Intercalation of Sodium Ions into Hollow Iron Oxide Nanoparticles

Abstract

Cation vacancies in hollow γ-Fe2O3 nanoparticles are utilized for efficient sodium ion transport. As a result, fast rechargeable cathodes can be assembled from Earth-abundant elements such as iron oxide and sodium. We monitored in situ structural and electronic transformations of hollow iron oxide nanoparticles by synchrotron X-ray adsorption and diffraction techniques. Our results revealed that the cation vacancies in hollow γ-Fe2O3 nanoparticles can serve as hosts for sodium ions in high voltage range (4.0–1.1 V), allowing utilization of γ-Fe2O3 nanoparticles as a cathode material with high capacity (up to 189 mAh/g), excellent Coulombic efficiency (99.0%), good capacity retention, and superior rate performance (up to 99 mAh/g at 3000 mA/g (50 C)). The appearance of the capacity at high voltage in iron oxide that is a typical anode and the fact that this capacity is comparable with the capacities observed in typical cathodes emphasize the importance of the proper understanding of the structure–propertie...