Dual-Function Electrolyte Design Enabling Sulfur Redox-Mediated Charging and Anode Stabilization in Zn-Air Batteries

Abstract

Rechargeable Zn-air batteries are limited by sluggish oxygen evolution reaction (OER) kinetics and Zn anode instability. Here, we report a thiourea-based electrolyte that enables sulfur redox-mediated charging while simultaneously stabilizing the Zn anode. Electrochemical and spectroscopic analyses reveal a reversible S2-/S2O32- redox cycle that provides a kinetically favourable oxidation pathway, partially replacing the high-overpotential OER during charging. Importantly, rotating ring-disk electrode measurements confirm that the discharge process remains dominated by the four-electron oxygen reduction reaction (ORR), preserving the fundamental Zn-air battery mechanism. In parallel, thiourea-derived carbonyl species regulate Zn2+ coordination, suppressing ZnO/ZnS formation and improving Zn utilization. As a result, the Zn-air battery exhibits a reduced voltage gap of 0.47 V and stable cycling over 330 h at 10 mA cm-2. This work demonstrates an effective electrolyte engineering strategy that enhances Zn-air battery performance through redox-mediated kinetic modulation without altering the core oxygen-based energy storage mechanism.