Enhanced energy storage properties of polypropylene/maleic anhydride-grafted polypropylene/nano-ZrO₂ ternary system

Extensive research studies have been carried out to enhance the energy storage density of polypropylene (PP) films for power capacitor application to cater to the development of power system. However, most of the research studies failed to balance the energy storage density and dielectric loss which generates heat and threatens the operation of power capacitor. In the present study, we proposed a ternary system composited of PP, maleic anhydride-grafted PP (PP-g-MAH), and nano-ZrO₂ with totally 25 compositions in an orthogonal ingredient system. Direct current (dc) breakdown test and dielectric spectra were measured and showed that the largest enhancement of 30.2% of energy storage density was achieved with both increased dielectric constant and dc breakdown strength (BDS), while the dielectric loss kept the same level of neat PP. This on the one hand was attributed to the orientation polarization, ionic polarization, and deep traps introduced by PP-g-MAH and nano-ZrO₂, evidenced by the thermal stimulated depolarization current test results. On the other hand, the results of dynamic mechanical analysis indicated that the compatibility of each phases was largely improved in the ternary system so that a high dc BDS was obtained due to the restricted segmental molecular motion.