Tough and recyclable hydrogel electrolytes with continuous ion migration pathways for dendrite-free zinc-ion batteries under harsh conditions

Abstract

Hydrogel electrolytes have been extensively explored for flexible zinc-ion batteries because of their exceptional mechanical adaptability, high safety, and customizable functionalities. However, water-induced side reactions and dendrite growth severely compromise the stability of zinc-ion batteries. Moreover, it remains challenging to prepare both tough and recyclable hydrogel electrolytes. This work developed tough and recyclable borate-crosslinked polyvinyl alcohol composite hydrogels (P₃B₂Z_x) through a one-pot method. These hydrogels were engineered through dynamic chemical crosslinking and entanglements of PVA chains induced by partial dehydration of the hydrogels, with continuous ion migration pathways. Borax not only is involved in chemical crosslinking but also regulates the solvation structure of hydrated Zn²⁺. The strong interactions between PVA and free water effectively reduced water molecule activity, thereby suppressing side reactions. Additionally, these hydrogel electrolytes exhibited good environmental adaptability, mechanical robustness, self-adhesiveness, recyclability, and self-regeneration. The Zn‖Zn symmetric batteries displayed stable performance at both −20 and 25 °C over 1500 h at 2 mA cm⁻². Even after recycling, symmetric batteries can still run stably over 1000 h at 2 mA cm⁻² without dendrite growth or side reactions. Moreover, flexible full batteries have demonstrated reliable operation under harsh conditions, including mechanical deformation and −20 °C.