High-Temperature Energy Storage Performance of Polyimide Nanocomposites Enhanced by Core–Shell BT-BMT@SiO2

Advanced electrical and electronic systems are placing increasingly stringent demands on high-temperature dielectric capacitors. Polyimide (PI) possesses excellent thermal stability, but its low dielectric constant and breakdown strength limit its energy storage performance. To address this, a nanocomposite was designed consisting of the amorphous SiO2-coated relaxor ferroelectric ceramic 0.6BaTiO3-0.4Bi(Mg0.5Ti0.5)O3 (BT-BMT@SiO2) and PI. This core–shell structure improves the organic-inorganic interface and mitigates dielectric mismatch, thereby synergistically enhancing the composite’s dielectric constant, breakdown strength, and energy storage performance. At 150 °C, the breakdown field strength and maximum discharge energy density of the 0.25 vol.% BT-BMT@SiO2/PI composite reached 381.81 MV/m and 1.14 J/cm3, respectively, representing increases of 32% and 67% compared to pure PI. These results indicate that the synergistic design of relaxor ferroelectric ceramics and core–shell interfaces is an effective strategy for enhancing the high-temperature energy storage performance of PI-based dielectric materials, providing important guidance for the development of high-performance capacitor materials.