PVDF-LiTFSI-based solid polymer electrolyte membranes for safer and more sustainable lithium-ion batteries: Thermal, mechanical, dielectric, and electrochemical properties

Solid polymer electrolytes (SPEs) are promising alternatives to conventional liquid electrolytes for lithium-ion batteries due to their enhanced safety, thermal stability, and reduced risk of electrolyte leakage. In this study, PVDF-based SPE membranes were prepared by blending poly(vinylidene fluoride) (PVDF) with poly(vinylpyrrolidone) (PVP) or poly(4-vinylpyridine) (P4VP) and incorporating lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a lithium-ion conducting salt. The effects of LiTFSI concentration and ceramic fillers (Al 2 O 3 , ZrO 2 , and SiO 2 ) on the structural, thermal, mechanical, dielectric, and electrochemical properties of the membranes were systematically investigated. X-ray diffraction, FTIR, and Raman spectroscopy confirmed successful incorporation of LiTFSI into the polymer matrix and revealed increased amorphization with increasing salt content. Thermal analysis demonstrated good thermal stability, while differential scanning calorimetry showed suppression of crystalline PVDF endotherms, indicating reduced crystallinity and enhanced polymer-chain mobility. Morphological analysis revealed increased pore size, grain coarsening, and surface porosity with increasing LiTFSI concentration. These structural changes enhanced dielectric performance but reduced tensile strength and Young’s modulus, highlighting a trade-off between ion-transport behavior and mechanical robustness. Dielectric spectroscopy showed significant increases in dielectric constant, dielectric loss, and conductance with increasing LiTFSI content, attributed to enhanced salt dissociation, interfacial polarization, and increased charge-carrier concentration within the amorphous polymer matrix. Among the investigated formulations, the PVDF/PVP/LiTFSI membrane exhibited the most balanced combination of thermal, mechanical, dielectric, and electrochemical properties. Linear sweep voltammetry demonstrated electrochemical stability up to approximately 3.64 V versus Li + /Li, while ceramic fillers further improved dielectric performance and oxidative stability. The findings provide valuable insights into the structure–property relationships governing PVDF-based SPEs and offer design guidelines for developing safer and more sustainable polymer electrolyte materials for next-generation solid-state lithium-ion batteries and energy-storage technologies.