Donor-acceptor π-stacking interactions boosting capacitive energy storage of g-C3N4/PEI composite films at elevated temperatures

Abstract

Polymer-based dielectric capacitors are crucial for modern electronics and power systems, but require performance optimization for high-temperature capacitive energy storage. Here, we report composite films prepared by doping sonication-exfoliated graphitic carbon nitride nanoplates (g-C₃N₄ NPLs) into polyetherimide (PEI). The benzene rings in PEI act as π-electron donors and triazine units in g-C₃N₄ serve as π-electron acceptors, forming strong donor-acceptor (D-A) π-stacking interactions that optimize the PEI chain conformation. With reduced d-spacing, dipole density is increased for strengthened polarization, and the shortened mean free path of carriers contributes to decreased mobility. A type-II band alignment at the PEI/g-C₃N₄ interface introduces interfacial traps that reduce free carrier concentration. With highly suppressed leakage current, the optimized 0.5 wt% film improves the breakdown strength to 613.5 kV/mm at 150°C and 517.6 kV/mm at 200°C, while the dielectric constant is 3.46 and 3.47, respectively. This enables a high discharge energy density of 5.10 J/cm³ at 150°C and 3.42 J/cm³ at 200°C with an efficiency over 90%, outperforming the pure PEI film. Additionally, the 0.5 wt% film exhibits uniformity in large-scale fabrication (27 cm × 10 cm) and sustains stable performance over 10⁶ cycles at 150°C and 400 kV/mm, highlighting its industrial applicability and reliability.