Influence of succinonitrile on structural, thermal, electrochemical and optical properties of sodium-ion conducting PVdF-HFP based gel polymer electrolyte membranes

A novel sodium (Na)-ion conducting gel polymer electrolyte composed of poly(vinylidine-fluoride-co-hexafluoropropylene) (PVdF-HFP) complexed with sodium tetrafluoro-borate (NaBF₄) and ethylene carbonate (EC)-propylene carbonate (PC) as a co-solvent, coupled via differing fractions of a non-ionic plastic crystal succinonitrile (SN) are developed and studied. X-ray diffraction and Fourier transform infra-red studies identifies significant structural alterations in terms of reduced crystallinity and the interactions among the polymeric components on incorporation of SN. The thermogravimetric and differential scanning calorimetry investigations indicate that the synthesized electrolytes experience a weight reduction of less than 5 % up to 100 °C and maintain the gel stage up to 125 °C, respectively. The elevated polarity and rotational disorder of the SN molecules in the plastic-crystalline phase facilitate the improvement of ionic conductivity in the PVdF-HFP/EC-PC/NaBF₄ complex system, achieving an optimal RT ionic conductivity of about 4.55 × 10⁻³ S cm⁻¹ with the incorporation of 50 wt% of SN with purely ionic character. The working voltage range for the optimized electrolyte specimen was 4.9 V. The UV–Vis studies demonstrate the enhancement in absorbance and the reduction of the optical band gap by adding SN up to 50 wt%. The experimental results of the contact angle indicated an improvement in hydrophobicity with higher concentrations of SN across the PVdF-HFP matrix. The operational attributes for the SN-incorporated polymeric system suggest their possible use as electrolytes in electrochemical energy storage applications.