Investigation of Thermal Aging Behavior and Energy Storage Performance via Polycarbonate/Fluorene Polyester All‐Organic Multilayer Composite Dielectrics

ABSTRACT Polymer dielectric capacitors have emerged as critical energy storage components in advanced applications such as new energy vehicles and smart grids, owing to their high‐power density, rapid charge–discharge capability. However, the increasingly demanding operational conditions, particularly elevated temperatures (> 80°C) and high electric fields (> 400 kV/mm)‐pose significant challenges to their performance stability and energy storage efficiency at elevated temperatures. In this work, a fully organic multilayer composite dielectric, denoted as PC/FPE/PC/FPE/PC (PFPFP), was designed using polycarbonate (PC), which exhibits high breakdown strength, and fluorene polyester (FPE), characterized by a high glass transition temperature. The high‐temperature aging behavior and energy storage stability of PFPFP were systematically evaluated under simulated real‐world operating conditions. The results indicate that during thermal aging at 150°C, the breakdown strength and energy storage performance of PFPFP, PC, and FPE all gradually deteriorated with prolonged aging time. Nevertheless, PFPFP consistently outperformed the individual constituent materials. Notably, after 28 days of thermal aging at 150°C, PFPFP retained an exceptionally high breakdown strength of 405.5 kV/mm, 28.89% and 35.85% greater than those of PC and FPE dielectrics, respectively. Concurrently, its maximum energy storage density reached 2.85 J/cm 3 , representing improvements of 103.57% and 69.64% over PC and FPE, respectively. These findings demonstrate that the fully organic multilayer architecture significantly enhances the high‐temperature energy storage stability of polymer dielectrics, thereby improving the performance under thermal conditions.