Freeze-Tolerant Hydrogel Electrolyte with High Strength for Stable Operation of Flexible Zinc-Ion Hybrid Supercapacitors

Abstract

Constructing ionic conductive hydrogels with diversified properties is crucial for portable zinc-ion hybrid supercapacitors (ZHSCs). Herein, a freeze-tolerant hydrogel electrolyte (AF PVA-CMC/Zn(CF3SO3)2) is developed by forming a semi-interpenetrating anti-freezing polyvinyl alcohol-carboxymethyl cellulose (AF PVA-CMC) network filled with the ethylene glycol (EG)-containing Zn(CF3SO3)2 aqueous solution. The semi-interpenetrating AF PVA-CMC/Zn(CF3SO3)2 possesses enhanced mechanical properties, realizes the uniform zinc deposition, and impedes the dendrite growth. Notably, the interaction between PVA and EG suppresses the ice crystal formation and prevents freezing at −20 °C. Due to these advantages, the designed hydrogel owns high ionic conductivity of 1.73/0.75 S m−1 at 20/−20 °C with excellent tensile/compression strength at 20 °C. Impressively, the flexible AF quasi-solid-state ZHSC employing the hydrogel electrolyte achieves a superior energy density at 20/−20 °C (87.9/60.7 Wh kg−1). It maintains nearly 84.8% of the initial capacity after 10 000 cycles and a low self-discharge rate (1.77 mV h−1) at 20 °C, together with great tolerance to corrosion. Moreover, this device demonstrates a stable electrochemical performance at −20 °C under deformation. The obtained results provide valuable insights for constructing durable hydrogel electrolytes in cold environments.