Enhanced high-temperature energy storage of polyetherimide nanocomposites via bonding molecular chains and reducing excitation entropy

To address the demand for efficient clean energy utilization, it is imperative to develop nanocomposites that are resistant to high temperatures while exhibiting both high breakdown strength and substantial energy storage density. Currently, a challenge involves regulating nanofiller/polymer interface structures and understanding carrier and dipole energy fluctuations affecting electrical breakdown and energy storage. Herein, polyetherimide (PEI) nanocomposites were synthesized using polyimide (PI)-coated Al₂O₃ core-shell structures. Experimental results demonstrate that PEI/Al₂O₃@PI nanocomposites, doped with 3 wt%, exhibit superior properties with a glass transition temperature of 224.65 °C, a Young's modulus of 3.01 GPa, a low conductivity of 1.92 × 10⁻¹⁵ S/m, and a high breakdown strength of 474.83 kV/mm. At 140 °C and 400 kV/mm, its energy storage density representing an 84.42 % increase compared to the undoped sample. The mesoscopic distributions of conductivity and Young's modulus within the interface zones was determined through the application of high-throughput electric and mechanical field simulations and inversion algorithms. It is found that there is a reduction in the excitation entropy of molecular motion, leading to an increase in the activation energy for charges and a subsequent decrease in the electrical conductivity. Furthermore, a joint simulation model for the conduction, electrical breakdown, and energy storage characteristics of nanocomposites is established based on the bipolar charge transport and molecular displacement. The model elucidated the mechanism behind the synergistic enhancement of thermal, mechanical, electrical, and energy storage properties in nanocomposites, attributing it to the strong capture of interfacial deep traps and tight molecular chain binding.