Significantly Enhanced Electrostatic Energy Density of a PVDF-Based Film with [001]-Oriented Rutile TiO₂ Fillers via Multilayer Interfacial Engineering

Introducing high dielectric-constant inorganic fillers into a high-broaden-strength polymer matrix is a crucial strategy to achieve a high-performance energy storage polymer composite. However, the interfacial coupling between the inorganic fillers and polymer matrix has always been a predicament for optimal performance. Herein, a multilayer interface structure, i.e., TiO2/SiO2, SiO2/polydopamine (PDA), and PDA/PVDF, are developed to resist the applied high electric field and improve the interfacial polarization simultaneously. TiO2 nanorods (NRs) with [001]-oriented rutile polymorph are synthesized by sodium dodecyl sulfate (SDS) assisted hydrothermal reaction, which is further decorated with a SiO2 layer and a subsequent PDA layer in order to incorporate well into the PVDF matrix using a solution casting process, finally forming the TiO2@SiO2@PDA/PVDF composite film. The optimal composite film incorporating [001]-TiO2 NRs exhibits an ultrahigh energy density (Ue) of 29.8 J/cm3 at a high Eb of 532 MV/m, sharply superior to the TiO2 counterpart-based films (e.g., TiO2 nanoparticle (NPs) based, and with or without the SiO2/PDA layer, which only gives a maximum Ue of 16 J/cm3 in TiO2@SiO2@PDA NPs/PVDF), and also the similarly inorganic-polymer systems previously reported. This work not only demonstrates an inorganic-polymer hybrid composite film with high electrostatic storage density but also highlights a multilayer interface structure route to alter interfacial microstructures and achieve superior energy storage performance.