Ultrahigh discharge efficiency and improved energy density in rationally designed bilayer polyetherimide–BaTiO3/P(VDF-HFP) composites

Abstract

Polymer dielectric composites are of great interest as film capacitors that are widely used in pulsed power systems. For a long time, huge efforts have been devoted to achieving energy densities as high as possible to satisfy the miniaturization and high integration of electronic devices. However, the discharge efficiency which is particularly crucial to practical applications has gained little attention. With the target of achieving concurrently improved energy density and efficiency, a class of rationally designed bilayer composites consisting of a pure polyetherimide layer and a BaTiO₃/P(VDF-HFP) composite layer were prepared. Interestingly, the bilayer composites exhibit ultrahigh discharge efficiencies η (>95%) under external electric fields up to 400 kV mm⁻¹ which are much higher than most of the so far reported results (η < 80%). Meanwhile, a low loss (tan δ < 0.05 @ 10 kHz) comparable to that of the pure polyetherimide is obtained. In addition, the bilayer composites show impressive improvements in breakdown strengths E_b, i.e., 285%, 363%, 366% and 567% for composites with 5 vol%, 10 vol%, 20 vol% and 40 vol% BaTiO₃, compared to their single layer counterparts, resulting in obviously improved energy densities U_d. In particular, the bilayer composite with 10 vol% BaTiO₃ displays the most prominent comprehensive energy storage performance, i.e., η ∼ 96.8% @ 450 kV mm⁻¹, U_d ∼ 6 J cm⁻³ @ 450 kV mm⁻¹, tan δ ∼ 0.025 @ 10 kHz, and E_b ∼ 483.18 kV mm⁻¹. The ultrahigh discharge efficiencies and high energy densities, along with low loss and breakdown strengths, make these bilayer composites ideal candidates for high-performance dielectric energy-storage capacitors.