One-Pot Synthesis of CoSe_x-rGO Composite Powders by Spray Pyrolysis and Their Application as Anode Material for Sodium-Ion Batteries

A simple one-pot synthesis of metal selenide/reduced graphene oxide (rGO) composite powders for application as anode materials in sodium-ion batteries was developed. The detailed mechanism of formation of the CoSe_x-rGO composite powders that were selected as the first target material in the spray pyrolysis process was studied. The crumple-structured CoSe_x-rGO composite powders prepared by spray pyrolysis at 800 °C had a crystal structure consisting mainly of Co_0.85Se with a minor phase of CoSe₂. The bare CoSe_x powders prepared for comparison had a spherical shape and hollow structure. The discharge capacities of the CoSe_x-rGO composite and bare CoSe_x powders in the 50th cycle at a constant current density of 0.3 A g^-1 were 420 and 215 mA h g^-1, respectively, and their capacity retentions measured from the second cycle were 80 and 46 %, respectively. The high structural stability of the CoSe_x-rGO composite powders for repeated sodium-ion charge and discharge processes resulted in superior sodium-ion storage properties compared to those of the bare CoSe_x powders. Spray composites: A simple one-pot synthesis of metal selenide/reduced graphene oxide (rGO) composite powders by a spray pyrolysis process was developed (see figure). This process could be applied in the preparation of crumple-structured cobalt selenide/rGO composite powders with various compositions for applications including anode materials for sodium-ion batteries.