Coupling of Mechanical, Self‐Healing, Adhesion, and High‐Ion Conducting Properties in Anti‐Freezing Hydrogel Electrolytes of Zinc Ion Batteries via Fe ³⁺ ‐Carboxylate Coordination

Abstract Aqueous zinc‐ion batteries (AZIBs) based on hydrogel electrolytes are considered promising flexible power supplies owing to their intrinsic safety, competent volumetric energy density, and eco‐friendliness. However, severe mechanical deterioration of the hydrogel electrolytes caused by insufficient inter‐component contact, zinc (Zn) dendrites, and freezing prevents their commercialization. Herein, it is found that, by doping a trace of Fe ³⁺ ions to afford Fe ³⁺ ‐carboxylate supramolecular interaction, the practicality of an archetypal cellulose nanofiber‐reinforced hydrogel electrolyte is significantly improved in a couple of aspects, including three and eight times increase in tensile strength and toughness without loss of ion conducting ability (up to 32 mS cm ⁻¹ ) and being room‐temperature self‐healable and strongly adhesive to various battery components. Together with the use of an anti‐freezing mixed Zn salt, the resulting hydrogel electrolyte is able to deliver ultrahigh Zn cycling reversibility (averaging 99.4%), the great cyclability of AZIBs (a high specific capacity of 180 mAh g ⁻¹ and capacity retention of 81%), and render the batteries operable under severe abuse conditions of 180° folding, exposure to liquid nitrogen, and cutting–rehealing cycles. This work unlocks the enormous potential of Fe ³⁺ ‐carboxylate chemistry in the development of self‐healable, anti‐freezing, and extreme‐environment‐adaptable gel electrolytes for flexible energy storage devices.