Interfacial electron regulation of Fe9Ni9S16/FeS heterostructure confined in N-doped carbon nanotube with enhanced reaction kinetics for efficient Na/Li-Ion storage

A novel type of Fe 9 Ni 9 S 16 /FeS heterostructure with sulfur vacancies in situ encapsulated within N-doped carbon nanotubes was initially prepared through a successive pyrolysis and sulfidation strategy. The heterostructure material, with a built-in electric field, not only enables fast ion diffusion and electron transfer , along with favorable capacitive behavior, but also enhances robust storage performance and cycle stability. Tailoring 1D nanotubes with refined interfacial interactions and optimized adsorption sites presents a highly promising yet challenging strategy for advancing Na/Li-ion batteries (SIBs/LIBs). Herein, the intertwined yardlong bean-like Fe 9 Ni 9 S 16 /FeS heterostructures with sulfur vacancies encapsulated in N-doped carbon nanotubes (3 N-Fe 9 Ni 9 S 16 /FeS-3@CNTs) are controllably synthesized through Fe/Ni-catalyzed pyrolysis of dicyandiamide followed by sulfidation strategies. 1D nanotubes with robust outer walls and internal cavity structures shorten the diffusion paths of ions/electrons and buffer volume expansion and aggregation of active materials. The Fe 9 Ni 9 S 16 /FeS heterostructure provides a powerful driving force for charge transfer by forming built-in electric fields, optimizing ion adsorption, while the Fe 9 Ni 9 S 16 features a wider interlayer spacing that allows for frequent Na + /Li + insertion and extraction, thereby enhancing the reaction kinetics within the electrode. Driven by these synergistic factors, the 3 N-Fe 9 Ni 9 S 16 /FeS-3@CNTs demonstrates remarkable electrochemical performance, achieving a substantial reversible capacity of up to 682.1mA h g −1 for SIBs at 0.1 A g −1 and 782.7 mA h g −1 for LIBs at 0.5 A g −1 , alongside exceptional cycling stability in SIBs, maintaining 78.7% of its capacity after 1500 cycles at 1 A g −1 coupling with the ether-based electrolyte. Employing various electrochemical analyses in conjunction with ex-situ characterization techniques and Density Functional Theory (DFT) calculations, the storage mechanisms and phase transition processes are investigated, elucidating the structure-composition-performance relationships. This work paves the way for a new strategy in designing advanced materials with engineered heterostructures and controllable defects for energy conversion and storage devices.