Rice straw -derived lignin-based carbon nanofibers as self-supporting electrodes for supercapacitors and lithium-ion batteries

Self-supporting carbon fibers are extensively employed as active components in energy storage systems due to their tunable microstructures, large specific surface area, affordability, and excellent electrical conductivity. Nevertheless, conventional methods for producing carbon fibers typically involve complicated synthesis processes, environmental pollution, and high energy consumption. In this study, lignin-based carbon nanofibers (LCNFs) were prepared through electrospinning and subsequent heat treatment. The morphologies, crystal structures, and specific surface area of the as-prepared LCNFs were characterized using scanning electron microscopy, X-ray diffraction and nitrogen sorption isotherms. The influence of lignin content on the on the structural, morphological, and electrochemical properties of the carbon nanofibers were examined, particularly in their applications as supercapacitor and lithium-ion battery anode materials. The as-prepared LCNF-2 possess the highest specific surface area of 468.3 m² g^-1. As a self-supporting electrode in supercapacitors (SCs), the LCNF-2 delivered 256.3 F g^-1 at 0.2 A g^-1, and capacitance retention of 62.0 % at the current density raised from 0.5 to 10 A g^-1. The assembled LCNF-2//LCNF-2 symmetric supercapacitor demonstrated a specific capacitance of 168 F g^-1 at 5 A g^-1, maintaining 100 % capacitance retention after 10,000 cycles. Additionally, it achieved an energy density of 5.6 Wh kg^-1 at a power density of 1250.0 W kg^-1. As a lithium-ion batteries (LIBs) anode, the LCNF-2 showed a discharge specific capacity of 1108.3 mAh g^-1 and a discharge specific capacity of 377.3 mAh g^-1 in the first cycle, with a capacity retention rate of 84.6 % after 100 cycles at 1C. This work offers a novel approach for the high-value utilization of agricultural waste straw lignin in energy storage devices.