Proline-Zwitterion Mediated Competitive Interactions Enabling Robust, Antifreezing, and Dendrite-Suppressing Hydrogel Electrolytes for Aqueous Zinc-Ion Batteries

Abstract

Aqueous zinc-ion batteries are promising for flexible energy storage; however, water-related issues such as electrolyte decomposition, dendrite growth, and anode corrosion impede practical application. Although hydrogel electrolytes can suppress water activity and guide zinc-ion transport to inhibit dendrites, achieving high strength, high conductivity, and low temperature tolerance together remains challenging. Inspired by natural cryoprotection, a competitive interaction strategy using natural proline is present to enhance the polyvinyl alcohol (PVA)/ZnSO₄ hydrogel electrolyte. The hydrogel is physically crosslinked by PVA crystallites and stabilized by noncovalent interactions among PVA, Zn²⁺, and proline, showing 0.9 MPa tensile strength and 403% elongation. Proline's zwitterionic groups compete with water molecules in zinc-ion solvation, with a higher binding energy of 222.15 kcal/mol compared to 100.42 for water, enabling uniform Zn deposition and dendrite suppression. Zn||MnO₂ cells with this hydrogel retained 61% capacity after 200 cycles at 0.5 C, much better than the 32% with a liquid electrolyte. Proline also breaks the hydrogen bonding network of water, lowering the freezing point of the hydrogel to −27°C and maintaining 1.95 mS/cm conductivity at −20°C. The hydrogel allows flexible pouch cells to operate reliably under deformation and freezing conditions, demonstrating great potential for wearable energy storage.