Enhancing the Energy Storage Performance of Flexible Na_0.5Bi_0.5TiO₃-Based Relaxor Thin Films Through a Relaxor Strategy

Abstract

Dielectric capacitors are employed in defense and automotive applications owing to their ultrahigh charge–discharge rates. To mitigate the high leakage current density of Na_0.5Bi_0.5TiO₃ (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(Na_0.5Bi_0.5)(Fe_0.02Ti_0.99)O₃-0.05SrTiO₃ thin film achieves a recoverable energy storage density (W_rec) 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.

1. Introduction

In recent years, with the advancement of electronic devices toward miniaturization and integration, dielectric thin-film capacitors, as an emerging high-speed energy storage technology, attracted widespread attention and held significant application prospects in fields such as defense, healthcare, and automotive [1,2,3]. Consequently, the dielectric energy storage film of this system exhibited a lower breakdown field strength, which hindered the achievement of excellent energy storage performance. Two key parameters characterize energy storage performance: energy storage density (W_rec) and efficiency (η). These could be calculated using the following formulas [4,5,6,7,8].

$$W_{\mathrm{rec}}={\int }_{P_r}^{P_m}Edp$$

(1)

η = W_rec/(W_rec + W_loss) × 100%

(2)

where P_m was the maximum polarization, P_r was the remanent polarization, and W_loss represented the energy dissipated during operation. Therefore, improving W_rec and η primarily relied on achieving both a large polarization difference (ΔP = P_m − P_r) and a high breakdown field strength (E_BD).

Relaxor ferroelectric materials possess fine ferroelectric domains, which can greatly reduce the cooperative coupling between ferroelectric domains. This gives the materials a high dielectric constant, high saturation polarization, and low remnant polarization, manifested as a slim hysteresis loop, and thus holds significant application potential in dielectric energy storage [9]. Na_0.5Bi_0.5TiO₃ (NBT), as an environmentally friendly relaxor ferroelectric material, offered advantages such as high saturation polarization (P_s~38 μC/cm²) and high Curie temperature (T_c~320 °C) for energy storage applications [10,11]; however, its application was greatly hindered by issues including large leakage current density (up to 3.1 × 10⁻³ A/cm²) and low breakdown field strength [12,13]. In response to this challenge, the 0.94BaZr_0.2Ti_0.8O₃-0.06Na_0.5Bi_0.5TiO₃ thin film was prepared, achieving a W_rec of 62.08 J/cm³ and η of 85.18% under an ultrahigh breakdown field strength (E_BD) of 6117 kV/cm [14]. Besides, Cheng obtained high P_m (112.7 µC/cm) and low P_r (14.9 µC/cm) by optimizing polarization response, ultimately achieving excellent energy storage properties with W_rec ≈ 81.9 J/cm³ and η ≈ 64.4% at an electric field of 2285 kV/cm in a flexible Mn-doped 0.97(0.93Na_0.5Bi_0.5TiO₃-0.07BaTiO₃)-0.03BiFeO₃ inorganic thin-film capacitor, with the assistance of a two-dimensional fluorophlogopite mica substrate. This was mainly attributed to the high degree of relaxor dispersion in the film, as well as the coexistence of ferroelectric and antiferroelectric phases [15]. In addition, Lee and Son incorporated BaTiO₃ into the lattice of NBT to optimize its relaxation properties, reducing the residual polarization of NBT from 28.4 to 4.7 µC/cm, ultimately achieving a W_rec of 54.3 J/cm³ and η of 89.5% in 0.94(Na_0.5Bi_0.5TiO₃-0.06BaTiO₃ thin film [16]. In addition to relaxor ferroelectrics, the high breakdown field strength and low P_r exhibited by paraelectric dielectrics in energy storage applications have also attracted considerable attention. For example, Peng et al. prepared Ba_0.7Sr_0.3Fe_xTi_1−xO₃ paraelectric thin film capacitors using the sol-gel method, achieving a W_rec of only 7.6 J/cm³ and an η of only 65% [17]. Furthermore, they introduced Al₂O₃ nanoparticles into the SrTiO₃ thin film. The Al₂O₃ nanoparticles created ion transport channels, which promoted an anodic oxidation reaction under an applied electric field, forming an Al₂O₃ − δ layer at the Al/SrTiO₃ interface. As a result, the breakdown field strength increased from 2330 kV/cm to 5070 kV/cm, and W_rec increased from 7.6 J/cm³ to 19.3 J/cm³. Moreover, guided by theoretical and phase-field simulations, remarkably superior comprehensive properties—including an ultrahigh η of 90~94% and a high W_rec of 85~90 J/cm³—were obtained in SrTiO₃ by manipulating local symmetry breaking via the introduction of Ti/O defects [18]. However, due to the ultra-low dielectric constant or polarization strength of paraelectric dielectrics, their W_rec remained relatively low, which significantly limited their development and application. Thus, integrating the high polarization strength of a relaxor ferroelectric phase (NBT, high saturation polarization, and Curie temperature) with the high breakdown field strength of a paraelectric phase (SrTiO₃, high E_BD but low P_m) offered a promising research direction for optimizing the energy storage performance of dielectric thin films.

In this work, SrTiO₃ was incorporated into the (Na_0.5Bi_0.5)TiO₃ lattice to fabricate (1 − x)(Na_0.5Bi_0.5)(Fe_0.02Ti_0.98)O_3−xSrTiO₃ (x = 0.00, 0.05, 0.10, 0.15) thin films. The effects of SrTiO₃ incorporation on domain response and relaxation behavior, as well as the underlying mechanism governing the energy storage performance, were systematically investigated. This study aims to enhance the E_BD and P_m of NBT-based thin-film capacitors, thereby improving their energy storage capability, and simultaneously provides both theoretical and experimental guidance for energy storage applications in the NBT system.

2. Experimental

The (1 − x)(Na_0.5Bi_0.5)(Fe_0.02Ti_0.98)O_3−xSrTiO₃ (x = 0.00, 0.05, 0.10, 0.15) thin films, designated as NBS₀FT, NBS₅FT, NBS₁₀FT, and NBS₁₅FT, respectively, are fabricated via the sol–gel method. The precursor solutions are prepared using raw materials including titanium (IV) butoxide [C₄H₉O)₄Ti] (Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai, China), bismuth nitrate pentahydrate (Bi(NO₃)·5H₂O) (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), iron (III) nitrate nonahydrate (Fe(NO₃)₃·9H₂O) (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), strontium acetate hemihydrate ((CH₃COO)₂Sr·½H₂O) (Shanghai Macklin Biochemical Co., Ltd., Shanghai, China), and sodium acetate (CH₃COONa) (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China). To stabilize the solution, C₄H₉O)₄Ti is dissolved in acetylacetone (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China). A mixture of ethanol and ethylene glycol (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) is used to dissolve (Bi(NO₃)·5H₂O), (Fe(NO₃)₃·9H₂O), and CH₃COONa, while ((CH₃COO)₂Sr·½H₂O) is dissolved in acetic acid (Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd., Tianjin, China). Each solution is magnetically stirred for 12 h, then combined and stirred for an additional 24 h. High-quality precursor solutions are obtained after allowing the mixture to stand for 48 h.

Flexible Pt/Mica substrates are employed to grow the thin films. The precursor solution is spin-coated at 3000 rpm for 30 s, dried at 200 °C for 3 min, and annealed at 600 °C for 15 min. This coating–drying–annealing cycle is repeated to achieve the desired film thickness. Gold top electrodes with a diameter of 0.4 mm are deposited onto the films through a shadow mask. The crystallinity of the films is analyzed by X-ray diffraction (XRD, D8, Bruker, Billerica, MA, USA). Morphology is examined using field-emission scanning electron microscopy (FESEM, S-4800, Hitachi, Tokyo, Japan) and atomic force microscopy (AFM, Dimension Edge, Santa Barbara, CA, USA). Domain structures are characterized via piezoelectric force microscopy (PFM, Dimension Edge, Santa Barbara, CA, USA). Ferroelectric and dielectric properties are evaluated using a ferroelectric tester (Radiant, RTI-Multiferroic, Albuquerque, NM, USA) and a dielectric analyzer (Concept 80, Novocontrol, Montabaur, Germany), respectively.

3. Results and Discussions

Figure 1 shows the grazing incidence X-ray diffraction (GIXRD) patterns of thin films with varying amounts of SrTiO₃ solid solution in (Na_0.5Bi_0.5)(Fe_0.02Ti_0.99)O₃. As can be seen from the figure, all (1 − x)(Na_0.5Bi_0.5)(Fe_0.02Ti_0.99)O_3−xSrTiO₃ flexible thin films exhibit a pure polycrystalline perovskite phase (Ref. ICSD #154040 of NBT phases), with no other impurity phases detected within the measurable range of the equipment. Additionally, as SrTiO₃ is introduced into the (Na_0.5Bi_0.5)(Fe_0.02Ti_0.99)O₃ lattice, the (110) peak shifts toward lower angles. This is due to the larger ionic radius of Sr²⁺ (r₁ = 0.1180 nm) compared to the average ionic radius of (NaBi)²⁺ (r₂ = 0.1025 nm). Therefore, when Sr²⁺ is incorporated into the (Na_0.5Bi_0.5)(Fe_0.02Ti_0.99)O₃ lattice, it causes lattice expansion. According to Bragg’s law ($2\mathrm{d}\sin \theta =n\lambda$, d is the distance between adjacent crystal planes, λ is the wavelength of the X-ray, θ is the angle between the X-ray and the crystal plane, and n is the diffraction order) [19], an increase in the d-spacing results in a decrease in the θ value, which manifests as a peak shift toward lower angles in the XRD pattern. This also confirms the successful incorporation of Sr²⁺ into the (Na_0.5Bi_0.5)(Fe_0.02Ti_0.99)O₃ lattice.

Figure 2 shows the surface and cross-sectional SEM morphologies of the (1 − x)(Na_0.5Bi_0.5)(Fe_0.02Ti_0.99)O₃ thin films. When x = 0.00, the NBS₀FT film surface exhibits a small number of pores and voids, which result from the volatilization or carbonization of organic compounds during the film preparation process [20], as shown in Figure 2(a₁). When x = 0.05, after SrTiO₃ is introduced into the (Na_0.5Bi_0.5)(Fe_0.02Ti_0.99)O₃ lattice, the pores on the film surface almost disappear, and the structure becomes dense, indicating that an appropriate amount of SrTiO₃ can promote grain growth, as shown in Figure 2(b₁). A dense structure can enhance the electrical insulation properties of the film, increase the breakdown field strength, and thereby improve the energy storage performance. However, as the SrTiO₃ content increases, pores and voids reappear on the surface. When the SrTiO₃ doping amount reaches 15%, the surface pores and voids significantly increase, as shown in Figure 2(c₁,d₁). This is because excess Sr²⁺ ions are not fully incorporated into the (Na_0.5Bi_0.5)(Fe_0.02Ti_0.99)O₃ lattice. These excess Sr²⁺ ions may accumulate at grain boundaries or interstitial sites, acting as defects that impede nucleation and growth of grains. Additionally, Figure 2(a₂,b₂,c₂,d₂) present the cross-sectional SEM images of the corresponding films. It can be observed that all films exhibit no obvious pores or voids in their cross-sections, indicating a dense internal structure. Furthermore, the thickness of all film samples is approximately 400 nm, and the similar thickness helps avoid errors in results and analysis due to size effects.

To further analyze the surface morphology and grain growth of the films, a 5 × 5 μm micro-area is scanned using AFM, as shown in Figure 3. From Figure 3a–d, it can be observed that the NBS₅FT film surface has fewer pores, while the other films exhibit pores and voids, which is consistent with the SEM results. The root mean square roughness (R_a) values for these films are 0.98 nm, 1.13 nm, 1.26 nm, and 2.11 nm, respectively. The R_a values of the first three samples are relatively close, while the roughness of the last sample shows a significant increase. The variation in roughness is closely related to grain size, morphology, and the presence of pores. Higher surface roughness can lead to the expansion of leakage current pathways, which in turn increases leakage current [21]. Figure 3e shows the statistical distribution of surface grains for all film samples, all of which follow a normal distribution, indicating uniform grain size distribution. The grains of the NBS₀FT and NBS₅FT films are significantly finer and more concentrated compared to the other two samples, suggesting that these films have smaller and more uniformly distributed grains. This trend is consistent with the R_a values.

Figure 4a shows the W_rec and η of all (1 − x)(Na_0.5Bi_0.5)(Fe_0.02Ti_0.98)O_3−xSrTiO₃ flexible thin-film capacitors. As can be seen, the η of all flexible thin-film capacitors is above 70% and increases with the SrTiO₃ solid solution content. Meanwhile, W_rec shows a trend of first increasing and then decreasing, with the NBS₅FT film achieving the highest W_rec of 43.88 μC/cm³. Simultaneously, the η of this film also reaches 73.95%. This excellent energy storage performance is primarily related to its high E_BD and (P_m − P_r) values. Figure 4b presents the corresponding hysteresis loops, all of which exhibit typical “slim” and “waist-pinched” hysteresis loops. Such hysteresis loops enable both high W_rec and η. To more intuitively demonstrate the performance of these flexible thin-film capacitors, their respective P_m, P_r, (P_m − P_r), E_BD, and E_c values are displayed in Figure 4c. As shown, with the introduction of SrTiO₃ into the (Na_0.5Bi_0.5)(Fe_0.02Ti_0.98)O₃ lattice, P_m first increases and then decreases, while P_r shows a continuous decreasing trend, resulting in (P_m − P_r) also first increasing and then decreasing. This indicates that an appropriate amount of SrTiO₃ solid solution (i.e., 5% wt.) can enhance the polarization intensity of (Na_0.5Bi_0.5)(Fe_0.02Ti_0.98)O₃ thin-film capacitors. This is because an appropriate amount of Sr²⁺ doping can disrupt the long-range ordered domains in the (Na_0.5Bi_0.5)(Fe_0.02Ti_0.98)O₃ film, forming fine ferroelectric domains, which is widely reported in previous studies [22,23,24,25,26]. Under an applied electric field, the reduced hindrance to reorientation allows fine ferroelectric domains to align at lower fields, yielding a higher maximum polarization (P_m) and a lower coercive field. Upon field removal, the fine ferroelectric domains readily return to their initial randomly oriented state with low energy, resulting in a low remnant polarization (P_r). The presence of fine ferroelectric domains thus increases P_m and decreases P_r, enhancing the recoverable energy density (W_rec) and efficiency (η) of flexible thin-film capacitors. However, excessive Sr²⁺ incorporation leads to the formation of a substantial amount of paraelectric SrTiO₃ [27], which increases the leakage current and reduces the breakdown strength, thereby deteriorating the energy storage density and efficiency. One of the typical characteristics of paraelectric dielectrics is their low polarization intensity, which also explains the reduction in P_m and P_r values in NBS₁₀FT and NBS₁₅FT films. The decrease in P_r is the main reason for the monotonic increase in η. Additionally, the E_BD of the flexible ferroelectric thin film capacitors first increases and then decreases, reaching its maximum value in the NBS₅FT film capacitor. This is because the NBS₅FT film has a smooth surface morphology, uniformly distributed grains, and a dense microstructure. However, when the Sr²⁺ doping amount reaches 15%, the E_BD increases again, which is attributed to the presence of a large amount of high-breakdown-performance SrTiO₃ in the film. The improvement in E_BD is the main reason for the enhanced W_rec in the NBS₅FT film capacitor.

Leakage current density is one of the important parameters characterizing ferroelectric thin films and can serve as a key indicator for assessing the quality of ferroelectric films. The relationship between leakage current density and electric field for different thin-film capacitors is shown in Figure 4d. As can be seen, the introduction of a certain amount of SrTiO₃ into the (Na_0.5Bi_0.5)(Fe_0.02Ti_0.98)O₃ lattice reduces the leakage current density from the order of 10⁻⁵ A/cm² to 10⁻⁷ A/cm². The NBS₅FT film capacitor exhibits the lowest leakage current density, which is closely related to its smooth surface morphology, uniformly distributed grains, and dense microstructure. In contrast, the leakage current density of NBS₁₀FT and NBS₁₅FT films increases, which is associated with the presence of numerous pores in these films.

To further investigate the polarization process of ferroelectric domains in the thin films, the amplitudes of the ferroelectric domains of several samples are measured using PFM. As shown in Figure 5(a₁–d₁), the four samples exhibit clear contrast between polarized and unpolarized regions, indicating the presence of ferroelectric domains in all samples. Additionally, ferroelectric domains align orderly under DC voltage excitation, while they vibrate under AC voltage. Under the same AC voltage, a larger vibration amplitude of the ferroelectric domains indicates a more significant response to the external electric field, suggesting higher polarization intensity. The NBS₅FT and NBS₁₀FT films display distinct “frame-like” patterns, with the NBS₅FT sample being particularly evident, while the other two samples show weaker electric field responses from their ferroelectric domains. To quantitatively describe the electric field response of these ferroelectric domains, the amplitude values of each sample are extracted using Nanoscope analysis software (Version 1.40) and plotted in Figure 5(a₂–d₂). Comparison reveals that the response amplitude of the ferroelectric domains in the NBS₅FT sample reaches 70 mV; the response amplitude of the ferroelectric domains in the NBS₁₀FT film is only about 20 mV, while the response amplitudes of the ferroelectric domains in the other two samples are even lower, around 15 mV. These results are consistent with the analysis in Figure 4.

Figure 6 shows the relationship between the dielectric constant and loss of all flexible thin films as a function of temperature. As observed, all films exhibit frequency dispersion in the range of 1~20.0 kHz, and the temperature corresponding to the maximum dielectric constant (T_m) shifts toward higher temperatures, indicating that these films are relaxor ferroelectrics. Additionally, with the introduction of SrTiO₃, the Tm values for the NBS₀FT, NBS₅FT, NBS₁₀FT, and NBS₁₅FT films are 278 °C, 266 °C, 248 °C, and 242 °C, respectively. Their T_m values are all above 240 °C, indicating good temperature stability of these relaxor ferroelectric thin films. Moreover, the Tm values show a decreasing trend, which is attributed to the reduction of Fe in the system as the SrTiO₃ content increases, leading to a decrease in the BiFeO₃ content in the system. The Curie temperature of pure BiFeO₃ is as high as 850 °C [28]; therefore, when the BiFeO₃ component in the system decreases, the Curie temperature of the entire system also decreases. The inset shows the relationship between ln(1/ε − 1/εm) and ln(T − T_m) for the corresponding films at 1.0 kHz, fitted according to the modified Curie-Weiss law ($1/{\epsilon }_{\mathrm{r}}-1/{\epsilon }_{\mathrm{m}}={\left(T-T_{\mathrm{m}}\right)}^{\mathsf{\gamma }}/C$) [22,29,30]. Clearly, the γ values for the flexible ferroelectric thin film capacitors are 1.63, 1.84, 1.78, and 1.73, respectively. All γ values are greater than 1.6, indicating good relaxor characteristics, and they show a trend of first increasing and then decreasing. Notably, the γ values of the films after SrTiO₃ solid solution are all greater than 1.7, indicating that the introduction of Sr²⁺ effectively enhances the relaxor properties of the films. Among them, the NBS₅FT film capacitor has a γ value of 1.84, indicating the best relaxor characteristics. This is because an appropriate amount of Sr²⁺ introduced into the lattice disrupts the long-range order of the lattice, forming a large number of fine ferroelectric domains.

To further study the relaxor properties of the flexible thin films, the phase evolution of the ferroelectric domains in each sample is tested. After removing the DC voltage, the same area is cyclically tested with an AC voltage amplitude of 6 V, obtaining phase diagrams of the ferroelectric domains at different times, as shown in Figure 7. Except for NBS₁₀FT, the phase diagrams of the ferroelectric domains in the other samples show relatively clear “frame-like” patterns, indicating low energy required for ferroelectric domain switching during polarization, as shown in Figure 7(a₁–a₄). Among them, the NBS₅FT film exhibits clear contrast, indicating that under the same polarization electric field, the domain wall movement in this film encounters less hindrance, and the ferroelectric domains switch more easily, corresponding to a higher polarization intensity. For NBS₁₀FT, a large number of ferroelectric domains do not switch, which may be due to domain wall pinning on one hand, and on the other hand, the switched ferroelectric domains may return to their initial state before testing. After the DC electric field is removed, the depolarization process begins, and most ferroelectric domains gradually return to their initial state. The depolarization times for the NBS₀FT, NBS₅FT, NBS₁₀FT, and NBS₁₅FT films are 40 min, 26 min, 20 min, and 12 min, respectively, showing a gradually shortening trend. With the introduction of SrTiO₃, the depolarization process of the films is effectively shortened, and the relaxor properties are enhanced, which is consistent with the results in Figure 6. However, although NBS₅FT has stronger relaxor properties, its depolarization time is longer than that of NBS₁₀FT and NBS₁₅FT; this is because the increase in SrTiO₃ content effectively reduces the P_r value of the material.

The NBS₅FT flexible thin film capacitor exhibits excellent relaxor properties and achieves superior energy storage performance. However, in practical applications, the impact of different application environments on the energy storage performance of this thin film capacitor must be considered. Evaluating its stability and reliability is an essential step.

First, the hysteresis loops of the flexible NBS₅FT thin film capacitor under different tensile and compressive radii, along with their corresponding W_rec and η, are shown in Figure 8. As observed, under tensile or compressive radii of 5 mm (R₅), 7 mm (R₇), 9 mm (R₉), 11 mm (R₁₁), 13 mm (R₁₃), and 15 mm (R₁₅), the hysteresis loops remain essentially unchanged; as a result, the W_rec and η of the thin film capacitor under different tensile and compressive radii are maintained at around 46 J/cm³ and 75%, respectively. The results indicate that this flexible thin film capacitor can leverage its good flexibility for application in specific environments involving stretching or compression, such as certain robotic arm joints.

In addition to bending resistance, temperature stability, frequency stability, and good fatigue resistance are also important indicators for evaluating energy storage thin films. Figure 9(a₁,a₂) show the hysteresis loops of the NBS₅FT thin film capacitor at a frequency of 2.0 kHz and the corresponding W_rec and η as a function of temperature. In the temperature range of 10 °C to 170 °C, the hysteresis loops gradually deform as the temperature increases, as shown in Figure 9(a₁). The W_rec and η of the NBS₅FT film show an initial improvement, which is due to the presence of fine ferroelectric domains, whose activity increases with rising temperature. As the temperature continues to rise, the leakage current of the system increases, leading to the degradation of W_rec and η, as shown in Figure 9(a₂,b₁,b₂), which displays the hysteresis loops at different frequencies (0.1 kHz to 2.0 kHz) and their corresponding W_rec and η. As the frequency increases, the W_rec remains around 45 J/cm³, while η increases from 70% to 74%, indicating that this thin film capacitor can be used at different frequencies. Fatigue resistance is another important application indicator for thin-film capacitors, characterizing the number of repeated switching cycles of ferroelectric domains. After 1 × 10⁸ charge-discharge cycles, the shape of the hysteresis loop of this thin film capacitor remains essentially unchanged, as shown in Figure 9(c₁). The corresponding W_rec remains stable above 46 J/cm³, while η decreases from 74.55% to 68.81%, a reduction of only 6%, as shown in Figure 9(c₂). It can be concluded that the NBS₅FT thin film capacitor exhibits good fatigue resistance.

4. Conclusions

The ferroelectric domain structure of the thin films is modulated by adjusting the SrTiO₃ content in the thin films. When the doping level is 5%, the 0.95(Na_0.5Bi_0.5)(Fe_0.02Ti_0.98)O₃-0.05SrTiO₃ film achieves a W_rec of 43.88 J/cm³ and an η of 73.95% under an electric field strength of 2692.29 kV/cm. Additionally, the NBS₅FT film exhibits outstanding temperature stability (10~170 °C), excellent frequency stability (0.1~2.0 kHz), and robust fatigue resistance (1 × 10⁸ charge-discharge cycles). Meanwhile, it also has excellent bendability performance (bending radius: 5~15 mm). This work promotes the theoretical and applied development of dielectric energy storage materials.