In-situ Green Gram Scale Synthesis of Carbon Sphere/Graphene for High-Performance Supercapacitors

Eco-friendly and low-cost methods for the scalable production of high-quality graphene are highly recommended for its use in electric or electronic applications, as the commonly employed graphene oxide (GO) route is associated with drastic oxidizing conditions and toxic reducing agents, where the resultant reduced graphene oxide (rGO) fails to display the electrical properties of pristine graphene. Herein, we present a new green and facile in-situ approach for the high-yielding synthesis of a carbon sphere/graphene nanocomposite through graphite exfoliation via a simple sucrose-mediated mechanical peel-off via ball-milling followed by hydrothermal treatment. The anchoring of carbon spheres on the graphene sheets and oxygen-containing functional groups on the carbon atoms have been revealed using FESEM imaging and XPS analysis respectively. The electrical double layer capacitance together with the pseudocapacitance make the carbon sphere/graphene electrodes promising for energy storage applications, with a high specific capacitance (511 F/g @2 A/g current density) and long-term stability (86.2% capacitance retention @10000 cycles). The high performance of the carbon sphere/graphene nanocomposite is achieved through improved hybridization of the two materials and the consequent synergistic effect as an outcome of the unique in-situ fabrication approach; in addition, insertion of the carbon spheres prevents the restacking of the graphene layers. A symmetric coin cell supercapacitor was constructed from the carbon sphere/graphene nanocomposite and the device displayed a high specific capacitance of 1344 mF/g at 8 mA/g and a good energy density of 186 mWh/kg at a high specific power of 4000 mW/kg. The practical applicability of the fabricated supercapacitor as an energy storage device has also been investigated.