Enhancing Electrolyte Stability and Performance in Vanadium Redox Flow Batteries through Inorganic Additives Investigation
Authors: Tian Yuheng , Xie Jiangzhou , Skyllas-Kazacos Maria , Xie Jiangzhou , Menictas Chris 
Published: December 2024

The electrolyte is a crucial component of the vanadium redox flow battery (VRFB), exerting a substantial influence on cell properties, performance, and cost. Its composition significantly impacts energy density, operational temperature range, and practical applications of the VRFB. Various strategies have been proposed to enhance energy density and broaden the temperature range.[1] For instance, the presence of electrolyte impurities or the addition of specific chemical compounds into the vanadium solution can modify electrolyte stability, affecting cell performance, temperature range, energy density, electrochemical kinetics, and cost-effectiveness. The practical composition of vanadium battery electrolytes typically maintains vanadium concentrations between 1.6 and 2 M within a total sulfate concentration of 4−5 M, with operational temperatures ranging between 10 and 40 °C.[2] At these levels, electrolyte operation typically remains in a supersaturated or supercritical state. Consequently, the research and development of additives have emerged as a focal point within electrolyte studies, aimed at sustaining stable operation with high-concentration electrolytes at a broader temperature range.
The current work involves a thorough investigation of various inorganic additives in vanadium electrolytes tailored for VRFBs, conducted across a range of temperatures and sulfuric acid concentrations. Specifically, the study targets distinct oxidation states of vanadium ions, including V(II), V(III), V(IV), and V(V), individually examined under different temperature and acid concentration conditions. This is because the dissolution behavior of V(V) ions can be enhanced by increasing sulfuric acid concentration or reducing the temperature, whereas V(IV), V(III), and V(II) ions can be stabilized by elevating temperature and decreasing sulfuric acid concentration. Additionally, the performance of these additives is evaluated in flow cells to gauge their effectiveness within the battery system, providing valuable insights into their real-world performance and potential for enhancing VRFB efficiency and reliability.
The expense associated with electrolyte production poses a significant barrier to the widespread deployment of vanadium redox flow batteries (VRFBs).[3] Even minor enhancements in electrolyte purity beyond the threshold of 98.5% can substantially inflate electrolyte costs. However, the presence of impurities within the electrolyte solution can trigger unwanted phenomena such as precipitation formation and hydrogen evolution, undermining battery performance and reliability. In response to this challenge, the research endeavors to identify additives capable of mitigating the adverse effects of impurities and sustaining optimal flow battery operation. The investigation has focused on the utilization of lead nitrate as an additive, revealing promising outcomes. Specifically, lead nitrate demonstrates the ability to suppress hydrogen evolution induced by select metal ions commonly found as impurities in electrolyte solutions. Furthermore, the experiments have shown that lead nitrate can enhance battery performance, particularly in scenarios where the concentration of metal ions is increased. These findings highlight the potential of lead nitrate as a viable additive for improving the operational efficiency and longevity of VRFBs, paving the way for more cost-effective and reliable energy storage solutions.
In conclusion, the research underscores the critical role of electrolyte composition in VRFBs. Thorough investigation of various inorganic additives and their impact on electrolyte stability and battery performance aims to address key challenges such as impurity-induced precipitation formation and hydrogen evolution. Additionally, it aims to improve electrolyte stability across a broader operating temperature range, particularly with high-concentration electrolytes. The findings highlight the potential of additives to enhance VRFB efficiency and reliability, offering promising avenues for the development of more cost-effective and reliable energy storage solutions. Through continued research and development in this field, significant advancements in VRFB technology is envisioned, facilitating its broader adoption and integration into various energy storage applications.

References

[1] L. Cao, M. Skyllas-Kazacos, C. Menictas, and J. Noack, “A review of electrolyte additives and impurities in vanadium redox flow batteries,” Journal of Energy Chemistry, vol. 27, no. 5, pp. 1269–1291, 2018, doi: 10.1016/j.jechem.2018.04.007.
[2] Y. Guo, J. Huang, and J. K. Feng, “Research progress in preparation of electrolyte for all-vanadium redox flow battery,” Journal of Industrial and Engineering Chemistry, vol. 118, pp. 33–43, 2023, doi: 10.1016/j.jiec.2022.11.037.
[3] M. Pahlevaninezhad, M. Pahlevani, and E. P. L. Roberts, “Effects of aluminum, iron, and manganese sulfate impurities on the vanadium redox flow battery,” J Power Sources, vol. 529, May 2022, doi: 10.1016/j.jpowsour.2022.231271.