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.