State-of-health monitoring is key for the correct operation of redox flow batteries, which are affected by parasite reactions like Faradaic imbalance. This work proposes a new non-invasive monitoring method based on the minimum derivative of the cell voltage, used as the input that controls a rebalancing device to recover the capacity loss, extending the battery lifetime.

Abstract

Aqueous Organic Redox Flow Batteries (AORFBs) have received much attention due to the accessibility of their active materials. However, among the key performance indicators that require improvement for AORFBs to become competitive against mature technologies, lifespan is especially critical for stationary energy storage. Faradaic imbalance driven by the occurrence of irreversible electrochemical processes decreases lifespan, so monitoring and correction of this parameter is required to prolong lifespan. This work presents a novel, simple and non-invasive automatized method to monitor the Faradaic imbalance. This method is based on detecting the variation of the minimum derivative of the cell voltage upon cycling, and it is used as the activation criterion for a rebalancing device. The system is tested using an alkaline flow battery consisting of ferrocyanide and 2,6-dihydroxyanthraquinone (2,6-DHAQ), extending the cycle life of the battery to 400 cycles (235 h) without any capacity decay and without Ar-filled glovebox. This demonstrates the feasibility of the proposed system to monitor the state-of-health (SOH) due to Faradaic imbalance and recover the capacity loss.