Structural Ordering and Polarizable Al³⁺ Solvation Induced via Amphiphilic Zwitterion for Highly-Reversible Zn-Al...

Aqueous aluminum-ion batteries face significant challenges in achieving stable plating/stripping owing to issues such as hydrogen evolution and corrosion. Although the in situ formation of Zn-Al alloys via Zn anodes and Al³⁺-based electrolytes enables a suitable operating potential, this approach is hindered by cycling deactivation caused by uneven deposition and side reactions. Herein, we employ an amphiphilic zwitterion (ZI-10) as an electrolyte additive to enhance the stability of Zn-Al alloy anodes. Small-angle X-ray scattering (SAXS) and sum frequency generation (SFG) spectroscopy reveal that the self-assembly of ZI-10 forms ordered aggregates, thereby constructing a dual-layered electric double layer (EDL) that excludes water from the electrode interface while facilitating reversible plating/stripping. The zwitterionic chelation further induces a polarizable Al³⁺ solvation shell that reduces the energy barrier for charge transfer. Ultimately, Zn-Al||Zn-Al symmetric cells achieve >2500 h of stable operation at 1 mA cm^-2 and 1 mAh cm^-2, outperforming the recently reported counterparts. Full cells paired with MnVO cathodes sustain stable cycling even under 10 mg cm^-2 cathode loading, while Zn-Al||I₂ full cells further demonstrate exceptional long-term durability. This work offers insights into the role of amphiphilic zwitterions in tailoring electrolyte nanostructure and interfacial reaction kinetics.