Significantly enhanced dielectric and energy storage performance of AlN/KNbO₃/PVDF sandwich-structured composites via introducing the AlN/PVDF insulating layers

Dielectric composites with a high dielectric constant and electric breakdown strength are highly desired for the excellent energy storage behavior of the microelectronic and electric power systems. Sandwich-structured composites with an insulating layer can provide a pathway to improve the dielectric and energy storage performance, and in general, the fillers design and volume control of the insulating layer are very important. Herein, we present a novel designed sandwich-structured aluminum nitride/potassium niobate/poly(vinylidene fluoride) (AlN/KNbO₃/PVDF) nanocomposites by the solution-casting and hot-pressing process. The effect of the introduction of an insulating phase AlN in the two outer layers and a different KNbO₃ volume fraction in the middle layer on the dielectric properties and energy storage behavior of the sandwich-structured composites were investigated in detail. The results demonstrate that dielectric constant, electric breakdown strength, energy storage density and discharged efficiency of the AlN/KNbO₃/PVDF sandwich-structured composites are significantly enhanced. Moreover, a high energy density of 10.54 J/cm³ and a superior discharged energy efficiency of 70% at the electric breakdown strength of 337 MV/m are achieved in the sandwich-structured nanocomposites with 1 vol% KNbO₃ in middle layer and with 1 vol% AlN in the outer layers, which are much higher than the conventional single-layered KNbO₃/PVDF composites. It is indicated that the introduction of insulating layers in sandwich-structure composites can improve the electric breakdown strength and discharge efficiency, as confirmed by analyzing results of the finite element simulations. This work may provide an effective approach to develop excellent performance dielectric composites for electrical energy storage applications.