A method for fabricating a scalable flexible thermoelectric device

Abstract

The application discloses a preparation method of a scalable flexible thermoelectric device. The prepared flexible thermoelectric film and flexible silver film are alternately pasted on a flexible substrate, conductive silver paste is brushed on the connecting part, the films are electrically connected in series, lead wires are drawn out from both ends, a strip-shaped thermoelectric device is obtained, the flexible insulating film is pasted on the front surface of the device, the device is folded along the center line of the silver film, and the scalable flexible thermoelectric device is obtained. The preparation method of the scalable flexible thermoelectric device is simple, high in efficiency, energy-saving and low in cost, the device has a wide application range, is high in production efficiency and low in defective product rate, and can be mass-produced. In addition, the scalable flexible thermoelectric device prepared by the application has excellent output performance and flexibility, is high in scalability, and has a 20% higher output power than a conventional in-plane pi-type device, and can be used for designing integrated wearable electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric conversion technology, and more specifically, relates to a method for preparing a stretchable and flexible thermoelectric device. Background Technology

[0002] In recent years, with the rapid development of wearable electronics and the Internet of Things (IoT), flexible thermoelectric technology, which can generate electricity using temperature differences, has attracted widespread attention. By converting the heat emitted from the surface of a living organism or IoT nodes into electrical energy, flexible thermoelectric devices can provide a long-lasting and reliable power source for small / micro electronic devices. Compared to currently used batteries that require frequent charging and replacement, flexible thermoelectric devices require almost no maintenance or human intervention, thus demonstrating broad application prospects.

[0003] Because the surface of living organisms is a curved heat source, with unstructured curved surfaces at joints and other locations, and because living organisms are generally flexible, flexible thermoelectric devices that are only bendable cannot adhere tightly to the skin surface when the skin is stretched or joints move, easily leading to detachment or damage. For example, Chinese invention patent application CN107046092A, published on August 15, 2017, discloses a method for manufacturing a wearable thermoelectric generator with a hollowed-out substrate. However, because it uses a flexible printed circuit board to fabricate an integrated hot-end electrode, the flexible thermoelectric device cannot be stretched or extended. At the same time, the separately processed cold-end copper conductive sheet requires secondary positioning using 3D printing, which increases the processing difficulty, easily introduces new processing errors, and reduces processing efficiency.

[0004] Employing stretchable and flexible thermoelectric devices can reduce damage from external impacts and vibrations, and improve wearability. Existing technologies, through improvements in structural design or manufacturing methods, can give flexible thermoelectric devices good bending characteristics. For example, Chinese invention patent application CN108649116A, published on October 12, 2018, discloses a stretchable, wearable, spring-shaped inorganic thermoelectric device and its fabrication method. Figure 1 As shown, a spring-shaped stretchable thermoelectric device is fabricated by sequentially coating a polymer substrate and a thermoelectric active material onto a spring template using a template method, followed by peeling. The use of commercially available screws as templates for the polymer substrate in this spring-shaped stretchable structure is not conducive to large-area manufacturing and arraying of the device. Furthermore, because it uses a mixture of polymer viscous liquid and thermoelectric material for coating, the device's output power is only in the nW range.

[0005] Chinese invention patent application CN106206923A, published on December 7, 2016, discloses a flexible wearable thermoelectric power generation device. For example... Figure 2As shown, this flexible wearable thermoelectric generator uses copper foil and flexible wires connecting the copper foils to form a copper foil conductor layer. The copper foil used for welding has the same shape as the surface of the semiconductor particles, and the flexible sinusoidal wires provide stretchability. However, since the copper foil conductor layer needs to be processed separately and then assembled, the processing is difficult and inefficient, which is not conducive to the integration and miniaturization of the device.

[0006] Therefore, there is an urgent need for an efficient and low-cost stretchable flexible thermoelectric device and its manufacturing method, which can solve the problems of large-area manufacturing difficulties, low connection efficiency of various devices, and high defect rate in the current process of stretchable flexible thermoelectric device manufacturing, and improve device reliability and output power density. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a stretchable and flexible thermoelectric device. This method achieves a simple, mild, efficient, and energy-saving preparation process with high productivity, low defect rate, and the ability to mass-produce. Furthermore, the prepared stretchable and flexible thermoelectric device has excellent output performance and flexibility, making it suitable for designing integrated wearable electronic devices.

[0008] To achieve the above-mentioned objective, the present invention provides a method for fabricating a stretchable flexible thermoelectric device, characterized by comprising the following steps:

[0009] (1) Preparation of flexible thermoelectric thin films and flexible silver thin films;

[0010] (2) Cut the flexible thermoelectric film and flexible silver film into long strips and alternately paste them onto the strip-shaped flexible substrate along the length direction;

[0011] (3) Apply conductive silver paste to the connection between the flexible thermoelectric film and the flexible silver film and dry it to make the films connected in series. Lead wires out from both ends of the connected films to obtain a strip thermoelectric device.

[0012] (4) A flexible insulating film is pasted onto the front of the strip thermoelectric device. After cold pressing or hot pressing, the strip thermoelectric device is folded along the center line of the flexible silver film to obtain a stretchable flexible thermoelectric device.

[0013] The objective of this invention is achieved as follows:

[0014] The method for fabricating the stretchable flexible thermoelectric device of this invention involves alternately bonding a prepared flexible thermoelectric thin film and a flexible silver thin film onto a flexible substrate, brushing conductive silver paste onto the connection points to create an electrical series connection between the films, and leading wires from both ends to obtain a strip-shaped thermoelectric device. A flexible insulating film is then bonded to the front of the device, and the device is folded along the center line of the silver thin film to obtain the stretchable flexible thermoelectric device. The fabrication method of the stretchable flexible thermoelectric device of this invention is simple, low-temperature, highly efficient, energy-saving, and low-cost. The device has a wide range of applications due to its stretchability, high production efficiency, low defect rate, and can be mass-produced. Furthermore, the stretchable flexible thermoelectric device prepared by this invention has excellent output performance and flexibility, strong stretchability, and an output power 20% higher than that of traditional in-planar π-type devices, making it suitable for designing integrated wearable electronic devices. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the existing technology for fabricating stretchable wearable spring-shaped inorganic thermoelectric devices;

[0016] Figure 2 This is an exploded view of the overall structure of an existing flexible wearable thermoelectric power generation device;

[0017] Figure 3 This is a flowchart of a specific embodiment of the method for preparing the stretchable flexible thermoelectric device of the present invention;

[0018] Figure 4 This is a schematic diagram of the structure of a stretchable flexible thermoelectric device prepared according to an embodiment of the present invention;

[0019] Figure 5 Example 1 shows the output voltage (a) and flexibility test results (b) of the stretchable thermoelectric device prepared from Bi2Te3 / PEDOT / CNT flexible thermoelectric film; Example 2 shows the output voltage (c) and flexibility test results (d) of the stretchable flexible thermoelectric device prepared from Ag2Se / PEDOT / graphene flexible thermoelectric film; Example 3 shows the output voltage (e) and flexibility test results (f) of the stretchable flexible thermoelectric device prepared from Ag2S / PEDOT / Mxene flexible thermoelectric film. Detailed Implementation

[0020] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0021] Figure 3 This is a flowchart of a specific embodiment of the fabrication method of the stretchable flexible thermoelectric device of the present invention.

[0022] In this embodiment, as Figure 3 As shown, the method for fabricating the stretchable flexible thermoelectric device of the present invention includes the following steps:

[0023] Step S1: Fabrication of flexible thermoelectric thin film and flexible silver thin film

[0024] In this embodiment, the flexible thermoelectric thin film is a nanocomposite material comprising chalcogenides (such as bismuth telluride Bi2Te3, bismuth selenide Bi2Se3, silver selenide Ag2Se, silver sulfide Ag2S, etc.), conductive polymers (such as polyethylene dioxythiophene PEDOT, polypyrrole PPy, etc.) and carbon materials (carbon nanotubes CNT, graphene rGO, and Mxene). The molar mass ratio of chalcogenides to conductive polymers is controlled at 1:2-10:1, and the molar mass ratio of chalcogenides to carbon materials is controlled at 1:3-8:1.

[0025] In this embodiment, the method for preparing the flexible thermoelectric thin film is as follows:

[0026] (1) The nanostructures of chalcogenides were synthesized by hydrothermal method, wherein the temperature range of the hydrothermal synthesis method was 100℃-1000℃ and the synthesis time was 20-600min;

[0027] (2) In a solution containing chalcogenide nanostructures, 3,4-ethylenedioxythiophene (PEDOT) or pyrrole (Py) monomers are polymerized in situ under the action of a strong oxidant; the polymerization reaction time is 5-600 min and the polymerization reaction temperature is -10℃-150℃.

[0028] (3) The product of the polymerization reaction is washed by alternating centrifugation with deionized water and anhydrous ethanol, and the product is redispersed in anhydrous ethanol. The centrifugation conditions are 2000-15000 rpm, 2-50 min, and 1-20 times.

[0029] (4) The carbon material powder is fully dispersed in anhydrous ethanol and mixed with the mixed solution in step (3) by heating and stirring. The stirring temperature is 25-200℃, the stirring speed is 50-500rpm, and the stirring time is 20-600min.

[0030] (5) The solution after heating and stirring in step (3) is vacuum filtered onto a porous filter membrane. After drying, the membrane is first post-treated by cold pressing technology. The cold pressing conditions are: pressure of 1 to 150 MPa and time of 5 to 60 min. Then, the membrane is post-treated by high temperature and high pressure technology. The high temperature and high pressure conditions are: pressure of 1 to 150 MPa, temperature of 50 to 300 °C and time of 5 to 600 min.

[0031] In this embodiment, the prepared flexible thermoelectric film has high density and excellent thermoelectric properties and flexibility. The flexible thermoelectric device can be bent and stretched at will and has high output performance. It can use the temperature difference between human skin and the external environment to power wearable electronic devices and provide a long-lasting and reliable power source for flexible electronic devices.

[0032] In this embodiment, the method for preparing the flexible silver film is as follows: silver nanowires are synthesized by wet chemical method, then the silver nanowires are vacuum filtered onto a porous filter membrane, and finally the film is post-treated by cold pressing. The cold pressing conditions are: pressure of 1 to 150 MPa and time of 5 to 600 min.

[0033] Step S2: Flexible thermoelectric film and flexible silver film are alternately bonded onto a strip-shaped flexible substrate.

[0034] Flexible thermoelectric films and flexible silver films are cut into strips and alternately pasted onto a strip-shaped flexible substrate along the length direction.

[0035] In this embodiment, the flexible thermoelectric film and silver film are cut to the following dimensions: length 0.5-5cm, width 0.1-5cm; the number of films pasted is not less than 4 pairs; the flexible substrate includes, but is not limited to, polyimide film, nylon film, copy paper, etc.

[0036] Step S3: Connect the thin films in series and lead wires out from both ends to obtain a strip-shaped thermoelectric device.

[0037] Conductive silver paste is brushed onto the junction of the flexible thermoelectric film and the flexible silver film and dried, thus connecting the films in series. Wires are then led out from both ends of the series-connected films to obtain a strip-shaped thermoelectric device. In this embodiment, the drying temperature of the conductive silver paste is 50–100°C.

[0038] Step S4: After attaching the flexible insulating film, cold-press or hot-press it, fold it along the center line of the flexible silver film to obtain a stretchable flexible thermoelectric device.

[0039] A flexible insulating film is adhered to the front of a strip-shaped thermoelectric device. After cold or hot pressing, the strip-shaped thermoelectric device is folded in half along the center line of the flexible silver film to obtain a stretchable flexible thermoelectric device.

[0040] In this embodiment, the flexible insulating film includes, but is not limited to, polyimide film, nylon film, and copy paper. The cold pressing and hot pressing conditions are the same as in step S1 (5).

[0041] This invention employs low-temperature, short-time heat treatment, a simple and mild process that is highly efficient and energy-saving, with a high productivity (device yield reaching 99.5%), enabling mass production. The flexible thermoelectric devices prepared using this method exhibit excellent output performance and flexibility, making them suitable for high-performance thermoelectric power generation, electric cooling, and thermoelectric sensors in various wearable electronic devices. Furthermore, wearable electronic products using the stretchable flexible thermoelectric device prepared by this invention can convert the heat emitted by the human body into electrical energy, thereby saving energy and being environmentally friendly.

[0042] Example 1

[0043] Step 1: Bismuth telluride Bi2Te3 nanostructures were synthesized by hydrothermal method (reaction temperature 500℃, 600 min). Then, PEDOT monomers were polymerized in situ in Bi2Te3 nanostructure solution under the action of strong oxidant concentrated sulfuric acid (reaction temperature: 150℃, time: 10 min), with a Bi2Te3:PEDOT molar ratio of 10:1.

[0044] Step 2: The polymerization product was washed 20 times alternately by centrifugation with deionized water and anhydrous ethanol at 15000 rpm for 2 min. The resulting product was then redispersed in anhydrous ethanol. Carbon nanotube (CNT) powder was thoroughly dispersed in the above solution and stirred at 500 rpm for 600 min at room temperature. The molar ratio of Bi2Te3 to CNT was 8:1.

[0045] Step 3: Vacuum filter the heated and stirred Bi2Te3 / PEDOT / CNT solution onto a nylon porous filter membrane. The membrane is then post-treated using a cold pressing method under the following conditions: pressure 50 MPa, time 10 min. Next, the membrane undergoes a high-temperature and high-pressure post-treatment under the following conditions: pressure 15 MPa, temperature 200 °C, time 20 min.

[0046] Step 4: Preparation of flexible silver film. Silver nanowires were synthesized by wet chemical method, and then the silver nanowires were vacuum filtered onto a nylon porous filter membrane. Finally, the film was post-treated by cold pressing. The cold pressing conditions were: pressure of 50 MPa and time of 5 min.

[0047] Step 5: Cut the flexible bismuth telluride thermoelectric film into 12 strips with a length of 5cm and a width of 0.5cm, and cut the silver film into 13 strips with a length of 2cm and a width of 0.5cm; then, alternately attach the strip films along their length to the strip-shaped flexible polyimide substrate.

[0048] Step 6: Apply conductive silver paste to the film joints and dry at 100°C to create an electrical series connection between the films. Lead wires out from both ends to obtain a strip-shaped thermoelectric device. Figure 4 The device is shown in a stretched state.

[0049] Step 7: Attach a flexible insulating film to the front of the strip-shaped thermoelectric device, cold press (1 MPa, 60 min), then fold the strip-shaped thermoelectric device along the center line of the flexible silver film to obtain a stretchable flexible thermoelectric device, such as... Figure 4 As shown, this includes the intermediate state and the device shrinkage state.

[0050] In this example, such as Figure 5 As shown in (a) and (b), when the temperature difference between the two ends of the stretchable thermoelectric device prepared by Bi2Te3 / PEDOT / CNT flexible thermoelectric film reaches 50K, the output voltage reaches 52mV. After the device is stretched 20,000 times, the resistance only increases by 3.5%, indicating that the stretchable flexible thermoelectric device prepared by the present invention has excellent output performance and flexibility.

[0051] Example 2

[0052] Step 1: Silver selenide (Ag2Se) nanostructures were synthesized by hydrothermal method (reaction temperature 100℃, 200 min). PEDOT monomers were polymerized in situ under the action of strong oxidant FeCl3 (reaction temperature: -10℃, time 600 min), with an Ag2Se:PEDOT molar ratio of 1:2.

[0053] Step 2: The polymerization product was washed 40 times alternately by centrifugation with deionized water and anhydrous ethanol at 2000 rpm for 50 min. The resulting product was then redispersed in anhydrous ethanol. Graphene powder was then fully dispersed in the above solution and stirred at 200°C at 50 rpm for 10 min. The molar ratio of Ag₂Se to graphene was 1:3.

[0054] Step 3: The heated and stirred Ag2Se / PEDOT / graphene product was vacuum filtered onto a nylon porous filter membrane. The membrane was then post-treated using a cold pressing method under the following conditions: pressure 150 MPa, time 5 min. Next, the membrane underwent a high-temperature and high-pressure post-treatment under the following conditions: pressure 150 MPa, temperature 50 °C, time 600 min.

[0055] The product polymer PEDOT was vacuum filtered onto a nylon porous filter membrane, and the membrane was post-treated by cold pressing. The cold pressing conditions were: pressure 50 MPa and time 10 min.

[0056] Step 4: Preparation of flexible silver film. Silver nanowires were synthesized by wet chemical method, and then the silver nanowires were vacuum filtered onto a polyimide porous filter membrane. Finally, the film was post-treated by cold pressing. The cold pressing conditions were: pressure of 150 MPa and time of 60 min.

[0057] Step 5: Cut the flexible PEDOT thermoelectric film and silver film into 20 strips, each 0.5cm long and 0.1cm wide. Then, alternately paste the strips of film along their length onto the strip of flexible copy paper.

[0058] Step 6: Apply conductive silver paste to the film joints and dry at 100°C to connect the films in series. Lead wires out from both ends to obtain a strip-shaped thermoelectric device.

[0059] Step 7: Attach a flexible insulating film to the front of the strip-shaped thermoelectric device, and after cold pressing (pressure 1MPa, time 60min), fold the strip-shaped thermoelectric device along the center line of the flexible silver film to obtain a stretchable flexible thermoelectric device.

[0060] In this example, such as Figure 5 As shown in (c) and (d), when the temperature difference between the two ends of the stretchable flexible thermoelectric device prepared by Ag2Se / PEDOT / graphene flexible thermoelectric film reaches 50K, the output voltage is 11.2mV. After the device is stretched 20,000 times, the resistance only increases by 2.7%.

[0061] Example 3

[0062] Step 1: Silver selenide (Ag2S) nanostructures were synthesized by hydrothermal method (reaction temperature 1000℃, 600 min). Py monomers were polymerized in situ under the action of strong oxidant FeCl3 (reaction temperature: 10℃, time: 300 min). The molar ratio of Ag2S to polypyrrole (PPy) was 5:1.

[0063] Step 2: The polymerization product was washed 10 times alternately by centrifugation with deionized water and anhydrous ethanol at 5000 rpm for 30 min. The resulting product was then redispersed in anhydrous ethanol. Mxene powder was then thoroughly dispersed in the above solution and stirred at 50°C at 200 rpm for 30 min. The Ag₂S:Mxene molar ratio was 1:3.

[0064] Step 3: Vacuum filter the heated and stirred Ag2S / PPy / Mxene mixture onto a nylon porous filter membrane. The membrane is then post-treated using a cold pressing method under the following conditions: pressure 20 MPa, time 50 min. Next, the membrane undergoes a high-temperature and high-pressure post-treatment under the following conditions: pressure 150 MPa, temperature 50 °C, time 600 min.

[0065] Carbon nanotube powder was dispersed in an ethanol solution, and carbon nanotubes were deposited on a porous filter membrane by vacuum filtration. Finally, the membrane was post-treated using high temperature and high pressure technology. The high temperature and high pressure conditions were: pressure of 50 MPa, temperature of 200 °C, and time of 300 min.

[0066] Step 2: Preparation of flexible silver film. Silver nanowires were synthesized by wet chemical method, and then the silver nanowires were vacuum filtered onto a polyimide porous filter membrane. Finally, the film was post-treated by cold pressing. The cold pressing conditions were: pressure of 20 MPa and time of 10 min.

[0067] Step 3: Cut the flexible carbon nanotube thermoelectric film and silver film into 50 strips, each 5cm long and 0.5cm wide. Then, alternately paste the strips along their length onto the strip-shaped flexible copy paper.

[0068] Step 4: Apply conductive silver paste to the film joints and dry at 80°C to connect the films in series. Lead wires out from both ends to obtain a strip-shaped thermoelectric device.

[0069] Step 5: Attach a flexible insulating film to the front of the device, cold press (pressure 10MPa, time 30min), then fold the device along the center line of the silver film to obtain a flexible telescopic thermoelectric device.

[0070] In this example, such as Figure 5 As shown in (e) and (f), when the temperature difference between the two ends of the stretchable flexible thermoelectric device prepared by the Ag2S / PEDOT / Mxene flexible thermoelectric film reaches 260K, the output voltage is 11.2mV. After the device is stretched and retracted 20,000 times, the resistance only increases by 2.8%. This indicates that the stretchable flexible thermoelectric device prepared by the present invention has excellent output performance and flexibility.

[0071] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A method for fabricating a stretchable flexible thermoelectric device, characterized in that, Includes the following steps: (1) Preparation of flexible thermoelectric thin films and flexible silver thin films; (2) Cut the flexible thermoelectric film and flexible silver film into long strips and alternately paste them onto the strip-shaped flexible substrate along the length direction; (3) Apply conductive silver paste to the connection between the flexible thermoelectric film and the flexible silver film and dry it to make the films connected in series. Lead wires out from both ends of the connected films to obtain a strip thermoelectric device. (4) A flexible insulating film is pasted on the front side of the strip thermoelectric device. After cold pressing or hot pressing, the strip thermoelectric device is folded along the center line of the flexible silver film to obtain a stretchable flexible thermoelectric device. The flexible thermoelectric film is made of a nanocomposite material comprising chalcogenides, conductive polymers and carbon materials, wherein the molar mass ratio of chalcogenides to conductive polymers is controlled at 1:2-10:1 and the molar mass ratio of chalcogenides to carbon materials is controlled at 1:3-8:

1. The preparation of the flexible thermoelectric thin film is as follows: 1.1) The nanostructures of chalcogenides were synthesized by a hydrothermal method, wherein the temperature range of the hydrothermal synthesis was 100℃-1000℃ and the synthesis time was 20-600 min; 1.2) In a solution containing chalcogenide nanostructures, 3,4-ethylenedioxythiophene or pyrrole monomers are polymerized in situ under the action of a strong oxidant; the polymerization reaction time is 5-600 min and the polymerization reaction temperature is -10℃ to 150℃. 1.3) The product of the polymerization reaction is washed by alternating centrifugation with deionized water and anhydrous ethanol, and the resulting product is redispersed in anhydrous ethanol; the centrifugation conditions are 2000-15000 rpm, 2-50 min, and 1-20 times. 1.

4. The carbon material powder is fully dispersed in anhydrous ethanol and mixed with the mixed solution in step (3) by heating and stirring. The stirring temperature is 25-200℃, the stirring speed is 50-500rpm, and the stirring time is 20-600min. 1.5) The solution after heating and stirring in step 1.3) is vacuum filtered onto a porous filter membrane. After drying, the membrane is first post-treated using cold pressing technology. The cold pressing conditions are: pressure of 1~150MPa and time of 5~60min. Then, the membrane is post-treated using high temperature and high pressure technology. The high temperature and high pressure conditions are: pressure of 1~150MPa, temperature of 50~300℃ and time of 5~600min.

2. The method for fabricating the stretchable flexible thermoelectric device according to claim 1, characterized in that, The chalcogenides are bismuth telluride, bismuth selenide, or silver selenide; the conductive polymers are polyethylene dioxythiophene or polypyrrole; and the carbon materials are carbon nanotubes, graphene, or Mxene.

3. The method for fabricating the stretchable flexible thermoelectric device according to claim 1, characterized in that, The method for preparing flexible silver films is as follows: silver nanowires are synthesized by wet chemical method, then the silver nanowires are vacuum filtered onto a porous filter membrane, and finally the film is post-treated by cold pressing. The cold pressing conditions are: pressure of 1~150MPa and time of 5~600min.

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