Ion‐Selective Membrane‐Free Dual Sulfur‐Iodine Catholyte for Low‐Cost and High‐Power Flow Battery Applications

Abstract Highly concentrated polysulfide‐ (PS) and iodide‐based (I₃⁻/I⁻) redox couples are promising active materials for redox flow battery applications owing to their high volumetric capacity. However, their applications in lithium redox flow batteries suffer from severe shuttle of iodine and PS and thus require the use of an ion‐selective ceramic membrane for stable operation. This inherent challenge critically limits the practical current density of the flow battery (<1 mA cm⁻²). Herein, we developed a dual PS‐LiI catholyte to simultaneously alleviate the shuttling of iodine and the passivation of Li₂S, demonstrating stable ion‐selective membrane‐free Li‐catholyte cells achieving volumetric capacity between 30–60 Ah L⁻¹_catholyte with long cycle life (>150 cycles) at high current densities (3.8 mA cm⁻² and 5.4 mA cm⁻²). The dual PS‐LiI catholyte not only increases the volumetric capacity and stability, but also removes the resistive and high‐cost ion‐selective membrane for low‐cost, high‐energy and high‐power flow battery applications.