Decoupling ferroelectric polarization and charge transport for thermally robust polymer dielectric energy storage.

Polymer dielectrics are vital for high-power electronics, yet their high-temperature application is fundamentally constrained by the inherent trade-offs among thermal stability, polarization retention, and conduction loss. Here, we mitigate these limitations by integrating high-entropy nanofillers with a preferentially oriented, wide-bandgap inorganic nanocoating to construct a multiscale heterointerfacial architecture. Within this design, entropy-driven compositional disorder enhances the structural stability and polarization response of the nanofillers, while the conformal inorganic network synergistically suppresses carrier injection and modulates bulk trap-mediated transport. Consequently, the engineered composites deliver a discharged energy density of 10.44 J cm-3 with 95% efficiency and a breakdown strength of 650 MV m-1 at room temperature. Notably, at 150 °C, the composites retain 8.35 J cm-3, 80% efficiency, and a breakdown strength of 610 MV m-1. First-principles calculations and phase-field simulations suggest multiscale field confinement that weakens electrothermal coupling and enhances high-temperature stability. This work establishes a comprehensive, multiscale design paradigm for next-generation polymer dielectric capacitors operating in extreme thermal environments.