Thermoelectric capacitors and methods of using thermoelectric capacitors

Abstract

To provide a thermoelectric capacitor that can be manufactured easily, has an excellent Seebeck coefficient, and can obtain electric energy intermittently from temperature differences, a thermoelectric conversion module and a temperature sensor using the same, and a method of using the same.SOLUTION: A thermoelectric capacitor includes at least a pair of electrodes and a thermoelectric conversion material sandwiched between them. The thermoelectric conversion material is composed of an ionic conductor containing a salt with a halogen anion.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a thermoelectric capacitor for use in energy harvesting and a method for using a thermoelectric capacitor. [Background technology]

[0002] The Internet of Things (IoT) is becoming more and more widespread, aiming to connect all things that surround us to the Internet and realize a safe, secure, and convenient society. However, since the IoT is expected to use trillions of sensors to obtain information about things, it is practically impossible to perform maintenance work such as battery replacement, charging, and wiring for each sensor, and maintenance-free power supply technology is required. In response to this, energy harvesting technology is being developed, which harvests unused energy such as heat, light, and vibration that is widely and thinly present in the environment on the spot, converts it into electricity, and uses it to operate electronic circuits. In recent years, technology development has been progressing to significantly reduce the power consumption of wireless sensors, and the applicability of energy harvesting, which enables local production and consumption of electricity, is also increasing. For example, thermoelectric conversion, which converts the temperature difference obtained from heat in the environment into electricity, is known as one form of energy harvesting.

[0003] Thermoelectric conversion is a technology that generates electricity from temperature differences, and its conversion characteristics are evaluated by the Seebeck coefficient (S), which is the voltage generated per unit temperature difference of a material, and the dimensionless figure of merit (ZT), which is calculated from the electrical conductivity (σ), thermal conductivity (κ), and absolute temperature (T). ZT is expressed as follows: ZT=S 2 It is calculated as σT / κ, and the larger ZT is, the higher the conversion performance of the material. In other words, to realize a thermoelectric generation element with high conversion efficiency, it is necessary to develop a material with a larger Seebeck coefficient and electrical conductivity, as well as a lower thermal conductivity.

[0004] In the past, inorganic materials containing bismuth, tellurium, lead, cobalt, etc. have been researched and developed as thermoelectric conversion materials that exhibit high ZT. However, these materials have the problem of containing toxic elements or rare elements. The sintering process used for the production is costly. In addition, they lack flexibility, making them difficult to attach to curved surfaces. Furthermore, for energy harvesting applications, it is desirable to effectively apply a temperature difference from a heat source in the medium-low temperature range from around room temperature to around 100 degrees Celsius to the element to generate electricity efficiently, so materials with low thermal conductivity are important.

[0005] Known examples of thermoelectric conversion materials that are flexible and have low thermal conductivity include conductive polymers, nanocarbon materials, and composites of these.

[0006] In addition to semiconductors, metals, conductive polymers, and nanocarbon materials, it is known that even substances in which the charge carriers are ions can generate electromotive force when subjected to a temperature difference. A thermochemical battery is a thermoelectric generating element that has a structure in which a solution of ions containing redox pairs is sandwiched between mainly platinum electrodes. When a temperature difference is applied to a thermochemical battery, an oxidation reaction (reduction reaction) of the reductant (oxidant) occurs at the high-temperature electrode, and a reduction reaction (oxidation reaction) of the oxidant (reductant) occurs at the low-temperature electrode, causing a continuous current to flow through the circuit, making it possible to use it as a generating element (see, for example, Patent Document 1). Non-Patent Document 1 reports that an ion conductor made of NaOH and PEO (polyethylene oxide) and an Au electrode or an Au / CNT electrode are used to function as a thermoelectric capacitor. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2017 / 155046 [Non-patent literature]

[0008] [Non-Patent Document 1] D. Zhao et al., Energy Environ. Sci. 2016, 9, 1450-1457 Summary of the Invention [Problem to be solved by the invention]

[0009] Thermoelectric conversion elements have traditionally been developed mainly for the purpose of reusing high-temperature waste heat emitted from power plants and other sources. For this reason, thermoelectric conversion materials using inorganic semiconductors have attracted attention. In recent years, there are growing expectations for them in the energy harvesting field as a power supply technology related to IoT. For these applications, materials that are low cost, lightweight, flexible, can be made large, and have few resource constraints are essential, and materials with low thermal conductivity are also important for generating electricity from low-temperature heat sources. Organic thermoelectric materials have attracted attention as flexible and low-thermal-conductivity materials, but at present, they have a small Seebeck coefficient and require the construction of modules made of multiple organic films to generate sufficient voltage. In addition, impedance matching with the boost circuit must be considered, which results in problems such as complicated manufacturing processes and device design.

[0010] In view of the above circumstances, an object of the present invention is to provide a thermoelectric capacitor that can be easily manufactured, has an excellent Seebeck coefficient, and is capable of obtaining electric energy intermittently from a temperature difference, and a method for using the thermoelectric capacitor. [Means for solving the problem]

[0011] As a result of extensive investigations aimed at solving the above problems, the present inventors discovered that when an ion conductor containing a salt having a halogen anion is sandwiched between electrodes and a temperature difference is applied, it is effective as a thermoelectric conversion material and has a large absolute value of the Seebeck coefficient, thereby completing the present invention. The present invention provides the following specific embodiments. <1> A thermoelectric capacitor including a cell including at least a pair of electrodes and a thermoelectric conversion material sandwiched between the electrodes, A thermoelectric capacitor, wherein the thermoelectric conversion material is an ion conductor containing a salt having a halogen anion. <2> The salt having a halogen anion is an imidazolium halide. <1> The thermoelectric capacitor according to claim 1. <3> The imidazolium halide is a compound represented by the following formula (1): <2> The thermoelectric capacitor according to claim 1. [ka] In formula (1), R 1 and R 2 each independently represents an alkyl group, and X represents a halogen anion. <4> In the formula (1), R 1 and R 2 each independently represents an alkyl group having 1 to 12 carbon atoms, and X represents a chloro anion; <3> The thermoelectric capacitor according to claim 1. <5> The ion conductor is an ionic liquid, an ionic solution or an ion gel. <1> ~ <4> 2. The thermoelectric capacitor according to claim 1 . <6> The electrode has a conductive polymer, silver or platinum at least on a surface thereof. <1> ~ <5> 2. The thermoelectric capacitor according to claim 1 . <7> The electrode is a conductive polymer electrode, a silver electrode, a platinum electrode, or an electrode formed by coating a nanocarbon material with silver or platinum. <6> The thermoelectric capacitor according to claim 1. <8> The absolute value of the Seebeck coefficient is 1mV / K or more. <1> ~ <7> 2. The thermoelectric capacitor according to claim 1 . <9> A plurality of cells electrically connected in series. <1> ~ <8> 2. The thermoelectric capacitor according to claim 1 . <10> It is p-type <1> ~ <9> 2. The thermoelectric capacitor according to claim 1 . <11> It is n-type <1> ~ <9> 2. The thermoelectric capacitor according to claim 1 . <12> One or more <10> The p-type thermoelectric capacitor according to claim 1, <11> and an n-type thermoelectric capacitor according to claim 1, wherein the p-type thermoelectric capacitor and the n-type thermoelectric capacitor are alternately and electrically connected in series. <13> <1> ~ <11> or <12> A temperature sensor comprising the thermoelectric capacitor module according to claim 1. <14> A method for using a thermoelectric capacitor including a cell composed of at least a pair of electrodes and a thermoelectric conversion material sandwiched between the electrodes, comprising: the thermoelectric conversion material is an ion conductor containing a salt having a halogen anion, The pair of electrodes maintains a constant temperature difference, A method for using a thermoelectric capacitor, characterized in that it outputs power intermittently. <15> The salt having a halogen anion is an imidazolium halide. <14> A method for using the thermoelectric capacitor according to claim 1. <16> The imidazolium halide is a compound represented by the following formula (1): <15> A method for using the thermoelectric capacitor according to claim 1. [ka] In formula (1), R 1 and R 2 each independently represents an alkyl group, and X represents a halogen anion. <17> In the formula (1), R 1 and R 2 each independently represents an alkyl group having 1 to 12 carbon atoms, and X represents a chloro anion; <16> A method for using the thermoelectric capacitor according to claim 1. <18> The ion conductor is an ionic liquid, an ionic solution or an ion gel. <14> ~ <17> 2. A method for using the thermoelectric capacitor according to claim 1 . <19> The electrode has a conductive polymer, silver or platinum on at least a surface thereof. <14> ~ <16> 2. A method for using the thermoelectric capacitor according to claim 1 . <20> The electrode is a conductive polymer electrode, a silver electrode, a platinum electrode, or an electrode formed by coating a nanocarbon material with silver or platinum. <19> A method for using the thermoelectric capacitor according to claim 1. Effect of the Invention

[0012] According to the present invention, it is possible to provide a thermoelectric capacitor that can be easily manufactured, has an excellent Seebeck coefficient, and is capable of obtaining electric energy intermittently, a temperature sensor using the thermoelectric capacitor, and methods of using the same. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a conceptual diagram of a thermochemical battery. [Diagram 2] FIG. 2 is a conceptual diagram of a thermoelectric capacitor according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a conceptual diagram of a thermoelectric capacitor according to one embodiment of the present invention. [Figure 4] FIG. 4 is a conceptual diagram showing a method of using a thermoelectric capacitor according to one embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram showing the element for evaluating the Seebeck coefficient of Example 1. As shown in FIG. [Figure 6] FIG. 6 is a diagram showing a method for measuring the Seebeck coefficient evaluation element of Example 1. [Figure 7] FIG. 7 is a graph showing the measurement results of the Seebeck coefficient of the Emim-Cl gel of Example 1. [Figure 8] FIG. 8 is a graph showing the change in voltage in an experiment in which a temperature difference was applied to the Emim-Cl / PVA gel of Example 1 and a load resistor was connected. [Figure 9] FIG. 9 is a graph showing voltage changes when a temperature difference is applied to the Emim-Cl / PVA gel of Example 1 and a load resistance is repeatedly connected and disconnected. [Figure 10] 1 is a graph showing an overall image of the Nyquist plot of Emim-Cl / PVA gel (measurement frequency: 1 to 105 Hz). [Figure 11]FIG. 13 is a magnified view of the high frequency region (near the origin) of the Nyquist plot of the Emim-Cl / PVA gel. [Figure 12] 1 is a graph showing an overall image of the Nyquist plot of Hmim-Cl / PVA gel (measurement frequency: 1 to 105 Hz). [Figure 13] FIG. 13 is a magnified view of the high frequency region (near the origin) of the Nyquist plot of the Hmim-Cl / PVA gel. [Figure 14] 1 is a graph showing an overall image of the Nyquist plot of Dmim-Cl / PVA gel (measurement frequency: 1 to 105 Hz). [Figure 15] FIG. 13 is a magnified view of the high frequency region (near the origin) of the Nyquist plot of the Dmim-Cl / PVA gel. [Figure 16] FIG. 16 is a diagram showing a Seebeck coefficient evaluation element in which a plurality of gels of Example 5 are connected in series with electrodes. [Figure 17] FIG. 17 is a graph showing the electromotive force of a thermoelectric capacitor in which multiple gels are connected in series with electrodes. [Figure 18] FIG. 18 is a graph showing the change in voltage in an experiment in which five gels were connected in series, a temperature difference was applied, and a load resistor was connected. [Figure 19] FIG. 19 shows an example of manufacturing a coin cell type thermoelectric capacitor (photograph in place of drawing). [Figure 20] FIG. 20 is a graph showing the change in voltage when a load resistance is repeatedly connected and disconnected in a coin cell type thermoelectric capacitor. [Figure 21] FIG. 21 is a graph showing the measurement results of the Seebeck coefficient of the Emim-Cl gel of Example 7. [Figure 22] FIG. 22 is a graph showing the change in voltage in an experiment in which a temperature difference was applied to the Emim-Cl / PVA gel of Example 7 and a load resistor was connected. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In explaining the details of the present invention, specific examples will be given. However, the present invention is not limited to the following contents as long as it does not deviate from the spirit of the present invention, and can be modified as appropriate.

[0015] 1. Thermoelectric capacitor and thermoelectric capacitor module A thermoelectric capacitor according to one aspect of the present invention includes a cell including at least a pair of electrodes and a thermoelectric conversion material sandwiched between the electrodes, the thermoelectric conversion material being made of an ion conductor including a salt having a halogen anion. FIG. 1 is a conceptual diagram of a thermochemical battery, and FIG. 2 is a conceptual diagram of a thermoelectric capacitor according to one embodiment of the present invention. As shown in FIG. 1, an electrolyte consisting of a semiconductor material and a redox pair behaves like a battery under a temperature difference, while as shown in FIG. 2, an ionically conductive material that does not have a redox pair behaves as a chargeable capacitor by being polarized under a temperature difference. In a thermoelectric capacitor according to one embodiment of the present invention, as shown in FIG. 3(A), by applying a temperature difference between the electrodes, As a result, ionic polarization due to the temperature difference occurs in the cell sandwiched between the electrodes, and an open circuit voltage is generated. When a load is connected to the cell, as shown in FIG. 3(B), a current flows in the circuit until the voltage becomes zero so as to compensate for the ionic polarization, and an electric charge accumulates in the electrodes. The current flows, and the voltage is converted into work. The present inventor has found that by using an ionic conductor containing a salt having a halogen anion, a huge Seebeck coefficient can be expressed, and a thermoelectric capacitor with excellent thermoelectric conversion characteristics that achieves both low impedance and extremely low thermal conductivity can be realized. Since the absolute value of the Seebeck coefficient of the thermoelectric capacitor according to the present invention (hereinafter, the "absolute value of the Seebeck coefficient" is also simply referred to as the "Seebeck coefficient") is huge, the number of thermoelectric modules, which have been complicated in the conventional manufacturing process, can be significantly reduced, or even modularization can be eliminated. The huge open circuit voltage can be converted into electrical work by connecting a load resistance to the thermoelectric capacitor, and further, after the conversion into work is completed, the open circuit voltage can be restored again by removing the load resistance while maintaining the temperature difference. Due to this property, the thermoelectric capacitor according to one embodiment of the present invention can provide a thermoelectric conversion device that can alternately repeat the generation of a huge voltage due to a temperature difference and the conversion to work by connecting a load. For example, it can be deployed in an application in which a voltage obtained from unused heat is used to intermittently supply power to a wireless sensor once every few seconds to several hours or days. Furthermore, the thermoelectric conversion material used in the present invention is flexible, such as a gel or liquid, and the thermoelectric capacitor can be made into a usable form by attaching it to a curved heat source. In addition, it can be made into an element by simply applying paint or sandwiching it between electrode materials, and it can be easily made to accommodate large areas and can be manufactured by a simple process. As an embodiment of the present invention, it is also preferable to use a thermoelectric capacitor having a plurality of cells electrically connected in series. By electrically connecting a plurality of cells in series, a thermoelectric capacitor having a larger electromotive force can be obtained. For example, in the example described below, five cells were connected in series and a Seebeck coefficient of 37 mV / K was obtained. This value can only be obtained by modularizing the device using about 150 pieces of bismuth tellurium, and this shows that the present invention is very effective in simplifying the device fabrication and reducing the cost. In addition, when a temperature difference of 33°C was applied to the capacitor, an open circuit voltage of about 1.1 V, which is comparable to the electromotive force of an alkaline dry battery, was obtained without using a boost circuit. Thus, since the electromotive force per unit temperature difference of the thermoelectric capacitor according to one embodiment of the present invention is large, a large electromotive force can be obtained by modularizing a small number of cells. The present inventor also found that the polarity of the thermoelectric capacitor can be controlled by using a specific ion conductor and changing the type of electrode. According to the present invention, it is possible to obtain a thermoelectric capacitor with p-type polarity or an n-type polarity by using the same ion conductor. Therefore, a thermoelectric capacitor module including one or more p-type thermoelectric capacitors and one or more n-type thermoelectric capacitors, in which the p-type thermoelectric capacitors and the n-type thermoelectric capacitors are alternately electrically connected in series, is also an aspect of the present invention. In this way, by forming a thermoelectric capacitor module by alternately connecting p-type thermoelectric capacitors and n-type thermoelectric capacitors in series, voltages can be added by electrically connecting them in series and thermally connecting them in parallel, and a larger voltage can be obtained. The "thermoelectric conversion material" and "electrode" used in the present invention will be described below.

[0016] 1-1. Thermoelectric conversion materials In the present invention, an ion conductor containing a salt having a halogen anion is used as the thermoelectric conversion material. The ionic conductor containing a salt having a halogen anion is not particularly limited as long as it is an ionic conductor containing a salt having a halogen anion, and a commercially available product may be used, or a synthesized product may be used. Examples of the halogen anion include a fluoro anion, a chloro anion, a bromo anion, and an iodo anion. From the viewpoint of achieving both a large Seebeck coefficient and a low thermal conductivity, and from the viewpoints of solubility and the Seebeck coefficient, the chloro anion is preferred. The counter cation of the salt having a halogen anion is not particularly limited, but from the viewpoint of achieving both a large Seebeck coefficient and low thermal conductivity, and realizing a relatively high electrical conductivity, it is preferably an imidazolium cation. From the viewpoint of availability, the imidazolium cation is preferably a 1,3-disubstituted imidazolium cation or a 1,2,3-trisubstituted imidazolium cation, more preferably a 1,3-disubstituted imidazolium cation, and further preferably a 1,3-dialkylimidazolium cation. Specific examples of the imidazolium cation include 1-ethyl-3-methylimidazolium cation, 1,3-dimethylimidazolium cation, 1-methyl-3-propylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-methyl-3-pentylimidazolium cation, 1-hexyl-3-methylimidazolium cation, 1-heptyl-3-methylimidazolium cation, 1-methyl-3-octylimidazolium cation, 1-decyl-3-methylimidazolium cation, 1-dodecyl-3-methylimidazolium cation, 1-ethyl-3-propylimidazolium, imidazolium cation, dialkylimidazolium cations such as 1-butyl-3-ethylimidazolium cation; and trialkylimidazolium cations such as 3-ethyl-1,2-dimethyl-imidazolium cation, 1,2-dimethyl-3-propylimidazolium cation, 1-butyl-2,3-dimethylimidazolium cation, 1,2-dimethyl-3-hexylimidazolium cation, 1,2-dimethyl-3-octylimidazolium cation, 1-ethyl-3,4-dimethylimidazolium cation, and 1-isopropyl-2,3-dimethylimidazolium cation.

[0017] The salt having a halogen anion is preferably a halogenated imidazolium, and more preferably a compound represented by formula (1) in which the counter cation is a 1,3-dialkylimidazolium cation. [ka] In formula (1), R 1 and R 2 each independently represents an alkyl group, and X represents a halogen anion. In this specification, the alkyl group is not limited to a linear alkyl group, and may have a branched structure and / or a cyclic structure. R 1 and R 2 is preferably an alkyl group having 1 to 18 carbon atoms, more preferably an alkyl group having 1 to 12 carbon atoms, and further preferably an alkyl group having 1 to 10 carbon atoms. Examples of the alkyl group having 1 to 18 carbon atoms include alkyl groups such as a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, a n-pentyl group, an isopentyl group, a neopentyl group, a n-hexyl group, a n-heptyl group, a n-octyl group, a n-nonyl group, a n-decyl group, a n-undecyl group, a n-dodecyl group, a n-tridecyl group, a n-tetradecyl group, a n-pentadecyl group, a n-hexadecyl group, a n-heptadecyl group, a n-octadecyl group, a n-nonadecyl group, and a n-docosyl group; and cycloalkyl groups such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group.

[0018] As the compound represented by formula (1), from the viewpoints of solubility, Seebeck coefficient, and electrical conductivity, R 1 and R 2 are each independently an alkyl group having 1 to 18 carbon atoms, and X is a chloro anion. More preferably, R 1 is a methyl group and X is a chloro anion, [ka] In formula (2), R 2 represents an alkyl group. In terms of solubility, Seebeck coefficient, and electrical conductivity, R 2 is preferably an alkyl group having 1 to 18 carbon atoms, more preferably an alkyl group having 1 to 12 carbon atoms, and further preferably an alkyl group having 1 to 10 carbon atoms. Among these, 1-ethyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-decyl-3-methylimidazolium cation are particularly preferred.

[0019] The ionic conductor may be either a liquid or a solid. If the salt having the above-mentioned halogen anion is an ionic liquid, it may be used as it is, or the salt having the halogen anion may be dissolved in a solvent such as water and used as an ionic solution, or the salt having the halogen anion may be gelled using a polymer such as polyvinyl alcohol (PVA) and used as an ionic gel. As the solvent for the ionic solution, for example, water or an aqueous solvent containing water and an organic solvent is used. As the ion gel, a gel of a salt having a halogen anion using a polymer such as polyvinyl alcohol; polyethylene glycol, polypropylene glycol; polyvinylpyrrolidone; amylose; or hydroxyalkylcellulose such as hydroxypropylmethylcellulose or hydroxypropylcellulose is preferred. A specific example of a method for preparing an ion gel is a method in which an aqueous solution containing a salt having a halogen anion at a concentration of about 0.1 g / mL is mixed with an aqueous PVA solution at a concentration of about 10 wt %, and then excess water is removed at 80° C. in an air atmosphere to prepare an ionic conductor of a thermoelectric conversion material. The ion conductor is preferably an ionic liquid, an ionic solution, or an ion gel, and more preferably an ion gel from the viewpoints of ease of handling, suppression of thermal expansion of the thermoelectric capacitor, and low thermal conductivity. From the viewpoint of increasing the Seebeck coefficient, the ratio of the weight of the salt having a halogen anion to the weight of the gel (weight [g] of the salt having a halogen anion / weight [g] of the gel) is preferably 0.5 or more, more preferably 0.7 or more, and even more preferably 1.0 or more.

[0020] 1-2. Electrode The electrodes used in the present invention are not particularly limited, and depending on the shape and size of the thermoelectric capacitor, commercially available products may be used as they are, commercially available products may be processed and used, or commercially available materials may be processed and used. From the viewpoint of achieving both a large Seebeck coefficient and low thermal conductivity, an electrode having a conductive polymer, silver or platinum on its surface is preferred, and a conductive polymer electrode, a silver electrode, a platinum electrode, or an electrode formed by coating a nanocarbon material with silver or platinum is more preferred. The silver and platinum electrodes may be porous. Commercially available electrodes include, for example, silver plate (AG-403324) manufactured by Nilaco Corporation, platinum plate (PT-353325) manufactured by Nilaco Corporation, silver paste (Dotite D-550) manufactured by Fujikura Kasei Co., Ltd., and silver porous body (Ag-MF80A-□50-1) manufactured by AS ONE Corporation. The conductive polymer is not particularly limited, and any known conductive polymer can be used. Examples of the π-conjugated polymer constituting the conductive polymer include polyacetylene and polyparaf Examples of the π-conjugated polymer include a polymer or a copolymer of two or more types selected from the group consisting of phenylene, polyaniline, polythiophene, polyethylenedioxythiophene, polyparaphenylenevinylene, polypyrrole, polyfluorene, and polythienylenevinylene. In addition, functional groups such as alkyl groups may be introduced into these π-conjugated polymers. The dopant added to the conductive polymer is not particularly limited, and may be appropriately selected based on the electronic level and chemical structure of the π-conjugated polymer. Examples of the dopant include halogen molecules, alkali metals, iron chloride, gold(III) chloride, arsenic pentafluoride, sulfuric acid, nitric acid, hydrochloric acid, acetic acid, Examples of the dopant include polystyrene sulfonic acid, p-toluenesulfonic acid, benzenesulfonic acid, nitrosonium tetrafluoroborate, nitrosonium hexafluorophosphate, bistrifluoromethanesulfonylsilver, and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole. The amount and method of addition of the dopant can also be determined appropriately. In the case of a p-type thermoelectric capacitor having a large Seebeck coefficient (high Seebeck coefficient) and low thermal conductivity, the electrode is preferably an electrode having silver or platinum on the surface, and more preferably a silver electrode, a platinum electrode, or an electrode formed by coating a nanocarbon material with silver or platinum. In the case of an n-type thermoelectric capacitor having a large absolute value of the Seebeck coefficient (low Seebeck coefficient) and low thermal conductivity, the electrode is preferably a conductive polymer electrode, the π-conjugated polymer constituting the conductive polymer is preferably polyethylenedioxythiophene, the dopant is preferably polystyrenesulfonic acid, and a conductive polymer consisting of polyethylenedioxythiophene and polystyrenesulfonic acid is particularly preferable. In addition, in order to impart higher conductivity, for example, a high boiling point polar solvent such as ethylene glycol may be mixed with PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid)). The pair of electrodes may be made of the same material or different materials, but preferably are made of the same material.

[0021] 1-3. Manufacturing method of thermoelectric capacitor The method for manufacturing a thermoelectric capacitor according to an embodiment of the present invention is not particularly limited as long as it includes the steps of preparing at least a pair of electrodes and a thermoelectric conversion material, and sandwiching the thermoelectric conversion material between the electrodes. For example, when manufacturing a coin cell type thermoelectric capacitor, a silver paste that serves as an electrode is applied to the inside of a stainless steel container used for the coin cell, and then an ion gel containing a salt having a halogen anion, which is a thermoelectric conversion material, is poured in and the capacitor is crimped with a crimping machine.

[0022] 1-4. Seebeck coefficient, AC conductivity, and thermal conductivity of thermoelectric capacitors The absolute value of the electromotive force per unit temperature difference of the thermoelectric capacitor according to one embodiment of the present invention is large, on the order of millivolts or more. The absolute value of the Seebeck coefficient of the thermoelectric capacitor according to one embodiment of the present invention is preferably 1 mV / K or more, more preferably 1.5 mV / K or more, even more preferably 2.0 mV / K or more, and particularly preferably 3.0 mV / K or more. In the case of inorganic thermoelectric materials, for example, bismuth-tellurium-based inorganic thermoelectric materials have a Seebeck coefficient of about 0.25 mV / K. In the examples described later, it is shown that a Seebeck coefficient of 10.1 mV / K can be obtained, which is about 40 times that of commercially available thermoelectric materials, making it an excellent thermoelectric conversion material.

[0023] In the thermoelectric capacitor according to one embodiment of the present invention, a thermoelectric conversion material has a relatively high AC conductivity as an ion conductor. The AC conductivity can be calculated by the following formula: AC conductivity = electrode gap / (internal resistance x cross-sectional area of ​​ionic conductor) The specific evaluation method is as described in the Examples below.

[0024] Moreover, the thermoelectric capacitor according to one embodiment of the present invention can achieve extremely low thermal conductivity, comparable to that of bismuth-tellurium-based inorganic thermoelectric materials and conductive polymer thermoelectric materials that have attracted attention in recent years. The thermal conductivity of the thermoelectric capacitor according to one embodiment of the present invention is preferably 0.35 Wm -1 K -1 or less, more preferably 0.33 Wm -1 K -1 or less, and more preferably 0.30 Wm -1 K -1 The low thermal conductivity reduces the temperature difference applied to the thermoelectric capacitor when it is placed on a heat source. It is effective for maintaining the temperature and increasing the amount of power generation. The thermal conductivity is measured according to ISO-22007-6. For example, the thermal conductivity can be measured using ai-Phase Mobile M10 manufactured by ai-Phase. The specific measurement method is as described in the examples below.

[0025] 2. How to use thermoelectric capacitors A method of using a thermoelectric capacitor according to one aspect of the present invention is a method of using a thermoelectric capacitor having a cell composed of at least a pair of electrodes and a thermoelectric conversion material sandwiched between them, characterized in that the thermoelectric conversion material is made of an ion conductor containing a salt having a halogen anion, and the electrodes of the thermoelectric capacitor output power intermittently while maintaining a constant temperature difference. The above descriptions of 1-1. Thermoelectric Conversion Material and 1-2. Electrode are applicable to the thermoelectric conversion material and the electrodes, respectively. A preferred embodiment of the present invention is a thermoelectric conversion device that includes a thermoelectric capacitor having a cell composed of at least a pair of electrodes and a thermoelectric conversion material sandwiched between them, and a heat transfer part that contacts the thermoelectric capacitor and transfers heat, in which the thermoelectric conversion material is an ion conductor containing a salt having a halogen anion, the heat transfer part controls the pair of electrodes to maintain a constant temperature difference, and outputs electric power intermittently. The heat transfer part may be appropriately selected depending on the target temperature. FIG. 4 is a conceptual diagram showing a method of using a thermoelectric capacitor according to one embodiment of the present invention. (i) shows the state where there is no temperature difference between the electrodes, i.e., the non-polarized state. As shown in (ii), by applying a temperature difference in an open circuit state, ionic polarization due to the temperature difference occurs, generating an open circuit voltage. As shown in (iii), by applying a temperature difference and keeping the circuit closed, ionic polarization is To compensate, a current flows through the load (circuit) and a charge accumulates on the electrode. The current flow converts the voltage into work, which means that this energy can be used to move the sensor. (iv) shows that the voltage recovers when a temperature difference is applied in an open circuit state. Even if the temperature difference is maintained, the charge accumulated in the electrodes disappears due to self-discharge of the capacitor, and the voltage recovers. Then, by connecting the load again, the recovered voltage can be converted back into work. In other words, intermittent charging and discharging can be repeated using heat as an energy source. FIG. 9 is a graph showing the voltage change in an example in which a load resistance is repeatedly connected and disconnected for a thermoelectric capacitor according to one embodiment of the present invention. As shown in FIG. 9, (iii) the temperature difference Since the (iv) temperature difference application (open circuit) and the (v) temperature difference application (open circuit) are reversible, it is possible to output intermittent power under a constant temperature difference between the electrodes by repeating the cycle of voltage recovery, conversion to work, and voltage recovery. For this reason, it is expected to be used as a power source for intermittently transmitting sensor information at a frequency of once every few minutes to several hours. Non-Patent Document 1 shows a method of use in which a capacitor generates a voltage by applying a temperature difference in an open state, and then converts this into work by connecting a load resistance to it. However, in this document, the open-end voltage generated by applying a temperature difference does not reach 0V even when a load is connected, and it is difficult to say that all of the generated voltage is effectively used as work. Furthermore, as a means of recovering the voltage, a method is taken in which the load is removed once to eliminate the temperature difference, the load is reconnected, and the capacitor is again placed in an open state, after which a temperature difference is applied again. In other words, this method is intended for use in situations where there is a fluctuation in temperature difference. This type of usage is effective in situations where the temperature difference fluctuates between day and night, such as with solar heat. However, it is difficult to apply this method when using heat sources with small temperature fluctuations, such as hot water pipes in factories or human body temperature. On the other hand, a thermoelectric capacitor according to one embodiment of the present invention can repeatedly convert the temperature difference into work and restore the voltage even while the temperature difference is maintained, and therefore can be used not only in such a manner but also when using a heat source with small temperature fluctuations, which is advantageous in practical use. In addition, in relation to IoT, in applications that wirelessly transmit environmental information, etc., in reality, it is not always necessary to transmit the acquired information at all times, and it is considered that the technology will be preferably applied to situations where the information is transmitted wirelessly using power obtained from thermal energy once every few minutes to several hours or days.

[0026] 3. Temperature Sensor A temperature sensor including the above-mentioned thermoelectric capacitor or thermoelectric capacitor module is also one of the preferred embodiments of the present invention. Pyroelectric sensors, which are widely used in automatic lighting and the like, can usually only sense temperature changes. On the other hand, existing thermocouples utilize the Seebeck effect of metals. The thermoelectric capacitor and thermoelectric capacitor module according to the present invention can generate a large thermoelectromotive force as long as there is a temperature difference, and are therefore preferably used in applications that require highly sensitive sensing of temperature itself. EXAMPLES

[0027] The present invention will be described in more detail below with reference to examples, but the examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited to the specific examples shown below.

[0028] <Example 1. Preparation and measurement of element for evaluating Seebeck coefficient> A gel precursor was prepared by mixing an aqueous solution of 1-ethyl-3-methylimidazolium chloride (Emim-Cl) (concentration: 0.1 g / mL) and an aqueous solution of polyvinyl alcohol (PVA) (concentration: 10 wt%) in a screw bottle so that the weight ratio of Emim-Cl:PVA was the weight ratio shown in Table 1. When the weight ratio of Emim-Cl:PVA was 10:1, the molar ratio of Emim-Cl:PVA was 1500:1. Two metal electrodes (silver-silver or platinum-platinum) were placed on a glass substrate with a gap of approximately 1 cm. As shown in Figure 5, approximately 50 μL of the gel precursor was dropped between the electrodes and heated on a hot plate at 80°C to evaporate excess water, producing a film of ion-conductive gel. Thermogravimetry showed that the water remaining in the gel was approximately 20% of the total weight of the gel. As shown in Figure 6, the element was placed so as to bridge the two Peltier elements, and the R thermocouple (for measuring temperature and voltage) was placed directly on the electrode. The R thermocouple was connected to a data logger (temperature and voltage measuring device). One Peltier element was set to high temperature and the other to low temperature, and a temperature difference (ΔT) was applied between the electrodes. At this time, the temperature difference was applied while adjusting the temperature of the low-temperature electrode to be constant at about 300 K. Temperature and open circuit voltage (V OC ) were simultaneously measured to determine the Seebeck coefficient. The results are shown in Table 1. A huge Seebeck coefficient of up to +10.1 mV / K was obtained with the Emim-Cl / PVA gel. Figure 7 shows the measurement results of the Seebeck coefficient (thermoelectromotive force: voltage generated per unit temperature difference) when Emim-Cl was used as the salt having a halogen anion. Figure 8 shows a graph of the voltage change when the Emim-Cl / PVA gel element was connected to a load resistance (100 Ω) from an open circuit state (open) where a temperature difference was applied. In Figure 3, the voltage (open end voltage) generated in the open circuit state (open) (A) immediately attenuated to 0 V by connecting a load resistance between the electrodes (B). This means that a current flows through the load to compensate for the polarization state generated by the temperature difference, and it can be said that it was converted into work. In the case of semiconductor or metal thermoelectric materials or thermochemical batteries, charges that can be extracted into the circuit, such as electrons and holes, flow continuously through the load resistance and thermoelectric material, so that the voltage does not return to zero even when a load is connected. From the above, it can be seen that when subjected to a temperature difference, the device behaves as a capacitor that can be charged by heat, rather than as a battery like ordinary thermoelectric materials. In addition, for the element using a gel with a molar ratio of Emim-Cl:PVA of 1500:1, the temperature difference was kept constant at about 3°C, and the load (100 Ω) was connected (Figure 4 (iii)), opened (Figure Figure 9 shows the voltage change when 4(iv)) was repeated. It can be seen from Figure 9 that the voltage, which was converted into work by connecting the load and decreased, recovered to the same level as before the load was connected by opening the load. In other words, it was shown that it is possible to repeatedly charge and discharge intermittently using heat as an energy source.

[0029] [Table 1]

[0030] <Example 2. Preparation and measurement of element for evaluating Seebeck coefficient> A Seebeck coefficient evaluation element was fabricated and measured in the same manner as in Example 1, except that the salt having a halogen anion was changed from 1-ethyl-3-methylimidazolium chloride (Emim-Cl) to 1-hexyl-3-methylimidazolium chloride (Hmim-Cl) or 1-decyl-3-methylimidazolium chloride (Dmim-Cl). In the ion gel, the molar ratio of the salt having a halogen anion to PVA was 1500:1. The measurement results are shown in Table 2 together with the results for 1-ethyl-3-methylimidazolium chloride.

[0031] [Table 2]

[0032] Example 3: Evaluation of AC Conductivity Using ion gels prepared by gelling 1-ethyl-3-methylimidazolium chloride (Emim-Cl), 1-hexyl-3-methylimidazolium chloride (Hmim-Cl), or 1-decyl-3-methylimidazolium chloride (Dmim-Cl) as a salt having a halogen anion with PVA, AC conductivity was evaluated as follows. In the ion gel, the molar ratio of the salt having a halogen anion to PVA was 1500:1. Two glass substrates with fluorine-doped tin oxide (transparent conductive film) were used as electrodes. Each gel was sandwiched between the electrodes via a 25 μm thick polyethylene terephthalate film spacer. The gap between the electrodes was set to 25 μm, and an AC voltage was applied. The internal resistance was calculated from the intersection point of a Nyquist plot created by impedance spectroscopy and extrapolated to the real axis. 5 Hz) in Fig. 10, and in the high frequency domain (near the origin) An enlarged view of the Nyquist plot of Hmim-Cl / PVA gel (measurement frequencies 1–10) is shown in Fig. 11. 5 The Nyquist plot of the Dmim-Cl / PVA gel (measurement frequencies 1–10 Hz) is shown in Fig. 12, and an enlarged view of the high-frequency region (near the origin) is shown in Fig. 13. 5 The AC conductivity of each gel is shown in Table 3. It was found that all of the gels had relatively high values ​​for ion conductors.

[0033] [Table 3]

[0034] Example 4: Evaluation of thermal conductivity The thermal conductivity was evaluated using ion gels prepared by gelling 1-ethyl-3-methylimidazolium chloride (Emim-Cl), 1-hexyl-3-methylimidazolium chloride (Hmim-Cl), or 1-decyl-3-methylimidazolium chloride (Dmim-Cl) with PVA as the salt having a halogen anion, as follows: The molar ratio of the salt having a halogen anion to PVA in the ion gel was 1500:1. The measurements were conducted in accordance with ISO-22007-6 using the ai-Phase Mobile M10 manufactured by ai-Phase. The evaluation gel was placed on a measurement section laminated in the order of thermopile (temperature sensor) / reference sample (polyethylene terephthalate film) / thermopile (temperature sensor), and an AC temperature wave with a frequency of 50 mHz and an amplitude of ±1°C was applied by a Peltier element, and the thermal conductivity was calculated from the amplitude attenuation rate. -1 K -1 It was confirmed that the values ​​were as low as those of bismuth telluride and organic thermoelectric materials. The results are shown in Table 4.

[0035] [Table 4]

[0036] <Example 5. Evaluation of a device in which multiple cells are electrically connected in series> As shown in Figure 16, multiple cells were electrically connected in series to measure the Seebeck coefficient. First, silver paste was applied to a glass substrate to make electrodes. Gel was applied between the electrodes. The cells were then connected in series, forming an electrical connection in series. The temperature difference was applied in the direction shown in the figure using two Peltier elements. As each cell is thermally arranged in parallel, the same temperature difference is applied to each cell, but since they are electrically connected in series, the voltage is added up according to the number of constituent cells, resulting in an increasing structure. As shown in the figure, R thermocouples were connected to the electrodes at both ends, and the temperature difference and voltage were measured simultaneously using a data logger to evaluate the thermoelectromotive force (generated voltage per unit temperature difference). An ion gel with a molar ratio of Emim-Cl:PVA of 1500:1 (weight ratio of 10:1) was used as the ionic conductor. The Seebeck coefficient of the ion gel (generated voltage per unit temperature difference; thermoelectric power) was a maximum of 10.1 mV / K for Emim-Cl / PVA, an enormous value that is about 40 times that of commercially available thermoelectric materials. This could be further increased by connecting multiple gels via electrodes. The relationship between the number of ion gels and the generated thermoelectromotive force is shown in Figure 17. An ion gel with a molar ratio of Emim-Cl:PVA of 1500:1 was used as the ion conductor. As the number of ion gels increased, the thermoelectromotive force also increased, and a maximum of 37 mV / K was obtained when five ion gels were connected. With bismuth-tellurium-based materials, a thermoelectromotive force that would normally be obtained by connecting approximately 150 ion gels could be achieved with just five wires, demonstrating that this is effective in simplifying the manufacturing process of thermoelectric elements. Next, a temperature difference of 33°C was applied to the element with five gels connected, and the open circuit voltage was measured, yielding a value of approximately 1.1 V, comparable to that of an alkaline dry cell. In addition, the energy gained by connecting to a load reached approximately 1.7 mJ. Figure 18 shows the voltage change. In order to obtain a voltage on the order of volts with a normal thermoelectric element, it is necessary to boost the voltage using a boost circuit. In this case, consideration must be given to impedance matching between the thermoelectric element and the boost circuit, but it has been shown that the thermoelectric capacitor according to the present invention can generate a voltage on the order of volts without using a boost circuit.

[0037] <Example 6. Fabrication and evaluation of coin cell type thermoelectric capacitor> After applying silver paste to the inside of a stainless steel container (LIR2450) used for the electrodes of a coin cell (button battery) (left side of Figure 19), an ion gel with a molar ratio of Emim-Cl:PVA of 1500:1 (weight ratio of 10:1) was poured in and crimped with a crimping machine to produce a coin cell type thermoelectric capacitor. The right side of Figure 19 shows the resulting coin cell type thermoelectric capacitor. The coin cell type thermoelectric capacitor obtained with two Peltier elements was sandwiched between the upper and lower electrodes, a temperature difference was applied between the upper and lower electrodes, and the voltage was measured with a data logger. At this time, the resistor box was used to repeatedly open and connect the load resistance. By repeatedly connecting and opening the load resistance, it was possible to alternately repeat the decrease in voltage (conversion to work) and the recovery of the voltage. The voltage change at this time is shown in Figure 20. By filling the coin cell, it is possible to prevent leakage of the ionic conductor.

[0038] <Example 7. Preparation and measurement of element for evaluating Seebeck coefficient> In the same manner as in Example 1, an aqueous solution of 1-ethyl-3-methylimidazolium chloride (Emim-Cl) (concentration: 0.1 g / mL) and an aqueous solution of polyvinyl alcohol (PVA) (concentration: 10 wt%) were mixed in a screw bottle to prepare a gel with a weight ratio of Emim-Cl:PVA of 10:1 (the molar ratio of Emim-Cl:PVA was 1500:1). A commercially available PEDOT:PSS dispersion (Clevios PH1000) was mixed with 3 weight percent ethylene glycol, cast into a polypropylene case, dried, and peeled off from the polypropylene case to produce a free-standing PEDOT:PSS film. This was cut into strips and placed on a glass substrate, a bank was made with adhesive, the above gel was poured, and the excess water was evaporated by heating to produce an ionically conductive gel film, which was used as a sample for measurement. As in Example 1, two Peltier elements were placed so as to bridge each other, and an R thermocouple (for measuring temperature and voltage) was placed directly on the electrode. The R thermocouple was connected to a data logger (temperature and voltage measuring instrument), and the Seebeck coefficient was determined as in Example 1. The Seebeck coefficient was -1 to -2 mV / K. The Seebeck coefficient of the Emim-Cl / PVA gel was measured using a PEDOT:PSS electrode (thermoelectromotive force: voltage generated per unit temperature difference). The measurement results are shown in Figure 21. Figure 22 shows a graph of the voltage change when the Emim-Cl / PVA gel element is connected to a load resistance (loading: 1 kΩ) from an open circuit state (open) where a temperature difference is applied. It should be noted that the sign of the open circuit voltage is reversed in the comparison between FIG. 7 and FIG. 21 or between FIG. 8 and FIG. 22. In Example 1, as shown in FIG. 7, the open circuit voltage increases to the positive side as the temperature difference is increased, so the Seebeck coefficient is positive and the polarity is p-type. On the other hand, in FIG. 21, the open circuit voltage increases to the negative side as the temperature difference is increased, so the Seebeck coefficient is negative. That is, by using the same Emim-Cl / PVA gel as in Example 1 and changing the electrode to a PEDOT:PSS electrode, the polarity is reversed and it becomes n-type. From FIG. 22, even if the electrode is changed to a PEDOT:PSS electrode, the open circuit voltage becomes 0 when connected to a load resistor, and it can be seen that it operates as a capacitor, not a mechanism in which electrons flow continuously like a thermoelectric element or a thermochemical battery. Note that in FIG. 22, the sign of the open circuit voltage in FIG. 8 of Example 1 is also reversed. That is, it is an n-type thermoelectric capacitor. [Industrial Applicability]

[0039] The present invention provides power for sensors and wireless transmission devices in the IoT (Internet of Things). This technology is useful as a power generation element that supplies heat to a variety of places, particularly in the low and medium temperature ranges, and is particularly useful as an element that uses unused heat. Potential applications include health care sensors, child monitoring sensors, power sources for automatic temperature and humidity monitors, and highly sensitive temperature sensors that use thermoelectromotive force.

Claims

1. A thermoelectric capacitor comprising at least a pair of electrodes and a cell formed of a thermoelectric conversion material sandwiched between the electrodes, the thermoelectric conversion material is an ion conductor containing a salt having a halogen anion, the salt having a halogen anion is an imidazolium halide, The thermoelectric capacitor, wherein the halogen anion is a chlorine anion.

2. 2. The thermoelectric capacitor according to claim 1, wherein the imidazolium halide is a compound represented by the following formula (1): 【Chemistry 1】 In formula (1), R １ and R ２ each independently represents an alkyl group, and X represents a chloro anion.

3. In the formula (1), R １ and R ２ The thermoelectric capacitor according to claim 2 , wherein each of the groups is independently an alkyl group having 1 to 12 carbon atoms.

4. The thermoelectric capacitor according to any one of claims 1 to 3, wherein the ion conductor is an ionic liquid, an ionic solution, or an ionic gel.

5. The thermoelectric capacitor of claim 4 , wherein the ionic conductor is an ion gel.

6. The thermoelectric capacitor according to any one of claims 1 to 5, wherein the electrodes have a conductive polymer, silver or platinum on at least a surface thereof.

7. 7. The thermoelectric capacitor according to claim 6, wherein the electrodes are conductive polymer electrodes, silver electrodes, platinum electrodes, or electrodes formed by coating a nanocarbon material with silver or platinum.

8. The thermoelectric capacitor according to any one of claims 1 to 7, wherein the absolute value of the Seebeck coefficient is 1 mV / K or more and 10.1 mV / K or less.

9. The thermoelectric capacitor of any one of claims 1 to 8, comprising a plurality of cells electrically connected in series.

10. The thermoelectric capacitor of any one of claims 1 to 9, which is p-type.

11. The thermoelectric capacitor of any one of claims 1 to 9, which is n-type.

12. A thermoelectric capacitor module comprising one or more p-type thermoelectric capacitors according to claim 10 and one or more n-type thermoelectric capacitors according to claim 11, wherein the p-type thermoelectric capacitors and the n-type thermoelectric capacitors are alternately and electrically connected in series.

13. A temperature sensor comprising the thermoelectric capacitor according to any one of claims 1 to 11 or the thermoelectric capacitor module according to claim 12.

14. A method for using a thermoelectric capacitor having a cell composed of at least a pair of electrodes and a thermoelectric conversion material sandwiched between the electrodes, comprising: the thermoelectric conversion material is an ion conductor containing a salt having a halogen anion, the salt having a halogen anion is an imidazolium halide, the halogen anion is a chloro anion, The pair of electrodes maintains a constant temperature difference, A method for using a thermoelectric capacitor, characterized in that it outputs power intermittently.

15. The method for using a thermoelectric capacitor according to claim 14, wherein the imidazolium halide is a compound represented by the following formula (1): 【Chemistry 2】 In formula (1), R １ and R ２ each independently represents an alkyl group, and X represents a chloro anion.

16. In the formula (1), R １ and R ２ The method for using a thermoelectric capacitor according to claim 15, wherein each of the groups is independently an alkyl group having 1 to 12 carbon atoms.

17. The method for using a thermoelectric capacitor according to any one of claims 14 to 16, wherein the ion conductor is an ion gel.

Images