The electrophoretic mobilities μ of all ion species in the lithium salt/ionic liquid mixtures LiTFSA/EmimTFSA and LiBF/EmimBF are determined by H,F and Li electrophoretic NMR. The average drift direction of Li is identical to that of the anions TFSA or BF. This proves a correlated ion motion of Li with the anions in negatively charged Li-containing clusters in both systems. The effective charge of these clusters is determined as -1, or -2 in the system with TFSA or BF, respectively, pointing at the existence of [Li(TFSA)] or [Li(BF)]. This behavior is described by a negative effective transference number of Li, resulting in a negative contribution of Li ions to the overall conductivity. Li effective transference numbers are in the range of -0.04 to -0.02, depending on Li salt concentration and anion type. Transference numbers thus clearly deviate from apparent transference numbers estimated from diffusion coefficients, as an effect of a vehicular transport mechanism. This has important implications for the mechanism of Li mass transport in Li ion batteries as the drift of charged clusters has to be overcompensated by diffusive mass transport of neutral, Li-containing aggregates.

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Lithium salt−glyme mixtures are interesting candidates as electrolytes for battery applications. Depending on the type of glyme or anion and the salt concentration, they either show ionic liquid-like behavior with stable lithium−glyme complex cations or concentrated salt solution-like behavior. Here, we apply electrophoretic NMR (eNMR) to elucidate transport mechanisms by observing the migration of the molecular species in an electric field. We investigate two solvate ionic liquids, i.e., lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and lithium tetrafluoroborate (LiBF 4 ), in tetraglyme (G4) at different glyme−salt molar ratios X. A fieldinduced migration of neutral glyme molecules is directly observed, which is due to stable solvate−Li complex formation. Transference numbers, effective charges, and ionicities are derived from electrophoretic mobilities and self-diffusion coefficients, respectively, for the nuclei 1 H, 7 Li, and 19 F. The effective charges are the highest at the equimolar mixture, X = 1, they differ strongly for lithium and anion, and they show large differences between both systems. These findings are qualitatively interpreted in a speciation model, suggesting anionic clusters and solvate cations as the species dominating charge transport. The resulting effective charges can only be explained taking into account ion−ion anticorrelations in the framework of the Onsager formalism, where anticorrelations between the solvate cation and the anionic complexes arise due to momentum conservation. The contributions to the anticorrelation are most dominant at high salt concentrations and in the system with the LiBF 4 − anion due to its lower mass and ability to form larger asymmetric clusters with Li + . Thus, in either system, also the lithium transference number is influenced to a different extent by ion−ion anticorrelations.

Electrophoretic nuclear magnetic resonance (eNMR) is a powerful tool in studies of nonaqueous electrolytes, such as ionic liquids. It delivers electrophoretic mobilities of the ionic constituents and thus sheds light on ion correlations. In applications of liquid electrolytes, uncharged additives are often employed, detectable via 1 H NMR. Characterizing their mobility and coordination to charged entities is desirable; however, it is often hampered by small intensities