Two-Dimensional High-k BaTiO3 for Capacitive High-Energy Storage

High-performance capacitors are essential for modern power electronics, yet the low energy density of conventional dielectrics largely restricts their further miniaturization. Incorporating nanostructured high-k materials offers a promising route to overcome this limitation. Here, we address this issue by producing high-quality 2D BaTiO3 via soft chemical growth at low temperatures. The formation of these ultrathin BaTiO3 nanosheets proceeds from TiO2 nanosheet precursors via a multi-stage pathway that couples an initial topochemical surface conversion with subsequent confinement-directed regrowth processes. The obtained nanosheets feature thickness of ~10 nm and lateral dimensions of several hundred nanometers. Subsequent annealing enhances their crystallinity, yielding a high k of ~70 at 1 kHz. To demonstrate their practical potential, stable aqueous dielectric inks composed of these nanosheets and poly(vinyl alcohol) were formulated, enabling the fabrication of waterborne polymer composites via a simple solution-casting process. These truly 2D high-k nanosheets result in a maximum recoverable energy density of 12 J cm⁻3 and a charge-discharge efficiency of 70% at an electric field of 632 MV m⁻1 in a composite film with record-low filling ratio (0.05 vol%). These energy storage metrics rival those of state-of-the-art waterborne dielectric materials and most of solvent-processed polymer composites based on BaTiO3 nanoparticles or nanofibers, highlighting the potential of the 2D BaTiO3 for flexible energy-storage devices.