Design of Tannic Acid-Regulated Zwitterionic Hydrogels as Low-Temperature-Tolerant High-Performance Electrolytes for Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) based on hydrogel electrolytes have emerged as promising candidates for flexible energy storage, combining high theoretical specific capacity, inherent safety, and low cost. However, the insufficient interfacial adhesion between the zinc anode and hydrogel electrolyte represents a major obstacle to fabricating batteries with satisfactory electrochemical performance. To address this issue, we herein propose a facile photoinitiated polymerization strategy to fabricate poly(acrylamide-co-2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide)/tannic acid (P(AM-co-SBMA)/TA) hydrogel electrolytes for high-performance ZIBs. The as-prepared hydrogel electrolyte establishes intimate and tight interfacial contact with the Zn anode, which not only accelerates interfacial ion transport but also effectively suppresses Zn dendrite growth and parasitic side reactions. Consequently, the optimized hydrogel electrolyte exhibits an outstanding ionic conductivity of 28.82 mS/cm and a high Zn2+ transference number of 0.71. Furthermore, the developed electrolyte enables the Zn//Zn symmetric cell to maintain stable and reversible Zn plating/stripping for over 700 h. The assembled Zn//MXene-decorated polyaniline (MXene@PANI) full cell delivers a high initial specific capacity of 185.4 mAh/g at 0.5 A/g, and retains a capacity retention of 77.1% after 1000 cycles at a high current density of 5 A/g. Impressively, even at an ultralow temperature of −20 °C, the full cell still achieves an initial specific capacity of 91.5 mAh/g at 1 A/g, accounting for 52.1% of its capacity at 20 °C. Moreover, the cell maintains stable electrochemical performance under various mechanical deformations, demonstrating great potential for flexible wearable applications. This strategy effectively mitigates the interfacial issues of hydrogel-based ZIBs, greatly improving interfacial compatibility and long-term cycling stability.