Inhomogeneous polarization configuration of high-entropy fillers boosting high-temperature capacitive performances of polymer nanocomposites

Advanced electronics and power systems urgently demand polymer nanocomposites with exceptional high-temperature capacitive performance. To achieve this goal, incorporated fillers must simultaneously enhance polarization and suppress loss of the nanocomposites at elevated temperatures. Herein, core-shell structured (Bi_0.2Na_0.2Ba_0.2Sr_0.2Ca_0.2)TiO₃@Al₂O₃ (BNBSCT@A) high-entropy ferroelectric fillers featuring inhomogeneous polarization configuration are designed. Multiphase polar nanoregions and random oxygen octahedral tilt in BNBSCT can effectively enhance dielectric constant (ε_r), refine electric displacement-electric field loops, reduce remnant electric displacement and delay polarization saturation of the nanocomposite. Meanwhile, suitable ε_r and high thermal conductivity of Al₂O₃ shell enable homogenous distribution of the external electric field and rapid dissipation of the generated Joule heating, thereby suppressing conduction loss and enhancing breakdown strength. Consequently, encouragingly, the BNBSCT@A/polyetherimide (B@A/PEI) nanocomposite displays an outstanding discharged energy density (U_dis) of 8.7 J cm⁻³ and high efficiency (η) of 90.4% at 150 °C, surpassing most of reported dielectric nanocomposites with η>90%. Additionally, by employing polyetherimide-riptycene (PEI-TE) polymers with dense physical crosslinking networks as the matrix to further suppress electrical and electromechanical breakdown, the B@A/PEI-TE nanocomposites achieve an impressive U_dis of 5.9 J cm⁻³ along with a high η of 90.6% at 200 °C.