Polymer-based composites with high discharged energy density and energy efficiency are tremendously desired for modern electronic systems. In this study, a bilayer heterostructural composite (named as THV/xBT) with excellent energy storage performances was constructed by one layer of a BaTiO 3 nanoparticles (BT nps)-filled P(VDF-HFP) composite and another layer of a pure poly(tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene) (THV) polymer with a moderate dielectric constant and high breakdown strength. The experimental and finite element simulation results indicate that the space charges could accumulate at the interfaces between THV/P(VDF-HFP) and BT nps/P(VDF-HFP) by regulating the dielectric contrast between these two adjacent layers. It improves not only the interfacial polarization but also the breakdown strength and limits the leakage current density of THV/xBT composites. As a result, the THV/5BT composite delivers the best energy storage performance with the discharged energy density of 22.7 J/cm 3 , and an energy efficiency of 79.0% is achieved. This work might open up a way for structural design of polymer-based composites with remarkable energy storage performances.
TiO2 nanoarray (TNA) is usually used to improve the
energy storage performance of the polymer composite; however, owing
to the paradox between polarization and breakdown strength, the discharged
energy density of TNA-based composite is always restricted. In this
study, a novel bilayer composite with excellent energy storage performance
has been designed and fabricated by combining aligned TNA and random
TiO2 nanowires (TO NWs) with poly(vinylidene fluoride)
(PVDF) matrix. Interestingly, a superior discharged energy density
of 16.13 J/cm3 was obtained in the (5 vol % TO NWs/TNA)–PVDF
composite, which is 2.0 times higher than that of pure PVDF matrix
(8.23 J/cm3) due to the simultaneously improved polarization
and breakdown strength. Additionally, the corresponding energy efficiency
remains high (77.37%) owing to the nonferroelectric characteristics
of the TO fillers and the suppressed leakage current density. Considering
the excellent and sharply incremental discharged energy density and
superior energy efficiency of the (5 vol % TO NWs/TNA)–PVDF
composite, this demonstrated work provides a method to obtain high
discharged energy density and energy efficiency simultaneously.
An enhanced energy storage ability, under a low operating electric field, was achieved in Fe3O4@TiO2-P(VDF-HFP) composite films. The low conductivity TiO2 layer was coated onto the high polarization Fe3O4 to construct Fe3O4@TiO2 core–shell fillers for decreasing filler fraction and alleviating conductivity contrast. For instance, the 2 vol.% Fe3O4@TiO2-P(VDF-HFP) film shows a discharged energy density and energy efficiency of 8.6 J cm−3 and 61.7%, respectively, under a low operating electric field of 261.9 kV mm−1. The coated TiO2 and modified –OH groups not only restrict the adverse effects (such as high conductivity, easy agglomeration, etc) caused by Fe3O4, but also contribute greatly to the improvement of polarization and breakdown strength, leading to a significantly improved energy storage performance. Additionally, the present work might possess great potential applications for energy storage owing to the low filler fraction, simple, and low electric filed operation.
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