Progress in flow-battery shunt current investigations: a species-resolved foundational approach

Shunt currents are elusive effects occurring in stacks of flow batteries which received partial attention despite being a major cause of internal losses, directly affecting efficiency and operability. Existing studies model them with electric networks of resistors. For the first time, this paper presents a foundational analysis of the charge carriers moving in the fluid electrolytes due to the electric potential differences among homologous electrodes. Taking the vanadium chemistry as a study case, the conductive, diffusive and convective motions of ions V2+, V3+, VO2+, VO2+, H+, HSO4–, SO42– were analyzed with Navier-Stokes, Nernst-Planck and conservation equations. 3D and 2D numerical implementations allowed analyzing both steady state and transient conditions. Shunt current contributions were computed in stacks of different sizes and under different loads, finding that they produce maximum relative power losses at lower loads, in the range from ~0.17 % in a 5-cell stack to ~6.7 % in a 40-cell stack. The methodology allows identifying the primary factors affecting shunt currents, such as membrane permeability, electrode porosity, and flow channel design. These results shed light on the advanced strategies to mitigate shunt currents in order to improve the battery efficiency.