Ultrahigh energy storage density and efficiency in facile dual-layered PVDF/PEI-based nanocomposites <i>via</i> an electrical/thermal synergistic effect

The implementation of high energy storage performance in polymer-based composite dielectrics under harsh environmental conditions is critical for the advancement of electronics and electric power systems. In this work, leveraging the principle of electrical/thermal synergistic enhancement, a series of facile dual-layered polymer-based nanocomposites are fabricated, with pure polyvinylidene fluoride (PVDF) as the top layer and boron nitride nanosheet (BNNS)/polyetherimide (PEI) as the bottom layer. Both the efficiency (<i>η</i>) and dielectric constant of the nanocomposites can be optimized simultaneously by harmonizing the dielectric mismatch through the construction of a macroscopic interface between different polymers. More importantly, a breakdown barrier and a heat transfer pathway can be created to elevate breakdown strength and improve high-temperature performance by embedding lay-flat BNNSs into the PEI layer. Further analyses through simulations and experimental characterization reveal the relationship between structural design and energy storage performance. Ultimately, the composites simultaneously achieved ultrahigh energy storage performance (energy storage density [<i>U</i>_e] = 28.38 J cm^-3, <i>η</i> = 96.2%) and excellent high-temperature performance (<i>U</i>_e = 12.69 J cm^-3 with <i>η</i> > 80%, maximum <i>U</i>_e = 14.02 J cm^-3, 150 °C), far exceeding recently reported advanced polymer composites. This facile structural design provides an innovative and effective design paradigm for advanced dielectric materials.