High‐Entropy‐Nanofibers Enhanced Polymer Nanocomposites for High‐Performance Energy Storage

Abstract Polymer composite dielectrics capable of high energy density, high efficiency, and high‐temperature stability are in high demand for application in various electronic vehicles and power systems. A major challenge, however, is the reasonable design of high‐performance nanofillers that are beneficial to the polarization and breakdown strength simultaneously. Here, high‐entropy‐induced ceramic nanofibers with a stable Bi 2 Ti 2 O 7 ‐type pyrochlore phase are developed as effective nanofillers to enhance the energy storage performance of polyetherimide (PEI) composites. Benefiting from the linear pyrochlore phase, refined grain size, and increased amorphous fraction of the high‐entropy nanofillers, the resultant PEI composites exhibit significantly improved energy storage performance over a wide temperature range of 25–150 °C. Notably, a high energy density of 6.46 J cm −3 under an electric field of 590 MV m −1 is achieved at 150 °C, which outperforms most of the reported PEI composites. This study provides a guideline for the development of dielectric fillers with tunable dielectric properties and microstructures, thus promoting the development of high‐performance polymer composites.