Lean-water hydrogel electrolyte for zinc ion batteries

Solid polymer electrolytes (SPEs) and hydrogel electrolytes were developed as electrolytes for zinc ion batteries (ZIBs). Hydrogels can retain water molecules and provide high ionic conductivities; however, they contain many free water molecules, inevitably causing side reactions on the zinc anode. SPEs can enhance the stability of anodes, but they typically possess low ionic conductivities and result in high impedance. Here, we develop a lean water hydrogel electrolyte, aiming to balance ion transfer, anode stability, electrochemical stability window and resistance. This hydrogel is equipped with a molecular lubrication mechanism to ensure fast ion transportation. Additionally, this design leads to a widened electrochemical stability window and highly reversible zinc plating/ stripping. The full cell shows excellent cycling stability and capacity retentions at high and low current rates, respectively. Moreover, superior adhesion ability can be achieved, meeting the needs of flexible devices. Excess water in hydrogel-based zinc ion batteries causes side reactions, but reduced water content results in low conductivities. Here, authors develop a lean-water hydrogel based on molecular lubrication mechanism for fast ion transportation, extended stability, and reversible Zinc plating/stripping.