Mediating dielectric/breakdown conflict in polydopamine@HfB₂ nanorod-filled polymer composites from rational meaty-sandwich structure

The contradiction between high permittivity and breakdown strength in dielectrics is acknowledged. Although a sandwich structure endows the nanocomposites with ultrahigh breakdown strengths, the permittivity is limited ascribed to series connection of layers. In this work, a novel strategy from “meaty-sandwich” food was utilized to prepare the multi-layer polymer nanocomposites with finely balanced high permittivity and breakdown strength. HfB₂ nanorods, BaTiO₃ nanoparticles, and BN nanosheets were used as fillers. HfB₂ were surface-coated by polydopamine to gain the core–shell nanorods. High-content middle-layer composite results in a large dielectric response, while low-content bilateral-layer composite leads to high breakdown strength. Tri-layer composites with core–shell filler show high breakdown strengths. Five-layer composite with four high-insulation thin layers exhibits an ultrahigh breakdown strength and favorable permittivity. Breakdown mechanisms of composites were proposed. The best tri-layer composite shows a high permittivity of ~ 136@100 Hz and breakdown strength of ~ 263 MV m⁻¹. This work might pave a road for fabrication of promising dielectrics.