Electrochemical Performance of Coaxially Wet-Spun Hierarchically Porous Lignin-Based Carbon/Graphene Fiber Electrodes for Flexible Supercapacitors

All-carbon flexible supercapacitors are highly promising in powering up wearable electronics in smart textiles. However, their low energy density hinders their practical application due to the lack of an effective fabrication method of highly conductive fiber electrodes with high specific capacitance. Herein, we develop a sustainable, scalable, and cost-effective method to fabricate lignin-based carbon/graphene fiber (GF) hybrid electrodes with a hierarchically porous structure. This engineered structure is achieved by coaxially wet spinning a graphene oxide fiber (GOF) as a core structural support and 0–10% lignin/graphene oxide (GO) as a surface layer, followed by carbonization and KOH activation processes. The obtained fiber electrodes exhibit the highest specific capacitance of 260.48 mF cm^–2 at a current density of 0.1 mA cm^–2, which is 11 times that of the neat GF from conventional wet spinning. The entire-device energy density of the assembled fiber-based flexible supercapacitors from the optimal fiber electrode is 5.79 μW h cm^–2 in a H₂SO₄/poly­(vinyl alcohol) electrolyte. Furthermore, the fiber-based flexible supercapacitors show ultralong cycling life and cycling stability (the capacitance retention rate is 98% after 7000 cycles of charge/discharge at a current density of 0.1 mA cm^–2). This work enables the high-value utilization of low-cost carbon precursors (lignin and GO) in potential applications such as energy storage devices for smart textiles.