Ultrahigh Energy Density of Scalable Thermal-Crosslinked Polyetherimides at 250 °C

Dielectric polymers must exhibit low conductivity and thermal stability to realize high-performance capacitive energy storage under high-temperature conditions. However, conventional heat-resistant polymers suffer from deteriorated insulation at elevated temperatures, limiting their practical applications. Here, it is proposed and demonstrated that a self-driven thermal crosslinking approach, without crosslinker, is highly efficient in breaking the adverse correlation between the insulation and thermal stability of dielectric polymers at high temperatures. By decarboxylation-driven crosslinking within polyetherimide (PEI) molecular chains, a robust network is formed, effectively suppressing charge carrier migration. The synergistic combination of decarboxylation-induced structural densification and residual carboxyl-enabled deep charge trapping synergistically reduces the electrical conductivity of the modified PEI by 3 orders of magnitude relative to conventional polyimide (Kapton PI) at 250 °C. Consequently, a significantly enhanced discharge energy density of 3.7 J cm⁻³ with a charge-discharge efficiency of 91% is achieved at 250 °C, outperforming existing pure polymer dielectrics. Furthermore, the scalability of this approach is demonstrated by producing a 100-meter-long modified film through an industrial-scale roll-to-roll solution-casting process, highlighting its compatibility with mass production. This strategy also proves to be universal to other dielectric polymers to achieve high insulation and heat resistance at elevated temperatures. © 2025 Wiley-VCH GmbH.