Ultrahigh Energy Storage Performance of BiFeO3‐BaTiO3 Flexible Film Capacitor with High‐Temperature Stability via Defect Design

Abstract Nanoengineering polar oxide films have attracted great attention in energy storage due to their high energy density. However, most of them are deposited on thick and rigid substrates, which is not conducive to the integration of capacitors and applications in flexible electronics. Here, an alternative strategy using van der Waals epitaxial oxide dielectrics on ultra‐thin flexible mica substrates is developed and increased the disorder within the system through high laser flux. The introduction of defects can efficiently weaken or destroy the long‐range ferroelectric ordering, ultimately leading to the emergence of a large numbers of weak‐coupling regions. Such polarization configuration ensures fast polarization response and significantly improves energy storage characteristics. A flexible BiFeO 3 ‐BaTiO 3 (BF‐BT) capacitor exhibits a total energy density of 43.5 J cm −3 and an efficiency of 66.7% and maintains good energy storage performance over a wide temperature range (20–200 °C) and under large bending deformation (bending radii ≈ 2 mm). This study provides a feasible approach to improve the energy storage characteristics of dielectric oxide films and paves the way for their practical application in high‐energy density capacitors.