Hybrid Core–Shell TiCN@SiO₂ Nanoparticles in Percolation-Based Polyvinylidene Fluoride Dielectrics for Improved High-Voltage Capacitive Energy Storage

Solid-state polymer dielectrics offer an exceptional dielectric breakdown, but require an enhanced energy density to be competitive with alternative electrolyte-based energy storage technologies. Therefore, this research introduces conductive titanium carbonitride (TiCN) nanoparticles in a polyvinylidene fluoride (PVDF) matrix to obtain flexible percolation-based nanodielectrics by ultrasonication-based suspension processing and hot pressing. Well-dispersed TiCN nanoparticles in PVDF were obtained for a wide range of filler volume fractions, and an exceptional peak in the dielectric constant equal to 1130 (0.1 Hz) and 29 (10 kHz) was observed near the percolation threshold (9.2 vol %). The enhanced dielectric constant was ascribed to massive interfacial polarization occurring, resulting from Maxwell-Wagner-Sillars (MWS) polarization and a nanocapacitor mechanism that are dominant at low and high frequencies, respectively. An improvement by 30% in the energy density (0.042 Wh kg^-1) compared with the neat PVDF matrix was achieved for the PVDF/TiCN nanodielectrics. The first successful uniform deposition of a nanometer-thin (3 nm) silica (SiO₂) shell via the Stöber process on TiCN nanoparticles significantly suppressed the dielectric losses near percolation for the PVDF/TiCN@SiO₂ nanodielectrics by more than 1 order of magnitude while offering dielectric constants of 34 (0.1 Hz) and 10 (10 kHz). This study demonstrates the potential of hybrid (core-shell) percolation-based dielectrics for an improved capacitive dielectric performance by an integrated dielectric characterization approach that simultaneously optimizes the dielectric constant, loss tangent, breakdown strength, and energy density.