Humidity-modulated synthesis of surface-oxidized nickel phosphide‑carbon nanofibers as multi-functional sulfur hosts for lithium‑sulfur batteries

Although lithium‑sulfur batteries offer high theoretical specific capacity and potential environmental benefits, they still suffer from the polysulfide shuttle effect, sluggish redox kinetics, and the intrinsically low electrical conductivity of sulfur. To overcome these limitations, free-standing nickel phosphide‑carbon nanofibers (Ni x P/C) were synthesized as efficient sulfur host materials. The nanofiber mats were fabricated by electrospinning at different relative humidity (RH) levels (25%, 30%, and 35%), followed by one-step thermal treatment, and were characterized using multiple techniques. The results showed that nanofibers prepared at 30% RH (Ni x P/C-30%) achieved the optimal structure, morphology, and surface oxidation, which in turn provided high electrical conductivity and a well-balanced surface area-pore volume ratio. Consequently, improved physicochemical properties promoted lithium polysulfide adsorption and catalytic conversion, delivering excellent electrochemical performance at both ambient and low temperatures. Notably, the Ni x P/C-30% electrode delivered 1344.9 mAh g −1 at 0.1C and retained 87% capacity after 100 cycles at 0.2C. It further achieved 830 mAh g −1 at 0.2C even at −20 °C, demonstrating its strong potential for practical use.