Conductive, flexible, and adhesive lignin-polyacrylic acid hydrogel crosslinked with aluminum ions for...

Hydrogel electrolytes have gained considerable attention as key components in flexible supercapacitors for electronic devices. However, traditional hydrogels face challenges due to inadequate mechanical properties and low energy density in supercapacitor applications. In this study, a highly conductive and flexible hydrogel (PAA-LS-Al³⁺) composed of polyacrylic acid (PAA), lignosulfonate (LS), and Al³⁺ was fabricated. The optimal ratio of LS to water, along with specific amount of AlCl₃·6H₂O contributed to rapid polymerization redox pairs of Al³⁺/Al²⁺ and hydroquinone/quinone, thus facilitating hydrogel preparation. High concentrations of LS and Al³⁺, along with effective Al³⁺ complexes, endowed the hydrogel with ionic conductivity of 5.80 S·m^-1, tensile strength of 420.64 kPa at 830 % elongation, and compressive strength of 2860 kPa with strain of 99.87 %. When assembled into a supercapacitor with moisture content of 25.12 %, the specific capacitance of hydrogel electrolyte exhibited 306.19 F·g^-1, maximum energy density of 27.22 Wh·kg^-1, and power density of 2398.39 W·kg^-1. After 5000 cycles, the supercapacitor maintained capacitance retention of 78.1 % and a coulombic efficiency of 99.8 %. The PAA-LS-Al³⁺ hydrogel with long lifespan and good stability showed great potential for practical applications in flexible power supplies.