Pitch-derived carbon coated SnO₂–CoO yolk–shell microspheres with excellent long-term cycling and rate performances as anode materials for lithium-ion batteries

SnO₂-based composite materials have been studied as efficient anode materials for lithium-ion batteries. In this study, pitch-derived carbon coated SnO₂–CoO yolk–shell microspheres were synthesized by a spray drying process. Pitch is a widely used source material for electrically conductive carbon. Pitch-infiltrated SnO₂–Co₃O₄ were transformed into SnO₂–CoO–C yolk–shell microspheres by a carbothermal reduction. SnO₂–CoO–C yolk–shell microspheres with a carbon content of 15 wt% exhibited superior cycling and rate performances compared with those of the bare SnO₂–Co₃O₄ microspheres with the same morphologies. The discharge capacities of SnO₂–Co₃O₄ and SnO₂–CoO–C at the 100th cycle were 565 and 812 mA h g⁻¹, while their capacity retentions calculated from the second cycle were 51 and 97%, respectively. Furthermore, SnO₂–CoO–C yolk–shell microspheres exhibited high and stable reversible capacities even at an extremely high current density of 30 A g⁻¹. The discharge capacity of SnO₂–CoO–C yolk–shell microspheres at the 1000th cycle at a current density of 3.0 A g⁻¹ was 775 mA h g⁻¹. The synergetic effect of the pitch-derived carbon with a high electrical conductivity, catalytic effect of the metallic Co, crystal growth minimization of metallic Co and Sn by reciprocal action, and yolk–shell structure with empty shells provided the SnO₂–CoO–C yolk–shell microspheres with excellent lithium-ion storage performances.