Self‐Assembled Liquid Crystal Interphase Enabling Long‐Life All‐Iron Redox Flow Batteries

ABSTRACT Aqueous all‐iron redox flow batteries (AIRFBs) are an attractive avenue for large‐scale energy storage due to the safety and cost‐effectiveness of iron. However, the performance and durability of AIRFBs are limited by nonuniform Fe plating, hydrogen evolution and corrosion reactions at the anodes. Herein, a non‐ionic surfactant, polyethylene glycol cetyl ether (Brij 56), is introduced into the electrolyte for stabilizing the anode, which can self‐assemble on the iron surface to form a dynamic liquid crystal interphase. This oriented interfacial layer not only inhibits H 2 O‐induced side reactions by efficient Fe 2+ ion desolvation at the anode interface, but also modulates Fe 2+ ion transport owing to its anisotropic properties, acting as a soft template for the uniform iron deposition. Consequently, the liquid crystal interphase increases the anode reversibility of the AIRFB, achieving a high Coulombic efficiency (CE) of 99.4% and an energy efficiency of 74.5% over 300 h (230 cycles) at 20 mA cm −2 . Furthermore, the AIRFB with liquid crystal interphase retained a CE of 98.2% at a high current density of 60 mA cm −2 and delivered a high capacity of 26 mAh cm −2 . These findings highlight the potential of interfacial engineering to promote performance for the next‐generation energy storage technologies.