Monomer Engineering of Polyimides for High-Temperature Capacitive Energy Storage

High-temperature dielectric polymers are critical for capacitors used in electric vehicles, aerospace electronics, renewable energy management and other power inverters. Nevertheless, conventional materials such as commercial polyetherimide (PEI) exhibit limited energy storage performance above 150° C. In this work, we propose a monomer-level design strategy to enhance the high-temperature performance of polyimides (PIs) by tailoring diamine structures with different polar functional groups. The results of PIs exhibit distinct glass transition temperatures, dielectric constants, and breakdown strengths, governed by the rigidity and polarity of the incorporated groups. Among them, the sulfone-functionalized PI (PEI-SO2) shows exceptional performance, reaching a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4.1 ~\mathrm{J} / \text{cm}^{3}$</tex> discharged energy density while maintaining 90 % efficiency at 200° C. The improved performance stems from the synergistic effect of high polarity and suppressed charge transportation due to strong intermolecular interactions. This research demonstrates that monomer-level structural engineering is an effective strategy for achieving thermally stable polymer dielectrics with enhanced energy storage capabilities.