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

Abstract

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.