Water in Solvate Ionic Liquids: Preserving Lithium Coordination While Enhancing Ionic Conductivity

This work investigates how the concepts of solvate ionic liquids (SILs) and water-in-salt (WIS) electrolytes can be combined to create hybrid electrolyte systems. We examine the neat SIL [Li(G3)][NTf₂], composed of a solvate cation and an anion, as well as its water-modified analog containing an equimolar amount of added water, using both molecular dynamics simulations and experiments. Introducing water markedly reduces the high viscosity of the neat SIL while substantially enhancing ionic conductivity. Structurally, each cationic complex incorporates on average a single water molecule, resulting in highly dispersed water and the absence of extended water networks. We refer to such systems as water-in-solvate-ionic-liquid (WISIL) electrolytes. Owing to the strongly coordination-dominated lithium environment, the WISIL retains a wide electrochemical stability window, decreasing only slightly from over 5 V in the neat SIL to 4.9 V at ambient conditions.