A Salt‐Templated Strategy toward Hollow Iron Selenides‐Graphitic Carbon Composite Microspheres with Interconnected Multicavities as High‐Performance Anode Materials for Sodium‐Ion Batteries

Abstract In this work, a facile salt‐templated approach is developed for the preparation of hollow FeSe 2 /graphitic carbon composite microspheres as sodium‐ion battery anodes; these are composed of interconnected multicavities and an enclosed surface in‐plane embedded with uniform hollow FeSe 2 nanoparticles. As the precursor, Fe 2 O 3 /carbon microspheres containing NaCl nanocrystals are obtained using one‐pot ultrasonic spray pyrolysis in which inexpensive NaCl and dextrin are used as a porogen and carbon source, respectively, enabling mass production of the composites. During post‐treatment, Fe 2 O 3 nanoparticles in the composites transform into hollow FeSe 2 nanospheres via the Kirkendall effect. These rational structures provide numerous conductive channels to facilitate ion/electron transport and enhance the capacitive contribution. Moreover, the synergistic effect between the hollow cavities within FeSe 2 and the outstanding mechanical strength of the porous carbon matrix can effectively accommodate the large volume changes during cycling. Correspondingly, the composite microsphere exhibits high discharge capacity of 510 mA h g −1 after 200 cycles at 0.2 A g −1 with capacity retention of 88% when calculated from the second cycle. Even at a high current density of 5.0 A g −1 , a high discharge capacity of 417 mA h g −1 can be achieved.