Reactant Flow in Flow Batteries

Electrolyte transport considerably affect a Redox Flow Battery (RFB) performance so that it has an important role in its design and operation. RFBs with similar electrodes are often supplied with the same electrolyte, so that unevenness issues have a minor relevance, conversely than non-flow battery such as Li-ion (Trovò and Guarnieri, 2020). However, the continuous flow of conductive liquid electrolytes through hydraulic pipes implies electrical and hydraulic losses (Sánchez-Díez et al., 2021). The former is caused by different cell potentials that drive the vanadium charged species to move along the flow paths inside the stack, resulting in parasitic by-pass currents known as “shunt currents” and consequent Joule losses. The latter are caused by flow friction in the porous electrodes, stack hydraulic paths, and external piping. The design of an RFB stack must take into account these aspects, because they strongly affect the battery operation. The flow field of the electrolytes in the porous electrodes and of their feeding channels have a significant impact on some features of the stack, such as the electrolyte mass transfer rate, the activation and concentration overpotentials and the stack current.