Enlarging ion-transfer micropore channels of hierarchical carbon nanocages for ultrahigh energy and power densities

Abstract

Increasing the energy density of supercapacitor without sacrificing its high power is an everlasting pursuit in energy storage. Using ionic liquid electrolyte with high operating voltage can increase the energy density but usually at the expense of power density due to the large ion size, low ionic conductivity and high viscosity. Herein we demonstrate a simultaneous increase of the energy and power densities with ionic liquid electrolyte (EMIMBF4) mainly by enlarging the ion-transfer micropore channels of the electrode material, i.e., the unique hierarchical carbon nanocages (hCNC). Boudouard reaction is adopted to tune the micropore size while remaining the hierarchical framework of hCNC. Meanwhile, the specific surface area, pore volume and conductivity are also increased under optimal activation temperature. Such a unique modification boosts the large-sized ion transfer, leading to the obvious decrease of equivalent series resistance and the dramatic increase of supercapacitive performance thereof. The optimized product exhibits an energy density up to 153.8 W h kg−1 at the power density of 1.8 kW kg−1, and maintains 54.0 W h kg−1 even at an ultrahigh power density of 480.1 kW kg−1. This study demonstrates an effective way to explore advanced electrode materials by the fine regulation of micropores and related properties.