Dielectric performance of all-organic polymer composites via incorporation of fluorinated molecules

All-organic polymer composites have garnered growing attention due to their improved dielectric performance and the compatibility between polymer matrix and fillers favorable for large-scale processing. Here, two fluorinated molecules with different numbers of fluorine atoms, namely 4,5,6,7-tetrafluoronaphtho [2,1-b:3,4-b’]dithio-phene (F₄NT) and 5,6-difluoronaphtho [2,1-b:3,4-b’]dithio-phene (F₂NT), are incorporated in polyetherimide (PEI). Traces of organic fillers decouple the conjugated structure of PEI chains, reducing the electron transmission channels under high electric fields. The FNTs with multi-ring coplanar structures enhance the insulation of composites due to the wide-bandgap nature and space-scattering electron effects. The molecular filler with more fluorine atoms proved to be more effective in inhibiting electron transmission and resulted in enhanced breakdown strength (approximately 30 %) and significantly reduced high-temperature dielectric loss. Moreover, sulfur atoms with higher polarizability in FNTs contribute to an improved dielectric constant. The simultaneously enhanced dielectric constant and breakdown strength in composite film capacitors result in a higher discharged energy density that is 1.9 times that of pure polymer, accompanied by a high efficiency of 90 %. Further preparation of composites based on polyvinylidene difluoride (PVDF) for mechanism investigation reveals that the enhanced dielectric performance is mainly due to enhanced insulation properties in the amorphous area.