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

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.