Regeneration method of failed electrolyte of vanadium battery

Abstract

The invention discloses a regeneration method of a failed electrolyte of a vanadium battery, which comprises the following steps: (1) adding an oxidant into the failed electrolyte to oxidize vanadium ions in the failed electrolyte to tetravalent to obtain a tetravalent vanadium solution; (2) adding sulfuric acid into the tetravalent vanadium solution, concentrating, crystallizing, aging, and carrying out solid-liquid separation to obtain vanadyl sulfate crystals and sulfuric acid waste liquid; (3) adding deionized water and sulfuric acid into the vanadyl sulfate crystal, and dissolving to obtain a tetravalent vanadium basic electrolyte; and (4) electrolyzing the tetravalent vanadium basic electrolyte to obtain a 3.5-valent vanadium electrolyte and a 4.5-valent vanadium electrolyte. According to the FF, a chemical method and an electrochemical method are organically combined, the process is clear, the steps are coherent, the regeneration of the failed vanadium battery electrolyte can be effectively realized, and the FF is suitable for centralized and batch regeneration treatment of the large-scale failed vanadium battery electrolyte; the internal recycling of the sulfuric acid is realized, the consumption of new acid and the discharge of waste liquid are greatly reduced, and the regeneration cost and the environmental burden are reduced.

Description

A method for regenerating the electrolyte of a vanadium battery that has failed. Technical Field

[0001] This invention relates to the field of vanadium battery technology, and in particular to a method for regenerating failed electrolyte in vanadium batteries. Background Technology

[0002] Vanadium redox flow batteries, as a large-scale, long-duration energy storage technology, have shown broad application prospects in renewable energy grid integration, grid peak shaving, and backup power due to their outstanding advantages such as independent power and capacity design, long cycle life, high safety, and environmental friendliness. Their working principle is based on the electrochemical redox reaction of vanadium ions between different valence states. The electrolyte, as the carrier and reaction medium of the active materials, is the core and value of the battery system.

[0003] However, in actual operation, vanadium battery electrolytes face unavoidable failure problems, mainly manifested as: (1) valence imbalance and cross-contamination of vanadium ions. Although the proton exchange membrane is designed to block the electrolytes of the positive and negative half-cells, the migration of trace amounts of vanadium ions across the membrane cannot be completely avoided. Long-term operation leads to a decrease in high-valence vanadium ions and an increase in low-valence vanadium ions in the positive electrode electrolyte, while the opposite is true for the negative electrode. This change in valence distribution directly leads to a continuous decrease in the battery system capacity and a decline in energy efficiency.

[0004] (2) Unstable precipitation of electrolyte. Under specific temperature (usually above 40°C) and concentration conditions, pentavalent vanadium in the positive electrode electrolyte is prone to form insoluble precipitates such as V2O5. This process is irreversible, which not only causes permanent loss of active material, but also blocks the flow channels and electrodes, increases system pressure, and in severe cases can even damage the battery stack, threatening the safe and stable operation of the battery.

[0005] (3) Introduction and accumulation of impurity ions. During long-term cycling or maintenance, impurity ions (such as Na+) from the membrane... + K + Impurities in the air may enter the electrolyte system, thereby altering the physicochemical properties of the electrolyte (such as conductivity and viscosity), and consequently affecting the battery's voltage efficiency and reaction kinetics.

[0006] The aforementioned failure mechanisms result in the actual usable capacity of the battery system being significantly lower than the design capacity, forcing operators to perform frequent maintenance and electrolyte replacements. Since vanadium resources are expensive, accounting for a large proportion of the initial investment in the entire battery system, directly discarding the failed electrolyte not only causes enormous economic waste but also contradicts the original intention of green energy storage.

[0007] Therefore, developing efficient, economical, and environmentally friendly electrolyte regeneration technologies for failed vanadium batteries, aiming to restore their electrochemical performance and achieve the recycling of active materials, is of paramount importance for reducing the total life-cycle cost of vanadium batteries, enhancing their economic competitiveness, and promoting the sustainable development of the large-scale energy storage industry. Currently, this technological field has become a research hotspot in both academia and industry, with main research directions including chemical rebalancing, electrolytic regeneration, and hybrid regeneration, aiming to provide customized solutions for different failure modes. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a regeneration method for vanadium battery electrolyte with high recovery efficiency.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes the following steps: (1) adding an oxidant to the failed electrolyte to oxidize the vanadium ions therein to the tetravalent valence to obtain a tetravalent vanadium solution; (2) adding sulfuric acid to the tetravalent vanadium solution, concentrating, crystallizing, aging, and separating solid and liquid to obtain vanadium oxysulfate crystals and sulfuric acid waste liquid; (3) adding deionized water and sulfuric acid to the vanadium oxysulfate crystals to dissolve them to obtain a tetravalent vanadium basic electrolyte; (4) electrolyzing the tetravalent vanadium basic electrolyte to obtain a 3.5 vanadium electrolyte and a 4.5 vanadium electrolyte.

[0010] Furthermore, in step (1), the oxidant used is hydrogen peroxide, potassium permanganate, or sodium hypochlorite.

[0011] Furthermore, in step (2), sulfuric acid is added until the sulfuric acid concentration reaches 5-7 mol / L.

[0012] Furthermore, in step (3), the total vanadium concentration of the tetravalent vanadium-based electrolyte is 1.6–2.0 mol / L, and the sulfate concentration is 3.0–4.0 mol / L.

[0013] Furthermore, in step (2), the resulting sulfuric acid waste liquid is added to a tetravalent vanadium solution for reuse.

[0014] Furthermore, in step (4), the resulting 4.5-valent vanadium electrolyte is returned to step (3) and dissolved together with the vanadium oxysulfate crystals.

[0015] The beneficial effects of adopting the above technical solution are as follows: This invention organically combines chemical and electrochemical methods, with a clear process and coherent steps, which can effectively realize the regeneration of failed vanadium battery electrolytes and is suitable for centralized and batch regeneration of large-scale failed vanadium battery electrolytes.

[0016] This invention enables the internal recycling of sulfuric acid, significantly reducing the consumption of new acid and the discharge of waste liquid, thereby lowering regeneration costs and environmental burden. Experimental verification shows that the vanadium recovery efficiency of this invention can reach over 95%. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to specific embodiments.

[0018] The regeneration method of the vanadium battery failure electrolyte includes the following steps: (1) Oxidation-reduction to 4 valence: The failure electrolyte comes from a full vanadium redox flow battery, and the valence state of its vanadium ions is +3.8 to +3.9. The average valence state and total vanadium concentration of the failure electrolyte are measured, and the theoretical amount of oxidant required to oxidize all vanadium ions to +4 valence is calculated based on the measured average valence state and total vanadium concentration. The calculated theoretical amount of oxidant is added to the failure electrolyte to oxidize the vanadium ions to 4 valence, and a 4-valent vanadium solution is obtained; the oxidant is hydrogen peroxide, potassium permanganate or sodium hypochlorite. The theoretical amount of oxidant is calculated based on the stoichiometric ratio of the redox reaction. For example, when using hydrogen peroxide, the theoretical amount of oxidant is calculated based on the stoichiometric ratio of the redox reaction. 3+ To V 4+ It requires 0.5 mol of H2O2, and the reaction temperature should be controlled between 10 and 40°C, with a reaction time of 0.5 to 2.0 hours.

[0019] (2) Crystallization separation of vanadium oxysulfate: Sulfuric acid is added to the tetravalent vanadium solution until the sulfuric acid concentration reaches 5-7 mol / L. The solution is concentrated under reduced pressure at 50-70℃ to 1 / 3-1 / 2 of its original volume. Then, the solution is cooled to 5-15℃ for crystallization and aged for 1-3 hours. Solid-liquid separation is performed, and the crystals are washed 2-3 times with concentrated cold sulfuric acid to remove surface impurities, yielding vanadium oxysulfate crystals and sulfuric acid waste liquid. The sulfuric acid waste liquid is added to the tetravalent vanadium solution obtained in step (1), and then the crystallization separation of vanadium oxysulfate in this step is carried out again, thereby realizing the reuse of sulfuric acid.

[0020] (3) Reconstructing the tetravalent electrolyte: The vanadium oxysulfate crystals are added to deionized water and sulfuric acid to dissolve and obtain a tetravalent vanadium basic electrolyte; the total vanadium concentration of the tetravalent vanadium basic electrolyte is 1.6 to 2.0 mol / L and the sulfate concentration is 3.0 to 4.0 mol / L.

[0021] (4) Electrochemical regeneration: The tetravalent vanadium base electrolyte is electrolyzed in an electrochemical reduction device to obtain a 3.5 vanadium electrolyte and a 4.5 vanadium electrolyte; the 3.5 vanadium electrolyte is used as the regenerated vanadium electrolyte for a full vanadium redox flow battery; the 4.5 vanadium electrolyte is returned to step (3), mixed with vanadium oxysulfate crystals, and then dissolved together with deionized water and sulfuric acid.

[0022] The electrolysis process involves using a Nafion membrane (perfluorosulfonic acid resin ion exchange membrane) as the diaphragm and a graphite plate as the electrode, operating at a constant current density of 20–50 mA / cm². 2 Electrolysis is carried out below; during the electrolysis process, tetravalent vanadium (VO₄) in the cathode chamber... 2+ Reduced to trivalent vanadium V 3+ In the anode chamber, tetravalent vanadium is oxidized to pentavalent vanadium VO2. + The cathode chamber yields an electrolyte with an average valence state of approximately +3.5 and rich in V(III); the anode chamber yields an electrolyte with an average valence state of approximately +4.5 and rich in V(V); the electrochemical reduction device may be an electrolytic cell.

[0023] Example 1: The failed electrolyte was derived from the failed positive electrode electrolyte of a vanadium redox flow battery energy storage power station after long-term operation. Chemical titration determined its total vanadium concentration to be 1.5 mol / L, with an average valence state of approximately +3.9. The electrolyte appeared slightly turbid, suggesting the formation of a small amount of fine V₂O₅ precipitate.

[0024] (1) Oxidation-reduction to +4 oxidation state: Based on the measured average oxidation state of +3.9 and the total vanadium concentration of 1.5 mol / L, calculate the theoretical amount of hydrogen peroxide required to oxidize all vanadium ions to +4 oxidation state. Oxidation of 1 mol V 3+ To V 4+ 0.5 mol of H₂O₂ is required, and the volume of 30 wt% hydrogen peroxide needed is calculated accordingly. In this example, approximately 12 mL of 30 wt% hydrogen peroxide is added per liter of spent electrolyte. Under continuous stirring and temperature control in an ice-water bath, maintaining the temperature below 40°C, the calculated hydrogen peroxide solution is slowly and dropwise added to the spent electrolyte. A color change and the generation of bubbles (oxygen) can be observed during the reaction. After the addition is complete, the reaction is continued with stirring for 1 hour to ensure complete oxidation. The final product is a clear solution mainly containing VO₂. 2+ Blue tetravalent vanadium solution.

[0025] (2) Crystallization and separation of vanadium oxysulfate: Concentrated sulfuric acid is added to the tetravalent vanadium solution to achieve a final sulfuric acid concentration of 6 mol / L; the solution is concentrated under reduced pressure at 60°C until the volume is reduced to one-third of its original volume, at which point the sulfuric acid concentration in the system increases significantly; the concentrated hot solution is then transferred to a crystallization vessel, cooled to 10°C, and aged at this temperature for 2 hours to allow vanadium oxysulfate to fully crystallize and precipitate. Finally, solid-liquid separation is performed using a vacuum filtration device to obtain blue vanadium oxysulfate crystals and sulfuric acid waste liquid. The crystals are then washed twice with a small amount of cold concentrated sulfuric acid to remove impurities adhering to the crystal surface. In addition, the collected sulfuric acid mother liquor can be stored in a waste acid tank and used as a source of part of the sulfuric acid in this step for the next batch of electrolyte, achieving recycling.

[0026] (3) Reconstructing the tetravalent electrolyte: Transfer the pure vanadium oxysulfate crystals obtained in step three to a dissolving tank, add deionized water and supplemented sulfuric acid, and adjust the solution system to restore the total vanadium concentration to 1.8 mol / L and the sulfate concentration to 3.5 mol / L. Mechanically stir at room temperature until the crystals are completely dissolved to obtain a homogeneous and clear tetravalent vanadium basic electrolyte.

[0027] (4) Electrochemical regeneration: A tetravalent vanadium-based electrolyte is pumped into the electrolytic cell; the electrolytic cell uses a Nafion membrane as the diaphragm and graphite plates as electrodes. A constant current density of 30 mA / cm² is maintained. 2+ Electrolysis is carried out below; during the electrolysis process, tetravalent vanadium (VO₄) in the cathode chamber... 2+ It is reduced to trivalent vanadium (V). 3+ In the anode chamber, tetravalent vanadium is oxidized to pentavalent vanadium (VO2). + ); Real-time monitoring of electrolyte potential; The electrolyte output from the cathode chamber, with an average valence state of approximately +3.5 and rich in V(III), is introduced into the finished product filling system and collected as a regenerated negative electrode electrolyte. The electrolyte output from the anode chamber, with an average valence state of approximately +4.5 and rich in V(V), is pumped back to the dissolving tank in step (3) through a circulation pipeline, where it is dissolved together with new vanadium oxysulfate crystals and participates in the electrolysis process again. This circulation operation continues until all tetravalent vanadium base electrolyte is converted into regenerated +3.5 vanadium electrolyte.

[0028] In this embodiment, 1L of spent electrolyte, after regeneration, yields 0.98L of regenerated vanadium trivalent electrolyte, with a vanadium recovery efficiency of 96.5%. Example 1

[0029] Potassium permanganate was used as the oxidant, and other conditions were the same as in Example 1. 2.8 g of potassium permanganate (stoichiometric calculation) was added per liter of spent electrolyte. The oxidation reaction was carried out at room temperature for 1.5 hours. After regeneration, 1 L of spent electrolyte yielded 0.97 L of regenerated vanadium 3.5-valent electrolyte, with a vanadium recovery efficiency of 95.8%. Example 2

[0030] Sodium hypochlorite (10% available chlorine content) was used as the oxidant, and other conditions were the same as in Example 1. 25 mL of sodium hypochlorite solution (stoichiometric calculation) was added per liter of spent electrolyte. The oxidation reaction was carried out at 20°C for 1 hour. After regeneration, 1 L of spent electrolyte yielded 0.96 L of regenerated vanadium 3.5-valent electrolyte, with a vanadium recovery efficiency of 95.2%.

Claims

1. A method for regenerating a failed electrolyte in a vanadium battery, characterized in that, The process includes the following steps: (1) adding an oxidant to the failed electrolyte to oxidize the vanadium ions to tetravalent to obtain a tetravalent vanadium solution; (2) adding sulfuric acid to the tetravalent vanadium solution, concentrating, crystallizing, aging, and separating solid and liquid to obtain vanadium oxysulfate crystals and sulfuric acid waste liquid; (3) adding deionized water and sulfuric acid to the vanadium oxysulfate crystals to dissolve them to obtain a tetravalent vanadium basic electrolyte; (4) electrolyzing the tetravalent vanadium basic electrolyte to obtain a 3.5 vanadium electrolyte and a 4.5 vanadium electrolyte.

2. The method for regenerating vanadium battery electrolyte according to claim 1, characterized in that: In step (1), the oxidant used is hydrogen peroxide, potassium permanganate, or sodium hypochlorite.

3. The method for regenerating vanadium battery electrolyte according to claim 1, characterized in that: In step (2), sulfuric acid is added until the sulfuric acid concentration reaches 5-7 mol / L.

4. The method for regenerating vanadium battery electrolyte according to claim 1, characterized in that: In step (3), the total vanadium concentration of the tetravalent vanadium-based electrolyte is 1.6–2.0 mol / L, and the sulfate concentration is 3.0–4.0 mol / L.

5. The method for regenerating vanadium battery electrolyte according to claim 1, characterized in that: In step (2), the resulting sulfuric acid waste liquid is added to a tetravalent vanadium solution for reuse.

6. A method for regenerating a failed electrolyte in a vanadium battery according to any one of claims 1-5, characterized in that: In step (4), the resulting vanadium 4,5-valent electrolyte is returned to step (3) and dissolved together with the vanadium oxysulfate crystals.