Hydrogel electrolytes for aqueous zinc metal batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) are promising for next-generation energy storage due to their safety, low cost, and sustainability, but they remain limited by water-driven instability, sluggish Zn2+ desolvation, parasitic reactions, and dendritic deposition. This thesis develops a progressive electrolyte design based on hydrophilic, hydrophobic, and amphiphilic hydrogel frameworks, combining molecular water regulation with interfacial chemical engineering to achieve dendrite-free cycling and long-term stability.

In Chapter 1, the functions and limitations of hydrophilic hydrogels are systematically examined. Hydrophilic networks immobilize water, provide ion-conduction channels, and homogenize Zn2+ flux, suppressing dendritic growth and reducing side reactions. However, their water-rich microenvironments sustain proton activity and corrosion, revealing a trade-off between ionic conductivity and interfacial stability. To overcome these constraints, the chapter discusses the advantages of incorporating hydrophobic domains.

Chapter 2 proposed a hydrophobic-spacer engineering strategy, in which fluorinated methacrylate monomers are incorporated into zwitterionic hydrogel networks to construct controlled amphiphilic microdomains. Spectroscopic, thermal, and molecular dynamics simulations demonstrated that hydrophobic microdomains can suppress the activity of free water and inhibit zwitterionic self-association. Electrochemical measurements demonstrate improved Zn2+ transference numbers, reduced interfacial charge-transfer barriers, and extended symmetric-cell cycling lifetimes exceeding 2500 h without dendritic failure.

In Chapter 3, the thesis concludes with a forward-looking outlook. This work demonstrates a paradigm shift from passive water immobilization to active interfacial chemical engineering.