Biomass-derived carbon nanofibers and electrolytes: Toward high-performance lignin-based supercapacitors with enhanced electrochemical performance

The practical use of lignin in energy storage systems faces several limitations. To improve its application, we undertook the fractionation of alkali lignin (AL) through acetone extraction, yielding two distinct fractions with different molecular weights and phenolic hydroxyl group contents, designated as F1 and F2. Lignin-derived carbon nanofibers (AL-C-800, F1-C-800, F2-C-700, F2-C-800, and F2-C-900) were prepared via electrospinning and subsequent carbonization of lignin fractions (AL, F1, and F2) alongside polyacrylonitrile (PAN). Additionally, three types of electrolytes (AL/KOH, F1/KOH, and F2/KOH) were developed, utilizing AL, F1, and F2 respectively. The all-lignin-based supercapacitor (F2-C-800/(KOH/F2)/F2-C-800) demonstrated enhancements in energy density and specific capacitance by 17.1 % and 17 % compared to the unmodified supercapacitor. Initially, the F2-C-800/(KOH/F2)/ F2-C-800 achieved an energy density of 25.6 Wh kg-1 at a power density of 509 W kg-1 . These results underscore the all-lignin-based supercapacitor's potential for practical applications. This study successfully employed lignin-derived materials in the synthesis of both electrolytes and carbon nanofiber electrodes, advancing the development of renewable supercapacitors with enhanced electrochemical performance. The findings provide valuable theoretical insights into the utilization of lignin for highperformance energy storage systems.