Shunt currents in vanadium redox flow batteries – a parametric and optimization study

Abstract Shunt currents can hinder the performance and reduce the lifespan of redox flow batteries. This work focuses on finding the best approach to mitigate the shunt currents in vanadium redox flow batteries. A 2-D dynamic phenomenological model was used to compute the shunt currents as a function of the design and operating conditions of a stack with 6 cells and 16 cm2 active area, operated at 80 mA cm−2. In parallel, an equivalent circuit model was used to compute the same shunt currents but with a far smaller computing time. Finally, an artificial intelligence-based software was used to obtain a simple mathematical correlation that best fit the simulated shunt currents, as a function of the external resistances (manifold and flow frame channels, from 0.08 Ω to 2621 Ω), operating current (from 4 A to 512 A) and number of cells (from 5 to 40) in a stack. The correlation was then used to perform a sensitivity analysis to the previous parameters. The results show that the shunt currents decrease with the internal resistances (activation, ohmic and mass transport). Nonetheless, the external resistances have the greatest impact in the shunt currents, particularly the manifold electrical resistance. Based on these findings, a novel redox flow battery stack design (343 cm2 active area), with a high manifold resistance and a low flow frame channel resistance, is proposed to mitigate the shunt currents; cells with no electrochemical activity (dumping cells), evenly inserted into the stack, were considered to increase the manifold resistance. This new stack displays 23.6% lower shunt current losses, 33% lower pressure drop and 19% higher nominal power output at 80 mA cm−2 when compared with a conventional stack.