Strategic molecular conformation engineering enables significantly enhanced high-temperature energy storage in polyetherimide

Abstract

To accommodate the advancement of next-generation power electronics toward high-level integration and miniaturization, it is imperative to develop polymer dielectrics that maintain superior energy storage performance under thermal extremes. Traditional aromatic polymers (e.g., polyetherimide, PEI) suffer from severe charge delocalization at elevated temperatures due to inherent charge-transfer complexes (CTCs) within their conjugated structures, resulting in sharply increased leakage current and deteriorated energy storage performance. In this work, we propose a molecular conformation engineering strategy that incorporates sterically hindered, twisted fluorine-substituted fluorene moieties into the PEI backbone, successfully decoupling the trade-off between thermal stability and high-efficiency energy storage. Integrating experimental characterization with theoretical calculations reveals the underlying mechanism by which molecular conformation engineering regulates macroscopic electrical performance from a multiscale perspective: the inherent rigidity of the fluorene skeleton provides a robust molecular scaffold that ensures thermomechanical reliability at elevated temperatures. Meanwhile, the non-coplanar, twisted geometry disrupts long-range π–π stacking, thereby hindering intermolecular charge transfer and synergizing with strategic fluorination to reduce leakage current through reinforced electron localization. Consequently, the optimized PEI-FFDA achieves a superior discharge energy density of 3.44 J cm⁻³ at 200 °C (10 Hz), approximately 2.5 times that of pristine PEI (1.38 J cm⁻³), with exceptional reliability over 10⁵ cycles. This work establishes an effective molecular design paradigm for intrinsically robust high-temperature dielectrics.