Zinc-oligoether carboxylate salts as electrolyte additives for aqueous Zn metal batteries

Aqueous zinc-metal batteries, which pair a water-based electrolyte with an earth-abundant metal, offer a sustainable energy storage platform. However, hydrogen evolution and dendrite growth during zinc plating limit stability and cycle life. Achieving durable performance requires a comprehensive approach that promotes forming a robust solid electrolyte interphase layer. Here, we introduce zinc oligoether carboxylates as tuneable dual-function electrolyte additives. The carboxylate group promotes the formation of a zinc sulphide-based interphase through the controlled decomposition of sulphate anions, while the oligoether chain suppresses water activity at the electrode surface, as revealed by spectroscopic and electrochemical microscopy analyses. By varying the chain length, we find that the longest compound, zinc (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]acetate)₂, extends the lifetime of symmetric zinc cells from 200 to 1000 hours at a current density of 0.624 mA.cm^-2 and a capacity of 2.5 mAh.cm^-2. Furthermore, zinc-copper cells achieve 99.6% efficiency at 5 mA.cm^-2 and 10 mAh.cm^-2. This improvement also benefits zinc-manganese dioxide, extending from 30 to 200 cycles. These results demonstrate a molecular strategy for stabilising zinc interfaces, hence advancing practical aqueous zinc-manganese dioxide batteries.