Microwave-irradiated reduced graphene oxide nanosheets for highly reversible and ultrafast sodium storage

In this study, we synthesize microwave-irradiated reduced graphene oxide with an open structure for the facile intercalation/deintercalation of sodium cations. Images obtained from a scanning electron microscope and a transmission electron microscope clearly showed that microwave-irradiated reduced graphene oxide consisted of finely divided stacks of graphene sheets with a thickness of a few nanometers, which remarkably increased its porosity as confirmed by nitrogen adsorption–desorption measurements. The galvanostatic charge/discharge measurements of microwave-irradiated reduced graphene oxide showed that after 100 cycles at 1 A/g, its discharge capacity (200 mAh/g) was two times higher than that of reduced graphene oxide (100 mAh/g). Furthermore, microwave-irradiated reduced graphene oxide exhibited excellent rate capability and stable cycling performance, even at an extremely high current density of 20 A/g. These results suggest that owing to its high specific surface area and short ion diffusion path, the nanoporous framework of microwave-irradiated reduced graphene oxide can provide a large number of intercalation sites easily accessible by sodium ions.