New operating strategy for all-vanadium redox flow batteries to mitigate electrolyte imbalance

Abstract

Despite the major advantage of an all-vanadium redox flow battery (VRFB) associated with the absence of cross-contamination between the anolyte and catholyte, VRFB systems still suffer from the issue of electrolyte imbalance. This is due mainly to the asymmetric water crossover between the charge and discharge operations, which is rectified only by costly periodic electrolyte rebalancing procedures during long-term usage. In this study, we attempt to mitigate the degree of electrolyte imbalance by designing different initial supporting electrolyte concentrations between the anolyte and catholyte. The new VRFB operating strategy is successfully verified using both 3-D numerical simulations and experimental tests at various charge/discharge current densities. With the same initial anolyte and catholyte compositions, the amount of catholyte and anolyte imbalance during a single charge-discharge cycle at 20 mA/cm2 is measured to be ±5.80ml based on a 50 ml external electrolyte tank. On the other hand, the amount of catholyte and anolyte imbalance is successfully reduced to ±0.70ml using appropriate control of the initial anolyte and catholyte compositions.