Voltage Loss and Capacity Fade Reduction in Vanadium Redox Battery by Electrolyte Flow Control

Capacity fade (loss) in Vanadium Redox Flow Batteries (VRFB) relies mainly on the loss of electrolyte volume in each charge and discharge cycle. The loss of volume in each cycle, also known as the bulk electrolyte osmosis, is due to Vanadium ions' diffusion from the membrane. The lower electrolyte flow rate in VRFB can reduce capacity fade as the electrolyte's velocity across the membrane decreases. However, the lower electrolyte flow increases the battery's voltage loss. A new electrolyte flow management is introduced in this study to address this trade-off, which considers the decrease of both capacity fade and voltage losses in VRFBs simultaneously. The proposed multi-objective flow management shows a significant reduction of both capacity and voltage losses in VRFBs. Moreover, typically complex electrochemical models and equations are needed to model capacity fade in VRFBs, which are not straightforward to model. The capacity fade modeling can lead to the estimation of available capacity and the battery's State of Health (SoH). Therefore, a new simplified mathematical model is proposed for the VRFB's available capacity based on the electrochemical-based capacity fade model results. The model is further developed to estimate the State of Charge (SoC) and the SoH of VRFBs per cycle of charge and discharge.