Composition-Driven Design of Solid Polymer Electrolytes: Effects of Non-coordinating and Coordinating Polymers on Ionic Transport in PVDF-HFP/PEG Blends

Abstract

This study performs in-depth investigation on how the interplay between coordinating and non-coordinating polymers governs ionic transport in solid polymer blend electrolytes (SPBEs). Coordinating fully amorphous, low-molecular-weight poly(ethylene glycol) (PEG) and non-coordinating low-crystallinity poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) were blended to form polymer matrices with suppressed crystallinity below 20%. The resulting SPBEs exhibited high ionic conductivity, reaching 2.21 × 10-4 S/cm at room temperature. Spectroscopic analysis revealed that increasing PEG content alters Li⁺ ion coordination from solvent-based complexes to PEG ether groups, promoting segmental motion-mediated ion hopping. X-ray scattering confirmed domain-level rearrangements with changing composition. While temperature-dependent ionic conductivity followed Vogel-Tammann-Fulcher (VTF) behavior, PEG-rich systems exhibited lower activation energies (Ea) and higher pre-exponential factors (A), deviating from the conventional compensation effect due to enhanced segmental mobility. A calculated reduced conductivity further confirmed that increasing PEG content leads to higher intrinsic ionic transport capability. Electrochemical experiments revealed stable Li plating/stripping behavior with low overpotentials, and a Li+ ion transference number of 0.18 was measured. These findings demonstrate that tuning the blend ratio of coordinating and non-coordinating polymers enables precise control over ion coordination and segmental dynamics. This composition-driven strategy provides a robust framework for designing high-performance SPBEs with enhanced ionic conductivity and interfacial stability, supporting their application in solid-state lithium batteries.