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

Abstract

The invention discloses a high-performance n-type bismuth telluride-based thermoelectric material and a preparation method thereof. The chemical formula of the n-type bismuth telluride-based thermoelectric material is Cu < 0.02 > Bi < 2 > Te < 2.7-x > Se < 0.3 + x + y% Bi < 2 > S3, x is greater than or equal to 0.1 and less than or equal to 0.25, and y is greater than or equal to 0 and less than or equal to 1. The n-type bismuth telluride-based thermoelectric material disclosed by the invention has relatively low thermal conductivity, and a relatively high thermoelectric figure of merit is obtained near the room temperature. Meanwhile, the mechanical property of the material is improved through multi-element solid solution collaborative optimization, and the structural defect that an n-type bismuth telluride-based thermoelectric material is prone to dissociation is overcome. The preparation method of the thermoelectric material only comprises the steps of high-temperature melting, ball milling, sintering and the like, and is simple in process, low in cost and beneficial to large-scale production and application.

Description

Technical Field

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

[0002] Thermoelectric materials are functional materials that use the movement of carriers (electrons and holes) in solids to achieve direct conversion between heat and electricity. In recent decades, the growing demand for green energy and the development of solid waste heat recovery systems have promoted the vigorous development of thermoelectric material research. Thermoelectric materials can achieve temperature difference power generation or electric refrigeration using the Seebeck effect and the Peltier effect. The devices use an all-solid-state electronic device structure, no working fluid, no moving components, no pollution during operation, no harmful chemical residues, noise and vibration, and reliable mechanical properties. They are widely used in automotive waste heat or industrial waste heat power generation, electronic device refrigeration and other fields. It is an environmentally friendly material with superior performance and extremely high application value.

[0003] Usually, the dimensionless thermoelectric figure of merit (ZT) is an important parameter for judging the thermoelectric performance of materials. For a long time, the research on thermoelectric materials has basically focused on how to improve the ZT value. According to its calculation formula ZT = S 2 From σT / к, we can see that a good thermoelectric material must have a large Seebeck coefficient S and a high electrical conductivity σ, in addition to a low thermal conductivity к. However, these physical parameters are closely related to each other, and the pursuit of increasing or decreasing one parameter alone often leads to non-synergistic changes in other parameters, which is also an important reason that currently limits the commercial application of thermoelectric materials.

[0004] Bismuth telluride (Bi2Te3)-based alloy is the most classic low-temperature thermoelectric material. It is also the best thermoelectric material at room temperature and the only one that has been commercialized. It has received widespread attention in the past few decades. Bi2Te3 belongs to the rhombohedral phase structure. The Bi atomic layer and the Te atomic layer are stacked in the order of Te1-Bi-Te2-Bi-Te1, forming a layered structure with five layers of atoms as a period. The atoms are bonded by mixed ion-covalent bonds, and the middle layers are connected by van der Waals interactions. Therefore, the material has obvious anisotropy and exhibits structural characteristics that are easily dissociated. Bi2Te 2.7 Se 0.3It is a typical n-type Bi2Te3-based material. Compared with p-type materials, its performance development lags seriously, which greatly hinders the further development of commercial applications of Bi2Te3-based thermoelectric devices. At present, n-type Bi2Te3-based thermoelectric materials are mainly prepared by zone melting, and their easily dissociated structural defects have not been solved, which is not conducive to the subsequent device processing, assembly and service; in addition, there are also works that have prepared n-type Bi2Te3-based thermoelectric materials with high texture by hot forging process, which successfully improved the ZT value of n-type Bi2Te3-based thermoelectric materials. However, the cumbersome and complex preparation process greatly increases the cost of device development, which seriously limits the commercial development of n-type Bi2Te3-based thermoelectric materials. Therefore, the development of an n-type Bi2Te3-based material with both high thermoelectric performance and mechanical properties can further promote the practical application of Bi2Te3-based thermoelectric materials and devices. Summary of the invention

[0005] In view of the deficiencies in the prior art, the object of the present invention is to provide an n-type bismuth telluride-based thermoelectric material having both high thermoelectric properties and mechanical properties, and to provide a preparation method thereof with simple process, good repeatability and low cost.

[0006] For the above purpose, the chemical formula of the n-type bismuth telluride-based thermoelectric material provided by the present invention is Cu 0.02 Bi2Te 2.7- x Se 0.3+x +y%Bi2S3, wherein 0.1≤x≤0.25, 0≤y≤1, preferably x=0.2, y=0.5.

[0007] The method for preparing the n-type bismuth telluride-based thermoelectric material of the present invention comprises the following steps:

[0008] Step 1: Follow Cu 0.02 Bi2Te 2.7-x Se 0.3+x +y%Bi2S3 stoichiometric ratio, weigh Bi, Cu, Te, Se, S respectively, mix the weighed raw materials evenly and put them into a quartz tube, seal it in vacuum and melt it at high temperature to obtain an alloy ingot.

[0009] Step 2: ball mill the alloy ingot obtained in step 1 to obtain uniform and refined powder.

[0010] Step 3: The powder obtained in step 2 is placed in a mold for sintering to obtain a dense bulk material, namely, an n-type bismuth telluride-based thermoelectric material.

[0011] In the above step 1, preferably, the purity of the single substances Bi, Cu, Se, Te and S is 99.99% or more.

[0012] In the above step 1, the weighed single substances are mixed evenly and then placed into a quartz tube for vacuum sealing. Preferably, the vacuum degree is ≤8×10 -4 Pa.

[0013] In the above step 1, the melting is preferably divided into two stages, the melting temperature of the first stage is 450-500°C, the holding time is 2-4 hours, and the melting temperature of the second stage is 800-1100°C, the holding time is 6-18 hours. It is further preferred that the melting temperature rise rate is 1-2°C / min.

[0014] In the above step 2, the ball milling is carried out under the protection of an inert atmosphere, the inert atmosphere includes: high vacuum, high purity nitrogen, high purity helium, high purity argon, etc., the ball milling method includes: planetary ball milling, high energy ball milling, oscillating ball milling, etc., preferably the ball milling speed is 400-600r / min, and the ball milling time is 30-90min.

[0015] In the above step 3, the sintering method is preferably spark plasma sintering, the sintering temperature is 400-480°C, the sintering time is 5-10 min, and the sintering pressure is 40-50 MPa. The sintering heating rate is further preferably 50-100°C / min.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The chemical formula of the n-type bismuth telluride-based thermoelectric material of the present invention is Cu 0.02 Bi2Te 2.7-x Se 0.3+x +y%Bi2S3, by finely controlling the Te and Se contents and further adding Bi2S3, the thermal conductivity is greatly reduced while maintaining a high power factor, which significantly improves the ZT value of the material. In addition, multi-element solid solution also synergistically improves the mechanical properties of the material, among which the Vickers hardness of the optimal component is increased by about 60% compared with the base material.

[0018] 2. The preparation method provided by the present invention only includes the steps of high-temperature melting combined with ball milling and sintering, and its process is simple and low-cost, which is conducive to large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 3 is a graph showing the relationship between the power factor of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1 to 8 and Comparative Examples 1 and 2 and the temperature.

[0020] Figure 2 3 is a graph showing the relationship between the thermal conductivity of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1 to 8 and Comparative Examples 1 and 2 and the temperature.

[0021] Figure 33 is a graph showing the relationship between the ZT values ​​of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1 to 8 and Comparative Examples 1 and 2 and the temperature.

[0022] Figure 4 It is the Vickers hardness of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 3 and 6 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0024] Comparative Example 1

[0025] Step 1: According to the chemical formula Bi2Te 2.7 Se 0.3 The stoichiometric ratio of each element in the mixture is 99.99% or more of Bi, Te, and Se. All the weighed elements are then placed in a quartz tube and sealed in vacuum. The vacuum degree is 8×10 -4 Pa; then the quartz tube was transferred to a muffle furnace, and the temperature was first increased to 500°C at a rate of 2°C / min and kept for 2h, and then increased to 1100°C at a rate of 1°C / min and kept for 12h, and the alloy ingot was obtained after cooling.

[0026] Step 2: The alloy ingot obtained in step 1 is crushed and loaded into a stainless steel ball mill, wherein the ball-to-material ratio is set to 10:1, and ball milled at a speed of 450 r / min for 60 min under a high-purity nitrogen protective atmosphere, and sieved with a 120-mesh sieve to obtain a uniformly refined powder.

[0027] Step 3: The powder obtained in step 2 is loaded into a graphite mold for spark plasma sintering, wherein the heating rate is 100°C / min, the sintering temperature is 450°C, the holding time is 5min, and the sintering pressure is 50MPa, and finally a dense bulk material, i.e., an n-type bismuth telluride-based thermoelectric material, is obtained.

[0028] Comparative Example 2

[0029] In step 1 of comparative example 1, according to the chemical formula Cu 0.02 Bi2Te 2.7 Se 0.3 The stoichiometric ratio of each element in the reaction mixture is as follows: Cu, Bi, Te, and Se single substances with a purity of more than 99.99% are weighed respectively, and the other steps are the same as those in Comparative Example 1 to obtain an n-type bismuth telluride-based thermoelectric material.

[0030] Example 1

[0031] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.6 Se0.4 The stoichiometric ratio of each element in the above-mentioned example is as follows: Bi, Cu, Te, and Se single substances with a purity of more than 99.99% are weighed respectively; the other steps are the same as those in Comparative Example 1, and an n-type bismuth telluride-based thermoelectric material is obtained.

[0032] Example 2

[0033] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.55 Se 0.45 The stoichiometric ratio of each element in the above-mentioned example is as follows: Bi, Cu, Te, and Se single substances with a purity of more than 99.99% are weighed respectively; the other steps are the same as those in Comparative Example 1, and an n-type bismuth telluride-based thermoelectric material is obtained.

[0034] Example 3

[0035] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.5 Se 0.5 The stoichiometric ratio of each element in the above-mentioned example is as follows: Bi, Cu, Te, and Se single substances with a purity of more than 99.99% are weighed respectively; the other steps are the same as those in Comparative Example 1, and an n-type bismuth telluride-based thermoelectric material is obtained.

[0036] Example 4

[0037] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.45 Se 0.55 The stoichiometric ratio of each element in the above-mentioned example is as follows: Bi, Cu, Te, and Se single substances with a purity of more than 99.99% are weighed respectively; the other steps are the same as those in Comparative Example 1, and an n-type bismuth telluride-based thermoelectric material is obtained.

[0038] Example 5

[0039] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.5 Se 0.5 +0.25% Bi2S3: weigh Bi, Cu, Te, Se, and S single substances with a purity of more than 99.99% respectively according to the stoichiometric ratio of each element in the Bi2S3; the other steps are the same as those in comparative example 1 to obtain an n-type bismuth telluride-based thermoelectric material.

[0040] Example 6

[0041] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.5 Se 0.5+0.5% Bi2S3: weigh Bi, Cu, Te, Se, and S single substances with a purity of more than 99.99% respectively according to the stoichiometric ratio of each element in the Bi2S3; the other steps are the same as those in comparative example 1 to obtain an n-type bismuth telluride-based thermoelectric material.

[0042] Example 7

[0043] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.5 Se 0.5 +0.75% Bi2S3: weigh Bi, Cu, Te, Se, and S single substances with a purity of more than 99.99% respectively in the stoichiometric ratio of each element in the Bi2S3, and the other steps are the same as those in comparative example 1 to obtain an n-type bismuth telluride-based thermoelectric material.

[0044] Example 8

[0045] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.5 Se 0.5 +1% Bi2S3: weigh Bi, Cu, Te, Se, and S single substances with a purity of more than 99.99% respectively in the stoichiometric ratio of each element in the Bi2S3, and the other steps are the same as those in comparative example 1 to obtain an n-type bismuth telluride-based thermoelectric material.

[0046] The block materials obtained in the above examples and comparative examples were cut according to the test specifications and then polished with 2000-grit sandpaper. The ZEM-3 (Ulvac-Riko, Japan) thermoelectric performance test system was used to measure the conductivity and Seebeck coefficient of the samples at 323K to 573K, and the corresponding power factor PF=S was calculated. 2 σ. The calculation method of thermal conductivity is k = D × C p ×ρ, where the thermal diffusion coefficient D was measured by laser flash thermal conductivity instrument LFA 467 (Netzsch, Germany), and the specific heat C p It is estimated by Dulong-Petit limit, and the density ρ is measured by Archimedes drainage method. Finally, the formula ZT=S 2 The thermoelectric figure of merit ZT of the sample is calculated by σT / к. The Vickers hardness tester is China HV-1000.

[0047] It is worth noting that, considering the anisotropy of bismuth telluride-based thermoelectric materials, in order to ensure the uniformity of the electrical and thermal performance test analysis of the samples, the performance tests of the above-mentioned embodiments and comparative examples were all conducted in the direction perpendicular to the sintering pressure. Figures 1 to 4 .

[0048] As can be seen from the figure, the thermoelectric material of comparative example 1 has a medium power factor, but its thermal conductivity is relatively high, reaching 1.4 Wm at room temperature.-1 K -1 , resulting in an extremely low ZT value. By adding additional Cu in Comparative Example 2, the special interstitial occupancy of Cu increases the carrier mobility of the material and significantly improves the power factor. However, the donor doping effect introduced by the interstitial Cu also increases the carrier concentration, so that the thermal conductivity is still high, which is 1.3 Wm at room temperature. -1 K -1 The higher thermal conductivity makes the ZT value limited to 0.9 at room temperature. Based on this, in Examples 1 to 4, by finely adjusting the Cu 0.02 Bi2Te 2.7-x Se 0.3+x (0.1≤x≤0.25) The Te and Se content of the material is used to optimize the carrier concentration, significantly reducing the thermal conductivity while maintaining a high power factor. In particular, when the optimal component x=0.2, the room temperature thermal conductivity of the material is reduced to 1.01Wm -1 K -1 , combined with the maintained power factor, the ZT value at room temperature is increased to 1.04, which is 57% and 15.5% higher than that of Comparative Example 1 and Comparative Example 2, respectively. In order to further improve the ZT value of the material, Examples 5 to 8 have the optimal component Cu 0.02 Bi2Te 2.5 Se 0.5 Bi2S3 is added to the material. The addition of Bi2S3 forms multi-scale microstructural defects in the material, further enhancing phonon scattering, which greatly reduces the lattice thermal conductivity and obtains an extremely low total thermal conductivity, while the power factor remains at a high level over the entire temperature range. In particular, when y=0.5, the room temperature thermal conductivity of the material is reduced to 0.9Wm -1 K -1 , which is 36% and 30% lower than that of Comparative Example 1 and Comparative Example 2, respectively. The ZT value at room temperature is increased to 1.12, and the maximum ZT value is 1.26 at 373K. The maximum ZT value is increased by about 40% and 14.5% compared with Comparative Example 1 and Comparative Example 2, respectively. In addition, by comparing the Vickers hardness of Comparative Example 1, Comparative Example 2 and the optimal components x=0.2 (Example 3) and y=0.5 (Example 6), it can be seen that the average Vickers hardness of Example 3 and Example 6 is 0.78GPa and 0.88GPa, respectively, which is significantly improved compared with Comparative Example 1 and Comparative Example 2, indicating that the mechanical properties of the material are significantly improved.

[0049] The above contents are some specific implementation schemes of the present invention, but the protection scope of the present invention is not limited to the above embodiments. It should be pointed out that for ordinary technicians in the technical field of the present invention, without departing from the concept of the present invention, simple replacement or improvement of the technical scheme of the present invention is made, which all belong to the protection scope of the present invention.

Claims

1. A high-performance n-type bismuth telluride-based thermoelectric material, characterized in that: The chemical formula of the thermoelectric material is Cu 0.02 Bi2Te 2.7-x Se 0.3+x +y%Bi2S3, where 0.1≤x≤0.25, 0≤y≤1.

2. The high performance n-type bismuth telluride-based thermoelectric material according to claim 1, characterized in that: x=0.2, y=0.

5.

3. A method for preparing a high-performance n-type bismuth telluride-based thermoelectric material according to claim 1, characterized in that: The preparation method comprises the following steps: Step 1: Follow Cu 0.02 Bi2Te 2.7-x Se 0.3+x +y%Bi2S3 stoichiometric ratio, weigh Bi, Cu, Te, Se, S respectively, where 0.1≤x≤0.25, 0≤y≤1; mix the weighed single substances evenly and put them into a quartz tube, seal it in vacuum and melt it to obtain an alloy ingot; Step 2: ball milling the alloy ingot obtained in step 1 to obtain uniform and refined powder; Step 3: The powder obtained in step 2 is placed in a mold for sintering to obtain a dense bulk material, namely, an n-type bismuth telluride-based thermoelectric material.

4. The method for preparing a high-performance n-type bismuth telluride-based thermoelectric material according to claim 3, characterized in that: In step 1, the purity of the single substances Bi, Cu, Se, Te and S is above 99.99%.

5. The method for preparing a high-performance n-type bismuth telluride-based thermoelectric material according to claim 3, characterized in that: Step 1: The vacuum degree of the vacuum seal is ≤ 8×10 -4 Pa.

6. The method for preparing a high-performance n-type bismuth telluride-based thermoelectric material according to claim 3, characterized in that: In step 1, the melting is divided into two stages. The melting temperature of the first stage is 450-500° C., and the insulation time is 2-4 hours. The melting temperature of the second stage is 800-1100° C., and the insulation time is 6-18 hours.

7. The method for preparing a high-performance n-type bismuth telluride-based thermoelectric material according to claim 6, characterized in that: In step 1, the heating rate of the melting is 1-2°C / min.

8. The method for preparing a high-performance n-type bismuth telluride-based thermoelectric material according to claim 3, characterized in that: In step 2, the ball milling is carried out under the protection of an inert atmosphere, the ball milling speed is 400 to 600 r / min, and the ball milling time is 30 to 90 min.

9. The method for preparing a high-performance n-type bismuth telluride-based thermoelectric material according to claim 3, characterized in that: In step 3, the sintering method is spark plasma sintering, the sintering temperature is 400-480° C., the sintering time is 5-10 min, and the sintering pressure is 40-50 MPa.

10. The method for preparing a high-performance n-type bismuth telluride-based thermoelectric material according to claim 9, characterized in that: The heating rate of the sintering is 50-100°C / min.

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