Journal
CHEMISTRY OF MATERIALS
Volume 25, Issue 2, Pages 245-252Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm303611z
Keywords
sodium ion battery; fast rechargeable cathode; hollow nanoparticle; iron oxide; cation vacancy; in situ study
Funding
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
- National Science Foundation - Earth Sciences [EAR-0622171]
- Department of Energy - Geosciences [DE-FG02-94ER14466]
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Cation vacancies in hollow gamma-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 gamma-Fe2O3 nanoparticles can serve as hosts for sodium ions in high voltage range (4.0-1.1 V), allowing utilization of gamma-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-properties correlation. In addition to that, encapsulation of hollow gamma-Fe2O3 nanoparticles between two layers of carbon nanotubes allows fabrication of lightweight, binder-free, flexible, and stable electrodes. We also discuss the effect of electrolyte salts such as NaClO4 and NaPF6 on the Coulombic efficiency at different cycling rates.
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