Preparation of Yolk-Shell and Filled Co9S8 Microspheres and Comparison of their Electrochemical Properties.

In this study, we report the first preparation of phase-pure Co9S8 yolk-shell microspheres in a facile two-step process and their improved electrochemical properties. Yolk-shell Co3O4 precursor microspheres are initially obtained by spray pyrolysis and are subsequently transformed into Co9S8 yolk-shell microspheres by simple sulfidation in the presence of thiourea as a sulfur source at 350 °C under a reducing atmosphere. For comparison, filled Co9S8 microspheres were also prepared using the same procedure but in the absence of sucrose during the spray pyrolysis. The prepared yolk-shell Co9S8 microspheres exhibited a Brunauer-Emmett-Teller (BET) specific surface area of 18 m2 g−1 with a mean pore size of 16 nm. The yolk-shell Co9S8 microspheres have initial discharge and charge capacities of 1008 and 767 mA h g−1 at a current density of 1000 mA g−1, respectively, while the filled Co9S8 microspheres have initial discharge and charge capacities of 838 and 638 mA h g−1, respectively. After 100 cycles, the discharge capacities of the yolk-shell and filled microspheres are 634 and 434 mA h g−1, respectively, and the corresponding capacity retentions after the first cycle are 82 % and 66 %. [ABSTRACT FROM AUTHOR]