No-mixing design of vanadium redox flow battery for enhanced effective energy capacity

Abstract

Abstract The increasing proliferation of intermittent renewables is driving great attention to grid-scale energy storage, particularly vanadium redox flow batteries. The performance of vanadium redox flow batteries has improved remarkably over the last few decades. However, due to the premature cut-off resulting from growing concentration overpotentials at low or high states-of-charge and the discrepancy of active reactants in the tank and stack, the energy capacity of the electrolytes has not yet been fully utilized. In this study, we develop a method for enhancing effective energy capacity of vanadium redox flow batteries, especially in applications with large amounts of electrolytes. The developed system uses four electrolyte tanks to achieve the objective through the avoidance of the mixing of the (dis-)charged and un(dis-)charged electrolytes in tanks. Both experimental and simulative studies are conducted to investigate the performance of the proposed system, which is confirmed to afford a significant increase in the effective energy capacity of more than 10% compared with a two-tank setup. And the enhancement increases with decreasing electrolyte flowrate and increasing electrolyte volume. Besides, the voltage efficiency can be also enhanced by more than 2%. The underlying mechanisms are analyzed in the present study.