Cation Solvation in Co-Solvent Doped Water-in-Salt Electrolytes

Water-in-salt electrolytes (WiSEs) are an exciting class of highly concentrated electrolyte. They have recently come to the forefront of battery research owing to their desirable properties: they can be safer, less expensive, and more environmentally friendly than traditional electrolytes currently used in state-of-the-art batteries. However, some hurdles remain before they become commonplace: namely, parasitic hydrogen evolution still limits their useable lifespan. One notable and highly scaleable way of mitigating this is to use an appropriate co-solvent. However, the mechanism of co-solvent action is still disputed. The aim of the experiment is to investigate the impact of the promising co-solvent candidate methyl urea on local and bulk structure in the archetypal WiSE formed of 20 molal lithium bistriflimide (NTf2) in water. We recently studied 20 molal lithium NTf2 in pure water only (manuscript in preparation) and we will draw comparison between these two cases. These results will have significant implications for the mechanism of co-solvation within WiSEs and will be key to the design of future batteries.