Simultaneously Enhanced Thermal Conductivity and Dielectric Breakdown Strength in Micro/Nano-BN/Epoxy/PC Multilayer Composites

Because of their significant application potential in both power electronic devices and power equipment, the development of polymer-based composites with high thermal conductivity and breakdown strength has gained increasing attention. In this study, multilayer structural composites were successfully prepared. Micro/Nano-BN was prepared by electrospinning technology, showing positive gradient (PGD) and inverse gradient (IGD) distribution in an epoxy and polycarbonate (PC) blended matrix. The gradient distribution of nanofillers fully filled in each layer greatly enhances the breakdown strength of the composite dielectric. In comparison to traditional composites, the bottleneck of increasing thermal conductivity and breakdown strength at the same time was successfully overcome. The breakdown strength of the 2–6–2 structure multilayer positive gradient composite dielectric reaches 107.1 kV/mm, 76.7% higher than the single-layer uniform composite dielectric and thermal conductivity of 0.38 W/(m·K) (2.11 times that of epoxy). The 6–2–6 structure obtains the highest breakdown strength of 110 kV/mm and a thermal conductivity of 0.33 W/(m·K). The thermal conductivity of the multilayer composite dielectric of both gradient structures changed; this phenomenon provides an idea for polymers to improve thermal conductivity.