Asymmetric variable flow-rate control enhances capacity and efficiency in vanadium redox flow batteries

Vanadium redox flow batteries (VRBs) are promising for large-scale energy storage, yet their long-term performance is often compromised by electrolyte volume imbalances induced by ion migration and self-discharge. Existing flow rate control strategies have primarily focused on enhancing system efficiency, often at the expense of capacity retention and system stability. In this work, we propose a novel flow control strategy that integrates asymmetric and variable flow-rate control strategies to dynamically counteract electrolyte migration during cycling. This asymmetrical variable flow-rate (AVF) strategy is supported by a high-fidelity VRB model developed based on Darcy’s law, which characterizes electrolyte volume variations by incorporating the effects of viscosity, flow rate, and migrated electrolyte volume. With this model, a direct link is established between the state of charge and electrolyte viscosity. We then formulate and solve a constrained optimization problem using a heuristic approach to achieve adaptive flow regulation. Experimental validation demonstrates that the proposed AVF control strategy outperforms existing strategies by significantly reducing electrolyte migration, increasing discharge capacity, and slowing capacity degradation, which offers a practical pathway to enhance VRB longevity and efficiency.