A kind of n-type bismuth telluride-based thermoelectric material and preparation method thereof

Abstract

The present invention discloses an n-type bismuth telluride-based thermoelectric material and a preparation method thereof, and relates to the field of thermoelectric materials. The present invention includes process steps such as component configuration, high-energy ball milling, SPS sintering, etc., and adopts a method of adding a certain specific gravity of a second phase material to a bismuth telluride matrix material. The prepared thermoelectric material is an n-type bismuth telluride-based thermoelectric material of Bi2Te 2.7 Se 0.3 +0.5wt% MgAgSb; the carrier concentration is adjusted by anion alloying and adding the prepared MgAgSb second phase, the grain boundaries are increased, and micro-nano powders of different sizes are obtained through high-energy ball milling combined with SPS sintering process, which effectively enhances the scattering of long and short wavelength phonons and obtains lower thermal conductivity. The prepared thermoelectric materials have good application prospects in the medium and low temperature range.

Description

Technical Field

[0001] The invention belongs to the field of thermoelectric materials, and in particular relates to an n-type bismuth telluride-based thermoelectric material and a preparation method thereof. Background Art

[0002] Thermoelectric materials are functional materials that can realize the conversion of heat energy and electrical energy. Thermoelectric conversion technology is based on the Seebeck effect. It can realize the mutual conversion of heat energy and electrical energy by driving the migration of carriers by temperature difference to form thermoelectric potential. Thermoelectric power generation devices made of thermoelectric materials can use industrial and commercial waste heat, geothermal heat, human body temperature, etc. as heat sources for thermoelectric conversion, and have the advantages of small size, high stability, long life, green environmental protection, and maintenance-free. Energy and environmental problems in the world today are becoming increasingly serious. Making full use of energy resources and improving energy utilization efficiency have become current research hotspots. Thermoelectric conversion technology can realize the conversion of low-grade heat sources and waste heat into electrical energy, and has broad application prospects in the field of energy resource utilization.

[0003] Thermoelectric figure of merit (dimensionless ZT value) is an indicator to measure the thermoelectric conversion efficiency of thermoelectric materials. Thermoelectric materials with high thermoelectric conversion efficiency often have larger thermoelectric figure of merit. ZT can be expressed as:

[0004]

[0005] Where S is the Seebeck coefficient, which is the electromotive force generated by the unit gradient temperature of the material. Its size depends on the carrier type and the temperature difference between the two ends of the material. σ is the electrical conductivity, which is related to the carrier concentration and carrier mobility. k is the thermal conductivity, which is composed of electronic thermal conductivity and lattice thermal conductivity. Thermoelectric materials with higher thermoelectric figures of merit often have higher Seebeck coefficients, larger electrical conductivity, and lower thermal conductivity, but the relationship between these three is mutually coupled and mutually influential, and comprehensive regulation is more difficult. Bismuth telluride-based materials are a kind of thermoelectric materials suitable for low temperatures (room temperature-200℃). They have the advantages of simple preparation, green environmental protection, and low cost. They are also the most commonly used low-temperature thermoelectric materials in business. In order to obtain a higher ZT value, in the coordinated regulation of S, σ, and K, we always hope to obtain larger S and σ and smaller K. At present, the ZT value of p-type bismuth telluride thermoelectric materials can reach above 1.5. However, the ZT value of the matching n-type bismuth telluride materials is still low, and the ZT value of the intrinsic n-type bismuth telluride materials is only about 0.5. The traditional melting method has a long cycle and low preparation efficiency. In addition, the thermal conductivity of bismuth telluride-based materials prepared by the melting method is mostly around 1.5W·m -1 ·K -1 How to further reduce the thermal conductivity of materials and improve their ZT values ​​has always been one of the research issues for this type of materials. Summary of the invention

[0006] The purpose of the present invention is to solve the problems that the existing traditional p-type bismuth telluride thermoelectric material has a large ZT value, the matching n-type bismuth telluride material has a relatively low ZT value, the traditional melting method has a long cycle, low preparation efficiency, and the thermal conductivity of the bismuth telluride-based material prepared by the melting method is relatively high. Provided are an n-type bismuth telluride material with a large ZT value and a bismuth telluride-based material with relatively low thermal conductivity, as well as a method for preparing the n-type bismuth telluride-based thermoelectric material.

[0007] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0008] The present invention discloses an n-type bismuth telluride-based thermoelectric material, wherein the chemical formula of the thermoelectric material is Bi2Te 2.7 Se 0.3 +0.5wt%MgAgSb; of which Bi2Te 2.7 Se 0.3 and MgAgSb are prepared separately.

[0009] A method for preparing an n-type bismuth telluride-based thermoelectric material comprises the following steps:

[0010] S1. Mg, Ag, and Sb are used as raw materials, weighed according to the chemical formula of MgAgSb thermoelectric material, mixed, and placed in a ball mill;

[0011] S2. Using a planetary ball mill to symmetrically take the materials after high-energy ball milling to obtain prefabricated MgAgSb powder;

[0012] S3, after the ball milling is completed, the prefabricated MgAgSb powder material is sintered by the SPS sintering method under vacuum pressure conditions;

[0013] S4, after sintering is completed, take an appropriate amount of MgAgSb block;

[0014] S5, according to Bi2Te 2.7 Se 0.3 Thermoelectric material chemical formula Weigh Bi, Te, Se and mix them, then weigh Bi, Te, Se and 0.5% of the mixed mass of MgAgSb block and put them into a ball mill;

[0015] S6. Use a planetary ball mill to symmetrically take the proportioned materials and perform high-energy ball milling to obtain prefabricated Bi2Te 2.7 Se 0.3 +0.5wt%MgAgSb powder;

[0016] S7. After ball milling, the prefabricated Bi2Te 2.7 Se 0.3 +0.5wt%MgAgSb powder material is sintered.

[0017] Furthermore, the weighing in step S5 is performed in a vacuum glove box under the protection of argon atmosphere.

[0018] Furthermore, in the step S7, the SPS sintering temperature is 450° C., the pressure is 60 MPa, and the holding time is 20 min.

[0019] Furthermore, the sintering process of the SPS sintering in the step S7 adopts gradient heating and full pressure maintenance, specifically, heating to 250°C for 10 minutes, then heating to 450°C for 10 minutes, keeping the temperature for 20 minutes, and then cooling with the furnace; the pressure is maintained during the whole sintering process.

[0020] Furthermore, the ball mill jar and the grinding balls inside are made of stainless steel, the grinding aid in the ball mill jar is anhydrous ethanol, and the ball mill jar after mixing is vacuum-sealed.

[0021] Furthermore, the total rotation speed of the planetary ball mill is 500 rpm, the rotation speed of the self-rotating disk is 800 rpm, and the rotation speed of the orbiting disk is 300 rpm.

[0022] Furthermore, the specific treatment method of the high-energy ball milling is intermittent ball milling; the intermittent ball milling is to pause for 10 minutes after each 50 minutes of ball milling, and the total ball milling time is 12 hours. The intermittent ball milling is to prevent the powder from sticking to the wall and affecting the ball milling efficiency on the one hand, and to protect the motor on the other hand.

[0023] Furthermore, the Bi2Te obtained in step S6 2.7 Se 0.3 +0.5wt% MgAgSb powder is dried in a vacuum drying oven; vacuum degree ≤ 0.1Pa, drying temperature 80-100℃, drying time ≥ 18h; the dried powder material is sieved using an ultrasonic vibrating screen; the vibrating screen mesh number ≥ 450 mesh, the purpose of the vibrating screen. Sieving can separate powders of different particle sizes and can also screen out impurities with larger particle sizes.

[0024] Furthermore, the temperature of the vacuum drying oven is increased by a gradient, specifically, the temperature is increased to 80°C for 20 minutes, kept at this temperature for 5 hours, then increased to 100°C for 1 hour, and kept at this temperature, and the total keeping time is more than 18 hours. The purpose of using the gradient temperature increase is to volatilize the ethanol liquid under low temperature vacuum conditions, and then completely dry the remaining powder at high temperature.

[0025] On the other hand, the present invention also provides an n-type bismuth telluride-based thermoelectric material prepared according to the above-mentioned preparation method; on the other hand, the present invention also provides an n-type bismuth telluride-based thermoelectric material dense block, using the above-mentioned n-type bismuth telluride-based thermoelectric material Bi2Te 2.7 Se 0.3+0.5wt%MgAgSb powder is used as raw material, and n-type bismuth telluride-based thermoelectric material Bi2Te is obtained by SPS sintering. 2.7 Se 0.3 +0.5wt%MgAgSb dense block; SPS sintering parameters are: sintering temperature is 450℃; pressure is 60MPa; holding time is 20min. The sintering process adopts gradient heating and full pressure holding; the gradient heating and full pressure holding are 10min heating to 250℃, then 10min heating to 450℃, holding for 20min, and then cooling with the furnace; the pressure is kept on during the whole sintering process.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The n-type bismuth telluride-based thermoelectric material prepared by this technical solution is finally prepared by the coordinated regulation of carrier concentration and micro-nanoscale to obtain Bi2Te 2.7 Se 0.3 The thermal conductivity of +0.5wt%MgAgSb at 473K is 1.25W·m -1 ·K -1 , the ZT value is 0.71, which is about 42% higher than the typical value in the literature;

[0028] (2) The method and process of this technical solution are simple, and high-energy ball milling does not require high-temperature reaction conditions, thus avoiding the vaporization of the reaction raw materials and causing excessive vapor pressure, which brings safety hazards. The traditional melting method requires a long insulation time and annealing time, and the general cycle takes 10 days or longer. Compared with the melting method, high-energy ball milling combined with SPS sintering process can greatly reduce the material preparation cycle and improve the preparation efficiency; thermoelectric materials are prepared by high-energy ball milling combined with SPS sintering. High-energy ball milling can greatly reduce the powder preparation cycle, and vacuum sealing can effectively prevent the volatilization of raw materials after the ball milling process; the use of high-energy ball milling and SPS sintering technology can better avoid the shortcomings of traditional synthesis methods. SPS has a fast sintering speed and the sintered bulk material has a good density, which greatly improves the preparation efficiency of thermoelectric materials;

[0029] (3) The method of this technical solution can quickly and efficiently prepare n-type bismuth telluride-based thermoelectric material Bi2Te 2.7 Se 0.3 +0.5wt% MgAgSb, through the alloying of anion sites and the introduction of the second phase component MgAgSb to regulate the carrier concentration, it is beneficial to reduce the electronic thermal conductivity; in addition, the melting method can produce nano-scale powders, which can enhance the scattering of short-wavelength phonons, while the high-energy ball milling combined with the SPS sintering process can produce micro-nanoscale powders, which have a good scattering effect on both short-wavelength and long-wavelength phonons, and can further reduce the thermal conductivity of the material;

[0030] (4) This technical solution can obtain micro-nanoscale thermoelectric materials by combining ball milling with SPS sintering process. The nanoscale structure can obtain a larger interface density at the interface, which helps to disperse phonons with nanoscale wavelengths, while the micron-scale structure can scatter long-wavelength phonons. Micro-nano powders containing different scales can scatter phonons of all scales, reduce their free path, and obtain lower thermal conductivity.

[0031] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0033] Figure 1 The n-type bismuth telluride-based Bi2Te mentioned in the embodiment 2.7 Se 0.3 +0.5wt%MgAgSb thermoelectric material preparation process flow chart

[0034] Figure 2 The n-type bismuth telluride-based Bi2Te mentioned in the embodiment 2.7 Se 0.3 SEM image of +0.5wt%MgAgSb thermoelectric material.

[0035] Figure 3 The n-type bismuth telluride-based Bi2Te mentioned in the embodiment 2.7 Se 0.3 +0.5wt%MgAgSb thermoelectric material is a graph showing the relationship between the Beck coefficient and temperature.

[0036] Figure 4 The n-type bismuth telluride-based Bi2Te mentioned in the embodiment 2.7 Se 0.3 The relationship between the conductivity and temperature of +0.5wt% MgAgSb thermoelectric material.

[0037] Figure 5 The n-type bismuth telluride-based Bi2Te mentioned in the embodiment 2.7 Se 0.3 The relationship between the power factor and temperature of +0.5wt% MgAgSb thermoelectric material.

[0038] Figure 6 The n-type bismuth telluride-based Bi2Te mentioned in the embodiment2.7 Se 0.3 The relationship between thermal conductivity and temperature of +0.5wt%MgAgSb thermoelectric material.

[0039] Figure 7 The n-type bismuth telluride-based Bi2Te mentioned in the embodiment 2.7 Se 0.3 Relationship between ZT value and temperature of +0.5wt%MgAgSb thermoelectric material. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] like Figure 1 As shown, the prepared material is Bi2Te 2.7 Se 0.3 +0.5wt%MgAgSb, the preparation method of n-type bismuth telluride-based thermoelectric material comprises:

[0042] S1. Mg, Ag, and Sb are used as raw materials, weighed according to the chemical formula of MgAgSb thermoelectric material, mixed, and placed in a ball mill;

[0043] S2. Using a planetary ball mill to perform high-energy ball milling on the proportioned materials to obtain prefabricated MgAgSb powder;

[0044] S3, after the ball milling is completed, the prefabricated MgAgSb powder material is sintered by the SPS sintering method under vacuum pressure conditions;

[0045] S4, after sintering is completed, take an appropriate amount of MgAgSb block;

[0046] S5, according to Bi2Te 2.7 Se 0.3 Thermoelectric material chemical formula Weigh Bi, Te, Se and mix them, then weigh 0.5% of the Bi, Te, Se mixed mass of MgAgSb block and put them into a ball mill;

[0047] S6. Use a planetary ball mill to perform high-energy ball milling on the proportioned materials to obtain prefabricated Bi2Te 2.7 Se 0.3 +0.5wt%MgAgSb powder;

[0048] S7. After ball milling, the prefabricated Bi2Te2.7 Se 0.3 +0.5wt%MgAgSb powder material is sintered.

[0049] Among them, in the component configuration step, the raw materials are weighed in a glove box protected by an argon atmosphere. First, according to the chemical formula MgAgSb, that is, according to the mass ratio of Mg: Ag: Sb = 24.305: 107.9: 121.8, the single-substance raw materials are weighed in the glove box and put into a stainless steel ball mill. The ball mill is equipped with three sizes of grinding balls, large, medium and small. The grinding ball specifications are 70g of Φ20mm grinding balls, 70g of Φ15mm grinding balls, 70g of Φ8mm grinding balls, 70g of Φ6mm grinding balls, and 30g of Φ4mm grinding balls. The total mass of the grinding balls is 310g, and the mass of the powder is controlled at 10g to 15g, and the ball-to-material ratio is about 1:20. Pour anhydrous ethanol into the ball mill, and the amount of anhydrous ethanol slightly covers all the fillers, but ensure that the liquid level of anhydrous ethanol does not exceed 1 / 3 of the volume of the ball mill. After all the materials are filled, the ball mill is placed in the transition chamber of the glove box, vacuumed and sealed, and then taken out for ball milling.

[0050] Among them, in the process of preparing MgAgSb powder, the ball milling treatment method selected is intermittent ball milling. The intermittent ball milling is to pause for 10 minutes after each ball milling for 50 minutes, and the total ball milling time is 12 hours. Intermittent ball milling is to prevent the powder from sticking to the wall and affecting the ball milling efficiency on the one hand, and to protect the motor on the other hand. The working parameters of the ball mill are set as follows: the total speed of the ball mill is 500rpm, the speed of the self-rotating disk is 800rpm, and the speed of the revolving disk is 300rpm. The powder after ball milling needs to be vacuum dried. The vacuum degree of the drying oven is ≤0.1Pa. It is first heated to 80℃ for 20min, kept warm for 5h, and then heated to 100℃ for 1h, and continued to keep warm. The total insulation time is more than 18h. The purpose of using the gradient heating method is to volatilize the ethanol liquid under low-temperature vacuum conditions, and then dry the remaining powder completely at high temperature. The dried powder material is sieved using an ultrasonic vibrating screen, and the mesh number of the vibrating screen is ≥450 mesh. Sieving can separate powders of different particle sizes and remove impurities with larger particle sizes.

[0051] In the sintering process of the MgAgSb block, SPS sintering is selected. In an optional embodiment, the SPS sintering parameters include: sintering temperature of 350°C; pressure of 60MPa; and holding time of 20min. The sintering process adopts gradient heating and full pressure holding; the gradient heating and full pressure holding are heating to 250°C for 10min, then heating to 450°C for 10min, holding for 20min, and then cooling with the furnace; the pressure is kept on during the whole sintering process.

[0052] After the preparation of the MgAgSb block is completed, a certain amount of MgAgSb material is weighed. According to the chemical formula Bi2Te2.7 Se 0.3 , that is, the mass ratio Bi:Te:Se=418:344.52:23.652. The single raw materials were weighed in the glove box and put into the stainless steel ball mill together with the prepared MgAgSb. All parameters and steps were consistent with the MgAgSb block preparation process. After ball milling, drying, sieving, SPS sintering, Bi2Te 2.7 Se 0.3 +0.5wt%MgAgSb material. Specific embodiments

[0054] In an argon atmosphere glove box, 1.62 g of Mg single substance raw material, 7.17 g of Ag single substance raw material, and 8.12 g of Sb single substance raw material were weighed in proportion and filled into a stainless steel ball mill.

[0055] The stainless steel ball mill is evacuated and sealed in the transition chamber, and then taken out for high-energy ball milling. In this embodiment, the speed of the revolution plate of the ball mill is 800rpm, the speed of the rotation plate is 300rpm, and the intermittent ball milling method is adopted. After each 50min of ball milling, it pauses for 10min, and the total ball milling time is 12h. After the ball milling is completed, the powder is taken out and placed in a vacuum drying oven for drying. The vacuum degree of the drying oven is ≤0.1Pa. It is first heated to 80℃ for 20min, kept warm for 5h, and then heated to 100℃ for 1h, and continued to be kept warm for 16h. After the dried powder is taken out, it is sieved through a 450-mesh sieve, and then an appropriate amount of powder is weighed and pressed into a Φ20×3mm block material.

[0056] The pressed MgAgSb material is placed in an SPS sintering furnace and sintered under vacuum. The sintering temperature is 450°C and the pressure applied during the sintering process is 60MPa. The sintering process adopts a gradient heating and full pressure maintenance method. The temperature is first raised to 250°C for 10 minutes, then raised to 450°C for 10 minutes, and kept at this temperature for 20 minutes, and then cooled with the furnace; the pressure load is maintained at 60Mpa during the whole sintering process.

[0057] Take 0.075 g of the sintered MgAgSb material for later use. In an argon atmosphere glove box, weigh 8.36 g of Bi single substance raw material, 6.89 g of Te single substance raw material, and 0.47 g of Se single substance raw material according to proportion, and put them together with 0.075 g of MgAgSb into a stainless steel ball mill.

[0058] The stainless steel ball mill is evacuated and sealed in the transition chamber, and then taken out for high-energy ball milling. In this embodiment, the speed of the revolution plate of the ball mill is 800rpm, the speed of the rotation plate is 300rpm, and the intermittent ball milling method is adopted. After each 50min of ball milling, it pauses for 10min, and the total ball milling time is 12h. After the ball milling is completed, the powder is taken out and placed in a vacuum drying oven for drying. The vacuum degree of the drying oven is ≤0.1Pa. It is first heated to 80℃ for 20min, kept warm for 5h, and then heated to 100℃ for 1h, and continued to be kept warm for 16h. After the dried powder is taken out, it is sieved through a 450-mesh sieve, and then an appropriate amount of powder is weighed and pressed into a Φ20×3mm block material.

[0059] The Bi2Te 2.7 Se 0.3 The +0.5wt% MgAgSb material was placed in an SPS sintering furnace and sintered under vacuum. The sintering temperature was 450°C and the pressure applied during the sintering process was 60MPa. The sintering process adopted a gradient heating method with full pressure maintenance. The temperature was first raised to 250°C for 10 minutes, then raised to 450°C for 10 minutes, and kept at this temperature for 20 minutes, and then cooled with the furnace; the pressure load was maintained at 60Mpa during the entire sintering process.

[0060] The Seebeck coefficient and electrical conductivity are measured by the ZEM-3 thermoelectric performance analysis system, and the thermal conductivity is further calculated by the thermal diffusion coefficient of the LFA-467 laser thermal conductivity meter. Finally, the n-type Bi2Te 2.7 Se 0.3 Power factor and ZT value of +0.5wt%MgAgSb thermoelectric materials.

[0061] The n-type bismuth telluride-based Bi2Te 2.7 Se 0.3 +0.5wt%MgAgSb thermoelectric material such as Figure 2 As shown in the SEM picture, Figure 3 As shown, the n-type bismuth telluride-based Bi2Te in this embodiment is shown. 2.7 Se 0.3 +0.5wt%MgAgSb thermoelectric material is the relationship between the Beck coefficient and temperature, such as Figure 4 As shown, the n-type bismuth telluride-based Bi2Te mentioned in this embodiment 2.7 Se 0.3 +0.5wt%MgAgSb thermoelectric material conductivity and temperature diagram; Figure 5 As shown, the n-type bismuth telluride-based Bi2Te mentioned in this embodiment is shown. 2.7 Se 0.3 +0.5wt% MgAgSb thermoelectric material power factor and temperature relationship diagram; Figure 6As shown, the n-type bismuth telluride-based Bi2Te mentioned in the embodiment is shown. 2.7 Se 0.3 The relationship between thermal conductivity and temperature of +0.5wt%MgAgSb thermoelectric material; Figure 7 As shown, the n-type bismuth telluride-based Bi2Te mentioned in the embodiment is shown. 2.7 Se 0.3 +0.5wt% MgAgSb thermoelectric material ZT value and temperature;

[0062] Depend on Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 It can be seen that according to, at T = 473K, Bi2Te 2.7 Se 0.3 The Seebeck coefficient of the +0.5wt% MgAgSb thermoelectric block is -0.000156 V / K and the electrical conductivity is 7.9×10 4 S / m, power factor is 0.0018W·m -1 ·K -2 , thermal conductivity is 1.25 W·m -1 ·K -1 , the ZT value is 0.71.

[0063] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. An n-type bismuth telluride-based thermoelectric material, characterized in that: The thermoelectric material chemical formula is Bi2Te 2.7 Se 0.3 +0.5wt%MgAgSb; Among them, Bi2Te 2.7 Se 0.3 and MgAgSb are prepared separately.

2. The method for preparing an n-type bismuth telluride-based thermoelectric material according to claim 1, characterized in that: The steps include: S1. Mg, Ag, and Sb are used as raw materials, weighed according to the chemical formula of MgAgSb thermoelectric material, mixed, and placed in a ball mill; S2. Using a planetary ball mill to symmetrically take the materials after high-energy ball milling to obtain prefabricated MgAgSb powder; S3, after the ball milling is completed, the prefabricated MgAgSb powder material is sintered by the SPS sintering method under vacuum pressure conditions; S4, after sintering is completed, take an appropriate amount of MgAgSb block; S5, according to Bi2Te 2.7 Se 0.3 Thermoelectric material chemical formula Weigh Bi, Te, Se and mix them, then weigh Bi, Te, Se and 0.5% of the mixed mass of MgAgSb block and put them into a ball mill; S6. Use a planetary ball mill to symmetrically take the proportioned materials and perform high-energy ball milling to obtain prefabricated Bi2Te 2.7 Se 0.3 +0.5wt%MgAgSb powder; S7. After ball milling, the prefabricated Bi2Te 2.7 Se 0.3 +0.5wt% MgAgSb powder material is sintered; the SPS sintering temperature in the S7 step is 450°C; the pressure is 60MPa; and the holding time is 20min; The specific treatment method of the high-energy ball milling is intermittent ball milling; the intermittent ball milling is to pause for 10 minutes after each 50 minutes of ball milling, and the total ball milling time is 12 hours; the total speed of the planetary ball mill is 500rpm, the speed of the self-rotating disk is 800rpm, and the speed of the orbiting disk is 300rpm.

3. The method for preparing an n-type bismuth telluride-based thermoelectric material according to claim 2, characterized in that: The weighing in step S5 is performed in a vacuum glove box under the protection of argon atmosphere.

4. The method for preparing an n-type bismuth telluride-based thermoelectric material according to claim 2, characterized in that: The sintering process of SPS sintering in step S7 adopts gradient heating and full pressure maintenance, specifically, heating to 250° C. for 10 minutes, then heating to 450° C. for 10 minutes, keeping the temperature for 20 minutes, and then cooling with the furnace; The pressure is maintained during the entire sintering process.

5. The method for preparing an n-type bismuth telluride-based thermoelectric material according to claim 2, characterized in that: The ball mill jar and the grinding balls inside are made of stainless steel, the grinding aid in the ball mill jar is anhydrous ethanol, and the ball mill jar after mixing is vacuum-sealed.

6. The method for preparing an n-type bismuth telluride-based thermoelectric material according to claim 2, characterized in that: The Bi2Te obtained in step S6 2.7 Se 0.3 +0.5wt% MgAgSb powder is dried in a vacuum drying oven; the vacuum degree is ≤0.1Pa, the drying temperature is 80-100°C, and the drying time is ≥18h; the dried powder material is sieved using an ultrasonic vibration screen; the mesh number of the vibration screen is ≥450 meshes.

7. The method for preparing an n-type bismuth telluride-based thermoelectric material according to claim 6, characterized in that: The temperature of the vacuum drying oven is increased by gradient heating, specifically, the temperature is increased to 80° C. in 20 minutes, kept at this temperature for 5 hours, and then increased to 100° C. in 1 hour, and continued to be kept at this temperature.

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