Preparation Method and Development Direction of Electrolyte for Vanadium Flow Battery
Classification：Industrial News
- Author：ZH Energy
- Release time：Nov-15-2023
【 Summary 】All vanadium flow batteries have advantages such as high safety, long service life, flexible energy storage capacity configuration, adjustable power, and ultra long charging and discharging cycles, ma
Exhibition Name: 25th China International High tech Fair - Global Clean Energy Innovation Expo Vanadium electrolyte is composed of vanadium electrolyte and acid supported electrolyte, with sulfuric acid currently the most common supported electrolyte. Vanadium electrolyte uses sulfuric acid as the supporting solution, mainly because sulfuric acid has the characteristics of good stability, weak volatility, and low price. The preparation of high concentration vanadium sulfate electrolyte to increase battery energy density plays an important role in the commercial application of all vanadium flow batteries, and is also a hot research direction at present. Changing the structure and proportion of supporting electrolytes is also an important research direction for increasing the concentration of vanadium electrolytes. At present, sulfuric acid is the most common supporting electrolyte, and the development of HCl/H2SO4 mixed supporting electrolytes is relatively mature and has moved towards commercial applications. The stable electrolyte concentration can reach 2.5 mol/L V. However, research on other supporting electrolytes is still in the laboratory stage, such as methylsulfonic acid aqueous solution, HCl/HBr mixed solution, etc. Research has shown that adjusting the concentration ratio of sulfuric acid and vanadium ions can improve the thermal stability of vanadium electrolytes, allowing them to operate over a wide temperature range. However, it may also have adverse effects on electrolyte viscosity changes, so certain trade-offs need to be made.
Exhibition time: November 15th to November 18th, 2023
All vanadium flow batteries have advantages such as high safety, long service life, flexible energy storage capacity configuration, adjustable power, and ultra long charging and discharging cycles, making them outstanding in large-scale energy storage. All vanadium flow batteries store vanadium ion solutions with high and low valence states as active substances for the positive and negative electrodes, respectively, in their respective electrolyte storage tanks. When the battery is charged and discharged, the positive and negative electrolytes undergo oxidation and reduction reactions on the electrode surface, respectively, to achieve the charging and discharging of the battery. The electrolyte is an electrolyte solution of various valence state ions of a single vanadium element, with a positive electrode pair of VO2+/VO2+and a negative electrode pair of V3+/V2+, which can avoid cross contamination caused by the permeation of different element ions through the ion exchange membrane. The battery has high cycling times and long service life. At present, the preparation of electrolytes with high stability, high concentration and purity, wide temperature adaptation range, and low cost is still a major issue in the development of all vanadium flow batteries.
The preparation methods of vanadium electrolyte can be divided into physical dissolution method, chemical reduction method, and electrolysis method [1]. The physical dissolution method is to directly dissolve high-purity VOSO4 solid in sulfuric acid to obtain an electrolyte. Chemical reduction method is the use of reducing agents (such as sulfur, alcohols, etc.) to reduce high valent vanadium oxides or vanadates to prepare an electrolyte. The electrolysis method can be further divided into two methods: direct electrolysis and indirect electrolysis. The direct electrolysis method is to introduce V2O5 dissolved in sulfuric acid into the negative electrode of the electrolysis cell. After being energized, the negative electrode undergoes a reduction reaction to obtain an equal amount of trivalent vanadium ions and tetravalent vanadium ions. The reaction principle is as follows [2]. The indirect electrolysis method utilizes a reducing substance (such as elemental S) to undergo an oxidation-reduction reaction with V2O5 dissolved in sulfuric acid to obtain a VO2+solution, which is then passed through the negative electrode for further electrolysis to obtain an equal amount of trivalent vanadium ions and tetravalent vanadium ions. Both methods have the characteristics of high energy consumption and slow kinetic processes, so researchers are constantly optimizing the preparation process and technology of vanadium electrolyte. The reported optimization of electrolyte preparation currently includes using high-purity VOCl3 as the precursor for direct electrolysis and using VOSO4 as the precursor for catalytic reduction to obtain equal amounts of trivalent and tetravalent vanadium ions, each with its own characteristics and advantages.
In addition, studies have shown that the concentration and performance of vanadium electrolytes can be improved by adding additives, which can be classified into dispersion, complexation, and threshold types according to their mechanism of action. Disperse additives are mainly low molecular weight polymers that can carry opposite charges to the nucleated particles formed by vanadium ion precipitation in electrolytes, thereby preventing the growth of nucleated particles, such as lignin and polyaminobenzenesulfonic acid. Complex type additives are organic ligands that coordinate with vanadium ions to reduce the precipitation activity of vanadium ions and improve the stability of electrolytes, such as EDTA, 8-hydroxyquinoline, etc. Threshold type additives can adsorb onto the surface of precipitated particles to prevent the growth of precipitate nuclei, and their addition amount has no fixed composition ratio to vanadium ions, such as pyrophosphate, sodium hexametaphosphate, etc. [3].
In summary, the efficient and low-energy preparation of vanadium electrolyte and the continuous optimization of its performance remain important issues in the development and iteration of all vanadium flow batteries for a long period of time in the future. With the continuous updating and iteration of technology, all vanadium flow batteries, as a new energy storage method, will also have broader application prospects.
[1] Yang Yang, Liu Na, Wei Yanhong, Li Aikui. Research progress on electrolytes for all vanadium flow batteries [J]. Power Technology, 2019, 43 (04): 706-709
[2] Guo Hui Preparation and Performance Study of Electrolyte for All Vanadium Flow Battery [D]. Beijing University of Chemical Technology, 2023. DOI: 10.26939/d.cnki.gbhgu.2022.001404
[3] Cao L, Skyllas Kazacos M, Menictas C, et al. A review of electrolyte additives and impurities in advanced redox flow batteries [J] Journal of Energy Chemistry, 2018,27 (05): 1269-1291
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