Coupling of Mechanical, Self-Healing, Adhesion, and High-Ion Conducting Properties in Anti-Freezing Hydrogel Electrolytes of Zinc Ion Batteries via Fe3+-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 Fe³⁺ ions to afford Fe³⁺-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 Fe³⁺-carboxylate chemistry in the development of self-healable, anti-freezing, and extreme-environment-adaptable gel electrolytes for flexible energy storage devices.