Suppressing Conduction Losses and Enhancing High-Temperature Capacitive Energy Storage Performance in Polymer Dielectrics through Maleic Anhydride Grafting at 200 °C

Polymer film capacitors are essential in modern electronics and power systems, but their limited thermal stability restricts their application in advanced energy storage systems under harsh conditions. At elevated temperatures, their capacitive performance degrades due to increased conduction losses in strong electric fields. In polymer dielectrics, these losses arise from two primary mechanisms: electrode-limited and bulk-limited conduction. Unlike previous approaches that target only one mechanism, this study introduces a dual-conduction loss reduction strategy. Maleic anhydride (MAH) is grafted onto high-glass transition temperature (<i>T</i>_g) poly(phenylene oxide) (PPO) chains via free-radical polymerization, effectively reducing both conduction mechanisms. The grafted polar MAH groups inhibit charge injection by creating an internal electric field from trapped charges, reducing electrode-limited conduction. Additionally, the grafted MAH creates deeper trap sites in the bulk, mitigating bulk-limited hopping conduction. As a result, PPO-g-MAH films demonstrate significantly reduced energy losses, achieving a discharged energy density of 3.12 J cm^-3 at 200 °C and an efficiency exceeding 90%, outperforming most existing dielectric polymers. This simple, cost-effective method supports the scalable fabrication of high-temperature dielectric polymers for film capacitors.