Migration mechanism of Li+ in sulfonated polyvinyl alcohol membrane by dielectric spectroscopy

Dielectric measurements were carried out for the sulfonated polyvinyl alcohol (SPVA) membrane in liquid electrolytes. A distinct Maxwell - Wagner relaxation is observed, which changes with the sulfonation degree of the membrane and the Li+ concentration. The permittivity and conductivity were calculated by a model free method. The results show that both the membrane conductivity and bulk solution conductivity increase first and then decrease with the Li+ concentration, but the maximum value appears at various concentration, suggesting different migration mechanism of Li+. The ion distribution coefficient, the volume charge density of the membrane and the solvation energy barrier of Li+ were calculated, and a possible mechanism has been suggested: the Li+ migration is essentially due to the interaction between the fixed charge in the membrane and the polarized charge at the interface, dominated by the Donnan equilibrium or dielectric repulsion in the lower or higher lithium salt concentration.