A dual strategy for enhancing the high-temperature electrostatic energy storage performance of polyetherimide -based composite films

Polyimide and its derivatives are high-temperature resistant yet show increased leakage current and reduced charge-discharge efficiency at high temperatures when used as dielectric spacers of film capacitors. Herein, a dual strategy is proposed to enhance the capacitive energy storage performance of polyetherimide (PEI)-based nanocomposites. ZnO@CaF₂ nanosheets are synthesized by a simple chemical bath method and filled into the PEI matrix. The nanocomposite film is further irradiated by UV light. Both ZnO@CaF₂ nanofillers and UV treatment show efficacies in increasing the breakdown strength and reducing the dielectric loss. The ZnO@CaF₂ nanostructure acts as a quantum well to trap electrons and holes hopping from the PEI molecule. UV irradiation cleaves partial C=C bonds in aromatic rings of the PEI macromolecules, thereby limiting the delocalization range of electrons along the molecular chain. With an optimal nanofiller content of 0.3 wt%, the UV-irradiated nanocomposite film shows a maximum discharged energy density of 5.7 J cm⁻³ at 150 °C, along with an efficiency of 85 %. If reducing the charging voltage to maintain the efficiency beyond 90 %, the discharged energy density still reaches to 4.80 J cm⁻³. Using the metallized nanocomposite films, a multilayered capacitor is fabricated and shows stable capacitance within a wide frequency range of 10²–10⁵ Hz, measured at different temperatures from 25 to 150 °C. © 2025 Elsevier B.V.