Water-In-Salt LiTFSI Aqueous Electrolytes (2): Transport Properties and Li Dynamics Based on Molecular Dynamics Simulations.

The transport properties of water-in-salt lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) aqueous electrolytes were studied using classical molecular dynamics (MD) simulations. At high salt concentrations of 20 m, the calculated viscosity, self-diffusion coefficients, ionic conductivity, the inverse Haven ratio, and the Li apparent transference number all agree with previous experimental results quantitatively. Furthermore, analyses show that the high apparent transference number for Li is due to the fact that the dynamics of TFSI decrease more quickly with increasing salt concentration than the dynamics of Li ions due to the formation of a TFSI network. In addition, it was shown that the conduction of Li ions through the highly concentrated electrolyte occurs mainly via a hopping mechanism instead of a vehicular mechanism hypothesized in earlier studies of this system.