We studied the conductivity of different ionic-liquid based electrolytes together with the Li ion diffusion coefficients obtained from field-gradient nuclear magnetic resonance spectroscopy. For different electrolytes, although having similar conductivities, drastic differences in the battery performance could be explained by the large differences in the Li ion diffusivities. While the diffusivity of the Li ions strongly depends on the nature of the solvent, the anion of the Li salt has only minor influence on the Li diffusion. (C) 2014 The Electrochemical Society. All rights reserved.