The Compensation Effect in the Vogel–Tammann–Fulcher (VTF) Equation for Polymer-Based Electrolytes

Single-ion conducting polymer electrolytes have been proposed to significantly enhance lithium ion battery performance by eliminating concentration gradients within the cell. Such electrolytes have universally suffered from poor conductivity at low to moderate temperatures. In an attempt to improve conductivity, numerous studies have sought to better understand the fundamental interplay of ion content and segmental motion, with typical analyses relying on a fit of temperature-dependent conductivity data using the Vogel–Tammann–Fulcher (VTF) equation to assist in separating these effects. In this study, we leverage the large accessible composition window of a newly synthesized, single ion conducting polysulfone–poly(ethylene glycol) (PSf-co-PEG) miscible random copolymer to more completely understand the interrelationship of glass transition temperature, ion content, and the polymer’s Li+ conductivity. It is demonstrated here that choice of fitting procedure and Vogel temperature plays a crucial role in th...