All-Organic Quantum Dots-Boosted Energy Storage Density in PVDF-Based Nanocomposites via Dielectric Enhancement and Loss Reduction

Dielectric capacitors offer immense application potential in advanced electrical and electronic systems with their unique ultrahigh power density. Polymer-based dielectric composites with high energy density are urgently needed to meet the ever-growing demand for the integration and miniaturization of electronic devices. However, the universal contradictory relationship between permittivity and breakdown strength in traditional ceramic/polymer nanocomposite still poses a huge challenge for a breakthrough in energy density. In this work, all-organic carbon quantum dot CDs were synthesized and introduced into a poly(vinylidene fluoride) PVDF polymer matrix to achieve significantly boosted energy storage performance. The ultrasmall and surface functionalized CDs facilitate the polar beta-phase transition and crystallinity of PVDF polymer and modulate the energy level and traps of the nanocomposite. Surprisingly, a synergistic dielectric enhancement and loss reduction were achieved in CD/PVDF nanocomposite. For one thing, the improvement in epsilon r and high-field Dm originates from the CD-induced polar transition and interface polarization. For another thing, the suppressed dielectric loss and high-field Dr are attributed to the conductive loss depression via the introduction of deep trap levels to capture charges. More importantly, Eb was largely strengthened from 521.9 kV mm-1 to 627.2 kV mm-1 by utilizing the coulomb-blockade effect of CDs to construct energy barriers and impede carrier migration. As a result, compared to the 9.9 J cm-3 for pristine PVDF, the highest discharge energy density of 18.3 J cm-3 was obtained in a 0.5 wt% CD/PVDF nanocomposite, which is competitive with most analogous PVDF-based nanocomposites. This study demonstrates a new paradigm of organic quantum dot-enhanced ferroelectric polymer-based dielectric energy storage performance and will promote its application for electrostatic film capacitors.