A method of improving electrode life of a vanadium flow battery

Abstract

The application discloses a method for prolonging the service life of a vanadium flow battery electrode, and comprises the following steps: (1) adding iron salt and strontium salt into a solvent, and then adding a dispersing agent and a complexing agent, and stirring under heating to obtain a precursor sol; (2) using the precursor sol to impregnate a vanadium flow battery electrode substrate; (3) performing freeze-drying on the impregnated vanadium flow battery electrode substrate to obtain a vanadium flow battery electrode composite; and (4) performing heat treatment on the vanadium flow battery electrode composite to obtain a vanadium flow battery composite electrode. The method selects a strontium iron calcium perovskite structure metal oxide as an electrode surface loading material, avoids oxidation deactivation of electrode material during use of the electrode, prevents corrosion of the electrode material, improves the oxidation resistance and electrocatalytic performance of the electrode material, and greatly improves the operation efficiency and service life of the vanadium flow battery electrode stack.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage devices, and particularly relates to a method for prolonging the service life of vanadium flow battery electrodes. BACKGROUND

[0002] Vanadium flow battery (VFB) is a kind of redox flow battery, which uses vanadium ions dissolved in aqueous sulfuric acid solution as electrolyte, uses vanadium redox couple in sulfuric acid solution as electrolyte, uses proton exchange membrane as a membrane device for conducting protons and isolating electrons, and the electrolyte between the positive and negative electrodes is stored in an electrolyte tank. The electrolyte outlet pipe is designed separately from the stack. As a long-acting energy storage device, vanadium flow battery has a series of excellent characteristics such as large energy storage capacity, large output power, high energy efficiency, good charge-discharge performance, and long cycle life in large-scale energy storage applications. The carbon electrode such as graphite is usually selected as the main base material for the electrode of vanadium flow battery stack. This kind of material has a larger porosity and a higher specific surface area, which can provide more active sites in the electrochemical reaction process and improve the efficiency and rate of electrochemical reaction. However, the carbon electrode of vanadium flow battery has oxidation corrosion phenomenon during the charging and discharging process, which will cause the deactivation of the electrode. Therefore, it is necessary to study and improve the carbon electrode of vanadium flow battery to improve its oxidation resistance and electrocatalytic performance, and prolong the service life of the electrode of vanadium flow battery. SUMMARY

[0003] The present application is based on the discovery and understanding of the inventors on the following facts and problems: In experiments, it is found that when the electrode potential of vanadium flow battery is lower than 0.4V, the pure carbon electrode is easy to be corroded in air, but not in nitrogen; when the electrode potential is higher than 0.9V, obvious carbon corrosion can be observed in both air and nitrogen environment. When the electrode potential is lower than 0.4V, the peak value of carbon dioxide emission is related to the chemical corrosion of oxygen to carbon, and when the electrode potential is higher than 1V, the peak value of carbon dioxide emission is related to the electrochemical oxidation of "stable" oxide C=O.

[0004] The present application aims to at least solve one of the technical problems in the related art. To this end, the embodiments of the present application propose a method for prolonging the service life of vanadium flow battery electrode, which selects strontium iron calcium perovskite structure metal oxide as the electrode surface loading material, avoids the oxidation deactivation of the electrode material during use, prevents the corrosion of the electrode material, improves the oxidation resistance and electrocatalytic performance of the electrode material, and greatly improves the operation efficiency and service life of the electrode of vanadium flow battery stack.

[0005] The method for prolonging the service life of vanadium flow battery electrode according to the embodiments of the present application comprises the following steps:

[0006] (1) adding iron salt and strontium salt into a solvent, then adding dispersant and complexing agent, heating and stirring to obtain a precursor sol;

[0007] (2) using the precursor sol to impregnate a vanadium flow battery electrode substrate;

[0008] (3) freezing and drying the impregnated vanadium flow battery electrode substrate to obtain a vanadium flow battery electrode composite;

[0009] (4) heat treating the vanadium flow battery electrode composite to obtain a vanadium flow battery composite electrode.

[0010] The method for prolonging the service life of a vanadium flow battery electrode according to the embodiments of the application has the following advantages and technical effects:

[0011] 1. The freezing and drying process is used, and the capillary action is used for adsorption and film formation during the impregnation process. In the process of removing solvent molecules, the precursor material can be uniformly distributed on the electrode substrate. The heat treatment process enables the strontium iron perovskite structure metal oxide to form a stable phase structure. Meanwhile, the metal oxide is loaded on the carbon electrode substrate. The carbon has reducing property, and the ion oxygen in the metal oxide has oxidizing property. The two can easily combine, so that the oxygen ions in the iron oxygen ion bond of the metal oxide combine with the carbon-carbon bond of the vanadium flow battery electrode to form a fixed heterojunction structure, thereby achieving the process effect of self-assembly and composite film formation. The strontium iron perovskite structure metal oxide has more intermetallic oxygen vacancy defects due to its unique crystal structure. The existence of these defects can effectively lead out the combined oxygen ions on the surface of the electrode material during the electrochemical reaction process, and can greatly avoid the phenomenon of oxidation corrosion and deactivation of the electrode material due to the combination of the electrode material and oxygen ions. The strontium iron perovskite structure metal oxide has high electronic conductivity, and the heterojunction formed with the electrode surface can significantly reduce the reaction barrier in the reaction process of the electrode material, thereby improving the reaction activity of the electrode. The strontium iron perovskite structure metal oxide has high electrochemical catalytic activity, which can greatly improve the catalytic performance of the electrode material. In the working process of the obtained composite electrode, a small amount of iron-based perovskite material loaded on the surface will be dissolved into the vanadium flow battery electrolyte. The dissolved iron ions can promote the working performance of the vanadium flow battery.

[0012] 2. The strontium iron perovskite structure metal oxide is selected as the electrode surface loading material, which has good coating effect on the electrode, avoids oxidation and deactivation of the electrode material during use, prevents corrosion of the electrode material, improves the oxidation resistance and electrocatalytic performance of the electrode material, and greatly improves the operation efficiency and service life of the vanadium flow battery electrode stack.

[0013] In some embodiments, in step (1), the iron salt comprises at least one of ferric nitrate hexahydrate, ferric chloride or ferric perchlorate; the strontium salt comprises at least one of strontium nitrate, strontium chloride or strontium chlorate; the solvent comprises water; the dispersant comprises at least one of butanediol, ethanol or ethylene glycol; and the complexing agent comprises at least one of EDTA or citric acid.

[0014] In some embodiments, in step (1), the concentration of the metal ion complex in the precursor sol is 1-1.5 mol / L; the molar ratio of strontium ions to iron ions is 0.8-0.9:1; the molar ratio of metal ions to complexing agent in the precursor sol is 7-10:1, the metal ions being the sum of iron ions and strontium ions; and the mass ratio of the complexing agent to the dispersant is 4-6:1.

[0015] In some embodiments, in step (1), the heating temperature is 80-90℃, and the heating time is 4-8h.

[0016] In some embodiments, in step (2), the vanadium flow battery electrode substrate is a carbon electrode substrate, preferably at least one of a graphite electrode, a carbon fiber carbon stick, graphene, a carbon nanotube or a glassy carbon electrode.

[0017] In some embodiments, in step (2), the single impregnation amount of the impregnation is 5-8 ml of the precursor sol per cm 3 a vanadium flow battery electrode substrate; the impregnation is a titration impregnation; and the number of times of impregnation is 1-3 times.

[0018] In some embodiments, in step (3), the freeze-drying temperature is 5-15℃, the freeze-drying time is 24-48h, and the freeze-drying pressure is -0.01 to -0.03 MP.

[0019] In some embodiments, in step (4), the heat treatment temperature is 600-650℃, the heat treatment time is 2-6h, the heat treatment rate is 3-8℃ / min, and the heat treatment atmosphere is a nitrogen atmosphere.

[0020] In some embodiments, in step (4), constant temperature thermal diffusion is performed before the heat treatment, the constant temperature thermal diffusion temperature is 80-120℃, and the constant temperature thermal diffusion time is 2-6h; annealing is performed after the heat treatment, the annealing temperature is 200-275℃, the annealing rate is 8-12℃ / min, and the annealing holding time is 1-3h, followed by natural cooling; the natural cooling atmosphere is a nitrogen atmosphere; and the nitrogen atmosphere flow rate is 60-100 mL / min.

[0021] In some embodiments, in step (4), the molar ratio of strontium ions to iron ions in the vanadium flow battery composite electrode is 0.8-0.9:1. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is the Raman spectrum test pattern of the graphite carbon felt for vanadium flow battery before loading strontium iron perovskite structure metal oxide in Example 1.

[0023] Figure 2 is the Raman spectrum test pattern of the graphite carbon felt for vanadium flow battery after loading strontium iron perovskite structure metal oxide in Example 1. DETAILED DESCRIPTION

[0024] The embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings. The embodiments described below by reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0025] A method for improving the service life of a vanadium flow battery electrode according to an embodiment of the present application includes the following steps:

[0026] (1) adding iron salt and strontium salt into a solvent, then adding a dispersing agent and a complexing agent, and heating and stirring to obtain a precursor sol;

[0027] (2) using the precursor sol to impregnate a vanadium flow battery electrode substrate;

[0028] (3) freeze-drying the impregnated vanadium flow battery electrode substrate to obtain a vanadium flow battery electrode composite;

[0029] (4) heat treating the vanadium flow battery electrode composite to obtain a vanadium flow battery composite electrode.

[0030] The method for prolonging the electrode life of a vanadium flow battery in the embodiment of the application adopts a freeze-drying process, and uses capillary action for adsorption and film formation during the impregnation process. In the process of removing solvent molecules, the precursor material can be uniformly distributed on the electrode substrate. The heat treatment process enables the strontium iron calcium perovskite structure metal oxide to form a stable phase structure. At the same time, the metal oxide is loaded on the carbon electrode substrate. Carbon has reducing properties, and the ion oxygen in the metal oxide has oxidizing properties. The two are easy to combine, so that the oxygen ions in the iron oxygen ion bond of the metal oxide combine with the carbon-carbon bond of the vanadium flow battery electrode to form a fixed heterojunction structure, achieving the process effect of self-assembly and composite film formation. The strontium iron calcium perovskite structure metal oxide has more intermetallic oxygen vacancy defects due to its unique crystal structure. The existence of these defects can effectively lead out the combined oxygen ions on the surface of the electrode material during the electrochemical reaction process, and can greatly avoid the phenomenon of oxidation corrosion and deactivation of the electrode material due to the combination of the electrode material and oxygen ions. The strontium iron calcium perovskite structure metal oxide has high electronic conductivity, and the heterojunction formed with the electrode surface can greatly reduce the reaction barrier in the reaction process of the electrode material, improve the reaction activity of the electrode, and greatly improve the catalytic performance of the electrode material. The surface of the obtained composite electrode will have a small amount of iron-based perovskite material loaded into the vanadium flow battery electrolyte during the working process. The dissolved iron ions can promote the working performance of the vanadium flow battery. In the embodiment of the application, the strontium iron calcium perovskite structure metal oxide is selected as the electrode surface loading material, which has a good coating effect on the electrode, avoids oxidation and deactivation of the electrode material during use, prevents corrosion of the electrode material, improves the oxidation resistance and electrocatalytic performance of the electrode material, and greatly improves the operating efficiency and service life of the vanadium flow battery electrode stack.

[0031] In some embodiments, in step (1), the iron salt includes at least one of ferric nitrate hexahydrate, ferric chloride or ferric perchlorate; the strontium salt includes at least one of strontium nitrate, strontium chloride or strontium chlorate; the solvent includes water; the dispersant includes at least one of butanediol, ethanol or ethylene glycol, preferably butanediol; and the complexing agent includes at least one of EDTA or citric acid, preferably EDTA. In the embodiment of the application, the selection of the dispersant and the complexing agent is crucial to the film formation effect of the precursor, and is conducive to the uniform and stable loading of the strontium iron calcium perovskite structure metal oxide on the electrode surface. Among them, the dispersant butanediol has better solubility and lower volatility, and can achieve better dispersion effect, and the complexing agent EDTA has better complexing rate.

[0032] In some embodiments, in the step (1), the concentration of the metal ion complex in the precursor sol is 1-1.5 mol / L, optionally 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L; the molar ratio of strontium ion to iron ion is 0.8-0.9:1, optionally 0.83:1, 0.85:1, 0.87:1; the molar ratio of metal ion to complexing agent in the precursor sol is 7-10:1, optionally 8:1, 8.5:1, 9:1, wherein the metal ion is the total of iron ion and strontium ion; the mass ratio of the complexing agent to the dispersing agent is 4-6:1, optionally 5:1, 5.2:1, 5.5:1. In the embodiments of the present application, by further optimizing the amounts of metal ion, complexing agent and dispersing agent, the metal element distribution is more uniform, and the phase structure of the product is more stable.

[0033] In some embodiments, in the step (1), the heating temperature is 80-90℃, optionally 85℃, and the heating time is 4-8h, optionally 5h, 6h, 7h. In some embodiments, in the step (1), the heating is carried out by placing in an oil bath or a water bath; and the stirring rate is 70-90r / min. In the embodiments of the present application, the complexing reaction by heating obtains a sol with uniform distribution of metal elements, which is helpful for forming a film layer with good uniformity in the subsequent calcination process.

[0034] In some embodiments, in the step (2), the vanadium flow battery electrode substrate is a carbon electrode substrate, which is preferably at least one of graphite electrode, carbon fiber carbon stick, graphene, carbon nanotube or glassy carbon electrode, and is further preferably graphite carbon felt. In the embodiments of the present application, the strontium iron calcium titanate structure metal oxide as the carbon electrode surface loading material has a good coating effect on the electrode, which can avoid the oxidation deactivation of the electrode material during use, prevent the corrosion of the electrode material, improve the oxidation resistance and electrocatalytic performance of the electrode material, and greatly improve the operation efficiency and service life of the vanadium flow battery electrode stack.

[0035] In some embodiments, in the step (2), the single impregnation amount of the impregnation is 5-8ml of the precursor sol per cm 3The vanadium flow battery electrode substrate; the impregnation is titration impregnation; the impregnation times are 1-3 times. In some embodiments, in the step (2), the impregnation utilizes a constant temperature titration device to perform titration impregnation. In the embodiments of the present application, when the impregnation amount is too high, the voids of the carbon electrode are easily blocked, which seriously reduces the specific surface area of the electrode reaction; when the impregnation amount is too low, a homogeneous and homogeneous film layer cannot be formed. The impregnation is repeated for 1-3 times, which can form a film layer with better performance without significantly affecting the specific surface area of the electrode reaction. In the embodiments of the present application, titration impregnation is adopted, and the process flow is shorter and the operation is simpler.

[0036] In some embodiments, in the step (3), the temperature of the freeze-drying is 5-15℃, optionally 8℃, 10℃, 12℃, the time of the freeze-drying is 24-48h, optionally 30h, 36h, 40h, 45h, and the pressure of the freeze-drying is -0.01 to -0.03MP, optionally -0.02MP. In the embodiments of the present application, the freeze-drying process is adopted, and the adsorption film forming is performed by capillary action. In the process of removing solvent molecules, the precursor material can be uniformly distributed on the electrode substrate. By optimizing the temperature, time and pressure of freeze-drying, the uniformity of the formed film layer can be optimized, and the decay of electrochemical performance caused by agglomeration and accumulation can be avoided.

[0037] In some embodiments, in the step (4), the temperature of the heat treatment is 600-650℃, optionally 625℃, the time of the heat treatment is 2-6h, optionally 3h, 4h, 5h, the heating rate of the heat treatment is 3-8℃ / min, optionally 5℃ / min, 7℃ / min, and the atmosphere of the heat treatment is nitrogen atmosphere. In some embodiments, before the heat treatment, constant temperature thermal diffusion is performed, the temperature of the constant temperature thermal diffusion is 80-120℃, optionally 90℃, 100℃, the time of the constant temperature thermal diffusion is 2-6h, optionally 3h, 4h, 5h; after the heat treatment, annealing is performed, the annealing temperature is 200-275℃, optionally 225℃, 250℃, the annealing rate is 8-12℃ / min, preferably 10℃ / min, the holding time of the annealing is 1-3h, preferably 2h, and then natural cooling is performed; the atmosphere of the natural cooling is nitrogen atmosphere; the flow rate of the nitrogen atmosphere is 60-100mL / min, preferably 80mL / min. In the embodiments of the present application, the heat treatment process enables the strontium iron calcium titanate structure metal oxide to form a stable phase structure, and enables the oxygen ions in the iron oxygen ion bond of the metal oxide to combine with the carbon-carbon bond of the carbon flow battery electrode to form a fixed heterojunction structure. When the heat treatment temperature is too low, the metal oxide film layer with a good phase structure cannot be formed; when the heat treatment temperature is too high, the metal oxide is prone to sintering and clumping. When the heating rate of the heat treatment is too high, the metal oxide film layer is prone to separation from the substrate and peeling off; when the heating rate is too low, the time is long and energy is wasted. In the embodiments of the present application, the constant temperature thermal diffusion can remove the crystal water. Annealing is beneficial to the further growth of the crystal. When the annealing rate is too high, the crystal film is prone to cracking; when the annealing rate is too low, the time is long and energy is wasted; when the holding time of the annealing is too short, the bubbles in the crystal gap are not completely removed, and the crystal film is prone to cracking in the later period; when the holding time is too long, the time is long and the cost is high.

[0038] In some embodiments, in the step (4), the molar ratio of strontium ions to iron ions in the vanadium flow battery composite electrode is 0.8-0.9:1, optionally 0.83:1, 0.85:1, 0.87:1. In the embodiments of the present application, strontium nitrate is selected as the A-site ion of the perovskite structure, and by optimizing the molar ratio of strontium ions to iron ions, the partial defects of A-site elements can increase the oxygen vacancy defect content of the perovskite structure metal oxide, effectively guide the combined oxygen ions on the surface of the electrode material in the electrochemical reaction process, avoid the oxidation corrosion and inactivation of the electrode material due to the combination with oxygen ions, and thus improve the electrochemical performance of the metal oxide.

[0039] The present application will be described in detail below with reference to specific embodiments, and it should be noted that these embodiments are merely descriptive and do not limit the present application in any way.

[0040] Example 1

[0041] 1. A method for preparing a vanadium redox flow battery composite electrode supported on a strontium-iron-perovskite structure metal oxide, comprising the following steps:

[0042] (1) Strontium nitrate and ferric nitrate hexahydrate were added to water and stirred with a magnetic stirrer to dissolve them completely. Butanediol was added as a dispersant and EDTA as a complexing agent. The mass ratio of EDTA to butanediol was 5.2:1, the molar ratio of iron ions and strontium ions to EDTA was 8.5:1, and the molar ratio of strontium ions to iron ions was 0.8:1. The addition was carried out under magnetic stirring at a constant speed. The resulting solution was placed in a water bath and stirred continuously at 90°C for 4 hours to obtain a precursor sol. The concentration of the metal ion complex in the precursor sol was 1.5 mol / L.

[0043] (2) Using the precursor sol as the impregnation liquid and the vanadium redox battery graphite carbon felt as the impregnation substrate, the impregnation was performed using a constant temperature titration device. The single impregnation volume was 8 ml of precursor sol / cm³. 3 The vanadium redox flow battery electrode substrate is impregnated twice.

[0044] (3) The graphite carbon felt impregnated with the precursor sol was placed in a freeze dryer for freeze drying. The drying state was a vacuum environment, the freeze drying temperature was 10 degrees Celsius, the freeze drying time was 36 hours, and the freeze drying pressure was -0.02 MPa.

[0045] (4) The obtained freeze-dried vanadium redox flow battery electrode composite was placed in a tube furnace under a nitrogen atmosphere. It was first subjected to isothermal thermal diffusion at 80°C for 3 hours. The heat treatment temperature was 650°C, the heating rate was 5°C / min, and the heat treatment time was 4 hours. Then, it was annealed at a rate of 10°C / min to 200°C and held for 2 hours. Then, it was naturally cooled under a nitrogen atmosphere to obtain the vanadium redox flow battery composite electrode, wherein the molar ratio of strontium ions to iron ions was 0.8:1.

[0046] 2. Raman spectroscopy test

[0047] Raman spectroscopy is primarily used for determining and confirming the composition of substances. Confocal micro-Raman optics systems have a wide operating wavenumber range, enabling microscopic detection of sample surfaces at the μm level and allowing for microscopic imaging measurements. Its basic working principle is based on determining the structure of the scattering molecules using Raman shifts. Raman shifts depend on changes in molecular vibrational energy levels; molecules with different structures exhibit corresponding molecular vibrations, which is the basis for Raman spectroscopy's qualitative characterization of molecular structure.

[0048] Figure 1This is the Raman spectrum of the graphite carbon felt used in the vanadium redox flow battery before loading the strontium-iron-perovskite structured metal oxide in Example 1. It can be seen that... Figure 1 The graphite carbon felt exhibits distinct carbon fiber peaks with a wide peak range, indicating that it has a high specific surface area and porosity, which facilitates the full wetting and loading of the impregnating precursor colloid.

[0049] Figure 2 This is the Raman spectrum of the graphite carbon felt electrode used in vanadium redox flow batteries after loading with strontium-iron-perovskite structured metal oxide in Example 1. It can be seen that no obvious Raman peaks of the carbon structure can be observed on the composite electrode after loading with the metal oxide matrix. This is because the electrode surface after loading with strontium-iron-perovskite structured metal oxide is well coated with the strontium-iron-perovskite structured metal oxide, making it impossible to detect the structural peaks of the graphite carbon felt in the Raman spectrum. This indicates that the surface of the composite electrode obtained in Example 1 is well coated and stably formed, which will greatly improve the electrochemical corrosion resistance of the graphite carbon felt electrode used in vanadium redox flow batteries.

[0050] 3. The electrochemical performance test results of the vanadium redox flow battery composite electrode are shown in Table 1.

[0051] Example 2

[0052] The preparation method is the same as that of the vanadium redox flow battery composite electrode in Example 1, except that in step (4), the heat treatment temperature is 625°C and the annealing temperature is 250°C.

[0053] Example 3

[0054] The method is the same as that used in Example 1 for preparing the vanadium redox flow battery composite electrode, except that in step (4), the heat treatment temperature is 600°C and the annealing temperature is 275°C.

[0055] Comparative Example 1

[0056] The method is the same as that used in Example 1 for preparing the vanadium redox flow battery composite electrode, except that: in step (3), freeze drying is not performed, and the graphite carbon felt impregnated with the precursor sol is placed in a dryer and dried at 80°C.

[0057] Comparative Example 2

[0058] The method is the same as that used in Example 1 for preparing the vanadium redox flow battery composite electrode, except that the freeze-drying temperature in step (3) is 25 degrees Celsius, the freeze-drying time is 10 hours, and the freeze-drying pressure is -0.05 MPa.

[0059] Comparative Example 3

[0060] The method is the same as that used in Example 1 for preparing the vanadium redox flow battery composite electrode, except that in step (1), strontium nitrate and cobalt nitrate are added to water, and the molar ratio of strontium ions to cobalt ions is 0.8:1.

[0061] Comparative Example 4

[0062] The method is the same as that used in Example 1 for preparing the vanadium redox flow battery composite electrode, except that in step (1), lanthanum nitrate and ferric nitrate hexahydrate are added to water, and the molar ratio of lanthanum ions to iron ions is 0.8:1.

[0063] Comparative Example 5

[0064] The method is the same as that used in Example 1 for preparing the vanadium redox flow battery composite electrode, except that in step (1), lanthanum nitrate and cobalt nitrate are added to water, and the molar ratio of lanthanum ions to cobalt ions is 0.8:1.

[0065] Comparative Example 6

[0066] The preparation method is the same as that of the vanadium redox flow battery composite electrode in Example 1, except that propylene glycol is added as a dispersant and citric acid monohydrate as a complexing agent in step (1).

[0067] Table 1. Zview Fitting Data Results During Electrode Operation

[0068]

[0069]

[0070] As shown in Table 1, Rs represents the solution resistance, which is the impedance between the working electrode and the counter electrode. The Rs of the electrode loaded with strontium-iron-perovskite metal oxide is lower than that of the electrode before loading, indicating that the loaded electrode has lower system resistance, lower charge transfer resistance (Rct), and lower solution resistance (Rs), proving that the loaded electrode has higher electronic conductivity in the electrolyte. Diffusion resistance is the impedance to diffusion to the reaction interface, also called concentration polarization resistance. The diffusion resistance at each step of the electrode loaded with strontium-iron-perovskite metal oxide is lower than that of the electrode before loading, proving that it has higher ion conductivity. Improved ion conductivity will greatly enhance its oxygen ion conduction rate and efficiency, effectively conducting oxygen ions from the carbon electrode surface, greatly improving the electrode's resistance to oxygen corrosion, and extending its service life. By comparing with the comparative example, it can be seen that the composite electrode of this invention has the best electrochemical performance and will maximize the electrode's service life.

[0071] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0072] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for improving the electrode life of a vanadium redox flow battery, characterized in that, Includes the following steps: (1) Add iron salt and strontium salt to a solvent, then add a dispersant and a complexing agent, heat and stir to obtain a precursor sol; the dispersant includes at least one of butanediol, ethanol and ethylene glycol; the complexing agent includes at least one of EDTA and citric acid; the concentration of the metal ion complex in the precursor sol is 1-1.5 mol / L; (2) The vanadium redox flow battery electrode substrate is impregnated with the precursor sol; the vanadium redox flow battery electrode substrate is a carbon electrode substrate; (3) The impregnated vanadium redox flow battery electrode substrate is freeze-dried to obtain a vanadium redox flow battery electrode composite. (4) The vanadium redox flow battery electrode composite is heat-treated to obtain a vanadium redox flow battery composite electrode; the heat treatment temperature is 600-650 ℃.

2. The method for improving the electrode life of a vanadium redox flow battery according to claim 1, characterized in that, In step (1), the iron salt includes at least one of ferric nitrate hexahydrate, ferric chloride, or ferric perchlorate; the strontium salt includes at least one of strontium nitrate, strontium chloride, or strontium chlorate; and the solvent includes water.

3. The method for improving the electrode life of a vanadium redox flow battery according to claim 1, characterized in that, In step (1), the molar ratio of strontium ions to iron ions is 0.8-0.9:1; the molar ratio of metal ions to complexing agent in the precursor sol is 7-10:1, and the metal ions are the sum of iron ions and strontium ions; the mass ratio of the complexing agent to the dispersant is 4-6:

1.

4. The method for improving the electrode life of a vanadium redox flow battery according to claim 1, characterized in that, In step (1), the heating temperature is 80-90℃ and the heating time is 4-8h.

5. The method for improving the electrode life of a vanadium redox flow battery according to claim 1, characterized in that, In step (2), the carbon electrode substrate is at least one of graphite electrode, carbon fiber carbon adhesive, graphene, carbon nanotube or glassy carbon electrode.

6. The method for improving the electrode life of a vanadium redox flow battery according to claim 1, characterized in that, In step (2), the single impregnation volume is 5-8 ml of precursor sol / cm³. 3 Vanadium redox battery electrode substrate; the impregnation is titration impregnation; the impregnation is performed 1-3 times.

7. The method for improving the electrode life of a vanadium redox flow battery according to claim 1, characterized in that, In step (3), the freeze-drying temperature is 5-15℃, the freeze-drying time is 24-48h, and the freeze-drying pressure is -0.01 to -0.03MPa.

8. The method for improving the electrode life of a vanadium redox flow battery according to claim 1, characterized in that, In step (4), the heat treatment time is 2-6 hours, the heating rate is 3-8℃ / min, and the atmosphere for the heat treatment is nitrogen atmosphere.

9. The method for improving the electrode life of a vanadium redox flow battery according to claim 1, characterized in that, In step (4), before the heat treatment, constant temperature heat diffusion is performed at a temperature of 80-120 ℃ and a time of 2-6 h; after the heat treatment, annealing is performed at a temperature of 200-275 ℃ at a rate of 8-12 ℃ / min and a holding time of 1-3 h, followed by natural cooling; the atmosphere for natural cooling is a nitrogen atmosphere; the nitrogen atmosphere is introduced at a rate of 60-100 mL / min.

10. The method for improving the electrode life of a vanadium redox flow battery according to claim 1, characterized in that, In step (4), the molar ratio of strontium ions to iron ions in the vanadium redox flow battery composite electrode is 0.8-0.9:1.

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