Disruption of short-range π–π stacking via a disordered spatial architecture for energy storage at 250 °C

Abstract

Film capacitors are indispensable in electrical engineering; however, balancing the insulation and thermal stability of polymer dielectrics remains a key challenge for high-temperature energy storage. Aromatic polyimide (PI) exhibits a high glass transition temperature (T_g, >300 °C), facilitating the formation of charge transfer complexes (CTCs). Semi-aromatic PIs mitigate this order, but insufficient thermal stability leads to poor performance above 200 °C. To resolve this contradiction, we incorporated a sp³-centered monomer, tris(4-aminophenyl)methane (TAPM), into a semi-aromatic PI (MPD-PI), constructing a spatially disordered architecture that suppresses short-range π–π stacking and CTCs, enhancing dielectric insulation and thermal stability. The resulting copolymer specifically achieves a discharged energy density of 7.13 J cm⁻³ at 200 °C with 90% efficiency and 5.18 J cm⁻³ at 250 °C, representing 341% and 280% improvements compared to those of MPD-PI, respectively. The improved thermal stability also imparts excellent cycling stability (3 × 10⁵ cycles at 200 °C and 300 MV m⁻¹) and a state-of-the-art breakdown strength of 596.2 MV m⁻¹ at 250 °C. The conformational-engineering strategy of this work provides a versatile route for high-temperature polymer dielectrics.