Optimised partial remixing procedure for mitigating capacity loss of imbalanced vanadium flow batteries

Abstract

Electrolyte imbalance is the main cause of capacity loss in Vanadium Flow Batteries (VFB). Imbalance can be classified into “stoichiometric imbalance” (or “mass imbalance”) and “faradaic imbalance” (or “oxidative/reductive imbalance”). The former is a consequence of vanadium crossover and electrolyte transfer through the membrane, that result in a different amount of vanadium moles on each side of the system. The latter is caused by several side reactions (oxidation with air, hydrogen/oxygen evolution, etc.), that result in a deviation from the ideal overall Average Oxidation State (AOS) of +3.5. Stoichiometric imbalance can be corrected in a simple way, by total or partial remixing the tanks’ contents. In contrast, faradaic imbalance can only be reverted by means of more complex chemical or electrochemical methods. Typically, both types of imbalance are addressed independently. To overcome this limitation, this work presents a novel strategy that considers their interaction for recovering the capacity of imbalanced VFB.

The project that gave rise to these results received the support of a fellowship from ”la Caixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/DI21/11860023.

Peer Reviewed

Postprint (published version)