Nitrogen-doped carbon coated sheet-like face-centered cubic cobalt sulfide for long-life and ultrafast sodium storage

Designing carbon-coated two-dimensional nanosheets is a key approach to enhancing the sodium storage performance of electrode materials. Therefore, this study successfully synthesized nitrogen-doped carbon-coated sheet-like face-centered cubic cobalt sulfide (Co₉S₈@NC) via a solvothermal method combined with sulfurization treatment. Kinetic analyses (including Density functional theory calculations and galvanostatic intermittent titration technique) reveal that this structural design endows the material with a dominant pseudocapacitive contribution and rapid Na⁺ diffusion kinetics. Benefiting from these synergistic effects, the Co₉S₈@NC electrode exhibits a high reversible specific capacity of 491.6 mAh g^-1 at a current density of 1.0 A g^-1, excellent cycling stability (a capacity of 432.2 mAh g^-1 after 400 cycles at 1.0 A g^-1), and superior rate capability (a capacity of 231.1 mAh g^-1 at 8.0 A g^-1). Furthermore, ex-situ X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM) characterizations elucidated the sodium-ion storage mechanism of the Co₉S₈@NC electrode. Importantly, the Na₃V₂(PO₄)₃@rGO//Co₉S₈@NC full cell delivers a robust capacity of 194.2 mAh g^-1 after 200 cycles at 0.5 A g^-1.