Improving the Performance of Dielectric Nanocomposites by Utilizing Highly Conductive Rigid Core and Extremely Low Loss Shell

Polymer nanocomposites filled with one-dimensional "reelable" carbon-based nanoparticles can exhibit a high dielectric constant (epsilon') with a small quantity of nanoparticles. However, this kind of nanoparticle easily forms a conductive network near the percolation threshold, resulting in a sharp increase in the dielectric loss (tan delta) and dramatic deterioration of the breakdown strength (E-b). In this work, the insulated silica (SiO2) nanoparticles were decorated on the surface of "rigid" carbon nanofibers (CNFs) that exhibit a similar geometric feature to that of the one-dimensional ceramic fiber by a sol-gel reaction, and then the SiO2@CNF hybrids were subsequently incorporated into poly(vinylidene fluoride) (PVDF) matrix to fabricate SiO2@CNF/PVDF dielectric nanocomposites. Compared with the CNF/PVDF nanocomposites, the presence of a SiO2 insulating barrier layer tremendously reduced the tan delta of the nanocomposites, and meanwhile, E-b of the nanocomposites was greatly enhanced. For example, the nanocomposite containing 3 wt % CNFs exhibited a tan delta of 62 at 10(3) Hz and E-b of 118.4 kV/mm; however, for the nanocomposite containing 3 wt % b-S@C, tan delta was reduced to 0.057 at 103 Hz while E-b was enhanced up to 290.9 kV/mm. This work confirms that coating the insulated SiO2 nanoparticles with extremely low tan delta onto the surface of the one-dimensional conductive nanoparticles is a promising way to prepare the excellent comprehensive performing dielectric nanocomposites, and such composites may have a bright future in the fields of energy storage, conversion, and release.