Thermoelectric conversion material layer

Abstract

The present invention provides a thermoelectric conversion material layer having improved electrical conductivity and high thermoelectric performance. Provided is a thermoelectric conversion material layer comprising thermoelectric semiconductor particles and monometallic particles, wherein, in a longitudinal cross-section that includes the center part of the thermoelectric conversion material layer, the area ratio of a region occupied by the monometallic particles to a region occupied by the thermoelectric semiconductor particles and the monometallic particles is 1-50%.

Description

Thermoelectric conversion material layer

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

[0002] As one of the means for effectively utilizing energy, there have been devices that directly convert thermal energy into electrical energy and vice versa using thermoelectric conversion modules with thermoelectric effects such as the Seebeck effect and the Peltier effect. A known thermoelectric conversion module is a so-called π-type thermoelectric conversion element. A π-type thermoelectric conversion element is configured by providing a pair of spaced-apart electrodes on a substrate, with, for example, a P-type thermoelectric element on one electrode and an N-type thermoelectric element on the other electrode, also spaced apart from each other, and connecting the top surfaces of both thermoelectric elements to a common electrode on the opposing substrate. Another known configuration is a so-called IP (in-plane) type thermoelectric conversion element. From the perspective of thermoelectric performance, IP-type thermoelectric conversion elements typically have P-type and N-type thermoelectric elements alternately arranged in the in-plane direction of the substrate, with the upper or lower portions of adjacent or abutting P-type and N-type thermoelectric elements connected in series via electrodes. Despite this, there remains a demand for improved thermoelectric performance in thermoelectric conversion modules. Patent Document 1 discloses a thermoelectric conversion material layer made of a sintered 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 less. ３－ｘ－ｙ Si ｘ Te ｙ A skutterudite thermoelectric semiconductor having a composition where 0.003<x<0.25 and 0.025<y<0.40 is disclosed.

[0003] International Publication No. 2022 / 071043 Japanese Patent Application Laid-Open No. 2016-066795

[0004] In the thermoelectric conversion material layer of Patent Document 1, the presence of an ionic liquid between thermoelectric semiconductor particles suppresses the 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, leading to improved thermoelectric performance. However, further improvement in thermoelectric performance is needed. 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 a skutterudite cage structure. Unlike Patent Document 1, this structure effectively introduces disorder that reduces thermal conductivity into the cage structure without compromising electrical conductivity, resulting in improved thermoelectric performance. However, further improvement in thermoelectric performance is needed.

[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.

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

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

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

[0009] [Thermoelectric Conversion Material Layer] The thermoelectric conversion material layer according to a first embodiment of the present invention is a thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometallic particles, characterized in that, in a longitudinal cross section including a central portion of the thermoelectric conversion material layer, the ratio of the area occupied by the monometallic particles to the area occupied by the thermoelectric semiconductor particles and monometallic particles is 1 to 50%. The thermoelectric conversion material layer according to the first embodiment of the present invention contains thermoelectric semiconductor particles and monometallic particles, and, in a longitudinal cross section including a central portion of the thermoelectric conversion material layer, the ratio of the area occupied by the monometallic particles to the area occupied by the thermoelectric semiconductor particles and monometallic particles is within the above range, so that the thermoelectric conversion material layer has high electrical conductivity and, as a result, achieves high thermoelectric performance. A thermoelectric conversion material layer according to a second embodiment of the present invention is a thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometal particles, characterized in that, 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 packing factor 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 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 within the above range, so that the thermoelectric conversion material layer has high electrical conductivity and, as a result, achieves high thermoelectric performance.

[0010] Herein, a film obtained by coating a thermoelectric semiconductor composition is sometimes referred to as a "composition film," a film obtained by drying the "composition film" is sometimes referred to as a "coated film," and a film obtained by firing the "coated film" is sometimes referred to as a "thermoelectric conversion material layer." Herein, the "ratio of the area occupied by the monometallic particles to the area occupied by the thermoelectric semiconductor particles and the monometallic particles in a longitudinal cross section including the center of the thermoelectric conversion material layer" (%) is sometimes simply referred to as the "ratio A1 of the area occupied by the monometallic particles" (%). Herein, the "ratio A2 of the area occupied by the monometallic particles to the area of ​​the longitudinal cross section including the center of the thermoelectric conversion material layer" (%) is sometimes 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 it can be said that a combination of preferred definitions is more preferable. In this specification, the expression "XX to YY" means "XX or more and YY or less." In this specification, for preferred numerical ranges (for example, ranges of content, etc.), lower and upper limits described in stages can be independently combined. For example, from the description "preferably 10 to 90, more preferably 30 to 60," the "preferable lower limit (10)" and the "more preferable upper limit (60)" can be combined 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 center of the thermoelectric conversion material layer, the ratio of the area occupied by the monometallic particles to the area occupied by the thermoelectric semiconductor particles and the monometallic particles (area ratio A1 of the area occupied by the monometallic particles) is 1 to 50%. If the area ratio A1 of the area occupied by the monometallic 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 is small. If the area ratio A1 of the area occupied by the monometallic particles is more than 50%, the electrical conductivity of the thermoelectric conversion material layer increases, but the total Seebeck coefficient decreases. In either case, this leads to a decrease in the power factor, which is an index of thermoelectric performance. The area ratio A1 of the area occupied by the monometallic 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 the ratio within 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] Furthermore, in the thermoelectric conversion material layer according to the second embodiment of the present invention, in a longitudinal cross section including the central portion of the thermoelectric conversion material layer, the ratio (filling rate) of the area of ​​the region other than voids, i.e., the region occupied by thermoelectric semiconductor particles and monometallic 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, monometallic particles, and voids, or may include regions occupied by other substances, but is preferably composed only of thermoelectric semiconductor particles, monometallic particles, and voids. The sum of the filling rate and void rate is preferably 90 to 100%, more preferably 99 to 100%, and may even be 100%.

[0016] In one embodiment, the thermoelectric conversion material layer is preferably made of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles and monometallic particles. The thermoelectric semiconductor composition may contain a binder resin in addition to the thermoelectric semiconductor particles and 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 the thermoelectric semiconductor material described below to a predetermined size using a pulverizer 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 taken as 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, Zn３ Sb ２、 Zn ４ Sb ３ Zinc-antimony based thermoelectric semiconductor materials such as silicon-germanium based thermoelectric semiconductor materials such as silicon germanium; Bi ２ Se ３ Bismuth selenide-based thermoelectric semiconductor materials such as β-FeSi ２ , CrSi ２ , MnSi １．７３ , Mg ２ Silicide-based thermoelectric semiconductor materials such as Si; oxide-based thermoelectric semiconductor materials; Heusler materials such as FeVAl, FeVAlSi, and FeVTiAl; TiS ２ Sulfide-based thermoelectric semiconductor materials, skutterudite materials, etc. are used. Among 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 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] 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 further, 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] <Monometallic 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, the monometallic particles melt, connecting the thermoelectric semiconductor particles and forming 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 connect and disperse thermoelectric semiconductor particles together, but are preferably selected from the group consisting of bismuth, tellurium, zinc, tin, indium, cadmium, selenium, thallium, and lithium, and more preferably at least one selected from bismuth, tellurium, selenium, zinc, tin, and indium from the viewpoints of low-temperature sintering properties and stability.

[0025] The average particle size of the monometallic 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, even 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 and efficiently connected between thermoelectric semiconductor particles, facilitating the formation of conductive paths. Furthermore, for example, during 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 facilitates filling of voids between the thermoelectric semiconductor particles, thereby further improving electrical conductivity. The average particle size (primary particles) of the monometallic particles in the thermoelectric semiconductor composition is the arithmetic mean of the average particle sizes of any 20 monometallic particles observed by transmission electron microscopy (TEM).

[0026] The resistivity of a single metal particle is 5 x 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 bonding 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 firing (annealing) a coating film made of the thermoelectric semiconductor composition to form a fired 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 preferably comprises a sintered body of a coating film of the thermoelectric semiconductor composition. From the viewpoint of obtaining a sintered body of monometal particles, the sintering 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 sintering 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 thermoelectric semiconductor particles together, and can increase the flexibility of the thermoelectric conversion module, and also makes 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 binder resin at a temperature higher than its decomposition temperature. Furthermore, a resin that maintains its physical properties, such as mechanical strength and thermal conductivity, without being impaired when a coating film made of a thermoelectric semiconductor composition is subjected to heat treatment or the like to cause crystal growth of the thermoelectric semiconductor particles, is more preferable. In this specification, the "decomposition temperature" refers to the temperature at which the mass loss rate measured 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 of two or more. 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% by mass, more preferably 0.5 to 15% by mass, and even more preferably 1.0 to 10% by mass.

[0034] [Method for producing a thermoelectric conversion material layer] In one embodiment, the method for producing a thermoelectric conversion material layer of the present invention includes the following steps (A) and (B): (A) obtaining a coating film formed from a thermoelectric semiconductor composition; and (B) firing the coating film to obtain a thermoelectric conversion material layer.

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

[0036] Step (A): Coating Step The method for producing a thermoelectric conversion material layer of the present invention includes a coating step, which, in one embodiment, comprises dispersing a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, monometal particles, and a binder resin in a dilution solvent on a support, adjusting the viscosity, coating the dispersion 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 that dissolves 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] Methods for applying the thermoelectric semiconductor composition as a composition film include, but are not limited to, well-known methods such as screen printing, flexographic printing, gravure printing, spin coating, dip coating, die coating, spray coating, bar coating, and doctor blade coating. 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 as the drying method. The heating temperature is typically 80 to 150°C, and the heating time, although varying depending on the heating method, is typically several seconds to several tens of minutes. Furthermore, 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 can completely dry the solvent used.

[0039] Step (B): Firing Step The method for producing a thermoelectric conversion material layer of the present invention preferably includes a firing step. The firing step is a step of firing the coating film obtained in step (A) 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 obtain a thermoelectric conversion material layer as a fired body, the monometallic particles melt, connecting the thermoelectric semiconductor particles and forming 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 typically stabilizes thermoelectric performance and promotes crystal growth of the thermoelectric semiconductor particles in the thermoelectric semiconductor composition in the coating film, further improving thermoelectric performance.

[0040] The firing treatment is not particularly limited, but is usually carried out under an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere, or a vacuum condition with the gas flow rate controlled. The firing temperature depends on the thermoelectric semiconductor particles, monometal particles, binder resin, etc. used in the thermoelectric semiconductor composition and is adjusted as appropriate, but in the present invention, as described above, it is set based on the melting temperature of the monometal particles. The firing 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 performed using a known method, such as a hydraulic press or an air press. The heating temperature must be set taking into consideration the melting temperature of the monometallic particles and the decomposition temperature of the binder resin. The heating temperature is typically 100 to 500°C, and the pressurizing is typically 20 to 300 MPa. The heating temperature is preferably 150 to 400°C, more preferably 200 to 400°C. The pressurizing 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 several seconds to several hours, more preferably several tens of seconds to several tens of minutes, and even more preferably several minutes to several tens of minutes. When the heating temperature, pressurizing, and heating and pressurizing treatment time are within the above ranges, if 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 pressurizing treatment due to the softening of the binder resin, which facilitates an improvement in the packing density and reduces internal defects in the precursor of the thermoelectric conversion material layer. Furthermore, when the 95% decomposition temperature of the binder resin is, for example, 350° C. or lower, the binder resin is decomposed during the heating and pressurizing treatment, and the filling rate of the precursor of the thermoelectric conversion material layer is further improved, resulting in a further reduction in internal defects.

[0043] The thermoelectric conversion material layer produced by the production method of the present invention may be further singulated in a dicing step. The dicing step is a step of singulating the thermoelectric conversion material layer into chips of thermoelectric conversion material. From the viewpoints of processing accuracy and process stability, the singulation is preferably performed using a dicing blade attached to a dicing tape.

[0044] [Thermoelectric Conversion Material Layer] The thermoelectric conversion material layer according to the third embodiment of the present invention is a thermoelectric material layer of the general formula CoSb (３-x-y) Te x Bi y(In the general formula, 0.02≦x≦1.0, 0≦y, 0.2≦x+y≦1.0.) As described above, the thermoelectric conversion material layer has a composition ratio of elements different 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 composition ratio of the elements. While a predetermined amount or more of Sb is present, Te and Bi are also 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.

[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 thermoelectric conversion material layers obtained in the examples and comparative examples were evaluated for electrical conductivity, Seebeck coefficient, P.F. (power factor), area ratio A1 of the region occupied by the monometal particles, area ratio A2 of the region occupied by the monometal particles, and filling rate 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: MCP-TP06P, product abbreviation: RMH112).

[0048] (b) Evaluation of Seebeck Coefficient The Seebeck coefficient S (μV / K) of the thermoelectric conversion material layers (sample: 15 mm × 5 mm × 0.05 mm thick) 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, and the temperature difference between the upper and lower blocks was set to 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 from the following formula (1): S = Vp / ΔT (μV / K) (1)

[0049] (c) Evaluation of P.F. (Power Factor) The P.F. 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. P.F. = S 2 ×σ [μW / cm K 2 ] (2)

[0050] (d) Evaluation of Area Proportion A1 of Region Occupied by Single Metal Particles, Area Proportion A2 of Region Occupied by Single Metal Particles, and Filling Rate (Vertical Section Along Thickness Direction) For each of the test pieces (25 mm × 25 mm × 50 μm thick) made of thermoelectric conversion material layers obtained in the Examples and Comparative Examples, a vertical 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 an image of the vertical section (image of the vertical section) taken at a magnification of 2000 times was observed using a scanning electron microscope energy dispersive X-ray spectrometer (manufactured by ZEISS Microscopy Co., Ltd., model name: GeminiSEM 560), and elemental mapping of the single metal was measured. 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), 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 the rest, and the area ratio (filling rate) X × 100 (%) of the filled regions in the image was calculated using "Measure." Next, the images obtained by elemental mapping of the single metal [(FIG. 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, and the proportion of the area of ​​the single metal particle distribution region Y x 100 (%), i.e., the proportion A2 (%) of the area of ​​the region occupied by the single metal particles, was calculated. The proportion of the area of ​​the single metal particle distribution region was calculated for each of the three mapping photographs and the average of these was used. The proportion of the area of ​​the region occupied by the single metal particles to the area of ​​the region occupied by the thermoelectric semiconductor particles and the single metal particles, i.e., the proportion A1 (%) of the area of ​​the region occupied by the single metal particles, was then calculated using (Y / X) x 100 (%).

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

[0052] Example 1 <Preparation of Thermoelectric Semiconductor Material Layer> (1) Preparation of Thermoelectric Semiconductor Particles N-type cobalt antimony telluride CoSb, which is a cobalt-antimony based thermoelectric semiconductor material, was prepared. ２．９ Te ０．１ Thermoelectric semiconductor particles with an average particle size of 2.2 μm were prepared by pulverizing N-type cobalt antimony telluride CoSb (manufactured by Kojundo Chemical Laboratory, particle size: 15 μm) 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 ０．１ A coating liquid comprising 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 liquid 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 a temperature of 120°C for 10 minutes to remove the N-methylpyrrolidone, thereby forming a coating film. The obtained coating film was heat-treated at 600°C for 180 minutes in an argon-hydrogen mixed gas atmosphere to prepare 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 ０．１A 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 71.1 parts by mass of the particles of CoSb, 17.8 parts by mass of a polyethylene carbonate solution, and 11.1 parts by mass of bismuth particles. 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 of CoSb, 16.1 parts by mass of a polyethylene carbonate solution, and 26.8 parts by mass of bismuth particles. 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 particles of CoSb, 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. 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 CeFe ３ CoSb １２ A coating film was prepared using a coating liquid in which 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 were mixed and dispersed, 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 CoSb２．９ 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 ０．１ 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 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 CeFe ３ CoSb 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, P.F. (power factor), area ratio A1 of the region occupied by the monometal particles, area ratio A2 of the region occupied by the monometal particles, and filling rate of the thermoelectric conversion material layers obtained in Examples 1 to 6 and Comparative Examples 1 to 4.

[0063]

[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 provisions 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 provisions of the invention according to the first embodiment or the invention according to the second embodiment, and therefore improved thermoelectric performance can be expected.

[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.

[0066] A: Sum of thermoelectric semiconductor particle distribution region and void distribution region A1: Thermoelectric semiconductor particle distribution region A2: Void distribution region B2: Monometal particle distribution region (bismuth distribution region)

Claims

1. A thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometallic particles, wherein in a longitudinal cross section including the center of the thermoelectric conversion material layer, the ratio of the area occupied by the monometallic particles to the area occupied by the thermoelectric semiconductor particles and monometallic particles is 1 to 50%.

2. A thermoelectric conversion material layer containing thermoelectric semiconductor particles and monometallic particles, wherein in a longitudinal cross section including the central portion of the thermoelectric conversion material layer, the ratio of the area occupied by the monometallic 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 claim 1 or 2, 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 following general formula: (wherein 0.02≦x≦1.00, 0.02≦x+y≦1.00, and 0≦y).

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