Inverse Opaline Metallic Membrane Addresses the Tradeoff Between Volumetric Capacitance and Areal Capacitance of Supercapacitor

Increasing the electrode thickness of energy‐storage devices can enhance the areal capacitance, but often results in a significant decrease in the volumetric capacitance. This tradeoff between the volumetric capacitance and electrode thickness, which is ascribed to the poor ion and charge transport in thick electrodes, has been a major obstacle to realizing high‐energy‐density of devices. Herein, an inverse opaline metallic membrane (IOMM) is reported as a stable and high‐rate electrode, which displays a linear increase in volumetric capacitance as a function of electrode thickness. The IOMM is fabricated through simple self‐assembly, photopolymerization, and subsequent chemical co‐deposition of metallic compounds to yield a 3D porous and interconnected construct of highly conductive and capacitive Ni/Ni(OH)2. IOMM can be used as a binder‐free and current‐collector‐free electrode of SC, which possesses an outstanding volumetric capacitance of more than 1500 F cm−3 over 18 000 charge/discharge cycles, and an ultrahigh areal capacitance of 18.2 F cm−2. An inverse opaline metallic membrane (IOMM) is reported as a binder‐free and current‐collector‐free electrode of supercapacitor. The interconnected porous scaffold and conformal coating of metallic compounds of the IOMM address the tradeoff between volumetric and areal capacitance in thick electrodes. The stable porous microstructure also ensures its outstanding capacitive retention during long charge/discharge cycles.