Significantly enhancing the dielectric constant and breakdown strength of linear dielectric polymers by utilizing ultralow loadings of nanofillers

Abstract

Dielectric polymers with high electrostatic energy storage capability are the enabling technology for advanced electronics and electric power systems. However, the development of dielectric polymers is rather limited by their undesired discharged energy density (U_e) due to the intrinsic low dielectric constant (K). Although large improvements of K can be achieved in dielectric polymers by introducing high filling ratios (>10 vol%) of high-K inorganic fillers, this approach has had only limited success in enhancing energy density due to the negative impact on the breakdown strength (E_b) and charge–discharge efficiency (η). Herein, we report that the incorporation of ultralow amounts (<1 vol%) of low-K quantum dot (QD) nanofillers into a linear polymer leads to pronounced and concurrent enhancements in both K and E_b, yielding a high U_e of 17.6 J cm⁻³ with an η of >87% at 800 MV m⁻¹. The improvement ratios of K (∼69%) and E_b (∼60%) reported in this work represent the record values in linear dielectric polymer composites with low filler content (≤5 vol%). The observed dielectric enhancement is rationalized by the significant contributions of the interface including enhanced polymer chain mobility and induced interfacial dipoles as revealed in the interphase dielectric model and interface simulations based on density functional theory (DFT). The improved mechanical strength and raised interface charge barriers are responsible for the high E_b. This contribution paves a new avenue for designing scalable polymer-based dielectric materials exhibiting high energy densities and efficiencies and provides fundamental insights into the dielectric behaviors at the interfaces in polymer nanocomposites.