JP6908256B2 - Thermoelectric element - Google Patents

Description

The present invention relates to a thermoelectric generator that converts thermal energy into electrical energy.

The amount of unused industrial waste heat in Japan is more than twice the amount of electricity used in Japan. In addition, the amount of solar thermal energy that falls on Japan is more than 1000 times the amount of electricity used in Japan. If some of these thermal energies can be converted into electrical energy, fossil energy consumption can be suppressed and carbon dioxide can be reduced.

In addition, since the human body also dissipates heat energy, if this heat energy can be converted into electrical energy, charging of mobile devices becomes unnecessary. For that purpose, a "thermoelectric power generation system" that can inexpensively convert thermal energy near room temperature into electrical energy is required.

As a technique for converting a temperature difference into electrical energy, for example, a thermoelectric power generation element using the Seebeck coefficient of a semiconductor is known. In this thermoelectric generation element, a material (Bi ₂ Te ₃ ) having high performance near room temperature is used. However, this material has the problem that it is expensive and contains toxic elements. Further, this thermoelectric generation element becomes bulky in order to provide a temperature gradient.

On the other hand, Patent Document 1 discloses a thermoelectric power generation element similar to a secondary battery utilizing the electrochemical Seebeck effect. In this thermoelectric generation element, the same active material is used for the positive electrode and the negative electrode. In this thermoelectric generation element, a current can be passed through an external circuit by causing a difference in electromotive force between both electrodes due to a temperature difference.

International Publication No. 2012/140856

In the temperature difference conversion type thermoelectric power generation element of Patent Document 1, it is necessary to make a large temperature difference in the element. For that purpose, it is necessary to use a material having a low thermal conductivity. In order to realize a semiconductor thermoelectric conversion element with high conversion efficiency from thermal energy to electrical energy, it is necessary to achieve both large electrical conductivity and small thermal conductivity. Therefore, development of a temperature difference conversion type thermal power generation element. Is making it difficult. Further, in the sheet-shaped temperature difference conversion type thermoelectric power generation element, in order to raise the voltage, a sheet-shaped cell having a pair of electrodes and an electrolyte interposed between them is connected in series (cells are stacked). There is a need. Then, the temperature difference between the front surface and the back surface of each cell is reduced.

The present invention has been made in view of the above circumstances, and is a thermal power generation element capable of converting thermal energy into electrical energy and making it thinner by utilizing the temperature change of the entire element. The purpose is to provide.

[1] A thermal power generation element in which a first electrode and a second electrode face each other via a single electrolyte, and the first electrode and the second electrode have the same metal ion. include a material that reversibly out, including the first electrode and the second electrode different the materials from each other, by the temperature change the overall device, the temperature of the second electrode and the first electrode is raised or lowered, together with causing one of the electromotive force of the negative and positive to the first electrode, to cause different other electromotive force from said first electrode to said second electrode A thermal power generation element characterized by generating electricity by means of.

[2] The first electrode contains a material A that generates a negative electromotive force as the temperature rises, and the second electrode contains a material B that generates a positive electromotive force as the temperature rises. The thermoelectric power generation element according to [1].

[3] The first electrode contains a material A that generates a negative electromotive force as the temperature rises or a material B that generates a positive electromotive force as the temperature rises, and the second electrode contains an alkali metal C. The thermoelectric power generation element according to [1].

[4] The material A is a material that generates a negative electromotive force at −20 ° C. or higher, and the material B is a material that generates a positive electromotive force at −20 ° C. or higher [2] or [ 3] The thermoelectric power generation element.

[5] The thermoelectric generation element according to [1], wherein the first electrode contains a material D that undergoes a structural phase transition with an increase in temperature, and the second electrode contains an alkali metal C.

[6] A plurality of units having the first electrode, the second electrode, and the electrolyte are laminated so that the first electrode of one unit and the second electrode of the other unit are adjacent to each other. The thermal power generation element according to any one of [1] to [5].

According to the present invention, it is possible to provide a thermal power generation element capable of converting thermal energy into electrical energy and making it thinner by utilizing the temperature change of the entire element.

It is sectional drawing of the thermoelectric generation element in one Embodiment of this invention. It is a schematic diagram of the thermoelectromotive force measuring apparatus used in the experimental example. It is a figure which shows the temperature dependence of the discharge curve of the electrochemical cell of Experimental Example 1. It is a figure which shows the result of having evaluated the electrochemical Seebeck coefficient of the electrochemical cell of Experimental Example 1. FIG. It is a figure which shows the temperature dependence of the discharge curve of the electrochemical cell of Experimental Example 2. It is a figure which shows the result of having evaluated the electrochemical Seebeck coefficient of the electrochemical cell of Experimental Example 2. It is a figure which shows the temperature dependence of the discharge curve of the electrochemical cell of Experimental Example 3. It is a figure which shows the result of having evaluated the electrochemical Seebeck coefficient of the electrochemical cell of Experimental Example 3. It is a schematic diagram of the electrochemical cell used in the experimental example. It is a figure which shows the electromotive force difference between the 1st electrode and the 2nd electrode with respect to the temperature difference between the 1st electrode and the 2nd electrode in the electrochemical cell of Experimental Example 4. FIG. It is a schematic diagram of the thermoelectromotive force measuring apparatus used in the experimental example. It is a figure which shows the result of having measured the temperature difference and the thermoelectromotive force difference of the 1st electrode and the 2nd electrode in Experimental Example 5. It is a figure which shows the result of having measured the temperature difference and the thermoelectromotive force difference of the 1st electrode and the 2nd electrode in Experimental Example 6. It is a figure which shows the result of having measured the temperature difference and the thermoelectromotive force difference of the 1st electrode and the 2nd electrode in Experimental Example 7. It is a figure which shows the result of having measured the temperature difference and the thermoelectromotive force difference of the 1st electrode and the 2nd electrode in Experimental Example 8. It is a figure which shows the temperature dependence of the discharge curve of the electrochemical cell of Experimental Example 9. It is a figure which shows the relationship between the Li concentration and the lattice constant at _{Li x} Co [Fe (CN) ₆ ] _0.9 in Experimental Example 9. It is a figure which shows the relationship between the Na concentration and the lattice constant at _{Na x} Co [Fe (CN) ₆ ] _0.9 in Experimental Example 10. It is a figure which shows the relationship between the Na concentration and the temperature at _{Na x} Co [Fe (CN) ₆ ] _0.9 in Experimental Example 10. It is a figure which shows the relationship between the capacitance of the electrode of the electrochemical cell of Experimental Example 11 and the discharge voltage. It is a schematic diagram which shows the arrangement of the sodium ion in _{P2-Na x} CoO ₂ in the case of x = 1/2. It is a schematic diagram which shows the arrangement of the sodium ion in _{P2-Na x} CoO ₂ in the case of x = 2/3. It is a figure which shows the result of having evaluated the crystal structure of _{P2-Na 0.59} CoO ₂ at 27 degreeC, 127 degreeC and 227 degreeC by X-ray diffraction.

An embodiment of the thermoelectric power generation element of the present invention will be described.
It should be noted that the present embodiment is specifically described in order to better understand the gist of the invention, and is not limited to the present invention unless otherwise specified.

[Thermal power generation element]
Hereinafter, the thermoelectric generation element of the present embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the thermoelectric power generation element of the present embodiment.
The thermoelectric generation element 1 of the present embodiment includes a unit 5 having a first electrode 2, a second electrode 3, and an electrolyte 4.
In the thermoelectric generation element 1, the first electrode 2 is provided on one surface 6a of the collecting electrode 6, the second electrode 3 is provided on the other surface 6b of the collecting electrode 6, and the first electrode 2 and the first electrode 2. The second electrode 3 is arranged so as to face each other via the collecting electrode 6. Further, the first electrode 2 and the second electrode 3 are arranged so as to face each other with the separator 7 interposed therebetween. Further, the first electrode 2 and the second electrode 3 are arranged so as to face each other at a predetermined interval via a single electrolyte 4 impregnated in the separator 7. Further, in the unit 5 having the first electrode 2, the second electrode 3, and the electrolyte 4, the first electrode 2 of one unit 5 and the second electrode 3 of the other unit 5 are adjacent to each other. Multiple layers are stacked. Further, the first electrode 2 and the second electrode 3 are electrically connected via a lead wire 8. Further, a circuit (not shown) or a device (not shown) for taking out the current generated by the thermoelectric generation element 1 may be provided in the middle of the lead wire 8. A heater (not shown) is attached to the first electrode 2. Further, these components are sealed with a laminate film 9.

Although the case where the heater is attached to the first electrode 2 is illustrated here, the present embodiment is not limited to this. In the thermoelectric generation element 1 of the present embodiment, the heater may be attached to the second electrode 3, or may be attached to both the first electrode 2 and the second electrode 3, and the laminate film 9 may be attached. It may be provided inside, or may be provided on the outer surface of the laminated film 9.

As the heater, for example, a general resistance heating type heater or the like is used. Further, as the heater, a heater using solar heat energy may be used. A heater using solar heat energy is a heater that uses heat energy sent from a device for collecting solar heat energy installed outdoors for heating. By using such a heater, a heat source using fossil energy becomes unnecessary in order to heat the first electrode 2 and the second electrode 3.

The first electrode 2 and the second electrode 3 include a material in which the same metal ion reversibly enters and exits. Further, the first electrode 2 and the second electrode 3 may contain a material in which the same metal ion is precipitated or alloyed.

It is preferable that the first electrode 2 contains a material A that generates a negative electromotive force as the temperature rises, and the second electrode 3 contains a material B that generates a positive electromotive force as the temperature rises. Alternatively, the first electrode 2 contains a material A that produces a negative electromotive force as the temperature rises or a material B that produces a positive electromotive force as the temperature rises, and the second electrode 3 contains an alkali metal C. It is preferable to include it. When the second electrode 3 contains the alkali metal C, the second electrode 3 is composed of substantially only the alkali metal C.

The material A is not particularly limited as long as it generates a negative electromotive force as the temperature rises, but for example, it is preferably a material that generates a negative electromotive force at −20 ° C. or higher, and at 0 ° C. or higher. A material that generates a negative electromotive force is more preferable, and a material that generates a negative electromotive force at 0 ° C. to 200 ° C. is further preferable.
If a material that generates a negative electromotive force at -20 ° C or higher is used as the material A, a large amount of thermal energy is not required to generate the electromotive force, so that the conversion from thermal energy to electrical energy is performed more efficiently. be able to.

Specific examples of the material A include _{layered oxides such as P2-Na x} CoO ₂ (0.5 ≦ x ≦ 1.0), Na _x Co [Fe (CN) ₆ ] _0.81 , and Na _x Ni [ Fe (CN) ₆ ] _Examples thereof include Prussian blue type complexes such as 0.68. "P2" in P2-Na _x CoO ₂ is the name of the crystal structure. P2-Na _x CoO ₂ is a layered substance, but the lamination pattern is ABBAABBA.

The material B is not particularly limited as long as it generates a positive electromotive force as the temperature rises, but for example, it is preferably a material that generates a positive electromotive force at −20 ° C. or higher, and at 0 ° C. or higher. A material that generates a positive electromotive force is more preferable, and a material that generates a positive electromotive force at 0 ° C. to 200 ° C. is further preferable.
If a material that generates a positive electromotive force at -20 ° C or higher is used as the material B, a large amount of thermal energy is not required to generate the electromotive force, so that the conversion from thermal energy to electrical energy is performed more efficiently. be able to.

Specific examples of the material B include _{a Prussian blue complex such as Na x} Co [Fe (CN) ₆ ] _0.9 and Na _x Mn [Fe (CN) ₆ ] _0.84 , and lithium cobalt oxide (Li _x CoO). ₂ (0.5 ≦ x ≦ 1.0)) and the like.

Examples of the alkali metal C include lithium (Li) and sodium (Na).

Further, it is preferable that the first electrode 2 contains a material D that undergoes a structural phase transition as the temperature rises, and the second electrode 3 contains an alkali metal C. When the second electrode 3 contains the alkali metal C, the second electrode 3 is composed of substantially only the alkali metal C.

As the material D, a material that undergoes a structural phase transition as the temperature rises is preferable.
If the material D is a material that undergoes a structural phase transition as the temperature rises, it is possible to efficiently convert thermal energy into electrical energy.

Specific examples of the material D include _{layered oxides such as P2-Na x} CoO ₂ (0.5 ≦ x ≦ 1.0), Li _x Co [Fe (CN) ₆ ] _{0.9 and the} like.

The first electrode 2 and the second electrode 3 may contain a binder resin (binding agent) and a conductive auxiliary agent in addition to the above-mentioned materials A, B, and D.
Examples of the binder resin include polyvinylidene fluoride (PVdF) resin, polytetrafluoroethylene (PTFE) resin, fluororubber and the like.
Examples of the conductive auxiliary agent include Ketjen black, acetylene black (AB), furnace black, vapor-grown carbon fiber (VGCF), carbon nanotubes and the like.

As the electrolyte 4, an electrolytic solution obtained by dissolving an alkali metal salt in a solvent is used.
Examples of the alkali metal salt include sodium perchlorate (NaClO ₄ ), sodium chloride (NaCl), lithium perchlorate (LiClO ₄ ) and the like.
Examples of the solvent include water, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC) and the like.
As the electrolyte 4, an aqueous electrolyte is preferable, and an aqueous sodium chloride solution is more preferable, because it is inexpensive.

Further, in FIG. 1, in the thermoelectric generation element 1, the unit 5 having the first electrode 2, the second electrode 3, and the electrolyte 4 is the first electrode 2 of one unit 5 and the other unit 5. Although a case where a plurality of the second electrodes 3 are laminated so as to be adjacent to each other has been illustrated, the present embodiment is not limited to this. The thermoelectric generation element 1 of the present embodiment may be composed of one unit 5 having a first electrode 2, a second electrode 3, and an electrolyte 4.

According to the thermoelectric generation element 1 of the present embodiment, it is possible to convert thermal energy into electrical energy by utilizing the temperature change of the entire element, and it is possible to reduce the thickness. Further, by using the water-based electrolyte, it is possible to obtain the thermoelectric power generation element 1 which is cheaper and has less environmental load when disposed of.

Specifically, when the first electrode 2 contains a material A that generates a negative electromotive force as the temperature rises, and the second electrode 3 contains a material B that generates a positive electromotive force as the temperature rises. Alternatively, the first electrode 2 contains a material A that generates a negative electromotive force as the temperature rises or a material B that generates a positive electromotive force as the temperature rises, and the second electrode 3 contains an alkali metal C. When the above is included, the thermal power generation element 1 can generate electric power as follows.
That is, by raising the temperature of the first electrode 2 to provide a temperature difference between the first electrode 2 and the second electrode 3, and generating a negative electromotive force in the first electrode 2. , The thermal power generation element 1 can generate electricity. Further, by raising the temperature of the second electrode 3 to provide a temperature difference between the first electrode 2 and the second electrode 3, and generating a positive electromotive force in the second electrode 3. , The thermal power generation element 1 can generate electricity. Further, the temperatures of the first electrode 2 and the second electrode 3 are raised (or lowered) to generate a negative (positive) electromotive force in the first electrode 2 and in the second electrode 3. By generating a positive (negative) electromotive force, the thermal power generation element 1 can generate electricity.

Further, when the first electrode 2 contains the material D that undergoes a structural phase transition as the temperature rises and the second electrode 3 contains the alkali metal C, the thermoelectric generation element 1 generates electricity as follows. Can be done.
That is, by raising (or lowering) the temperature of the first electrode 2, the material D contained in the first electrode 2 undergoes a structural phase transition, and a negative electromotive force is generated in the first electrode 2. , The thermoelectric generation element 1 can generate electricity. Further, by raising (or lowering) the temperature of the first electrode 2 and causing a structural phase transition of the material D contained in the first electrode 2, a positive electromotive force is generated in the first electrode 2. , The thermoelectric generation element 1 can generate electricity.
Further, since the first electrode 2 and the second electrode 3 are arranged via a single electrolyte 4, the thermoelectric generation element 1 can be miniaturized.

Hereinafter, the present invention will be described in more detail with reference to Experimental Examples, but the present invention is not limited to the following Experimental Examples.

[Experimental Example 1]
"Preparation of electrochemical cell"
The thermoelectromotive force of the electrode was measured using the electrochemical cell 100 shown in FIG.
The electrochemical cell 100 includes a first electrode 101, a second electrode 102, and an electrolyte 103.
In the electrochemical cell 100, the first electrode 101 and the second electrode 102 are arranged to face each other at predetermined intervals via a single electrolyte 103 housed in the case 104. Further, the first electrode 101 and the second electrode 102 are electrically connected via a lead wire 105. Further, the case 104 is arranged on the heater 106.

As the P2-Na _x CoO ₂ powder, a powder obtained by mixing a raw material oxide and firing in air at 700 ° C. for 24 hours was used.
P2-Na _x CoO ₂ powder, polyvinylidene fluoride, and Ketjen black are mixed at a mass ratio of 8: 1: 1, and the mixture is applied onto an aluminum electrode plate to form a coating film. The coating film was dried to obtain an electrode having an electrode mixture layer containing _{P2-N x} CoO _{2 on an aluminum electrode plate.} This electrode was designated as the first electrode 101.
As the second electrode 102, metallic sodium was used.
As the electrolyte 103, a propylene carbonate solution having a sodium perchlorate concentration of 1 mol / L was used.
Using these first electrode 101, second electrode 102, and electrolyte 103, the electrochemical cell 100 of Experimental Example 1 was prepared.

"Evaluation of temperature dependence of discharge curve / Evaluation of electromotive force"
The temperature dependence of the discharge curve of the electrochemical cell of Experimental Example 1 was evaluated.
The evaluation procedure is as follows.
The temperature of the entire case 104 is controlled to 35 ° C. or 55 ° C., and in this state, a current is passed from the first electrode 101 to the second electrode 102 to be between the first electrode 101 and the second electrode 102. The generated electromotive force was measured.
The results of measuring the discharge curves at 35 ° C and 55 ° C are shown in FIG. In FIG. 3, x on the horizontal axis indicates x of _{P2-Na x} CoO _2. That is, x on the horizontal axis indicates the Na concentration (molar ratio) in _{P2-Na x} CoO _2.
In FIG. 3, the reason why the electromotive force changes significantly at x = 1/2 and 2/3 is that P2-Na _x CoO ₂ undergoes a structural phase transition.

The electrochemical Seebeck coefficient was evaluated from the discharge curve shown in FIG.
The evaluation procedure is as follows.
The Electrochemical Seebeck coefficient is the difference in electromotive force divided by the temperature difference. The electromotive force difference was calculated by subtracting the 35 ° C. discharge curve from the 55 ° C. discharge curve, and the electromotive force difference was divided by the temperature difference (15 ° C.) to obtain the electrochemical Seebeck coefficient.
The results are shown in FIG. In FIG. 4, x on the horizontal axis indicates x of _{P2-Na x} CoO _2. That is, x on the horizontal axis indicates the Na concentration (molar ratio) in _{P2-Na x} CoO _2.
From the result of FIG. 4, it was found that a negative electromotive force was observed. Further, from the results of FIG. 4, P2-Na _x CoO ₂ has a thermoelectromotive force (0.2 mV / K) at around room temperature as compared with the thermoelectromotive force (0.2 mV / K) of the semiconductor thermoelectric material (Bi ₂ Te _{3) near room temperature.} It was found that the absolute value of was large.

[Experimental Example 2]
"Preparation of electrochemical cell"
_{Na x Co [Fe (CN)} 6] The thin film made of _0.9, by electrolytic deposition, indium tin oxide (ITO) was formed on the electrode plates, on the ITO electrode plate _Na x Co [Fe (CN) ₆ ] An electrode having an electrode layer made of _{0.9 was obtained.} This electrode was designated as the first electrode 101.
An electrochemical cell of Experimental Example 2 was produced in the same manner as in Experimental Example 1 except that the first electrode 101 was used.

"Evaluation of temperature dependence of discharge curve / Evaluation of electromotive force"
In the same manner as in Experimental Example 1, the temperature dependence of the discharge curve of the electrochemical cell of Experimental Example 2 was evaluated.
The results of measuring the discharge curves at 35 ° C and 55 ° C are shown in FIG. In FIG. 5, x on the horizontal axis represents x of Na _x Co [Fe (CN) ₆ ] _0.9 . That is, x on the horizontal axis indicates the Na concentration (molar ratio) at _{Na x} Co [Fe (CN) ₆ ] _0.9.

The electrochemical Seebeck coefficient was evaluated from the discharge curve shown in FIG. 5 in the same manner as in Experimental Example 1.
The results are shown in FIG. In FIG. 6, x on the horizontal axis represents x of Na _x Co [Fe (CN) ₆ ] _0.9 . That is, x on the horizontal axis indicates the Na concentration (molar ratio) at _{Na x} Co [Fe (CN) ₆ ] _0.9.
From the result of FIG. 6, it was found that a positive electromotive force was observed. Further, from the results of FIG. 6, Na _x Co [Fe (CN) ₆ ] _0.9 is a thermoelectromotive force (-0.2 mV / K) of the semiconductor thermoelectric material (Bi ₂ Te _{3) near room temperature near room temperature.} ), It was found that the absolute value of the thermoelectromotive force was larger.

[Experimental Example 3]
"Preparation of electrochemical cell"
_{Na x Mn [Fe (CN)} 6] The thin film made of _0.84, by electrolytic deposition, indium tin oxide (ITO) was formed on the electrode plates, on the ITO electrode plate _Na x Mn [Fe (CN) ₆ ] An electrode having an electrode layer made of _{0.84 was obtained.} This electrode was designated as the first electrode 2.
An electrochemical cell of Experimental Example 3 was produced in the same manner as in Experimental Example 1 except that the first electrode 2 was used.

"Evaluation of temperature dependence of discharge curve / Evaluation of electromotive force"
In the same manner as in Experimental Example 1, the temperature dependence of the discharge curve of the electrochemical cell of Experimental Example 3 was evaluated.
The results of measuring the discharge curves at 35 ° C and 55 ° C are shown in FIG. In FIG. 7, x on the horizontal axis represents x of Na _x Mn [Fe (CN) ₆ ] _0.84 . That is, x on the horizontal axis indicates the Na concentration (molar ratio) at _{Na x} Mn [Fe (CN) ₆ ] _0.84.

The electrochemical Seebeck coefficient was evaluated from the discharge curve shown in FIG. 7 in the same manner as in Experimental Example 1.
The results are shown in FIG. In FIG. 8, x on the horizontal axis represents x of Na _x Mn [Fe (CN) ₆ ] _0.84 . That is, x on the horizontal axis indicates the Na concentration (molar ratio) at _{Na x} Mn [Fe (CN) ₆ ] _0.84.
From the result of FIG. 8, it was found that a positive electromotive force was observed. Further, from the results of FIG. 8, Na _x Mn [Fe (CN) ₆ ] _0.84 is the thermoelectromotive force (-0.2 mV / K) of the semiconductor thermoelectric material (Bi ₂ Te _{3) near room temperature near room temperature.} ), It was found that the absolute value of the thermoelectromotive force was larger.

[Experimental Example 4]
"Preparation of electrochemical cell"
The thermoelectromotive force of the electrode was measured using the electrochemical cell 200 shown in FIG.
The electrochemical cell 200 was inserted into the cell 210, a pair of fixing plates 220 and 220 for fixing the first electrode 301, the second electrode 302 and the electrolyte 303 housed in the cell 210, and the cell 210. It includes a pair of thermocouples 230, 230 and a pair of heaters 240, 240 screwed into the cell 210.

The first electrode 301 and the second electrode 302 housed in the cell 200 are arranged so as to face each other via the electrolyte 303. The distance between the first electrode 301 and the second electrode 302 is 2 mm.

One of the thermocouples 230 has its tip arranged in the vicinity of the first electrode 301 housed in the cell 200 and measures the temperature of the first electrode 301. Further, the other end of the thermocouple 230 is arranged in the vicinity of the second electrode 302 housed in the cell 200, and the temperature of the second electrode 3022 is measured.

The heater 240 includes a coupling portion 241 screwed into the cell 200, a Perche element 242 and a heat sink 243 stacked in this order from the coupling portion 241.

As the P2-Na _x CoO ₂ powder, a powder obtained by mixing a raw material oxide and firing in air at 700 ° C. for 24 hours was used.
P2-Na _x CoO ₂ powder, polyvinylidene fluoride, and Ketjen black are mixed at a mass ratio of 8: 1: 1, and the mixture is applied onto an aluminum electrode plate to form a coating film. The coating film was dried to obtain an electrode having an electrode mixture layer containing _{P2-N x} CoO _{2 on an aluminum electrode plate.} These electrodes were designated as the first electrode 301 and the second electrode 302.
As the electrolyte 303, a propylene carbonate solution having a sodium perchlorate concentration of 1 mol / L was used.
Using these first electrode 301, second electrode 302, and electrolyte 303, the electrochemical cell 200 of Experimental Example 1 was prepared.

"Evaluation of electromotive force difference"
A temperature difference is provided between the first electrode 301 and the second electrode 302, and the temperature difference and the electromotive force difference between the first electrode 301 and the second electrode 302 are actually measured, and the first electrode is measured. The electromotive force difference between the first electrode 301 and the second electrode 302 was calculated with respect to the temperature difference between the 301 and the second electrode 302.
The results are shown in FIG. In FIG. 10, x represents x of P2-Na _x CoO ₂ . That is, x indicates the Na concentration (molar ratio) in _{P2-Na x} CoO _2.
From the results of FIG. 10, it was found that the electrochemical Seebeck coefficient was -0.720 mV / K when the Na concentration was 1/2, and the electrochemical Seebeck coefficient was -0.167 mV / K when the Na concentration was 2/3. rice field. These values were found to be comparable to the electrochemical Seebeck coefficient of semiconductor thermoelectric materials. For example, when the semiconductor thermoelectric material is Bi ₂ Te ₃ , the electrochemical Seebeck coefficient is -0.2 mV / K (300K), and when the semiconductor thermoelectric material is Na _1/2 CoO ₂ , the electrochemical Seebeck coefficient is 0. It is 2 mV / K (300K).

[Experimental Example 5]
"Manufacturing of thermoelectromotive force measuring device"
The thermoelectromotive force of the electrode was measured using the thermoelectromotive force measuring device 400 shown in FIG.
The thermoelectromotive force measuring device 400 includes a first electrode 401, a second electrode 402, and an electrolyte 403.
In the thermoelectromotive force measuring device 400, the first electrode 401 and the second electrode 402 are arranged to face each other at predetermined intervals via a single electrolyte 403 housed in the case 404. .. Further, the first electrode 401 and the second electrode 402 are electrically connected via a lead wire 405. A heater 406 is attached to the first electrode 401. Further, thermocouples 407 and 407 are attached to the first electrode 401 and the second electrode 402. Further, the case 404 is arranged on the magnetic stirrer main body 408, and the rotor 409 is arranged in the electrolyte 403 housed in the case 404.

_{Na x Co [Fe (CN)} 6] The thin film made of _0.9, by electrolytic deposition, indium tin oxide (ITO) was formed on the electrode plates, on the ITO electrode plate _Na x Co [Fe (CN) ₆ ] An electrode having an electrode layer made of _{0.9 was obtained.} These electrodes were designated as the first electrode 401 and the second electrode 402.
As the electrolyte 403, a 1 mol / L sodium chloride aqueous solution was used.
Using these first electrode 401, second electrode 402, and electrolyte 403, the thermoelectromotive force measuring device 400 of Experimental Example 5 was produced.

"Evaluation of thermoelectromotive force difference"
A temperature difference was provided between the first electrode 401 and the second electrode 402, and the temperature difference and the thermoelectromotive force difference between the first electrode 401 and the second electrode 402 were measured.
The results are shown in FIG.
From the results of FIG. 12, it was found that the electrochemical Seebeck coefficient was 0.7 mV / K.

[Experimental Example 6]
"Manufacturing of thermoelectromotive force measuring device"
_{Na x Co [Fe (CN)} 6] The thin film made of _0.81, by electrolytic deposition, indium tin oxide (ITO) was formed on the electrode plates, on the ITO electrode plate _Na x Co [Fe (CN) ₆ ] An electrode having an electrode layer made of _{0.81 was obtained.} The thermoelectromotive force measuring device 400 of Experimental Example 6 was produced in the same manner as in Experimental Example 5 except that this electrode was used as the first electrode 401 and the second electrode 402.

"Evaluation of electromotive force difference"
A temperature difference was provided between the first electrode 401 and the second electrode 402, and the temperature difference and the thermoelectromotive force difference between the first electrode 401 and the second electrode 402 were measured.
The results are shown in FIG.
From the results of FIG. 13, it was found that the electrochemical Seebeck coefficient was −0.85 mV / K.

[Experimental Example 7]
"Manufacturing of thermoelectromotive force measuring device"
_{Na x Ni [Fe (CN)} 6] The thin film made of _0.68, by electrolytic deposition, indium tin oxide (ITO) was formed on the electrode plates, on the ITO electrode plate _Na x Ni [Fe (CN) ₆ ] An electrode having an electrode layer made of _{0.68 was obtained.} The thermoelectromotive force measuring device 400 of Experimental Example 7 was produced in the same manner as in Experimental Example 5 except that this electrode was used as the first electrode 401 and the second electrode 402.

"Evaluation of electromotive force difference"
A temperature difference was provided between the first electrode 401 and the second electrode 402, and the temperature difference and the thermoelectromotive force difference between the first electrode 401 and the second electrode 402 were measured.
The results are shown in FIG.
From the results of FIG. 14, it was found that the electrochemical Seebeck coefficient was −0.70 mV / K.

[Experimental Example 8]
"Manufacturing of thermoelectromotive force measuring device"
As the Li _x CoO ₂ powder, a powder obtained by mixing a raw material oxide and firing in air at 900 ° C. for 10 hours was used.
Li _x CoO ₂ powder, polyvinylidene fluoride, and Ketjen black are mixed at a mass ratio of 8: 1: 1, and the mixture is applied onto an aluminum electrode plate to form a coating film. The coating film was dried to obtain an electrode having an electrode mixture layer containing _{Li x} CoO _{2 on an aluminum electrode plate.} This electrode was used as the first electrode 401 and the second electrode 402.
As the electrolyte 403, a mixed solution of ethylene carbonate and diethyl carbonate having a lithium perchlorate concentration of 1 mol / L was used.
The thermoelectromotive force measuring device 400 of Experimental Example 8 was produced in the same manner as in Experimental Example 5 except that the first electrode 401, the second electrode 402, and the electrolyte 403 were used.

"Evaluation of electromotive force difference"
A temperature difference was provided between the first electrode 401 and the second electrode 402, and the temperature difference and the thermoelectromotive force difference between the first electrode 401 and the second electrode 402 were measured.
The results are shown in FIG.
From the results of FIG. 15, it was found that the electrochemical Seebeck coefficient was 1.0 mV / K (x = 1.0).

"Experimental Example 9"
"Preparation of electrochemical cell"
The thermoelectromotive force of the electrode was measured using the electrochemical cell 100 shown in FIG.
A _{thin film consisting of Li x} Co [Fe (CN) ₆ ] _0.9 was formed on the ITO electrode plate by the electrolytic precipitation method, and Li _x Co [Fe (CN) ₆ ] _{0.9 was formed on the ITO electrode plate.} An electrode having an electrode layer made of the above was obtained. This electrode was designated as the first electrode 101.
As the second electrode 102, metallic lithium was used.
As the electrolyte 103, a mixed solution of ethylene carbonate and diethyl carbonate having a lithium perchlorate concentration of 1 mol / L was used.
Using these first electrode 101, second electrode 102, and electrolyte 103, the electrochemical cell 100 of Experimental Example 9 was prepared.

"Evaluation of electromotive force / evaluation of lattice constant"
In the same manner as in Experimental Example 1, the temperature dependence of the discharge curve of the electrochemical cell of Experimental Example 9 was evaluated.
The result of measuring the discharge curve is shown in FIG. In FIG. 16, x on the horizontal axis represents x of Li _x Co [Fe (CN) ₆ ] _0.9 . That is, x on the horizontal axis indicates the Li concentration (molar ratio) at _{Li x} Co [Fe (CN) ₆ ] _0.9.
In FIG. 16, the reason why there is a change in electromotive force of about 0.1 V between the low spin phase (LS) and the high spin phase (HS) is that Li _x Co [Fe (CN) ₆ ] _0.9 is the structural phase transition. Because it is.
In addition, the relationship between the Li concentration and the lattice constant at _{Li x} Co [Fe (CN) ₆ ] _{0.9 was evaluated.}
The evaluation procedure is as follows.
At each x, the electrochemical cell was disassembled in the glove box and Li _x Co [Fe (CN) ₆ ] _0.9 powder was encapsulated in the capillary. The X-ray diffraction pattern was measured using the synchrotron radiation X-ray as a light source. The lattice constant of the obtained diffraction pattern was determined from the diffraction angle 2θ using the black equation (2dsinθ = λ: d is the plane spacing and λ is the wavelength of the X-ray).
The results are shown in FIG. In FIG. 17, x on the horizontal axis represents x of Li _x Co [Fe (CN) ₆ ] _0.9 . That is, x on the horizontal axis indicates the Li concentration (molar ratio) at _{Li x} Co [Fe (CN) ₆ ] _0.9.
From the results shown in FIG. 17, it was found that the lattice constant increases by about 0.2 Å (0.02 nm) when the phase transition from the low spin phase (LS) to the high spin phase (HS) occurs.

"Experimental Example 10"
"Preparation of electrochemical cell"
The thermoelectromotive force of the electrode was measured using the electrochemical cell 100 shown in FIG.
A _{thin film consisting of Na x} Co [Fe (CN) ₆ ] _0.9 was formed on the ITO electrode plate by the electrolytic precipitation method, and Na _x Co [Fe (CN) ₆ ] _{0.9 was formed on the ITO electrode plate.} An electrode having an electrode layer made of the above was obtained. This electrode was designated as the first electrode 101.
As the second electrode 102, metallic sodium was used.
As the electrolyte 103, a mixed solution of ethylene carbonate and diethyl carbonate having a lithium perchlorate concentration of 1 mol / L was used.
Using these first electrode 101, second electrode 102, and electrolyte 103, the electrochemical cell 100 of Experimental Example 9 was prepared.

"Evaluation of lattice constant / Evaluation of temperature dependence of Na concentration"
In the same manner as in Experimental Example 9, _{the relationship between the Na concentration of Na x} Co [Fe (CN) ₆ ] _0.9 of Experimental Example 10 and the lattice constant was evaluated.
The results are shown in FIG. In FIG. 18, x on the horizontal axis represents x of Na _x Co [Fe (CN) ₆ ] _0.9 . That is, x on the horizontal axis indicates the Na concentration (molar ratio) at _{Na x} Co [Fe (CN) ₆ ] _0.9.
From the results shown in FIG. 18, it was found that the lattice constant increases by about 0.2 Å (0.02 nm) when the phase transition from the low spin phase (LS) to the high spin phase (HS) occurs.
Moreover, the relationship between the Na concentration and the temperature at _{Na x} Co [Fe (CN) ₆ ] _{0.9 was evaluated.}
The evaluation procedure is as follows.
In each x, dismantled electrochemical cell in a glove _box filled with _{Na x Co [Fe (CN)} 6] 0.9 powder capillary. The X-ray diffraction pattern was measured using the synchrotron radiation X-ray as a light source. The measurement temperatures were 100 K (-173 ° C) and 300 K (27 ° C). The lattice constant of the obtained diffraction pattern was determined from the diffraction angle 2θ using the black equation (2dsinθ = λ: d is the plane spacing and λ is the wavelength of the X-ray).
The results are shown in FIG. In FIG. 19, x on the horizontal axis represents x of Na _x Co [Fe (CN) ₆ ] _0.9 . That is, x on the horizontal axis indicates the Na concentration (molar ratio) at _{Na x} Co [Fe (CN) ₆ ] _0.9.
From the results shown in FIG. 19, it was found that the phase transition from the low spin phase (LS) to the high spin phase (HS) occurs at the boundary of 200 K. It is expected that there will be a change in electromotive force of about 0.1 V due to this phase transition.

[Experimental Example 11]
"Preparation of electrochemical cell"
Using the electrochemical cell 100 shown in FIG. 2, the relationship between the capacitance of the electrode and the discharge voltage was evaluated.
As the P2-Na _x CoO ₂ powder, a powder obtained by mixing a raw material oxide and firing in air at 700 ° C. for 24 hours was used.
P2-Na _x CoO ₂ calcined powder, polyvinylidene fluoride, and Ketjen black are mixed at a mass ratio of 8: 1: 1, and the mixture is applied onto an aluminum electrode plate to form a coating film. Then, the coating film was dried to obtain an electrode having an electrode mixture layer containing _{P2-Na x} CoO _{2 on an aluminum electrode plate.} This electrode was designated as the first electrode 101.
As the second electrode 102, metallic sodium was used.
As the electrolyte 103, a propylene carbonate solution having a sodium perchlorate concentration of 1 mol / L was used.
Using these first electrode 101, second electrode 102, and electrolyte 103, the electrochemical cell 100 of Experimental Example 11 was prepared.

"Evaluating the relationship between electrode capacitance and discharge voltage"
The relationship between the capacitance of the electrode of the electrochemical cell of Experimental Example 11 and the discharge voltage was evaluated.
The evaluation procedure is as follows.
The temperature of the entire case 104 is controlled to 35 ° C. or 55 ° C., and in this state, a current is passed from the first electrode 101 to the second electrode 102 to be between the first electrode 101 and the second electrode 102. The generated electromotive force was measured.
The results are shown in FIG. In FIG. 20, x on the horizontal axis represents x of P2-Na _x CoO ₂ . That is, x on the horizontal axis indicates the Na concentration (molar ratio) in _{P2-Na x} CoO _2.
In FIG. 20, the reason why the electromotive force changes significantly at x = 1/2 and 2/3 is that P2-Na _x CoO ₂ undergoes a structural phase transition.
The arrangement of sodium ions (Na ⁺ _{) in P2-Na x} CoO ₂ when x = 1/2 predicted from the calculation is shown in FIG. In addition, the arrangement of sodium ions in _{P2-Na x} CoO ₂ when x = 2/3 predicted from the calculation is shown in FIG. In FIGS. 21 and 22, Na ⁺ 1 is located directly above the cobalt atom and Na ⁺ 2 is located above the cobalt atom gap. Further, in FIGS. 21 and 22, x indicates x of P2-Na _x CoO ₂ . That is, x indicates the Na concentration (molar ratio) in _{P2-Na x} CoO _2.
The electromotive force changes greatly depending on the arrangement of the sodium ions. It is expected that the sodium ion sequence disappears at a high temperature of about 100 ° C. to 200 ° C.
In addition, the crystal structure of _{P2-Na 0.59} CoO ₂ was evaluated at 27 ° C., 127 ° C. and 227 ° C. by X-ray diffraction. The results are shown in FIG. From the results of FIG. 23, it was confirmed that the peak related to the order of Na with an index disappeared at 227 ° C.
From the above, a huge electromotive force can be expected due to the structural phase transition accompanying the temperature rise of _{P2-Na x} CoO _2.

The thermoelectric generator of the present invention can be used as a stationary thermoelectric generator, a mobile generator, a hybrid solar energy generator, or the like.

1 ... Thermoelectric element, 2 ... 1st electrode, 3 ... 2nd electrode, 4 ... Electrolyte, 5 ... Unit, 6 ... Collecting electrode, 7 ... Separator, 8 ... Lead wire, 9 ... Laminated film.

Claims (6)

A thermoelectric element in which the first electrode and the second electrode face each other via a single electrolyte.
The first electrode and the second electrode contain a material in which the same metal ion reversibly enters and exits.
The first electrode and the second electrode contain said materials that are different from each other.
The temperature of the entire element is changed to raise or lower the temperature of the first electrode and the second electrode to generate either negative or positive electromotive force in the first electrode, and the above-mentioned heat generating elements, characterized by generating by producing different other electromotive force from the first electrode to the second electrode. The first electrode contains a material A that generates a negative electromotive force as the temperature rises, and the second electrode contains a material B that generates a positive electromotive force as the temperature rises. The thermoelectric power generation element according to claim 1. The first electrode contains a material A that produces a negative electromotive force as the temperature rises or a material B that produces a positive electromotive force as the temperature rises, and the second electrode contains an alkali metal C. The thermal power generation element according to claim 1. The material A is a material that generates a negative electromotive force at −20 ° C. or higher, and the material B is a material that generates a positive electromotive force at −20 ° C. or higher. Thermoelectric element. The thermoelectric generator according to claim 1, wherein the first electrode contains a material D that undergoes a structural phase transition with an increase in temperature, and the second electrode contains an alkali metal C. A plurality of units having the first electrode, the second electrode, and the electrolyte are laminated so that the first electrode of one unit and the second electrode of the other unit are adjacent to each other. The thermal power generation element according to any one of claims 1 to 5, characterized in that.

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