Confined Water Molecules of Ionic Conductive Hydrogel Electrolyte for the High-Performance, Dendrite-Free, and Safe Flexible Supercapacitor

Hydrogels have emerged as promising electrolyte candidates for flexible energy storage due to their excellent flexibility and high ionic conductivity. However, their practical applications are limited by intrinsic drawbacks such as low energy density and poor cycling stability, primarily attributed to the narrow electrochemical stability window (1.23 V) of water and uncontrolled dendrite growth. Additionally, the susceptibility to water loss and icing at low temperatures further restricts their widespread application. Herein, a facile and effective strategy was provided for the preparation a sodium alginate (SA)/LiCl hydrogel electrolyte (SAL) by leveraging the unique polymer chain aggregation behavior of SA in LiCl aqueous solutions, which could control water molecules’ movements within the hydrogel frame structure. Benefiting from the confined water molecules, the working voltage range of the hydrogel electrolyte was significantly extended, and the ability to inhibit dendrite growth was improved. Moreover, LiCl not only provided high ionic conductivity (68.85 mS/cm) but also served as a water-retaining and antifreeze agent, ensuring long-term operational stability. The assembled symmetric supercapacitors (SALs) demonstrated excellent electrochemical performance with a wide working voltage range (0–1.8 V), high energy density (53.01 Wh/kg at 1800 W/kg power density), and stable temperature-dependent specific capacitance. Additionally, it exhibited exceptional long-term cycling stability, robust Li deposition regulation, flame retardant properties, and reliable power output even under mechanical damage, ensuring safety and stability over a wide working temperature range. This work proposes a simple and versatile method for preparing hydrogel electrolytes to address the existing problems in high-performance flexible energy storage.