HighlightsA bilayer dielectric film is prepared via coating boron nitride nanosheets (BNNSs) by solution casting on the surface of polyethylene terephthalate (PET) film.The BNNS layer acts as the efficient barrier layer to suppress the charge injection, thereby making the surface-modified PET films exhibit excellent breakdown strength and electrostatic energy storage performance.The surface coating methods are accessible and suitable for large-scale roll-to-roll process production of dielectric films.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40820-023-01121-6.