Semi‐Alicyclic Dipolar Glass Dielectric Polymer Capacitors for Superior High‐Temperature Capacitive Energy Storage

Abstract Ultrahigh‐power‐density metallized film capacitors at elevated temperatures and electric field extremes are key components in electrical and electronic systems. The miniaturization, integration, and cost‐effectiveness of the systems demand high‐energy‐density, high‐efficiency, and reliable dielectrics. A major challenge is to concurrently break multiple paradoxes of bandgap ( E g ) with glass transition temperature ( T g ), dielectric constant ( ɛ r ) with E g, and self‐healing capability with T g . In this contribution, a class of semi‐alicyclic dipolar glass dielectric polymers (sAl‐DG) is developed, with an alternating non‐conjugated alicyclic unit and a strong dipolar group aromatic unit. The alicyclic unit synergistically confers a large E g and the potential for strong self‐healing while the other unit concurrently endows high polarization and thermal stability, effectively decoupling the multiple paradoxes. As a result, sAl‐DG delivers large E g with 3.99–4.26 eV, high T g with 218–387 °C, high ɛ r with 3.39–3.71 (200°C, 1 kHz) and simultaneously excellent self‐healing ability with self‐healing energy of 15.03 mJ. Hence, this molecular decoupling strategy enables a superior discharge energy density with 90% discharge efficiency ( U η90 ) of up to 6.2 J cm −3 at 200 °C, and state‐of‐the‐art 3.94 J cm −3 at 250 °C. Plus, a stacked sAl‐DG capacitor demonstrates 1.06 J cm − 3 at 94% efficiency under 250 MV m −1 and 200°C, showcasing operational viability.