Enhancing the Energy Storage Performance of Flexible Na0.5Bi0.5TiO3-Based Relaxor Thin Films Through a Relaxor Strategy

Dielectric capacitors are employed in defense and automotive applications owing to their ultrahigh charge–discharge rates. To mitigate the high leakage current density of Na0.5Bi0.5TiO3 (NBT), SrTiO3 (STO), which exhibits excellent insulation performance, is incorporated into the NBT lattice to enhance both the breakdown field strength and the relaxor characteristics. Furthermore, the ionic radius of Sr2+ (0.1180 nm) is slightly larger than the average ionic radius of (NaBi)2+ (0.1025 nm). As a result, the introduction of STO induces lattice distortion, disrupts long-range ordering, and promotes the formation of short-range ordered domains, thereby strengthening the relaxor behavior (the relaxation degree γ increased from 1.63 to 1.84). Consequently, the 0.95(Na0.5Bi0.5)(Fe0.02Ti0.99)O3-0.05SrTiO3 thin film achieves a recoverable energy storage density (Wrec) of 43.88 J/cm3 and an efficiency (η) of 73.95%. In addition, the thin film exhibits excellent temperature stability over a range of 10 to 170 °C, good frequency stability from 0.1 to 2.0 kHz, and robust fatigue endurance up to 1 × 108 switching cycles. This work provides reliable technical and theoretical guidance for the application of NBT-based materials in energy storage.