Enhancing Dielectric and High-Temperature Energy Storage Capability for Benzoxazole Polymer Films Featuring Naphthalene Ring Blocks

All-organic polymer dielectrics used in electrical and electronic systems have been proven to be an efficient option for large-scale industrial production. Modifying the side chain of polymers can improve the energy storage performance of polymers, but it can hardly solve the problem of failure under high-temperature application. Herein, an innovative approach is proposed to introduce a group with high temperature resistance into the main chain to reconstruct the chain structure to solve the abovementioned problem. Concretely, a naphthalene ring was introduced to the chain of polyphenylene benzodioxazole (PBO) that is the most promising polymer applied in a high-temperature environment. The naphthalene ring endows the molecular structure with both enhanced permittivity and breakdown strength by decoupling the conjugation of the main chain, increasing the dielectric constant. Meanwhile, an appropriate ratio of benzene–naphthalene as deep traps enables reduced carriers’ mobility and an increased band gap, thereby enhancing the breakdown strength. The discharged energy density of the copolymer reached 5.26 J/cm3 with a charge–discharge efficiency of 91.8% under 450 MV/m at room temperature. Simultaneously, a discharged energy density of 3.1 J/cm3 was also obtained at 150 °C. This work provides a scalable approach to explore polymer dielectrics by freely introducing a small amount of local structural modifications.