Significantly improved breakdown strength and energy density in high-temperature polymer dielectric enabled by bilayered nanocoatings

Abstract

Dielectric materials with superior high-temperature energy storage capability are of critical importance for the development of modern power electronic systems. However, polymer dielectrics generally suffer from rapid performance degradation under high temperature and strong electric fields due to charge injection, which is particularly severe for highly aromatic, high-temperature-resistant polymers such as polyimide. Owing to their intrinsically low bandgap and limited charge-injection barriers, pronounced conductive losses can occur even under moderate electric fields. Conventional methods to address this issue involve coating the polymer surface with highly insulating nanomaterials; while this can suppress charge injection, it simultaneously triggers space charge accumulation and local electric-field distortion. To address these challenges, a novel bilayer nanocoated polyimide (Kapton PI)–based multilayer architecture is designed in this work to synergistically integrate charge-blocking and charge-dissipation functionalities. The boron nitride nanosheets (BNNSs) layer adjacent to the electrodes effectively increases the charge-injection barrier, while the montmorillonite (MMT) nanosheets layer near the polymer substrate facilitates in-plane charge dissipation and alleviates local electric-field distortion. Plasma treatment is strategically employed to optimize the interfacial chemistry, further enhancing interfacial polarization and interfacial interactions to ensure a robust synergistic effect. Benefiting from this comprehensive interfacial engineering, the bilayer nanocoatings simultaneously achieve suppressed electrical breakdown and enhanced polarization at elevated temperatures. Remarkably, it delivers a high discharged energy density (Ue) of 1.6 J cm−3 with an outstanding charge–discharge efficiency (η) of 90.1% at 200 ◦C under a low electric field of 250 MV m−1. This work demonstrates an effective strategy based on bilayer nanocoatings for improving the high-temperature energy storage performance of polymer films, showing great potential for harsh environment applications.