Significantly Enhanced High-Temperature Energy Storage Properties of Poly(ether imide) Dielectrics Enabled by Ultralow Content of Ni@Al ₂ O ₃ Nanofibers

Polymer dielectrics play an indispensable role in electrostatic energy storage due to their merits of high voltage resistance, lightweight, excellent flexibility, and easy processability. However, the deterioration in dielectric reliability and energy loss at high temperatures limit their versatility for broader applications. Herein, Ni@Al 2 O 3 NFs are fabricated by encapsulating different content of nickel (Ni) nanoparticles into alumina nanofibers (Al 2 O 3 NFs) via the electrospinning technique and employed to simultaneously improve the dielectric constant and breakdown strength of poly(ether imide) (PEI). This is realized by the coupling action of the increased interfacial polarization, Coulomb blockade effect of Ni nanoparticles, and wide bandgap of Al 2 O 3 NFs. Notably, the PEI nanocomposite films containing 0.50 vol % Ni@Al 2 O 3 NFs exhibit an excellent discharge energy density ( U d ) of 5.8 J/cm 3 at 150 °C, 262% higher than that of pristine PEI ( U d = 1.6 J/cm 3 ), accompanied by a high efficiency of 81.3%. This work provides a promising strategy to improve the high-temperature energy storage performance of polymer-based dielectrics by exerting the synergistic effect of fillers at ultralow content.