Pitch-derived yolk-shell-structured carbon microspheres as efficient sulfur host materials and their application as cathode material for Li–S batteries

Submicron and micron-sized carbon spheres with high electrical conductivity, micro–mesoporous structure, and empty space are considered ideal sulfur host materials for Li–S batteries. In this study, a new and efficient strategy for the synthesis of yolk-shell-structured carbon microspheres with multishells is introduced. Pitch-derived carbon microspheres with yolk-shell structure, high pore volume, and high electrical conductivity are synthesized by applying yolk-shell-structured Fe₂O₃ microspheres as a sacrificial template. Pitch-infiltrated Fe₂O₃ microspheres transform into yolk-shell-structured carbon (YS_C) microspheres with a specific conductivity of 0.9 S cm⁻¹ after post-treatment and etching with an HCl solution. The discharge capacity of the sulfur-loaded YS_C microspheres for the 200th cycle at a current density of 0.5 C is 686 mA h g⁻¹, and their reversible capacity after 800 cycles at a high current density of 2 C is 412 mA h g⁻¹. In addition, the sulfur-loaded YS_C microspheres show excellent cycling performance, despite their very high sulfur loading of 70 wt%. The excellent cycling and rate performances of the sulfur-loaded YS_C microspheres are attributed to the synergistic effect of the high electrical conductivity of YS_C microspheres, loading of amorphous and ultrafine sulfur, and empty shell layers.