High-performance n-type bismuth telluride-based thermoelectric material and preparation method thereof

Abstract

This invention discloses a high-performance n-type bismuth telluride-based thermoelectric material and its preparation method. The preparation method of the thermoelectric material includes the following steps: weighing Ag powder and Se powder according to a stoichiometric ratio and mixing them to obtain a mixed powder; the mixed powder is then subjected to melting and ball milling to obtain Ag2Se powder; and n-type Bi2Te... 3‑x Se x The powder and the Ag2Se powder prepared above are mixed evenly, and after sintering, a high-performance n-type bismuth telluride-based thermoelectric material is obtained; the n-type Bi2Te 3‑x Se x The value of x in the powder ranges from 0 to 1.0. A high-performance n-type bismuth telluride-based thermoelectric material with improved power factor and reduced thermal conductivity was prepared. This invention achieves optimized electrical and thermal properties of an n-type bismuth telluride-based thermoelectric material by compositing nano-Ag₂Se material with an n-type bismuth telluride thermoelectric material.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of new energy materials, and particularly relates to a high-performance n-type bismuth telluride-based thermoelectric material and a preparation method thereof. BACKGROUND

[0002] Thermoelectric materials are materials that can directly convert waste heat into electricity or be used for thermoelectric refrigeration. In recent years, they have attracted extensive attention due to their scalability, noiselessness, simple operation, high reliability, environmental friendliness and other advantages. The thermoelectric performance of a material is usually evaluated by a figure of merit ZT, ZT = S 2 σT / κ, where S is the Seebeck coefficient, σ is the electrical conductivity, the product S 2 σ is the power factor (PF), κ is the thermal conductivity, and T is the absolute temperature. A thermoelectric material with superior performance should have a high power factor and a low thermal conductivity.

[0003] Although new thermoelectric materials are emerging, bismuth telluride (Bi2Te3)-based alloys are still the most promising and the only commercially available thermoelectric materials near room temperature. Bi x Sb 2-x Te3 and Bi2Te 3-x Se x (BTS) are typical p-type and n-type thermoelectric materials, respectively. Compared with the p-type Bi x Sb 2-x Te3 material with a ZT as high as 1.4-1.8, the ZT of the n-type Bi2Te 3-x Se x material is rarely higher than 1.0. By introducing a nanostructured second phase, the ZT of the p-type Bi x Sb 2-x Te3 material is greatly improved. However, in the n-type Bi2Te 3-x Se x material, the introduction of a nano second phase usually causes a rapid decrease in the power factor of the material due to the decrease in mobility, making it difficult to simultaneously optimize the electrical and thermal properties of the n-type Bi2Te 3-x Se x material through nanocomposites.

[0004] Therefore, obtaining a high-performance n-type bismuth telluride thermoelectric material is of great significance for breaking the serious imbalance in thermoelectric performance between p-type and n-type bismuth telluride-based materials. SUMMARY

[0005] In view of the above existing problems, the present application provides a method for simultaneously improving the electrical and thermal properties of n-type bismuth telluride and further improving the thermoelectric performance thereof.The method has a short preparation time and simple operation, and the bulk density of the prepared bulk is greater than 96%, and the power factor and thermal conductivity are simultaneously effectively improved by appropriate Ag2Se compounding, so that the dimensionless thermoelectric figure of merit ZT reaches 0.85 at 350 K.

[0006] To achieve the above object, the technical scheme adopted by the present application is:

[0007] A preparation method of high-performance n-type bismuth telluride-based thermoelectric material, comprising the following steps:

[0008] Ag powder and Se powder are weighed according to the stoichiometric ratio and mixed to obtain a mixed powder, and the mixed powder is subjected to melting treatment and ball milling treatment in sequence to obtain Ag2Se powder with a particle size of less than 1 μm; preferably, the melting treatment process is that the mixed powder is heated to 1100-1300 K and kept for 8-14 hours, and then annealed at 723 K for 3-10 days; the ball milling treatment time is 1-30 h.

[0009] n-type Bi2Te 3-x Se x powder and the Ag2Se powder prepared above are mixed uniformly at a volume ratio of 100:(0.1-0.35), and high-performance n-type bismuth telluride-based thermoelectric material is obtained after sintering; the value of x in the n-type Bi2Te 3-x Se x powder is 0-1.0. Preferably, the sintering is spark plasma sintering or hot-pressing sintering; the sintering temperature is 350-450 ℃, the pressure is 50-600 Mpa, and the holding time is 5-60 minutes. The spark plasma sintering time is short, only 5 minutes, and the high-performance n-type bismuth telluride-based thermoelectric material can be quickly obtained in a short time; the hot-pressing sintering can prolong the sintering time, and on the basis of increasing the pressure, the high-toughness n-type Bi2Te 3-x Se x -based thermoelectric material with a compression strength increased by more than 4 times that of commercial material can be obtained.

[0010] The bulk density of the n-type bismuth telluride-based thermoelectric material prepared by the above method is greater than 96%. The present application finds that by compounding the Bi2Te 3-x Se x powder with appropriate Ag2Se as a second phase, the power factor and thermal conductivity of the bismuth telluride-based thermoelectric material can be simultaneously effectively improved, so that the dimensionless thermoelectric figure of merit ZT reaches 0.85 at 350 K.

[0011] Compared with the prior art, the present application has the following beneficial effects:

[0012] Firstly, the prepared Ag2Se powder is an n-type Ag2Se material with excellent thermoelectric performance near room temperature, and the n-type Ag2Se is used as a second phase to mix with an n-type Bi2Te 3-x Se x matrix to prepare a dense n-type bismuth telluride-based thermoelectric material through a spark plasma sintering or hot-pressing sintering technology.

[0013] Secondly, the carrier concentration and mobility are comprehensively controlled by compounding the nano Ag2Se phase with the n-type bismuth telluride thermoelectric material, and the Seebeck coefficient is greatly improved through energy filtering effect, so that the power factor of the Bi2Te 3-x Se x material is greatly improved; meanwhile, the nano Ag2Se powder compounded in the material scatters phonons, so that the thermal conductivity of the material is significantly reduced.

[0014] Thirdly, the Ag2Se material has good thermoelectric performance and mechanical properties at room temperature, and the Ag2Se material is compounded with the Bi2Te 3-x Se x powder, so that the thermoelectric performance of the n-type bismuth telluride thermoelectric material is improved, and the compressive strength is obviously improved, thereby further improving the mechanical properties, and laying a good foundation for more efficient industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Figure 1 is a particle size analysis diagram of the prepared Ag2Se material;

[0016] Figure 2 Figure 2 is a diagram of the relationship between the thermoelectric performance of the Ag2Se material and temperature;

[0017] Figure 3 Figure 3 is an XRD spectrum of the bismuth telluride-based thermoelectric material prepared by mixing Bi2Te 2.5 Se 0.5 and Ag2Se in different proportions;

[0018] Figure 4 Figure 4 is a FESEM diagram of the high-performance n-type bismuth telluride-based thermoelectric material prepared when the volume percentage of the Ag2Se powder is 0.35 vol% under different magnifications;

[0019] Figure 5 Figure 5 is a FESEM diagram of the high-performance n-type bismuth telluride-based thermoelectric material prepared when the volume percentage of the Ag2Se powder is 0.5 vol% under different magnifications; 2.5 Se 0.5The figure of the power factor of the Bi2Te

[0020] Figure 6 Bi2Te 2.5 Se 0.5 The figure of the thermal conductivity of the Bi2Te

[0021] Figure 7 Bi2Te 2.5 Se 0.5 The figure of the ZT value of the Bi2Te

[0022] Figure 8 The figure of the compressive strength of the commercial BTS prepared by the zone melting method, the BTS and the BTS / Ag2Se prepared by the present application. DETAILED DESCRIPTION

[0023] In order to better understand the present application, the present application will be further illustrated by the following examples, but the present application is not limited to the following examples. The materials used in the following examples are commercially available products unless otherwise specified.

[0024] Preparation of Ag2Se powder: Ag and Se were sealed in a quartz tube in a stoichiometric ratio of 2:1. Then, the quartz tube was slowly heated to 1273 K and kept at this temperature for 12 hours, and then annealed at 723 K for 7 days. The obtained Ag2Se was ground into powder. The Ag2Se powder was then put into a ball mill jar and ball-milled for 30 hours. The Ag2Se powder with a particle size less than 1 μm was screened out and ready for use.

[0025] The particle size of the Ag2Se powder prepared above is shown in Figure 1 It can be seen that the obtained Ag2Se powder has a nanometer size and belongs to a nanometer material. The properties of the obtained Ag2Se material are shown in Figure 2 It can be seen from the figure that the Seebeck coefficient is negative, which indicates that it is an n-type material. It can also be seen from the figure that the Ag2Se synthesized by the method has excellent thermoelectric properties, which will be beneficial to the composite of Bi2Te 3-x Se x and significantly improve the thermoelectric properties of the matrix.

[0026] Preparation of n-type Bi2Te 2.5 Se 0.5 : Commercial Bi2Te 2.5 Se 0.5After grinding, the material is placed into a mold with an inner diameter of 15 mm and then placed in a discharge plasma furnace. The temperature is raised to 400℃ and the pressure is increased to 50 MPa. The temperature and pressure are maintained for 5 minutes to obtain a material with a diameter of 15 mm and a thickness of about 10 mm. The prepared product is n-type Bi2Te. 2.5 Se 0.5 This is denoted as BTS (SPS).

[0027] Preparation of high-performance n-type bismuth telluride-based thermoelectric materials: Commercially available Bi₂Te₂ prepared by zone melting (ZM) was used. 2.5 Se 0.5 After grinding, the powder was compounded with the prepared Ag₂Se powder at different volume ratios to obtain mixed powders with different proportions. Then, 14g of each mixed powder was weighed and mixed evenly in an agate mortar. In different embodiments, the Ag₂Se powder accounted for a certain percentage of the Bi₂Te content in the mixed powder. 2.5 Se 0.5 The powder volume percentages were 0.1 vol%, 0.15 vol%, 0.2 vol%, 0.25 vol%, and 0.35 vol%. The mixed powder was placed into a mold with an inner diameter of 15 mm and placed in a plasma furnace. The temperature was raised to 400 °C and the pressure was increased to 50 MPa. The temperature and pressure were maintained for 5 minutes to obtain a high-performance n-type bismuth telluride-based thermoelectric material with a diameter of 15 mm and a thickness of about 10 mm, denoted as BTS / Ag2Se(SPS).

[0028] Figure 3 The above-mentioned Bi2Te 2.5 Se 0.5 The XRD patterns of bismuth telluride-based thermoelectric materials prepared by mixing bismuth telluride and Ag2Se in different proportions show that the main phase in the obtained materials is Bi2Te. 2.5 Se 0.5 The second phase Ag2Se was not observed in XRD due to its low content.

[0029] Figure 4 The images show FESEM images of high-performance n-type bismuth telluride-based thermoelectric materials prepared with Ag2Se powder at a volume percentage of 0.35 vol% at different magnifications. The images show that the grains have a typical layered structure and exhibit a certain degree of orientation.

[0030] Figures 5-7 These are the Bi2Te mentioned above. 2.5 Se 0.5The graphs show the in-plane power factor, thermal conductivity, and ZT value of bismuth telluride-based thermoelectric materials prepared by mixing Ag₂Se in different proportions as a function of temperature. The thermoelectric properties of these materials were measured along the direction perpendicular to the SPS pressure (in-plane direction). By combining Ag₂Se, the power factor (PF) of the material reached 35.2 μW / cm². -1 K -2 Meanwhile, the thermal conductivity of the composite material was effectively reduced. Through synergistic optimization of electrical and thermal properties, the ZT value of the material prepared by this invention reached a maximum of 0.85 when composited with 0.15 vol% Ag₂Se.

[0031] Figure 8 A comparison of the compressive strength of commercially prepared BTS (Bioblast-Semiconductor Metallic Acid) by zone melting (ZM) and BTS / Ag₂Se (BTSS) prepared by spark plasma sintering (SPS) is presented. Cylindrical test specimens with a height of 6 mm and a diameter of 3 mm were prepared for testing. Figure 8 It can be seen that by preparing the composite nano-Ag2Se phase through spark plasma sintering (SPS), the compressive strength of the n-type bismuth telluride thermoelectric material is significantly improved, thereby further enhancing its mechanical properties.

[0032] It should be noted that in other embodiments, the objective of this invention can be achieved when the experimental process meets the following conditions:

[0033] The preferred heating temperature for the mixed powder is 1100-1300K, specifically 1100K, 1200K, or 1300K; the preferred holding time is 8-14 hours, specifically 8h, 10h, or 14h; and the preferred annealing time is 3-10 days, specifically 3 days, 5 days, 7 days, or 10 days.

[0034] The preferred time for ball milling is 1-30 hours, specifically 1 hour, 5 hours, 20 hours, or 30 hours. For those skilled in the art, an appropriate ball milling time can be selected according to the specific ball milling parameters, as long as Ag2Se powder with a particle size of less than 1 μm can be obtained.

[0035] For sintering parameters, the preferred sintering temperature is 350-450℃, specifically 350℃, 400℃, or 450℃; the preferred sintering pressure is 50-600 MPa, specifically 50 MPa, 200 MPa, 400 MPa, or 600 MPa; the preferred holding time is 5-60 minutes, specifically 5 minutes, 20 minutes, 40 minutes, or 60 minutes.

[0036] For n-type Bi2Te3-x Se x The powder, wherein the value of x is preferably 0-1.0, specifically it can be 0.1, 0.4, 0.6 or 1.0, etc.

[0037] Those skilled in the art can make appropriate selections of the above process parameters according to actual needs, and all of them can achieve the purpose of this invention.

[0038] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance n-type bismuth telluride-based thermoelectric material, characterized in that: Includes the following steps: Ag powder and Se powder were weighed according to the stoichiometric ratio and mixed to obtain a mixed powder. The mixed powder was then subjected to melting and ball milling to obtain Ag2Se powder. n-type Bi2Te 3-x Se x The powder and the Ag2Se powder prepared above are mixed evenly, and then sintered to obtain a high-performance n-type bismuth telluride-based thermoelectric material; the n-type Bi2Te 3-x Se x The value of x in the powder ranges from 0.1 to 1.0; The Ag2Se powder has a particle size of less than 1 μm.

2. The method for preparing high-performance n-type bismuth telluride-based thermoelectric materials according to claim 1, characterized in that: The smelting process is as follows: the mixed powder is heated to 1100-1300K and held for 8-14 hours, and then annealed at 723K for 3-10 days.

3. The method for preparing high-performance n-type bismuth telluride-based thermoelectric materials according to claim 1, characterized in that: The ball milling process takes 1-30 hours.

4. The preparation method of the high-performance n-type bismuth telluride-based thermoelectric material according to claim 1, characterized in that: The Bi2Te 3-x Se x The volume ratio of powder to Ag2Se powder is 100:(0.1-0.35).

5. The method for preparing high-performance n-type bismuth telluride-based thermoelectric materials according to claim 1, characterized in that: The sintering is either discharge plasma sintering or hot pressing sintering; the sintering temperature is 350-450℃, the pressure is 50-600 MPa, and the holding time is 5-60 minutes.

6. A high-performance n-type bismuth telluride-based thermoelectric material, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 5.

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