Ultrahigh energy storage capability of trilayered polyetherimide/poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) with low loading of boron nitride nanosheets

Abstract

Polymer dielectrics demonstrate great potential in advanced energy storage capacitors due to their huge power density and flexibility. Various effective strategies have been proposed to improve the inherently low energy density of film capacitors. However, developing polymer films with high charge–discharge efficiency and large energy density is an issue worthy of attention. In this work, we have developed a trilayered dielectric film with linear polyetherimide (PEI) dielectrics as outer layers and poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) composites as middle layers. With such a tailored sandwiched architecture, the fluoropolymer delivers high energy density due to large electrical displacement, and the PEI linear layer delivers high charge–discharge efficiency with low hysteresis loss. A hyperbranched polyethylene grafted hexafluorobutyl acrylate (HBPE-g-HFBA) copolymer is utilized to functionalize boron nitride nanosheets (BNNSs), and the presence of fluorine-containing copolymer enhances the compatibility between nanosheets and the fluoropolymer matrix. For the trilayered composite with 0.5 wt% BNNSs/P(VDF-TrFE-CFE) as the inner layer, the energy density at 550 MV m⁻¹ increases to 16.9 J cm⁻³ with an efficiency of 80.1% due to the improvement of interfacial polarization. In particular, the trilayered architecture contributes to the redistribution of the local field by a large injection of electrical voltage, thereby greatly improving breakdown strength and energy density. The maximum energy density of 18.9 J cm⁻³ with an efficiency of 85.0% at 625 MV m⁻¹ is achieved in the optimized trilayered film. This work provides an efficient route to develop a flexible polymer film capacitor with large energy storage capability.