Tailoring cellulose hydrogel electrolyte using deep eutectic solvent for stable zinc-ion hybrid supercapacitors with enhanced ionic transport.

Zinc-ion hybrid supercapacitors (ZHSs) are considered promising candidates for large-scale energy storage because of their low cost, high safety, and excellent power density. However, in practical applications, the capacity and cycling stability of zinc-ion capacitors are hindered by issues such as dendrite growth and parasitic side reactions. This inherently requires the gel electrolyte to possess excellent mechanical strength and tunable interfacial properties to effectively regulate the electrochemical deposition of zinc. We developed a cellulose-based hydrogel (DES-gel-2) electrolyte prepared via NaOH-urea treatment followed by immersion in a ZnCl2/urea deep eutectic solvent (DES). The experimental results indicate that urea molecules in DES-gel-2 coordinate with Zn2+ and water molecules, leading to a more uniform Zn2+ electric field distribution and effectively suppressing Zn dendrite growth. Meanwhile, residual Na+ ions in the hydrogel electrolyte enhance ionic conductivity and facilitate fast interfacial charge transport, thereby improving electrochemical kinetics. The ZHS based on DES-gel-2 retained over 86.7% of its capacity after 10,000 cycles at a high current density of 10 A·g-1, demonstrating excellent cycling stability. This study presents a novel and effective strategy for regulating Zn deposition behavior through DES-cellulose hydrogel electrolytes, offering new opportunities for the development of high-performance zinc-based energy storage systems.