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.