Breakthroughs in Designing Commercial-Level Mass-Loading Graphene Electrodes for Electrochemical Double-Layer Capacitors

Since the first exploration of graphene as an electrode material for electrochemical double-layer capacitors (EDLCs) in 2008, great effort has been made to develop high-performance graphene-based electrodes with commercial-level mass loading up to 10 mg/cm(2) or thickness up to 200 mu m. However, a thick electrode usually possesses a long diffusion distance for electrolyte ions and a low accessible surface area, leading to gravimetric capacitance degradation, especially at high current density. In recent years, novel techniques have emerged to solve these issues and have brought significant breakthroughs for graphene-based EDLCs. An ultra-high areal capacitance (>2 F/cm(2)) has been achieved at a large graphene mass loading (>10 mg/cm(2)) without sacrificing gravimetric capacitance. This article reviews this recent significant progress and emphatically discusses challenges and strategies for highly efficient graphene electrodes to achieve high values for three types of capacitance (gravimetric, volumetric, and areal) at commercial-level mass loadings from the viewpoint of materials design.