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

Abstract

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 degrees 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 degrees 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 degrees 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 degrees C. The initial discharge and charge capacities of the composite powders sulfidated at 300 degrees C at a current density of 1000 mAg(-1) were 1089 and 878 mA h g(-1), respectively. The discharge capacity of the composite powders sulfidated at 300 degrees C became stable at around 790mA h g(-1) for up to 70 cycles. (C) 2014 Elsevier Ltd. All rights reserved.