High-purity defect-engineered porous carbons from cellulose amorphization and steam activation for one-million-cycle supercapacitor durability

In this study, we propose a crystallinity-engineering strategy for developing high-purity activated carbon (AC) with a hierarchical pore structure for high-performance supercapacitor electrodes. Our results demonstrate that the precursor's amorphization is critical in determining the activation efficiency and the defect density of the resultant AC materials. By combining ultrasonic-assisted amorphization of cellulose with hydrothermal purification, activation efficiency was significantly enhanced, enabling the formation of highly defective carbon surfaces and optimized pore structures suitable for organic electrolytes. The resulting ACs (Sono-p2-AC) exhibited excellent electrochemical performance, including high capacitance retention (87.1% after 1,000,000 cycles at 3.3 V), low internal resistance, and stable electric double-layer (EDL) behavior under high-voltage operation. Notably, the well-developed porous structure not only improved ion accessibility but also facilitated deep solvent penetration, achieving high purity (∼1026 ppm) during purification. This dual functionality effectively overcomes key limitations of conventional ACs, highlighting the critical role of microstructural and chemical optimization in advancing next-generation energy storage materials.