Investigating the Correlation of Segmental Dynamics, Free Volume Characteristics, and Ionic Conductivity in Poly(ethylene oxide)-Based Electrolyte: A Broadband Dielectric and Positron Annihilation Spectroscopy Study

Abstract

Poly(ethylene oxide), PEO, based solid polymer electrolyte with different loadings of a lithium salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), has been investigated to study the role of PEO–Li cross-linking on segmental dynamics and free volume structure of PEO which consequently determine thermal, mechanical, and ion conduction properties of the electrolyte. In order to investigate the interrelation between segmental dynamics, free volume structure, and ion conduction mechanism, broadband dielectric spectroscopy and positron annihilation spectroscopy have been employed. The ion conduction process in the polymer electrolyte has been explained according to Almond–West formalism considering two different universalities dominating at different temperature or frequency regimes. Ionic conductivity was observed to increase in a nonlinear trend with salt loading, confirming the additional role of the ion diffusion process. The present study has shown that segmental dynamics and free volume structure of PEO-electrolyte which primarily govern the ion diffusion process are interrelated. These have been invoked to explain the observed variations in ionic conductivity, crystallinity, ductility, and thermal stability of PEO–LiTFSI electrolytes.