Modulation of individual-layer properties results in excellent discharged energy density of sandwich-structured composite films

Sandwich-structured composite films have been regarded as an effective route to resolve the paradox between polarization increase and breakdown strength decrease, and achieve the excellent energy storage performances. However, there are few studies focused on optimizing the individual-layer properties and obtaining satisfactory energy storage performances in the sandwich-structured composite films. In this study, the xTBT (where x is the TO nw fractions, T and B are the TO nws and BT nps filled layers, respectively) sandwich-structured composite films with excellent energy storage performance have been realized though regulating each individual-layer properties, including the dielectric properties, polarization, leakage current and breakdown strength and so on. Notably, the maximum discharged energy density of the 2TBT composite film reaches up to 13.7 J/cm(3) at 400 MV/m, and maintains a relatively high energy efficiency of 65%. The enhanced discharged energy density of 2TBT composite film represents a great improvement of 137% higher than that of the neat PVDF (5.8 J/cm(3) at 345 MV/m) due to the simultaneously improved breakdown strength and polarization. The preliminary results might pave the way for future designing and optimizing discharged energy density and energy efficiency of sandwich-structured films.