Achieving High Energy Storage Capability of Polypropylene Films through Clean Electron Beam Irradiation Induced Grafting Strategy

In order to develop polypropylene (PP) based dielectric materials with high dielectric and energy storage properties, PP grafted polystyrene films (PP-g-PS) with different grafting content have been prepared by electron beam irradiation grafting method. Free radicals were generated in the PP chains during irradiation and also enhanced the polarity of PP due to the oxidation reaction. The results have shown that the presence of grafted PS introduced smaller spherical crystals, which led to more interfacial regions and increased the interfacial polarization. DFT simulations and TSDC proved that the grafted PS introduced deeper traps, which could effectively trap carriers at high speeds and reduce the carrier mobility. When the content of PS was 8 wt %, the PP-g-PS film achieved 600 MV/m breakdown strength, 5.43 J/cm3 discharge energy density, and more than 96% charge–discharge efficiency. What’s more, the grafting of PS significantly improved the high-temperature energy storage properties of PP. At 110 °C, the discharge energy density of the PP-g-PS (8%) film is 3.44 J/cm3, which is 93% higher than that of the PP film (1.78 J/cm3). And at the electric field strength of 440 MV/m, the efficiency still exceeds 96%. This study provides a simple and feasible strategy for the development of high-performance PP-based dielectric films.