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.