Ionic transport and pair formation in polymer electrolytes

Common analysis (level 1) characterizes the degree of ion association in polymer electrolytes by the Nernst-Einstein deviation parameter ∆ which quantifies the relative difference between the true ionic conductivity directly measured by electrical methods and the hypothetical maximum conductivity calculated from the individual ionic self-diffusion coefficients. Alternatively, the Haven ratio HR may be used as key figure to specify the association degree. Despite their unambiguous definitions, ∆ and HR are global quantities with limited explanatory power. Similar is true for the cation transport number t∗ cat which relies on the same ionic diffusion coefficients usually measured by nuclear magnetic resonance or radiotracer methods.