Boosted energy storage density of sandwich-structurecomposites: A unique strategy via introducing negative permittivity layer

Abstract

Dielectric materials exhibiting high power densities have garnered significant interest as crucial constituents for capacitors employed in energy storage systems and diverse electronic devices. Regrettably, the intrinsic low energy densities of dielectrics pose significant limitations to their practical application. Hence, the pursuit of enhanced energy storage properties and superior dielectric performance in dielectric materials necessitates the exploration of novel approaches to material design and processing. Here, a special design that introduces a negative-ε´ layer in a sandwich structure is explored for simultaneously realising high breakdown strength and permittivity, which are two critical factors influencing energy density. In a tri-layer composite, the outer positive-ε´ layer consisting of BN/PVDF offers high breakdown strength due to the presence of abundant BN sheets and micro-interfaces in the composite can effectively block the electric trees expansion. Simultaneously, the negative-ε´ layer of MWCNTs/PVDF provides elevated permittivity and enhanced energy density due to the synergistic effect between the positive and negative-ε´ layers, along with interfacial polarizations in the micro-interfaces connecting adjacent layers. As a result, the tri-layer composite, with a thickness ratio of 1:20:1, achieves an extraordinary permittivity of 432. Importantly, a high discharge energy density of approximately 27 J/cm3 is obtained by carefully balancing the dielectric properties of single layers. This investigation presents a novel insight on the design of high-energy-density dielectric materials through introducing a negative ε´ layer, offering significant benefits for energy storage applications.