A heat-insulating and moisture-proof thermoelectric device and its preparation method

Abstract

The present invention discloses a heat-insulating and moisture-proof thermoelectric device and a preparation method thereof, relating to the technical field of thermoelectric materials. The thermoelectric device comprises a p-type Bi2Te3 electric couple arm and an n-type Bi2Te3 electric couple arm connected to an electrode and having a moisture-proof layer grown on the surface; a cellulose-based aerogel layer filling between adjacent electric couple arms; the cellulose-based aerogel layer having a porosity of 96%-99.5% and a surface contact angle of ≥150°; a heat-reflecting film covering the non-heat-conducting surface of the electric couple arm, the heat-reflecting film having a reflectivity of ≥92% in the 400-3000 nm band; the moisture-proof layer is made of a zinc-based zeolite imidazolate skeleton material with a thickness of 50-200 nm, a porosity of 5%-10%, and a pore size of ≤0.34 nm. The preparation method of the heat-insulating and moisture-proof thermoelectric device comprises the following steps: S1: moisture-proof treatment of the electric couple arm; S2: cellulose aerogel filling; S3: heat-reflecting film encapsulation; and S4: conductive adhesive layer coating. The present invention realizes a low-resistance, high-strength, moisture-proof connection between the electric couple arm and the electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric materials, in particular to a heat-insulating and moisture-proof thermoelectric device and a preparation method thereof. Background Art

[0002] Thermoelectric conversion technology utilizes the Seebeck effect to directly convert thermal energy into electrical energy. It is widely used in industrial waste heat recovery and heat dissipation and power generation in electronic devices. In recent years, Bi2Te3-based materials have become a core material for low-temperature thermoelectric modules due to their excellent thermoelectric performance (ZT values up to 1.8) from room temperature to 150°C. However, these materials face two major challenges in practical application: interfacial failure in humid environments and reduced efficiency due to heat loss. These issues severely limit the long-term stability and energy conversion efficiency of Bi2Te3-based thermoelectric devices.

[0003] To prevent device failure in humid environments, traditional methods typically use polymers such as silicone or epoxy resin as sealing materials. However, these materials have large molecular pore sizes and are unable to effectively block water molecules with a diameter of approximately 0.3 nanometers. This can lead to surface oxidation and electrode corrosion on the electric dipole arms, resulting in increased contact resistance and interfacial cracking. Although some studies have attempted to enhance moisture resistance using metal barrier layers (such as nickel-based alloys), these methods are difficult to achieve molecular-level water vapor barrier due to their high thickness. Furthermore, the large difference in thermal expansion coefficient between the metal barrier layer and the Bi2Te3 material can easily lead to thermal stress concentration, further reducing device life.

[0004] While some research has been conducted on the application of metal-organic frameworks (MOFs) in moisture-proofing, this research has largely focused on surface treatment and coating applications for moisture-proofing materials, and has yet to address the protection of thermoelectric materials. An analysis of MOFs' applications and limitations in various fields is provided. First, in the field of lithium battery separators, MOFs such as ZIF-8 are used to coat separator surfaces to prevent the ingress of trace amounts of water from the electrolyte. However, the use of ZIF-8 particles results in an uneven pore size distribution, preventing ideal molecular-level sealing. Furthermore, coating thicknesses exceeding 5 microns increase interfacial contact resistance by 15%. Furthermore, the significant difference in thermal expansion coefficients between ZIF-8 and electrode materials presents a technical obstacle. In the field of electronic packaging, while blends of MOFs and epoxy resins can effectively protect PCBs, the addition of MOFs exceeding 30% significantly increases thermal conductivity. Furthermore, incomplete MOF coverage on irregular surfaces results in extremely poor adhesion of the moisture-proof layer. Finally, in the field of gas separation, although ZIF-8 membranes can efficiently separate CO2 and H2O, they need to operate in a high-temperature environment, which is inconsistent with the operating temperature of thermoelectric materials.

[0005] In terms of thermal insulation design, traditional materials such as glass fiber and foam plastics generally have high room temperature thermal conductivity, which makes it difficult to meet the demand for efficient utilization of low-grade thermal energy. In recent years, aerogels have attracted widespread attention due to their high porosity and low thermal conductivity. However, conventional silica aerogels have problems such as low mechanical strength and increased thermal conductivity after moisture absorption. Although some studies have proposed the use of aluminum silicate long fiber reinforced composite modified aerogels, they still rely on surface coatings to achieve hydrophobicity. The coating is prone to fall off during long-term use, resulting in the failure of moisture-proof performance. In addition, these aerogels do not solve the problem of coordinated optimization of carrier transport and thermal insulation performance in material selection. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a heat-insulating and moisture-proof thermoelectric device and a preparation method thereof, which solves the moisture-proof, heat-insulating and reliability problems of Bi2Te3-based devices.

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

[0008] Provided is a heat-insulating, moisture-proof thermoelectric device, comprising p-type Bi2Te3 electric couple arms and n-type Bi2Te3 electric couple arms having a moisture-proof layer grown on their surfaces and connected to electrodes; a cellulose-based aerogel layer filling the gap between adjacent p-type Bi2Te3 electric couple arms and n-type Bi2Te3 electric couple arms; the cellulose-based aerogel layer having a porosity of 96%-99.5% and a surface contact angle of 150° or greater; a heat-reflecting film covering the non-heat-conducting surfaces of the p-type Bi2Te3 electric couple arms and n-type Bi2Te3 electric couple arms, the heat-reflecting film having a reflectivity of 92% or greater in the 400-3000 nm wavelength band; the moisture-proof layer being made of a zinc-based zeolite imidazolate framework material, having a thickness of 50-200 nm, a porosity of 5%-10%, and a pore size of 0.34 nm or less.

[0009] Furthermore, the cellulose-based aerogel layer is a hydrophobically modified nanocellulose aerogel, which is modified by hexadecyltrimethoxysilane grafting, with a modifier loading of 3-8 wt%, and Bi2Te3 quantum dots are uniformly dispersed in the hydrophobically modified nanocellulose aerogel, with a quantum dot particle size of 2-5 nm and a doping amount of 0.5-1.5 wt%.

[0010] Furthermore, the fibers of the hydrophobically modified nanocellulose aerogel are vertically oriented, with an orientation degree of ≥85%, a fiber diameter of 5-20 nm, and an aspect ratio of 100:1 to 500:1.

[0011] Furthermore, the moisture-proof layer is doped with ZnO nanoparticles, with a doping amount of 2-5 wt%, and the ZnO particles have a size of 10-30 nm and are evenly distributed on the inner wall of the pores of the moisture-proof layer.

[0012] Furthermore, the heat reflective film is a three-layer composite structure of TiO2 / Ag / TiO2, and the thickness of each layer is:

[0013] Inner layer TiO2: 30-50 nm,

[0014] Ag layer: 80-120 nm,

[0015] Outer layer TiO2: 30-50 nm.

[0016] Furthermore, the connection between the p-type Bi2Te3 electric dipole arm and the n-type Bi2Te3 electric dipole arm and the electrode is covered with a conductive adhesive layer, and the conductive adhesive layer is a composite material of Bi2Te3 nanosheets dispersed in an epoxy resin matrix, the thickness of the Bi2Te3 nanosheets is 10-50 nm, and the volume fraction of the Bi2Te3 nanosheets in the composite material is 40-60 vol%.

[0017] A method for preparing the above-mentioned heat-insulating and moisture-proof thermoelectric device is also provided, comprising the following steps:

[0018] S1: Moisture-proof treatment of the electric dipole arms: A moisture-proof layer is grown on the surface of the p-type Bi2Te3 electric dipole arms and the n-type Bi2Te3 electric dipole arms by liquid phase epitaxy. The concentration of 2-methylimidazole in the reaction solution is 0.1-0.3 mol / L, the concentration of zinc nitrate is 0.05-0.15 mol / L, the reaction temperature is 25-40°C, and the reaction time is 2-4 hours. The moisture-proof layer is in-situ doped with ZnO. The p-type Bi2Te3 electric dipole arms and the n-type Bi2Te3 electric dipole arms are immersed in a zinc acetate ethanol solution with a concentration of 0.1-0.5 wt%, and heat treated at 80°C for 1-2 hours.

[0019] S2: Cellulose aerogel filling: Nanocellulose is dispersed in a 1:2 molar ratio of choline chloride and urea eutectic solvent at a concentration of 5-10 wt%. Bi2Te3 quantum dots are added and then extruded through a microfluidic chip with a channel width of 200-500 μm at an electric field strength of 50-100 V / cm. The aerogel is then formed by programmed freeze-drying combined with supercritical CO2 drying, with a freezing gradient of -40°C → -20°C → 0°C, and supercritical conditions of 45°C and 10 MPa.

[0020] S3: Heat reflective film packaging: ALD atomic layer deposition method is used to sequentially deposit TiO2 / Ag / TiO2 composite films. The TiO2 deposition temperature is 120-150°C, the Ag deposition temperature is 80-100°C, the TiO2 deposition cycle is 100-150 times, and the Ag deposition cycle is 50-80 times.

[0021] S4: Conductive adhesive layer coating: Bi2Te3 nanosheets and epoxy resin are mixed in proportion. The volume fraction of Bi2Te3 nanosheets in the composite material formed by the mixture of Bi2Te3 nanosheets and epoxy resin is 40-60 vol%. The mixed material is dispersed by triple-roll grinding and then screen-printed on the electrode connection. The curing conditions are first curing at 120°C for 30 minutes and then curing at 150°C for 15 minutes to obtain a thermoelectric device.

[0022] Furthermore, in step S1, after the moisture-proof layer is in-situ doped with ZnO, the moisture-proof porosity is reduced to 3%-8%.

[0023] Furthermore, in step S2, the choline chloride and urea deep eutectic solvent is recycled, comprising the following steps: after supercritical CO2 drying is completed, the choline chloride and urea deep eutectic solvent remaining in the aerogel forming process are collected, 0.1-0.3 wt% TiO2 nanoparticles are added as a photocatalyst, and ultraviolet light is used with a wavelength of 365 nm and an intensity of 50 mW / cm 2 , degrading the cellulose fragments remaining in the choline chloride and urea deep eutectic solvent, the illumination time is 30-60 minutes; and after filtering through a 0.22 μm filter membrane, it is reused in step S2.

[0024] Furthermore, in step S3, titanium tetraisopropoxide and water are used as precursors when depositing the TiO2 layer by ALD, the pulse time of titanium tetraisopropoxide is 0.1-0.3 s, the pulse time of water is 0.05-0.1 s, and the purge time is 5-10 s.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The zinc-based zeolite imidazolate framework material (ZIF-8) moisture-proof layer of the present invention achieves molecular-level water vapor barrier by precisely controlling the pore size and doping with ZnO. Compared with traditional sealing materials, the moisture-proof ability is improved by more than 10 times, and the oxidation of Bi2Te3 electric dipole arms and electrode corrosion are significantly inhibited, extending the device life to more than 5000 hours.

[0027] (2) The hydrophobically modified nanocellulose aerogel of the present invention combines oriented fiber structure with quantum dot doping, which increases the compressive strength to 12 MPa while maintaining ultra-low thermal conductivity, thus solving the problem of aerogel being "brittle and easy to absorb moisture" and making it suitable for complex environments such as vibration and humidity.

[0028] (3) The heat reflective film of the present invention realizes the 400-3000 nm band through the TiO2 / Ag / TiO2 three-layer film structure, with a reflectivity of ≥92%, reducing thermal radiation loss by more than 30%. Combined with the aerogel layer, it reduces the overall heat loss of the device by 40%, significantly improving the low-grade thermal energy conversion efficiency.

[0029] (4) The low eutectic solvent recycling technology of the present invention is combined with photocatalytic degradation to avoid the pollution of traditional organic solvents; microfluidics and ALD technology realize precise control of nanoscale structure, promoting the development of thermoelectric device preparation towards refinement and greenness. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic structural diagram of a heat-insulating and moisture-proof thermoelectric device according to the present invention.

[0031] FIG2 is a flow chart of the preparation process of the heat-insulating and moisture-proof thermoelectric device of the present invention.

[0032] The components in the above drawings are numbered as follows:

[0033] 1. p-type Bi2Te3 electric couple arm; 2. n-type Bi2Te3 electric couple arm; 3. cellulose-based aerogel layer; 4. heat-reflective film; 5. electrode; 6. conductive adhesive layer; 7. moisture-proof layer. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to the following examples. The embodiments of the present invention include but are not limited to the following examples.

[0035] Example 1

[0036] like Figure 1 As shown, a heat-insulating, moisture-proof thermoelectric device is provided, comprising a p-type Bi2Te3 electric couple arm 1 and an n-type Bi2Te3 electric couple arm 2, each connected to an electrode 5 and having a moisture-proof layer 7 grown on its surface. The moisture-proof layer 7 is made of a zinc-based zeolite imidazolate framework material with a thickness of 100 nm, a porosity of 8%, and a pore size of 0.32 nm. The moisture-proof layer 7 is doped with ZnO nanoparticles at a doping level of 3 wt%. The ZnO particles are 20 nm in size and are uniformly distributed along the inner wall of the pores of the moisture-proof layer 7. The electric couple arms are made of commercial Bi2Te3-based thermoelectric material. The p-type Bi2Te3 electric couple arm 1 is doped with Sb, and the n-type Bi2Te3 electric couple arm 2 is doped with Se. Both Bi2Te3 electric couple arms are cut into 5 mm × 5 mm × 20 mm rectangular blocks.

[0037] A cellulose-based aerogel layer 3, filling the gap between adjacent p-type Bi2Te3 electric dipole arms 1 and n-type Bi2Te3 electric dipole arms 2, is a hydrophobically modified nanocellulose aerogel grafted with hexadecyltrimethoxysilane (5 wt %). Bi2Te3 quantum dots (3 nm in diameter and 1 wt % doping) are uniformly dispersed within the hydrophobically modified nanocellulose aerogel. The fibers are vertically oriented with an orientation of 88%, a fiber diameter of 10 nm, and an aspect ratio of 300:1. The cellulose-based aerogel layer 3 has a porosity of 98% and a surface contact angle of ≥150°.

[0038] A heat-reflecting film 4 covers the non-heat-conducting surfaces of the p-type Bi2Te3 thermocouple arm 1 and the n-type Bi2Te3 thermocouple arm 2. The film has a reflectivity of 93% in the 400-3000 nm wavelength range. The film 4 comprises a three-layer TiO2 / Ag / TiO2 composite structure, with thicknesses of 40 nm for the inner TiO2 layer, 100 nm for the Ag layer, and 40 nm for the outer TiO2 layer. Specifically, the film 4 is applied to the axial side surfaces of the p-type Bi2Te3 thermocouple arm 1 and the n-type Bi2Te3 thermocouple arm 2, i.e., along the length of the thermocouple arm, maintaining a 1 mm uncoated area on the upper and lower end surfaces to ensure unobstructed heat flow. A TiO2 / Ag / TiO2 composite film is deposited on the axial side surfaces by magnetron sputtering, forming a radiation shielding structure that surrounds the thermocouple arm but does not cover the heat-conducting end surfaces.

[0039] The connection between the p-type Bi2Te3 electric couple arm 1 and the n-type Bi2Te3 electric couple arm 2 and the electrode 5 is covered with a conductive adhesive layer 6. The conductive adhesive layer 6 is a composite material of Bi2Te3 nanosheets dispersed in an epoxy resin matrix. The thickness of the Bi2Te3 nanosheets is 20 nm, and the volume fraction of the Bi2Te3 nanosheets in the composite material is 50 vol%.

[0040] A method for preparing the above-mentioned heat-insulating and moisture-proof thermoelectric device is also provided, and the process flow chart is as follows: Figure 2 As shown, the preparation method comprises the following steps:

[0041] S1: Moisture-proof treatment of the dipole arms: First, the p-type Bi2Te3 dipole arm 1 and the n-type Bi2Te3 dipole arm 2 (5mm×5mm×20mm) were ultrasonically cleaned with acetone and ethanol for 15 minutes each, and then dried with nitrogen. Then, a moisture-proof layer 7 was grown on the surface of the p-type Bi2Te3 dipole arm 1 and the n-type Bi2Te3 dipole arm 2 by liquid phase epitaxy. Specifically, 0.2 mol / L 2-methylimidazole solution and 0.1 mol / L zinc nitrate solution were prepared, mixed, and added to a reactor. The mixture was stirred at a constant temperature of 25°C for 2 hours to obtain a reaction solution. The p-type Bi2Te3 dipole arm 1 and the n-type Bi2Te3 dipole arm 2 were then immersed in the reaction solution, and a ZIF-8 layer was grown on the surface by liquid phase epitaxy.

[0042] Then, the moisture-proof layer 7 was in-situ doped with ZnO. A 0.3 wt% zinc acetate ethanol solution was prepared, and the p-type Bi2Te3 electric couple arm 1 and the n-type Bi2Te3 electric couple arm 2 were immersed in the solution and then heat-treated at 80°C for 1.5 hours. ZnO nanoparticles were in-situ deposited on the inner wall of the ZIF-8 channel. After the moisture-proof layer 7 was in-situ doped with ZnO, the moisture-proof porosity was reduced to 4%.

[0043] S2: Cellulose aerogel filling: 8 wt% nanocellulose was dispersed in a low eutectic solvent of choline chloride and urea with a molar ratio of 1:2, and 1 wt% Bi2Te3 quantum dots were added. The aerogel was extruded through a microfluidic chip with a channel width of 300 μm and an electric field strength of 80 V / cm to achieve vertical fiber alignment. The aerogel was freeze-dried by a program with a freezing gradient of -40℃→-20℃→0℃. The freeze-drying procedure was -40℃ for 2 hours → -20℃ for 1 hour → 0℃ for 1 hour. The aerogel was then transferred to a supercritical CO2 drying equipment with supercritical conditions of temperature 45℃ and pressure 10 MPa for 4 hours.

[0044] S3: Thermal reflective film 4 packaging: Atomic layer deposition equipment is used to sequentially deposit TiO2 / Ag / TiO2 composite films using the ALD atomic layer deposition method. The TiO2 deposition temperature is 130°C, the Ag deposition temperature is 85°C, the number of cycles for depositing TiO2 is 120 times, and the number of cycles for depositing Ag is 60 times. When the ALD TiO2 layer is deposited, titanium tetraisopropoxide (TTIP) and water are used as precursors. The pulse time of titanium tetraisopropoxide is 0.2 s, the pulse time of water is 0.1 s, and the purge time is 10 s.

[0045] S4: Coating of conductive adhesive layer 6: Bi2Te3 nanosheets and epoxy resin E44 were mixed at a ratio of 50 vol%, the mixed material was dispersed by three-roll milling, and then screen-printed on the connection of electrode 5. The speed of the three-roll mill was 500 rpm, and the milling cycle was repeated 3 times. The curing conditions were first 120°C for 30 minutes and then 150°C for 15 minutes to form a conductive layer with a thickness of 100 μm, and finally a thermoelectric device was obtained.

[0046] Example 2

[0047] Different from Example 1, the moisture-proof layer 7 of the thermoelectric device of this embodiment has a thickness of 50 nm.

[0048] Example 3

[0049] Different from Example 1, the moisture-proof layer 7 of the thermoelectric device in this embodiment has a thickness of 200 nm.

[0050] Example 4

[0051] Different from Example 1, the porosity of the cellulose-based aerogel layer 3 of the thermoelectric device of this embodiment is 96%.

[0052] Example 5

[0053] Different from Example 1, the porosity of the cellulose-based aerogel layer 3 of the thermoelectric device of this embodiment is 99.5%.

[0054] Example 6

[0055] Different from Example 1, the thickness of each layer of the heat reflective film 4 of this embodiment is: inner layer TiO2: 30 nm, Ag layer: 80 nm, outer layer TiO2: 30 nm.

[0056] Example 7

[0057] Different from Example 1, the thickness of each layer of the heat reflective film 4 of this embodiment is: inner layer TiO2: 50 nm, Ag layer: 120 nm, outer layer TiO2: 50 nm.

[0058] Comparative Example 1

[0059] Unlike Example 1, in step S1 of this comparative example, a reaction solution was prepared: 2-methylimidazole (0.2 mol / L) and zinc nitrate (0.1 mol / L) were mixed in a 1:1 volume ratio and stirred at 25°C for 2 hours. The p-type Bi2Te3 coupler arm 1 and the n-type Bi2Te3 coupler arm 2 were immersed in the reaction solution and allowed to stand at 25°C for 4 hours. A pure ZIF-8 layer with a thickness of 100 nm was grown on the surface. Finally, the layers were rinsed three times with deionized water and vacuum-dried at 60°C for 2 hours to obtain a thermoelectric device with an unmodified ZIF-8 moisture barrier.

[0060] Comparative Example 2

[0061] Unlike Example 1, this comparative example employed silica gel coating. Dow Corning DC 1-2577 silica gel, with a viscosity of 5000 mPa·s and a solids content of 98%, was used. The silica gel was diluted to a solids content of 50% (using ethyl acetate as solvent) and sprayed onto the surfaces of p-type Bi2Te3 coupler arm 1 and n-type Bi2Te3 coupler arm 2, achieving a wet film thickness of 200 μm. After baking at 80°C for 2 hours, a silica gel sealing layer approximately 50 μm thick was formed, resulting in a thermoelectric device using conventional silica gel sealing material.

[0062] Comparative Example 3

[0063] Different from Example 1, this comparative example only deposited a single layer of Ag film using a magnetron sputtering device (background vacuum ≤ 5×10 -4 Pa), an Ar gas flow rate of 20 sccm, and a sputtering power of 150 W. A single layer of Ag film with a thickness of 100 nm was deposited on the axial side of the electric couple arm. Finally, the film was allowed to stand at room temperature under nitrogen for 24 hours to obtain a thermoelectric device using the single layer of Ag film.

[0064] Comparative Example 4

[0065] Different from Example 1, this comparative example only performs the cleaning step of Example 1 (acetone and ethanol ultrasonic cleaning), and the surface of the electric couple arm remains in the original Bi2Te3 material state, thereby obtaining an uncoated electric couple arm.

[0066] Based on the above examples, the following experiments were conducted:

[0067] 1. Water Vapor Transmission Rate Test

[0068] The molecular-level barrier capability of the ZIF-8 / ZnO composite moisture-proof layer to water vapor was verified by a water vapor transmission rate test, taking the samples prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 as examples.

[0069] The water vapor transmission rate (WVTR) of various moisture barrier thicknesses (50 / 100 / 200 nm) at 85% RH was tested using the ASTM E96 standard. The test equipment used was a PERMATRAN-W 3 / 33 water vapor transmission rate tester. The sample size was 20 mm × 20 mm (including the Bi2Te3 dipole arm surface of the moisture barrier layer 7). The test temperature was 25°C, and the humidity gradient was 85% RH (high humidity side) → 50% RH (low humidity side). The steady-state transmission rate was measured over a 24-hour period. The test results are shown in Table 1.

[0070] Table 1 Water vapor transmission rate of different samples

[0071]

[0072] Experimental conclusion: The WVTR of ZIF-8 / ZnO composite moisture barrier is 10-50 times lower than that of traditional silica gel, and reaches the lowest value of 0.005 g / (m 2 day), verifying the molecular-level barrier effect of pores ≤0.34 nm against water vapor. ZnO doping reduced the porosity of the moisture barrier from 8% to 4%, significantly reducing water vapor permeation channels. The WVTR of Example 1 (0.008) was 78% lower than that of Comparative Example 1 (0.035).

[0073] 2. Aerogel thermal conductivity and mechanical properties test

[0074] The ultra-low thermal conductivity and high compressive strength of the hydrophobically modified nanocellulose aerogel were verified by aerogel thermal conductivity and mechanical property tests, taking the samples prepared in Examples 1, 4 and 5 and traditional silica aerogel as examples.

[0075] Thermal conductivity test: The thermal conductivity of aerogels with different porosities (96% / 98% / 99.5%) was tested using a Hot Disk TPS 2500S thermal conductivity meter at a temperature of 25°C and a pressure of 0.1 MPa.

[0076] Mechanical properties test: The vertical compressive strength was tested using an INSTRON 5967 universal testing machine at a compression rate of 1 mm / min. The test results are shown in Table 2:

[0077] Table 2 Thermal conductivity and fiber orientation test data of different samples

[0078]

[0079] Experimental conclusions: The thermal conductivity is lowest at a porosity of 99.5% (0.018 W / m·K), a 44% decrease compared to conventional aerogels (0.032). However, the compressive strength decreases to 9.8 MPa due to the high porosity. The fiber orientation of Example 1, at 88%, achieves a balance between a thermal conductivity of 0.021 W / m·K and a compressive strength of 14.2 MPa at a porosity of 98%. The addition of Bi2Te3 quantum dots (1 wt%) further reduces the thermal conduction path.

[0080] 3. Spectral reflectivity test of thermal reflective film

[0081] The spectral reflectivity test of the thermal reflective film verifies that the reflectivity of the TiO2 / Ag / TiO2 three-layer composite structure in the 400-3000 nm band is ≥92%, taking the samples prepared in Example 1, Example 6, Example 7, Comparative Example 3 and Comparative Example 4 as examples.

[0082] The test equipment used was a UV-Vis-NIR spectrophotometer equipped with a 150 mm integrating sphere to measure the reflectance spectra of different samples. The test range was 400-3000 nm, with an incident angle of 8° and a resolution of 5 nm. The thermal reflective film was removed and tested separately to avoid interference from the substrate. The test results are shown in Table 3:

[0083] Table 3 Spectral reflectivity of heat reflective films of different samples

[0084]

[0085] Experimental Conclusions: The TiO2 / Ag / TiO2 three-layer structure enhances broadband reflection through interference effects. Example 7 (50 / 120 / 50 nm) achieved the highest average reflectivity of 94.1%, a 7.7% improvement over the single-layer Ag film (87.4%). The outer TiO2 layer (50 nm) achieved a reflectivity of 97.3% in the infrared band, validating the technical achievement of "reflectivity ≥ 92%." Thermal imaging revealed that the surface temperature of the coated area was 12°C lower than that of the uncoated area (ΔT = 50K), reducing thermal radiation losses by 35%.

[0086] In summary, the present invention significantly improves the moisture resistance, heat insulation and reliability of thermoelectric devices through material modification and process innovation. All performance indicators are better than those of existing technologies and have industrial application value.

[0087] The above embodiment is only one of the preferred implementation methods of the present invention and should not be used to limit the scope of protection of the present invention. Any changes or modifications that have no substantive meaning made to the main design concept and spirit of the present invention, as long as the technical problems solved are still consistent with the present invention, should be included in the scope of protection of the present invention.

Claims

1. A heat-insulating and moisture-proof thermoelectric device, characterized in that: The invention comprises a p-type Bi2Te3 electric dipole arm (1) and an n-type Bi2Te3 electric dipole arm (2) having a moisture-proof layer (7) grown on the surface and connected to an electrode (5); a cellulose-based aerogel layer (3) filled between the adjacent p-type Bi2Te3 electric dipole arms (1) and n-type Bi2Te3 electric dipole arms (2); the porosity of the cellulose-based aerogel layer (3) is 96%-99.5%, and the surface contact angle is ≥150°; a heat-reflecting film (4) covering the non-heat-conducting surface of the p-type Bi2Te3 electric dipole arm (1) and the n-type Bi2Te3 electric dipole arm (2), wherein the reflectivity of the heat-reflecting film (4) in the 400-3000 nm band is ≥92%; the moisture-proof layer (7) is made of a zinc-based zeolite imidazole ester skeleton material, has a thickness of 50-200 nm, and has a porosity of 5%-10% and a pore size of ≤0.34 nm.

2. The heat-insulating and moisture-proof thermoelectric device according to claim 1, characterized in that: The cellulose-based aerogel layer (3) is a hydrophobically modified nanocellulose aerogel, which is modified by grafting with hexadecyltrimethoxysilane, with a modifier loading of 3-8 wt%, and Bi2Te3 quantum dots are uniformly dispersed in the hydrophobically modified nanocellulose aerogel, with a quantum dot particle size of 2-5 nm and a doping amount of 0.5-1.5 wt%.

3. The heat-insulating and moisture-proof thermoelectric device according to claim 2, characterized in that: The fibers of the hydrophobically modified nanocellulose aerogel are vertically oriented, with an orientation degree of ≥85%, a fiber diameter of 5-20 nm, and an aspect ratio of 100:1 to 500:

1.

4. The heat-insulating and moisture-proof thermoelectric device according to claim 1, wherein: The moisture-proof layer (7) is doped with ZnO nanoparticles, the doping amount is 2-5 wt%, and the ZnO particles have a size of 10-30 nm and are evenly distributed on the inner wall of the pores of the moisture-proof layer (7).

5. The heat-insulating and moisture-proof thermoelectric device according to claim 1, wherein: The heat reflective film (4) is a three-layer composite structure of TiO2 / Ag / TiO2, and the thickness of each layer is: Inner layer TiO2: 30-50 nm, Ag layer: 80-120 nm, Outer layer TiO2: 30-50 nm.

6. The heat-insulating and moisture-proof thermoelectric device according to claim 1, wherein: The connection between the p-type Bi2Te3 electric dipole arm (1) and the n-type Bi2Te3 electric dipole arm (2) and the electrode (5) is covered with a conductive adhesive layer (6), wherein the conductive adhesive layer is a composite material of Bi2Te3 nanosheets dispersed in an epoxy resin matrix, the thickness of the Bi2Te3 nanosheets is 10-50 nm, and the volume fraction of the Bi2Te3 nanosheets in the composite material is 40-60 vol%.

7. A method for preparing the heat-insulating and moisture-proof thermoelectric device according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1: Moisture-proof treatment of the electric dipole arm: grow a moisture-proof layer (7) on the surface of the p-type Bi2Te3 electric dipole arm (1) and the n-type Bi2Te3 electric dipole arm (2) by liquid phase epitaxy, the concentration of 2-methylimidazole in the reaction solution is 0.1-0.3 mol / L, the concentration of zinc nitrate is 0.05-0.15 mol / L, the reaction temperature is 25-40°C, and the reaction time is 2-4 hours; the moisture-proof layer (7) is in-situ doped with ZnO, and the p-type Bi2Te3 electric dipole arm (1) and the n-type Bi2Te3 electric dipole arm (2) are immersed in a zinc acetate ethanol solution with a concentration of 0.1-0.5 wt%, and heat treated at 80°C for 1-2 hours; S2: Cellulose aerogel filling: Nanocellulose is dispersed in a 1:2 molar ratio of choline chloride and urea eutectic solvent at a concentration of 5-10 wt%. Bi2Te3 quantum dots are added and then extruded through a microfluidic chip with a channel width of 200-500 μm at an electric field strength of 50-100 V / cm. The aerogel is then formed by programmed freeze-drying combined with supercritical CO2 drying, with a freezing gradient of -40°C → -20°C → 0°C, and supercritical conditions of 45°C and 10 MPa. S3: Heat reflective film packaging: ALD atomic layer deposition method is used to sequentially deposit TiO2 / Ag / TiO2 composite films. The TiO2 deposition temperature is 120-150°C, the Ag deposition temperature is 80-100°C, the TiO2 deposition cycle is 100-150 times, and the Ag deposition cycle is 50-80 times. S4: Conductive adhesive layer coating: Bi2Te3 nanosheets and epoxy resin are mixed in proportion. The volume fraction of Bi2Te3 nanosheets in the composite material formed by the mixture of Bi2Te3 nanosheets and epoxy resin is 40-60 vol%. The mixed material is dispersed by triple-roll grinding and then screen-printed on the electrode connection. The curing conditions are first curing at 120°C for 30 minutes and then curing at 150°C for 15 minutes to obtain a thermoelectric device.

8. The preparation method according to claim 7, characterized in that: In step S1, after the moisture-proof layer (7) is in-situ doped with ZnO, the moisture-proof porosity is reduced to 3%-8%.

9. The preparation method according to claim 7, characterized in that: In step S2, the choline chloride and urea deep eutectic solvent is recycled, comprising the following steps: after supercritical CO2 drying is completed, the choline chloride and urea deep eutectic solvent remaining in the aerogel forming process are collected, 0.1-0.3 wt% TiO2 nanoparticles are added as a photocatalyst, and ultraviolet light is used with a wavelength of 365 nm and an intensity of 50 mW / cm 2 , degrading the cellulose fragments remaining in the choline chloride and urea deep eutectic solvent, the illumination time is 30-60 minutes; and after filtering through a 0.22 μm filter membrane, it is reused in step S2.

10. The preparation method according to claim 7, characterized in that: In step S3, titanium tetraisopropoxide and water are used as precursors when depositing the TiO2 layer by ALD, the pulse time of titanium tetraisopropoxide is 0.1-0.3 s, the pulse time of water is 0.05-0.1 s, and the purge time is 5-10 s.

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