Electrochemical properties of cobalt sulfide-carbon composite powders prepared by simple sulfidation process of spray-dried precursor powders

Cobalt sulfide-carbon composite powders were prepared by sulfidation of precursor powders obtained by spray drying. The precursor powders were composed of large particles with dimensions of several tens of micrometers and a hollow morphology with a thin-walled structure. The XRD pattern of the powders sulfidated at 200 °C showed Co9S8 as the main phase and CoS as the minor phase. However, the XRD patterns of the powders sulfidated at 300 and 400 °C showed CoS as the main phase and Co9S8, Co3S4, and CoS2 as the minor phases. The primary particle sizes of the powders sulfidated at 200, 300, and 400 °C were 80, 190, and 230 nm, respectively. Ultrafine cobalt sulfide crystals, a few nanometers in size, were uniformly distributed across the cobalt sulfide-carbon composite sheet. Dot-mapping images revealed that the carbon component was uniformly distributed throughout the composite powder. The optimum sulfidation temperature to obtain the composite powders with superior electrochemical properties was 300 °C. The initial discharge and charge capacities of the composite powders sulfidated at 300 °C at a current density of 1000 mA g−1 were 1089 and 878 mA h g−1, respectively. The discharge capacity of the composite powders sulfidated at 300 °C became stable at around 790 mA h g−1 for up to 70 cycles.