Polyimides Physically Crosslinked by Aromatic Molecules Exhibit Ultrahigh Energy Density at 200 °C

Polymer dielectrics possess significant advantages in electrostatic energy storage applications, such as high breakdown strength (E_b) and efficiency (η), while their discharged energy density (U_d) at high temperature is limited by the decrease in E_b and η. Several strategies including introducing inorganic components and crosslinking have been investigated to improve the U_d of polymer dielectrics, but new issues will be encountered, e.g., the sacrifice of flexibility, the degradation of the interfacial insulating property and the complex preparation process. In this work, 3D rigid aromatic molecules are introduced into aromatic polyimides to form physical crosslinking networks through electrostatic interactions between their oppositely charged phenyl groups. The dense physical crosslinking networks strengthen the polyimides to boost the E_b, and the aromatic molecules trap the charge carriers to suppress the loss, allowing the strategy to combine the advantages of inorganic incorporation and crosslinking. This study demonstrates that this strategy is well applicable to a number of representative aromatic polyimides, and ultrahigh U_d of 8.05 J cm⁻³ (150 °C) and 5.12 J cm⁻³ (200 °C) is achieved. Furthermore, the all-organic composites exhibit stable performances during ultralong 10⁵ charge–discharge cycles in harsh environments (500 MV m⁻¹ and 200 °C) and prospects for large-scale preparation.