Flexible wearable thermoelectric device based on hydrogel-foamy copper and method

Abstract

The invention provides a flexible wearable thermoelectric device based on hydrogel-foamy copper, a preparation method and a performance evaluation method. The flexible wearable thermoelectric device comprises a flexible thermoelectric substrate layer made of a PI film, and a plurality of thermoelectric units prepared on the flexible thermoelectric substrate layer. The thermoelectric unit comprises a hot end electrode, an N-type thermoelectric arm, a P-type thermoelectric arm and a cold end hydrogel-foamy copper composite heat dissipation electrode; the cold-end hydrogel-foamy copper composite heat dissipation electrode comprises a cold-end copper electrode and a foamy copper layer-hydrogel layer conjugate; the flexible thermoelectric substrate layer comprises two layers of PI films, and a hot end electrode of the thermoelectric unit is clamped between the two layers of PI films; the hot end electrode is welded with the N-type thermoelectric arm and the P-type thermoelectric arm; and cold end hydrogel-foamy copper composite heat dissipation electrodes are welded at the cold ends of the N-type thermoelectric arm and the P-type thermoelectric arm. According to the invention, the thermoelectric conversion efficiency can be improved, and the requirements of limited space, light weight and flexibility of the flexible wearable equipment are met.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric devices, and in particular to a flexible wearable thermoelectric device based on hydrogel-copper foam, a preparation method and a performance evaluation method. Background Art

[0002] In the field of flexible wearable electronic devices, with the increasing integration and functional complexity, thermal management issues have become a key factor restricting their performance improvement and long-term stable operation. Especially in the application of thermoelectric devices, due to the large amount of waste heat generated during the energy conversion process, if there is a lack of an effective heat dissipation mechanism, the working efficiency of the thermoelectric devices will decrease, the stability will be damaged, and it may even cause safety hazards such as overheating of the equipment. Although traditional heat dissipation technologies, such as metal heat sinks, air cooling or liquid cooling systems, perform well in rigid electronic devices, they are unable to meet the limited space, lightweight and flexibility requirements of flexible wearable devices.

[0003] Hydrogels have shown great potential in the field of flexible heat dissipation due to their unique heat absorption and water retention properties and good biocompatibility. Hydrogels can absorb and store a large amount of heat, and through their internal microstructure and the movement of water molecules, they can slowly release and evenly distribute the heat, thereby effectively slowing down the accumulation of heat and providing a continuous heat dissipation effect for the device. However, the thermal conductivity of a single hydrogel material is limited, and it is difficult to meet the efficient heat dissipation requirements of high heat flux density thermoelectric devices.

[0004] On the other hand, copper foam, as a porous metal material, has significant advantages in the field of heat dissipation due to its high porosity, large specific surface area and excellent thermal conductivity. Especially in thermoelectric devices, copper foam can quickly transfer heat from the heat source to the heat dissipation surface, achieving rapid heat dissipation, thereby effectively reducing the operating temperature of the thermoelectric device and improving its working efficiency and stability. However, there is a significant mismatch between the rigid structure of copper foam and its application requirements in flexible wearable devices. How to combine it with a flexible substrate to achieve the dual goals of efficient heat dissipation and good flexibility has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] In view of this, the present invention provides a flexible wearable thermoelectric device and method based on hydrogel-copper foam, which can improve the thermoelectric conversion efficiency and meet the limited space, lightweight and flexibility requirements of flexible wearable devices.

[0006] In order to solve the above technical problems, the present invention is implemented as follows.

[0007] A flexible wearable thermoelectric device based on hydrogel-copper foam, comprising: a flexible thermoelectric substrate layer made of PI film, and a plurality of thermoelectric units prepared on the flexible thermoelectric substrate layer; the thermoelectric unit comprises a hot end electrode, an N-type thermoelectric arm, a P-type thermoelectric arm, and a cold end hydrogel-copper foam composite heat dissipation electrode; the cold end hydrogel-copper foam composite heat dissipation electrode comprises a cold end copper electrode and a combination of a copper foam layer and a hydrogel layer;

[0008] The flexible thermoelectric substrate layer includes a lower PI film and an upper PI film, and the hot end electrode of the thermoelectric unit is sandwiched between the two PI films;

[0009] Hot end electrode welding N-type thermoelectric arm and P-type thermoelectric arm;

[0010] The cold ends of the N-type thermoelectric arm and the P-type thermoelectric arm are welded with a cold-end hydrogel-foam copper composite heat dissipation electrode; wherein the cold-end copper electrode is welded to the hot ends of the N-type thermoelectric arm and the P-type thermoelectric arm, and a combination of a foam copper layer and a hydrogel layer is fixed on the cold-end copper electrode; the combination of the foam copper layer and the hydrogel layer includes a foam copper layer whose pores are filled with a hydrogel material in a lower layer, and an upper hydrogel layer.

[0011] Preferably, the thickness of the lower PI film is 25 μm, and the thickness of the upper PI film is 50 μm.

[0012] Preferably, the foam copper layer is made of 40-90 PPM foam metal, and the pores are filled with hydrogel material; the foam copper layer has a thickness of 4 mm, a pore size of 0.1 mm to 10 mm, and a porosity of 60% to 98%.

[0013] Preferably, the hydrogel layer material and the hydrogel material used to fill the pores of the foam copper layer are both cross-linked by acrylamide, agar, N,N'-methylenebisacrylamide and sodium persulfate.

[0014] Preferably, the cold-end hydrogel-foam copper composite heat dissipation electrode is a strip structure, and one cold-end hydrogel-foam copper composite heat dissipation electrode covers two columns of thermoelectric arms.

[0015] The present invention also provides a method for preparing a flexible wearable thermoelectric device based on hydrogel-copper foam, which is used to prepare the above-mentioned flexible wearable thermoelectric device based on hydrogel-copper foam; the method comprises the following steps:

[0016] Step 1: Prepare a flexible thermoelectric substrate layer containing a hot-end electrode: deposit a patterned copper layer on the lower PI film and perform electroplating to form a hot-end electrode, and then cover it with a layer of PI film as an upper PI film; open a window in the contact area between the hot-end electrode and the thermoelectric arm on the upper PI film for welding the thermoelectric arm and the hot-end electrode, thereby obtaining a flexible thermoelectric substrate layer containing a hot-end electrode;

[0017] Step 2: coating a hot-end electrode solder paste on the exposed hot-end electrode at the window position of the flexible thermoelectric substrate layer containing the hot-end electrode;

[0018] Step 3: Place the N-type thermoelectric arm and the P-type thermoelectric arm at intervals at the location where the hot end electrode solder paste is applied, and place them in a reflow furnace to complete the welding;

[0019] Step 4: Print the cold end electrode solder paste on the cold end of the N-type thermoelectric arm and the P-type thermoelectric arm, place the cold end electrode, and then put it into the reflow furnace to complete the welding;

[0020] Step 5: Fix the combination of the hydrogel layer and the foam copper layer to the cold end electrodes of the N-type thermoelectric arm and the P-type thermoelectric arm one by one through thermal conductive silicone. The foam copper layer contacts the cold end electrode to form a cold end hydrogel-foam copper composite heat dissipation electrode, completing the preparation of the hydrogel-foam copper flexible wearable thermoelectric device.

[0021] Preferably, in step 1, the thickness of the lower PI film is 25 μm, and the thickness of the upper PI film is 50 μm.

[0022] Preferably, the hot end electrode solder paste used in step 2 has a thickness of 0.1 mm and a composition of Sn. 99 Ag 0.3 Cu 0.7 The cold end electrode solder paste used in step 4 has a thickness of 0.1 mm and a composition of Sn 42 Bi 58 Low temperature solder paste.

[0023] Preferably, in step 5, the preparation process of the combination of the hydrogel layer and the copper foam layer is:

[0024] Step 501: Weigh 14.97% by mass of acrylamide AM, 1.66% by mass of agar Agar, and 0.05% by mass of N,N'-methylenebisacrylamide MBA, add these raw materials into deionized water, and perform ultrasonic grinding and stirring to form a mixed solution;

[0025] Step 502: transferring the mixed solution obtained in step 501 to a reaction kettle, placing it in a vacuum drying oven, performing a hydrothermal reaction, and then cooling; after cooling, adding 0.15% by mass of sodium persulfate APS as an initiator for the polymerization reaction;

[0026] Step 503: placing a foam copper sheet at the bottom of the mold, introducing a mixed solution containing APS into the mold, and fully blending the mixed solution with the foam copper sheet;

[0027] Step 504: placing the mold in a vacuum drying oven and heating it to allow the hydrogel to completely polymerize and solidify, while forming a strong bond between the hydrogel and the copper foam to form a combination of the hydrogel layer and the copper foam layer.

[0028] The present invention provides a performance evaluation method for a flexible wearable thermoelectric device based on hydrogel-copper foam, which is used to evaluate or optimize the above-mentioned flexible wearable thermoelectric device based on hydrogel-copper foam; the method comprises:

[0029] Determine key parameters, including heat source temperature, cold end temperature, material thermal resistance, Seebeck coefficient, material thermal conductivity, and electrical conductivity of metal materials, and input them into the analysis software;

[0030] Constructing a structural model of the flexible wearable thermoelectric device and inputting it into analysis software;

[0031] Determine the first physical field model of the solid-fluid heat transfer and laminar flow interaction of the flexible wearable thermoelectric device and input it into the analysis software; the first physical field model includes the total heat flow Q entering the flexible wearable thermoelectric device H The model of the hot end of the flexible wearable thermoelectric device is the heat flow Q lost by heat conduction of the PI film and heat exchange with the air. air The model, the heat flux Q entering each pair of thermoelectric arms h The model, the heat flux Q flowing out of each pair of thermoelectric arms C The model of

[0032]

[0033] Among them, T h is the temperature of the hot end of the thermoelectric arm, T air is the ambient temperature, R 2 is the thermal resistance of the upper PI film, R air is the air convection heat transfer thermal resistance of the hot end of the flexible wearable thermoelectric device; S pn is the relative Seebeck coefficient of the thermoelectric arm, I is the current passing through the loop, T C is the cold end temperature of the thermoelectric arm, K is the total thermal conductivity of the two thermoelectric arms, R Con is the thermal resistance of the cold-end connection electrode of the flexible wearable thermoelectric device; R Cu is the thermal resistance of copper foam; R HG is the thermal resistance of the hydrogel;

[0034] The thermal resistance of copper foam is determined by the thermal resistance R Cu，solid and the thermal resistance R of the hydrogel part filled in the pores of the copper foam gel composition:

[0035]

[0036] Among them, LCu is the total thickness of the copper foam layer; A is the thermal conductivity area of ​​the hydrogel-copper foam composite heat dissipation electrode; is the porosity of copper foam; k Cu k is the thermal conductivity of the solid part of the copper foam; gel·eff is the effective thermal conductivity of hydrogel in copper foam;

[0037] Determine a second physical field model of thermoelectric and current interaction of the flexible wearable thermoelectric device and input it into the analysis software; the second physical field model includes an open circuit voltage model, a loop current model, a maximum output power model and a thermoelectric conversion efficiency;

[0038] The analysis software uses the first physics model and the second physics to perform performance evaluation;

[0039] By adjusting the thermal conductivity area A of the foam copper material, the hydrogel-foam copper composite heat dissipation electrode, the porosity of the foam copper The total thickness of the copper foam layer is L Cu By changing the materials and / or dimensions of each component of the flexible wearable thermoelectric device, the performance of the flexible wearable thermoelectric device can be changed to meet the design requirements.

[0040] Beneficial effects:

[0041] (1) The present invention optimizes the thermal management design. The hot end uses PI material, whose excellent thermal stability and medium thermal conductivity enable it to effectively withstand high temperatures and stably conduct heat to the cold end; the cold end uses a copper foam-hydrogel composite electrode, in which the porous structure of the copper foam increases the heat exchange area, the high thermal conductivity of the copper foam quickly diffuses heat, and the hydrogel further enhances the heat dissipation efficiency by slowly releasing and storing heat, thereby significantly improving the overall heat dissipation performance. This design achieves a good balance between flexibility and performance. The PI material is flexible and has high mechanical strength, which is suitable for the needs of a flexible hot end; the copper foam provides structural support for the cold end, and the hydrogel enhances flexibility, so that the cold end has both excellent heat dissipation performance and flexible adaptability. In addition, the PI material is resistant to high temperatures and aging, ensuring the mechanical stability of the hot end during long-term operation; the corrosion resistance of the copper foam and the moisture absorption and regeneration function of the hydrogel effectively maintain the long-term stability of the cold end and extend the service life of the device. Through the above design, the PI material can maintain a higher temperature at the hot end, and the copper foam-hydrogel composite structure at the cold end maintains a low temperature state, forming a larger temperature difference, thereby significantly improving the thermoelectric conversion efficiency.

[0042] (2) This composite structure optimizes the thermoelectric conversion process, improves the conversion efficiency, and enhances the stability and durability of the electrode, avoiding the stress concentration phenomenon caused by the introduction of hydrogel.

[0043] (3) This composite structure enhances the stability of the heat dissipation system. The structural stability of the copper foam and the durability of the hydrogel ensure long-term stable heat dissipation performance.

[0044] (4) In addition, the processability of copper foam and the flexibility of hydrogel enable the heat dissipation system to adapt to thermoelectric devices of different shapes and sizes, improving the adaptability of the system.

[0045] (5) The flexible thermoelectric substrate layer adopts a two-layer PI film design, and the hot end electrode of the thermoelectric unit is sandwiched between the two PI films, which not only improves the flexibility and high-temperature stability of the electrode, but also enhances its insulation and chemical stability. In a preferred embodiment, the thickness of the lower PI film is preferably 25 μm, and the thickness of the upper PI film is preferably 50 μm. The thickness of the lower layer of 25 μm helps to optimize the electrical performance of the thermoelectric substrate layer; the thickness of the upper layer of 50 μm provides stronger structural support, which helps to protect the thermoelectric unit and the electroplated copper layer from damage.

[0046] (6) In a preferred embodiment, the thickness of the copper foam is 4 mm, the pore size is 0.2 mm, the porosity is about 96%, the surface density is relatively large, and it has a good heat dissipation effect.

[0047] (7) In terms of preparation and processing technology, this patent combines hydrogel and copper foam to form a composite heat dissipation electrode, making full use of the high thermal conductivity of copper foam and the heat absorption and slow release characteristics of hydrogel to achieve rapid heat conduction and uniform heat dissipation. The patterned copper layer is deposited on the PI film through electroplating technology, and combined with precise solder paste coating and reflow soldering, which significantly improves the contact quality and thermoelectric conversion efficiency between the thermoelectric arm and the electrode. At the same time, vacuum pumping and low-temperature curing processes are used to ensure the stability of the combination of copper foam and hydrogel. The composite design of copper foam and hydrogel is introduced at the cold end to improve the heat dissipation efficiency and continuous heat dissipation capacity, and extend the stable working time of the equipment. In addition, the mechanical properties and adaptability are also enhanced. The combination of PI film and copper foam improves the flexibility and durability of the device, better meeting the use requirements of flexible wearable devices in dynamic environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a schematic diagram of the preparation process of the flexible wearable thermoelectric device based on hydrogel-copper foam of the present invention.

[0049] Figure 2 Schematic diagram of a flexible thermoelectric substrate layer containing electroplated copper electrodes.

[0050] Figure 3 Schematic diagram of the structure with thermoelectric arms placed without adding hydrogel-foam copper.

[0051] Figure 4 Schematic diagram of the structure with added hydrogel layer-foam copper.

[0052] Figure 5 This is a schematic diagram of the preparation of the flexible wearable thermoelectric device based on hydrogel-copper foam of the present invention.

[0053] Figure 6 This is the theoretical model of the flexible wearable thermoelectric device based on hydrogel-copper foam of the present invention.

[0054] Figure 7 It is a schematic diagram of the power-current change of the hydrogel-foam copper electrode and the copper metal electrode of the present invention.

[0055] Among them, 1-flexible thermoelectric substrate layer; 2-hot end electrode; 3-N-type thermoelectric arm / P-type thermoelectric arm; 4-cold end hydrogel-foam copper composite heat dissipation electrode; 41-foam copper layer; 42-hydrogel layer. DETAILED DESCRIPTION

[0056] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0057] At present, flexible wearable thermoelectric devices generate a large amount of waste heat during operation. If the heat dissipation is not sufficient, the temperature of the hot end will increase, affecting the temperature difference efficiency of the device, thereby significantly reducing the thermoelectric conversion performance. However, traditional high-efficiency heat dissipation materials (such as metals) are rigid and do not match the flexible substrate, which limits their application in wearable devices; and overly soft materials (such as single hydrogels) have good flexibility, but due to poor thermal conductivity, it is difficult to meet the heat dissipation requirements of high heat flux density scenarios. In addition, the device is prone to mechanical stress concentration or material aging problems under long-term high temperature or dynamic environment, which in turn affects the durability of the heat dissipation structure and the overall performance of the device. More importantly, the fluctuation of the hot end temperature may weaken the efficiency of the entire thermoelectric circuit, and if the cold end cannot maintain a continuous low temperature state, it is difficult to ensure effective temperature difference generation, thereby restricting the stability and long-term application performance of the device.

[0058] In view of the above problems, the present invention first analyzes the material selection of flexible wearable thermoelectric devices. The thermoelectric device includes a cold end and a hot end. The present invention designs the hot end material and the cold end electrode material by optimizing thermal management.

[0059] For the hot end, the present invention uses polyimide (PI) material, whose excellent thermal stability and medium thermal conductivity enable it to effectively withstand high temperatures and stably conduct heat to the cold end. In addition, PI material is flexible and has high mechanical strength, which is suitable for the needs of flexible hot ends; PI material is also resistant to high temperatures and aging, ensuring the mechanical stability of the hot end during long-term operation.

[0060] For the cold-end electrode material, the present invention combines copper foam with hydrogel as the heat dissipation part of the cold end of the thermoelectric device. Compared with using copper foam or hydrogel alone as a heat dissipation electrode, copper foam has high thermal conductivity, but it is relatively rigid and difficult to adapt to flexible devices. At the same time, a single heat conduction mechanism is not enough to effectively alleviate local overheating, while hydrogel has good flexibility and heat absorption and slow release characteristics, but its thermal conductivity is insufficient and it cannot quickly transfer heat from the heat source to the heat dissipation surface. In the combination of hydrogel and copper foam, the porous structure of copper foam increases the heat exchange area, and the high thermal conductivity quickly diffuses heat, while the hydrogel further enhances the heat dissipation efficiency by slow release and storage of heat. The two combine the efficient heat transfer of copper foam and the continuous and uniform heat dissipation function of hydrogel, achieving the dual effects of rapid heat conduction and delayed heat accumulation, which not only improves the temperature difference between the hot end and the cold end of the thermoelectric device, optimizes the thermoelectric conversion efficiency, and jointly improves the heat dissipation efficiency and conversion efficiency, thereby significantly improving the overall heat dissipation performance. At the same time, the stability and durability of the electrode are enhanced, the stress concentration caused by the introduction of hydrogel is avoided, and the mechanical strength and environmental adaptability of the heat dissipation system are enhanced, thereby meeting the needs of efficient heat dissipation and flexible dynamic applications, with a longer service life and a wider range of application scenarios. In addition, the processability of copper foam and the flexibility of hydrogel enable the heat dissipation system to adapt to thermoelectric devices of different shapes and sizes, improving the adaptability of the system.

[0061] For the combination of PI + copper foam + hydrogel, this design achieves a good balance between flexibility and performance. The PI material is flexible and has high mechanical strength, which is suitable for the needs of flexible hot ends; copper foam provides structural support for the cold end, and hydrogel enhances flexibility, so that the cold end has both excellent heat dissipation performance and flexible adaptability. In addition, the PI material is resistant to high temperatures and aging, ensuring the mechanical stability of the hot end during long-term operation; the corrosion resistance of copper foam and the moisture absorption and regeneration function of hydrogel effectively maintain the long-term stability of the cold end and extend the service life of the device. Through the above design, the PI material can maintain a higher temperature at the hot end, and the copper foam-hydrogel composite structure at the cold end maintains a low temperature state, forming a larger temperature difference, thereby significantly improving the thermoelectric conversion efficiency.

[0062] Based on the above analysis, the flexible wearable thermoelectric device based on hydrogel-foam copper provided in the embodiment of the present invention includes a flexible thermoelectric substrate layer 1 made of PI film, and a plurality of thermoelectric units are prepared on the flexible circuit substrate layer. Each thermoelectric unit is composed of a hot end electrode 2, an N-type thermoelectric arm 3, a P-type thermoelectric arm 3, and a cold end hydrogel-foam copper composite heat dissipation electrode 4. The hot end electrode 2 can be an electroplated copper electrode. This structure effectively improves the thermoelectric conversion efficiency of the thermoelectric device, and by enhancing the heat dissipation performance, ensures the stability and reliability of the device during high-efficiency operation.

[0063] The flexible thermoelectric substrate layer 1 is the part of the thermoelectric device that bears the bending deformation, and its main material is PI (polyimide). The flexible thermoelectric substrate layer includes a lower PI film and an upper PI film, and the electroplated copper electrode of the thermoelectric unit is sandwiched between the two PI films. The specific preparation of the flexible thermoelectric substrate layer is designed through nine steps of cutting, film pasting, exposure, development, etching, film stripping, covering layer pasting, hot pressing and reinforcing plate pasting. The thickness of the lower PI film is preferably 25μm, and the thickness of the upper PI film is preferably 50μm. The thickness of the lower layer of 25μm helps to optimize the electrical performance of the thermoelectric substrate layer; the thickness of the upper layer of 50μm provides stronger structural support, which helps to protect the thermoelectric unit and the electroplated copper layer from damage.

[0064] The N-type thermoelectric arm and the P-type thermoelectric arm are welded between the hot-end electrode 2 and the cold-end hydrogel-foam copper composite heat dissipation electrode 4. The N-type thermoelectric arm and the P-type thermoelectric arm are arranged at intervals.

[0065] The cold-end hydrogel-foam copper composite heat dissipation electrode 4 includes a cold-end copper electrode and a combination of a foam copper layer and a hydrogel layer. The cold-end copper electrode is welded to the cold end of the thermoelectric arm, and the other side of the cold-end copper electrode is fixed with the combination of a foam copper layer and a hydrogel layer. The combination of a foam copper layer and a hydrogel layer mainly includes a foam copper layer 41 whose pores are filled with a hydrogel material in a lower layer, and a hydrogel layer 42 in an upper layer.

[0066] The copper foam layer is made of 40-90 ppm of metal foam, and the pores are filled with hydrogel material. The copper foam thickness is 4 mm, the pore size is 0.1 mm to 10 mm, and the porosity is 60% to 98%. In a preferred embodiment, the copper foam layer is made of 90 ppm of metal foam, the copper foam thickness is 4 mm, the pore size is 0.2 mm, and the porosity is about 96%.

[0067] In a preferred embodiment, the hydrogel layer material and the hydrogel material used to fill the pores of the foam copper layer are both cross-linked by acrylamide, agar, N,N'-methylenebisacrylamide and sodium persulfate.

[0068] The embodiment of the present invention further provides a method for preparing a flexible wearable thermoelectric device based on hydrogel-copper foam. Figure 1 The preparation process is shown. As shown in the figure, the method includes the following steps:

[0069] Step 1: Prepare a flexible thermoelectric substrate layer containing a hot end electrode, and open windows to form welding locations.

[0070] In a preferred embodiment, this step first deposits a patterned copper layer as the hot end electrode part on a polyimide (PI) film with a thickness of 25 μm by electroplating. After electroplating to form an electroplated copper electrode, a layer of PI film with a thickness of 50 μm is covered on the surface of the lower PI film with the electroplated copper electrode as the upper PI film. Then, a window treatment is performed on the upper PI film in the contact area between the electroplated copper electrode and the thermoelectric arm to facilitate the welding of the thermoelectric arm and the electroplated copper electrode. At this point, a flexible thermoelectric substrate layer containing electroplated copper electrodes is manufactured, such as Figure 2 shown.

[0071] Step 2: Apply hot-end electrode solder paste to the exposed hot-end electrode at the window position of the flexible thermoelectric substrate layer.

[0072] Among them, the hot end electrode solder paste can use high tin solder paste, and the high temperature solder paste composition is Sn 99 Ag 0.3 Cu 0.7 .

[0073] To ensure a good coating effect, the surface of the flexible thermoelectric substrate layer containing the hot end electrode must be thoroughly cleaned with alcohol to remove all impurities. Subsequently, the flexible thermoelectric substrate layer containing the hot end electrode is firmly mounted on the stainless steel base plate to avoid any movement during coating. Next, a stainless steel mask with a mesh size of 1.4mm×1.4mm is used to accurately print a high-temperature solder paste with a thickness of about 0.1mm on the welding area. After completion, the mask is removed, marking the completion of the hot end electrode solder paste coating.

[0074] Step 3: Place the N-type thermoelectric arm and the P-type thermoelectric arm at intervals at the location where the hot end electrode solder paste is applied to the flexible printed circuit substrate, and then place them in a reflow furnace to complete the welding.

[0075] In this step, according to the design circuit, the N-type thermoelectric arm and the P-type thermoelectric arm are sequentially placed on the flexible printed circuit substrate coated with solder paste. Figure 3 As shown. During this process, ensure that the thermoelectric arm is positioned accurately to avoid the adverse effects of open circuit or tilt caused by misalignment on cold end welding. Finally, put the components to be welded into the reflow furnace to complete the welding.

[0076] Step 4: Print cold end electrode solder paste on the cold end of the N-type thermoelectric arm and the P-type thermoelectric arm, place the cold end electrode, and then put it into the reflow furnace to complete the welding.

[0077] Among them, the cold end electrode solder paste can use low-tin solder paste, and the low-temperature solder paste composition is Sn 42 Bi 58 .

[0078] Before cold-end welding, the flexible thermoelectric device components with welded thermoelectric arms need to be fixed on the base plate to prevent movement in subsequent operations. Subsequently, similar to the coating step of the hot end, a layer of cold-end electrode solder paste with a thickness of about 0.1 mm is printed on the cold-end welding area using a stainless steel mask positioned by a fixture, and the mask is removed after coating. Next, the cold-end electrode is accurately placed on the cold end of the thermoelectric arm coated with solder paste. Finally, the entire device and fixture are placed in the reflow oven to complete the welding process.

[0079] Step 5: Fix the combination of the hydrogel layer and the copper foam layer to the cold end electrodes of the N-type thermoelectric arm and the P-type thermoelectric arm one by one through thermal conductive silicone. The copper foam layer contacts the cold end electrode to form a cold end hydrogel-copper foam composite heat dissipation electrode. This is the preparation of a flexible wearable thermoelectric device of hydrogel-copper foam.

[0080] In this embodiment, if Figure 4 As shown, the combination of the hydrogel layer and the copper foam layer is not a whole structure, but a strip structure, and a strip of the combination of the hydrogel layer and the copper foam layer covers two columns of thermoelectric arms.

[0081] In a preferred embodiment, the preparation process of the combination of the hydrogel layer and the copper foam layer includes:

[0082] Step 501: Weigh acrylamide (AM), agar (Agar) and N,N'-methylenebisacrylamide (MBA) in mass percentages of 14.97%, 1.66% and 0.05%, respectively, and add these raw materials into deionized water. Then, use an ultrasonic pulverizer to efficiently treat the mixed solution for 1 minute to ensure that the raw materials are fully dissolved and evenly dispersed to form a stable mixed solution.

[0083] Taking 12.5 ml of deionized water as an example, 2.25 g of acrylamide (AM), 0.25 g of agar (Agar) and 0.0075 g of N,N'-methylenebisacrylamide (MBA) need to be weighed, and these raw materials are added to 12.5 ml of deionized water, and stirred to form a mixed solution.

[0084] Step 502: The mixed solution obtained in step 501 is transferred to a reaction kettle and placed in a vacuum drying oven for hydrothermal reaction and then cooled; after cooling, 0.15% by mass of sodium persulfate (APS) is added as an initiator for the polymerization reaction.

[0085] In a preferred embodiment, in this step, the mixed solution is transferred to a reaction kettle and placed in a vacuum drying oven for a hydrothermal reaction at 95° C. for 2 hours, laying the foundation for the subsequent hydrogel formation. After the hydrothermal reaction is completed and the mixed solution is cooled, 0.0225 g of APS is slowly added as an initiator for the polymerization reaction.

[0086] Step 503: Place a foam copper sheet at the bottom of the mold, introduce the mixed solution containing APS into the mold, and fully blend the mixed solution with the foam copper sheet.

[0087] In a preferred embodiment, the mold used in this step can be made of silicone material. The silicone mold has multiple grooves, and foam copper sheets are placed in the grooves. Then the mixed solution containing APS is poured into the mold one by one and slowly to ensure that the mixed solution and foam copper are fully integrated.

[0088] The copper foam sheet can be pre-treated before being placed in the groove. The pre-treatment method can be: ultrasonic cleaning with organic solvents such as acetone and ethanol to remove organic impurities and oil stains on the surface. Then, the copper foam is further cleaned with an acidic solution (such as hydrochloric acid or acetic acid aqueous solution) to remove surface oxides. Finally, the copper foam sheet is blown dry with nitrogen to ensure that there is no moisture residue on its surface.

[0089] Step 504: placing the mold in a vacuum drying oven and heating it to allow the hydrogel to completely polymerize and solidify, while forming a strong bond between the hydrogel and the copper foam to form a combination of the hydrogel layer and the copper foam layer.

[0090] In a preferred embodiment, in this step, the mold is placed in a vacuum drying oven, and after vacuuming, heated at 65° C. for 2 hours to promote complete polymerization and curing of the hydrogel, and at the same time to form a strong bond between the hydrogel and the foam copper. After cooling, the foam copper with the hydrogel is formed.

[0091] The cooled copper foam with hydrogel, i.e., the combination of the hydrogel layer and the copper foam layer, is fixed to the cold end electrode of the thermoelectric arm one by one through thermal conductive silicone. The copper foam layer contacts the cold end electrode to form a cold end hydrogel-copper foam composite heat dissipation electrode, thereby completing the preparation of the hydrogel-copper foam flexible wearable thermoelectric device. The prepared structure is as follows: Figure 5 shown.

[0092] The present invention combines copper foam and hydrogel as the heat dissipation part of the cold end of the thermoelectric device, which can significantly improve the heat dissipation efficiency. Thanks to the excellent thermal conductivity of copper foam and the heat absorption and water retention characteristics of hydrogel, the two work together to quickly and effectively remove heat and extend the heat dissipation time. At the same time, this combination enhances the stability of the heat dissipation system. The structural stability of copper foam and the durability of hydrogel ensure long-term stable heat dissipation performance.

[0093] The present invention further constructs a systematic evaluation method based on a mathematical model to comprehensively characterize the performance of the hydrogel-copper foam flexible wearable thermoelectric device, which can be used to evaluate or optimize the flexible wearable thermoelectric device of the present invention. The method uses inputs including the heat source temperature Ts, the cold end temperature T c 、Ambient temperature T air, material thermal resistance, Seebeck coefficient, material thermal conductivity, electrical conductivity of metal materials and other key parameters. Relying on the established mathematical model, it is possible to quantitatively calculate important performance indicators such as the total heat flow, open circuit voltage, maximum output power and thermoelectric conversion efficiency of the device, thereby providing rigorous theoretical support and technical support for the in-depth evaluation and optimization design of device performance.

[0094] The evaluation method includes the following steps:

[0095] Determine key parameters, including heat source temperature, cold end temperature, material thermal resistance, Seebeck coefficient, material thermal conductivity, and electrical conductivity of metal materials, and input them into analysis software. The analysis software may be finite element analysis software.

[0096] Construct a structural model of the flexible wearable thermoelectric device and input it into the analysis software; SolidWorks software can be used to build the model.

[0097] Determine the first physical field model of the solid-fluid heat transfer and laminar flow interaction of the flexible wearable thermoelectric device and input it into the analysis software; the first physical field model includes the total heat flow Q entering the flexible wearable thermoelectric device H The model of the hot end of the flexible wearable thermoelectric device is the heat flow Q lost by heat conduction and heat exchange with air through PI Harima air The model, the heat flux Q entering each pair of thermoelectric arms h The model, the heat flux Q flowing out of each pair of thermoelectric arms C The model of

[0098] The total heat flow Q into the flexible thermoelectric device H It can be expressed as:

[0099]

[0100] In the formula, Q air The heat flow lost at the hot end of the thermoelectric device; Q h represents the heat flow into a single thermoelectric arm; N is the total number of thermoelectric arms; T S Indicates the temperature of the heat source; T h Indicates the temperature of the hot end of the thermoelectric arm; R 1 Represents the thermal resistance of the underlying PI film.

[0101] The heat loss at the hot end of the thermoelectric device through heat conduction of the polyimide film and heat exchange with the air is:

[0102]

[0103] Where, T air is the ambient temperature; R 2 Represents the thermal resistance of the upper PI film; R air It is the thermal resistance of air convection heat transfer at the hot end of the device.

[0104] The heat flux Q entering each pair of thermoelectric arms h and the outflowing heat flux Q C It can be expressed as:

[0105]

[0106] In the formula, S pn is the relative Seebeck coefficient of the thermoelectric arm; I is the current passing through the loop; K is the total thermal conductivity of the two thermoelectric arms; T C is the cold end temperature of the thermoelectric arm, that is, the cold end temperature of the device; R Con R is the thermal resistance of the device’s cold-end connection electrode; Cu is the thermal resistance of the device’s copper foam; R HG is the thermal resistance of the device hydrogel.

[0107] The thermal resistance of the solid part of the foam copper layer is R Cu，solid and the thermal resistance of the hydrogel part R gel They can be expressed as:

[0108]

[0109] However, since the heat is in series inside the copper foam, the two are added together to get the total thermal resistance of the copper foam layer:

[0110]

[0111] In the formula, R Cu，solid is the thermal resistance of the solid part of the copper foam; R gel Thermal resistance of the part of hydrogel filled in the pores of copper foam; A is the thermal conduction area of ​​the hydrogel-copper foam electrode; L Cu The total thickness of the copper foam; k Cu k is the thermal conductivity of the solid part of the copper foam; gel·eff is the effective thermal conductivity of the hydrogel in the copper foam, is the porosity of copper foam (0-100%).

[0112] Determine the second physical field model of the thermoelectric and current interaction of the flexible wearable thermoelectric device and input it into the analysis software; the second physical field model includes an open circuit voltage model, a loop current model, a maximum output power model and a thermoelectric conversion efficiency; wherein,

[0113] The open circuit voltage in the loop is:

[0114] V=NS pn (T h -T C ) (8)

[0115] When the output power in the loop is maximum, the current in the loop can be expressed as:

[0116]

[0117] Where R is the internal resistance of the thermoelectric device, which is the sum of the resistance of the metal electrode and the thermoelectric arm. Resistance is the reciprocal of conductivity.

[0118] The maximum output power of the device can be expressed as:

[0119]

[0120] The thermoelectric conversion efficiency of the device can be expressed as:

[0121]

[0122] Based on the above modeling, the analysis software can evaluate the performance of flexible wearable thermoelectric devices.

[0123] The performance evaluation results can be used to determine whether the design requirements are met. If the design requirements are not met or there is still room for optimization, the performance of the flexible wearable thermoelectric device can be changed by adjusting the materials and / or dimensions of the components of the flexible wearable thermoelectric device; in the present invention, for the hydrogel-foam copper composite heat dissipation electrode, the adjustment parameters may include the foam copper material, the thermal conductivity area A of the hydrogel-foam copper composite heat dissipation electrode, the porosity of the foam copper, and the thermal conductivity of ... The total thickness of the copper foam layer is L Cu .

[0124] Based on the above performance parameters calculation and analysis, such as Figure 6 The data graph of a flexible wearable thermoelectric device and a manufacturing method based on hydrogel-copper foam enhanced heat dissipation is shown. Without the addition of hydrogel-copper foam enhanced heat dissipation electrodes, the maximum output power is 0.007mw under human body conditions of 37°C, while the maximum output power of the addition of hydrogel-copper foam enhanced heat dissipation electrodes is 0.3mW, which can meet the working needs of some low-power wearable sensors such as temperature sensors, heart rate sensors and humidity sensors to a certain extent.

[0125] The above specific embodiments only describe the design principle of the present invention. The shapes and names of the components in the description may be different and are not limited. Therefore, those skilled in the art in the field of the present invention may modify or replace the technical solutions recorded in the above embodiments; and these modifications and replacements do not deviate from the creative purpose and technical solutions of the present invention and should all fall within the protection scope of the present invention.

Claims

1. A flexible wearable thermoelectric device based on hydrogel-copper foam, characterized in that: include: A flexible thermoelectric substrate layer made of PI film, and a plurality of thermoelectric units prepared on the flexible thermoelectric substrate layer; the thermoelectric unit comprises a hot end electrode, an N-type thermoelectric arm, a P-type thermoelectric arm, and a cold end hydrogel-foam copper composite heat dissipation electrode; the cold end hydrogel-foam copper composite heat dissipation electrode comprises a cold end copper electrode and a combination of a foam copper layer and a hydrogel layer; The flexible thermoelectric substrate layer includes a lower PI film and an upper PI film, and the hot end electrode of the thermoelectric unit is sandwiched between the two PI films; Hot end electrode welding N-type thermoelectric arm and P-type thermoelectric arm; The cold ends of the N-type thermoelectric arm and the P-type thermoelectric arm are welded with a cold-end hydrogel-foam copper composite heat dissipation electrode; wherein the cold-end copper electrode is welded to the hot ends of the N-type thermoelectric arm and the P-type thermoelectric arm, and a combination of a foam copper layer and a hydrogel layer is fixed on the cold-end copper electrode; the combination of the foam copper layer and the hydrogel layer includes a foam copper layer whose pores are filled with a hydrogel material in a lower layer, and an upper hydrogel layer.

2. The flexible wearable thermoelectric device based on hydrogel-copper foam according to claim 1, characterized in that: The thickness of the lower PI film is 25 μm, and the thickness of the upper PI film is 50 μm.

3. The flexible wearable thermoelectric device based on hydrogel-copper foam according to claim 1, characterized in that: The foam copper layer is made of 40-90 PPM foam metal, and the pores are filled with hydrogel material; the thickness of the foam copper layer is 4 mm, the pore diameter is selected from 0.1 mm to 10 mm, and the porosity is selected from 60% to 98%.

4. The flexible wearable thermoelectric device based on hydrogel-copper foam according to claim 1, characterized in that: The hydrogel layer material and the hydrogel material for filling the pores of the foam copper layer are both cross-linked by acrylamide, agar, N,N'-methylenebisacrylamide and sodium persulfate.

5. The flexible wearable thermoelectric device based on hydrogel-copper foam according to claim 1, characterized in that: The cold-end hydrogel-foam copper composite heat dissipation electrode is a strip structure, and one cold-end hydrogel-foam copper composite heat dissipation electrode covers two columns of thermoelectric arms.

6. A method for preparing a flexible wearable thermoelectric device based on hydrogel-copper foam, characterized in that: Used to prepare a flexible wearable thermoelectric device based on hydrogel-copper foam as described in any one of claims 1 to 5; the method comprises the following steps: Step 1: Prepare a flexible thermoelectric substrate layer containing a hot-end electrode: deposit a patterned copper layer on the lower PI film and perform electroplating to form a hot-end electrode, and then cover it with a layer of PI film as an upper PI film; open a window in the contact area between the hot-end electrode and the thermoelectric arm on the upper PI film for welding the thermoelectric arm and the hot-end electrode, thereby obtaining a flexible thermoelectric substrate layer containing a hot-end electrode; Step 2: coating a hot-end electrode solder paste on the exposed hot-end electrode at the window position of the flexible thermoelectric substrate layer containing the hot-end electrode; Step 3: Place the N-type thermoelectric arm and the P-type thermoelectric arm at intervals at the location where the hot end electrode solder paste is applied, and place them in a reflow furnace to complete the welding; Step 4: Print the cold end electrode solder paste on the cold end of the N-type thermoelectric arm and the P-type thermoelectric arm, place the cold end electrode, and then put it into the reflow furnace to complete the welding; Step 5: Fix the combination of the hydrogel layer and the foam copper layer to the cold end electrodes of the N-type thermoelectric arm and the P-type thermoelectric arm one by one through thermal conductive silicone. The foam copper layer contacts the cold end electrode to form a cold end hydrogel-foam copper composite heat dissipation electrode, completing the preparation of the hydrogel-foam copper flexible wearable thermoelectric device.

7. The method for preparing a flexible wearable thermoelectric device based on hydrogel-copper foam according to claim 6, characterized in that: In step 1, the thickness of the lower PI film is 25 μm, and the thickness of the upper PI film is 50 μm.

8. The method for preparing a flexible wearable thermoelectric device based on hydrogel-copper foam according to claim 6, characterized in that: The hot end electrode solder paste used in step 2 has a thickness of 0.1 mm and a composition of Sn. 99 Ag 0.3 Cu 0.7 The cold end electrode solder paste used in step 4 has a thickness of 0.1 mm and a composition of Sn 42 Bi 58 Low temperature solder paste.

9. The method for preparing a flexible wearable thermoelectric device based on hydrogel-copper foam according to claim 6, characterized in that: In step 5, the preparation process of the combination of the hydrogel layer and the copper foam layer is as follows: Step 501: Weigh 14.97% by mass of acrylamide AM, 1.66% by mass of agar Agar, and 0.05% by mass of N,N'-methylenebisacrylamide MBA, add these raw materials into deionized water, and perform ultrasonic grinding and stirring to form a mixed solution; Step 502: transferring the mixed solution obtained in step 501 to a reaction kettle, placing it in a vacuum drying oven, performing a hydrothermal reaction, and then cooling; after cooling, adding 0.15% by mass of sodium persulfate APS as an initiator for the polymerization reaction; Step 503: placing a foam copper sheet at the bottom of the mold, introducing a mixed solution containing APS into the mold, and fully blending the mixed solution with the foam copper sheet; Step 504: placing the mold in a vacuum drying oven and heating it to allow the hydrogel to completely polymerize and solidify, while forming a strong bond between the hydrogel and the copper foam to form a combination of the hydrogel layer and the copper foam layer.

10. A method for evaluating the performance of a flexible wearable thermoelectric device based on hydrogel-copper foam, for evaluating or optimizing the flexible wearable thermoelectric device based on hydrogel-copper foam as claimed in any one of claims 1 to 5; the method comprising: Determine key parameters, including heat source temperature, cold end temperature, material thermal resistance, Seebeck coefficient, material thermal conductivity, and electrical conductivity of metal materials, and input them into the analysis software; Constructing a structural model of the flexible wearable thermoelectric device and inputting it into analysis software; Determine the first physical field model of the solid-fluid heat transfer and laminar flow interaction of the flexible wearable thermoelectric device and input it into the analysis software; the first physical field model includes the total heat flow Q entering the flexible wearable thermoelectric device H The model of the hot end of the flexible wearable thermoelectric device is the heat flow Q lost by heat conduction of the PI film and heat exchange with the air. air The model, the heat flux Q entering each pair of thermoelectric arms h The model, the heat flux Q flowing out of each pair of thermoelectric arms C The model of Among them, T h is the temperature of the hot end of the thermoelectric arm, T air is the ambient temperature, R2 is the thermal resistance of the upper PI film, R air is the air convection heat transfer thermal resistance of the hot end of the flexible wearable thermoelectric device; S pn is the relative Seebeck coefficient of the thermoelectric arm, I is the current passing through the loop, T C is the cold end temperature of the thermoelectric arm, K is the total thermal conductivity of the two thermoelectric arms, R Con is the thermal resistance of the cold-end connection electrode of the flexible wearable thermoelectric device; R Cu is the thermal resistance of copper foam; R HG is the thermal resistance of the hydrogel; The thermal resistance of copper foam is determined by the thermal resistance R Cu,solid and the thermal resistance R of the hydrogel part filled in the pores of the copper foam gel composition: Among them, L Cu is the total thickness of the copper foam layer; A is the thermal conductivity area of ​​the hydrogel-copper foam composite heat dissipation electrode; is the porosity of the copper foam; k Cu k is the thermal conductivity of the solid part of the copper foam; gel·eff is the effective thermal conductivity of hydrogel in copper foam; Determine a second physical field model of thermoelectric and current interaction of the flexible wearable thermoelectric device and input it into the analysis software; the second physical field model includes an open circuit voltage model, a loop current model, a maximum output power model and a thermoelectric conversion efficiency; The analysis software uses the first physics model and the second physics to perform performance evaluation; By adjusting the thermal conductivity area A of the foam copper material, the hydrogel-foam copper composite heat dissipation electrode, the porosity of the foam copper The total thickness of the copper foam layer is L Cu By changing the materials and / or dimensions of each component of the flexible wearable thermoelectric device, the performance of the flexible wearable thermoelectric device can be changed to meet the design requirements.

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