Dynamic Mechanism of Short Peptide Additive Regulating Solvation Microenvironment of Zinc Ions

Abstract The optimization electrolyte strategy through molecular additives to improve the stability of aqueous zinc‐ion batteries (AZIBs), which changes the solvation structure of hydrated zinc ions (Zn 2+ ), generally relies on experimental trial and error, because the precise mechanism by which these additives alter the coordination environment of Zn 2+ remains elusive. Here, we select the oligopeptide of mono‐, di‐, tri‐, and tetra‐glycine, as electrolyte additives to optimize the Zn 2+ solvation microenvironment in AZIBs. Contrary to traditional views, we find that these additives modify the solvated structure of the Zn 2+ by substituting sulfate ion (SO 4 2− ) in the preexistence of Zn 2+ ‐SO 4 2− ion pair, rather than water molecules in the first solvation shell, due to a high energy barrier to replace one of the coordinated water molecules of Zn 2+ . This observation is consistent with recent experimental result of the attenuating influence of glycine on the interaction between Zn 2+ and SO 4 2− confirmed by Fourier‐transform infrared spectroscopy. For the multifunctional triglycine, its favorable conformation is disrupted to accommodate the direct coordination of oxygen atoms with Zn 2+ , and Zn 2+ is observed to migrate between distinct sites along the triglycine backbone. This work provides theoretical principles to rationally design advanced electrolytes for solvation modulation with high performance AZIBs.