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

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.