On the structure of hybrid water-in-salt electrolytes

Water-in-salt electrolytes are promising candidates for next-generation lithium-ion batteries due to their enhanced safety and cost-effectiveness. However, optimizing the performance of hybrid aqueous/non-aqueous water-in-salt electrolytes remains a challenge. This work investigates the structural characteristics of mixtures of a LiTFSI water-in-salt based electrolyte (21 m) with several common solvents (<i>e.g.</i> carbonates, dimethyl sulfoxide, acetonitrile) using molecular dynamics simulations combined with experimental measurements. Our analysis reveals a correlation between the ability of a given cosolvent to solvate lithium cations and its Lewis basicity. A strong Lewis basicity favours the formation of free water cluster aggregates in the system, which reduces the electrochemical performance of the electrolyte. Moreover, the relative permittivity of the cosolvents also plays an important role in modifying the ionic interaction.