Stable Hydrogel Electrolytes for Flexible and Submarine-Use Zn-Ion Batteries

Abstract Due to their intrinsic safety, low cost, and eco-friendliness, aqueous Zn-ion batteries (ZIBs) have shown significant potential for wearable and flexible electronic devices. However, the lack of a stable and durable electrolyte for flexible ZIBs greatly hampers their applications in harsh conditions during daily use. In this work, we reported a stable hydrogel electrolyte, fabricated by coupling the grafted copolymer xanthan gum–polyacrylamide (XG–PAM) with cotton cellulose nanofiber (CNF), denoted XG–PAM/CNF. The designed XG–PAM/CNF hydrogel electrolyte exhibited high ionic conductivity (28.8 mS cm–1), good adhesion, high mechanical strength, and strong ion adsorption. In addition, it also shows an inhibition effect on the generation of dendrites. The flexible ZIBs with the XG–PAM/CNF hydrogel electrolyte achieved high specific capacity (237 mA·h g–1) and excellent cycling stability (86.2% retention over 1000 cycles at 4 C). Notably, flexible ZIBs withstand severe conditions, such as bending, folding, poking, washing, soaking, and underwater usage. Furthermore, an underwater warning rescue system application was proposed. Consequently, this work provides a new approach and application for the development of reliable and durable wearable energy storage devices.