Engineering hierarchical interfaces in high-temperature polymer dielectrics for electrostatic supercapacitors†

Dielectric capacitors are pivotal elements in advanced pulsed power devices and high-voltage, high-capacity power electronic converters, crucial for efficient energy storage. However, a major challenge remains the significant reduction in energy density and charge–discharged efficiency of dielectric polymers under high temperatures, primarily due to heightened electrical conduction losses. This study introduces a universal approach of heterojunction interface engineering in polyethersulfone (PESU) composites, aimed at improving capacitive performance across a broad temperature range. The introduction of one-dimensional heterojunction BaTiO₃@Al₂O₃ nanofibers with large aspect ratios could enhance both the dielectric constant (ε_r) and breakdown strength (E_b). Specifically, the creation of hierarchical interfaces increases the trap density and energy levels for mobile charges, effectively reducing conduction losses and improving E_b under high-temperature conditions. Consequently, the PESU-3 vol% BaTiO₃@Al₂O₃ nanocomposite achieves an excellent energy density of 7.3 J cm⁻³ with over 90% retention at 150 °C and 550 MV m⁻¹. Finite element simulations further confirm that the heterojunction structure of BaTiO₃@Al₂O₃ nanofibers effectively inhibits the growth of breakdown paths. This work demonstrates that hierarchical interface engineering offers a powerful strategy to enhance capacitive performance in dielectric polymer composites under harsh conditions.