Ultra‐High Capacitance Energy Storage Enabled by Weakening the π – π Stacking Effect in Novel Polynorbornene

Abstract The increasing demand for high‐power‐density energy storage in advanced pulsed power systems necessitates polymer film capacitors exhibiting superior energy storage capabilities. Aromatic dielectric polymers, such as polyimide and polycarbonate, despite extensive research, exhibit a significant surge in conductivity loss under high electric fields due to their strong π – π stacking interactions. Herein, a novel norbornene polymer (PNB2APS) is prepared, and its strong π – π stacking interactions are effectively weakened through copolymerization with adamantylated norbornene (NBAd), thereby yielding a novel copolymer with ultrahigh breakdown strength (BDS) and enhanced discharge energy efficiency ( η ) under high electric fields, as demonstrated both experimentally and theoretically. A discharge energy density ( U _d ) of 23.5 J cm ⁻³ is achieved at 1000 MV m ⁻¹ , while maintaining U _d = 15 J cm ⁻³ even when η exceeded 90%, surpassing the energy storage performance of state‐of‐the‐art commercial polymers. The film exhibits cost‐effectiveness and facile processability, with high homogeneity and outstanding capacitance stability (>100 000 cycles), providing a practical pathway for scalable polymer dielectrics in high‐performance electrical energy storage applications.