Sulfonyl manipulation for enhancing energy storage of flexible epoxy based capacitive films

Polymer based dielectric film capacitors with enhanced energy density and high temperature resistance are urgently required to replace the general used biaxially oriented polypropylene (BOPP) dielectric counterparts in power grid and electrical vehicles. This study reports the development of sulfonated flexible epoxy polymers, which demonstrate excellent properties including high dielectric constant (4.9–6.0), low dielectric loss, high charge–discharge efficiency and desirable thermal stability. The obtained epoxy film achieves an impressive efficiency of 91.5 %, accompanied by discharge energy density up to 8.78 J/cm3 at 550MV/m at room temperature, nearly twice that of BOPP. While the prepared film still possesses discharge energy density of 1.01 J/cm3 at 200MV/m, even when exposed to temperatures up to 150 °C, which is nearly twice that of PEI under same conditions. Simulation results reveal that sulfonyl groups can effectively improve dielectric performance without sacrificing heat resistance of epoxy polymers. The influence of sulfonated groups and positions are figured out by constructing epoxy film with pendant and bridging sulfonyl groups. It is concluded that the enhanced dipole moments caused by pendant sulfonyl group is preferred in improving energy density, while the increased rotational energy barrier attributed to bridging sulfonyl group is critical to the enhancement of temperature tolerance. The manipulation of sulfonation in polymer dielectrics’ design introduces a deep perspective for advancing high energy storage films.