Ionic conduction and self-diffusion near infinitesimal concentration in lithium salt-organic solvent electrolytes

The Debye-Huckel-Onsager and Nernst-Einstein equations, which are based on two different conceptual approaches, constitute the most widely used equati ons for relating ionic conduction to ionic mobility. However, both of these classical (simple) equations are predictive of ionic conductivity only at very low salt concentrations. In the present work the ionic conductivity of four organic solvent-lithium salt-based electrolytes were measured. These experimental conductivity values were then contrasted with theoretical valu es calculated using the translational diffusion (also known as self-diffusi on or intradiffusion) coefficients of all of the species present obtained u sing pulsed-gradient spin-echo (H-1, F-19 and Li-7) nuclear magnetic resona nce self-diffusion measurements. The experimental results verified the appl icability of both theoretical approaches at very low salt concentrations fo r these particular systems as well as helping to clarify the reasons for th e divergence between theory and experiment. In particular, it was found tha t the correspondence between the Debye-Huckel-Onsager equation and experime ntal values could be improved by using the measured solvent self-diffusion values to correct for salt-induced changes in the solution viscosity. The c oncentration dependence of the self-diffusion coefficients is discussed in terms of the Jones-Dole equation. (C) 2000 American Institute of Physics. [ S0021-9606(00)50625-4].