Fabrication of Antifreezing and Adhesive Hydrogel Electrolytes Based on Zwitterionic Proline for Flexible Zinc Ion Batteries with Low-Temperature Tolerance

Hydrogel-based zinc–ion batteries (ZIBs) stand out as promising flexible energy storage devices, benefiting from their synergistic advantages of high theoretical specific capacity, reliable safety performance, and cost-effectiveness. However, conventional hydrogel-based ZIBs are plagued by inadequate ionic conductivity and structural instability at subzero temperatures, which consequently lead to sluggish Zn-ion migration kinetics and severe capacity decay. Herein, we introduced zwitterionic proline (PL) as an antifreezing additive into cross-linked polyacrylamide/carboxymethyl chitosan (PAM/CMCS) to address the above-mentioned challenges. PL can reduce hydrogen bonds between free water, thus endowing the hydrogel electrolyte (HE) with good antifreezing and antidrying performance, interfacial adhesive, high ionic conductivity (30.20 ± 0.47 mS/cm), and enhanced interfacial adhesion. Notably, the PL additive facilitates more uniform zinc deposition in the PAM/CMCS/PL electrolyte relative to the bare PAM/CMCS electrolyte and the ZnSO4 aqueous electrolyte. Accordingly, the PAM/CMCS/PL HE confers outstanding long-term cycling stability on the Zn//Zn symmetric cell. The asymmetrical Zn//MXene@PANI flexible ZIBs can deliver a specific capacity of 154.8 mAh/g at 0.5 A/g and maintain 84.9% capacity with an excellent Coulombic efficiency above 99% after 500 cycles. This flexible ZIB can withstand severe deformations and operate normally at low temperatures (75.2 mAh/g at 1.0 A/g, even at −30 °C). High-performance flexible ZIBs with outstanding low-temperature tolerance are successfully fabricated in this work, providing insightful references for advancing multifunctional flexible energy storage systems and wearable electronics.