Locking Water Molecules Loss of PAA Hydrogel for Flexible Zinc-Air Battery with NaCl Doping

Abstract

Flexible zinc-air batteries have received widespread attention due to their high specific energy and eco-friendly environment. However, the water in the hydrogel is easily lost to the external environment because of the semi-open structure zinc-air batteries, leading to performance degradation of the batteries. Here a saline gel of NaCl-KOH-PAA (sodium chloride-potassium hydroxide-polyacrylic acid) without soaking in the alkaline solution before use is designed, refining the grid structure of the hydrogel and reducing water loss through NaCl doping. Meanwhile, the gel exhibits no significant decrease in ion conductivity before and after NaCl doping and can maintain stability of around 170 and 150 mS cm−1 at room temperature and −20 °C, respectively. The results demonstrate that the lifetime of flexible zinc-air batteries with NaCl-doped hydrogel can be extended by nearly 50%. The NaCl doping gel also displays superior flexibility under extreme physical deformation conditions. Moreover, the phenomenon of hydrogel delamination with NaCl doping is observed and the mechanism of gel water retention is uncovered. These findings will pave the way for developing flexible zinc-air battery.