High-mass-density nanographene frameworks for compact capacitive energy storage

Graphene-based supercapacitors are one of highly promising electrochemical energy-storage devices, but remain great challenges in achieving high volumetric energy density due to lacking of the efficient strategy in optimal balance between the mass density and the gravimetric capacitance of graphene electrodes. Here we demonstrate a novel strategy involving smashing the conventional graphene oxide (GO) into nano-sized graphene oxide (NGO) for the fabrication of high-mass-density nano-sized graphene frameworks (NGFs). The NGFs can simultaneously deliver a high mass density of 1.2 g cm−3, high specific surface area of ∼196 m2 g−1, large cumulative pore volume of ∼0.55 cm3 g−1 and interlinked ion transport channels. These features endow the NGF electrode with a volumetric capacitance of 230 F cm−3 at 1 A g−1 in ionic liquid electrolyte, which is among the highest reported values for all carbon-based materials reported so far. Moreover, the fully packaged NGF-supercapacitors using two NGF electrodes with an areal mass loading of 15 mg cm−2 show a stacked volumetric energy density of 52 Wh·L−1, which is comparable to the lead-acid batteries. The innovative strategy demonstrated in this work can be utilized to fabricate high-mass-density graphene-based materials for the development of not only supercapacitors but also other energy-storage devices.