Zinc-Ion–Cross-Linked Sodium Alginate-Wood Hydrogel Electrolyte for Supercapacitors via a Top-Down Design

Cellulose-based hydrogels have gained prominence in hydrogel electrolyte substrate research due to their remarkable flexibility and renewable raw materials. However, cellulose hydrogels produced by traditional bottom-up synthesis strategies generally suffer from insufficient mechanical properties and low areal-specific capacitance in constructed capacitors. This study employs a top-down strategy, utilizing the natural cellulose framework of delignified wood as a structural substrate. Through the synergistic effects of in situ sodium alginate filling and gradient zinc perchlorate cross-linking, a zinc-ion–cross-linked wood-based hydrogel electrolyte (ZWH) was constructed. When the Zn 2+ concentration in the hydrogel electrolyte was 2 mol·L −1 , the resulting ZWH-2 material demonstrated breakthrough performance enhancements: achieving a mechanical strength of 9.47 MPa and exhibiting an ionic conductivity as high as 68.97 mS·cm −1 . Energy storage systems utilizing this electrolyte exhibited exceptional electrochemical performance. The activated carbon symmetric supercapacitor and zinc-activated carbon asymmetric supercapacitor achieved areal-specific capacitances of 165 and 361 mF·cm −2 at a current density of 2 mA·cm −2 . In this study, zinc ions serve dual roles as both cross-linkers for the hydrogel and electrolyte components, facilitating a multifunctional electrolyte system with bend resistance. This study offers innovative perspectives for creating sustainable, adaptable energy storage devices suitable for a broad temperature spectrum.