In Figure in the SI, we directly compare the Einstein-Helfland and Nernst-Einstein conductivities. Note that the NE approximation, which neglects contributions from ion-ion correlations, leads to a significant overestimation of the true ionic conductivity with σ NE > σ EH . This effect has been observed in molten salt alkali halides and has been reported for many ionic liquids. To quantify the ion-ion correlation effect, we compute ratios σ EH /σ NE which are shown in Figure in the SI. Since σ EH /σ NE is sensitive to ion pair formation, it is also referred to as "ionicty". The data in Figure scatter quite a bit due to the rather large uncertainties associated with σ EH and σ NE . However, we can denote a substantial ionion correlation contribution, centering around a value of σ EH /σ NE ≈ 0.6, and ranging mostly between 0.3 ≤ σ EH /σ NE ≤ 0.8. This is perfectly in line with the value of 0.68 at 303 K obtained by Tamura et al., determined from conductivity measurements and PFG NMR data. With increasing temperature, the ioncorrelation increases significantly. This is in accordance with the enhanced stability of direct ion-ion contacts at elevated temperatures due to the decline of the static dielectric constant with increasing temperature, which has been observed for both molecular and ionic liquids. Figure S12 also suggests that the magnitude of the ion-ion correlation scales roughly inversely proportional with the G3 content. This would imply the formation of neutral ion aggregates at low salt concentrations, albeit structurally less well-organized than those in the 1:1 mixtures.