Facile Synthesis of FeSe ₂ /rGO with High Reaction Kinetics for Simultaneously Ultrafast and Durable Sodium Storage

Iron selenides are promising anode materials for high performance sodium storage due to their high theoretical capacities, cost-effectiveness, and natural abundance. Nevertheless, their practical applications are severely constrained by intrinsically low electronic conductivity, sluggish Na+ diffusion kinetics, and structural instability during repeated cycling. In this work, sandwiched structure FeSe2/rGO nanocomposite is prepared with a facile microwave-assisted hydrothermal method within only 5 min. The rationally designed layered structure not only suppresses nanoparticle agglomeration but also enlarges the specific surface area, thereby maximizing the accessibility of electrochemical active sites throughout the charge/discharge process. Benefiting from this architecture, FeSe2/rGO exhibits accelerated reaction kinetics in ether-based electrolyte, characterized by reduced activation energy, enhanced Na+ diffusion coefficients, and improved charge transfer dynamics. When employed as an anode for sodium ion batteries (SIBs), FeSe2/rGO demonstrates outstanding electrochemical performance. The underlying Na-storage mechanism was further elucidated through comprehensive ex-situ characterizations. Moreover, by coupling FeSe2/rGO with active carbon (AC) as the cathode to construct sodium-ion capacitors (SICs), the assembled device delivers an impressive energy density of 124.2 Wh kg–1 and a high power density of 9975 W kg–1, along with excellent long-term durability (70.7% capacity retention after 8000 cycles). These results highlight the potential of the FeSe2/rGO-based architecture for next-generation high-performance electrochemical energy storage systems and offer valuable insights into the design of advanced electrode materials.