High-Temperature Energy Storage in Semi-Aromatic Polyimide with Dual Crosslinking Networks

Abstract To address the degradation issues of conventional polyimides under high-temperature and high-field energy storage conditions, this study synthesized a semi-aromatic polyimide featuring both hydrogen-bonding and chemically cross-linked networks. The chemically cross-linked structure anchors the high-temperature-resistant segments, while the dynamic hydrogen bonds further restrict chain mobility and provide additional charge trapping sites, which may contribute to shortening the mean free path of electrons and suppressing long-range carrier transport. Molecular dynamics simulations and X-ray diffraction indicate that the interchain distance shortens from 4.66 Å to 4.18 Å, with a corresponding decrease in free volume and thermal expansion coefficient. TSDC testing shows that the trap depth increases from 1.08 eV to 1.14 eV, and the leakage current density is as low as 1.98×10-7 A cm-2 at 200 MV m-1. Finally, the discharge energy density of the bis-crosslinked semi-aromatic PI reached 6.63 J cm-3 and 4.80 J cm-3 at 150 °C and 200 °C, respectively, with an efficiency >90%, and a maximum energy density of 5.08 J cm-3 at 250 °C (87.3% efficiency). This work provides new insights into the molecular engineering design of high-temperature polymer dielectric films.