An elastic compressible bismuth telluride composite thermoelectric material, its preparation method and application

Abstract

The present invention relates to the technical field of thermoelectric materials, and discloses an elastic compressible bismuth telluride composite thermoelectric material, a preparation method thereof and an application thereof. The preparation method includes: uniformly mixing bismuth telluride powder, graphene, a pore-forming agent and a polyurethane prepolymer, compacting and curing in a mold; then soaking in water to remove sodium chloride; then performing high-temperature treatment in a protective atmosphere to remove polyurethane to obtain a porous sample; then immersing the porous sample in an Ecoflex solution diluted with n-hexane and curing in an oven to finally obtain an elastic compressible bismuth telluride composite thermoelectric material. The preparation process of the present invention is simple, and the prepared elastic bismuth telluride composite thermoelectric material has good thermoelectric performance and compressibility, and has broad application prospects as a thermoelectric material in the fields of flexible thermoelectricity, heat energy collection and wearable devices.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric materials, and particularly relates to an elastic compressible bismuth telluride composite thermoelectric material, a preparation method thereof, and an application thereof. Background Art

[0002] As an innovative material that can directly convert thermal energy into electrical energy, thermoelectric materials provide a new way for the collection and utilization of thermal energy. However, due to the rigid and brittle characteristics of traditional inorganic semiconductor thermoelectric materials, their wide application in practical applications is limited, making it difficult to effectively collect many low-grade thermal energies. In view of this, it is particularly important to develop flexible thermoelectric materials, which can not only broaden the application scope of thermoelectric materials but also realize the innovation of flexible wearable devices, thereby more effectively collecting low-grade thermal energies in the human body and daily life. Bismuth telluride is currently the only commercially applied semiconductor thermoelectric material with good thermoelectric performance and is widely used in thermoelectric power generation and thermoelectric refrigeration. However, traditional bismuth telluride-based thermoelectric materials and devices usually require high-temperature synthesis experimental devices, plasma-activated sintering equipment, grinding and polishing equipment, etc. during the preparation process, resulting in a complex and cumbersome preparation process and high costs. More importantly, due to its large rigidity and poor flexibility, the application of bismuth telluride in the fields of flexible electronics and wearable devices is limited. Based on the above considerations, it is of great significance to design and prepare high-performance flexible bismuth telluride-based thermoelectric materials, which will promote their broad application prospects in the fields of flexible inorganic thermoelectrics, self-powered sensing and monitoring, and wearable devices. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a preparation method of a high-performance elastic compressible bismuth telluride composite thermoelectric material. Through design and regulation, the obtained thermoelectric material can obtain good thermoelectric performance and compression performance.

[0004] To achieve the above object, the present invention provides a preparation method of an elastic compressible bismuth telluride composite thermoelectric material, which includes the following steps:

[0005] 1) Mix bismuth telluride powder, graphene, pore-forming agent, and polyurethane prepolymer evenly, and press and compact them tightly in a mold for curing;

[0006] Wherein: based on 1 g of the mass of the polyurethane prepolymer, the corresponding mass of the bismuth telluride powder is 0.5 - 10 g, the mass of the pore-forming agent is 2 - 15 g, and the mass of the graphene is 10 - 100 mg; the pore-forming agent is one or several of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate;

[0007] 2) Immerse the sample obtained by curing in step 1) in water to remove sodium chloride, and then after drying, perform high-temperature treatment at 400 - 560 °C in a protective atmosphere to remove polyurethane, obtaining a porous sample;

[0008] 3) Immerse the porous sample obtained in step 2) in an Ecoflex solution diluted with n-hexane at a temperature of -10 to 5 °C to allow Ecoflex to completely fill the pores of the sample, then take out the sample and place it in an oven for curing to finally obtain an elastic and compressible bismuth telluride composite thermoelectric material.

[0009] As a further preferred technical solution of the present invention, the type of polyurethane corresponding to the polyurethane prepolymer is one or a mixture of several of Clearflex PU95, Clearflex PU30, Clearflex PU60, and Clearflex PU200.

[0010] As a further preferred technical solution of the present invention, in step 1), based on 1 g of the mass of the polyurethane prepolymer, the mass of the bismuth telluride powder is 5 to 8 g.

[0011] As a further preferred technical solution of the present invention, in step 1), the curing temperature is 60 - 80 °C and the curing time is 8 - 12 h.

[0012] As a further preferred technical solution of the present invention, in step 2), the temperature for soaking the sample to remove sodium chloride is 80 - 100 °C and the soaking time is 24 - 48 h; and / or, the drying temperature for drying is 60 - 80 °C and the time is 2 - 4 h; and / or, the high-temperature treatment time is 2 - 6 h.

[0013] As a further preferred technical solution of the present invention, in step 3), the soaking time of the porous sample in the Ecoflex solution diluted with n-hexane is 8 - 12 h.

[0014] As a further preferred technical solution of the present invention, in step 3), the curing temperature is 60 - 80 °C and the curing time is 0.5 - 2 h.

[0015] As a further preferred technical solution of the present invention, in the Ecoflex solution, the mass ratio of n-hexane to the prepolymer of Ecoflex is 1:1 to 1:2.

[0016] According to another aspect of the present invention, the present invention also provides a bismuth telluride composite thermoelectric material prepared by the above method.

[0017] According to another aspect of the present invention, the present invention also provides an application of a bismuth telluride composite thermoelectric material as a thermoelectric material. Specifically, it can be applied to the fields of sensing monitoring and flexible wearable.

[0018] The preparation method of the elastic and compressible bismuth telluride composite thermoelectric material of the present invention, adopting the above technical solution, can achieve the following beneficial effects:

[0019] (1) The preparation method of the present invention is simple and easy to implement, and has the potential for mass production;

[0020] (2) The elastic and compressible bismuth telluride composite thermoelectric material of the present invention has good thermoelectric performance and compression performance;

[0021] (3) Based on the elastic and compressible bismuth telluride composite thermoelectric material, the present invention can prepare high-performance thermoelectric devices, which have good application prospects in the fields of low-grade heat energy collection, temperature monitoring, and wearable electronics. Description of the Drawings

[0022] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0023] Figure 1 It is a flow chart for the present invention to prepare an elastic and compressible bismuth telluride composite thermoelectric material by using bismuth telluride powder, graphene, sodium chloride and polyurethane;

[0024] Figure 2 It is the microscopic structure (SEM photo) of the porous bismuth telluride composite material and the distribution maps of Bi, Sb and Te elements in Example 1;

[0025] Figure 3 It is the optical photo of the elastic and compressible bismuth telluride composite thermoelectric material in Example 1;

[0026] Figure 4 It is the Seebeck coefficient of the high-performance porous bismuth telluride composite thermoelectric material after high-temperature treatment in Example 1 before and after immersion in Ecoflex;

[0027] Figure 5 It is the test result of the elastic and compressible bismuth telluride composite thermoelectric material in Example 1, including the stress-strain curves (A) with different compression degrees, and the Seebeck coefficient after 1000 cycles of cyclic compression at 20% strain (B);

[0028] Figure 6 It is the test of the response of the elastic and compressible bismuth telluride composite thermoelectric material to minute temperature changes in Example 1;

[0029] Figure 7 It is the photos of the porous bismuth telluride composite thermoelectric materials obtained in Examples 1 to 5 with different bismuth telluride contents;

[0030] Figure 8 It is the Seebeck coefficient of the elastic and compressible bismuth telluride composite thermoelectric materials obtained under different high-temperature treatments in Examples 6 and 7.

[0031] The realization of the object, functional features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. Detailed Embodiments

[0032] The following further describes in detail the detailed embodiments of the present invention with reference to the accompanying drawings. It should be understood that the detailed embodiments described herein are only for the purpose of illustration and explanation of the present invention, and are not used to limit the present invention.

[0033] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods used are all conventional methods unless otherwise specified.

[0034] The bismuth telluride (Bi2Te3) used in the following embodiments was purchased from Zhongnuo New Materials (Beijing) Technology Co., Ltd., graphene was purchased from Sichuan Kenye Technology Development Co., Ltd., polyurethane (Clearflex-95) was purchased from Shanghai Zhixin Technology Co., Ltd., sodium chloride particles were purchased from Shanghai Salt Industry Co., Ltd. of China National Salt Industry Corporation, and Ecoflex-0030 was purchased from SMOOTH-ON Company in the United States.

[0035] The test methods involved in the following embodiments: The Seebeck coefficient of the thermoelectric composite material was tested using a self-built test device. A low-voltage power supply, a commercial Peltier heating module, and TEC Service software were used to control the temperature (temperature difference) at both ends of the thermoelectric device. The open-circuit voltage at both ends of the thermoelectric device was measured using a Keithley 2450 data acquisition system, and the Seebeck coefficient was calculated. For the thermoelectric composite material designed in the embodiments of the present invention, taking the cylindrical structure as an example, the compression strain test of the bismuth telluride composite thermoelectric material was realized by a universal testing machine test system, which was connected to the Keithley 2450 system to record all electrical signals in real time.

[0036] Embodiment 1

[0037] The preparation method of the elastic and compressible bismuth telluride thermoelectric material and device of the present invention is as follows:

[0038] (1) Pour 5 g of commercial p-type bismuth telluride powder, 30 mg of graphene, 9 g of sodium chloride particles, 0.4 g of precursor A component and 0.6 g of precursor B component of polyurethane (Clearflex PU95) into a cylindrical mold, stir and mix well, then compact the mixture, and then take it out (diameter 16 mm, height 16 mm) to obtain an uncured bismuth telluride composite material;

[0039] (2) Place the uncured bismuth telluride composite material in step (1) in an oven at 60 °C for 12 h. After curing, take it out and then soak it in hot water at 80 °C for 48 h to remove salt.

[0040] (3) Put the desalted bismuth telluride composite material in step (2) into the oven again to dry, the temperature is 60 °C, and the drying time is 4 h.

[0041] (4) Perform high-temperature treatment on the bismuth telluride composite material in step (3), keep it at 560 °C for 3 h, and the heating rate is 4.5 °C / min. After the reaction is completed, take it out to obtain a porous bismuth telluride composite material.

[0042] (5) Immerse the porous bismuth telluride composite material obtained in step (4) in an Ecoflex-0030 solution diluted with n-hexane (2.5 g) (the mass ratio of n-hexane to Ecoflex prepolymer is 1:2), and put it in a refrigerator (temperature is -10~5 °C) to prevent Ecoflex from curing at room temperature. After Ecoflex completely enters the pores of the porous bismuth telluride, remove the excess Ecoflex on the surface and put it in the oven again for curing. The curing temperature is 60 °C, and the curing time is 1 h. Finally, a high-performance elastic and compressible bismuth telluride composite thermoelectric material is obtained.

[0043] Figure 1 The flow chart shows the preparation of a compressible bismuth telluride thermoelectric composite material using commercial p-type bismuth telluride powder (Bi2Te3), high graphene, polyurethane (PU) and sodium chloride (NaCl) in Example 1, including several main steps such as curing, soaking, high-temperature sintering, and dipping in glue.

[0044] Figure 2 It is the microstructure and EDS element distribution map of the porous bismuth telluride composite material in Example 1. It can be seen that the material has a porous structure and the element distribution is uniform.

[0045] Figure 3 It is the optical photo of the elastic and compressible bismuth telluride composite thermoelectric material after being immersed in Ecoflex glue in Example 1, showing the good compressibility and resilience of the porous bismuth telluride thermoelectric composite material after dipping in glue. Specifically, when compressed by hand, it can be seen that the height is almost unchanged before and after compression, indicating good resilience.

[0046] Figure 4 It is the test result (V-t graph) of the Seebeck coefficient of the high-performance porous bismuth telluride composite thermoelectric material before and after dipping in glue in Example 1. The Seebeck coefficient before dipping in Ecoflex glue is 206.22 μV / K ( Figure 4 A), and the Seebeck coefficient after dipping in glue is 195.87 μV / K ( Figure 4B). Before impregnation, the porous bismuth telluride is incompressible and is easily crushed when pressed forcefully; after impregnation, since the Ecoflex glue enters the pores of the bismuth telluride and plays a supporting role, and since the Ecoflex glue will wrap up a very small part of the bismuth telluride, the Seebeck coefficient will be slightly reduced. In addition, the compression test will damage the three-dimensional network structure of the bismuth telluride, but the degree of damage is very small, and it will also cause the Seebeck coefficient to decrease slightly.

[0047] Figure 5 For the mechanical properties of the elastic compressible bismuth telluride composite thermoelectric material with different compression strains and the thermoelectric properties under compression cycles in Example 1, it can be seen that under the compression tests of 10%, 20% and 30% using a universal testing machine, the bismuth telluride composite thermoelectric material maintains good resilience and no strain hysteresis behavior occurs ( Figure 5 A). Among them, after 1000 cycles of 20% compression strain, the Seebeck coefficient only drops from 197.37 μV / K to 186.32 μV / K, showing good thermoelectric stability ( Figure 5 B).

[0048] Figure 6 For the micro temperature response test of the elastic compressible bismuth telluride composite thermoelectric material in Example 1; Figure 6 A is the test schematic diagram. Two commercial Peltier patches (which can achieve heating or cooling functions) are used, one on top and one on the bottom. The one on top keeps the temperature constant, fixed at 20 °C here, and the heating element below changes from 20 °C to 20.05 °C, 20.10 °C, 20.15 °C, 20.20 °C in sequence, and the corresponding temperature differences are 0.05, 0.10, 0.15, 0.2 K respectively. The upper and lower electrodes of the bismuth telluride are connected to the test instrument Keithley 2450 to record the voltage change, and the test data is as Figure 6 B. The test results show that the composite thermoelectric material can have regular changes in the thermoelectric signal under the change of a small temperature difference, and the minimum monitored temperature difference can reach 0.05 K. The micro temperature response test is often used in wearable electronic devices, such as for monitoring human body temperature changes; it is also often used in the field of artificial intelligence. For example, temperature monitoring is one of the most basic functions of bionic robots and can be used to identify the external temperature and the temperature of a certain object. Currently, most temperature sensors have a resolution greater than 0.1 K, and very few can achieve 0.05 K. The present invention can reach 0.05 K, indicating excellent temperature monitoring ability.

[0049] Examples 2 - 5

[0050] Five groups of examples are provided, and elastic compressible bismuth telluride composite thermoelectric materials are prepared respectively. The specific method is as follows:

[0051] The amount of p-type bismuth telluride powder in step (1) of Example 1 was changed to 1 g, 2 g, 3 g, 4 g, and 10 g respectively, and the remaining steps were the same as those in Example 1.

[0052] By adjusting the content of bismuth telluride, when the dosage of p-type bismuth telluride powder is 1-5 g, the morphological changes of the obtained thermoelectric materials are as Figure 7 shown. It can be seen that only when the mass of bismuth telluride is greater than 4 g, the thermoelectric properties of the prepared thermoelectric materials can maintain the same size and morphology as the initial ones after sintering. Among them, when the content of bismuth telluride is small (1-4 g), the prepared bismuth telluride composite thermoelectric materials will collapse after high-temperature treatment, and the thermoelectric properties are relatively small. The specific test results are as follows (the following results are all for the case without dipping in glue):

[0053] At a bismuth telluride content of 1 g, the Seebeck coefficient of the corresponding composite thermoelectric material is 130 μV / K;

[0054] At a bismuth telluride content of 2 g, the Seebeck coefficient of the corresponding composite thermoelectric material is 150 μV / K;

[0055] At a bismuth telluride content of 3 g, the Seebeck coefficient of the corresponding composite thermoelectric material is 170 μV / K;

[0056] At a bismuth telluride content of 4 g, the Seebeck coefficient of the corresponding composite thermoelectric material is 180 μV / K;

[0057] At a bismuth telluride content of 10 g, the Seebeck coefficient of the corresponding composite thermoelectric material is 220 µV / K.

[0058] It can be seen that compared with Example 1, the comprehensive performance of Examples 2-5 becomes worse, but still has certain elastic compressibility and certain thermoelectric properties. In addition, the excessive amount of p-type bismuth telluride powder was also tested. After a large number of experiments, when the dosage exceeds 10 g, due to excessive use, the porosity is very low and it is difficult to dip in glue. Although a part of the glue can be dipped, it results in a large rigidity of the sample and almost no flexibility and compressibility. Therefore, in order to ensure the comprehensive performance, based on the mass of 1 g of polyurethane prepolymer in the present invention, the mass of the corresponding bismuth telluride powder is preferably 5-8 g.

[0059] Examples 6-7

[0060] Two groups of examples were provided to prepare elastic compressible bismuth telluride composite thermoelectric materials, and the specific methods are as follows:

[0061] The high-temperature treatment temperature (560 °C) in step (4) of Example 1 was changed to 400 °C and 300 °C respectively, and the remaining steps were the same as those in Example 1.

[0062] According to the voltage-temperature difference fitting results, it can be seen that the Seebeck coefficient obtained under the high-temperature treatment at 400 °C is approximately 191.42 μV / K ( Figure 8 A); under the high-temperature treatment at 300 °C, the Seebeck coefficient of the corresponding composite thermoelectric material is approximately 163.63 μV / K ( Figure 8 B), indicating that a lower treatment temperature will reduce the thermoelectric performance of the elastic compressible bismuth telluride composite thermoelectric material. By changing the high-temperature treatment temperature, the elastic compressible bismuth telluride composite thermoelectric material obtained in the present invention exhibits different thermoelectric performances. Lowering the high-temperature treatment temperature will gradually reduce the Seebeck coefficient. The high-temperature treatment is mainly to remove the polyurethane binder inside, so that good contact is maintained between bismuth telluride. However, too low a temperature will cause incomplete removal of polyurethane and reduce the thermoelectric performance. Too high a temperature will cause bismuth telluride to melt (melting point 573 °C). Therefore, 560 °C is preferably set as the upper limit temperature. Therefore, the preferred temperature range for high-temperature heat treatment in the present invention is 400 - 560 °C.

[0063] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to these embodiments without departing from the principle and essence of the present invention. The protection scope of the present invention is only defined by the appended claims.

Claims

1. A method for preparing an elastically compressible bismuth telluride composite thermoelectric material, characterized in that: The following steps are involved: 1) Mix bismuth telluride powder, graphene, pore-forming agent and polyurethane prepolymer evenly, and compact them in a mold for curing at a temperature of 60-80 °C for 8-12 h; Wherein: based on the mass of 1 g of the polyurethane prepolymer, the mass of the corresponding bismuth telluride powder is 5-8 g, the mass of the pore-forming agent is 2-15 g, and the mass of the graphene is 10-100 mg; the pore-forming agent is one or more of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate; the polyurethane type corresponding to the polyurethane prepolymer is one or a mixture of Clearflex PU95, Clearflex PU30, Clearflex PU60, and Clearflex PU200; 2) soaking the sample obtained by curing in step 1) in water to remove the pore-forming agent, drying it, and then subjecting it to high-temperature treatment at 400-560° C. in a protective atmosphere to remove the polyurethane, thereby obtaining a porous sample; 3) The porous sample of step 2) is immersed in an Ecoflex prepolymer solution diluted with n-hexane at a temperature of -10 to 5 °C, so that the Ecoflex prepolymer completely fills the pores of the sample, and then the sample is taken out and placed in an oven for curing, and finally an elastically compressible bismuth telluride composite thermoelectric material is obtained.

2. The method for preparing the elastically compressible bismuth telluride composite thermoelectric material according to claim 1, characterized in that: In step 2), when the pore-forming agent is sodium chloride, the temperature for soaking the sample to remove the sodium chloride is 80-100°C, and the soaking time is 24-48 hours; and / or, the drying temperature for drying is 60-80°C, and the time is 2-4 hours; and / or, the high temperature treatment time is 2-6 hours.

3. The method for preparing the elastically compressible bismuth telluride composite thermoelectric material according to claim 1, characterized in that: In step 3), the porous sample is immersed in the Ecoflex prepolymer solution diluted with n-hexane for 8-12 h.

4. The method for preparing the elastically compressible bismuth telluride composite thermoelectric material according to claim 1, characterized in that: In step 3), the curing temperature is 60-80°C and the curing time is 0.5-2 h.

5. The method for preparing the elastically compressible bismuth telluride composite thermoelectric material according to claim 1, characterized in that: In the Ecoflex prepolymer solution, the mass ratio of n-hexane to Ecoflex prepolymer is 1:1-1:

2.

6. A bismuth telluride composite thermoelectric material, characterized in that: It is prepared by the method described in any one of claims 1 to 5.

7. Use of the bismuth telluride composite thermoelectric material according to claim 6 as a thermoelectric material.

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