Composite modified aerogel materials, their preparation methods, thermoelectric devices and thermoelectric modules

Abstract

This invention provides a composite modified aerogel material, its preparation method, a thermoelectric device, and a thermoelectric module. The composite modified aerogel material comprises a first modified aerogel layer and a second modified aerogel layer stacked together; the first modified aerogel layer includes a first aerogel and a first filler filled within the first aerogel; the second modified aerogel layer includes a second aerogel and a second filler filled within the second aerogel; the first filler is an inorganic long fiber, and the second filler is an inorganic particle and / or an inorganic short fiber. The thermoelectric device comprises a hot-end electrode, a thermoelectric arm, and a cold-end electrode stacked sequentially, and the composite modified aerogel material covering part or all of the side surface of the thermoelectric arm. The thermoelectric device coated with the composite modified aerogel material provided by this invention can effectively suppress the sublimation of elements in the thermoelectric material, improve the high-temperature stability of the thermoelectric material, and ensure the reliability of the thermoelectric module during long-term service.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric device technology, specifically relating to a composite modified aerogel material, its preparation method, thermoelectric devices, and thermoelectric modules. Background Technology

[0002] Thermoelectric materials are functional materials that utilize the thermoelectric effect to directly convert heat energy into electrical energy and vice versa. Thermoelectric modules are the basic units for the engineering application of thermoelectric materials, consisting of metal electrodes, n-type thermoelectric arms, and p-type thermoelectric arms connected in series and parallel according to a specific distribution. Thermoelectric materials are typically semiconductor materials, and can be classified according to their operating temperature into low-temperature thermoelectric materials (<300℃), medium-temperature thermoelectric materials (400~800℃), and high-temperature thermoelectric materials (>800℃).

[0003] The long-term stability of thermoelectric modules used for power generation has always been a major concern, especially for radioisotope thermoelectric generators (RTGs) used in deep space exploration, where long-term stability is paramount. A radioisotope thermoelectric generator (RTG) is a device that converts the heat energy generated by the decay of radioisotopes into electrical energy. It mainly consists of three parts: a radioisotope heat source, a thermoelectric converter, and a heat sink. RTGs typically use medium-to-high temperature thermoelectric modules; the higher the temperature, the higher the overall power utilization efficiency. However, the higher the service temperature of medium-to-high temperature thermoelectric modules, the more severe phenomena such as element diffusion and sublimation become. This can lead to a gradual decrease in power output and even internal short-circuit failure during long-term use.

[0004] According to research, the service reliability of thermoelectric modules is determined by a combination of factors, including the high-temperature stability of the thermoelectric materials, the reliability of the welding interface between the barrier layer and the electrode, and the reliability of the sintering interface between the thermoelectric materials and the barrier layer. Among these, the high-temperature stability of the thermoelectric materials is a crucial influencing factor. The main reason affecting the high-temperature stability of thermoelectric materials is that they typically contain high vapor pressure semiconductor elements such as Ge, Sn, As, Sb, Se, and Te. These elements are prone to sublimation at medium to high temperatures, causing the thermoelectric materials to decompose and thus degrade their performance.

[0005] Therefore, overcoming the aforementioned shortcomings of thermoelectric modules and improving their long-term reliability is an urgent problem to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a composite modified aerogel material, its preparation method, a thermoelectric device, and a thermoelectric module. The composite modified aerogel material provided by the present invention has a stable structure and can be used to coat thermoelectric devices. It can effectively inhibit the sublimation of elements in the thermoelectric material, improve the high-temperature stability of the thermoelectric material, and ensure the reliability of the thermoelectric module during long-term service.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a composite modified aerogel material, the composite modified aerogel material comprising a first modified aerogel layer and a second modified aerogel layer stacked together.

[0009] The first modified aerogel layer includes a first aerogel and a first filler filled within the first aerogel;

[0010] The second modified aerogel layer includes a second aerogel and a second filler filled within the second aerogel;

[0011] The first filler is an inorganic long fiber, and the second filler is an inorganic particle and / or an inorganic short fiber.

[0012] The composite modified aerogel material provided by this invention can be used in thermoelectric devices to coat thermoelectric materials (the first modified aerogel layer is the outer layer, and the second modified aerogel layer is the inner layer), thereby inhibiting the sublimation of elements in the thermoelectric material and extending the service life of the thermoelectric device.

[0013] The principle by which the composite modified aerogel material provided by this invention inhibits elemental sublimation is as follows:

[0014] Aerogels possess a three-dimensional network structure composed of nanoscale pores. This structure gives aerogels very low density and high porosity, as well as excellent insulation properties and a high specific surface area. When fluids (elemental vapors) enter the microporous structure of an aerogel, they are restricted by the microporous surface and cannot move freely, but can only diffuse within a tiny space. The microporous structure of an aerogel can be viewed as a series of narrow channels and pores. As gas molecules move within them, they constantly collide and bounce against the pore walls, slowing down the diffusion and movement speed, thereby reducing element sublimation. According to the laws governing the permeation of fluids (elemental vapors) through matter, the smaller the pore size, the lower the porosity, and the greater the tortuosity of the channels, the better the inhibition effect.

[0015] However, pure aerogels have very low mechanical strength and are easily broken in engineering applications. More seriously, pure aerogels are prone to shrinkage at high temperatures. This is because finished aerogels usually contain a large number of organic groups (such as methoxy and ethoxy groups), which will decompose when heated at high temperatures, causing the aerogel nanostructure to shrink and collapse, resulting in cracks or even complete breakage, thus rendering the function of inhibiting element sublimation ineffective.

[0016] This invention incorporates inorganic particles, short inorganic fibers, or long inorganic fibers into aerogel. The filler not only fills the microporous structure of the aerogel but also reacts with the hydroxyl functional groups on the aerogel surface to form an interfacial layer. This not only creates a "bridging" effect but also reduces the content of organic groups. The combined effect effectively regulates the thermal shrinkage of the aerogel, allowing the composite modified aerogel material to maintain its mesoporous structure at high temperatures, thus preventing high-temperature shrinkage and cracking. Specifically, the inner second modified aerogel layer, incorporating inorganic particles and / or short inorganic fibers, more uniformly fills the aerogel micropores, forming a "supported" nanoporous structure internally. This evenly regulates the thermal shrinkage of the aerogel, preventing the nanostructure from collapsing and inhibiting elemental sublimation. The outer second modified aerogel layer, incorporating long inorganic fibers, can nest with the inner layer at the interface between the inner and outer layers, forming a "micron-nano" transition layer. This further enhances the effect of inhibiting elemental sublimation and provides better encapsulation, support, and thermal insulation.

[0017] In some embodiments of the present invention, the thickness of the first modified aerogel layer is 2-20 mm; for example, it can be 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 13 mm, 15 mm, 16 mm, 18 mm or 20 mm, etc.

[0018] In some embodiments of the present invention, the apparent density of the first modified aerogel layer is 200-500 mg / cm³. 3 For example, it could be 200 mg / cm³. 3 220mg / cm 3 250mg / cm 3 280mg / cm 3 300mg / cm 3 320mg / cm 3 350mg / cm 3 380mg / cm 3 400mg / cm 3 420mg / cm 3 450mg / cm 3 480mg / cm 3 Or 500mg / cm 3 wait.

[0019] In this invention, if the apparent density of the first modified aerogel layer is too high, it is easy to have a high thermal conductivity and poor heat insulation effect; if the apparent density of the first modified aerogel layer is too low, it has more pores, which makes it easier for volatile elements to diffuse out through the large pores, which will reduce the inhibitory effect of the first modified aerogel layer on element sublimation, and will also lead to lower strength of the first modified aerogel layer, making it more prone to collapse during use.

[0020] In some embodiments of the present invention, the first aerogel is a silica aerogel.

[0021] In some embodiments of the present invention, the first filler accounts for 40-80% of the volume fraction of the first modified aerogel layer; for example, it can be 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, or 80%, etc.

[0022] In this invention, if too little first filler is incorporated into the first modified aerogel layer, the strength of the first modified aerogel layer will be reduced, making it brittle during use; if too much first filler is incorporated into the first modified aerogel layer, the sol will not penetrate sufficiently, resulting in large pores, which will reduce the effect of inhibiting element sublimation.

[0023] In some embodiments of the present invention, the length of the inorganic long fiber is 0.1-100 mm, for example, it can be 0.1 mm, 0.3 mm, 0.5 mm, 0.8 mm, 1 mm, 3 mm, 5 mm, 8 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm, etc.; the diameter is 1-50 μm, for example, it can be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, etc.

[0024] In some embodiments of the present invention, the inorganic long fiber is aluminum silicate long fiber and / or quartz long fiber.

[0025] In some embodiments of the present invention, the thickness of the second modified aerogel layer is 2-10 mm; for example, it can be 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm, etc.

[0026] In some embodiments of the present invention, the apparent density of the second modified aerogel layer is 100-500 mg / cm³. 3 For example, it could be 100 mg / cm³.3 120mg / cm 3 150mg / cm 3 180mg / cm 3 200mg / cm 3 220mg / cm 3 250mg / cm 3 280mg / cm 3 300mg / cm 3 320mg / cm 3 350mg / cm 3 380mg / cm 3 400mg / cm 3 420mg / cm 3 450mg / cm 3 480mg / cm 3 Or 500mg / cm 3 wait.

[0027] In this invention, if the apparent density of the second modified aerogel layer is too high, it will easily lead to an increase in its thermal conductivity and a decrease in its heat insulation effect; if the apparent density of the second modified aerogel layer is too low, it will have more pores, and volatile elements can more easily escape through the large pores, which will reduce the ability of the second modified aerogel layer to inhibit element sublimation, and the strength of the second modified aerogel layer will also decrease, making it more prone to collapse during use.

[0028] In some embodiments of the present invention, the pore diameter in the second modified aerogel layer is ≤100nm.

[0029] In some embodiments of the present invention, the second aerogel is a silica aerogel.

[0030] In some embodiments of the present invention, the second filler accounts for 5-40% of the volume fraction of the second modified aerogel layer; for example, it can be 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, or 40%, etc.

[0031] In this invention, if too little second filler is incorporated into the second modified aerogel layer, it may lead to insufficient support for the nanopores, resulting in a larger high-temperature shrinkage rate of the second modified aerogel layer, which may easily cause cracking during use; if too much second filler is incorporated into the second modified aerogel layer, it may destroy the continuous structure of the aerogel, leading to a decrease in the mechanical properties of the second modified aerogel layer, which may make it brittle during use.

[0032] In some embodiments of the present invention, the particle size of the inorganic particles is 1-200 nm; for example, it can be 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm or 200 nm, etc.

[0033] In some embodiments of the present invention, the inorganic particles are one or more of fumed silica particles, silicon carbide particles, metal oxide particles (e.g., alumina, titanium dioxide, etc.) and carbon black particles.

[0034] In some embodiments of the present invention, the length of the inorganic short fiber is 50-200 nm, for example, it can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, or 200 nm; the diameter is 1-50 nm, for example, it can be 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm. Those skilled in the art will readily understand that, since the inorganic short fiber has a non-fibrous structure, its length should be greater than its diameter.

[0035] In some embodiments of the present invention, the inorganic short fibers are quartz short fibers and / or silica short fibers.

[0036] In a second aspect, the present invention provides a method for preparing a composite modified aerogel material as described in the first aspect, the method comprising the following steps:

[0037] (1) Mix the first aerogel precursor and the first solvent, add the first catalyst to react and obtain the first sol; impregnate the first filler with the first sol, and then age and dry it in sequence to form the first modified aerogel layer.

[0038] (2) The second aerogel precursor and the second solvent are mixed and the second catalyst is added to react to obtain the second sol; the second sol is mixed with the second filler and then attached to the preset space on the surface of the first modified aerogel layer, and aged and dried in sequence to form the second modified aerogel layer, thereby obtaining the composite modified aerogel material.

[0039] In some embodiments of the present invention, the first aerogel precursor and the second aerogel precursor are each independently selected from one or more of silicates, silicates and silanes, preferably selected from one or more of sodium tetrasilicate, tetraethyl silicate, diethyl silicate and ethyl silicate.

[0040] In some embodiments of the present invention, the first solvent and the second solvent are each independently selected from one or more of water, methanol, ethanol, isopropanol, n-propanol, n-butanol, acetone and acetonitrile.

[0041] In some embodiments of the present invention, the volume ratio of the first aerogel precursor to the first solvent and the volume ratio of the second aerogel precursor to the second solvent are each independently (5%-20%):(80%-95%); for example, they can be 5%:95%, 8%:92%, 10%:90%, 12%:88%, 15%:85%, 18%:82%, or 20%:80%, etc.

[0042] In this invention, the types of the first solvent and the second solvent need to be selected according to the types of the first aerogel precursor and the second aerogel precursor. Generally, when the first aerogel precursor and the second aerogel precursor are inorganic substances (e.g., silicates), the first solvent and the second solvent can be water; the volume ratio of the first aerogel precursor to the first solvent and the volume ratio of the second aerogel precursor to the second solvent are each independently (5%-20%):(80%-95%). When the first aerogel precursor and the second aerogel precursor are organic materials (e.g., silicates, silanes), the solvent can be a mixture of an organic solvent (i.e., one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, acetone, and acetonitrile) and water; the volume ratio of the first aerogel precursor, the organic solvent, and water, and the volume ratio of the second aerogel precursor, the organic solvent, and water are each independently (5%-20%):(50%-80%):(10%-45%); for example, it can be 5%:80%:15%, 10%:70%:20%, 15%:60%:25%, 20%:50%:30%, etc.

[0043] In this invention, if the content of aerogel precursor in the reaction system is too low, the hydrolysis and condensation reactions will not proceed sufficiently, resulting in a smaller three-dimensional network structure, making it difficult or even impossible to form an aerogel. At the same time, if the content of precursor is too low, the porosity of the aerogel will increase, and the effect of inhibiting element volatilization will be worse. If the content of aerogel precursor is too high, the viscosity of the solution will be too high, affecting the hydrolysis and condensation reactions, thereby affecting the formation of the aerogel.

[0044] In some embodiments of the present invention, the first catalyst and the second catalyst are each independently selected from one or more of ammonia, sodium hydroxide, ammonium hydroxide, potassium hydroxide, hydrochloric acid and sulfuric acid.

[0045] In some embodiments of the present invention, the first catalyst and the second catalyst are added in solution form, each with a concentration independently of 0.05-0.5 mol / L (e.g., 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, etc.). If the catalyst concentration is too high, it will cause the hydrolysis and condensation reactions of the local aerogel precursor to be too rapid, resulting in an uneven reaction system and affecting the formation and properties of the aerogel.

[0046] In some embodiments of the present invention, the amount of the first catalyst and the second catalyst added is independently set such that the pH of the reaction system reaches 1-4 or 8-11; for example, it can be 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.3, 3.5, 3.8, 4, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 9.8, 10, 10.2, 10.5, 10.7 or 11, etc.

[0047] In this invention, the pH of the reaction system needs to be selected according to the types of the first and second aerogel precursors. If the aerogel precursor is a silicate, the pH of the reaction system is 1-4; if the aerogel precursor is a silicate ester and / or a silane, the pH of the reaction system is 8-11.

[0048] In some embodiments of the present invention, the temperature of the reaction in steps (1) and (2) is independently 20-60°C and the time is independently 0.5-6h.

[0049] In this invention, aging refers to a static reaction. In some embodiments of this invention, the aging temperature in steps (1) and (2) is independently 20-60°C, and the aging time is independently 6-72h.

[0050] In some embodiments of the present invention, the impregnation in step (1) is carried out under vacuum conditions for 0.5-6 hours. Vacuum conditions help the first sol to fully penetrate into the voids of the first filler.

[0051] Thirdly, the present invention provides a thermoelectric device comprising a hot-end electrode, a thermoelectric arm and a cold-end electrode stacked sequentially, and a composite modified aerogel material as described in the first aspect or a composite modified aerogel material prepared by the preparation method described in the second aspect.

[0052] The composite modified aerogel material is coated on part or all of the surface of the side of the thermoelectric arm;

[0053] The second modified aerogel layer in the composite modified aerogel material is bonded to the thermoelectric arm.

[0054] In this invention, the thermoelectric arm comprises, in sequence, an electrode connection layer, a barrier layer, a thermoelectric material layer, another barrier layer, and an electrode connection layer. Thermoelectric materials are classified into N-type thermoelectric materials and P-type thermoelectric materials. A thermoelectric arm containing N-type thermoelectric material is an N-type thermoelectric arm, and the corresponding thermoelectric device is an N-type thermoelectric device; a thermoelectric arm containing P-type thermoelectric material is a P-type thermoelectric arm, and the corresponding thermoelectric device is a P-type thermoelectric device.

[0055] In some embodiments of the present invention, the composite modified aerogel material is disposed around the side of a section of the thermoelectric arm near the hot end.

[0056] In this invention, the hot end of the thermoelectric arm refers to the end closest to the hot end electrode, and the cold end refers to the end closest to the cold end electrode. When the thermoelectric device is working, the hot end is in a high-temperature environment, and the cold end is in a low-temperature environment. The section of the thermoelectric arm near the hot end refers to a section extending from the hot end of the thermoelectric arm to the cold end at a certain height; this "section" includes the entire thermoelectric arm.

[0057] In some embodiments of the present invention, the height of the second modified aerogel layer in the composite modified aerogel material is more than 2 / 3 of the height of the thermoelectric arm, and the height of the first modified aerogel layer in the composite modified aerogel material is greater than or equal to the height of the second modified aerogel layer.

[0058] When a thermoelectric device is operating, the temperature decreases from the hot end to the cold end. Since elements in the thermoelectric material only sublimate above a certain temperature, the composite modified aerogel material does not need to cover the entire side of the thermoelectric arm. Actual measurements show that the height enclosed by the second modified aerogel layer is more than 2 / 3 of the height of the thermoelectric arm, which is sufficient to cover most of the sublimation temperature range. In this invention, it is preferable that the height enclosed by the first modified aerogel layer is equal to the height enclosed by the second modified aerogel layer.

[0059] In some embodiments of the present invention, at any temperature within the operating temperature range of the thermoelectric device, relative to room temperature, the volume change rate η of the second modified aerogel layer in the composite modified aerogel material satisfies the same condition as the volume change rate δ of the thermoelectric material in the thermoelectric arm: |η+δ|≤15%, for example, it can be 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or 0%, etc.

[0060] In this invention, the operating temperature range refers to the temperature range between the hot end temperature and the cold end temperature (including both the hot and cold end temperatures) during the operation of the thermoelectric device. Volume change rate = (volume at a certain temperature - volume at room temperature) / volume at room temperature × 100%. Composite modified aerogel materials and thermoelectric materials will expand or contract at high temperatures. If the difference between η and δ is too large, the thermal stress may exceed the aerogel's strength limit, leading to cracking and rendering its function of inhibiting elemental sublimation ineffective.

[0061] In some embodiments of the present invention, the surface roughness of the thermoelectric arm's side surface satisfies Rz≤3.2μm and Ra≤0.4μm. Polishing the side surface of the thermoelectric arm reduces its surface roughness, which helps to improve the tightness of the bond between the composite modified aerogel material and the thermoelectric arm, preventing defects such as pores and cracks from occurring between them.

[0062] In some embodiments of the present invention, the thermoelectric material in the thermoelectric arm contains one or more elements that readily sublimate, such as Ge, Sn, As, Sb, Se, and Te. Corresponding thermoelectric materials may be CoSb3, PbTe, TAGS (Te-Sb-Ge-Ag), half-Heusler, SiGe, SnSe, Zintl phase compounds (an intermetallic compound containing both ionic and covalent bond characteristics), Cu, etc. 2-x Se, Cu 2-x One or more of Te(0<x<2).

[0063] Fourthly, a thermoelectric module, the thermoelectric module comprising a thermocouple, or multiple thermocouples connected in series or in parallel;

[0064] The thermocouple includes an N-type thermoelectric element and a P-type thermoelectric element;

[0065] In each of the thermocouples, the hot end electrode of the N-type thermoelectric device is connected to the hot end electrode of the P-type thermoelectric device, or the cold end electrode of the N-type thermoelectric device is connected to the cold end electrode of the P-type thermoelectric device.

[0066] The N-type thermoelectric device and the P-type thermoelectric device are thermoelectric devices as described in the third aspect.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] The composite modified aerogel material provided by this invention has a stable structure and can be used to coat thermoelectric devices. It can effectively inhibit the sublimation of elements in thermoelectric materials, improve the high-temperature stability of thermoelectric materials, and ensure the reliability of thermoelectric modules during long-term service. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the composite barrier layer in a thermoelectric module provided in an embodiment of the present invention;

[0070] Figure 2 This is a flowchart illustrating the fabrication process of the thermoelectric arm in an embodiment of the present invention;

[0071] Figure 3 This is a schematic diagram of the thermoelectric pair in the thermoelectric module provided in an embodiment of the present invention;

[0072] Figure 4 This is a schematic diagram of the structure of the first modified aerogel layer in the thermoelectric module provided in an embodiment of the present invention;

[0073] Figure 5 This is a schematic diagram of the structure of the first modified aerogel layer into which thermoelectric pairs are inserted in an embodiment of the present invention;

[0074] Figure 6a This is a schematic diagram of the cross-sectional structure of the thermoelectric module intermediate body perpendicular to the side of the thermoelectric arm in an embodiment of the present invention;

[0075] Figure 6b This is a schematic diagram of the cross-sectional structure of the thermoelectric module intermediate body parallel to the side of the thermoelectric arm in an embodiment of the present invention;

[0076] Figure 7 This is a schematic diagram of the thermoelectric module with a series structure provided in an embodiment of the present invention;

[0077] Figure 8 Optical photographs of the composite modified aerogel material in Example 1 of this invention before and after testing;

[0078] Figure 9 Optical photographs of the composite modified aerogel material in Comparative Example 1 of this invention before and after testing;

[0079] Figure 10 Metallographic micrograph of the thermoelectric module after testing, provided in Embodiment 1 of the present invention;

[0080] Figure 11 The above is a metallographic micrograph of the thermoelectric module after testing, provided in Comparative Example 2 of this invention.

[0081] The reference numerals in the attached figures are as follows: 101-Electrode connection layer, 102-Blocking layer, 11-Composite blocking layer, 12-Thermoelectric material layer, 13-Thermoelectric arm block, 14-P-type thermoelectric arm, 15-N-type thermoelectric arm, 16-Hot end electrode, 17-First modified aerogel layer, 18-Second modified aerogel layer, 19-Thermoelectric module intermediate, 20-Cold end electrode. Detailed Implementation

[0082] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the specific embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0083] Example 1

[0084] This embodiment provides a thermoelectric module, the preparation method of which is as follows;

[0085] (1) Preparation of composite barrier layer 11

[0086] The structure of the composite barrier layer 11 is as follows Figure 1 As shown, the composite barrier layer 11 includes a stacked electrode connection layer 101 and a barrier layer 102. The electrode connection layer 101 is made of pure copper, and the barrier layer 102 is made of an iron-nickel-chromium alloy. The surfaces of the electrode connection layer 101 and the barrier layer 102 are sequentially polished with 800-grit, 1200-grit, 1500-grit, and 2000-grit sandpaper, and ultrasonically cleaned. Then, the electrode connection layer 101 and the barrier layer 102 are composited together using a solid-phase diffusion method at a temperature of 700℃, a pressure of 50MPa, and a holding time of 30min to obtain a composite barrier layer 11.

[0087] (2) Fabrication of thermoelectric arms

[0088] The fabrication process of the thermoelectric arm is as follows: Figure 2 As shown, the composite barrier layer 11, thermoelectric material (P-type CoSb3 powder or N-type CoSb3 powder), and composite barrier layer 11 are placed sequentially into a mold (barrier layer 102 is close to the thermoelectric material). SPS sintering is performed at a sintering temperature of 700℃, a pressure of 40MPa, and a holding time of 25min to prepare a thermoelectric arm block 13 with a height of 15mm. This block includes two composite barrier layers 11 and a thermoelectric material layer 12 sandwiched between the two composite barrier layers 11. The thermoelectric arm block 13 is then divided, ground, and polished until the surface roughness reaches Rz = 3.2μm and Ra = 0.4μm, resulting in a P-type thermoelectric arm 14 and an N-type thermoelectric arm 15, with dimensions of 6.5mm × 6.5mm × 15mm.

[0089] (3) Preparation of thermoelectric pairs

[0090] The structure of a thermoelectric pair is as follows Figure 3 As shown, it includes a P-type thermoelectric arm 14, an N-type thermoelectric arm 15, and a hot-end electrode 16. The electrode connection layer 101 at one end of the P-type thermoelectric arm 14 and the N-type thermoelectric arm 15 is connected to the hot-end electrode 16 by vacuum brazing.

[0091] (4) Preparation of the first modified aerogel layer 17

[0092] The structure of the first modified aerogel layer 17 is as follows: Figure 4 As shown, its shape is a cuboid with multiple through holes arranged in an array. Its height (i.e., the depth of the through holes) is 13 mm. The shape of the through holes is square with a side length of 12.5 mm. The spacing between two adjacent through holes (i.e., the thickness of the first modified aerogel layer 17) is 5 mm. The distance between the through holes located at the edge and the edge is 5 mm.

[0093] Alumina silicate long fibers (40 mm in length and 20 μm in diameter) were pre-formed into the shape of the first modified aerogel layer 17. Tetraethyl silicate, methanol, and deionized water were mixed in a volume fraction of 15%:55%:30%, and the pH was adjusted to 9 with 0.5 mol / L ammonia. The mixture was allowed to stand at room temperature for 30 min to obtain silica sol. The pre-formed alumina silicate long fibers were immersed in the silica sol and impregnated in a vacuum for 1 h. Then, the mixture was allowed to stand at room temperature for 10 h to age. Finally, the mixture was subjected to supercritical carbon dioxide drying at 40 °C and 8 MPa to remove residual aerogel inside the pores and on the surface, resulting in the first modified aerogel layer 17, in which the alumina silicate long fibers accounted for 50% of the volume fraction of the first modified aerogel layer 17.

[0094] (5) Preparation of thermoelectric module intermediate 19

[0095] The structure of the thermoelectric module intermediate 19 is as follows Figure 6a and Figure 6b As shown, it includes a first modified aerogel layer 17, a second modified aerogel layer 18, and a thermoelectric pair; wherein the P-type thermoelectric arm 14 and the N-type thermoelectric arm 15 of the thermoelectric pair are inserted into the through hole of the first modified aerogel layer 17, and the second modified aerogel layer 18 fills the gap between the thermoelectric arm and the through hole, forming a structure in which the composite modified aerogel material surrounds the side of the thermoelectric arm near the hot end.

[0096] The thermoelectric arms are inserted sequentially into the through holes of the first modified aerogel layer 17. The gap between the thermoelectric arms and the periphery of the through holes (i.e., the thickness of the second modified aerogel layer 18) is 3 mm. The structure is as follows: Figure 5 As shown.

[0097] Tetraethyl silicate, methanol, and deionized water were mixed in a volume ratio of 20%:50%:30%, and the pH was adjusted to 9 with 0.5 mol / L ammonia. The mixture was allowed to stand at room temperature for 30 min to obtain a silica sol. Vaporized silica particles with a diameter of 20 nm (controlling their volume fraction in the second modified aerogel layer 18 to be 10%) and titanium dioxide particles with a diameter of 50 nm (controlling their volume fraction in the second modified aerogel layer 18 to be 10%) were added to the silica sol and stirred evenly. The mixture was then injected into the gap between the thermoelectric arm and the through hole, with a liquid level of 13 mm. The mixture was allowed to stand at room temperature for 10 h to age, and then subjected to supercritical carbon dioxide drying at a temperature of 40 °C and a pressure of 8 MPa to form the second modified aerogel layer 18, thus obtaining the thermoelectric module intermediate 19.

[0098] (6) Fabrication of thermoelectric modules

[0099] The structure of the thermoelectric module is as follows Figure 7 As shown, it includes a thermoelectric module intermediate 19 and a cold end electrode 20. The cold end electrode 20 is a connection method that allows thermoelectric pairs to be connected in series and is welded to the exposed electrode connection layer 101 of the P-type thermoelectric arm 14 and the N-type thermoelectric arm 15.

[0100] Example 2

[0101] This embodiment provides a thermoelectric module, the preparation method of which differs from that of Embodiment 1 in that:

[0102] The thermoelectric materials used in step (2) are P-type SnSe and N-type SnSe;

[0103] Step (4): The structure of the first modified aerogel layer 17 is as follows Figure 4 As shown, its shape is a cuboid with multiple through holes arranged in an array. Its height (i.e., the depth of the through holes) is 13 mm. The shape of the through holes is square with a side length of 10.5 mm. The spacing between two adjacent through holes (i.e., the thickness of the first modified aerogel layer 17) is 20 mm. The distance between the through holes located at the edge and the edge is 20 mm.

[0104] Aluminum silicate long fibers (0.01 mm in length and 20 μm in diameter) are preformed into the shape of the first modified aerogel layer 17;

[0105] Sodium tetrasilicate and deionized water were mixed in a volume ratio of 20%:80%, and the pH was adjusted to 2 with 0.1 mol / L sulfuric acid. The mixture was allowed to stand at room temperature for 1 hour to obtain silica sol. Pre-formed aluminosilicate long fibers were immersed in the silica sol and impregnated in a vacuum for 2 hours. Then, the mixture was allowed to stand at room temperature for 10 hours to age. The mixture was then subjected to supercritical carbon dioxide drying at 40°C and 10 MPa to remove residual aerogel from the pores and surface, resulting in a first modified aerogel layer 17, in which the aluminosilicate long fibers accounted for 40% of the volume of the first modified aerogel layer 17.

[0106] Step (5): Insert the thermoelectric arms sequentially into the through holes of the first modified aerogel layer 17. The gap between the thermoelectric arms and the perimeter of the through holes (i.e., the thickness of the second modified aerogel layer 18) is 2 mm. The structure is as follows: Figure 5 As shown. Sodium tetrasilicate and deionized water were mixed in a volume fraction of 5%:95%, and the pH was adjusted to 2 with 0.1 mol / L sulfuric acid. The mixture was allowed to stand at room temperature for 1 hour to obtain silica sol. Alumina particles with a diameter of 200 nm were added to the silica sol (controlling their volume fraction in the second modified aerogel layer 18 to be 40%), stirred evenly, and then injected into the gap between the thermoelectric arm and the through hole, with a liquid level of 13 mm. The mixture was allowed to stand at room temperature for 6 hours to age, and then subjected to supercritical carbon dioxide drying at a temperature of 40 °C and a pressure of 10 MPa to form the second modified aerogel layer 18, thus obtaining the thermoelectric module intermediate 19.

[0107] Example 3

[0108] This embodiment provides a thermoelectric module, the preparation method of which differs from that of Embodiment 1 in that:

[0109] The thermoelectric materials used in step (2) are P-type SiGe and N-type SiGe;

[0110] Step (4): The structure of the first modified aerogel layer 17 is as follows Figure 4 As shown, its shape is a cuboid with multiple through holes arranged in an array. Its height (i.e., the depth of the through holes) is 13 mm. The shape of the through holes is square with a side length of 26.5 mm. The spacing between two adjacent through holes (i.e., the thickness of the first modified aerogel layer 17) is 2 mm. The distance between the through holes located at the edge and the edge is 2 mm.

[0111] Quartz long fibers (100 mm in length and 20 μm in diameter) were pre-formed into the shape of the first modified aerogel layer 17. Diethyl silicate, acetonitrile, and deionized water were mixed in a volume fraction of 12%:50%:38%, and the pH was adjusted to 9 with 0.2 mol / L sodium hydroxide. The mixture was allowed to stand at room temperature for 40 min to obtain silica sol. The pre-formed quartz long fibers were immersed in silica sol and impregnated in a vacuum for 1 h. Then, the mixture was allowed to stand at room temperature for 6 h to age. Finally, the mixture was subjected to supercritical carbon dioxide drying at 45 °C and 8 MPa to remove residual aerogel inside the pores and on the surface, resulting in the first modified aerogel layer 17, in which the aluminum silicate long fibers accounted for 80% of the volume fraction of the first modified aerogel layer 17.

[0112] Step (5): Insert the thermoelectric arms sequentially into the through holes of the first modified aerogel layer 17. The gap between the thermoelectric arms and the perimeter of the through holes (i.e., the thickness of the second modified aerogel layer 18) is 10 mm. The structure is as follows: Figure 5 As shown, diethyl silicate, acetonitrile, and deionized water were mixed in a volume fraction of 15%:50%:35%, and the pH was adjusted to 9 with 0.2 mol / L sodium hydroxide. The mixture was allowed to stand at room temperature for 1 hour to obtain silica sol. Short quartz fibers with a length of 200 nm and a diameter of 20 nm (controlling their volume fraction in the second modified aerogel layer 18 to be 5%) were added to the silica sol and stirred evenly. The mixture was then injected into the gap between the thermoelectric arm and the through hole, with a liquid level of 13 mm. The mixture was allowed to stand at room temperature for 6 hours and then subjected to supercritical carbon dioxide drying at a temperature of 45 °C and a pressure of 8 MPa to form the second modified aerogel layer 18, thus obtaining the thermoelectric module intermediate 19.

[0113] Comparative Example 1

[0114] This comparative example provides a thermoelectric module, which differs from Example 1 only in that, in step (5), silica sol is directly injected into the gap between the thermoelectric arm and the through hole, and the second modified aerogel layer 18 becomes a silica aerogel without filler.

[0115] Comparative Example 2

[0116] This comparative example provides a thermoelectric module, which differs from Example 1 only in that the thermoelectric module does not have the first modified aerogel layer 17 and the second modified aerogel layer 18.

[0117] Performance testing:

[0118] The thermoelectric modules provided in Example 1 and Comparative Example 1 were tested for 60 hours under conditions of a hot-end temperature of 650°C, a cold-end temperature of 40°C, and a vacuum degree of 10 Pa. The morphology of the composite modified aerogel material before and after the test was observed. The results showed that the composite modified aerogel material in Example 1 did not show significant structural changes before and after the test. Figure 8 ), while the composite modified aerogel material in Comparative Example 1 cracked after aging. Figure 9 This cannot meet the long-term use requirements of CoSb3 thermoelectric modules.

[0119] The thermoelectric modules provided in Example 1 and Comparative Example 2 were tested for 2000 hours under the conditions of a hot end temperature of 650°C, a cold end temperature of 40°C, and a vacuum degree of 10Pa. The volatilization of elements on the surface of the thermoelectric arm was observed after the test.

[0120] After the test, the composite modified aerogel material wrapped around the thermoelectric arm was removed, and the surface of the thermoelectric arm was polished with a nylon polishing cloth. The thermoelectric arms in Example 1 and Comparative Example 2 were observed using a metallographic microscope. The results showed that in Comparative Example 2, the thermoelectric arm not wrapped with the composite modified aerogel material had a distinct porous layer in the hot end region after the test, caused by Sb volatilization, with the most severe pores on both sides. Figure 10 In Example 1, the thermoelectric arm wrapped with a composite modified aerogel material showed a significant reduction in porosity in the hot-end region due to Sb volatilization after testing. Figure 11 This demonstrates that the composite modified aerogel material has a significant effect in inhibiting Sb volatilization.

[0121] The apparent density, porosity, pore size, and volume shrinkage rate of the second modified aerogel layer 18 in Examples 1 and 2 (Comparative Example 1) were tested. The test methods are as follows:

[0122] (1) Density test

[0123] The material of the second modified aerogel layer 18 was prepared into a regular cube, the mass of the block was weighed, and its mass (g) and volume ratio (cm³) were calculated. 3 The value of ).

[0124] (2) Rate of change of volume

[0125] The material of the second modified aerogel layer 18 was prepared into a test block, and its volume V1 (cm³) at room temperature (25℃) was measured. 3 Then, it undergoes high-temperature treatment (25-1000℃) under vacuum, and the volume V2 (cm³) after high-temperature treatment is measured. 3 The volume change rate η can be calculated using the following formula.

[0126]

[0127] The same method was used to test the volume change rate δ of thermoelectric materials at 25-650℃.

[0128] (3) Specific surface area and pore structure (BET) analysis

[0129] The micro-nano porous structure of the modified aerogel was analyzed using a specific surface area analyzer through nitrogen isothermal adsorption-desorption curves and pore size distribution curves.

[0130] The test results for the above properties are shown in Table 1 below.

[0131] Table 1

[0132]

[0133] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A composite modified aerogel material for coating thermoelectric devices, characterized in that, The composite modified aerogel material comprises a first modified aerogel layer and a second modified aerogel layer stacked together. The first modified aerogel layer includes a first aerogel and a first filler filled within the first aerogel; The second modified aerogel layer includes a second aerogel and a second filler filled within the second aerogel; The first filler is an inorganic long fiber, and the second filler is an inorganic particle and / or an inorganic short fiber; The apparent density of the first modified aerogel layer is 200-500 mg / cm³. 3 The first aerogel is a silica aerogel, and the length of the inorganic long fiber is 0.1-100 mm; The apparent density of the second modified aerogel layer is 100-500 mg / cm³. 3 The second aerogel is a silica aerogel, and the inorganic particles are one or more of fumed silica particles, silicon carbide particles, metal oxide particles and carbon black particles, and the length of the inorganic short fibers is 50-200 nm.

2. The composite modified aerogel material according to claim 1, characterized in that, The thickness of the first modified aerogel layer is 2-20 mm.

3. The composite modified aerogel material according to claim 1 or 2, characterized in that, The first filler accounts for 40-80% of the volume fraction of the first modified aerogel layer.

4. The composite modified aerogel material according to claim 1 or 2, characterized in that, The diameter of the inorganic long fibers is 1-50 μm.

5. The composite modified aerogel material according to claim 1 or 2, characterized in that, The inorganic long fibers are aluminum silicate long fibers and / or quartz long fibers.

6. The composite modified aerogel material according to claim 1, characterized in that, The thickness of the second modified aerogel layer is 2-10 mm; And / or, the pore diameter in the second modified aerogel layer is ≤100nm.

7. The composite modified aerogel material according to claim 1 or 6, characterized in that, The second filler accounts for 5-40% of the volume fraction of the second modified aerogel layer.

8. The composite modified aerogel material according to claim 1 or 6, characterized in that, The inorganic particles have a particle size of 1-200 nm.

9. The composite modified aerogel material according to claim 1 or 6, characterized in that, The diameter of the inorganic short fibers is 1-50 nm.

10. The composite modified aerogel material according to claim 1 or 6, characterized in that, The inorganic short fibers are quartz short fibers and / or silica short fibers.

11. A method for preparing a composite modified aerogel material according to any one of claims 1-10, characterized in that, The preparation method includes the following steps: (1) Mix the first aerogel precursor and the first solvent, add the first catalyst to react and obtain the first sol; impregnate the first filler with the first sol, and then age and dry it in sequence to form the first modified aerogel layer. (2) The second aerogel precursor and the second solvent are mixed and the second catalyst is added to react to obtain the second sol; the second sol is mixed with the second filler and then attached to the preset space on the surface of the first modified aerogel layer, and aged and dried in sequence to form the second modified aerogel layer, thereby obtaining the composite modified aerogel material.

12. The preparation method according to claim 11, characterized in that, The first aerogel precursor and the second aerogel precursor are each independently selected from one or more of silicates, silicates and silanes.

13. The preparation method according to claim 12, characterized in that, The first aerogel precursor and the second aerogel precursor are each independently selected from one or more of sodium tetrasilicate, tetraethyl silicate, diethyl silicate and ethyl silicate.

14. The preparation method according to claim 11, characterized in that, The first solvent and the second solvent are each independently selected from one or more of water, methanol, ethanol, isopropanol, n-propanol, n-butanol, acetone and acetonitrile.

15. The preparation method according to claim 11, characterized in that, The volume ratio of the first aerogel precursor to the first solvent and the volume ratio of the second aerogel precursor to the second solvent are each independently (5%-20%):(80%-95%).

16. The preparation method according to claim 11, characterized in that, The first catalyst and the second catalyst are each independently selected from one or more of ammonia, sodium hydroxide, ammonium hydroxide, potassium hydroxide, hydrochloric acid, and sulfuric acid.

17. The preparation method according to claim 11 or 16, characterized in that, The first catalyst and the second catalyst are added in solution form, each with a concentration of 0.05-0.5 mol / L.

18. The preparation method according to claim 11 or 16, characterized in that, The amount of the first catalyst and the second catalyst added is independently determined to bring the pH of the reaction system to 1-4 or 8-11.

19. The preparation method according to claim 11, characterized in that, The temperature of the reaction described in steps (1) and (2) is 20-60℃ and the time is 0.5-6h.

20. The preparation method according to claim 11, characterized in that, The aging temperatures described in steps (1) and (2) are each 20-60°C and the aging times are each 6-72h.

21. The preparation method according to claim 11, characterized in that, The impregnation described in step (1) is carried out under vacuum conditions for 0.5-6 hours.

22. A thermoelectric device, characterized in that, The thermoelectric device includes a hot-end electrode, a thermoelectric arm, and a cold-end electrode stacked sequentially, as well as a composite modified aerogel material as described in any one of claims 1-10 or a composite modified aerogel material prepared by the preparation method as described in any one of claims 11-21. The composite modified aerogel material is coated on part or all of the surface of the side of the thermoelectric arm; The second modified aerogel layer in the composite modified aerogel material is bonded to the thermoelectric arm.

23. The thermoelectric device according to claim 22, characterized in that, The composite modified aerogel material is disposed around the side of a section of the thermoelectric arm near the hot end.

24. The thermoelectric device according to claim 22, characterized in that, The height of the second modified aerogel layer in the composite modified aerogel material is more than 2 / 3 of the height of the thermoelectric arm, and the height of the first modified aerogel layer in the composite modified aerogel material is greater than or equal to the height of the second modified aerogel layer.

25. The thermoelectric device according to claim 22, characterized in that, Compared to room temperature, at any temperature within the operating temperature range of the thermoelectric device, the volume change rate η of the second modified aerogel layer in the composite modified aerogel material satisfies the same condition as the volume change rate δ of the thermoelectric material in the thermoelectric arm: |η+δ|≤15%.

26. The thermoelectric device according to claim 22, characterized in that, The surface roughness of the thermoelectric arm meets the requirements of Rz≤3.2μm and Ra≤0.4μm.

27. The thermoelectric device according to claim 22, characterized in that, The thermoelectric material in the thermoelectric arm contains one or more of the elements Ge, Sn, As, Sb, Se, and Te.

28. A thermoelectric module, characterized in that, The thermoelectric module includes one thermocouple, or multiple thermocouples connected in series or in parallel. The thermocouple includes an N-type thermoelectric element and a P-type thermoelectric element; In each of the thermocouples, the hot end electrode of the N-type thermoelectric device is connected to the hot end electrode of the P-type thermoelectric device, or the cold end electrode of the N-type thermoelectric device is connected to the cold end electrode of the P-type thermoelectric device. The N-type thermoelectric device and the P-type thermoelectric device are thermoelectric devices as described in any one of claims 22-27.

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