Coupled polarization dynamics and ion mobility in PVDF-HFP/ionic liquid/TiSiO4 composite electrolytes

In this study, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based composite polymer electrolytes containing ionic liquid (IL) and TiSiO 4 nanofiller are developed to determine the coupled effects of filler content, temperature and frequency on dielectric characteristics and ion transport. Membranes are prepared by the conventional solution-casting method and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy tests. The characterizations confirm strong IL-polymer interactions, reduced crystallinity, effective filler dispersion and sufficient thermal stability. AC conductivity ( σ ac ) measurements show that IL incorporation improves conductivity, while TiSiO 4 further enhances the physical film properties. The TiSiO 4 filler maintained ionic conductivity at comparable levels while modifying interfacial polarization behavior and the dielectric response of the composite electrolyte. At 430 K, the highest DC conductivities ( σ dc ) are observed for the PVDF-HFP/IL and PVDF-HFP/IL/TiSiO 4 (1.5) composite membranes, reaching 8.03 × 10 −4 and 6.86 × 10 −4 S/m, respectively, which are nearly three orders of magnitude higher than that of pure PVDF-HFP (3.58 × 10 −7 S/m). Dielectric analyses reveal pronounced low-frequency permittivity amplification, with the dielectric constant ( ε ′) reaching 1.51 × 10 4 at 20 Hz and 430 K for PVDF-HFP/IL/TiSiO 4 (2.0). Loss tangent (tan δ ) profiles exhibit composition- and temperature-dependent relaxation behavior and indicate thermally-activated dipolar reorientation. Unlike conventional oxide fillers, TiSiO 4 acts as an active interfacial component that modulates coupling between polarization dynamics and ion transport. The IL–TiSiO 4 interaction optimizes conductivity and dielectric behavior, demonstrating promising potential for high-performance composite electrolytes.