Cross-linking effect on dielectric properties of polypropylene thin films and applications in electric energy storage

A family of cross-linked polypropylene (x-PP) thin film dielectrics is systematically studied to understand the cross-linking effect on the dielectric properties. Evidently, the butylstyrene (BSt) cross-linkers increase both the dielectric constant (ε) and breakdown strength (E), without increasing energy loss. An x-PP dielectric, with 3.65 mol % BSt cross-linkers, exhibits a ε∼3, which is independent of a wide range of temperatures and frequencies, slim D-E hysteresis loops, high breakdown strength (E=650 MV/m), narrow breakdown distribution, and reliable energy storage capacity ≥5 J/ ^cm3 (double that of state-of-the-art biaxially oriented polypropylene capacitors), without showing any increase in energy loss.