Gradient-layered polymer nanocomposites with significantly improved insulation performance for dielectric energy storage

Dielectric polymer composites with high power densities and ultrafast charge-discharge rates hold the promise of storing and converting renewable energies to address growing environmental challenges. Many efforts have been devoted to improving the energy storage capability of polymer composites in the past few years. However, there is an ever-existing tradeoff between dielectric permittivity and breakdown strength, which are two key factors determining the energy density. Here, inspired by the hierarchical structure of bamboo culms, the gradient-layered ceramic nanowires/polymer composites are designed and prepared, where the contents of ceramic fillers are increased gradually from the upper to bottom layers. It is demonstrated that the gradient electric fields formed at the interfaces between the adjacent layers play an important role to impede the breakdown process, thus leading to a significantly enhanced breakdown strength even at large amounts of high-dielectric permittivity (k) fillers. Consequently, a remarkable energy density of 17.6 J/cm accompanied with a high charge-discharge efficiency of 71.2% has been obtained, which significantly outperform the traditional single-layered films. This gradient-layered polymer nanocomposite represents a new class of hierarchically-structured multicomponent materials, whose design strategy is applicable to a variety of advanced composites with integrated contradictory characteristics for outstanding combined performance.