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.