Thermoelectric conversion element and method for manufacturing the same

Abstract

The present invention provides a thermoelectric conversion element which is provided with: a p-type thermoelectric conversion layer that contains a p-type material which contains carbon nanotubes and a conductive resin; and an n-type thermoelectric conversion layer that is in contact with the p-type thermoelectric conversion layer, while containing an n-type material that is obtained by doping the p-type material, which contains carbon nanotubes and a conductive resin, with a dopant. With respect to this thermoelectric conversion element, the dopant contains: anions that are complex ions; alkali metal cations; and a cation scavenger.

Description

Technical Field

[0001] The present invention relates to a thermoelectric conversion element and a method for manufacturing the same.

Background Art

[0002] Thermoelectric conversion is a technology that directly converts heat into electricity using the Seebeck effect, and has attracted attention as an energy recovery technology that converts waste heat generated when using fossil fuels into electricity.

[0003] As thermoelectric conversion materials, inorganic materials have conventionally been mainly studied, but there are problems such as difficulty in installing on curved surfaces, using rare elements or toxic elements, and not being suitable for installation on a large area.

[0004] Therefore, in recent years, organic materials have attracted attention as thermoelectric conversion materials that solve the above-described problems (for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a thermoelectric conversion element having low element resistance and high output, and a method for manufacturing the same.

Means for Solving the Problems

[0007] One aspect of the present invention relates to, for example, the following [1] to [8]. [1] A p-type thermoelectric conversion layer including a p-type material containing carbon nanotubes and a conductive resin, An n-type thermoelectric conversion layer in contact with the p-type thermoelectric conversion layer and including an n-type material obtained by doping a p-type material containing carbon nanotubes and a conductive resin with a dopant, Comprising, The dopant contains an anion that is a complex ion, an alkali metal cation, and a cation scavenger, a thermoelectric conversion element. [2] The thermoelectric conversion element according to [1], wherein the anion is selected from the group consisting of ferrocyanide ions, ferricyanide ions, tetrachloroferrate(III) ions, and tetrachloroferrate(II) ions. [3] The thermoelectric conversion element according to [1] or [2], wherein the cation scavenger is a crown ether-based compound. [4] The thermoelectric conversion element according to any one of [1] to [3], wherein the cation scavenger is a crown ether-based compound having a benzene ring in the molecule. [5] The thermoelectric conversion element according to any one of [1] to [4], wherein the conductive resin is composed of poly(3,4-ethylenedioxythiophene) and an electron acceptor. [6] The thermoelectric conversion element according to any one of [1] to [5], wherein the thicknesses of the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer are 1 to 500 μm. [7] A method for manufacturing a thermoelectric conversion element including a p-type thermoelectric conversion layer and an n-type thermoelectric conversion layer, Including a step of doping a part of a p-type material layer including a p-type material containing carbon nanotubes and a conductive resin with a dopant, The p-type thermoelectric conversion layer includes the p-type material, The n-type thermoelectric conversion layer includes an n-type material obtained by doping the p-type material with the dopant, The dopant contains an anion that is a complex ion, an alkali metal cation, and a cation scavenger, a method for manufacturing a thermoelectric conversion element. [8] The above process is an impregnation step of impregnating a part of the p-type material layer with a dopant solution containing the dopant and a solvent, a solvent removal step of removing at least a part of the solvent, The manufacturing method according to [7], which comprises the above steps.

Advantages of the Invention

[0008] According to the present invention, there are provided a thermoelectric conversion element with low element resistance and high output, and a method for manufacturing the same.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0011] (Thermoelectric Conversion Element) The thermoelectric conversion element of the present embodiment includes a p-type thermoelectric conversion layer and an n-type thermoelectric conversion layer in contact with the p-type thermoelectric conversion layer. The p-type thermoelectric conversion layer is a layer containing a p-type material containing carbon nanotubes and a conductive resin. The n-type thermoelectric conversion layer is a layer containing an n-type material obtained by doping a dopant into a p-type material containing carbon nanotubes and a conductive resin. The dopant contains an anion which is a complex ion, an alkali metal cation, and a cation scavenger.

[0012] The thermoelectric conversion element of this embodiment has low element resistance and high output. Although the reason for such an effect is not necessarily clear, the thermoelectric conversion element of this embodiment is formed based on a p-type material containing carbon nanotubes and a conductive resin for both the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer. Therefore, it is considered that the affinity between the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer is good, and an increase in element resistance due to the interface of the layers can be avoided.

[0013] <p-type material> The p-type material contains carbon nanotubes (CNT) and a conductive resin.

[0014] The carbon nanotubes may be any of single-layer, double-layer, and multi-layer. From the viewpoint of further improving the electrical conductivity, a single layer is preferable.

[0015] The carbon nanotubes preferably include single-walled carbon nanotubes. The content ratio of single-walled carbon nanotubes to the total amount of carbon nanotubes is preferably, for example, 25% by mass or more, more preferably 50% by mass or more, and may be 100% by mass.

[0016] The diameter of the single-walled carbon nanotubes is not particularly limited. For example, it may be 20 nm or less, preferably 10 nm or less, and more preferably 3 nm or less. There is no particular limitation on the lower limit of the diameter of the single-walled carbon nanotubes. For example, it may be 0.4 nm or more, or may be 0.5 nm or more. That is, the diameter of the single-walled carbon nanotubes may be, for example, 0.4 to 20 nm, 0.4 to 10 nm, 0.4 to 3 nm, 0.5 to 20 nm, 0.5 to 10 nm, or 0.5 to 3 nm.

[0017] In this specification, the diameter of the single-walled carbon nanotubes can be obtained from the wave number (ω (cm -1 )) of the peak appearing at 100 to 300 cm by Raman spectroscopy using the formula diameter (nm) = 248 / ω. -1 )) from the formula diameter (nm) = 248 / ω.

[0018] As an evaluation method of single-walled carbon nanotubes, the G / D ratio in laser Raman spectroscopy is known. In the present embodiment, the single-walled carbon nanotubes preferably have a G / D ratio of 10 or more, more preferably 20 or more, in laser Raman spectroscopy with a wavelength of 532 nm. By using such single-walled carbon nanotubes, a thermoelectric conversion material with even better electrical conductivity tends to be obtained. Note that the upper limit of the G / D ratio is not particularly limited, and the G / D ratio may be, for example, 500 or less, or may be 300 or less. That is, the G / D ratio may be, for example, 10 to 500, 10 to 300, 20 to 500, or 20 to 300.

[0019] The content of carbon nanotubes may be, for example, 20% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more, based on the total amount of the p-type material. Also, the content of carbon nanotubes may be, for example, 99% by mass or less, preferably 95% by mass or less, and more preferably 90% by mass or less, based on the total amount of the p-type material. That is, the content of carbon nanotubes may be, for example, 20 to 99% by mass, 20 to 95% by mass, 20 to 90% by mass, 30 to 99% by mass, 30 to 95% by mass, 30 to 90% by mass, 40 to 99% by mass, 40 to 95% by mass, or 40 to 90% by mass, based on the total amount of the p-type material.

[0020] The conductive resin is not particularly limited, and known conductive resins used in thermoelectric conversion materials can be used without particular limitation. Examples of the conductive resin include those containing polyaniline-based conductive polymers, polythiophene-based conductive polymers, polypyrrole-based conductive polymers, polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, polyphenylene vinylene-based conductive polymers, and the like. Examples of the polythiophene-based conductive polymer include poly(3,4-ethylenedioxythiophene).

[0021] As the conductive resin, a conductive resin composed of poly(3,4-ethylenedioxythiophene) (hereinafter may be referred to as PEDOT) and an electron acceptor is preferable. With such a conductive resin, the electrical conductivity tends to be further improved.

[0022] Examples of the electron acceptor include polystyrene sulfonic acid, polyvinyl sulfonic acid, poly(meth)acrylic acid, polyvinyl sulfonic acid, toluene sulfonic acid, dodecylbenzene sulfonic acid, camphor sulfonic acid, bis(2-ethylhexyl) sulfosuccinate, chlorine, bromine, iodine, phosphorus pentafluoride, arsenic pentafluoride, boron trifluoride, hydrogen chloride, sulfuric acid, nitric acid, tetrafluoroboric acid, perchloric acid, iron(III) chloride, tetracyanoquinodimethane, etc. From the viewpoint of further improving the electrical conductivity, as the electron acceptor, polystyrene sulfonic acid (hereinafter may be referred to as PSS) is preferable.

[0023] The content of the conductive resin may be, for example, 1% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, based on the total amount of the p-type material. Also, the content of the conductive resin may be, for example, 80% by mass or less, preferably 70% by mass or less, more preferably 60% by mass or less, based on the total amount of the p-type material. That is, the content of the conductive resin may be, for example, 1 to 80% by mass, 1 to 70% by mass, 1 to 60% by mass, 5 to 80% by mass, 5 to 70% by mass, 5 to 60% by mass, 10 to 80% by mass, 10 to 70% by mass, or 10 to 60% by mass, based on the total amount of the p-type material.

[0024] The total content of the carbon nanotubes and the conductive resin in the p-type material may be, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, may be 99% by mass or more, or may be 100% by mass, based on the total amount of the p-type material.

[0025] The p-type material may further contain other components other than those described above. Examples of other components include residual solvents, carbon-based conductive materials, inorganic conductive materials, inorganic thermoelectric materials, binder resins, surfactants, defoaming agents, coupling agents, antioxidants, ultraviolet absorbers, viscosity modifiers, leveling agents, and the like. The content of other components may be, for example, 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, may be 1% by mass or less, or may be 0% by mass, based on the total amount of the p-type material.

[0026] <p-type thermoelectric conversion layer> The p-type thermoelectric conversion layer is a layer containing a p-type material. The content of the p-type material in the p-type thermoelectric conversion layer may be, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, may be 99% by mass or more, or may be 100% by mass, based on the total amount of the p-type thermoelectric conversion layer.

[0027] The p-type thermoelectric conversion layer may further contain other components other than the p-type material. Examples of other components other than the p-type material include residual solvents, binder resins, surfactants, defoaming agents, coupling agents, antioxidants, ultraviolet absorbers, viscosity modifiers, leveling agents, and the like. The content of other components may be, for example, 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, may be 1% by mass or less, or may be 0% by mass, based on the total amount of the p-type thermoelectric conversion layer.

[0028] The thickness of the p-type thermoelectric conversion layer is preferably from 100 nm to 1 mm, more preferably from 200 nm to 800 μm, still more preferably from 300 nm to 600 μm, and even more preferably from 1 to 500 μm, from the viewpoint of obtaining appropriate electrical resistance and excellent flexibility. That is, the thickness of the p-type thermoelectric conversion layer may be, for example, from 100 nm to 1 mm, from 100 nm to 800 μm, from 100 nm to 600 μm, from 100 nm to 500 μm, from 200 nm to 1 mm, from 200 nm to 800 μm, from 200 nm to 600 μm, from 200 nm to 500 μm, from 300 nm to 1 mm, from 300 nm to 800 μm, from 300 nm to 600 μm, from 300 nm to 500 μm, from 1 μm to 1 mm, from 1 μm to 800 μm, from 1 μm to 600 μm, or from 1 μm to 500 μm.

[0029] The p-type thermoelectric conversion layer may be formed, for example, by applying a coating liquid containing a p-type material and a solvent onto a support and removing the solvent. Further, the p-type thermoelectric conversion layer may be formed by performing a solvent treatment on a p-type material layer formed by applying a coating liquid containing a p-type material and a solvent onto a support and removing the solvent.

[0030] The solvent is not particularly limited as long as it can dissolve the conductive resin and disperse the carbon nanotubes. The solvent may be, for example, water, alcohols (such as methanol and ethanol), amides (such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone), ketones (such as acetone and methyl ethyl ketone), glycols (such as ethylene glycol and diethylene glycol), dimethyl sulfoxide, acetonitrile, or the like. From the viewpoints of reducing environmental impact and handleability, one or more of water, methanol, and ethanol are preferable, and water is more preferable. From the viewpoint of the dispersibility of the carbon nanotubes, one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide are preferable.

[0031] The solid content concentration of the coating liquid (for example, it may be the content of the p-type material or the total content of the carbon nanotubes and the conductive resin) is not particularly limited and may be, for example, 0.1 mass% or more, preferably 0.2 mass% or more, and more preferably 0.3 mass% or more. The solid content concentration of the coating liquid may be, for example, 10 mass% or less, preferably 7 mass% or less, and more preferably 5 mass% or less. That is, the solid content concentration of the coating liquid may be, for example, 0.1 to 10 mass%, 0.1 to 7 mass%, 0.1 to 5 mass%, 0.2 to 10 mass%, 0.2 to 7 mass%, 0.2 to 5 mass%, 0.3 to 10 mass%, 0.3 to 7 mass%, or 0.3 to 5 mass%.

[0032] The solvent treatment may be carried out, for example, by a first step of impregnating the p-type material layer with a solvent, and a second step of removing the solvent from the p-type material layer after the first step.

[0033] Solvent treatment removes impurities such as low molecular weight components and metal ions that are mixed in the p-type material, strengthens the interaction between the carbon nanotubes and the conductive resin, and tends to improve the thermoelectric conversion properties. It is also believed that the solvent treatment causes the conductive resin in the p-type material to flow, filling the gaps between the carbon nanotubes and forming a denser structure.

[0034] The solvent is preferably a polar solvent. The relative dielectric constant of the solvent may be, for example, 10 or more, preferably 15 or more, and more preferably 20 or more. The solvent may be a protic solvent or an aprotic solvent, and is preferably an aprotic solvent.

[0035] The boiling point of the solvent is preferably 70° C. or higher, more preferably 90° C. or higher, further preferably 110° C. or higher, and may be 150° C. or higher. When a heat treatment is performed in the second step described below, if the boiling point of the solvent is high, the solvent does not volatilize in the early stage of the heat treatment, and the effect of the heat treatment is more pronounced.

[0036] Examples of the solvent include water (relative dielectric constant 78, boiling point 100°C), acetonitrile, ethanol, ethylene glycol, dimethyl sulfoxide (DMSO, relative dielectric constant 49, boiling point 189°C), N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and the like. The solvent may be used alone or in combination of two or more.

[0037] The solvent used in the first step may be the same as or different from the solvent of the coating solution, but it is preferably different. By using a solvent different from the solvent of the coating solution as the solvent in the first step, structural changes that did not occur during the formation of the p-type material layer can be caused, and the thermoelectric conversion performance tends to be further improved.

[0038] The second step may be, for example, a step of removing the solvent by natural drying, or a step of removing the solvent by performing heat treatment, reduced pressure treatment, or the like.

[0039] The second step preferably includes a step of heat-treating the p-type material layer impregnated with the solvent. It is considered that by heat treatment, the solvent with improved compatibility with the conductive resin causes the conductive resin in the material to flow, filling the gaps between the carbon nanotubes and forming a denser structure.

[0040] In the second step, the temperature of the heat treatment is not particularly limited and may be, for example, 40°C or higher, preferably 50°C or higher, and more preferably 60°C or higher. By increasing the temperature of the heat treatment, the Seebeck coefficient tends to be further improved. Also, the temperature of the heat treatment may be, for example, 250°C or lower, preferably 225°C or lower, and more preferably 200°C or lower. By decreasing the temperature of the heat treatment, the electrical conductivity tends to be further improved. That is, the Seebeck coefficient and the electrical conductivity tend to vary depending on the temperature of the heat treatment. Therefore, the temperature of the heat treatment may be appropriately selected, for example, within the above-mentioned range, by looking at the balance of the numerical values of the Seebeck coefficient and the electrical conductivity. The heating temperature may be, for example, 40 to 250°C, 40 to 225°C, 40 to 200°C, 50 to 250°C, 50 to 225°C, 50 to 200°C, 60 to 250°C, 60 to 225°C, or 60 to 200°C.

[0041] The time of the heat treatment is not particularly limited. The time of the heat treatment may be, for example, 1 minute or longer, preferably 10 minutes or longer, and may be 12 hours or shorter, preferably 6 hours or shorter. That is, the time of the heat treatment may be, for example, 1 minute to 12 hours, 1 minute to 6 hours, 10 minutes to 12 hours, or 10 minutes to 6 hours.

[0042] Note that the heat treatment in the second step does not necessarily have to be for the purpose of removing the solvent, and the second step may be a step of further performing a treatment for removing the solvent after the heat treatment.

[0043] In a preferred embodiment, the ratio (V1 / V0) of the volume (V1) of the p-type material layer after solvent treatment to the volume (V0) of the p-type material layer before solvent treatment may be, for example, 0.6 or less, preferably 0.5 or less. Also, the ratio (V1 / V0) may be, for example, 0.1 or more, preferably 0.2 or more. That is, the solvent treatment may be, for example, a process of subjecting the p-type material to solvent treatment such that the ratio (V1 / V0) falls within the above range. Note that the above ratio (V1 / V0) can also be referred to as the ratio of the thicknesses of the p-type material layer before and after solvent treatment. The ratio (V1 / V0) may be, for example, 0.1 to 0.6, 0.1 to 0.5, 0.2 to 0.6, or 0.2 to 0.5.

[0044] <n-type material> The n-type material is obtained by doping a dopant into a p-type material containing carbon nanotubes and a conductive resin. Examples of the p-type material include the same materials as those contained in the above-described p-type thermoelectric conversion layer. The p-type material for forming the n-type material preferably contains the same conductive resin as the p-type material of the p-type thermoelectric conversion layer, more preferably contains the same carbon nanotubes and the same conductive resin as the p-type material of the p-type thermoelectric conversion layer, and even more preferably has the same composition as the p-type material of the p-type thermoelectric conversion layer.

[0045] In this specification, the dopant is intended to be a substance that changes the Seebeck coefficient of the material to which the dopant is doped.

[0046] In this specification, "changing the Seebeck coefficient" is intended to mean decreasing the value of the Seebeck coefficient or changing the value of the Seebeck coefficient from a positive value to a negative value. A thermoelectric conversion material having a positive Seebeck coefficient has p-type conductivity, and a thermoelectric conversion material having a negative Seebeck coefficient has n-type conductivity. The Seebeck coefficient can be measured, for example, by the measurement method described below, and the polarity of the thermoelectric conversion material can be determined from the positive or negative of the measured value.

[0047] <Measurement of Seebeck coefficient> The polyimide plate coated with the measurement target is cut into pieces of 20 mm × 10 mm. One end of the test piece is cooled (to about 5°C), and the other end is heated (to about 5°C). The temperature difference and voltage generated at both ends are measured with a chromel-alumel thermocouple, and the Seebeck coefficient is calculated from the slopes of the temperature difference and voltage.

[0048] In this embodiment, the dopant contains an anion that is a complex ion (hereinafter, also simply referred to as "anion"), an alkali metal cation (hereinafter, also simply referred to as "cation"), and a cation scavenger (hereinafter, also simply referred to as "scavenger"). By doping the p-type material with the dopant, the Seebeck coefficient of the p-type material changes, and an n-type material showing n-type conductivity can be obtained. Further, by containing the specific components in the dopant, excellent thermoelectric conversion performance is realized.

[0049] The reason for the above effects is not particularly limited, but it is considered that one of the reasons is that the scavenger contained in the dopant captures the cation, dissociates the anion, and the anion changes the carrier of the carbon nanotube from a hole to an electron. At this time, in this embodiment, since the anion is a complex ion having a metal atom at the center, it is considered that n-type doping is significantly achieved by the interaction between the metal atom and the carbon nanotube. Further, since the complex ion has a large ionic size, it is also considered that one of the reasons for the above effects is that the dissociation property with the cation captured by the scavenger is good.

[0050] Further, since the anion of the dopant in this embodiment is a complex ion, metal atoms derived from the complex ion remain in the n-type material. In this embodiment, the metal atoms remaining in the n-type material function as an antioxidant, suppressing the change in physical properties over time and improving the storage stability.

[0051] Examples of the anion that is a complex ion include anions selected from the group consisting of ferrocyanide ion, ferricyanide ion, tetrachloroferrate(III) ion, tetrachloroferrate(II) ion, tetracyanonickelate(II) ion, tetrachloronickelate(II) ion, tetracyanocobaltate(II) ion, tetrachlorocobaltate(II) ion, tetracyanocuprate(I) ion, tetrachlorocuprate(II) ion, hexacyanochromium(III) ion, tetrahydroxozincate(II) ion, and tetrahydroxoaluminate(III) ion. Among these, ferrocyanide ion is preferred. When the anion is ferrocyanide ion, an n-type material having better characteristics can be obtained. Further, when the anion is ferrocyanide ion, iron atoms remaining in the n-type material function suitably as an antioxidant, physical property changes over time are more suppressed, and the storage stability tends to be further improved.

[0052] The anion that is a complex ion may contain iron atoms and is preferably selected from the group consisting of, for example, ferrocyanide ion, ferricyanide ion, tetrachloroferrate(III) ion, and tetrachloroferrate(II) ion. Since an n-type material having better characteristics can be obtained, the anion containing iron atoms is preferably ferrocyanide ion. Further, from the viewpoint of the antioxidant effect, the content of iron atoms in the n-type material is preferably 0.001% by mass to 15% by mass, more preferably 0.005% by mass to 12% by mass, and still more preferably 0.01% by mass to 10% by mass. That is, the content of iron atoms in the n-type material may be, for example, 0.001 to 15% by mass, 0.001 to 12% by mass, 0.001 to 10% by mass, 0.005 to 15% by mass, 0.005 to 12% by mass, 0.005 to 10% by mass, 0.01 to 15% by mass, 0.01 to 12% by mass, or 0.01 to 10% by mass. In the present specification, the content of iron atoms indicates a value measured by scanning electron microscope (SEM)-energy dispersive X-ray spectroscopy (EDS).

[0053] The anion may be an anion generated by dissociation of the complex salt in the dopant solution. Examples of the complex salt include potassium ferrocyanide, sodium ferrocyanide, potassium ferricyanide, sodium ferricyanide, potassium tetrachloroferrate(III), sodium tetrachloroferrate(III), potassium tetrachloroferrate(II), sodium tetrachloroferrate(II), and the like. The complex salt may be a hydrate.

[0054] Examples of the alkali metal cation include sodium ion, potassium ion, lithium ion, and the like.

[0055] The cation scavenger is not particularly limited as long as it is a substance having the ability to capture cations. For example, crown ether compounds, cyclodextrins, calixarenes, ethylenediaminetetraacetic acid, porphyrins, phthalocyanines, and their derivatives can be mentioned. In an organic solvent, it is preferable to use a crown ether compound.

[0056] Examples of the crown ether compound include 15-crown-5-ether, 18-crown-6-ether, 12-crown-4-ether, benzo-18-crown-6-ether, benzo-15-crown-5-ether, benzo-12-crown-4-ether, and the like. The crown ether used as the scavenger may have its ring size selected according to the size of the metal ion to be captured. For example, when the metal ion is a potassium ion, an 18-membered crown ether is preferable; when the metal ion is a sodium ion, a 15-membered crown ether is preferable; and when the metal ion is a lithium ion, a 12-membered crown ether is preferable.

[0057] The crown ether-based compound preferably has a benzene ring in the molecule. By using such a crown ether-based compound, p-type formation due to oxidation is suppressed, and the storage stability tends to be further improved. Examples of the crown ether-based compound having a benzene ring include benzo-18-crown-6-ether, benzo-15-crown-5-ether, benzo-12-crown-4-ether, and the like.

[0058] The molar ratio (C2 / C1) of the content C2 of the scavenger to the content C1 of the cation may be, for example, from 0.1 to 5, preferably from 0.3 to 3, and more preferably from 0.5 to 2. That is, the molar ratio (C2 / C1) may be, for example, 0.1 to 5, 0.1 to 3, 0.1 to 2, 0.3 to 5, 0.3 to 3, 0.3 to 2, 0.5 to 5, 0.5 to 3, or 0.5 to 2.

[0059] The dopant may optionally contain substances other than the above-described anions, cations, and scavengers. Such substances are not particularly limited as long as they do not inhibit the function of the dopant, and examples thereof include water, organic solvents, and the like.

[0060] The dopant may contain a plurality of types of anions, cations, and scavengers, respectively.

[0061] The method for producing the n-type material may include a step of doping the p-type material with a dopant (n-type formation step).

[0062] The method for doping the p-type material with the dopant in the n-type formation step is not particularly limited, and examples thereof include a method of bringing a dopant solution containing the dopant into contact with the p-type material.

[0063] In a preferred embodiment, the n-type formation step may include an impregnation step of impregnating at least a part of the p-type material with a dopant solution containing the dopant and a solvent, and a solvent removal step of removing the solvent from the material after impregnation with the dopant solution.

[0064] The boiling point of the solvent is preferably 70° C. or higher, more preferably 90° C. or higher, even more preferably 110° C. or higher, and may be 150° C. or higher. When a heat treatment is performed in the solvent removal step described below, if the boiling point of the solvent is high, most of the solvent is not removed in the early stage of the heat treatment, and the effect of the heat treatment is fully exerted. By using a solvent having the above-mentioned suitable boiling point range, the effect of the heat treatment is more significantly exerted.

[0065] Examples of the solvent include water, acetonitrile, ethanol, ethylene glycol, dimethylsulfoxide (DMSO), N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, etc. The solvent may be used alone or in combination of two or more.

[0066] The dopant solution may contain other components in addition to the dopant and the solvent, as long as the effects of the present invention are not impaired. Examples of other components include a binder resin, an antioxidant, a thickener, and a surfactant.

[0067] The method for impregnating the p-type material with the dopant solution is not particularly limited, and examples thereof include a method of immersing the p-type material in the dopant solution, and a method of applying the dopant solution to the p-type material.

[0068] The dopant of this embodiment has excellent doping efficiency, so that doping can be completed in a short time. The time for impregnating the p-type material with the dopant solution may be, for example, 10 minutes or more. The time for impregnating the p-type material with the dopant solution may be, for example, 72 hours or less, or 24 hours or less. When the time for impregnating the dopant solution is within the above range, the productivity of the n-type material is excellent.

[0069] In the impregnation step, a material impregnated with a dopant solution is obtained, and this material is subjected to a solvent removal step. Of the solvents used in the impregnation step, those other than those impregnated or adhered to the material may be removed at the end of the impregnation step. For example, when a p-type material is immersed in a dopant solution in the impregnation step, the material may be taken out of the dopant solution and subjected to a solvent removal step.

[0070] In the solvent removal step, at least a part of the solvent is removed from the material after impregnation with the above-described dopant solution. In the solvent removal step, it is not necessarily required to remove all of the solvent, and the solvent may remain as long as it functions sufficiently as an n-type material.

[0071] The solvent removal step may be, for example, a step of removing the solvent by natural drying, or may be a step of removing the solvent by performing heat treatment, reduced pressure treatment, or the like.

[0072] In a preferred embodiment, the solvent removal step may include a step of heat-treating the material impregnated with the solvent. In this embodiment, it is considered that the solvent with improved compatibility with the conductive resin due to heating causes the conductive resin in the material to flow, filling the gaps between the carbon nanotubes and forming a denser structure. Therefore, in this embodiment, there is a tendency for the thermoelectric conversion characteristics to be more significantly improved.

[0073] In this aspect, the temperature of the heat treatment is not particularly limited. For example, it may be 40°C or higher, preferably 50°C or higher, and more preferably 60°C or higher. By increasing the temperature of the heat treatment, the Seebeck coefficient tends to be further improved. Also, the temperature of the heat treatment may be, for example, 250°C or lower, preferably 225°C or lower, and more preferably 200°C or lower. By decreasing the temperature of the heat treatment, the electrical conductivity tends to be further improved. That is, the heat treatment temperature may be, for example, 40 - 250°C, 40 - 225°C, 40 - 200°C, 50 - 250°C, 50 - 225°C, 50 - 200°C, 60 - 250°C, 60 - 225°C, or 60 - 200°C. In this aspect, the Seebeck coefficient and the electrical conductivity tend to vary depending on the temperature of the heat treatment. Therefore, the temperature of the heat treatment may be appropriately selected, for example, within the above-mentioned range, by looking at the balance of the numerical values of the Seebeck coefficient and the electrical conductivity.

[0074] In this aspect, the time of the heat treatment is not particularly limited. The time of the heat treatment may be, for example, 1 minute or longer, preferably 10 minutes or longer, and may be 12 hours or shorter, preferably 6 hours or shorter. That is, the time of the heat treatment may be, for example, 1 minute - 12 hours, 1 minute - 6 hours, 10 minutes - 12 hours, or 10 minutes - 6 hours.

[0075] Note that the heat treatment in this aspect does not necessarily have to be for the purpose of removing the solvent, and the solvent removal step according to this aspect may be a step of further performing a treatment for removing the solvent after the heat treatment.

[0076] In this embodiment, among the p-type materials, the portion doped with the dopant becomes an n-type material. In this embodiment, all of the p-type materials may be doped with the dopant to form an n-type material, or a part of the p-type materials may be doped with the dopant to form a composite of the p-type material and the n-type material.

[0077] <n-type thermoelectric conversion layer> The n-type thermoelectric conversion layer is a layer containing an n-type material. The content of the n-type material in the n-type thermoelectric conversion layer may be, for example, 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, may be 99% by mass or more, or may be 100% by mass, based on the total amount of the n-type thermoelectric conversion layer.

[0078] The n-type thermoelectric conversion layer may further contain other components other than the n-type material. Examples of other components other than the n-type material include residual solvents, binder resins, surfactants, defoaming agents, coupling agents, antioxidants, ultraviolet absorbers, viscosity modifiers, leveling agents, and the like. The content of other components may be, for example, 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, may be 1% by mass or less, or may be 0% by mass, based on the total amount of the n-type thermoelectric conversion layer.

[0079] From the viewpoint of obtaining appropriate electrical resistance and excellent flexibility, the thickness of the n-type thermoelectric conversion layer is preferably 100 nm to 1 mm, more preferably 200 nm to 800 μm, still more preferably 300 nm to 600 μm, and even more preferably 1 to 500 μm. That is, the thickness of the n-type thermoelectric conversion layer may be, for example, 100 nm to 1 mm, 100 nm to 800 μm, 100 nm to 600 μm, 100 nm to 500 μm, 200 nm to 1 mm, 200 nm to 800 μm, 200 nm to 600 μm, 200 nm to 500 μm, 300 nm to 1 mm, 300 nm to 800 μm, 300 nm to 600 μm, 300 nm to 500 μm, 1 μm to 1 mm, 1 μm to 800 μm, 1 μm to 600 μm, or 1 μm to 500 μm.

[0080] For example, the n-type thermoelectric conversion layer can be formed by coating a coating liquid containing a p-type material and a solvent on a support, removing the solvent to form a p-type material layer, and doping the p-type material layer with a dopant. Further, the n-type thermoelectric conversion layer can also be formed by coating a coating liquid containing a p-type material and a solvent on a support, removing the solvent to form a p-type material layer, performing a solvent treatment on the p-type material layer, and doping the p-type material layer after the solvent treatment with a dopant.

[0081] <Thermoelectric conversion element> The thermoelectric conversion element of the present embodiment includes a p-type thermoelectric conversion layer and an n-type thermoelectric conversion layer in contact with the p-type thermoelectric conversion layer.

[0082] In the thermoelectric conversion element of the present embodiment, the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer may be disposed on a support. Examples of the support include polyimide, polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, polybutylene terephthalate, polycarbonate, polyether ether ketone, polyphenyl sulfide, polysulfone, glass, copper, silver, gold, aluminum, and the like. Among these, it is preferably selected from the group consisting of polyimide, polyethylene terephthalate, and polyethylene naphthalate because of its good flexibility.

[0083] In the thermoelectric conversion element of the present embodiment, the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer may be laminated in the thickness direction or may be disposed adjacent to each other in the in-plane direction. Further, the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer may be disposed so that a part thereof overlaps.

[0084] The thermoelectric conversion element of the present embodiment may include a plurality of p-type thermoelectric conversion layers and n-type thermoelectric conversion layers, respectively.

[0085] FIG. 1(a) is a top view showing one form of the thermoelectric conversion element, and FIG. 1(b) is a cross-sectional view showing the Ib-Ib cross-section of FIG. 1(a). The thermoelectric conversion element 10 shown in FIGS. 1(a) and 1(b) includes a p-type thermoelectric conversion layer 11 and an n-type thermoelectric conversion layer 12. The p-type thermoelectric conversion layer 11 and the n-type thermoelectric conversion layer 12 are disposed adjacent to each other on a support 13.

[0086] The thermoelectric conversion element 10 can be manufactured, for example, by forming a layer of a p-type material on a support 13 and doping a part of the layer with a dopant. A part of the layer (the part doped with the dopant) becomes the n-type thermoelectric conversion layer 12, and the other part (the part not doped with the dopant) is used as the p-type thermoelectric conversion layer 11.

[0087] FIG. 2(a) is a top view showing another form of the thermoelectric conversion element, and FIG. 2(b) is a cross-sectional view showing the IIb-IIb cross-section of FIG. 2(a). The thermoelectric conversion element 20 shown in FIGS. 2(a) and 2(b) includes a p-type thermoelectric conversion layer 21 and an n-type thermoelectric conversion layer 22. The p-type thermoelectric conversion layer 21 and the n-type thermoelectric conversion layer 22 are arranged on the support 23 such that a part of the n-type thermoelectric conversion layer 22 overlaps the p-type thermoelectric conversion layer 21.

[0088] The thermoelectric conversion element 20 can be manufactured, for example, by forming the p-type thermoelectric conversion layer 21 on the support 23 and then forming the n-type thermoelectric conversion layer 22 so as to overlap the p-type thermoelectric conversion layer 21.

[0089] The thermoelectric conversion element of the present embodiment may further include other members other than the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer.

[0090] The thermoelectric conversion element of the present embodiment may further include, for example, a first conductive substrate electrically connected to the p-type thermoelectric conversion layer side and a second conductive substrate electrically connected to the n-type thermoelectric conversion layer side. The first conductive substrate and the second conductive substrate can also be referred to as the first electrode and the second electrode, respectively.

[0091] Further, the thermoelectric conversion element of the present embodiment may further include a sealing material for sealing the thermoelectric conversion material, wiring for electrically connecting the thermoelectric conversion elements to each other or taking out power to an external circuit, and a heat insulating material or a heat conductive material for controlling the heat conductivity of the thermoelectric conversion element.

[0092] In the thermoelectric conversion element of the present embodiment, other members other than the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer may be the same as those of a known thermoelectric conversion element, for example. That is, the thermoelectric conversion element of the present embodiment may be one in which the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer in a known thermoelectric conversion element are replaced with the above-described p-type thermoelectric conversion layer and n-type thermoelectric conversion layer, respectively.

[0093] (Method for manufacturing a thermoelectric conversion element) The manufacturing method of the thermoelectric conversion element of the present embodiment includes a step (n-type conversion step) of doping a dopant into a part of a p-type material layer containing a p-type material containing carbon nanotubes and a conductive resin. Among the p-type material layer, the part doped with the dopant becomes an n-type thermoelectric conversion layer, and the other part (the part not doped with the dopant) becomes a p-type thermoelectric conversion layer.

[0094] The n-type conversion step may include an impregnation step of impregnating a part of the p-type material layer with a dopant solution containing a dopant and a solvent, and a solvent removal step of removing at least a part of the solvent.

[0095] The p-type material, the dopant, the n-type conversion step, the impregnation step, and the solvent removal step may be the same as the above-described p-type material, the dopant, the n-type conversion step, the impregnation step, and the solvent removal step.

[0096] According to the manufacturing method of the thermoelectric conversion element of the present embodiment, the above-described thermoelectric conversion element (particularly, the thermoelectric conversion element 10 shown in Fig. 1(a)) can be efficiently manufactured.

[0097] As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to the above embodiments.

Examples

[0098] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0099] [Example 1] (Preparation of coating solution) A single-layer CNT aqueous dispersion (G / D ratio of single-layer CNT: 41, diameter: 0.9 - 1.7 nm) with a single-layer CNT concentration of 0.4 mass% was prepared. 0.56 g of "Clevios PH1000" (PEDOT / PSS aqueous dispersion, solid content concentration: 1.2 mass%) manufactured by Heraeus and 5 g of the single-layer CNT aqueous dispersion were mixed and stirred at a stirring temperature of 30 °C with a rotation-revolution mixer ("Avatori Renkitaro ARE-310" manufactured by Shinki) for 10 minutes to prepare a coating solution.

[0100] (Formation of p-type material layer) A polyimide film (thickness: 100 μm) was attached to a stainless steel plate with a thickness of 500 μm, and a range with a width of 10 mm and a length of 60 mm was formed on the polyimide film using masking tape. A coating solution was applied using a doctor blade to a thickness of 2.8 mm and dried at 60 °C for 2 hours. After drying, the masking tape was peeled off to obtain a p-type material layer with a width of 10 mm and a length of 60 mm.

[0101] (Solvent treatment) The p-type material layer obtained above was immersed in dimethyl sulfoxide (DMSO) as a solvent at room temperature (25 °C) for 5 minutes. Then, it was heat-dried at 60 °C for 120 minutes to fabricate a p-type thermoelectric conversion layer. The thickness of the p-type thermoelectric conversion layer was 15 μm, and V1 / V0 was 0.1.

[0102] (Preparation of dopant solution) 0.106 g of potassium ferrocyanide trihydrate and 0.312 g of benzo-18-crown-6-ether were dissolved in 5 mL of ultrapure water (the concentrations of potassium ions and benzo-18-crown-6-ether were 0.2 M each) to obtain a dopant solution.

[0103] (Doping treatment) 120 μL of the dopant solution was dropped onto a partial region (width 10 mm × length 30 mm) of the obtained p-type thermoelectric conversion layer. Then, after heat-drying at 60 °C for 30 minutes, it was heated at 100 °C for 60 minutes to n-type a part of the p-type thermoelectric conversion layer, and a thermoelectric conversion element 1 was obtained.

[0104] [Example 2] (Formation of p-type thermoelectric conversion layer) The same operations as in Example 1 were performed except that the coating range of the coating solution was changed to a width of 10 mm and a length of 31 mm to obtain a p-type thermoelectric conversion layer.

[0105] (Formation of n-type thermoelectric conversion layer) The same coating solution as in Example 1 was applied in a range of 10 mm in width and 31 mm in length so as to overlap the end portion 1 mm in the length direction of the p-type thermoelectric conversion layer, and a p-type material layer was formed. Next, the p-type material layer was immersed in DMSO for 30 minutes, and then heated and dried at 60 °C for 120 minutes. Next, 124 μL of the same dopant solution as in Example 1 was dropped onto the p-type material layer, and after being heated and dried at 60 °C for 30 minutes, it was heated at 100 °C for 60 minutes to form an n-type thermoelectric conversion layer. Thus, a thermoelectric conversion element 2 was obtained.

[0106] [Example 3] In the preparation of the coating solution, the same operations as in Example 1 were performed except that the amount of the PEDOT / PSS dispersion was changed to 0.087 g, and a thermoelectric conversion element 3 was obtained.

[0107] [Example 4] In the preparation of the coating solution, the same operations as in Example 1 were performed except that the amount of the PEDOT / PSS dispersion was changed to 1.667 g, and a thermoelectric conversion element 3 was obtained.

[0108] [Example 5] In the preparation of the dopant solution, the same operations as in Example 1 were performed except that 0.121 g of sodium ferrocyanide decahydrate was used instead of potassium ferrocyanide trihydrate and 0.268 g of benzo-15-crown-5-ether was used instead of benzo-18-crown-6-ether, and a thermoelectric conversion element 5 was obtained.

[0109] [Comparative Example 1] As Comparative Example 1, a thermoelectric conversion element shown in FIGS. 3(a) and 3(b) was fabricated. FIG. 3(a) is a top view showing the thermoelectric conversion element of Comparative Example 1, and FIG. 3(b) is a cross-sectional view showing the IIIb-IIIb cross-section of FIG. 3(a). In the thermoelectric conversion element 30 shown in FIGS. 3(a) and 3(b), a p-type thermoelectric conversion layer 31 and an n-type thermoelectric conversion layer 32 are spaced apart and arranged on a support 33, and the p-type thermoelectric conversion layer 31 and the n-type thermoelectric conversion layer 32 are electrically connected by an electrode 34.

[0110] (Formation of gold electrode) A copper tape (manufactured by Teraoka Seisakusho) with a width of 10 mm and a length of 2 mm was attached onto a polyimide film. After nickel plating the copper surface, gold plating was further performed thereon to form a gold electrode.

[0111] (Formation of p-type thermoelectric conversion layer) A masking tape with a width of 1 mm was attached to the center of the gold electrode. Next, a region with a width of 1 mm and a length of 31 mm was formed on the polyimide film such that the center of the region coincided with the center of the gold electrode by means of the masking tape. The coating solution prepared in the same manner as in Example 1 was applied to this region, dried, and the masking tape was peeled off. Next, solvent treatment was performed in the same manner as in Example 1 to obtain a p-type thermoelectric conversion layer formed separately into two through the gold electrode.

[0112] (Formation of n-type thermoelectric conversion layer) 120 μL of the dopant solution prepared in the same manner as in Example 1 was dropped onto one of the two p-type thermoelectric conversion layers. Then, after heating and drying at 60 °C for 30 minutes, it was heated at 100 °C for 60 minutes to obtain a thermoelectric conversion element 6.

[0113] [Comparative Example 2] (Formation of p-type thermoelectric conversion layer) The same operations as in Example 1 were performed except that the coating range of the coating solution was changed to a width of 10 mm and a length of 31 mm to obtain a p-type thermoelectric conversion layer.

[0114] (Formation of n-type thermoelectric conversion layer) 2.9 g of titanium disulfide (manufactured by Kojundo Chemical Laboratory Co., Ltd.) and 3.9 g of an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride (resin concentration: 4 mass%) were mixed and stirred at a stirring temperature of 30 °C using a rotation-revolution mixer (Shinki "Avatore Rentaro ARE-310") for 10 minutes to prepare a titanium disulfide dispersion. Next, the titanium disulfide dispersion was applied to a region with a width of 10 mm × length of 31 mm so as to overlap the end portion 1 mm in the length direction of the p-type thermoelectric conversion layer, and heated at 80 °C for 120 minutes to remove the solvent and form an n-type thermoelectric conversion layer. Thereby, a thermoelectric conversion element 7 was obtained.

[0115] (Evaluation of element resistance) For each of the thermoelectric conversion elements 1 to 7, probe 1 and probe 2 were brought into contact with the positions 2 mm from both ends, respectively, and probe 3 and probe 4 were brought into contact with the positions 5 mm from both ends, respectively. While sweeping the current flowing between probe 1 and probe 2 between -10 mA and 10 mA, the voltage between probe 3 and probe 4 was measured, and the resistance of the element was calculated from the slope of the obtained current-voltage straight line. The results are shown in Table 1.

[0116] In Table 1, the values of the element resistance are shown as relative values with the element resistance of Example 1 being 100. Also, in Table 1, the items of "CNT" and "conductive resin" indicate the content ratios of the respective components in the p-type material. Further, in Table 1, the item of "dopant" indicates the type of dopant used, with the dopant used in Example 1 being A and the dopant used in Example 5 being B. Also, in Table 1, the item of "element configuration" indicates the configuration of the corresponding element, with the thermoelectric conversion element 10 in FIG. 1 being 10, the thermoelectric conversion element 20 in FIG. 2 being 20, and the thermoelectric conversion element 30 in FIG. 3 being 30.

[0117]

Table 1

[0118] As shown in Table 1, it was confirmed that the thermoelectric conversion elements of the examples have low element resistance and are high-output thermoelectric conversion elements.

Explanation of Reference Signs

[0119] 10, 20, 30... thermoelectric conversion elements, 11, 21, 31... p-type thermoelectric conversion layers, 12, 22, 32... n-type thermoelectric conversion layers, 13, 23, 33... supports, 34... electrodes.

Claims

1. A p-type thermoelectric conversion layer including a p-type material containing carbon nanotubes and a conductive resin, An n-type thermoelectric conversion layer in contact with the p-type thermoelectric conversion layer and including an n-type material obtained by doping a p-type material containing carbon nanotubes and a conductive resin with a dopant, provided with The dopant is a complex ion and contains an anion containing an iron atom, an alkali metal cation, and a cation trapping agent that traps the alkali metal cation and dissociates the anion. A thermoelectric conversion element.

2. The thermoelectric conversion element according to claim 1, wherein the anion is selected from the group consisting of ferrocyanide ions, ferricyanide ions, tetrachloroferrate (III) ions, and tetrachloroferrate (II) ions.

3. The thermoelectric conversion element according to claim 1, wherein the cation trapping agent is a crown ether-based compound.

4. The thermoelectric conversion element according to claim 1, wherein the cation trapping agent is a crown ether-based compound having a benzene ring in the molecule.

5. The thermoelectric conversion element according to claim 1, wherein the conductive resin is composed of poly(3,4-ethylenedioxythiophene) and an electron acceptor.

6. The thermoelectric conversion element according to any one of claims 1 to 5, wherein the thicknesses of the p-type thermoelectric conversion layer and the n-type thermoelectric conversion layer are 1 to 500 μm.

7. A method for manufacturing a thermoelectric conversion element including a p-type thermoelectric conversion layer and an n-type thermoelectric conversion layer, including a step of doping a part of a p-type material layer including a p-type material containing carbon nanotubes and a conductive resin with a dopant, the p-type thermoelectric conversion layer includes the p-type material, the n-type thermoelectric conversion layer includes an n-type material obtained by doping the p-type material with the dopant, The method for manufacturing a thermoelectric conversion element, wherein the dopant is a complex ion and contains an anion containing an iron atom, an alkali metal cation, and a cation scavenger that captures the alkali metal cation and dissociates the anion.

8. The step is An impregnation step of impregnating a part of the p-type material layer with a dopant solution containing the dopant and a solvent, A solvent removal step of removing at least a part of the solvent, The manufacturing method according to claim 7, comprising:

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