Side group induced steric hindrance effect in polyetherimide derived polymers for high-temperature capacitive energy storage performance

Benzene rings in polymer chains providing rigidity enable conformation stability at high temperatures. However, the exponential increase in leakage current of benzene-ring-rich polymers under elevated temperatures and strong electric fields has become the main bottleneck for their application in electrostatic capacitors. Herein, four side groups with different electronegativity were substituted in the benzene rings of polyetherimide (PEI) to suppress leakage current. Molecular dynamic simulation reveals that the potential difference between benzene rings is decreased with chlorine (PEICl) and trifluoromethyl (PEI-CF3) side groups. Moreover, the variation of interchain spacing at elevated temperatures is reduced, as evidenced by in-situ XRD, indicating a temperature-stable steric hindrance effect. Further thermal stimulated depolarization current measurements indicated that those side groups in PEI-derived polymers construct deeper trap energy levels to hinder the transportation of carriers. Accordingly, the conductivity at 150 °C and 200 °C is suppressed, and an optimal discharge energy density of 5.53 J/cm3 at 150 °C and 3.87 J/cm3 at 200 °C with a charge-discharge efficiency exceeding 90% is achieved for PEI-CF3. Our results demonstrate the potential of modified PEI materials with steric side groups as high-temperature dielectric polymers for practical applications and lead the way in improving high-energy density capacitor films.