Surface‐coated polymer nanocomposites containing z‐aligned high‐k nanowires as high‐performance dielectrics at elevated temperatures

Abstract Recently, demands for high‐performance polymer film capacitors at elevated temperatures have become more urgent. High dielectric constant is essential for dielectric materials to achieve substantial energy density at relatively low electric fields, which is of great significance to practical applications, while improving the permittivity of high‐temperature polymer dielectrics without a remarkable deterioration in other electrical properties still remains a challenge. Here, a polymer nanocomposite containing z‐aligned high‐k nanowires sandwiched by e‐beam evaporation deposited Al 2 O 3 films was developed based on the optimal structure proposed by the phase‐field simulation. It is found that z‐aligned nanowires are more effective in promoting the dielectric constant than random‐aligned ones, and a large increase in dielectric constant is observed at relatively low content of nanofillers. Outer insulating layers effectively suppress the electric conduction and improve the breakdown strength. Consequently, the nanocomposite with only 1 volume fraction of z‐aligned nanowires exhibits a breakdown strength, electrical resistance, and charge–discharge efficiency as high as neat PEI, but more than twice the discharged energy density than it at 150 °C. This study realises the optimal structure predicted by simulation in experiment, obtaining high‐permittivity, high‐temperature nanocomposites at no expense of other electrical properties, and making it possible to achieve high discharged energy density at relatively low electric fields.