Tuning the structure-activity of fillers and matrix is crucial for designing polymer-based dielectric capacitors with high energy storage performance. Up to date, how the fillers’ structural characteristics (surface/interface configurations, dimensions, orientations etc.) contribute to the overall energy storage is far from unveiled. To this end, a combined filler-polymer dual-side design strategy is developed, which involves the DFT guidance for the electronic transport criteria for the designable synthesis of KNb₃O₈ fillers. Four different structural configurations are constructed, which are surface-modified with polydopamine (PDA) to fabricate the final composite films, i.e. PDA@KNb₃O₈/PVDF-P(VDF-HFP)-PMMA with particular orientations and arrangements, through a well-controlled solution casting method. Comprehensive structural and electrical investigations reveal that 1D/2D-orientated PDA@KNb₃O₈ fillers could obviously enhance the breakdown field and energy storage performance. The difference is that the 1D fillers more effectively improve the energy efficiency (up to 72%), while the 2D fillers more steadily achieve high energy density (U_e = 28.35 J/cm³) among the highest U_e reported for the composites. This work not only uncovers the structural origin of the electrostatic storage in inorganic-polymer composite films but also provides critical insights in designing high-energy-density film capacitors.

What is the nature of the electric (dielectric/ferroelectric) properties of CuInP₂S₆ (CIPS)? CIPS, considered an emerging two-dimensional (2D) ferroelectric, has been well explored in various properties and applications. However, the most important and fundamental nature, i.e. dielectric/ferroelectric property, has been controversial, because high-quality CIPS samples are grossly deficient. In this work, single crystal CIPS is successfully synthesized by the chemical vapour transport method, which presents “high quality” in terms of high purity, excellent crystallinity, uniform composition, and defect-free structure etc. that are confirmed through comprehensive characterization techniques. With performing high-quality single crystal, we fully uncover the intrinsic electric properties of CIPS through accurately identifying the atomic arrangement, electron configuration, magnetic, dielectric, and ferroelectric properties that should reach a consensus on such a disputed CIPS material. These findings serve as a pivotal benchmark for a comprehensive understanding of the inherent electric characteristics of CIPS, offering valuable insights for its future modifications and applications in various applications.