Impact of hydrogel microstructure and mechanics on the growth of zinc dendrites towards long-life flexible batteries

Flexible zinc-ion batteries with hydrogel electrolytes are the most perspective energy-storage systems for wearable applications because of their low cost, safety, abundant zinc reserves, and environmental compatibility. Hydrogel electrolytes have been shown to mitigate the growth of zinc dendrites compared with liquid electrolytes, but dendrites remain the main issue limiting the lifespan of flexible batteries. The relationship between structural and mechanical properties of hydrogels and dendrite growth is unclear, which hinders the efficient development of long-life flexible batteries. Herein, the impact of the microstructure and mechanics of hydrogels on the morphology of zinc deposition was investigated systematically, as well as the influence of current density. Hydrogels with lower porosity allowed for denser zinc plating during initial and long-term cycles since their high Young's modulus and the uniform distribution of micropores led to dendrite suppression by mechanical pressure and regulated ion transport, respectively. However, hydrogel electrolytes with higher porosity resulted in higher stability after long-term cycles because of enhanced mechanical recovery and because the voids generated between the hydrogel and electrode during electroplating and stripping were recovered. Besides, with increasing current density, the deposition layer became thicker and more uneven, thereby reducing the lifetime of zinc batteries. Our study depicts the desired microstructure and mechanical features of hydrogel electrolytes, and could pave the way for the development of flexible long-life zinc-ion batteries. © The Royal Society of Chemistry 2023