Improved energy density and efficiency of polymer nanocomposites by filling ultralow amounts of 2D Ni(OH)2 nanosheets and building sandwich structure

Currently, the application of polymer dielectric capacitors is largely limited by their low energy storage density. Herein, novel sandwich-structured composite films with simultaneously enhanced energy storage density and efficiency are fabricated, which combine outer layers of inorganic nanosheets Ni(OH) 2 /poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) with high permittivity and intermediate layer of polycarbonate (PC) with high breakdown strength. The trilayer film with only 1 vol% Ni(OH) 2 exhibits an excellent energy storage density of 7.322 J/cm 3 accompanied with a high efficiency of 72.1 % at 605 kV/mm, which are 120 % and 113 % of pure P(VDF-HFP). Furthermore, hindrance effect of micro-interfaces and macroscopical-interfaces on electrical trees is well revealed through finite element simulation. These excellent characteristics of composite films suggest that this design strategy is effective to realize concurrent high energy density and efficiency.