Finally, we determine x Roling as a measure for the ratio of mass vs. charge transport. For some examples the data are listed in Tab.1. Interestingly in the whole range of compositions, the transport is always limited by the charge transport, resulting from a stronger interaction between cations and anions. Most importantly, for salt concentrations of around 1 M and higher as well as for EC contents above 24% the transport coefficient is within a factor of 3 close to an ideal strong electrolyte. Apart from the application-driven perspective (good transport behavior for anion blocking conditions), the transport coefficient x Roling is a versatile dimensionless parameter, characterizing the nature of the transport process. The viscosity η is calculated using Einstein's relation Eq.( ), based on the polarizable force field. This approach is very sensitive to the chosen trajectory storing frequency as discussed in the supplementary. Fig. (a) shows η vs. 1/T for two compositions, reflecting a low and a high salt concentration. This data is compared with experimentally measured viscosities, measured at a slightly different EC:EMC ratio (as above) and molalities (0.44 m vs 0.5 m and 2.0 m vs. 2.1 m, respectively). It turns out that extrapolation of the simulated viscosities to lower temperatures yields very good agreement with the experimental data.