Direct Coal Liquefication Asphalt-Based Mesoporous Carbon Prepared by the MgO Template Method for High-Performance Supercapacitors

High-performance supercapacitor electrode materials were prepared using laboratory-synthesized nano-MgO as a template and refined direct coal liquefaction asphalt as a carbon source. Attributed to the graphitization of the raw asphalt, activation of KOH, and the occupying effect of the nano-MgO template, the obtained porous carbons exhibited a certain degree of graphitization and perfectly replicated the structure of the nano-MgO template. The carbon nanoparticles assembled into a 3D hollow structure derived from interconnected mesopores and micropores with a specific surface area of 2408.37 m2·g–1 and a mesoporous volume ratio of 81.46%. This composite pore structure is conducive to the infiltration and transmission of the electrolyte. In a 6 M KOH electrolyte, the specific capacitance of the electrode prepared from PCs–MgO0.5-T900 was 404.63 F·g–1 at 0.5 A·g–1, and it still maintained a specific capacitance of 306.71 F·g–1 at 50 A·g–1, with a capacitance retention rate of 75.80%. In the EMIMBF4 system, the symmetrical supercapacitor assembled by PCs–MgO1-T900 had a specific capacitance of 82.12 F·g–1 at 0.5 A·g–1, and the transfer of the ions was significantly affected by the viscosity of the electrolyte. The long-cycle test shows that PCs–MgO0.5-T900//PCs–MgO0.5-T900 maintained 98.97% performance after 5000 cycles at 5 A·g–1 with 6 M KOH as the electrolyte.