Polymer dielectrics enabled by molecular engineering design and charge trap regulation for high-temperature energy storage

Abstract

Aromatic polyimides (PIs) are widely regarded as promising high-temperature polymer dielectric films because of their excellent thermal stability. However, the extensive intra- and inter-chain migration of delocalized π-electrons through aromatic rings, coupled with a sharp increase in the density of injected and thermally activated charge carriers, significantly weakens the high-temperature energy storage performance of conventional PI. In this work, a novel strategy combining molecular engineering design with modulation of charge trap levels was employed to fabricate a series of fluorinated polyimide/magnesium oxide (FPI/MgO) dielectric films incorporating –CF₃ groups and wide-bandgap MgO nanoparticles. Compared with conventional PI, the introduction of –CF₃ and MgO effectively suppresses π-electron migration and thermally excited charge carriers and hinders the propagation and development of breakdown pathways along the electric field direction. These synergistic effects effectively inhibit bulk-limited hopping conduction, leading to significantly improved breakdown strength (E_b) and enhanced high-temperature capacitive performance of the FPI/MgO dielectric film. At 150 °C, the FPI dielectric film with 0.10 wt% MgO exhibits a high E_b of 508 MV m⁻¹, representing an enhancement of 46.4% over that of conventional PI (347 MV m⁻¹). Benefiting from the superior E_b and suppressed leakage current density, the FPI dielectric film with 0.10 wt% MgO achieves a maximal discharge energy density (U_d) of 4.97 J cm⁻³ at 150 °C, which is 4.3 times that of conventional PI (1.15 J cm⁻³) and exceeds that of most previously reported high-temperature polymer dielectric films. This work presents a new paradigm for developing PI-based dielectrics with superior high-temperature energy storage performance.