Significant Improvements in Dielectric Constant and Energy Density of Ferroelectric Polymer Nanocomposites Enabled by Ultralow Contents of Nanofillers

Abstract Polymer dielectrics with excellent processability and high breakdown strength ( E b ) enable the development of high‐energy‐density capacitors. Although the improvement of dielectric constant ( K ) of polymer dielectric has been realized by adding high‐ K inorganic fillers with high contents (>10 vol%), this approach faces significant challenges in scalable film processing. Here, the incorporation of ultralow ratios (<1 vol%) of low‐ K Cd 1− x Zn x Se 1− y S y nanodots into a ferroelectric polymer is reported. The polymer composites exhibit substantial and concurrent increase in both K and E b , yielding a discharged energy density of 26.0 J cm −3 , outperforming the current dielectric polymers and nanocomposites measured at ≤600 MV m −1 . The observed unconventional dielectric enhancement is attributed to the structural changes induced by the nanodot fillers, including transformation of polymer chain conformation and induced interfacial dipoles, which have been confirmed by density function theory calculations. The dielectric model established in this work addresses the limitations of the current volume‐average models on the polymer composites with low filler contents and gives excellent agreement to the experimental results. This work provides a new experimental route to scalable high‐energy‐density polymer dielectrics and also advances the fundamental understanding of the dielectric behavior of polymer nanocomposites at atomistic scales.