Superior high-temperature energy storage of polypropylene enabled by coating rectorite nanosheets and γ-irradiation

Biaxially oriented polypropylene (BOPP), a state-of-the-art commercially benchmark dielectric material for thin-film capacitors dominating modern electrostatic capacitor technologies, suffers from performance degradation above 85 °C. To address the limitation, a scalable strategy combining bulk γ-ray irradiation and surface nano-coating is developed to enhance the high-temperature capacitive energy storage performance. At 125 °C, the irradiated BOPP film coated with rectorite nanosheets (RNs) achieves a high energy density of 2.8 J cm −3 at 500 MV m −1 with 95% efficiency, representing a 250% enhancement relative to pristine BOPP and outperforming reported PP-based dielectrics. Notably, the composite film sustains 1.8 J cm −3 energy density at 98% efficiency through 30,000 charge-and-discharge cycles under 400 MV m −1 at 125 °C. Experimental and theoretical analyses reveal the underlying mechanism that the negatively charged and wide-bandgap RNs suppress charge injection, while the polar groups in BOPP introduced by γ-irradiation provide deep-energy traps to block the movement of charge carriers within the dielectric. This optimization approach establishes a design paradigm for high-temperature polymer dielectrics and brings new insights into bulk and interfacial engineering.