High-temperature polymer-based nanocomposites for high energy storage performance with robust cycling stability

High-power capacitors are highly demanded in advanced electronics and power systems, where rising concerns on the operating temperatures have evoked the attention on developing highly reliable high-temperature dielectric polymers. Herein, polyetherimide (PEI) filled with highly insulating Al₂O₃ (AO) nanoparticles dielectric composite films have been fabricated aiming for high thermal stability and reliability operated under high cycling electric field and elevated temperature. At room temperature, incorporating a small fraction of 0.5 vol% AO nanoparticles gives rise to a highest discharged energy density (U_e) of 5.57 J·cm⁻³ and efficiency (η) of 90.9% at 650 MV·m⁻¹, and a robust cycling stability up to 10⁷ cycles at 400 MV·m⁻¹. Due to the substantially reduced dielectric loss, 2.0 vol% AO/PEI nanocomposite film exhibits excellent high-temperature capacitive performances, delivering U_e ~ 7.33 J·cm⁻³ with η ~ 88.8% under 700 MV·m⁻¹, and cycling stability up to 10⁶ cycles under 400 MV·m⁻¹ at 100 °C, and U_e ~ 5.57 J·cm⁻³ with η ~ 84.7% under 620 MV·m⁻¹ at 150 °C. Molecular dynamic simulations are performed to understand the microscopic mechanism via revealing the polymer relaxation process in the AO/PEI composite at elevated temperatures. Our results are therefore very encouraging for high-temperature high-power capacitor application.