An Entropy–Enthalpy‐Guided Molecular‐Brake Strategy for High‐Temperature Capacitive Energy Storage

The growing demand for electrified technologies operating in thermally harsh environments, ranging from electric vehicles to aerospace power systems, requires polymer dielectrics that can sustain high energy density and reliability at elevated temperatures. However, the performance of biaxially oriented polypropylene (BOPP), the industrial standard for capacitor films, is fundamentally limited by thermally activated segmental motion in its amorphous regions, which accelerates charge carrier transport and leads to premature electrical failure. Here, we present a scalable, all‐organic molecular design strategy that leverages entropy–enthalpy–driven miscibility to suppress this thermally induced conduction. Low‐molecular‐weight poly(phenylene oxide) oligomers, which act as “molecular brakes”, are incorporated into a maleic‐anhydride‐functionalized PP matrix to restrict chain mobility, promote the formation of well‐developed crystalline lamellae, and introduce deep traps. Molecular simulations and experimental characterization confirm that this synergistic confinement effectively stabilizes the amorphous phase and hinders charge carrier transport at high temperature. At 120°C, modified BOPP films achieve a discharged energy density of 4.6 J cm −3 with 96.2% charge–discharge efficiency at 715 MV m −1 . This entropy–enthalpy‐guided molecular design provides a practical and generalizable pathway for engineering heat‐resilient polymer dielectrics using fully scalable, industry‐compatible materials.