In-situ solid-state growth of N, S codoped carbon nanotubes encapsulating metal sulfides for high-efficient-stable sodium ion storage

A self-catalyzed solid-state growth method was developed for the synthesis of N, S codoped carbon nanotubes (NS-CNTs) in-situ encapsulating strings of metal sulfide nanocrystals. In this facile one-pot synthesis, the cross-linking reactions at the initial stage enable a well dispersion of metal ions (further metal sulfide clusters) in the chelate complex. By using the surrounding solid carbon as feedstocks, the metal sulfide clusters on the surface can catalyze the continuous growth of ultralong NS-CNTs in-situ encapsulating strings of metal sulfide nanocrystals. The representative Ni3S2-encapsulated NS-CNTs can deliver reversible capacitances of 500 mAh g−1 (@0.03 A/g) and 463 mAh g−1 (@0.2 A/g) when investigated as anode materials in sodium-ion batteries. In particular, an outstanding initial Coulombic efficiency of 93% is achieved at a current density of 200 mA g−1 together with a long-term stability of over 300 cycles, attributing to the unique core-shell nanostructures with long tubes of over 10 μm and rich N, S co-dopants. Meanwhile, the generated ultrathin solid electrolyte interphases (SEI), consisting of robust inorganics and highly reversible species, such as polyethers, -CFx and carbonate, could successfully afford high stable and efficient sodium ion storage.