Broadening the Horizons of Fe-Metal in Static Batteries with Anion Exchange Membranes

Abstract

Iron-based batteries are attracting growing attention as sustainable and cost-effective systems for large-scale energy storage. Iron offers key advantages in aqueous environments, including natural abundance, high theoretical capacity, and environmental safety. However, the practical deployment of Fe-based batteries is hindered by parasitic hydrogen evolution, dendritic Fe deposition, and the narrow electrochemical window governed by the Fe²⁺/Fe3⁺ redox couple. To address these intrinsic challenges, we introduce a new cell design that employs an anion-exchange membrane (AEM) to separate the Fe anode from the catholyte. The AEM selectively conducts anions while blocking Fe²⁺ migration toward the cathode compartment, effectively preventing cross-contamination. This configuration enables the Fe anode to be coupled with a wide range of aqueous cathodes without mutual interference, thereby broadening the design flexibility of iron-based systems. Using concentrated LiCl or NaCl electrolytes as the catholyte and mixed FeCl₂–LiCl/NaCl solutions as the anolyte, we demonstrate stable operation of electrochemical cells composed of Fe anodes and LiMn₂O₄ or NiFe(CN)₆ cathodes. These systems deliver a capacity of 120 and 60 mAh g⁻¹, respectively, based on the cathode mass. We believe that this newly developed concept provides a practical route to stabilize iron electrochemistry in aqueous media, offering a platform for the design of scalable, low-cost, and environmentally benign energy storage technologies suitable for grid applications.