An extensive scaling-up oriented investigation on carbon felt flow- through and interdigitated Vanadium Flow Batteries cells

In this work, 3D multiphysics model for Vanadium flow batteries (VFBs) was formulated and validated to computationally predict battery performance. The model showed an accuracy >2 % on the cell polarization curve. The electrode permeability, conductivity and internal cell resistance were experimentally measured while electrolyte density and viscosity were identified through novel empirical formulations. An extensive comparative analysis was performed between the flow-through (FTFF) and flow-by interdigitated (IDFF) flow field configurations for a 50 cm2 cell, varying the number and width of channels for the latter. A total of 90 3D simulations were conducted, first imposing constant flow rates of 20, 50 and 80 mL min−1 and subsequently using the resulting pressure drops for the flow-trough cell as input condition. At imposed flow rates, the FTFF configuration demonstrates superior perfor- mance, achieving a peak net power up to 6 % higher than the interdigitated configuration at 50 mL min−1. Conversely, under imposed pressure drop con- ditions, the behavior is more nuanced, showing that IDFF cells can deliver higher net peak power (up to 10 %) for intermediate imposed pressure. This operating condition, rarely investigated in the literature for medium-sized cells, matches closely the working conditions of industrial-scale VFB stacks. Our work aims to provide a detailed explanation of the interplay between fluid dynamics and electrochemical phenomena for the FTFF and the IDFF flow-by configuration cells, focusing on operational aspects and providing valuable scaling-up guidelines.