Enhanced Low-Temperature performance of flexible Zinc-Air batteries via High-Concentration ZnCl₂ and lignin modified polyacrylamide hydrogels

The crosslinked polymer hydrogels with porous structure have great application potentials in flexible metal-air batteries due to the matrix of soft and water-containing characteristics improving the ionic conductivity and stability of the electrolyte. However, the hydrogel degrades significantly at low temperatures, seriously influencing the batteries’ performance. Here we report a hydrogel of PAM modulated with high concentration of ZnCl₂ and lignin (M−DPAM−3), where the high concentration of ZnCl₂ is introduced as a pore-forming agent and salt additive, and lignin serves as a skeleton repairing agent, thus achieving an alkali absorption of 25.74 g/g and an ionic conductivity of 440.91 mS cm^–1. The results demonstrate that the additives of ZnCl₂ together with lignin can effectively improve the PAM hydrogel stability, and the addition of lignin induces the electrodeposited zinc atoms adhered to the (002) crystal plane, inhibit dendrites growth and achieve a symmetric cycling of 150 h. The assembled flexible Zn-air battery reaches a high power density of 136.2 mW cm^–2 and a cycling performance of 55 h at room temperature. Moreover, the flexible Zn-air battery can output a power density of 115.6 mW cm^–2 at −20℃, and the battery may run stably for 72 h. These findings reveal the modification effects of ZnCl₂ and lignin on the gel matrix, which is conducive to promoting the application of hydrogels in flexible batteries.