Preparation of lignite-based porous carbon for high performance supercapacitor and the correlation between pore structures and electrochemical performance

Porous carbon exhibits considerable potential in energy storage field due to its remarkable electrical conductivity and adjustable pore structure. Nevertheless, the electrochemical performance of the material will be significantly impacted by its unreasonable pore structure. In this study, lignite was used as raw material to prepare lignite-based porous carbon by one-step activation method and the pore structure was optimized to improve its electrochemical performance and expand the utilization of low-rank coal. The results reveal that the porous carbon prepared at 600 °C has a higher specific surface area (940 m² g⁻¹) and a suitable pore structure (71 % mesopore), which enable adequate charge storage and fast transport of electrolyte ions, resulting in excellent electrochemical performance. In the three-electrode system, the lignite-based porous carbon exhibits a notable specific capacity of 331 F g⁻¹ at the current density of 0.5 A g⁻¹ and retains 96.4 % initial capacitance after undergoing 10,000 cycles. When assembled into a symmetrical supercapacitor, the device provides an energy density of 6.5 Wh kg⁻¹ at a power density of 250 W kg⁻¹. Even after 10,000 cycles, the capacitance retention rate is kept at 91 %, and the coulombic efficiency remains close to 100 %. These findings demonstrate that cost-effective porous carbon can be prepared by a simple route using lignite, hence exhibiting promise as electrode materials for high-performance supercapacitors.