Sodium bismuth titanate-based lead-free energy storage ceramic and preparation method thereof

Abstract

The application belongs to the technical field of lead-free energy storage ceramics, and discloses a sodium bismuth titanate-based lead-free energy storage ceramic and a preparation method. 0.47 Na 0.47 Ba 0.06 )TiO3 matrix, and the ceramic can release energy storage density and energy storage efficiency which are significantly improved, and has high breakdown field and good temperature stability, and the comprehensive performance is better than that of the same kind of material prepared by a conventional solid-phase method in the prior art. 0.06 1‑x Sr x (Ti 1‑x Mg x / 3 Nb 2x / 3 )O3, wherein 0.06≤x<0.18. The preparation method comprises the following steps: mixing raw materials, performing first ball milling, drying, pre-sintering, performing second ball milling, drying, forming, degumming, and finally performing segmented sintering; wherein the segmented sintering is: first heating to 1000 DEG C at a heating rate of 5 DEG C / min, and then heating to 1100-1150 DEG C at a heating rate of 3 DEG C / min and keeping the temperature. The application introduces Sr, Mg and Nb elements with different ferroelectric activities into the (Bi 0.47 Na 0.47 Ba 0.06

Description

Technical Field

[0001] This invention relates to the field of dielectric energy storage ceramics technology, specifically to sodium bismuth titanate-based lead-free energy storage ceramics and their preparation methods. Background Technology

[0002] Dielectric ceramic energy storage materials have important applications in pulsed power systems due to their high power density, fast charge-discharge characteristics, and excellent stability, such as electromagnetic weapons, medical defibrillators, new energy vehicles, and industrial processing equipment. Ideal energy storage ceramics must simultaneously possess high breakdown field strength, high releaseable energy density, and high energy storage efficiency to meet the demands of compact and highly reliable electronic devices. In lead-free energy storage ceramic systems, barium titanate (BaTiO3)-based, potassium sodium niobate (KNN)-based, and sodium bismuthate (Bi)-based materials are commonly used. 0.47 Na 0.47 Ba 0.06 Barium titanate (BNBT) based materials are currently a hot research topic. Among them, barium titanate-based ceramics have attracted attention early on due to their high dielectric constant and ferroelectricity, but their low breakdown field strength and energy storage density limit their practical applications.

[0003] To improve the energy storage performance of BNBT-based ceramics, the existing technologies mainly adopt the following strategies: (1) Element doping modification: Chinese patent CN104891989A discloses a Sr x (Bi0. 47 Na0. 47 Ba0. 06 ) 1-x M x Ti 1-x O3 ceramics, in which M includes options such as (Mg1 / 3Nb2 / 3), are prepared by spark plasma sintering (SPS). Although this method achieves certain ferroelectric properties, its energy storage density is only 1.56 J / cm³ (when x=0.12), which is still far from the actual application requirements. In addition, the SPS process equipment is expensive and difficult to scale up, which limits its industrial application. (2) Traditional solid-state method: The traditional solid-state method for preparing BNBT-based ceramics usually adopts a single ball milling and direct heating sintering process. For example, the batching-pre-firing-ball milling-pressing-sintering process disclosed in CN118894722A is simple, but the resulting ceramics have an uneven microstructure, with pores and abnormal grain growth, resulting in a low breakdown field strength (usually <300 kV / cm) and an energy storage density that is difficult to exceed 5 J / cm³.

[0004] In summary, the existing technologies still have the following technical problems: (1) Element doping and process disconnect: Although some studies have disclosed the doping scheme of (Mg1 / 3Nb2 / 3) composite ions, they have not disclosed how to control the uniform distribution and specific occupancy of the composite ions in the matrix through conventional solid-state process, resulting in limited performance improvement; (2) High cost and complex process: Although the use of Ta element or special processes such as SPS and tape casting can improve performance, the cost is high and industrialization is difficult; (3) Difficulty in microstructure control: Traditional processes are difficult to form uniformly sized and evenly distributed nanoscale polar microregions in BNBT matrix, and cannot simultaneously achieve high polarization intensity and low hysteresis loss.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] To address the problems in the background art, the present invention provides a sodium bismuth titanate-based energy storage ceramic and its preparation method, which has both high energy storage density and high energy storage efficiency.

[0007] To achieve the above objectives, the first technical solution adopted by the present invention is as follows: Sodium bismuth titanate energy storage ceramics, with the general formula: (Bi 0.47 Na 0.47 Ba 0.06 ) 1-x Sr x (Ti 1-x Mg x / 3 Nb 2x / 3 O3, where 0.06 ≤ x 0.18; The ceramic preparation method includes the following steps: mixing the raw materials and then ball milling them for the first time, drying and pre-firing them, then ball milling them for the second time, drying and shaping them and then removing the binder, and finally sintering them in sections. The segmented sintering process involves first heating to 1000°C at a heating rate of 5°C / min, then heating to 1100-1150°C at a heating rate of 3°C / min and holding at that temperature.

[0008] Preferably, x=0.14.

[0009] Preferably, the ceramic has polar nanoregions with a size of 1-2 nm and exhibits relaxed state characteristics under a piezoelectric response force microscope, without obvious long-range ordered domain contrast.

[0010] The second technical solution adopted in this invention is: The preparation method of sodium bismuth titanate energy storage ceramics includes: After mixing the raw materials, the mixture is ball-milled for the first time, dried and pre-fired, then ball-milled for the second time, dried and shaped, and then debinded. Finally, the mixture is sintered in sections. The segmented sintering process involves first heating to 1000°C at a heating rate of 5°C / min, then heating to 1100-1150°C at a heating rate of 3°C / min and holding at that temperature.

[0011] Preferably, the raw materials are Na2CO3, SrCO3, BaCO3, MgO, Nb2O5, TiO2 and Bi2O3.

[0012] Preferably, anhydrous ethanol is used as the milling medium for the first ball milling, and the milling time is 12-14 hours.

[0013] Preferably, the second ball milling time is 10-12 hours.

[0014] Preferably, the pre-firing method is to heat the room temperature to 800-850°C at a heating rate of 3°C / min, hold the temperature at the highest temperature for 4-6 hours, and then allow it to cool naturally.

[0015] Preferably, the heat preservation time at 1100-1150℃ is 120-180 min.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes (Bi) with high polarization intensity 0.47 Na 0.47 Ba 0.06 The TiO3 matrix was doped with Sr, Mg and Nb elements with different ferroelectric activities. By controlling the doping amount and using a process that combines two ball millings with specific segmented sintering (heating to 1000℃ at 5℃ / min and then to 1100-1150℃ at 3℃ / min), the ceramic prepared can release energy density and energy storage efficiency are significantly improved. At the same time, it has a high breakdown field and good temperature stability. Its comprehensive performance is better than that of similar materials prepared by conventional solid-state methods in the prior art.

[0017] This invention ensures thorough refinement and uniform mixing of raw materials through two ball milling processes (first 12-14 h, second 10-12 h), particularly ensuring uniform dispersion of (Mg1 / 3Nb2 / 3) composite ions. Segmented heating sintering (fast at first, then slow) achieves initial grain densification at 1000℃, and controls uniform grain growth at 1100-1150℃, avoiding abnormal grain growth and residual pores. The resulting ceramic exhibits a breakdown field strength ≥400 kV / cm, significantly higher than samples prepared using traditional processes, which is crucial for achieving high energy density. Attached Figure Description

[0018] Figure 1(a) The figure shows the hysteresis loop of the ceramic samples in experimental groups 1-4 under the maximum electric field. (b) The energy storage density and efficiency of the ceramic samples in experimental groups 1-4 under the maximum electric field. Figure 2 (ab) shows the amplitude and phase diagrams of the ceramics in experimental group 1, and (cd) shows the amplitude and phase diagrams of the ceramics in experimental group 3. Figure 3 The results are the STEM test results for experimental group 3. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to specific implementation examples. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the following description, to avoid unnecessary obscuring of the core concepts of this invention, structural and technical details well-known to those skilled in the art will not be repeated. Where experimental conditions are not explicitly specified in the embodiments, they are performed according to conventional experimental conditions in the art or conditions recommended by the equipment manufacturer. Unless otherwise specified, the reagents and instruments involved are all commercially available products.

[0020] The present invention provides a sodium bismuth titanate energy storage ceramic, the general formula of which is: (Bi 0.47 Na 0.47 Ba 0.06 ) 1-x Sr x (Ti 1-x Mg x / 3 Nb 2x / 3 O3, where 0.06 ≤ x 0.18; The ceramic preparation method includes the following steps: mixing the raw materials and then ball milling them for the first time, drying and pre-firing them, then ball milling them for the second time, drying and shaping them and then removing the binder, and finally sintering them in sections. The segmented sintering process involves first heating to 1000°C at a heating rate of 5°C / min, then heating to 1100-1150°C at a heating rate of 3°C / min and holding at that temperature.

[0021] This invention utilizes (Bi) with high polarization intensity 0.47 Na 0.47 Ba 0.06The TiO3 matrix is ​​doped with Sr, Mg, and Nb elements, which have different ferroelectric activities. By controlling the doping amount, local polarization fluctuations can be achieved in the ceramic, where ultra-weak polarity regions and short-range polarity regions coexist. This local polarization fluctuation refers to the simultaneous existence of ultra-weak polarity regions (regions with extremely weak polarization induced by Mg doping) and short-range polarity regions (regions with short-range ordered polarization but no long-range ferroelectric domain structure induced by Nb doping) within the material at the nanoscale. These two regions are spatially alternating, coexisting, and coupled, forming a dynamic polarization fluctuation state. This structure differs from traditional ferroelectric domains and simple relaxation states; it is a multi-scale polarity coexistence state. This coexisting local polarization fluctuation exhibits good flexibility, enabling rapid polarization reversal upon application of an electric field and rapid recovery after removal of the electric field, thus achieving high polarization intensity and low hysteresis.

[0022] To ensure the formation of the specific local polarization wave structure described above, the preparation method of this ceramic needs to be precisely controlled, requiring two ball milling processes and segmented sintering.

[0023] Specifically, after mixing the raw materials, the purpose of the first ball milling is to achieve uniform mixing and particle size reduction of the primary powder. After the first ball milling, pre-calcination is performed. The pre-calcined powder exhibits hard agglomerates, and the (Mg / Nb) composite ions need to be more uniformly dispersed around the Ti sites. Therefore, a second ball milling is necessary. This second ball milling is essential for forming localized polarization fluctuations: only through sufficient secondary ball milling can the uniform mixing of Mg and Nb at the atomic scale be ensured, thereby forming uniformly sized ultra-weakly polar regions and short-range polar regions after sintering. If this step is omitted, the uneven distribution of Mg and Nb will lead to excessively large or unevenly distributed polar regions, forming traditional ferroelectric domains, losing the characteristics of localized polarization fluctuations, and significantly reducing the energy storage density.

[0024] Then, after molding and debinding, segmented sintering is performed. Segmented sintering is a key step in forming localized polarization fluctuations, employing a segmented heating method: First stage: heating to 1000℃ at 5℃ / min, achieving initial densification of the green body; grains begin to form but have not yet grown rapidly. Second stage: heating to 1100-1150℃ at 3℃ / min, holding for 120-180 min. During the heating process from 1000℃ to 1100-1150℃, the relatively slow heating rate (3℃ / min) provides sufficient kinetic conditions for the diffusion and occupancy of Sr, Mg, and Nb in the crystal lattice. In particular, the random occupancy of Mg and Nb at B sites and the substitution of Sr at A sites, within this temperature range, by controlling the heating rate and holding time, forms polar nanoregions with a size of 1-2 nm, namely the aforementioned ultra-weakly polar region and short-range polar region. If a direct and rapid heating method is used (e.g., directly heating to 1150℃ at 5℃ / min), the grains will grow too fast, and the polar regions will merge and grow to form stable ferroelectric domains, which will disrupt the local polarization fluctuations, resulting in increased hysteresis and reduced efficiency.

[0025] For the raw materials, Na2CO3, SrCO3, BaCO3, MgO, Nb2O5, TiO2 and Bi2O3 are weighed according to the stoichiometric ratio. The purity of each raw material is preferably ≥99% to reduce impurities.

[0026] For the first ball milling, a conventional planetary ball mill can be used, with anhydrous ethanol as the medium and zirconia balls as the grinding balls. In some preferred embodiments, a rotation speed of 250 r / min and a time of 12-14 h can ensure thorough mixing of the raw materials.

[0027] For pre-calcination, it is preferable to pre-calcine the dried powder at 800-850℃ for 4-6 h, with a heating rate of 3℃ / min. The purpose of this step is to decompose the carbonate and form a perovskite phase precursor.

[0028] For the second ball milling, the preferred time is 10-12 hours.

[0029] For molding and debinding, the conventional method of adding 8 wt% PVA binder for granulation, pressing and molding (10 MPa), and then debinding at 850℃ for 120 min, followed by slow heating (17-19 h).

[0030] The ceramics prepared by the above process, according to STEM results, show that: along the

[001] zone axis, polar nano-regions with a size of about 1-2 nm are visible. The atomic displacement vector diagram shows that the local structure exhibits multiple symmetries coexisting, and the polarization intensity is significantly inconsistent in space, exhibiting strong polarization fluctuations. PFM results show that the amplitude diagram presents "ice-sand-like" dotted signals, and the phase diagram does not show obvious long-range ordered domain contrast, exhibiting typical highly relaxed state characteristics. This microstructure indicates that the polar structure is in a highly dynamic polarization fluctuation state, without stable ferroelectric domains, and can achieve rapid polarization reversal under the action of an external electric field and recover quickly after the field is removed.

[0031] To make the present invention clearer, the following detailed description of lead-free sodium bismuth titanate energy storage ceramics and their performance is provided through several specific embodiments.

[0032] Example 1 Sodium bismuth titanate-based lead-free energy storage ceramics, with the general formula: (Bi 0.47 Na 0.47 Ba 0.06 ) 1-x Sr x (Ti 1-x Mg x / 3 Nb 2x / 3 O3. Multiple specific instances are set up as follows: Experimental group 1: x=0.06; Experimental group 2: x=0.10; Experimental group 3: x=0.14; Experimental group 4: x=0.18.

[0033] The preparation method of sodium bismuth titanate-based lead-free energy storage ceramics is as follows: (1) Ingredient preparation and ball milling Na₂CO₃ (99.8%), SrCO₃ (99%), BaCO₃ (99%), MgO (99%), Nb₂O₅ (99.95%), TiO₂ (99.9%), and Bi₂O₃ (99.999%) were used as raw materials and mixed separately according to stoichiometric ratios. After mixing, anhydrous ethanol was used as the ball milling medium, and the mixture was ball-milled in a planetary ball mill at a speed of 250 r / min for 12-14 h.

[0034] (2) Pre-firing and secondary ball milling The thoroughly mixed slurry was dried and transferred to a crucible. The temperature was increased from room temperature to 850°C at a rate of 3°C / min, and then held at the highest temperature for 6 hours before being allowed to cool naturally. The pre-calcined powder was then subjected to a second ball milling process for 12 hours to refine the powder particles and ensure uniform mixing.

[0035] (3) Mechanical forming After drying the well-mixed slurry, add an appropriate amount of 8wt% polyvinyl alcohol (PVA) aqueous solution and mix thoroughly. Sift the dried powder, then use a mold and tablet press to press it into discs with a diameter of approximately 8mm and a thickness of approximately 1mm under a pressure of 10MPa. Place the pressed discs in a muffle furnace and slowly heat to 850℃ over 17-19 hours, hold for 120 minutes, and then allow to cool naturally. This slow heating and long holding time ultimately removes excess adhesive and moisture from the discs, achieving the debinding step.

[0036] (4) Sintering After debinding, the disc is first heated to 1000℃ at a heating rate of 5℃ / min, then heated to 1120℃ at a heating rate of 3℃ / min, held at that temperature for 120 minutes, and then cooled in the furnace.

[0037] The performance of the lead-free sodium bismuth titanate energy storage ceramics prepared in the above experimental groups was tested, and the results are as follows: Figure 1 As shown.

[0038] like Figure 1 As shown, the polarization intensity and hysteresis generally decrease with increasing doping concentration. When the doping concentration x increases from 0.06 to 0.18, the maximum polarization intensity gradually decreases from 61.2 μC cm⁻² to 46.3 μC cm⁻², and the hysteresis correspondingly decreases from 8.8 μC cm⁻² to 4.0 μC cm⁻². Notably, the breakdown field strength first increases and then decreases with doping concentration, reaching a peak of 560 kV cm⁻¹ at x=0.14, which is the highest value among all concentrations. This demonstrates that doping is beneficial for ceramics to achieve good energy storage performance.

[0039] Piezoelectric force microscopy (PFM) tests were performed on experimental groups 1 and 3 to observe the domain configuration of the ceramic samples. The results are as follows: Figure 2 As shown in the diagram, (a) and (c) are the piezoelectric response diagrams (Amplitude), and (b) and (d) are the phase diagrams (Phase). It can be observed that the domain configuration of the ceramic in experimental group 1 is a fine, fragmented nanodomain resembling ice crystals. The domain configuration of the ceramic in experimental group 3 exhibits typical highly relaxed state characteristics; the phase diagram shows no obvious long-range ordered domain contrast, indicating that it possesses highly dynamic polarization response behavior.

[0040] Scanning transmission electron microscopy (STEM) was performed on experimental group 3 to observe the local polar structure of the ceramic samples. The results are as follows: Figure 3As shown in Figure (a), the atomic structure of the ceramic along the 001 zone axis is shown in Figure (b). The atomic displacement vector can be calculated by determining the offset of the B / A site atom from the centers of the four adjacent A / B site atom atoms. The mapping of the atomic displacement vector is shown in Figure (b). It can be observed that the local structure exhibits multiple symmetries, and the size of the polar nanoregions is about 1-2 nm. Different regions show significant inconsistencies in polarization intensity, exhibiting strong polarization fluctuations. This polarization structure is easily rotated by electric field disturbances, thus promoting polarization. When polarization reorientation occurs under an external field, stable bulk domains are not formed. After the electric field is removed, the initial state can be quickly restored, thus obtaining large polarization and small hysteresis. Therefore, this is beneficial for ceramic samples to achieve good energy storage performance.

[0041] Finally, it should be noted that the above embodiments are only used to explain the technical solutions of the present invention and are not intended to limit the scope of protection thereof. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical details stated in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lead-free energy storage ceramic based on sodium bismuth titanate, characterized in that, Its general formula is: (Night 0.47 In 0.47 Consider 0.06 ) 1-x Sr x (A 1-x Mg x / 3 Nb 2x / 3 )O3, 0.06≤x<0.18; The ceramic preparation method includes the following steps: mixing the raw materials and then ball milling them for the first time, drying and pre-firing them, then ball milling them for the second time, drying and shaping them and then removing the binder, and finally sintering them in sections. The segmented sintering process involves first heating to 1000°C at a heating rate of 5°C / min, then heating to 1100-1150°C at a heating rate of 3°C / min and holding at that temperature.

2. The sodium bismuth titanate lead-free energy storage ceramic as described in claim 1, characterized in that, x=0.14。 3. The sodium bismuth titanate lead-free energy storage ceramic as described in claim 1, characterized in that... The ceramic has polar nanoregions with a size of 1-2 nm and exhibits relaxed state characteristics under piezoelectric response force microscopy, without obvious long-range ordered domain contrast.

4. The method for preparing the lead-free sodium bismuth titanate energy storage ceramic as described in any one of claims 1-3, characterized in that, Include: After mixing the raw materials, the mixture is ball-milled for the first time, dried and pre-fired, then ball-milled for the second time, dried and shaped, and then debinded. Finally, the mixture is sintered in sections. The segmented sintering process involves first heating to 1000°C at a heating rate of 5°C / min, then heating to 1100-1150°C at a heating rate of 3°C / min and holding at that temperature.

5. The preparation method according to claim 4, characterized in that, The raw materials are Na2CO3, SrCO3, BaCO3, MgO, Nb2O5, TiO2 and Bi2O3.

6. The preparation method according to claim 4, characterized in that, The first ball milling was performed using anhydrous ethanol as the milling medium, and the milling time was 12-14 hours.

7. The preparation method according to claim 4, characterized in that, The second ball milling time is 10-12 hours.

8. The preparation method according to claim 4, characterized in that, The preheating method involves heating from room temperature to 800-850℃ at a heating rate of 3℃ / min, holding at the highest temperature for 4-6 hours, and then allowing it to cool naturally.

9. The preparation method according to claim 4, characterized in that, The heat preservation time is 120-180 min.

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