"Salting out" in Hofmeister Effect Enhancing Mechanical and Electrochemical Performance of Amide-based Hydrogel Electrolytes for Flexible Zinc-Ion Battery

With the development of flexible and wearable electronic devices, it is a new challenge for polymer hydrogel electrolytes to combine high mechanical flexibility and electrochemical performance into one membrane. In general, the high content of water in hydrogel electrolyte membranes always leads to poor mechanical strength, and limits their applications in flexible energy storage devices. In this work, based on the "salting out" phenomenon in Hofmeister effect, a kind of gelatin-based hydrogel electrolyte membrane is fabricated with high mechanical strength and ionic conductivity by soaking pre-gelated gelatin hydrogel in 2 m ZnSO4 aqueous. Among various gelatin-based electrolyte membranes, the gelatin-ZnSO4 electrolyte membrane delivers the "salting out" property of Hofmeister effect, which improves both the mechanical strength and electrochemical performance of gelatin-based electrolyte membranes. The breaking strength reaches 1.5 MPa. When applied to supercapacitors and zinc-ion batteries, it can sustain over 7500 and 9300 cycles for repeated charging and discharging processes. This study provides a very simple and universal method to prepare polymer hydrogel electrolytes with high strength, toughness, and stability, and its applications in flexible energy storage devices provide a new idea for the construction of secure and stable flexible and wearable electronic devices.