Antifreezing Zwitterionic-Based Hydrogel Electrolyte for Aqueous Zn Ion Batteries

Hydrogel electrolytes have attracted great attention because the properties of integrated conductivity and mechanical flexibility endow them with potential applications in flexible solid-state batteries. However, hydrogels are easy to freeze when the temperature drops below zero, resulting in the reduction of ionic conductivity and mechanical strength of hydrogels. Herein, an antifreezing polymer hydrogel electrolyte was developed by introducing a zwitterionic group and salt into the double-network polymer. The polymer hydrogel electrolyte possessed a perfect ionic conductivity of 10.38 mS cm–1 at −20 °C and could remain unfrozen until −50 °C. A flexible solid-state Zn//LiFePO4 battery assembled with the prepared hydrogel electrolyte exhibited a discharge capacity of 126.1 and 75.1 mAh g–1 at 20 and −20 °C at 1 C, respectively. In addition, it showed quite perfect cycling performance and maintained a capacity retention of 72.6% after 1000 cycles with a favorable Coulombic efficiency (∼100%) at −20 °C at 1 C. The hydrogel electrolyte with perfect antifreezing performance is supposed to broaden the range of working temperature and practical applications of the zinc ion battery.