A Model for All-Vanadium Redox Flow Batteries: Introducing Electrode-Compression Effects on Voltage Losses and Hydraulics

In this study, a 2D-model of an all-vanadium redox flow battery is presented including effects of electrode compression on voltage losses and hydraulics. A parametric study has been performed to investigate the influence of different parameters (such as material properties, geometric data, and operating conditions) on the cell performance. The model equations were solved by using COMSOL Multiphysics software. The results of the study show that a reduction of the electrode thickness by compression lowers the area specific resistance (ASR), the porosity and the hydraulic permeability, which results in a better cell performance but also a higher pressure drop. The electrode compression mainly re-duces the ohmic losses. Furthermore, the ASR has a high sensitivity to changes of the specific surface area a(0) and the reaction constant k(0). These material parameters control the activation overpotentials of the reactions and are independent of the compression. Due to the high ohmic losses, the goal for further developments in redox-flow-cell design should be to minimize the electrode thickness and to maximize the hydraulic permeability along with the surface area of the electrode. The optimal compression rate depends strongly on the material properties and has to be a trade-off between electrical and hydraulic performance.