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

Abstract 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 Al 2 O 3 (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 10 7 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 10 6 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.