Exploring Antiperovskite Cathodes for Na‐Ion Batteries

Recently discovered cathode materials with antiperovskite (AP) structure have shown a promising performance in Li‐ion batteries. However, their applicability in other battery chemistries have not been well explored. In this work, an AP‐based cathode material, Li 2 FeSeO, was systematically studied for application in Na‐ion batteries (NIBs). Delithiated Li 0.8 FeSeO was used as a precursor for preparing an Na‐ion analog. The electrochemical characterization of Na‐based AP cathode revealed a reversible galvanostatic cycling behavior with an initial capacity of 129 mA g −1 and a capacity retention of 57% after 200 cycles when cycled at a current density of 10 mA g −1 . Up to 0.75 Na + can be reversibly inserted into the AP framework. Synchrotron operando and ex situ X‐ray studies revealed a working mechanism based on a dual redox behavior including both Fe and Se, with Se being the main redox actor. The (de)sodiation capacity below expected value is possibly attributed to the formation of a core–shell structure formed due to kinetic limitation of Na + diffusion into bulk structure, thus preventing a full utilization of the available redox activity. These findings establish AP cathodes as viable candidates for NIBs and provide mechanistic insights that can guide their future structural optimization.