Preparation of lignite-based porous carbon for high-performance supercapacitors by supercritical chemical tailoring method

Lignite, a low-rank coal with abundant reserves, plays a crucial role in enhancing energy efficiency and mitigating environmental pollution through quality enhancement and improved utilization. Its large supply, low cost, well-developed pore structure, and functional groups make it a valuable starting material for fabricating porous carbon materials used in supercapacitors. During the preparation, a special chemical treatment can create the appropriate pore structure and a large surface area, which helps to speed up ion transport and enhances the supercapacitor performance. This study presents an innovative method for producing coal-based activated carbon (PAC) using an optimized supercritical methanol/alkali treatment. The resulting PAC exhibited a high surface area of 1616.9 m 2  g −1 , a significant microporous volume of 0.78 cm 3  g −1 , and an appropriate percentage of micropores (85.71 %). The PAC electrode achieved a specific capacitance of 263.2 F g −1 at 1 A g −1 , while a PAC//PAC symmetric supercapacitor exhibited an exceptional performance, with an energy density of 16.48 Wh kg −1 at 500 W kg −1 and 1 A g −1 , along with a 98 % capacity retention after 20,000 cycles at 5 A g −1 . This method enables the precise removal of certain oxygen-containing groups from lignite, making it a more environmentally friendly and cost-effective option than traditional chemical activation, while also using less acid and creating a higher number of defective sites. The resulting porous carbon material features a larger specific surface area, a lower ash content, and superior properties.