Significantly Enhanced Energy Density in Nanocomposite Capacitors Combining the TiO₂ Nanorod Array with Poly(vinylidene fluoride)

A novel inorganic/polymer nanocomposite, using 1-dimensional TiO₂ nanorod array as fillers (TNA) and poly­(vinylidene fluoride) (PVDF) as matrix, has been successfully synthesized for the first time. A carefully designed process sequence includes several steps with the initial epitaxial growth of highly oriented TNA on the fluorine-doped tin oxide (FTO) conductive glass. Subsequently, PVDF is embedded into the nanorods by the spin-coating method followed by annealing and quenching processes. This novel structure with dispersive fillers demonstrates a successful compromise between the electric displacement and breakdown strength, resulting in a dramatic increase in the electric polarization which leads to a significant improvement on the energy density and discharge efficiency. The nanocomposites with various height ratios of fillers between the TNA and total film thickness were investigated by us. The results show that nanocomposite with 18% height ratio fillers obtains maximum increase in the energy density (10.62 J cm^–3) at a lower applied electric field of 340 MV m^–1, and it also illustrates a higher efficiency (>85%) under the electric field less than 100 MV m^–1. Even when the electric field reached 340 MV m^–1, the efficiency of nanocomposites can still maintained at ∼70%. This energy density exceeds most of the previously reported TiO₂-based nanocomposite values at such a breakdown strength, which provides another promising design for the next generation of dielectric nanocomposite material, by using the highly oriented nanorod array as fillers for the higher energy density capacitors. Additionally, the finite element simulation has been employed to analyze the distribution of electric fields and electric flux density to explore the inherent mechanism of the higher performance of the TNA/PVDF nanocomposites.