Superior High-Temperature Capacitive Energy Storage in Dielectric Random Copolymer by Constructing Staggered Barriers

Dielectric polymers with high glass transition temperatures (T_g) are widely employed in capacitive energy storage applications for electronic equipment and power systems. However, polyetherimide (PEI) suffers from significant leakage current and a pronounced increase in conductivity loss at high temperatures, which prominently restricts its operational reliability under extreme conditions. In this work, an all-organic strategy is proposed by random blocking the 2, 2-Bis [4-(4-aminophenoxy) phenyl] propane (BAPP) into the PEI backbones. The staggered potential barriers between distinct chains create local electronic trap states and increase the energy barrier for trapped carriers to escape. Furthermore, the incorporation of the BAPP segments effectively decreases the interchain spacing and fractional free volume (FFV). Experimental studies and density functional theory (DFT) calculations reveal that a large number of deep traps combined with a reduced FFV, enhance electron capture capability and restrict charge transport. As a result, the random copolymer with 50 mol% BAPP segments (C50PEI) exhibits superior high-temperature capacitive performance, delivering an exceptional discharged energy density (U_e) of 4.68 J/cm³ with a charge–discharge efficiency (η) exceeding 90% at 200°C. This work provides an all-organic design strategy for the development of dielectric capacitors under extreme high-temperature conditions.