Double-Cross-linking Strengthened Cellulose Nanofibrils/Poly(vinyl alcohol) Hydrogel Electrolyte for All-Climate Supercapacitors

An environmentally adaptive and mechanically strengthened binary solvent hydrogel, leveraging double-cross-linking modified and hydrated salt incorporated poly(vinyl alcohol) (PVA) matrix, has been developed for comprehensive property improvement as flexible electronics. Ethylene glycol (EG) as an organic solvent facilitated the formation of bound water. LiCl served as the ionic solute to mitigate volatilization and crystallization through its ion hydration effect while concurrently modifying the ionic conductivity. Further mechanical reinforcement by cellulose nanofibrils (CNFs) created double-cross-linked networks between CNFs and PVA chains in the resultant hydrogel, with tensile strength, elongation at break, and toughness reaching 1.38 MPa, 313%, and 1.79 MJ m–3, respectively. PCEL (PVA/CNFs/EG/LiCl) hydrogel exhibited high conductivity (61.2 mS cm–1) and outstanding antifreezing properties (the ionic conductivity reached 6.5 mS cm–1 at −40 °C). Meanwhile, the PCEL hydrogel maintained ionic conductivities of 28.18 mS cm–1 after 30 days in an evaporative environment. Following assembly into an all-hydrogel-state supercapacitor via in situ polymerization of polyaniline, the supercapacitor exhibited a specific capacitance of 127 mF cm–2 at a current density of 0.2 mA cm–2 while maintaining 81.4% and 80.1% of its initial capacitance at −20 °C and after 30 days of exposure to an evaporative environment, respectively. This method markedly enhanced the environmental adaptability of conductive hydrogels, offering a straightforward approach for the development of supercapacitors for use in all-climate conditions.