Zinc-based flow batteries, such as alkaline zinc–iron flow batteries (AZIFB), are gaining considerable interest in stationary energy storage applications due to their low cost, high safety, and high power density. A typical AZIFB employs Zn(OH)42−/Zn as the negative redox couple, and as such, it suffers from the formation of Zn dendrites during the charging process (that is, Zn electrodeposition), leading to deteriorated electrochemical performance. Despite tremendous efforts in tackling the issue, it remains a challenge to ensure controllable Zn electrodeposition while achieving high storage performance, especially under practical conditions. Now, Xianfeng Li and colleagues at the Dalian Institute of Chemical Physics and the University of Chinese Academy of Sciences engineer an interfacial bridge — based on an organic compound (ethylenediaminetetraacetic acid, EDTA) — between the negative electrode and the negolyte to address this challenge.
Li and team demonstrated that when used as a negolyte additive, EDTA reacts with Zn(OH)42− via the coordination between the carboxyl oxygen of EDTA and the Zn ion to form EDTA·Zn(OH)3−. EDTA·Zn(OH)3− exhibits a stronger binding interaction with the negative electrode than Zn(OH)42−, creating a bridge at the negolyte-electrode interface. This enhances the desolvation kinetics of Zn ions and facilitates their directional transport towards the electrode surface, enabling uniform and dense Zn electrodeposition with minimal dendrite formation. The effectiveness was manifested by 500 cycles with a Coulombic efficiency of 99.7% in the Zn||Zn symmetric cell, under stringent conditions (current density of 80 mA cm–2 and areal capacity of 25 mAh cm–2). Li and team paired the negolyte with a Fe(CN)64−/ Fe(CN)63− posolyte, showcasing a hundred-watt-level AZIFB stack. The stack, consisting of ten single cells each with an effective electrode area of 1,000 cm2, maintains stable operation for ~30 days.
This is a preview of subscription content, access via your institution