PN‐Cage‐Based Hybrid Inorganic–Organic Polymers for Self‐Healing High‐Energy Density Capacitors

ABSTRACT Polymer dielectrics are indispensable for modern electronics and power systems, yet achieving high energy density together with long‐term reliability remains a persistent challenge. Conventional organic polymers frequently degrade under intense electric fields with compromised breakdown strength and cycling stability, highlighting the urgent need for polymers with intrinsic self‐healing capabilities. Distinct from well‐known dielectric polymers featuring carbon‐rich backbones and side groups, which are vulnerable in high‐energy operating conditions, polymers containing phosphorus‐nitrogen (PN) bonds and a rigid 3D structure in the main chain offer enhanced environmental robustness and stability. Their potential for applications in electrostatic energy storage, however, remains unexplored. Herein, we present poly(hydrazinophosphine diazide) (PHPD‐CO), a PN cage‐integrated organic–inorganic hybrid polymer readily synthesized by Staudinger polycondensation, as an exceptional dielectric polymer for electrostatic energy storage. PHPD‐CO thin films fabricated through simple solution processing achieve a breakdown strength above 700 MV m −1 and a discharge energy density of ∼7.7 J cm −3 at an efficiency of 96%. Unlike carbon‐rich dielectrics, decomposition of PHPD‐CO during dielectric breakdown produces nonvolatile, inorganic‐dominant passivation layers that effectively preserve energy storage performance after self‐healing. These features not only endow PHPD‐CO‐based capacitors with long‐term cycling stability with minimal performance degradation, but also position PN‐cage‐based hybrid inorganic–organic polymers as promising candidates for next‐generation dielectric polymers.