Single‐Crystalline BaZr0.2Ti0.8O3 Membranes Enabled High Energy Density in PEI‐Based Composites for High‐Temperature Electrostatic Capacitors

Dielectric capacitors are promising for high power energy storage, but their breakdown strength (Eb ) and energy density (Ue ) usually degrade rapidly at high temperatures. Adding boron nitride (BN) nanosheets can improve the Eb and high-temperature endurance but with a limited Ue due to its low dielectric constant. Here, freestanding single-crystalline BaZr0.2 Ti0.8 O3 (BZT) membranes with high dielectric constant are fabricated, and introduced into BN doped polyetherimide (PEI) to obtain laminated PEI-BN/BZT/PEI-BN composites. At room temperature, the composite shows a maximum Ue of 17.94 J cm-3 at 730 MV m-1 , which is more than two times the pure PEI. Particularly, the composites exhibit excellent dielectric-temperature stability between 25 and 150 °C. An outstanding Ue = 7.90 J cm-3 is obtained at a relatively large electric field of 650 MV m-1 under 150 °C, which is superior to the most high-temperature dielectric capacitors reported so far. Phase-field simulation reveals that the depolarization electric field generated at the BZT/PEI-BN interfaces can effectively reduce carrier mobility, leading to the remarkable enhancement of the Eb and Ue over a wide temperature range. This work provides a promising and scalable route to develop sandwich-structured composites with prominent energy storage performances for high-temperature capacitive applications.