Cluster level entropy enhancement in neutral acetate electrolytes enables economical and durable zinc air batteries.

Abstract

Neutral zinc-air batteries provide a viable alternative to alkaline systems by avoiding salt creep and carbonate passivation. Among candidate electrolytes, acetate-based formulations are particularly attractive for their low cost, sustainability, and compatibility with ambient-air operation. However, their widespread adoption is limited by a trade-off between two concentration regimes. Dilute electrolytes trigger side reactions and lack ionic strength, while concentrated ones suffer from kinetic limitations due to contact ion pair clustering. Here, we propose a cluster-level entropy enhancement strategy that optimizes the mesoscopic configuration of the electrolyte by disrupting large clusters in concentrated acetate electrolytes. This entropy enhancement improves zinc ion diffusivity and kinetics, mitigates interfacial concentration gradients, and maintains local ionic strength for fast electrochemical reactions, as evidenced by various synchrotron X-ray techniques and theoretical simulations. Consequently, the zinc-air batteries in neutral electrolyte deliver over 1800 hours at 0.1 mA cm^-2 (1 mAh cm^-2, 61.4% round-trip efficiency) and 500 hours at 1 mA cm^-2 (12 mAh cm^-2, 51.2% round-trip efficiency) in ambient air. This study extends the application of sustainable acetate electrolytes in neutral zinc-air batteries and illustrates a mesoscopic tuning approach applicable to aqueous energy systems with metal electrodes and concentrated solvents.