All-Organic Sandwich-Structured Dielectric Films Based on Aramid Nanofibers and Polyimide for High-Temperature Electrical Energy Storage

To meet the urgent requirements of cutting-edge power electronics and electrical systems at elevated temperatures, all-organic sandwich-structured dielectric films were successfully designed and fabricated based on the aramid nanofiber film (ANFm) and polyimide (PI) layer via the convenient “dipping and pulling” technique. On account of the flat surface and formed electron traps, the PI-ANFm-PI (P-A-P) dielectric films exhibit enhanced breakdown strength (Eb) and reduced leakage current density compared to the single-layered ANFm at elevated temperatures. The P-A-P dielectric film shows a maximal discharge energy density (Ud) of 3.68 J/cm3 with a charge–discharge efficiency (η) exceeding 80% at 25 °C and an impressive Ud of 1.76 J/cm3 with η above 70% at 150 °C, outstandingly surpassing the performances of single-layered ANFm and pure PI dielectric film. With the exceptional energy-storage properties, the all-organic sandwich-structured P-A-P films have been demonstrated to be promising candidates for high-temperature electrical energy storage.