High-performance Ag2Se-based block thermoelectric material and preparation method thereof

Abstract

The invention relates to a high-performance Ag2Se-based block thermoelectric material and a preparation method thereof. The preparation method of the high-performance Ag2Se-based block thermoelectric material comprises the following steps: weighing high-purity elementary substance raw materials Ag particles and Se particles or Ag particles, Se particles and S particles according to the stoichiometric ratio of Ag2Se1 + x or Ag2Se1-ySy, mixing the raw materials, packaging the mixed raw materials into a carbon-plated vacuum quartz tube, and carrying out high-temperature reaction and annealing treatment to obtain an Ag2Se-based thermoelectric material cast ingot; wherein in the Ag2Se1 + x, x is greater than or equal to 0 and less than or equal to 0.05; in the Ag2Se1-ySy, y is more than or equal to 0 and less than or equal to 0.1; the obtained Ag2Se-based thermoelectric material cast ingot is subjected to crushing, sieving and cold pressing, and an Ag2Se-based block after cold pressing is obtained; and carrying out hot extrusion on the Ag2Se-based block after cold pressing to obtain the high-performance Ag2Se-based block thermoelectric material.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy materials, and relates to a high-performance Ag2Se-based bulk thermoelectric material and a preparation method thereof. Background Art

[0002] Thermoelectric energy conversion technology can directly convert thermal energy into electrical energy based on semiconductor materials, and has important application values in special power supplies, efficient utilization of industrial waste heat, self-power supply of electronic devices, micro-space refrigeration, local high heat flux density active thermal control and other fields.

[0003] Ag2Se is a typical liquid-like superionic conductor thermoelectric material, and a phase change will occur near 407K, changing from a low-temperature orthorhombic phase to a high-temperature cubic phase with liquid-like superionic characteristics. The Ag2Se material has a low lattice thermal conductivity and a high electrical conductivity at room temperature, and as a narrow-bandgap semiconductor itself, it has a relatively high Seebeck coefficient. Therefore, it has high thermoelectric potential near room temperature.

[0004] In recent years, researchers have used different processes to prepare Ag2Se-based bulk thermoelectric materials, including zone melting, mechanical alloying, hydrothermal synthesis, cold pressing-sintering, melting-annealing-sintering, liquid-phase sintering, etc. However, the thermoelectric performance of the prepared Ag2Se-based materials has not made a major breakthrough. The room-temperature zT value is 0.5 - 0.8, and the sample performance repeatability is poor. These factors have greatly restricted the application and development of Ag2Se-based thermoelectric materials.

[0005] Therefore, there is an urgent need to develop a method for preparing high-performance Ag2Se-based bulk thermoelectric materials with stable processes to meet the requirements of large-scale commercial production, so as to promote the application of Ag2Se-based bulk thermoelectric materials in the room-temperature region. Summary of the Invention

[0006] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a high-performance Ag2Se-based bulk thermoelectric material and a preparation method thereof. The preparation method provided by the present invention can significantly improve the thermoelectric performance of the Ag2Se-based bulk material, and the dimensionless thermoelectric figure of merit zT reaches 1.1 at room temperature of 300K, which is much higher than that of Ag2Se-based bulk thermoelectric materials prepared by other processes.

[0007] On the one hand, the present invention provides a preparation method of a high-performance Ag2Se-based bulk thermoelectric material, comprising the following steps: According to Ag2Se 1+x or Ag2Se 1-y S yWeigh high-purity elemental raw materials, i.e., Ag grains and Se grains, or Ag grains, Se grains and S grains, according to the stoichiometric ratio. Mix the raw materials and encapsulate them into a carbon-coated vacuum quartz tube, and then conduct high-temperature reaction and annealing treatment to obtain an Ag2Se-based thermoelectric material ingot. Among them, for the Ag2Se 1+x in which, 0 ≤ x ≤ 0.05; for the Ag2Se 1-y S y in which, 0 ≤ y ≤ 0.1; Crush, sieve and cold-press the obtained Ag2Se-based thermoelectric material ingot to obtain a cold-pressed Ag2Se-based bulk; conduct hot extrusion on the cold-pressed Ag2Se-based bulk to obtain the high-performance Ag2Se-based bulk thermoelectric material.

[0008] Preferably, the purity of the raw materials Ag grains, Se grains and S grains is ≥ 99.999%.

[0009] Preferably, the temperature of the high-temperature reaction is 1273 - 1373K, and the time is 10 - 20 hours.

[0010] Preferably, the parameters of the high-temperature reaction and annealing treatment include: first, heat up to 1273 - 1373K at a rate of 40 - 60K per hour, hold for 10 - 20 hours, then cool down to 723 - 823K at a rate of 15 - 25K per hour, then conduct annealing treatment at 723 - 823K for 72 - 96 hours, and then naturally cool to room temperature.

[0011] Preferably, after crushing the Ag2Se-based thermoelectric material ingot, sieve it using a 100-mesh sieve.

[0012] Preferably, the pressure of the cold pressing is 250 - 350Mpa; the diameter of the cold pressing die is Φ20 - 30mm.

[0013] Preferably, the parameters of the hot extrusion include: the hot extrusion temperature is 473 - 673K, the extrusion ratio is 3 - 12:1, the extrusion rate is 0.8 - 1.5mm / min, and the extrusion angle is 30° - 60°.

[0014] On the other hand, the present invention provides a high-performance Ag2Se-based bulk thermoelectric material prepared by the above preparation method. The density of the high-performance Ag2Se-based bulk thermoelectric material is higher than 95%, the highest power factor is 25.2 - 32.5 μWcm -1 K -2 , the lowest thermal conductivity is 0.8 - 1.0 Wm -1 K -1 , the thermoelectric figure of merit zT at 300K is 0.7 - 1.1, and the highest thermoelectric figure of merit zT is 0.8 - 1.2.

[0015] Beneficial effects: The present invention first uses a hot extrusion process to prepare Ag2Se-based bulk thermoelectric materials, generating a fine-grained microstructure with high orientation and strong texture through hot extrusion. The highly oriented texture can ensure high mobility, while grain refinement significantly reduces the lattice thermal conductivity, thereby ultimately improving the thermoelectric performance of the Ag2Se-based materials. The thermoelectric figure of merit zT reaches a maximum of 1.1 at room temperature of 300K, which is much higher than that of Ag2Se-based bulk thermoelectric materials prepared by other processes, meeting the requirements of large-scale commercial production. Description of the Drawings

[0016] Figure 1 XRD patterns of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5; Figure 2 Backscattered electron image (BSE) and energy dispersive spectroscopy surface scan image (EDS) of the Ag2Se-based bulk thermoelectric material prepared in Example 2; Figure 3 Pole figure and grain orientation map of the Ag2Se-based bulk thermoelectric material prepared in Example 2; Figure 4 Graph showing the relationship between the conductivity and temperature of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2; Figure 5 Graph showing the relationship between the Seebeck coefficient and temperature of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2; Figure 6 Graph showing the relationship between the power factor PF and temperature of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2; Figure 7 Graph showing the relationship between the thermal conductivity and temperature of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2; Figure 8 Graph showing the relationship between the thermoelectric figure of merit zT and temperature of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2. Detailed Description of the Invention

[0017] To further illustrate the content, features, and actual effects of the present invention, the present invention will be described in detail below with reference to the examples. It should be noted that the modified methods designed in the present invention are not limited to these specific embodiments. Without departing from the spirit and connotation of the design of the present invention, equivalent replacements and modifications made by those skilled in the art on the basis of reading the content of the present invention are also within the scope of protection required by the present invention.

[0018] In the present invention, a hot extrusion process is adopted for the first time to prepare Ag2Se-based bulk thermoelectric materials. Through hot extrusion, a fine-grained microstructure with high orientation and strong texture can be produced. The highly oriented texture can ensure high mobility, while grain refinement significantly reduces the lattice thermal conductivity, thereby ultimately improving the thermoelectric performance of the Ag2Se-based materials. Compared with the traditional preparation methods (only high-temperature reaction and annealing treatment), the hot extrusion process adopted in the present invention causes the material to further undergo plastic deformation at high temperature and high pressure, the grains are elongated and a large number of dislocations are generated. With the accumulation of strain energy, the material undergoes dynamic recrystallization to form new fine grains. During the extrusion process, the grains are arranged along the extrusion direction to form a specific fiber texture. This orientation is beneficial to the transmission of electrons, thereby increasing the electrical conductivity; and the high density of dislocations and twin boundaries introduced by hot extrusion further reduces the lattice thermal conductivity, thereby optimizing the final performance of the Ag2Se-based materials.

[0019] In the present invention, during the hot extrusion process, complex grain evolution processes such as plastic deformation and dynamic recrystallization are experienced, and each process is affected by factors such as extrusion temperature, extrusion speed, and extrusion ratio. For example, the extrusion temperature affects the grain size and the proportion of small-angle grain boundaries in the material; the extrusion speed affects the strain rate, dislocation accumulation, and recrystallization initiation; the extrusion ratio affects the degree of plastic deformation and texture strength of the material. Therefore, we deeply analyzed the influence of different parameters in hot extrusion on the microstructure and thermoelectric performance of the Ag2Se-based materials, and comprehensively optimized the process parameters of hot extrusion, and finally obtained high-performance Ag2Se-based bulk materials.

[0020] In an alternative embodiment, the density of the high-performance Ag2Se-based bulk thermoelectric material is higher than 95%, the highest power factor is 25.2 - 32.5 μWcm -1 K -2 , the lowest thermal conductivity is 0.8 - 1.0 Wm -1 K -1 , the thermoelectric figure of merit zT at 300K is 0.7 - 1.1, and the highest thermoelectric figure of merit zT is 0.8 - 1.2.

[0021] As a classic processing method in the traditional metallurgy field, the hot extrusion process has been very maturely applied in metal processing, but it has never been applied to the preparation of Ag2Se-based bulk thermoelectric materials. The following exemplarily describes the preparation method of the high-performance Ag2Se-based bulk thermoelectric material provided by the present invention.

[0022] According to Ag2Se 1+x (0 ≤ x ≤ 0.05) or Ag2Se 1-y S yWeigh high-purity elemental raw materials, Ag grains and Se grains or Ag grains, Se grains and S grains, according to the stoichiometric ratio of (0≤y≤0.1). Mix the raw materials and encapsulate them into a carbon-coated vacuum quartz tube, and then place them in a melting furnace for high-temperature reaction and annealing treatment to obtain an Ag2Se-based thermoelectric material ingot.

[0023] In an alternative embodiment, the purity of the raw materials Ag grains, Se grains and S grains is ≥99.999%. The purpose of mixing the raw materials and encapsulating them into a carbon-coated vacuum quartz tube is to prevent the reaction and rupture of the raw materials with the quartz tube during the melting process.

[0024] In an alternative embodiment, the parameters of the high-temperature melting and annealing treatment include: first heating at a rate of 40 - 60 K / hour to 1273 - 1373 K, holding for 10 - 20 hours, then cooling at a rate of 15 - 25 K / hour to 723 - 823 K, and then annealing at 723 - 823 K for 72 - 96 hours. For example, first heat at a rate of 50 K / hour to 1273 K, hold for 12 hours, then cool at a rate of 18 K / hour to 500 °C, and then anneal at 773 K for 72 hours.

[0025] Crush, sieve and cold press the obtained Ag2Se-based thermoelectric material ingot to obtain a cold-pressed Ag2Se-based bulk.

[0026] In an alternative embodiment, the crushed ingot is sieved using a 100-mesh sieve. The diameter of the die for the cold pressing is Φ20 - 30 mm; the pressure for the cold pressing is 250 - 350 Mpa.

[0027] Hot extrude the cold-pressed Ag2Se-based bulk to obtain the high-performance Ag2Se-based bulk thermoelectric material.

[0028] In an alternative embodiment, the parameters of the hot extrusion include: the temperature of the hot extrusion is 473 - 673 K, the extrusion ratio is 3 - 12:1, the extrusion rate is 0.8 - 1.5 mm / min, and the extrusion angle is 30° - 60°. Among them, too low an extrusion temperature will cause cracks on the material surface, while too high an extrusion temperature will accelerate recrystallization, grain coarsening, and weaken the material texture. Too high an extrusion rate will increase the strain rate, promote dislocation accumulation and the formation of small-angle grain boundaries, but is not conducive to the formation of a high-orientation texture of the material.

[0029] The present invention first uses a hot extrusion process to prepare an Ag2Se-based bulk thermoelectric material. By hot extrusion, a fine-grained microstructure with high orientation and strong texture is generated, significantly improving the thermoelectric performance of the material. The dimensionless thermoelectric figure of merit zT reaches 1.1 at room temperature of 300 K, which is much higher than that of Ag2Se-based bulk thermoelectric materials prepared by other processes.

[0030] In the present invention, the Archimedes drainage method is used to test the density of the high-performance Ag2Se-based bulk thermoelectric material; the Seebeck coefficient / resistance measurement system (ZEM) is used to test the highest power factor of the high-performance Ag2Se-based bulk thermoelectric material; the laser thermal conductivity method / NETZSCH LFA-457 instrument is used to test the lowest thermal diffusivity of the high-performance Ag2Se-based bulk thermoelectric material; the thermoelectric figure of merit zT of the high-performance Ag2Se-based bulk thermoelectric material is calculated by the formula zT = σS 2 T / κ; the highest thermoelectric figure of merit zT of the high-performance Ag2Se-based bulk thermoelectric material is calculated by the formula zT = σS 2 T / κ.

[0031] The following further gives examples to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, rather than being limited to the specific values in the following examples.

[0032] Example 1

[0033] The preparation method of the high-performance Ag2Se-based bulk thermoelectric material provided in this Example 1 includes the following steps: (1) Weigh high-purity elemental raw materials, Ag grains and Se grains, according to the stoichiometric ratio of Ag2Se; (2) Mix the raw materials and encapsulate them into a carbon-coated vacuum quartz tube, and then put them into a melting furnace for high-temperature reaction and annealing treatment to obtain an Ag2Se-based thermoelectric material ingot; among them, the parameters of the high-temperature reaction and annealing treatment process include: heating to 1273K at a rate of 50K per hour, holding for 12 hours, then cooling to 773K at a rate of 18K per hour, and then annealing at 773K for 72 hours; (3) Use a crusher to fully crush the Ag2Se-based thermoelectric material ingot and sieve it through a 100-mesh sieve, then put the sieved powder into a cold pressing mold with a diameter of Φ24mm, and use a press to press it into a block at a pressure of 300Mpa; (4) Put the cold-pressed Ag2Se-based block into a mold for hot extrusion to obtain a high-performance Ag2Se-based bulk thermoelectric material; among them, the hot extrusion temperature is 523K, the extrusion ratio is 9:1, the extrusion rate is 1.4mm / min, and the extrusion angle is 45°.

[0034] Example 2

[0035] In Example 2, the preparation process of the high-performance Ag2Se-based bulk thermoelectric material refers to Example 1, with the only difference being that in step (1), according to the stoichiometric ratio of Ag2Se 1.02 high-purity elemental raw materials, Ag grains and Se grains, are weighed.

[0036] Example 3

[0037] In Example 3, the preparation process of the high-performance Ag2Se-based bulk thermoelectric material refers to Example 1, with the only difference being that in step (4), the hot extrusion temperature is 673K.

[0038] Example 4

[0039] In Example 4, the preparation process of the high-performance Ag2Se-based bulk thermoelectric material refers to Example 1, with the only difference being that in step (4), the hot extrusion rate is 1.2 mm / min.

[0040] Example 5

[0041] In Example 5, the preparation process of the high-performance Ag2Se-based bulk thermoelectric material refers to Example 1, with the only difference being that in step (1), according to the stoichiometric ratio of Ag2Se 0.9 S 0.1 high-purity elemental raw materials, Ag grains, Se grains and S grains, are weighed.

[0042] Comparative Example 1

[0043] The preparation method of the Ag2Se-based bulk thermoelectric material provided in this Comparative Example 1 includes the following steps: (1) According to the stoichiometric ratio of Ag2Se 1.02 high-purity elemental raw materials, Ag grains and Se grains, are weighed; (2) The raw materials are mixed and encapsulated in a vacuum quartz tube, and then placed in a melting furnace for high-temperature reaction and annealing treatment to obtain an Ag2Se-based thermoelectric material ingot; among them, the parameters of the high-temperature reaction and annealing treatment process include: heating to 1273K at a rate of 50K per hour, holding for 12 hours, then cooling to 773K at a rate of 18°C per hour, and then annealing at 773K for 72 hours; (3) The Ag2Se-based thermoelectric material ingot is directly cut for subsequent test characterization.

[0044] Comparative Example 2

[0045] The preparation method of the Ag2Se-based bulk thermoelectric material provided in this Comparative Example 2 includes the following steps: (1) According to the stoichiometric ratio of Ag2Se 1.02 high-purity elemental raw materials, Ag grains and Se grains, are weighed; (2) Mix the raw materials and encapsulate them in a vacuum quartz tube, then place it in a melting furnace for high-temperature reaction and annealing treatment to obtain an Ag2Se-based thermoelectric material ingot; among them, the parameters of the high-temperature reaction and annealing treatment process include: heating to 1273K at a rate of 50K per hour, holding for 12 hours, then cooling to 773K at a rate of 18K per hour, and then annealing at 773K for 72 hours; (3) Grind the Ag2Se-based thermoelectric material ingot into powder in a mortar and place it in a graphite mold with a diameter of 10mm, and perform spark plasma sintering in a vacuum environment; among them, the sintering temperature is 573K, the sintering pressure is 60MPa, the heating rate is 40K / min, and the holding time is 10min.

[0046] Perform density and thermoelectric performance tests on the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2, and the test results are shown in Table 1.

[0047] Table 1:

[0048] As can be seen from Table 1, in Examples 1-5 of the present invention, compared with Comparative Examples 1-2, the thermoelectric performance is significantly improved, the power factor increases, and the thermal conductivity decreases. Among them, the thermoelectric performance of Example 2 is the highest, and the thermoelectric figure of merit zT reaches 1.1 at 300K, which is 175% higher than that of Comparative Example 1. This is because in Comparative Example 1, only high-temperature reaction and annealing treatment are used, and the prepared material has no texture, no orientation, low mobility, which affects its electrical transport performance, and the grain size is large, and the lattice thermal conductivity is high, resulting in low thermoelectric performance; compared with Comparative Example 2, it is 57% higher. This is because in Comparative Example 2, although the steps of grinding and spark plasma sintering are added after high-temperature reaction and annealing treatment, the grains are refined, but the grains still have no orientation and cannot obtain a high mobility, so the thermoelectric performance is also low. However, in Example 2, after the hot extrusion process, a fine-grained microstructure with high orientation and strong texture is produced. Among them, the highly oriented texture can ensure high mobility, and at the same time, the grain refinement significantly reduces the lattice thermal conductivity, thus finally improving the thermoelectric performance of the Ag2Se-based material.

[0049] Figure 1 XRD pattern of the Ag2Se-based bulk thermoelectric material prepared for Examples 1-5. As can be seen from the figure, the preparation method provided by the present invention can obtain a high-purity Ag2Se-based bulk thermoelectric material.

[0050] Figure 2 Backscattered electron image (BSE) and energy-dispersive spectroscopy surface scan image (EDS) of the Ag2Se-based bulk thermoelectric material prepared for Example 2. As can be seen from the figure, the preparation method provided by the present invention can obtain a pure-phase Ag2Se-based bulk material with uniform composition.

[0051] Figure 3 The pole figure and grain orientation map of the Ag2Se-based bulk thermoelectric material prepared in Example 2. It can be seen from the figure that the Ag2Se-based bulk thermoelectric material prepared in Example 2 has a preferred orientation in the (031) crystal direction.

[0052] Figure 4 The relationship diagram of the electrical conductivity of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2 changing with temperature. It can be seen from the figure that the electrical conductivities of Examples 1-5 and Comparative Examples 1-2 increase with the increase of temperature. The electrical conductivity of Example 2 is the highest at 300K, reaching 1137.4 S cm -1 .

[0053] Figure 5 The relationship diagram of the Seebeck coefficient of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2 changing with temperature. It can be seen from the figure that as the temperature increases, the Seebeck coefficient shows a downward trend. The Seebeck coefficient of Example 2 is the largest at 300K, reaching -164.1 μV K -1 .

[0054] Figure 6 The relationship diagram of the power factor PF of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2 changing with temperature. It can be seen from the figure that the power factor of Example 2 is generally higher than that of Examples 1, 3-5, and Comparative Examples 1-2. The power factor of Example 2 at 300K is 30.6 μV K -1 , and the highest power factor reaches 32.5 μV K -1 (360K).

[0055] Figure 7 The relationship diagram of the thermal conductivity of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2 changing with temperature. It can be seen from the figure that as the temperature increases, the thermal conductivity shows an upward trend. The thermal conductivity of Example 2 is generally lower than that of Examples 1, 3-5, and Comparative Examples 1-2. The thermal conductivity of Example 2 at 300K is 0.83 W m -1 K -1 .

[0056] Figure 8Relationship diagram of the thermoelectric figure of merit zT of the Ag2Se-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2 varying with temperature. As can be seen from the figure, the thermoelectric figure of merit zT of Example 2 is overall higher than that of Examples 1, 3-5 and Comparative Examples 1-2. The thermoelectric figure of merit zT of Example 2 at 300K is 1.1, and the maximum thermoelectric figure of merit zT reaches 1.2 (380K). The average thermoelectric figure of merit zT within the range of 300K to 380K avg is 1.14.

Claims

1. A preparation method of a high-performance Ag2Se-based bulk thermoelectric material, characterized in that It includes the following steps: According to the stoichiometric ratio of Ag2Se 1+x or Ag2Se 1-y S y Weigh high-purity elemental raw materials, Ag grains and Se grains or Ag grains, Se grains and S grains, according to the stoichiometric ratio. Mix the raw materials and encapsulate them in a carbon-coated vacuum quartz tube, and then carry out high-temperature reaction and annealing treatment to obtain an Ag2Se-based thermoelectric material ingot. Among them, in the Ag2Se 1+x , 0 ≤ x ≤ 0.05; in the Ag2Se 1-y S y , 0 ≤ y ≤ 0.1; Crush, sieve and cold press the obtained Ag2Se-based thermoelectric material ingot to obtain the cold-pressed Ag2Se-based bulk; subject the cold-pressed Ag2Se-based bulk to hot extrusion to obtain the high-performance Ag2Se-based bulk thermoelectric material.

2. The preparation method according to claim 1, wherein The purity of the raw material Ag particles, Se particles and S particles is ≥99.999%.

3. The preparation method according to claim 1 or 2, characterized in that, The temperature of the high-temperature reaction is 1273 - 1373K, and the time is 10 - 20 hours.

4. The preparation method according to any one of claims 1-3, characterized in that, The parameters of the high-temperature reaction and annealing treatment include: first heating to 1273 - 1373K at a rate of 40 - 60K per hour, holding for 10 - 20 hours, then cooling to 723 - 823K at a rate of 15 - 25K per hour, then annealing at 723 - 823K for 72 - 96 hours, and then naturally cooling to room temperature.

5. The preparation method according to any one of claims 1-4, characterized in that, After crushing the Ag2Se-based thermoelectric material ingot, sieve it using a 100-mesh sieve.

6. The preparation method according to any one of claims 1-5, characterized in that, The pressure of the cold pressing is 250 - 350 Mpa; the diameter of the cold pressing die is Φ20 - 30 mm.

7. The preparation method according to any one of claims 1-6, characterized in that, The parameters of the hot extrusion include: the hot extrusion temperature is 473 - 673K, the extrusion ratio is 3 - 12:1, the extrusion rate is 0.8 - 1.5 mm / min, and the extrusion angle is 30° - 60°.

8. A high-performance Ag2Se-based bulk thermoelectric material prepared by the preparation method according to any one of claims 1-7, characterized in that, The relative density of the high-performance Ag2Se-based bulk thermoelectric material is higher than 95%, the maximum power factor is 25.2 - 32.5 μWcm -1 K -2 , the minimum thermal conductivity is 0.8 - 1.0 Wm -1 K -1 , the thermoelectric figure of merit zT at 300 K is 0.7 - 1.1, and the maximum thermoelectric figure of merit zT is 0.8 - 1.2.

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