Thermoelectric conversion material layer

Abstract

To provide a thermoelectric conversion material layer with enhanced electrical conductivity and high thermoelectric performance.SOLUTION: In a thermoelectric conversion layer containing thermoelectric semiconductor particles and single metal particles, in a longitudinal section including a central portion of the thermoelectric conversion material layer, the area occupied by the single metal particles relative to the total area occupied by the thermoelectric semiconductor particles and single metal particles is 1 to 50%.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a thermoelectric conversion material layer.

Background Art

[0002] Conventionally, as one means for effectively utilizing energy, there is a device that directly converts thermal energy and electrical energy with a thermoelectric conversion module having a thermoelectric effect such as the Seebeck effect or the Peltier effect. As a thermoelectric conversion module, a configuration of a so-called π-type thermoelectric conversion element is known. The π-type thermoelectric conversion element is provided with a pair of electrodes spaced apart from each other on a substrate. For example, a P-type thermoelectric element is provided on one electrode, and an N-type thermoelectric element is provided on the other electrode, also spaced apart from each other, and the upper surfaces of both thermoelectric elements are connected to a common electrode of the opposing substrate. Further, a configuration of a so-called IP (in-plane) type thermoelectric conversion element is known. From the viewpoint of thermoelectric performance, the IP-type thermoelectric conversion element usually has P-type thermoelectric elements and N-type thermoelectric elements alternately provided in the in-plane direction of the substrate. For example, the upper or lower parts of adjacent or abutting P-type thermoelectric elements and N-type thermoelectric elements are connected in series via electrodes. Under such circumstances, there is still a demand for improving the thermoelectric performance of thermoelectric conversion modules. In Patent Document 1, there is disclosed a thermoelectric conversion material layer composed of a fired body of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles, wherein the metal nanoparticles are particles that sinter at 450°C or lower. In Patent Document 2, CoSb 3-x-y Si x Te y (where 0.003 < x < 0.25, 0.025 < y < 0.40) having a composition of skutterudite thermoelectric semiconductor is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0004] In the thermoelectric conversion material layer of Patent Document 1, the presence of an ionic liquid between thermoelectric semiconductor particles suppresses a decrease in electrical conductivity, and the presence of metal nanoparticles reduces internal defects (presence of voids) in the thermoelectric conversion material layer, thereby increasing electrical conductivity. As a result, this can lead to improved thermoelectric performance, but further improvement in thermoelectric performance is necessary. Furthermore, the skutterudite thermoelectric semiconductor of Patent Document 2 is known as a system that exhibits extremely high thermoelectric performance in the medium-to-high temperature range. This structure is obtained by doping both Si and Te into the cage structure of skutterudite, and unlike Patent Document 1, it is possible to effectively introduce disorder that reduces thermal conductivity into the cage structure without compromising electrical conductivity, resulting in improved thermoelectric performance. However, further improvement in the thermoelectric performance is also required.

[0005] In view of the above, an object of the present invention is to provide a thermoelectric conversion material layer having improved electrical conductivity and high thermoelectric performance. [Means for solving the problem]

[0006] As a result of extensive research into solving the above problems, the inventors have found that a thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometal particles, in which the ratio of the area occupied by the monometal particles to the area occupied by the thermoelectric semiconductor particles and monometal particles in a longitudinal cross section including the center of the thermoelectric conversion material layer is within a specific range, has high thermoelectric performance with improved electrical conductivity, and have completed the present invention. That is, the present invention provides the following [1] to [5]. [1] A thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometal particles, wherein in a longitudinal cross section including a central portion of the thermoelectric conversion material layer, the ratio of the area occupied by the monometal particles to the area occupied by the thermoelectric semiconductor particles and the monometal particles is 1 to 50%. [2] A thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometal particles, wherein in a longitudinal cross section including a central portion of the thermoelectric conversion material layer, the ratio of the area occupied by the monometal particles to the area of ​​the longitudinal cross section is 1 to 48%, and the filling rate is 70 to 99%. [3] The thermoelectric conversion material layer according to the above [1] or [2], wherein the melting temperature of the monometallic particles is 130 to 550°C. [4] The thermoelectric conversion material layer according to any one of the above [1] to [3], which is made of a sintered body of a coating film of a thermoelectric semiconductor composition. [5] General formula CoSb (3-x-y) Te x Bi y A thermoelectric conversion material layer having a composition represented by the formula: (In the general formula, 0.02≦x≦1.00, 0.02≦x+y≦1.00, and 0≦y.) [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a thermoelectric conversion material layer having improved electrical conductivity and high thermoelectric performance. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an SEM image of a vertical cross section of a test piece (thermoelectric conversion material layer) of Comparative Example 1. [Figure 2] 1 is an SEM image of a vertical cross section of a test piece (thermoelectric conversion material layer) of Example 2. [Figure 3] 1 shows the element distribution of single metal particles in a vertical cross section of a test piece (thermoelectric conversion material layer) of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Thermoelectric conversion material layer] The thermoelectric conversion material layer according to the first embodiment of the present invention is a thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometal particles, and is characterized in that in a longitudinal cross section including the central portion of the thermoelectric conversion material layer, the ratio of the area occupied by the monometal particles to the area occupied by the thermoelectric semiconductor particles and monometal particles is 1 to 50%. The thermoelectric conversion material layer according to the first embodiment of the present invention contains thermoelectric semiconductor particles and monometal particles, and in a longitudinal cross section including the center of the thermoelectric conversion material layer, the ratio of the area occupied by the monometal particles to the area occupied by the thermoelectric semiconductor particles and the monometal particles is within the above-mentioned range, so that the thermoelectric conversion material layer has high electrical conductivity and, as a result, high thermoelectric performance is obtained. A thermoelectric conversion material layer according to a second embodiment of the present invention is a thermoelectric conversion material layer including thermoelectric semiconductor particles and single metal particles, In a longitudinal section including the central portion of the thermoelectric conversion material layer, the ratio of the area occupied by the single metal particles to the area of ​​the longitudinal section is 1 to 48%, and the filling rate is 70 to 99%. The thermoelectric conversion material layer according to the second embodiment of the present invention contains thermoelectric semiconductor particles and monometal particles, and in a longitudinal cross section including the central portion of the thermoelectric conversion material layer, the ratio of the area occupied by the monometal particles to the area of ​​the longitudinal cross section is within the above range, so that the thermoelectric conversion material layer has high electrical conductivity and, as a result, high thermoelectric performance is obtained.

[0010] In this specification, a film obtained after forming a thermoelectric semiconductor composition by coating may be referred to as a "composition film," a film obtained after drying the "composition film" may be referred to as a "coated film," and a film obtained after firing the "coated film" may be referred to as a "thermoelectric conversion material layer." In this specification, the "ratio of the area occupied by the monometal particles to the area occupied by the thermoelectric semiconductor particles and the monometal particles in a longitudinal cross section including the central portion of the thermoelectric conversion material layer" (%) may be simply referred to as the "ratio A1 of the area occupied by the monometal particles" (%). In this specification, the "ratio of the area occupied by the region occupied by the single metal particles to the area of ​​the longitudinal cross section including the central portion of the thermoelectric conversion material layer" (%) may be simply referred to as the "ratio A2 of the area occupied by the single metal particles" (%). In this specification, the "ratio of the area of ​​the region occupied by thermoelectric semiconductor particles and single metal particles to the area of ​​the longitudinal cross section including the center of the thermoelectric conversion material layer" (%) may be simply referred to as the "filling ratio" (%). In this specification, the "proportion of voids to the area of ​​a vertical cross section including the center of a thermoelectric conversion material layer" (%) may be simply referred to as "porosity" (%).

[0011] In this specification, preferred definitions can be selected arbitrarily, and combinations of preferred definitions can be considered more preferred. In this specification, the expression "XX to YY" means "XX or more and YY or less." In this specification, for preferred numerical ranges (e.g., ranges of content, etc.), the lower and upper limits described in stages can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60."

[0012] The thermoelectric conversion material layer of the present invention contains thermoelectric semiconductor particles and monometal particles.

[0013] In the thermoelectric conversion material layer according to the first embodiment of the present invention, in a longitudinal section including the central portion of the thermoelectric conversion material layer, the ratio of the area occupied by the monometal particles to the area occupied by the thermoelectric semiconductor particles and the monometal particles (area ratio A1 of the area occupied by the monometal particles) is 1 to 50%. If the ratio A1 of the area of ​​the region occupied by the single metal particles is less than 1%, the decrease in the total Seebeck coefficient of the thermoelectric conversion material layer can be suppressed, but the increase in electrical conductivity becomes small. If the area ratio A1 of the region occupied by single metal particles exceeds 50%, the electrical conductivity of the thermoelectric conversion material layer increases but the total Seebeck coefficient decreases, leading to a decrease in the power factor, which is an index of thermoelectric performance. The area ratio A1 of the region occupied by the single metal particles is preferably 3 to 45%, more preferably 4 to 30%, and even more preferably 5 to 20%. When the area ratio A1 of the region occupied by the single metal particles is within this range, the trade-off in the power factor between the increase in electrical conductivity and the decrease in the total Seebeck coefficient is minimized, and the power factor can be increased.

[0014] In the thermoelectric conversion material layer according to the second embodiment of the present invention, the ratio of the area occupied by the monometal particles to the area of ​​a longitudinal cross section including the center of the thermoelectric conversion material layer (area ratio A2 of the area occupied by the monometal particles) is 1 to 48%. Keeping this range makes it easier to increase the power factor of the thermoelectric conversion material layer. From this perspective, the area ratio A2 of the area occupied by the monometal particles is more preferably 2 to 35%, particularly preferably 4 to 25%, and even more preferably 6 to 20%.

[0015] In the thermoelectric conversion material layer according to the second embodiment of the present invention, the ratio (filling rate) of the area of ​​the region other than voids, i.e., the area of ​​the region occupied by thermoelectric semiconductor particles and monometal particles to the area of ​​the longitudinal cross section including the central portion of the thermoelectric conversion material layer, is 70 to 99%. A filling rate within this range facilitates increasing the power factor of the thermoelectric conversion material layer. From this perspective, the filling rate is preferably 72 to 96%, more preferably 74 to 90%, and even more preferably 77 to 84%. In the thermoelectric conversion material layers according to the first and second embodiments of the present invention, the longitudinal cross section may be composed only of thermoelectric semiconductor particles, monometal particles, and voids, or may have regions occupied by other substances, but is preferably composed only of thermoelectric semiconductor particles, monometal particles, and voids. The sum of the filling rate and porosity is preferably 90 to 100%, more preferably 99 to 100%, and may be 100%.

[0016] In one embodiment, the thermoelectric conversion material layer is preferably made of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles and monometal particles. The thermoelectric semiconductor composition may contain a binder resin in addition to the thermoelectric semiconductor particles and the monometallic particles.

[0017] <Thermoelectric semiconductor particles> The thermoelectric conversion material layer of the present invention contains thermoelectric semiconductor particles. The thermoelectric semiconductor particles are used, for example, by pulverizing a thermoelectric semiconductor material, which will be described later, to a predetermined size using a fine grinding device or the like. The average particle size of the thermoelectric semiconductor particles is preferably 10 nm to 100 μm, more preferably 50 nm to 50 μm, and even more preferably 1 μm to 4 μm. The average particle size of the thermoelectric semiconductor particles is obtained by measurement using a laser diffraction particle size analyzer, and is the median value of the particle size distribution.

[0018] The thermoelectric semiconductor material is not particularly limited as long as it is a material that can generate thermoelectric power by applying a temperature difference, and examples thereof include bismuth-tellurium-based thermoelectric semiconductor materials such as P-type bismuth telluride and N-type bismuth telluride; telluride-based thermoelectric semiconductor materials such as GeTe and PbTe; antimony-tellurium-based thermoelectric semiconductor materials; ZnSb, Zn3Sb 2、 Zinc-antimony thermoelectric semiconductor materials such as Zn4Sb3; silicon-germanium thermoelectric semiconductor materials such as SiGe; bismuth selenide thermoelectric semiconductor materials such as Bi2Se3; β-FeSi2, CrSi2, MnSi 1.73Examples of materials that can be used include silicide-based thermoelectric semiconductor materials such as MgSi, oxide-based thermoelectric semiconductor materials, Heusler materials such as FeVAl, FeVAlSi, and FeVTiAl, sulfide-based thermoelectric semiconductor materials such as TiS, and skutterudite materials. Of these, silicide-based thermoelectric semiconductor materials are preferred from the viewpoint of not containing rare metals whose supply is unstable due to geopolitical issues, and skutterudite materials having a CoSb-based skutterudite crystal structure are preferred from the viewpoint of making it easier to make the thermoelectric conversion module function in a high-temperature environment.

[0019] Furthermore, from the viewpoint of high thermoelectric conversion performance in a low-temperature environment, the thermoelectric semiconductor material is preferably a bismuth-tellurium-based thermoelectric semiconductor material such as P-type bismuth telluride or N-type bismuth telluride.

[0020] The content of the thermoelectric semiconductor particles in the thermoelectric semiconductor composition is preferably 30 to 99% by mass, more preferably 60 to 95% by mass, and even more preferably 75 to 90% by mass. If the content of the thermoelectric semiconductor particles is within the above range, it is easy to set the area ratio of the monometal particles in the cross section within the above range, and it is easy to obtain a thermoelectric conversion material layer with an excellent power factor. Note that the content of each component in the thermoelectric semiconductor composition is based on the pure content or solid content, excluding the dilution solvent (the same applies hereinafter).

[0021] Furthermore, the thermoelectric semiconductor particles are preferably subjected to an annealing treatment (hereinafter sometimes referred to as "annealing treatment A"). By performing annealing treatment A, the crystallinity of the thermoelectric semiconductor particles is improved, and furthermore, the surface oxide film of the thermoelectric semiconductor particles is removed, thereby increasing the Seebeck coefficient (absolute value of the Peltier coefficient) of the thermoelectric conversion material layer and further improving the thermoelectric figure of merit.

[0022] <Single metal particles> The thermoelectric conversion material layer according to the present invention contains monometallic particles. In the process of sintering a thermoelectric semiconductor composition containing thermoelectric semiconductor particles and monometallic particles to form a sintered body as a thermoelectric conversion material layer, the monometallic particles melt, connecting the thermoelectric semiconductor particles to form conductive paths. At the same time, this also makes it easier to fill voids between the thermoelectric semiconductor particles, thereby further improving electrical conductivity.

[0023] The melting temperature (melting point) of the monometallic particles is preferably 130 to 550°C, more preferably 150 to 500°C, even more preferably 170 to 440°C, and particularly preferably 190 to 350°C. If the monometallic particles melt within the above range, they can connect the thermoelectric semiconductor particles in the thermoelectric conversion material layer to form conductive paths. At the same time, they also make it easier to fill the voids between the thermoelectric semiconductor particles, thereby further improving electrical conductivity.

[0024] The single metal particles are not particularly limited as long as they satisfy the melting temperature described above and can disperse the thermoelectric semiconductor particles while connecting them to each other. However, they are preferably selected from the group consisting of bismuth, tellurium, zinc, tin, indium, cadmium, selenium, thallium, and lithium, and from the viewpoint of low-temperature sintering properties and stability, they are more preferably selected from at least one of bismuth, tellurium, selenium, zinc, tin, and indium.

[0025] The average particle size of the single metal particles in the thermoelectric semiconductor composition is not particularly limited, but is preferably 12 μm or less, more preferably 0.10 to 12 μm, even more preferably 0.20 to 10 μm, still more preferably 0.30 to 8 μm, particularly preferably 0.40 to 6 μm, and most preferably 0.50 to 4 μm. When the average particle size of the monometallic particles is within the above range, they can be dispersed among the thermoelectric semiconductor particles and efficiently connected to form conductive paths. Furthermore, for example, in the process of sintering (annealing) a coating film made of the thermoelectric semiconductor composition to form a thermoelectric conversion material layer as a sintered body, the sintering of the monometallic particles progresses, which simultaneously makes it easier to fill the voids between the thermoelectric semiconductor particles, thereby further improving the electrical conductivity. The average particle size (primary particles) of the monometallic particles in the thermoelectric semiconductor composition is the arithmetic mean value of the average particle sizes of any 20 monometallic particles observed under a transmission electron microscope (TEM).

[0026] The resistivity of a single metal particle is 5×10 -4 Ω·cm or less, and more preferably 5×10 -5 Ω·cm or less, and more preferably 5×10 -6 Ω·cm or less, and particularly preferably 5×10 -7 If the resistivity of the single metal particles is within the above range, the electrical bond between the thermoelectric semiconductor particles is improved, and the electrical resistance value of the thermoelectric conversion material layer is likely to decrease.

[0027] The content of the monometallic particles in the thermoelectric semiconductor composition is preferably 0.01 to 35% by mass, more preferably 0.50 to 30% by mass, even more preferably 1.00 to 25.00% by mass, particularly preferably 4.00 to 20.00% by mass, and most preferably 8.00 to 15.00% by mass. When the content of the monometallic particles in the thermoelectric semiconductor composition is within the above range, the monometallic particles are dispersed properly among the thermoelectric semiconductor particles, efficiently connecting them to form conductive paths. Furthermore, for example, during the process of sintering (annealing) a coating film made of the thermoelectric semiconductor composition to form a sintered thermoelectric conversion material layer, the monometallic particles are sintered properly, which simultaneously makes it easier to fill voids between the thermoelectric semiconductor particles and, as a result, further improves electrical conductivity.

[0028] The thermoelectric conversion material layer is preferably made of a sintered body of a coating film of a thermoelectric semiconductor composition. From the viewpoint of obtaining a sintered body of single metal particles, the firing temperature is usually 100 to 800° C., preferably 130 to 700° C., more preferably 200 to 650° C., even more preferably 300 to 620° C., and particularly preferably 460 to 620° C. The firing time is not particularly limited, but is usually several minutes to several tens of hours, preferably several minutes to several hours.

[0029] The thickness of the thermoelectric conversion material layer obtained by the firing treatment is preferably 5 to 800 μm, more preferably 10 to 200 μm, and even more preferably 20 to 80 μm.

[0030] (binder resin) The binder resin has the effect of physically binding the thermoelectric semiconductor particles together, and can increase the flexibility of the thermoelectric conversion module, as well as making it easier to form a thin film by coating or the like.

[0031] The binder resin is appropriately selected depending on the temperature of the heat treatment of the thermoelectric semiconductor particles and the baking (annealing) temperature. It is preferable to heat the thermoelectric semiconductor particles at a temperature higher than the decomposition temperature of the binder resin. Furthermore, a resin that maintains various physical properties such as mechanical strength and thermal conductivity without being impaired when the thermoelectric semiconductor particles are crystallized by heat treatment or the like of a coating film made of the thermoelectric semiconductor composition is more preferable. In this specification, the term "decomposition temperature" refers to the temperature at which the mass loss rate by thermogravimetry (TG) is 100% (the mass after decomposition is less than 1% of the mass before decomposition). The decomposition temperature of the binder resin is preferably 150 to 500°C.

[0032] Thermoplastic resins and curable resins can be used as such binder resins. Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, polyisobutylene, and polymethylpentene; aromatic polycarbonates; aliphatic polycarbonates such as polyethylene carbonate and polypropylene carbonate; thermoplastic polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyvinyl polymers such as polystyrene, acrylonitrile-styrene copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer, vinyl chloride, polyvinylpyridine, polyvinyl alcohol, and polyvinylpyrrolidone; polyurethane; and cellulose derivatives such as ethyl cellulose. Examples of curable resins include thermosetting resins and photocurable resins. Examples of thermosetting resins include epoxy resins and phenolic resins. Examples of photocurable resins include photocurable acrylic resins, photocurable urethane resins, and photocurable epoxy resins. These resins may be used alone or in combination. Among these, thermoplastic resins are preferred, and aromatic polycarbonates, aliphatic polycarbonates such as polyethylene carbonate and polypropylene carbonate, and cellulose derivatives such as ethyl cellulose are more preferred, with polyethylene carbonate being particularly preferred.

[0033] The content of the binder resin in the thermoelectric semiconductor composition is preferably 0.1 to 20 mass %, more preferably 0.5 to 15 mass %, and even more preferably 1.0 to 10 mass %.

[0034] [Method of manufacturing the thermoelectric conversion material layer] One embodiment of the method for producing a thermoelectric conversion material layer of the present invention includes the following steps (A) and (B). (A) Step of Obtaining a Coating Film Formed from a Thermoelectric Semiconductor Composition (B) A step of calcining the coating film to obtain a thermoelectric conversion material layer

[0035] In the following description, step (A) may also be referred to as the "coating step" and step (B) as the "firing step." The method for producing a thermoelectric conversion material layer in the present invention will be described below.

[0036] Process (A): Coating process The method for producing a thermoelectric conversion material layer of the present invention includes a coating step. In one embodiment, the coating step is a step of dispersing a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, single metal particles, and a binder resin in a dilution solvent on a support, adjusting the viscosity, coating the composition to form a composition film, and drying the composition film to obtain a coating film.

[0037] The details of the thermoelectric semiconductor composition containing thermoelectric semiconductor particles, monometallic particles, and a binder resin used to form the coating film are as described above. It is preferable to use an organic solvent capable of dissolving the binder resin as the dilution solvent. Examples include toluene, ethyl acetate, methyl ethyl ketone, alcohol, tetrahydrofuran, N-methylpyrrolidone, and ethyl cellosolve. These may be used alone or in combination of two or more.

[0038] The method for applying the thermoelectric semiconductor composition as a composition film includes known methods such as screen printing, flexographic printing, gravure printing, spin coating, dip coating, die coating, spray coating, bar coating, and doctor blade, and is not particularly limited. The resulting composition film is then dried to form a coating film. Conventional drying methods, such as hot air drying, hot roll drying, and infrared irradiation, can be used. The heating temperature is typically 80 to 150°C, and the heating time, which varies depending on the heating method, is typically several seconds to several tens of minutes. When a solvent is used in preparing the thermoelectric semiconductor composition, the heating temperature is not particularly limited as long as it is within a temperature range that allows the solvent used to be completely dried.

[0039] Step (B): Firing process The method for producing a thermoelectric conversion material layer of the present invention preferably includes a firing treatment step. The firing treatment step is a step in which the coating film obtained in step (A) is fired to obtain a thermoelectric conversion material layer as a fired body. In the process of firing a coating film made of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles and monometallic particles to form a fired body, the monometallic particles melt, connecting the thermoelectric semiconductor particles to form conductive paths. At the same time, this also makes it easier to fill voids between the thermoelectric semiconductor particles, thereby further improving electrical conductivity. In addition, firing treatment usually stabilizes the thermoelectric performance and also allows the thermoelectric semiconductor particles in the thermoelectric semiconductor composition in the coating film to undergo crystal growth, thereby further improving the thermoelectric performance.

[0040] The firing treatment is not particularly limited, but is usually carried out in an inert gas atmosphere such as nitrogen or argon, in a reducing gas atmosphere, or under vacuum conditions, with the gas flow rate controlled. The temperature of the firing treatment depends on the thermoelectric semiconductor particles, monometal particles, binder resin, etc. used in the thermoelectric semiconductor composition and is adjusted appropriately, but in the present invention, as described above, it is set based on the melting temperature of the monometal particles. The baking time is as described above.

[0041] In one embodiment, the method for producing a thermoelectric conversion material layer of the present invention may include a heating and pressurizing step between step (A) and step (B). The heating and pressurizing step is a step of subjecting the coating film to a heating and pressurizing treatment to obtain a precursor of the thermoelectric conversion material layer before firing.

[0042] The heating and pressurizing treatment in the heating and pressurizing step can be carried out by a known method, for example, by using a hydraulic press, an air press, or the like. The heating temperature must be set taking into consideration the melting temperature of the single metal particles and the decomposition temperature of the binder resin, but the heating temperature is usually 100 to 500° C., and the pressure is usually 20 to 300 MPa. The heating temperature is preferably 150 to 400°C, more preferably 200 to 400°C. The pressure is preferably 45 to 250 MPa, more preferably 50 to 200 MPa. The heating and pressurizing treatment time is not particularly limited, but is preferably from several seconds to several hours, more preferably from several tens of seconds to several tens of minutes, and even more preferably from several minutes to several tens of minutes. When the heating temperature, pressure application, and heating and pressure application time are within the above ranges, and the softening point of the binder resin is, for example, 250°C or lower, the thermoelectric semiconductor particles flow at the beginning of the heating and pressure application due to the softening of the binder resin, making it easier to improve the filling rate and reducing internal defects in the precursor of the thermoelectric conversion material layer. Furthermore, if the 95% decomposition temperature of the binder resin is, for example, 350°C or lower, the binder resin is decomposed during the heat and pressure treatment, further improving the packing rate of the precursor of the thermoelectric conversion material layer, and as a result, further reducing internal defects.

[0043] The thermoelectric conversion material layer produced by the production method of the present invention may be further divided into individual pieces in a dicing step. The dicing step is a step of dividing the thermoelectric conversion material layer into chips of thermoelectric conversion material. From the viewpoint of processing accuracy and process stability, the dividing step is preferably performed using a dicing blade with a dicing tape attached.

[0044] [Thermoelectric conversion material layer] The thermoelectric conversion material layer according to the third embodiment of the present invention is a material having the general formula CoSb (3-x-y) Te x Bi y It has a composition represented by the formula: (In the general formula, 0.02≦x≦1.0, 0≦y, and 0.2≦x+y≦1.0.) As described above, the thermoelectric conversion material layer has a different element composition ratio from that of conventional thermoelectric conversion material layers by adding Te or Bi, which has a low melting temperature, to a conventional skutterudite crystal. This is specified by the element composition ratio. While a predetermined amount or more of Sb is present, Te and Bi are present in predetermined proportions. From this perspective, it is more preferable that 0.03≦x≦0.08, 0.20≦y, and 0.23≦x+y≦0.70. [Example]

[0045] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0046] The electrical conductivity, Seebeck coefficient, PF (power factor), area ratio A1 of the region occupied by the single metal particles, area ratio A2 of the region occupied by the single metal particles, and filling rate of the thermoelectric conversion material layers obtained in the examples and comparative examples were evaluated by the following methods.

[0047] (a) Evaluation of electrical conductivity The electrical conductivity σ (S / cm) of the thermoelectric conversion material layers (sample: 25 mm × 25 mm × thickness 0.05 mm) obtained in the examples and comparative examples was evaluated by a four-terminal method using a resistivity meter (manufactured by Nitto Seiko Analytech Co., Ltd., Loresta GP, model number: MCP-600T) and a PSP probe (manufactured by Nitto Seiko Analytech Co., Ltd., model number: MCP-TP06P, product code: RMH112).

[0048] (b) Evaluation of the Seebeck coefficient The Seebeck coefficient S (μV / K) of the thermoelectric conversion material layers (sample: 15 mm × 5 mm × thickness 0.05 mm) obtained in the examples and comparative examples was evaluated as follows using a thermoelectric property evaluation device ZME-3 (manufactured by Advance Riko Co., Ltd.). The sample was sandwiched between upper and lower blocks (material: ceramic) and fixed vertically, and the heating temperature was set to 85°C, with a temperature difference between the upper and lower blocks of 40°C (temperature difference ΔT between the upper and lower surfaces within the sample: 3°C). The electromotive force Vp (V) generated by the temperature gradient within the sample was measured under reduced pressure, and the Seebeck coefficient S was calculated using the following formula (1). S=Vp / ΔT(μV / K) (1)

[0049] (c) PF (Power Factor) evaluation The PF of the thermoelectric conversion material layers obtained in the examples and comparative examples was calculated from the following formula (2) using the values ​​obtained in the evaluation of the electrical conductivity and the evaluation of the Seebeck coefficient. PF=S 2 ×σ[μW / cm K 2 ] (2)

[0050] (d) Evaluation of the area ratio A1 of the region occupied by the single metal particles, the area ratio A2 of the region occupied by the single metal particles, and the filling rate (longitudinal cross section along the thickness direction) For each of the test pieces (25 mm × 25 mm × 50 μm thick) made of the thermoelectric conversion material layer obtained in the examples and comparative examples, a longitudinal section including the center of the thermoelectric conversion material layer was prepared using a polishing machine (manufactured by Refine Tech Co., Ltd., model name: Refine Polisher HV), and images of the longitudinal section (longitudinal cross-section image) taken at a magnification of 2000 times were observed using a scanning electron microscope energy dispersive X-ray spectrometer (manufactured by ZEISS Microscopy, model name: GeminiSEM 560), and elemental mapping measurements of the single metals were performed. Using image processing software (ImageJ ver. 1.44P, manufactured by the National Institutes of Health), images of the longitudinal cross section of the thermoelectric conversion material layer [Comparative Example 1 (Fig. 1: A1 is the thermoelectric semiconductor particle distribution region, A2 is the void distribution region), and Example 2 (Fig. 2: B2 is the monometal particle distribution region (bismuth distribution region), the sum of A1 and B2 corresponds to the thermoelectric semiconductor particle distribution region and the monometal particle distribution region)] were binarized using "Threshold." The bright areas in the binarization process were considered to be filled regions (thermoelectric semiconductor particle distribution region and monometal particle distribution region), and the dark areas were considered to be other regions, and the area ratio of the filled regions in the image (filling rate) X × 100 (%) was calculated using "Measure." Next, the images obtained by elemental mapping of the single metal [(Figure 3: A is the sum of the thermoelectric semiconductor particle distribution region and the void distribution region, B2 is the single metal particle distribution region (bismuth distribution region)], and the photographs obtained by the mapping measurement were binarized using a "Threshold." The bright areas in the binarization process were considered to be the single metal particle distribution region, and the dark areas were considered to be the rest. The area proportion of the single metal particle distribution region, Y x 100 (%), i.e., the area proportion A2 (%) of the region occupied by single metal particles, was calculated. The area proportion of the single metal particle distribution region was calculated for each of the three mapping photographs and used as the average. The ratio of the area occupied by single metal particles to the area occupied by thermoelectric semiconductor particles and single metal particles, i.e., the area proportion A1 (%) of the region occupied by single metal particles, was then calculated using (Y / X) x 100 (%).

[0051] (e) Component analysis of the thermoelectric conversion material layer <Elemental analysis> Next, using the same device, the atomic concentration (%) of Co, Sb, Te, and Bi contained in the thermoelectric conversion material layer was evaluated by EDX analysis in the measured area of ​​the vertical cross section. The composition ratios of Sb, Te, and Bi were calculated from the obtained atomic concentration % ratio of each atom, with the atomic concentration of Co set to 1.

[0052] Example 1 <Fabrication of thermoelectric semiconductor material layer> (1) Preparation of thermoelectric semiconductor particles N-type cobalt antimony telluride CoSb, a cobalt-antimony based thermoelectric semiconductor material 2.9 Te 0.1 Thermoelectric semiconductor particles with an average particle size of 2.2 μm were produced by pulverizing 15 μm-sized sintered body (manufactured by Kojundo Chemical Laboratory) in air using a planetary ball mill (manufactured by Fritsch Japan, Premium line P-7). The particle size distribution of the obtained thermoelectric semiconductor particles was measured using a laser diffraction particle size analyzer (manufactured by Malvern, Mastersizer 3000). (2) Preparation of thermoelectric semiconductor composition N-type cobalt antimony telluride CoSb 2.9 Te 0.1A coating liquid consisting of a thermoelectric semiconductor composition was prepared by mixing and dispersing 78.0 parts by mass of the particles, 19.5 parts by mass of a polyethylene carbonate (PEC) solution (manufactured by Empower Materials, solvent: N-methylpyrrolidone, solid content: 15% by mass), and 2.5 parts by mass of bismuth particles (manufactured by Kojundo Chemical Laboratory, average particle size 1 μm) as an additive metal. (3) Preparation of thermoelectric conversion material layer The coating solution prepared in (2) was applied to a glass substrate with a thickness of 1.1 mm using an applicator, and then heated and dried at 120°C for 10 minutes to remove N-methylpyrrolidone, forming a coating film. The resulting coating film was heat-treated at 600°C for 180 minutes in an argon-hydrogen mixed gas atmosphere to produce a thermoelectric conversion material layer with a thickness of 50 μm. The elemental composition of the thermoelectric conversion material layer was CoSb 2.63 Te 0.07 Bi 0.30 It was.

[0053] Example 2 N-type cobalt antimony telluride CoSb 2.9 Te 0.1 A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that a coating liquid was prepared by mixing and dispersing 71.1 parts by mass of the particles, 17.8 parts by mass of a polyethylene carbonate solution, and 11.1 parts by mass of bismuth particles. The elemental composition of the thermoelectric conversion material layer is CoSb 2.81 Te 0.07 Bi 0.84 It was.

[0054] Example 3 N-type cobalt antimony telluride CoSb 2.9 Te 0.1 A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that a coating liquid was prepared by mixing and dispersing 57.1 parts by mass of the particles, 16.1 parts by mass of a polyethylene carbonate solution, and 26.8 parts by mass of bismuth particles. The elemental composition of the thermoelectric conversion material layer is CoSb 2.15 Te 0.02 Bi 0.12 It was.

[0055] Example 4 N-type cobalt antimony telluride CoSb 2.9 Te 0.1 A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that a coating liquid was prepared by mixing and dispersing 71.1 parts by mass of the particles, 17.8 parts by mass of a polyethylene carbonate solution, and 11.1 parts by mass of tellurium particles (manufactured by Kojundo Chemical Laboratory, powder, average particle size 7 μm) instead of bismuth particles. The elemental composition of the thermoelectric conversion material layer was CoSb 2.8 Te 0.2 It was.

[0056] Example 5 N-type cobalt antimony telluride CoSb 2.9 Te 0.1 Instead of P-type cerium iron cobalt antimony CeFe3CoSb 12 A coating film was prepared using a coating liquid prepared by mixing and dispersing 76.2 parts by mass of the particles, 19.0 parts by mass of a polyethylene carbonate solution, and 4.8 parts by mass of bismuth particles, and a thermoelectric conversion material layer was prepared in the same manner as in Example 1, except that the heat treatment temperature was 500°C.

[0057] Example 6 N-type cobalt antimony telluride CoSb 2.9 Te 0.1 Instead of N-type cobalt antimony silicon telluride Co 23.4 Sb 69.1 Si 1.5 Te 6.0 A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that a coating liquid was prepared by mixing and dispersing 71.1 parts by mass of the particles, 17.8 parts by mass of a polyethylene carbonate solution, and 11.1 parts by mass of bismuth particles.

[0058] (Comparative Example 1) N-type cobalt antimony telluride CoSb 2.9 Te 0.1A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that a coating liquid was prepared by mixing and dispersing 80.0 parts by mass of the particles and 20.0 parts by mass of a polyethylene carbonate solution. The elemental composition of the thermoelectric conversion material layer was CoSb 2.9 Te 0.1 It was.

[0059] (Comparative Example 2) N-type cobalt antimony telluride CoSb 2.9 Te 0.1 A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that a coating liquid was prepared by mixing and dispersing 51.6 parts by mass of the particles, 16.0 parts by mass of a polyethylene carbonate solution (manufactured by Empower Materials, solvent: N-methylpyrrolidone, solid content: 15% by mass), and 32.4 parts by mass of bismuth particles (manufactured by Kojundo Chemical Laboratory, powder, average particle size 1 μm) as an additive metal. The elemental composition of the thermoelectric conversion material layer was CoSb 1.9 Te 0.01 Bi 1.09 It was.

[0060] (Comparative Example 3) N-type cobalt antimony telluride CoSb 2.9 Te 0.1 Instead of P-type cerium iron cobalt antimony CeFe3CoSb 12 A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that a coating liquid was prepared by mixing and dispersing 80.0 parts by mass of the particles and 20.0 parts by mass of a polyethylene carbonate solution.

[0061] Comparative Example 4 N-type cobalt antimony telluride CoSb 2.9 Te 0.1 Instead of N-type cobalt antimony silicon telluride Co 23.4 Sb 69.1 Si 1.5 Te 6.0 A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that a coating liquid was prepared by mixing and dispersing 80.0 parts by mass of the particles and 20.0 parts by mass of a polyethylene carbonate solution.

[0062] Table 1 shows the evaluation results of the electrical conductivity, Seebeck coefficient, PF (power factor), area ratio A1 of the region occupied by the single metal particles, area ratio A2 of the region occupied by the single metal particles, and filling rate of the thermoelectric conversion material layers obtained in Examples 1 to 6 and Comparative Examples 1 to 4.

[0063] [Table 1]

[0064] According to Table 1, in the present invention, the power factors of the thermoelectric conversion material layers of Examples 1 to 6, which satisfy the requirements of the invention according to the first embodiment or the invention according to the second embodiment, are higher than the power factors of the thermoelectric conversion material layers of Comparative Examples 1 to 4, which do not satisfy the requirements of the invention according to the first embodiment or the invention according to the second embodiment, and therefore improved thermoelectric performance can be expected. [Industrial Applicability]

[0065] According to the thermoelectric conversion material layer of the present invention, a thermoelectric conversion material layer having improved electrical conductivity and high thermoelectric performance can be obtained, and therefore can be used as a thermoelectric conversion layer constituting a thermoelectric conversion module. [Explanation of symbols]

[0066] A: The sum of the thermoelectric semiconductor particle distribution region and the void distribution region A1: Thermoelectric semiconductor particle distribution region A2:Void distribution area B2: Monometallic particle distribution region (bismuth distribution region)

Claims

1. A thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometal particles, a ratio of an area occupied by the monometal particles to an area occupied by the thermoelectric semiconductor particles and the monometal particles in a longitudinal cross section including a central portion of the thermoelectric conversion material layer being 1 to 50%.

2. A thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometal particles, A thermoelectric conversion material layer, in which, in a longitudinal cross section including a central portion of the thermoelectric conversion material layer, the ratio of an area occupied by the single metal particles to an area of ​​the longitudinal cross section is 1 to 48%, and the filling rate is 70 to 99%.

3. 3. The thermoelectric conversion material layer according to claim 1, wherein the melting temperature of the monometallic particles is 130 to 550°C.

4. The thermoelectric conversion material layer according to claim 1 or 2, wherein the thermoelectric conversion material layer is made of a sintered body of a coating film of a thermoelectric semiconductor composition.

5. General formula CoSb (３-x-y) Te x Bi y A thermoelectric conversion material layer having a composition represented by the formula: (In the general formula, 0.02≦x≦1.00, 0.02≦x+y≦1.00, and 0≦y.)

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