Simultaneous Ultrahigh Energy Density and High Efficiency Achieved in Dipole-Glass Polyimide Dielectrics

Polymer-based film capacitors are crucial components for modern electronic devices and advanced pulse power systems, but their performance is fundamentally constrained by the long-standing trade-off between high energy density and high charge-discharge efficiency. Here, a dipole-glass polymer design is introduced, in which the active dipolar side groups are incorporated into a rigid polyimide backbone through flexible spacers. The rigid polyimide backbone provides a wide bandgap and a glassy matrix that suppresses leakage current and enables an ultrahigh breakdown strength of 964 MV m^-1, while the active acetyl side groups deliver easy and reversible orientational polarization with minimal steric hindrance. As a result, the optimized DGPI-Ac film achieves a record-high discharged energy density of 15.3 J cm^-3 with a charge-discharge efficiency higher than 95% at room temperature, and it also shows excellent high-temperature capacitive performance up to 200°C. This work establishes rational side-chain engineering as an effective strategy, thereby unlocking the inherent energy storage potential of polymer dielectrics and advancing high-power electrostatic energy storage technologies.