Spiral-Twisted Poly(ether imide) Copolymer Dielectrics with Synergistically Modulated Interchain Spacing and Charge Transfer for High-Temperature Capacitive Energy Storage
Abstract
Poly(ether imide) (PEI) is a promising high-temperature dielectric material, yet its application is limited by severe intrachain and interchain charge transfer (CT) effects, which give rise to high leakage currents at elevated temperatures. Tuning interchain spacing has been recognized as an effective strategy to suppress CT effects, but it entails an intrinsic tradeoff: excessively large spacing facilitates free charge transport, whereas overly compact chain packing exacerbates CT interactions. Herein, we report a series of spiral-twisted PEI copolymers synthesized by incorporating the bulky, twisted BAFL diamine and the planar PPDA diamine with BPADA dianhydride. By systematically varying the BAFL/PPDA molar ratio, we identified that the cPEI-5 composition (50 mol % BAFL and 50 mol % PPDA) as possessing the most favorable interchain spacing, which effectively suppresses CT without unduly weakening interchain coupling, thereby yielding the widest bandgap (3.37 eV) and the deepest trap level (2.19 eV). This optimal spacing, enabled by the spiral-twisted backbone, concurrently shortens the hopping distance and lowers the carrier mobility, leading to a substantial reduction in leakage current. Consequently, cPEI-5 achieves a breakdown strength of 610 MV m–1 at 150 °C, which is 36.2% higher than cPEI-0 and 9.5% higher than cPEI-10, and delivers a discharged energy density of 5.5 J cm–3 at > 90% efficiency, surpassing the room-temperature performance of biaxially oriented polypropylene (BOPP, 4.0 J cm–3). Moreover, cPEI-5 demonstrates excellent cycling stability (over 50 000 cycles, 0.8% loss) and fast discharge capability (t95 = 2.47 μs, power density = 0.28 MW cm–3). This work underscores that rational engineering of spiral-twisted structures enables a synergistic balance between CT suppression and charge transport, offering a new paradigm for high-performance polymer dielectrics under harsh operating conditions.