Three-phases Fe3O4@TiO2-P(VDF-HFP) composite films with high energy storage density at low filler fraction under low operating electric field

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.