Improved Dielectric and Energy Storage Properties of Polypropylene-Based Organic Films through Construction of a Microcompatible “Sea–Island” Structure

With the development of modern power systems, advanced energy storage polymer films are receiving attention. As an important energy storage dielectric material, polypropylene (PP) film has the advantages of low dielectric loss and high charge/discharge efficiency. Nevertheless, its inherent low dielectric constant (∼2.0) severely hampers the enhancement of energy storage density (∼1–2 J/cm3). Herein, all-organic PP-based ternary composite films with the "sea–island" structure were designed to improve the dielectric and energy storage properties of PP. In this research, PP formed the sea phase. In contrast, the methyl methacrylate-co-glycidyl methacrylate (MG) copolymer formed the island phase with polypropylene-grafted maleic anhydride (PP-g-MAH) as the compatibilizer. The higher polarity of MG, PP-g-MAH, and the interfacial polarization between the "sea–island" two-phase interface improved the dielectric constant to 3.8, while the dielectric loss remained almost unchanged compared to PP itself. When the loading of MG was 12 wt %, the discharge energy density of the PP/MG/PP-g-MAH composite film reached 5.87 J/cm3 with a 610 MV/m breakdown strength; furthermore, the charge/discharge efficiency still remained at about 96%, which shows a good application prospect in the field of thin film capacitors.