Shunt current associated bipolar plate degradation in a multi-cell vanadium redox flow battery

Vanadium redox flow battery (VRFB) has been emerging as the best candidate for large-scale renewable energy storage, which is critical for development of key renewable infrastructures such as e-vehicle charging stations, replacement of diesel generators, power-backup services, etc. However, it is necessary to address certain technological challenges to boost its commercialization. This work emphasizes on the detrimental role of shunt current in scaled-up multi-cell flow systems. It is shown that the uneven single cell voltage distribution in a multi-cell stack, due to very high shunt currents, could lead to graphite degradation near the extreme sides of the positive terminal. A plate and frame-type VRFB stack is deliberately designed with short-flow flow frames in which the shunt current effect is most prominent. It is observed that during charge-discharge cycling, graphitic bipolar plates nearest to the positive terminal are exfoliated, which propagates away from the positive terminal with cycling, and the VRFB ceases to work. The corrosion investigation reveal that the plates are not prone to degradation in the relevant cycling voltage range. This corrosion is successfully linked with high shunt currents in a multi-cell system, which can be mitigated by proper designing of the flow frames. Therefore, using equivalent circuit modeling, the shunt current is estimated for re-designed flow frame. The stack with modified flow frames shows no signs of graphitic corrosion. This work presents an important insight into shunt-current linked bipolar plate degradation which acts as an important design parameter for various stakeholders involved in development of electrochemical flow systems. • Construction of a plate and frame 10-cell VRFB stack • Corrosion of bipolar plates due to high shunt currents in constructed stack • Mitigation of corrosion by redesigning flow frame with low shunt current • Performance analysis of 10-cell and 20-cell VRFB stack