Flexible High-Energy-Density Hybrid Supercapacitors with Alkaline Hydrogel Electrolytes

Ionic hydrogel electrolyte supercapacitors are the next-generation flexible wearable devices for energy storage, which have superb conductivity and mechanical performance, thus arousing great attention. However, existing hydrogel electrolyte supercapacitors exhibit obvious limitations in electrochemical performance (e.g., narrow working voltage range, low power density and energy density, and unstable cycle life at high current density). In this work, an alkaline ionic conductive hydrogel (PEGMA) was prepared by copolymerization of acrylamide (AM), ethylene glycol methyl ether acrylate (MEA), and poly(ethylene glycol) methyl ether acrylate (PEGA), and potassium hydroxide (KOH) was selected as a conductive substance to form hydrogel electrolytes that could be used in flexible hybrid supercapacitors. The assembled supercapacitor (PEGMA-ZHS) exhibited superb electrochemical properties, such as a high energy density (356.6 Wh kg–1) at 2647.4 W kg–1 powder density and a wide (0.2–2.0 V) operating voltage range and high stability with a capacity retention of nearly 100% after charging/discharging for 10,000 cycles at 10 A g–1 current density. The strategy would make progress in exploring hydrogel-based flexible supercapacitors with excellent electrochemical performance for electronic devices.