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Owing to its fascinating properties (such as high theoretical specific capacity and considerable conductivity), nickel sulfide (NiS) was investigated comprehensively as an anode material in sodium-ion batteries. However, they still suffered from volume expansion and sluggish kinetics, resulting in serious cycle capabilities. Herein, through controlling the kind of molten salts (Na 2 SO 4 , NaCl, and Na 2 CO 3 ) in salt melt synthesis (SMS), a series of NiS with an N, S-codoped carbon layer was successfully prepared, accompanied with different morphologies and structures (earthworm-like belts and triangular and spherical particles). Tailored by the ionic strength and viscosity of molten salts, the as-prepared samples displayed different crystallization behaviors, bringing about a difference in electrochemical performance. As earthworm-like NiS@C was explored as an anode material for SIBs, an initial capacity of 712.5 mAh g −1 at 0.5 A g −1 could be obtained, and it still kept 527.4 mAh g −1 after 100 cycles. Even at 2.0 A g −1 , a capacity of 508.6 mAh g −1 could be achieved. Meanwhile, with the assistance of detailed kinetic analysis, the rapid diffusion behaviors of Na + and redox reaction mechanisms of as-fabricated samples were proven for the enhanced electrochemical properties. Given this, this work is expected to provide a method for designing the morphology and structure of metal sulfides, while shedding light on the orientation of fabricating advanced electrode materials for SIBs.

Iron disulfide (FeS 2 ), a low-cost material, displays considerable theoretical specific capacity (894 mA h g −1 ) but still suffers from shuttling of polysulfides and sluggish kinetics. The MoO 2 electrocatalyst has been successfully applied in Li−S systems, bringing about fascinated electrochemical improvements. Herein, through the gasification coating manners, the ultra-uniform distribution of MoO 2 with abundant catalytic sites is surprisingly obtained, incorporating with the establishment of interfacial Fe− O−Mo bonds. Benefiting from the unique structural traits, optimized FeS 2 @MoO 2 delivers an initial discharge capacity of 1271 mA h g −1 . In addition, after 100 cycles, the capacity of FeS 2 @ MoO 2 could reach ∼308 mA h g −1 , larger than that of pristine FeS 2 . Supported by the kinetic analysis, it could be found that the existing Fe−O−Mo bonds contribute to enhanced ion/e − diffusion behaviors during the intercalation/deintercalation process, ultimately resulting in outstanding lithium-ion storage capacity. Moreover, benefitting from the detailed resistance analysis and the galvanostatic intermittent titration technique test, the existence of MoO 2 and Fe−O−Mo interfacial bonds could facilitate the diffusion of ions/electrons transferring and structural stability. Thus, this work is expected to provide insights into the construction of MoO 2 ultra-uniformly coated FeS 2 with tailored interfacial traits in energy storage systems.

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