Electrochemical\nPerformance of Coaxially Wet-Spun\nHierarchically Porous Lignin-Based Carbon/Graphene Fiber Electrodes\nfor Flexible Supercapacitors

Abstract

All-carbon\nflexible supercapacitors are highly promising in powering\nup wearable electronics in smart textiles. However, their low energy\ndensity hinders their practical application due to the lack of an\neffective fabrication method of highly conductive fiber electrodes\nwith high specific capacitance. Herein, we develop a sustainable,\nscalable, and cost-effective method to fabricate lignin-based carbon/graphene\nfiber (GF) hybrid electrodes with a hierarchically porous structure.\nThis engineered structure is achieved by coaxially wet spinning a\ngraphene oxide fiber (GOF) as a core structural support and 0–10%\nlignin/graphene oxide (GO) as a surface layer, followed by carbonization\nand KOH activation processes. The obtained fiber electrodes exhibit\nthe highest specific capacitance of 260.48 mF cm^–2 at a current density of 0.1 mA cm^–2, which is\n11 times that of the neat GF from conventional wet spinning. The entire-device\nenergy density of the assembled fiber-based flexible supercapacitors\nfrom the optimal fiber electrode is 5.79 μW h cm^–2 in a H₂SO₄/poly­(vinyl alcohol) electrolyte.\nFurthermore, the fiber-based flexible supercapacitors show ultralong\ncycling life and cycling stability (the capacitance retention rate\nis 98% after 7000 cycles of charge/discharge at a current density\nof 0.1 mA cm^–2). This work enables the high-value\nutilization of low-cost carbon precursors (lignin and GO) in potential\napplications such as energy storage devices for smart textiles.