Natural lignite derived porous foam for all-solid-state supercapacitors†

The conventional production of heteroatom-doped porous carbon typically involves complex multi-step synthesis processes, which significantly restrict its application in supercapacitors. In this study, we developed a straightforward and efficient method for preparing S/N self-doped lignite-based three-dimensional carbon microfoam (SNCF) for supercapacitor applications. X-ray photoelectron spectroscopy analysis reveals that the incorporation of S/N species significantly enhances the electrochemical performance of supercapacitors by improving the hydrophilicity of the carbon materials. The calcined coal-based three-dimensional carbon microfoam exhibits exceptional capabilities in rapid ion transmission and storage, while its robust three-dimensional cross-linked structure effectively facilitates electron transmission. The optimal electrochemical performance was achieved at a calcination temperature of 800 °C. In a three-electrode system, the material demonstrated a remarkable specific capacitance of 222.16 F g⁻¹ at a current density of 1 A g⁻¹, along with excellent electrochemical reversibility and rate performance. Using PVA–KOH as the electrolyte, we assembled an SNCF-800//SNCF-800 all-solid-state symmetric supercapacitor device. This device achieved a specific capacitance of 82.6 F g⁻¹ at a charging voltage of 1.4 V and an energy density of 22.5 Wh kg⁻¹. Notably, the device maintained 99.3% coulombic efficiency even after 10 000 charge/discharge cycles at high current densities, demonstrating exceptional cycle stability. Considering its cost-effectiveness and superior performance, the SNCF-800 material shows great promise for practical applications in energy storage systems. This study provides a valuable approach for developing high-performance supercapacitor materials from low-cost coal resources, potentially paving the way for more sustainable energy storage solutions.