Redox flow batteries for hybrid electric vehicles: Progress and challenges

Electric vehicles have been the focus of much research over the last two decades as the world has sought improved energy utilization and reduced emissions. However, the lengthy charging time, modest range and relatively sluggish performance of batteries have restricted the commercialization of electric vehicles. Hybrid propulsion can overcome most of these shortcomings, with improved energy efficiency and reduced emissions compared to conventional internal combustion engine vehicles (ICEVs). Nonetheless, energy storage issues are still critical. Redox flow batteries (RFB), which continue to mature, have the potential to be fast recharging contenders. Refuelling is possible by rapid pumping of the reactants into the batteries´ tanks. Another feature of RFBs that makes them attractive for EV applications is the separation, in terms of physical location and sizing, of the energy and power components. This adds a degree of flexibility that allows the optimization of the power and energy components for a specific vehicle configuration and performance. This paper concisely reviews RFBs and assesses their potential as a power source for hybrid electric vehicles. Experimental performance data from a 100 cm² laboratory, unit cell, allvanadium redox flow battery (V-RFB) are presented. Based on these results, the size and performance of a V-RFB, suitable for a series hybrid electric vehicle, are estimated and compared with lithium-ion and conventional lead-acid alternatives. The results suggest that V-RFB performance could be improved to match that of the conventional lead-acid, with the added advantage of very rapid recharging.