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

ABSTRACT 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.