All-Organic Sandwich-Structured Polymer Dielectric Films with Aramid Nanofiber and Polyimide for High-Temperature Electrical Energy Storage

To address the urgent requirements of cutting-edge power electronics and electrical systems, it is of great significance to develop advanced polymer dielectric films that exhibit superior energy storage properties over a broad temperature range. However, the leakage current density, which escalate dramatically at elevated temperatures, often significantly diminish the energy storage performance. In this work, novel all-organic polymer dielectric films with sandwich structures were successfully fabricated by utilizing polyimide (PI) and aramid nanofibers films (ANFm) via "dipping and pulling" technique. The results indicate that the sandwich-structured PI-ANFm- PI (P-A-P) films exhibit enhanced breakdown strength (Eb) and reduced leakage current density compared to single-layered ANFm. 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 performance of ANFm and pure PI dielectric films. With the exceptional energy storage properties, the sandwich-structured P-A-P film is demonstrated to be a promising candidate for high-temperature electrical energy storage.