It has recently been shown, in the case of the bisfluorosulfonamide (FSI) based ionic liquids, that as the concentration of the alkali metal salt (LiFSI or NaFSI) is increased, the alkali metal cation transport number increases, along with an increase in viscosity and decrease in conductivity. At the same time, significant enhancements in electrochemical stability and rate performance of devices are also observed. The ion structuring and dynamics are shown to be very dependent on salt concentration as observed from NMR diffusion measurements and also verified by bulk MD simulations. As the alkali metal salt concentration increases towards 50 mol%, or even higher, the available anions required to satisfy the coordination environment (between 3 and 5) will become fewer and insufficient unless each anion begins to coordinate more than one metal cation, for example by bridging two or even three Li<sup>+</sup> or Na<sup>+</sup> ions. This results in significant aggregation and structuring of the ionic liquid as observed via our MD simulations which also likely influences the electrochemical processes at the Li or Na metal electrodes. Interfacial structuring at a charged electrode has also be shown to depend on IL chemistry, salt concentration and the applied charge density (or voltage) at the electrode. We investigate these phenomena using AFM and MD simulations and correlate this to electrochemical cycling of various metal electrodes.

Ion structure and dynamics in ionic liquids and the effect of salt concentration and chemistry on structuring at an electrified interface

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.