Hydrothermal preparation and electrochemical properties of Co-S alloys

The Co-S alloys were prepared by a hydrothermal method and the process parameters were optimized. The surface morphology and phase structure of Co-S alloys were characterized by SEM and XRD. The electrochemical properties of Co-S alloys were investigated by galvanostatic charge and discharge tests, cyclic voltammetry and AC impedance. The results indicated that the as-prepared Co-S alloy, which was synthesized using a 70% packing volume of the reaction solution at 160°C for 12 h, showed good crystallinity. This alloy consisted of metallic Co and Co₉S₈ phases with a cross-linked lamellar morphology of about 50 nm in thickness. It possessed a maximum discharge capacity of 536 mAh/g at charge and discharge current density of 150 mA/g and a good cycling stability with capacity retention rate of 77.4% after 50 cycles. The redox reactions between Co and Co(OH)₂ were the main reaction during charge and discharge. Partial dissolution of Co reduced the active material and led to capacity decay.