Preparation method of vanadium battery electrolyte with adjustable concentration and electrolyte additive

Abstract

This invention discloses a method for preparing a vanadium battery electrolyte with adjustable concentration and electrolyte additives, relating to the field of vanadium battery electrolyte preparation. The specific steps include: feeding reaction and reduction reaction, two-stage filtration, first valence state adjustment, batch concentration adjustment, second valence state adjustment, addition of additives, and obtaining the product. This invention solves the problems of inflexible adjustment of total vanadium ion concentration and valence state, low vanadium ion utilization, and poor stability in existing vanadium battery electrolytes. This invention can adjust different vanadium ion concentrations and valence states. Through the organic combination of centralized production of high-concentration mother liquor and customized dilution, it not only optimizes the costs of equipment, logistics, and energy consumption, but also builds a competitive advantage in terms of quality stability, production efficiency, market response speed, and environmental friendliness. Simultaneously adding high-efficiency additives ultimately provides process assurance for the "high activity, high stability, and high energy efficiency" of vanadium redox flow battery electrolytes.

Description

Technical Field

[0001] This invention relates to the field of vanadium battery electrolyte preparation, specifically to a vanadium battery electrolyte with adjustable concentration, its preparation method, and electrolyte additives. Background Technology

[0002] Vanadium redox flow batteries are currently the most widely researched and applied flow batteries. Their main advantages are: (1) They can easily achieve large-scale energy storage: all the energy of vanadium batteries is stored in the electrolyte. The capacity of vanadium batteries is determined by the tank volume and electrolyte concentration. Moreover, the electrolyte has good consistency, which can achieve large-scale energy storage at the GWh level (1 million kWh); (2) They have a long service life: vanadium batteries can be deeply discharged without damaging the battery. The battery has a long service life, with a charge-discharge cycle life of more than 20,000 times; (3) They have good safety: vanadium batteries have no risk of explosion or fire. Even if the positive and negative electrolytes are mixed, there is no danger. Only the electrolyte temperature rises slightly. They are batteries that will never explode and are intrinsically safe. In addition, vanadium batteries also have advantages such as fast response speed, high power, high efficiency, and no memory effect. They are considered to be the "perfect battery" for large-scale energy storage.

[0003] However, the total vanadium ion concentration of currently available mainstream vanadium batteries is generally around 1.50~1.70 mol / L, and the total vanadium ion valence state is generally 3.5 (i.e., V). 3.5+ vanadium trivalent ion V 3+ and vanadium tetravalent ions V 4+ While vanadium redox flow batteries (with the same concentration) have drawbacks such as difficulty in adjusting vanadium ion concentration (energy density), low vanadium ion utilization in the electrolyte, and low energy efficiency, they also suffer from other drawbacks. Since the energy density of vanadium batteries is directly proportional to vanadium ion concentration and utilization, quickly meeting customer requirements for energy density and efficiency is a challenge faced by every vanadium redox flow battery manufacturer. The real challenge for vanadium battery development lies in how to flexibly configure electrolytes with different concentrations and total vanadium ion valence states according to user needs, improving the utilization and stability of vanadium ions in electrochemical reactions, significantly increasing vanadium ion utilization and energy efficiency, and further reducing costs.

[0004] Therefore, this application is hereby submitted. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a vanadium battery electrolyte with adjustable concentration, its preparation method, and electrolyte additives. This process adopts a "concentrated at the beginning and diluted at the end" model, organically combining centralized production of high-concentration mother liquor with customized dilution. This not only optimizes costs in equipment, logistics, and energy consumption, but also builds a competitive advantage in terms of quality stability, production efficiency, market responsiveness, and environmental friendliness. Ultimately, it provides process assurance for the "high activity, high stability, and high energy efficiency" of vanadium redox flow battery electrolytes, while laying the foundation for large-scale, flexible production. It is an efficient configuration model adapted to the industrialization needs of vanadium redox flow batteries.

[0006] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a vanadium battery electrolyte with adjustable concentration, comprising the following steps: Vanadium ion electrolyte was prepared by a combination of feeding and reduction reactions, with the total vanadium ion concentration controlled at 2.0 mol / L to 5.0 mol / L. After two stages of filtration, namely coarse filtration and fine filtration, the obtained V 4+ The electrolyte undergoes a first valence state adjustment to achieve a final average vanadium valence state of 3.5. By adding pure water and sulfuric acid in batches, the concentrations of sulfate and vanadium ions were adjusted to the target values. V 4+ Electrolyte and V 3.5+ The electrolytes are mixed to undergo a second valence state adjustment. After adding additives and mixing well, the finished product is obtained.

[0007] In this scheme, the process flow for preparing vanadium battery electrolyte with adjustable concentration includes: ① Feeding reaction + reduction reaction → ② Two-stage filtration → ③ First adjustment of valence state → ④ Batch concentration adjustment → ⑤ Second adjustment of valence state → ⑦ Addition of additives → ⑧ Product. All added raw materials and additives should be of superior purity or analytical purity.

[0008] The electrolyte for the vanadium redox flow battery configured in processes ① to ③ is a high-concentration vanadium ion electrolyte preparation process. The total vanadium ion concentration of the prepared electrolyte is 2.0 mol / L-5.0 mol / L, which is a concentrated-then-dilute configuration mode. Its advantages are: due to the increased concentration, the volume of equipment for the "feeding reaction + reduction reaction → two-stage filtration → one-time adjustment of valence state" process is reduced, which can significantly reduce investment costs. The material conveying volume is also greatly reduced, thereby greatly reducing equipment investment and logistics costs.

[0009] In a specific embodiment, the process of the feeding reaction stage is as follows: the substances added to the reaction vessel in the following order are: pure water, sulfuric acid, vanadium pentoxide, and reducing agent, and the molar ratio of the added reactants is: n 硫酸 ∶n五氧化二钒 ∶n 还原剂 =2~3∶1∶1~4.5; where the purity of all added substances must meet the standards of superior grade or analytical grade, and the temperature of the materials in the reactor is 60-95℃.

[0010] The specific operating procedure in this scheme is as follows: ① Add high-purity water. Turn on the stirring of the reactor (low speed 50 rpm) and inject the calculated amount of deionized water (60% of the reactor volume) into the reactor through the automatic water pump. Turn on the jacket circulating water / hot oil to preheat to 30℃ (to avoid violent exothermic reactions during subsequent acid addition). ② Slowly add concentrated sulfuric acid. Slowly drip concentrated sulfuric acid along the inner wall of the reactor (or add it metered through an acid-resistant pump), with a feeding time of ≥30 minutes (to prevent local overheating). Maintain the stirring speed at 80-100 rpm during the feeding process and monitor the temperature inside the reactor in real time. ③ Add vanadium pentoxide. After the sulfuric acid is added and the temperature stabilizes at 60-98℃, slowly add V2O5 powder into the reactor through a vacuum feeder and suction pump to avoid powder flying. After the addition is complete, increase the stirring speed to 150 rpm to fully disperse the solid (observable through an electronic lens that there is no obvious powder accumulation inside the reactor). ④ Fourth step: Add reducing agent. The amount of reducing agent added is 1-4.5 times the amount of vanadium pentoxide (calculated based on the molar mass of formic acid). Formic acid and pyruvic acid are added in a volume ratio of "V..." 甲酸 ∶V 丙酮酸 Mix 8.0-9.8 ∶ 2.0-0.2” and add slowly over 30 minutes, controlled directly by a flow meter (avoid adding all at once to prevent a violent reaction). Maintain a stirring rate of 150-200 rpm during the addition process and turn on the jacket heating to maintain the reactor temperature (60-98℃). ⑤ Reaction process control. Temperature control: Stabilize the reactor temperature at the set value (60-98℃) using the jacket heating / cooling system, and record the temperature data every 15 minutes. Stirring rate: Maintain a uniform stirring speed (180-200 rpm) to ensure sufficient solid-liquid contact (mixing uniformity can be judged by observing the depth of the vortex inside the reactor). Reaction time monitoring: Start timing after the reducing agent is added; the reaction time is 6-10 hours.

[0011] In one specific embodiment, the reducing agent in the reduction reaction is one or a mixture of formic acid and pyruvic acid.

[0012] In one specific embodiment, in the two-stage filtration process, the coarse filtration is a bag filter with a filter mesh filtration accuracy of ≤25μm; the fine filtration is a membrane filter with a filter mesh filtration accuracy of ≤1μm.

[0013] Specifically, the primary bag filter uses nylon (PA) or polypropylene (PP) mesh; the membrane filter uses an acid-resistant organic membrane. A very small amount of filter residue remains after filtration and is sent to a third party for centralized, harmless treatment.

[0014] In one specific implementation, the temperature during the batch addition of pure water and sulfuric acid is 15-40°C.

[0015] In one specific implementation, the first valence state adjustment is achieved by electrolysis to reduce the total vanadium ion valence state to 3.5.

[0016] In this scheme, a reduction reaction (V) occurs at the cathode during electrolysis. 4+ →V 3+ An oxidation reaction occurs at the anode (usually oxygen evolution of water, to avoid introducing impurities). The reaction principle is as follows: Cathode (reduction): VO 2+ (V) 4+ )+2H + +e - →V 3+ +H2O (For every 1 mol of electrons transferred, 1 mol of V is generated) 3+ Consume 1 mol VO 2+ ) Anode (oxidation, inert electrode): 2H₂O - 4e⁻ - →O2↑+4H + (For every 4 mol of electrons transferred, 1 mol of O2 is generated. Note that H2 needs to be added at the anode.) + (Sulfuric acid) maintains its acidity. The core reason: the cathode reaction affects H₂. + The consumption of vanadium ions far exceeds the amount generated at the anode, and an acidic environment is key to the stable existence of vanadium ions. The initial solution is the single V produced in step 2. 4+ (VO) 2+ ) solution, VO during electrolysis 2+ The cathode is continuously reduced to V 3 + As the reaction proceeds, [VO 2+ [V] gradually decreases, 3+ The concentration gradually increases. When the concentrations of both are equal, the total vanadium valence reaches 3.5, at which point electrolysis is stopped.

[0017] In one specific embodiment, the second valence state adjustment is performed using an electrolyte mixing method to adjust the valence state, V V4+ Electrolyte and V V3.5+ The electrolyte mixing volume ratio is 0.00-0.57:1.

[0018] Secondly, the present invention also provides an electrolyte additive, comprising additive No. 1 and additive No. 2, wherein additive No. 1 is high-purity nitrobenzoic acid, and additive No. 2 is one or a mixture of high-purity oxalic acid and anhydrous tartaric acid.

[0019] In one specific embodiment, the No. 1 additive is a liquid, and its addition amount is 1L to 20L per 1000L of electrolyte; the No. 2 additive is a solid, and its addition amount is 5kg to 25kg per 1000L of electrolyte.

[0020] In a specific embodiment, the nitrobenzoic acid used in this invention comprises three isomers: ortho, meta, and para; the tartaric acid used in this invention is two optical isomers: L-tartaric acid (levo-tartaric acid) and DL-tartaric acid (racemic tartaric acid), both commonly used high-purity industrial products.

[0021] The beneficial effects of adding additive #1 (in very small amounts) to the electrolyte are: First, it significantly improves thermal stability and inhibits vanadium ion precipitation. It significantly reduces V(V) precipitation under high-temperature conditions, ensuring the electrolyte remains stable during long-term use and reducing maintenance frequency and costs. The nitro (-NO2) and carboxyl (-COOH) bifunctional groups form stable five-membered ring chelates with vanadium ions, blocking the aggregation and precipitation pathways of vanadium ions, allowing V(V) to exist in a soluble complex form, thus improving the thermal stability of the electrolyte. Second, it enhances electrochemical reversibility and conductivity. It improves the conductivity and redox reversibility of the electrolyte, making the charge-discharge process more efficient, increasing energy efficiency by approximately 5-10%. The nitro group has two-electron redox activity, which can serve as an additional electrochemical active site, increasing the overall specific capacity. After the carboxyl group coordinates with vanadium ions, it reduces the degree of solvation, increases ion mobility, and improves conductivity. The benzene ring structure provides an electron conduction channel, optimizing the electron transfer process.

[0022] The beneficial effects of adding additive #2 to the electrolyte are: firstly, it complexes with vanadium ions, improving the stability of the electrolyte. Oxalate (C2O4) 2⁻ ) can be with V 3+ V 4+ Vanadium ions form a stable complex [V(C2O4)3]. 3- [VO(C2O4)2] 2- This complexation significantly improves the solubility of vanadium ions in the electrolyte, especially under high concentration or high temperature conditions, and can effectively suppress the solubility of vanadium ions (such as V). 3+ VO 2+ Hydrolysis and precipitation of V in solution. 2+ Theoretically, it can form [V(C2O4)2] with oxalate. 2- However, V²⁺ has strong reducing properties and is easily oxidized in acidic electrolytes, resulting in a weak complexation reaction. The V²⁺ in the solution... 5+ (VO) 2+ Tartaric acid has extremely strong oxidizing properties and frequently undergoes redox reactions with oxalic acid, while its complexation reaction is very weak. Similarly, the carboxyl group (-COOH) of tartaric acid partially dissociates into a carboxyl anion (-COO-) in acidic electrolytes. -The hydroxyl group (-OH) retains a lone pair of electrons, and both can act as coordinating atoms to form coordinate bonds with vanadium ions (transition metal ions with empty orbitals). This polydentate coordination can form stable five- or six-membered ring structures (chelation effect), significantly improving the stability of the complex. VO in solution 2+ With tartrate (C4H4O6) 2- ) forms a 1:1 chelate [VO(C4H4O6)], V 3+ It forms a more stable complex with tartrate (possibly in a 1:1 or 1:2 ratio) [V(C4H4O6)]. + The complexation of oxalic acid and tartaric acid can also regulate the solvation structure of vanadium ions, reducing their transmembrane migration and thus reducing cross-contamination between the positive and negative electrode electrolytes. Secondly, it regulates valence state and restores capacity. Oxalic acid has strong reducing properties and can reduce pentavalent vanadium (VO₂) to its solvation state. + ) is reduced to tetravalent vanadium (VO) 2+ This effectively adjusts the average valence state of the electrolyte and restores battery capacity. The reducing properties of tartaric acid, to some extent, assist oxalic acid in regulating the valence state of vanadium ions, further optimizing the redox balance of the electrolyte. During charging, if VO2 in the positive electrode electrolyte... ⁺ If the concentration is too high, adding oxalic acid can partially convert it into VO through a reduction reaction. 2+ This avoids energy loss due to valence imbalance. Field experiments show that the reducing effect of oxalic acid and tartaric acid can reduce the average valence state of the electrolyte from a high valence state to around 3.5, significantly improving the cycle stability of the battery. Thirdly, it optimizes electrochemical performance. The addition of oxalic acid improves the ion conductivity of the electrolyte and electrode reaction kinetics. In cyclic voltammetry tests, the redox peak current of the electrolyte with added oxalic acid increased, and the potential difference decreased, indicating a significant improvement in the reversibility of the electrode reaction. Furthermore, oxalic acid can reduce the viscosity of the electrolyte and promote the diffusion of vanadium ions, thereby improving the charge-discharge efficiency of the battery. Fourthly, it suppresses side reactions and extends battery life. Oxalic acid can suppress the occurrence of hydrogen evolution side reactions at the negative electrode. In a full vanadium redox flow battery, the negative electrode V... 2+ / V 3+ The standard potential of the redox couple is lower than that of the hydrogen electrode, which easily leads to the hydrogen evolution reaction, while the presence of oxalic acid can stabilize V through complexation. 2+ This reduces hydrogen evolution. At the same time, oxalic acid and tartaric acid can also inhibit the oxidation of V by oxygen in the air. 2+ The oxidation process further extends the electrolyte's lifespan. The synergistic use of both can further improve electrolyte stability and battery efficiency, but requires fine-tuning in terms of concentration, temperature, and compatibility with other additives.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) Improve production efficiency and economies of scale. Centralized production of high-concentration mother liquor can significantly improve the vanadium ion production efficiency per unit time. The process of "feeding reaction + reduction reaction → two-stage filtration → one-time adjustment of valence state" is designed for high-concentration systems. The reactants (V2O5, reducing agent, acid, etc.) have high concentrations and sufficient contact, resulting in a faster reaction rate (reducing diffusion mass transfer resistance) and a shorter single-batch reaction time. At the same time, the vanadium ion content per unit volume of electrolyte is higher at high concentrations. Under the same equipment capacity, the total amount of vanadium that can be produced per unit time (e.g., tons of vanadium / day) is more than 50% higher than that of directly producing low-concentration electrolyte, making it suitable for large-scale industrial mass production. Centralized production of high-concentration mother liquor can form standardized production modules. Continuous production can be achieved by fixing process parameters (e.g., reaction temperature, stirring rate, filtration accuracy), reducing the debugging time for batch switching, and further amplifying economies of scale.

[0024] (2) Enhance quality consistency and stability. High-concentration mother liquor serves as a "standardized base," providing a stable quality benchmark for subsequent customized products. The preceding process involves rigorous two-stage filtration (removing unreacted particles and impurities) and a single valence adjustment (ensuring V... 2+ / V 3+ V 4+ / V 5+ With precise proportions, vanadium ions in the mother liquor exist in a stable complex form, exhibiting high compositional uniformity and extremely low impurity content (due to the easier filtration and retention of impurities at high concentrations, and more complete reactions). Subsequent customized production is achieved solely through "dilution + fine-tuning of valence state," a simple process with easily controllable parameters (e.g., dilution requires only precise addition of water or dilute sulfuric acid, and valence state adjustment is achieved through trace additives). This avoids quality fluctuations caused by batch differences in raw materials and reaction conditions during the production of low-concentration electrolytes from scratch, ensuring consistent performance across different batches of customized products (e.g., vanadium ion utilization rate, cycle stability).

[0025] (3) Improve the speed of customized response and market adaptability. The “concentrated first, diluted later” model separates the complex core reaction from the simple customized adjustment, which greatly shortens the delivery cycle of customized products. High-concentration mother liquor can be pre-produced and stored in batches. When the user’s demand (such as the user needs 1.6mol / L 3.5 valence electrolyte) is issued, there is no need to repeat the time-consuming reduction reaction, filtration and other core processes. The target product can be quickly generated by dilution (controlling the amount of water added / dilute acid added), fine-tuning the valence state and activating vanadium ions. The response cycle can be shortened to 1 / 3 to 1 / 5 of the traditional “one-order production” model. There is no need to reconstruct the core equipment. It is extremely flexible and can quickly adapt to diversified market demands.

[0026] (4) Optimize impurity control and product purity. High-concentration systems provide a more efficient process window for impurity removal. The higher the ion concentration, the more effective the removal of impurities (such as Fe introduced from raw materials). 3+ Si4+ The higher concentration of impurities (or reaction byproducts) in the system makes them more easily retained by filter media (such as precision filter membranes) (at high concentrations, impurity particles are more likely to aggregate, resulting in lower filtration resistance and higher retention rates). In contrast, when low-concentration electrolytes are produced from scratch, impurities are highly dispersed, have low filtration efficiency, and are prone to remaining in the product. After rigorous purification of the preceding high-concentration mother liquor, the subsequent dilution process only introduces pure water or high-purity acid and additives, hardly adding any new impurities. The final product purity (most cationic impurities ≤1ppm) is much higher than that of low-concentration electrolytes produced by the "one-step" method. High purity is key to ensuring the electrolyte's "high activity" (vanadium ion utilization rate) and "high stability" (reducing vanadium ion disproportionation catalyzed by impurities).

[0027] (5) Reduce overall energy consumption and carbon footprint. The production and treatment of high-concentration mother liquor can significantly reduce the energy consumption of the entire process. Reaction stage: The heat transfer efficiency of the high-concentration system is higher (the thermal conductivity increases with the concentration), and the energy consumption required for heating / cooling is reduced by 20%~30% compared with the low-concentration system. Transportation and stirring: Under the same vanadium content, the volume of the high-concentration electrolyte is only 1 / 2~1 / 3 of that of the 1.5mol / L electrolyte, and the pump power and energy consumption of the stirring equipment can be reduced proportionally, which is especially suitable for long-distance material transportation scenarios. Subsequent customization: The dilution process only requires simple mixing, without additional heating or chemical reaction, and the energy consumption is much lower than that of preparing low-concentration electrolyte from scratch. The unit vanadium energy consumption of the overall process can be reduced by more than 30%, which meets the green production requirements under the "dual carbon" target.

[0028] (6) Enhanced process tolerance and scalability. The "concentrated at the beginning and diluted at the end" model provides the production line with stronger anti-interference capabilities and expansion space. Even if there are slight fluctuations in the production parameters of the high-concentration mother liquor (such as reaction time and temperature), they can be "diluted and buffered" by subsequent dilution, reducing the impact on the performance of the final product (for example, if the vanadium concentration of the mother liquor fluctuates by ±0.2mol / L, when diluted to 2.0mol / L, the final concentration fluctuation is only ±0.05mol / L), resulting in higher process tolerance. The production line can achieve rapid capacity expansion through the flexible design of "mother liquor storage tank + customized module": only the mother liquor production unit needs to be added, and the subsequent customized module can be expanded in parallel without reconstructing the entire production line. Compared with the fixed concentration production line of "one production and one sale", the expansion cost is reduced by more than 40%, and it can quickly respond to the explosive growth of market demand.

[0029] (7) Additives further improve electrolyte stability and electrochemical performance. Oxalic acid and tartaric acid enhance battery performance in vanadium redox flow battery electrolytes through multiple mechanisms such as complexation, reduction, and interface modification. Oxalic acid mainly functions by stabilizing vanadium ions, adjusting valence state, and improving electrochemical activity, while tartaric acid optimizes electrolyte performance through complexation, redox mediation, and pH buffering. Both form stable complexes with vanadium ions through complexation, significantly improving vanadium ion solubility, especially inhibiting hydrolysis and precipitation at high concentrations or high temperatures. They can also regulate the solvation structure of vanadium ions, reduce transmembrane migration, and reduce cross-contamination between positive and negative electrode electrolytes. Oxalic acid can reduce pentavalent vanadium to tetravalent vanadium, and tartaric acid assists in adjusting the valence state, reducing the average valence state of the electrolyte, restoring battery capacity, and improving cycle stability. Oxalic acid can improve ion conductivity and electrode reaction kinetics, increasing charge and discharge efficiency; pyruvate adsorbs on the electrode surface to reduce polarization resistance, improve membrane selectivity, and optimize electrochemical reaction pathways. In addition, oxalic acid can stabilize vanadium ions. 2+ Reducing hydrogen evolution, both inhibit V together. 2+ Oxidation by oxygen extends the electrolyte's lifespan and synergistically improves battery performance. Adding a very small amount of nitrobenzoic acid to the electrolyte of a vanadium redox flow battery can enhance battery performance through different mechanisms: nitrobenzoic acid inhibits precipitation and optimizes the electrochemical environment through chelation, significantly improving the electrolyte's thermal stability, electrochemical activity, and cycle life, providing a strong guarantee for the efficient and stable operation of vanadium redox flow batteries.

[0030] (8) Ensure the matching of sulfate ion concentration and vanadium ion concentration. Based on the sulfate concentration calculation formula developed based on a large amount of experimental data, the sulfate concentration can be controlled synchronously and precisely by adjusting in batches to ensure the coordination balance between vanadium ions and sulfate ions (e.g., high vanadium concentration electrolytes require higher sulfate concentrations to inhibit hydrolysis). This avoids vanadium ion precipitation due to insufficient sulfate ions, while ensuring the ionic conductivity and electrical conductivity of the electrolyte, thereby improving the utilization rate of vanadium ions.

[0031] (9) Ensuring product performance consistency and traceability. High-concentration mother liquor, as a standardized intermediate product, facilitates the establishment of a full life-cycle quality traceability system: key parameters of each batch of mother liquor (such as vanadium concentration, valence distribution, impurity content, and viscosity) can be accurately recorded, and the performance of subsequent customized products can be inferred from the mother liquor parameters. Once a quality problem occurs, it can be quickly located to the preceding or subsequent stages, solving the problem of difficult quality traceability in traditional "one-step" production. Different batches of products customized with the same mother liquor have higher consistency in electrochemical performance (such as cyclic voltammetry curves and charge-discharge efficiency) due to the consistent substrate, which can provide a stable raw material base for downstream battery manufacturers and reduce battery performance differences caused by electrolyte fluctuations. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0034] It should be noted that this process has already achieved large-scale production in Ya'an City, Sichuan Province (annual output of 3000m³). 3 It has successful industrial-scale implementation cases for both batch delivery to users and delivery to users in batches.

[0035] In the attached diagram: the gray box represents the high-vanadium-ion concentration section, where the total vanadium-ion concentration in the electrolyte is 2.0–5.0 mol / L. Example 1

[0036] This embodiment provides a method for preparing a vanadium battery electrolyte with adjustable concentration, including the following steps: 1. Feeding reaction and reduction reaction: 5m 3 Pure water, sulfuric acid, vanadium pentoxide, and a reducing agent were added sequentially to the reactor. The total volume of the high-concentration electrolyte was set to 3 m³. 3 The total vanadium ion concentration is 2.0 mol / L, and the final product electrolyte concentration is 1.7 mol / L. All added substances must meet the standards of superior purity or analytical purity. The ratio of the amount of substance added during the first feeding and the reduction reaction stage (based on the molar mass of vanadium pentoxide added) is: n 硫酸 ∶n 五氧化二钒 ∶n 还原剂 The ratio is 2:1:1. The entire reaction must be carried out under uniform stirring. The temperature of the materials in the reactor must be controlled between 60-98℃, and the stirring time in the reactor is 6-10 hours. The reducing agent is composed of one or a mixture of formic acid and pyruvic acid. The specific preparation method is to mix formic acid and pyruvic acid in a volume ratio of "V". 甲酸 ∶V 丙酮酸The reaction mixture was prepared with a ratio of 8.0:2.0. The amount of reducing agent added to the reactor was calculated based on the molar mass of formic acid. Therefore, the ratio of nformic acid to nvanadium pentoxide was 1:1. The chemical reaction equation occurring in the reactor under heating conditions is as follows: V2O5+3HCOOH+3H2SO4→2VOSO4+3CO2↑+5H2O V2O5+CH3COCOOH+2H2SO4→2VOSO4+CH3COOH+CO2↑+2H2O 4V2O5+CH3COOH+8H2SO4→8VOSO4+2CO2↑+10H2O In the reaction, sulfuric acid mainly provides the acidic environment, while formic acid and pyruvic acid are mainly used as reducing agents, reducing V... 5+ Restore to V 4+ .

[0037] The calculated volume of sulfuric acid added in the first addition is 320,000 L, the mass of vanadium pentoxide added is 546.745 kg, and the total amount of reducing agent added is 114.257 L (calculated based on 99% formic acid by mass). The specific operating procedure is as follows: ① Add high-purity water. Turn on the reactor stirring (low speed 50 rpm) and inject the calculated amount of deionized water (60% of the reactor volume) into the reactor through the automatic water pump. Turn on the jacket circulating water / hot oil to preheat to 30℃ (to avoid violent exothermic reactions during subsequent acid addition). ② Slowly add concentrated sulfuric acid. Slowly drip concentrated sulfuric acid along the inner wall of the reactor (or meter it using an acid-resistant pump), with a feeding time ≥30 minutes (to prevent local overheating). Maintain a stirring speed of 80-100 rpm during the feeding process and monitor the reactor temperature in real time (the temperature rise must not exceed 100℃; if it exceeds the temperature, stop feeding). ③ Add vanadium pentoxide. After the sulfuric acid has been added and the temperature has stabilized at 40-50℃, V2O5 powder is slowly added to the reactor via a vacuum feeder and suction pump to prevent powder from flying. After the addition is complete, the stirring speed is increased to 150 rpm to ensure the solid is fully dispersed (observable through an electron microscope to ensure no obvious powder accumulation in the reactor). ④ Fourth step: Add the reducing agent. Formic acid and pyruvic acid are added according to V... 甲酸 ∶V 酒石酸After mixing at a volume ratio of 8.0:2.0, add the solution directly over 30 minutes, controlled by a flow meter (avoiding a violent reaction caused by adding all at once). Maintain a stirring rate of 150-200 rpm during the addition process, and activate the jacket heating to reach the target temperature range (50-100℃). ⑤ Reaction Process Control. Temperature Control: Stabilize the temperature inside the reactor at the set value (±2℃ fluctuation) using the jacket heating / cooling system, recording temperature data every 15 minutes. Stirring Rate: Maintain uniform stirring (180-200 rpm) to ensure sufficient solid-liquid contact (mixing uniformity can be judged by observing the depth of the vortex inside the reactor). Reaction Time Monitoring: Start timing after the reducing agent is added; the reaction time is 6-10 hours.

[0038] 2. Two-stage filtration: coarse filtration and fine filtration The vanadium battery electrolyte produced in step (1) is subjected to two-stage filtration: primary filtration is bag filtration (coarse filtration), and secondary filtration is membrane filtration (fine filtration). The primary bag filter has a filtration accuracy of ≤25μm and is made of nylon (PA) or polypropylene (PP) filter mesh; the secondary membrane filter has a filtration accuracy of ≤1μm and is made of acid-resistant organic membrane. A very small amount of filter residue remains after filtration and is sent to a third party for centralized harmless treatment.

[0039] 3. First adjustment of price status The primary valence state adjustment is achieved by electrolysis to reduce the total vanadium ion valence state to 3.5 (V2). 3.5+ V 4+ Ion concentration and V 3+ (equal ion concentrations); this process uses the V prepared in step 2. 4+ Vanadium ion electrolyte is used as the mother electrolyte.

[0040] V in step 3 above 4+ The solution is added to the electrolytic cell, and the cathode and anode are inserted (the spacing is generally 3 to 5 cm). The cathode is connected to the negative terminal of the power supply, and the anode is connected to the positive terminal. Nitrogen gas is introduced to remove dissolved oxygen from the solution (to prevent V). 3+ (Oxidized), and continuously stirred to ensure uniform solution concentration. Start the electrolytic cell to begin electrolysis, using constant current electrolysis (current density controlled at 5-10 mA / cm²). 2 To avoid excessive current causing H + (Reduced to H2), the voltage of the single electrode plate is typically 1.5-3.0V (adjusted according to the solution resistance). Monitor electrolysis parameters: Measure V every 10-15 minutes. 3+ and V 4+ Concentration (spectrophotometric method). When [V] is detected... 3+ ]=[V 4+ If the electrolysis fails, immediately turn off the power and stop the electrolysis. After electrolysis is complete, continue to purge with nitrogen for protection, transfer the solution to a container, and store it in a sealed, light-protected environment at a low temperature (to prevent V). 3+Oxidation or valence change). When the valence adjustment device shows an average valence of 3.5+, stop electrolysis, and the first valence adjustment is completed.

[0041] 4. Batch concentration adjustment The concentration adjustment is carried out in two batches. The first batch is the V produced in process 2 4+ The vanadium battery electrolyte is adjusted from a high concentration to the target concentration by adding pure water and the sulfate ion concentration is adjusted by adding sulfuric acid; the second batch is the V produced in process 3 3.5+ The vanadium battery electrolyte is adjusted from a high concentration to the target concentration by adding pure water and the sulfate ion concentration is adjusted by adding sulfuric acid. The target electrolyte sulfate ion concentration is set to 3.40 mol / L. The V produced in process 2 and process 3 4+ 、V 3.5+ The vanadium battery electrolytes are respectively pumped into different dilution tanks. Under the condition of stirring, slowly add 336.04 L of electronic grade concentrated sulfuric acid and 186.372 L of ultrapure water according to the above calculation results to adjust the vanadium ion concentration to the vanadium ion concentration and sulfate ion concentration required by the customer. The specific operation process is as follows: electrolyte transfer. Carefully check the V 4+ vanadium battery electrolyte produced in process 2 and the V 3+ vanadium battery electrolyte produced in process 3. After ensuring that there is no error, accurately pump them into different marked, clean and dry dilution tanks through pipelines respectively. Start stirring: Turn on the stirring device supporting the dilution tank and adjust the stirring speed to a uniform state (the stirring rate is controlled at 50 - 200 rpm) to ensure the normal operation of the stirring paddle and make the electrolyte in the tank preliminarily mixed evenly to prepare for the subsequent addition of acid and water. Add acid and water: Prepare the required acid and water strictly according to the previous calculation results. When adding, keep a slow and uniform speed and pour the acid and water into the dilution tank through a special feeding port. During the addition process, continuously observe the stirring state to ensure that the newly added acid and water are fully mixed with the electrolyte and avoid too high local concentration. Concentration adjustment and temperature control: Continuously stir the electrolyte, and at the same time use professional concentration detection equipment (such as an ion concentration analyzer) to monitor the vanadium ion concentration and sulfate ion concentration in real time until they are adjusted to the standard values required by the customer. During the whole operation process, control the electrolyte temperature stably within the range of 15 - 40 °C through a temperature control system (such as a cooling or heating device). If the temperature fluctuates abnormally, adjust the parameters of the temperature control equipment in time to ensure the smooth progress of the operation process.

[0042] 5. Secondary valence adjustment The secondary valence adjustment uses the electrolyte mixing method to adjust the valence. Mix the electrolytes of V 4+ with the electrolytes of V 3.5+ in a certain volume ratio. The electrolyte mixing volume ratio is: V V4+ ∶VV3.5+ =0∶1. The electrolyte mixing ratio is calculated in reverse based on the user's requirements for the electrolyte valence state. The specific calculation formula is: Let V in the electrolyte... 3+ and V 4+ If the concentrations are C3 and C4 respectively, then the average valence state of the vanadium electrolyte can be calculated by the following formula: Average valence state of vanadium electrolyte = (3*C3+4*C4) / (C3+C4).

[0043] 6. Add additives Under normal temperature conditions, additive #1 and additive #2 are slowly added sequentially to the activation reactor for activation, with stirring during the addition process: Additive #1 is added at a rate of 7L (liquid) per 1000L of electrolyte; additive #1 is high-purity nitrobenzoic acid. Additive #2 is added at a rate of 16kg (solid) per 1000L of electrolyte; additive #2 is a mixture of one or both analytical grade oxalic acid and tartaric acid, with 8kg of oxalic acid and 8kg of tartaric acid added. Stirring is required during the addition of the additives.

[0044] 7. Place at room temperature After sealing or nitrogen-sealing the electrolyte at room temperature for 48 hours, the finished product can be obtained.

[0045] 8. Testing The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.7 mol / L was 21.20 Wh / L, the average energy density after 50 cycles was 21.39 Wh / L, the average vanadium ion utilization rate was 75.12%, the average energy efficiency (DC side) was 80.24%, and the capacity retention rate after 50 cycles was 100.38%.

[0046] Example 2 Based on Example 1, the method for preparing the vanadium battery electrolyte with adjustable concentration provided in this example is largely the same as the steps in Example 1, except that: (1) During the feeding reaction and reduction reaction, the total vanadium ion concentration in the high-concentration electrolyte is 3.0 mol / L, and the molar ratio n 硫酸 :n 五氧化二钒 :n 还原剂 =2.1∶1∶2; Formic acid and pyruvic acid in the reducing agent are in a volume ratio of "V 甲酸 V 丙酮酸 The mixture was prepared at a ratio of 9.8:0.2; the initial addition of sulfuric acid was 336.000 L, the initial addition of vanadium pentoxide was 546.745 kg, and the total amount of reducing agent added was 228.515 L. (2) The target electrolyte sulfate ion concentration in the batch concentration adjustment was set to 3.465 mol / L. Based on the above calculation results, 352.842 L of electronic grade concentrated sulfuric acid and 1273.521 L of ultrapure water were slowly added.

[0047] (3) V in the second-order valence state adjustment 4+ electrolyte and V 3.5+ The volume ratio of the electrolyte mixture is 0.11:1.

[0048] (4) The amount of additive 1 is 10L of additive 1 (liquid) per 1000L of electrolyte. Additive 1 is high-purity nitrobenzoic acid. The amount of additive 2 is 8kg of additive 2 (solid) per 1000L of electrolyte. Among them, the amount of oxalic acid and tartaric acid added is 4kg each.

[0049] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the electrolyte with a total vanadium ion concentration of 1.65 mol / L had the following characteristics: initial energy density of 22.40 Wh / L, average energy density of 23.2 Wh / L after 50 cycles, average vanadium ion utilization rate of 83.94%, average energy efficiency (DC side) of 81.30%, and capacity retention rate of 101.92% after 50 cycles.

[0050] Example 3 Based on Example 1, the method for preparing the vanadium battery electrolyte with adjustable concentration provided in this example is largely the same as the steps in Example 1, except that: (1) During the feeding reaction and reduction reaction, the total vanadium ion concentration in the high-concentration electrolyte was 3.2 mol / L, and the molar ratio n 硫酸 :n 五氧化二钒 :n 还原剂 =2.3∶1∶3; Formic acid and pyruvic acid in the reducing agent are in a volume ratio of "V 甲酸 V 丙酮酸 The mixture was prepared in a ratio of 8.5:1.5. The volume of sulfuric acid added in the first batch was 392.553 L, the mass of vanadium pentoxide added was 583.195 kg, and the total amount of reducing agent added was 365.623 L.

[0051] (2) The target electrolyte sulfate ion concentration was set to 4.000 mol / L during batch concentration adjustment. Based on the above calculations, 482.193 L of electronic-grade concentrated sulfuric acid and 1502.807 L of ultrapure water were slowly added. (3) V in the second-order valence state adjustment 4+ electrolyte and V 3.5+ The volume ratio of the electrolyte mixture is 0.25:1.

[0052] (4) The amount of additive 1 is 15L of additive 1 (liquid) per 1000L of electrolyte. Additive 1 is high-purity nitrobenzoic acid. The amount of additive 2 is 10kg of additive 2 (solid) per 1000L of electrolyte. The amount of oxalic acid and tartaric acid added are 6kg and 4kg respectively.

[0053] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.60 mol / L was 25.53 Wh / L, the average energy density after 50 cycles was 23.47 Wh / L, the average vanadium ion utilization rate was 87.57%, the average energy efficiency (DC side) was 82.14%, and the capacity retention rate after 50 charge-discharge cycles was 95.43%.

[0054] Example 4 Based on Example 1, the method for preparing the vanadium battery electrolyte with adjustable concentration provided in this example is largely the same as the steps in Example 1, except that: (1) During the feeding reaction and reduction reaction, the total vanadium ion concentration in the high-concentration electrolyte is 3.5 mol / L, and the molar ratio n 硫酸 :n 五氧化二钒 :n 还原剂 =2.6∶1∶4; Formic acid and pyruvic acid in the reducing agent are in a volume ratio of "V 甲酸 V 丙酮酸 The mixture was prepared in a ratio of 9.0:1.0. The volume of sulfuric acid added for the first time was 485.333 L, the mass of vanadium pentoxide added was 637.870 kg, and the total amount of reducing agent added was 533.201 L.

[0055] (2) The target electrolyte sulfate ion concentration was set to 4.340 mol / L during batch concentration adjustment. Based on the above calculation results, 586.206 L of electronic grade concentrated sulfuric acid and 1928.923 L of ultrapure water were slowly added.

[0056] (3) V in the second-order valence state adjustment 4+ electrolyte and V 3.5+ The volume ratio of the electrolyte mixture is 0.56:1.

[0057] (4) The amount of additive 1 is 1L of additive 1 (liquid) per 1000L of electrolyte. Additive 1 is high-purity nitrobenzoic acid. The amount of additive 2 is 15kg of additive 2 (solid) per 1000L of electrolyte. The amount of oxalic acid and tartaric acid added are 8kg and 7kg respectively.

[0058] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.55 mol / L was 20.23 Wh / L, the average energy density after 50 cycles was 20.29 Wh / L, the average vanadium ion utilization rate was 78.15%, the average energy efficiency (DC side) was 82.96%, and the capacity retention rate after 50 charge-discharge cycles was 97.83%.

[0059] Example 5 Based on Example 1, the method for preparing the vanadium battery electrolyte with adjustable concentration provided in this example is largely the same as the steps in Example 1, except that: (1) During the feeding reaction and reduction reaction, the total vanadium ion concentration in the high-concentration electrolyte was 3.3 mol / L, and the molar ratio n 硫酸 :n 五氧化二钒 ∶n 还原剂 =3.0∶1∶4.5; Formic acid and pyruvic acid in the reducing agent are in a volume ratio of "V 甲酸 V 丙酮酸 The mixture was prepared in a ratio of 8.8:0.8; the volume of sulfuric acid added for the first time was 528.000L, the mass of vanadium pentoxide added was 601.420kg, and the total amount of reducing agent added was 565.574L.

[0060] (2) The target electrolyte sulfate ion concentration in the batch concentration adjustment was set to 4.500 mol / L. Based on the above calculation results, 554.466 L of electronic grade concentrated sulfuric acid and 1843.534 L of ultrapure water were slowly added.

[0061] (3) V in the second-order valence state adjustment 4+ electrolyte and V 3.5+ The volume ratio of the electrolyte mixture is 0.16:1.

[0062] (4) The amount of additive 1 is 2L of additive 1 (liquid) per 1000L of electrolyte. Additive 1 is high-purity nitrobenzoic acid. The amount of additive 2 is 20kg of additive 2 (solid) per 1000L of electrolyte. The amount of oxalic acid and tartaric acid added are 12kg and 8kg respectively.

[0063] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.50 mol / L was 19.85 Wh / L, the average energy density after 50 cycles was 20.01 Wh / L, the average vanadium ion utilization rate was 79.64%, the average energy efficiency (DC side) was 82.16%, and the capacity retention rate after 50 cycles was 99.55%.

[0064] Example 6 Based on Example 1, the method for preparing the vanadium battery electrolyte with adjustable concentration provided in this example is largely the same as the steps in Example 1, except that: (1) During the feeding reaction and reduction reaction, the total vanadium ion concentration in the high-concentration electrolyte is 3.0 mol / L, and the molar ratio n 硫酸 ∶n 五氧化二钒 ∶n 还原剂 =2∶1∶3.5; Formic acid and pyruvic acid in the reducing agent are in a volume ratio of "V 甲酸 ∶V 丙酮酸 The mixture was prepared in a ratio of 9.5:0.5; the volume of sulfuric acid added for the first time was 320.000L, the mass of vanadium pentoxide added was 546.745kg, and the total amount of reducing agent added was 399.901L.

[0065] (2) The target electrolyte sulfate ion concentration in the batch concentration adjustment was set to 4.500 mol / L. Based on the above calculation results, 500.064 L of electronic grade concentrated sulfuric acid and 828.269 L of ultrapure water were slowly added.

[0066] (3) V in the second-order valence state adjustment 4+ electrolyte and V 3.5+ The volume ratio of the electrolyte mixture is 0.06:1.

[0067] (4) The amount of additive 1 is 5L of additive 1 (liquid) per 1000L of electrolyte. Additive 1 is high-purity nitrobenzoic acid. The amount of additive 2 is 25kg of additive 2 (solid) per 1000L of electrolyte. The amount of oxalic acid and tartaric acid added are 13kg and 12kg respectively.

[0068] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.80 mol / L was 23.54 Wh / L, the average energy density after 50 cycles was 24.13 Wh / L, the average vanadium ion utilization rate was 80.03%, the average energy efficiency (DC side) was 80.42%, and the capacity retention rate after 50 charge-discharge cycles was 98.81%.

[0069] Example 7 Based on Example 1, the method for preparing the vanadium battery electrolyte with adjustable concentration provided in this example is largely the same as the steps in Example 1, except that: (1) During the feeding reaction and reduction reaction, the total vanadium ion concentration in the high-concentration electrolyte was 3.6 mol / L, and the molar ratio n 硫酸 :n 五氧化二钒 :n 还原剂 =2.5∶1∶3.1; Formic acid and pyruvic acid in the reducing agent are in a volume ratio of "V 甲酸 V 丙酮酸 The mixture was prepared in a ratio of 9.3:0.7”; the volume of sulfuric acid added for the first time was 480.000L, the mass of vanadium pentoxide added was 656.095kg, and the total amount of reducing agent added was 425.037L.

[0070] (2) The target electrolyte sulfate ion concentration in the batch concentration adjustment was set to 4.900 mol / L. Based on the above calculation results, 622.158 L of electronic grade concentrated sulfuric acid and 1477.128 L of ultrapure water were slowly added.

[0071] (3) V in the second-order valence state adjustment 4+ electrolyte and V 3.5+ The volume ratio of the electrolyte mixture is 0.22:1.

[0072] (4) The amount of additive 1 is 15L of additive 1 (liquid) per 1000L of electrolyte. Additive 1 is high-purity nitrobenzoic acid. The amount of additive 2 is 15kg of additive 2 (solid) per 1000L of electrolyte. The amount of oxalic acid and tartaric acid added are 5kg and 10kg respectively.

[0073] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.75 mol / L was 22.74 Wh / L, the average energy density after 50 cycles was 22.88 Wh / L, the average vanadium ion utilization rate was 78.06%, the average energy efficiency (DC side) was 78.91%, and the capacity retention rate after 50 charge-discharge cycles was 98.24%.

[0074] Example 8 Based on Example 1, the method for preparing the vanadium battery electrolyte with adjustable concentration provided in this example is largely the same as the steps in Example 1, except that: (1) During the feeding reaction and reduction reaction, the total vanadium ion concentration in the high-concentration electrolyte was 2.1 mol / L, and the molar ratio n 硫酸 :n 五氧化二钒 :n 还原剂 =2∶1∶2.5; Formic acid and pyruvic acid in the reducing agent are in a volume ratio of "V 甲酸 V 丙酮酸 The mixture was prepared in a ratio of 9.0:1.0. The volume of sulfuric acid added for the first time was 280.000L, the mass of vanadium pentoxide added was 382.722kg, and the total amount of reducing agent added was 199.950L.

[0075] (2) The target electrolyte sulfate ion concentration in the batch concentration adjustment was set to 3.30 mol / L. Based on the above calculation results, 179.218 L of electronic grade concentrated sulfuric acid and 358.236 L of ultrapure water were slowly added.

[0076] (3) V in the second-order valence state adjustment 4+ electrolyte and V 3.5+ The volume ratio of the electrolyte mixture is 0.04:1.

[0077] (4) The amount of additive 1 is 8L of additive 1 (liquid) per 1000L of electrolyte. Additive 1 is high-purity nitrobenzoic acid. The amount of additive 2 is 13kg of additive 2 (solid) per 1000L of electrolyte. The amount of oxalic acid and tartaric acid added are 8kg and 5kg respectively.

[0078] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the electrolyte with a total vanadium ion concentration of 1.65 mol / L had the following characteristics: initial energy density of 20.23 Wh / L, average energy density of 20.82 Wh / L after 50 cycles, average vanadium ion utilization rate of 75.33%, average energy efficiency (DC side) of 76.56%, and capacity retention rate of 98.76% after 50 cycles.

[0079] Comparative Example 1 Based on Example 6, the preparation method of the concentration-adjustable vanadium battery electrolyte provided in this comparative example is roughly the same as the steps in Example 6, except that: (1) the target electrolyte sulfate ion concentration is set to 3.30 mol / L in the batch concentration adjustment. 833.269 L of ultrapure water is slowly added according to the above calculation result. (2) No additive #1 is added, and the amount of additive #2 added is 25 kg of additive #2 per 1000 L of electrolyte, the same as in Example 6.

[0080] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.80 mol / L was 20.04 Wh / L, the average energy density after 50 cycles was 20.05 Wh / L, the average vanadium ion utilization rate was 66.50%, the average energy efficiency (DC side) was 66.42%, and the capacity retention rate after 50 cycles was 90.32%.

[0081] Comparative Example 2 Based on Example 7, the preparation method of the vanadium battery electrolyte with adjustable concentration provided in this comparative example is roughly the same as the steps in Example 7, except that the amount of additive #2 is different. In this example, 10 kg of additive #2 is added per 1000 L of electrolyte, and additive #2 does not contain oxalic acid.

[0082] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.75 mol / L was 19.74 Wh / L, the average energy density after 50 cycles was 19.81 Wh / L, the average vanadium ion utilization rate was 67.58%, the average energy efficiency (DC side) was 68.91%, and the capacity retention rate after 50 charge-discharge cycles was 87.84%.

[0083] Comparative Example 3 Based on Example 8, the preparation method of the vanadium battery electrolyte with adjustable concentration provided in this comparative example is roughly the same as the steps in Example 8, except that the amount of additive #2 is different. In this example, 8 kg of additive #2 is added per 1000 L of electrolyte. Additive #2 does not contain tartaric acid.

[0084] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the electrolyte with a total vanadium ion concentration of 1.65 mol / L had the following characteristics: initial energy density of 18.23 Wh / L, average energy density of 18.38 Wh / L after 50 cycles, average vanadium ion utilization rate of 66.50%, average energy efficiency (DC side) of 72.56%, and capacity retention rate of 90.07% after 50 cycles.

[0085] Comparative Example 4: Based on Example 6, the preparation method of the vanadium battery electrolyte with adjustable concentration provided in this comparative example is roughly the same as the steps in Example 6, except that additive #2 is not added.

[0086] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.80 mol / L was 19.34 Wh / L, the average energy density after 50 cycles was 19.02 Wh / L, the average vanadium ion utilization rate was 62.58%, the average energy efficiency (DC side) was 76.33%, and the capacity retention rate after 50 charge-discharge cycles was 78.20%.

[0087] Comparative Example 5 Based on Example 6, the preparation method of the vanadium battery electrolyte with adjustable concentration provided in this comparative example is roughly the same as the steps in Example 6, except that: no additives 1# and 2# are added, that is, additives 1# and 2# are zero.

[0088] Test results: The electrolyte was tested using a 0.5 kW small-scale vanadium redox flow system. The average value was obtained after 50 consecutive charge-discharge cycles. The results showed that the initial energy density of this batch of electrolyte with a total vanadium ion concentration of 1.80 mol / L was 17.89 Wh / L, the average energy density after 50 cycles was 16.69 Wh / L, the average vanadium ion utilization rate was 54.92%, the average energy efficiency (DC side) was 75.98%, and the capacity retention rate after 50 charge-discharge cycles was 76.32%.

[0089] Based on Examples 6, 1, 4 and 5, additive #1 and additive #2 have a significant synergistic effect: when either additive is added alone or not added at all, the electrolyte energy density, vanadium ion utilization rate, energy efficiency and cycle capacity retention rate are all low; when the two are used together, all performances are improved significantly in a simultaneous manner, showing a synergistic effect.

[0090] Compared with Comparative Example 1, which only reduced the sulfate concentration without adding additive #1, Example 6, after adding both additives #1 and #2, showed that the average vanadium ion utilization rate increased from 66.50% to 80.03%, and the average energy efficiency increased from 66.42% to 80.42%, indicating that additive #1 can significantly improve the electrochemical utilization efficiency and energy conversion efficiency of vanadium ions.

[0091] Compared with Comparative Example 4, which did not add Additive 2, Example 6, after using Additive 1 and Additive 2 in combination, showed a significant increase in capacity retention from 78.20% to 98.81% after 50 cycles. At the same time, energy density and vanadium utilization were also significantly improved, indicating that Additive 2 plays a key role in stabilizing the electrolyte structure and inhibiting capacity decay.

[0092] Compared with Comparative Example 5 (without any additives), Example 6 showed comprehensive improvements in initial energy density, average energy density, vanadium ion utilization, energy efficiency, and cycle capacity retention. In particular, the capacity retention increased from 76.32% to 98.81%, a very significant improvement.

[0093] Conclusion: The data above shows that Examples 2 and 6 achieve the best balance between energy density, utilization rate, efficiency, and stability, representing the optimal formulation. Comparative Examples 1-5 show lower performance across all indicators, indicating poor overall performance.

[0094] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific 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 should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a vanadium battery electrolyte with adjustable concentration, characterized in that, Includes the following steps: Vanadium ion electrolyte was prepared by a combination of feeding and reduction reactions, with the total vanadium ion concentration controlled at 2.0 mol / L to 5.0 mol / L. After two stages of filtration, namely coarse filtration and fine filtration, the obtained V 4+ The electrolyte undergoes a first valence state adjustment to achieve a final average vanadium valence state of 3.

5. By adding pure water and sulfuric acid in batches, the concentrations of sulfate and vanadium ions were adjusted to the target values. V 4+ Electrolyte and V 3.5+ The electrolytes are mixed to undergo a second valence state adjustment. After adding additives and mixing well, the finished product is obtained.

2. The method for preparing the vanadium battery electrolyte with adjustable concentration according to claim 1, characterized in that, The reaction process during the feeding stage is as follows: the substances added to the reactor in the following order are: pure water, sulfuric acid, vanadium pentoxide, and reducing agent. The molar ratio of the reactants is: n 硫酸 ∶n 五氧化二钒 ∶n 还原剂 =2~3∶1∶1~4.5; where the purity of all added substances must meet the standards of superior grade or analytical grade, and the temperature of the materials in the reactor is 60~95℃.

3. The method for preparing the concentration-adjustable vanadium battery electrolyte according to claim 1 or 2, characterized in that, In the reduction reaction, the reducing agent is composed of one or a mixture of formic acid and pyruvic acid.

4. The method for preparing the vanadium battery electrolyte with adjustable concentration according to claim 1, characterized in that, In the two-stage filtration process, the coarse filtration is a bag filter with a filter mesh filtration accuracy of ≤25μm; the fine filtration is a membrane filter with a filter mesh filtration accuracy of ≤1μm.

5. The method for preparing the vanadium battery electrolyte with adjustable concentration according to claim 1, characterized in that, The temperature during the batch addition of pure water and sulfuric acid is 15-40℃.

6. The method for preparing the vanadium battery electrolyte with adjustable concentration according to claim 1, characterized in that, The first valence state adjustment was achieved by electrolysis to reduce the total vanadium ion valence state to 3.

5.

7. The method for preparing the vanadium battery electrolyte with adjustable concentration according to claim 1, characterized in that, The second oxidation state adjustment uses an electrolyte mixing method to adjust the oxidation state, V V4+ Electrolyte and V V3.5+ The electrolyte mixing volume ratio is 0.00~0.57∶1.

8. An electrolyte additive, characterized in that, It includes Additive No. 1 and Additive No. 2, wherein Additive No. 1 is high-purity nitrobenzoic acid, and Additive No. 2 is one or a mixture of high-purity oxalic acid and anhydrous tartaric acid.

9. The electrolyte additive according to claim 8, characterized in that, Additive No. 1 is a liquid, and its addition amount is 1L to 20L per 1000L of electrolyte; Additive No. 2 is a solid, and its addition amount is 5kg to 25kg per 1000L of electrolyte.

10. The electrolyte additive according to claim 8, characterized in that, The tartaric acid is a combination of two optical isomers: levotartaric acid and racemic tartaric acid.

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