Quantum‐Confined Boron Nitride Quantum Dots–Polyimide Composites Achieve Exceptional Dielectric Strength, Energy Density, and Thermal Dissipation at Ultralow Loading

Abstract Polymer dielectric materials are highly promising for capacitive energy storage in electronics and pulsed‐power devices thanks to their flexibility, low loss, high voltage tolerance, and cost‐effectiveness. Yet balancing dielectric constant and breakdown strength, managing space charge accumulation and thermal dissipation, and maintaining electrical reliability and long‐term aging remain formidable challenges, especially for high‐power applications. In this work, by embedding just 0.06 wt.% boron nitride quantum dots (BNQDs) into polyimide (PI), this study harnesses quantum confinement, enhances interfacial polarization, and a Coulomb‑blockade effect to simultaneously boost dielectric properties, energy storage, cycling stability, and thermal dissipation. The resulting BNQDs/PI dielectric films exhibit exceptional energy storage densities of 9.57 J·cm −3 ( η = 90%) at room temperature and 5.46 J·cm −3 ( η = 86%) at 200 °C under its maximum breakdown strength of 632.0 and 591.9 kV·mm −1 , respectively, surpassing most reported PI systems. Moreover, the thermal conductivity increases by 121.7% (to 0.229 W·(m·K) −1 ) compared to pristine PI, effectively mitigating heat accumulation and ensuring cycling reliability as confirmed by both experiments and simulations. Acting as efficient electron traps of BNQDs, this synergistic integration addresses key electrical, thermal, and reliability bottlenecks, offering a compelling route toward advanced, high‐power dielectric systems.