Method for improving performance of bismuth telluride-based thermoelectric material by introducing micropores

Abstract

The invention relates to the technical field of preparation of new energy materials, in particular to a method for improving the performance of a bismuth telluride-based thermoelectric material by introducing micropores, a series of xwt% Zn / Bi < 0.34 > Sb < 1.66 > Te3 (x = 0-0.4) composite samples are synthesized by combining melting-quenching with a spark plasma sintering (SPS) technology, then sublimation of a ZnSb second phase in the composite samples is induced by combining an annealing process, and the performance of the bismuth telluride-based thermoelectric material is improved. And the Bi < 0.34 > Sb < 1.66 > Te3 material with a porous structure is obtained. The result shows that the Seebeck coefficient is obviously increased due to the energy filtering effect induced by the nano structure on the inner surface of the micropore; the lattice thermal conductivity is remarkably reduced by the strong phonon scattering effect of the micropores and the nanoparticles on the inner surfaces of the micropores. It is lucky that the randomly distributed porous structure does not cause significant deterioration of the electrical performance, and the significant reduction of the thermal conductivity compensates for the reduction of the conductivity, thereby resulting in a significant increase in the ZT value. As a result, the porous material having a Zn mass percent of 0.2 wt% has a high ZT value of 1.27.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy material preparation, and specifically relates to a method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials. Background Art

[0002] Under the background of the global energy crisis, it is extremely urgent to develop new energy. Thermoelectric materials are new energy functional materials that utilize the thermoelectric physical effect to realize the mutual conversion between thermal energy and electrical energy. Compared with traditional heat engines, devices made of thermoelectric materials have the advantages of no mechanical transmission components, no pollution, no noise, no vibration, and small space occupancy, and will play an important role in future energy utilization and management.

[0003] The conversion efficiency of thermoelectric materials is usually evaluated by the dimensionless thermoelectric figure of merit ZT. The larger the ZT value, the higher the conversion efficiency. An ideal high-efficiency thermoelectric material needs to have excellent electrical transport properties, that is, a large Seebeck coefficient and high electrical conductivity, and at the same time have low thermal conductivity, that is, have the characteristics of "electronic crystal - phonon glass". Therefore, the optimization of the thermoelectric properties of materials is determined by these three parameters: the Seebeck coefficient, electrical conductivity, and thermal conductivity (the sum of the electronic thermal conductivity and the lattice thermal conductivity). However, these three parameters are interrelated and interact with each other through the energy band structure and scattering mechanism. Therefore, decoupling these three parameters is the key to improving the ZT value of the material. The correlation between the lattice thermal conductivity and other parameters is relatively weak. Therefore, reducing the lattice thermal conductivity is an important means to improve the thermoelectric performance. Bi2Te3-based materials are considered to be the best thermoelectric materials near room temperature due to their unique crystal structure and excellent performance. Creating a multi-scale pore structure in bulk thermoelectric materials and enhancing broadband phonon scattering are important means to reduce the lattice thermal conductivity and improve the thermoelectric performance of the materials.

[0004] In view of the above defects, the creator of the present invention finally obtained the present invention through long-term research and practice. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of how to improve the thermoelectric performance of Bi2Te3-based materials by reducing the lattice thermal conductivity, and provides a method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials.

[0006] To achieve the above purpose, the present invention discloses a method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials, including the following steps:

[0007] S1, using Bi, Te, and Sb as starting materials, mixing the weighed powders and putting them into a quartz tube, evacuating the quartz tube and then melting it with a hydrogen-oxygen flame and sealing it to obtain a quartz ampoule;

[0008] S2. Place the quartz ampoule obtained in step S1 into a programmable furnace, slowly raise the temperature to the quenching temperature, perform vacuum melting, and then quench the melt in saturated salt water to obtain an initial ingot.

[0009] S3. Grind the initial ingot obtained in step S2 to obtain Bi 0.34 Sb 1.66 Te3 powder. At the same time, put Zn powder into a vacuum ball milling jar for ball milling to obtain a Zn micro-nano suspension.

[0010] S4. Ultrasonically mix the Bi 0.34 Sb 1.66 Te3 powder and the Zn micro-nano suspension, and place them in a vacuum drying oven for drying to obtain micro-nano composite powder.

[0011] S5. Sinter the micro-nano composite powder obtained in step S4 by spark plasma sintering method under vacuum to obtain a dense p-type Zn / Bi 0.34 Sb 1.66 Te3 thermoelectric material.

[0012] S6. Anneal the p-type Zn / Bi 0.34 Sb 1.66 Te3 thermoelectric material in a vacuum furnace to obtain a porous Bi 0.34 Sb 1.66 Te3 thermoelectric material.

[0013] In step S1, the mixing time is 5 - 10 min, and the vacuum condition is that the vacuum degree is less than 0.1 MPa.

[0014] In step S2, the melting time is 9 - 12 h, and the quenching temperature is 800 - 830 °C.

[0015] In step S3, the vacuum degree in the vacuum ball milling jar is less than 0.1 MPa.

[0016] In step S3, the ball milling time is 24 h, and the ball milling speed is 200 r / min.

[0017] In step S4, the mass percentage of Zn in the Zn micro-nano suspension and Bi 0.34 Sb 1.66 Te3 powder satisfies the following conditions: Zn / Bi 0.34 Sb 1.66 Te3 is 0 - 0.4%, and the ultrasonic dispersion time is 5 - 10 min.

[0018] In step S5, the sintering temperature is 425 - 430 °C, the sintering pressure is 30 - 40 MPa, and the sintering time is 5 - 10 min.

[0019] In step S6, the annealing temperature is 440 - 455 °C and the annealing time is 70 - 73 h.

[0020] The present invention utilizes the characteristic that the ZnSb second phase is easily decomposed and volatilized at high temperatures (annealing process) to prepare a porous high-performance bismuth telluride-based thermoelectric material Bi 0.34 Sb 1.66 Te3 material. Specifically: First, Zn reacts with Sb in the Bi 0.34 Sb 1.66 Te3 material to form ZnSb. By selecting an appropriate annealing temperature (above the decomposition temperature of ZnSb), ZnSb will decompose and volatilize, leaving micropores in the Bi 0.34 Sb 1.66 Te3 material.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention introduces micropores through annealing to prepare a porous high-performance bismuth telluride-based thermoelectric material Bi 0.34 Sb 1.66 Te3. This p-type bismuth telluride-based thermoelectric material has the following advantages:

[0022] 1. Due to the energy filtering effect induced by the nano-structure on the inner surface of the pores, the Seebeck coefficient of this p-type bismuth telluride-based thermoelectric material is significantly increased;

[0023] 2. The strong phonon scattering effect of the micropores and the nanoparticles on their surfaces in this p-type bismuth telluride-based thermoelectric material significantly reduces the lattice thermal conductivity;

[0024] 3. Compared with the dense p-type bismuth telluride-based material, this porous p-type bismuth telluride-based material has a higher ZT value and a higher average ZT value in the entire test temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the process flow chart of the present invention;

[0026] Figure 2 is the field emission scanning electron microscope (FESEM) image of the sample of the embodiment;

[0027] Figure 3 is the XRD pattern of the samples of each embodiment;

[0028] Figure 4 is the relationship curve graph of the ZT value and temperature of the samples of each embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0029] The following further elaborates on the above and other technical features and advantages of the present invention with reference to the accompanying drawings.

[0030] Example 1

[0031] As shown Figure 1 in the figure, a preparation method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials consists of the following steps:

[0032] (1) Using high-purity Bi (99.99% powder), Sb (99.999% powder), and Te (99.99% powder) as raw materials, weigh the powders according to the nominal composition Bi 0.34 Sb 1.66 Te3.

[0033] (2) Mix the weighed powders for 10 minutes to make them evenly mixed. Then place the mixed powders into a quartz tube; under the condition that the vacuum degree is less than 0.1 MPa, use a hydrogen-oxygen flame to melt the quartz glass tube until it melts and then seal it. Put the quartz tube into a programmable furnace and heat it to 830 °C. Vacuum melt for 10 h at this temperature, and then quench in saturated salt water to obtain the initial Bi 0.34 Sb 1.66 Te3 ingot block, and manually grind the ingot block into uniform powders.

[0034] (3) Sinter the quenched powders obtained in step (2) by SPS sintering method under vacuum. The sintering temperature is 430 °C, the sintering pressure is 30 MPa, and the sintering time is 5 minutes to obtain a highly dense Bi 0.34 Sb 1.66 Te3 thermoelectric bulk material. Heat the dense material to 723 K in a vacuum furnace and anneal for 72 h to obtain the Bi 0.34 Sb 1.66 Te3 annealed material (denoted as Pm00), as shown in Figure 2 (a).

[0035] Bi 0.34 Sb 1.66 The XRD pattern analysis results of the Bi Figure 3 Sb 4 Te3 annealed powders show that the main phase of the sintered body in this example is the bismuth telluride phase without other impurity phases, as shown in Figure 4 . After annealing, the maximum electrical conductivity of the sample reaches 8.95×10

[0036] Example 2

[0037] The difference between this example and Example 1 is that: add the ball-milled Zn micro-nano suspension (the Zn powder and Bi in the suspension 0.34 Sb 1.66The mass percentage of Te3 satisfies the following conditions: Zn / Bi 0.34 Sb 1.66 Te3 is 0.2%). Then, it is ultrasonically stirred and mixed evenly, placed in a vacuum drying oven to dry, and micro-nano composite powder is obtained; the micro-nano composite powder is sintered by SPS technology to obtain a p-type 0.2 wt% Zn / Bi 0.34 Sb 1.66 Te3 dense bulk material; the dense material is heated to 723 K in a vacuum furnace and annealed for 72 h to obtain 0.2 wt% Zn / Bi 0.34 Sb 1.66 Te porous material (denoted as Pm02), as Figure 2 (b) shown.

[0038] The XRD pattern analysis results of the porous material powder show that the main phase of the sintered body in this example is bismuth telluride phase, without other impurity phases, as Figure 3 shown. After annealing, the conductivity test results show that the conductivity of the sample in this example is not much different from that of Example 1, but due to the 50 - 250 nm particles generated in the micropores formed by annealing, the Seebeck coefficient is significantly increased due to the energy filtering effect, which is 208 μV / K at 350 K, an increase of 14% compared with Example 2. The sample in this example obtains the minimum lattice thermal conductivity of 0.47 W / mK at 340 K, a decrease of 44% compared with Example 1. Coupled with the decrease in carrier thermal conductivity caused by the decrease in conductivity, the total thermal conductivity of the sample in this example is significantly lower than that of Example 1. Finally, the sample in this example obtains a maximum ZT value of 1.27 at 350 K. The ZT value of the sample in this example is increased by 29% compared with Example 1. And the sample has a larger average ZT value of 1.10 in the temperature range of 300 - 500 K, as Figure 4 shown.

[0039] Example 3

[0040] The difference between this example and Example 1 is that: in the sample in step (2), the ball-milled Zn micro-nano suspension is added (the mass percentage of Zn powder and Bi 0.34 Sb 1.66 Te3 in the suspension satisfies the following conditions: Zn / Bi 0.34 Sb 1.66 Te3 is 0.4%). Then, it is ultrasonically stirred and mixed evenly, placed in a vacuum drying oven to dry, and micro-nano composite powder is obtained; the micro-nano composite powder is sintered by SPS technology to obtain a p-type 0.4 wt% Zn / Bi 0.34 Sb 1.66 Te3 dense bulk material; the dense material is heated to 723 K in a vacuum furnace and annealed for 72 h to obtain 0.4 wt% Zn / Bi 0.34 Sb 1.66A Te porous material (denoted as Pm04), such as Figure 2 shown in (c).

[0041] The XRD pattern analysis results of the porous material powder show that the main phase of the sintered body in this example is the bismuth telluride phase, without other impurity phases, as Figure 3 shown. After annealing, the results of the electrical transport property test show that the conductivity of this example is slightly lower than that of Example 2. However, the Seebeck coefficient is not much different. Due to the increase in the lattice thermal conductivity, the total thermal conductivity is promoted to be higher than that of Example 2. The finally obtained maximum ZT value is lower than that of Example 2, being 1.10, which is higher than that of Example 1. The average ZT value in the temperature range of 300 - 500K is 0.95, as Figure 4 shown.

[0042] In summary, the present invention utilizes the characteristic that the ZnSb second phase is easily decomposed and volatilized at high temperatures to develop a new method for preparing p-type bismuth telluride thermoelectric materials with a microporous structure by means of melt quenching - SPS - high-temperature annealing. The microporous materials have similar conductivities, and the energy filtering effect of the nanoparticles on the inner wall of the micropores can significantly improve the Seebeck coefficient. In addition, the micropores and the nanoparticles on the inner wall of the micropores can enhance phonon scattering and significantly reduce the lattice thermal conductivity, enabling the porous material to have a relatively high ZT peak value. 0.2wt% Zn / Bi 0.34 Sb 1.66 Te porous material simultaneously has the maximum ZT value of 1.27 at 350K and a larger average ZT value of 1.10 in the temperature range of 300 - 500K.

[0043] The present invention shows that introducing a pore structure into bismuth telluride materials can utilize the boundary scattering of long-wavelength phonons by the micropore boundaries to reduce the lattice thermal conductivity, and at the same time utilize the nanoparticles on the inner wall of the pores to enhance the Seebeck coefficient through energy filtering; realizing the collaborative regulation of electricity and heat and significantly optimizing the ZT value of bismuth telluride-based materials. 0.2wt% / Bi 0.34 Sb 1.66 The 0.2wt% / Bi

[0044] The above are only the preferred embodiments of the present invention, which are illustrative rather than restrictive to the present invention. Those skilled in the art understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, but all will fall within the protection scope of the present invention.

Claims

1. A method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials, characterized in that, It includes the following steps: S1. Using Bi, Te and Sb as the initial raw materials, putting the weighed powders into a quartz tube, evacuating the quartz tube, melting it with a hydrogen-oxygen flame until it melts and then sealing it to obtain a quartz ampoule; S2. Placing the quartz ampoule obtained in step S1 in a programmable furnace, slowly raising the temperature to the quenching temperature, quenching the melt in saturated salt water after vacuum melting to obtain an initial ingot; S3. Grind the initial ingot obtained in step S2 to obtain Bi 0.34 Sb 1.66 Te3 powder. At the same time, put Zn powder into a vacuum ball milling jar for ball milling to obtain a Zn micro-nano suspension; S4. Mix the Bi 0.34 Sb 1.66 Te3 powder and the Zn micro-nano suspension by ultrasonic waves, then place them in a vacuum drying oven for drying to obtain a micro-nano composite powder; S5. Sinter the micro-nano composite powder obtained in step S4 by spark plasma sintering method under vacuum to obtain a dense p-type Zn / Bi 0.34 Sb 1.66 Te3 thermoelectric material; S6. Anneal the p-type Zn / Bi 0.34 Sb 1.66 Te3 thermoelectric material in a vacuum furnace to obtain a porous Bi 0.34 Sb 1.66 Te3 thermoelectric material.

2. A method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials as claimed in claim 1, wherein, In step S1, the mixing time is 5 to 10 minutes, and the vacuum condition is that the vacuum degree is less than 0.1 MPa.

3. The method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials according to claim 1, characterized in that In step S2, the melting time is 9 to 12 hours, and the quenching temperature is 800 to 830 °C.

4. A method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials according to claim 1, characterized in that, In step S3, the vacuum degree in the vacuum ball milling tank is less than 0.1 MPa.

5. A method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials as claimed in claim 1, characterized in that, In step S3, the ball milling time is 24 hours, and the ball milling speed is 200 r / min.

6. The method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials according to claim 1, wherein, In the step S4, the mass percentage of Zn in the Zn micro-nano suspension and Bi 0.34 Sb 1.66 Te3 powder satisfies the following conditions: Zn / Bi 0.34 Sb 1.66 Te3 is 0 - 0.4%, and the ultrasonic dispersion time is 5 - 10 min.

7. A method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials as described in claim 1, characterized in that, In step S5, the sintering temperature is 425 to 430 °C, the sintering pressure is 30 to 40 MPa, and the sintering time is 5 to 10 minutes.

8. A method for introducing micropores to improve the performance of bismuth telluride-based thermoelectric materials according to claim 1, characterized in that, In step S6, the annealing temperature is 440 to 455 °C, and the annealing time is 70 - 73 hours.

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