Significant enhancement of high-temperature capacitive energy storage in dielectric films through surface self-assembly of BNNS coatings

Polymer dielectrics, serving as integral components in electrostatic capacitors, must meet the escalating demands for electrical energy storage and conversion in harsh environments. However, the current enhancement of breakdown strength in polymer composite materials often relies on intricate nanostructure designs or inorganic deposition methods, which result in high production costs, slow processing, and hinder industrial scalability. Here, we present an economically efficient and easily implementable surface modification approach. This method induces the self-assembly of high-insulation-performance boron nitride nanosheets (BNNS) on the film surface through electrostatic interactions, thereby enhancing the high-temperature electrical insulation and energy storage performance of polymer dielectrics. At room temperature, the breakdown strength of the BNNS-coated polyetherimide (PEI) significantly increased to 544 MV/m, representing a 100 MV/m improvement compared to pure PEI. At elevated temperatures (200 °C), the organic insulator achieved a high breakdown strength of 439 MV/m and a high energy density of 2.59 J/cm3. The tangential orientation of the nanosheets effectively impedes charge injection from electrodes while promoting charge dissipation and heat transfer. This work provides a novel avenue for the design of high-performance polymer dielectrics for high-temperature energy storage through surface engineering.