Mesoporous graphitic carbon microspheres with a controlled amount of amorphous carbon as an efficient Se host material for Li–Se batteries

Abstract

Synthesis of graphitic carbon (GC) microspheres with well-developed mesopores, high pore volumes, and high electrical conductivities remains a challenge in the energy storage field including Li–Se batteries. In this study, GC–TiO microspheres with optimum structures are synthesized as host materials for amorphous elemental Se by the modification of activated carbon (A-C) microspheres. Some amount of amorphous carbon (AC) is transformed into GC using Fe nanocatalysts. TiO nanocrystals reduced the crystal growth of Fe nanocatalysts during the formation of GC layers. The selective oxidation of AC in the microporous GC–AC–Fe–TiO composite microspheres at 350 °C with a controlled oxygen content and the subsequent HCl etching process produced mesoporous GC–TiO composite microspheres with a controlled amount of AC. High-volume mesopores with pore sizes ranging between 4 and 50 nm are generated after the formation of GC–TiO microspheres. The GC–TiO/Se microspheres with a high Se loading of 70 wt%, which is achieved by the melt inclusion process, exhibit excellent electrochemical properties as a cathode material for Li–Se batteries. The discharge capacities of GC–TiO/Se microspheres for the 850^th cycle at a current density of 0.5C is 584 mA h g⁻¹, and the capacity retention measured from the second cycle is 84%.