Rod-like Ni-CoS@NC@C: Structural design, heteroatom doping and carbon confinement engineering to synergistically boost sodium storage performance.

Currently, conversion-type transition metal sulfides have been extensively favored as the anodes for sodium-ion batteries due to their excellent redox reversibility and high theoretical capacity; however, they generally suffer from large volume expansion and structural instability during repeatedly Na de/intercalation. Herein, spatially dual-confined Ni-doped CoS@NC@C microrods (Ni-CoS@NC@C) are developed via structural design, heteroatom doping and carbon confinement to boost sodium storage performance of the material. The morphology of one-dimensional-structured microrods effectively enlarges the electrode/electrolyte contact area, while the confinement of dual-carbon layers greatly alleviates the volume change-induced stress, pulverization, agglomeration of the material during charging and discharging. Moreover, the introduction of Ni improves the electrical conductivity of the material by modulating the electronic structure and enlarges the interlayer distance to accelerate Na diffusion. Accordingly, the as-prepared Ni-CoS@NC@C exhibits superb electrochemical properties, delivering the satisfactory cycling performance of 526.6 mA h g after 250 cycles at 1 A g, excellent rate performance of 410.9 mA h g at 5 A g and superior long cycling life of 502.5 mA h g after 1,500 cycles at 5 A g. This study provides an innovative idea to improve sodium storage performance of conversion-type transition metal sulfides through the comprehensive strategy of structural design, heteroatom doping and carbon confinement.