Synergistic engineering of electronic traps and free volume in fluorinated polynorbornene for high-temperature capacitive energy storage

Abstract

Polymer capacitor energy storage is widely employed in electric vehicles, power systems, and aerospace owing to its exceptional electrical breakdown strength and high-power density. Polynorbornene, characterized by a cycloolefin backbone and a wide bandgap, has attracted increasing attention for use in polymer capacitor energy storage. Herein, we modify polynorbornene by grafting various fluorine-containing groups (–F, –CF3, –SF5) onto its side chains to synergistically engineer electronic traps and free volume, thereby enhancing its high-temperature energy storage performance. Computational and experimental investigations reveal that fluorinated groups, owing to their distinct electron-withdrawing capabilities and molar volumes, induce deep electron traps and side-chain disorientation. The synergy between these counteracting effects governs the high-temperature breakdown strength and energy storage efficiency. At 150 °C, the polymer bearing –SF5 groups exhibits the most outstanding comprehensive dielectric energy storage performance, achieving a discharge energy density of 5.9 J cm−3 at 600 MV m−1, which is 2.4 times that of polynorbornene. This work elucidates the synergistic interplay between side-chain electronic traps and free volume in regulating charge transport, providing a viable side-chain engineering strategy for designing high-temperature polymer dielectrics with enhanced capacitive performance.