Operando XANES and EXAFS on High Valence Iron Redox in Na-Rich Cathode Materials

Next-generation battery materials, composed of earth-abundant elements, are required to complement current Li-ion technologies. Here we developed novel Na-rich Fe-based oxide cathodes based on Fe redox couples above Fe (III), exhibiting reversible multi-electron transfer, which are promising for improving the achievable energy density of Na-ion batteries. However, the charge-compensation mechanism and the stabilization of high-valence Fe remain unresolved. In this proposal, we will perform operando Fe K-edge XANES and EXAFS to directly track the evolution of Fe oxidation states and local coordination during electrochemical cycling. Our validated operando coin-cell design can ensure reliable, high-quality transmission data. The results will clarify the stability mechanisms of high-valence Fe, and provide critical design principles for next-generation Fe-based cathodes in sustainable Na-ion batteries.