A holey graphene-based hybrid supercapacitor

Holey graphene with nano-sized holes has numerous electrochemically active sites and an open porous structure, imparting a higher electrocatalytic activity and faster electron and ion transport compared with basal planes in graphene. In this study, holey graphene-based electrode materials, prepared using holey graphene as building blocks, are applied in both electric double-layer capacitor- and lithium-ion battery-type electrodes, because holey graphene possesses more electrochemically active sites originating from the edge sites and facilitates faster electron/ion transport through the holes. The enhanced specific capacity of holey graphene can be attributed to its edge sites, because an additional electric double-layer is formed at the edges. The enhanced rate capability of the Li4Ti5O12/holey graphene composite can be attributed to the in-plane holes, because they enhance lithium-ion transport across the graphene to Li4Ti5O12. We successfully design a hybrid supercapacitor consisting of holey graphene and the Li4Ti5O12/holey graphene composite. The hybrid supercapacitor delivers a maximum energy density of 117.3 Wh·kg−1 at a power density of 0.1 kW·kg−1, and a maximum power density of 19.7 kW·kg−1 is achieved at an energy density of 43.1 Wh·kg−1. The outstanding energy and power density demonstrate the increased specific capacitance of the capacitor-type electrode and rate capability of the battery-type electrode.