Freeze-thawed polyacrylamide-polyvinyl alcohol double network with enhanced mechanical properties as hydrogel electrolyte for zinc-ion battery

Hydrogel electrolytes have received increasing attention for their potential applications in the flexible aqueous energy storage devices. An ideal gel electrolyte should deliver both high ionic conductivity and mechanical robustness. In this study, a chemical combined physical cross-linking strategy has been carried out to successfully synthesize polyacrylamide (PAM)-polyvinyl alcohol (PVA) network as hydrogel electrolyte. The fabrication process contains two steps: Firstly, chemical cross-linked (polymerized) acrylamide (polyacrylamide) as the main chain is wrapped by polyvinyl alcohol via a hydrogen bond interaction to form a double network (PAM-PVA). Secondly, the PAM-PVA polymer undergoes freeze-thawed (physical) cross-link (FT-PAM-PVA) to achieve improved mechanical strength without sacrificing the ionic conductivity. Moreover, the internal pore size of FT-PAM-PVA is enlarged as compared to the PAM-PVA that only contains direct hydrogen bond interaction without cross-link. The ionic conductivity of FT-PAM-PVA is as high as 14.63 mS cm−1. And the diffusion coefficients of Zn2+ for Zn-MnO2 battery assembled with FT-PAM-PVA is also improved due to the freeze-thawing operation. This study provides insights to developing high-performance hydrogel electrolytes for aqueous batteries.