Electret behavior in dielectric polymers for superior high-temperature capacitive performance

Dielectric polymers for electrostatic energy storage suffer from low energy density and reduced efficiency at elevated temperatures, limiting their practical application. Here, we introduce an electret-enhancement strategy that suppresses conduction losses and enhances energy density under high-temperature conditions. By exploiting intrinsic electret behavior to form an internal negative charge layer via corona-discharge charging, electrostatic assembly, and thermal aging, our approach impedes electron injection and transport. As a result, at 200°C, the discharged energy density of aged polyetherimide (PEI) (at >90% efficiency) increases by 394%—from 0.32 J/cm 3 (pristine PEI) to 1.58 J/cm 3 —and reaches a maximum of 1.90 J/cm 3 . Demonstrating its universality, this strategy boosts the maximum energy densities of biaxially oriented polypropylene (BOPP) and polyethylene terephthalate (PET) by over 51% relative to their pristine counterparts. Finally, we demonstrate scalable fabrication of large-area (>1 m 2 ) electret-enhanced BOPP films, underscoring their potential for high-temperature energy storage and power-electronics applications.