Nonpolar sub-10 nm TiO2 nanocrystal for high energy density polypropylene nanocomposites

Abstract

Film capacitors have shown great potential in high-power energy storage devices due to their high breakdown strength and low dielectric loss. However, the state-of-the-art commercial capacitor dielectric, biaxially oriented polypropylene (BOPP), exhibits limited energy storage density below 2 J cm−3 because of its low dielectric constant (approximately 2.2 at 103 Hz). In this work, we present a novel PP-based nanocomposites by incorporating nonpolar sub-10 nm sized TiO2 nanoparticles into the PP matrix for the first time. The nonpolar TiO2 nanoparticles are functionalized with Trioctylphosphine oxide (TOPO) ligands, ensuring excellent compatibility and dispersion of the TiO2 fillers in the PP matrix, resulting in a homogeneous dielectric PP nanocomposite. Moreover, the TOPO ligand, with lower LUMO energy level and higher HOMO level than that of PP matrix, serves as an energy trap to capture carriers upon their occurrence. Furthermore, the well-dispersed sub-10 nm sized TiO2 nanoparticles enlarges the interfacial area, thereby increasing the interfacial polarization and the dielectric constant. The resultant PP nanocomposites exhibit a high discharged energy density of 4.19 J cm−3 at 600 MV m−1, representing a remarkable 74.9% increase compared to that of the pure PP films. This work provides a brand-new strategy for constructing homogeneous PP nanocomposite dielectrics by incorporating nonpolar sub-10 nm sized TiO2 nanoparticles as fillers. And this approach is critical for the design of high energy density PP-based nanocomposites.