High-Temperature Energy Storage in Poly(ether imide) via Molecular-Engineered Naphthalene Traps

Aromatic poly(ether imide) (PEI) film capacitors are promising for high-temperature applications due to their thermal stability and flexibility. This study first designed and synthesized three PEIs based on different diamine monomer structures, then introduced 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) during their polymerization to construct copolymer systems. Experiments and density functional theory (DFT) analysis show that NTCDA, with a lower lowest unoccupied molecular orbital (LUMO) energy level, can form moderately deep electron traps in the PEIs bandgap. These traps effectively capture free carriers at high temperatures, suppressing their migration and hopping conduction, thereby reducing leakage current and dielectric loss. Meanwhile, the rigid naphthalene ring structure of NTCDA enhances intermolecular interactions, inhibiting segmental motion at high temperatures and reducing energy dissipation. Performance tests indicate that the three copolymers exhibit energy densities (Ue) of 3.7 J/cm3, 3.22 J/cm3, and 3.56 J/cm3 at 150 °C, with corresponding charge–discharge efficiencies (η) of 87%, 75%, and 79%. These results confirm that regulating the energy bands and trap distribution of PEIs with different structures via NTCDA is an effective strategy to enhance high-temperature energy storage performance, providing references for related material design.