A design method and application of an all-vanadium redox flow battery electrolyte with high capacity retention.

Abstract

This invention relates to the field of electrochemical energy storage, specifically disclosing a design method and application of a high-capacity-retention electrolyte for vanadium redox flow batteries. Addressing the problem of rapid capacity decay in vanadium redox flow batteries during long-cycle operation, this invention increases the average valence state of the electrolyte, causing the positive electrode to generate excess VO2 during the first charge. + This avoids the problem caused by V 2+ Diffusion to the positive electrode for VO2 + The VO2 available at the positive electrode due to consumption + The shortcomings of this method also reduce the unavailable V in the negative electrode solution. 2+ The accumulation of these factors significantly improves the capacity retention of vanadium redox flow batteries. Without optimization, the non-equilibrium valence electrolyte (V0.05) designed in this invention outperforms conventional electrolytes. 3 . 68+ After 400 cycles, the corresponding cumulative capacity increased by 52.33%.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage, specifically to a design method and application of an all-vanadium redox flow battery electrolyte with high capacity retention. Background Technology

[0002] In recent years, to address global warming, governments and industries worldwide have set goals for energy conservation, emission reduction, and CO2 reduction. Against this backdrop, renewable energy power generation projects, represented by wind and solar power, have sprung up rapidly. However, wind and solar power are heavily influenced by weather, leading to instability in renewable energy generation. Therefore, establishing safe and efficient energy storage systems to store surplus solar and wind power has become crucial for efficiently increasing the proportion of renewable energy. Among these, vanadium redox flow batteries (VRBs) have shown great promise in large-scale energy storage systems due to their excellent safety, long operating life, and good battery performance. Currently, DuPont's Nafion series proton exchange membranes, with their good proton conductivity and excellent stability, dominate the ion exchange membrane market for VRBs. However, due to the different diffusion rates of vanadium ions in different valence states within the Nafion membrane (V0...),... 2+ >VO 2+ >VO2 + >V 3+ This leads to a gradual increase in the volume of the positive electrode electrolyte in vanadium redox flow batteries during long-term cycling, but... The content gradually decreases. Conversely, the volume of the negative electrode electrolyte gradually decreases, but the unusable V... 2+ The gradual accumulation of electrolyte imbalance leads to a significant reduction in battery capacity. While the capacity decay caused by the imbalance of positive and negative electrolyte volumes can be mitigated to some extent by mixing the electrolytes, this process requires additional equipment, consuming substantial manpower and resources. Furthermore, the battery must be shut down during mixing, undoubtedly increasing maintenance costs. In addition, mixing can only partially restore electrolyte utilization but cannot suppress capacity decay. Rapid capacity decay further reduces electrolyte utilization during charge-discharge cycles, further increasing the energy storage cost of vanadium batteries. Summary of the Invention

[0003] This invention provides a design method and application of an all-vanadium redox flow battery electrolyte with high capacity retention. The method is effective, simple and easy to control, highly operable, and easy to promote and industrialize.

[0004] The technical solution of this invention is:

[0005] A design method for a high-capacity-retention electrolyte in vanadium redox flow batteries addresses the significant capacity decay caused by severe imbalances in the concentration and valence state of the positive and negative electrode electrolytes during long-cycle operation. This method increases the average valence state of the electrolyte, causing the positive electrode to generate excess VO2 during the first charge. + To avoid V 2+ Diffusion to the positive electrode for VO2 + The VO2 available at the positive electrode due to consumption + The shortcomings; at the same time, reduce the unavailable V in the negative electrode liquid. 2+ The accumulation of V, thereby slowing down 2+ By migrating the membrane towards the positive electrode, the diffusion and convection of active materials on both sides of the membrane reach a stable state in the early stages of charging and discharging, thus achieving a high capacity retention rate for vanadium redox flow batteries.

[0006] Furthermore, the above-mentioned design method for a high capacity retention vanadium redox flow battery electrolyte, which improves the average valence state of the electrolyte, is achieved through the following three methods based on commercially available 3.5 valence vanadium electrolyte: (1) adding VO₂ with the same supporting electrolyte concentration to the electrolyte. 2+ Solution, or VO2 + Solution, or VO 2+ and VO2 + A mixed solution, or a V solution with an average valence state higher than 3.5. 3+ and VO 2+ (1) Mixed solution; (2) Add anhydrous or aqueous VOSO4 directly to the electrolyte; (3) Add a combination of two or more solutions described in (1) and (2) to the electrolyte to increase the valence state of the mixed electrolyte to >3.5.

[0007] Furthermore, in the above-mentioned design method for a high-capacity-retention all-vanadium redox flow battery electrolyte, the average valence state of the electrolyte is improved in the positive electrode electrolyte V0 2+ Solution, negative electrode electrolyte V 3+ Based on the solution, VO2 with the same supporting electrolyte concentration is added to the positive electrode solution. + Solution, VO 2+ and VO2 + One or two solutions in the mixed solution are used to raise the valence state of the mixed electrolyte to >3.5.

[0008] Furthermore, in the above-mentioned design method for a high-capacity-retention all-vanadium redox flow battery electrolyte, the average valence state of the electrolyte is improved in the positive electrode electrolyte V0 2+ Solution, negative electrode electrolyte V 3+ Based on the solution, it can be achieved through the following three methods: (1) by adding VO with the same supporting electrolyte concentration to the negative electrode solution.2+ Solution, or VO2 + Solution, or V 3+ and VO 2+ A mixed solution, or VO 2+ and VO2 + (1) A mixed solution; (2) Adding anhydrous or aqueous VOSO4 directly to the negative electrode solution; (3) Adding a combination of two or more solutions described in (1) and (2) to the negative electrode solution to increase the valence state of the mixed electrolyte to >3.5.

[0009] Furthermore, in the above-mentioned design method for a high-capacity-retention all-vanadium redox flow battery electrolyte, the average valence state of the electrolyte is improved in the positive electrode electrolyte V0 2+ Solution, negative electrode electrolyte V 3+ Based on the solution, add VO2 with the same supporting electrolyte concentration to the positive electrode solution. + Solution, VO 2+ and VO2 + One or two solutions from the mixed solution, and simultaneously, the following solutions are added to the negative electrode solution: (1) Adding VO with the same supporting electrolyte concentration 2+ Solution, or VO2 + Solution, or V 3+ and VO 2+ A mixed solution, or VO 2+ and VO2 + (1) A mixed solution; (2) or anhydrous / aqueous VOSO4; (3) or a combination of two or more solutions described in (1) and (2) to increase the valence state of the mixed electrolyte to >3.5.

[0010] Furthermore, in the aforementioned design method for a high-capacity-retention all-vanadium redox flow battery electrolyte, the method for improving the average valence state of the electrolyte can be based on the positive and negative electrode electrolytes with valence state balance, i.e., VO 2+ :V 3+ =1:1, or it can be based on the imbalance of valence states in the positive and negative electrolytes, i.e., VO 2+ :V 3+ ≠1:1.

[0011] Furthermore, the above-mentioned design method for a high capacity retention vanadium redox flow battery electrolyte, wherein the method for improving the average valence state of the electrolyte can be operated before the vanadium battery electrolyte is charged or discharged, or during or after the vanadium battery electrolyte is charged or discharged.

[0012] Furthermore, the above-mentioned design method for a high capacity retention vanadium redox flow battery electrolyte is applicable to electrolytes with unbalanced valence states, as well as electrolytes with unbalanced volume and concentration.

[0013] The above-described design method provides an application of a high-capacity-retention vanadium redox flow battery electrolyte. This electrolyte is suitable for vanadium redox flow batteries equipped with Nafion series proton exchange membranes, as well as vanadium redox flow batteries equipped with any combination of other proton exchange membranes, amphoteric membranes, or porous membranes.

[0014] The design concept of this invention is:

[0015] Nafion series proton exchange membranes are widely used in vanadium redox flow batteries due to their excellent chemical stability and proton conductivity. However, the diffusion rates of vanadium ions in different valence states within the Nafion membrane vary (V0). 2+ >VO 2+ >VO2 + >V 3+ This leads to a gradual increase in the positive electrode electrolyte in vanadium redox flow batteries during long-term cycling, but... Gradually decrease. Conversely, the negative electrode electrolyte gradually decreases, but the unusable V... 2+ The amount of [something] gradually accumulates, leading to a significant reduction in battery capacity. This invention, without altering the original structure and operating conditions of the vanadium redox flow battery, increases the average valence state of the positive and negative electrode electrolytes through various methods, thereby generating an excess of [something] in the positive electrode electrolyte. At the same time, it will reduce the V in the negative electrode liquid. 2+ The accumulation of V slowed down 2+ The transfer from the negative electrode to the positive electrode achieves the goal of high capacity retention in vanadium redox flow batteries.

[0016] The present invention has the following advantages and beneficial effects:

[0017] 1. This invention achieves its goal by increasing the average valence state of the positive and negative electrode electrolytes through the introduction of excess electrolyte on the positive electrode side. This reduces the unusable V 2+ The accumulation on the negative electrode side also slows down V. 2+ The flow from the negative electrode side to the positive electrode side achieves the goal of high capacity retention in vanadium redox flow batteries. This method is virtually cost-free, simple to operate, and can be used in newly assembled vanadium redox flow batteries as well as in vanadium redox flow batteries undergoing charge-discharge cycles. It is flexible, efficient, and has great application potential.

[0018] 2. This invention enables the production of vanadium redox flow batteries with high capacity retention. For new or operating vanadium redox flow batteries, increasing the average valence state of the electrolyte can significantly improve the battery's capacity retention, thereby increasing electrolyte utilization and reducing maintenance costs. This invention can be widely used in fields such as vanadium redox flow batteries.

[0019] 3. Without optimization, the present invention can increase the cumulative capacity of a full vanadium redox flow battery equipped with Nafion 212 by 52.33% over 400 cycles. Attached Figure Description

[0020] Figure 1 The diagram shows the evolution of different vanadium ions in the positive and negative electrode electrolytes during the operation of a vanadium redox flow battery equipped with a Nafion proton exchange membrane, where n% represents the state of charge.

[0021] Figure 2 Figure showing the changes in the concentrations of active materials at the positive and negative electrodes of a non-equilibrium electrolyte with an enhanced valence state during operation of a vanadium redox flow battery.

[0022] Figure 3 For traditional electrolytes in valence equilibrium (V 3.50+ ) and non-equilibrium electrolytes with increased valence state (V 3.68+ UV curves;

[0023] Figure 4 To use a conventional electrolyte in valence equilibrium (V 3.50+ ) and non-equilibrium electrolytes with increased valence state (V 3.68+ The graph shows the capacity change of a vanadium redox flow battery during 400 cycles. Detailed Implementation

[0024] To facilitate understanding of the present invention, a more comprehensive description will be provided below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] In specific implementation, this invention targets V 2+ The transmembrane diffusion rate is much higher than that of vanadium ions in other valence states, resulting in a higher Vo in the all-vanadium redox flow battery during long-term cycling. 2+ They gradually migrate from the negative electrode to the positive electrode and... The reaction ultimately leads to the problem of rapid battery capacity decay. This paper proposes to increase the valence state of the mixed electrolyte of positive and negative electrodes, causing the positive electrode to generate excess electrolyte during the first charge. This reduces the unusable V during operation. 2+Accumulation at the negative electrode simultaneously reduces V. 2+ The transfer to the positive electrode achieves the goal of high capacity retention in vanadium redox flow batteries.

[0027] The Nafion series proton exchange membrane involved in this invention is the commercially available Nafion 212, which was used without any prior treatment. Additionally, the electrolyte used in this invention is in valence equilibrium (V... 3.50+ The concentration is 1.70 mol / L. -1 Commercial electrolytes using VO 2+ The electrolyte was obtained by electrolyzing a commercially available equilibrium electrolyte. The non-equilibrium electrolyte used, which increased the valence state, consisted of 51.66 mL of the equilibrium electrolyte and 28.34 mL of VOCs. 2+ It is obtained by mixing electrolytes.

[0028] The present invention will now be described in further detail with reference to embodiments and accompanying drawings.

[0029] like Figure 1 The above describes the evolution of different vanadium ions in the positive and negative electrode electrolytes of a vanadium redox flow battery equipped with a Nafion proton exchange membrane during operation. Initially, the content and valence state of vanadium ions in the positive and negative electrode electrolytes are in equilibrium. As charging and discharging proceed, V... 2+ It continuously diffuses from the negative electrode to the positive electrode, causing the positive electrode side to... It is consumed many times over, thus creating a positive electrode. The content is reduced and lower than V on the negative electrode side. 2+ The content of V0. Therefore, during long-cycle operation, the unusable V0 on the negative electrode side of the all-vanadium redox flow battery. 2+ Gradually accumulating, thus accelerating V 2+ The migration from the negative electrode side to the positive electrode side ultimately exacerbates the capacity decay of the vanadium redox flow battery.

[0030] like Figure 2 The figure shows the changes in the concentrations of active materials at the positive and negative electrodes of a non-equilibrium electrolyte with increased valence state during operation of a vanadium redox flow battery. Compared to a traditional electrolyte in valence equilibrium, the non-equilibrium electrolyte with increased valence state exhibits higher VO2 levels in the initial stage. 2+ The content is higher than that of V 3+ Therefore, after charging is complete, the vanadium ions on the positive electrode side are all converted first. At this time, there is still some V on the negative electrode side. 3+ Therefore, unusable V was avoided in the subsequent discharge process. 2+ Accumulation on the negative electrode side, thereby reducing V 2+ The migration rate from the negative electrode to the positive electrode ultimately improves the capacity retention rate of vanadium redox flow batteries.

[0031] Example 1:

[0032] First, in traditional valence equilibrium electrolytes (V 3.50+ Based on this, a non-equilibrium electrolyte with enhanced valence state (V) is provided. 3.68+ ),like Figure 3 As shown.

[0033] Secondly, a Nafion 212 proton exchange membrane was used to assemble an all-vanadium redox flow battery. The electrolyte was a conventional valence equilibrium electrolyte (V0.05). 3.50+ The total vanadium concentration was 1.7 mol / L. -1 Next, 40 mL of the above electrolyte was taken as the positive and negative electrolytes, respectively, with graphite felt as both electrodes. Similarly, a non-equilibrium electrolyte with increased valence state (V0) was used. 3.68+ A vanadium redox flow battery is assembled using vanadium redox fluid as the electrolyte. A graphite plate with serpentine flow channels is used as the bipolar plate, with an effective flow channel area of ​​16 cm². 2 (4×4cm 2 A gold-plated copper plate was used as the current collector, and a peristaltic pump was used as the electrolyte supply device for the flow battery. The electrolyte flow rate during the experiment was 2.50 mL / min. -1 cm -2 .

[0034] Finally, a comprehensive comparison was made between the use of traditional valence equilibrium electrolytes (V... 3.50+ ) and non-equilibrium electrolyte (V 3.68+ The all-vanadium redox flow battery at 200 mA / cm² -2 The relationship between discharge capacity at current density and cycle number, such as Figure 4 As shown, during 400 cycles, the electrolyte (V) in equilibrium with the conventional valence state... 3.50+ Compared to non-equilibrium electrolytes, which initially lose some capacity due to the increased valence state, V increases with the subsequent cycle count. 3.68+ It can quickly reach a stable state, ultimately leading to the non-equilibrium electrolyte (V) designed in this invention. 3.68+ The cumulative capacity increased by 52.33% after 400 cycles.

[0035] The experimental results of this embodiment demonstrate that the design method for a high-capacity-retention electrolyte in a vanadium redox flow battery proposed in this invention can effectively improve the capacity retention of the vanadium redox flow battery. This method has advantages such as simplicity, low cost, good economic benefits, no special requirements for the working environment, and significant effects, making it suitable for applications in flow batteries and related fields.

[0036] Example 2:

[0037] In this embodiment, the non-equilibrium electrolyte is applied to a single cell of a vanadium redox flow battery, and can also be used in a stack of vanadium redox flow batteries.

[0038] Example 3:

[0039] In this embodiment, a non-equilibrium electrolyte is applied to a vanadium redox flow battery / stack containing a Nafion series proton exchange mode, applicable but not limited to Nafion membranes.

[0040] Example 4:

[0041] In this embodiment, the valence state is V 3.68+ The non-equilibrium valence state electrolyte is used in all-vanadium redox flow batteries / stacks, applicable but not limited to V 3.68+ Price state.

[0042] The experimental results of Examples 2-4 demonstrate that the design and application of the high capacity retention electrolyte for vanadium redox flow batteries proposed in this invention can significantly reduce the capacity decay rate of vanadium redox flow batteries and achieve online capacity recovery, thereby greatly reducing the operation and maintenance costs of vanadium redox flow batteries and improving economic efficiency.

Claims

1. A method for preparing a high-capacity-retention all-vanadium redox flow battery electrolyte, characterized in that, By increasing the average valence state of the electrolyte, the positive electrode liquid generates excess VO2 during the first charge. + To avoid V 2+ Diffusion to the positive electrode for VO2 + The VO2 available at the positive electrode due to consumption + The shortcomings; at the same time, reduce the unavailable V in the negative electrode liquid. 2+ The accumulation of V, thereby slowing down 2+ The migration of the membrane to the positive electrode allows the diffusion and convection of active materials on both sides of the membrane to reach a stable state in the early stages of charging and discharging, thus achieving a high capacity retention rate for the vanadium redox flow battery. The method for improving the average valence state of the electrolyte includes the following: At a total vanadium concentration of 1.7 mol L -1 Based on commercial vanadium 3.5 electrolyte, the following three methods are used to achieve this: (1) Adding VO with the same supporting electrolyte concentration to the electrolyte. 2+ Solution, or VO2 + Solution, or VO 2+ and VO2 + A mixed solution, or a V solution with an average valence state higher than 3.

5. 3+ and VO 2+ (1) Mixed solution; (2) Add anhydrous or aqueous VOSO4 directly to the electrolyte; (3) Add a combination of two or more solutions described in (1) and (2) to the electrolyte to increase the valence state of the mixed electrolyte to 3.

68.

2. The method for preparing a high-capacity-retention all-vanadium redox flow battery electrolyte according to claim 1, characterized in that, The method for improving the average valence state of the electrolyte can be based on the positive and negative electrode electrolytes in valence state equilibrium, i.e., VO 2+ :V 3 + =1:1, or it can be based on the positive and negative electrolytes with unbalanced valence states, i.e., VO 2+ :V 3+ ≠1:

1.

3. The application of a high-capacity-retention all-vanadium redox flow battery electrolyte prepared according to the preparation method of claim 1, characterized in that, The electrolyte is suitable for vanadium redox flow batteries equipped with Nafion series proton exchange membranes.

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