Diol-based Deep Eutectic Solvent for Cellulose Hydrogels from Corncob as Solid Electrolytes for Zinc-Ion Hybrid Supercapacitors

Green solvent pretreatment of biomass represents a promising approach for enhancing the economic value of lignocellulosic derivatives. In this study, corncob biomass was treated with a diol-based deep eutectic solvent (DES) under mild conditions, facilitating efficient cellulose separation. The extracted cellulose was subsequently used to fabricate cellulose hydrogels in an aqueous zinc chloride solution. The resulting hydrogel exhibited a "water-in-salt" effect due to the high concentration of ZnCl₂.Leveraging the antifreeze properties of sorbitol, the system demonstrated outstanding low-temperature electrochemical performance, including a broad operating voltage window and an ionic conductivity of 38.4 mS•cm -1 at -20 °C. At 20 °C, the device achieved an energy density of 206 Wh•kg -1 and a power density of 2701.05 W•kg -1 at a current density of 1 A•g -1 . Moreover, the flexible zinc-ion hybrid supercapacitor (ZHSC) maintained 89% of its capacitance and nearly 100% Coulombic efficiency after 5500 cycles at 20 °C. This work not only advances the development of zinc-ion energy storage devices but also establishes a new paradigm for the green and direct utilization of biomass-derived materials.