Na0. 5Bi0. 5TiO3-based energy storage dielectric ceramic with heterostructure and preparation

Abstract

The invention discloses a Na0. 5Bi0. 5TiO3-based energy storage dielectric ceramic with a heterostructure and preparation thereof, the structural general formula of the energy storage dielectric ceramic is (1-x) (Bi0. 5Na0. 5) 0.96 Ba0. 04TiO3-xSm1 / 3TaO3, x is more than or equal to 0.04 and less than 0.16, and x is more than or equal to 0.05 and less than or equal to 0.16. The energy storage dielectric ceramic has a multiphase polycrystalline structure; the relaxation degree value gamma is equal to 1.91-2; the maximum total energy storage density under the ultrahigh electric field of 693 kV / cm is 11.7 J / cm < 3 >, and the maximum recoverable energy storage density is 9.8 J / cm < 3 >. According to the preparation method, a domain structure-grain size-energy band characteristic multi-scale cooperative regulation and control system is constructed, a grain refinement and out-phase composite cooperative mechanism is adopted, a composite ceramic system with rodlike grain morphology and BNBTT-based Aurivillius phase coexisting is obtained, and the breakdown field strength of the material is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of energy storage medium ceramics, specifically relating to Na with a heterostructure. 0.5 Bi 0.5 TiO3-based energy storage medium ceramics and their preparation. Background Technology

[0002] Currently, the main energy storage devices include dielectric capacitors, supercapacitors, and batteries. Among them, ceramic dielectric capacitors exhibit excellent charge-discharge performance and fatigue resistance in advanced pulse power systems, such as power electronics, electromagnetic equipment, pulse power weapons, and hybrid vehicles. Therefore, ceramic dielectric materials with high energy density have become the inevitable choice for high-performance pulse energy storage capacitor applications.

[0003] Research on perovskite-structured ceramics constitutes a major part of dielectric material research, such as BaNaTiO3-based, NaNbO-based, BaTiO3-based, SrTiO3-based, BiFeO3-based, and AgNbO3-based energy storage dielectric ceramics, among which Bi... 0.5 Na 0.5 TiO3 has become a research hotspot in energy storage materials due to its excellent piezoelectric effect and electrostriction. However, perovskite ceramics exhibit significant remanent polarization, which affects their energy storage properties.

[0004] Energy storage dielectric ceramics possess the characteristics of high-current discharge and rapid charge-discharge, and are widely used in military, medical, and environmental treatment fields. Their energy storage density is directly proportional to the dielectric constant of the dielectric ceramic and the square of the breakdown field strength. Therefore, to obtain dielectric ceramic materials with high energy storage density, it is necessary to increase their dielectric constant and their breakdown field strength.

[0005] Pure BNT ceramics exhibit unique advantages in dielectric energy storage materials due to their significant spontaneous polarization intensity, but their high remanent polarization and large coercive field strength (E) are also significant challenges. c ≈3.5 kV / mm) and low breakdown field strength (E b <200 kV / cm) severely restricts energy storage performance.

[0006] For conventional ceramic dielectric materials, energy storage efficiency and energy storage density are negatively correlated. How to obtain higher energy storage density while ensuring a certain level of energy storage efficiency is a key research and development direction in the field of ceramic energy storage materials. Summary of the Invention

[0007] This invention discloses a Na with a heterostructure 0.5 Bi 0.5 TiO3-based energy storage medium ceramics and their preparation, in order to solve any of the above-mentioned and other potential problems of the prior art.

[0008] To achieve the above objectives, the technical solution of the present invention is: a Na with a heterostructure 0.5 Bi 0.5 TiO3-based energy storage medium ceramics have the following general structural formula: (1-x)(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-xSm 1 / 3 TaO3, wherein 0.04 ≤ x < 0.16; the energy storage medium ceramic has a multiphase polycrystalline structure; the relaxation value of the energy storage medium ceramic is γ = 1.91-2; the maximum total energy storage density of the energy storage medium ceramic under an ultra-high electric field of 693 kV / cm is 11.7 J / cm³. 3 The maximum recoverable energy storage density is 9.8 J / cm³. 3 The energy storage efficiency is 83.3%.

[0009] Furthermore, the polycrystalline structure includes a main crystalline phase, a second phase, and a third phase; the main crystalline phase is a perovskite pseudocubic structure; the second phase consists of rod-shaped grains; and the third phase consists of rhombic grains.

[0010] Furthermore, the chemical formula of the rod-shaped grains is BaTiO3, and the chemical formula of the rhombic grains is BaNa. 1.8 Bi 2.2 (Ta 1.5 Ti 3.5 )O 15.95 .

[0011] Furthermore, when x=0.04, the general structural formula of the energy storage medium ceramic is: 0.96(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.04Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.86, and its maximum total energy storage density is 9.04 J / cm² under a high electric field of 480 kV / cm. 3 The maximum recoverable energy storage density is 6.9 J / cm³. 3 The energy storage efficiency is 76.8%.

[0012] Furthermore, when x=0.08, the general structural formula of the energy storage medium ceramic is: 0.92(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.08Sm 1 / 3The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.93, and its maximum total energy storage density is 11.7 J / cm² under an ultra-high electric field of 693 kV / cm. 3 The maximum recoverable energy storage density is 9.8 J / cm³. 3 The energy storage efficiency is 83.3%.

[0013] Furthermore, when x=0.10, the general structural formula of the energy storage medium ceramic is: 0.90(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.10Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.99, and its maximum total energy storage density is 8.66 J / cm² under a high electric field of 620 kV / cm. 3 The maximum recoverable energy storage density is 7.3 J / cm³. 3 The energy storage efficiency is 84.6%.

[0014] Furthermore, when x=0.12, the general structural formula of the energy storage medium ceramic is: 0.88(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.12Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.92, and its maximum total energy storage density is 7.65 J / cm² under a high electric field of 620 kV / cm. 3 The maximum recoverable energy storage density is 6.6 J / cm³. 3 The energy storage efficiency is 86.2%.

[0015] Furthermore, when x=0.16, the general structural formula of the energy storage medium ceramic is: 0.84(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.16Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.92, and its maximum total energy storage density is 6.07 J / cm² under a high electric field of 660 kV / cm. 3 The maximum recoverable energy storage density is 5.4 J / cm³. 3 The energy storage efficiency is 89.6%.

[0016] Another object of the present invention is to provide a method for preparing the above-mentioned energy storage medium ceramic, the method specifically including the following steps: S1) Weigh out Na2CO3, Bi2O3, BaCO3, TiO2, Sm2O3 and Ta2O5 according to the design ratio of the general structural formula, and set aside for later use; S2) Place the raw materials weighed in S1) into a ball mill jar, add 70 mL of anhydrous ethanol as the ball milling medium, and use a planetary ball mill with zirconia balls to ball mill for 16-24 h to ensure that the raw materials are fully mixed and uniform, and obtain a mixed slurry; dry the obtained mixed slurry, and grind and mix it using a mortar and pestle. The powder after sieving is shaped under a pressure of 5 MPa, the shaped block is placed in a crucible, and calcined using a box furnace to obtain a first-calcined block; S4) After the first-calcined block obtained in S3) is initially ground in a mortar, the process of S3) is repeated to obtain the second-calcined block; S5) The calcined block obtained in S4) is placed in a mortar, a binder is added, and the mixture is ground to obtain powder. The powder is then sieved and pre-pressed under a pressure of 5 MPa. The block is then crushed, ground again, and sieved. The sieved powder is pressed into discs using a 10 / 15 mm diameter mold under a pressure of 2.5 MPa. S6) The shaped disc obtained in S5) is placed in a box-type high-temperature furnace and heated to 610 ℃ at a heating rate of 1.5 ℃ / min and held for 300 min to remove the added organic binder; S7) The discs treated in S6) are placed in a crucible covered with ZrO2 powder and sintered in a box furnace to obtain energy storage medium ceramics with high density.

[0017] Furthermore, the sintering process parameters in S2) and S7) are: heating to 850°C at a heating rate of 3°C / min and holding for 2 hours.

[0018] The beneficial effects of this invention are: by adopting the above technical solution, this invention successfully prepared (1-x)(Bi) by a high-temperature solid-state reaction method. 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-xSm 1 / 3 TaO3 energy storage dielectric ceramics were used to construct a multi-scale synergistic control system for domain structure, grain size, and band structure characteristics. Employing a synergistic mechanism of grain refinement and heterogeneous composite synthesis, a composite ceramic system (1-x)BNBT-xST with rod-shaped grain morphology and the coexistence of a BNBTT-based Aurivillius phase was successfully prepared. This structural feature significantly enhances the breakdown field strength of the material. The results show that the 0.92BNBT-0.08ST ceramic exhibits excellent energy storage characteristics: under an ultra-high breakdown electric field of 690 kV / cm, its W... rec Reaching 9.8 J / cm 3The η value remained at 83.3%, while exhibiting excellent charge-discharge characteristics. Notably, this material system demonstrates excellent thermal stability (20-120 °C), frequency stability (1-100 Hz), and fatigue resistance (10 Hz). 6 The study demonstrates promising application potential in various aspects, including secondary cycles. Finite element numerical simulations revealed the synergistic regulation mechanism of electric field distribution by the geometric anisotropy of rod-shaped grains and the intrinsic properties of the Aurivillius phase, providing a theoretical basis for improving the breakdown field strength. This work not only verifies the applicability of relaxor ferroelectric design theory in binary ceramic systems, but more importantly, establishes the structure-property relationship between heterogeneous grain engineering and energy storage performance, providing a crucial material foundation for developing next-generation high-power pulsed energy storage devices. Attached Figure Description

[0019] Figure 1 This invention relates to a Na with a heterostructure. 0.5 Bi 0.5 XRD pattern of TiO3-based energy storage medium ceramic.

[0020] Figure 2 The surface SEM and grain size distribution of (1-x)BNBT-xST ceramic are shown. (a)-(e) Surface SEM images of (1-x)BNBT-xST ceramics, (f) Average grain size distribution.

[0021] Figure 3 Cross-sectional SEM images and EDS elemental mapping distribution diagrams of 0.92BNBT-0.08ST ceramics.

[0022] Figure 4 The surface SEM image and EDS elemental mapping distribution of 0.92BNBT-0.08ST ceramic are shown.

[0023] Figure 5 Bright-field TEM images and surface-scanned EDS images of 0.92BNBT-0.08ST ceramics.

[0024] Figure 6 The diagram shows a spot scan of 0.92BNBT-0.08ST ceramic and its corresponding SAED.

[0025] Figure 7 Na with a heterostructure 0.5 Bi 0.5 Schematic diagram of relaxation behavior analysis of TiO3-based energy storage medium ceramics; (a) ε of ceramics with x=0.04-0.16 at 100KHz. r (a) Temperature dependence of tanδ; (b) ε at room temperature rFrequency dependence of tanδ; (c) ln(1 / ε - 1 / ε) for x = 0.04, x = 0.08 and x = 0.10 m )vs.ln(TT m (d) Density of states of BNBT and BNBT-Ta; (e)-(f) SAED and HR-TEM images of the x=0.08 ceramic.

[0026] Figure 8 Na with a heterostructure 0.5 Bi 0.5 Schematic diagram of energy storage performance analysis of TiO3-based energy storage medium ceramics; (a)-(b) PE loop and W of (1-x)BNBT-xST ceramics under breakdown field. rec E corresponding to different components and η value (c) b The Weibull distribution and fitted line; (d) UV-Vis absorption spectrum and (αhν) of (1-x)BNBT-xST ceramic. 2 vs. hν plot; (e) unipolar PE loop of x=0.08 ceramic under different electric fields and (f) corresponding W rec W tol and η value; (g) W of BNT-BT based ceramics rec η and E b Comparison; (h) W of different endmember numbers in BNT-based materials rec Comparison diagram. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] This invention provides a Na with a heterostructure 0.5 Bi 0.5 TiO3-based energy storage medium ceramics have the following general structural formula: (1-x)(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-xSm 1 / 3 TaO3, wherein 0.04 ≤ x < 0.16; the energy storage medium ceramic has a multiphase polycrystalline structure; the relaxation value of the energy storage medium ceramic is γ = 1.91-2; the maximum total energy storage density of the energy storage medium ceramic under an ultra-high electric field of 693 kV / cm is 11.7 J / cm³. 3 The maximum recoverable energy storage density is 9.8 J / cm³. 3 The energy storage efficiency is 83.3%.

[0029] The polycrystalline structure includes a main crystalline phase, a second phase, and a third phase; the main crystalline phase is a perovskite pseudocubic structure; the second phase consists of rod-shaped grains; and the third phase consists of rhombic grains.

[0030] The chemical formula of the rod-shaped grains is BaTiO3, and the chemical formula of the rhombic grains is BaNa. 1.8 Bi 2.2 (Ta 1.5 Ti 3.5 )O 15.95 .

[0031] Example 1: When x = 0.04, the general structural formula of the energy storage medium ceramic is: 0.96(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.04Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.86, and its maximum total energy storage density is 9.04 J / cm² under a high electric field of 480 kV / cm. 3 The maximum recoverable energy storage density is 6.9 J / cm³. 3 The energy storage efficiency is 76.8%.

[0032] Example 2: When x = 0.08, the general structural formula of the energy storage medium ceramic is: 0.92(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.08Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.93, and its maximum total energy storage density is 11.7 J / cm² under an ultra-high electric field of 693 kV / cm. 3 The maximum recoverable energy storage density is 9.8 J / cm³. 3 The energy storage efficiency is 83.3%.

[0033] Example 3: When x = 0.10, the general structural formula of the energy storage medium ceramic is: 0.90(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.10Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.99, and its maximum total energy storage density is 8.66 J / cm² under a high electric field of 620 kV / cm. 3The maximum recoverable energy storage density is 7.3 J / cm³. 3 The energy storage efficiency is 84.6%.

[0034] Example 4: When x=0.12, the general structural formula of the energy storage medium ceramic is: 0.88(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.12Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.92, and its maximum total energy storage density is 7.65 J / cm² under a high electric field of 620 kV / cm. 3 The maximum recoverable energy storage density is 6.6 J / cm³. 3 The energy storage efficiency is 86.2%.

[0035] Example 5: When x = 0.16, the general structural formula of the energy storage medium ceramic is: 0.84(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.16Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.92, and its maximum total energy storage density is 6.07 J / cm² under a high electric field of 660 kV / cm. 3 The maximum recoverable energy storage density is 5.4 J / cm³. 3 The energy storage efficiency is 89.6%.

[0036] The above-mentioned Na with heterostructure 0.5 Bi 0.5 A method for preparing TiO3-based energy storage medium ceramics, comprising the following steps: Table 1 Raw materials used in the experiment raw material molecular weight purity(%) Manufacturer <![CDATA[Na2CO3]]> 105.99 99.80 Sinopharm Group Chemical Reagents <![CDATA[Bi2O3]]> 465.96 99.00 Sinopharm Group Chemical Reagents <![CDATA[BaCO3]]> 197.34 99.00 Sinopharm Group Chemical Reagents <![CDATA[TiO2]]> 79.87 98.00 Sinopharm Group Chemical Reagents <![CDATA[Sm2O3]]> 137.91 99.99 Aladdin <![CDATA[Ta2O5]]> 441.89 99.99 Aladdin Raw material drying Before weighing the raw materials, the required raw materials were placed in an oven and dried at 80 ℃ for 6 hours to remove moisture, thus ensuring the accuracy of the weighing results.

[0037] Calculation, weighing Calculate the required mass (0.05 mol) of each component and each raw material based on the chemical formula of the components. Weigh the dried raw materials to the nearest ten-thousandth, with an error not exceeding ±0.0005 g.

[0038] ball milling Place the weighed raw materials into a ball mill jar, add 70 mL of anhydrous ethanol as the ball milling medium, and use a planetary ball mill with zirconia balls to ball mill for 16 / 24 h to ensure that the raw materials are fully mixed and homogeneous.

[0039] Pre-synthesis The ball-milled slurry was dried and further ground and mixed using a mortar and pestle. The sieved powder was then molded under a pressure of 5 MPa. The molded blocks were placed in crucibles and calcined using a box-type high-temperature furnace. The synthesis temperature of each component was 850 ℃ and the holding time was 2 h, with a heating rate of 3 ℃ / min.

[0040] Secondary ball mill After the pre-fired blocks are initially ground in a mortar, step (3) is repeated for ball milling to ensure uniform mixing.

[0041] Granulation and molding After the ball-milled slurry was dried, it was ground and mixed in a mortar. To increase the flowability of the powder and facilitate subsequent molding, an 8% (w / w) aqueous solution of polyvinyl alcohol (PVA) was added as a binder. After thorough grinding, the powder was sieved, pre-compressed under a pressure of 5 MPa, and the lumps were crushed, ground again, and sieved. The sieved powder was then pressed into small discs using a 10 / 15 mm diameter mold under a pressure of 2.5 MPa.

[0042] Plastic removal The shaped discs are placed in a box-type high-temperature furnace and heated to 610 ℃ at a heating rate of 1.5 ℃ / min and held for 300 min to remove the added organic binder.

[0043] sintering The plasticized discs were placed in crucibles covered with ZrO2 powder and sintered in a box furnace under suitable sintering conditions to obtain highly dense ceramic samples. The sintering heating rate of each component was 3 ℃ / min.

[0044] Based on the characteristics of each system, we adjusted the sintering process parameters accordingly. The specific values ​​of the pre-synthesis temperature, sintering temperature, and holding time for each system are detailed in Table 2.

[0045] Table 2. Pre-synthesis and sintering temperatures and holding times for each system system <![CDATA[Synthesis temperature ( o °C)]]> Insulation time (h) <![CDATA[Sintering temperature ( o °C)]]> Insulation time (h) BNBT-ST 850 2 1170 2 Sample surface optimization and electrode preparation Ceramic samples were mechanically thinned and mirror-polished using diamond abrasive slurry, followed by 15 minutes of ultrasonic cleaning in deionized water to remove surface residues. After drying, metal electrodes (Au / Ag) were fabricated on the sample surface, and sintering processes were completed in a tube furnace (Au electrode: 250 ℃, 5 ℃ / min heating rate, air atmosphere) and a box furnace (Ag electrode: 630 ℃, 1.5 ℃ / min heating rate, 20-30 min holding time). Relevant performance tests were then conducted.

[0046] like Figure 1 The image shows a Na with a heterostructure according to the present invention. 0.5 Bi 0.5 XRD pattern of TiO3-based energy storage medium ceramics. The main crystal phase of all samples exhibits a typical perovskite pseudocubic structure, consistent with the reference card in the standard PDF database. The formation of secondary phases can be observed in the range of x = 0.04 to 0.16, and the diffraction peaks of the secondary phases gradually increase with increasing x. By magnifying the (200) diffraction peaks of BNBT ceramics with different ST contents, the trend of their structural evolution was revealed: with increasing ST content, the diffraction peaks first shift to higher angles, while at x > 0.12, they begin to shift to lower angles. This phenomenon can be attributed to the substitution effect of ions in the lattice. When x ≤ 0.12, the diffraction peaks shift to higher angles, indicating a reduction in unit cell volume, possibly due to the smaller radius of the Sm... 3+ The ion replaces Na at the A site + Bi 3+ Or Ba 2+ This is due to the presence of ions. When x > 0.12, the diffraction peaks begin to shift to lower angles, which is due to the larger Ta content. 5+ An ion (ionic radius 1.44 Å) substituted Ti at the B site. 4+ (Ionic radius 1.44 Å), indicating that substitution at the B site plays a major role in the chemical modification. Of particular note is... Figure 1 No splitting of the (200) diffraction peak was observed, indicating that the solid solution has a high degree of symmetry. Furthermore, analysis of the impurity phase peaks in the XRD pattern revealed that they correspond to PDF#97-018-3932 (BaTiO3) and PDF#97-015-0928 (Bi), respectively. 1.86 Ti2O 6.884 The results are consistent with the standard phase in the original text, further verifying the compositional origin of the secondary phase.

[0047] All samples exhibited good crystallinity and a relatively dense microstructure. Notably, except for the sample with x = 0.04, which showed only rod-shaped grains, all other samples exhibited both rod-shaped and rhombic grains. With increasing x, the average equiaxed grain sizes were 2.18 μm, 1.95 μm, 2.08 μm, 2.09 μm, and 1.97 μm, respectively. SEM images of the BNBT-ST ceramics at x = 0.04 and x = 0.08 revealed three different grain morphologies: equiaxed grains, rod-shaped grains, and rhombic grains. These grain morphologies correspond to the three types observed in the XRD results, such as... Figure 2 and Figure 3 As shown.

[0048] like Figure 4 As shown, the elements are uniformly distributed in the equiaxed grains, while Ba and Ti are enriched in the rod-shaped grains, and Bi, Ti, and Ta are enriched in the rhombic grains. It is noteworthy that although the EDS results for the equiaxed and rod-shaped grains are consistent with the XRD analysis results, no impurity phase corresponding to Ta was detected in the XRD for the rhombic grains. Therefore, the composition and structural characteristics of the rhombic grains require further in-depth analysis to clarify their specific origin and correlation with the microstructure.

[0049] Heterogeneous phase analysis To further explore the differences and elemental composition among equiaxed polygonal grains, rod-shaped grains, and rhombic grains, transmission electron microscopy (TEM) analysis was performed on the three grain regions in 0.92BNBT-0.08ST ceramics. Elemental distribution was investigated using surface scanning and point scanning methods, such as... Figure 5 and Figure 6 As shown.

[0050] The results showed that the elemental distribution in the TEM and SEM surface scan images was consistent. Subsequently, point scans were performed on the rod-shaped and rhombic grains to obtain the atomic percentages of each element (see Tables 4.1 and 4.2). Based on the atomic percentages, the chemical formulas of the rod-shaped and rhombic grains were determined to be Ba(TiO3) and BaNa, respectively. 1.8 Bi 2.2 (Ta 1.5 Ti 3.5 )O 15.95 (BNBTT). The chemical formula of the rhombic grains is close to that of BaBi4Ti4O. 15 (BBT), but different from the third phase Bi in XRD analysis 1.86 Ti2O 6.884 Not entirely corresponding REF _Ref192444505 \r \h \* MERGEFORMAT

[135] This difference may be attributed to the similarity in diffraction patterns corresponding to the crystal structures of the two. Further SAED tests were performed on the rod-shaped and rhombic grain regions, revealing that the crystal structure of the rod-shaped grains is consistent with Ba(TiO3), while the rhombic grains are consistent with BBT. This is consistent with the aforementioned analytical results.

[0051] Table 4.1 Peak fitting results of rod-shaped grains Element Weight (%) Atomic (%) Uncert. (%) k-Factor O(K) 14.63 47.97 0.15 1.889 Na(K) 0.64 1.47 0.03 1.174 Ti(K) 26.15 28.63 0.20 1.227 Ba(L) 54.00 20.61 0.27 3.148 Sm(L) 0.44 0.15 0.04 3.369 Ta(L) 3.05 0.88 0.07 3.811 Bi(L) 1.05 0.26 0.05 4.797 Based on the above results, it can be inferred that the rod-shaped and rhombic grains are physically similar to BaTiO3 and BaBi4Ti4O3, respectively. 15 REF _Ref192444524 \r \h \* MERGEFORMAT It has played an important role in regulating the energy storage performance of ceramic samples and provided new insights for optimizing ceramic energy storage materials.

[0052] Table 4.2 Peak fitting results of rhombic grains Element Weight (%) Atomic (%) Uncert. (%) k-Factor O(K) 30.34 74.42 0.39 1.889 Na(K) 2.71 4.63 0.09 1.174 Ti(K) 10.71 8.77 0.24 1.227 Ba(L) 9.58 2.73 0.25 3.148 Sm(L) 2.75 0.71 0.14 3.369 Ta(L) 16.01 3.47 0.31 3.811 Bi(L) 27.87 5.23 0.47 4.797 4.3.6 Relaxation Behavior Analysis Figure 7 (a) shows the ε of (1-x)BNBT-xST ceramic at 100 kHz. r The relationship between ε and tanδ as a function of temperature. With increasing doping concentration, ε... m The dielectric gradually decreases while the dielectric plateau widens, indicating a reduction in polarity coupling. This phenomenon can be attributed to Sr 2+ and Ta 5+ The introduction of these substances leads to cation disorder and charge fluctuations, thereby enhancing relaxation behavior. REF _Ref192444539 \r \h \* MERGEFORMAT] . Figure 7 (b) further demonstrates the stability of the dielectric constant of the sample in the frequency range of 1 kHz to 1000 kHz, while tanδ remains at a low level throughout, indicating that the ceramic sample has excellent insulation properties and thermal stability. In addition, the relaxation degree (γ) was determined by a modified Curie-Weiss law, where a γ value between 1 and 2 indicates that the material is in a relaxed ferroelectric state.

[0053] The calculated γ is as follows Figure 7 As shown in (c), the density of states is 1.91 at x=0.04, 1.95 at x=0.08, and 1.99 at x=0.10, indicating that the material has strong relaxation characteristics. First-principles calculations based on DFT further theoretically verified the relaxation enhancement behavior and its correlation mechanism with bandgap changes. The projected density of states of BNBT and its A-site / B-site doped ceramics are shown in (c). Figure 7As shown in (d), for pure BNBT, the valence band is mainly contributed by the cooperative hybridization of O 2p orbitals and the 3d and 6s orbitals of Ti and Bi ions, while the conduction band bottom (CBM) is mainly composed of Bi 6s and O 2p states. Strong hybridization between Ti 3d and Bi 6p states and O 2p states forms a high conduction band in the 2-3 eV range, while the valence band top (VBM) is mainly contributed by Ti 3d states. Near the CBM, the density of d orbitals at B sites is higher than that of O 2p orbitals, while near the VBM, this trend is reversed, indicating the electron transition process from the valence band to the conduction band. In Sm and Ta-doped BNBT, the hybridization characteristics near the CBM are similar to those in pure BNBT, while near the VBM, the main contribution to the conduction band comes from Ti 3d and Ta 5d states. Compared to BNBT, the PDOS distribution of the doped system extends to a higher energy range. This distribution reduces the role of d-orbital hybridization of B-site Ti in maintaining ferroelectric stability, leading to a weakening of ferroelectricity and thus inducing the coupled relaxation behavior observed in BNBT-ST ceramics. (Selected area electron diffraction (SAED) pattern) Figure 7 (e) further verified the relaxation behavior of the ceramic at x=0.08.

[111] c The SAED image shows typical 1 / 2{ooe} superlattice diffraction spots (where o and e represent odd and even Miller indices, respectively), indicating the presence of the T phase in the sample. Meanwhile, in

[110] c A small amount of R phase was observed in the SAED image, characterized by weak 1 / 2{ooo} superlattice diffraction spots. Further calculations of the interplanar spacing ( Figure 7 The results (f) show that d(001) and d(110) are 0.3878 nm and 0.2748 nm, respectively, which are consistent with the interplanar spacing of the C phase, thus confirming the multiphase coexistence structure in the 0.92BNBT-0.08ST ceramic.

[0054] Energy storage performance analysis like Figure 8 As shown in (a)-(b), the unipolar PE loop and its corresponding W of (1-x)BNBT-xST ceramic under the critical electric field are... rec The analysis was performed on η. This was due to the large polarization hysteresis and low E. b The ceramic with x=0.04 exhibits a lower W. rec and E b As x increases, W rec and E b All showed varying degrees of growth. In particular, when x=0.08, the 0.92BNBT-0.08ST ceramic achieved 9.8 J / cm² at an ultra-high electric field of 693 kV / cm. 3The ultra-high energy storage density is likely due to the presence of a third phase and changes in the rod-shaped grain morphology in the ceramic sample. However, with further increases in ST doping, the W of the ceramic sample... rec The abnormal decrease was mainly attributed to P. max and E b The value of η decreased significantly. Nevertheless, as x increases, the η of the ceramic sample shows a continuous increasing trend, indicating that its relaxation behavior is enhanced. Figure 8 (c) shows the Weber distribution of different ceramic samples. The β value of all samples is greater than 10, indicating that the measured E b It has high reliability and average E b It reaches its maximum value at x=0.08, which is consistent with the PE test results. Furthermore, the Esample was obtained by measuring the UV-Vis absorption spectrum and fitting it. g The result is as follows Figure 8 As shown in (d). The E of the sample at x=0.08 g It reached its maximum value (2.834 eV), and the E values ​​of other samples were also higher. g The trend of change and its corresponding E b The patterns of change are consistent. Generally, higher E values... g The values ​​indicate that the sample has a larger band gap, making it more difficult for electrons to transition from the valence band to the conduction band, thus achieving a higher breakdown strength. To further investigate the excellent energy storage performance of 0.92BNBT-0.08ST ceramic, its PE curve and corresponding W were measured under different electric fields. rec And efficiency, the results are as follows Figure 8 As shown in (e)-(f), the W of the 0.92BNBT-0.08ST ceramic increases from 100 kV / cm to 690 kV / cm. tot and W rec From 0.39 J / cm 3 and 0.34 J / cm 3 Gradually increased to 9.8 J / cm 3 and 11.7 J / cm 3 And P r Maintaining a small electric field value throughout the test range is beneficial for sustaining a large ΔP, thus achieving a fine PE loop. Furthermore, research on BNT-BT-based ceramics shows that co-doping with Ta significantly improves the W of the ceramic compared to Sm doping alone. rec η and E b ,like Figure 8 As shown in (g). By co-doping ST into 0.94BNT-0.06BT ceramics, W rec η and E bThe increases were approximately 612%, 179%, and 531%, respectively. Figure 8 (h) gives the W between x=0.3 ceramic and current lead-free dielectric ceramic. rec Comparison. Achieving high W in BNBT-ST binary ceramics with relatively simple chemical composition. rec In stark contrast to the current situation where high energy storage performance requires extremely complex components, this highlights the enormous potential of binary ceramics in energy storage applications.

[0055] PFM Analysis The formation of nanoscale domains (PNRs) is crucial for achieving excellent overall energy storage performance in the RFE (Resource-Free Energy) model. To further investigate nanoscale domains and their dynamic response, PFM (Programmable Magnetic Membrane) tests were conducted. These tests were performed on nanoscale domains at a density of 10 × 10 μm. 2 Different voltages (+15 V, +30 V, +60 V, +90 V) were applied to the square surface area of ​​ceramics with x=0.04 and x=0.08, and the domain structure evolution was obtained. For the x=0.08 ceramic, its out-of-plane phase diagram showed that due to the low energy barrier and strong dynamic characteristics of PNRs and nanodomains, some domains could switch at low voltage. When the voltage increased to above 30 V, most nanodomains flipped, and with further increases in voltage, a stronger piezoelectric response could be observed in the amplitude and phase images. Notably, after the external electric field was removed, the flipped domains could quickly recover to their initial state. After 5 minutes of relaxation, the domain structure of the polarized sample was almost identical to that of the unpolarized sample. These results indicate that the gradual enhancement of the local random field and the reduction of the hysteresis effect enable the PNRs and nanodomains in the x=0.08 ceramic to exhibit highly dynamic characteristics, contributing to its excellent overall energy storage performance. In contrast, the domains in the x=0.04 ceramic exhibited more stable characteristics and were difficult to recover to their initial state quickly. These phenomena indicate that the introduction of ST significantly disrupts the long-range ferroelectric domains in the BNBT matrix. Although similar domain structures exist in both ceramics, the dynamic response of the domains is enhanced with increasing ST content, thereby effectively reducing P. r This plays a crucial role in improving ESPs.

[0056] Breakdown field strength enhancement mechanism In addition to high dynamic PNRs and nanodomains, there is a huge E of approximately 690 kV / cm. b For achieving ultra-high W in ceramics with x=0.08 rec This is also crucial because it is a necessary condition for obtaining high electric fields in large ΔP and PE loops. It is well known that many factors affect the E of dielectric ceramics. bFactors affecting the electrical properties of ceramics include grain size, porosity, band gap, electrical conductivity, second phase (impurities), and sample thickness. To further investigate the influence of grain size and shape, as well as other factors, on the electrical properties of ceramics, finite element analysis (FEM) calculations were performed on 0.96BNBT-0.04ST and 0.92BNBT-0.08ST ceramics. FEM-based simulations were used to visualize the electric field, potential, and polarization distribution of electric tree propagation under an external electric field. This model primarily considers the physical properties and microstructure characteristics of the material to further simulate the most realistic results. Typically, grains and grain boundaries exhibit weak and strong electric field concentrations, respectively, due to the ε-coefficient of electric field concentration. r Higher, while the ε of the grain boundaries is higher. r The lower voltage significantly affects the formation of breakdown paths. Under an applied electric field, electrical dendrites typically begin to grow from the grain region, and their growth is hindered when the breakdown path encounters grain boundaries. At an electric field strength of 690 kV / cm, 0.96BNBT-0.04ST ceramics achieved complete breakdown, while 0.92BNBT-0.08ST ceramics did not. Furthermore, the number of electrical dendrite branches inside 0.92BNBT-0.08ST ceramics was significantly greater than that in 0.96BNBT-0.04ST ceramics, indicating that the grain boundaries and grains in the former have a stronger hindering effect on electrical dendrite growth. Due to the presence of rod-shaped grains, a large number of small dendrites are generated during electrical dendrite growth, resulting in significant energy loss and affecting energy dispersion performance. Therefore, compared with pure BNBT ceramics without rod-shaped grains, rod-shaped grains hinder the evolution of electrical dendrites. Although rod-shaped grains have a higher dielectric constant than equiaxed grains, their unique shape significantly hinders the growth of electrical trees. The role of rhombic grains in 0.92BNBT-0.08ST ceramics was also investigated. The study showed that rhombic grains (BNBTT) have a much lower dielectric constant than ordinary grains, thus enabling them to withstand higher voltages than equiaxed grains. The x=0.08 ceramic had the smallest average grain size, resulting in the highest grain boundary density among all samples. These properties indicate that in 0.92BNBT-0.08ST ceramics possessing both rod-shaped and rhombic grains, these factors work together to significantly improve the dielectric constant (E0.08). b This achieves a qualitative leap in energy storage performance. The 0.92BNBT-0.08ST ceramic exhibits a more uniform potential distribution at the tip of the electric tree, indicating that the potential difference gradually decreases due to energy dissipation, effectively mitigating the phenomenon of excessive local electric field concentration. The sample, near E... bThe polarization distribution at different critical electric fields is observed. Notably, during breakdown, the polarization distribution of the x=0.04 sample exhibits significant inhomogeneity, accompanied by marked localized polarization enhancement. Even at higher critical electric fields, the x=0.08 sample maintains a uniform polarization distribution, further demonstrating the intrinsic reason for its enhanced breakdown field strength. It is noteworthy that the increased presence of rod-shaped and rhombohedral grains leads to a gradual decrease in sample density and a corresponding increase in porosity, which has a significant impact on E. b The increase in [something] has an adverse effect. Furthermore, the average size of equiaxed grains also increases accordingly. The combined effect of these factors leads to a decrease in the E [something] of ceramic samples with x > 0.08. b The decline.

[0057] The above describes a Na with a heterostructure provided in the embodiments of this application. 0.5 Bi 0.5 The preparation of TiO3-based energy storage dielectric ceramics is described in detail. The above descriptions of the embodiments are merely for the purpose of helping to understand the methods and core ideas of this application; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0058] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0059] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0060] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0061] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A Na with a heterostructure 0.5 Bi 0.5 TiO3-based energy storage medium ceramic, characterized in that... The general structural formula of the energy storage medium ceramic is: (1-x)(Bi) 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-xSm 1 / 3 TaO3, wherein 0.04 ≤ x < 0.16; the energy storage medium ceramic has a multiphase polycrystalline structure; the relaxation value of the energy storage medium ceramic is γ = 1.91-2; the maximum total energy storage density of the energy storage medium ceramic under an ultra-high electric field of 693 kV / cm is 11.7 J / cm³. 3 The maximum recoverable energy storage density is 9.8 J / cm³. 3 The energy storage efficiency is 83.3%.

2. The energy storage medium ceramic according to claim 1, characterized in that, The polycrystalline structure includes a main crystalline phase, a second phase, and a third phase; the main crystalline phase is a perovskite pseudocubic structure; the second phase consists of rod-shaped grains; and the third phase consists of rhombic grains.

3. The energy storage medium ceramic according to claim 2, characterized in that, The chemical formula of the rod-shaped grains is BaTiO3, and the chemical formula of the rhombic grains is BaNa. 1.8 Bi 2.2 (Ta 1.5 Ti 3.5 )O 15.95 .

4. The energy storage medium ceramic according to claim 1, characterized in that, When x = 0.04, the general structural formula of the energy storage medium ceramic is: 0.96(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.04Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.86, and its maximum total energy storage density is 9.04 J / cm² under a high electric field of 480 kV / cm. 3 The maximum recoverable energy storage density is 6.9 J / cm³. 3 The energy storage efficiency is 76.8%.

5. The energy storage medium ceramic according to claim 1, characterized in that, When x = 0.08, the general structural formula of the energy storage medium ceramic is: 0.92(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.08Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.93, and its maximum total energy storage density is 11.7 J / cm² under an ultra-high electric field of 693 kV / cm. 3 The maximum recoverable energy storage density is 9.8 J / cm³. 3 The energy storage efficiency is 83.3%.

6. The energy storage medium ceramic according to claim 1, characterized in that, When x = 0.10, the general structural formula of the energy storage medium ceramic is: 0.90(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.10Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.99, and its maximum total energy storage density is 8.66 J / cm² under a high electric field of 620 kV / cm. 3 The maximum recoverable energy storage density is 7.3 J / cm³. 3 The energy storage efficiency is 84.6%.

7. The energy storage medium ceramic according to claim 1, characterized in that, When x=0.12, the general structural formula of the energy storage medium ceramic is: 0.88(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.12Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.92, and its maximum total energy storage density is 7.65 J / cm² under a high electric field of 620 kV / cm. 3 The maximum recoverable energy storage density is 6.6 J / cm³. 3 The energy storage efficiency is 86.2%.

8. The energy storage medium ceramic according to claim 1, characterized in that, When x = 0.16, the general structural formula of the energy storage medium ceramic is: 0.84(Bi 0.5 Na 0.5 ) 0.96 Ba 0.04 TiO3-0.16Sm 1 / 3 The energy storage medium ceramic, TaO3, has a relaxation value γ of 1.92, and its maximum total energy storage density is 6.07 J / cm² under a high electric field of 660 kV / cm. 3 The maximum recoverable energy storage density is 5.4 J / cm³. 3 The energy storage efficiency is 89.6%.

9. A method for preparing an energy storage medium ceramic as described in any one of claims 1-8, characterized in that, The method specifically includes the following steps: S1) Weigh out Na2CO3, Bi2O3, BaCO3, TiO2, Sm2O3 and Ta2O5 according to the design ratio of the general structural formula, and set aside for later use; S2) Place the raw materials weighed in S1) into a ball mill jar, add 70 mL of anhydrous ethanol as the ball milling medium, and use a planetary ball mill with zirconia balls to ball mill for 16-24 h to ensure that the raw materials are fully mixed and uniform, and obtain a mixed slurry; dry the obtained mixed slurry, and grind and mix it using a mortar and pestle. The powder after sieving is shaped under a pressure of 5 MPa, the shaped block is placed in a crucible, and calcined using a box furnace to obtain a first-calcined block; S4) After the first-calcined block obtained in S3) is initially ground in a mortar, the process of S3) is repeated to obtain the second-calcined block; S5) The calcined block obtained in S4) is placed in a mortar, a binder is added, and the mixture is ground to obtain powder. The powder is then sieved and pre-pressed under a pressure of 5 MPa. The block is then crushed, ground again, and sieved. The sieved powder is pressed into discs using a mold with a diameter of 10 / 15 mm under a pressure of 2.5 MPa. S6) The shaped disc obtained in S5) is placed in a box-type high-temperature furnace and heated to 610 ℃ at a heating rate of 1.5 ℃ / min and held for 300 min to remove the added organic binder; S7) The discs treated in S6) are placed in a crucible covered with ZrO2 powder and sintered in a box furnace to obtain energy storage medium ceramics with high density.

10. The method according to claim 9, characterized in that, The sintering process parameters in S2) and S7) are: heating to 850 ℃ at a heating rate of 3 ℃ / min and holding for 2 h.

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