Surface Strengthening of Polymer Composite Dielectrics for Superior High‐Temperature Capacitive Energy Storage

Abstract Polymer dielectrics for high‐temperature capacitive energy storage suffer from low energy density and poor efficiency, which is mainly attributed to the exponential growth of conduction loss at high electric fields. Here, a surface strengthening strategy to inhibit the electrode‐limited conduction loss of polymer composite dielectrics is reported. The surface phase of polymer composite dielectrics is strengthened by the in situ generated ultrafine silicon oxide (SiO₂) nanoparticles while the bulk phase is strengthened by incorporating commercially available SiO₂ nanoparticles. These wide bandgap SiO₂ nanoparticles can not only restrict the movement of macromolecular chains, but also act as deep traps to capture the charge carriers. As a result, the charge transport at the electrode/dielectric interface and in the bulk phase of dielectric is significantly restrained, thereby leading to a decrease in conduction loss. The resultant film can deliver a discharged energy density of 4.26 J cm⁻³ at 200 °C, which increased by 1274.19% compared with that of pristine film. The strategy of employing surface strengthening to suppress the conduction loss of polymer composite dielectrics can be easily extended to other polymers to improve the high‐temperature insulation and capacitive energy storage performances.