Excellent Energy Storage Performance in Bilayer Composites Combining Aligned TiO2 Nanoarray and Random TiO2 Nanowires with Poly(vinylidene fluoride)

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.