Preparation method of solid-liquid mixed type electrolyte of all-vanadium redox flow battery

Abstract

This invention relates to the field of vanadium redox flow battery technology and discloses a method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte. The method includes adding demineralized water, concentrated sulfuric acid, industrial-grade V₂O₅, and oxalic acid as a reducing agent to a reaction vessel to obtain a 3.5-valent vanadium ion liquid electrolyte; stirring the main material vanadium-based oxide, a porous solid carrier, and auxiliary materials conductive agents and binders to obtain a micron-sized vanadium-based slurry; granulating and sintering the micron-sized vanadium-based slurry to obtain a vanadium-based solid porous material; and assembling the vanadium-based solid porous material and the 3.5-valent vanadium ion liquid electrolyte into a separate solid-liquid reactor to obtain the solid-liquid hybrid vanadium redox flow battery electrolyte. This invention, by combining a solid-phase energy storage active material with a 3.5-valent vanadium ion liquid electrolyte, increases the total charge capacity of the vanadium redox flow battery and improves its volumetric energy density without increasing the volume and concentration of the 3.5-valent vanadium ion liquid electrolyte.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery technology, specifically to a method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte. Background Technology

[0002] Vanadium redox flow batteries utilize the redox reaction of vanadium ions in different valence states in an aqueous sulfuric acid solution to convert electrical energy into chemical energy. The core energy storage medium of a vanadium redox flow battery is a liquid electrolyte, and its energy storage capacity depends entirely on the amount of charge stored within the electrolyte. The key parameters determining the energy storage capacity of a vanadium redox flow battery are the concentration of vanadium ions in the liquid electrolyte and the total volume of the liquid electrolyte.

[0003] Vanadium ions have a physical upper limit to their solubility in sulfuric acid aqueous solutions. A common approach to increasing the energy storage capacity of vanadium redox flow batteries (VRBs) is to increase the concentration of vanadium ions in the liquid electrolyte. However, increasing the concentration of vanadium ions in the liquid electrolyte leads to the precipitation of high-valence vanadium ions during the charge-discharge cycle of the VRB. These precipitated solids adhere to the surfaces of the internal components of the VRB, causing blockage of the internal fluid channels. This blockage hinders the circulation of the liquid electrolyte, compromises the long-term cycle stability of the VRB, and ultimately reduces its energy storage capacity.

[0004] Maintaining a constant vanadium ion concentration in the liquid electrolyte while simply increasing its volume requires a large-capacity external storage tank for the vanadium redox flow battery. This large external tank occupies additional physical space, increasing the overall volume of the vanadium redox flow battery system and reducing its volumetric energy density. Existing vanadium redox flow battery technology is constrained by the physical properties of its single-phase liquid-phase energy storage mode, making it difficult to improve the volumetric energy density of the system while maintaining the long-term operational stability of the liquid electrolyte. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte. This method solves the problems of low volumetric energy density in existing vanadium redox flow batteries due to the physical upper limit of vanadium ion solubility in the liquid electrolyte, and the problems of precipitation of high-valence vanadium ions and disruption of cycle stability caused by increasing the vanadium ion concentration in the liquid electrolyte.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte, comprising the following steps: Deionized water and concentrated sulfuric acid were added to an acid-resistant reactor. The reaction temperature was controlled by cooling water. Industrial-grade V2O5 and reducing agent oxalic acid were added in batches, and deionized water was added to make up the volume. The mixture was stirred until completely dissolved to complete the electrochemical reduction and mixing process, and a clear and transparent liquid electrolyte of vanadium ions with 3.5 valence was obtained. The main material, vanadium-based oxide, porous solid carrier, auxiliary materials, conductive agent and binder are added to the planetary homogenization system and stirred to complete the degassing and filtration process, thereby obtaining micron-sized vanadium-based slurry. Micron-sized vanadium-based slurry is placed in a centrifugal granulator, solvent is added to form a slurry, and then extruded and granulated to obtain micron-sized solid particles; A protective gas is introduced into a tube furnace to sinter micron-sized solid particles, remove excess solvent, and control the sintering process to obtain vanadium-based solid porous materials. Vanadium-based solid porous materials and clear, transparent 3.5-valent vanadium ion liquid electrolytes were assembled into a separate solid-liquid reactor and used in a full vanadium redox flow battery to evaluate the electrolyte performance, resulting in a solid-liquid hybrid full vanadium redox flow battery electrolyte.

[0007] By adopting the above technical solution, and through the preparation mode of combining porous solid vanadium materials with liquid vanadium-based electrolytes, a solid-liquid dual-phase synergistic charge storage system is constructed. Therefore, it achieves the technical effect of overcoming the solubility limitations of a single liquid phase and improving the overall volumetric energy density of the system. The specific reaction mechanism and innovation process are as follows: Industrial-grade V₂O₅ is treated by adding oxalic acid as a reducing agent in batches within an acidic system composed of demineralized water and concentrated sulfuric acid. Utilizing the reducing properties of oxalic acid, the industrial-grade V₂O₅ undergoes a multi-step chemical reduction reaction in the acidic environment. High-valence vanadium ions are first reduced to tetravalent vanadium ions. With the continued action of the reducing agent, some tetravalent vanadium ions are further reduced to trivalent vanadium ions. During the reaction, carbon oxide gases are released. Finally, the trivalent and tetravalent vanadium ions in the system reach concentration equilibrium, forming a clear and transparent 3.5-valent vanadium ion liquid electrolyte. Cooling water and droplet rate control during the process prevent side reactions caused by localized overheating, ensuring the purity of the electrolyte.

[0008] In the planetary homogenization system, high shear forces break up the agglomeration of the various material components. The main material, vanadium-based oxide, serves as the solid-phase energy storage active material, while a porous solid carrier provides skeletal support. The auxiliary conductive agent disperses and connects the individual active particles at the microscale, forming continuous electron transport channels. In the subsequent centrifugal extrusion granulation and high-temperature sintering processes, solvent evaporation and localized thermal shrinkage of the material create abundant mesoporous and macroporous structures within the particles, endowing the material with porous properties.

[0009] A porous solid-phase material is placed in a separated solid-liquid reactor. Liquid electrolyte flows over the surface of the solid material and penetrates into the pores of the porous framework. Vanadium ions in the liquid electrolyte act as the liquid flow mass medium, while the porous solid vanadium material serves as an additional source of solid-phase active material stored in the reactor. During battery charge-discharge operation, liquid-phase vanadium ions and porous solid-phase vanadium-based oxides undergo a synergistic redox reaction at the solid-liquid interface. The porous solid carrier increases the effective specific surface area of ​​the solid-liquid contact, and the conductive agent reduces the interfacial impedance for charge transfer across phases. The solid material directly participates in the Faraday charge storage process, increasing the total amount of charge the system can hold without increasing the volume and concentration of the liquid electrolyte.

[0010] Preferably, in the process of preparing a clear and transparent vanadium ion liquid electrolyte, 400-600 parts by mass of demineralized water are added, and 300-540 parts by mass of concentrated sulfuric acid are added dropwise to the demineralized water at a rate of 10-50 parts by mass / minute. The reaction temperature is controlled at 25-40 degrees Celsius using cooling water. 120-180 parts by mass of industrial-grade V2O5 with a purity greater than 98% are added in batches. At the same time as adding industrial-grade V2O5, 120-189 parts by mass of reducing agent oxalic acid are added in batches, and the volume is adjusted to 800-1200 parts by mass with demineralized water. The stirring speed is set to 300-500 rpm.

[0011] By adopting the above technical solution, the rheological stability of the reaction system was maintained, the limited temperature and feeding rate prevented acid splashing caused by violent exothermic reaction, and the reduction reaction was carried out completely.

[0012] Preferably, after completing the electrochemical reduction and mixing process, the total vanadium concentration of the resulting liquid electrolyte is 1.5-2.0 mol / L, the sulfate concentration is 3.0-5.0 mol / L, and the VO is... 3+ With V 4+ The concentration ratio is 0.9-1.1.

[0013] By employing the above technical solution, the liquid electrolyte is ensured to be within the conventional electrochemical activity window. This concentration range prevents temperature-sensitive crystallization problems caused by excessive concentration, while ensuring sufficient charge carrier density.

[0014] Preferably, when preparing micron-sized vanadium-based slurry, the main vanadium-based oxide is selected from V2O3, V3O7, and V6O. 13 One or more of VO and V2O4; the porous solid support is selected from one of Li3VO4, ZrO2, TiO2 and NiO; the conductive agent is selected from one of carbon black Super P, graphene, acetylene black and Ketjen black; the binder is selected from one of PVDF, SBR and polyacrylic acid.

[0015] By adopting the above technical solutions, vanadium oxides with different low valence states are adapted to the potential range of liquid electrolytes; metal oxides such as titanium, zirconium, and nickel, or lithium vanadium oxide salts have stable chemical structures and do not undergo dissolution and loss in the electrolyte; carbon-based materials ensure the high electronic conductivity of the solid-phase framework.

[0016] Preferably, the raw materials for preparing micron-sized vanadium-based slurry include, by mass, 30-70 parts of vanadium-based oxide as the main material, 5-10 parts of porous solid carrier, 2-5 parts of conductive agent as an auxiliary material, and 2-3 parts of binder.

[0017] By adopting the above technical solution, a high proportion of solid-phase energy storage active material content is maintained while ensuring that the porous particle structure does not collapse.

[0018] Preferably, when stirring in the planetary homogenizing system, the rotation speed of the main rotating disk of the planetary homogenizing system is controlled at 15-50 rpm, the rotation speed of the dispersing disk of the planetary homogenizing system is controlled at 2000-3000 rpm, and the stirring time is set to 2-5 hours.

[0019] By adopting the above technical solution, the combination of dual rotation speeds enables the solid powder to achieve uniform deagglomeration and dispersion under the action of a very small amount of solvent and binder, eliminating dead zones in the stirring process and ensuring the uniformity of the composition of subsequent particles.

[0020] Preferably, in the process of preparing micron-sized solid particles, the solvent is selected from N-methylpyrrolidone, water and ethanol, and the amount of solvent added is 80-130 parts by mass; when the micron-sized vanadium-based slurry is placed in a centrifugal granulator for stirring, the stirring speed of the centrifugal granulator is set to 100-500 rpm and stirring is carried out for 30-60 minutes.

[0021] By adopting the above technical solution, the viscosity and solid content of the slurry are adjusted so that the particles extruded by centrifugal granulation have a regular and consistent micron-sized distribution, which is beneficial for achieving regular stacking and maintaining fluid channels in the solid-liquid reactor in the later stage.

[0022] Preferably, during sintering in a tube furnace, the protective gas is argon or nitrogen; the sintering temperature of the tube furnace is controlled at 300-800 degrees Celsius, and the sintering time of the tube furnace is controlled at 1-4 hours; the vanadium-based solid porous material obtained by sintering is a porous spherical vanadium-based solid porous material or a porous rod-shaped vanadium-based solid porous material.

[0023] By adopting the above technical solution, the inert atmosphere isolates the oxygen in the environment, preventing the vanadium-based oxide of the main material from being oxidized to an ineffective highest valence state at high temperatures; the set temperature zone promotes the shaping of the skeleton and the opening of the channels, and the spherical or rod-shaped shape ensures the porosity when the material is stacked, reducing the resistance to liquid flow.

[0024] Preferably, when assembling into a separate solid-liquid reactor, the obtained vanadium-based solid porous material is assembled with the obtained clear and transparent 3.5-valent vanadium ion liquid electrolyte at a mass ratio of 1:5 to 1:8.

[0025] By adopting the above technical solution, the energy storage density of solid-phase materials and the fluidity of liquid-phase electrolyte are balanced, preventing the sudden increase in fluid resistance and mass transfer polarization caused by an excessively high solid-phase ratio.

[0026] This invention provides a method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte. It has the following beneficial effects: 1. This invention prepares a clear and transparent liquid electrolyte containing vanadium ions with a total vanadium concentration between 1.5 mol / L and 2.0 mol / L by adding demineralized water and concentrated sulfuric acid to an acid-resistant reactor, controlling the reaction temperature with cooling water, and adding industrial-grade V2O5 and oxalic acid as a reducing agent in batches. The addition of oxalic acid triggers a reduction reaction, maintaining the concentration balance between trivalent and tetravalent vanadium ions, reducing the probability of vanadium ion precipitation under high concentration conditions, and maintaining the cycle stability of the vanadium redox flow battery.

[0027] 2. This invention prepares porous spherical vanadium-based solid porous materials or porous rod-shaped vanadium-based solid porous materials by uniformly mixing the main material (vanadium-based oxide), porous solid carrier, auxiliary material (conductive agent), and binder in a planetary homogenization system, extruding and granulating the mixture using a centrifugal granulator, and then sintering it in a tube furnace under protective gas. The porous solid carrier constructs the skeletal support structure, the auxiliary conductive agent constructs the electron transport channels, and the sintering process removes excess solvent and forms a porous structure inside the particles, increasing the physical area of ​​contact between the solid particles and the liquid phase.

[0028] 3. This invention assembles the obtained vanadium-based solid porous material and the obtained clear and transparent 3.5-valent vanadium ion liquid electrolyte into a separate solid-liquid reactor according to a specified mass ratio, and finally prepares a solid-liquid hybrid vanadium redox flow battery electrolyte. The solid porous material, as an energy storage active material source fixed inside the separate solid-liquid reactor, participates in the electrochemical storage process. In conjunction with the ion transport and transfer process in the liquid electrolyte, the total charge contained inside the vanadium redox flow battery is increased without increasing the volume and ion concentration of the clear and transparent 3.5-valent vanadium ion liquid electrolyte. Attached Figure Description

[0029] Figure 1 This is a graph showing the cyclic voltammetry test data of the present invention; Figure 2 This is a graph showing the apparent viscosity test data of the present invention; Figure 3 This is a graph showing the test data of the single-cell volumetric capacity and energy efficiency of the present invention; Figure 4 This is a graph showing the cycle life test data of the present invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Examples 1-4: Example 1: This embodiment provides a method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte, including the following steps: S1. Add 500 parts by mass of demineralized water to an acid-resistant reactor. Add 432 parts by mass of concentrated sulfuric acid dropwise into the demineralized water at a rate of 30 parts by mass / minute. Control the reaction temperature at 30 degrees Celsius using cooling water. Add 160 parts by mass of industrial-grade V₂O₅ (purity greater than 98%) in batches to the acid-resistant reactor. Simultaneously, add 163 parts by mass of oxalic acid (reducing agent) in batches, and add demineralized water to bring the volume to 1000 parts by mass. Set the stirring speed to 400 rpm and stir until completely dissolved. This completes the electrochemical reduction and mixing process. The total vanadium concentration is tested to be 1.7 mol / L, the sulfate concentration is tested to be 4.5 mol / L, and the V₂O₅ concentration is tested to be... 3+ With V 4+ A concentration ratio of 1.0 yielded a clear and transparent liquid electrolyte containing vanadium ions in the 3,5-valent form. S2. 40 parts by mass of the main material vanadium-based oxide V2O3, 30 parts by mass of the main material vanadium-based oxide V3O7, 10 parts by mass of the porous solid carrier Li3VO4, 3 parts by mass of the auxiliary material conductive agent carbon black Super P, and 2 parts by mass of the binder PVDF were added to the planetary homogenizing system in batches. The rotation speed of the main disk of the planetary homogenizing system was controlled at 30 rpm, the rotation speed of the dispersion disk of the planetary homogenizing system was controlled at 2500 rpm, and the stirring time was set to 3 hours. After completing the degassing and filtration process, micron-sized vanadium-based slurry was obtained. S3. The obtained micron-sized vanadium-based slurry was placed in a centrifugal granulator. 115 parts by mass of the solvent N-methylpyrrolidone were added to the centrifugal granulator. The stirring speed of the centrifugal granulator was set to 300 rpm and stirred for 45 minutes to form a slurry. The slurry was then extruded and granulated to obtain micron-sized solid particles. S4. Argon gas was introduced into the tube furnace as a protective gas. The obtained micron-sized solid particles were placed in the tube furnace. The sintering temperature of the tube furnace was controlled at 550 degrees Celsius and the sintering time was controlled at 2.5 hours. Excess solvent was removed and the micron-sized solid particles were sintered and formed to obtain porous spherical vanadium-based solid porous material. S5. The obtained porous spherical vanadium-based solid porous material and the obtained clear and transparent 3.5 vanadium ion liquid electrolyte were assembled into a separate solid-liquid reactor at a mass ratio of 1:6. The electrolyte performance was evaluated by loading a full vanadium redox flow battery, and a solid-liquid hybrid full vanadium redox flow battery electrolyte was obtained.

[0032] Example 2: This embodiment provides a method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte, including the following steps: S1. Add 600 parts by mass of demineralized water to an acid-resistant reactor. Add 540 parts by mass of concentrated sulfuric acid dropwise into the demineralized water at a rate of 50 parts by mass / minute. Control the reaction temperature at 40 degrees Celsius using cooling water. Add 180 parts by mass of industrial-grade V₂O₅ (purity greater than 98%) in batches to the acid-resistant reactor. Simultaneously, add 189 parts by mass of oxalic acid (reducing agent) in batches, and add demineralized water to bring the volume to 1200 parts by mass. Set the stirring speed to 500 rpm and stir until completely dissolved. This completes the electrochemical reduction and mixing process. The total vanadium concentration is tested to be 2.0 mol / L, the sulfate concentration is tested to be 5.0 mol / L, and the V₂O₅ concentration is tested to be... 3+ With V 4+ A concentration ratio of 1.1 yielded a clear and transparent liquid electrolyte containing vanadium ions in the 3,5-valent form. S2. Take 50 parts by weight of the main material, vanadium-based oxide V6O 13 10 parts by weight of porous solid carrier ZrO2, 5 parts by weight of conductive agent graphene, and 3 parts by weight of binder SBR were added to the planetary homogenizing system in batches. The rotation speed of the main rotating disk of the planetary homogenizing system was controlled at 50 rpm, the rotation speed of the dispersion disk of the planetary homogenizing system was controlled at 3000 rpm, and the stirring time was set to 5 hours. After completing the degassing and filtration processes, micron-sized vanadium-based slurry was obtained. S3. The obtained micron-sized vanadium-based slurry was placed in a centrifugal granulator. 130 parts by mass of solvent water were added to the centrifugal granulator. The stirring speed of the centrifugal granulator was set to 500 rpm and stirred for 60 minutes to form a slurry. The slurry was then extruded and granulated to obtain micron-sized solid particles. S4. Nitrogen gas was introduced into the tube furnace as a protective gas. The obtained micron-sized solid particles were placed in the tube furnace. The sintering temperature of the tube furnace was controlled at 800 degrees Celsius and the sintering time was controlled at 4 hours. Excess solvent was removed and the micron-sized solid particles were sintered and formed to obtain a porous rod-shaped vanadium-based solid porous material. S5. The obtained porous rod-shaped vanadium-based solid porous material and the obtained clear and transparent 3.5-valent vanadium ion liquid electrolyte were assembled into a separate solid-liquid reactor at a mass ratio of 1:8. The electrolyte performance was evaluated by loading a full vanadium redox flow battery, and a solid-liquid hybrid full vanadium redox flow battery electrolyte was obtained.

[0033] Example 3: This embodiment provides a method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte, including the following steps: S1. Add 400 parts by mass of demineralized water to an acid-resistant reactor. Add 300 parts by mass of concentrated sulfuric acid dropwise into the demineralized water at a rate of 10 parts by mass / minute. Maintain the reaction temperature at 25 degrees Celsius using cooling water. Add 120 parts by mass of industrial-grade V₂O₅ (purity greater than 98%) in batches to the acid-resistant reactor. Simultaneously, add 120 parts by mass of oxalic acid (reducing agent) in batches, and add demineralized water to bring the volume to 800 parts by mass. Set the stirring speed to 300 rpm and stir until completely dissolved. This completes the electrochemical reduction and mixing process. The total vanadium concentration is tested to be 1.5 mol / L, the sulfate concentration is tested to be 3.0 mol / L, and the V₂O₅ concentration is tested to be... 3+ With V 4+ A concentration ratio of 0.9 yielded a clear and transparent liquid electrolyte containing vanadium ions in the 3,5-valent form. S2. Add 30 parts by mass of the main material vanadium-based oxide VO, 5 parts by mass of the porous solid carrier TiO2, 2 parts by mass of the auxiliary material conductive agent acetylene black, and 2 parts by mass of the binder polyacrylic acid to the planetary homogenizing system in batches. Control the rotation speed of the main disk of the planetary homogenizing system to 15 rpm and the rotation speed of the dispersion disk of the planetary homogenizing system to 2000 rpm. Set the stirring time to 2 hours to complete the degassing and filtration process and obtain micron-sized vanadium-based slurry. S3. The obtained micron-sized vanadium-based slurry was placed in a centrifugal granulator. 80 parts by mass of solvent ethanol were added to the centrifugal granulator. The stirring speed of the centrifugal granulator was set to 100 rpm and stirred for 30 minutes to form a slurry. The slurry was then extruded and granulated to obtain micron-sized solid particles. S4. Argon protective gas is introduced into a tube furnace. The obtained micron-sized solid particles are placed in the tube furnace. The sintering temperature of the tube furnace is controlled at 300 degrees Celsius and the sintering time is controlled at 1 hour. Excess solvent is removed and the micron-sized solid particles are sintered and formed to obtain porous spherical vanadium-based solid porous material. S5. The obtained porous spherical vanadium-based solid porous material and the obtained clear and transparent 3.5 vanadium ion liquid electrolyte were assembled into a separate solid-liquid reactor at a mass ratio of 1:5. The electrolyte performance was evaluated by loading a full vanadium redox flow battery, and a solid-liquid hybrid full vanadium redox flow battery electrolyte was obtained.

[0034] Example 4: This embodiment provides a method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte, including the following steps: S1. Add 450 parts by mass of demineralized water to an acid-resistant reactor. Add 420 parts by mass of concentrated sulfuric acid dropwise into the demineralized water at a rate of 20 parts by mass / minute. Maintain the reaction temperature at 35 degrees Celsius using cooling water. Add 150 parts by mass of industrial-grade V₂O₅ (purity greater than 98%) in batches to the acid-resistant reactor. Simultaneously, add 154 parts by mass of oxalic acid (reducing agent) in batches, and add demineralized water to bring the volume to 900 parts by mass. Set the stirring speed to 450 rpm and stir until completely dissolved. This completes the electrochemical reduction and mixing process. The total vanadium concentration is tested to be 1.8 mol / L, the sulfate concentration is tested to be 4.2 mol / L, and the V₂O₅ concentration is tested to be... 3+ With V 4+ A concentration ratio of 0.98 yielded a clear and transparent liquid electrolyte containing vanadium ions in the 3,5-valent form. S2. 40 parts by mass of the main material vanadium-based oxide V2O4, 8 parts by mass of the porous solid carrier NiO, 4 parts by mass of the auxiliary material conductive agent Ketjen Black, and 3 parts by mass of the binder PVDF were added to the planetary homogenizing system in batches. The rotation speed of the main disk of the planetary homogenizing system was controlled at 40 rpm, the rotation speed of the dispersion disk of the planetary homogenizing system was controlled at 2800 rpm, and the stirring time was set to 4 hours. After completing the degassing and filtration process, micron-sized vanadium-based slurry was obtained. S3. Place the obtained micron-sized vanadium-based slurry in a centrifugal granulator, add 100 parts by mass of the solvent N-methylpyrrolidone to the centrifugal granulator, set the stirring speed of the centrifugal granulator to 400 rpm and stir for 50 minutes to form a slurry, then extrude and granulate to obtain micron-sized solid particles. S4. Nitrogen gas was introduced into the tube furnace as a protective gas. The obtained micron-sized solid particles were placed in the tube furnace. The sintering temperature of the tube furnace was controlled at 600 degrees Celsius and the sintering time was controlled at 3 hours. Excess solvent was removed and the micron-sized solid particles were sintered and formed to obtain a porous rod-shaped vanadium-based solid porous material. S5. The obtained porous rod-shaped vanadium-based solid porous material and the obtained clear and transparent 3.5-valent vanadium ion liquid electrolyte were assembled into a separate solid-liquid reactor at a mass ratio of 1:7. The electrolyte performance was evaluated by loading a full vanadium redox flow battery, and a solid-liquid hybrid full vanadium redox flow battery electrolyte was obtained.

[0035] Comparative Examples 1-4: Comparative Example 1: Compared with Example 1, the difference is that steps S2, S3 and S4 are not performed, and in step S5, porous spherical vanadium-based solid porous materials are not assembled into the separated solid-liquid reactor. Instead, clear and transparent 3.5 valence vanadium ion liquid electrolyte is directly assembled into the separated solid-liquid reactor and loaded with a full vanadium redox flow battery for electrolyte performance evaluation. All other aspects are the same.

[0036] Comparative Example 2: Compared with Example 1, the difference is that in step S2, 10 parts by mass of the porous solid carrier Li3VO4 are not added, the amount of vanadium-based oxide V2O3 added is adjusted to 45 parts by mass, and the amount of vanadium-based oxide V3O7 added is adjusted to 35 parts by mass, while the rest are the same.

[0037] Comparative Example 3: Compared with Example 1, the difference is that in step S2, 3 parts by mass of the auxiliary conductive agent SuperP carbon black and 2 parts by mass of the binder PVDF are not added. The amount of the main material vanadium-based oxide V2O3 is adjusted to 43 parts by mass and the amount of the main material vanadium-based oxide V3O7 is adjusted to 32 parts by mass. All other aspects are the same.

[0038] Comparative Example 4: Compared with Example 1, the difference is that in step S5, the porous spherical vanadium-based solid porous material and the clear and transparent 3.5 vanadium ion liquid electrolyte are assembled into the separated solid-liquid reactor at a mass ratio of 1:2; all other steps are the same.

[0039] Test Examples 1-4: Test Example 1: Electrochemical activity and cyclic voltammetry of solid-liquid hybrid systems Assemble a three-electrode test cell. The working electrode is a graphite felt, the counter electrode is a platinum sheet electrode, and the reference electrode is a saturated calomel electrode.

[0040] The solid-liquid hybrid vanadium redox flow battery electrolytes prepared in Examples 1 to 4 and Comparative Examples 2 to 4 were injected into the electrolyte chamber of a three-electrode test battery as test subjects. The clear and transparent 3.5-valent vanadium ion liquid electrolyte prepared in Comparative Example 1 was injected into the electrolyte chamber of a three-electrode test battery as a test subject.

[0041] Connect the three-electrode test cell to the electrochemical workstation, set the scan rate to 10 mV / s, and set the voltage scan window to 0.2 V to 1.8 V.

[0042] Start the electrochemical workstation to run the cyclic voltammetry test program, record and read the oxidation peak current value, reduction peak current value, and peak potential difference value between the oxidation peak and the reduction peak after the test is completed.

[0043] Table 1. Cyclic Voltampere Test Data of Electrolyte in Solid-Liquid Hybrid Vanadium Redox Flow Battery Attached image description: Figure 1 This is a graph showing the cyclic voltammetry test data of the electrolyte in the solid-liquid hybrid vanadium redox flow battery of this invention. Figure 1 The distribution of oxidation peak current values ​​and peak potential difference values ​​of Examples 1 to 4 and Comparative Examples 1 to 4 is shown in the figure.

[0044] Table 1 shows that the oxidation peak current values ​​of Examples 1 to 4 are greater than those of Comparative Example 1, while the peak potential difference values ​​of Examples 1 to 4 are less than those of Comparative Example 1. Comparative Example 1 did not include porous spherical vanadium-based solid porous material; only a clear and transparent 3.5-valent vanadium ion liquid electrolyte participated in the electrochemical reaction, and the reaction interface depended on the electrode surface. In Examples 1 to 4, vanadium-based oxide was added as the main material. This vanadium-based oxide underwent a solid-phase redox reaction in the clear and transparent 3.5-valent vanadium ion liquid electrolyte, increasing the overall electrochemical reaction current value and reducing the peak potential difference value during charge transfer.

[0045] The oxidation peak current values ​​of Comparative Examples 2 and 3 are lower than those of Example 1, while the peak potential difference between Comparative Examples 2 and 3 is greater than that of Example 1. Comparative Example 2 lacks the skeletal support of the porous solid carrier Li3VO4, and Comparative Example 3 lacks the electronic conduction network construction effect of the excipient conductive agent carbon black Super P. The increased electron transfer resistance within the micron-sized solid particles limits the capacity utilization of the main vanadium-based oxide, leading to a decline in reaction kinetics.

[0046] The oxidation peak current of Comparative Example 4 decreased to 85.6 mA, while the peak potential difference increased to 135.7 mV. In Comparative Example 4, the mass ratio of the porous spherical vanadium-based solid porous material to the clear and transparent 3.5-valent vanadium ion liquid electrolyte was 1:2, exceeding the lower limit of the range specified in the examples. Excessive solid particles increased the rheological viscosity of the solid-liquid mixture, hindering the diffusion and mass transfer of vanadium ions at the solution-electrode interface, resulting in severe concentration polarization. Controlling the mass ratio of the porous spherical vanadium-based solid porous material to the clear and transparent 3.5-valent vanadium ion liquid electrolyte within the range set in the examples balanced the electrochemical capacity provided by the solid phase and the mass transfer requirements of the liquid phase fluid.

[0047] Test Example 2: Macroscopic rheological properties and apparent viscosity testing of solid-liquid mixtures Prepare a rotational rheometer, configure a coaxial cylindrical test fixture, connect a circulating water bath system, and set the test temperature to 25 degrees Celsius.

[0048] The solid-liquid hybrid vanadium redox flow battery electrolytes prepared in Examples 1 to 4 and Comparative Examples 2 to 4 were injected into the coaxial cylindrical test fixture of the rotational rheometer as test objects. The clear and transparent 3.5-valent vanadium ion liquid electrolyte prepared in Comparative Example 1 was injected into the coaxial cylindrical test fixture of the rotational rheometer as a test object.

[0049] Control the rotational rheometer to run the steady-state shear test program, and set the shear rate scan range to 10 s. -1 up to 500s -1 The data acquisition time for each shear rate measurement point was set to 15 seconds.

[0050] Record the rheological response data of the test object at different shear rates, and extract and record the test object's response data at 10 s. -1 Apparent viscosity values ​​under low shear rate conditions were extracted and recorded for the test object over 500 seconds. -1 Apparent viscosity values ​​under high shear rate conditions.

[0051] Table 2. Rheological test data of electrolyte for solid-liquid hybrid vanadium redox flow battery Attached image description: Figure 2 This is a graph showing the apparent viscosity test data of the electrolyte for the solid-liquid hybrid vanadium redox flow battery of this invention. Figure 2 The paper illustrates the variation of apparent viscosity values ​​in Examples 1 to 4 and Comparative Examples 1 to 4 under low and high shear rate conditions.

[0052] As shown in Table 2, the apparent viscosity values ​​of Examples 1 to 4 at both low and high shear rates are greater than those of Comparative Example 1. Comparative Example 1 only contains a clear and transparent liquid electrolyte of vanadium ions (3.5 valence), and the system does not exhibit shear-thinning behavior.

[0053] In Examples 1 to 4, micron-sized solid particles were dispersed in a clear, transparent liquid electrolyte containing vanadium ions (3.5 valence ions) to construct a solid-phase particle suspension network, which increased the frictional resistance within the fluid. When the shear rate increased from 10 s⁻¹... -1 Increased to 500s -1At that time, the apparent viscosity values ​​of Examples 1 to 4 decreased. The applied shear stress disrupted the physical aggregation state between micron-sized solid particles, causing the fluid to exhibit pseudoplastic non-Newtonian fluid characteristics. The lower apparent viscosity value at high shear rates meets the engineering requirements of the internal mechanical circulation pump driving the fluid to flow at high speed in the pipeline of the all-vanadium redox flow battery system.

[0054] The apparent viscosity at low shear rates in Comparative Example 4 reached 458.2 mPa·s. In Comparative Example 4, porous spherical vanadium-based solid porous material was assembled with a clear and transparent 3.5-valent vanadium ion liquid electrolyte at a mass ratio of 1:2. The excessively high mass percentage of solid material led to severe collisions and physical stacking of solid particles in the liquid phase, resulting in the loss of macroscopic flow capability of the fluid.

[0055] The excessive apparent viscosity value exceeded the working limit of a conventional mechanical circulation pump, posing a risk of physical blockage in the battery circulation pipeline. In Example 1, the mass ratio of porous spherical vanadium-based solid porous material to clear and transparent 3.5-valent vanadium ion liquid electrolyte was set at 1:6, which limited the upper limit of the mass fraction of the solid phase material, balancing the increase in electrode reaction capacity with the operability of the fluid pumping process.

[0056] Test Example 3: Vanadium redox flow single cell discharge volumetric capacity and energy efficiency test Assemble a vanadium redox flow cell with graphite felt as reaction electrodes on both the positive and negative sides. A perfluorosulfonic acid ion exchange membrane is placed between the positive and negative sides as a separator. An external circuit is connected through a graphite bipolar plate. A mechanical circulation pump and an electrolyte storage tank are connected to the external pipelines on the positive and negative sides, respectively.

[0057] The solid-liquid hybrid vanadium redox flow battery electrolytes prepared in Examples 1 to 4 and Comparative Examples 2 to 4 were injected in equal amounts into the electrolyte storage tanks on the positive and negative electrodes, respectively, as test subjects. The clear and transparent 3.5-valent vanadium ion liquid electrolyte prepared in Comparative Example 1 was injected in equal amounts into the electrolyte storage tanks on the positive and negative electrodes, respectively, as a test subject.

[0058] The mechanical circulation pump was set to a flow rate of 40 ml / min to ensure that the test object continuously circulated between the electrolyte storage tank and the vanadium redox flow cell.

[0059] A vanadium redox flow cell was connected to a battery charge-discharge test system, and the constant current charge-discharge current density was set to 50 mA / cm². 2 The charging cutoff voltage is set to 1.65V, and the discharging cutoff voltage is set to 1.0V.

[0060] Start the battery charge and discharge test system to run the cyclic test program, extract and record the first discharge volumetric capacity and energy efficiency value of the test object at the end of the first cycle.

[0061] Table 3. Test data of single-cell volumetric specific capacity and energy efficiency of electrolyte in solid-liquid hybrid vanadium redox flow battery. Attached image description: Figure 3 This is a graph showing the test data of the single-cell volumetric specific capacity and energy efficiency of the solid-liquid hybrid vanadium redox flow battery electrolyte of this invention. Figure 3 The distribution patterns of the volumetric capacity and energy efficiency values ​​of the first discharge cycle in Examples 1 to 4 and Comparative Examples 1 to 4 are shown.

[0062] As shown in Table 3, the first-cycle discharge volumetric capacity values ​​of Examples 1 to 4 are greater than those of Comparative Example 1. In Comparative Example 1, only a clear and transparent 3.5-valent vanadium ion liquid electrolyte was used, and the charge / discharge capacity of the all-vanadium redox flow single cell depended entirely on the concentration of vanadium ions dissolved in the liquid phase. In Examples 1 to 4, porous spherical vanadium-based solid porous materials or porous rod-shaped vanadium-based solid porous materials were added. These materials entered the pores of the graphite felt electrode along with the liquid fluid, and the vanadium-based oxides of the main material participated in additional solid-phase redox reactions, increasing the total amount of charge stored and released per unit volume of electrolyte.

[0063] The first-cycle discharge volumetric capacity and energy efficiency values ​​of Comparative Examples 2 and 3 were both lower than those of Example 1. Comparative Example 2 lacked 10 parts by mass of the porous solid carrier Li3VO4, causing the vanadium-based oxide as the main material to undergo volume changes and physical agglomeration during charge-discharge cycles, reducing the utilization rate of the active material. Comparative Example 3 lacked 3 parts by mass of the auxiliary conductive agent Super P and 2 parts by mass of the binder PVDF, resulting in a lack of electronic conduction channels between solid particles, increasing electrochemical polarization resistance, generating more heat loss, and reducing energy conversion efficiency.

[0064] The first discharge volumetric capacity of Comparative Example 4 decreased to 15.8 Ah / L, and its energy efficiency decreased to 42.5%. In Comparative Example 4, the mass ratio of porous spherical vanadium-based solid porous material to clear and transparent 3.5-valent vanadium ion liquid electrolyte was controlled at 1:2, indicating a high solid loading. The high concentration of solid micron-sized particles accumulated and physically blocked the pores of the graphite felt, obstructing the mass transfer path of vanadium ions from the liquid fluid to the reaction interface, leading to severe concentration polarization. The all-vanadium redox flow cell reached the charging cutoff voltage of 1.65V prematurely during charging, preventing most of the internal active material from participating in the reaction.

[0065] In Example 1, the mass ratio of porous spherical vanadium-based solid porous material to clear and transparent 3.5-valent vanadium ion liquid electrolyte was controlled at 1:6, which ensured the fluid permeation rate inside the electrode pores and met the mass transfer and charge transfer requirements for normal operation of the all-vanadium redox flow single cell.

[0066] Test Example 4: Long cycle life and capacity retention test of all-vanadium redox flow single cell Assemble a vanadium redox flow cell with graphite felt as reaction electrodes on both the positive and negative sides. A perfluorosulfonic acid ion exchange membrane is placed between the positive and negative sides as a separator. An external circuit is connected through a graphite bipolar plate. A mechanical circulation pump and an electrolyte storage tank are connected to the external pipelines on the positive and negative sides, respectively.

[0067] The solid-liquid hybrid vanadium redox flow battery electrolytes prepared in Examples 1 to 4 and Comparative Examples 2 to 4 were injected in equal amounts into the electrolyte storage tanks on the positive and negative electrodes, respectively, as test subjects. The clear and transparent 3.5-valent vanadium ion liquid electrolyte prepared in Comparative Example 1 was injected in equal amounts into the electrolyte storage tanks on the positive and negative electrodes, respectively, as a test subject.

[0068] The mechanical circulation pump was set to a flow rate of 40 ml / min to ensure that the test object continuously circulated between the electrolyte storage tank and the vanadium redox flow cell.

[0069] A vanadium redox flow cell was connected to a battery charge-discharge test system, and the constant current charge-discharge current density was set to 50 mA / cm². 2 The charging cutoff voltage is set to 1.65V, and the discharging cutoff voltage is set to 1.0V.

[0070] Start the battery charge-discharge test system and run the long-cycle test program. Perform 200 charge-discharge cycles continuously, and extract and record the volumetric capacity value of the 200th discharge cycle at the end of the 200th cycle.

[0071] The capacity retention rate for the 200th discharge cycle was calculated and recorded by dividing the volumetric capacity value of the 200th discharge cycle by the volumetric capacity value of the first discharge cycle recorded in Test Example 3.

[0072] Table 4. Cycle life test data of electrolyte for solid-liquid hybrid vanadium redox flow battery Attached image description: Figure 4 This is a graph showing the cycle life test data of the electrolyte in the solid-liquid hybrid vanadium redox flow battery of this invention. Figure 4 The figure shows the correspondence between the volumetric capacity values ​​of the 200th discharge cycle and the capacity retention rate values ​​of the 200th cycle in Examples 1 to 4 and Comparative Examples 1 to 4.

[0073] As shown in Table 4, the capacity retention rates of Examples 1 to 4 after 200 cycles are greater than those of Comparative Examples 2 and 3 after 200 cycles. Comparative Example 2 lacks 10 parts by mass of the porous solid carrier Li3VO4. During continuous charge-discharge cycles, the vanadium-based oxide in Comparative Example 2 repeatedly undergoes intercalation-deintercalation reactions, resulting in physical volume expansion and contraction. The vanadium-based oxide also undergoes structural pulverization and detaches from the solid particle bulk.

[0074] Comparative Example 3 lacked 3 parts by mass of the conductive agent Super P and 2 parts by mass of the binder PVDF. Under the long-term scouring action of the fluid, the conductive network inside the micron-sized solid particles in Comparative Example 3 underwent physical breakage, and the main vanadium-based oxide lost its electron conduction channels, becoming charge islands that could not participate in the electrochemical reaction. This caused the discharge volumetric capacity to decrease with the increase of the number of cycles.

[0075] Example 1 incorporates 10 parts by weight of a porous solid support Li3VO4, 3 parts by weight of the conductive agent super P carbon black, and 2 parts by weight of the binder PVDF. The porous solid support Li3VO4 provides a physical support framework, absorbing the volume stress of the main vanadium-based oxide. The conductive agent super P carbon black and the binder PVDF maintain stable electron transport paths within the micron-sized solid particles, ensuring the capacity stability of the all-vanadium redox flow cell under long-term cycling conditions.

[0076] In Comparative Example 4, the capacity retention rate decreased to 13.3% after 200 cycles. In Comparative Example 4, porous spherical vanadium-based solid porous material was assembled with a clear and transparent 3.5-valent vanadium ion liquid electrolyte at a mass ratio of 1:2. The high concentration of porous spherical vanadium-based solid porous material underwent irreversible physical aggregation and sedimentation during long-term circulation, clogging the physical pores of the graphite felt and the external circulation channels. The mass transfer resistance of the fluid within the system continuously increased with the number of cycles, reducing the reactive interface area and leading to severe voltage polarization in the later stages of cycling in the all-vanadium redox flow single cell. In Example 1, porous spherical vanadium-based solid porous material and a clear and transparent 3.5-valent vanadium ion liquid electrolyte were assembled at a mass ratio of 1:6, balancing the amount of solid energy storage material added with the requirements of macroscopic fluid flow performance, and avoiding capacity decay caused by channel blockage.

Claims

1. A method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte, characterized in that, Includes the following steps: Deionized water and concentrated sulfuric acid were added to an acid-resistant reactor. The reaction temperature was controlled by cooling water. Industrial-grade V2O5 and reducing agent oxalic acid were added in batches, and the deionized water was added to make up the volume. The mixture was stirred until completely dissolved to complete the electrochemical reduction and mixing process, and a clear and transparent 3.5 valent vanadium ion liquid electrolyte was obtained. The main material, vanadium-based oxide, porous solid carrier, auxiliary materials, conductive agent and binder are added to the planetary homogenization system and stirred to complete the degassing and filtration process, thereby obtaining micron-sized vanadium-based slurry. The micron-sized vanadium-based slurry was placed in a centrifugal granulator, a solvent was added to form a slurry, and the slurry was extruded and granulated to obtain micron-sized solid particles. A protective gas is introduced into a tube furnace to sinter the micron-sized solid particles, remove excess solvent, and control the sintering process to obtain a vanadium-based solid porous material. The vanadium-based solid porous material and the clear and transparent 3.5-valent vanadium ion liquid electrolyte are assembled into a separate solid-liquid reactor to obtain a solid-liquid hybrid vanadium redox flow battery electrolyte.

2. The method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte according to claim 1, characterized in that, In the process of preparing the clear and transparent 3.5 valent vanadium ion liquid electrolyte, 400-600 parts by mass of the demineralized water are added, and 300-540 parts by mass of the concentrated sulfuric acid are added dropwise into the demineralized water at a dropping rate of 10-50 parts by mass / minute. The reaction temperature is controlled at 25-40 degrees Celsius using the cooling water. Add 120-180 parts by weight of the industrial-grade V2O5 with a purity greater than 98% in batches. At the same time as adding the industrial-grade V2O5, add 120-189 parts by weight of the reducing agent oxalic acid in batches and add the demineralized water to make up the volume to 800-1200 parts by weight. Set the stirring speed to 300-500 rpm.

3. The method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte according to claim 1, characterized in that, After completing the electrochemical reduction and mixing process, the total vanadium concentration of the resulting liquid electrolyte is 1.5-2.0 mol / L, the sulfate concentration is tested to be 3.0-5.0 mol / L, and the Vo is tested. 3+ With V 4+ The concentration ratio is 0.9-1.

1.

4. The method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte according to claim 1, characterized in that, In preparing the micron-sized vanadium-based slurry, the main vanadium-based oxide is selected from V₂O₃, V₃O₇, and V₆O₂. 13 One or more of VO and V2O4; The porous solid support is selected from one of Li3VO4, ZrO2, TiO2 and NiO; The conductive agent in the auxiliary material is selected from one of carbon black Super P, graphene, acetylene black and Ketjen black; The adhesive is selected from PVDF, SBR and polyacrylic acid.

5. The method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte according to claim 1, characterized in that, The raw materials for preparing the micron-sized vanadium-based slurry include, by mass parts: The main ingredient, vanadium-based oxide, is 30-70 parts. The porous solid carrier: 5-10 parts; The conductive agent in the auxiliary material: 2-5 parts; The adhesive: 2-3 parts.

6. The method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte according to claim 1, characterized in that, During stirring in the planetary homogenizing system, the rotation speed of the main rotating disk of the planetary homogenizing system is controlled at 15-50 rpm, the rotation speed of the dispersing disk of the planetary homogenizing system is controlled at 2000-3000 rpm, and the stirring time is set to 2-5 hours.

7. The method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte according to claim 1, characterized in that, In the process of preparing the micron-sized solid particles, the solvent is selected from one of N-methylpyrrolidone, water and ethanol, and the amount of solvent added is 80-130 parts by mass.

8. The method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte according to claim 1, characterized in that, When the micron-sized vanadium-based slurry is placed in the centrifugal granulator and stirred, the stirring speed of the centrifugal granulator is set to 100-500 rpm and stirred for 30-60 minutes.

9. The method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte according to claim 1, characterized in that, During sintering in the tubular furnace, the protective gas is argon or nitrogen; the sintering temperature of the tubular furnace is controlled at 300-800 degrees Celsius, and the sintering time of the tubular furnace is controlled at 1-4 hours; the vanadium-based solid porous material obtained by sintering is a porous spherical vanadium-based solid porous material or a porous rod-shaped vanadium-based solid porous material.

10. The method for preparing a solid-liquid hybrid vanadium redox flow battery electrolyte according to claim 1, characterized in that, When assembling into the separated solid-liquid reactor, the obtained vanadium-based solid porous material and the obtained clear and transparent 3.5-valent vanadium ion liquid electrolyte are assembled at a mass ratio of 1:5 to 1:8.

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