Electrothermal Aging of All-Organic PEI/ITIC Composite Films for Dielectric Energy Storage

Recently, polyetherimide (PEI) polymer films have attracted increasing attention due to their excellent energy storage performance at high temperature. However, most research work has focused on improving the dielectric property and lacks investigation of the aging law and aging mechanism of dielectric films under the elevated temperature and high electric field. In this study, PEI dielectric films doped with the molecular semiconductor (ITIC) are subjected to electrothermal aging. The results show that surface defects of the composite dielectric increase due to aging in the absence of oxygen, but this does not alter the crystal phase structure. After aging for 500 h at 150 MV/m and 150 °C, the breakdown strength and energy storage efficiency decrease, the leakage current density increases by more than one order of magnitude, and the energy storage density decreases from 4.26 to 3.06 J/cm3. Furthermore, based on the numerical analysis and SIMONI model, the electrothermal lifetime prediction model of PEI/ITIC composite dielectric is established. It is found that the charge–discharge efficiency can serve as a physical criterion for the end of the lifetime of energy storage dielectric compared to breakdown strength, and the aging electric field has a greater impact on the lifetime of PEI/ITIC composite dielectric compared to the aging temperature.