JP7790716B2 - thermoelectric conversion module - Google Patents

Description

The present invention relates to a sheet-like thermoelectric conversion module in which thermoelectric elements are arranged across a pair of main surfaces to which a temperature difference can be applied.

A sheet-like thermoelectric conversion module is known in which multiple thermoelectric elements that utilize the Seebeck effect are arranged across a pair of main surfaces that are provided with an interface with a temperature difference and that are exposed to this temperature difference. Such thermoelectric conversion elements are commonly made up of small semiconductor thermoelectric elements formed into rectangular chips with pairs of p-type and n-type semiconductor pieces. A large number of such small semiconductor thermoelectric elements can be electrically connected together with appropriate wiring to extract a specified amount of power.

For example, Patent Document 1 discloses a thermoelectric conversion module with a cooling surface on one of the front and back sides and a heating surface on the other. This thermoelectric conversion module includes multiple thermoelectric elements that use the Seebeck effect, a pair of flexible substrates that sandwich the thermoelectric elements and form the cooling and heating surfaces, multiple inter-element electrodes provided on the opposing surfaces of the flexible substrates and electrically connecting the thermoelectric elements, and lead wires electrically connected to the end electrodes that connect the end elements located at the ends of the electrical arrangement. By providing the thermoelectric elements on the flexible substrate, the flexible substrate is given the ability to deform, allowing it to be attached to fit the shape of a heating element.

JP 2016-171230 A

However, if the sheet of a sheet-type thermoelectric conversion module is made thin to improve flexibility and deformability, a sufficient temperature difference between the pair of main surfaces cannot be achieved, resulting in a decrease in power generation. Furthermore, when considering attachment to curved surfaces of various shapes and surfaces that undergo dynamic deformation, it is necessary to provide not only flexibility but also stretchability, as well as shape stability, which allows the module to return to its original shape when the load is removed after deformation.

The present invention was made in consideration of the above-mentioned circumstances, and its purpose is to provide a thermoelectric conversion module that has flexibility, including flexibility and stretchability, high deformability, excellent shape stability, and can generate a high amount of power.

The present invention is a sheet-like thermoelectric conversion module in which thermoelectric elements are arranged across a pair of main surfaces across which a temperature difference can be applied, and in which metal wiring is provided alternately on the first and second main surfaces to electrically connect p-type and n-type thermoelectric element pieces provided across the first and second main surfaces, and at least the metal wiring on the second main surface side is a serpentine wiring, allowing the distance between the p-type and n-type thermoelectric element pieces connected to both ends to be variable, and the p-type and n-type thermoelectric element pieces are inserted into a sheet made of a rubber elastic material containing bubbles, and at least the sides of the sheet are sealed.

With these features, the sheet made of rubber elastic material and the serpentine wiring provide flexibility, including flexibility and stretchability, and high deformability, while the rubber elastic material containing air bubbles provides excellent shape stability. A sufficient temperature difference can be achieved between the pair of main surfaces, resulting in a high amount of power generation.

In the above invention, the rubber elastic body may be an elastomer sponge with open cells that connect the cells to the surface. The elastomer sponge may also have a modulus of elasticity in the range of 1 to 100 kPa. This feature allows for high power generation while maintaining flexibility and high deformability.

In the above invention, a support substrate may be provided along one of the main surfaces below the thermoelectric element and the metal wiring. The support substrate may be made of polyimide. This feature provides flexibility, high deformability, and excellent shape stability.
That is why.

The above invention may also be characterized in that it includes a chip-shaped element in which the metal wiring on the first principal surface and the p-type thermoelectric element component and the n-type thermoelectric element component on both sides of the metal wiring are sealed and integrated. This characteristic allows for a high amount of power generation while maintaining flexibility and high deformability.

In the above invention, the thermal conductivity of the elastomer sponge may be in the range of 0.01 to 0.1 W/m·K. The electrical conductivity of the metal wiring may be in the range of 1.0×10 ⁴ to 1.0×10 ⁸ S/m. The Seebeck coefficient of the p-type thermoelectric element piece may be in the range of 1 to 1000 μV/K. The Seebeck coefficient of the n-type thermoelectric element piece may be in the range of -1000 to -1 μV/K. These characteristics enable a higher power generation capacity to be obtained while maintaining flexibility and high deformability.

The above invention may be characterized in that the sheet body is sandwiched between a pair of surface sheet bodies made of a rubber elastic material with higher thermal conductivity than the sheet body. This characteristic allows for high power generation while maintaining flexibility and high deformability.

1 is a photograph showing the appearance of a thermoelectric conversion module as an example according to the present invention. 1A and 1B are a top view and a side view, respectively, of a sheet body of a thermoelectric conversion module, which is transparently displayed; FIG. 2 is a top view of a main part of the thermoelectric conversion module when a sheet body is displayed in a transparent manner. FIG. 2 is a cross-sectional view of a main part of a thermoelectric power generation module. 10 is a photograph showing a state in which a thermoelectric power generation module is deformed by hand. 1 is a photograph showing the appearance of a test specimen for a stretch durability test. 1 is a table showing the measurement results of the elastic modulus and thermal conductivity of the sheet body used for each test specimen. 1A is a graph showing the results of a stretch durability test, and FIG. 1B is a graph showing the resistance change rate indicating breakage in the same test. This is a photograph of the exterior of a test specimen used in power generation performance tests. 1 is a graph showing the relationship between heat source temperature and open-circuit voltage. 10 is a graph showing the amount of power generated in a test specimen having a flexible rubber sponge sealing structure.

Below, a thermoelectric conversion module, which is one embodiment of the present invention, will be described using Figures 1 to 4.

As shown in Figures 1 and 2, the thermoelectric conversion module 10 comprises a plurality of thermoelectric elements 1 arranged along the main surface of a sheet body 2, with each element penetrating the sheet body 2. Each thermoelectric element 1 is electrically connected by metal wiring 3, and is connected to a terminal electrode 4 for extracting power to the outside. Here, an example is shown in which 30 thermoelectric elements 1 are arranged in 5 columns and 6 rows, all of which are connected in series.

Each thermoelectric element 1 is oriented and positioned so that it generates electromotive force due to the temperature difference between the front and back sides of the sheet 2. Furthermore, as described above, the thermoelectric elements 1 are inserted into the sheet 2, and at least their sides are enclosed by the sheet 2. By creating a temperature difference between the high-temperature and low-temperature sides of the pair of main surfaces of the sheet 2, the thermoelectric elements 1 positioned across both main surfaces generate electricity, resulting in a sheet-like thermoelectric conversion module 10.

The sheet body 2 is made of a rubber elastic material containing air bubbles, which provides excellent thermal insulation between the two main surfaces, as well as bendability (flexibility) in the direction of bending the main surfaces and stretchability in the direction along the main surfaces. In particular, the sheet body 2 preferably has open cells, with the interiors of the cells connected to the surface. By using open cells, the Young's modulus of the thermoelectric conversion module 10 can be reduced compared to when a sheet body with closed cells is used. In other words, open cells are preferable because they can further improve stretchability and bendability. For example, an elastomer sponge such as a flexible silicone rubber sponge can be suitably used as this sheet body 2.

It is preferable that the modulus of elasticity of the sheet body 2 be selected from the range of 1 to 100 kPa. In particular, if the modulus of elasticity of the sheet body 2 is low, excessive stress is not applied to the internal wiring 3 when the thermoelectric conversion module 10 is deformed, and inhibition of deformation of the wiring 3 can be suppressed. In other words, a low modulus of elasticity of the sheet body 2 is preferable, as it not only increases the deformability of the thermoelectric conversion module but also contributes to an improved lifespan.

Furthermore, it is preferable that the thermal conductivity of the sheet member 2 be selected from the range of 0.01 to 0.1 W/m·K. In particular, by keeping the thermal conductivity low, it is possible to maintain a large temperature difference between the two main surfaces of the thermoelectric conversion module, thereby increasing the amount of power generation.

As shown in FIG. 3 , the wiring 3 is a serpentine wiring made of a metal thin film that can change the distance between the thermoelectric elements 1. Such serpentine wiring allows the thermoelectric elements to easily follow the expansion and bending of the thermoelectric conversion module 10. Copper, which has a relatively low electrical resistance and is inexpensive, is preferably used as the material for the wiring 3. By using copper foil for the wiring 3, the width of the wiring 3 can be increased, and the electrical resistance of the wiring can be reduced while maintaining high deformability against bending. In other words, the internal resistance of the thermoelectric conversion module 10 can be reduced, and the amount of power generation can be increased. It is also preferable that the electrical conductivity of the wiring 3 is selected from the range of 1.0×10 ⁴ to 1.0×10 ⁸ S/m. In particular, a higher electrical conductivity is preferable, as it allows the internal resistance of the thermoelectric conversion module 10 to be reduced.

Referring also to Figure 4, the thermoelectric element 1 can be, for example, a chip-shaped element with a π-type structure, in which two types of thermoelectric element pieces, a p-type semiconductor piece 11p and an n-type semiconductor piece 11n, are sealed with a sealing material 15 and connected at their low-temperature sides to form an integrated unit. In the case of semiconductors, a Bi-Te thermoelectric material, for example, is preferably used to achieve high thermoelectric conversion efficiency. The sealing material 15 can be an insulating material such as epoxy resin. The p-type semiconductor piece 11p and the n-type semiconductor piece 11n are arranged so as to be separated on the left and right by the sealing material 15, and their low-temperature sides (upper side of the drawing) are connected to each other by a low-temperature electrode 14 made of copper. The low-temperature electrode 14 made of copper is connected via low-melting-point solder 13 to a high-temperature electrode 12 made of, for example, Ni, attached to the top surfaces of the p-type semiconductor piece 11p and the n-type semiconductor piece 11n. On the other hand, on the high-temperature side (the lower side of the drawing), wiring 3 is connected via low-melting-point solder 13 to high-temperature electrodes 12 attached to the undersides of the p-type semiconductor piece 11p and the n-type semiconductor piece 11n, and they are separated by a sealing material 15.

The p-type and n-type semiconductor pieces do not necessarily have to be encapsulated in a chip-type element, but may be individually arranged. For example, the p-type and n-type semiconductor pieces are arranged across both the high-temperature and low-temperature main surfaces, and the p-type and n-type semiconductor pieces are electrically connected alternately. In this case, such connections are made using metal wiring provided alternately on both main surfaces. The metal wiring on at least one of the main surfaces is made serpentine. In other words, a thermoelectric conversion module is made using p-type and n-type semiconductor pieces, and the distance between the p-type and n-type semiconductor pieces connected to both ends of the serpentine wiring is variable. This also results in a thermoelectric conversion module similar to that using the chip-type element described above. The electrical wiring on both main surfaces may be made serpentine, making the distance between all of the p-type and n-type semiconductor pieces variable.

It is also preferable that the Seebeck coefficients of the p-type semiconductor piece 11p and the n-type semiconductor piece 11n are each selected from the range of 1 to 1000 μV/K. In both cases, a large Seebeck coefficient is preferable, as it allows for greater power generation.

Furthermore, the wiring 3 and thermoelectric element 1 are provided with a support substrate 17 adhered to their lower portions by an adhesive layer 16. The support substrate 17 is arranged along the high-temperature side of the main surface of the sheet member 2, and preferably has flexibility and shape stability. Polyimide can be suitably used as such a support substrate 17. The two-layer structure of the polyimide support substrate 17 and the copper foil wiring 3 can give the thermoelectric conversion module 10 flexibility, high deformability, and excellent shape stability. The support substrate 17 also contributes to the shape stability of the thermoelectric conversion module 10 during its fabrication.

The thermoelectric elements 1 and wiring 3 are placed inside the sheet 2, completely covered with an insulating film 18. Considering the possibility that the thermoelectric elements 1 and wiring 3 may come into contact beyond the bubbles when the sheet 2, which has open cells, is bent excessively, the insulating film 18 can prevent short circuits caused by such contact. Furthermore, using a paraxylylene-based polymer as the insulating film 18 is preferable as it also acts as a protective film against the humidity of the outside air.

The thermoelectric conversion module 10 further includes a pair of surface sheets 2a and 2b, which sandwich the entire module. The surface sheets 2a and 2b are preferably made of a rubber elastic material with higher thermal conductivity than the sheet 2, and by increasing the thermal conductivity in the direction along the main surface, a high temperature difference can be maintained between the high-temperature side and the low-temperature side of the thermoelectric element 1. From the perspective of thermal conductivity, it is preferable that the surface sheets 2a and 2b do not contain air bubbles. For example, the surface sheets 2a and 2b are preferably made of a silicone elastomer mixed with a material with high thermal conductivity, such as silver flakes, in a sheet shape, which further increases the thermal conductivity.

[Manufacturing test]
Next, the results of a test conducted to evaluate the performance of the actually manufactured thermoelectric conversion module 10 will be described with reference to FIGS.

As shown in Figure 5, a thermoelectric conversion module 10 was actually manufactured and a deformation test was conducted. The thermoelectric conversion module 10 had the same structure as that shown in the previous drawing, and the sheet body 2 was made of a flexible silicone rubber sponge with open cells. The wiring 3 was made of copper foil, the support substrate 17 was made of polyimide, and the insulating film 18 was made of a paraxylylene-based polymer. A chip-type thermoelectric element made of a Bi-Te-based semiconductor was used for the thermoelectric element 1. The surface sheet bodies 2a and 2b were made of silicone rubber, with no other materials mixed in.

The thermoelectric conversion module 10, which has a roughly rectangular, flat plate shape, was bent as shown in Figure 1(a), pulled as shown in Figure 1(b), and randomly rolled and folded as shown in Figure 1(c). After each deformation was applied with fingers, the deforming force was removed. The module then returned to its original roughly rectangular, flat plate shape as shown in Figure 1(d). In other words, it was found that the thermoelectric conversion module 10 has excellent shape stability while possessing flexibility, including flexibility and stretchability, and high deformability.

Next, three types of test specimens were fabricated by changing the material of the thermoelectric conversion module sheet, and comparative tests were conducted. The three types of test specimens were: Test specimen Ta, in which the sheet material was hard silicone rubber; Test specimen Tb, in which the sheet material was soft silicone rubber; and Test specimen Tc, in which the sheet material was soft silicone rubber sponge, a rubber elastic body containing air bubbles. The other materials were the same as those used in the deformation test described above.

First, we created specimens Ta to Tc for the expansion and contraction durability test, each consisting of three thermoelectric elements, as shown in Figure 6. The symbols Ta to Tc are also used commonly for the specimens for the power generation performance test (see Figure 9), which will be described later.

As shown in Figure 7, the elastic modulus and thermal conductivity of each sheet used for specimens Ta to Tc were measured. The results showed that the hard silicone rubber used for specimen Ta had a higher elastic modulus of 1.32 MPa than the other two, while the soft silicone rubber sponge used for specimen Tc had the lowest. In other words, it was estimated that specimen Tc had the greatest deformability for a given stress. The hard silicone rubber used for specimen Ta and the soft silicone rubber used for specimen Tb had high thermal conductivities of 0.16 and 0.20 W/m·K, respectively, while the soft silicone rubber sponge used for specimen Tc had a low thermal conductivity of 0.08 W/m·K. In other words, a thermoelectric conversion module using soft silicone rubber sponge is believed to be able to maintain a high temperature difference between the high-temperature side and the low-temperature side, resulting in high power generation.

Figure 8(a) shows the results of a stretching durability test using specimens Ta (made of hard silicone rubber), Tb (made of soft silicone rubber), and Tc (made of soft silicone rubber sponge). In the stretching durability test, the specimens were attached to a tensile testing machine and repeatedly subjected to tensile deformation to achieve a predetermined elongation rate while measuring the internal resistance of the specimen as a thermoelectric conversion module using the four-terminal method. The number of repetitions required for failure was recorded. The rate of change in internal resistance was monitored during the test, and failure was determined when the rate of change in internal resistance reached 100% or greater. In other words, failure was determined as electrical insulation. For example, Figure 8(b) shows the rate of change in internal resistance at plotted point P. In this example, when the elongation rate for specimen Ta, made of hard silicone rubber, was set to 20%, the rate of change in internal resistance suddenly increased to 100% at 78 cycles (repetitions), leading to a failure determination.

In the stretch durability test, specimen Ta, which used hard silicone rubber, was found to have the lowest durability, while specimen Tc, which used soft silicone rubber sponge, was found to have the highest durability. For specimen Tc, the maximum elongation was set to 125%, and the number of repetitions until breakage at an elongation rate of 50% was 1,025. Note that the maximum elongation rate was defined as the elongation rate when stretched until breakage occurred after a single tensile deformation.

Figure 9 shows the appearance of test specimens Ta to Tc used for the power generation performance test. Each test specimen had 30 thermoelectric elements arranged in 5 columns and 6 rows. The high-temperature side of each test specimen was placed in close contact with the hot plate, which served as the heat source, and the low-temperature side was placed so that it was exposed to the room air, creating a temperature difference. The surface temperature of the hot plate was measured as the heat source temperature, and the open-circuit voltage of each specimen was measured. Each test specimen was also placed on the hot plate, and the power generation amount was measured while measuring the temperatures of its top and bottom surfaces.

As shown in Figure 10, at heat source temperatures between 60 and 100°C, the open-circuit voltage was greatest for test specimen Tc, which used soft silicone rubber sponge, while test specimen Ta, which used hard silicone rubber, and test specimen Tb, which used soft silicone rubber, had similar values. This is thought to be because a temperature difference corresponding to the difference in thermal conductivity (see Figure 7) described above occurred between the high-temperature side and the low-temperature side. In other words, it is thought that a high thermal conductivity reduces the temperature difference and reduces the open-circuit voltage, and a low thermal conductivity increases the temperature difference and increases the open-circuit voltage.

Figure 11 shows the power generation capacity of test specimen Tc, which uses a flexible silicone rubber sponge. It was confirmed that the power generation capacity can be increased by increasing the temperature difference between the high-temperature side (bottom surface) and the low-temperature side (top surface). In this case, a maximum power generation capacity of 32.2 μW was achieved at a temperature difference of 8.6°C.

As described above, it was found that test specimen Tc, which uses a flexible silicone rubber sponge, has flexibility, including flexibility and stretchability, and high deformability, while also producing a high amount of power generation.

The above describes embodiments of the present invention and variations based thereon, but the present invention is not necessarily limited to these, and those skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the appended claims.

REFERENCE SIGNS LIST 1 thermoelectric element 2 sheet body 3 wiring 10 thermoelectric conversion module

Claims (10)

A sheet-like thermoelectric conversion module in which thermoelectric elements are arranged across a pair of main surfaces that can be given a temperature difference,
metal wiring is provided alternately on the first main surface side and the second main surface side so as to electrically connect alternately p-type thermoelectric element components and n-type thermoelectric element components provided across a first main surface and a second main surface of the main surfaces,
The metal wiring on at least the second main surface side is formed as a meandering wiring, and the distance between the p-type thermoelectric element component and the n-type thermoelectric element component connected to both ends of the meandering wiring is variable;
the p-type thermoelectric element pieces and the n-type thermoelectric element pieces are inserted into a sheet made of a rubber elastic material containing bubbles, and at least the side surfaces of the sheet are sealed;
The thermoelectric conversion module is characterized in that the rubber elastic body is an elastomer sponge having open cells that connect the cells to the surface . 2. The thermoelectric conversion module according to claim 1 , wherein the modulus of elasticity of the elastomer sponge is within a range of 1 to 100 kPa. The thermoelectric conversion module described in claim 1, characterized in that a support substrate is provided on the metal wiring along one of the main surfaces. 4. The thermoelectric conversion module according to claim 3 , wherein the support substrate is made of polyimide. The thermoelectric conversion module of claim 1, characterized in that it includes a chip-shaped element in which the metal wiring on the first main surface and the p-type thermoelectric element piece and the n-type thermoelectric element piece on both sides of the metal wiring are sealed and integrated. 2. The thermoelectric conversion module according to claim 1 , wherein the thermal conductivity of the elastomer sponge is within a range of 0.01 to 0.1 W/m·K. 2. The thermoelectric conversion module according to claim 1, wherein the electrical conductivity of the metal wiring is in the range of 1.0×10 ⁴ to 1.0×10 ⁸ S/m. The thermoelectric conversion module described in claim 1, characterized in that the Seebeck coefficient of the p-type thermoelectric element piece is in the range of 1 to 1000 μV/K. The thermoelectric conversion module described in claim 1, characterized in that the Seebeck coefficient of the n-type thermoelectric element piece is in the range of -1000 to -1 μV/K. 10. The thermoelectric conversion module according to claim 1 , wherein the thermoelectric conversion module is sandwiched between a pair of surface layer sheets made of a rubber elastic material having a higher thermal conductivity than the sheet body.