Unveiling the Critical Influence of EDTA Additives on Modulating Solvation Structure and Solid Electrolyte Interphase Formation in Water‐in‐Salt Electrolytes for Aqueous Batteries

Abstract Water‐in‐salt ( WIS ) electrolytes confer a wide voltage window to aqueous batteries. However, the dynamic solid electrolyte interphase ( SEI ) is adversely affected by LiTFSI precipitation/dissolution and continuous reforming issues, causing electrolyte dryness. Here, the aminopolycarboxylic (Ethylenediaminetetraacetic acid, EDTA ) additive is introduced to WIS electrolytes. An intriguing solvation phenomenon is observed wherein EDTA exhibited insolubility in a low‐concentrated (7m) solution while achieving certain solubility in a high‐concentrated (21m) one. The assembled full cell with EDTA exhibited good cycling stability at a low 0.5 C. To elucidate the unique solvation phenomenon and unravel the mechanism of SEI formation, experimental characterizations, and simulations are conducted. Molecular Dynamics ( MD ) and physical measurements disclosed that sufficient Li + acts as a bridge connecting EDTA with TFSI − ‐H 2 O . The simulated electrode/electrolyte interface investigated the dynamics, showing the difference in the activity and density of molecules after adding EDTA . Density Functional Theory ( DFT ) calculations together with physical measurements discovered EDTA ‐ species are prone to facile reduction during cycling, and the products facilitated the formation of a robust fluorine–oxygen–sulfur‐based SEI , outstanding critical roles of EDTA in forming the interphase compared with the unstable dynamic SEI . This work directs an alternative way and clear formation mechanism of the interphase for building stable aqueous batteries.