Ni3S2@S-carbon nanotubes synthesized using NiS2 as sulfur source and precursor for high performance sodium-ion half/full cells

Nickle sulfides are attractive anode materials for sodium-ion batteries (SIBs) due to their rich structures and natural abundance. However, their applications are greatly hindered by the large volume expansion and poor cycling properties. The introduction of hollow structures and heteroatom-doped carbon layers are effective ways to solve these issues. Here, nitrogen, sulfur co-doped carbon coated Ni3S2 (abbreviated as, Ni3S2@NSC) nanotubes were prepared by a novel templating route. During the annealing process, NiS2 acts as both a precursor to Ni3S2 and an S-doped sulfur source. No additional sulfur source was used during the S-doping procedure, suggesting an atomically economic synthesis process. As anodes for sodium-ion half-cells, Ni3S2@NSCs exhibited high discharge capacity of 481 mA h g-1 at 0.1 A g-1 after 100 cycles with exceptional capacity retention of 98.6%. Furthermore, they maintained excellent rate capability of 318 mA h g-1 even at elevated current density of 5 A g-1. Sodium-ion full-cells assembled from the Ni3S2@NSC anodes and Na3V2(PO4)3 (NVP@C) cathodes also presented superior capacities and cyclabilities. These features can be attributed to the N, S co-doped carbon coated hollow structure that provided sufficient contact between the electrode and electrolyte, enhanced surface ion storage performance (capacitive effect), and improved structural stability of electrode materials.