An Automatized Rebalancing System to Address Faradaic Imbalance and Prolong Cycle Life in Alkaline Ferrocyanide – Anthraquinone Redox Flow Batteries

Aqueous Organic Redox Flow Batteries are a family of promising energy storage systems. However, they face various challenges related to their lifetime, such as the Faradaic imbalance due to the occurrence of parasitic reaction leading to the fading of its energy storage capacity. Herein, automatization of a rebalancing system to reverse the detrimental effects of  Faradaic imbalance due to the unavoidable presence of small quantities of oxygen in the negative reservoir or hydrogen evolution reaction is developed and implemented in an alkaline flow battery. A membrane-free rebalancing cell is proposed to promote the oxygen evolution reaction and reverse the accumulated charge in the catholyte showing a 100% coulombic efficiency. The programmable logic controller monitors the open circuit voltage to calculate the charge stored in each charge / discharge step and closes a circuit so a fixed voltage is applied to the rebalancing cell when the battery needs to be rebalanced. The system is tested using an alkaline flow battery consisting of ferrocyanide and 2,6-dihydroxyanthraquinone, improving the energy capacity retention from 0.27 % cycle-1 and 0.47 % h-1 without rebalancing system to 100% retention after > 850 cycles and > 24 days (without Ar-filled glovebox), demonstrating the feasibility of this proposed system to address the Faradaic imbalance.