Insights into low-impurity activated carbon materials for supercapacitors with high-voltage and ultra-long cycle stability

Ensuring the long-term cycling stability of energy storage devices requires rigorous purity control of active carbon (AC) materials, making it a critical aspect of the manufacturing process. However, despite the presence of naturally occurring impurities in biomass-derived ACs, limited research has focused on effective purification methods for ACs used in supercapacitor applications. In this study, we present a simple hydrothermal purification method using only deionized (DI) water to remove both metallic and non-metallic impurities. By utilizing the enhanced self-ionization and high fluidity of water molecules under elevated hydrothermal conditions, this process achieved a higher purification efficiency (∼94.5 %) than conventional chemical purification methods (∼92.1 %), with minimal textural changes of the ACs. Quantitative analysis of 17 impurity elements via ICP-OES, along with excellent capacitance retention of 86.7 % after 100,000 cycles in an acetonitrile-based electrolyte, demonstrates the effectiveness of this straightforward, environmentally friendly strategy for impurity control and long-term electrochemical stability.