Ultra‐Low Loading Fillers Induced Excellent Capacitive Performance in Polymer‐Based Multilayer Nanocomposites under Harsh Environments

Abstract Multilayer‐structured nanocomposites are recognized as a prominent strategy for overcoming the paradox between the breakdown strength ( E b ) and polarization ( P ) to achieve superior energy storage performance. However, current multilayer‐structured nanocomposites involving substantial quantities of nanofillers (>10 vol.%) for high dielectric constant as polarization layer will inevitably deteriorate mechanical properties and breakdown strength. Herein, an innovative approach is reported to breaking conventional rules by designing a multilayered polymer composite with ultralow loading of Al 2 O 3 nanoparticles, i.e., 0.3 vol.% for polarization layers and 2 vol.% for insulation layers. By modulating the spatial distribution of Al 2 O 3 nanoparticles in polymer, a significantly increased interfacial dipole response is induced, and deep interfacial traps are constructed to capture the mobile charges, thereby suppressing high‐temperature conduction loss. The resulting multilayered polymer composite exhibits an unparalleled discharged energy density of 7.8 J cm −3 with a charging/discharging efficiency exceeding 90% at 150 °C. This work provides valuable insights into achieving superior capacitive performance in multilayer composite films operating under extreme conditions.