Intercalation pseudocapacitance of expanded graphite in sodium-ion capacitors

The intercalation pseudocapacitance of expanded graphite (EG) which was prepared by a process of oxidation and partial reduction on pristine graphite was investigated in this work. The structure of EG was characterised by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM), and the electrochemical performance of EG was measured by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The interlayer distance of EG is enlarged from 0.34 to 0.40 nm, which is demonstrated by XRD and HRTEM. EG electrode exhibits a specific capacitance of 228 F/g at current density of 0.5 A/g. Moreover, the material shows excellent cycle stability after 2000 charge-discharge cycles at a current density of 1 A/g. EG could be a very promising material for the supercapacitors industry.