Uncovering Structural Mechanisms in Anionic Redox Process in Na-Rich Iron Based Cathode Materials using Neutron Diffraction

Na-ion batteries are emerging as a cost-effective and sustainable alternative to lithium-ion batteries, particularly for large-scale energy storage. We have developed new Na-rich iron-based cathode materials, analogous to Li-rich compounds, which show promise for higher capacities by exploiting high valence Fe redox and additional charge compensation through anionic (O²⁻) redox, but have larger voltage hysteresis. Preliminary characterizations—including XRD, STEM, and XAS—suggest reversible phase transitions and anionic redox, but X-rays are limited in probing light elements and differentiating cation disorder. The neutron diffraction offers significant advantages over the lab X-ray data in its ability to collect high-quality diffraction data to high Q, which can help determine site occupancies where species are disordered over various crystallographic sites. We propose to use high-resolution neutron powder diffraction to uncover its structural mechanisms by quantifying Na site occupancy and tracking potential Fe/Sb disorder or migration for the samples at different states of charge. The results will provide critical insight into structural changes driving reversibility in the Na-rich compounds and establish structure–property relationships governing anionic redox.