Rational Defect and Fluorine Chemistry in Tin Oxide Enables Reversible Na Intercalation with a Stable NaF-Rich SEI Formation.

Significant efforts have been devoted to optimizing the morphology and synthesizing composite materials to activate SnO for sodium-ion batteries. However, challenges arising from its intrinsic crystal structure remain insufficiently addressed. This study aims to introduce both oxygen vacancies and fluorine ions into the SnO lattice, yielding a modified compound with a chemical composition of SnO£F. Notably, SnO£F anode exhibits an enhanced discharge capacity and improved cycling stability. These enhancements are attributed to the accelerated Na diffusion and increased electrochemical activity, as confirmed by kinetics investigations and in situ X-ray diffraction (XRD) characterizations. Furthermore, cryogenic transmission electron microscopy (cryo-TEM) analyses reveal that the coexistence of oxygen vacancies and fluorine anions promotes the formation of a NaF-rich solid electrolyte interface (SEI) layer, showing an excellent compatibility in sodium-ion batteries, which holds prospects for the realization of the next generation of energy storage systems.