Enhanced Na⁺ transport and dielectric performance of PVDF/zeolite composites for solid-state sodium battery electrolytes

Polymer electrolytes based on polyvinylidene fluoride (PVDF) are promising candidates for solid-state sodium batteries, yet achieving high ionic conductivity with stable dielectric properties remains challenging. In this study, PVDF composites containing 0–50 wt.% Zeolite Na-X composites were investigated to understand their dielectric relaxation and ionic transport behavior. Incorporation of Zeolite Na-X significantly enhanced dielectric permittivity and ionic conductivity by supplying mobile Na⁺ ions and promoting interfacial polarization at PVDF/Zeolite Na-X interfaces. Structural and surface analyses using X-ray diffraction (XRD) and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) demonstrated a quasi-uniform distribution of the filler. Dielectric relaxation spectroscopy indicated non-Debye behavior, with broad distributions of relaxation times, reflecting heterogeneous charge transport and strong interfacial polarization. Relaxation peaks shifted to higher frequencies as temperature increased, consistent with thermally activated Na⁺ hopping. The highest ionic conductivity was observed at 40 wt.% Zeolite Na-X, with the lowest activation energy of 0.498 eV, while 50 wt.% Zeolite Na-X reduced ionic mobility due to particle clustering. The intrinsic porosity of zeolite enhanced ion transport by providing additional pathways for Na⁺ migration, thereby improving ionic conductivity in the composite. These findings demonstrate that zeolite effectively tailors dielectric relaxation and ionic transport in PVDF-based composites. These analyses provide a basis for further electrochemical testing to evaluate their performance in solid-state sodium batteries. • PVDF composites with Na-X zeolite (0–50 wt%) were systematically investigated as polymer-based solid electrolytes for sodium-ion batteries. • Optimal filler loading of 40 wt% Na-X forms continuous ion-conducting pathways, achieving the lowest activation energy (0.498 eV) and enhanced Na⁺ mobility. • Dielectric relaxation spectroscopy revealed non-Debye behavior and strong interfacial polarization, highlighting heterogeneous charge transport. • Higher Na-X content (50 wt%) causes particle agglomeration, reducing ionic mobility and conduction efficiency. • Thermal effects on conductivity were identified, including a drop near 90 °C due to partial dehydration and interfacial restructuring. • The system demonstrates superior ionic transport and dielectric performance compared with previously reported polymer/zeolite and MOF-based electrolytes.