High-performance symmetrical supercapacitor based on coal-derived porous carbon materials prepared via pyrolysis and KOH activation

The high value-added utilization of traditional coal resources is one of the important ways to achieve the strategic goals of carbon peaking and carbon neutrality. Simultaneously, coal-based carbon materials, noted for their cost-effectiveness, superior conductivity, and inherent stability, are emerging as promising candidates for next-generation capacitor technologies. This research presents a series of coal-derived porous carbon by pyrolysis using low rank lignite as raw material and KOH as activator, which are employed in symmetrical supercapacitors filled with liquid electrolytes. The physicochemical properties of the as-prepared electrode materials are characterized by means of scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and their supercapacitive performance are evaluated through cyclic voltammetry and galvanostatic charge–discharge tests. The coal-based porous carbon electrode prepared at an activation temperature of 800 °C (KOH-800) exhibits a specific capacitance of 142.2 F g⁻¹ at a current density of 1 A g⁻¹, and retaining 80% of its capacitance (114.0 F g⁻¹) even at 10 A g⁻¹. The fabricated liquid supercapacitor displays a power density of 999.8 W kg⁻¹ and an energy density of 19.4 Wh kg⁻¹ at a current density of 1 A g⁻¹. Undergoing 10,000 cycles at 2 A g⁻¹, the supercapacitor maintains near-perfect capacitance retention and coulombic efficiency close to 100%, demonstrating its excellent durability and stability for supercapacitor applications.