Flexible BaTiO3/PVDF gradated multilayer nanocomposite film with enhanced dielectric strength and high energy density

Organic–inorganic 0–3 nanocomposites, which combine the potentially high dielectric strength of the organic matrix and the high dielectric permittivity of the inorganic filler, are extensively studied as energy-storage dielectrics in high-performance capacitors. In this study, a gradated multilayer BaTiO3/poly(vinylidene fluoride) thin film structure is presented as a means to achieve both a higher breakdown strength and a superior energy-storage capability. The central layer of this film, designed to provide high electric displacement, is composed of a high volume fraction of 6–10 nm BTO nanocrystals produced by a TEG-sol method. The small particle size contributes to a high dispersibility of the nanocrystals in polymer media, as well as a high interfacial area to mitigate the local electric field concentration. The outer layers of the structure are predominantly PVDF, with a significantly low volume fraction of BTO, taking advantage of the high dielectric strength of pure PVDF at the electrode–nanocomposite interface. The film is mechanically flexible, and can be removed from the substrate, with total thicknesses in the range of 1.2–1.5 μm. Parallel plate capacitance devices exhibit highly improved dielectric performances with low-frequency permittivity values of 20–25, a maximal discharge energy density of 19.37 J cm−3 and dielectric (breakdown) strengths of up to 495 kV mm−1.