Study of Enhancing Energy Storage Density of Polypropylene Film Capacitors by Modified BaTiO3 Nano-fillers

[Objective] Polypropylene （PP） film capacitors are widely used in critical power equipment due to their excellent characteristics such as low loss and high voltage endurance. However， their low dielectric constant limits performance enhancement. [Methods] Increasing the dielectric constant of films is the core approach to maximizing capacitor performance. While conventional methods employing high-dielectric ceramic nanoparticles can improve dielectric constants， they often lead to reduced breakdown field strength. As such， how to keep a high breakdown field strength while improving dielectric performance becomes a challenge. This paper innovatively designs a core-shell structured nanofiller system， featuring a high-dielectric barium titanate （BaTiO₃） core and a low-dielectric disordered shell， to construct hierarchically structured composite films. [Results] Experimental results demonstrate that the composite film achieves an energy storage density of 10.6 J/cc， representing a 5-fold improvement over pure PP films， while synergistically optimizing both dielectric constant and breakdown field strength. Mechanistic analysis reveals：1） The low-dielectric shell buffers the organic-inorganic interfacial dielectric mismatch， suppressing electric field distortion and significantly enhancing breakdown field strength； 2） Space charges induced at the core-shell interface form unique distributions under the effect of electric field， generating strong interfacial polarization during migration to substantially boost dielectric constant. [Conclusions] By precisely controlling nanofiller microstructure， this study successfully resolves the conflict between dielectric performance and insulation strength. The work provides new insights for the design of high-performance capacitor films.