Flexible lead-free Na_0.5Bi_0.5TiO₃-based film capacitor with stable energy storage performances

The important application potential of flexible energy storage materials in new portable and wearable electronic devices has aroused a research upsurge in performance optimization. Here, the flexible (1−x)Na_0.5Bi_0.5TiO₃−xBi(Mg_0.5Zr_0.5)O₃ (NBT-xBMZ) film capacitors were obtained via a simple sol–gel method based on a nickel foil substrate. The addition of BMZ content strengthens the relaxor behavior of NBT-based film, which is conducive to producing substantial polarization differences (P_max−P_r). Mg²⁺ and Zr⁴⁺, on the other hand, help to minimize leakage current density and boost breakdown field strength (BDS). As a result, a large recoverable energy storage density of ~ 51.5 J cm^{− 3} with a large energy efficiency of 60.4% under 2000 kV cm^{− 1} was detected in the flexible film for x = 0.4. In addition, the NBT-0.4BMZ film exhibits great frequency (1–5 kHz), temperature (25–205 °C) stability, and antifatigue property (10⁵ cycles). Besides, the energy storage performances in NBT-0.4BMZ films are almost free from the mechanical bending processes even if it is cycled for 20,000 times at a small radii of 2 mm. The results indicate that the NBT-0.4BMZ flexible film is a promising energy storage material for the flexible electronics fields.