Mitigation of water and electrolyte imbalance in all-vanadium redox flow batteries

Abstract In all-vanadium redox flow battery (VRFB) systems, the electrolyte imbalance between the negative and positive electrodes inevitably occurs and subsequently necessitates costly electrolyte rebalancing procedures for long-term VRFB operation. We propose a new operating strategy for VRFBs that alleviates the electrolyte imbalance issue, which is to employ water and sulfuric acid at different concentrations as initial supporting electrolytes between the negative and positive electrodes. Using a three-dimensional VRFB model that was developed and validated in our previous study, we numerically demonstrate that the degree of electrolyte imbalance can be reduced by using appropriate compositions of the initial anolyte and catholyte. Detailed simulation results reveal that the diffusive water crossover flux between the negative and positive electrodes, which is a main contributor to electrolyte imbalance during charge-discharge cyclic operations, can be effectively suppressed by controlling the initial anolyte and catholyte compositions.