Single-crystalline BaZr 0.2 Ti 0.8 O 3 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 (E b ) and energy density (U e ) usually degrade rapidly at high temperatures. Adding boron nitride (BN) nanosheets could improve the E b and high-temperature endurance but with a limited U e due to its low dielectric constant. Here, we fabricate freestanding single-crystalline BaZr 0.2 Ti 0.8 O 3 (BZT) membranes with high dielectric constant, and introduce them into BN doped polyetherimide (PEI) to obtain laminated PEI-BN/BZT/PEI-BN composites. At room temperature, the composite shows a maximum U e of 17.94 J cm -3 with the highest E b of 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 U e = 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 could effectively reduce carrier mobility, leading to the remarkable enhancement of the E b and U e 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. This article is protected by copyright. All rights reserved.