A bismuth telluride-based thermoelectric material, a preparation method and application thereof

Abstract

This invention relates to the field of thermoelectric materials technology, and discloses a bismuth telluride-based thermoelectric material, its preparation method, and its applications. It includes a matrix and a dopant material; the matrix is ​​bismuth telluride; the dopant material is selected from binary compound materials. The thermoelectric material of this application improves electrical transport performance and increases the power factor by incorporating binary compound materials into the matrix material and combining zone melting, ultrasonic exfoliation, and hot-pressing sintering processes. It also introduces numerous dislocations, grain boundaries, and other defects to effectively reduce lattice thermal conductivity and optimize thermoelectric performance; simultaneously, it significantly improves the Vickers hardness of the bismuth telluride-based thermoelectric material.

Description

Technical Field

[0001] This invention relates to a bismuth telluride-based thermoelectric material, its preparation method, and its application. This material belongs to the field of thermoelectric materials. Background Technology

[0002] Thermoelectric materials utilize the Seebeck effect to directly convert heat energy into electrical energy. Given the current shortage of fossil fuels and the increasing prominence of environmental pollution problems, thermoelectric materials, as a green, environmentally friendly, and reliable solid-state energy material, have received widespread attention and rapid development in recent years. Achieving high thermoelectric conversion efficiency requires a high thermoelectric figure of merit, ZT = S. 2 σT / κ, where S, σ, T, and κ are the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity, respectively. Therefore, achieving a high ZT value requires high electrical conductivity, a Seebeck coefficient, and low thermal conductivity. However, these three factors are interdependent, which is a major reason why it is currently difficult to significantly improve the ZT value.

[0003] Bi2Te3, as the earliest studied and best-performing near-room temperature thermoelectric material, and currently the only commercially available thermoelectric material, has attracted widespread attention from researchers. The Bi2Te3 crystal structure belongs to the R-3m trigonal crystal system, and viewed along the c-axis, it exhibits a hexahedral layered structure with five layers of atoms arranged in a repeating stacking pattern: Te1-Bi-Te2-Bi-Te1. Bi atoms are covalently bonded to Te atoms, while adjacent Te1 atomic layers are connected by van der Waals forces, making cleavage along the (001) plane very easy. Due to the layered crystal structure of Bi2Te3, its electrical and thermal conductivity exhibit significant anisotropy in both in-plane and out-of-plane directions. For example, the ratio of electrical conductivity parallel to and perpendicular to the bismuth telluride crystal growth direction is 3–7, and the ratio of thermal conductivity is 2–2.5. The Seebeck coefficient is almost isotropic in the eigenregion. Along the crystal growth direction, the increase in electrical conductivity is greater than the increase in thermal conductivity, so strong texture is beneficial for obtaining good thermoelectric figures of merit.

[0004] Compared to p-type bismuth telluride, n-type bismuth telluride exhibits a more pronounced need for texturing. A good degree of texturing is essential for obtaining high-performance n-type bismuth telluride materials. Currently, common methods for preparing n-type bismuth telluride include zone melting and powder metallurgy. While zone-melted n-type Bi₂Te₃ exhibits a high degree of texturing, its high thermal conductivity, poor thermoelectric properties, and poor mechanical properties present significant challenges in device fabrication, limiting its widespread application. Powder metallurgy preparations of n-type bismuth telluride often suffer from "donor-like effects," resulting in carrier concentrations deviating from the optimal range and leading to extremely low thermoelectric performance. Therefore, a process that achieves both high texturing and high mechanical strength is needed to prepare bismuth telluride materials. Summary of the Invention

[0005] Liquid-phase ultrasonic exfoliation technology is mainly based on the ultrasonic cavitation effect. When ultrasound acts on a liquid medium, bubbles dissolved in the liquid will contract under high pressure and expand under low pressure due to the ultrasonic vibration. When the sound pressure is high enough, the bubbles will burst rapidly, a process accompanied by a huge amount of energy. When the bubbles burst on the surface of bismuth telluride, liquid molecules or ions enter the interlayer of bismuth telluride, overcoming the van der Waals forces between the layers to achieve the exfoliation of bismuth telluride into sheet-like structures. At the same time, ultrasonic cavitation is a physical phenomenon that can produce bismuth telluride sheet materials with very few structural defects. It can effectively compensate for the shortcomings of conventional ball milling processes, which introduce too many structural defects into bismuth telluride, disrupting its texture and causing the carrier concentration to deviate from the optimal range, resulting in poor thermoelectric performance. Furthermore, ultrasonic exfoliation technology is inexpensive and is an effective method for large-scale batch production.

[0006] According to one aspect of this application, a bismuth telluride-based thermoelectric material is provided, the bismuth telluride-based thermoelectric material comprising a matrix and a dopant material. This thermoelectric material possesses both good thermoelectric and mechanical properties.

[0007] The matrix is ​​bismuth telluride. It is an N-type thermoelectric material.

[0008] Currently, the commonly referred to bismuth telluride is not just Bi₂Te₃; for the n-type, it is Bi₂Te₃. 3-x Se x , the p-type is Bi x Sb 2-x Te3 is a general term, and the matrix used in this study is Bi2Te. 2.7 Se 0.3 .

[0009] Optionally, the matrix material has the chemical formula Bi2Te. 3-x Se x , where x ranges from 0.1 to 1.0.

[0010] The doping material is selected from binary compound materials.

[0011] The doped material accounts for 0.02 to 10 wt% of the matrix mass.

[0012] Optionally, the doped material may be any value or a range between any two of 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt% of the matrix mass.

[0013] The binary compound material includes metallic elements and halogen elements.

[0014] The metallic element is selected from at least one of bismuth, tellurium, and antimony.

[0015] The halogen element is selected from at least one of fluorine, chlorine, bromine, and iodine.

[0016] Optionally, the binary compound material is selected from BiI3, BiCl3, TeI4, and SbI3.

[0017] According to another aspect of this application, a method for preparing the above-mentioned bismuth telluride-based thermoelectric material is provided, comprising the following steps:

[0018] The raw materials containing elemental tellurium, elemental bismuth, elemental selenium, and dopant materials are mixed, melted, zone-melted, subjected to liquid-phase ultrasonic exfoliation, and sintered to obtain the bismuth telluride-based thermoelectric material. The mixture is then placed under vacuum conditions for further processing.

[0019] The melting temperature is 700–1050°C.

[0020] Optionally, the melting temperature is any value or a range between 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, and 1050°C.

[0021] The melting time is 0.5 to 15 hours.

[0022] Optionally, the melting time is any value or a range between 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, and 15 hours.

[0023] The zone melting temperature is 600–900°C.

[0024] Optionally, the zone melting temperature is any value among 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, and 900℃, or a range between any two.

[0025] The melting rate of the zone is 0.5–8 cm / h.

[0026] Optionally, the melting rate is any value or a range between 0.5 cm / h, 1 cm / h, 2 cm / h, 3 cm / h, 4 cm / h, 5 cm / h, 6 cm / h, 7 cm / h, and 8 cm / h.

[0027] The frequency of the liquid phase ultrasonic ablation is 20–150 kHz.

[0028] Optionally, the frequency of the liquid phase ultrasonic ablation is any value or a range between any two of 20kHz, 30kHz, 40kHz, 50kHz, 60kHz, 70kHz, 80kHz, 90kHz, 100kHz, 110kHz, 120kHz, 130kHz, 140kHz, and 150kHz.

[0029] The liquid phase ultrasonic ablation time is 5s to 100min.

[0030] Optionally, the liquid phase ultrasonic ablation time is any value or a range between any two of 5s, 1min, 5min, 10min, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, and 100min.

[0031] The sintering temperature is 350–530°C.

[0032] Optionally, the sintering temperature is any value among 350°C, 400°C, 450°C, 500°C, and 530°C, or a range between any two.

[0033] The sintering pressure is 50–80 MPa.

[0034] Optionally, the sintering pressure is any value among 50MPa, 60MPa, 70MPa, and 80MPa, or a range between any two.

[0035] Specifically, the method includes at least the following steps:

[0036] Step 1: Mix the bismuth telluride matrix element and the binary compound raw material under vacuum conditions;

[0037] Step 2: The obtained mixture is melted, zone melted, ultrasonically exfoliated in liquid phase, and sintered to obtain the bismuth telluride-based thermoelectric material.

[0038] Optionally, the particle size of the mixture in step one is 20–100 μm.

[0039] Optionally, the purity of the binary compound in step one is between 95% and 99.999%.

[0040] Optionally, the melting method in step two includes placing the raw materials into quartz glass tubes according to the stoichiometric ratio of the prepared material, then sealing the quartz glass tubes under vacuum and placing them in a swinging melting furnace. The furnace is heated and swung to 700–1050°C, held for 0.5–15 hours, then cooled to 300–400°C over 0.5–4 hours, held at this temperature for 0.5–2 hours, and then rapidly cooled to room temperature to obtain the corresponding material.

[0041] Optionally, the solvent selected in the liquid phase ultrasound in step two is water or ethanol;

[0042] Optionally, step 2 further includes: drying the mixture obtained by liquid phase ultrasonic exfoliation;

[0043] The drying conditions are: drying temperature of 50-80℃ and drying time of 0.5-10 hours;

[0044] Optionally, the drying process is carried out under vacuum conditions.

[0045] Optionally, the sintering method in step two can be any one of vacuum hot pressing sintering, electric discharge plasma sintering, or microwave sintering.

[0046] Optionally, the sintering conditions are:

[0047] The sintering temperature is 350–530℃, the sintering pressure is 50–80MPa, and the holding time is 5–60 minutes.

[0048] Optionally, the heating rate during the sintering process is 30–70 °C / min.

[0049] The density of the bismuth telluride-based thermoelectric materials obtained after sintering is all above 95%.

[0050] According to another aspect of this application, an application is provided for the above-described bismuth telluride-based thermoelectric material or the bismuth telluride-based thermoelectric material prepared by the above-described preparation method, for waste heat power generation and thermoelectric refrigeration.

[0051] Compared with commonly used bismuth telluride-based thermoelectric materials, the method in this application combines both thermoelectric and mechanical properties, showing broad application prospects. Due to the low carrier concentration in the bismuth telluride matrix, this application first selects a binary compound material to optimize its carrier concentration, and then uses a zone melting process to obtain high orientation, thereby improving its thermoelectric performance to a certain extent. To overcome the poor mechanical properties of zone-melted bismuth telluride materials, the zone-melted material is further subjected to ultrasonic exfoliation and sintering. Ultrasonic exfoliation can largely maintain the high texture of bismuth telluride, and it can introduce numerous grain boundary scattering phonons, effectively reducing the lattice thermal conductivity, thereby further optimizing the thermoelectric properties of bismuth telluride and greatly enhancing its mechanical properties, achieving synergistic optimization of both thermoelectric and mechanical properties.

[0052] The thermoelectric material of this application improves electrical transport performance and increases the power factor by incorporating binary compound materials into the matrix material and combining zone melting, ultrasonic exfoliation and hot pressing sintering processes. It also introduces numerous defects such as dislocations and grain boundaries to effectively reduce lattice thermal conductivity and optimize thermoelectric performance. At the same time, it greatly improves the Vickers hardness of bismuth telluride-based thermoelectric materials.

[0053] The beneficial effects that this application can produce include:

[0054] 1) This application effectively optimizes the electron carrier concentration in bismuth telluride materials by incorporating binary compound materials, thereby improving the electrical transport performance;

[0055] 2) This application uses zone melting, liquid-phase ultrasonic exfoliation and sintering processes to effectively introduce grain boundaries, dislocations, stress and strain, which can greatly enhance phonon scattering, effectively reduce the lattice thermal conductivity of bismuth telluride-based thermoelectric materials, and optimize thermal transport performance.

[0056] 3) This application achieves high orientation while increasing Vickers hardness by 50% compared to materials prepared by commercial zone melting processes through zone melting, liquid-phase ultrasonic exfoliation, and sintering.

[0057] 4) This application achieves synergistic optimization of thermoelectric and mechanical properties through zone melting, liquid-phase ultrasonic exfoliation and sintering processes. The thermoelectric figure of merit (ZT) and the average ZT at 300K to 500K of the bismuth telluride-based thermoelectric material are significantly improved. These synergistic optimizations effectively broaden the application prospects of bismuth telluride-based thermoelectric materials. Attached Figure Description

[0058] Figure 1 The graph shows the electrical conductivity (Fig. a), Seebeck coefficient (Fig. b), power factor (Fig. c), thermal conductivity (Fig. d), and thermoelectric figure of merit (Fig. e) of Comparative Example 1 of this application as a function of temperature.

[0059] Figure 2 The graphs show the conductivity versus temperature for Examples 1 and 2 of this application.

[0060] Figure 3 The graphs show the Seebeck coefficient as a function of temperature for Examples 1 and 2 of this application.

[0061] Figure 4 The following are graphs showing the power factor variation with temperature in Examples 1 and 2 of this application;

[0062] Figure 5 The graphs show the changes in total thermal conductivity and lattice thermal conductivity as a function of temperature for Examples 1 and 2 of this application.

[0063] Figure 6 The graphs show the thermoelectric figure of merit as a function of temperature in Examples 1 and 2 of this application.

[0064] Figure 7 This is a comparison chart of Vickers hardness between Comparative Example 1 and Examples 1 and 2 of this application;

[0065] Figure 8 The Vickers hardness curves are for the thermoelectric materials prepared in Comparative Example 1 and Examples 1-2 of this invention. Detailed Implementation

[0066] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0067] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0068] Thermal conductivity was tested using a laser thermal conductivity meter (Netzsch, LFA-457, Germany).

[0069] Conductivity and Seebeck coefficient were tested using a ZEM-3 instrument (ULVAC, Japan).

[0070] Liquid phase ultrasonic ablation was performed using a self-made ultrasonic device.

[0071] Zone melting was performed using a self-made zone melting furnace.

[0072] Hot sintering was carried out using an induction hot pressing sintering furnace (Shanghai Shilu Vacuum Technology Engineering Co., Ltd.).

[0073] Comparative Example 1

[0074] Weigh the raw material Bi2Te 2.7 Se 0.3 Weigh out 50g of tellurium granules (99.999%), bismuth granules (99.999%), and selenium granules (99.999%). Place the raw materials into a clean quartz glass tube and fix it in a sealing device. Seal the quartz glass tube while ensuring that the vacuum negative pressure does not exceed 0.8Pa.

[0075] The sealed quartz tube was placed in a swing furnace and heated with the furnace at a rate of 100℃ / hour to 800℃. It was held at this temperature for 2 hours, and the tube was swung every 30 minutes during the holding period to make it more uniform. Then it was air-cooled to room temperature (25℃) to obtain a bismuth telluride-based alloy.

[0076] Bismuth telluride alloy was zone melted at 850℃ at a rate of 4 cm / h to obtain Comparative Example 1.

[0077] Example 1 and Comparative Example 1 were prepared in exactly the same way, while Example 2 was slightly different. In Example 2, ultrasonic liquid phase exfoliation was added during the zone melting and sintering process.

[0078] Example 1

[0079] In this embodiment, a combination of melting, rocking, and zone melting was used to prepare a binary compound BiCl3 material composite bismuth telluride-based thermoelectric material. The process was basically the same as that of Comparative Example 1, wherein the content of the binary compound was 0.025g.

[0080] Example 2

[0081] In this embodiment, a thermoelectric material composed of binary compound material bismuth telluride was prepared by combining melting, oscillation, zone melting, ultrasonic liquid phase exfoliation, and hot pressing sintering. The melting, oscillation, and zone melting processes were basically the same as those in Comparative Example 1, wherein the content of the binary compound was 0.025 g; the ultrasonic liquid phase exfoliation involved breaking the zone-melted bismuth telluride material into large blocks and ultrasonicating them for 0.5 min, followed by drying the ultrasonically exfoliated sheets at 80°C for 1 h.

[0082] 10g of the material prepared by ultrasonication was weighed and placed into a graphite mold. It was pre-compacted by holding the pressure at 20MPa for 3 minutes. Then, the mold and the material were placed into a vacuum hot press furnace. The temperature was raised to 480℃ at a rate of 30℃ / min under a vacuum of <10Pa for sintering. The temperature was held at this temperature and pressure for 10 minutes. After sintering, the bulk sample was removed from the furnace and a sintered bismuth telluride bulk thermoelectric material with a diameter of approximately 12.7×10mm was obtained.

[0083] Test Example 1

[0084] The thermoelectric material samples obtained in Comparative Example 1 and Examples 1-2 were cut into strips of 2.5×2.5×12mm and circular pieces of Φ12.7×1.5mm, respectively. The electrical conductivity, Zebeck coefficient, lattice thermal conductivity, total thermal conductivity and ZT value of the thermoelectric materials were measured and calculated as a function of temperature.

[0085] Figure 1The electrical conductivity (Fig. a), Seebeck coefficient (Fig. b), power factor (Fig. c), total thermal conductivity (Fig. d), and thermoelectric figure of merit (Fig. e) of Comparative Example 1 as a function of temperature show that the electrical conductivity of Comparative Example 1 decreases with increasing temperature. The Seebeck coefficient is initially positive but gradually becomes negative as the temperature rises, indicating that the bismuth telluride matrix thermoelectric material is a weak p-material with a low power factor. Ultimately, the thermoelectric figure of merit of the bismuth telluride matrix reaches 0.7.

[0086] Figures 2-4 The graphs show the relationship between the conductivity, Seebeck coefficient, and power factor of the thermoelectric materials prepared in Examples 1-2 of this invention and temperature. After the addition of the binary compound, the conductivity of the bismuth telluride material in Example 1 is significantly improved compared to the matrix comparative example 1, mainly due to the increased carrier concentration after the addition of the binary compound. The conductivity of the material obtained by sintering after ultrasonic liquid phase exfoliation in Example 2 is slightly improved compared to Example 1, mainly due to the "donor-like effect" of bismuth telluride, which to some extent increases the carrier concentration. However, the conductivity of Example 2 is still within the optimal range, and the Seebeck coefficient of Example 2 does not decrease significantly compared to Example 1, resulting in a room temperature power factor of 42 μW·cm for Example 2. -1 K -2 Such a high power factor is extremely rare in the literature on n-type sintered bismuth telluride materials. This indicates that the ultrasonic liquid phase exfoliation technology does not introduce too many structural defects into the bismuth telluride material, but maintains the mobility under the zone melting process well, so that its power factor is still at a higher level than that of the conventional zone melting process, such as in Example 1.

[0087] Figures 5-7 The graphs show the relationship between the total thermal conductivity, lattice thermal conductivity, and thermoelectric figure of merit of the thermoelectric materials prepared in Examples 1 and 2 of this invention and temperature. Example 2 shows a significant reduction in both total thermal conductivity and lattice thermal conductivity compared to Example 1. This is mainly because Example 2 introduces a large number of lattice defect-scattered phonons, and the increased carrier concentration also suppresses the bipolar effect. At 300 K, the lattice thermal conductivity decreases from 0.9 W·m⁻². -1 ·K -1 Reduced to 0.65 W·m -1 ·K -1 Ultimately, through synergistic optimization of electrical and thermal performance, the ZT in Example 2... max The value reached 1.08, which is an 8% improvement compared to Example 1 and a 54% improvement compared to Comparative Example 1.

[0088] Figure 8This is a Vickers hardness curve of the thermoelectric materials prepared in Comparative Example 1 and Examples 1-2 of this invention. Vickers hardness measurement is used to measure the hardness of a sample. Conventional zone-melted bismuth telluride materials have poor mechanical properties, which severely restricts their widespread commercial application. Improving their mechanical strength is a hot research topic for many researchers. In Example 2, under the sintering process, the Vickers hardness increased from 0.36 GPa in Example 1 to 0.48 GPa, an increase of 50%.

[0089] In summary, bismuth telluride prepared by ultrasonic liquid phase exfoliation technology has significantly improved mechanical strength and thermoelectric properties, which provides an effective approach for the widespread application of bismuth telluride.

[0090] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a bismuth telluride-based thermoelectric material, characterized in that, The bismuth telluride-based thermoelectric material includes a matrix and a dopant material; The matrix is ​​Bi2Te 3-x Se3, x takes values ​​from 0.1 to 1.0; The doping material is selected from binary compound materials, and the doping material accounts for 0.02~0.1wt% of the mass of the matrix; the binary compound material is selected from one of BiI3, BiCl3, TeI4, and SbI3; The thermoelectric material is prepared by a method comprising the following steps: The raw materials containing elemental tellurium, elemental bismuth, elemental selenium, and doped materials are mixed. Melt at 700~1050℃ for 0.5~15 hours; Zone melting was carried out at 600~900℃, with a melting rate of 0.5~8 cm / h; The thermoelectric material is obtained by liquid-phase ultrasonic exfoliation for 5 s to 100 min and vacuum hot pressing sintering at 350 to 530℃ with a sintering pressure of 50 to 80 MPa and a holding time of 5 to 60 minutes.

2. The preparation method according to claim 1, characterized in that, The sintering was carried out under a vacuum condition of <10 Pa.

3. The preparation method according to claim 1, characterized in that, The melting temperature is 750~850℃; The melting time is 1 to 3 hours.

4. The preparation method according to claim 1, characterized in that, The zone melting temperature is 800~900℃; The melting rate of the zone is 3~5 cm / h.

5. The preparation method according to claim 1, characterized in that, The frequency of the liquid phase ultrasonic ablation is 20~150 kHz; The liquid phase ultrasonic ablation time is 5s to 1min.

6. The preparation method according to claim 1, characterized in that, The sintering temperature is 450~500℃.

7. The application of a bismuth telluride-based thermoelectric material prepared by the preparation method according to any one of claims 1 to 6, characterized in that, Used for waste heat power generation and thermoelectric refrigeration.

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