Synthesis of the Carbon-Coated Nanoparticle Co₉S₈ and Its Electrochemical Performance as an Anode Material for Sodium-Ion Batteries

Abstract

A Co₉S₈/C nanocomposite is prepared using a solid-state reaction followed by a facile mechanical ball-milling treatment, with sucrose as the carbon source. The phases, morphologies, and detailed structures of the Co₉S₈/C nanocomposite are well-characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. When evaluated as an anode material for sodium-ion batteries, the Co₉S₈/C nanocomposite electrode displays a reversible capacity of ∼567 mA h g^-1 in the initial cycle and maintains a reversible capacity of ∼320 mA h g^-1 after 30 cycles, indicating a larger capacity and a stable cycling performance. For comparison, the electrochemical performances of Co₉S₈ and Co₉S₈/C samples synthesized using the solid-state reaction are also displayed. The ex situ XRD and transmission electron microscopy tests demonstrate that Co₉S₈ undergoes a conversion-type sodium storage mechanism.