Environmentally Benign Natural Hydrogel Electrolyte Enables Wide Operating Potential Window for Energy Storage Devices

The development of energy-efficient storage platforms is of paramount importance. Specifically, wearable, smart, flexible, and portable electronic devices with small size, lightweight, and high safety are of urgent need for several applications. To achieve these criteria, green, sustainable, nonflammable, and biodegradable hydrogel electrolytes are essential. To this end, we developed a LiCl@starch-based hydrogel via readily gelatinization of starch. The ionic conductivity of the synthesized gel was tuned via controlled variation of the LiCl content, as revealed by the electrochemical impedance spectroscopy (EIS) measurements. The developed starch gel network with 2 M LiCl showed ultrahigh ionic conductivity of 0.079 Scm^–1 with excellent thermal stability and nonflammability. The rheological characteristics are aligned with enhanced ionic conductivity. Using the commercially available activated carbon (AC), the assembled supercapacitor symmetric device (AC//2-LiCl@starch//AC) withstands a wide operating voltage window of 2.4 V with outstanding specific capacitance (62.3 F/g), energy density, and reliable self-discharge time. These findings imply that this quasi-solid biopolymer gel can be a viable electrolyte for various energy storage devices.