Achieving superior high-temperature capacitance performance in aromatic polyetherimide with bulky fluorine substituent

The rapid development of electronic and electrical power equipment has increased the demand for dielectric materials with high-temperature energy storage performances. However, the mutual restrictions imposed by the glass transition temperature (T_g) and bandgap (E_g) limit the use of commercial polyetherimide (PEI) under extreme conditions. In this work, we propose a strategic modular structure design to balance a high T_g and large E_g by modulating the substituents in the biphenyl structure of modified PEI. Both experimental results and theoretical simulations indicates that owing to its electron-withdrawing nature, a bulky -CF₃ substituent not only increases the bandgap but also decreases the conjugation effect of the biphenyl structure, while having a minimal effect on T_g. This significantly shortens the hopping distance of the carriers, ultimately improving the high-temperature breakdown strength (E_b) and thus the capacitance performance of PEI. The modified PEI with the bulky -CF₃ achieves a discharge energy density (U_e) of 8.01 J/cm³ with an efficiency (η) of 91.9 % at 150 °C and an U_e of 5.3 J/cm³ with an η of 90.4 % at 200 °C, which exceeds the performance of most of current high-temperature dielectric polymers. The results of this study provide technical support for the developing of high-performance, flexible dielectric capacitors.