A high-performance N-type bismuth telluride, its preparation method and application

Abstract

This invention discloses a high-performance N-type bismuth telluride, its preparation method, and its applications, relating to the field of thermoelectric materials technology. The preparation method of the high-performance N-type bismuth telluride provided by this invention involves incorporating a certain amount of TeO2 during the batching process to balance the intrinsic oxygen defects of N-type bismuth telluride and the donor-like effect induced by Te vacancies. Subsequently, the N-type bismuth telluride powder is ball-milled in the presence of liquid nitrogen. Liquid nitrogen simultaneously provides a stable phase structure and promotes material shrinkage to generate cracks. Therefore, this invention can improve the thermoelectric performance of bismuth telluride while ensuring the uniformity and stability of its properties.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric materials technology, specifically to a high-performance N-type bismuth telluride, its preparation method, and its applications. Background Technology

[0002] Bismuth telluride-based thermoelectric materials possess good electrical conductivity and low thermal conductivity, making them among the most widely used commercial thermoelectric materials. However, thermoelectric devices require the use of both P-type and N-type thermoelectric materials with matching performance, and current N-type bismuth telluride materials still fall short of P-type bismuth telluride in terms of thermoelectric performance. Furthermore, N-type bismuth telluride has a narrow process window, and even under the same process conditions, its performance can exhibit random fluctuations. This is primarily because, under the influence of a donor-like effect, the thermoelectric performance of N-type bismuth telluride is highly sensitive to doping with impurities (such as oxygen). This random fluctuation leads to significant performance differences between different production batches of N-type bismuth telluride, limiting its large-scale commercialization. Therefore, there is an urgent need to provide a production process that can simultaneously improve the thermoelectric performance and performance stability of N-type bismuth telluride materials. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a high-performance N-type bismuth telluride, its preparation method, and its applications.

[0004] The above-mentioned objective of this invention is achieved through the following technical solution: A method for preparing high-performance N-type bismuth telluride includes the following steps: S1. Mix the raw materials for preparing N-type bismuth telluride and TeO2 at a volume ratio of 100:(0.05-0.5), melt, cast into an ingot, and then mechanically crush to obtain bismuth telluride precursor powder; the raw materials for preparing N-type bismuth telluride include elemental Bi, elemental Se and elemental Te; S2. The bismuth telluride precursor powder obtained in step S1 is ball-milled in a closed environment in the presence of liquid nitrogen until the particle size D50 ≤ 10 μm, thus obtaining high-performance N-type bismuth telluride; the amount of liquid nitrogen filling in the closed environment is 65-85 vol.

[0005] The method for preparing N-type bismuth telluride provided by this invention incorporates a certain amount of TeO2 during the batching process to balance the intrinsic oxygen defects of N-type bismuth telluride and the donor-like effect induced by Te vacancies, thereby synergistically optimizing the carrier concentration and phonon transport behavior of the N-type bismuth telluride thermoelectric material. Subsequently, the N-type bismuth telluride powder is ball-milled in the presence of liquid nitrogen. This not only prevents the bismuth telluride material from being oxidized and from introducing other impurities, but also, as a cooling medium, liquid nitrogen has a "quenching" effect on the bismuth telluride precursor powder, enabling the N-type bismuth telluride that undergoes mechanical alloying during ball milling to transform into a stable phase structure with high thermoelectric performance. Simultaneously, the cooling effect of the low temperature of liquid nitrogen causes the N-type bismuth telluride powder to shrink and crack, reducing the particle size and improving the uniformity of the obtained material. Based on the above operations, this invention can improve the thermoelectric performance of bismuth telluride while ensuring the uniformity and stability of the N-type bismuth telluride properties.

[0006] It should be noted that the ball milling in step S2 is required to achieve a particle size D50 ≤ 10 μm in order to improve the uniformity of the microstructure of the obtained N-type bismuth telluride product. This uniformity is a prerequisite for improving the batch stability of bismuth telluride alloy production.

[0007] It should be noted that in step S2, in order to ensure that liquid nitrogen simultaneously provides an inert atmosphere, cooling, and stabilization, its introduction into the sealed environment needs to be limited to a specific range. If the amount of liquid nitrogen filling in the sealed environment is too low, the liquid nitrogen will not be able to play its due role; however, if the amount of liquid nitrogen filling is too high, the powder particles will shrink too much, which can easily lead to over-activation, resulting in agglomeration or oxidation, which will also affect the performance of the obtained N-type bismuth telluride.

[0008] In a specific embodiment of the present invention, the gas atmosphere in the sealed environment described in step S2 is provided by a mixture of liquid nitrogen and air, and the air filling volume in the sealed environment is 15-35 vol.

[0009] Preferably, in the raw material element for preparing N-type bismuth telluride in step S1, the stoichiometric ratio of each element element is Bi element: Se element: Te element = (2+x): y: (3-y), where 0≤x≤0.3, 0≤y≤1.

[0010] Typical, but not restrictive, stoichiometric ratios of the elements in their elemental forms are: Bi:Se:Te = 2.02:0.3:2.7, Bi:Se:Te = 2.015:0.3:2.7, Bi:Se:Te = 2:0.3:2.7, and Bi:Se:Te = 2.015:0.2:2.8.

[0011] Preferably, the volume ratio of the raw material element and TeO2 in step S1 for preparing N-type bismuth telluride is 100:(0.2-0.3).

[0012] Preferably, the melting in step S1 is carried out at a temperature of 500-1000°C for a time of 2-20 hours.

[0013] Preferably, the melting in step S1 is carried out under a vacuum degree ≤ 5 × 10⁻⁶. -4 The experiment was conducted under the condition of Pa.

[0014] Preferably, the heating rate during melting in step S1 is 1~5℃ / min.

[0015] Preferably, the melting in step S1 is carried out in a swaying furnace, wherein the swaying angle of the swaying furnace is 30°-70°.

[0016] Preferably, the particle size D50 of the bismuth telluride precursor powder in step S1 is ≤500μm.

[0017] Limiting the particle size of the bismuth telluride precursor powder before ball milling helps to improve the overall preparation efficiency while further preventing the oxidation of bismuth telluride.

[0018] Preferably, the D50 particle size of the bismuth telluride precursor powder in step S1 is 100-350 μm.

[0019] Preferably, the mechanical crushing in step S1 includes a jaw crusher and / or a disc mill.

[0020] Preferably, after mechanical crushing in step S1, a screening step is further included, wherein the screening is performed using a sieve with a mesh size of 15-60 mesh.

[0021] More preferably, the mechanical crushing in step S1 is as follows: the ingot is crushed by jaw crusher to obtain large particles, and then subjected to disc milling; the jaw crusher is used for crushing, and the gap of the jaw crusher is ≤5 mm; the disc milling is used for disc grinding, and the grinding spacing of the disc grinding is 0.15-0.35 mm.

[0022] Preferably, the amount of liquid nitrogen filling the sealed environment in step S2 is 70-80 vol%.

[0023] Preferably, the rotational speed of the ball mill in step S2 is 200-400 rpm.

[0024] Preferably, the ball-to-material ratio in step S2 is (2-4):(1-4).

[0025] Preferably, the ball milling time in step S2 is 8-14 hours.

[0026] More preferably, the ball milling in step S2 is performed using a planetary ball mill.

[0027] More preferably, the D50 particle size of the high-performance N-type bismuth telluride after ball milling in step S2 is 1-5 μm.

[0028] Preferably, step S2 further includes a sieving step after ball milling, wherein the sieving is performed using a sieve with a mesh size of 2000-12500.

[0029] More preferably, the step after screening further includes a forming step, wherein the forming includes hot pressing, and the hot pressing pressure is 100-200 MPa.

[0030] This invention also protects a high-performance N-type bismuth telluride prepared by the above preparation method.

[0031] This invention also protects the application of the above-mentioned high-performance N-type bismuth telluride in thermoelectric devices.

[0032] Compared with the prior art, the present invention has the following beneficial effects: The preparation method provided by this invention can produce N-type bismuth telluride materials with both high thermoelectric properties and production stability, and the power factor of the obtained N-type bismuth telluride is as high as 41.55 μW cm⁻¹. -1 K -2 The thermoelectric figure of merit is as high as 0.95, and the performance variation rate between different batches in actual production is no higher than ±4%. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0034] Example 1 A method for preparing high-performance N-type bismuth telluride includes the following steps: S1. According to Bi 2.02 Te 2.7 Se 0.3 The stoichiometric ratio of the raw material for preparing N-type bismuth telluride, as shown in the chemical formula, was weighed. Then, TeO2 was weighed according to a volume ratio of 100:0.2 (N-type bismuth telluride raw material to TeO2), mixed thoroughly, and placed into a quartz tube. The tube was then vacuum-sealed at a vacuum degree of 5 × 10⁻⁶. -4 Pa; The quartz tube was transferred to a swing muffle furnace and heated to 700℃ at a rate of 1℃ / min, held for 4 h to melt. After cooling in the furnace, an alloy ingot was obtained, which was then placed in a jaw crusher to crush large particles (jaw crusher gap 2 mm). The large particles were then placed in a disc mill for disc grinding, with the disc mill spacing set to 0.2 mm. After disc grinding, the particles were passed through a 40-mesh sieve to obtain bismuth telluride precursor powder with a particle size ≤425μm (D50 particle size is 185μm). S2. The bismuth telluride precursor powder obtained in step S1 is loaded into a ball mill jar, and the ball mill jar is filled with liquid nitrogen (the liquid nitrogen filling rate is 75 vol%) and then sealed. Ball milling is carried out at a ball milling speed of 250 rpm and a ball-to-powder ratio of 3:2 for 10 h. After ball milling, the high-performance N-type bismuth telluride (D50 particle size is 2.5 μm) is obtained by sieving.

[0035] Example 2 A method for preparing high-performance N-type bismuth telluride, wherein the only difference from Example 1 is: In step S1, according to Bi 2.15 Te 2.8 Se 0.2 The raw material for the preparation of N-type bismuth telluride was weighed according to the stoichiometric ratio shown in the chemical formula. Then, TeO2 was weighed according to the volume ratio of the raw material for the preparation of N-type bismuth telluride to TeO2 of 100:0.5. After disc milling, the powder was passed through a 16-mesh sieve to obtain bismuth telluride precursor powder with a particle size ≤1000μm (D50 particle size is 326μm). In step S2, the ball mill jar is filled with 65 vol% liquid nitrogen, the ball milling speed is 400 rpm, the ball-to-material ratio is 4:4, and the time is 14 h. After ball milling, the high-performance N-type bismuth telluride (D50 particle size is 1.5 μm) can be obtained by sieving.

[0036] Example 3 A method for preparing high-performance N-type bismuth telluride, wherein the only difference from Example 1 is: In step S1, according to Bi 2.3 The chemical formula of Te2Se shows the stoichiometric ratio of the raw material for the preparation of N-type bismuth telluride. Then, TeO2 is weighed according to the volume ratio of the raw material for the preparation of N-type bismuth telluride to TeO2 of 100:0.05. After disc milling, the powder is passed through a 60-mesh sieve to obtain bismuth telluride precursor powder with a particle size ≤250μm (D50 particle size is 147.8μm). In step S2, the ball mill jar is filled with 85 vol% liquid nitrogen, the ball milling speed is 200 rpm, the ball-to-material ratio is 4:4, and the time is 8h. After ball milling, the high-performance N-type bismuth telluride (D50 particle size is 5μm) can be obtained by sieving.

[0037] Example 4 A method for preparing high-performance N-type bismuth telluride, wherein the only difference from Example 1 is: In step S1, TeO2 is weighed according to the volume ratio of the raw material element for the preparation of N-type bismuth telluride to TeO2 of 100:0.3.

[0038] Example 5 A method for preparing high-performance N-type bismuth telluride, wherein the only difference from Example 1 is: In step S1, TeO2 is weighed according to the volume ratio of elemental raw material for the preparation of N-type bismuth telluride to TeO2 of 100:0.4.

[0039] Example 6 A method for preparing high-performance N-type bismuth telluride, wherein the only difference from Example 1 is: In step S1, according to Bi2Te 2.64 Se 0.3 The chemical formula shows the stoichiometric ratio of the raw material for the preparation of N-type bismuth telluride.

[0040] Comparative Example 1 A method for preparing N-type bismuth telluride, wherein the only difference from Example 1 is: TeO2 is not added in step S1.

[0041] Comparative Example 2 A method for preparing N-type bismuth telluride, wherein the only difference from Example 1 is: In step S1, TeO2 is weighed according to the volume ratio of elemental raw material for the preparation of N-type bismuth telluride to TeO2 of 100:0.6.

[0042] Comparative Example 3 A method for preparing N-type bismuth telluride, wherein the only difference from Example 1 is: In step S2, the amount of liquid nitrogen filled is 60 vol.

[0043] Comparative Example 4 A method for preparing N-type bismuth telluride, wherein the only difference from Example 1 is: In step S2, the amount of liquid nitrogen filled is 100 vol.

[0044] Comparative Example 5 A method for preparing N-type bismuth telluride, wherein the only difference from Example 1 is: In step S2, after ball milling and sieving, high-performance N-type bismuth telluride with a D50 particle size of 50 μm is obtained.

[0045] Comparative Example 6 A method for preparing N-type bismuth telluride, wherein the only difference from Example 2 is: TeO2 is not added in step S1.

[0046] Comparative Example 7 A method for preparing N-type bismuth telluride, wherein the only difference from Example 3 is: TeO2 is not added in step S1.

[0047] Comparative Example 8 A method for preparing N-type bismuth telluride, wherein the only difference from Example 6 is: TeO2 is not added in step S1.

[0048] Performance testing Thermoelectric performance testing: The N-type bismuth telluride samples obtained in the examples and comparative examples were hot-pressed under a pressure of 150 MPa to obtain test samples. The electrical conductivity and Seebeck coefficient of the thermoelectric material at 300 K to 400 K were measured using a CTA thermoelectric testing system, and the thermal conductivity of the samples was measured using a CLA laser thermal conductivity meter. The results were obtained using the formula PF=S 2 σ and zT=S 2 The power factor and thermoelectric figure of merit of the thermoelectric material are obtained by σT / κ calculation.

[0049] Performance stability test: Five groups of N-type bismuth telluride were prepared according to the method provided in Example 1, and hot-pressed under 150 MPa pressure to obtain test samples. The performance of the five groups of samples was tested according to the "Thermoelectric Performance Test" method.

[0050] The results of the above performance tests are shown in Table 1-2 below: Table 1. Table 2. Note: In the table above, "Performance Change Rate" refers to the deviation between the power factor of this group and the average power factor of the five groups. The calculation method is: (Power factor of this group - average power factor of the five groups) / average power factor of the five groups.

[0051] As can be seen from Tables 1-2 above, the preparation method provided by this invention can prepare N-type bismuth telluride materials with both high thermoelectric properties and production stability. The power factor of the obtained N-type bismuth telluride is as high as 41.55 μW cm⁻¹. -1 K -2 The thermoelectric figure of merit is as high as 0.95, and the performance variation rate between different batches in actual production is no higher than ±4%.

[0052] According to Comparative Examples 1, 6-8, the introduction of TeO2 is key to this application.

[0053] According to Comparative Example 2, excessive addition of TeO2 can also lead to a decrease in the performance of thermoelectric materials.

[0054] According to Comparative Examples 3-4, the unsuitable amount of liquid nitrogen filling cannot achieve the desired effect.

[0055] According to Comparative Example 5, when the particle size of bismuth telluride powder is too large, it will affect the uniformity of the properties of the obtained material.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing high-performance N-type bismuth telluride, characterized in that, Includes the following steps: S1. Mix the raw materials for preparing N-type bismuth telluride and TeO2 at a volume ratio of 100:(0.05-0.5), melt, cast into an ingot, and then mechanically crush to obtain bismuth telluride precursor powder; the raw materials for preparing N-type bismuth telluride include elemental Bi, elemental Se and elemental Te; S2. The bismuth telluride precursor powder obtained in step S1 is ball-milled in a closed environment in the presence of liquid nitrogen until the particle size D50 ≤ 10 μm, thus obtaining high-performance N-type bismuth telluride; the amount of liquid nitrogen filling in the closed environment is 65-85 vol.

2. The method for preparing high-performance N-type bismuth telluride as described in claim 1, characterized in that, In step S1, the stoichiometric ratio of each element in the raw material for preparing N-type bismuth telluride is Bi:Se:Te = (2+x):y:(3-y), where 0≤x≤0.3 and 0≤y≤1.

3. The method for preparing high-performance N-type bismuth telluride as described in claim 1, characterized in that, The melting in step S1 is carried out at a temperature of 500-1000℃ for a time of 2-20 h. And / or, the melting in step S1 is performed under a vacuum degree ≤ 5 × 10⁻⁶. -4 Under the condition of Pa; And / or, the heating rate during melting in step S1 is 1~5℃ / min; And / or, the melting described in step S1 is carried out in a swaying furnace, wherein the swaying angle of the swaying furnace is 30°-70°.

4. The method for preparing high-performance N-type bismuth telluride as described in claim 1, characterized in that, The particle size D50 of the bismuth telluride precursor powder in step S1 is ≤500μm.

5. The method for preparing high-performance N-type bismuth telluride as described in claim 1 or 4, characterized in that, The mechanical crushing described in step S1 includes a jaw crusher and / or a disc mill; And / or, the mechanical crushing described in step S1 may further include a screening step.

6. The method for preparing high-performance N-type bismuth telluride as described in claim 5, characterized in that, The mechanical crushing in step S1 is as follows: the ingot is crushed by jaw crusher to obtain large particles, and then the particles are ground by disc milling; the jaw crusher is used for crushing, and the gap of the jaw crusher is ≤5 mm; the disc milling is used for grinding, and the grinding gap of the disc mill is 0.15-0.35 mm.

7. The method for preparing high-performance N-type bismuth telluride as described in claim 1, characterized in that, The rotational speed of the ball mill in step S2 is 200-400 rpm; And / or, the ball-to-material ratio of the ball mill in step S2 is (2-4):(1-4); And / or, the ball milling time in step S2 is 8-14 hours.

8. The method for preparing high-performance N-type bismuth telluride as described in claim 1, characterized in that, Step S2, after ball milling, also includes a forming step, which includes hot pressing forming with a hot pressing pressure of 100-200 MPa.

9. High-performance N-type bismuth telluride prepared by the preparation method according to any one of claims 1-8.

10. The application of the high-performance N-type bismuth telluride as described in claim 9 in thermoelectric devices.

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