given here for spherical particles with "stick" boundary conditions, with R hyd denoting the hydrodynamic radius of the diffusing particles. The calculated hydrodynamic radius R hyd for the G3 species remains small between 1.7 Å and 1.9 Å for the entire composition range (excluding the 0.75 mole fraction), whereas the hydrodynamic radii of the ions nearly decreases by 50 % from values of 3.5 Å and 3.1 Å at x([Li][NTf 2 ])= 0.037 to 1.7 Å and 1.9 Å at x([Li][NTf 2 ])= 0.45 for the [Li] + and the [NTf 2 ] - ions, respectively. The strongly changing hydrodynamic radii are related to a change in the diffusion mechanism and correlate with the formation of 1:1 complexes. Both the unphysically small radii of G3 and the similarly unphysically large values for [Li] + , however, suggest a "breakdown" of the SE relation for these systems, similar to what was previously observed for mixtures of ionic liquids with chloroform. Moreover, a breakdown of the SE relation is a staple feature of supercooled liquids and is linked to the presence of dynamic heterogeneities due to a broad distribution of relaxation processes with different rates. 0.0 0.1 0.2 0.3 0.4 0.5 0.6