Polymer‐Based Dielectric Composite Films with Excellent Dielectric Energy Storage and Thermal Management Capabilities

Abstract The drive toward miniaturization, integration, and extreme environmental adaptability in electronic devices imposes stringent demands on the energy density and thermal conductivity of polymer dielectric materials. Here, the long‐standing challenge of simultaneously improving dielectric constant and thermal conductivity through a “heterogeneous interface enhancement‐dual filler synergy” strategy is addressed. Hydroxylated boron nitride nanosheets (BNNS) and reduced graphene oxide (rGO) are codispersed within a polyimide (PI) matrix, forming continuous networks that facilitate efficient dielectric and thermal transport. Robust hydrogen bonding among hydroxylated BNNS, rGO, and PI establishes stable interfaces, while the permittivity mismatch between BNNS and rGO induces interfacial polarization, yielding a dielectric constant of 12.6 at 1 kHz. The interpenetrating BNNS/rGO network facilitates efficient phonon transport, resulting in a thermal conductivity of 13.6 W (m K) −1 . Furthermore, the large lateral size of ultrathin BNNS suppresses breakdown channel propagation, maintaining a high breakdown strength of 440 kV mm −1 . Notably, the composite exhibits a discharge energy density of 4.6 J cm − 3 with charge–discharge efficiency over 90% at 150 °C, surpassing most advanced polymer dielectrics. This work overcomes the trade‐off between dielectric and thermal properties of polymer‐inorganic nanocomposites, offering a compelling strategy for developing high‐performance dielectric films for advanced electronics.