Capacity fade during long-term charge/discharge cycling is considered as one of the key issues that limits the long-term performance and lifetime of vanadium redox flow batteries (VRFBs) [1]. This issue is primarily caused by oxygen and hydrogen gas evolution as well as vanadium crossover and leads to a decrease in battery performance through its lifetime [2]. One potential solution to address the problem of vanadium crossover is remixing the electrolyte, i.e. transferring a portion of electrolyte from one tank to the other (Figure 1a), to balance the total vanadium concentration in both tanks [3]. Although this approach has been widely implemented in recent studies, the literature still lacks a descriptive theoretical framework to accurately assess the connection between electrolyte remixing and VRFB performance both in a specific cycle and during exhaustive cycling. If this relationship could be understood, then more effective strategies to reduce the negative impacts of crossover and related capacity fade could be developed.

In this talk, we will present a modeling study to establish a fundamental understanding of electrolyte remixing as a capacity fade mitigation strategy. The effects of remixing frequency (Figure 1b) and the amount of electrolyte remixed on the long-term performance of these systems will be reported. Additionally, the trade-off between improved capacity fade during long-term cycling and reduced single-cycle performance at which remixing applied will be discussed.

References

[1] Boettcher, P. A., Agar, E., Dennison, C. R., Kumbur, E. C. J. Electrochem. Soc. 2016, 163 (1), A5244-A5252.

[2] Knehr, K. W., Agar, E. Dennison, C. R., Kalidindi, A. R., Kumbur, E. C. J. Electrochem. Soc. 2012, 159 (9), A1446-A1459.

[3] Wang, K., Liu, L., Xi, J., Wu, Z., Qui, X. J. Power Sources, 2017, 338, 17-25.