Polyamideimide dielectric with montmorillonite nanosheets coating for high-temperature energy storage

• MMT nanocoatings were prepared on dielectric Kapton films by a versatile dip-coating method. • A high energy density of 2.9 J cm −3 with an efficiency higher than 80% was achieved at 150 °C. • The charge blocking/regulating effect of nanocoatings was revealed by high-field characterization and finite element simulation. To meet the ever-increasing demand for electric power storage and conversion under harsh environment, polymer dielectrics, as the functional component in electrostatic capacitors, are required to serve at high temperatures. However, it is challenging to maintain favorable electrical insulation in polymer dielectrics with the temperature rise because of the high conduction loss at elevated temperature, which will lead to reduced breakdown strength, energy density, and service life. Here, a versatile surface engineering method is presented to enhance the high-temperature electrical insulation and energy storage performance of polymer dielectric via dip-coating montmorillonite (MMT) nanosheets. At 150 °C, a significantly enhanced breakdown strength of 551MV/m is achieved in a MMT coated polyamideimide (PAI) with optimized coating thickness and MMT content, resulting in a high energy density of 2.9 J cm −3 and a charge-discharge efficiency >80% that outperform existing high-temperature polymers and polyimide-based composites. Finite element simulation demonstrates that this superior performance is attributed to the anisotropic electrical properties of MMT nanosheets, which not only blocks charges injected from electrodes but also regulates the transport of charges to dissipate along the in-plane direction. This work offers a versatile and scalable approach for enabling high-temperature electrostatic energy storage and high-temperature insulation of a wide range of polymer dielectrics.