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 an ideal blueprint for sustainable battery technology. However, intrinsic instability owing to hydrogen evolution and dendrite formation during the plating process severely compromise the stability of the Zn anode and drastically limit cycling performance. Extending the battery's lifetime at such a complex interface requires a comprehensive approach promotes the formation of a stable and robust solid electrolyte interphase (SEI) layer. Here, we introduce zinc oligoether carboxylates as tuneable dual-function electrolyte additives. The carboxylate group acts as a proton donor, inducing the decomposition of sulfate salt anions to form a ZnS-based SEI, while the oligoether moiety mitigates water activity at the electrode interface, as deduced from the combination of spectroscopic techniques with scanning electrochemical microscopy. By varying the chain length, we find that the longest chain, Zinc (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]acetate)₂, enables long-term cycling under harsher conditions than previously reported, extending cycle life fivefold, sustaining 1000 hours at low current density and high capacity with excellent CE%. This enhancement translates into 98 mAh Zn-MnO2 full pouch cells, supporting the scalability of commercial Zn-based devices by delivering a promising cycle life at low C-rates and high cumulative charge capacity. We hope this discovery will speed up the development of commercial Zn-MnO2 aqueous batteries.