Significantly Improved Energy Storage Density of Polypropylene Nanocomposites via Macroscopic and Mesoscopic Structure Designs

Polymer dielectrics with high breakdown strength are very competitively used in the dielectric capacitor, which is widely applied in pulsed power devices and power systems due to their ultra-high power density. The polypropylene (PP) film is the most popularly used polymer for the dielectric capacitor in the market. However, its low energy density cannot meet the emerging demand for miniaturized, compact, and high-energy performance dielectrics. Therefore, it is urgent to raise the energy storage density of the polypropylene film. Here, this study described the improved energy storage density of polypropylene nanocomposites via macroscopic and mesoscopic structure designs. The ABA-structured, BAB-structured, and single-layered nanocomposites were prepared by melting blending and hot-pressing methods, where “A” and “B” films refer to PP/MgO and PP/BaTO ₃ nanocomposite dielectrics, respectively. Then, the microstructure, dielectric, breakdown, and energy storage properties of these nanocomposite dielectrics were tested. According to the test results, for the sandwich-structured dielectrics, the B layer and the interface between adjacent layers can increase the polarization, and the A layer and the barrier at the interface can reduce the charge mobility. In addition, the sandwich structures can redistribute the electric field. Correspondingly, the breakdown strength and permittivity of PP dielectrics are improved synergistically. Compared to the PP nanocomposite dielectrics with the BAB structure, the dielectric with the ABA structure exhibits more excellent energy storage performance. The largest energy storage density of ABA films with a BaTO ₃ content of 45 wt% in the B layer is 3.10 J/cm ³, which is 67% higher than that of pure PP. The study provides a new concept for improving the energy storage performance of polymer nanocomposite dielectrics from the perspective of macroscopic and mesoscopic structure designs.