CN113380941B - Out-of-plane thermoelectric device with stretchable porous structure - Google Patents
Out-of-plane thermoelectric device with stretchable porous structure Download PDFInfo
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Abstract
The invention relates to an out-of-plane type thermoelectric device with a stretchable porous structure, and belongs to the technical field of flexible thermoelectric energy conversion. The thermoelectric device is composed of the following structures: the thermoelectric module comprises a top electrode (1) and a bottom electrode (4) which are composed of conductive cloth, a p-type thermoelectric arm (2) and an n-type thermoelectric arm (3) which are composed of flexible porous materials with low heat conductivity and thermoelectric materials, and a flexible high heat conduction substrate which is composed of a flexible stretchable high heat conduction film (5) and a high heat conduction metal interface layer (6). The technical problem to be solved by the invention is as follows: constructing an elastic material with thermoelectric energy conversion function and three-dimensional porous structure integrated to obtain a stretchable thermoelectric material; the electrode structure of the thermoelectric device is designed, the interface thermal resistance between the thermoelectric device and a heat source is reduced, the actual temperature difference of the cold side and the hot side of the thermoelectric device is improved, the output voltage performance of the device is improved, and the stretchable application of the wearable power supply for generating electricity by utilizing the body temperature of a human body is realized.
Description
Technical Field
The invention relates to an out-of-plane thermoelectric device with a stretchable porous structure, and belongs to the technical field of flexible thermoelectric energy conversion.
Background
Devices used in wearable sensing systems should be sustainable, self-contained, maintenance free, mechanically flexible, and the like. It is needless to say that the power supply is an indispensable part in the sensing and signal transmission processes. But the current power supply unit becomes the biggest limitation of the wearable sensing network to realize the functions, because the power supply system which is most widely applied at present is a block battery, which brings a series of problems such as wearable flexibility problem, frequent charging problem and battery replacement. Self-powered sensing devices that do not require an external power supply unit supply are becoming especially important as more and more sensors are being applied in remote control scenarios. In other words, practical application requirements place ever higher demands on self-powered sensing systems.
Wearable flexible sensors mostly require micro-to milliwatt power supplies in the process of acquiring and transmitting signals. Therefore, an energy device capable of collecting low-grade energy (waste heat energy and human body movement mechanical energy) is very important for driving the wearable flexible sensing device. The micro energy harvesting device may be based on a variety of principles: such as piezoelectric effect and triboelectric effect, collecting mechanical energy, thermoelectric effect, collecting waste heat energy, and photovoltaic effect, collecting solar energy, and such micro-energy collecting devices have been widely studied in wearable flexible sensing systems. The thermoelectric power generation device converts heat energy into electric energy based on the Seebeck effect of thermoelectric materials, and has the advantages of environmental friendliness, small volume, compact structure, no moving parts and the like. The specific principle is as follows: when heat flows from the hot side of the thermoelectric material to the cold side of the thermoelectric material, the free charges (electrons or holes) inside the semiconductor thermoelectric material also follow the directional movement, and the heat energy is converted into electric energy through the charge movement. The temperature difference established between the human body and the external environment is used for power generation, and self-power supply of the flexible wearable equipment is achieved.
At present, a rigid human body thermoelectric power generation device applied to human body surface heat collection has the problems of high device manufacturing cost, poor reliability, inconvenience in wearing and the like. In addition, people look to flexible wearable thermoelectric devices. Although international research into flexible thermoelectric devices has progressed, four major challenges remain. Firstly, due to the high thermal conductivity of the thermoelectric material, the temperature difference is difficult to establish on the two sides of the thermoelectric material in human body application; secondly, the conventional flexible thermoelectric device uses a polymer substrate with low thermal conductivity, which causes large heat loss and is not favorable for heat energy utilization. Third, the existing flexible thermoelectric devices are limited by the inextensibility of the electrodes, and thus the devices themselves do not have stretchability; fourthly, the contact thermal resistance between the flexible thermoelectric device substrate and the heat source is large, so that the actual temperature difference between two sides of the thermoelectric arm is small, and the thermoelectric conversion efficiency is influenced.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: constructing an elastic material with a thermoelectric energy conversion function and a three-dimensional porous structure integrated to obtain a stretchable thermoelectric material; the design of the electrode structure of the thermoelectric device can reduce the interface thermal resistance between the thermoelectric device and a heat source, improve the actual temperature difference of the cold side and the hot side of the thermoelectric device, improve the output voltage performance of the device, and realize the stretchable application of the wearable power supply which generates electricity by utilizing the body temperature of a human body.
An out-of-plane thermoelectric device of stretchable porous structure, the thermoelectric device consisting of: the thermoelectric module comprises a top electrode (1) and a bottom electrode (4) which are composed of conductive cloth, a p-type thermoelectric arm (2) and an n-type thermoelectric arm (3) which are composed of flexible porous materials with low heat conductivity and thermoelectric materials, and a flexible high heat conduction substrate which is composed of a flexible stretchable high heat conduction film (5) and a high heat conduction metal interface layer (6).
The p-type thermoelectric arm (2) and the n-type thermoelectric arm (3) are connected with the top electrode (1) and the bottom electrode (4) through silver paste, and the contact resistance can be effectively reduced by using the silver paste. The bottom electrode (4) is adhered to the upper surface of the high heat-conducting film (5) through the adhesive surface of the conductive cloth. The metal interface layer (6) is fixed on the lower surface of the high heat conduction film (5) through in-situ growth.
The preparation sequence of the device is that a flexible and stretchable high-thermal-conductivity film (5) is prepared firstly, a metal interface layer (6) grows in situ on the lower surface of the high-thermal-conductivity film (5), a cut bottom electrode (4) is adhered to the fixed position of the upper surface of the high-thermal-conductivity film (5) according to a mask plate, silver paste is coated at the fixed position of the surface of the bottom electrode (4) according to the mask plate, a p-type thermoelectric arm (2) is fixed on the silver paste at the fixed position of the surface of the bottom electrode (4), an n-type thermoelectric arm (3) is fixed on the silver paste at the fixed position of the surface of the bottom electrode (4), the fixed position of a top electrode (1) is coated with the silver paste, and then the top electrode (1) coated with the silver paste is placed on the upper surfaces of the p-type thermoelectric arm (2) and the n-type thermoelectric arm (3).
The thermoelectric device is formed by connecting a bottom electrode, a p-type thermoelectric arm, an n-type thermoelectric arm and a top electrode in a pi-type manner, wherein the p-type thermoelectric arm and the n-type thermoelectric arm are connected in series in a cross manner, and the size of the thermoelectric arm is (3 multiplied by 5 mm) 3 ) The spacing between the thermoelectric arms was 2 mm.
The electrode material used by the thermoelectric device is conductive cloth, the upper surface of the conductive cloth is interwoven yarns coated with conductive particles, and the lower surface of the conductive cloth is conductive adhesive. The conductive cloth has good flexibility and deformability and excellent conductivity. Cutting the electrode size by laser engraving technique, wherein the size of the conductive cloth electrode is 8X 3mm 2 。
The p-type thermoelectric arm (2) and the n-type thermoelectric arm (3) used by the thermoelectric device are polyurethane/single-walled carbon nanotube (PU/SWCNT) porous materials, the thermoelectric material SWCNT is coated on the surface of the flexible PU porous material through an ultrasonic technology, so that electric-thermal separation is promoted, and the thermoelectric device has high thermal resistance and good electrical conductivity. The thermal conductivity of the PU/SWCNT porous material is far lower than that of an inorganic thermoelectric material and a conventional organic thermoelectric material, and the PU/SWCNT porous material provides guarantee for establishing a large temperature difference on two sides of a thermoelectric arm. The specific preparation process of the thermoelectric arm comprises the following steps:
(1) preparation of p-type thermoelectric arms
20mg of SWCNT powder was weighed into a crucible and heat-treated in a nitrogen atmosphere using a tube furnace. The temperature was raised from room temperature to 400 ℃ within 60 min. Keeping the temperature at 400 ℃ for 20 min. Then, the SWCNTs are cooled naturally, cooled to room temperature, and then taken out.
The heat-treated SWCNT was added to 50g of ethanol solution and subjected to ultrasonic dispersion for 30min to sufficiently disperse the SWCNT solution.
The cut PU porous cube (3X 5 mm) 3 ) Put into the dispersed SWCNT solution and continue to carry out ultrasonic treatment for 60 min. The PU/SWCNT block was then removed and dried in an oven at 60 ℃ for 6h, resulting in a p-type thermoelectric arm with low thermal conductivity.
(2) Preparation of n-type thermoelectric arm
50g of ethanol and 0.1g of Polyethyleneimine (PEI) were weighed and stirred on a magnetic stirrer for 30min to disperse the PEI in the ethanol solution. 20mg of SWCNT was weighed into PEI-ethanol solution and stirred magnetically for 24h to aminate the SWCNT. The stirred SWCNT solution was then ultrasonically dispersed for 30min to fully disperse the SWCNTs in the solution.
The cut PU porous cubic blocks (3X 5 mm) 3 ) The solution was added and sonication continued for 60 min. The PU/SWCNT block was then removed and dried in an oven at 60 ℃ for 6h, resulting in an n-type thermoelectric arm with low thermal conductivity.
The high heat-conducting film (5) used by the thermoelectric device is polydimethylsiloxane/boron nitride-ferroferric oxide (PDMS/BN-Fe) 3 O 4 ) By passingSynthesis of magnetic substance Fe on surface of high-heat-conductivity BN powder 3 O 4 Then mixing PDMS solution with BN-Fe 3 O 4 Mixing the powders, and curing under the action of magnetic field to obtain PDMS/BN-Fe 3 O 4 Internal BN-Fe 3 O 4 Micron sheet perpendicular to PDMS/BN-Fe 3 O 4 The surface of the film is further improved by PDMS/BN-Fe 3 O 4 Out-of-plane thermal conductivity. Subjecting PDMS/BN-Fe 3 O 4 While having large stretchability and high out-of-plane thermal conductivity. PDMS/BN-Fe 3 O 4 The preparation process of the film comprises the following steps:
the surface treatment of Boron Nitride (BN) powder was performed using a sodium hydroxide solution. The BN particle has few surface functional groups and strong chemical resistance. Therefore, a surface treatment is required to prepare the particles for chemical or physical bonding. BN particles were suspended in 5M NaOH solution at 90 ℃ for 48 hours to achieve surface attachment of hydroxide functional groups. Then, carrying out suction filtration and washing by using deionized water until the pH value of the suction filtration solution at the last time is neutral. Borohydride (BN-OH) nitride particles were placed in a furnace at 80 ℃ for 5 hours, cooled to room temperature, and then stored in a desiccator.
Next, iron oxide nanoparticles were added to the boron nitride surface by hydrolysis in a deionized water solution. First, 1.5g of polyvinylpyrrolidone was dissolved in 100 ml of deionized water, and 1g of BN-OH powder was added with magnetic stirring. After 2 hours, 4 g FeCl was added to the solution 3 ·6H 2 O, and then stirred at 90 ℃ for 12 hours. Subsequently, 20ml of hydrazine hydrate solution was added and the mixture was stirred at 90 ℃ for 4 hours. Finally, the product was washed with deionized water, filtered several times, and dried under vacuum at 80 ℃ for 5 hours to remove the solvent. Finally obtaining magnetic BN-Fe 3 O 4 And (3) powder.
Mixing PDMS solution with BN-Fe 3 O 4 The powders were mixed in a weight ratio of 10:4, stirred, degassed, and processed into a film having a thickness of 220 μm using a film coater. Then curing for 1 hour at 80 ℃ under the action of a magnetic field to obtain the flexible high-thermal-conductivity substrate PDMS/BN-Fe with boron nitride orientation distribution 3 O 4 。
A layer of Cu with high thermal conductivity is grown on the lower surface of the flexible substrate of the thermoelectric device in situ through magnetron sputtering, and interface thermal resistance is reduced. The preparation process of the interface layer comprises the following steps:
mixing PDMS/BN-Fe 3 O 4 The film is fixed on a sample holder in the sputtering instrument. Vacuumizing to the vacuum degree of 4.0 multiplied by 10 - 4 And when Pa is needed, opening the autorotation electrode of the sample table, introducing high-purity argon, fixing the flow of the argon to be 25sccm, and adjusting the air pressure to be 1 Pa. And adjusting the sputtering power, pre-sputtering for 5 minutes to remove oxides or impurities on the surface of the copper target, and opening a sample baffle to sputter for 30 minutes at 20W after the glow of the target is stable. And after the sputtering is finished, the sputtering power supply is turned off. Taking out the sample (PDMS/BN-Fe) 3 O 4 Cu film) to be used in the next step.
Compared with the prior art, the invention has the following beneficial effects:
and the preparation of the out-of-plane thermoelectric device with a stretchable porous structure is realized through the design of a three-dimensional structure. By using the porous structure, the electro-thermal separation is realized, and the thermoelectric arm with low thermal conductivity is prepared. By using the high thermal conductivity flexible substrate and the copper interface layer, the interface thermal resistance is significantly reduced. Because of the conductive cloth, PU/SWCNT porous material, PDMS/BN-Fe 3 O 4 The flexible high-heat-conductivity substrate consisting of the Cu interface layer is a flexible variable material, the thermoelectric device is stretched, and the conductive cloth and the PU/SWCNT porous material adapt to PDMS/BN-Fe through self deformation 3 O 4 The stretching process of the substrate realizes large deformation and stretchability of the device, which are not possessed by other flexible devices.
Drawings
Fig. 1 is a schematic view of a pair of thermoelectric legs.
Figure 2 is a front view of a pair of thermoelectric leg structures.
Fig. 3 is a schematic view of an out-of-plane type thermoelectric device structure.
Fig. 4 is a flow chart of an out-of-plane type thermoelectric device fabrication. 4a is PDMS/BN-Fe plated with copper on one side 3 O 4 the/Cu film, 4b is a physical diagram of the bottom electrode fixed on the upper surface of the flexible substrate. FIG. 4c is a pictorial view of a P-type thermoelectric leg coated with silver paste and FIG. 4d is a pictorial view of an out-of-plane type thermoelectric deviceFigure (a).
FIGS. 5a-b are PDMS/BN-Fe 3 O 4 The microscopic appearance of the film section.
Fig. 6 is the thermal conductivity of different materials.
FIGS. 7a-c are PDMS/BN-Fe after copper plating 3 O 4 The microscopic appearance of the Cu film.
FIG. 8 is a PDMS/BN-Fe plated with copper on one side 3 O 4 Stress-strain curve of Cu thin film.
Fig. 9a-c are microstructures of the surface of the conductive cloth.
Fig. 9d is a microstructure of a cross section of the conductive cloth.
FIG. 10 is a schematic diagram of a PU/SWCNT thermoelectric arm.
FIGS. 11a-c are microstructures of PU/SWCNT porous materials.
Fig. 12 is the thermal conductivity of different materials.
FIGS. 13a-b are graphs of the output performance of PDMS/BN based thermoelectric devices at different temperature differences.
FIGS. 14a-b are graphs of PDMS/BN-Fe 3 O 4 The output performance of the thermoelectric device as a substrate under different temperature differences.
FIGS. 15a-b are graphs of plated copper PDMS/BN-Fe 3 O 4 The output performance of the thermoelectric device with Cu as the substrate under different temperature differences.
Fig. 16a is the relative change in device resistance during a single bend in the X-axis direction of the device.
Fig. 16b is the relative change in resistance during 1000 cycles of bending (distance between clamps from 70mm to 50mm) along the X-axis of the device.
Fig. 17a is the relative change in resistance of the device during a single bend in the Y-axis direction of the device.
Figure 17b is the relative change in resistance during 1000 cycles of bending (distance between clamps from 70mm to 50mm) in the Y-axis direction of the device.
Fig. 18a is the relative change in resistance of the device during a single stretch in the X-axis direction of the device.
Figure 18b is the relative change in resistance during 1000 cycles of stretching (distance between clamps from 60mm to 70mm) along the X-axis of the device.
Figure 19a shows the device applied directly to the skin surface.
FIG. 19b shows the thermoelectric voltage generated during the thermal protection.
Detailed Description
Fig. 1 is a structural diagram of a pair of thermoelectric arms, which is composed of a top electrode (1) and a bottom electrode (4) made of conductive fabrics, a p-type thermoelectric arm (2) and an n-type thermoelectric arm (3) made of flexible porous materials and thermoelectric materials with low thermal conductivity, and a flexible high thermal conductive substrate made of a flexible stretchable high thermal conductive film (5) and a high thermal conductive metal interface layer (6).
Fig. 2 is a front view of a device with a pair of thermoelectric legs, the p-type thermoelectric leg (2) and the n-type thermoelectric leg (3) being connected to the top electrode (1) and the bottom electrode (4) by silver paste. The bottom electrode (4) is adhered to the upper surface of the flexible film (5) through the adhesive surface of the conductive cloth. The metal interface layer (6) is fixed on the lower surface of the flexible film (5) through in-situ growth.
FIG. 3 is a diagram showing a device structure of 50 pairs of thermoelectric legs, the device is connected in a pi-type manner by a bottom electrode, a p-type thermoelectric leg, an n-type thermoelectric leg and a top electrode, wherein the p-type thermoelectric leg and the n-type thermoelectric leg are arranged in a crossed manner and connected in series, and the size of the thermoelectric leg is (3X 5 mm) 3 ) The spacing between the thermoelectric legs was 2 mm.
Fig. 4 is a flow chart of an out-of-plane type thermoelectric device fabrication. The preparation sequence of the device is that a flexible and stretchable high-heat-conductivity film (5) is prepared first, and a metal interface layer (6) grows in situ on the lower surface of the high-heat-conductivity film (5) (figure 4 a);
sticking the cut bottom electrode (4) on the upper surface of the high thermal conductive film (5) according to the mask plate (figure 4b), wherein the size of the bottom electrode in figure 4b is 8 x 3mm 2 And cutting the bottom electrode in size by using a laser engraving technology. The distance between the electrodes is equal to 2 mm;
coating silver paste (3 × 3 mm) on the surface of the bottom electrode through a mask (FIG. 4c) 2 The distance between the silver pastes is 2 mm. The p-type thermoelectric arm (2) is fixed on the silver paste at the fixed position on the surface of the bottom electrode (4) (figure 4c), and the p-type thermoelectric arm and the n-type thermoelectric arm are arranged in a crossed mode, so that the p-type thermoelectric arm is placed in a vacant position.
Then the n-type thermoelectric legs (3) are fixedCoating the silver paste at the rest fixed position on the surface of the bottom electrode (4) with a top electrode fixed position through a mask plate, wherein the coating area is 3 multiplied by 3mm 2 After a distance of 2mm, the top electrode (1) coated with silver paste was placed on the upper surfaces of the p-type (2) and n-type (3) thermoelectric legs (fig. 4 d).
FIG. 5 shows PDMS/BN-Fe 3 O 4 Microscopic morphology of film section, PDMS/BN-Fe 3 O 4 BN-Fe in thin film 3 O 4 All perpendicular to the surface direction, which is beneficial to heat transfer.
Fig. 6 shows the thermal conductivity of different flexible substrates, the thermal conductivity of the substrates has a large influence on the establishment of the temperature difference of the thermoelectric device, and the thermal conductivity of PDMS is only 0.16W/(mK), so that the improvement of the substrates is carried out, and high-thermal-conductivity fillers such as BN, GO, CNTs, Al sheets and the like are respectively tried to be mixed with PDMS to increase the thermal conductivity of the matrix, and preferably, BN is used.
The mass ratio of the PDMS solution to the BN powder can be 10:1, 10:2, 10:3 and 10:4, and preferably 10:3 is used, so that the thermal conductivity of the matrix is improved while the elasticity is ensured.
By synthesizing Fe on the surface of BN powder 3 O 4 ,PDMS/BN-Fe 3 O 4 The mixture is solidified by applying a magnetic field to BN-Fe 3 O 4 The thermal conductivity can be further improved in the direction perpendicular to the surface. As shown in FIG. 6, PDMS/BN-Fe 3 O 4 The thermal conductivity of the film (0.84W/(mK)) is much greater than that of PDMS/BN (0.47W/(mK)).
Respectively preparing PDMS/BN-Fe oriented by magnetic field 3 O 4 Thin film and conventional PDMS/BN-Fe 3 O 4 Thin film, then testing the thermal conductivity of the two, PDMS/BN-Fe oriented by magnetic field 3 O 4 The thermal conductivity (0.84W/(mK)) of the film is larger than that of PDMS/BN-Fe prepared by a conventional method 3 O 4 Thermal conductivity of the film (0.56W/(mK)).
FIG. 7 is PDMS/BN-Fe 3 O 4 The microstructure of the/Cu film section can be seen as PDMS/BN-Fe 3 O 4 The film thickness was 220 μm, and the thickness of the interface layer Cu sputtered on the lower surface was 300 nm.
The selected metal interface layer can use high heat-conducting metal such as Fe, Ag, Al, Au and the like, and Cu is preferably used.
PDMS/BN-Fe 3 O 4 The thickness of the film may be 50 μm to 500. mu.m, and preferably 220 μm is used.
The thickness of the metallic interfacial layer is in the range of 100nm to 1000nm, preferably 300nm is used.
FIG. 8 shows PDMS/BN-Fe 3 O 4 The stress-strain curve of the/Cu thin film is shown by the data, and the elongation at break is 131%.
Fig. 9 shows a microstructure of a conductive cloth, the thickness of which is 100 μm, the upper surface of the conductive cloth is interwoven yarns coated with conductive particles, and the lower surface of the conductive cloth is conductive adhesive. The conductive cloth has good flexibility and deformability and excellent conductivity. Cutting the electrode size by laser engraving technique, wherein the size of the conductive cloth electrode is 8X 3mm 2 。
The electrodes can be made of copper adhesive tapes, conductive silver paste and conductive cloth, preferably, the conductive cloth is used, has certain deformability and certain support property, and can be used as a top electrode. The conductive cloth is carved by laser, so that the precision is ensured and the efficiency is improved. When the substrate is stretched, the flexible conductive cloth can deform according to the flexible conductive cloth so as to adapt to the stretching of the device.
FIG. 10 is a schematic diagram of a PU/SWCNT thermoelectric arm with dimensions of 3X 5mm 3 The PU/SWCNT thermoelectric arms had a porosity of 97.28% and the mass fraction of SWCNTs in the PU/SWCNT thermoelectric arms was 1.9%.
Increasing the height of the thermoelectric arms can significantly increase the temperature difference across the thermoelectric arms. However, the thermoelectric arms are too high for the wearing of the device. A balance is chosen between high temperature difference and wearability, i.e. taking an intermediate value. Thermoelectric legs having a height of 3mm, 4mm, 5mm, 6mm, 7mm are prepared separately, preferably, the thermoelectric leg height is selected to be 5 mm.
FIG. 11 shows the micro-topography of PU/SWCNT thermoelectric arms, the PU foam pore size is between 200 and 500 μm. The surface of the PU foam framework is uniformly coated with a layer of SWCNT.
Fig. 12 shows the thermal conductivity of different materials, the high porosity realizes the low thermal conductivity of the device, and the uniformly coated SWCNT layer on the PU skeleton surface ensures the good transmission of electrical signals, i.e. the structure realizes the electrical-thermal separation. As can be seen from fig. 12, the thermal conductivity of the PU foam (0.04W/(mK)) is much lower than that of the PU bulk (0.25W/(mK)), and even with SWCNT coating, the thermal conductivity of the PU/SWCNT foam is only 0.06W/(mK).
And (3) performance testing:
FIGS. 13-15 are PDMS/BN substrates, PDMS/BN-Fe, respectively 3 O 4 Substrate and copper plated PDMS/BN-Fe 3 O 4 Output performance test of three devices of a Cu substrate. The output performance was tested by placing 50 pairs of thermoelectric devices of the thermoelectric arms on a high and low temperature platform (with the cold side forcibly cooled to 20 ℃), and the output voltage and power of the devices at different temperature differences are shown in fig. 13-15. The maximum output power produced by the device at a temperature difference of 50 ℃ is 1.75 muW, 2.03 muW and 2.17 muW. The Seebeck coefficients of the devices were 74.4. mu. VK -1 /couple、78.3μVK -1 (couple and 81.3. mu. VK) -1 (couple). Calculated, the copper plated PDMS/BN-Fe 3 O 4 Compared with a PDMS/BN substrate device, the output power of the device is improved by 24%, and the Seebeck coefficient of the device is improved by 9%.
Fig. 16-17 are flexural performance tests of the devices. The device is fixed on a linear electrode and bent along the X-axis direction (figure 16a) and the Y-axis direction (figure 17a) of the device respectively, the original distance between the clamps is 70mm, the distance between the clamps is 20mm, the total resistance of the device in the process is changed as shown in figures 16a and 17a, and then the device is bent for 1000 times (the distance between the clamps is 70mm-50mm), and the internal resistance of the device is changed as shown in figures 16b and 17 b. The results show that there is little change in device resistance during bending.
Fig. 18 shows the tensile properties of the devices tested. When the original distance between the clamps is 60mm and the distance between the clamps is 86mm (45% strain), the substrate of the device is broken, and although the substrate is broken, the device still has the bottom electrode connected with the top electrode, and the resistance increases only by a small amount during the substrate breaking process, as shown in fig. 18 a. The device was then subjected to 1000 cycles of tensile testing (distance between clamps from 60mm to 70mm) and the internal resistance of the device varied as shown in figure 18 b.
Figure 19 is a human thermal power generation application. The device was placed directly on the arm and the thermoelectric voltage that the device could generate was 16.3mV (fig. 19 a). When a human body is in a low-temperature environment, the temperature of the skin surface is lower than the normal temperature of the human body, so that the arm at the periphery of the device is insulated and protected. As shown in FIG. 19b, the thermoelectric device generates a thermoelectric voltage of 19.5mV, which is 3.2mV higher than when not protected.
Claims (6)
1. An out-of-plane thermoelectric device of stretchable porous structure characterized by: the thermoelectric device is composed of the following structures: the thermoelectric module comprises a top electrode (1) and a bottom electrode (4) which are composed of conductive cloth, a p-type thermoelectric arm (2) and an n-type thermoelectric arm (3) which are composed of flexible porous materials with low thermal conductivity and thermoelectric materials, and a flexible high thermal conductive substrate which is composed of a flexible stretchable high thermal conductive film (5) and a high thermal conductive metal interface layer (6); the p-type thermoelectric arm (2) and the n-type thermoelectric arm (3) are connected with the top electrode (1) and the bottom electrode (4) through silver paste, and the contact resistance can be effectively reduced by using the silver paste; the bottom electrode (4) is adhered to the upper surface of the high-heat-conductivity film (5) through the adhesive surface of the conductive cloth; the metal interface layer (6) is fixed on the lower surface of the high heat conduction film (5) through in-situ growth;
the p-type thermoelectric arm (2) and the n-type thermoelectric arm (3) used by the thermoelectric device are polyurethane/single-walled carbon nanotube PU/SWCNT porous materials, and the thermoelectric material SWCNT is coated on the surface of the flexible PU porous material through an ultrasonic technology to promote electric-heat separation;
the specific preparation process of the p-type thermoelectric arm (2) is as follows:
weighing 20mg of SWCNT powder into a crucible, and performing heat treatment in a nitrogen atmosphere using a tube furnace; raising the temperature from room temperature to 400 ℃ within 60 min; keeping the temperature at 400 ℃ for 20 min; then naturally cooling, and taking out the SWCNT after the temperature is reduced to the room temperature;
adding the heat-treated SWCNT into 50g of ethanol solution, and performing ultrasonic dispersion for 30min to fully disperse the SWCNT solution;
the cut PU porous cube is 3X 5mm 3 Putting into the dispersed SWCNT solution, and continuing to perform ultrasonic treatment for 60 min; then taking out the PU/SWCNT blockDrying in an oven at 60 ℃ for 6h to obtain a p-type thermoelectric arm with low thermal conductivity;
the specific preparation process of the n-type thermoelectric arm (3) is as follows:
weighing 50g of ethanol and 0.1g of polyethyleneimine PEI, and stirring for 30min on a magnetic stirrer to disperse the PEI in the ethanol solution; weighing 20mg of SWCNT (Single-walled carbon nanotube) and pouring the SWCNT into a PEI-ethanol solution, and magnetically stirring for 24 hours to aminate the SWCNT; then, carrying out ultrasonic dispersion on the stirred SWCNT solution for 30min to ensure that the SWCNTs are fully dispersed in the solution;
the cut PU porous cube is 3X 5mm 3 Putting into the solution, and continuing to perform ultrasonic treatment for 60 min; then taking out the PU/SWCNT block, and drying in an oven at 60 ℃ for 6h to obtain an n-type thermoelectric arm with low thermal conductivity;
the high heat-conducting film (5) used by the thermoelectric device is polydimethylsiloxane/boron nitride-ferroferric oxide PDMS/BN-Fe 3 O 4 By synthesizing magnetic substance Fe on the surface of high heat conductive BN powder 3 O 4 Then mixing the PDMS solution with BN-Fe 3 O 4 Mixing the powders, and curing under the action of magnetic field to obtain PDMS/BN-Fe 3 O 4 Internal BN-Fe 3 O 4 Micron sheet perpendicular to PDMS/BN-Fe 3 O 4 The surface of the film is further improved by PDMS/BN-Fe 3 O 4 Out-of-plane thermal conductivity; subjecting PDMS/BN-Fe 3 O 4 While having stretchability and out-of-plane thermal conductivity.
2. An out-of-plane thermoelectric device of stretchable porous structure as claimed in claim 1 wherein: the preparation sequence comprises the steps of firstly preparing a flexible and stretchable high-thermal-conductivity film (5), growing a metal interface layer (6) on the lower surface of the high-thermal-conductivity film (5) in situ, adhering the cut bottom electrode (4) to the upper surface of the high-thermal-conductivity film (5) according to a mask plate, coating silver paste on the surface of the bottom electrode (4) according to the mask plate, fixing the p-type thermoelectric arm (2) on the silver paste at the surface fixed position of the bottom electrode (4), fixing the n-type thermoelectric arm (3) on the silver paste at the surface fixed position of the bottom electrode (4), coating the silver paste on the fixed position of the top electrode (1), and placing the top electrode (1) coated with the silver paste on the upper surfaces of the p-type thermoelectric arm (2) and the n-type thermoelectric arm (3).
3. An out-of-plane thermoelectric device of stretchable porous structure as claimed in claim 1 or 2 wherein: the thermoelectric device is formed by connecting bottom electrode, p-type thermoelectric arm, n-type thermoelectric arm and top electrode in pi-type manner, wherein the p-type thermoelectric arm and n-type thermoelectric arm are connected in series and are connected in cross, and the size of the thermoelectric arm is 3 × 3 × 5mm 3 The spacing between the thermoelectric legs was 2 mm.
4. An out-of-plane thermoelectric device of stretchable porous structure as claimed in claim 1 or 2 wherein: the electrode material used by the thermoelectric device is conductive cloth, the upper surface of the conductive cloth is interwoven yarns coated with conductive particles, and the lower surface of the conductive cloth is conductive adhesive; the conductive cloth has flexibility and deformability and conductivity; cutting the electrode size by laser engraving technique, wherein the size of the conductive cloth electrode is 8 × 3mm 2 。
5. An out-of-plane thermoelectric device of stretchable porous structure as claimed in claim 1 wherein: PDMS/BN-Fe 3 O 4 The preparation process of the film comprises the following steps:
performing surface treatment on the boron nitride BN powder by using a sodium hydroxide solution; BN particles were suspended in 5M NaOH solution at 90 ℃ for 48 hours to achieve surface attachment of hydroxide functional groups; then, carrying out suction filtration and washing by using deionized water until the pH value of the suction filtration solution at the last time is neutral; placing boron nitride hydroxide BN-OH particles in a furnace at 80 ℃ for 5 hours, cooling to room temperature, and then storing in a dryer;
next, Fe was hydrolyzed in deionized water solution 3 O 4 Adding nano particles to the surface of boron nitride; firstly, 1.5g of polyvinylpyrrolidone is dissolved in 100 ml of deionized water, and 1g of BN-OH powder is added under magnetic stirring; after 2 hours, 4 g FeCl was added to the solution 3 ·6H 2 O, then at 90 DEG CStirring for 12 hours; then, 20ml of hydrazine hydrate solution was added, and the mixture was stirred at 90 ℃ for 4 hours; finally, the product was washed with deionized water and filtered and dried under vacuum at 80 ℃ for 5 hours to remove the solvent; finally obtaining magnetic BN-Fe 3 O 4 Powder;
mixing PDMS solution with BN-Fe 3 O 4 Mixing the powder according to the weight ratio of 10:4, stirring, removing bubbles, and preparing a film with the thickness of 220 microns by using a film coating machine; then curing the mixture for 1 hour at 80 ℃ under the action of a magnetic field to obtain the flexible high-thermal-conductivity substrate PDMS/BN-Fe with boron nitride orientation distribution 3 O 4 。
6. An out-of-plane thermoelectric device of stretchable porous structure as claimed in claim 1 or 2, characterized in that: a layer of high-thermal-conductivity Cu grows on the lower surface of the flexible substrate of the thermoelectric device in situ through magnetron sputtering, and interface thermal resistance is reduced; the preparation process of the interface layer comprises the following steps:
mixing PDMS/BN-Fe 3 O 4 The film is fixed on a sample rack in the sputtering instrument; vacuumizing to the vacuum degree of 4.0 multiplied by 10 -4 When the pressure is Pa, opening the sample table autorotation electrode, introducing high-purity argon, fixing the flow of the argon to be 25sccm, and adjusting the pressure to be 1 Pa; adjusting sputtering power, pre-sputtering for 5 minutes to remove oxides or impurities on the surface of the copper target, and opening a sample baffle to sputter for 30 minutes at 20W after the glow of the target is stable; after sputtering is finished, a sputtering power supply is closed; taking out a sample PDMS/BN-Fe 3 O 4 the/Cu film is used in the next step.
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