Dual function zinc-oligoether carboxylate salts enabling highly reversible 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 chemical approach that promotes the formation of a stable and robust solid electrolyte interphase (SEI) layer while enabling homogeneous deposition by favouring the growth of Zn facets with low surface energy. Here, we introduce zinc oligoether carboxylates as tuneable dual-function electrolyte component. 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 70 mAh Zn-MnO2 full pouch cells, supporting the scalability of commercial Zn-based devices by delivering a promising cycle life with practical C-rates and charge capacity.