Method for producing thermoelectric conversion element and thermoelectric conversion element

Abstract

A thermoelectric conversion element according to the present invention is constituted by laminating an electrode material that contains an alloy of copper (Cu) and nickel (Ni) on a thermoelectric conversion layer that is made of a thermoelectric conversion material which contains magnesium (Mg) and antimony (Sb). Further, a production method according to the present invention is for producing a thermoelectric conversion element that has a thermoelectric conversion layer and an electrode layer which is laminated on the thermoelectric conversion layer, said production method comprising: a first sintering step for sintering a thermoelectric conversion material to form a pellet; a lamination step for forming a layer of an electrode material on the pellet; and a second sintering step for heat-treating the pellet on which the layer of the electrode material has been formed, wherein the first sintering step is executed at a temperature higher than a reaction start temperature at which the electrode material starts to react with the thermoelectric conversion material, and the second sintering step is executed at a temperature lower than the reaction start temperature. The magnesium antimony (MgSb)-based thermoelectric conversion element has both low contact resistance and affinity for solder.

Description

Method for manufacturing a thermoelectric conversion element and the thermoelectric conversion element

[0001] The present invention relates to a method for manufacturing a thermoelectric conversion element and the thermoelectric conversion element, and is particularly suitable for use in a thermoelectric conversion element that also takes into consideration good electrical connection with circuit wiring.

[0002] As research into the efficient use of energy, including energy conservation and the use of renewable energy, progress is being made, and thermoelectric elements are attracting attention as devices that can directly convert waste thermal energy into electrical energy and make it possible to reuse it.

[0003] n-type magnesium antimony (Mg ３ Sb ２ By adding copper (Cu) to a thermoelectric material based on copper (Cu), a thermoelectric material has been developed that achieves both reduced thermal conductivity and improved charge mobility (see Non-Patent Document 1). However, in order to extract the converted electrical energy, the thermoelectric material needs to be connected to circuit wiring.

[0004] Non-Patent Document 2 describes n-type magnesium antimony bismuth (Mg ３ Sb １．５ Bi ０．５ As an interface material to be laminated on the thermoelectric conversion layer of the ferroelectric material, a ternary alloy mainly composed of iron (Fe), iron magnesium chromium (Fe ７ Mg ２ Cr) and iron magnesium titanium (Fe ７ Mg ２ According to Fig. 4 of the same document, when these materials are used as the interface layer, the specific contact resistivity can be reduced to 10 μΩcm. ２ It is said that it is possible to achieve a shear strength of 30 MPa or more while keeping the shear strength below 30 MPa.

[0005] Patent Document 1 discloses a technique for reducing electrical resistance in a thermoelectric conversion element using a magnesium antimony bismuth telluride (MgSbBiTe)-based thermoelectric conversion material. When electrode layers made of a copper (Cu) and zinc (Zn) alloy are formed on both ends of a thermoelectric conversion layer, which is an MgSbBiTe-based sintered body, using a spark plasma sintering apparatus, an intermediate layer is formed between the thermoelectric conversion layer and the electrode layer. It is said that a thermoelectric conversion element with significantly lower resistivity was realized compared to a comparative example in which nickel (Ni) electrode layers were formed by electrolytic plating on both ends of a thermoelectric conversion layer, which is an MgSbBiTe-based sintered body.

[0006] In the invention disclosed in Patent Document 2, a thermoelectric conversion element using an MgSbBiTe-based thermoelectric conversion material has transitional layers and electrode layers formed on both ends of a thermoelectric conversion layer. The transition layers are made of an alloy of copper (Cu) and titanium (Ti) and / or magnesium (Mg), and the electrode layers are made of Cu and / or Ni. In each example, a temperature difference of 50°C or more was measured when 12 V was applied.

[0007] In the invention disclosed in Patent Document 3, Mg ３ Sb ２ As an interface layer material for a thermoelectric conversion element using a base conversion material, the chemical formula Fe ｘ Mg ｙ A ｚ (where A is a transition metal, x=3-10, y=1-5, z=1-3) is preferred, and in the examples, ２ The following low contact resistances were reportedly measured:

[0008] US Publication US2020 / 0006616 International Publication WO2021 / 036544 Chinese Publication CN115020577A

[0009] Z. Liu, et al. , “Demonstration of Ultrahigh Thermoelectric Efficiency of ~7.3% in Mg3Sb2 / MgAgSb Module for Low Temperature Energy Harvesting”, Joule 5, May 19, 2021, pp. 1196-1208X. Wu, et al. , “A general design strategy for thermoelectric interface materials in n-type Mg3Sb1.5Bi0.5 single leg used in Acta Materialia, 226 (2022) 117616

[0010] As a result of the inventor's investigation of Patent Documents 1, 2, and 3 and Non-Patent Documents 1 and 2, it was found that there existed the following new problems.

[0011] As shown in Non-Patent Document 2 and Patent Document 3, by providing an alloy containing iron as the main component in the interface layer of an MgSb-based thermoelectric conversion layer, it is possible to achieve a resistance of 10 μΩcm ２ However, since alloys primarily composed of iron have low affinity with solder, it is difficult to stably form low-resistance, highly reliable connections with circuit wiring. In this specification, affinity with solder means ease of soldering, and more specifically, means that the wettability of molten solder is high and the wet solder easily spreads.

[0012] On the other hand, the interface layers of the thermoelectric conversion elements shown in Patent Documents 1 and 2 have high affinity with solder, and are therefore expected to be able to stably form low-resistance, highly reliable connections with circuit wiring. The thermoelectric conversion element described in Patent Document 1 has electrode layers made of a CuZn alloy formed on both ends of the thermoelectric conversion layer via an intermediate layer made of CuZnMg. The thermoelectric conversion element described in Patent Document 2 has transitional layers made of an alloy of Cu and Ti and / or Mg and Cu and / or Ni electrode layers formed on both ends of the thermoelectric conversion layer.

[0013] However, the present inventors have found that the interface layer materials disclosed in Patent Documents 1 and 2 have a problem in that they have high contact resistance with the thermoelectric conversion layer. Patent Document 1 reports resistance values ​​of 16.4 mΩ and 7.05 mΩ and resistivities of 50.2 μΩm and 21.6 μΩm in two examples, but does not report the value of contact resistance. The contact resistance of the interface between electrode layers made of various materials and MgSb-based thermoelectric conversion layers is reported in the above-mentioned Non-Patent Document 2. Fig. 4 of the same document shows a contact resistance of about 80 Ωcm when Cu is used as the interface layer material. ２ It has been reported that, in this way, the electrode layer containing Cu, which has a high affinity with solder, as its main component, does not allow the contact resistance between the thermoelectric conversion layers to be sufficiently low.

[0014] From the above investigation, the inventors have determined that the ２ We have discovered a new challenge: achieving both low contact resistance and solder affinity.

[0015] The object of the present invention is to achieve both low contact resistance and solder affinity in an MgSb-based thermoelectric conversion element, and one of the objects is to provide a manufacturing method that can solve this problem, and another object is to identify an electrode material that can solve this problem.

[0016] According to one embodiment, the invention is as follows: That is, a method for manufacturing a thermoelectric conversion element having a thermoelectric conversion layer and an electrode layer laminated on the thermoelectric conversion layer, the method including: a first sintering step of sintering a thermoelectric conversion material to form a pellet; a laminating step of forming an electrode material layer on at least one of two opposing surfaces of the pellet; and a second sintering step of heat-treating the pellet on which the electrode material layer has been formed, the first sintering step being performed at a temperature higher than a reaction initiation temperature at which the electrode material begins to react with the thermoelectric conversion material, and the second sintering step being performed at a temperature lower than the reaction initiation temperature. According to another embodiment, the invention is as follows: A thermoelectric conversion element having a thermoelectric conversion layer and first and second electrode layers laminated on either side of the thermoelectric conversion layer, the thermoelectric conversion layer being made of a thermoelectric conversion material containing magnesium (Mg) and antimony (Sb), and the first and / or second electrode layers being made of an electrode material containing an alloy of copper (Cu) and nickel (Ni).

[0017] The effects obtained by the embodiment are briefly explained as follows: In other words, in an MgSb-based thermoelectric conversion element, both low contact resistance and affinity with solder can be achieved.

[0018] FIG. 1 is an explanatory diagram showing an example of the configuration of a thermoelectric conversion element of the present invention. FIG. 2 is a flowchart showing an example of a manufacturing method for a thermoelectric conversion element of the present invention. FIG. 3 is a graph showing a sintering curve representing experimental results. FIG. 4A is a cross-sectional SEM (scanning electron microscope) photograph showing the interface between an MgSb-based thermoelectric conversion layer and a cupronickel electrode layer. FIG. 4B is a cross-sectional SEM photograph showing the interface between an MgSb-based thermoelectric conversion layer and an Fe electrode layer. FIG. 4C is a cross-sectional SEM photograph showing the interface between an MgSb-based thermoelectric conversion layer and a stainless steel electrode layer. FIG. 5 is a graph showing the measurement results of electrode contact resistance in a thermoelectric conversion element prototyped as an example. FIG. 6 is a graph showing the measurement results of thermoelectric conversion efficiency of a thermoelectric conversion element prototyped as an example.

[0019] 1. Overview of the Embodiments First, an overview of the representative embodiments disclosed in the present application will be described. Reference numerals in parentheses in the drawings used in the overview of the representative embodiments merely illustrate components included in the concept of the components to which they are attached.

[0020] [1] Thermoelectric conversion element having an MgSb-based thermoelectric conversion layer and a CuNi alloy electrode layer (FIG. 1) A representative embodiment disclosed in the present application is a thermoelectric conversion element (1) having a thermoelectric conversion layer (2) and an electrode layer (3) laminated on the thermoelectric conversion layer, and is configured as follows: The thermoelectric conversion layer is made of a thermoelectric conversion material containing Mg and Sb, and the electrode layer is made of an electrode material containing an alloy of Cu and Ni.

[0021] This allows the MgSb-based thermoelectric conversion element to achieve both low contact resistance and solder affinity. The Cu—Ni alloy (cupronickel) can form a low-resistance ohmic contact with the MgSb-based thermoelectric conversion layer and has high solder affinity.

[0022] [2] When the thermoelectric conversion material is MgSbBi: In the thermoelectric conversion element according to [1], the thermoelectric conversion material further contains bismuth (Bi), and Mg ３＋ｖ Sb ｗ Bi ｘ (where 0.1<v<0.3, 1.35<w<1.65, 0.45<x<0.55).

[0023] This allows for both low contact resistance and solder affinity even in MgSbBi thermoelectric materials, i.e., Sb-rich MgSb-based thermoelectric elements. However, this does not exclude Bi-rich cases (2.7<v<3.3, 0.45<w<0.55, 1.35<x<1.65). Furthermore, by adding an excess of Mg, as in [2], the thermoelectric element can be made to behave as an n-type.

[0024] [3] When the thermoelectric conversion material is MgSbBTe: In the thermoelectric conversion element according to [1], the thermoelectric conversion material further contains Bi and tellurium (Te), and Mg ３＋ｖ Sb ｗBi ｘ Te ｙ (where 0.1<v<0.3, 1.35<w<1.65, 0.44<x<0.54, 0.001<y<0.011). This makes it possible to achieve both low contact resistance and affinity with solder even when the thermoelectric conversion material is MgSbBiTe.

[0025] [4] When the thermoelectric conversion material is MgSbBiTeCu: In the thermoelectric conversion element according to [1], the thermoelectric conversion material further contains Bi, Te, and Cu, and Mg ３＋ｖ Sb ｗ Bi ｘ Te ｙ Cu ｚ (where 0.1<v<0.3, 1.35<w<1.65, 0.43<x<0.53, 0.001<y<0.011, 0.009<z<0.011). This makes it possible to achieve both low contact resistance and affinity with solder even when the thermoelectric conversion material is MgSbBiTeCu.

[0026] [5] Method for manufacturing a thermoelectric conversion element including a two-step sintering process (FIG. 2) A representative embodiment disclosed in the present application is a method for manufacturing a thermoelectric conversion element having a thermoelectric conversion layer and an electrode layer laminated on the thermoelectric conversion layer, and is configured to include the following steps. First sintering step (S2): Sintering a thermoelectric conversion material to form a pellet. Laminating step (S3): Laminating an electrode material on at least one of two opposing surfaces of the pellet. Second sintering step (S4): Heat-treating the pellet on which the electrode material layer has been formed. Here, the first sintering step is performed at a temperature higher than the reaction initiation temperature at which the electrode material starts to react with the thermoelectric conversion material, and the second sintering step is performed at a temperature lower than the reaction initiation temperature.

[0027] This makes it possible to manufacture a thermoelectric conversion element that achieves both low contact resistance and solder affinity. This is because by selecting a material with high solder affinity for the electrode layer, the sintering temperature at which low-resistance ohmic contact can be formed with the thermoelectric conversion layer can be determined independently of the optimum temperature for sintering the thermoelectric conversion layer. It should be noted that the thermoelectric conversion material of the present invention is not limited to MgSb-based materials. For any thermoelectric conversion material, a material with high solder affinity can be selected for the electrode layer, and the optimum sintering temperature can be set for each.

[0028] [6] The method for manufacturing a thermoelectric conversion element according to [5], wherein the second sintering step is performed at a temperature equal to or lower than the temperature at which the Cu-Ni alloy starts to react with the MgSb-based thermoelectric conversion material, the thermoelectric conversion material containing Mg and Sb, the electrode material containing a Cu-Ni alloy, and the reaction initiation temperature is the temperature at which a reaction between the thermoelectric conversion material and Cu and / or Ni starts. This makes the electrode layer of Cu-Ni alloy (cupronickel) compatible with solder and allows for the formation of a low-resistance ohmic contact with the MgSb-based thermoelectric conversion layer, so that the MgSb-based thermoelectric conversion element can achieve both low contact resistance and affinity with solder.

[0029] [7] In the case where the thermoelectric conversion material is MgSbBiTeCu, the method for producing a thermoelectric conversion element according to [6] is characterized in that the thermoelectric conversion material is Mg ３＋ｖ Sb ｗ Bi ｘ Te ｙ Cu ｚ (However, 0.1<v<0.3, 1.35<w<1.65, 0.43<x<0.53, 0.001<y<0.011, 0.009<z<0.011) This makes it possible to manufacture an MgSb-based thermoelectric conversion element that has both low contact resistance and affinity with solder, even when the thermoelectric conversion material is MgSbBiTeCu.

[0030] 2. Details of the embodiment The embodiment will be described in further detail.

[0031] 1 is an explanatory diagram showing an example of the configuration of a thermoelectric conversion element 1 of the present invention. The thermoelectric conversion element 1 is a thermoelectric conversion element including an MgSb-based thermoelectric conversion layer and a CuNi alloy electrode layer.

[0032] That is, the thermoelectric conversion element 1 includes a thermoelectric conversion layer 2 and electrode layers 3 laminated on the thermoelectric conversion layer 2. The thermoelectric conversion layer 2 is made of a thermoelectric conversion material containing Mg and Sb, and the electrode layers 3 are made of an electrode material containing an alloy of Cu and Ni. The electrode layers 3 may be laminated so as to sandwich the upper and lower surfaces of the thermoelectric conversion layer 2, which has been sintered into a pellet shape, for example.

[0033] This allows the MgSb-based thermoelectric conversion element to achieve both low contact resistance and solder affinity. The Cu-Ni alloy (cupronickel) can form a low-resistance ohmic contact with the MgSb-based thermoelectric conversion layer and has high solder affinity. If only one surface is soldered to the circuit wiring, the cupronickel electrode layer 3 is formed only on that surface, and the other surface may be electrically connected separately.

[0034] The thermoelectric conversion layer 2 contains bismuth (Bi) in addition to Mg and Sb, and Mg ３＋ｖ Sb ｗ Bi ｘ (wherein 0.1<v<0.3, 1.35<w<1.65, 0.45<x<0.55), and further contains tellurium (Te), and Mg ３＋ｖ Sb ｗ Bi ｘ Te ｙ (where 0.1<v<0.3, 1.35<w<1.65, 0.44<x<0.54, 0.001<y<0.011). Here, by increasing the Mg composition in excess of the stoichiometric ratio of 3 to, for example, 3.1 to 3.3, the behavior of the thermoelectric conversion layer can be adjusted to n-type.

[0035] The thermoelectric conversion layer 2 contains Bi, Te, and Cu in addition to Mg and Sb. ３＋ｖ Sb ｗ Bi ｘ Te ｙ Cuｚ (wherein 0.1<v<0.3, 1.35<w<1.65, 0.43<x<0.53, 0.001<y<0.011, 0.009<z<0.011) is more preferable.

[0036] [Embodiment 2] Fig. 2 is a flowchart showing an example of a method for manufacturing a thermoelectric conversion element of the present invention. The manufacturing method of the present invention is a method for manufacturing a thermoelectric conversion element having a thermoelectric conversion layer and an electrode layer laminated on the thermoelectric conversion layer, and is configured to include the following steps. Note that the thermoelectric conversion layer is not limited to the thermoelectric conversion material containing Mg and Sb exemplified in Embodiment 1.

[0037] Preparation step (S1): Prepare a thermoelectric conversion material. The substances that make up the thermoelectric conversion material are prepared in accordance with the desired stoichiometric ratio. The prepared materials are mixed and processed into powder using a grinder. First sintering step (S2): The prepared thermoelectric conversion material is placed in, for example, a graphite crucible and sintered at high pressure and high temperature to form a pellet. The pellet is, for example, cylindrical. Layering step (S3): Form a layer of electrode material on the pellet. For example, the pellet is sandwiched between powdered electrode material from above and below and filled into a graphite crucible, thereby layering the electrode material on the pellet. Second sintering step (S4): The pellet with the layered electrode material is heat-treated.

[0038] Here, the first sintering step (S2) is carried out at a temperature higher than the reaction initiation temperature at which the electrode material starts to react with the thermoelectric conversion material, and the second sintering step (S4) is carried out at a temperature lower than the reaction initiation temperature.

[0039] This makes it possible to manufacture a thermoelectric conversion element that achieves both low contact resistance and solder affinity, because by selecting a material with high solder affinity for the electrode layer, the sintering temperature at which a low-resistance ohmic contact can be formed with the thermoelectric conversion layer can be determined independently of the optimum temperature for sintering the thermoelectric conversion layer.

[0040] It is preferable that the thermoelectric conversion layer is formed of an MgSb-based thermoelectric conversion material and that an electrode material of cupro-nickel (Cu—Ni alloy) is laminated thereon. In this case, the reaction initiation temperature is the temperature at which the reaction between the MgSb-based thermoelectric conversion material and the cupro-nickel begins. The cupro-nickel electrode layer not only forms a low-resistance ohmic contact with the MgSb-based thermoelectric conversion layer, but also has solder affinity and is easy to solder to external circuit wiring, so that the MgSb-based thermoelectric conversion element can achieve both low contact resistance and solder affinity.

[0041] The reaction initiation temperature may be determined, for example, by referring to a sintering curve. Fig. 3 is a graph showing the sintering curve obtained as an experimental result. The horizontal axis represents temperature, and the vertical axis represents the displacement of the sample.

[0042] When the temperature is gradually increased from room temperature, an inflection point is observed around 575°C, where the change in displacement per unit temperature change suddenly increases. This temperature is thought to be the starting point for the reaction between the cupronickel (Cu-Ni alloy) electrode material and the MgSb-based thermoelectric conversion material. When the temperature is further increased, the original slope returns at around 585°C, and the slope gradually increases until the cupronickel melts when the temperature exceeds around 750°C. Even if the temperature is subsequently lowered, the displacement does not return to its original state.

[0043] When the thermoelectric conversion layer is formed of an MgSb-based thermoelectric conversion material, a sintering temperature of approximately 750°C is suitable. However, the above sintering curve shows that if Cu is included in the electrode material, a reaction with the thermoelectric conversion material may begin, and even melt.

[0044] In the manufacturing method of the second embodiment, in the example of the electrode material of the above-mentioned MgSb-based thermoelectric conversion material and cupro-nickel (Cu—Ni alloy), the first sintering step (S2) sinters the thermoelectric conversion layer, so the sintering temperature is set to 750° C., and the second sintering step (S4) mainly sinters the electrode layer, so it is understood that the sintering temperature should be kept below 575° C., which is the reaction start temperature.

[0045] As described above, MgSb-based thermoelectric conversion materials include Mg ３＋ｖ Sb ｗ Biｘ Te ｙ Cu ｚ (where 0.1<v<0.3, 1.35<w<1.65, 0.43<x<0.53, 0.001<y<0.011, 0.009<z<0.011) and cupronickel (Cu—Ni alloy) are suitable electrode materials. This makes it possible to manufacture an MgSb-based thermoelectric conversion element that has both low contact resistance and affinity with solder, even when the thermoelectric conversion material is MgSbBiTeCu.

[0046] The present invention will now be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples.

[0047] Example 1 As an example of the present invention, the present inventors have ３．２ Sb １．５ Bi ０．４９ Te ０．０１ Cu ０．０１ On both sides of the thermoelectric conversion layer, Cu ７０ Ni ３０ A thermoelectric conversion element was prototyped with electrode layers stacked, and the contact resistance was 5.1 μΩcm. ２ At a temperature difference of 273 K, the conversion efficiency is 8%, and the maximum output power density at a temperature difference of 273 K is 0.94 W cm －２ The results obtained were as follows.

[0048] [Prototype Method] Preparation step (S1): Mg (99.95%, Sigma-Aldrich), Sb (99.999%, 5N Plus), Bi (99.999%, 5N Plus), Te (99.999%, 5N Plus), and Cu (99.9995%, Sigma-Aldrich) were weighed and prepared according to a predetermined stoichiometric ratio. The prepared materials were pulverized for 5 hours using a SPEX SamplePrep 8000D ball mill, mixed, and processed into a powder.

[0049] First sintering step (S2): The powdered material was filled into a graphite crucible with a diameter of 10 mm, and the sample was heated at 100 K / min using a spark plasma sintering device SPS-1080 manufactured by SPS SYNTEX, and sintered at a temperature of 1023 K and a pressure of 60 MPa for 5 minutes. The thickness of the obtained sintered body was approximately 2.9 mm.

[0050] Lamination step (S3) and second sintering step (S4): The obtained sintered body was sandwiched between cupronickel powder (99.9%, manufactured by Nilaco), and the sample was heated at 100 K / min using the same SPS SYNTEX spark plasma sintering device SPS-1080, and sintered at a temperature of 773 K and a pressure of 60 MPa for 10 minutes. The thickness of the obtained sintered body was approximately 4.4 mm, which was the original thickness of 2.9 mm plus 0.75 mm on each of the front and back surfaces.

[0051] As a comparative example, Mg ３．２ Sb １．５ Bi ０．４９ Te ０．０１ Cu ０．０１ A sample (Comparative Example 1) in which an electrode layer of Fe was laminated on a thermoelectric conversion layer of Mg ３．２ Sb １．５ Bi ０．４９ Te ０．０１ Cu ０．０１ A sample (Comparative Example 2) was produced in which a stainless steel electrode layer was laminated on the thermoelectric conversion layer.

[0052] [Measurement Results] First, cross sections of the prototype samples and prototype examples 1 and 2 were observed with a scanning electron microscope (SEM).

[0053] 4A, 4B, and 4C are cross-sectional SEM photographs showing the interface between the thermoelectric conversion layer and the cupronickel electrode layer, the interface between the thermoelectric conversion layer and the Fe electrode layer, and the interface between the thermoelectric conversion layer and the stainless steel electrode layer, respectively. In Comparative Example 1 (FIG. 4B), a layer was observed in which it was recognized that there had been a reaction between the Fe and the MgSb-based thermoelectric conversion layer (shown as "Reaction layer" in FIG. 4B). Also, in Comparative Example 2 (FIG. 4C), a layer was observed in which it was recognized that there had been a reaction between the stainless steel and the MgSb-based thermoelectric conversion layer (shown as "Reaction layer" in FIG. 4C). On the other hand, in the sample of this example (FIG. 4A), no reaction between the electrode material and the thermoelectric conversion layer was observed, and it can be seen that a sharp interface was formed.

[0054] 5 is a graph showing the results of measuring the electrode contact resistance of a prototype thermoelectric conversion element. A rectangular parallelepiped with a cross section of 2.90 mm x 2.94 mm x 4.4 mm length was cut out from a prototype thermoelectric conversion element (10 mm diameter, 4.4 mm thickness). Electrodes were placed in contact with both ends of the thermoelectric conversion element, where the cupronickel electrode layer was formed, and a current was passed through the electrodes. The potential appearing on a probe placed in contact with the side surface (corresponding to the cross section of the prototype thermoelectric conversion element) was measured while the probe was moved. The horizontal axis represents the probe position, and the vertical axis represents the measured resistance (the measured potential divided by the current value).

[0055] The contact resistance was measured to be 0.06 mΩ. Multiplying this by the cross-sectional area (0.290 cm × 0.294 cm), the contact resistance was calculated to be 5.1 μΩ cm. ２ was obtained.

[0056] 6 is a graph showing the results of measuring the thermoelectric conversion efficiency of the prototype thermoelectric conversion element. The horizontal axis represents the temperature difference, and the vertical axis represents the thermoelectric conversion efficiency. The measured thermoelectric conversion efficiency was 1.8% at a temperature difference of 75 K, 4.9% at a temperature difference of 173 K, and 8.0% at a temperature difference of 273 K. For comparison, samples (Comparative Examples 1 and 2) were prepared using Fe and stainless steel as electrode layer materials, respectively, and measurements were performed, resulting in comparable thermoelectric conversion efficiencies.

[0057] As described above, by using cupronickel as the electrode layer in an MgSb-based thermoelectric conversion element, while employing a Cu-based electrode material that is easy to solder, a conversion efficiency comparable to or even higher than that of thermoelectric conversion elements that use Fe, stainless steel, FeCrTiMnMg, etc. as interface layers, as reported in many papers, etc., was obtained. This result demonstrates that cupronickel and similar alloys have extremely excellent capabilities as interface materials for extracting electricity from MgSb-based thermoelectric conversion materials.

[0058] The invention made by the inventor has been specifically described above based on an embodiment, but it goes without saying that the invention is not limited thereto and can be modified in various ways without departing from the spirit of the invention.

[0059] 1 Thermoelectric conversion element 2 Thermoelectric conversion layer 3 Electrode layer

Claims

1. A thermoelectric conversion element having a thermoelectric conversion layer and an electrode layer laminated on the thermoelectric conversion layer, wherein the thermoelectric conversion layer is made of a thermoelectric conversion material containing magnesium (Mg) and antimony (Sb), and the electrode layer is made of an electrode material containing an alloy of copper (Cu) and nickel (Ni).

2. The thermoelectric conversion element according to claim 1, wherein the thermoelectric conversion material further contains bismuth (Bi) and Mg ３＋ｖ Sb ｗ Bi ｘ (wherein 0.1<v<0.3, 1.35<w<1.65, 0.45<x<0.55).

3. The thermoelectric conversion element according to claim 1, wherein the thermoelectric conversion material further contains Bi and tellurium (Te), and Mg ３＋ｖ Sb ｗ Bi ｘ Te ｙ (wherein 0.1<v<0.3, 1.35<w<1.65, 0.44<x<0.54, and 0.001<y<0.011).

4. The thermoelectric conversion element according to claim 1, wherein the thermoelectric conversion material further contains Bi, Te and Cu, and Mg ３＋ｖ Sb ｗ Bi ｘ Te ｙ Cu ｚ (wherein 0.1<v<0.3, 1.35<w<1.65, 0.43<x<0.53, 0.001<y<0.011, 0.009<z<0.011).

5. A method for manufacturing a thermoelectric conversion element having a thermoelectric conversion layer and an electrode layer laminated on the thermoelectric conversion layer, comprising: a first sintering step of sintering a thermoelectric conversion material to form a pellet; a lamination step of forming a layer of electrode material on at least one of two opposing surfaces of the pellet; and a second sintering step of heat-treating the pellet on which the layer of electrode material has been formed, wherein the first sintering step is performed at a temperature higher than a reaction initiation temperature at which the electrode material starts to react with the thermoelectric conversion material, and the second sintering step is performed at a temperature lower than the reaction initiation temperature.

6. A method for manufacturing a thermoelectric conversion element as described in claim 5, wherein the thermoelectric conversion material contains Mg and Sb, the electrode material contains a CuNi alloy, and the reaction initiation temperature is a temperature at which a reaction begins between the thermoelectric conversion material and Cu and / or Ni constituting the CuNi alloy.

7. The method for producing a thermoelectric conversion element according to claim 6, wherein the thermoelectric conversion material is Mg ３＋ｖ Sb ｗ Bi ｘ Te ｙ Cu ｚ (wherein 0.1<v<0.3, 1.35<w<1.65, 0.43<x<0.53, 0.001<y<0.011, and 0.009<z<0.011).