Significantly enhanced dielectric constant and energy storage properties in polyimide/reduced BaTiO3 composite films with excellent thermal stability

In this work, reduced BaTiO3 (rBT) particles with a large number of defects sintered in a reducing atmosphere (95N2/5H2) were introduced into polyimide (PI) matrix without using any modifier or surfactant components. The rBT/PI composite films fabricated by an in situ polymerization method showed significantly enhanced dielectric constant and energy storage density. The dielectric constant of the rBT/PI composite with 30 wt% rBT reached up to 31.6, while maintaining lower loss (tg δ = 0.031@1000 kHz) compared to pure PI (εr = 4.1). Its energy storage density (9.7 J cm−3 at 2628 kV cm−1) was enhanced by more than 400% over that of pure PI (1.9 J cm−3 at 3251 kV cm−1), and was greater than the energy density of the best commercial biaxially-oriented-polypropylenes (BOPP) (1.2 J cm−3 at 6400 kV cm−1). The energy storage efficiency was around 90% due to the linear dielectric performance of rBT/PI composite films. The improved dielectric constant and energy storage density could be attributed to the combined effect of the interface interaction between two phases and the surface defects of rBT induced by the reducing atmosphere. Therefore, rBT/PI composite films with high dielectric constant, energy storage density and storage efficiency may have potential applications in the preparation of embedded capacitors.