A flow battery

Abstract

The application discloses a kind of liquid flow battery, electrolyte uses VO 2+ Positive electrolyte and Cd 2+ Negative electrolyte, and places cadmium plate on negative electrode.Preparation negative electrolyte, concentrated sulfuric acid or concentrated sulfuric acid and concentrated hydrochloric acid mixed solution is added dropwise to stirring deionized water, obtains uniform sulfuric acid aqueous solution bottom liquid or mixed acid bottom liquid, then battery grade crystal grain is added to acid bottom liquid, stirs until solid is completely dissolved, after cooling to room temperature, it is transferred to volumetric flask and constant volume, obtains Cd 2+ Negative electrolyte.The application overcomes the problems of hydrogen evolution reaction and low energy efficiency in the prior art liquid flow battery technology, improves the energy efficiency of the liquid flow battery, and the highest energy efficiency can reach more than 93%.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, and in particular relates to a flow battery. Background Technology

[0002] Flow batteries possess advantages such as long cycle life, flexible design, safety, reliability, and rapid response, making them promising for large-scale energy storage applications. Among them, the all-vanadium redox flow battery is one of the technologies with the fastest industrialization progress. The core reasons for the current low energy efficiency of flow batteries are multifaceted: First, significant electrode polarization losses occur, with slow negative electrode kinetics and high reaction resistance in some positive electrode pairs. This, combined with activation polarization and concentration polarization, leads to a widening of the charge-discharge voltage difference. Second, insufficient electrolyte mass transfer efficiency hinders the diffusion of active materials in the flow channels and electrode pores, resulting in uneven local concentrations and reduced reaction utilization. Third, limited electrode catalytic activity; traditional carbon-based electrodes lack sufficient catalytic sites for redox reactions, exacerbating reaction lag. Fourth, side reactions exist in some systems, leading to charge loss and further reducing energy conversion efficiency. These problems collectively constrain the performance upgrade of flow batteries.

[0003] Vanadium redox flow batteries, due to their negative electrode V 2+ / V 3+ Insufficient redox kinetics, manifested as low exchange current density and high activation polarization, limit the energy efficiency of batteries at high current densities, making it difficult to further improve power density. Existing technologies for addressing this problem all have significant shortcomings. For example, while doping carbon-based electrodes with noble metals or loading them with nanoparticles can improve catalytic activity, noble metals are expensive, particles are prone to dissolution and aggregation, resulting in poor long-term cycle stability and potential membrane blockage. Adding inorganic or organic additives to the electrolyte can slightly improve ion mass transfer, but these additives are prone to loss, excessive addition can increase ionic strength and decrease ion mobility, and they cannot suppress hydrogen evolution side reactions. Developing novel electrode materials such as MOF-derived carbon and MXene can improve reaction kinetics, but these suffer from complex preparation processes, high scalability costs, and easy degradation in strongly acidic systems. Therefore, current improvement solutions have many shortcomings and cannot fundamentally solve the problem, failing to meet the demands of high performance and low cost for large-scale applications. Summary of the Invention

[0004] The purpose of this invention is to provide a flow battery to overcome the problems of hydrogen evolution reaction and low energy efficiency in existing flow battery technology, and to improve the energy efficiency and power density of flow batteries.

[0005] To address the aforementioned technical problems, the present invention provides a flow battery, comprising a positive electrode, a negative electrode, a proton exchange membrane, and a VOCs. 2+ Positive electrode electrolyte, Cd2+ The negative electrode electrolyte is prepared by placing a cadmium plate on the negative electrode, wherein Cd... 2+ The preparation steps of the negative electrode electrolyte are as follows:

[0006] S21. Add deionized water to a polytetrafluoroethylene beaker and stir continuously at room temperature. Then, add concentrated sulfuric acid or a mixed solution dropwise to the stirred deionized water and continue stirring to obtain a uniform sulfuric acid aqueous solution or a mixed acid solution.

[0007] S22, battery level Add the crystals to the base liquid and stir until the solid is completely dissolved. Continue stirring to dissolve the Cd. 2+ With ligand Cl - , The solvent water molecules are fully combined, and then cooled to room temperature to obtain a colorless and transparent solution;

[0008] S23, transfer the colorless, transparent solution to a volumetric flask and dilute to volume. After shaking well, obtain Cd. 2+ Negative electrode electrolyte.

[0009] Furthermore, in S21, the concentrated sulfuric acid is taken as 20.4~40.8 mL, and in S22, the battery grade... The grain size is 17.12~34.25g.

[0010] Furthermore, in step S21, the mixed solution is concentrated sulfuric acid and concentrated hydrochloric acid, with 20.4~40.8 mL of concentrated sulfuric acid and 10.4~41.7 mL of concentrated hydrochloric acid. In step S22, the battery-grade... The grain size is 17.12~34.25g.

[0011] Furthermore, the Cd 2+ In the negative electrode electrolyte, the concentration of total dissolved cadmium is 0.3~0.6 mol / L, H + The concentration is 3~8 mol / L.

[0012] Furthermore, in step S21, during the dropwise addition of concentrated sulfuric acid or mixed solution, the solution temperature is controlled at 30~40℃.

[0013] The proton exchange membrane needs to be immersed in deionized water for 1 to 1.5 hours at 60 to 80°C, then transferred to a 1 to 2 mol / L H2SO4 solution for 1.5 to 2 hours at 60 to 80°C, and finally soaked in deionized water at room temperature for later use.

[0014] Cadmium plates need to be polished until they are shiny and free of scratches, then immersed in 0.5~1 mol / L HCl solution for 30~40 seconds for acid washing. After taking them out, rinse them with deionized water immediately, let them dry, and then seal them for storage.

[0015] VO2+ The preparation steps of the positive electrode electrolyte are as follows:

[0016] S11. Add deionized water to a polytetrafluoroethylene beaker and stir continuously at room temperature. Then, add concentrated sulfuric acid dropwise to the stirred deionized water and stir to obtain a uniform sulfuric acid aqueous solution.

[0017] S12, add battery-grade VOSO4 crystals to the sulfuric acid aqueous solution base, stir until the solid is completely dissolved to obtain a bright blue solution, continue stirring to fully mix the system, and then cool naturally to room temperature;

[0018] S13, after cooling to room temperature, transfer the entire bright blue solution to a volumetric flask and dilute to volume. Shake well to obtain a homogeneous VO solution. 2+ Positive electrode electrolyte.

[0019] Furthermore, the VO 2+ In the positive electrode electrolyte, VO 2+ The concentration is 1~2 mol / L, and the sulfuric acid concentration is 3~4 mol / L.

[0020] The beneficial effects of this invention are:

[0021] 1. The vanadium-cadmium redox flow battery provided by this invention has a significantly higher energy efficiency than other flow battery systems due to the rapid kinetic reaction of the cadmium anode.

[0022] 2. The cadmium negative electrode in this invention has a high hydrogen evolution overpotential, which fully ensures that the battery can operate stably under high voltage conditions and improves the power density of the flow battery.

[0023] 3. This invention adopts the process of adding a zinc plate in zinc-based flow batteries. After adding a cadmium plate, hydrogen evolution is further suppressed, cadmium dendrite growth is suppressed, and the cycle life of the battery is extended.

[0024] 4. The vanadium-cadmium redox flow battery of the present invention has low cost, convenient operation and maintenance, and inherits the high safety of flow batteries without thermal runaway. It is a high-quality system that can be adapted to large-scale electrochemical energy storage. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of the vanadium-cadmium redox flow battery of the present invention.

[0027] Figure 2The cyclic voltammetry curves of the cadmium negative electrode electrolyte in Example 1 of this invention are within 20 mV / s.

[0028] Figure 3 These are the electrochemical test results of the vanadium-cadmium redox flow battery assembled in Example 1 of this invention and the all-vanadium redox flow battery assembled in Comparative Example 1.

[0029] Figure 4 The vanadium-cadmium redox flow batteries assembled in Example 1 and Comparative Example 2 of this invention operate at 100 mA / cm². 2 The first cycle charge-discharge capacity-voltage curve under current density cyclic testing.

[0030] Figure 5 The vanadium-cadmium redox flow battery assembled in Embodiment 1 of this invention operates at 100 mA / cm². 2 Results of cyclic testing at current density.

[0031] Figure 6 The vanadium-cadmium redox flow battery assembled in Embodiment 1 of this invention operates at 300 mA / cm². 2 Results of cyclic testing at current density.

[0032] Figure 7 The vanadium-cadmium redox flow battery assembled in Embodiment 1 of this invention operates at 500 mA / cm². 2 Results of cyclic testing at current density.

[0033] Figure 8 The vanadium-cadmium redox flow batteries assembled in Examples 1, 2, 3, 4, 5, and 6 of this invention operate at 100 mA / cm². 2 Energy efficiency test results at current density.

[0034] Figure 9 The vanadium-cadmium redox flow batteries assembled in Examples 1, 2, 3, 4, 5, and 6 of this invention operate at 100 mA / cm². 2 Capacity decay rate test results under current density.

[0035] Figure 10 The vanadium-cadmium redox flow battery assembled in Embodiment 2 of this invention operates at 100 mA / cm². 2 Results of cyclic testing at current density.

[0036] Figure 11 The vanadium-cadmium redox flow battery assembled in Embodiment 3 of this invention operates at 100 mA / cm². 2 Results of cyclic testing at current density.

[0037] Figure 12 The vanadium-cadmium redox flow battery assembled in Embodiment 4 of this invention operates at 100 mA / cm². 2 Results of cyclic testing at current density.

[0038] Figure 13 The vanadium-cadmium redox flow battery assembled in Embodiment 5 of this invention operates at 100 mA / cm². 2 Results of cyclic testing at current density.

[0039] Figure 14 The vanadium-cadmium redox flow battery assembled in Embodiment 6 of this invention operates at 100 mA / cm². 2 Results of cyclic testing at current density.

[0040] Figure 15 The vanadium-cadmium redox flow battery assembled in Embodiment 7 of this invention operates at 100 mA / cm². 2 Results of cyclic testing at current density.

[0041] Figure 16 This is a scanning electron microscope (SEM) image of the surface of the negative electrode material after a complete charge following a test of the vanadium-cadmium redox flow battery assembled in Embodiment 1 of the present invention. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0043] An embodiment of the present invention provides a flow battery in which the positive electrode electrolyte is prepared using VOSO4 crystals. A negative electrode electrolyte was prepared by grain preparation, and a cadmium plate was placed on the negative electrode. The positive electrode electrolyte, negative electrode electrolyte, electrode materials, proton exchange membrane, and cadmium plate were then assembled to form a vanadium-cadmium redox flow battery. A schematic diagram of the prepared vanadium-cadmium redox flow battery is shown below. Figure 1 As shown, the specific preparation method is as follows:

[0044] S1, Preparation of the positive electrode electrolyte:

[0045] S11. Add 150 mL of deionized water to a polytetrafluoroethylene beaker and stir continuously at a stirring speed of 300-500 r / min at room temperature to ensure that the subsequently added concentrated sulfuric acid can be quickly and evenly dispersed in the solution, preventing the solution temperature from rising too high locally due to exothermic reactions. Then, measure 40.8-54.3 mL of 98% concentrated sulfuric acid and slowly add it dropwise along the beaker wall to the stirred deionized water. Continue stirring for 5-10 min to obtain a uniform sulfuric acid aqueous solution. Control the solution temperature at 30-40℃ during the dropwise addition process.

[0046] S12: Take 40.75~81.5g of battery-grade VOSO4 crystals and slowly add them to the sulfuric acid aqueous solution in 3~5 portions. After each addition, stir at 300~500 rpm until the solid is completely dissolved before adding the next batch. This is to avoid excessively high local vanadium ion concentration, which could lead to hydrolysis and the formation of vanadium hydroxide precipitate. After the VOSO4 is completely dissolved, a bright blue solution is obtained. Continue stirring at 300~500 rpm for 10~15 minutes to ensure thorough mixing, and then allow it to cool naturally to room temperature. During this process, the temperature should be maintained at 30~40℃.

[0047] S13. Transfer the entire bright blue solution, cooled to room temperature, to a 250 mL brown volumetric flask. Slowly add deionized water dropwise to the flask until it reaches the 250 mL mark. Stopper the flask, seal the opening with sealing film, and invert the flask to shake thoroughly, ensuring complete dispersion of vanadium ions in the sulfuric acid solution, thus obtaining a homogeneous VO4 solution. 2+ The positive electrode electrolyte, after measurement, contains VO 2+ The concentration is 1~2 mol / L, and the sulfuric acid concentration is 3~4 mol / L.

[0048] S2, Preparation of negative electrode electrolyte:

[0049] S21. Add 150 mL of deionized water to a polytetrafluoroethylene beaker and stir continuously at a stirring speed of 300-500 r / min at room temperature. Then measure 98% concentrated sulfuric acid or a mixed solution of concentrated sulfuric acid and concentrated hydrochloric acid (choosing a mixed acid can further improve the energy efficiency of the flow battery) and slowly add it dropwise along the beaker wall to the stirred deionized water. Then continue stirring for 5-10 min to obtain a uniform sulfuric acid aqueous solution or mixed acid solution. Control the solution temperature at 30-40℃ during the dropwise addition process.

[0050] If only 98% concentrated sulfuric acid is selected, measure 20.4~40.8 mL;

[0051] If a mixed solution of concentrated sulfuric acid and concentrated hydrochloric acid is chosen, measure 20.4~40.8 mL of 98% concentrated sulfuric acid and 10.4~41.7 mL of commercially available concentrated hydrochloric acid (36%~38% by mass) to control the H+ concentration in the mixed acid solution. + The concentration is between 3 and 8 mol / L. Below 3 mol / L, the electrolyte conductivity will be relatively low, the ohmic polarization will be large, and the energy efficiency will be reduced. Above 8 mol / L, the electrolyte viscosity will be large, which will lead to increased concentration polarization. At the same time, the higher starting voltage will lead to a decrease in discharge capacity.

[0052] S22, with a battery weight of 17.12~34.25g. The crystals were slowly added to the acid base solution in 3-4 batches, stirring until the solid was completely dissolved after each addition before adding the next batch. After all the crystals had dissolved, stirring was continued for 15-20 minutes to allow the Cd to dissolve. 2+ With ligand Cl - , The solvent water molecules fully combine to form stable solvated coordination complex ions, and then the solution is naturally cooled to room temperature. Because CdCl2 has high solubility in highly acidic mixtures, and H2O, Cl - Can quickly connect with Cd 2+ It forms complex ions, eliminating the risk of hydrolysis, so the solution remains colorless and transparent during the dissolution process.

[0053] The invention provided The amount of cadmium used is only within a safe range. In actual applications, because a cadmium plate is placed on the negative electrode, the cadmium in the battery is in an excessive state, hence the addition here. The amount of crystal grains has no effect on the final anti-cadmium flow battery; only the H2O needs to be controlled. + Concentration is sufficient.

[0054] S23. Transfer the cooled, colorless, transparent solution entirely to a 250 mL volumetric flask, and slowly add deionized water dropwise to bring the volume to the 250 mL mark. Stopper the flask, invert it, and shake repeatedly to mix the Cd solution. 2+ Uniformly dispersed, Cd is obtained 2+ The negative electrode electrolyte, after testing, showed a total dissolved cadmium concentration of 0.3~0.6 mol / L. + The concentration is 3~8 mol / L.

[0055] S3, Preparation of electrode materials:

[0056] The carbon felt is immersed in a 1-2 mol / L H2SO4 solution and acidified in a water bath at 50-60℃ for 20-24 hours to remove surface ash and metal impurities, resulting in acid-washed carbon felt, which is used as the positive and negative electrode material of the battery. The surface of the cadmium plate is polished with sandpaper until it is bright and free of scratches to remove the oxide layer and surface burrs. The polished cadmium plate is then immersed in a 0.5-1 mol / L HCl solution for 30-40 seconds to remove residual metal debris and oxide film. After removal, it is immediately rinsed with deionized water, dried, and sealed for storage to prevent secondary oxidation, resulting in the treated cadmium plate, which is then placed on the negative electrode.

[0057] S4. Immerse the proton exchange membrane in deionized water and bathe it in a water bath at 60-80℃ for 1-1.5 hours. Then, transfer it to a 1-2 mol / L H2SO4 solution and bathe it in a water bath at 60-80℃ for 1.5-2 hours. Finally, soak it in deionized water at room temperature for later use.

[0058] S5 assembles positive and negative electrolytes, electrode materials, and a treated proton exchange membrane into a vanadium-cadmium redox flow battery.

[0059] Example 1

[0060] S1, Preparation of the positive electrode electrolyte:

[0061] S11. Add 150 mL of deionized water to a polytetrafluoroethylene beaker and stir continuously at 400 r / min at room temperature. Then, measure 40.8 mL of concentrated sulfuric acid and slowly add it dropwise along the beaker wall to the stirred deionized water. Continue stirring for 8 min to obtain a uniform sulfuric acid aqueous solution. Control the solution temperature at 35℃ during the dropwise addition process.

[0062] S12, take 60g of battery-grade VOSO4 crystals and slowly add them to the sulfuric acid aqueous solution in four portions. After each addition, stir at 400r / min until the solid is completely dissolved before adding the next batch. After the VOSO4 is completely dissolved, a bright blue solution is obtained. Continue stirring at 400r / min for 12 min to ensure the system is thoroughly mixed, and then allow it to cool naturally to room temperature. During this process, the temperature is maintained at 35℃.

[0063] S13. Transfer the entire bright blue solution, cooled to room temperature, to a 250 mL brown volumetric flask. Then, slowly add deionized water dropwise to the 250 mL mark, cap the flask, seal the opening with sealing film, invert the flask, and shake repeatedly to obtain a homogeneous VO solution. 2+ Positive electrode electrolyte.

[0064] S2, Preparation of negative electrode electrolyte:

[0065] S21. Add 150 mL of deionized water to a polytetrafluoroethylene beaker and stir continuously at 400 r / min at room temperature. Then measure 40.8 mL of 98% concentrated sulfuric acid and slowly add it dropwise along the beaker wall to the stirred deionized water. Continue stirring for 8 min to obtain a uniform sulfuric acid aqueous solution. Control the solution temperature at 35℃ during the dropwise addition process.

[0066] S22, 25.6 g battery grade The crystals were slowly added to the sulfuric acid aqueous solution in three portions. After all the crystals were completely dissolved, the mixture was stirred for 18 minutes to obtain a colorless and transparent solution. The solution was then allowed to cool naturally to room temperature.

[0067] S23. Transfer the cooled, colorless, transparent solution entirely to a 250 mL volumetric flask, and slowly add deionized water dropwise to bring the volume to the 250 mL mark. Stopper the flask, invert it, and shake repeatedly to obtain Cd. 2+ Negative electrode electrolyte.

[0068] S3, Preparation of electrode materials:

[0069] The carbon felt was immersed in a 1.5 mol / L H2SO4 solution and acidified in a water bath at 55°C for 22 hours. The surface of the cadmium plate was polished with sandpaper until it was smooth and free of scratches. Then, it was immersed in a 0.8 mol / L HCl solution for 35 seconds for acid washing. After removal, it was immediately rinsed with deionized water, dried, and sealed for storage. The treated cadmium plate was then placed on the negative electrode.

[0070] S4. Immerse the proton exchange membrane in deionized water and bathe it in a water bath at 70°C for 1.2 h. Then, transfer it to a 1.5 mol / L H2SO4 solution and bathe it in a water bath at 70°C for 1.7 h. Finally, place it in deionized water and soak it at room temperature for later use.

[0071] S5 assembles positive and negative electrolytes, electrode materials, and a treated proton exchange membrane into a vanadium-cadmium redox flow battery.

[0072] Measurements showed that the positive electrode electrolyte obtained in this embodiment contained VO 2+ The vanadium ion concentration is 1.5 mol / L, the sulfuric acid concentration is 3 mol / L, and the total dissolved cadmium concentration in the negative electrode electrolyte is 0.5 mol / L, while the H+ concentration is 6 mol / L.

[0073] Cyclic voltammetry tests were performed on the negative electrode electrolyte of this embodiment using a mercurous sulfate electrode, with a test range of -1.35 to -1V (vs. Hg / Hg2SO4). This range did not exceed the stable potential range of the electrode, and no side reactions occurred. The test results are as follows: Figure 2 As shown. Considering the symmetry of the peak shape and the magnitude of the potential shift, the combined influence of diffusion and surface nucleation processes indicates that the deposition / dissolution process of Cd exhibits good electrochemical reversibility in this system.

[0074] Electrochemical tests were conducted on the vanadium-cadmium redox flow battery obtained in this embodiment at different current densities. The test results for coulombic efficiency, average energy efficiency, and capacity retention are as follows: Figure 3 As shown, at 100mA / cm 2 The first charge-discharge capacity-voltage curve of the current density cycle test is shown below. Figure 4 As shown, 100mA / cm 2 300mA / cm 2 500mA / cm 2 The efficiency graphs for cyclic testing at current density are as follows: Figures 5-7 As shown. At 100mA / cm 2At the specified current density, with the charging cutoff voltage set to 1.9V, no bubbles were generated in the negative electrolyte storage tank, indicating a significant effect in suppressing hydrogen evolution. The average coulombic efficiency after 350 cycles was 98.87%, the average energy efficiency was 91.26%, and the capacity retention was 65.78%. At 300 mA / cm², the performance was as follows: 2 At the current density, the average coulombic efficiency after 5000 cycles is 98.63%, the average energy efficiency is 80.12%, and the average voltage efficiency is 81.23%; at 500 mA / cm², the average energy efficiency is 98.63%, the average energy efficiency is 80.12%, and the average voltage efficiency is 81.23%. 2 At current density, the average coulombic efficiency over 5000 cycles is 97.04%, the average energy efficiency is 74.41%, and the average voltage efficiency is 76.68%.

[0075] The vanadium-cadmium redox flow battery obtained in this embodiment was tested for rate performance at an initial 100 mA / cm. 2 During this phase, the coulombic efficiency stabilizes at 98-100%, charge transfer remains highly reversible, and there is almost no charge loss caused by side reactions; the energy efficiency is above 90%, and the voltage efficiency can reach 92%, indicating that the polarization loss of the battery is small, the interfacial performance between the electrode and the ion exchange membrane is excellent, and the reaction kinetics and mass transfer process are well matched. When the current density increases from 100 mA / cm², the efficiency of the battery is significantly improved. 2 Gradually increase to 500mA / cm 2 At that time, the coulombic efficiency remained in the range of 95-100%, at 500 mA / cm². 2 No significant attenuation was observed even at ultra-high current densities, indicating that the reversibility of charge transfer remained intact across the entire rate range. (100 mA / cm²) 2 At current density, the average energy efficiency is 92.94%, improved to 500 mA / cm². 2 The current density then decreased to 75%, with a gradual decline, reflecting that the system still possesses good polarization control capability at high rates; when the current density decreased from 500 mA / cm²... 2 It fell back to the initial 100 mA / cm 2 When the coulombic efficiency can be quickly restored to the initial level of 98~100%, the energy efficiency and voltage efficiency also recover to close to the initial value, proving that the polarization loss under high current density is completely reversible. No irreversible structural damage or degradation of active materials occurred in the electrode and ion exchange membrane. The vanadium-cadmium system flow battery has excellent rate recovery capability.

[0076] After the vanadium-cadmium redox flow battery obtained in this embodiment underwent its final full charge, the extracted negative electrode material was processed and subjected to SEM testing. The results are as follows: Figure 16 As shown, Figure 16The image clearly shows the directional stacking of lamellar deposits after charging of the cadmium anode. The raised areas are the exposed sides of densely packed lamellar layers, which are of uniform thickness and consistent orientation. This lamellar growth pattern indicates the presence of H2O and SO4. 2- Cl - with cd 2+ The formed complex ions alter the crystal growth energy barrier of cadmium, inducing the crystal to preferentially grow along low-energy crystal planes, ultimately forming a directionally stacked layered structure rather than random dendrites. Simultaneously, the current distribution on the electrode surface and the electrolyte flow state further enhance this banded layered morphology; the raised areas, with their uniform current density and ample mass transfer, promote the directional growth of the layers.

[0077] Example 2

[0078] S1, Preparation of the positive electrode electrolyte:

[0079] S11. Add 150 mL of deionized water to a polytetrafluoroethylene beaker and stir continuously at 300 r / min at room temperature. Then, measure 48 mL of concentrated sulfuric acid and slowly add it dropwise along the beaker wall to the stirred deionized water. Continue stirring for 5 min to obtain a uniform sulfuric acid aqueous solution. Control the solution temperature at 30℃ during the dropwise addition process.

[0080] S12, take 40.75g of battery-grade VOSO4 crystals and slowly add them to the sulfuric acid aqueous solution in three portions. After each addition, stir at 300r / min until the solid is completely dissolved. After the VOSO4 is completely dissolved, a bright blue solution is obtained. Continue stirring at 300r / min for 10min, and then allow it to cool naturally to room temperature. During this process, the temperature is maintained at 30℃.

[0081] S13. Transfer the entire bright blue solution, cooled to room temperature, to a 250 mL brown volumetric flask. Slowly add deionized water dropwise to the flask until it reaches the 250 mL mark. Stopper the flask, seal the opening with sealing film, and invert the flask to shake thoroughly, ensuring complete dispersion of vanadium ions in the sulfuric acid solution, thus obtaining a homogeneous VO4 solution. 2+ Positive electrode electrolyte.

[0082] S2, Preparation of negative electrode electrolyte:

[0083] S21. Add 150 mL of deionized water to a polytetrafluoroethylene beaker and stir continuously at 300 r / min at room temperature. Then, measure 40.8 mL of a mixed solution of concentrated sulfuric acid and 10.4 mL of concentrated hydrochloric acid and slowly add it dropwise along the beaker wall to the stirred deionized water. Continue stirring for 5 min to obtain a uniform mixed acid solution. Control the solution temperature at 30℃ during the dropwise addition process.

[0084] S22, 17.12g battery capacity The crystals were slowly added to the acidic solution in three portions. After all the crystals had dissolved, the solution was stirred for another 15 minutes. The solution was then allowed to cool naturally to room temperature, resulting in a cooled, colorless, and transparent solution.

[0085] S23. Transfer the cooled, colorless, transparent solution entirely to a 250 mL volumetric flask, and slowly add deionized water dropwise to bring the volume to the 250 mL mark. Stopper the flask, invert it, and shake repeatedly to mix the Cd solution. 2+ After uniform dispersion, Cd is obtained. 2+ Negative electrode electrolyte.

[0086] S3, Preparation of electrode materials:

[0087] The carbon felt was immersed in a 1 mol / L H2SO4 solution and acidified in a water bath at 50°C for 20 h to obtain acid-washed carbon felt, which was used as the positive and negative electrode materials of the battery. The surface of the cadmium plate was polished with sandpaper until it was bright and free of scratches. Then the polished cadmium plate was immersed in a 0.5 mol / L HCl solution for 30 s for acid washing. After taking it out, it was immediately rinsed with deionized water, dried, and sealed for storage to obtain the treated cadmium plate, which was placed on the negative electrode.

[0088] S4. Immerse the proton exchange membrane in deionized water and bathe it in a water bath at 60°C for 1 hour. Then, transfer it to a 1 mol / L H2SO4 solution and bathe it in a water bath at 60°C for 1.5 hours. Finally, place it in deionized water to soak at room temperature for later use.

[0089] S5 assembles positive and negative electrolytes, electrode materials, and a treated proton exchange membrane into a vanadium-cadmium redox flow battery.

[0090] Measurements showed that the positive electrode electrolyte obtained in this embodiment contained VO 2+ The concentration of cadmium in the negative electrode electrolyte is 0.3 mol / L, the concentration of sulfuric acid is 3.5 mol / L, and the concentration of total dissolved cadmium is 0.3 mol / L. + The concentration was 7.5 mol / L. The vanadium-cadmium redox flow battery obtained in this example operated at 100 mA / cm². 2 Electrochemical tests were performed at current density, and the results are as follows: Figure 10 As shown, the average coulombic efficiency over 150 cycles is 98.84%, the average energy efficiency is 91.70%, and the capacity retention rate is 83.99%.

[0091] Example 3

[0092] S1, Preparation of the positive electrode electrolyte:

[0093] S11. Add 150 mL of deionized water to a polytetrafluoroethylene beaker and stir continuously at 500 r / min at room temperature. Then, measure 54.3 mL of 98% concentrated sulfuric acid and slowly add it dropwise along the beaker wall to the stirred deionized water. Continue stirring for 10 min to obtain a uniform sulfuric acid aqueous solution. Control the solution temperature at 40℃ during the dropwise addition process.

[0094] S12, take 81.5g of battery-grade VOSO4 crystals and slowly add them to the sulfuric acid aqueous solution in 5 portions. After each addition, stir at 500r / min until the solid is completely dissolved. After the VOSO4 is completely dissolved, a bright blue solution is obtained. Continue stirring at 500r / min for 15min, and then allow it to cool naturally to room temperature. During this process, the temperature is maintained at 40℃.

[0095] S13. Transfer the entire bright blue solution, cooled to room temperature, to a 250 mL brown volumetric flask. Slowly add deionized water dropwise to the flask until it reaches the 250 mL mark. Stopper the flask, seal the opening with sealing film, and invert the flask to shake thoroughly, ensuring complete dispersion of vanadium ions in the sulfuric acid solution, thus obtaining a homogeneous VO4 solution. 2+ Positive electrode electrolyte.

[0096] S2, Preparation of negative electrode electrolyte:

[0097] S21. Add 150 mL of deionized water to a polytetrafluoroethylene beaker and stir continuously at 500 r / min at room temperature. Then, take a mixed solution of 40.8 mL of concentrated sulfuric acid and 41.7 mL of concentrated hydrochloric acid and slowly add it dropwise along the beaker wall to the stirred deionized water. Continue stirring for 10 min to obtain a uniform mixed acid solution. Control the solution temperature at 40℃ during the dropwise addition process.

[0098] S22, 34.25g battery capacity The crystals were slowly added to the acidic base solution in four portions. After all the crystals had dissolved, the solution was stirred for another 20 minutes. The solution was then allowed to cool naturally to room temperature, resulting in a cooled, colorless, and transparent solution.

[0099] S23. Transfer the cooled, colorless, transparent solution entirely to a 250 mL volumetric flask, and slowly add deionized water dropwise to bring the volume to the 250 mL mark. Stopper the flask, invert it, and shake repeatedly to mix the Cd solution. 2+ Uniformly dispersed, Cd is obtained 2+ Negative electrode electrolyte.

[0100] S3, Preparation of electrode materials:

[0101] The carbon felt was immersed in a 2 mol / L H2SO4 solution and acidified in a water bath at 60°C for 24 h to obtain acid-washed carbon felt, which was used as the positive and negative electrode materials of the battery. The surface of the cadmium plate was polished with sandpaper until it was bright and free of scratches. Then the polished cadmium plate was immersed in a 1 mol / L HCl solution for acid washing for 40 s. After taking it out, it was immediately rinsed with deionized water and dried to obtain the treated cadmium plate, which was placed on the negative electrode.

[0102] S4. Immerse the proton exchange membrane in deionized water and bathe it in a water bath at 80°C for 1.5 hours. Then, transfer it to a 2 mol / L H2SO4 solution and bathe it in a water bath at 80°C for 2 hours. Finally, place it in deionized water to soak at room temperature for later use.

[0103] S5 assembles positive and negative electrolytes, electrode materials, and a treated proton exchange membrane into a vanadium-cadmium redox flow battery.

[0104] Measurements showed that the positive electrode electrolyte obtained in this embodiment contained VO 2+ The concentration of cadmium in the negative electrode electrolyte is 0.6 mol / L, the concentration of sulfuric acid is 4 mol / L, and the concentration of total dissolved cadmium is 0.6 mol / L. + The concentration was 8 mol / L. The vanadium-cadmium redox flow battery obtained in this example operated at 100 mA / cm². 2 Electrochemical tests were performed at current density, and the results are as follows: Figure 11 As shown, the average coulombic efficiency over 150 cycles is 99.25%, the average energy efficiency is 91.79%, and the capacity retention rate is 83.17%.

[0105] Example 4

[0106] The difference from Example 1 is that: 20.4 mL of concentrated sulfuric acid was used in S21; and 17.12 g of battery-grade [substance] was used in S22. Grains.

[0107] Everything else is the same as in Example 1.

[0108] Measurements showed that the total dissolved cadmium concentration in the negative electrode electrolyte obtained in this embodiment was 0.3 mol / L. + The concentration was 3 mol / L. The vanadium-cadmium redox flow battery obtained in this example was tested at 100 mA / cm². 2 Electrochemical tests were performed at current density, and the results are as follows: Figure 12 As shown, the average coulombic efficiency over 150 cycles is 97.81%, the average energy efficiency is 90.16%, and the capacity retention rate is 82.37%.

[0109] Example 5

[0110] The difference from Example 1 is that in S21, a mixed acid solution of concentrated sulfuric acid and concentrated hydrochloric acid is selected, wherein the concentrated sulfuric acid is 20.4 mL and the hydrochloric acid is 20.83 mL.

[0111] Everything else is the same as in Example 1.

[0112] Measurements showed that the total dissolved cadmium concentration in the negative electrode electrolyte obtained in this embodiment was 0.5 mol / L. + The concentration was 4 mol / L. The vanadium-cadmium redox flow battery obtained in this example was tested at 100 mA / cm². 2 Electrochemical tests were performed at current density, and the results are as follows: Figure 13 As shown, within 250 cycles, the highest energy efficiency after battery activation and stabilization can reach 93.07%, the average coulombic efficiency is 98.4%, the average energy efficiency is 92.08%, and the capacity retention rate is 44.25%.

[0113] Example 6

[0114] The difference from Example 1 is that 30 mL of concentrated sulfuric acid is taken in S21.

[0115] Everything else is the same as in Example 1.

[0116] Measurements showed that the negative electrode electrolyte obtained in this embodiment contained H... + With a concentration of 4.42 mol / L, the vanadium-cadmium redox flow battery obtained in this example operates at 100 mA / cm². 2 Electrochemical tests were performed at current density, and the results are as follows: Figure 14 As shown, the average coulombic efficiency over 150 cycles is 99.34%, the average energy efficiency is 91.97%, and the average voltage efficiency is 92.59%.

[0117] Example 7

[0118] The difference from Example 1 is that in S21, a mixed acid solution of concentrated sulfuric acid and concentrated hydrochloric acid is selected, wherein 30 mL of concentrated sulfuric acid and 25 mL of hydrochloric acid are used.

[0119] Everything else is the same as in Example 1.

[0120] Measurements showed that the negative electrode electrolyte obtained in this embodiment contained H... + With a concentration of 5.62 mol / L, the vanadium-cadmium redox flow battery obtained in this example operates at 100 mA / cm². 2 Electrochemical tests were performed at current density, and the results are as follows: Figure 15 As shown, the average coulombic efficiency over 150 cycles is 99.31%, the average energy efficiency is 92.01%, and the average voltage efficiency is 92.65%.

[0121] Comparative Example 1

[0122] The difference from Example 2 is that the negative electrode electrolyte is replaced with the existing vanadium electrolyte, and finally assembled into a full vanadium redox flow battery.

[0123] Everything else is the same as in Example 2.

[0124] Electrochemical tests were conducted on the vanadium redox flow battery obtained in this comparative example at different current densities. The test results for coulombic efficiency, average energy efficiency, and capacity retention are as follows: Figure 3 As shown, the initial current density is set to 100 mA / cm². 2 The current density is increased by 1 time every 5 cycles, until the current density reaches 500 mA / cm². 2 The return current density is then 100 mA / cm². 2 Perform 5 more cycles. A comparison was made at the initial 100 mA / cm². 2 At the current density, the energy efficiency is below 90%, and the voltage efficiency is less than 88%, and the attenuation rate is much greater than in Example 2 as the current density increases; when the current density increases to 500 mA / cm², the energy efficiency is less than 90%, and the voltage efficiency is less than 88%, and the voltage efficiency decreases much more than in Example 2. 2 At that time, the energy efficiency had dropped to about 60%, and the voltage efficiency dropped significantly at the same time, reflecting that the polarization loss of the all-vanadium redox flow battery in Comparative Example 1 was serious. Whether it was ohmic polarization, activation polarization or concentration polarization, it was much greater than that in Example 2. This was due to the insufficient kinetics of the negative electrode electrochemical process, which further confirmed that its system had poor adaptability under high power conditions. The rate performance had multiple defects such as low energy efficiency level and fast decay, serious polarization loss and insufficient recovery ability.

[0125] Comparative Example 2

[0126] The difference from Example 1 is that 61.1 mL of concentrated sulfuric acid is taken in S21.

[0127] Everything else is the same as in Example 1.

[0128] Measurements showed that the negative electrode electrolyte obtained in this comparative example contained H... + The concentration was 9 mol / L. The vanadium-cadmium redox flow battery obtained in this comparative example operated at 100 mA / cm². 2 Electrochemical tests were conducted at a safe cutoff voltage, from Figure 4 The initial charge-discharge curves show that the battery's charge and discharge voltages have increased, while its charge and discharge capacity has decreased. The energy efficiency test results for this comparative example are as follows: Figure 8 As shown, the capacity retention test results are as follows: Figure 9 As shown, the average energy efficiency over 60 cycles was 92.54%, and the capacity retention decreased by 18.81%, which is significantly lower than the 12.63% decrease in capacity retention measured in Implementation 1. The capacity decay in this comparison is obvious.

[0129] Comparative Example 3

[0130] The difference from Example 1 is that 17 mL of concentrated sulfuric acid is taken in S21.

[0131] Everything else is the same as in Example 1.

[0132] The concentration of total dissolved cadmium in the negative electrode electrolyte obtained in this comparative example was determined to be 1 mol / L. + The concentration was 2.5 mol / L. Electrochemical tests were performed on the vanadium-cadmium redox flow battery obtained in this comparative example at 100 mA / cm². 2 The energy efficiency test results at current density are as follows: Figure 8 As shown, the capacity retention test results are as follows: Figure 9 As shown, the energy efficiency decreased significantly within 60 cycles, by approximately 3%, and the capacity retention decreased by 42%, indicating that the performance was significantly inferior to that of Example 1 in all aspects.

[0133] Comparative Example 4

[0134] The difference from Example 1 is that: in S21, a mixed acid solution of concentrated sulfuric acid and concentrated hydrochloric acid is selected, wherein 34 mL of concentrated sulfuric acid and 83.3 mL of concentrated hydrochloric acid are used.

[0135] Everything else is the same as in Example 1.

[0136] Measurements showed that the negative electrode electrolyte obtained in this embodiment contained H... + The concentration was 9 mol / L. Electrochemical tests were performed on the vanadium-cadmium redox flow battery obtained in this example at 100 mA / cm². 2 The energy efficiency test results at current density are as follows: Figure 8 As shown, the capacity retention test results are as follows: Figure 9 As shown, the energy efficiency fluctuates significantly within 60 cycles, with the maximum fluctuation being 4.82%, while the maximum fluctuation in Example 1 is only 0.02%, and the capacity retention rate also decreases relatively significantly, with a decrease of 34.07%.

[0137] Comparative Example 5

[0138] The difference from Example 1 is that in S21, a mixed acid solution of concentrated sulfuric acid and concentrated hydrochloric acid is selected, wherein 6.8 mL of concentrated sulfuric acid and 6.25 mL of concentrated hydrochloric acid are used.

[0139] Everything else is the same as in Example 1.

[0140] Measurements showed that the total dissolved cadmium concentration in the negative electrode electrolyte obtained in this embodiment was 1 mol / L. + The concentration was 1.3 mol / L. Electrochemical tests were performed on the vanadium-cadmium redox flow battery obtained in this example at 100 mA / cm². 2The energy efficiency test results at current density are as follows: Figure 8 As shown, the capacity retention test results are as follows: Figure 9 As shown, the average energy efficiency over 60 laps was only 88.47%, and the energy efficiency decreased significantly, with a drop of 2.69%, while the capacity retention rate decreased by 13.69%.

[0141] Comparative Example 6

[0142] The difference from Example 1 is that no cadmium plate is placed on the negative electrode.

[0143] Everything else is the same as in Example 1.

[0144] Electrochemical tests were performed on the vanadium-cadmium redox flow battery obtained in this comparative example at 100 mA / cm². 2 The energy efficiency test results at current density are as follows: Figure 8 As shown, the capacity retention test results are as follows: Figure 9 As shown, the average energy efficiency within 60 cycles is only 89.3%, the capacity retention rate is 24.42%, and the battery cycle life is far less than that of Example 1.

[0145] The energy efficiency of the vanadium-cadmium flow battery of the present invention was compared with that of existing mainstream flow battery systems such as all-vanadium, complex all-iron, zinc-iron, iron-chromium, and zinc-bromine. The results are shown in Table 1.

[0146] Table 1 Performance Comparison of Vanadium-Cd Redox Flow Batteries and Different Flow Battery Systems

[0147]

[0148] The above results demonstrate that the vanadium-cadmium redox flow battery of this invention has significant advantages in core performance indicators. Its commonly used current density is 100 mA / cm², which not only covers the upper limit of the 60~100 mA / cm² range of all vanadium redox flow batteries, but also significantly outperforms the levels of complexed all-iron flow batteries (60~80 mA / cm²), zinc-iron flow batteries (60 mA / cm²), iron-chromium flow batteries (40~60 mA / cm²), and zinc-bromine flow batteries (60~80 mA / cm²). It possesses superior power output capability, and its DC energy efficiency can reach 90%~93%, significantly exceeding the efficiency ranges of 80%~85% for all vanadium redox flow batteries, 79%~83% for complexed all-iron flow batteries, 78%~82% for zinc-iron flow batteries, 65%~75% for iron-chromium flow batteries, and 75%~78% for zinc-bromine flow batteries. This achieves higher energy conversion and utilization efficiency, fully demonstrating the technological advancement and practical value of the vanadium-cadmium redox flow battery of this invention in the field of energy storage.

[0149] The electrochemical test results of each embodiment of the present invention at a current density of 100 mA / cm² are shown in Table 2:

[0150] Table 2 Electrochemical test results of each example at a current density of 100 mA / cm²

[0151]

[0152] In this invention, Examples 1, 4, and 6 used only concentrated sulfuric acid in the negative electrode electrolyte, while Examples 2, 3, 5, and 7 used mixed acid in the negative electrode electrolyte. Comparing Examples 1 and 5, Example 1 used only concentrated sulfuric acid in the negative electrode electrolyte, while Example 5 used mixed acid. Using mixed acid can further improve energy efficiency, but it will aggravate side reactions (chlorine gas evolution), damage the membrane and electrode, and reduce battery stability and lifespan. Therefore, the capacity retention rate of Example 1 is higher than that of Example 5.

[0153] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0154] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A flow battery, characterized in that, Including positive electrode, negative electrode, proton exchange membrane, VO 2+ Positive electrode electrolyte, Cd 2+ A vanadium-cadmium redox flow battery is assembled by adding a negative electrode electrolyte and placing a cadmium plate on the negative electrode. The Cd 2+ The preparation method of the negative electrode electrolyte is as follows: S21. Add deionized water to a polytetrafluoroethylene beaker and stir continuously at room temperature. Then, add concentrated sulfuric acid or a mixed solution dropwise to the stirred deionized water and continue stirring to obtain a uniform sulfuric acid aqueous solution or a mixed acid solution. S22, battery level Add the crystals to the base liquid and stir until the solid is completely dissolved. Continue stirring to dissolve the Cd. 2+ With ligand Cl - , The solvent water molecules are fully combined, and then cooled to room temperature to obtain a colorless and transparent solution; S23, transfer the colorless, transparent solution to a volumetric flask and dilute to volume. After shaking well, obtain Cd. 2+ Negative electrode electrolyte; In step S21, if concentrated sulfuric acid is selected, take 20.4~40.8 mL; if mixed solution is selected, take 20.4~40.8 mL of concentrated sulfuric acid and 10.4~41.7 mL of concentrated hydrochloric acid. During the addition of concentrated sulfuric acid or mixed solution, control the solution temperature to 30~40℃. The battery level in S22 The grain size is 17.12~34.25g; The Cd 2+ In the negative electrode electrolyte, the concentration of total dissolved cadmium is 0.3~0.6 mol / L, H + The concentration is 3~8 mol / L.

2. A flow battery as described in claim 1, characterized in that, The proton exchange membrane needs to be immersed in deionized water for 1 to 1.5 hours at 60 to 80°C, then transferred to a 1 to 2 mol / L H2SO4 solution for 1.5 to 2 hours at 60 to 80°C, and finally soaked in deionized water at room temperature for later use.

3. A flow battery according to claim 1, characterized in that, The cadmium plate needs to be polished until it is shiny and free of scratches, then immersed in 0.5~1 mol / L HCl solution for 30~40 seconds for acid washing. After taking it out, it should be rinsed with deionized water immediately, dried, and then sealed for storage.

4. A flow battery according to claim 1, characterized in that, The VO 2+ The preparation steps of the positive electrode electrolyte are as follows: S11. Add deionized water to a polytetrafluoroethylene beaker and stir continuously at room temperature. Then, add concentrated sulfuric acid dropwise to the stirred deionized water and stir to obtain a uniform sulfuric acid aqueous solution. S12, add battery-grade VOSO4 crystals to the sulfuric acid aqueous solution base, stir until the solid is completely dissolved to obtain a bright blue solution, continue stirring to fully mix the system, and then cool naturally to room temperature; S13, after cooling to room temperature, transfer the entire bright blue solution to a volumetric flask and dilute to volume. Shake well to obtain a homogeneous VO solution. 2+ Positive electrode electrolyte.

5. A flow battery according to claim 4, characterized in that, The VO 2+ In the positive electrode electrolyte, VO 2+ The concentration is 1~2 mol / L, and the sulfuric acid concentration is 3~4 mol / L.

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