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Polyimide (PI) films with extremely high breakdown strength (451 kV/mm), energy density (5.2 J/cm3), and discharge efficiency (86.7%) at the room temperature are fabricated by simple solution casting method. Barium titanate (BaTiO3) nanoparticles are introduced into PI matrix, giving rise to enhanced dielectric permittivity (6.8) and low dielectric loss (0.012). Dielectric and energy storage performances of the BTO/PI nanocomposites are thoroughly investigated up to 200 °C. The breakdown strengths of both pure PI and BTO/PI nanocomposites decrease dramatically with the increase in the temperature, owing to the low thermal conductivity of PI and the consequent thermal runaway caused by the accumulation of Joule heat under high electric field. Despite of the enhanced electric displacement, BTO/PI nanocomposites exhibit low discharge energy density due to the substantially compromised breakdown strength induced by the BTO nanoparticles.
Sun et al. (Thu,) studied this question.