Impact of polymer blending on ionic conductivity and dielectric polarization of TiO2 incorporated SPEEK/PVDF electrolytes

Abstract

In the present study, the effect of varying polyvinylidene fluoride (PVDF) content and blend ratios on the ionic conductivity and dielectric properties of titanium dioxide (TiO₂) incorporated blend membrane electrolytes has been investigated. Various characterizations were used to determine the structural, morphological and thermal characteristics of the prepared composite electrolytes. Proton conductivity, relaxation dynamics and dielectric measurements on polymer composites were performed by varying blend compositions with a constant weight ratio of TiO₂ filler. With respect to the pure sulfonated polyether ether ketone (SPEEK), blend ratios including 5 % and 10 % PVDF improved the ionic conductivity and dielectric response. Nevertheless, compositions with 15 % or more PVDF showed notable decreases in both characteristics. The SP10-TO electrolyte exhibited the highest conductivity, reaching 2.47 × 10⁻⁴ S/m at 1 MHz and 300 K. By hydrogen bonding, the ideal PVDF content enhanced ion transport and water retention in the SPEEK matrix. Ionic mobility was supported by TiO₂, which further improved water dispersion. However, too much PVDF stiffened the polymer structure, which reduced conductivity and limited water movement. SP10-TO showed the highest dielectric constant (ε') value of 6052.5 at 300 K and 20 Hz. ε' decreased with increasing temperature and frequency due to reduced dipole alignment. Loss tangent (tanδ), a measure of relaxation dynamics, showed that the ideal blend composition had the shortest relaxation time, as 4.91 × 10⁻⁵ s. Increased ionic conductivity was strongly correlated with this drop, which suggests rapid dipole relaxation. The results highlight PVDF role in optimizing SP-TO polymer electrolytes for energy storage and conversion.