ABSTRACT The low energy density, inefficient operation, and thermal instability of polymer dielectrics hinder the deployment of film capacitors under harsh environmental conditions. Interface engineering has emerged as a powerful strategy to introduce charge traps or construct interfacial barriers, thereby regulating carrier dynamics and enhancing energy storage. Here, we propose a multilevel heterointerface engineering strategy that integrates boron nitride and barium niobate nanosheets through lattice interlocking. The large work‐function offset and bandgap contrast induce interfacial band bending and a built‐in electric field, forming a complementary trap‐barrier network that guides, blocks, and confines charge carriers. This design effectively suppresses charge injection and mobility, enhances interfacial polarization, and mitigates the propagation of breakdown pathways. Consequently, BNO@BN/PEI composites achieve exceptional energy storage performance, delivering 9.02 J cm −3 ( η = 92%) at room temperature and sustaining 6.1 J cm −3 ( η ≈ 90%) at 150°C, while still preserving 4.6 J cm −3 at 200°C. First‐principles calculations and finite element simulations further validate the structural and functional superiority of the multilevel heterointerface. This work establishes multilevel heterointerface engineering as a generalizable paradigm for breaking the trap‐barrier trade‐off in conventional dielectric design and paves the way for next‐generation high‐energy‐density and thermally robust polymer capacitors.
Liu et al. (2026) studied this question.