Boosting reaction kinetics via heterojunction engineering of transition metal selenides for sodium-ion batteries

Transition metal selenides (TMSes), recognized for their high theoretical capacities, are considered attractive anode candidates for sodium-ion batteries (SIBs), yet their performance is often impeded by slow charge/ion transport and pronounced volume changes caused by repeated sodiation/desodiation. To address these issues, we herein report the rational synthesis of a freestanding three-dimensional membrane comprising CoSe 2 /FeSe 2 heterojunction nanoparticles uniformly encapsulated within an interconnected carbon nanofiber network (denoted as CoSe 2 /FeSe 2 @CNFs). Theoretical and experimental results indicate that the abundant CoSe 2 /FeSe 2 heterointerfaces facilitate interfacial charge redistribution and strengthen Na + adsorption, synergistically boosting the reaction kinetics. Benefiting from these structural merits, the CoSe 2 /FeSe 2 @CNFs anode achieves outstanding sodium storage performance, retaining 349.1 mAh g −1 after 600 cycles at 2 A g −1 and preserving 288.5 mAh g −1 even after 2500 cycles under a high current density of 5 A g −1 . Furthermore, the reversible conversion mechanism is directly elucidated through in-situ and ex-situ characterizations and analyses. This work not only demonstrates an effective heterostructure engineering strategy, but also offers a viable pathway toward developing high-performing binder-free anodes for advanced energy storage applications.