 75°C for 2 hours. Then transfer to a sealed container and react at 140°C for 12 hours. Separate and collect the solid. After washing, dry the solid at 100°C for 7 hours to obtain the precursor of tin carbide / bismuth stannate heterojunction. (4) The precursor is placed in a tube furnace and heated to 750°C at 9°C / min under an argon protective atmosphere. The temperature is maintained and 8% ammonia is immediately introduced to form a mixture of ammonia and argon. Nitriding is carried out for 4 hours to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction. (5) 2g of nitrogen-doped tin carbide / bismuth stannate heterojunction was mixed with 1mmol of potassium bromide and 60mL of N,N-dimethylformamide, and then 0.178g of hard carbon was added. The mixture was transferred to a sealed container and reacted at 170°C for 16h. The solid was separated and collected. After washing, the solid was dried at 140°C for 16h to obtain nitrogen-doped tin carbide / bismuth stannate heterojunction with hard carbon coating, which is the positive electrode material of zinc bromine flow battery.

[0048] Example 7 This embodiment provides a method for preparing a positive electrode material for a zinc-bromine flow battery, the specific steps of which are as follows: (1) Mix 10 mmol tin dioxide, 6.5 mmol bismuth hydroxide and 10 mL deionized water, and mill the mixture in a high-energy vibratory ball mill (MH100) at 2500 r / min for 30 min. Mix the resulting mixture with 4 mmol soluble starch and mill it in a three-dimensional vibratory planetary ball mill (MSK-SFM-3-Ⅱ) at 800 r / min for 16 h to form system A. (2) Mix 0.1g PEG-2000 with 60mL ethanol to form system B; (3) Add all of system A to system B and stir at 70°C for 2 hours. Then transfer to a sealed container and react at 160°C for 16 hours. Separate and collect the solid. After washing, dry the solid at 90°C for 6 hours to obtain the precursor of tin carbide / bismuth stannate heterojunction. (4) The precursor is placed in a tube furnace and heated to 650°C at 5°C / min under an argon protective atmosphere. The temperature is maintained and ammonia with a volume ratio of 7% is immediately introduced to form a mixture of ammonia and argon. Nitriding is carried out for 3 hours to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction. (5) 2g of nitrogen-doped tin carbide / bismuth stannate heterojunction was mixed with 1mmol sodium bromide and 40mL N,N-dimethylformamide, and then 0.102g of hard carbon was added. The mixture was transferred to a sealed container and reacted at 180°C for 18h. The solid was separated and collected. After washing, the solid was dried at 130°C for 12h to obtain nitrogen-doped tin carbide / bismuth stannate heterojunction with hard carbon coating, which is the positive electrode material of zinc bromine flow battery.

[0049] Comparative Example 1 This comparative example adopts the technical solution of Example 1, except that steps (1), (2), and (3) are changed to a single wet ball milling operation. That is, 10 mmol of tin dioxide, 6.5 mmol of bismuth oxide, 3.5 mmol of soluble starch, 0.1 g of PVP-K90 and 20 mL of ethanol are mixed and ball-milled at 2000 r / min for 30 min in a high-energy vibration ball mill (MH100). The resulting mixture is then dried at 100°C for 5 h to obtain the precursor. All other processes are the same as in Example 1.

[0050] Comparative Example 2 This comparative example adopts the technical solution of Example 1, except that the addition of the polymeric surfactant PVP-K90 is omitted in step (2). That is, 10 mmol of tin dioxide, 6.5 mmol of bismuth oxide and 20 mL of ethanol are mixed and ball-milled for 30 min at 2000 r / min using a high-energy vibration ball mill (MH100). The resulting mixture is then mixed with 3.5 mmol of soluble starch and ball-milled for 12 h at 750 r / min using a three-dimensional vibration planetary ball mill (MSK-SFM-3-Ⅱ) to form system A. System A is added to 50 mL of ethylene glycol and stirred at 80 °C for 2 h. Then it is transferred to a sealed container and reacted at 180 °C for 16 h. The solid is separated and collected. After washing, the solid is dried at 100 °C for 5 h to obtain the precursor of tin carbide / bismuth stannate heterojunction. All other processes are the same as in Example 1.

[0051] Comparative Example 3 This comparative example adopts the technical solution of Example 1. The difference is that a mixture of ammonia and argon is not used in step (4). The entire process is carried out in a pure argon atmosphere, that is: the precursor is placed in a tube furnace and heated to 700°C at 5°C / min under an argon protective atmosphere and held for 3 hours. All other processes are the same as those in Example 1.

[0052] Comparative Example 4 This comparative example uses the technical solution of Example 1, the difference being that no bromine source is added in step (5), that is: 2g of nitrogen-doped tin carbide / bismuth stannate heterojunction is mixed with 50mL of N,N-dimethylformamide, then 0.205g of hard carbon is added, and the mixture is transferred to a sealed container and reacted at 160°C for 18h. The solid is then separated and collected, washed, and dried at 150°C for 12h to obtain the zinc-bromine flow battery cathode material. All other processes are consistent with those of Example 1.

[0053] Comparative Example 5 This comparative example uses the technical solution of Example 1, the difference being that hard carbon is not added in step (5), that is: 2g of nitrogen-doped tin carbide / bismuth stannate heterojunction is mixed with 1mmol sodium bromide and 50mL N,N-dimethylformamide, transferred to a sealed container and reacted at 160°C for 18h, the solid is separated and collected, and after washing, the solid is dried at 150°C for 12h to obtain the zinc-bromine flow battery cathode material. All other processes are the same as in Example 1.

[0054] Application Example 1 The application of the zinc-bromine flow battery cathode material prepared in the above embodiments is carried out through the following specific steps: The positive electrode material for a zinc-bromine flow battery (i.e., a nitrogen-doped tin carbide / bismuth stannate composite material coated with hard carbon) was deposited onto a carbon felt via electrochemical deposition, with the current density of the electrochemical deposition controlled at 1.5 mA / cm². 2The deposition time was 15 min, and the loading of nitrogen-doped tin carbide / bismuth stannate composite material coated with hard carbon on the carbon felt surface was controlled to be 1.1-1.8 mg / cm³. 2 After deposition, the carbon felt is rinsed with ethanol and then vacuum dried to obtain the positive electrode sheet for zinc-bromine flow batteries.

[0055] Using the above application method, the zinc-bromine flow battery cathode materials of Examples 1-7 and Comparative Examples 1-5 were respectively prepared at a concentration of 1.5 mg / cm³. 2 The loading was deposited on carbon felt to form a positive electrode for zinc-bromine flow battery testing. Each electrode sheet served as the positive electrode, with an electrolyte consisting of 2.5 mol / L zinc bromide + 3 mol / L potassium chloride + 0.8 mol / L 1-methyl-1-ethylpyrrolidine bromide. A microporous polyolefin membrane was used as the separator, and a conventionally heat-treated graphite felt was used as the negative electrode (heat treatment conditions: 500℃, 4h). The zinc-bromine flow battery was then subjected to charge-discharge cycle testing. During the test, the charge-discharge current density was controlled at 30 mA / cm². 2 The discharge cutoff voltage was 0.6V. After 200 cycles, the coulombic efficiency, voltage efficiency, and energy efficiency of the zinc-bromine flow battery were tested.

[0056] The electrochemical performance of the electrode materials obtained from Examples 1-7 and Comparative Examples 1-5 is summarized in Table 1 below.

[0057] Table 1. Summary of electrochemical performance of each example and comparative example after 200 cycles.

[0058] Figure 1 The images in a and b represent the SEM spectra of the zinc-bromine flow battery cathode materials prepared in Example 1 and Comparative Examples 1-3, respectively; it can be seen that Example 1 ( Figure 1 -a) A blocky structure with good uniformity and dispersion was obtained. The raw materials underwent wet ball milling in the ball mill jar, which resulted in gentle mechanical collisions and effectively reduced agglomeration. The polymeric surfactant also effectively controlled the uniformity of the precursor material. The composite material obtained after treatment had a highly consistent morphology and could stably adhere to the carbon felt material during the electrochemical reaction, exhibiting excellent electrochemical performance; while Comparative Example 1 ( Figure 1 -b) Only one wet ball milling is performed, and all raw materials react directly, which tends to form a mixture of bismuth tin carbide and bismuth stannate. This tends to form aggregate structures, and adhesion to the carbon felt surface requires large bond energies and forces, thus causing electrochemical performance degradation; Comparative Example 2 ( Figure 1 -c) No surfactant was used. During the stirring reaction of the mixture, the mutual forces attracted each other to form large-scale material structures. The non-uniform structure also caused different forces on the positive electrode material to bromine, thus reducing the electrochemical performance; Comparative Example 3 ( Figure 1-d) Without using a mixture of ammonia and argon, there is no ammonia nitriding effect to increase the electronegativity of the material. The resulting composite material changes towards the Gibbs free energy stable state, forming agglomerates with low uniformity.

[0059] Figure 2 The XRD patterns of the zinc-bromine flow battery cathode materials prepared in Example 1 and Comparative Example 1 are shown. The XRD curve of Example 1 shows that the diffraction peaks correspond well to the diffraction peaks of bismuth stannate, tin carbide, and carbon materials, indicating that this method can successfully synthesize nitrogen-doped tin carbide / bismuth stannate heterojunction composite materials coated with hard carbon. Comparative Example 1 involves a one-pot ball milling process to prepare the precursor material from tin, bismuth, and carbon sources. This method allows for interaction between the three materials, ultimately yielding a mixture of tin carbide and bismuth stannate. In the XRD pattern, 26.45° and 51.71° correspond to characteristic peaks of tin oxide, 30.24° and 49.73° to characteristic peaks of tin carbide, and 37.84° and 39.49° to characteristic peaks of bismuth, along with some characteristic peaks of bismuth stannate. This verifies the possibility of synthesizing tin carbide using a one-pot process, but it cannot form a uniform heterojunction material.

[0060] Figure 3 The XPS spectrum of the zinc-bromine flow battery cathode material prepared in Example 1 mainly consists of a spin-orbit doublet state with Sn 3d binding energies of 486 and 494 eV, and a Bi 4f core structure with energies of 158 eV and 163 eV. Bulges of C 1s and N 1s were observed at 285 eV and 400 eV, indicating the successful addition of hard carbon and calcined nitrogen doping. The appearance of Br 3d at 69 eV indicates the successful addition of sodium bromide to obtain Bi-O-Br. Furthermore, the peak intensity of Br is lower than that of Bi, indicating that the addition of sodium bromide occupies some vacancy sites, and the remaining vacancy sites are used to store Br migrating during the electrochemical reaction, thereby improving electrochemical performance.

[0061] Figure 4 The image shows the TEM spectrum of the zinc-bromine flow battery cathode material prepared in Example 1. The image reveals that the heterojunction is coated with a hard carbon protective layer, and the lattice in this protective layer exhibits a discontinuous turbulent and closed-pore structure, consistent with the characteristics of hard carbon. This demonstrates that this method can effectively coat carbon materials onto heterojunctions. The interplanar spacing of the material was calculated from the spectrum. The interplanar spacing of the bismuth stannate (111) material is 0.28 nm, less than the theoretical value of 0.31 nm. This indicates that the addition of sodium bromide forms the Bi-O-Br structure, and the bromine is converted into Br... - It exists in the form of Br3, without complexing into Br3. ⁻ This caused lattice distortion in the material, further validating the results in XPS.

[0062] Figure 5 The zinc-bromine flow battery cathode material prepared in Example 1 operates at 30 mA / cm².2 The energy efficiency curve after 200 cycles at current density is obtained by... Figure 5 As shown in Table 1, the energy efficiency of the material in Example 1 only decreased to 82.8% after 200 cycles as the number of cycles increased, demonstrating excellent cycle stability.

[0063] A comparison of Example 1 with Comparative Examples 1-5 shows that the composite material prepared in Example 1 has the advantages of good morphological uniformity and few defects, and can continuously and stably participate in electrochemical reactions. In Example 1, a two-stage wet ball milling process was used to first thoroughly mix the tin source and bismuth source to form a bismuth stannate precursor. Then, a second wet ball milling process was used to mix the unreacted tin source with a sugar-based carbon source. The wet ball milling process is gentle in the liquid medium, and the mechanical force can reduce the occurrence of agglomeration. Then, a polymeric surfactant was used to connect the bismuth stannate and tin carbide materials. The surfactant provides sufficient kinetic conditions for the uniform growth of the heterojunction, and at the same time reduces the particle size change caused by crystal refinement during calcination, avoiding the formation of agglomerates between the materials themselves. The calcination process adopted argon calcination + ammonia-argon mixing. The combined gas insulated nitriding process not only ensures perfect heterojunction formation and crystal integrity, but also achieves nitrogen doping by controlling the amount of nitrogen used. Nitrogen doping also works synergistically with tin carbide to accelerate the migration of Br to the electrode material surface and its connection with oxygen vacancies and the porous structure of hard carbon in bismuth stannate, thus improving the electrochemical performance of zinc-bromine flow batteries. Adding a bromine source during the closed-container reaction process can improve the battery's energy efficiency. The addition of bromine can form covalent bonds with bismuth in bismuth stannate, creating Bi-O-Br connections at vacancies. Furthermore, continuous adsorption and desorption during the electrochemical reaction ensures the smooth flow of Br. - Concentration stability; the addition of hard carbon can also form a protective coating, and the unique turbulent structure of hard carbon can stably adsorb Br. - And capillary aggregation occurs within the pores; the closed-pore nanocages of hard carbon can also alleviate the effects of Br - Transformation into Br3 - The resulting volume expansion ensures that the volume change occurs only in the coating layer, avoiding the expansion of Br in the substrate material. - It shuttles towards the negative electrode. Through electrochemical performance testing, after 200 cycles, the coulombic efficiency increased from 67.5% to 92.8%, the voltage efficiency increased from 70.1% to 89.5%, and the energy efficiency increased from 60.5% to 82.8%.

[0064] Compared to Comparative Example 1, Example 1, with its two-stage wet ball milling process, achieves stable and efficient synthesis of tin carbide / bismuth stannate heterojunction materials. However, Example 1 only involves one wet ball milling process, where the tin, bismuth, and carbon sources are milled in a single operation. In the initial stage of milling, the high carbon source concentration and strong reducing ability preferentially induce the carbonization reaction, yielding tin carbide / bismuth stannate. In the later stage, the low carbon source concentration and weak reducing ability tend to generate bismuth stannate and tin oxide. Tin carbide / bismuth stannate is more prone to catalytic side reactions, consuming active materials and causing significant polarization, resulting in abnormal deposition with dendrite formation. Tin oxide itself has strong binding energy and low conductivity, exhibiting weak adsorption and complexation capabilities for bromine. During electrochemical testing, the weakest link effect leads to electrochemical performance degradation. Compared to Comparative Example 2, Example 1, without the addition of a polymeric surfactant, results in the formation of a bulk structure due to the inherent attraction of the material itself. This structural inhomogeneity also causes variations in the interaction force of the cathode material with bromine, thus reducing electrochemical performance. Compared to Comparative Example 3, Example 1 did not use mixed gas nitriding, and the calcination and heat preservation processes were carried out under an argon protective atmosphere. This process can only ensure the formation of heterogeneous crystals and cannot perform nitrogen doping, resulting in poor electrochemical performance. Compared to Comparative Examples 4-5, Comparative Example 4 did not add a bromine source, which would increase the number of vacancies in the composite material. During the electrochemical reaction, the ability of Br to occupy vacancies was limited, and the electrochemical performance was reduced due to Br loss during adsorption and desorption. Comparative Example 5 did not add hard carbon. Hard carbon, as a coating and protective layer of the composite material, can not only adsorb Br but also alleviate volume expansion. The absence of hard carbon would reduce the Br storage effect and decrease the electrochemical performance.

[0065] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0066] 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 positive electrode material for a zinc-bromine flow battery, characterized in that, Includes the following steps: Step S01: The tin source, bismuth source and polar solvent are subjected to a first wet ball milling to obtain a mixture; the mixture is then subjected to a second wet ball milling with a sugar carbon source to obtain system A; Step S02: Mix the polymeric surfactant with a polar organic solvent to obtain system B; Step S03: Add system A to system B, stir and react at 70-80℃, transfer to a sealed container, and after solvothermal reaction at 140-180℃, separate and collect the solid. The solid is washed and dried to obtain the precursor. Step S04: The precursor is heated to 600-750℃ in an argon atmosphere, kept at the temperature, and nitrided by introducing a mixed atmosphere of ammonia and argon to obtain a nitrogen-doped tin carbide / bismuth stannate heterojunction. Step S05: After mixing the nitrogen-doped tin carbide / bismuth stannate heterojunction with a bromine source and a polar organic solvent, hard carbon is added, and the mixture is transferred to a sealed container. After a sealed reaction at 140-180℃, the solids are separated and collected. The solids are then washed and dried to obtain the zinc-bromine flow battery cathode material. In step S05, the bromine source is sodium bromide or potassium bromide.

2. The method for preparing the zinc-bromine flow battery cathode material according to claim 1, characterized in that, In step S01, the tin source is one of tin dioxide, tin tetrachloride, and tin acetate. The bismuth source is one of bismuth oxide, bismuth trichloride, or bismuth hydroxide; The carbohydrate carbon source is one of glucose, sucrose, or soluble starch; The polar solvent is deionized water or ethanol.

3. The method for preparing the zinc-bromine flow battery cathode material according to claim 1, characterized in that, In step S01, the molar ratio of tin source, bismuth source, and carbohydrate carbon source is 1:0.65-0.7:0.33-0.4; The concentration of the tin source in the polar solvent is 0.5-1 mol / L.

4. The method for preparing the zinc-bromine flow battery cathode material according to claim 1, characterized in that, In step S01, the vibration frequency of the first wet ball mill is 1500-2500 r / min, and the time of the first wet ball mill is 20-30 min; the vibration frequency of the second wet ball mill is 700-950 r / min, and the time of the second wet ball mill is 9-16 h.

5. The method for preparing the zinc-bromine flow battery cathode material according to claim 1, characterized in that, In step S02, the polymeric surfactant is one of PVP-K90 and PEG-2000; The polar organic solvent is ethanol or ethylene glycol; The concentration of polymeric surfactants in polar organic solvents is 0.625-4 g / L.

6. The method for preparing the zinc-bromine flow battery cathode material according to claim 1, characterized in that, In step S03, the concentration of the tin source in system A within the polar organic solvent in system B is 0.125-0.2 mmol / mL; The stirring reaction time is 1-2 hours; the solvothermal reaction time is 10-16 hours.

7. The method for preparing the zinc-bromine flow battery cathode material according to claim 1, characterized in that, In step S04, the heating rate to 600-750℃ is 5-10℃ / min; The nitriding process is carried out under heat and in a mixed atmosphere of ammonia and argon for 2-4 hours. In a mixed atmosphere of ammonia and argon, the volume percentage of ammonia is 3-8%.

8. The method for preparing the zinc-bromine flow battery cathode material according to claim 1, characterized in that, In step S05, the polar organic solvent is one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; The concentration of nitrogen-doped tin carbide / bismuth stannate heterojunction in polar organic solvent is 0.033-0.05 g / mL; the concentration of bromine source in polar organic solvent is 0.0165-0.05 mol / L; and the mass ratio of hard carbon to bromine source is 1-2:

1.

9. The method for preparing the zinc-bromine flow battery cathode material according to claim 1, characterized in that, In step S05, the reaction time in a sealed environment at 140-180℃ is 12-18 hours.

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

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