Nitrogen-doped carbon encapsulating FeSe anode with core-shell structure enables high-performance sodium-ion capacitors.

With the associated advantages of low costs and abundant resources, sodium-ion capacitors (SICs) present a suitable means for large-scale energy storage. However, their practical application is still significantly limited by the sluggish electrochemical reaction kinetics of battery-type anodes. Herein, the nitrogen-doped carbon-encapsulated FeSe nanorods (FeSe@NC) with a core-shell structure were prepared via an in-situ self-polymerization and carbonization-selenization approach, which improves ion transport and maintains the structural stability of the nanorods. The designed FeSe@NC nanorods exhibit desirable rate capability with a capacity of 290.7 mAh/g at 10 A/g and long-term cyclability with 84.6 % retention over 6000 cycles at 5 A/g. Moreover, research has shown that the diffusion dynamics of Na is improved in ether-based electrolytes and that the irreversible reactions at low voltages can be inhibited by a high discharge cut-off voltage. Furthermore, we demonstrated the specific sodium storage mechanism and excellent electrochemical reversibility of the FeSe@NC electrode through in-situ and ex-situ characterization techniques. As expected, the assembled SICs with the FeSe@NC anode and active carbon cathode deliver prominent energy/power densities and an ultra-long cycle life over 5000 cycles, shedding new light on the design of transition metal dichalcogenides as anode materials for advanced energy storage systems.