Double Morphology of Co9S8 Coated by N, S Co-doped Carbon as Efficient Anode Materials for Sodium-Ion Batteries.

Co9S8 is a potential anode material for its high sodium storage performance, easy accessibility, and thermostability. However, the volume expansion is a great hindrance to its development. Herein, a composite containing Co9S8 nanofibers and hollow Co9S8 nanospheres with N, S co-doped carbon layer (Co9S8@NSC) is successfully synthesized through a facile solvothermal process and a high-temperature carbonization. Ascribed to the carbon coating and the large specific surface area, severe volume stress can be effectively alleviated. In particular, with N and S heteroatoms introduced into the carbon layer, which is conducive to the Na+ adsorption and diffusion on the carbon surface, Co9S8@NSC can perform more capacitive sodium storage mechanism. As a result, the electrode can exhibit a favorable reversible capacity of 226 mA h g-1 at 5 A g-1 and a favorable capacity retention of 83.1% at 1 A g-1 after 800 cycles. The unique design provides an innovative thought for enhancing the sodium storage performance.