Robust Hydrogel Electrolyte for Extra-Low Temperature Zinc Ion Storage Enabled by Nanoconfinement Effect

The growing demand for energy storage in extreme environments, including aerospace, polar regions, and deep sea, necessitates batteries that can operate reliably at ultra-low temperatures. Zinc-ion batteries (ZIBs) have emerged as promising candidates for such applications, with hydrogel electrolytes offering an appealing combination of safety, flexibility, and stability. However, conventional hydrogel electrolytes, containing high proportions of free water (> 80 wt.%), suffer from critical limitations, including narrow electrochemical stability windows, unwanted metal-anode side reactions, and freezing at subzero temperatures. To address these critical challenges, we introduce a novel nanoconfinement strategy that restricts free water mobility by embedding ∼60 nm polystyrene within a polyacrylamide (PAM)-based hydrogel matrix. The resulting 30PS-nc-PAM hydrogel electrolyte exhibited high zinc ionic conductivity and mechanical robustness. Demonstrating practical application at -40°C, an ultralong lifespan of 5000 cycles was achieved in a Zn|30PS-nc-PAM|PANI flexible cell. Even at -70°C, a Zn|30PS-nc-PAM|VO₂ coin cell exhibited a high specific capacity of 131.1 mAh g^-1 at 0.1 A g^-1, outperforming most of the recently reported low-temperature ZIBs based on hydrogel electrolytes. The nanoconfinement strategy effectively addresses major limitations of conventional hydrogels in terms of low-temperature ionic conductivity, salt segregation, and mechanical properties, thereby opening new avenues for energy storage in extreme environments.