Regulating Water Activity and Solvation Structure via Zwitterion‐Enhanced Polymer Electrolyte for Long‐Life Zn‐Ion Hybrid Capacitors with Low‐Temperature Applicability

Abstract The development of aqueous Zn‐based energy storage systems is plagued by poor cyclability and limited operating temperatures caused by Zn anode issues and highly active water. Herein, a frost‐tolerant hydrogel electrolyte (PABCHE) promoted by hydroxyl‐rich β‐cyclodextrin (β‐CD) and zwitterionic betaine (BA) additives is fabricated in situ to protect Zn anodes and enhance low‐temperature adaptability. Both additives synergistically disrupt the hydrogen‐bonding network between water molecules to remarkably reduce the freezing point of PABCHE and alleviate water‐associated side effects. Zwitterionic BA constructs ion‐migration channels and regulate Zn 2+ solvation structure, promoting uniform and rapid transport of Zn 2+ . Additionally, PABCHE renders the Zn 2+ homoepitaxially depositing along the (002) plane to achieve dendrite‐free Zn anodes. As a result, versatile PABCHE enables Zn//Zn cells to cycle stably for 1100 and 3600 h at 20 and −20 °C, respectively. Furthermore, the Zn‐ion hybrid capacitors optimized by PABCHE deliver favorable cyclability over 30000 cycles at 20 °C (with a capacity retention of 81.8%) and −20 °C (with a capacity retention of 84.2%). Additionally, PABCHE can be applied as a flexible strain sensor for real‐time monitoring of physiological activities. This work offers valuable insights for developing antifreeze hydrogel electrolytes toward applications of dendrite‐free low‐temperature Zn‐based devices and strain sensors.