Thermoelectric conversion film, thermoelectric conversion element, and method for producing thermoelectric conversion film

Abstract

Provided is a thermoelectric conversion film capable of having improved thermoelectric conversion characteristics while inhibiting an increase in cost.　A thermoelectric conversion film according to the present technology comprises: a plurality of graphene layers laminated on top of each other; and a metal complex group including a plurality of metal complexes. The metal complex group is provided between at least one pair of two adjacent ones of the graphene layers, and the plurality of metal complexes are irregularly arranged. According to the thermoelectric conversion film of the present technology, it is possible to provide a thermoelectric conversion film capable of having improved thermoelectric conversion characteristics while inhibiting an increase in cost.

Description

Thermoelectric conversion film, thermoelectric conversion element, and method for manufacturing thermoelectric conversion film

[0001] The present technology relates to a thermoelectric conversion film, a thermoelectric conversion element, and a method for manufacturing a thermoelectric conversion film.

[0002] 2. Description of the Related Art Thermoelectric conversion films that convert heat into electricity are known.

[0003] For example, Patent Document 1 discloses a thermoelectric conversion film made of carbon nanotubes.

[0004] For example, Patent Document 2 discloses a thermoelectric conversion film composed of graphene oxide and an aromatic polymer.

[0005] For example, Patent Document 3 discloses a thermoelectric conversion film made of carbon nanotubes and various polymers.

[0006] For example, Patent Document 4 discloses a thermoelectric conversion film made of graphite powder and a surfactant.

[0007] For example, Non-Patent Document 1 discloses a thermoelectric conversion film composed of graphite powder and a metal complex. In this thermoelectric conversion film, the metal complex is arranged orderly (regularly) between graphene layers.

[0008] International Publication No. 2017 / 119361 Japanese Patent Application Laid-Open No. 2016-127210 International Publication No. 2016 / 039225 Japanese Patent Application Laid-Open No. 2021-48280

[0009] W. Xu and MM Learner, A new and facile route using electride solutions to intercalate alkaline earth ions into graphite, Chem. Mater. 30 (2018) 6930

[0010] However, Patent Documents 1 to 4 and Non-Patent Document 1 leave room for improvement in terms of improving thermoelectric conversion characteristics while suppressing increases in cost.

[0011] Therefore, a main object of the present technology is to provide a thermoelectric conversion film that can improve thermoelectric conversion characteristics while suppressing an increase in cost.

[0012] The present technology provides a thermoelectric conversion film comprising: a plurality of two-dimensional nanosheet layers stacked on top of each other; and a metal complex group containing a plurality of metal complexes, wherein the metal complex group is provided between at least one pair of adjacent graphene layers, and the plurality of metal complexes are irregularly arranged. The two-dimensional nanosheet layer may be a graphene layer. The plurality of metal complexes may be arranged along an in-plane direction. The arrangement pitch of the plurality of metal complexes may not be constant. The spacing between the two-dimensional nanosheet layers may not be constant. The spacing difference between the two-dimensional nanosheet layers may be 0.3 nm or more. The metal complex group may be periodically stacked via at least one of the two-dimensional nanosheet layers so that the d value of the 001 peak in XRD (X-ray diffraction) is 0.6 nm or more and 3.5 nm or less. The plurality of metal complexes may include at least two of the metal complexes having different sizes. The plurality of two-dimensional nanosheet layers may be at least three two-dimensional nanosheet layers, and the metal complex group may be disposed between at least two pairs of adjacent two two-dimensional nanosheet layers. At least two two-dimensional nanosheet layers may be disposed between two adjacent two metal complex groups. The ligand of the metal complex may be a chelate complex. The chelate complex may be ethylenediamine. The central metal of the metal complex may be an alkaline earth metal. The central metal may be Ca or Ba. The central metal may be Sr. The conductivity type may be n-type. The electrical conductivity σ is σ≧2550 S·cm －１ The Seebeck coefficient S may be |S|≧24 μV·K. －１ The power factor PF may be PF≧190 μW m ー１ ・K －２The total amount of the metal may be less than 2.9% by mole fraction. The two-dimensional nanosheet layer may be any one of a metal oxide, a double hydroxide, and a chalcogenide-based compound. The present technology also provides a thermoelectric conversion element comprising: a thermoelectric conversion film; a first electrode arranged on one side of the thermoelectric conversion film; and a second electrode arranged on the other side of the thermoelectric conversion film, wherein the thermoelectric conversion film comprises: a plurality of two-dimensional nanosheet layers stacked on top of each other; and at least one metal complex group containing a plurality of metal complexes, wherein the metal complex group is provided between at least one pair of adjacent two two-dimensional nanosheet layers, and the plurality of metal complexes are irregularly arranged. The present technology also provides a method for producing a thermoelectric conversion film, including: generating a metal complex solution using a metal and a ligand; and immersing a graphite sheet in the metal complex solution. In the producing step, the concentration of the metal and / or the ligand in the metal complex solution may be adjusted depending on the type of graphite in the graphite sheet and / or the purity of carbon contained in the graphite.

[0013] 1 is a cross-sectional view schematically showing a thermoelectric conversion film according to Example 1 of the first embodiment of the present technology. FIG. 2 is a graph showing an example of change in Seebeck coefficient over time when each GIC (graphite intercalation compound) is stored in the atmosphere. FIG. 3 is a graph showing an example of change in thermal conductivity over time when each GIC (graphite intercalation compound) is stored in the atmosphere. FIG. 4 is a graph showing an example of change in power factor over time when each GIC (graphite intercalation compound) is stored in the atmosphere. FIG. 5 is a graph showing an example of change in weight over time when each GIC (graphite intercalation compound) is stored in the atmosphere. FIG. 6 is a flowchart showing an example of a method for manufacturing a thermoelectric conversion film according to the first embodiment of the present technology. FIG. 7 is a diagram showing a stage transition process during the manufacture of the thermoelectric conversion film of FIG. 1. FIG. 8 is a graph showing the relationship between diffraction angle and diffracted X-ray intensity when XRD is performed on PGS (registered trademark: Pyrolytic Graphite Sheet). FIG. 9 is a graph showing the relationship between diffraction angle and diffracted X-ray intensity when XRD is performed on Ca-en-GIC. 10A is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Ca-en-GIC stored in the atmosphere for three days. FIG. 10B is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Ca-en-GIC stored in the atmosphere for two weeks. FIG. 10C is a cross-sectional view schematically showing a thermoelectric conversion film according to a modified example of Example 1 of the first embodiment of the present technology. FIG. 11 is a diagram showing a stage transition process during the manufacture of the thermoelectric conversion film of FIG. 11. FIG. 11D is a cross-sectional view schematically showing a thermoelectric conversion film according to Example 2 of the first embodiment of the present technology. FIG. 13 is a diagram showing a stage transition process during the manufacture of the thermoelectric conversion film of FIG. 13. FIG. 16A is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Sr-en-GIC stored in the atmosphere for three days. 16B is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD is performed on Sr-en-GIC stored in the atmosphere for two weeks. It is a cross-sectional view schematically showing a thermoelectric conversion film according to Example 3 of the first embodiment of the present technology. It is a graph showing the change over time in the mole fractions of carbon, oxygen, nitrogen, and barium contained in Ba-en-GIC when the GIC is stored in the atmosphere.17 is a diagram showing a stage transition process during the production of the thermoelectric conversion film of FIG. 17. FIG. 21A is a graph showing the relationship between the diffraction angle and diffracted X-ray intensity when XRD was performed on Ba-en-GIC stored in the atmosphere for three days. FIG. 21B is a graph showing the relationship between the diffraction angle and diffracted X-ray intensity when XRD was performed on Ba-en-GIC stored in the atmosphere for three weeks ...C is a cross-sectional view schematically showing a thermoelectric conversion film according to a modified example of Example 3 of the first embodiment of the present technology. FIG. 22 is a diagram showing a stage transition process during the production of the thermoelectric conversion film of FIG. 22. FIG. 22 is a diagram showing, in numerical form, an example of the change in Seebeck coefficient over time when each GIC is stored in the atmosphere for a predetermined period or in argon for four months. FIG. 22 is a diagram showing, in numerical form, an example of the change in electrical conductivity over time when each GIC is stored in the atmosphere for a predetermined period or in argon for four months. FIG. 22 is a diagram showing, in numerical form, an example of the change in power factor over time when each GIC is stored in the atmosphere for a predetermined period or in argon for four months. 1 is a diagram for explaining the definition of a GIC in which metal complexes are randomly arranged; FIG. 2 is a diagram for explaining the definition of a thermoelectric conversion film in which metal complexes are randomly arranged; and FIG. 3 is a diagram for explaining the spacing between two adjacent graphene layers.

[0014] Preferred embodiments of the present technology will be described in detail below with reference to the accompanying drawings. Note that in this specification and the drawings, components having substantially the same functional configurations are denoted by the same reference numerals, and redundant description will be omitted. The embodiments described below are representative embodiments of the present technology, and are not intended to narrow the scope of the present technology. Even when the present specification describes that the thermoelectric conversion film, thermoelectric conversion element, and thermoelectric conversion film manufacturing method according to the present technology achieve multiple effects, it is sufficient that the thermoelectric conversion film, thermoelectric conversion element, and thermoelectric conversion film manufacturing method according to the present technology achieve at least one effect. The effects described in this specification are merely examples and are not limiting, and other effects may also be achieved.

[0015] (0) Introduction (1) Thermoelectric conversion film according to Example 1 of the first embodiment of the present technology (1.5) Thermoelectric conversion film according to a modified example of Example 1 of the first embodiment of the present technology (2) Thermoelectric conversion film according to Example 2 of the first embodiment of the present technology (3) Thermoelectric conversion film according to Example 3 of the first embodiment of the present technology (3.5) Thermoelectric conversion film according to a modified example of Example 3 of the first embodiment of the present technology (4) Thermoelectric conversion element according to the second embodiment of the present technology (5) Other modified examples of the present technology

[0016] <0. Introduction> In recent years, the demand for thermoelectric conversion films has been expanding for applications in waste heat power generation / thermal sensing in wearable devices and IoT equipment. The thermoelectric conversion principle of thermoelectric conversion films is based on the Seebeck effect, in which the temperature gradient within the thermoelectric conversion film is converted into voltage.

[0017] Although soft and safe carbon-based materials are suitable for the thermoelectric conversion film, Bi ２ Te ３ However, there are concerns that the thermoelectric properties (PF: power factor, S: Seebeck coefficient, σ: electrical conductivity, etc.) of carbon nanotubes are smaller than those of inorganic materials such as carbon nanotubes. On the other hand, carbon nanotubes, which have relatively large thermoelectric properties, can also be used as a material for thermoelectric conversion films, but there are concerns that carbon nanotubes do not exist in nature and are expensive, costing over $100 / kg.

[0018] Previously, soft and safe thermoelectric conversion films have been proposed using graphite, a naturally occurring and inexpensive material costing approximately $1 / kg. These thermoelectric conversion films can improve their thermoelectric properties by heterogeneously laminating the graphene layer with a guest compound that controls the charge characteristics. However, because graphite is chemically stable, most thermoelectric conversion films are manufactured using high-temperature vapor-phase processes or highly reactive chemical reagents. Furthermore, many reports have revealed that the stability of these thermoelectric conversion films in air is unclear, posing practical challenges.

[0019] Therefore, the inventors focused on a known liquid phase process for introducing a metal complex into graphite powder, and by adjusting the amount and chemical state of the metal complex introduced into the graphite, they succeeded in obtaining very high thermoelectric properties in a graphite-based thermoelectric conversion film.

[0020] The inventors have found that thermoelectric properties can be improved by reducing the amount of metal complex introduced into graphite and lowering the crystallinity. Furthermore, the inventors have confirmed that such a thermoelectric conversion film with low crystallinity exhibits stable performance even after storage in the air.

[0021] The inventors then developed a thermoelectric conversion film according to the present technology as a thermoelectric conversion film that embodies this new finding. Furthermore, the inventors developed a method for manufacturing a thermoelectric conversion film according to the present technology as a method for manufacturing a thermoelectric conversion film that embodies this new finding.

[0022] According to the thermoelectric conversion film of the present technology, it is possible to provide a thermoelectric conversion film that can improve thermoelectric conversion characteristics while suppressing an increase in cost. Here, "thermoelectric conversion characteristics" broadly means all characteristics related to thermoelectric conversion, including thermoelectric properties.

[0023] Furthermore, the thermoelectric conversion film according to the present technology can have the advantages of being easy to manufacture, having few restrictions on use, and being able to exhibit stable performance even in the atmosphere.

[0024] Hereinafter, the thermoelectric conversion film according to the first embodiment of the present technology will be described in detail with reference to several examples.

[0025] (1) Thermoelectric Conversion Film According to Example 1 of First Embodiment of the Present Technology Configuration of Thermoelectric Conversion Film FIG. 1 is a cross-sectional view schematically illustrating a thermoelectric conversion film 10 according to Example 1 of the first embodiment of the present technology.

[0026] As shown in FIG. 1 , the thermoelectric conversion film 10 includes a plurality of (e.g., 10) graphene layers 100 (two-dimensional nanosheet layers) stacked on top of each other, and a metal complex group 200G including a plurality of metal complexes (e.g., metal complexes 200, 200′). The metal complex group is disposed between at least one pair of adjacent graphene layers 100. That is, the thermoelectric conversion film 10 is a graphite intercalation compound (GIC) in which a metal complex (guest layer) is inserted between graphene layers (host layers) of graphite. Hereinafter, the direction in which the plurality of graphene layers 100 are stacked on top of each other will also be referred to as the “stacking direction.”

[0027] In the thermoelectric conversion film 10, for example, each metal complex has an alkaline earth metal, such as Ca, as the central metal, and a chelate complex, such as ethylenediamine, as the ligand. Therefore, hereinafter, the thermoelectric conversion film 10 is also referred to as Ca-en-GIC, where en means ethylenediamine (the same applies hereinafter).

[0028] As an example, the thermoelectric conversion film 10 has a Seebeck coefficient S<0, that is, an n-type conductivity.

[0029] In the thermoelectric conversion film 10, as an example, the plurality of graphene layers 100 are at least three (e.g., ten) graphene layers 100, and the metal complex groups 200G are arranged between at least two (e.g., three) pairs of adjacent graphene layers 100. In the thermoelectric conversion film 10, the metal complex groups 200G are not arranged between some (e.g., six) pairs of adjacent graphene layers 100.

[0030] At least two graphene layers 100, for example, four graphene layers 100, are arranged between two adjacent metal complex groups 200G. That is, the thermoelectric conversion film 10 is a stage 4 Ca-en-GIC.

[0031] The metal complexes in the metal complex group 200G are arranged irregularly (randomly) (not arranged in an orderly manner) along the in-plane direction (the direction perpendicular to the stacking direction).

[0032] The plurality of metal complexes in the metal complex group 200G includes at least two metal complexes of different sizes (for example, a small-diameter metal complex 200 and a large-diameter metal complex 200').

[0033] The arrangement pitch (the center-to-center distance between two adjacent metal complexes) of the plurality of metal complexes in the metal complex group 200G is not constant, i.e., the plurality of metal complexes are arranged irregularly (randomly) along the in-plane direction.

[0034] In the thermoelectric conversion film 10, the distance between two adjacent graphene layers 100 is not constant (uneven). More specifically, each graphene layer 100 has a randomly distorted shape.

[0035] As can be seen from the above description, the thermoelectric conversion film 10 is a low-crystalline GIC in which at least a portion (for example, a majority) is in an amorphous state (non-crystalline state).

[0036] The thermoelectric conversion film 10 can achieve higher thermoelectric properties by having a structure with low crystallinity and a small amount of metal complex incorporated, compared to a highly crystalline structure in which graphene and metal complex groups are alternately stacked. Furthermore, the thermoelectric conversion film 10 has further improved thermoelectric properties due to the disordering of the structure caused by chemical reactions of the metal complexes upon exposure to the atmosphere. The thermoelectric conversion film 10 does not require high crystallinity, can be stored and used in the atmosphere, has a versatile manufacturing process, and is suitable for a variety of use cases. The large-diameter metal complex 200' has a diameter similar to that of the small-diameter metal complex 200 when the thermoelectric conversion film 10 is produced, but has grown larger over time.

[0037] FIG. 2 is a graph showing an example of the change over time in the Seebeck coefficient S of each GIC (specifically, the change over time from the time of production of each GIC up to 20 weeks later). FIG. 24 is a diagram showing an example of the change over time in the Seebeck coefficient of each GIC in numerical form. From FIGS. 2 and 24, it can be seen that in the thermoelectric conversion film 10 (Ca-en-GIC), the Seebeck coefficient S satisfies |S|≧24 μV·K. －１ |S|≧30 μV·K －１ |S|≧35 μV·K －１ |S|≧40 μV·K －１ |S|≧45 μV·K －１ |S|≦50 μV·K －１ It is possible.

[0038] FIG. 3 is a graph showing an example of the change in electrical conductivity σ of each GIC over time (specifically, the change over time from the time of production of each GIC up to 20 weeks later). FIG. 25 is a diagram showing an example of the change in electrical conductivity of each GIC over time in numerical terms. From FIGS. 3 and 25, it can be seen that the electrical conductivity σ of the thermoelectric conversion film 10 (Ca-en-GIC) is σ≧2550 S cm －１ σ≧3000 S cm －１ σ≧3500 S cm －１ σ≧5000 S cm －１σ≦5500 S cm －１ It is possible.

[0039] Figure 4 shows the power factor PF (σS ２ 26 is a graph showing an example of the change over time in the power factor of each GIC (specifically, the change over time from the time of production to 20 weeks after the production of each GIC). FIG. 26 is a graph showing an example of the change over time in the power factor of each GIC in numerical terms. From FIGS. 4 and 26, it can be seen that the thermoelectric conversion film 10 (Ca-en-GIC) has a power factor PF of PF≧190 μW m ー１ ・K －２ PF≧300 μW m ー１ ・K －２ PF≧400 μW m ー１ ・K －２ PF≧450 μW m ー１ ・K －２ PF≧500 μW m ー１ ・K －２ PF≧600 μW m ー１ ・K －２ PF≧700 μW m ー１ ・K －２ PF≧750 μW m ー１ ・K －２ PF≦800 μW m ー１ ・K －２ It is possible.

[0040] 5 is a graph showing an example of the change in weight of each GIC over time (more specifically, the change over time from the time of production of each GIC up to 20 weeks later). From FIG. 5, it can be seen that the weight of the thermoelectric conversion film 10 (Ca-en-GIC) can be w≦3.5 mg, w≦3 mg, or w≧2.5 mg.

[0041] The total amount of metal (here, Ca) in the thermoelectric conversion film 10 (Ca-en-GIC) is preferably less than 2.9% in molar fraction, more preferably 2.5% or less in molar fraction, more preferably 2% or less in molar fraction, more preferably 1.5% or less in molar fraction, and more preferably 1% or less in molar fraction.

[0042] The structure of the thermoelectric conversion film 10 (Ca-en-GIC) can be analyzed by structural analysis (for example, XRD: X-ray diffraction) or elemental analysis (for example, EDX: Energy Dispersive X-ray Spectroscopy, ICP: Inductively Coupled Plasma).

[0043] <<Method for Manufacturing Thermoelectric Conversion Film>> A description will now be given of a method for manufacturing the thermoelectric conversion film 10. Fig. 6 is a flowchart showing an example of a method for manufacturing the thermoelectric conversion film 10 according to Example 1 of the first embodiment of the present technology.

[0044] In step S1, a metal complex solution is produced using a metal and a ligand. In step S2, a graphite sheet is immersed in the metal complex solution. Steps S1 and S2 may be performed sequentially or in parallel.

[0045] As an example, the starting materials used here were commercially available graphite sheets (PGS, registered trademark: Pyrolytic Graphite Sheet, 25 mm x 5 mm, 0.1 mm thick), metallic calcium (Aldrich, dendritic pieces, 99.5%), and anhydrous ethylenediamine (98%). Two sheets of PGS (24 mg), 0.5 g of calcium, 4 mL of ethylenediamine, and a stir bar were introduced into a Schlenk tube in a glove box with an Ar atmosphere containing less than 2% oxygen. The Schlenk tube was then purged with pure Ar and placed on a hot stirrer. The temperature was set to 80°C during the addition of calcium, and the mixture was stirred for 7 days. The bottom of the Schlenk tube was covered with aluminum foil to efficiently utilize the heat. After the reaction, the sheet sample was washed with acetone and air-blown to obtain a sample with a clean sheet surface.

[0046] Table 1 below shows the amounts of raw materials charged and reaction conditions for two graphite sheets (total 24 mg) in Examples 1 to 3 (Examples 2 and 3 will be described later).

[0047]

[0048] As described above, a thermoelectric conversion film (Ca-en-GIC) with the desired heterogeneous layer structure was successfully produced by immersing a commercially available graphite sheet in an ethylenediamine metal complex solution. While the recipe using graphite powder as the starting material is publicly known in papers published in international academic journals, the reaction did not proceed using this recipe when graphite sheets were used. For the first time, the reaction was successfully promoted by increasing the metal loading amount by 10 times or more. This means that even if the form or type of graphite used as the starting material changes, a thermoelectric conversion film can be produced by increasing the metal concentration in the metal complex solution. Therefore, in step S1, it is preferable to adjust the metal concentration in the metal complex solution depending on the type of graphite and / or the purity of the carbon contained in the graphite. Additionally or alternatively, the ligand concentration in the metal complex solution may be adjusted depending on the type of graphite and / or the purity of the carbon contained in the graphite. Factors such as the size and shape of the graphite (e.g., sheet, flake, powder, etc.), origin, manufacturing method, crystallinity, crystallite size, orientation, and interlayer distance of the graphene layers vary depending on the type of graphite. The purity of the graphite contained in the graphite sheet varies depending on whether it is natural graphite or artificial graphite, and further varies depending on the place of origin, etc. for natural graphite, and varies depending on the manufacturing method, etc. for artificial graphite. Examples of artificial graphite include graphitized polyimide sheets and highly crystalline kish graphite produced during steelmaking.

[0049] Fig. 7 is a diagram showing a stage transition process during the production of the thermoelectric conversion film of Fig. 1. Fig. 8 is a graph showing the relationship between the diffraction angle (horizontal axis) and the diffracted X-ray intensity (vertical axis) when XRD was performed on PGS (registered trademark: Pyrolytic Graphite Sheet). Fig. 9 is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Ca-en-GIC.

[0050] (Sample Evaluation by XRD) During the production of the thermoelectric conversion film 10, the progress of the intercalation reaction (stages 1 to 4 in FIG. 7 ) using PGS (registered trademark: Pyrolytic Graphite Sheet) as the host layer was confirmed by XRD analysis. XRD analysis of PGS revealed a sharp peak in diffracted X-ray intensity at a diffraction angle 2θ = 26.7° (see FIG. 8 ), and the d value was calculated to be 0.33 nm based on the Bragg diffraction condition. This is due to a periodic structure in which two-dimensional graphene layers are stacked in multiple layers, indicating a layer spacing of 0.33 nm. As shown in FIG. 9 , after intercalation, a new peak in diffracted X-ray intensity was observed at a lower diffraction angle. This indicates that ethylenediamine and Ca were introduced between the graphene layers, resulting in the production of Ca-en-GIC. In the example shown in Figure 9, the Ca-en-GIC exhibits the largest peak in diffracted X-ray intensity attributable to the stage 4 structure (stage 4 in Figure 7), indicating a high content of the stage 4 structure. In other words, in the example shown in Figure 9, the Ca-en-GIC exhibits a tendency toward a lower amount of metal complexes, i.e., a higher stage, compared to the stage 1 structure in which graphene layers, a highly crystalline GIC, and metal complex groups, a guest compound, are alternately stacked. Note that in a report by Lerner et al. (W. Xu and MM Learner, Chem. Mater. 30 (2018) 6930.), stage 1 GIC was successfully produced using natural graphite powder (SP-1 grade with an average diameter of 100 μm, Union Carbide) as a host layer. However, in this study, the use of PGS with a highly oriented graphene layer prepared by pyrolysis as the host layer likely altered the stage structure of the resulting GIC.

[0051] (Sample Evaluation by XRD After Storage in Air)

[0052] Figure 10A is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Ca-en-GIC stored in air for 3 days, and Figure 10B is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Ca-en-GIC stored in air for 2 weeks.

[0053] After the above sample evaluation, to verify the stability of the generated Ca-en-GIC, we performed time-dependent XRD measurements on Ca-en-GIC that had been left in an air atmosphere after generation. After leaving the Ca-en-GIC for three days, the low-angle peaks at 0-20 deg disappeared, and the 006 and 007 peaks of stage 4 were observed (see Figure 10A). This suggests that exposure to air promoted amorphization. After two weeks, the stage had progressed to stage 6, but the graphite (Gr) peak did not become larger, and the GIC structure was maintained (see Figure 10B).

[0054] As can be seen from the above explanation, the final form of the thermoelectric conversion film 10 (Ca-en-GIC) can be not only the final form of Stage 4 in FIG. 7 (after aging in the atmosphere) but also any of the initial forms of Stages 1, 2, 3, and 4 (before aging in the atmosphere) depending on the type of graphite in the graphite sheet used as the material, the amount of metal and ligand added, the manufacturing conditions, and the like.

[0055] <Effects of Thermoelectric Conversion Film and Method for Manufacturing Thermoelectric Conversion Film> The thermoelectric conversion film 10 according to Example 1 of the present technology includes a plurality of graphene layers 100 stacked on top of each other and a metal complex group 200G including a plurality of metal complexes, and the metal complex group 200G is arranged between at least one pair of two adjacent graphene layers 100, and the plurality of metal complexes are arranged irregularly.

[0056] The thermoelectric conversion film 10 has a structure (low crystalline structure) that provides high thermoelectric properties, based on graphite, which is a relatively inexpensive material.

[0057] As a result, the thermoelectric conversion film 10 can provide a thermoelectric conversion film that can improve thermoelectric conversion characteristics while suppressing an increase in cost.

[0058] On the other hand, a thermoelectric conversion film containing carbon nanotubes can be expected to have a certain degree of performance, but the thermoelectric conversion performance is lower than that of the thermoelectric conversion film 10, and furthermore, the cost and environmental load are increased. In addition, other carbon-based thermoelectric conversion films (thermoelectric conversion films containing aromatic polymers, graphene oxide, etc.) and the carbon-based thermoelectric conversion film and Bi ２ Te ３ A thermoelectric conversion film formed by combining an inorganic material such as a silicon dioxide powder and an aluminum alloy can suppress an increase in cost, but has poorer thermoelectric conversion properties than the thermoelectric conversion film 10 .

[0059] The method for manufacturing the thermoelectric conversion film 10 includes a step of producing a metal complex solution using a metal (e.g., Ca) and a ligand (e.g., ethylenediamine), and a step of immersing a graphite sheet in the metal complex solution.

[0060] According to the method for manufacturing the thermoelectric conversion film 10, the thermoelectric conversion film 10 can be easily manufactured.

[0061] <(1.5) Thermoelectric Conversion Film According to Modification of Example 1 of First Embodiment of the Present Technology> Fig. 11 is a cross-sectional view schematically showing a thermoelectric conversion film 15 according to a modification of Example 1 of the first embodiment of the present technology. Fig. 12 is a diagram showing a stage transition process during the manufacture of the thermoelectric conversion film 15 of Fig. 11 .

[0062] 11 and 12 , the thermoelectric conversion film 15 has the same configuration as the thermoelectric conversion film 10 according to Example 1, except that it is a Ca-en-GIC at the end of stage 6. That is, in the thermoelectric conversion film 15, for example, six graphene layers 100 are arranged between two adjacent metal complex groups 200G.

[0063] The thermoelectric conversion film 15 has a highly crystalline structure, for example, in which graphene and metal complex groups are alternately stacked, but has a structure with a very low amount of metal complexes incorporated and very low crystallinity, thereby enabling the film to achieve significantly higher thermoelectric properties. Furthermore, the thermoelectric conversion film 15 has further improved thermoelectric properties due to structural disorder caused by chemical reactions and desorption of the complexes upon exposure to the atmosphere. The thermoelectric conversion film 15 does not require high crystallinity, can be stored and used in the atmosphere, has a versatile manufacturing process, and has a wide range of use cases. The large-diameter metal complexes 200' have a diameter similar to that of the small-diameter metal complexes 200 when the thermoelectric conversion film 15 is produced, but have grown larger over time. Here, the property of claim 1, "the plurality of metal complexes are irregularly arranged," is explained as an example.

[0064] The final form of the thermoelectric conversion film 15 (Ca-en-GIC) can be not only the final form of Stage 6 in FIG. 12 (after aging in the atmosphere and after desorption), but also the initial form of Stages 1, 2, 3, 4, 5, and 6 (before aging in the atmosphere and before desorption), depending on the type of graphite in the graphite sheet used as the material, the amount of metal and ligand added, the manufacturing conditions, and the like.

[0065] The thermoelectric conversion film 15 can be manufactured by substantially the same manufacturing method as that for the thermoelectric conversion film 10 according to the first embodiment.

[0066] According to the thermoelectric conversion film 15, it is possible to obtain thermoelectric conversion characteristics equal to or better than those of the thermoelectric conversion film 10 according to the first embodiment.

[0067] 2. Thermoelectric Conversion Film According to Example 2 of First Embodiment of the Present Technology FIG. 13 is a cross-sectional view schematically showing a thermoelectric conversion film 20 according to Example 2 of the first embodiment of the present technology.

[0068] As shown in Fig. 13, the thermoelectric conversion film 20 includes a plurality of (e.g., 10) graphene layers 100 stacked on top of each other and a metal complex group 200G including a plurality of metal complexes (e.g., metal complexes 200, 200'). The metal complex group 200G is disposed between at least one pair (e.g., two pairs) of adjacent graphene layers 100. That is, the thermoelectric conversion film 20 is a graphite intercalation compound (GIC) in which a metal complex (guest layer) is inserted between graphene layers (host layers) of graphite. Hereinafter, the direction in which the plurality of graphene layers 100 are stacked on top of each other will also be referred to as the "stacking direction."

[0069] In the thermoelectric conversion film 20, as an example, each metal complex has an alkaline earth metal, such as Sr, as the central metal, and a chelate complex, such as ethylenediamine, as the ligand. Therefore, hereinafter, the thermoelectric conversion film 20 is also referred to as Sr-en-GIC.

[0070] As an example, the thermoelectric conversion film 20 has a Seebeck coefficient S<0, that is, an n-type conductivity.

[0071] In the thermoelectric conversion film 20, as an example, the plurality of graphene layers 100 are at least three (e.g., ten) graphene layers 100, and the metal complex groups 200G are arranged between at least two (e.g., two) pairs of adjacent graphene layers 100. In the thermoelectric conversion film 10, the metal complex groups 200G are not arranged between some (e.g., seven) pairs of adjacent graphene layers 100.

[0072] At least two graphene layers 100, for example, five graphene layers 100, are arranged between two adjacent metal complex groups 200G. That is, the thermoelectric conversion film 20 is a stage 5 Sr-en-GIC.

[0073] The metal complexes in the metal complex group 200G are arranged irregularly (randomly) (not arranged in an orderly manner) along the in-plane direction (the direction perpendicular to the stacking direction).

[0074] The plurality of metal complexes in the metal complex group 200G includes at least two metal complexes of different sizes (for example, a small-diameter metal complex 200 and a large-diameter metal complex 200').

[0075] The arrangement pitch (the center-to-center distance between two adjacent metal complexes) of the plurality of metal complexes in the metal complex group 200G is not constant, i.e., the plurality of metal complexes are arranged irregularly (randomly) along the in-plane direction.

[0076] In the thermoelectric conversion film 20, the distance between two adjacent graphene layers 100 is not constant (uneven). More specifically, each graphene layer 100 has a randomly distorted shape.

[0077] As can be seen from the above description, the thermoelectric conversion film 20 is a low-crystalline GIC in which at least a portion (for example, a majority) is in an amorphous state (non-crystalline state).

[0078] The thermoelectric conversion film 20 can achieve higher thermoelectric properties by having a structure with low crystallinity and a small amount of metal complex incorporated, compared to a highly crystalline structure in which graphene and metal complex groups are alternately stacked. Furthermore, the thermoelectric conversion film 20 has further improved thermoelectric properties due to the disordering of the structure caused by chemical reactions of the metal complexes due to exposure to the atmosphere. The thermoelectric conversion film 20 does not require high crystallinity, can be stored / used in the atmosphere, has a versatile manufacturing process, and has a wide range of use cases. The large-diameter metal complex 200' has a diameter similar to that of the small-diameter metal complex 200 before the thermoelectric conversion film 20 is produced, but has grown larger over time.

[0079] 2 and 24, the Seebeck coefficient S of the thermoelectric conversion film 20 (Sr-en-GIC) is |S|≧24 μV·K. －１ |S|≧27 μV·K －１ |S|≧30 μV·K －１ |S|≧35 μV·K －１ |S|≦40 μV·K －１ It is possible.

[0080] 3 and 25, the thermoelectric conversion film 20 (Sr-en-GIC) has an electrical conductivity σ of σ≧2550 S cm－１ σ≧3000 S cm －１ σ≧3500 S cm －１ σ≧4000 S cm －１ σ≦4500 S cm －１ It could be more than that.

[0081] 4 and 26, the thermoelectric conversion film 20 (Sr-en-GIC) has a power factor PF (σS ２ ) but PF ≥ 190 μW m ー１ ・K －２ PF≧250 μW m ー１ ・K －２ PF≧300 μW m ー１ ・K －２ PF≧350 μW m ー１ ・K －２ PF≧400 μW m ー１ ・K －２ PF≦450 μW m ー１ ・K －２ It is possible.

[0082] 5, the weight w of the thermoelectric conversion film 20 (Sr-en-GIC) can be w≦4 mg or w≦3.7 mg.

[0083] The total amount of metal (here, Sr) in the thermoelectric conversion film 20 (Sr-en-GIC) is preferably less than 2.9% in molar fraction, more preferably 2.5% or less in molar fraction, more preferably 2% or less in molar fraction, more preferably 1.5% or less in molar fraction, and more preferably 1% or less in molar fraction.

[0084] The structure of the thermoelectric conversion film 20 (Sr-en-GIC) can be analyzed by structural analysis (for example, X-ray diffraction (XRD)) or elemental analysis (for example, energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma (ICP)).

[0085] The following describes a method for manufacturing the thermoelectric conversion film 20. The thermoelectric conversion film 20 is manufactured by a manufacturing method that is generally similar to the manufacturing method for the thermoelectric conversion film 10 according to the first embodiment.

[0086] As an example, the starting materials used here were commercially available graphite sheets (PGS, registered trademark: Pyrolityc Graphite Sheet, 25 mm x 5 mm, 0.1 mm thick), metallic calcium (Aldrich, dendritic pieces, 99.5%), and anhydrous ethylenediamine (98%). Two sheets of PGS (24 mg), 0.5 g of Sr, 4 mL of ethylenediamine, and a stir bar were introduced into a Schlenk tube in a glove box with an Ar atmosphere containing less than 2% oxygen. The Schlenk tube was then purged with pure Ar and placed on a hot stirrer. The temperature was set to 50°C during the addition of Sr, and the mixture was stirred for 3 days (see Table 1). The bottom of the Schlenk tube was covered with aluminum foil to efficiently utilize the heat. After the reaction, the sheet sample was washed with acetone and air-blown to obtain a sample with a clean sheet surface.

[0087] Fig. 14 is a diagram showing a stage transition process during the manufacture of the thermoelectric conversion film 20 of Fig. 13. Fig. 15 is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD is performed on Sr-en-GIC.

[0088] (Sample Evaluation by XRD) During the production of the thermoelectric conversion film 20, the progress of the intercalation reaction (stages 1 to 5 in FIG. 14 ) using PGS (registered trademark: Pyrolytic Graphite Sheet) as the host layer was confirmed by XRD analysis. XRD analysis of PGS revealed a sharp peak in diffracted X-ray intensity at a diffraction angle 2θ = 26.7° (see FIG. 8 ), and the d value was calculated to be 0.33 nm based on the Bragg diffraction condition. This is due to a periodic structure in which two-dimensional graphene layers are stacked in multiple layers, and indicates that the layer spacing is 0.33 nm. As shown in FIG. 15 , after intercalation, a new peak in diffracted X-ray intensity was observed at a lower diffraction angle. This indicates that ethylenediamine and Sr were introduced between the graphene layers, resulting in the production of Sr-en-GIC. In the example shown in Figure 15, the Sr-en-GIC exhibits the largest peak in the diffracted X-ray intensity due to the stage 2 structure (stage 2 in Figure 14), indicating a high content of the stage 2 structure. In other words, in the example shown in Figure 15, the Sr-en-GIC exhibits a tendency toward a decrease in the amount of metal complex guest compound incorporated, i.e., a slower tendency toward a higher stage. Note that in a report by Lerner et al. (W. Xu and M. M. Learner, Chem. Mater. 30 (2018) 6930.), stage 1 GIC was successfully produced using natural graphite powder (SP-1 grade with an average diameter of 100 μm, Union Carbide) as the host layer. However, in this study, the use of PGS with a highly oriented graphene layer prepared by pyrolysis as the host layer likely altered the stage structure of the resulting GIC.

[0089] (Sample Evaluation by XRD After Storage in Air)

[0090] Figure 16A is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Sr-en-GIC stored in air for 3 days, and Figure 16B is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Sr-en-GIC stored in air for 2 weeks.

[0091] After the above sample evaluation, to verify the stability of the generated Sr-en-GIC, we performed time-dependent XRD measurements on Sr-en-GIC that had been left in an air atmosphere after generation. After leaving the Sr-en-GIC for three days, the low-angle peaks at 0-20 deg disappeared, and the 007 and 008 peaks of stage 5 were observed (see Figure 16A). It is believed that exposure to air promoted the progression to higher stages and amorphization. After two weeks, the GIC structure was maintained, with no further increase in the graphite (Gr) peaks (see Figure 16B).

[0092] As can be seen from the above explanation, the final form of the thermoelectric conversion film 20 (Sr-en-GIC) can be not only the end of Stage 5 (after changes over time in the atmosphere) in FIG. 14 but also any of the early stages of Stages 1, 2, 3, 4, and 5 (before changes over time in the atmosphere) and Stage 6, depending on the type of graphite in the graphite sheet that is the material, the amounts of metals and ligands charged, the manufacturing conditions, and the like.

[0093] According to the thermoelectric conversion film 20 described above, although the thermoelectric conversion characteristics are slightly inferior to those of the thermoelectric conversion film 10 according to Example 1, substantially the same effects can be obtained.

[0094] 3. Thermoelectric Conversion Film According to Example 3 of First Embodiment of Present Technology FIG. 17 is a cross-sectional view schematically showing a thermoelectric conversion film 30 according to Example 3 of the first embodiment of the present technology.

[0095] As shown in FIG. 17 , the thermoelectric conversion film 30 includes a plurality of (e.g., 10) graphene layers 100 stacked on top of each other, and a metal complex group 200G including a plurality of metal complexes (e.g., metal complexes 200, 200′). The metal complex group is disposed between at least one pair of adjacent graphene layers 100. That is, the thermoelectric conversion film 30 is a graphite intercalation compound (GIC) in which a metal complex (guest layer) is inserted between graphene layers (host layers) of graphite. Hereinafter, the direction in which the plurality of graphene layers 100 are stacked on top of each other will also be referred to as the “stacking direction.”

[0096] In the thermoelectric conversion film 30, for example, each metal complex has an alkaline earth metal, such as Ba, as the central metal, and a chelate complex, such as ethylenediamine, as the ligand. Therefore, hereinafter, the thermoelectric conversion film 30 is also referred to as Ba-en-GIC.

[0097] As an example, the thermoelectric conversion film 30 has a Seebeck coefficient S<0, that is, an n-type conductivity.

[0098] In the thermoelectric conversion film 30, as an example, the plurality of graphene layers 100 are at least three (e.g., ten) graphene layers 100, and the metal complex groups 200G are arranged between at least two (e.g., two) pairs of adjacent graphene layers 100. In the thermoelectric conversion film 30, the metal complex groups 200G are not arranged between some (e.g., seven) pairs of adjacent graphene layers 100.

[0099] At least two graphene layers 100, for example, seven graphene layers 100, are arranged between two adjacent metal complex groups 200G. That is, the thermoelectric conversion film 30 is a stage 7 Ba-en-GIC.

[0100] The metal complexes in the metal complex group 200G are arranged irregularly (randomly) (not arranged in an orderly manner) along the in-plane direction (the direction perpendicular to the stacking direction).

[0101] The plurality of metal complexes in the metal complex group 200G includes at least two metal complexes of different sizes (for example, a small-diameter metal complex 200 and a large-diameter metal complex 200').

[0102] The arrangement pitch (the center-to-center distance between two adjacent metal complexes) of the plurality of metal complexes in the metal complex group 200G is not constant, i.e., the plurality of metal complexes are arranged irregularly (randomly) along the in-plane direction.

[0103] In the thermoelectric conversion film 30, the distance between two adjacent graphene layers 100 is not constant (uneven). More specifically, each graphene layer 100 has a randomly distorted shape.

[0104] As can be seen from the above description, the thermoelectric conversion film 30 is a low-crystalline GIC in which at least a portion (for example, a majority) is in an amorphous state (non-crystalline state).

[0105] The thermoelectric conversion film 30 has a highly crystalline structure in which, for example, graphene and metal complex groups are alternately stacked, but has a structure with a very low amount of metal complexes incorporated and very low crystallinity, which enables it to achieve very high thermoelectric properties. Furthermore, the thermoelectric conversion film 30 has further improved thermoelectric properties due to structural disorder caused by chemical reactions and desorption of the metal complexes upon exposure to the atmosphere. The thermoelectric conversion film 30 does not require high crystallinity, can be stored and used in the atmosphere, has a versatile manufacturing process, and has a wide range of use cases. The large-diameter metal complexes 200' were approximately the same diameter as the small-diameter metal complexes 200 when the thermoelectric conversion film 30 was produced, but have grown larger over time.

[0106] 2 and 24, the Seebeck coefficient S of the thermoelectric conversion film 30 (Ba-en-GIC) is |S|≧24 μV·K. －１ |S|≧30 μV·K －１ |S|≧35 μV·K －１ |S|≧40 μV·K －１ |S|≧45 μV·K －１ |S|≦50 μV·K －１ It is possible.

[0107] 3 and 25, the thermoelectric conversion film 30 (Ba-en-GIC) has an electrical conductivity σ of σ≧2550 S·cm －１ σ≧3000 S cm －１ σ≧3500 S cm －１ σ≧4000 S cm －１ σ≧6000 S cm －１ σ≦6500 S cm －１ It is possible.

[0108] 4 and 26, the thermoelectric conversion film 30 (Ba-en-GIC) has a power factor PF (σS ２ ) but PF ≥ 190 μW m ー１ ・K －２PF≧300 μW m ー１ ・K －２ PF≧400 μW m ー１ ・K －２ PF≧450 μW m ー１ ・K －２ PF≧500 μW m ー１ ・K －２ PF≧550 μW m ー１ ・K －２ PF≧600 μW m ー１ ・K －２ PF≧700 μW m ー１ ・K －２ PF≧800 μW m ー１ ・K －２ PF≧900 μW m ー１ ・K －２ PF≦1000 μW m ー１ ・K －２ It is possible.

[0109] 5, the weight w of the thermoelectric conversion film 30 (Ba-en-GIC) can be w≦3.5 mg, w≦3 mg, w≦2.7 mg, or w≧2.2 mg.

[0110] Figure 18 is a graph showing the change in the mole fraction of Ba-en-GIC over time. In Figure 18, C1s, O1s, N1s, and Ba3d5 represent the electron orbitals of the elements (C, O, N, Ba), respectively. For example, C1s corresponds to the 1s electron orbital of a carbon atom. Additionally, X-ray photoelectron spectroscopy (XPS) detects the count and energy of electrons emitted when irradiated with X-rays, allowing the original electron orbitals and chemical state of each element to be determined. The total amount of metal (here, Ba) in the thermoelectric conversion film 30 (Ba-en-GIC) is preferably less than 2.9% molar fraction, more preferably 2.5% or less, even more preferably 2% or less, even more preferably 1.5% or less, and even more preferably 1% or less. In the example of FIG. 18, Ba-en-GIC contained Ba at a molar fraction of 2.2% the day after production, and after one week the molar fraction of Ba was 1% or less.

[0111] The structure of the thermoelectric conversion film 30 (Sr-en-GIC) can be analyzed by structural analysis (for example, X-ray diffraction (XRD)) or elemental analysis (for example, energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma (ICP)).

[0112] The thermoelectric conversion film 30 can be manufactured by a manufacturing method that is generally similar to the manufacturing method of the thermoelectric conversion film 30 according to the first embodiment.

[0113] As an example, the starting materials used here were commercially available graphite sheets (PGS, registered trademark: Pyrolytic Graphite Sheet, 25 mm x 5 mm, 0.1 mm thick), metallic calcium (Aldrich, dendritic pieces, 99.5%), and anhydrous ethylenediamine (98%). Two PGS sheets (24 mg), 1.5 g of barium, 4 mL of ethylenediamine, and a stir bar were introduced into a Schlenk tube in a glove box with an Ar atmosphere containing less than 2% oxygen. The Schlenk tube was then purged with pure Ar and placed on a hot stirrer. The temperature was set to 50°C during the addition of barium, and the mixture was stirred for 3 days (see Table 1). The bottom of the Schlenk tube was covered with aluminum foil to efficiently utilize the heat. After the reaction, the sheet sample was washed with acetone and air-blown to obtain a sample with a clean sheet surface.

[0114] Fig. 19 is a diagram showing a stage transition process during the manufacture of the thermoelectric conversion film 30 of Fig. 17. Fig. 20 is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD is performed on Ba-en-GIC.

[0115] (Sample Evaluation by XRD) During the production of the thermoelectric conversion film 30, the progress of the intercalation reaction (stages 1 to 7 in FIG. 19 ) using PGS (registered trademark: Pyrolytic Graphite Sheet) as the host layer was confirmed by XRD analysis. XRD analysis of PGS revealed a sharp peak in diffracted X-ray intensity at a diffraction angle 2θ = 26.7° (see FIG. 8 ), and the d value was calculated to be 0.33 nm based on the Bragg diffraction condition. This is due to a periodic structure in which two-dimensional graphene layers are stacked in multiple layers, and indicates that the layer spacing is 0.33 nm. As shown in FIG. 20 , after intercalation, a new peak in diffracted X-ray intensity was observed at a lower diffraction angle. This indicates that ethylenediamine and Ba were introduced between the graphene layers, resulting in the production of Ba-en-GIC. In the example shown in Figure 20, the Ba-en-GIC exhibits the largest peak in the diffracted X-ray intensity due to the stage 4 structure (stage 4 in Figure 19), indicating a high content of stage 4 structure. In other words, in the example shown in Figure 20, Ba-en-GIC exhibits a tendency toward a decrease in the amount of metal complex guest compound incorporated, i.e., a tendency toward a higher stage structure. In a report by Lerner et al. (W. Xu and MM Learner, Chem. Mater. 30 (2018) 6930.), stage 1 GIC was successfully produced using natural graphite powder (SP-1 grade with an average diameter of 100 μm, Union Carbide) as the host layer. However, in this study, the use of PGS with a highly oriented graphene layer prepared by pyrolysis as the host layer likely altered the stage structure of the resulting GIC.

[0116] (Sample Evaluation by XRD After Storage in Air)

[0117] Figure 21A is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Ba-en-GIC stored in air for 3 days, and Figure 21B is a graph showing the relationship between the diffraction angle and the diffracted X-ray intensity when XRD was performed on Ba-en-GIC stored in air for 2 weeks.

[0118] After the above sample evaluation, we performed time-dependent XRD measurements on Ba-en-GIC samples left in the atmosphere after production to verify their stability. After leaving the Ba-en-GIC for three days, the low-angle peaks at 0-20 deg disappeared, and peaks derived from stages 6 to 8 were observed (see Figure 21A). It is believed that exposure to the atmosphere promoted the progression to higher stages and amorphization. Even after three weeks, stages 6 to 8 were maintained, and the GIC structure was maintained without the graphite (Gr) peaks becoming larger (see Figure 21B).

[0119] As can be seen from the above explanation, the final form of the thermoelectric conversion film 30 (Ba-en-GIC) can be not only the final form of Stage 7 in FIG. 19 (after aging in the atmosphere and after desorption), but also any of the initial forms of Stages 1, 2, 3, 4, 5, 6, and 7 (before aging in the atmosphere and before desorption), depending on the type of graphite in the graphite sheet used as the material, the amount of metal and ligand charged, the manufacturing conditions, and the like.

[0120] According to the thermoelectric conversion film 30 described above, it is possible to provide a thermoelectric conversion film that can obtain thermoelectric conversion characteristics equal to or better than those of the thermoelectric conversion film 10 according to the first embodiment.

[0121] <(3.5) Thermoelectric Conversion Film According to Modification of Example 3 of First Embodiment of the Present Technology> Fig. 22 is a cross-sectional view schematically showing a thermoelectric conversion film 35 according to a modification of Example 3 of the first embodiment of the present technology. Fig. 23 is a diagram showing a stage transition process during the manufacture of the thermoelectric conversion film 35 of Fig. 22 .

[0122] 22 and 23 , the thermoelectric conversion film 35 has the same configuration as the thermoelectric conversion film 30 according to Example 3, except that it is Ba-en-GIC at the end of stage 8. That is, in the thermoelectric conversion film 35, for example, eight graphene layers 100 are arranged between two adjacent metal complex groups 200G.

[0123] The thermoelectric conversion film 35 has a highly crystalline structure in which, for example, graphene and metal complex groups are alternately stacked, but by having a structure with a very low amount of metal complexes incorporated and a very low crystallinity, it is possible to obtain significantly high thermoelectric properties. Furthermore, the thermoelectric conversion film 35 has further improved thermoelectric properties due to structural disorder caused by chemical reactions and desorption of the complexes upon exposure to the atmosphere. The thermoelectric conversion film 35 does not require high crystallinity, can be stored and used in the atmosphere, has a versatile manufacturing process, and has a wide range of use cases. The large-diameter metal complexes 200' have a diameter similar to that of the small-diameter metal complexes 200 when the thermoelectric conversion film 35 is produced, but have grown larger over time.

[0124] The final form of the thermoelectric conversion film 35 (Ba-en-GIC) can be not only the final form of Stage 8 in FIG. 23 (after aging in the atmosphere and after desorption), but also any of the initial forms of Stages 1, 2, 3, 4, 5, 6, 7, and 8 (before aging in the atmosphere and before desorption), depending on the type of graphite in the graphite sheet used as the material, the amount of metal and ligand added, the manufacturing conditions, and the like.

[0125] The thermoelectric conversion film 35 can be manufactured by substantially the same manufacturing method as that for the thermoelectric conversion film 10 according to the first embodiment.

[0126] According to the thermoelectric conversion film 35 described above, it is possible to provide a thermoelectric conversion film that can obtain thermoelectric conversion characteristics equal to or better than those of the thermoelectric conversion film 10 according to the first embodiment.

[0127] (Overall Consideration) From the examples and modifications of the first embodiment described above, it was found that the stage-highering and amorphous phases change more rapidly in the order of Ca<Sr<Ba. It is generally believed that alkaline earth metals, which are guest chemical species, have higher chemical reactivity, such as being more likely to form oxides, in the order of Ca<Sr<Ba, and this characteristic is reflected in the first embodiment described above.

[0128] Referring to Figures 2 to 5, each GIC exhibits thermoelectric conversion characteristics of the S<0 type. The Ca and Ba GIC materials show a significant increase in |S| value over time, reaching |S|=48 μV·K after 16 weeks of atmospheric storage. -1In a previous report, GICs in which alkali metals or metal chlorides were introduced between layers using PGS (registered trademark: Pyrolytic Graphite Sheet) as the starting material showed a value of |S| = 17-27 μV・K. -1 The |S| values ​​obtained for Ca-en-GIC and Ba-en-GIC in this study were significantly large, and to the best of the inventors' knowledge, were the highest among n-type GIC thermoelectric materials. On the other hand, the |S| value of Sr-en-GIC showed little change over time, at |S| = 28 μV·K. -1 The power factor (PF) that contributes to the energy efficiency of thermoelectric conversion is σS. 2 The value of Ba-en-GIC stored in air for 16 weeks reached a maximum value of 950 μW m -1 ・K -2 and Ca-en-GIC also increased to 700 μW m after 4 weeks. -1 ・K -2 The PF values ​​were higher than those reported in international academic papers. While the thermoelectric properties of Ca-en-GIC and Ba-en-GIC were similar, the behavior of Sr-en-GIC differed slightly. Reviewing the XRD results, only Sr-en-GIC tended to adopt a low-stage structure after synthesis and was relatively heavy. These results suggest that alkaline-earth metal-centered GICs, such as Ca-en-GIC, Ba-en-GIC, and Sr-en-GIC, which exhibit low crystallinity due to some degree of aging and desorption of guest species, exhibit better thermoelectric conversion properties than samples with a high crystallinity and a high concentration of guest species. These differences in stage structure and doping level likely modulated carrier concentration and mobility, affecting the development of thermoelectric properties.

[0129] <(4) Thermoelectric Conversion Element According to a Second Embodiment of the Present Technology> A thermoelectric conversion element according to a second embodiment can be configured including the thermoelectric conversion film according to the first embodiment (any of thermoelectric conversion films 10, 15, 20, 30, and 35), a first electrode arranged on one side of the thermoelectric conversion film, and a second electrode arranged on the other side of the thermoelectric conversion film. In the thermoelectric conversion element, electric power (electromotive force) corresponding to a temperature difference (temperature gradient) that occurs between one side and the other side when heat is absorbed can be extracted and utilized by the first and second electrodes.

[0130] (Definition of a GIC in which metal complexes are randomly arranged) Figure 27 is a diagram for explaining the definition of a GIC in which metal complexes are randomly arranged. Figure 27 lists peaks from Figures 9, 10, 15, 16, 20, and 21 that have relatively high peak intensities and whose full width at half maximum (FWHM) can be accurately calculated by separating them from other peaks. From these results, GICs (graphite intercalation compounds) that have peaks with a full width at half maximum (FWHM) of 0.26° or more can be defined as "GICs in which metal complexes are randomly arranged."

[0131] FIG. 28 is a diagram for explaining the definition of a thermoelectric conversion film in which metal complexes are randomly arranged. From the results of FIG. 28, for example, Reference ([Ba2(en)2]C 34 ), a layered compound (storage in air for 1 day, 1 week, and 2 days in Figure 28) that contains metal elements at an elemental ratio of 51% or less of the elemental ratio of the metal elements of guest chemical species in a highly crystalline GIC that exhibits multiple XRD peaks derived from the (001), (002), (003), (004), and (005) planes in Stage 1 can be defined as a "thermoelectric conversion film in which metal complexes are randomly arranged."

[0132] (Regarding the Spacing Between Two Adjacent Graphene Layers) FIG. 29 is a diagram illustrating the spacing between two adjacent graphene layers. FIG. 29 shows the spacing (interlayer distance) between two adjacent graphene layers derived from the (001) plane of each stage, based on the XRD results of the as-prepared GICs in FIGS. 9, 15, and 20. According to the XRD results of the examples, the d values ​​of the 001 peaks derived from stages 1 to 8 were 0.6 nm to 3.5 nm. This means that the metal complex groups are periodically stacked, with at least one graphene layer between them, such that the d value of the 001 peak in XRD (X-ray diffraction) is 0.6 nm or more and 3.5 nm or less. Additionally, the d value is the average perpendicular length of the multiple unit structures (one period is from the appearance of one metal complex group to the appearance of the next metal complex group) in each stage structure, in which multiple unit structures are periodically stacked. This is the average distance between two adjacent metal complex groups in each of the multiple unit structures. The thickness of a single graphene layer is 0.33 nm (the thickness of one carbon atom). Taking into account the error, the presence of multiple XRD peaks resulting from heterogeneous stacked structures with interlayer distances differing by 0.3 nm or more (i.e., a spacing difference of 0.3 nm or more) can be defined as "the spacing between two adjacent graphene layers is not constant." It is also possible to use a two-dimensional nanosheet layer other than graphene as the host layer. Since a single host layer always has a thickness of 0.3 nm or more, this definition can also be applied to layered compounds composed of two-dimensional nanosheets other than graphene. Therefore, in cases with multiple stage structures (stages 2 and beyond), a difference in interlayer distance (spacing difference) of 0.3 nm or more is always present. The spacing difference can be defined as the difference between the maximum spacing and the minimum spacing between two adjacent graphene layers.

[0133] (5) Other Modifications of the Present Technology The thermoelectric conversion film according to the first embodiment and the thermoelectric conversion element according to the second embodiment can be modified as appropriate.

[0134] As the host layer of the thermoelectric conversion film, a two-dimensional nanosheet layer of, for example, a metal oxide, a double hydroxide, a chalcogenide compound, or the like may be used instead of the graphene layer.

[0135] The central metal of the metal complex in the thermoelectric conversion film may be, for example, Li, Na, Mg, or the like.

[0136] The ligand of the metal complex in the thermoelectric conversion film may be a chain ligand other than ethylenediamine (for example, bipyridine, ethylenediaminetetraacetic acid, phenanthroline), or a cyclic ligand such as porphyrin or crown ether.

[0137] Parts of the configurations of the examples and modifications of the first embodiment may be combined to the extent that they are not contradictory to one another.

[0138] (Examples of applications of thermoelectric conversion film and thermoelectric conversion element) The thermoelectric conversion film according to the first embodiment, the thermoelectric conversion element according to the second embodiment, and the thermoelectric conversion films according to other modified examples described above are suitable for use in wearable devices such as smart watches, and waste heat power generation / thermal sensing in IoT devices.

[0139] The present technology can have the following configurations. (1) A thermoelectric conversion film comprising: a plurality of two-dimensional nanosheet layers stacked on top of each other; and a metal complex group containing a plurality of metal complexes, wherein the metal complex group is provided between at least one pair of adjacent two of the two-dimensional nanosheet layers, and the plurality of metal complexes are irregularly arranged. (2) The thermoelectric conversion film according to (1), wherein the two-dimensional nanosheet layer is a graphene layer. (3) The thermoelectric conversion film according to (1) or (2), wherein the plurality of metal complexes are arranged along an in-plane direction. (4) The thermoelectric conversion film according to any one of (1) to (3), wherein the arrangement pitch of the plurality of metal complexes is not constant. (5) The thermoelectric conversion film according to any one of (1) to (4), wherein the spacing between the two-dimensional nanosheet layers is not constant. (6) The thermoelectric conversion film according to any one of (1) to (5), wherein the spacing difference between the two-dimensional nanosheet layers is 0.3 nm or more. (7) The thermoelectric conversion film according to any one of (1) to (6), wherein the metal complex groups are periodically laminated via at least one of the two-dimensional nanosheet layers so that the d value of the 001 peak in XRD (X-ray diffraction) is 0.6 nm or more and 3.5 nm or less. (8) The thermoelectric conversion film according to any one of (1) to (7), wherein the plurality of metal complexes include at least two metal complexes having different sizes. (9) The thermoelectric conversion film according to any one of (1) to (8), wherein the plurality of two-dimensional nanosheet layers are at least three two-dimensional nanosheet layers, and the metal complex groups are disposed between at least two pairs of adjacent two two-dimensional nanosheet layers. (10) The thermoelectric conversion film according to any one of (1) to (9), wherein at least two two-dimensional nanosheet layers are disposed between two adjacent two metal complex groups. (11) The thermoelectric conversion film according to any one of (1) to (10), wherein the ligand of the metal complex is a chelate complex. (12) The thermoelectric conversion film according to (11), wherein the chelate complex is ethylenediamine. (13) The thermoelectric conversion film according to any one of (1) to (12), wherein the central metal of the metal complex is an alkaline earth metal. (14) The thermoelectric conversion film according to (13), wherein the central metal is Ca or Ba. (15) The thermoelectric conversion film according to (13), wherein the central metal is Sr.(16) The thermoelectric conversion film according to any one of (1) to (15), which has an n-type conductivity. (17) The thermoelectric conversion film has an electrical conductivity σ of σ≧2550 S·cm. －１ (18) The thermoelectric conversion film according to any one of (1) to (16), wherein the Seebeck coefficient S is |S|≧24 μV·K. －１ (19) The thermoelectric conversion film according to any one of (1) to (17), wherein the power factor PF is PF≧190 μW m ー１ ・K －２ (20) The thermoelectric conversion film according to any one of (1) to (19), wherein the total amount of the metals is less than 2.9% by mole fraction. (21) The thermoelectric conversion film according to any one of (1) to (20), wherein the two-dimensional nanosheet layer is any one of a metal oxide, a double hydroxide, and a chalcogenide-based compound. (22) A thermoelectric conversion element comprising: a thermoelectric conversion film; a first electrode arranged on one side of the thermoelectric conversion film; and a second electrode arranged on the other side of the thermoelectric conversion film, wherein the thermoelectric conversion film comprises: a plurality of two-dimensional nanosheet layers stacked on top of each other; and at least one metal complex group containing a plurality of metal complexes, wherein the metal complex group is provided between at least one pair of adjacent two of the two-dimensional nanosheet layers, and the plurality of metal complexes are irregularly arranged. (23) A method for producing a thermoelectric conversion film, comprising: a step of generating a metal complex solution using a metal and a ligand; and a step of immersing a graphite sheet in the metal complex solution. (24) The method for producing a thermoelectric conversion film according to (23), wherein in the generating step, the concentrations of the metal and / or the ligand in the metal complex solution are adjusted depending on the type of graphite in the graphite sheet and / or the purity of carbon contained in the graphite.

[0140] 10, 15, 20, 30, 35: Thermoelectric conversion film 100: Graphene layer (two-dimensional nanosheet layer) 200: Metal complex 200': Metal complex 200G: Metal complex group

Claims

1. A thermoelectric conversion film comprising: a plurality of two-dimensional nanosheet layers stacked on top of each other; and a metal complex group containing a plurality of metal complexes, wherein the metal complex group is provided between at least one pair of adjacent two of the two-dimensional nanosheet layers, and the plurality of metal complexes are irregularly arranged.

2. The thermoelectric conversion film according to claim 1, wherein the two-dimensional nanosheet layer is a graphene layer.

3. The thermoelectric conversion film according to claim 1, wherein the plurality of metal complexes are arranged along an in-plane direction.

4. The thermoelectric conversion film according to claim 3, wherein the arrangement pitch of the plurality of metal complexes is not constant.

5. The thermoelectric conversion film described in claim 1, wherein the spacing between the two-dimensional nanosheet layers is not constant.

6. The thermoelectric conversion film according to claim 5, wherein the spacing between the two-dimensional nanosheet layers has a spacing difference of 0.3 nm or more.

7. The thermoelectric conversion film according to claim 6, wherein the metal complex group is periodically laminated in a plurality of layers via at least one of the two-dimensional nanosheet layers so that the d value of the 001 peak of XRD (X-ray diffraction) is 0.6 nm or more and 3.5 nm or less.

8. The thermoelectric conversion film according to claim 1, wherein the plurality of metal complexes include at least two of the metal complexes having different sizes.

9. The thermoelectric conversion film described in claim 1, wherein the multiple two-dimensional nanosheet layers are at least three two-dimensional nanosheet layers, and the metal complex group is arranged between at least two pairs of adjacent two of the two-dimensional nanosheet layers.

10. The thermoelectric conversion film according to claim 9, wherein at least two of the two-dimensional nanosheet layers are arranged between two adjacent metal complex groups.

11. The thermoelectric conversion film according to claim 1, wherein the ligand of the metal complex is a chelate complex.

12. The thermoelectric conversion film according to claim 11, wherein the chelate complex is ethylenediamine.

13. The thermoelectric conversion film according to claim 1, wherein the central metal of the metal complex is an alkaline earth metal.

14. The thermoelectric conversion film according to claim 13, wherein the central metal is Ca or Ba.

15. The thermoelectric conversion film according to claim 13, wherein the central metal is Sr.

16. The thermoelectric conversion film according to claim 1, which has an n-type conductivity.

17. Electrical conductivity σ is σ≧2550 S cm －１ The thermoelectric conversion film according to claim 1 .

18. The Seebeck coefficient S is |S| ≧ 24 μV・K －１ The thermoelectric conversion film according to claim 1 .

19. Power factor PF is PF≧190μW・m ー１ K －２ The thermoelectric conversion film according to claim 1 .

20. The thermoelectric conversion film according to claim 1, wherein the total amount of the metals is less than 2.9% by mole fraction.

21. The thermoelectric conversion film according to claim 1, wherein the two-dimensional nanosheet layer is any one of a metal oxide, a double hydroxide, and a chalcogenide compound.

22. A thermoelectric conversion element comprising: a thermoelectric conversion film; a first electrode arranged on one side of the thermoelectric conversion film; and a second electrode arranged on the other side of the thermoelectric conversion film, wherein the thermoelectric conversion film comprises: a plurality of two-dimensional nanosheet layers stacked on each other; and at least one metal complex group containing a plurality of metal complexes, wherein the metal complex group is provided between at least one pair of adjacent two of the two-dimensional nanosheet layers, and the plurality of metal complexes are irregularly arranged.

23. A method for producing a thermoelectric conversion film, comprising: generating a metal complex solution using a metal and a ligand; and immersing a graphite sheet in the metal complex solution.

24. A method for producing a thermoelectric conversion film as described in claim 23, wherein in the generating step, the concentration of the metal and / or the ligand in the metal complex solution is adjusted depending on the type of graphite in the graphite sheet and / or the purity of carbon contained in the graphite.

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