Lignin‐Alkali Metal Ion Self‐Catalytic System Initiated Rapid Polymerization of Hydrogel Electrolyte with High Strength and Anti‐Freezing Ability

Abstract Hydrogel electrolyte is not resistant to freezing and has weak mechanical properties, and its fabrication is time‐consuming and energy‐consuming, limiting its application. Here, a simple, universal, and fast gelation based on dealkaline lignin (DL) ‐alkali metal ions is developed. The complex formed by catechol and alkali metal ions promotes the equilibrium of redox reactions. The produced SO 4 − ·, OH· and singlet oxygen ( 1 O 2 ) radicals are responsible for the rapid polymerization of vinyl monomers. Alkali metal ions play a dual role in the rapid polymerization and frost resistance of hydrogel electrolytes. By modulating the mass ratio of DL and metal ion concentration, the preferred hydrogel electrolyte can be fabricated in an alkaline aqueous solution for 4 min at room temperature and possesses excellent anti‐freezing performance (0.51 mS cm −1 at −40 °C) and strong mechanical properties (tensile stress: 0.4 MPa, strain: 1125%). The hydrogel electrolyte‐assembled supercapacitor exhibits high stability at low temperatures. The specific capacitance retention is 89.7 % and 88.7 % after 5000 charge/discharge cycles at 25 and −20 °C, respectively. The lignin‐alkali metal ions self‐catalytic system completely different from the reported lignin‐oxidizing metal ion system will open up a new way for the fabrication of anti‐freezing ionic conductors and energy storage devices.