Supramolecularly Assembled Noncarbonized Lignin-Based Fiber Electrodes with Hierarchical Structure for Flexible Supercapacitors

Fiber-shaped supercapacitors (FSSCs) hold immense potential for wearable electronics, yet balancing electrochemical performance, mechanical flexibility, and sustainability remains a challenging. While lignin is a sustainable biomass precursor, conventional carbonization strategies inevitably compromise the intrinsic functional groups and mechanical integrity. Herein, we report a sustainable “supramolecular interaction–structural regulation” strategy to fabricate noncarbonized lignin-based fiber electrodes. Hierarchical porous polypyrrole (PPy)/poly(vinyl alcohol) (PVA)/alkali lignin (AL) fibers are fabricated via wet spinning, freeze-drying, and low-temperature in situ polymerization. The abundant hydroxyl (−OH) groups in the PVA/AL matrix enhance the fiber hydrophilicity and provide supramolecular anchoring sites. Combined with capillary effects from the hierarchical porous structure, these sites promote the uniform in situ polymerization of pyrrole (Py) and form a continuous 3D conductive network for efficient charge transfer. Furthermore, the hierarchical porosity reduces the ion diffusion resistance and facilitates rapid electrolyte transport while maintaining fiber flexibility. The optimized fibers deliver high conductivity (424.4 S/m), fast ion transport kinetics (relaxation time constant of 11.6 s), and a high volumetric capacitance (163.1 F/cm3), significantly outperforming the nonporous control (27.3 F/cm3). The assembled symmetric device delivers a high energy density of 9.3 mWh/cm3 and retains 94.2% of its capacitance under 180° bending, demonstrating a stable electrochemical performance under mechanical deformation. This work provides a feasible noncarbonized strategy for sustainable lignin-based flexible energy storage devices.