Cellulose-based water-in-salt ZnBr2 hydrogels with multiple functions for energy storage devices

A new simple preparation method for water-in-salt-type cellulose hydrogels filled with ZnBr 2 is reported. The ZnBr 2 hydrogel electrolyte can be applied to zinc-ion hybrid supercapacitors and Zn–Br interfacial batteries. The water-in-salt ZnBr 2 hydrogel serves as a stable electrolyte for good electrochemical performance in zinc-ion hybrid supercapacitors without redox reactions and can participate in the charging/discharging process of the Zn–Br interfacial battery through the redox reaction of halogen anions. The assembled zinc-ion hybrid supercapacitor exhibits a specific capacitance of 241.8 F g −1 at 0.5 A g −1 . Furthermore, after a 10,000-cycle-long charging/discharging test at 5 A g −1 , the coulombic efficiency is found at nearly 100 %. The interfacial battery reaches the highest energy efficiency of 66 % at a current density of 3 mA cm −2 at 0–1.8 V and displays a good cycle life with an 88 % average coulombic efficiency at 3 mA cm −2 . This work expands the application of hydrogels and provides new possibilities for optimizing the high performance of electrolytes.