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 (eta) and high energy density (Ue). 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 Ue of 16.38 J cm-3, and an ultrahigh eta of 97.79%, far exceeding previously reported polymer nanocomposites. Furthermore, this nanocomposite also demonstrates satisfactory high-temperature energy storage performances, achieving a Ue of 7.36 J cm-3 and an eta of 83.12% at 150 degrees C. This gradient layered structure design opens a new way to explore high-performance dielectric polymer nanocomposite with both ultrahigh Ue and eta. Ultrahigh energy density and efficiency from room temperature to 150 degrees C are achieved in a precisely designed gradient-layered BaTiO3/PEI composite. The particle sizes of BaTiO3 are regulated in the middle three layers to construct multistage gradient interfaces, contributing to both high interfacial polarization and the effect of blocking electrical breakdown. image