Lithium Polymer Gel Electrolytes Designed to Control Ionic Mobility

Abstract

We prepared new lithium polymer gel electrolytes with Lewis acid ionic groups on the PVB polymer chain (ionic PVB gel) with the goal of attracting anions to restrict their mobility. The cation and anion diffusion coefficients (Dcation and Danion), dissociation degree of the salt (x), interactive forces between the ion and polar groups on the polymer (βcation and βanion), and interactive forces between the cation and anion (α) were estimated based on measurements of the diffusion coefficients (DLi, DF, and DH) and ionic conductivity (σ). The Dcation and Danion of the ionic PVB gel increased and decreased, respectively, compared to the values in the original PVB gel that did not contain an ionic group, which led to the enhanced cation transport number. The interactions between the mobile ions and polar groups depended on the solvation structure of the lithium cation, Li(EC)n+, which is associated with the polarity of the gel solvent. The solvating EC species around Li+ is the barrier for weakening Li+/OH– and Li+/TFSI– interactions and consequently activating the TFSI–/ionic group interaction.