Surface-tension-induced high packing density carbon nanoribbon films with ultrahigh volumetric capacitance

Abstract

For ultrafast-response supercapacitors, it is very challenging for typical porous carbon electrodes to exhibit both high volumetric (C_v) and areal (C_a) capacitances, especially under high rates, due to inefficient pore utilization. Here, a surface tension strategy is deployed to achieve high-density carbon electrodes by eliminating hollow voids, resulting in maximum densification and enhanced ion transport. Specifically, the hollow nanofibers transform into self-compressed nanoribbons with a volume shrinkage of 96.9% and an increase in elastic modulus by six times and electronic conductivity by eleven times. As a result, the volumetric capacitance of carbon nanoribbons (142 F cm⁻³) in an aqueous electrolyte largely exceeded those of the state-of the-art active carbon (62 F cm⁻³) and graphene films (41 F cm⁻³). At an extremely high power of 5 V s⁻¹, the 200-µm-thick nanoribbon film maintained an areal capacitance of 0.68 F cm⁻². Full devices in organic electrolytes delivered volumetric energies up to 18.9 Wh L⁻¹, more than double that of commercial supercapacitors (5–8 Wh L⁻¹) and other frontier ones. Additionally, 50 F soft-pack supercapacitors are fabricated to demonstrate their versatility in practical applications.