Composite thermoelectric material and preparation method thereof

Abstract

The invention discloses a composite thermoelectric material and a preparation method thereof, and relates to the technical field of thermoelectric materials. The method comprises the following steps: (1) carrying out ultrasonic treatment on nylon nanofibers in a solvent to obtain a nylon nanofiber dispersion liquid; (2) adding Bi2Te3 powder into the nylon nanofiber dispersion liquid, and uniformly mixing to obtain a mixed solution; and (3) drying and grinding the mixed solution to obtain composite thermoelectric material powder, and finally performing SPS sintering to obtain the composite thermoelectric material. Or carrying out silk-screen printing treatment on the mixed solution to obtain a composite thermoelectric material film, and finally carrying out cold pressing sintering treatment to obtain the composite thermoelectric material. According to the method, the thermoelectric performance of the composite thermoelectric material can be effectively improved, meanwhile, the mechanical performance of the composite thermoelectric material is improved compared with that of pure Bi2Te3, material assembly and device service are facilitated, and the method plays a positive role in device preparation and practical application.

Description

Technical Field

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

[0002] The thermoelectric effect includes the Seebeck effect, the Peltier effect, and the Thomson effect. All three originate from the difference in the energy carried by carriers in a conductor, and together they constitute a complete system of physical effects for the direct conversion of heat and electricity. Through the thermoelectric effect, waste heat utilization and thermoelectric refrigeration can be achieved, improving energy utilization efficiency while enhancing economic benefits, which is of great significance for alleviating energy and environmental protection.

[0003] The performance of thermoelectric materials mainly depends on the dimensionless thermoelectric figure of merit ZT, where S, σ, T, and κ are the Seebeck coefficient, electrical conductivity, thermodynamic temperature, and thermal conductivity, respectively. As is well known, a high ZT value means high thermoelectric conversion efficiency. Under the same temperature conditions, increasing the electrical conductivity and Seebeck coefficient and decreasing the thermal conductivity can increase the ZT value. However, the strong correlation between these three main thermoelectric parameters makes it difficult to independently optimize one parameter without ignoring unexpected changes in other parameters. Therefore, the decoupling of thermoelectric parameters and the synchronous regulation of electrical and thermal properties are major challenges faced by high-performance thermoelectric materials.

[0004] Among the currently well-studied thermoelectric materials, bismuth telluride (Bi2Te3) and its alloy materials are particularly prominent. Technical strategies for improving the performance of these materials usually include multi-band degeneracy, electron resonant states, and phonon resonant scattering, etc. Multi-band degeneracy and electron resonant states mainly aim to increase the Seebeck coefficient. The former is achieved by increasing the carrier mobility and carrier concentration, and the latter is achieved by introducing foreign energy levels to increase the density of states of the energy band near the Fermi surface. However, the introduction of electron resonant states may strongly scatter carriers, resulting in deterioration of the electrical conductivity. Therefore, when applying this strategy, it is necessary to carefully balance its enhancement effect on the Seebeck coefficient and its potential negative impact on the electrical conductivity.

[0005] Although the above strategies have improved the thermoelectric performance of materials to a certain extent, for inorganic materials, their inherent mechanical brittleness limits their application in flexible and wearable thermoelectric devices. Therefore, one of the key future development directions is to construct a new type of composite thermoelectric material with both high flexibility and thermoelectric performance by organically combining the flexibility of organic materials with the high thermoelectric performance of inorganic materials. For example, developers have compounded Bi2Te3 materials with organic materials such as nanocellulose and conductive polymers in order to improve the mechanical properties of the composite thermoelectric material while maintaining its thermoelectric performance. However, due to the low heat resistance of cellulose, it cannot be subjected to high-temperature annealing treatment, resulting in a sharp deterioration of its thermoelectric performance. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the prior art and provide a composite thermoelectric material and a preparation method thereof. The method of the present invention can effectively improve the thermoelectric performance of the composite thermoelectric material, and at the same time improve the mechanical properties compared with pure Bi2Te3, which is beneficial to the assembly of the material and the service of the device, and has a positive effect on the preparation and practical application of the device.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] In the first aspect, the present invention provides a preparation method of a composite thermoelectric material, comprising the following steps:

[0009] (1) Ultrasonically treat nylon nanofibers in a solvent to obtain a nylon nanofiber dispersion;

[0010] (2) Add Bi2Te3 powder to the nylon nanofiber dispersion, and after mixing evenly, obtain a mixed solution, wherein the mass fraction of nylon nanofibers in the mixed solution is 0.1-2 wt%;

[0011] (3) Dry and grind the mixed solution to obtain a composite thermoelectric material powder, and finally obtain a composite thermoelectric material by SPS sintering;

[0012] Alternatively, perform screen printing on the mixed solution to obtain a composite thermoelectric material film, and finally obtain a composite thermoelectric material by cold pressing and sintering.

[0013] The present invention first ultrasonically treats nylon nanofibers in a solvent to obtain a nylon nanofiber dispersion, then adds Bi2Te3 powder to the nylon nanofiber dispersion to obtain a mixed solution, and finally obtains a composite thermoelectric material by vacuum drying, grinding and sintering or screen printing and sintering of the mixed solution.

[0014] In the present invention, the nylon nanofibers as the reinforcing body can optimize the transport properties of phonons and electrons in the thermoelectric material through the quantum confinement effect and the confinement effect, thereby maintaining the Seebeck coefficient of the composite thermoelectric material and suppressing the lattice thermal conductivity; at the same time, the nylon nanofibers improve the toughness and flexibility of the inorganic thermoelectric material to a certain extent, which has a positive effect on the assembly of the material and the service of the device, the preparation and practical application of the device.

[0015] If the mass fraction of nylon nanofibers is too large, a continuous film will be formed to wrap the Bi2Te3 particles, resulting in a rapid decrease in conductivity; if the mass fraction of nylon nanofibers is too small, the interfacial effect will be weakened, which is not conducive to the synergistic improvement of mechanical properties. Therefore, by controlling the mass fraction of nylon nanofibers within the above range, the present invention is beneficial to improving the thermoelectric performance and mechanical properties of the composite thermoelectric material simultaneously.

[0016] Preferably, in the step (1), the mass fraction of nylon nanofibers in the mixed solution is any one or the range value of two of 0.1wt%, 0.25wt%, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%.

[0017] Preferably, in the step (1), the average diameter of the nylon nanofibers is 80 - 120nm, and the specific surface area is 12 - 15m 2 / g.

[0018] Preferably, in the step (1), the preparation method of the nylon nanofibers is as follows: first, add nylon fibers into an acidic solution to dissolve and obtain a spinning solution; then, obtain nylon nanofibers by electrospinning the spinning solution.

[0019] Preferably, the acidic solution includes at least one of formic acid and acetic acid.

[0020] Preferably, pre-treat the nylon fibers, and the method is as follows: perform ultrasonic cleaning on the nylon fibers in a solvent, the ultrasonic power is 100%, the ultrasonic time is 25 - 30min, and the ultrasonic times are 2 - 3 times.

[0021] Preferably, the mass fraction of nylon fibers in the spinning solution is 5 - 30wt%.

[0022] In the present invention, if the concentration of nylon fibers is too small, it will cause uneven electrostatic stretching, resulting in too thin and uneven diameters of nanofibers; if the concentration of nylon fibers is too high, it will cause a relatively large viscosity of the dispersion liquid, an increase in the adhesion force between molecules, and resulting in too large diameters of nanofibers. Therefore, by controlling the mass fraction of nylon fibers within the above range in the present invention, it is beneficial to improve the thermoelectric performance and mechanical properties of the composite thermoelectric material.

[0023] Preferably, the mass fraction of nylon fibers in the spinning solution is any one or the range value of two of 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%.

[0024] Preferably, the average molecular weight of the nylon fibers is 25000 - 30000.

[0025] If the molecular weight of the nylon fibers is too small, the viscosity of the spinning solution is relatively low, resulting in uneven spinning and poor strength and mechanical properties of the composite thermoelectric material; if the molecular weight of the nylon fibers is too large, the viscosity of the spinning solution is relatively large, making spinning difficult. Therefore, by controlling the molecular weight of the nylon fibers, it is beneficial to improve the mechanical properties of the composite thermoelectric material.

[0026] Preferably, the average molecular weight of the nylon fiber is any one or the range value of two of 25000, 26000, 27000, 28000, 29000, 30000.

[0027] Preferably, the nylon fiber comprises at least one of PA66, PA6, and PA56.

[0028] Preferably, during the electrospinning process, the applied high voltage ranges from 30 to 45 kV, the receiving distance is 18 to 20 cm, and the spinning speed is 10 to 15 μL / min.

[0029] When the voltage is low, electrospinning does not occur. When the voltage is too high, nanofibers or beads with a larger diameter will be formed; when the receiving distance is too short, the electric field strength will increase, the ejection speed of the spinning solution from the needle will accelerate, and the fibers are likely to stack, resulting in a larger diameter and a decrease in uniformity; when the spinning speed is too fast, the fiber diameter becomes larger and the uniformity decreases. Therefore, by controlling the voltage, receiving distance, and spinning speed within the above ranges during electrospinning in the present invention, it is beneficial to form nanofibers with a uniform diameter distribution, thereby improving the performance of the composite thermoelectric material.

[0030] Preferably, in the step (1), the diameter of the probe for ultrasonic treatment is 6 cm and the ultrasonic power is 100%.

[0031] Preferably, in the step (1), the solvent comprises ethanol or deionized water.

[0032] Preferably, in the step (2), the average diameter of the Bi2Te3 powder is 10 - 50 μm.

[0033] If the diameter of the Bi2Te3 powder is too small, it is easily coated by nylon nanofibers, resulting in a decrease in conductivity; if the diameter of the Bi2Te3 powder is too large, it will lead to uneven dispersion of the nanofibers, causing a decrease in the mechanical properties of the composite thermoelectric material. Therefore, by controlling the diameter of the Bi2Te3 powder in the present invention, it is beneficial to improve the thermoelectric performance and mechanical properties of the composite thermoelectric material.

[0034] Preferably, in the step (2), the average diameter of the Bi2Te3 powder is any one or the range value of two of 10 μm, 20 μm, 30 μm, 40 μm, 50 μm.

[0035] Preferably, in the step (2), the mass fraction of the Bi2Te3 powder in the mixed solution is 98 - 99.9 wt%.

[0036] Preferably, in the step (2), the Bi2Te3 powder is preheated to 350 - 380 °C under a mixed gas of hydrogen and argon and held for 8 - 10 h.

[0037] Preferably, the mixed gas comprises hydrogen with a volume fraction of 5-15% and argon with a volume fraction of 85-95%.

[0038] Preferably, the temperature during heating is 380 °C and the heat preservation time is 8 h.

[0039] Preferably, in step (3), the mixed solution is dried under vacuum, the vacuum pressure is -0.1 MPa to 0.09 MPa, and the drying temperature is 60-70 °C.

[0040] Preferably, in step (3), the temperature during SPS sintering is 400-450 °C and the pressure is 45-100 MPa.

[0041] If the temperature or pressure during SPS sintering is too low, the compactness of the composite thermoelectric material will be poor; if the temperature during SPS sintering is too high, metallic tellurium will precipitate in bismuth telluride, resulting in sintering failure; if the pressure is too high, it is not conducive to sample forming. Therefore, by controlling the temperature and pressure during SPS sintering within the above ranges in the present invention, it is beneficial to improve the compactness of the structure and enhance the performance of the composite thermoelectric material.

[0042] Preferably, in step (3), the temperature during cold pressing sintering is 400-450 °C and the pressure is 45-100 MPa.

[0043] In the second aspect, the present invention also provides a composite thermoelectric material prepared by the above method.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] In the present invention, high-temperature annealing is carried out by utilizing the high-temperature resistance characteristic of nylon nanofibers. Chemical bond binding is generated between the nylon nanofibers and the interface of Bi2Te3, which can regulate the electronic energy band structure and phonon transport, thereby maintaining the electrical properties and reducing the thermal conductivity, so as to improve the thermoelectric performance of the composite thermoelectric material. At the same time, the strong interfacial interaction between the nylon nanofibers and Bi2Te3 can effectively transfer the load borne by the composite thermoelectric material to the nylon nanofibers, thereby enhancing the mechanical flexibility performance of the composite thermoelectric material, so as to realize the synergistic improvement of the thermoelectric performance and flexibility performance of the composite thermoelectric material. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is the preparation flow chart of the composite thermoelectric material described in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the protection scope and implementation manners of the present invention are not limited thereto.

[0048] The materials, reagents, etc. used in the following examples are commercially available reagents and materials unless otherwise specified.

[0049] Example 1

[0050] A preparation method of a composite thermoelectric material, comprising the following steps:

[0051] (1) Ultrasonically clean nylon fiber PA66 (the average molecular weight of the nylon fiber is 25,000) in an acetone solution, with an ultrasonic power of 100%, an ultrasonic time of 30 min, and an ultrasonic frequency of 3 times; then add the cleaned nylon fiber to a formic acid solution to dissolve it to obtain a spinning solution, and the mass fraction of nylon fiber in the spinning solution is 5 wt%.

[0052] (2) Spin the spinning solution through an electrospinning device, with a high voltage range of 30 kv, a receiving distance of 20 cm, and a spinning speed of 10 μL / min to obtain nylon nanofibers, where the average diameter of the nylon nanofibers is 80 - 120 nm and the specific surface area is 12 - 15 m 2 / g.

[0053] (3) Ultrasonically treat the nylon nanofibers in an ethanol solution, with a probe diameter of 6 cm for ultrasonic treatment and an ultrasonic power of 100% to obtain a nylon nanofiber dispersion, and the concentration of nylon nanofibers in the nylon nanofiber dispersion is 1.25 wt%.

[0054] (4) Heat the Bi2Te3 powder to 380 °C under a mixed gas of hydrogen and argon and keep it for 8 h for surface reduction treatment; the volume fractions of hydrogen and argon in the mixed gas are 5% and 95% respectively.

[0055] (5) Add the reduced Bi2Te3 powder to the nylon nanofiber dispersion and perform ultrasonic stirring. After mixing evenly, a mixed solution is obtained; the average diameter of the Bi2Te3 powder is 10 μm, ultrasonic bath for 6 h, and magnetic stirring for 8 h; the mass fraction of nylon nanofibers in the mixed solution is 0.1 wt%, and the mass fraction of Bi2Te3 powder is 99.9 wt%, where nylon nanofibers / (nylon nanofibers + Bi2Te3) = 0.1% wt.

[0056] (6) Dry the mixed solution in a vacuum oven with a vacuum pressure of -0.1 MPa and a drying temperature of 70 °C, then grind it with an agate mortar for 30 min to obtain a composite thermoelectric material powder, and finally obtain a composite thermoelectric material by SPS sintering. The temperature during SPS sintering is 450 °C, the pressure is 100 MPa, and the sintering time is 5 min.

[0057] Example 2

[0058] A preparation method of a composite thermoelectric material, comprising the following steps:

[0059] (1) Ultrasonically clean nylon fiber PA66 (the average molecular weight of the nylon fiber is 30,000) in an acetone solution, with an ultrasonic power of 100%, an ultrasonic time of 30 min, and an ultrasonic frequency of 3 times; then add the cleaned nylon fiber to a formic acid solution to dissolve it, obtaining a spinning solution, and the mass fraction of nylon fiber in the spinning solution is 30 wt%.

[0060] (2) Spin the spinning solution through an electrospinning device, with a high voltage range of 45 kv, a receiving distance of 20 cm, and a spinning speed of 15 μL / min, obtaining nylon nanofibers, where the average diameter of the nylon nanofibers is 80 - 120 nm, and the specific surface area is 12 - 15 m 2 / g.

[0061] (3) Ultrasonically treat the nylon nanofibers in an ethanol solution, with the diameter of the ultrasonic treatment probe being 6 cm and the ultrasonic power being 100%, obtaining a nylon nanofiber dispersion, and the concentration of nylon nanofibers in the nylon nanofiber dispersion is 1.25 wt%.

[0062] (4) Heat Bi2Te3 powder to 380 °C under a mixed gas of hydrogen and argon and hold for 8 h for surface reduction treatment; the volume fractions of hydrogen and argon in the mixed gas are 15% and 85% respectively.

[0063] (5) Add the reduced Bi2Te3 powder to the nylon nanofiber dispersion and perform ultrasonic stirring. After mixing evenly, a mixed solution is obtained; the average diameter of the Bi2Te3 powder is 50 μm, ultrasonic bath for 6 h, and magnetic stirring for 8 h; the mass fraction of nylon nanofibers in the mixed solution is 0.1 wt%, and the mass fraction of Bi2Te3 powder is 99.9 wt%, where nylon nanofibers / (nylon nanofibers + Bi2Te3) = 0.1% wt.

[0064] (6) Perform screen printing on the mixed solution. Customize screen printing molds of different sizes during the screen printing process, and use a squeegee for scraping and printing to obtain a composite thermoelectric material film. Finally, obtain the composite thermoelectric material through cold pressing and sintering treatment. During the cold pressing and sintering process, use a universal testing machine to apply pressure to the printed film, with a pressure of 100 MPa. Then, use two carbon papers (length 70 mm, width 12 mm, thickness 0.20 mm), pass an electric current through the carbon papers for sintering, with a sintering temperature of 450 °C and a sintering time of 5 min.

[0065] Example 3

[0066] A preparation method of a composite thermoelectric material, comprising the following steps:

[0067] (1) The nylon fiber PA66 (the average molecular weight of the nylon fiber is 25,000) is ultrasonically cleaned in an acetone solution. The ultrasonic power is 100%, the ultrasonic time is 30 min, and the number of ultrasonic times is 3 times. Then, the cleaned nylon fiber is added to a formic acid solution for dissolution to obtain a spinning solution, and the mass fraction of the nylon fiber in the spinning solution is 5 wt%.

[0068] (2) The spinning solution is spun through an electrospinning device. The applied high voltage ranges from 30 kV, the receiving distance is 20 cm, and the spinning speed is 10 μL / min to obtain nylon nanofibers. The average diameter of the nylon nanofibers is 80 - 120 nm, and the specific surface area is 12 - 15 m 2 / g.

[0069] (3) The nylon nanofibers are ultrasonically treated in an ethanol solution. The diameter of the ultrasonic treatment probe is 6 cm, and the ultrasonic power is 100% to obtain a nylon nanofiber dispersion. The concentration of the nylon nanofibers in the nylon nanofiber dispersion is 1.25 wt%.

[0070] (4) The Bi2Te3 powder is heated to 380 °C under a mixed gas of hydrogen and argon and held for 8 h for surface reduction treatment. The volume fractions of hydrogen and argon in the mixed gas are 5% and 95% respectively.

[0071] (5) The reduced Bi2Te3 powder is added to the nylon nanofiber dispersion and ultrasonically stirred. After mixing evenly, a mixed solution is obtained. The average diameter of the Bi2Te3 powder is 10 μm, ultrasonic bath is carried out for 6 h, and magnetic stirring is carried out for 8 h. The mass fraction of the nylon nanofibers in the mixed solution is 0.25 wt%, and the mass fraction of the Bi2Te3 powder is 99.75 wt%. Among them, nylon nanofibers / (nylon nanofibers + Bi2Te3) = 0.25% wt.

[0072] (6) The mixed solution is dried in a vacuum oven. The vacuum pressure is -0.1 MPa, and the drying temperature is 70 °C. Then, it is ground in an agate mortar for 30 min to obtain a composite thermoelectric material powder. Finally, the composite thermoelectric material is obtained by SPS sintering. The temperature during SPS sintering is 450 °C, the pressure is 100 MPa, and the sintering time is 5 min.

[0073] The difference between this example and Example 1 is that in step (5), the mass fraction of the nylon nanofibers is 0.25 wt%, and the mass fraction of the Bi2Te3 powder is 99.75 wt%.

[0074] Example 4

[0075] A preparation method of a composite thermoelectric material, comprising the following steps:

[0076] (1) Ultrasonically clean nylon fiber PA66 (the average molecular weight of the nylon fiber is 25,000) in an acetone solution, with an ultrasonic power of 100%, an ultrasonic time of 30 min, and an ultrasonic frequency of 3 times; then add the cleaned nylon fiber to a formic acid solution to dissolve it, obtaining a spinning solution, and the mass fraction of nylon fiber in the spinning solution is 5 wt%.

[0077] (2) Spin the spinning solution through an electrospinning device, with a high voltage range of 30 kV, a receiving distance of 20 cm, and a spinning speed of 10 μL / min, obtaining nylon nanofibers, where the average diameter of the nylon nanofibers is 80 - 120 nm, and the specific surface area is 12 - 15 m 2 / g.

[0078] (3) Ultrasonically treat the nylon nanofibers in an ethanol solution, with the diameter of the ultrasonic probe being 6 cm and the ultrasonic power being 100%, obtaining a nylon nanofiber dispersion, and the concentration of nylon nanofibers in the nylon nanofiber dispersion is 1.25 wt%.

[0079] (4) Heat the Bi2Te3 powder to 380 °C under a mixed gas of hydrogen and argon and hold for 8 h for surface reduction treatment; the volume fractions of hydrogen and argon in the mixed gas are 5% and 95% respectively.

[0080] (5) Add the reduced Bi2Te3 powder to the nylon nanofiber dispersion and perform ultrasonic stirring. After mixing evenly, a mixed solution is obtained; the average diameter of the Bi2Te3 powder is 10 μm, ultrasonic bath for 6 h, and magnetic stirring for 8 h; the mass fraction of nylon nanofibers in the mixed solution is 0.5 wt%, and the mass fraction of Bi2Te3 powder is 99.5 wt%, where nylon nanofibers / (nylon nanofibers + Bi2Te3) = 0.5% wt.

[0081] (6) Dry the mixed solution in a vacuum oven, with a vacuum pressure of -0.1 MPa and a drying temperature of 70 °C, then grind it with an agate mortar for 30 min to obtain a composite thermoelectric material powder, and finally obtain the composite thermoelectric material through SPS sintering. The temperature during SPS sintering is 450 °C, the pressure is 100 MPa, and the sintering time is 5 min.

[0082] The difference between this example and Example 1 is that in step (5), the mass fraction of nylon nanofibers is 0.5 wt%, and the mass fraction of Bi2Te3 powder is 99.5 wt%.

[0083] Example 5

[0084] A preparation method of a composite thermoelectric material, comprising the following steps:

[0085] (1) Ultrasonically clean nylon fiber PA66 (the average molecular weight of the nylon fiber is 25,000) in an acetone solution, with an ultrasonic power of 100%, an ultrasonic time of 30 min, and an ultrasonic frequency of 3 times; then add the cleaned nylon fiber to a formic acid solution to dissolve it, obtaining a spinning solution, and the mass fraction of nylon fiber in the spinning solution is 5 wt%.

[0086] (2) Spin the spinning solution through an electrospinning device, with a high voltage range of 30 kv, a receiving distance of 20 cm, and a spinning speed of 10 μL / min, obtaining nylon nanofibers, where the average diameter of the nylon nanofibers is 80 - 120 nm, and the specific surface area is 12 - 15 m 2 / g.

[0087] (3) Ultrasonically treat the nylon nanofibers in an ethanol solution, with the diameter of the ultrasonic treatment probe being 6 cm and the ultrasonic power being 100%, obtaining a nylon nanofiber dispersion, and the concentration of nylon nanofibers in the nylon nanofiber dispersion is 1.25 wt%.

[0088] (4) Heat Bi2Te3 powder to 380 °C under a mixed gas of hydrogen and argon and hold for 8 h for surface reduction treatment; the volume fractions of hydrogen and argon in the mixed gas are 5% and 95% respectively.

[0089] (5) Add the reduced Bi2Te3 powder to the nylon nanofiber dispersion and perform ultrasonic stirring. After mixing evenly, a mixed solution is obtained; the average diameter of the Bi2Te3 powder is 10 μm, ultrasonic bath for 6 h, and magnetic stirring for 8 h; the mass fraction of nylon nanofibers in the mixed solution is 1.0 wt%, and the mass fraction of Bi2Te3 powder is 99.0 wt%, where nylon nanofibers / (nylon nanofibers + Bi2Te3) = 1.0% wt.

[0090] (6) Dry the mixed solution in a vacuum oven, with a vacuum pressure of -0.1 MPa and a drying temperature of 70 °C, then grind it with an agate mortar for 30 min to obtain a composite thermoelectric material powder, and finally obtain a composite thermoelectric material through SPS sintering. The temperature during SPS sintering is 450 °C, the pressure is 100 MPa, and the sintering time is 5 min.

[0091] The difference between this example and Example 1 is that in step (5), the mass fraction of nylon nanofibers is 1.0 wt%, and the mass fraction of Bi2Te3 powder is 99.0 wt%.

[0092] Example 6

[0093] A preparation method of a composite thermoelectric material, comprising the following steps:

[0094] (1) Ultrasonically clean nylon fiber PA66 (the average molecular weight of the nylon fiber is 25,000) in an acetone solution, with an ultrasonic power of 100%, an ultrasonic time of 30 min, and an ultrasonic frequency of 3 times; then add the cleaned nylon fiber to a formic acid solution to dissolve it to obtain a spinning solution, and the mass fraction of the nylon fiber in the spinning solution is 5 wt%.

[0095] (2) Spin the spinning solution through an electrospinning device, with a high voltage range of 30 kv, a receiving distance of 20 cm, and a spinning speed of 10 μL / min to obtain nylon nanofibers, wherein the average diameter of the nylon nanofibers is 80 - 120 nm, and the specific surface area is 12 - 15 m 2 / g.

[0096] (3) Ultrasonically treat the nylon nanofibers in an ethanol solution, with the diameter of the ultrasonic treatment probe being 6 cm and the ultrasonic power being 100% to obtain a nylon nanofiber dispersion, and the concentration of the nylon nanofibers in the nylon nanofiber dispersion is 1.25 wt%.

[0097] (4) Heat the Bi2Te3 powder to 380 °C under a mixed gas of hydrogen and argon and keep it for 8 h for surface reduction treatment; the volume fractions of hydrogen and argon in the mixed gas are 5% and 95% respectively.

[0098] (5) Add the reduced Bi2Te3 powder to the nylon nanofiber dispersion and perform ultrasonic stirring. After mixing evenly, a mixed solution is obtained; the average diameter of the Bi2Te3 powder is 10 μm, ultrasonic bath for 6 h, and magnetic stirring for 8 h; the mass fraction of the nylon nanofibers in the mixed solution is 2.0 wt%, and the mass fraction of the Bi2Te3 powder is 98.0 wt%, wherein, nylon nanofibers / (nylon nanofibers + Bi2Te3) = 2.0% wt.

[0099] (6) Dry the mixed solution in a vacuum oven, with a vacuum pressure of -0.1 MPa and a drying temperature of 70 °C, then grind it with an agate mortar for 30 min to obtain a composite thermoelectric material powder, and finally obtain the composite thermoelectric material by SPS sintering. The temperature during SPS sintering is 450 °C, the pressure is 100 MPa, and the sintering time is 5 min.

[0100] The difference between this example and Example 1 is that in step (5), the mass fraction of the nylon nanofibers is 2.0 wt%, and the mass fraction of the Bi2Te3 powder is 98.0 wt%.

[0101] Comparative Example 1

[0102] It is different from Example 1 in that in step (5), the mass fraction of nylon nanofibers is 0.05 wt%, and the mass fraction of Bi2Te3 powder is 99.95 wt%.

[0103] Comparative Example 2

[0104] It is different from Example 1 in that in step (5), the mass fraction of nylon nanofibers is 3 wt%, and the mass fraction of Bi2Te3 powder is 97 wt%.

[0105] Performance Detection

[0106] 1. Conductivity σ (S / cm): Cut the sample into a square, make Ohmic contact connections between the four test electrodes and the four corners (A, B, C, D) of the sample, and measure the conductivity using the Van der Pauw method: Pass a constant current between two adjacent electrodes, measure the voltage between the other pair of electrodes, and calculate the corresponding resistance; Pass a constant current between another group of two adjacent electrodes, measure the voltage between the other pair of electrodes, and calculate the corresponding resistance. Note: During the test, it is necessary to reverse the current direction and take the average value of the resistance to eliminate the influence of the thermoelectric potential. Finally, calculate the resistivity using the following formula:

[0107]

[0108] In the formula, ρ is the resistivity (the conductivity σ takes its reciprocal), d is the sample thickness, f is the Van der Pauw factor, and when the above test resistances are the same, f can be taken as 1.

[0109] 2. Seebeck coefficient S (μV / K): Measured by the dynamic method, by measuring the potential difference across the sample at a temperature difference (0 - 20 K), and fitting and calculating to obtain the slope, which is the Seebeck coefficient. The calculation formula is: S = -V / ΔT.

[0110] 3. Power factor PF (mW / m·K 2 ) : Calculated according to the formula PF = S 2 σ.

[0111] 4. Bending strength (MPa): Measured according to the ASTM D7264 / D7264M - 07 Standard Test Method for Flexural Properties of Polymer Matrix Composites.

[0112] The above test results are shown in Table 1.

[0113] Table 1

[0114]

[0115] As can be seen from Examples 1 - 6, the composite thermoelectric material prepared by the present invention has excellent thermoelectric performance and mechanical properties.

[0116] Comparing Comparative Examples 1-2 with Example 1 respectively, it can be seen that when the mass fraction of nylon nanofibers is too low, it is easy to cause the weakening of the interfacial interaction between nylon nanofibers and Bi2Te3, resulting in a decrease in the bending strength of the composite thermoelectric material; when the mass fraction of nylon nanofibers is too high, a continuous film will form to wrap the Bi2Te3 particles, leading to a decrease in the conductivity of the composite thermoelectric material. Therefore, by controlling the mass fraction of nylon nanofibers in the present invention, it is beneficial to improve the thermoelectric performance and mechanical properties of the composite thermoelectric material simultaneously.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A preparation method of a composite thermoelectric material, characterized in that, It includes the following steps: (1) Ultrasonically treat nylon nanofibers in a solvent to obtain a nylon nanofiber dispersion; (2) Add Bi2Te3 powder to the nylon nanofiber dispersion, and after mixing evenly, obtain a mixed solution, where the mass fraction of nylon nanofibers in the mixed solution is 0.1 - 2 wt%; (3) Dry and grind the mixed solution to obtain a composite thermoelectric material powder, and finally obtain the composite thermoelectric material through SPS sintering; Alternatively, perform screen printing on the mixed solution to obtain a composite thermoelectric material film, and finally obtain the composite thermoelectric material through cold - press sintering.

2. The preparation method of the composite thermoelectric material according to claim 1, characterized in that In the step (1), the average diameter of the nylon nanofibers is 80-120 nm, and the specific surface area is 12-15 m 2 / g.

3. The preparation method of the composite thermoelectric material according to claim 1, characterized in that In the step (1), the preparation method of the nylon nanofibers is as follows: First, dissolve nylon fibers in an acidic solution to obtain a spinning solution; then obtain nylon nanofibers by electrospinning the spinning solution.

4. The preparation method of the composite thermoelectric material according to claim 3, characterized in that, The acidic solution includes at least one of formic acid and acetic acid.

5. The preparation method of the composite thermoelectric material according to claim 3, wherein The mass fraction of nylon fibers in the spinning solution is 5 - 30 wt%; and / or, The average molecular weight of the nylon fibers is 25000 - 30000.

6. The preparation method of the composite thermoelectric material according to claim 3, characterized in that, Pre - treat the nylon fibers in advance, and the method is as follows: Ultrasonically clean the nylon fibers in a solvent, the ultrasonic power is 100%, the ultrasonic time is 25 - 30 min, and the number of ultrasonic times is 2 - 3 times.

7. The preparation method of the composite thermoelectric material according to claim 3, characterized in that, During the electrospinning process, the applied high - voltage range is 30 - 45 kv, the receiving distance is 18 - 20 cm, and the spinning speed is 10 - 15 μL / min.

8. The preparation method of the composite thermoelectric material according to claim 1, characterized in that, In the step (2), pre - heat the Bi2Te3 powder to 350 - 380 °C under a mixed gas of hydrogen and argon and keep it warm for 8 - 10 h.

9. The preparation method of the composite thermoelectric material according to claim 1, characterized in that, In the step (3), perform vacuum drying on the mixed solution, the vacuum pressure is - 0.1 MPa to 0.09 MPa, and the drying temperature is 60 - 70 °C; and / or, The temperature during SPS sintering is 400 - 450 °C, and the pressure is 45 - 100 MPa; and / or, The temperature during cold - press sintering is 400 - 450 °C, and the pressure is 45 - 100 MPa.

10. A composite thermoelectric material prepared by the preparation method of the composite thermoelectric material according to any one of claims 1 - 9.

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