Designing Aqueous Organic Electrolytes for Zinc-Air Batteries: Method, Simulation, and Validation

TL;DR

This study develops a computational and experimental framework for designing halide-free aqueous electrolytes for zinc-air batteries, demonstrating their potential for improved stability and longevity through organic salts.

Contribution

It introduces a thermodynamic screening method for halide-free electrolytes and validates a new organic salt-based electrolyte with comprehensive simulations and experiments.

Findings

ZnO is confirmed as the main discharge product.

The organic salt electrolyte maintains stable pH during cycling.

Long-term cycling shows promising battery performance.

Abstract

Aqueous zinc-air batteries (ZABs) are a low-cost, safe, and sustainable technology for stationary energy storage. ZABs with pH-buffered near-neutral electrolytes have the potential for longer lifetime compared to traditional alkaline ZABs due to the slower absorption of carbonates at non-alkaline pH values. However, existing near-neutral electrolytes often contain halide salts, which are corrosive and threaten the precipitation of ZnO as the dominant discharge product. This paper presents a method for designing halide-free aqueous ZAB electrolytes using thermodynamic descriptors to computationally screen components. The dynamic performance of a ZAB with one possible halide-free aqueous electrolyte based on organic salts is simulated using an advanced method of continuum modeling, and the results are validated by experiments. XRD, SEM, and EDS measurements of Zn electrodes show that ZnO is the dominant discharge product, and operando pH measurements confirm the stability of the electrolyte pH during cell cycling. Long-term full cell cycling tests are performed, and RRDE measurements elucidate the mechanism of ORR and OER. Our analysis shows that aqueous electrolytes containing organic salts could be a promising field of research for zinc-based batteries, due to their Zn$^{2+}$ chelating and pH buffering properties. We discuss the remaining challenges including the electrochemical stability of the electrolyte components.