A preparation method of a barrier layer of a bismuth telluride-based thermoelectric material with low contact resistance, high bonding strength and high thermal stability

Abstract

The application relates to a preparation method of a barrier layer of a bismuth telluride-based thermoelectric material with low contact resistance, high bonding strength and high thermal stability. The application aims to solve the problem that the existing barrier layer of the bismuth telluride-based thermoelectric material cannot simultaneously realize long-term thermal stability above 200 DEG C and high strength and low resistance. The method comprises the following steps: 1, preparing a Ti / bismuth telluride p-type / Ti test piece; 2, preparing a Ti / bismuth telluride n-type / Ti test piece; and 3, preparing a bismuth telluride power generation device. The application is used for preparing the barrier layer of the bismuth telluride-based thermoelectric material with low contact resistance, high bonding strength and high thermal stability.

Description

Technical Field

[0001] This invention relates to a method for preparing a barrier layer. Background Technology

[0002] Thermoelectric materials are energy materials that enable the direct conversion between thermal and electrical energy. Thermoelectric devices are generally constructed by soldering a copper-clad ceramic substrate to p-type or n-type thermoelectric materials containing a barrier layer. The barrier layer is introduced to suppress the diffusion of interfacial elements during soldering or service, preventing performance degradation or even failure. A heterogeneous interface with low contact resistance, high bonding strength, and high thermal stability is a prerequisite for high reliability, stability, and efficiency in thermoelectric devices.

[0003] For bismuth telluride-based thermoelectric materials, metallic Ni is currently the most widely used barrier layer. Below 200°C, the interfacial contact resistivity with Ni as the barrier layer is typically less than 10 μΩ·cm. 2 However, when the operating temperature exceeds 200℃, the interdiffusion between Ni and bismuth telluride accelerates, generating various interfacial compounds, which causes a sharp increase in contact resistivity. Although barrier layer materials such as elemental Fe and Ni-based alloys have emerged in recent years, there is still no barrier layer material that meets the requirements of long-term thermal stability above 200℃ and high strength with low resistivity. Summary of the Invention

[0004] This invention aims to solve the problem that existing bismuth telluride-based thermoelectric material barrier layers cannot simultaneously achieve long-term thermal stability above 200°C and high strength with low resistance, and thus provides a method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability for bismuth telluride-based thermoelectric materials.

[0005] A method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material is disclosed, comprising the following steps:

[0006] 1. Using Ti as a barrier layer for bismuth telluride-based p-type material, and then sintering for 5 min to 10 min under vacuum, pressure of 60 MPa to 100 MPa and temperature of 400℃ to 450℃ to obtain Ti / bismuth telluride p-type / Ti specimens;

[0007] 2. Using Ti as the barrier layer of bismuth telluride-based n-type material, and then sintering for 5 min to 10 min under vacuum, pressure of 60 MPa to 100 MPa and temperature of 400℃ to 450℃ to obtain Ti / bismuth telluride n-type / Ti specimens;

[0008] 3. Nickel is electroplated onto the Ti surface of the Ti / bismuth telluride p-type / Ti specimen and the Ti / bismuth telluride n-type / Ti specimen, respectively, and then soldered to the upper and lower substrates to obtain the bismuth telluride power generation device.

[0009] The beneficial effects of this invention are:

[0010] 1. Ti metal has a low Young's modulus, and bismuth telluride has a low sintering temperature. When Ti metal powder is directly sintered on the surface of bismuth telluride, Ti will form a loose structure with an even lower Young's modulus. At the same time, the phenomenon of particle sliding occurs during cooling, which helps to release the interfacial stress caused by the mismatch of thermal expansion coefficients. Therefore, the mechanical structure is stable.

[0011] 2. During the sintering process, Ti and bismuth telluride form a TiTe2 nano-reaction layer, and a metallurgical bond is formed at the interface, resulting in a bonding strength greater than 10 MPa, which meets the requirements of thermoelectric devices in practical use.

[0012] 3. The junction contact resistance between Ti and both p-type and n-type bismuth telluride is less than 3 μΩ·cm. 2 Furthermore, it remains essentially unchanged after annealing at 250℃ for 45 days, ensuring the stability of bismuth telluride power generation devices.

[0013] 4. The output voltage (U) and conversion efficiency (η) of the prepared bismuth telluride power generation device remained stable at 0.6V and 6.6% respectively after 15 days of service under hot-end temperature of 250℃ and cold-end temperature of 20℃, and did not decrease significantly with service time. This indicates that the thermoelectric device prepared by this barrier layer has excellent device performance and extremely good thermal stability.

[0014] This invention relates to a method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material. Attached Figure Description

[0015] Figure 1 The images show the backscattered electron scanning images and line scan energy dispersive spectroscopy results of the Ti / bismuth telluride / Ti specimens prepared in Example 1 before and after annealing. (a) Ti / bismuth telluride p-type / Ti specimen before annealing, (b) Ti / bismuth telluride n-type / Ti specimen before annealing, (c) Ti / bismuth telluride p-type / Ti specimen after annealing for 45 days, and (d) Ti / bismuth telluride n-type / Ti specimen after annealing for 45 days.

[0016] Figure 2 The contact resistance results of the Ti / bismuth telluride / Ti specimens prepared in Example 1 before and after annealing are shown in (a) before annealing of the Ti / bismuth telluride p-type / Ti specimen, (b) before annealing of the Ti / bismuth telluride n-type / Ti specimen, (c) after annealing of the Ti / bismuth telluride p-type / Ti specimen for 45 days, and (d) after annealing of the Ti / bismuth telluride n-type / Ti specimen for 45 days.

[0017] Figure 3 This is a comparison chart of Young's modulus, where 1 represents Bi. 0.399 Sb 1.596 Pb 0.005 Te3 bismuth telluride p-type material bulk, 2 is Bi2Te2.6975 Se 0.3 (SbI3) 0.0025 Bismuth telluride n-type material bulk, 3 is loose and porous Ti, 4 is dense Ti;

[0018] Figure 4 The results of the Ti / bismuth telluride interface stress simulated using the finite element solver (ABAQUS) are as follows: A represents the dense Ti / bismuth telluride p-type interface stress, B represents the loose and porous Ti / bismuth telluride p-type interface stress, C represents the dense Ti / bismuth telluride n-type interface stress, and D represents the loose and porous Ti / bismuth telluride n-type interface stress.

[0019] Figure 5 The fracture morphology of porous Ti is shown.

[0020] Figure 6 The images shown are scanning images of the Ti surface of the etched n-type specimen prepared in step three of Example 1 at room temperature and at varying temperatures. (a) is a scanning image at room temperature, (b) is a scanning image at 300°C, (c), (d) and (e) are magnified images of the dashed box in (a), and (f), (g) and (h) are magnified images of the dashed box in (b).

[0021] Figure 7 The images are high-resolution transmission electron microscope images of the Ti / bismuth telluride / Ti specimens prepared in Example 1. (a) is a Ti / bismuth telluride p-type / Ti specimen, and (b) is a Ti / bismuth telluride n-type / Ti specimen.

[0022] Figure 8 The results show the test results of the bonding strength of the Ti / bismuth telluride / Ti specimen prepared in Example 1 as a function of annealing time. ■ represents the shear strength of the Ti / bismuth telluride p-type / Ti specimen, and ★ represents the shear strength of the Ti / bismuth telluride n-type / Ti specimen. ● represents the tensile strength of the Ti / bismuth telluride p-type / Ti specimen, and ● represents the tensile strength of the Ti / bismuth telluride n-type / Ti specimen.

[0023] Figure 9 A photograph of the bismuth telluride power generation device prepared in Example 1;

[0024] Figure 10 The hot-end temperature of the bismuth telluride power generation device prepared in Example 1 changes over time during service.

[0025] Figure 11 The output voltage (U) and conversion efficiency (η) of the bismuth telluride power generation device prepared in Example 1 after 15 days of operation under the conditions of hot end temperature of 250°C and cold end temperature of 20°C are shown. 1 represents the output voltage and 2 represents the conversion efficiency. Detailed Implementation

[0026] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0027] Specific Implementation Method 1: This implementation method provides a method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material. It is carried out according to the following steps:

[0028] 1. Using Ti as a barrier layer for bismuth telluride-based p-type material, and then sintering for 5 min to 10 min under vacuum, pressure of 60 MPa to 100 MPa and temperature of 400℃ to 450℃ to obtain Ti / bismuth telluride p-type / Ti specimens;

[0029] 2. Using Ti as the barrier layer of bismuth telluride-based n-type material, and then sintering for 5 min to 10 min under vacuum, pressure of 60 MPa to 100 MPa and temperature of 400℃ to 450℃ to obtain Ti / bismuth telluride n-type / Ti specimens;

[0030] 3. Nickel is electroplated onto the Ti surface of the Ti / bismuth telluride p-type / Ti specimen and the Ti / bismuth telluride n-type / Ti specimen, respectively, and then soldered to the upper and lower substrates to obtain the bismuth telluride power generation device.

[0031] The beneficial effects of this embodiment are:

[0032] 1. Ti metal has a low Young's modulus, and bismuth telluride has a low sintering temperature. When Ti metal powder is directly sintered on the surface of bismuth telluride, Ti will form a loose structure with an even lower Young's modulus. At the same time, the phenomenon of particle sliding occurs during cooling, which helps to release the interfacial stress caused by the mismatch of thermal expansion coefficients. Therefore, the mechanical structure is stable.

[0033] 2. During the sintering process, Ti and bismuth telluride form a TiTe2 nano-reaction layer, and a metallurgical bond is formed at the interface, resulting in a bonding strength greater than 10 MPa, which meets the requirements of thermoelectric devices in practical use.

[0034] 3. The junction contact resistance between Ti and both p-type and n-type bismuth telluride is less than 3 μΩ·cm. 2 Furthermore, it remains essentially unchanged after annealing at 250℃ for 45 days, ensuring the stability of bismuth telluride power generation devices.

[0035] 4. The output voltage (U) and conversion efficiency (η) of the prepared bismuth telluride power generation device remained stable at 0.6V and 6.6% respectively after 15 days of service under hot-end temperature of 250℃ and cold-end temperature of 20℃, and did not decrease significantly with service time. This indicates that the thermoelectric device prepared by this barrier layer has excellent device performance and extremely good thermal stability.

[0036] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the bismuth telluride-based p-type material mentioned in step one is a Bi material doped with Pb, Mn, Mg, Zn, or Cd. 0.4 Sb 1.6 Te3, or Bi modified by doping with Pb, Mn, Mg, Zn or Cd. 0.5 Sb 1.5 Te3; the bismuth telluride-based n-type material mentioned in step two is Bi2Te doped with one or two of Br and I. 2.7 Se 0.3 Or it could be Bi2Te modified by one or both of Br and I. 2.8 Se 0.2 Everything else is the same as in Specific Implementation Method 1.

[0037] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the Ti / bismuth telluride p-type / Ti specimen described in step one is prepared according to the following steps: Ti powder is placed in a graphite mold and flattened to obtain a first Ti layer; bismuth telluride-based p-type material powder is placed on top of the first Ti layer and flattened to obtain a bismuth telluride-based p-type layer; then Ti powder is placed on top of the bismuth telluride-based p-type layer and flattened to obtain a second Ti layer, thus obtaining a mold containing Ti / bismuth telluride p-type / Ti. The mold is then sintered for 5-10 minutes under vacuum conditions with a pressure of 60-100 MPa and a temperature of 400-450°C. Finally, the mold is cut to obtain the Ti / bismuth telluride p-type / Ti specimen. The rest is the same as in Specific Implementation Method One or Two.

[0038] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the particle size of the bismuth telluride-based p-type material powder is 100 nanometers to 5 micrometers. Everything else is the same as in Specific Implementation Methods One to Three.

[0039] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the Ti / bismuth telluride n-type / Ti specimen described in step two is prepared according to the following steps: Ti powder is placed in a graphite mold and flattened to obtain a first Ti layer; bismuth telluride-based n-type material powder is placed on top of the first Ti layer and flattened to obtain a bismuth telluride-based n-type layer; then Ti powder is placed on top of the bismuth telluride-based n-type layer and flattened to obtain a second Ti layer, thus obtaining a mold containing Ti / bismuth telluride n-type / Ti. The mold is then sintered for 5 to 10 minutes under vacuum, a pressure of 60 MPa to 100 MPa, and a temperature of 400°C to 450°C. Finally, the mold is cut to obtain the Ti / bismuth telluride n-type / Ti specimen. Everything else is the same as in Specific Implementation Methods One to Four.

[0040] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the particle size of the bismuth telluride-based n-type material powder is 100 nanometers to 5 micrometers. Everything else is the same as in Specific Implementation Methods One to Five.

[0041] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the particle size of the Ti powder is 15μm to 75μm. Otherwise, it is the same as Specific Implementation Methods One to Six.

[0042] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One through Seven in that: in step three, nickel is electroplated onto the Ti surface of the Ti / bismuth telluride p-type / Ti specimen and the Ti / bismuth telluride n-type / Ti specimen, respectively. Specifically, this is carried out as follows: At room temperature, the Ti / bismuth telluride p-type / Ti specimen or the Ti / bismuth telluride n-type / Ti specimen is immersed in a mixed acid of hydrofluoric acid and nitric acid to corrode the Ti surface for 10s to 30s, followed by ultrasonic cleaning to obtain the corroded p-type specimen and the corroded n-type specimen. Under a temperature of 50℃ to 60℃, the corroded p-type specimen or the corroded n-type specimen is immersed in an electroplating solution as a cathode, and a Ni plate is used as an anode for nickel electroplating for 5m. The process takes 10 minutes to 10 minutes. The mixed acid of hydrofluoric acid and nitric acid is composed of 40%–50% hydrofluoric acid, 86%–98% nitric acid, and water by mass, with a volume ratio of 40%–50% hydrofluoric acid to 86%–98% nitric acid of 1:(3.5–4.5) and a volume ratio of 40%–50% hydrofluoric acid to water of 1:(4.5–5.5). The electroplating solution contains Ni(NH₂SO₃)₂ at a concentration of 280 g / L–320 g / L, NiCl₂·6H₂O at a concentration of 25 g / L–35 g / L, and H₃BO₃ at a concentration of 35 g / L–45 g / L. Other aspects are the same as in embodiments one through seven.

[0043] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: in step three, Al2O3 ceramic is used as the upper and lower substrates, with seven Cu sheets attached to the upper substrate and eight Cu sheets attached to the lower substrate. Everything else is the same as in Specific Implementation Methods One to Eight.

[0044] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the bismuth telluride power generation device in step three is assembled from 7 pn pairs. Everything else is the same as in Specific Implementation Methods One to Nine.

[0045] The beneficial effects of the present invention are verified using the following embodiments:

[0046] Example 1:

[0047] A method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material is disclosed, comprising the following steps:

[0048] 1. Place 0.12g of Ti powder in a graphite mold and flatten it to obtain the first Ti layer. Place 2.8g of bismuth telluride-based p-type material powder on the first Ti layer and flatten it to obtain the bismuth telluride-based p-type layer. Then place 0.12g of Ti powder on the bismuth telluride-based p-type layer and flatten it to obtain the second Ti layer. This yields a mold containing Ti / bismuth telluride p-type / Ti. Then, sinter it for 5 minutes under vacuum, pressure of 80MPa and temperature of 400℃. Finally, cut it to obtain the Ti / bismuth telluride p-type / Ti specimen.

[0049] The bismuth telluride-based p-type material powder has a particle size of 500 nanometers to 1 micrometer; the Ti powder has a particle size of 45 μm.

[0050] 2. Place 0.12g of Ti powder in a graphite mold and flatten it to obtain the first Ti layer. Place 3g of bismuth telluride-based n-type material powder on the first Ti layer and flatten it to obtain the bismuth telluride-based n-type layer. Then place 0.12g of Ti powder on the bismuth telluride-based n-type layer and flatten it to obtain the second Ti layer. This yields a mold containing Ti / bismuth telluride n-type / Ti. Then, sinter it for 5 minutes under vacuum, pressure of 80MPa and temperature of 400℃. Finally, cut it to obtain the Ti / bismuth telluride n-type / Ti specimen.

[0051] The particle size of the bismuth telluride-based n-type material powder is 500 nanometers to 1 micrometer; the particle size of the Ti powder is 45 μm.

[0052] III. At room temperature, immerse Ti / bismuth telluride p-type / Ti specimens or Ti / bismuth telluride n-type / Ti specimens in a mixed acid of hydrofluoric acid and nitric acid to etch the Ti surface for 30 seconds, followed by ultrasonic cleaning to obtain etched p-type and n-type specimens. At 55℃, immerse the etched p-type or n-type specimens in an electroplating solution as cathodes and a Ni plate as anode for nickel plating for 5 minutes to obtain nickel-plated p-type and n-type specimens. Then, using Al2O3 ceramic as the upper and lower substrates, attach seven Cu sheets to the upper substrate and eight Cu sheets to the lower substrate. Each nickel-plated p-type specimen and each nickel-plated n-type specimen constitute a pair of specimens. Utilize Pb... 92.5 Sn5Ag 2.5 The solder was used to solder seven pairs of test pieces onto seven Cu sheets on the upper substrate, resulting in a device with the upper end soldered. Sn was then used to... 42 Bi 58Solder is used to solder the device with the upper end soldered to the lower substrate, and finally copper wires are soldered to lead out the electrodes to obtain the bismuth telluride power generation device.

[0053] The mixed acid of hydrofluoric acid and nitric acid is composed of 48% hydrofluoric acid, 90% nitric acid, and water by mass percentage. The volume ratio of the 48% hydrofluoric acid to the 90% nitric acid is 1:4, and the volume ratio of the 48% hydrofluoric acid to water is 1:5. The concentration of Ni(NH2SO3)2 in the electroplating solution is 300 g / L, the concentration of NiCl2·6H2O is 30 g / L, and the concentration of H3BO3 is 40 g / L.

[0054] The bismuth telluride-based p-type material mentioned in step one is Bi 0.399 Sb 1.596 Pb 0.005 Te3; the bismuth telluride-based n-type material mentioned in step two is Bi2Te 2.6975 Se 0.3 (SbI3) 0.0025 .

[0055] The Ti / bismuth telluride p-type / Ti specimen mentioned in step one has a height of 3 mm, a length of 1.6 mm, and a width of 1.6 mm.

[0056] The Ti / bismuth telluride n-type / Ti specimen mentioned in step two has a height of 3 mm, a length of 1.6 mm, and a width of 1.6 mm.

[0057] In step three, the Cu sheet and a pair of test pieces form a π-shape; the upper welding in step three is specifically done on a heating table at a temperature of 300℃, and left to stand for 1 minute; the lower welding is specifically done on a heating table at a temperature of 140℃, and left to stand for 1 minute.

[0058] The substrate dimensions mentioned in step three are 10×10×0.63mm. 3 The Cu sheet mentioned in step three has dimensions of 1.6 × 1.6 × 4.2 mm. 3 .

[0059] In step three, the bismuth telluride power generation device is assembled from 7 pn pairs.

[0060] The Ti / bismuth telluride p-type / Ti and Ti / bismuth telluride n-type / Ti specimens, obtained from steps one and two of Example 1, were cut into 2.5mm × 2.5mm × 3mm pieces. After cleaning, they were placed in quartz tubes, and quartz columns were inserted. The tubes were then evacuated and heated with a high-temperature flame until they were sealed. The sealed quartz tubes were placed in a muffle furnace, heated to 250°C for one hour, and maintained at 250°C for annealing for 45 days. Afterward, they were cooled with the furnace to assess their thermal stability. The contact resistance of the 2.5mm × 2.5mm × 3mm connector block was tested using the four-probe method.

[0061] Figure 1 The images show the backscattered electron scanning image and line scan energy dispersive spectroscopy (ESD) results of the Ti / bismuth telluride / Ti specimen prepared in Example 1 before and after annealing. (a) Ti / bismuth telluride p-type / Ti specimen before annealing, (b) Ti / bismuth telluride n-type / Ti specimen before annealing, (c) Ti / bismuth telluride p-type / Ti specimen after annealing for 45 days, and (d) Ti / bismuth telluride n-type / Ti specimen after annealing for 45 days. As can be seen from the figures, there is no obvious reaction between the barrier layer and the material interface, and the bonding is good. No cracks appear inside the material, indicating a stable structure and good thermal stability.

[0062] Figure 2 The figures show the contact resistance of the Ti / bismuth telluride / Ti specimens prepared in Example 1 before and after annealing. (a) Ti / bismuth telluride p-type / Ti specimen before annealing, (b) Ti / bismuth telluride n-type / Ti specimen before annealing, (c) Ti / bismuth telluride p-type / Ti specimen after annealing for 45 days, and (d) Ti / bismuth telluride n-type / Ti specimen after annealing for 45 days. As shown in the figures, the contact resistance between the p-type bismuth telluride and the barrier layer is 2.5 μΩcm. 2 The contact resistance between n-type bismuth telluride and the barrier layer is 2.33 μΩcm. 2 The temperature did not increase after 45 days of annealing, indicating that the barrier layer has good contact with the bismuth telluride material and good thermal stability.

[0063] For individual Bi 0.399 Sb 1.596 Pb 0.005 Te3 bismuth telluride p-type material bulk, Bi2Te 2.6975 Se 0.3 (SbI3) 0.0025Young's modulus tests were performed on bismuth telluride n-type material bulk, porous Ti, and dense Ti. The dense Ti was prepared as follows: 0.8g of Ti powder was placed in a graphite mold and flattened, then sintered for 20 min under vacuum, pressure of 80 MPa, and temperature of 900℃ to obtain dense Ti (density 98%). The porous Ti was prepared as follows: 0.8g of Ti powder was placed in a graphite mold and flattened, then sintered for 5 min under vacuum, pressure of 80 MPa, and temperature of 400℃ to obtain porous Ti (density 75%). Bin... 0.399 Sb 1.596 Pb 0.005 Te3 bismuth telluride p-type material bulk was prepared according to the following steps: 3g of bismuth telluride-based p-type material powder with a particle size of 500 nm to 1 μm was placed in a graphite mold and flattened. Then, it was sintered for 5 min under vacuum, pressure of 80 MPa, and temperature of 400 °C to obtain Bi 0.399 Sb 1.596 Pb 0.005 Te3 bismuth telluride p-type material bulk; Bi2Te 2.6975 Se 0.3 (SbI3) 0.0025 The bismuth telluride n-type material bulk was prepared according to the following steps: 2.7g of bismuth telluride n-type powder with a particle size of 500 nm to 1 μm was placed in a graphite mold and flattened. Then, it was sintered for 5 min under vacuum, pressure of 80 MPa and temperature of 400℃ to obtain Bi2Te. 2.6975 Se 0.3 (SbI3) 0.0025 Bismuth telluride n-type material bulk.

[0064] Figure 3 This is a comparison chart of Young's modulus, where 1 represents Bi. 0.399 Sb 1.596 Pb 0.005 Te3 bismuth telluride p-type material bulk, 2 is Bi2Te 2.6975 Se 0.3 (SbI3) 0.0025 The figure shows a bulk bismuth telluride n-type material, where 3 is porous Ti and 4 is dense Ti. As can be seen from the figure, the porous Ti has a lower Young's modulus of about 40 MPa, which can release the interfacial stress caused by the mismatch of thermal expansion coefficients at the interface.

[0065] The finite element method (ABAQUS) was used to solve the problems of dense Ti (98% density) and porous Ti (75% density) with bismuth telluride (Bi). 0.399 Sb 1.596 Pb 0.005Te3 bismuth telluride p-type material bulk and Bi2Te 2.6975 Se 0.3 (SbI3) 0.0025 Stress analysis was performed on a bulk bismuth telluride n-type material, where the boundary condition used was the variable-temperature Young's modulus ( ). Figure 4 The dense Ti (98% density) and porous Ti (75% density) used in the simulation both had dimensions of 1.6 mm × 1.6 mm × 250 μm, and the p-type and n-type bismuth telluride had dimensions of 1.6 mm × 1.6 mm × 3 mm.

[0066] Figure 4 The figures show the results of Ti / bismuth telluride interface stress simulations using the finite element method (ABAQUS). A represents the stress at the dense Ti / bismuth telluride p-type interface, B represents the stress at the porous Ti / bismuth telluride p-type interface, C represents the stress at the dense Ti / bismuth telluride n-type interface, and D represents the stress at the porous Ti / bismuth telluride n-type interface. As shown in the figures, the porous structure of Ti reduces the interfacial stress between the bismuth telluride p-type and n-type interfaces from 289.5 MPa (dense Ti) and 251.4 MPa (dense Ti) to 189 MPa and 159.4 MPa, respectively. This indicates that the porous structure helps reduce interfacial stress.

[0067] Figure 5 The figure shows the fracture morphology of loose and porous Ti; as can be seen from the figure, it reflects low density, which provides the necessary conditions for particle sliding.

[0068] Figure 6 The images show scanning images of the Ti surface of the corrosion-treated n-type specimen prepared in step three of Example 1 at room temperature and at varying temperatures. (a) is the scanning image at room temperature, (b) is the scanning image at 300°C, (c), (d), and (e) are magnified images of the dashed boxes in (a), and (f), (g), and (h) are magnified images of the dashed boxes in (b). As can be seen from the figures, the Ti particles slid after heating to 300°C, a process that also helps reduce interfacial stress.

[0069] Figure 3 , Figure 4 , Figure 5 and Figure 6 The results show that the combined effect of loose porous Ti with low Young's modulus and its particle sliding reduces the interfacial stress between the barrier layer and bismuth telluride, thereby ensuring the stability of the mechanical structure.

[0070] Figure 7High-resolution transmission electron microscope images of the Ti / bismuth telluride / Ti specimens prepared in Example 1 are shown. (a) shows the Ti / bismuth telluride p-type / Ti specimen, and (b) shows the Ti / bismuth telluride n-type / Ti specimen. Calibration of the inverse Fourier transform images (inset) confirmed that TiTe2 was generated at both the Ti / bismuth telluride p-type and Ti / bismuth telluride n-type interfaces. This microreaction helps ensure bonding strength.

[0071] Figure 8 The results show the test results of the bonding strength of the Ti / bismuth telluride / Ti specimen prepared in Example 1 as a function of annealing time. ■ represents the shear strength of the Ti / bismuth telluride p-type / Ti specimen, and ★ represents the shear strength of the Ti / bismuth telluride n-type / Ti specimen. ● represents the tensile strength of Ti / bismuth telluride p-type / Ti specimens, and ● represents the tensile strength of Ti / bismuth telluride n-type / Ti specimens. Tests were conducted at room temperature using a universal testing machine with a moving speed of 0.005 mm / min. Before annealing, the shear strength of Ti / bismuth telluride p-type was 12.29 MPa, the shear strength of Ti / bismuth telluride n-type was 12.54 MPa, the tensile strength of Ti / bismuth telluride p-type was 10.34 MPa, and the tensile strength of Ti / bismuth telluride n-type was 10.62 MPa. After annealing for 45 days, the shear strength of Ti / bismuth telluride p-type was 12.2 MPa, the shear strength of Ti / bismuth telluride n-type was 11.78 MPa, the tensile strength of Ti / bismuth telluride p-type was 10 MPa, and the tensile strength of Ti / bismuth telluride n-type was 11.04 MPa. This indicates that the bonding strength does not decrease with annealing time, meeting the requirements of thermoelectric devices for joint strength, and demonstrating that the mechanical structure is robust and reliable.

[0072] Figure 9 This is a physical image of the bismuth telluride power generation device prepared in Example 1.

[0073] Figure 10 This describes the change in hot-junction temperature over time during the service life of the bismuth telluride power generation device prepared in Example 1. The hot-junction temperature was maintained at 523 K for 12 hours, then cooled down and maintained at room temperature for 12 hours, and this cycle was repeated to test the effect of thermal cycling on device performance. Simultaneously, the conversion efficiency was tested every 12 hours. The test results are as follows: Figure 11 As shown, each conversion efficiency point represents one test, so a total of 30 tests were conducted over 15 days.

[0074] Figure 11The output voltage (U) and conversion efficiency (η) of the bismuth telluride power generation device prepared in Example 1 after 15 days of service under the conditions of hot end temperature of 250°C and cold end temperature of 20°C are shown in the figure. 1 represents the output voltage and 2 represents the conversion efficiency. As can be seen from the figure, the output voltage (U) and conversion efficiency (η) stabilized at 0.6V and 6.6% respectively after 15 days of service, and there was no significant decrease with the service time. This indicates that the thermoelectric device prepared by this barrier layer has excellent device performance and extremely good thermal stability.

Claims

1. A method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material, characterized in that... It is done in the following steps:

1. Using Ti as a barrier layer for bismuth telluride-based p-type material, and then sintering for 5 min to 10 min under vacuum, pressure of 60 MPa to 100 MPa and temperature of 400℃ to 450℃ to obtain Ti / bismuth telluride p-type / Ti specimens; 2. Using Ti as the barrier layer of bismuth telluride-based n-type material, and then sintering for 5 min to 10 min under vacuum, pressure of 60 MPa to 100 MPa and temperature of 400℃ to 450℃ to obtain Ti / bismuth telluride n-type / Ti specimens; 3. Nickel is electroplated onto the Ti surface of the Ti / bismuth telluride p-type / Ti specimen and the Ti / bismuth telluride n-type / Ti specimen, respectively, and then soldered to the upper and lower substrates to obtain the bismuth telluride power generation device.

2. The method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material according to claim 1, characterized in that... The bismuth telluride-based p-type material mentioned in step one is a Pb, Mn, Mg, Zn, or Cd-doped Bi. 0.4 Sb 1.6 Te3, or Bi modified by doping with Pb, Mn, Mg, Zn or Cd. 0.5 Sb 1.5 Te3; the bismuth telluride-based n-type material mentioned in step two is Bi2Te doped with one or two of Br and I. 2.7 Se 0.3 Or it could be Bi2Te modified by one or both of Br and I. 2.8 Se 0.2 .

3. The method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material according to claim 1, characterized in that... The Ti / bismuth telluride p-type / Ti specimen mentioned in step one is prepared according to the following steps: Ti powder is placed in a graphite mold and flattened to obtain the first Ti layer; bismuth telluride-based p-type material powder is placed on the first Ti layer and flattened to obtain the bismuth telluride-based p-type layer; Ti powder is then placed on the bismuth telluride-based p-type layer and flattened to obtain the second Ti layer, thus obtaining a mold containing Ti / bismuth telluride p-type / Ti. Then, under vacuum, pressure of 60MPa~100MPa and temperature of 400℃~450℃, it is sintered for 5min~10min. Finally, it is cut to obtain the Ti / bismuth telluride p-type / Ti specimen.

4. The method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material according to claim 3, characterized in that... The particle size of the bismuth telluride-based p-type material powder is 100 nanometers to 5 micrometers.

5. The method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material according to claim 1, characterized in that... The Ti / bismuth telluride n-type / Ti specimen mentioned in step two is prepared according to the following steps: Ti powder is placed in a graphite mold and flattened to obtain the first Ti layer; bismuth telluride-based n-type material powder is placed on the first Ti layer and flattened to obtain the bismuth telluride-based n-type layer; Ti powder is then placed on the bismuth telluride-based n-type layer and flattened to obtain the second Ti layer, thus obtaining the mold containing Ti / bismuth telluride n-type / Ti. Then, under vacuum, pressure of 60MPa~100MPa and temperature of 400℃~450℃, it is sintered for 5min~10min. Finally, it is cut to obtain the Ti / bismuth telluride n-type / Ti specimen.

6. The method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material according to claim 5, characterized in that... The particle size of the bismuth telluride-based n-type material powder is 100 nanometers to 5 micrometers.

7. A method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability for a bismuth telluride-based thermoelectric material according to claim 3 or 5, characterized in that... The particle size of the Ti powder is 15μm to 75μm.

8. The method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material according to claim 1, characterized in that... Step three involves electroplating nickel onto the Ti surface of both the Ti / bismuth telluride p-type / Ti and Ti / bismuth telluride n-type / Ti specimens. Specifically, this is performed as follows: At room temperature, the Ti / bismuth telluride p-type / Ti or Ti / bismuth telluride n-type / Ti specimens are immersed in a mixed acid solution of hydrofluoric acid and nitric acid to corrode the Ti surface for 10-30 seconds. Then, they are ultrasonically cleaned to obtain the corroded p-type and n-type specimens. At a temperature of 50-60°C, the corroded p-type or n-type specimens are immersed in an electroplating solution as the cathode, with a Ni plate as the anode, for nickel electroplating for 5-10 minutes. The hydrofluoric acid... The mixed acid with nitric acid is composed of 40%–50% hydrofluoric acid, 86%–98% nitric acid, and water by mass, wherein the volume ratio of the 40%–50% hydrofluoric acid to the 86%–98% nitric acid is 1:(3.5–4.5), and the volume ratio of the 40%–50% hydrofluoric acid to water is 1:(4.5–5.5); the concentration of Ni(NH2SO3)2 in the electroplating solution is 280 g / L–320 g / L, the concentration of NiCl2·6H2O is 25 g / L–35 g / L, and the concentration of H3BO3 is 35 g / L–45 g / L.

9. The method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material according to claim 1, characterized in that... In step three, Al2O3 ceramic is used as the upper and lower substrates. Seven Cu sheets are attached to the upper substrate and eight Cu sheets are attached to the lower substrate.

10. The method for preparing a barrier layer with low contact resistance, high bonding strength, and high thermal stability in a bismuth telluride-based thermoelectric material according to claim 1, characterized in that... In step three, the bismuth telluride power generation device is assembled from 7 pn pairs.

Images