Flexible and self-standing polyimide/lignin-derived carbon nanofibers for high-performance supercapacitor electrode material applications

For attaining flexible and self-standing electrode materials for advanced energy storage devices, we herein report the fabrication and electrochemical properties of carbon nanofibers (CNFs) derived from polyimide (PI) and lignin precursors with different mass ratios (10/0, 9/1, 8/2, and 7/3) via electrospinning and carbonization at 1000 °C. The electron microscopic and photographic images exhibit that the average diameter and flexibility of PI/lignin-derived CNFs decreases and increases, respectively, with increasing the lignin mass ratio in the precursors. The EDS, XRD and Raman analyses confirm that PI/lignin-derived CNFs possess a partially ordered graphitic structure with oxygen self-doping. The electrical conductivity of the CNFs increases from 1.5 S/cm to 2.8 S/cm with the increment of the lignin mass ratio in the precursors. Accordingly, PI/lignin (7/3)-derived CNF is found to have the most excellent electrochemical properties from the analyses using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) test, and electrochemical impedance spectroscopy (EIS). For a symmetric two-electrode supercapacitor based on PI/lignin (7/3)-derived CNFs, high specific capacitance of 83.6 F/g at 1 A/g, power density of 5000 W/kg, energy density of 13.3 Wh/kg, and capacitance retention of ∼100% after 1000 GCD cycle are attained.