Significantly improved high-temperature capacitive performance in polypropylene based on molecular semiconductor grafting

Abstract

The high-temperature dielectric properties and energy storage performance of capacitive materials are of great significance for the sustainable development of new energy-related fields. However, the most widely used commercial capacitor dielectric biaxially oriented polypropylene (BOPP) films fail to satisfy the requirements of continuous operation above 105 °C at high electric fields. Here we demonstrate a molecular semiconductor-grafted polypropylene (PP) composite that possesses substantially enhanced dielectric and capacitive performance up to 120 °C by virtue of the modulated carrier transport behavior. The organic molecular semiconductor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is chemically grafted onto PP chains (PCBM-g-PP) to achieve strong interaction and decent compatibility between the PCBM and the polymer matrix. Based on computational simulation and experimental verification, it is confirmed that the grafted molecular semiconductor introduces deep traps to inhibit the migration of high-energy charge carriers excited by heat. In the meantime, the grafting also helps to intensify the regulation effect by exerting positive influences on the microstructure of the polymer. The PCBM-g-PP/PP composite films possess reduced leakage current and dielectric loss, as well as suppressed electric field distortion and elevated breakdown strength. At 120 °C, the energy storage density of the composite with an efficiency above 90% reaches 1.59 J/cm3, which is 683.62% that of the original PP film. The reported molecular semiconductor-grafting strategy is expected to promote the capacitive performance of polypropylene under hash-temperature conditions, facilitating the development of lightweight and compact-size dielectric capacitors.