Covalent POSS End‐Capping of Polyurea Enables Suppression of Conduction Loss for High‐Temperature Capacitive Energy Storage

High‐temperature polymer dielectrics hold broad application prospects in next‐generation power electronics, yet their energy densities at elevated temperatures are severely limited by thermally activated carrier transport and conduction loss. Herein, we develop a molecular engineering strategy to regulate the bulk‐limited conduction in polyurea via covalent end‐capping with wide‐bandgap amino‐functionalized polyhedral oligomeric silsesquioxane (NH 2 ‐POSS). Experimental and theoretical results demonstrate that NH 2 ‐POSS end‐capping broadens the bandgap, induces deep charge trap effects, weakens intermolecular electrostatic interactions, and significantly suppresses high‐temperature conduction loss. The optimized hybrid film (with only 3wt.% NH 2 ‐POSS) delivers an ultrahigh discharged energy density of 7.02 J/cm 3 with a charge–discharge efficiency above 90% at 150°C, along with excellent cycling stability over 10 000 cycles. This strategy features outstanding scalability for potentially industrial production, providing a promising candidate for high‐temperature, high‐energy‐density capacitor applications.