A promising mechanical ball-milling method to synthesize carbon-coated Co9S8 nanoparticles as high-performance electrode for supercapacitor

A Co9S8/C nanocomposite has been prepared using a solid-state reaction followed by a facile mechanical ball-milling treatment with sucrose as the carbon source. The phases, morphology, and detailed structures of Co9S8/C nanocomposite are well characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. Our experimental results show that not only a process of particle size reduction, the ball-milling treatment also promotes the carbon and Co9S8 combining with each other more effectively to form an ultrafine nanocomposite. When used as an electrode material in supercapacitor, Co9S8/C nanocomposite exhibits a high initial specific capacitance of 756.2 F g−1 at 1 A g−1 and excellent cycling stability with 73.4% retention after 2000 cycles. Its outstanding electrochemical properties are mainly attributed to the nanosize of particles and amorphous carbon layer coating on its surface.