Investigation of the Effect of the Flow Rate Control on Capacity Decay in Vanadium Redox Flow Battery

Redox Flow Batteries(RFBs) have been considered as a promising energy storage technology that would be easy to be expanded into large-scale applications such as load leveling, peak shaving, uninterruptable power supplies, emergency backup and renewable integration and so on. RFBs could be classified into Fe-Cr, Zn-Br and V-V RFBs depending on their redox-couple. Among them, Critical attention has been directed to VRFB due to the fact that it produces less mix-up between both sides of electrolytes during cycles.

 In VRFB, differential transfer rate of vanadium ions across the membrane can lead to capacity decay attributing to an increase of vanadium ions in one half-cell compared with the other. The capacity loss can significantly be restored in the physical way which is the remixing of two electrolytes, using a chemical technique, or an electrochemical method.

 In this study, the correlation between the flow rate control of each half-cell side electrolyte and the capacity decay of VRFB is investigated to improve a cycle-life. Under the same flow rate condition, the two half-cell electrolytes respectively have different pressures due to their viscosity. The pressures could be adjusted by controlling the flow rate. Hence, the level control of both electrolytes could be maintained equally through the above methods. The level control can reduce the amount of vanadium ions that transfer to the other side across the membrane compared with the previous way and it can both improve a cycle-life of VRFB and minimize the additional energy for rebalancing.