Delayed and Partial Mixing Method of Operating Multi-Tank Redox Flow Battery Systems

Abstract

To reap the benefits of conventional single and multi-tank redox flow battery (RFB) fluid systems, we investigate a delayed and partial mixing methodology for operating RFB tank systems to maximise electrolyte utilisation and storage capacity. The method modulates an optimised mixing timeframe and mixed amounts of momentarily (un)circulated electrolytes in two vertically separated tank sections. The gravity-assisted mixing between the tank sections achieved by siphon or automatic valve ensures continuous uninterrupted flow occurs in a single direction within the cell while lowering additional auxiliary components/energy and system complexity/cost. We applied a detailed Multiphysics simulation of a test vanadium RFB cell to demonstrate the methodology and its capabilities - especially for larger tank volumes. Significant concentration overpotential reduction with the delayed and partial mixing leads to an increment in discharge capacity and energy efficiency up to 6.5% and 2%, respectively, compared to the conventional single tank system. The practical applicability of the investigated system was also discussed as promising for commercial RFB deployments.