Enhanced cycle performance of Li ion battery by graphene sheets covering with SnO@SnO₂ anode materials

The Sn based materials have a high theoretical capacity, but undergo a volume change of about 300% during charge/discharge process in Li ion battery application. In this study, the anode material of SnO@SnO₂ thin film was directly grown on Cu foil by vapor transport method using two zone furnace system. To prevent physical collapse of the electrode due to volume expansion, graphene sheets were covered on SnO@SnO₂ electrode (layer controlled graphene/SnO@SnO₂/Cu structure). The high quality uniform graphene sheets were synthesized using thermal chemical vapor deposition (CVD) system. We investigated the effect of graphene sheets covering for cycle performance improvement of Li ion battery with SnO@SnO₂ anode material. As a result, the cycle performance (80% retention cycle of the initial capacity) was increased from 80 to 210 cycles by graphene sheets covering. The few layer graphene (FLG) sheets covering with moderate defects exhibits the lowest interfacial resistance attributed to easy immersion of electrolyte due to surface functional groups and rise of Li⁺ ion diffusion velocity. The FLG/SnO@SnO₂/Cu electrode exhibits the largest capacity of 288 mAh g⁻¹ due to the surface defect effect.