Weakly solvating effect optimized hydrated eutectic electrolyte towards reliable zinc anode interfacial chemistry

The inherent issues of aqueous Zn-ion batteries, including side reactions and dendrite growth, can be effectively addressed through designing solvation structures enriched with anions to facilitate the formation of an anion-derived solid electrolyte interphase (SEI) layer. Here, the weakly solvating effect is utilized to modulate Zn²⁺ solvation structure for constructing an anion-derived SEI layer. Trifluoroacetamide (TFACE), with a specific weak solvating ability, serves as an ideal ligand for preparing hydrated eutectic electrolytes (HEEs) combining the anion-containing solvation structures and high ionic conductivity. The results demonstrate that coordinated anions preferentially decompose and generate an inorganic/organic hybrid SEI layer on the Zn anode, which efficiently suppresses both side reactions and dendritic growth. Such an electrolyte enables assembled Zn//polyaniline (PANI) full cells to process an impressive capacity retention, maintaining 80 % after 3000 cycles at 0.5 A g^-1. This work provides a fundamental insight into building the anion-derived SEI by the weakly solvating effect and gives a viable route for designing advanced aqueous electrolytes.