Ultrafast Preparation of Semicoke-Based Carbon Material with Large-Micropores Structure to Optimize Ion Transport and Enhance Supercapacitor Performance

Electrochemical double-layer capacitors (EDLCs), featuring high power density and excellent cycling stability, typically adopt porous carbon with a tunable morphology and high SSA as electrode material. In this study, semicoke, a high-fixed-carbon coal pyrolysis product, was used as a precursor to prepare large-microporous (1–2 nm) carbon material (SC-3–800) via FJH in 30 s. SC-3–800 shows a total SSA of 1695 m 2 /g, a total pore volume of 0.81 cm 3 /g, and a micropore volume of 0.66 cm 3 /g. The large micropores contribute 881 m 2 /g of SSA (52% of total) and 0.35 cm 3 /g of pore volume (53% of micropore volume), representing the dominant pore structure. FJH enables rapid heating, short-time treatment, and fast cooling. Instantaneous current expands carbon layers and loosens stacking, preventing pore shrinkage and providing sufficient space for gas release and pore formation. Instant high temperature rapidly melts KOH into uniform droplets, forming abundant large micropores with a narrow size distribution. Fast cooling preserves the structure well, finally producing large micropore-dominated porous carbon. This large-micropore structure is highly matched with the size of electrolyte ions, providing abundant active sites, shortening the ion diffusion path, and significantly reducing the transmission resistance. At a 6 M KOH three-electrode system with a current density of 1 A/g, the specific capacitance of SC-3–800 reaches 380 F/g, and the initial Coulombic efficiency is 97%. A button supercapacitor assembled from SC-3–800 and 1 M TEATFB/AN electrolyte achieves a high energy density of 27.0 Wh/kg at 699.1 W/kg. This work presents an efficient method to synthesize large-microporous carbon with high surface area and controlled pores.