Numerical study on vanadium redox flow battery performance with non-uniformly compressed electrode and serpentine flow field

Electrode compression is an effective approach to enhance the performance of vanadium redox flow battery (VRFB). Electrode compression can decrease the contact resistance between the electrode and the current collector. Porous electrode compression and deformation are not uniform because of the rib-channel patterns and part of the fibers pressed into the channel. The effects of the non-uniform deformation of a compressed electrode on the performance of a VRFB with flow field are not fully analyzed. In this study, a non-uniform model is proposed to consider the electrode shape deformation and non-uniformity of physical properties inside a compressed electrode. Morphological features of a deformed electrode including the intrusion ratio and local porosities under compression are investigated. Non-uniformly compressed electrodes with different local porosity and permeability are obtained. The predicted cell performance is initially validated using experiment data. The performance of VRFB with non-uniformly compressed electrode and serpentine flow field are investigated under different compression ratios (CRs). The non-uniform model can reasonably predict the charge/discharge and flow behavior. The velocity profile, local current density, and overpotential fluctuation along the rib and channel regions are obtained. The bulk velocity associated with species transport is improved because of the decreased cross-section areas of the flow channel inside the compressed electrode. An appropriate compression can improve the VRFB performance because of the enhanced species transport and increased reaction area when the intrusion part is considered. An optimized electrode CR of 55.7% is found to exhibit the maximum concentration uniformity as well as the minimum current density and overpotential. The present model can guide the VRFB design when the compressed electrode is considered.