Cation and anion diffusion coefficients in a solid polymer electrolyte measured by pulsed-field-gradient nuclear magnetic resonance

Abstract

Diffusion of Li+-based and PF6--based species in an amorphous polymer electrolyte has been explored by pulsed-field-gradient (PFG) nuclear magnetic resonance. The experiments were undertaken over a range of salt concentrations and temperature extending to lower values of both variables than in previous studies. Features of the results include a demonstration of different mechanisms for anion and cation transport at high concentration, as shown by their different temperature dependences, a reduced sensitivity of cation diffusion to salt concentration and a failure of the Nernst-Einstein relationship. Cation hopping between ionic clusters and the diffusion of neutral ion pairs are advanced as microscopic mechanisms to explain the data.