Lignocellulose nanofiber-enhanced hydrogel electrolytes with lignin-Al3+ in metal-based neutral deep eutectic solvent for flexible supercapacitors

The mechanical flexibility and high conductivity of hydrogel electrolytes are crucial for their application in supercapacitors. In this study, we developed hydrogel electrolyte based on lignocellulose nanofibers (LCNFs) through nanofibrillation and self-catalytic gelation in a glycerinum/choline chloride/aluminum chloride hexahydrate (Gly/ChCl/AlCl 3 ·6H 2 O) metal-based neutral deep eutectic solvent (DES) system. The lignin-Al 3+ self-catalytic mechanism offered an eco-friendly and sustainable method for synthesizing hydrogel electrolytes, while enhancing their ionic conductivity. The high aspect ratio of LCNFs significantly improved the mechanical strength of the hydrogel electrolyte by facilitating the intertwining of LCNFs with acrylamide molecules. The resulting hydrogel electrolyte demonstrated exceptional mechanical strength (485 kPa), high ionic conductivity (26.1 ms/cm), strong adhesion (225 kPa), and excellent environmental stability (up to −80 °C). A supercapacitor assembled with this hydrogel showed a remarkable specific capacitance (200 F/g) and exhibited high sensitivity in electrical signal applications. This work demonstrates the transformation of wood fiber into functional lignocellulose-based materials, highlighting the high-value utilization of lignocellulose resources for energy storage and other applications.