Ultrahigh Dielectric Energy Density and Efficiency in PEI-Based Gradient Layered Polymer Nanocomposite

Dielectrics with high-energy-storage performance are highly desired for increasing compact-size energy storage, and integration of modern power electronics. However, an ever-existing challenge is to achieve both high efficiency (η) and high energy density (U_e). Here, a gradient-layered (five-layer) polyetherimide (PEI)-based nanocomposite is presented. Different from traditional layered structures (modulation of filler volume fraction), multistage gradient interfaces are constructed by modulating the particle sizes of barium titanate nanoparticles (BaTiO₃ NPs) to decrease sequentially from top to bottom. In this structure, three BaTiO₃ NPs/PEI layers are clamped by two boron nitride nanosheets (BNNSs)/PEI layers. It is demonstrated that the gradient structure can suppress breakdown and confer high interfacial polarization, simultaneously. Consequently, the nanocomposite possesses an enhanced U_e of 16.38 J cm⁻³, and an ultrahigh η of 97.79%, far exceeding previously reported polymer nanocomposites. Furthermore, this nanocomposite also demonstrates satisfactory high-temperature energy storage performances, achieving a U_e of 7.36 J cm⁻³ and an η of 83.12% at 150 °C. This gradient layered structure design opens a new way to explore high-performance dielectric polymer nanocomposite with both ultrahigh U_e and η.