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

Abstract

The application 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 Bi2Te 2.7‑x Se 0.3+x +y%Bi2S3, wherein 0.1<=x<=0.25 and 0<=y<=1. The n-type bismuth telluride-based thermoelectric material has low thermal conductivity and high thermoelectric figure of merit near room temperature. Meanwhile, the multi-element solid solution synergistically optimizes the mechanical properties of the material and overcomes the structural defect that the n-type bismuth telluride-based thermoelectric material is easy to dissociate. The preparation method of the thermoelectric material only comprises steps of high-temperature melting, ball milling and sintering, and has the advantages of simple process, low cost and favorable large-scale production and application.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, specifically relating to a high-performance n-type bismuth telluride-based thermoelectric material and its preparation method. Background Technology

[0002] Thermoelectric materials are functional materials that utilize the movement of charge carriers (electrons and holes) in a solid to directly convert between thermal energy and electrical energy. In recent decades, the increasing demand for green energy and the development of solid-state waste heat recovery systems have spurred the vigorous development of thermoelectric material research. Thermoelectric materials can achieve thermoelectric power generation or electric cooling using the Seebeck and Peltier effects. Their devices employ an all-solid-state electronic device structure, with no working fluid, requiring no moving parts, and emitting no pollution, harmful chemical residues, noise, or vibration during operation. They exhibit reliable mechanical properties and are widely used in fields such as automotive waste heat or industrial waste heat power generation and electronic device cooling. They are high-performance, environmentally friendly materials with extremely high application value.

[0003] The dimensionless thermoelectric figure of merit (ZT) is typically an important parameter for evaluating the thermoelectric properties of materials. For a long time, research on thermoelectric materials has primarily focused on improving the ZT value. According to its calculation formula, ZT = S... 2 As can be seen from σT / к, 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, and pursuing an increase or decrease in one parameter alone often leads to non-cooperative changes in other parameters, which is also an important reason that currently limits the commercial application of thermoelectric materials.

[0004] Bismuth telluride (Bi₂Te₃)-based alloys are the most classic low-temperature thermoelectric materials and currently the best-performing thermoelectric material at room temperature, and the only one that has achieved commercial application. They have received widespread attention over the past few decades. Bi₂Te₃ belongs to a rhombohedral phase structure, with Bi and Te atomic layers stacked in the order Te₁-Bi-Te₂-Bi-Te₁, forming a layered structure with a period of five atomic layers. The atoms are bonded together by mixed ion-covalent bonds, and the middle layers are connected by van der Waals interactions. Therefore, this material exhibits significant anisotropy and readily dissociable structural characteristics. Bi₂Te₃ 2.7 Se 0.3As a typical n-type Bi₂Te₃-based material, its performance development lags significantly behind that of p-type materials, greatly hindering the further commercial application of Bi₂Te₃-based thermoelectric devices. Currently, n-type Bi₂Te₃-based thermoelectric materials are mainly prepared through zone melting, but their easily dissociated structural defects remain unresolved, which is detrimental to subsequent device processing, assembly, and service. In addition, some studies have successfully improved the ZT value of n-type Bi₂Te₃-based thermoelectric materials by preparing them with high texture through hot forging. However, the cumbersome and complex preparation process greatly increases the cost of device development, severely limiting the commercialization of n-type Bi₂Te₃-based thermoelectric materials. Therefore, developing an n-type Bi₂Te₃-based material with both high thermoelectric 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 shortcomings of the prior art, the purpose of this invention is to provide an n-type bismuth telluride-based thermoelectric material with both high thermoelectric and mechanical properties, and to provide a simple, reproducible and low-cost preparation method for it.

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

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

[0008] Step 1: According to Cu 0.02 Bi2Te 2.7-x Se 0.3+x The stoichiometric ratio of Bi₂S₃ is used to weigh out Bi, Cu, Te, Se, and S elements respectively. After mixing the weighed raw materials evenly, they are placed into a quartz tube, sealed under vacuum, and melted at high temperature to obtain an alloy ingot.

[0009] Step 2: Ball mill the alloy ingot obtained in Step 1 to obtain a uniform and fine powder.

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

[0011] In step 1 above, it is preferred that the purity of the Bi, Cu, Se, Te, and S elements is 99.99% or higher.

[0012] In step 1 above, the weighed elements are mixed evenly and then placed into a quartz tube for vacuum sealing, preferably with a vacuum degree ≤ 8 × 10⁻⁶. -4 Pa.

[0013] In step 1 above, the melting is preferably divided into two stages: the melting temperature of the first stage is 450–500°C, and the holding time is 2–4 hours; the melting temperature of the second stage is 800–1100°C, and the holding time is 6–18 hours. More preferably, the heating rate of the melting is 1–2°C / min.

[0014] In step 2 above, the ball milling is carried out under an inert atmosphere, which 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. The preferred ball milling speed is 400-600 r / min and the ball milling time is 30-90 min.

[0015] In step 3 above, the preferred sintering method is spark plasma sintering, with a sintering temperature of 400–480°C, a sintering time of 5–10 min, and a sintering pressure of 40–50 MPa. More preferably, the sintering heating rate is 50–100°C / min.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] 1. The chemical formula of the n-type bismuth telluride-based thermoelectric material of this invention is Cu. 0.02 Bi2Te 2.7-x Se 0.3+x By precisely controlling the Te and Se contents and further adding Bi₂S₃, the thermal conductivity is significantly reduced while maintaining a high power factor, resulting in a significant improvement in the ZT value of the material. Furthermore, multi-element solid solution synergistically improves the mechanical properties of the material, with the optimal composition showing an approximately 60% increase in Vickers hardness compared to the matrix material.

[0018] 2. The preparation method provided by the present invention only includes steps such as high-temperature melting and ball milling and sintering. Its process is simple and low-cost, which is conducive to large-scale production and application. Attached Figure Description

[0019] Figure 1 The graph shows the power factor of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 and Comparative Examples 1 and 2 as a function of temperature.

[0020] Figure 2 The graphs show the relationship between the thermal conductivity and temperature of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 and Comparative Examples 1 and 2.

[0021] Figure 3The graphs show the relationship between the ZT values ​​and temperature of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 and Comparative Examples 1 and 2.

[0022] Figure 4 The Vickers hardness is the same as that of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 3 and 6 and Comparative Examples 1 and 2. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection 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 Bi, Te, and Se elements with a purity of ≥99.99% were weighed separately according to their stoichiometric ratios. The weighed elements were then placed into a quartz tube and vacuum-sealed at a vacuum level of 8 × 10⁻⁶. -4 Pa; then the quartz tube was transferred to a muffle furnace, heated to 500℃ at a rate of 2℃ / min and held for 2h, then heated to 1100℃ at a rate of 1℃ / min and held for 12h, and then cooled to obtain an alloy ingot.

[0026] Step 2: After crushing the alloy ingot obtained in Step 1, it is loaded into a stainless steel ball mill jar with a ball-to-material ratio of 10:1. The ball mill is then run at 450 r / min for 60 min under a high-purity nitrogen protective atmosphere. After sieving through a 120-mesh sieve, a uniform and fine powder is obtained.

[0027] Step 3: The powder obtained in Step 2 is loaded into a graphite mold for spark plasma sintering. The heating rate is 100℃ / min, the sintering temperature is 450℃, the holding time is 5min, and the sintering pressure is 50MPa. Finally, a dense bulk material, namely 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 ratios of each element were used to weigh out Cu, Bi, Te, and Se elements with a purity of ≥99.99%. The other steps were the same as 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 Bi, Cu, Te, and Se with a purity of 99.99% or higher were weighed out according to the stoichiometric ratio of each element. The other steps were the same as in Comparative Example 1 to obtain n-type bismuth telluride-based thermoelectric material.

[0032] Example 2

[0033] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.55 Se 0.45 Bi, Cu, Te, and Se with a purity of 99.99% or higher were weighed out according to the stoichiometric ratio of each element. The other steps were the same as in Comparative Example 1 to obtain n-type bismuth telluride-based thermoelectric material.

[0034] Example 3

[0035] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.5 Se 0.5 Bi, Cu, Te, and Se with a purity of 99.99% or higher were weighed out according to the stoichiometric ratio of each element. The other steps were the same as in Comparative Example 1 to obtain n-type bismuth telluride-based thermoelectric material.

[0036] Example 4

[0037] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.45 Se 0.55 Bi, Cu, Te, and Se with a purity of 99.99% or higher were weighed out according to the stoichiometric ratio of each element. The other steps were the same as in Comparative Example 1 to obtain n-type bismuth telluride-based thermoelectric material.

[0038] Example 5

[0039] In step 1 of this embodiment, according to the chemical formula Cu 0.02 Bi2Te 2.5 Se 0.5 In +0.25%Bi2S3, Bi, Cu, Te, Se, and S elements with a purity of ≥99.99% were weighed out according to their stoichiometric ratios. The other steps were the same as 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 0.5In +0.5% Bi2S3, Bi, Cu, Te, Se, and S elements with a purity of ≥99.99% were weighed out according to their stoichiometric ratios. The other steps were the same as in Comparative Example 1 to obtain 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 In +0.75%Bi2S3, Bi, Cu, Te, Se, and S elements with a purity of ≥99.99% were weighed out according to their stoichiometric ratios. The other steps were the same as in Comparative Example 1 to obtain 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 In +1%Bi2S3, Bi, Cu, Te, Se, and S elements with a purity of ≥99.99% were weighed out according to their stoichiometric ratios. The other steps were the same as in Comparative Example 1 to obtain n-type bismuth telluride-based thermoelectric material.

[0046] The bulk materials obtained in the above embodiments and comparative examples were cut according to the test specifications and then polished with 2000-grit sandpaper. The conductivity and Seebeck coefficient of the samples from 323 K to 573 K were measured using a ZEM-3 (Ulvac-Riko, Japan) thermoelectric performance testing system, and the corresponding power factor PF = S was calculated. 2 σ. The method for calculating thermal conductivity is k = D × C. p ×ρ, where the thermal diffusivity D is measured using a laser flare thermal conductivity meter LFA 467 (Netzsch, Germany), and the specific heat C is... p The density ρ was obtained through the Dulong-Petit limit estimation and measured using the Archimedes displacement method. Finally, the formula ZT = S was used. 2 The thermoelectric figure of merit ZT of the sample was calculated using σT / к. The Vickers hardness tester was a Chinese HV-1000.

[0047] It is worth noting that, considering the anisotropy of bismuth telluride-based thermoelectric materials, to ensure the consistency of electrical and thermal performance testing and analysis, the performance tests for the above examples and comparative examples were all conducted perpendicular to the sintering pressure. The test results are shown below. Figures 1-4 .

[0048] As shown in the figure, the thermoelectric material in Comparative Example 1 has a moderate power factor, but its thermal conductivity is high, reaching 1.4 W / m² at room temperature.-1 K -1 This resulted in an extremely low ZT value. By adding additional Cu to Comparative Example 2, the power factor was significantly improved due to the increased carrier mobility caused by the special interstitial sites of Cu. However, the donor doping effect introduced by the interstitial Cu also increased the carrier concentration, resulting in a still relatively high thermal conductivity of 1.3 W / m² at room temperature. -1 K -1 The high thermal conductivity limits the improvement of the ZT value, which is only 0.9 at room temperature. Based on this, in Examples 1-4, the ZT value was precisely controlled... 0.02 Bi2Te 2.7-x Se 0.3+x The carrier concentration was optimized by adjusting the Te and Se content of the material (0.1≤x≤0.25), significantly reducing thermal conductivity while maintaining a high power factor. In particular, with the optimal composition x=0.2, the room temperature thermal conductivity of the material decreased to 1.01 W / m². -1 K -1 Combined with the maintained power factor, the ZT value at room temperature was increased to 1.04, representing increases of 57% and 15.5% compared to Comparative Example 1 and Comparative Example 2, respectively. To further improve the ZT value of the material, Examples 5-8 used the optimal Cu composition... 0.02 Bi2Te 2.5 Se 0.5 The addition of Bi₂S₃ further enhances phonon scattering by creating multi-scale microstructural defects in the material, leading to a significant reduction in lattice thermal conductivity and resulting in extremely low overall thermal conductivity, while maintaining a high power factor across the entire temperature range. Particularly at y = 0.5, the room-temperature thermal conductivity decreases to 0.9 W / m². -1 K -1 Compared to Comparative Examples 1 and 2, the ZT values ​​were reduced by 36% and 30%, respectively, with the ZT value increasing to 1.12 at room temperature and reaching a maximum ZT value of 1.26 at 373 K. The maximum ZT value was approximately 40% and 14.5% higher than that of Comparative Examples 1 and 2, respectively. Furthermore, by comparing the Vickers hardness of Comparative Examples 1, 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 Examples 3 and 6 were 0.78 GPa and 0.88 GPa, respectively, which were significantly improved compared to Comparative Examples 1 and 2, indicating that the mechanical properties of the material were significantly improved.

[0049] The above description describes some specific embodiments of the present invention, but the scope of protection of the present invention is not limited to the above embodiments. It should be noted that for those skilled in the art, simple substitutions or improvements made to the technical solutions of the present invention without departing from the concept of the present invention are all within the scope of protection of the present invention.

Claims

1. A high-performance n Bismuth telluride-based thermoelectric materials, 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 according to claim 1 n Bismuth telluride-based thermoelectric materials, characterized in that: x =0.2， y =0.5。 3. A high-performance [device] according to claim 1 n A method for preparing bismuth telluride-based thermoelectric materials, characterized in that: The preparation method includes the following steps: Step 1: According to Cu 0.02 Bi2Te 2.7-x Se 0.3+x + y% Bi₂S₃ stoichiometry: Weigh out elements Bi, Cu, Te, Se, and S respectively, where 0.1 ≤ x ≤ 0.25, 0 ≤ y ≤ 1; After the weighed elements are mixed evenly, they are placed into a quartz tube, sealed under vacuum, and then melted to obtain an alloy ingot; The melting is divided into two stages, the melting temperature of the first stage is 450~500℃, the holding time is 2~4h, and the melting temperature of the second stage is 800~1100℃, the holding time is 6~18h. Step 2: Ball mill the alloy ingot obtained in Step 1 to obtain a uniform and fine powder; Step 3: The powder obtained in Step 2 is loaded into a mold for sintering to obtain a dense bulk material, i.e. n The bismuth telluride-based thermoelectric material is sintered by spark plasma sintering at a temperature of 400–480°C, a sintering time of 5–10 min, and a sintering pressure of 40–50 MPa.

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

5. The high-performance according to claim 3 n A method for preparing bismuth telluride-based thermoelectric materials, characterized in that: Step 1, the vacuum degree of the vacuum seal is ≤8 × 10⁻⁶ -4 Pa.

6. The high-performance according to claim 3 n A method for preparing bismuth telluride-based thermoelectric materials, characterized in that: In step 1, the heating rate of the melt is 1 to 2 °C / min.

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

8. The high-performance according to claim 3 n A method for preparing bismuth telluride-based thermoelectric materials, characterized in that: The sintering heating rate is 50–100 °C / min.

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