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 an 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⁻¹ at room temperature. Spectroscopic analysis revealed that increasing the PEG content alters Li⁺ ion coordination from solvent-based complexes to PEG ether groups, promoting segmental motion-mediated ionic transport. 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 (E_a) 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 the 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.