Electrode for liquid thermoelectric conversion element, liquid thermoelectric conversion element, method for manufacturing electrode for liquid thermoelectric conversion element

Abstract

To provide an electrode for a liquid thermoelectric conversion element consisting of a coating film with excellent flexibility, a liquid thermoelectric conversion element having the electrode for liquid thermoelectric conversion element, and a method for manufacturing the electrode for liquid thermoelectric conversion element.SOLUTION: An electrode 1 for a liquid thermoelectric conversion element consists of a coating film 3 containing carbon powder and a high molecule binder. The coating film 3 may be formed on one side 2a of an electrode holder 2. The liquid thermoelectric conversion element comprises a first electrode, a second electrode and an electrolyte interposed between the first and second electrodes. The electrolyte contains organic solvents and oxidized and reduced ions. The first and second electrodes consist of the electrodes for the liquid thermoelectric conversion element.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrode for a liquid thermoelectric conversion element, a liquid thermoelectric conversion element, and a method for manufacturing an electrode for a liquid thermoelectric conversion element. [Background technology]

[0002] A liquid thermoelectric conversion element is one of the energy harvesting technologies that converts temperature differences in the environment into electrical energy. A liquid thermoelectric conversion element includes a first electrode, a second electrode, and an electrolyte interposed between the first electrode and the second electrode. The first electrode and the second electrode are made of the same material and have the same structure.

[0003] The performance of a liquid thermoelectric conversion element is governed by the electrochemical Seebeck coefficient (S), the electrical conductivity (σ) of the electrolyte, and the thermal conductivity (k) of the electrolyte. The resistance of the electrolyte can be expressed as the sum of the solution resistance Rs due to the movement of ions driven by the potential gradient, the charge transfer resistance Rct due to the electron movement on the electrode surface, and the diffusion resistance Rdif associated with the ion movement near the electrode driven by the concentration gradient. The solution resistance Rs is determined by the composition of the electrolyte, the distance between the electrodes, and the electrode area. On the other hand, the charge transfer resistance Rct and the diffusion resistance Rdif depend on the electrode material and the electrode structure. Conventionally, platinum (see, for example, Non-Patent Document 1) and graphite sheets (see, for example, Non-Patent Document 2) have been used as electrodes for liquid thermoelectric conversion elements. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] A.Waki,et al,Jpn.J.Appl.Phys.62,014002(2023). [Non-Patent Document 2] W.Li,et al.Materials Today Energy,30,101147(2022). Summary of the Invention [Problem to be solved by the invention]

[0005] The greatest feature of liquid thermoelectric conversion elements is their simple structure. By utilizing this simple structure, it is possible to realize large or flexible liquid thermoelectric conversion elements. In order to enlarge the liquid thermoelectric conversion element, it is necessary to attach large electrodes to the inner surface of the container that contains the electrolyte. In order to make the liquid thermoelectric conversion element flexible, it is necessary for the electrodes to be attached to the inner surface of the container with sufficient strength. Furthermore, in order to reduce the manufacturing cost of liquid thermoelectric conversion elements, it is necessary to be able to easily manufacture the electrodes at low cost.

[0006] The electrodes of liquid thermoelectric conversion elements are made of platinum or carbon electrodes such as commercially available graphite sheets. Platinum is not flexible, while carbon electrodes such as graphite sheets are flexible.

[0007] However, a complex element structure is required to attach the graphite sheet to the inside surface of the container that contains the electrolyte and to seal the container that contains the electrolyte. In addition, although the graphite sheet is flexible, there is an issue that it is difficult to bend it to a large degree (large curvature).

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide an electrode for a liquid thermoelectric conversion element made of a coating film having excellent flexibility, a liquid thermoelectric conversion element equipped with an electrode for a liquid thermoelectric conversion element, and a method for manufacturing an electrode for a liquid thermoelectric conversion element. [Means for solving the problem]

[0009] The present invention has the following aspects. [1] An electrode for a liquid thermoelectric conversion element, comprising a coating film containing carbon powder and a polymer binder. [2] The electrode for a liquid thermoelectric conversion element according to [1], wherein the coating film is formed on one surface of an electrode holder. [3] A battery comprising a first electrode, a second electrode, and an electrolyte interposed between the first electrode and the second electrode; The electrolyte solution includes an organic solvent, an oxidizing ion, and a reducing ion; A liquid thermoelectric conversion element, wherein the first electrode and the second electrode are the electrodes for a liquid thermoelectric conversion element according to [1] or [2]. [4] preparing an electrode-forming composition containing carbon powder, a polymer binder, and an organic solvent; applying the electrode-forming composition to one surface of an electrode holder; and drying the electrode-forming composition to form a coating film on one surface of the electrode holder. Effect of the Invention

[0010] According to the present invention, it is possible to provide an electrode for a liquid thermoelectric conversion element made of a coating film having excellent flexibility, a liquid thermoelectric conversion element including an electrode for a liquid thermoelectric conversion element, and a method for manufacturing an electrode for a liquid thermoelectric conversion element. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view that illustrates a schematic diagram of an electrode for a liquid thermoelectric conversion element according to one embodiment of the present invention. [Diagram 2] 1 is a schematic diagram showing a liquid thermoelectric conversion element according to an embodiment of the present invention. [Diagram 3] FIG. 1 is a diagram showing the relationship between charge transfer resistance (Rct) and coating thickness in Experimental Examples 7 to 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an electrode for a liquid thermoelectric conversion element, ... and a method for manufacturing an electrode for a liquid thermoelectric conversion element according to the present invention will be described. It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0013] [Electrodes for liquid thermoelectric conversion elements] Hereinafter, an electrode for a liquid thermoelectric conversion element according to one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view that illustrates a schematic diagram of an electrode for a liquid thermoelectric conversion element according to the present embodiment. 1, the electrode 1 for a liquid thermoelectric conversion element of this embodiment includes an electrode holder 2 and a coating film 3. The coating film 3 is formed on one surface 2a of the electrode holder 2. The electrode 1 for a liquid thermoelectric conversion element of this embodiment may be composed of only the coating film 3, or may be composed of the electrode holder 2 and the coating film 3.

[0014] "Electrode holder" Examples of the electrode holder 2 include a resin substrate, a flexible plastic sheet, a stainless steel foil, a glass substrate, etc. Here, the electrode holder may be a substrate on which a coating film is provided, or an insulating structure (for example, a container (housing) that contains electrodes and an electrolyte in a liquid thermoelectric conversion element described later).

[0015] The thickness of the electrode holder 2 is not particularly limited, but is preferably 1 μm or more and 100 μm or less, and more preferably 1 μm or more and 10 μm or less. If the thickness of the electrode holder 2 exceeds the upper limit, the flexibility of the electrode is impaired. If the thickness of the electrode holder 2 is equal to or less than the upper limit, the liquid thermoelectric conversion element electrode 1 has flexibility. In order to further increase the flexibility of the liquid thermoelectric conversion element electrode 1, it is preferable not to use the electrode holder 2.

[0016] "Paint film" The coating 3 contains carbon powder and a polymer binder.

[0017] Examples of carbon powder include graphite powder, acetylene black (AB) powder, and carbon nanotubes (CNT).

[0018] An example of the polymer binder is polyvinylidene fluoride (PVDF).

[0019] In the coating film 3, the ratio of the carbon powder content to the polymer binder content (carbon powder content / polymer binder content) is preferably 4 to 49, more preferably 9 to 19. If the ratio is below the lower limit, the polymer binder content is high, resulting in high resistance of the electrode. If the ratio exceeds the upper limit, the carbon powder content is high, resulting in loss of mechanical strength of the electrode.

[0020] It is preferable that the coating film 3 does not contain any components other than the carbon powder and the polymer binder.

[0021] The thickness of the coating film 3 is not particularly limited, but is preferably 0.03 mm to 1 mm, and more preferably 0.1 mm to 0.3 mm. If the thickness of the coating film 3 is less than the lower limit, the resistance of the electrode increases. If the thickness of the coating film 3 exceeds the upper limit, the flexibility of the electrode is impaired.

[0022] The electrode 1 for liquid thermoelectric conversion elements of this embodiment has a coating film 3 containing carbon powder and a polymer binder, and therefore has superior flexibility to conventional carbon electrodes such as graphite sheets. In addition, when the coating film 3 is formed on one surface 2a of the electrode holder 2, the coating film 3 has high adhesion to the electrode holder 2, so that the coating film 3 is unlikely to peel off from the electrode holder 2 even when the electrode 1 for liquid thermoelectric conversion elements is curved.

[0023] [Method of manufacturing electrodes for liquid thermoelectric conversion elements] A method for manufacturing an electrode for a liquid thermoelectric conversion element according to one embodiment of the present invention includes the steps of preparing an electrode-forming composition containing carbon powder, a polymer binder, and an organic solvent (hereinafter referred to as the "first step"), applying the electrode-forming composition to one side of an electrode holder (hereinafter referred to as the "second step"), and drying the electrode-forming composition to form a coating film on one side of the electrode holder (hereinafter referred to as the "third step").

[0024] "First step" In the first step, an electrode-forming composition containing carbon powder, a polymer binder, and an organic solvent is prepared.

[0025] Examples of carbon powder include graphite powder, acetylene black (AB) powder, and carbon nanotubes (CNT).

[0026] An example of the polymer binder is polyvinylidene fluoride (PVDF).

[0027] An example of the organic solvent is N-methyl-2-pyrrolidone (NMP).

[0028] The content of carbon powder relative to the total mass (100 mass%) of the electrode-forming composition is preferably 80 mass% or more and 98 mass% or less, and more preferably 90 mass% or more and 95 mass% or less. If the content of carbon powder is less than the lower limit, the resistance of the electrode increases due to the reduced carbon powder content. If the content of carbon powder is more than the upper limit, the mechanical strength of the electrode is lost due to the increased carbon powder content.

[0029] The content of the polymer binder relative to the total mass (100 mass%) of the electrode-forming composition is preferably 2 mass% to 20 mass%, more preferably 5 mass% to 10 mass%. If the content of the polymer binder is less than the lower limit, the mechanical strength of the electrode is lost due to the reduced content of the polymer binder. If the content of the polymer binder exceeds the upper limit, the resistance of the electrode is increased due to the increased content of the polymer binder.

[0030] In the electrode-forming composition, the ratio of the carbon powder content to the polymer binder content (carbon powder content / polymer binder content) is preferably 4 to 49, more preferably 9 to 19. If the ratio is below the lower limit, the polymer binder content is high, resulting in high electrode resistance. If the ratio is above the upper limit, the carbon powder content is high, resulting in a loss of mechanical strength of the electrode.

[0031] "Second step" In the second step, the electrode-forming composition prepared in the first step is applied to one surface of the electrode holder. Examples of the electrode holder include a resin substrate, a flexible plastic sheet, a stainless steel foil, a glass substrate, etc. Here, the electrode holder may be a substrate on which a coating film is provided, or an insulating structure (for example, a container (housing) that contains electrodes and an electrolyte in a liquid thermoelectric conversion element described later). Examples of the method for applying the electrode-forming composition include roll coating, spray coating, spin coating, dropping, inkjet coating, and screen printing.

[0032] The amount of the electrode-forming composition applied to one surface of the electrode holder is appropriately adjusted depending on the desired thickness of the coating film. For example, 2 More than 30g / m 2 Less than 1 g / m is preferable. 2 More than 10g / m 2 The following is more preferable: if the coating amount is less than the lower limit, the resistance of the electrode increases, and if the coating amount is more than the upper limit, the mechanical strength of the electrode is lost.

[0033] "The third step" In the third step, the electrode-forming composition applied to one surface of the electrode holder in the second step is dried to form a coating film on one surface of the electrode holder.

[0034] The temperature for drying the electrode-forming composition is preferably 40° C. to 100° C., more preferably 60° C. to 80° C. If the temperature is below the lower limit, drying takes too long, and if the temperature is above the upper limit, mechanical strength may be impaired.

[0035] The time for drying the electrode-forming composition is preferably 1 hour or more and 20 hours or less, more preferably 2 hours or more and 10 hours or less. If the time is less than the lower limit, the mechanical strength may be impaired. If the time is less than the upper limit, the electrode may deteriorate.

[0036] The atmosphere in which the electrode-forming composition is dried is not particularly limited, and may be an air atmosphere or an inert gas atmosphere.

[0037] According to the manufacturing method of the electrode for liquid thermoelectric conversion element of this embodiment, a coating film is formed using an electrode forming composition containing carbon powder, a polymer binder, and an organic solvent, so that the electrode for liquid thermoelectric conversion element made of the obtained coating film has better flexibility than conventional carbon electrodes such as graphite sheets. Furthermore, when the coating film is formed on one side of the electrode holder, the adhesion of the coating film to the electrode holder is high. Therefore, the coating film of the obtained electrode for liquid thermoelectric conversion element is less likely to peel off from the electrode holder even when it is curved.

[0038] [Liquid thermoelectric conversion element] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid thermoelectric conversion element according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic diagram showing the liquid thermoelectric conversion element of this embodiment. As shown in FIG. 2, the liquid thermoelectric conversion element 10 of this embodiment includes a first electrode 21, a second electrode 22, and an electrolyte 30. In the liquid thermoelectric conversion element 10 of this embodiment, the electrolyte 30 is sandwiched between the first electrode 21 and the second electrode 22. In other words, the first electrode 21 and the second electrode 22 face each other with the electrolyte 30 interposed therebetween. The liquid thermoelectric conversion element 10 may also have a container (housing) 40 that contains the first electrode 21, the second electrode 22, and the electrolyte 30. By providing the container 40, the entire liquid thermoelectric conversion element 10 can be sealed to prevent the electrolyte 30 from leaking.

[0039] "First electrode, second electrode" The first electrode 21 and the second electrode 22 are made of the liquid thermoelectric conversion element electrodes of the above-mentioned embodiment.

[0040] The distance (spacing) between the first electrode 21 and the second electrode 22 is preferably 1 mm or more and 20 mm or less, more preferably 2 mm or more and 10 mm or less, and even more preferably 3 mm or more and 5 mm or less. If the distance between the first electrode 21 and the second electrode 22 is equal to or more than the lower limit, a temperature difference is likely to occur between the electrodes, and the liquid thermoelectric conversion element 10 is likely to generate an electromotive force. If the distance between the first electrode 21 and the second electrode 22 is equal to or less than the upper limit, a temperature difference is unlikely to occur between the electrodes. However, a current easily flows between the first electrode 21 and the second electrode 22, and a large output can be obtained.

[0041] "Electrolyte" An electrolyte solution containing an organic solvent, and oxide ions and reduced ions is used as the electrolyte solution 30. That is, the electrolyte solution 30 is obtained by dissolving oxide ions and reduced ions in an organic solvent. The electrolyte solution 30 may also contain a mixed solvent, oxide ions and reduced ions, and the mixed solvent may contain water and at least one organic solvent, or at least two different organic solvents.

[0042] The thermal conductivity of the electrolyte 30 is preferably less than that of water. The organic solvent is not particularly limited as long as its thermal conductivity is less than that of water (0.602 W / mK (20°C)), but examples thereof include methanol (0.212 W / mK), ethanol (0.183 W / mK), 1-propanol (0.161 W / mK), 2-propanol, 1-butene (0.167 W / mK), 2-butene, isobutene (0.134 W / mK), ethylene glycol (0.243 W / mK), glycerin (0.143 W / mK), acetone (0.18 W / mK), N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, propylene carbonate, tetrahydrofuran, acetonitrile, and ethyl acetate (0.137 W / mK). These organic solvents may be used alone or in combination of two or more.

[0043] The electrochemical Seebeck coefficient of the electrolyte 30 is preferably 1.23 mV / K or more and 3.60 mV / K or less. The organic solvent preferably has an electrochemical Seebeck coefficient of 1.23 mV / K or more and 3.60 mV / K or less. Examples of organic solvents having an electrochemical Seebeck coefficient of 1.23 mV / K or more and 3.60 mV / K or less include 1-propanol (1.24 mV / K), 1-butene (1.34 mV / K), acetone (3.60 mV / K), N,N-dimethylformamide (1.35 mV / K), N-methyl-2-pyrrolidone (1.39 mV / K), dimethyl sulfoxide (1.23 mV / K), propylene carbonate (1.78 mV / K), tetrahydrofuran (2.70 mV / K), acetonitrile (2.16 mV / K), and ethyl acetate (2.57 mV / K). These organic solvents may be used alone or in combination of two or more.

[0044] The electrolyte 30 may contain an additive such as sodium chloride (NaCl).

[0045] "Oxidized ions, reduced ions" The oxide ion is not particularly limited as long as it is soluble in the organic solvent. For example, iron (III) ion (Fe 3+ ), iron cyanide(III) ion ([Fe(CN)6] 3- Specifically, salts containing oxide ions are used, such as iron(III) perchlorate (Fe(ClO4)3) and sodium cyanide(III) (Na3[Fe(CN)6]). The reducing ion is not particularly limited as long as it is soluble in the organic solvent. For example, iron (II) ion (Fe 2+ ), iron cyanide (II) ion ([Fe(CN)6] 4- Specifically, salts containing reducing ions are used, such as iron(II) perchlorate (Fe(ClO4)2) and sodium cyanide(II) (Na4[Fe(CN)6]).

[0046] The concentration of the oxidizing ions or reducing ions in the electrolytic solution 30 is not particularly limited, but the solubility of each ion in an organic solvent is the upper limit of the concentration. Furthermore, the concentration of oxidizing ions in the electrolytic solution 30 and the concentration of reducing ions in the electrolytic solution 30 may be equal to or different from each other.

[0047] 2 illustrates an example in which the liquid thermoelectric conversion element 10 is composed of one unit having the first electrode 21, the second electrode 22, and the electrolyte 30, but this embodiment is not limited to this. The liquid thermoelectric conversion element of the present invention may have a plurality of units, each of which may be connected in series. "Series" refers to connecting the negative electrode of a unit to the positive electrode of an adjacent unit.

[0048] According to the liquid thermoelectric conversion element 10 of this embodiment, the first electrode 21 and the second electrode 22 are made of the electrodes for the liquid thermoelectric conversion element of the above-mentioned embodiment, and since the coating film on the first electrode 21 and the second electrode 22 has excellent adhesion to the electrode holder, the coating film is unlikely to peel off from the electrode holder even when the element is curved, and a liquid thermoelectric conversion element with excellent flexibility is obtained.

[0049] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. EXAMPLES

[0050] The present invention will be described in more detail below with reference to experimental examples, but the present invention is not limited to the following experimental examples.

[0051] [Experimental Example 1] Acetylene black (AB) powder and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 4:1, and the mixture was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an electrode-forming composition. The obtained electrode-forming composition was applied onto a stainless steel foil having a thickness of 0.01 mm using a coater (model name (product name): small sheet coater, manufactured by Hosen Co., Ltd.). The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 10 mil on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by electrochemical impedance spectroscopy. The electrode distance was 10 mm, and the electrode area was 42 mm 2 It was. The electrolyte used was an aqueous solution containing 1.0 mol / L Fe(ClO4)2 and 1.0 mol / L Fe(ClO4)3. The results are shown in Table 1.

[0052] [Experimental Example 2] Graphite powder and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 4:1, and the mixture was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an electrode-forming composition. The obtained electrode-forming composition was applied onto a stainless steel foil having a thickness of 0.01 mm in the same manner as in Experimental Example 1. The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 10 mil on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by an electrochemical impedance method in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0053] [Experimental Example 3] Carbon nanotubes (CNT) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 1:2, and the mixture was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an electrode-forming composition. The obtained electrode-forming composition was applied onto a stainless steel foil having a thickness of 0.01 mm in the same manner as in Experimental Example 1. The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 10 mil on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by an electrochemical impedance method in the same manner as in Experimental Example 1. The results are shown in Table 1.

[0054] [Experimental Example 4] In the same manner as in Experimental Example 1, two platinum (Pt) electrodes with a thickness of 0.01 mm were immersed in the electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by the electrochemical impedance method. The results are shown in Table 1.

[0055] [Experimental Example 5] In the same manner as in Experimental Example 1, two graphite sheets (trade name: PREMA-FOIL (registered trademark), manufactured by Toyo Tanso Co., Ltd.) with a thickness of 0.22 mm were immersed in the electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by the electrochemical impedance method. The results are shown in Table 1.

[0056] [Experimental Example 6] In the same manner as in Experimental Example 1, two graphite sheets (trade name: Graphite TIM, manufactured by Panasonic) with a thickness of 0.22 mm were immersed in the electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by the electrochemical impedance method. The results are shown in Table 1.

[0057] [Table 1]

[0058] From the results shown in Table 1, it was found that the charge transfer resistance (Rct) of Experimental Example 2 using graphite powder was the second lowest after the charge transfer resistance (Rct) of the graphite sheet.

[0059] [Experimental Example 7] Graphite powder and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 9:1, and the mixture was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an electrode-forming composition. The obtained electrode-forming composition was applied onto a stainless steel foil having a thickness of 0.01 mm using a coater (model name (product name): small sheet coater, manufactured by Hosen Co., Ltd.). The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 10 mil on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by electrochemical impedance spectroscopy. The electrode distance was 10 mm, and the electrode area was 42 mm 2 It was. The electrolyte used was an aqueous solution containing 1.0 mol / L Fe(ClO4)2 and 1.0 mol / L Fe(ClO4)3. The results are shown in Table 2 and Figure 3. Table 2 shows the actual measured values ​​of the coating thickness. These values ​​were measured using a micrometer.

[0060] [Experimental Example 8] An electrode-forming composition having the same composition as in Experimental Example 7 was used and applied to a stainless steel foil having a thickness of 0.01 mm in the same manner as in Experimental Example 7. The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 5 mil on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte solution and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by the electrochemical impedance method in the same manner as in Experimental Example 7. The results are shown in Table 2 and Figure 3. Table 2 shows the actual measured values ​​of the thickness of the coating film.

[0061] [Experimental Example 9] An electrode-forming composition having the same composition as in Experimental Example 7 was used and applied to a stainless steel foil having a thickness of 0.01 mm in the same manner as in Experimental Example 7. The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 3 mil on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte solution and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by the electrochemical impedance method in the same manner as in Experimental Example 7. The results are shown in Table 2 and Figure 3. Table 2 shows the actual measured values ​​of the thickness of the coating film.

[0062] [Experimental Example 10] In the same manner as in Experimental Example 7, two graphite sheets (trade name: PREMA-FOIL (registered trademark), manufactured by Toyo Tanso Co., Ltd.) having a thickness of 0.216 mm were immersed in the electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by the electrochemical impedance method. The results are shown in Table 2.

[0063] [Table 2]

[0064] From the results shown in Table 2, it was found that the charge transfer resistance (Rct) of the 36 μm thick coating film (Experimental Example 7) was comparable to that of the graphite sheet by making the thickness about 20 μm. Also, from the results shown in Figure 3, it was found that the charge transfer resistance (Rct) decreased as the coating film thickness increased.

[0065] [Experimental Example 11] Graphite powder and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:5, and the mixture was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an electrode-forming composition. The obtained electrode-forming composition was applied onto a stainless steel foil having a thickness of 0.01 mm using a coater (model name (product name): small sheet coater, manufactured by Hosen Co., Ltd.). The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 10 mil on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by electrochemical impedance spectroscopy. The electrode distance was 10 mm, and the electrode area was 42 mm 2 It was. The electrolyte used was an aqueous solution containing 1.0 mol / L Fe(ClO4)2 and 1.0 mol / L Fe(ClO4)3. The results are shown in Table 3.

[0066] [Experimental Example 12] Graphite powder and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 90:10, and the mixture was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an electrode-forming composition. The obtained electrode-forming composition was applied onto a stainless steel foil having a thickness of 0.01 mm in the same manner as in Experimental Example 11. The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 10 mil on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by an electrochemical impedance method in the same manner as in Experimental Example 11. The results are shown in Table 3.

[0067] [Experimental Example 13] Graphite powder and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 80:20, and the mixture was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an electrode-forming composition. The obtained electrode-forming composition was applied onto a stainless steel foil having a thickness of 0.01 mm in the same manner as in Experimental Example 11. The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 10 mil on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by an electrochemical impedance method in the same manner as in Experimental Example 11. The results are shown in Table 3.

[0068] [Table 3]

[0069] The results shown in Table 3 show that the charge transfer resistance (Rct) decreases with increasing graphite powder content.

[0070] [Experimental Example 14] Graphite powder and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 4:1, and the mixture was dissolved in N-methyl-2-pyrrolidone (NMP) to prepare an electrode-forming composition. The obtained electrode-forming composition was applied onto a stainless steel foil having a thickness of 0.01 mm using a coater (model name (product name): small sheet coater, manufactured by Hosen Co., Ltd.). The electrode-forming composition applied onto the stainless steel foil was dried at 60° C. for 10 hours to form a coating film having a thickness of 40 μm on the stainless steel foil, thereby obtaining an electrode. The two electrodes were immersed in an electrolyte, and the solution resistance (Rs) and charge transfer resistance (Rct) were evaluated by electrochemical impedance spectroscopy. The electrode distance was 10 mm, and the electrode area was 42 mm 2 It was. The two electrodes were immersed in an electrolyte to evaluate the DC resistance (R). The diffusion resistance (Rdif) was evaluated from the DC resistance (R) - solution resistance (Rs) - charge transfer resistance (Rct). The electrode distance was 10 mm, and the electrode area was 42 mm 2 It was. The electrolyte used was an aqueous solution containing 1.0 mol / L Fe(ClO4)2 and 1.0 mol / L Fe(ClO4)3. The results are shown in Table 4.

[0071] [Experimental Example 15] Except for changing the thickness of the coating film to 36 μm, the solution resistance (Rs), charge transfer resistance (Rct), DC resistance (R), and diffusion resistance (Rdif) were evaluated in the same manner as in Experimental Example 14. The results are shown in Table 4.

[0072] [Experimental Example 16] Except for changing the thickness of the coating film to 25 μm, the solution resistance (Rs), charge transfer resistance (Rct), DC resistance (R), and diffusion resistance (Rdif) were evaluated in the same manner as in Experimental Example 14. The results are shown in Table 4.

[0073] [Experimental Example 17] Except for changing the thickness of the coating film to 23 μm, the solution resistance (Rs), charge transfer resistance (Rct), DC resistance (R), and diffusion resistance (Rdif) were evaluated in the same manner as in Experimental Example 14. The results are shown in Table 4.

[0074] [Experimental Example 18] Except for changing the thickness of the coating film to 17 μm, the solution resistance (Rs), charge transfer resistance (Rct), DC resistance (R), and diffusion resistance (Rdif) were evaluated in the same manner as in Experimental Example 14. The results are shown in Table 4.

[0075] [Experimental Example 19] Except for changing the thickness of the coating film to 13 μm, the solution resistance (Rs), charge transfer resistance (Rct), DC resistance (R), and diffusion resistance (Rdif) were evaluated in the same manner as in Experimental Example 14. The results are shown in Table 4.

[0076] [Experimental Example 20] Two graphite sheets (trade name: PREMA-FOIL (registered trademark), manufactured by Toyo Tanso Co., Ltd.) with a thickness of 220 μm were immersed in the electrolyte, and the solution resistance (Rs), charge transfer resistance (Rct), DC resistance (R), and diffusion resistance (Rdif) were evaluated in the same manner as in Experimental Example 14. The results are shown in Table 4.

[0077] [Table 4]

[0078] From the results shown in Table 4, the thickest electrode (40 μm) of Experimental Example 14 had a DC resistance R (=35.8 Ω) lower than the value of the graphite sheet of Experimental Example 20. It was also found that the diffusion resistance (Rdif) increased as the thickness of the electrode increased. [Industrial Applicability]

[0079] The liquid thermoelectric conversion element of the present invention can be used in wearable IoT devices and the like that can permanently transmit, receive, and relay information without using a power supply or primary batteries. [Explanation of symbols]

[0080] 1. Electrodes for liquid thermoelectric conversion elements 2 Electrode holder 3. Coating 10 Liquid thermoelectric conversion element 21 First electrode 22 Second electrode 30 Electrolyte 40 containers

Claims

1. An electrode for a liquid thermoelectric conversion element, comprising a coating film containing carbon powder and a polymer binder.

2. 2. The electrode for a liquid thermoelectric conversion element according to claim 1, wherein the coating film is formed on one surface of an electrode holder.

3. A first electrode, a second electrode, and an electrolyte solution interposed between the first electrode and the second electrode, The electrolyte solution includes an organic solvent, an oxidizing ion, and a reducing ion; A liquid thermoelectric conversion element, wherein the first electrode and the second electrode are the electrodes for a liquid thermoelectric conversion element according to claim 1 .

4. preparing an electrode-forming composition including carbon powder, a polymer binder, and an organic solvent; applying the electrode-forming composition to one surface of an electrode holder; and drying the electrode-forming composition to form a coating film on one surface of the electrode holder.

Images