Design and experimental validation of an optimal remixing procedure for vanadium flow batteries affected by faradaic imbalance

A novel optimised partial remixing procedure for recovering the capacity loss in vanadium flow batteries that suffer from electrolyte imbalance is implemented and its practical performance is thoroughly evaluated in this paper. The proposed optimal remixing method is assessed by means of experimental tests and compared to the conventional total remixing and to the hydraulic bypass connection between the electrolyte tanks. Special attention is given to the interaction between stoichiometric imbalance, caused by crossover through the membrane, and faradaic imbalance, caused by side reactions that produce a shift in the average oxidation state of the electrolyte. Consistently with the theoretical predictions, it is shown that in actual flow batteries operation, the effectiveness of the conventional remixing methods is very limited when oxidation constitutes the main source of imbalance. In contrast, the proposed optimal remixing allows a substantial capacity recovery, mitigating up to a 67% of the capacity loss originated by oxidation without requiring any additional equipment.