Squeezing excess meso/macropores via self-assembly of zeolitic imidazolate framework units to synthesize dense carbon for high-volume supercapacitors

Abstract

The presence of excess meso/macropores accounts for the low density of porous carbon. Large-size meso/macropores can be easily compressed, for example, mechanically, increasing density to nearly 1.0 g cm−3. However, exceeding 1.0 g cm−3 density requires further compression of small-size meso/macropores, which is a challenge for dense carbon synthesis. Herein, we present a high-density zeolitic imidazolate framework-8 derived carbon (ZIF-8-DC) from the standpoint of carbon nano-unit ordering, that is, the self-assembly of ZIF-8 nano-units caused by solvent volatilization. Excess voids between nano-units are squeezed to increase density to 1.15 g cm−3. The low heating rate in the carbonization step ensures that ZIF-8-DC inherits the highly ordered assembly structure. Face-to-face close contact between carbon nano-units caused by self-assembly not only increases density but also establishes interconnected electron transport channels with extended widths via carbonization welding. More micropores and suitable mesopores created during carbonization give electrode/electrolyte systems a balance of electron and ion carrier densities. Supercapacitors made with symmetric ZIF-8-DC electrodes have a very high volumetric capacitance (195 F cm−3) and rate performance while maintaining a high volumetric power (3.55 kW L−1) and a long lifetime (>60 000 cycles). This strategy provides a new insight into the synthesis of high-volume-performance dense carbon.