Supercapacitors, also known as electrochemical capacitors, can provide much faster charge–discharge, greater power density, and cyclability than batteries,but they are still limited by lower energy densities (or the amount of energy
stored per unit volume). Here, a novel strategy for the synthesis of functional pillared graphene frameworks, in which graphene fragments in-between graphene sheets, through simple thermal-treatment of ozone (O 3 )-treated
graphene oxide at very low temperature of 200 °C is reported. Due to its high packing density, high content of stable oxygen species, and continues ion transport network in-between graphene sheets, the functional pillaredgraphene
framework delivers not only high gravimetric capacitance (353 F g −1 based on the mass of the active material) and ultrahigh volumetric capacitance (400 F cm −3 based on total mass of electrode material) in aqueous electrolyte but also excellent cyclic stability with 104% of its initial capacitance retention after 10 000 cycles. Moreover, the assembled symmetric supercapacitor achieves as high as 27 Wh L −1 of volumetric energy density at a power density of 272 W L −1 . This novel strategy holds great promise for future design of high volumetric capacitance supercapacitors.