CN113632252A

CN113632252A - Thermoelectric conversion material layer and method for producing same

Info

Publication number: CN113632252A
Application number: CN202080024639.7A
Authority: CN
Inventors: 关佑太; 户高昌也; 加藤邦久
Original assignee: Lintec Corp
Current assignee: Lintec Corp
Priority date: 2019-03-29
Filing date: 2020-03-26
Publication date: 2021-11-09
Also published as: JPWO2020203612A1; TW202105778A; WO2020203612A1

Abstract

The present invention provides a thermoelectric conversion material layer having high thermoelectric performance and improved electrical conductivity of a thermoelectric conversion material in a thermoelectric conversion material layer formed from a coating film of a thermoelectric semiconductor composition, wherein the thermoelectric conversion material layer has a void portion, and the filling ratio is 0.800 or more and less than 1.000 when the ratio of the area of the thermoelectric semiconductor composition in the area of a vertical cross section including a central portion of the thermoelectric conversion material layer is taken as the filling ratio, and a method for manufacturing the same.

Description

Thermoelectric conversion material layer and method for producing same

Technical Field

The invention relates to a thermoelectric conversion material layer and a method for manufacturing the same.

Background

Conventionally, as one of the effective utilization methods of energy, there is a device that directly converts thermal energy and electric energy to each other by using a thermoelectric conversion module having thermoelectric effects such as the seebeck effect and the peltier effect.

Among them, as the thermoelectric conversion module, a so-called pi-type thermoelectric conversion element is known. Pi-type is composed as follows: a pair of electrodes separated from each other are provided on a substrate, for example, a P-type thermoelectric element is provided on one electrode and an N-type thermoelectric element is provided on the other electrode, which are similarly separated from each other, and the upper surfaces of the thermoelectric materials of both are connected to the electrodes of the opposing substrate. In addition, it is known to use a so-called in-plane (in-plane) type thermoelectric conversion element. The in-plane type is constituted as follows: the P-type thermoelectric elements and the N-type thermoelectric elements are alternately arranged in the in-plane direction of the substrate, and for example, the lower portions of the junctions between the two thermoelectric elements are connected in series via electrodes.

Among them, there are demands for improvement in bendability, thinning, and thermoelectric performance of thermoelectric conversion modules. In order to meet these requirements, for example, resin substrates such as polyimide are used as substrates used in thermoelectric conversion modules from the viewpoint of heat resistance and flexibility. As the n-type thermoelectric semiconductor material and the p-type thermoelectric semiconductor material, a bismuth telluride-based material is used from the viewpoint of thermoelectric performance, and for example, a thermoelectric semiconductor composition containing a resin and a thermoelectric semiconductor material is prepared from the viewpoint of flexibility and reduction in thickness, and is formed as a coating film by a screen printing method or the like (patent document 1 and the like).

Documents of the prior art

Patent document

Patent document 1: international publication No. 2016/104615

Disclosure of Invention

Problems to be solved by the invention

However, since the thermoelectric semiconductor material used in the thermoelectric conversion module is formed as a thermoelectric conversion material layer from a thermoelectric semiconductor composition containing a resin, a thermoelectric semiconductor material, and the like, in the form of a coating film, the resulting thermoelectric conversion material layer cannot sufficiently obtain high electrical conductivity, and thus has insufficient thermoelectric performance.

In view of the above circumstances, an object of the present invention is to provide a thermoelectric conversion material layer having high thermoelectric performance in which the electrical conductivity of a thermoelectric conversion material in the thermoelectric conversion material layer formed of a coating film of a thermoelectric semiconductor composition is improved, and a method for producing the same.

Means for solving the problems

As a result of intensive studies to solve the above problems, the present inventors have found that a thermoelectric conversion material layer having a high filling rate of a thermoelectric conversion material can provide high electrical conductivity by embedding a large number of voids in a coating film of a thermoelectric semiconductor composition and reducing the volume thereof, and have completed the present invention.

That is, the present invention provides the following (1) to (10).

(1) A thermoelectric conversion material layer formed of a coating film of a thermoelectric semiconductor composition, wherein the thermoelectric conversion material layer has voids, and the filling ratio is 0.800 or more and less than 1.000 when the ratio of the area of the thermoelectric semiconductor composition in the area of a vertical cross section including a central portion of the thermoelectric conversion material layer is a filling ratio.

(2) The thermoelectric conversion material layer according to the above (1), wherein the thermoelectric semiconductor composition comprises a thermoelectric semiconductor material which is a bismuth-tellurium-based thermoelectric semiconductor material, a telluride-based thermoelectric semiconductor material, an antimony-tellurium-based thermoelectric semiconductor material, or a bismuth selenide-based thermoelectric semiconductor material.

(3) The thermoelectric conversion material layer according to the above (1) or (2), wherein the thermoelectric semiconductor composition further comprises a heat-resistant resin.

(4) The thermoelectric conversion material layer according to any one of the above (1) to (3), wherein the heat-resistant resin is a polyimide resin, a polyamide resin, a polyamideimide resin, or an epoxy resin.

(5) The thermoelectric conversion material layer according to any one of the above (1) to (4), wherein the thermoelectric semiconductor composition further contains an ionic liquid and/or an inorganic ionic compound.

(6) The thermoelectric conversion material layer according to any one of the above (1) to (5), wherein the thickness of the thermoelectric conversion material layer is 1 to 1000 μm.

(7) The thermoelectric conversion material layer according to any one of the above (1) to (6), wherein the filling ratio is 0.850 to 0.999.

(8) A method for producing a thermoelectric conversion material layer formed of a coating film of a thermoelectric semiconductor composition, the method comprising:

(A) a step of forming a thermoelectric conversion material layer;

(B) drying the thermoelectric conversion material layer obtained in the step (a);

(C) a step of pressurizing the dried thermoelectric conversion material layer obtained in the step (B); and

(D) and (C) annealing the pressed thermoelectric conversion material layer obtained in the step (C).

(9) The method for producing a thermoelectric conversion material layer according to item (8) above, wherein the annealing is performed at a temperature of 250 to 600 ℃.

(10) The method for producing a thermoelectric conversion material layer according to the above (8) or (9), wherein the pressing is performed at 1.0 to 60 MPa.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a thermoelectric conversion material layer having high thermoelectric performance in which the electrical conductivity of a thermoelectric conversion material in the thermoelectric conversion material layer formed of a coating film of a thermoelectric semiconductor composition is improved, and a method for producing the same.

Drawings

Fig. 1 is a diagram for explaining the definition of a longitudinal section of a thermoelectric conversion material layer of the present invention.

Fig. 2 is a schematic cross-sectional view for explaining a vertical cross-section of a thermoelectric conversion element layer obtained in an example of the present invention or a comparative example.

Fig. 3 is an explanatory view showing an example of the method for producing a thermoelectric conversion material layer according to the present invention in accordance with the steps.

Description of the symbols

1 a: substrate

1 b: alumina substrate

2. 2s, 2 t: thermoelectric conversion material layer

3: void part

3a, 4 a: void part

3 b: void part (comparative example 1)

4 b: void portion (example 1)

5: pressing part

X: length (width direction)

Y: length (height direction)

D: thickness (thickness direction)

Dmax: maximum thickness in thickness direction (longitudinal section)

Dmin: thickness minimum in thickness direction (longitudinal section)

C: central part of thermoelectric conversion material layer

Detailed Description

[ thermoelectric conversion material layer ]

The thermoelectric conversion material layer of the present invention is a thermoelectric conversion material layer formed of a coating film of a thermoelectric semiconductor composition, wherein the thermoelectric conversion material layer has voids, and the filling ratio is 0.800 or more and less than 1.000 when the ratio of the area of the thermoelectric semiconductor composition to the area of a vertical cross section including a central portion of the thermoelectric conversion material layer is defined as the filling ratio.

Longitudinal section of thermoelectric conversion material layer

In this specification, "a vertical cross section including a central portion of a thermoelectric conversion material layer" will be described with reference to the drawings.

Fig. 1 is a plan view of a thermoelectric conversion material layer 2, the thermoelectric conversion material layer 2 having a length X in the width direction and a length Y in the depth direction, and (b) is a vertical cross section of the thermoelectric conversion material layer 2 including a void portion 3 formed on a substrate 1a, the vertical cross section including a central portion C of the thermoelectric conversion material layer (a), and including a length X and a thickness D (rectangular in the drawing) obtained when the thermoelectric conversion material layer is cut between a and a' in the width direction.

The vertical cross section of the thermoelectric conversion material layer of the present invention will be described with reference to the drawings.

Fig. 2 is a schematic cross-sectional view for explaining a vertical cross-section of a thermoelectric conversion material layer according to an example of the present invention or a comparative example, (a) is a vertical cross-section of a thermoelectric conversion material layer 2s formed on an alumina substrate 1b obtained in comparative example 1, the thermoelectric conversion material layer 2s has a vertical cross-section having a length X in the width direction and a curve having values of Dmin and Dmax in the thickness direction, a concave portion and a convex portion are provided in an upper portion of the vertical cross-section, and a void portion 3b is present in the vertical cross-section. In addition, (b) is a vertical cross section of the thermoelectric conversion material layer 2t formed on the alumina substrate 1b in example 1, and the vertical cross section of the thermoelectric conversion material layer 2t includes a length X in the width direction and a thickness D in the thickness direction [ in the case where the values of Dmin and Dmax in fig. 2(a) are slightly different ], and the upper portion of the vertical cross section is substantially linear, and there is a void portion 4b in which the number of voids and the volume are suppressed in the vertical cross section. Dmin is the minimum thickness in the thickness direction of the longitudinal section, and Dmax is the maximum thickness in the thickness direction of the longitudinal section.

In the thermoelectric conversion material layer of the present invention, the filling ratio of the thermoelectric semiconductor composition in the thermoelectric conversion material layer, which is defined as the ratio of the area of the thermoelectric semiconductor composition to the area of the vertical cross section including the central portion of the thermoelectric conversion material layer, is 0.800 or more and less than 1.000, and the voids in the thermoelectric conversion material layer are small.

When the filling ratio of the thermoelectric semiconductor composition in the thermoelectric conversion material layer is less than 0.800, voids in the thermoelectric conversion material layer are large, and it is difficult to obtain excellent electrical conductivity, and high thermoelectric performance cannot be obtained. The filling rate is preferably 0.810 to 0.999, more preferably 0.850 to 0.999, further preferably 0.900 to 0.999, and particularly preferably 0.950 to 0.999, and when the filling rate is in this range, excellent electrical conductivity can be obtained, and a thermoelectric conversion material layer having high thermoelectric performance can be obtained.

The thermoelectric conversion material layer (hereinafter, also referred to as "thin film formed of a thermoelectric conversion material layer") of the present invention is formed of a coating film of a thermoelectric semiconductor composition. The thermoelectric semiconductor composition preferably contains a thermoelectric semiconductor material, and from the viewpoint of shape stability of the thermoelectric conversion material layer, preferably contains a heat-resistant resin, and from the viewpoint of thermoelectric performance, more preferably is formed of a thermoelectric semiconductor composition containing a thermoelectric semiconductor material, a heat-resistant resin, and an ionic liquid and/or an inorganic ionic compound.

The thermoelectric semiconductor material is preferably used as thermoelectric semiconductor particles from the viewpoint of thermoelectric performance (hereinafter, the thermoelectric semiconductor material may be referred to as "thermoelectric semiconductor particles").

The thickness of the thermoelectric conversion material layer is not particularly limited, but is preferably 1nm to 1000 μm, more preferably 3 to 600 μm, and still more preferably 5 to 400 μm, from the viewpoint of flexibility, thermoelectric performance, and coating strength.

(thermoelectric semiconductor Material)

The thermoelectric semiconductor material used in the present invention is not particularly limited as long as it can generate a thermoelectromotive force by imparting a temperature difference, and for example, a bismuth-tellurium-based thermoelectric semiconductor material such as P-type bismuth telluride or N-type bismuth telluride; telluride-based thermoelectric semiconductor materials such as GeTe and PbTe; an antimony-tellurium-based thermoelectric semiconductor material; ZnSb, Zn₃Sb₂、Zn₄Sb₃An isozinc-antimony-based thermoelectric semiconductor material; silicon-germanium thermoelectric semiconductor materials such as SiGe; bi₂Se₃Bismuth selenide-based thermoelectric semiconductor materials; beta-FeSi₂、CrSi₂、MnSi_1.73、Mg₂Silicide thermoelectric semiconductor material such as SiFeeding; an oxide-based thermoelectric semiconductor material; hastelloy materials such as FeVAl, FeVAlSi, FeVTiAl, TiS₂And sulfide-based thermoelectric semiconductor materials.

Among them, a bismuth-tellurium-based thermoelectric semiconductor material, a telluride-based thermoelectric semiconductor material, an antimony-tellurium-based thermoelectric semiconductor material, or a bismuth selenide-based thermoelectric semiconductor material is preferable.

In addition, from the viewpoint of thermoelectric performance, a bismuth-tellurium-based thermoelectric semiconductor material such as P-type bismuth telluride or N-type bismuth telluride is more preferable.

The P-type bismuth telluride has positive values of carriers and seebeck coefficient, and for example, Bi can be preferably used_XTe₃Sb_2-XThe compound shown in the specification. In this case, X is preferably 0 < X.ltoreq.0.8, more preferably 0.4. ltoreq.X.ltoreq.0.6. When X is more than 0 and 0.8 or less, the seebeck coefficient and the electrical conductivity increase, and the characteristics as a p-type thermoelectric element can be maintained, which is preferable.

In addition, the N-type bismuth telluride described above has a negative seebeck coefficient and a negative carrier, and Bi, for example, can be preferably used₂Te_3-YSe_YThe compound shown in the specification. In this case, Y is preferably 0. ltoreq. Y.ltoreq.3 (when Y is 0: Bi)₂Te₃) More preferably 0 < Y.ltoreq.2.7. When Y is 0 or more and 3 or less, the seebeck coefficient and the electrical conductivity increase, and the characteristics as an n-type thermoelectric element can be maintained, which is preferable.

The thermoelectric semiconductor particles used in the thermoelectric semiconductor composition are obtained by pulverizing the above-mentioned thermoelectric semiconductor material to a predetermined size using a micro-pulverizer or the like.

The amount of thermoelectric semiconductor particles blended in the thermoelectric semiconductor composition is preferably 30 to 99% by mass, more preferably 50 to 96% by mass, and still more preferably 70 to 95% by mass. When the amount of the thermoelectric semiconductor particles is within the above range, the seebeck coefficient (absolute value of the peltier coefficient) is large, and since only the thermal conductivity is reduced while the decrease in the electrical conductivity is suppressed, a film having not only high thermoelectric performance but also sufficient film strength and flexibility can be obtained.

The thermoelectric semiconductor particles preferably have an average particle diameter of 10nm to 200 μm, more preferably 10nm to 30 μm, still more preferably 50nm to 10 μm, and particularly preferably 1 to 6 μm. When the amount is within the above range, uniform dispersion is facilitated, and the conductivity can be improved.

The method for obtaining thermoelectric semiconductor particles by pulverizing the thermoelectric semiconductor material is not particularly limited, and the thermoelectric semiconductor particles can be pulverized into a predetermined size by a known micro-pulverizing device such as a jet mill, a ball mill, a bead mill, a colloid mill, or a roll mill.

The average particle size of the thermoelectric semiconductor fine particles can be measured by a laser diffraction particle size analyzer (Mastersizer 3000, manufactured by Malvern) and is a median of the particle size distribution.

The thermoelectric semiconductor particles are preferably subjected to a heat treatment in advance (here, the "heat treatment" is different from the "annealing treatment" performed in the annealing treatment step in the method for producing a thermoelectric conversion material layer of the present invention described later). By performing the heat treatment, crystallinity of the thermoelectric semiconductor particles is improved, and the surface oxide film of the thermoelectric semiconductor particles is removed, so that the seebeck coefficient or peltier coefficient of the thermoelectric conversion material is increased, and the thermoelectric performance index can be further improved. The heat treatment is not particularly limited, and is preferably performed in an inert gas atmosphere such as nitrogen or argon in which a gas flow rate is controlled, a reducing gas atmosphere such as hydrogen in the same manner, or a vacuum condition so as not to adversely affect the thermoelectric semiconductor particles before the thermoelectric semiconductor composition is produced, and more preferably in a mixed gas atmosphere of an inert gas and a reducing gas. The specific temperature condition depends on the thermoelectric semiconductor fine particles used, and is usually a temperature equal to or lower than the melting point of the particles, and is preferably 100 to 1500 ℃ for several minutes to several tens of hours.

(Heat-resistant resin)

The thermoelectric semiconductor composition used in the present invention is preferably a heat-resistant resin, from the viewpoint of annealing the thermoelectric semiconductor material at a high temperature. The thermoelectric semiconductor particles function as a binder between thermoelectric semiconductor materials (thermoelectric semiconductor particles), and can improve the flexibility of a thermoelectric conversion module, and can be easily formed into a thin film by coating or the like. The heat-resistant resin is not particularly limited, and is preferably a heat-resistant resin that maintains and does not impair physical properties such as mechanical strength and thermal conductivity as a resin when thermoelectric semiconductor particles are subjected to crystal growth by annealing or the like of a thin film formed of a thermoelectric semiconductor composition.

The heat-resistant resin is preferably a polyamide resin, a polyamideimide resin, a polyimide resin, or an epoxy resin from the viewpoint of higher heat resistance and no adverse effect on crystal growth of thermoelectric semiconductor particles in the film, and more preferably a polyamide resin, a polyamideimide resin, or a polyimide resin from the viewpoint of excellent bendability. In the present invention, the polyimide resin is a generic name of polyimide and a precursor thereof.

The decomposition temperature of the heat-resistant resin is more preferably 300 ℃ or higher. When the decomposition temperature is within the above range, as described later, the film formed from the thermoelectric semiconductor composition can maintain its flexibility without losing its function as a binder when subjected to an annealing treatment.

The weight loss at 300 ℃ of the heat-resistant resin obtained by Thermogravimetry (TG) is preferably 10% or less, more preferably 5% or less, and still more preferably 1% or less. When the weight reduction ratio is within the above range, as described later, even when the thin film formed of the thermoelectric semiconductor composition is subjected to annealing treatment, the flexibility of the thermoelectric conversion material layer can be maintained without losing the function as a binder.

The amount of the heat-resistant resin blended in the thermoelectric semiconductor composition is 0.1 to 40 mass%, preferably 0.5 to 20 mass%, more preferably 1 to 20 mass%, and still more preferably 2 to 15 mass%. When the amount of the heat-resistant resin is within the above range, a film that functions as a binder for thermoelectric semiconductor materials, is easily formed into a thin film, and has both high thermoelectric performance and film strength can be obtained.

(Ionic liquid)

The ionic liquid used in the present invention is a molten salt in which a cation and an anion are combined, and is a salt that can exist as a liquid at any temperature range from-50 to 400 ℃. In other words, the ionic liquid is an ionic compound having a melting point in the range of-50 ℃ or higher and lower than 400 ℃. The melting point of the ionic liquid is preferably-25 ℃ or higher and 200 ℃ or lower, and more preferably 0 ℃ or higher and 150 ℃ or lower. The ionic liquid has the following characteristics: the low vapor pressure is nonvolatile, has excellent thermal stability and electrochemical stability, low viscosity, and high ionic conductivity, and therefore, can effectively suppress a decrease in conductivity between thermoelectric semiconductor particles as a conductive aid. In addition, the ionic liquid exhibits high polarity due to the aprotic ionic structure and is excellent in compatibility with the heat-resistant resin, and therefore, the electrical conductivity of the thermoelectric conversion material layer can be made uniform.

As the ionic liquid, known or commercially available ionic liquids can be used. Examples thereof include: pyridine compound

Pyrimidine, pyrimidine

Pyrazoles

Pyrrolidine, pyrrolidine

Piperidine, piperidine and their use as a medicament

Imidazole, imidazole

Nitrogen-containing cyclic cationic compounds and derivatives thereof; ammonium cations such as tetraalkylammonium cations and derivatives thereof;

trialkyl(s)

Tetra-alkyl, tetra-alkyl

Etc. of

A cation-like and derivatives thereof; a compound comprising a cation component such as a lithium cation or a derivative thereof and an anion component comprising: cl^-、AlCl₄ ^-、Al₂Cl₇ ^-、ClO₄ ^-Plasma chloride ion, Br^-Plasma bromide ion, I^-Plasma iodide ion, BF₄ ^-、PF₆ ^-Plasma fluoride ion, F (HF)_n ^-Isohalide anion, BF₄ ^-、PF₆ ^-、ClO₄ ^-、NO₃ ^-、CH₃COO^-、CF₃COO^-、CH₃SO₃ ^-、CF₃SO₃ ^-、(FSO₂)₂N^-、(CF₃SO₂)₂N^-、(CF₃SO₂)₃C^-、AsF₆ ^-、SbF₆ ^-、NbF₆ ^-、TaF₆ ^-、F(HF)_n ^-、(CN)₂N^-、C₄F₉SO₃ ^-、(C₂F₅SO₂)₂N^-、C₃F₇COO^-、(CF₃SO₂)(CF₃CO)N^-And the like.

In the ionic liquid, the cation component of the ionic liquid preferably contains a compound selected from pyridine from the viewpoints of high-temperature stability, compatibility with thermoelectric semiconductor particles and resins, and suppression of decrease in electrical conductivity in gaps between thermoelectric semiconductor particles

Cation and its derivative, imidazole

At least one of a cation and a derivative thereof. The anionic component of the ionic liquid preferably comprises halide anions, more preferably comprises a compound selected from the group consisting of Cl^-、Br^-And I^-At least one of (1).

Containing pyridine as a cationic component

Specific examples of the ionic liquid of the cation and the derivative thereof include: 4-methylbutylpyridinium chloride, 3-methylbutylpyridinium chloride, 4-methylhexylpyridinium chloride, 3-methylhexylpyridinium chloride, 4-methyloctylpyridinium chloride, 3, 4-dimethylbutylpyridinium chloride, 3, 5-dimethylbutylpyridinium chloride, 4-methylbutylpyridinium tetrafluoroborate, 4-methylbutylpyridinium hexafluorophosphate, 1-butylpyridinium bromide, 1-butyl-4-methylpyridinium hexafluorophosphate, 1-butyl-4-methylpyridinium iodide and the like. Among them, 1-butylpyridinium bromide, 1-butyl-4-methylpyridinium hexafluorophosphate and 1-butyl-4-methylpyridinium iodide are preferable.

Further, the cationic component contains imidazole

Specific examples of the ionic liquid of the cation and the derivative thereof include: [ 1-butyl-3- (2-hydroxyethyl) imidazolium bromide][ 1-butyl-3- (2-hydroxyethyl) imidazole tetrafluoroborate]1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium chloride, 1-decyl-3-methylimidazolium bromide, 1-dodecyl-3-methylimidazolium chloride, 1-tetradecyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrakisFluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-methyl-3-butylimidazolium methanesulfonate, 1, 3-dibutylimidazolium methanesulfonate, and the like. Among them, [ 1-butyl-3- (2-hydroxyethyl) imidazolium bromide is preferable][ 1-butyl-3- (2-hydroxyethyl) imidazole tetrafluoroborate]。

The ionic liquid preferably has a conductivity of 10^-7S/cm or more, more preferably 10^-6And more than S/cm. When the electrical conductivity is within the above range, a decrease in electrical conductivity between the thermoelectric semiconductor particles can be effectively suppressed as the conductive aid.

The decomposition temperature of the ionic liquid is preferably 300 ℃ or higher. When the decomposition temperature is in the above range, as will be described later, the effect as a conductive aid can be maintained even when the thin film formed of the thermoelectric semiconductor composition is subjected to annealing treatment.

The weight loss of the ionic liquid at 300 ℃ as measured by thermogravimetric analysis (TG) is preferably 10% or less, more preferably 5% or less, and still more preferably 1% or less. When the weight reduction ratio is within the above range, as described later, the effect as a conductive aid can be maintained even when the thin film formed of the thermoelectric semiconductor composition is subjected to annealing treatment.

The amount of the ionic liquid blended in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.5 to 30 mass%, and still more preferably 1.0 to 20 mass%. When the amount of the ionic liquid is within the above range, a decrease in conductivity can be effectively suppressed, and a film having high thermoelectric performance can be obtained.

(inorganic Ionic Compound)

The inorganic ionic compound used in the present invention is a compound composed of at least a cation and an anion. The inorganic ionic compound is solid at room temperature, has a melting point at any temperature in the temperature range of 400 to 900 ℃, has high ionic conductivity, and the like, and can inhibit the decrease in conductivity between thermoelectric semiconductor particles as a conductive aid.

As the cation, a metal cation is used.

Examples of the metal cation include: alkali metal cations, alkaline earth metal cations, typical metal cations and transition metal cations, more preferably alkali metal cations or alkaline earth metal cations.

Examples of the alkali metal cation include: li⁺、Na⁺、K⁺、Rb⁺、Cs⁺And Fr⁺And the like.

As the alkaline earth metal cation, for example: mg (magnesium)²⁺、Ca²⁺、Sr²⁺And Ba²⁺And the like.

Examples of anions include: f^-、Cl^-、Br^-、I^-、OH^-、CN^-、NO^3-、NO^2-、ClO^-、ClO^2-、ClO^3-、ClO^4-、CrO₄ ^2-、HSO₄ ^-、SCN^-、BF₄ ^-、PF₆ ^-And the like.

As the inorganic ionic compound, known or commercially available compounds can be used. Examples thereof include: formed by reacting a cation component such as potassium cation, sodium cation or lithium cation with Cl^-、AlCl₄ ^-、Al₂Cl₇ ^-、ClO₄ ^-Plasma chloride ion, Br^-Plasma bromide ion, I^-Plasma iodide ion, BF₄ ^-、PF₆ ^-Plasma fluoride ion, F (HF)_n ^-Isohalide anion, NO₃ ^-、OH^-、CN^-And a compound composed of an anionic component.

Among the above inorganic ionic compounds, the cationic component of the inorganic ionic compound preferably contains at least one selected from potassium, sodium and lithium from the viewpoints of high-temperature stability, compatibility with the thermoelectric semiconductor particles and the resin, suppression of decrease in electrical conductivity in the gaps between the thermoelectric semiconductor particles, and the like. In addition, the anion component of the inorganic ionic compound preferably contains a halide anion, and more preferably containsContaining elements selected from Cl^-、Br^-And I^-At least one of (1).

Specific examples of the inorganic ionic compound having a potassium cation as a cation component include: KBr, KI, KCl, KF, KOH, K₂CO₃And the like. Among them, KBr and KI are preferable.

Specific examples of the inorganic ionic compound containing a sodium cation as the cationic component include: NaBr, NaI, NaOH, NaF, Na₂CO₃And the like. Among them, NaBr and NaI are preferable.

Specific examples of the inorganic ionic compound having a lithium cation as a cationic component include: LiF, LiOH, LiNO₃And the like. Among them, LiF and LiOH are preferable.

The conductivity of the inorganic ionic compound is preferably 10^-7S/cm or more, more preferably 10^-6And more than S/cm. When the electrical conductivity is within the above range, a decrease in electrical conductivity between the thermoelectric semiconductor particles can be effectively suppressed as the conductive aid.

The decomposition temperature of the inorganic ionic compound is preferably 400 ℃ or higher. When the decomposition temperature is in the above range, the effect as a conductive aid can be maintained even when the thin film formed of the thermoelectric semiconductor composition is subjected to annealing treatment as described later.

The weight loss at 400 ℃ of the inorganic ionic compound according to thermogravimetric analysis (TG) is preferably 10% or less, more preferably 5% or less, and still more preferably 1% or less. When the weight reduction ratio is within the above range, as described later, even when the thin film formed of the thermoelectric semiconductor composition is subjected to annealing treatment, the effect as the conductive aid can be maintained.

The amount of the inorganic ionic compound blended in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.5 to 30 mass%, and still more preferably 1.0 to 10 mass%. When the amount of the inorganic ionic compound is within the above range, the decrease in conductivity can be effectively suppressed, and as a result, a film having improved thermoelectric performance can be obtained.

When an inorganic ionic compound and an ionic liquid are used in combination, the total content of the inorganic ionic compound and the ionic liquid in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.5 to 30 mass%, and still more preferably 1.0 to 10 mass%.

(other additives)

The thermoelectric semiconductor composition used in the present invention may further contain, in addition to the above-mentioned components, other additives such as a dispersant, a film-forming aid, a light stabilizer, an antioxidant, a thickener, a plasticizer, a colorant, a resin stabilizer, a filler, a pigment, a conductive filler, a conductive polymer, and a curing agent, if necessary. These additives may be used alone in 1 kind, or in combination of 2 or more kinds.

The thermoelectric conversion material layer of the present invention has improved electrical conductivity, and a thermoelectric conversion module having high thermoelectric performance can be obtained by using the thermoelectric conversion material layer as a thermoelectric conversion module.

[ method for producing thermoelectric conversion Material layer ]

The method for producing a thermoelectric conversion material layer of the present invention is a method for producing a thermoelectric conversion material layer formed of a coating film of a thermoelectric semiconductor composition, the method comprising: (A) a step of forming a thermoelectric conversion material layer, (B) a step of drying the thermoelectric conversion material layer obtained in the step (a), (C) a step of pressurizing the dried thermoelectric conversion material layer obtained in the step (B), and (D) a step of annealing the pressurized thermoelectric conversion material layer obtained in the step (C).

In the method for producing a thermoelectric conversion material layer according to the present invention, after the thermoelectric conversion material layer is formed, drying is performed at a predetermined temperature, then the upper surface of the thermoelectric conversion material layer is pressed at a predetermined pressure to reduce the volume of voids in the thermoelectric conversion material layer, and then annealing is performed, thereby obtaining a thermoelectric conversion material layer having improved electrical conductivity.

Fig. 3 is an explanatory view showing an example of the method for producing a thermoelectric conversion material layer according to the present invention in steps, (a) is a cross-sectional view showing a mode in which the thermoelectric conversion material layer 2s is formed on the substrate 1a, the thermoelectric conversion material layer 2s is formed as a coating film (including the void portion 3a) on the substrate 1a, and dried at a predetermined temperature;

(b) a cross-sectional view showing a mode in which the pressing and pressing portion 5 is opposed to the upper surface of the thermoelectric conversion material layer 2s, and after cooling the dried thermoelectric conversion material layer 2s obtained in (a) to normal temperature, the thermoelectric conversion material layer 2s is opposed to the pressing and pressing portion 5;

(c) is a cross-sectional view showing a mode in which the upper surface of the thermoelectric conversion material layer 2s is pressed by the pressing portion 5, and then the pressing portion 5 is separated from the thermoelectric conversion material layer 2 s.

Then, annealing treatment is performed to obtain the thermoelectric conversion material layer 2t (including the void portions 4a with a reduced number of voids and volume) of the present invention.

Preferably, the thermoelectric conversion material layer is formed in a solid film shape on the substrate and then singulated into a desired chip size. In another preferred embodiment, the coating film may be formed on a substrate in the size of a chip of the thermoelectric conversion material. In addition, from the viewpoint of shape controllability of the thermoelectric conversion material layer, as a more preferable aspect, the thermoelectric conversion material layer may be produced using a lattice-like pattern frame member including separate openings having a chip shape of the thermoelectric conversion material.

The chip size is, for example, about 0.1 to 20mm in the short side and about 0.2 to 25mm in the long side.

The method for producing the thermoelectric conversion material layer when using the above-described lattice-like pattern frame member including the separated openings having the chip shape of the thermoelectric conversion material is, for example, as follows.

(p) standing a lattice-like pattern frame member including separated openings having a chip shape of a thermoelectric conversion material on a substrate;

(q) forming a coating film of the thermoelectric conversion material layer at an opening of the pattern frame member and drying the coating film at a predetermined temperature;

(r) cooling the dried thermoelectric conversion material layer obtained in (q) to normal temperature, and then facing the thermoelectric conversion material layer to a press portion (corresponding to the press portion 5 in fig. 3);

(t) pressing the upper surface of the thermoelectric conversion material layer by the pressing and pressing portion to reduce the number of voids and the volume of the thermoelectric conversion material layer, detaching the pressing and pressing portion from the thermoelectric conversion material layer, and further detaching the pattern frame member;

(u) then, the thermoelectric conversion material layer obtained on the substrate reflecting the shape of the opening of the pattern frame member is subjected to annealing treatment, thereby obtaining a chip-like thermoelectric conversion material layer of the present invention.

The opening is not particularly limited as long as the opening has a shape that reflects the shape of the chip of the thermoelectric conversion material after the pattern frame member is detached, and is preferably rectangular, square, or circular, and more preferably rectangular or square.

In addition, from the viewpoint of ease of formation, stainless steel, copper, or the like may be used as the pattern frame member.

(A) Thermoelectric conversion material layer formation step

The thermoelectric conversion material layer forming step is a step of forming a thermoelectric conversion material layer on a substrate, and for example, in fig. 3(a), is a step of forming a thermoelectric conversion material layer 2s by coating a thermoelectric semiconductor composition on a substrate 1 a.

(substrate)

The substrate is not particularly limited, and examples thereof include: glass, silicon, ceramic, metal, or plastic, etc. Glass, silicon, ceramic, and metal are preferable from the viewpoint of annealing treatment at high temperature, and glass, silicon, and ceramic are more preferable from the viewpoint of dimensional stability after heat treatment.

The thickness of the substrate can be 100 to 10000 μm from the viewpoint of process and dimensional stability.

(thermoelectric semiconductor composition)

The same thermoelectric semiconductor composition as described above can be used as the thermoelectric semiconductor composition used in the present invention. The same applies to the preferred materials and amounts of the thermoelectric semiconductor material, the heat-resistant resin, the ionic liquid, the inorganic ionic compound, and the like.

(method for producing thermoelectric semiconductor composition)

The method for producing the thermoelectric semiconductor composition used in the present invention is not particularly limited, and the thermoelectric semiconductor composition can be produced by adding one or both of the thermoelectric semiconductor particles, the heat-resistant resin, the ionic liquid and the inorganic ionic compound, the other additives used as needed, and a solvent by a known method such as an ultrasonic homogenizer, a helical stirrer, a planetary stirrer, a disperser, a mixing stirrer, and the like, and mixing and dispersing the mixture.

Examples of the solvent include: and solvents such as toluene, ethyl acetate, methyl ethyl ketone, alcohol, tetrahydrofuran, methyl pyrrolidone, and ethyl cellosolve. These solvents may be used alone in 1 kind, or may be used in combination of 2 or more kinds. The solid content concentration of the thermoelectric semiconductor composition is not particularly limited as long as it is a viscosity suitable for application of the composition.

The thin film formed of the thermoelectric semiconductor composition may be formed by, for example, applying the thermoelectric semiconductor composition on the substrate and drying the applied composition.

Examples of the method for applying the thermoelectric semiconductor composition to the substrate include: known methods such as screen printing, flexography, gravure, spin coating, dip coating, die coating, spray coating, bar coating, blade coating, and applicator are not particularly limited. When the coating film is formed in a pattern, screen printing, stencil printing, slit die coating (slot die coat), or the like, which enables a pattern to be easily formed by a screen having a desired pattern, is preferably used.

(B) Thermoelectric conversion material layer drying process

The thermoelectric conversion material layer drying step is a step of drying the thermoelectric conversion material layer obtained in the step (a), and for example, in fig. 3(a), is a step of drying the thermoelectric conversion material layer 2s on the substrate 1 a.

As the drying method, conventionally known drying methods such as a hot air drying method, a hot roll drying method, an infrared irradiation method, and the like can be used. The heating temperature is usually 80 to 170 ℃, preferably 100 to 150 ℃, more preferably 110 to 145 ℃, and still more preferably 120 to 140 ℃.

The heating time varies depending on the heating method, and is usually 30 seconds to 5 hours, preferably 1 minute to 3 hours, more preferably 5 minutes to 2 hours, and further preferably 10 minutes to 50 minutes.

When the heating temperature and the heating time are within these ranges, the electrical conductivity of the thermoelectric conversion material layer after the pressurization and the annealing treatment is easily improved.

When a solvent is used for the production of the thermoelectric semiconductor composition, the heating temperature may be in a temperature range in which the solvent to be used can be dried, or in a temperature range below the temperature range.

(C) Thermoelectric conversion material layer pressing step

The thermoelectric conversion material layer pressing step is a step of pressing the dried thermoelectric conversion material layer obtained in the step (B), and for example, in fig. 3(B), the upper surface of the thermoelectric conversion material layer 2s is pressed by the pressing and pressing portion 5.

As one embodiment, the pressurization is preferably performed in an atmospheric pressure gas atmosphere after cooling the dried thermoelectric conversion material layer obtained in the step (B) to room temperature. In another embodiment, the pressing is preferably performed while maintaining the drying temperature without cooling the dried thermoelectric conversion material layer obtained in step (B) to room temperature, and the subsequent annealing step is performed.

Examples of the pressing method include a method using a physical pressing system such as a hydraulic press, a vacuum press, and a weight. The amount of pressurization varies depending on the viscosity of the thermoelectric conversion material layer, the amount of voids, and the like, and is usually 0.1 to 80MPa, preferably 1.0 to 60MPa, more preferably 5 to 50MPa, and still more preferably 10 to 42 MPa. The pressurization can be increased to a predetermined amount at a time, but from the viewpoint of maintaining the shape stability of the thermoelectric conversion material layer and reducing more voids in the thermoelectric conversion material layer to increase the filling rate of the thermoelectric conversion material, the pressurization can be appropriately adjusted, and the amount of pressurization is increased to a predetermined amount of pressurization, usually 0.1 to 50 MPa/min, preferably 0.5 to 30 MPa/min, and more preferably 1.0 to 10 MPa/min.

The pressing time varies depending on the pressing method, and is usually 5 seconds to 5 hours, preferably 30 seconds to 3 hours, more preferably 5 minutes to 2 hours, and further preferably 10 minutes to 1 hour.

When the pressing amount and the pressing time are within this range, the filling ratio increases, and the electrical conductivity of the thermoelectric conversion material layer after the annealing treatment is likely to be improved.

(D) Annealing step

The step of annealing the pressed thermoelectric conversion material layer obtained in the step (C) in the annealing step is, for example, a step of annealing the pressed thermoelectric conversion material layer 2s at the temperature of the annealing treatment in fig. 3(C) (the thermoelectric conversion material layer 2t obtained after the annealing treatment).

The thermoelectric conversion material layer is dried after forming a thin film, and then annealed, thereby stabilizing thermoelectric performance and further improving thermoelectric performance by growing crystals of thermoelectric semiconductor particles in the thin film.

The annealing treatment is performed in a state where the thermoelectric conversion material layer is pressurized or in a state where it is not pressurized. The amount of pressurization in the pressurization is usually 0.1 to 80MPa, preferably 1.0 to 60MPa, more preferably 5 to 50MPa, and still more preferably 10 to 42 MPa.

The annealing is usually performed in an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere, or a vacuum condition with a controlled gas flow rate, and the annealing temperature depends on the thermoelectric semiconductor material, heat-resistant resin, ionic liquid, inorganic ionic compound, and the like used in the thermoelectric semiconductor composition, and is usually performed at 100 to 600 ℃ for several minutes to several tens of hours, preferably at 250 to 450 ℃ for several minutes to several tens of hours.

The thickness of the thermoelectric conversion material layer is not particularly limited as long as the shape stability and thermoelectric performance are not impaired by the pressure, as described above.

According to the method for producing a thermoelectric conversion material layer of the present invention, a thermoelectric conversion material layer having improved electrical conductivity can be produced by a simple method.

Examples

The present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

The filling rate of the thermoelectric semiconductor composition in the thermoelectric conversion material layers produced in examples and comparative examples and the electric conductivity were evaluated by the following methods.

(a) Evaluation of filling Rate

The thermoelectric conversion material layers produced in examples and comparative examples were subjected to observation of a vertical cross section including the central portion of the thermoelectric conversion material layer using an FE-SEM/EDX (FE-SEM: High-Tech, model: S-4700) while exposing the vertical cross section including the central portion thereof by a polishing apparatus (RefineTec, model: Refine Polisher HV), and then a filling ratio defined as a ratio of an area of the thermoelectric semiconductor composition in the vertical cross section of the thermoelectric conversion material layer was calculated using Image J (Image processing software, ver.1.44P).

In the measurement of the filling factor, an SEM image (vertical cross section) of 500 × magnification was used, and the image was cut out with the measurement range being a range surrounded by 1280 pixels in the width direction and 220 pixels in the thickness direction with respect to the boundary between the thermoelectric conversion material layer and the alumina substrate. The Contrast was set to the maximum value by "Brightness/Contrast", the cut image was subjected to binarization processing, the dark portion in the binarization processing was regarded as a void portion, the bright portion was regarded as a thermoelectric semiconductor composition, and the filling ratio of the thermoelectric semiconductor composition was calculated by "Threshold". The filling factor was calculated for 3 SEM images, and their average value was taken.

The cut-out image is an image selected in a region portion of the vertical section, and for example, in fig. 2(a), a region not exceeding the width direction X and the thickness direction Dmin of the vertical section is selected so as not to introduce a void portion (air layer portion) around the thermoelectric conversion material layer.

(b) Evaluation of conductivity

The thermoelectric conversion material layers prepared in examples and comparative examples were measured for surface resistance value by a four-terminal method at 25 ℃ and 60% RH using a low resistance measuring apparatus (model No. RM3545, manufactured by Nikkiso Co., Ltd.), and the electric conductivity was calculated.

(example 1)

< production of thermoelectric conversion Material layer >

(1) Fabrication of thermoelectric semiconductor compositions

(production of thermoelectric semiconductor particles)

P-type bismuth telluride Bi as a bismuth-tellurium-based thermoelectric semiconductor material was pulverized in a nitrogen atmosphere using a planetary ball mill (Premiumline P-7, manufactured by Fritsch Japan Co., Ltd.)_0.4Te₃Sb_1.6Thermoelectric semiconductor particles having an average particle size of 2.0 μm were produced (particle size: 180 μm, manufactured by high purity chemical research). The thermoelectric semiconductor particles obtained by the pulverization were subjected to particle size distribution measurement using a laser diffraction particle size analyzer (Mastersizer 3000, manufactured by Malvern corporation).

(preparation of coating liquid for thermoelectric semiconductor composition)

A coating liquid comprising a thermoelectric semiconductor composition obtained by subjecting the above-obtained P-type bismuth telluride Bi was prepared_0.4Te₃Sb_1.6Particles 82.5 mass%, polyimide as a heat-resistant resin precursor, namely polyamic acid (U-Varnish A, product of Utsu corporation, solvent N-methyl pyrrolidone, solid content concentration: 18 mass%) 3.2 mass% (solid content), and ionic liquid of 1-butyl pyridine bromide 14.3 mass% mixed and dispersed.

(2) Formation of thermoelectric conversion material layer and pressure treatment

The coating liquid prepared in (1) above was printed on an alumina substrate (product name: alumina substrate A0476T, 100 mm. times.100 mm, thickness: 1mm, manufactured by KYOCERA) using a coater to form a solid film, and the solid film was dried at 140 ℃ for 40 minutes in an argon atmosphere to form a thin film (thermoelectric conversion material layer before annealing) having a thickness of 37 μm.

Next, the dried thermoelectric conversion material layer was cooled to room temperature, and the alumina substrate on which the thermoelectric conversion material layer was printed was cut into a size of 5mm × 15 mm. Then, the entire upper surface of the thermoelectric conversion material layer was uniformly pressed at 40.0MPa for 1 minute at room temperature in an atmospheric atmosphere using a hydraulic Press (model SA-30Table Type Test Press manufactured by TESTER SANGYO).

Further, the thermoelectric conversion material layer obtained by the pressure treatment was heated at a heating rate of 5K/min in a gas atmosphere of a mixed gas of hydrogen and argon (hydrogen: argon: 3 vol%: 97 vol%), and held at 430 ℃ for 30 minutes, and the thermoelectric conversion material layer was annealed to grow crystals of the particles of the thermoelectric semiconductor material, thereby producing the thermoelectric conversion material layer. The obtained thermoelectric conversion material layer was evaluated for filling rate and electric conductivity. The results are shown in Table 1.

(example 2)

A thermoelectric conversion material layer was produced in the same manner as in example 1, except that the entire upper surface of the thermoelectric conversion material layer was uniformly subjected to a pressing treatment at 30.0MPa in example 1. The obtained thermoelectric conversion material layer was evaluated for filling rate and electric conductivity. The results are shown in Table 1.

Comparative example 1

A thermoelectric conversion material layer was produced in the same manner as in example 1 except that the pressure treatment was not performed in example 1, and the obtained thermoelectric conversion material layer was evaluated for filling rate and electric conductivity. The results are shown in Table 1.

It is found that the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer formed of the coating film of the thermoelectric semiconductor composition satisfies the electric conductivity increase of 50 to 118% in examples 1 to 2 defined by the present invention, as compared with comparative example 1 in which the filling rate is outside the range defined by the present invention. Therefore, by applying the thermoelectric conversion material layer and the method for manufacturing the same of the present invention to a thermoelectric conversion module, thermoelectric performance of the thermoelectric conversion module can be improved.

Industrial applicability

According to the thermoelectric conversion material layer formed of the coating film of the thermoelectric semiconductor composition of the present invention and the method for producing the same, since the electric conductivity of the thermoelectric conversion material layer is increased, it is expected that the thermoelectric performance is improved by introducing the thermoelectric conversion material layer of the present invention into a thermoelectric conversion module. Meanwhile, the obtained thermoelectric conversion module has flexibility and can be made thin (small and light) as compared with a thermoelectric conversion module using a conventional sintered body of a thermoelectric semiconductor material.

The thermoelectric conversion module using the thermoelectric conversion material layer is suitable for power generation applications in which heat discharged from various combustion furnaces such as factories, waste combustion furnaces, and cement combustion furnaces, heat discharged from combustion gas of automobiles, and heat discharged from electrical equipment are converted into electricity. In the field of electronic devices, for example, applications to temperature control of various sensors such as a CCD (Charge Coupled Device), an MEMS (Micro Electro Mechanical system), and a light receiving element, which are semiconductor elements, are conceivable as cooling applications.

Claims

1. A thermoelectric conversion material layer formed of a coating film of a thermoelectric semiconductor composition, wherein,

the thermoelectric conversion material layer has a void,

the filling ratio is 0.800 or more and less than 1.000, where the ratio of the area of the thermoelectric semiconductor composition in the area of the vertical cross section including the central portion of the thermoelectric conversion material layer is defined as the filling ratio.

2. The thermoelectric conversion material layer according to claim 1, wherein the thermoelectric semiconductor composition comprises a thermoelectric semiconductor material which is a bismuth-tellurium-based thermoelectric semiconductor material, a telluride-based thermoelectric semiconductor material, an antimony-tellurium-based thermoelectric semiconductor material, or a bismuth selenide-based thermoelectric semiconductor material.

3. The thermoelectric conversion material layer according to claim 1 or 2, wherein the thermoelectric semiconductor composition further comprises a heat-resistant resin.

4. The thermoelectric conversion material layer according to any one of claims 1 to 3, wherein the heat-resistant resin is a polyimide resin, a polyamide resin, a polyamideimide resin, or an epoxy resin.

5. The thermoelectric conversion material layer according to any one of claims 1 to 4, wherein the thermoelectric semiconductor composition further comprises an ionic liquid and/or an inorganic ionic compound.

6. The thermoelectric conversion material layer according to any one of claims 1 to 5, wherein a thickness of the thermoelectric conversion material layer is 1 to 1000 μm.

7. The thermoelectric conversion material layer according to any one of claims 1 to 6, wherein the filling ratio is 0.850 to 0.999.

8. A method for producing a thermoelectric conversion material layer formed of a coating film of a thermoelectric semiconductor composition, the method comprising:

(A) a step of forming a thermoelectric conversion material layer;

9. The method for manufacturing a thermoelectric conversion material layer according to claim 8, wherein the annealing is performed at a temperature of 250 to 600 ℃.

10. The method for producing a thermoelectric conversion material layer according to claim 8 or 9, wherein the pressurization is performed at 1.0 to 60 MPa.