Thermoelectric converter

Abstract

To provide a thermoelectric conversion device that can easily generate electricity in environments with fluctuating temperatures. [Solution] The thermoelectric converter comprises a first element and a second element that convert chemical energy into electrical energy, wherein at least one of the first element and the second element changes electromotive force with temperature, and when the first element and the second element are electrically insulated from each other, the difference in electromotive force before and after the temperature of the first element changes is different from the difference in electromotive force before and after the temperature of the second element changes. After the temperature of at least one of the first element and the second element changes, they are connected in parallel and output the voltage difference between the first element and the second element as current.

Description

[Technical Field]

[0001] This invention relates to a thermoelectric conversion device that converts thermal energy into electrical energy. [Background technology]

[0002] Prior art that converts thermal energy into electrical energy by applying a temperature difference to an element having a pn junction and utilizing the Seebeck effect is disclosed in Patent Document 1. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2009 / 063805 [Overview of the project] [Problems that the invention aims to solve]

[0004] Prior technology generates electricity by applying a temperature difference to the element, which presents a problem in that it is difficult to generate electricity in environments where the temperature of the element changes over time.

[0005] This invention was made to solve this problem and aims to provide a thermoelectric conversion device that can easily generate electricity in environments where the temperature changes. [Means for solving the problem]

[0006] A first embodiment for achieving this objective comprises a first element and a second element that convert chemical energy into electrical energy, wherein at least one of the first element and the second element changes electromotive force with temperature, and in a state where the first element and the second element are electrically insulated from each other, the difference in electromotive force before and after the temperature change of the first element is different from the difference in electromotive force before and after the temperature change of the second element.

[0007] In the second embodiment, the first element and the second element are connected in parallel after the temperature of at least one of the first element and the second element has changed, and the voltage difference between the first element and the second element is output as a current.

[0008] A third aspect is that, in the first or second aspect, the first element and the second element have the same sign in the slope of the temperature dependence of the electromotive force.

[0009] A fourth aspect is the first or second aspect wherein the first element and the second element have different signs in the slope of the temperature dependence of their electromotive force.

[0010] The fifth aspect is that, in any of the first to fourth aspects, at least one of the first element and the second element is placed in an environment in which the ambient temperature changes cyclically.

[0011] The sixth aspect is that, in any of the first to fifth aspects, at least one of the first element and the second element is covered with a material whose heat capacity is greater than the internal heat capacity.

[0012] The seventh aspect is that in any of the first to sixth aspects, at least one of the first element and the second element is a lithium-ion secondary battery. [Effects of the Invention]

[0013] According to the present invention, when the first element and the second element are electrically insulated from each other, the difference in electromotive force before and after a change in the temperature of the first element is different from the difference in electromotive force before and after a change in the temperature of the second element. Since the voltage difference between the first element and the second element that occurs in a temperature-changing environment can be output as a current, power generation can be easily performed in a temperature-changing environment. [Brief explanation of the drawing]

[0014] [Figure 1](a) is a schematic diagram of the thermoelectric converter in the first embodiment, (b) is a schematic diagram of the thermoelectric converter when the ambient temperature changes, and (c) is a schematic diagram of the thermoelectric converter when electrical energy is extracted. [Figure 2] This figure shows the temperature dependence of the electromotive force of the first and second elements. [Figure 3] (a) is a schematic diagram of the thermoelectric converter in the second embodiment, (b) is a schematic diagram of the thermoelectric converter when the ambient temperature changes, and (c) is a schematic diagram of the thermoelectric converter when electrical energy is extracted. [Figure 4] This figure shows the temperature dependence of the electromotive force of the first and second elements. [Figure 5] (a) is a schematic diagram of the thermoelectric converter in the third embodiment, and (b) is a schematic diagram of the thermoelectric converter when the ambient temperature changes. [Figure 6] This is the dQ / dv curve for the first element in the embodiment. [Figure 7] This figure shows the relationship between the voltage of the first element and the slope of the temperature dependence of the electromotive force. [Figure 8] This figure shows the change in the voltage difference between the first element and the second element. [Figure 9] This figure shows the change in the voltage difference between the first element and the second element. [Modes for carrying out the invention]

[0015] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1(a) is a schematic diagram of a thermoelectric converter 10 in the first embodiment. The thermoelectric converter 10 comprises a first element 11 and a second element 12. The thermoelectric converter 10 is placed in an environment in which the temperature of the first element 11 periodically changes between room temperature and low temperature, and the temperature of the second element 12 periodically changes between room temperature and high temperature, such as indoors where a high-temperature heat source and a low-temperature heat source are arranged. The first element 11 and the second element 12 are electrochemical elements that convert chemical energy into electrical energy.

[0016] Examples of electrochemical elements include rechargeable energy storage devices such as lithium-ion secondary batteries, lead-acid batteries, nickel-metal hydride batteries, electric double-layer capacitors, and asymmetric electrochemical capacitors, as well as primary batteries (energy storage devices) such as alkaline batteries and manganese batteries. The first element 11 and the second element 12 may each consist of a single electrochemical element, or multiple electrochemical elements may be connected in series, parallel, or in combination thereof.

[0017] The first element 11 and the second element 12 employ general-purpose electrochemical elements such as those found in energy storage devices. Conventional thermoelectric converters, including pn junctions, often use rare elements, including rare metals. Therefore, the thermoelectric converter 10, which uses general-purpose electrochemical elements, has advantages in that it can conserve natural resources and reduce the costs associated with rare metals.

[0018] The first element 11 and the second element 12 are circuit elements to which a conductor 13 is connected, and a switch 14 and a load 15 are connected to the conductor 13 to form a circuit. The switch 14 is a device for switching an electrical circuit on or off. The load 15 is any device that consumes the electrical energy emitted from the thermoelectric converter 10. Alternatively, a battery may be connected instead of the load 15, and the electrical energy emitted from the thermoelectric converter 10 may be stored in the battery. The first element 11 and the second element 12 are connected in parallel when the switch 14 connects the electrical circuit. Preferably, the thermoelectric converter 10 is equipped with a control device that operates the switch 14 according to changes in the thermal environment and the operating status of the thermoelectric converter 10, and a control device that monitors the temperature, current, and voltage of the first element 11 and the second element 12 and can safely shut them down as needed.

[0019] Figure 2 shows the temperature dependence of the electromotive force of the first element 11 and the second element 12. The electromotive force between the electrodes of the electrochemical elements constituting the first element 11 and the second element 12 is proportional to the change in the free energy of the electrochemical reaction.

[0020] Let E be the electromotive force (V) between the electrodes of an electrochemical element, n be the number of electrons involved in the electrochemical reaction, F be the Faraday constant (C / mol), T be the temperature (K), ΔH be the change in the enthalpy of the reaction (J / mol), ΔS be the change in the entropy of the reaction (JK , , A0 ,

[0022] ,

[0023] , , A1 , B0 mol -1 )、ΔG be the change in the Gibbs energy (J / mol) during discharge. Then, from ΔG = -nFE and ΔG = ΔH - TΔS, it is generally known that ΔS is calculated based on the temperature dependence of the electromotive force obtained by plotting the electromotive force E against the temperature T.

[0021] In the case of an electrochemical element with ΔS < 0, the sign of the slope ΔS / nF of the temperature dependence of the electromotive force is negative. An electrochemical element with ΔS < is exemplified by a lithium-ion secondary battery that uses LiNi 0.6 Mn 0.2 Co 0.2 O2 as the positive electrode active material, uses graphite as the negative electrode active material, and has a natural potential of 3.6V. In the case of an electrochemical element with ΔS > 0, the sign of the slope ΔS / nF of the temperature dependence of the electromotive force is positive. An electrochemical element with ΔS > 0 is exemplified by a lithium-ion secondary battery that uses LiNi 0.6 Mn 0.2 Co 0.2 O2 as the positive electrode active material, uses graphite as the negative electrode active material, and has a natural potential of 3.0V.

[0022] The first element 11 and the second element 12 have the same sign for the slope of the temperature dependence of the electromotive force. In this embodiment, both the first element 11 and the second element 12 have ΔS < 0 and the sign of the slope of the temperature dependence of the electromotive force is negative. However, it is of course possible to set both the first element 11 and the second element 12 to ΔS > 0 and make the signs of the slopes of the temperature dependence of the electromotive force both positive.

[0023] Returning to FIG. 1 for explanation. FIG. 1(b) is a schematic diagram of the thermoelectric conversion device 10 when the ambient temperature changes. Compared with the state of FIG. 1(a), the temperature of the periphery 16 of the first element 11 changes from T A0 (e.g., normal temperature) to T A1 and decreases, and the temperature of the periphery 17 of the second element 12 changes from T B0 (e.g., normal temperature) to TB1 The temperature is rising. As the ambient temperature changes in 16 and 17, the first element 11 releases heat to the ambient temperature 16, and because ΔS < 0, the electromotive force of the first element 11 is V A0 From V A1 It rises to V. Meanwhile, the second element 12 receives heat from the surroundings 17, and since ΔS < 0, the electromotive force of the second element 12 is V B0 From V B1 It decreases.

[0024] When the switch 14 is in the state where the electrical circuit is closed (the first element 11 and the second element 12 are electrically insulated from each other), the temperature of the first element 11 is T A0 From T A1 The difference V in electromotive force before and after the change. A1 -V A0 Then, the temperature of the second element 12 is T B0 From T B1 The difference V in electromotive force before and after the change. B1 -V B0 And are different.

[0025] Figure 1(c) is a schematic diagram of the thermoelectric converter 10 when electrical energy is extracted. After a difference in electromotive force is created between the first element 11 and the second element 12, the switch 14 connects the electrical circuit and connects the first element 11 and the second element 12 in parallel, V A1 -V A0 ≠V B1 -V B0 Therefore, a voltage difference ΔV is generated between the first element 11 and the second element 12. This allows electrical energy proportional to the voltage difference ΔV, which depends on the capacitance C of the first element 11 and the second element 12, to be supplied to the load 15.

[0026] After electrical energy is extracted from the thermoelectric converter 10, the switch 14 turns off the electrical circuit, and the state changes from Figure 1(c) to Figure 1(a). At this point, the temperature of the first element 11 is T A1 From T A0 The temperature rises to T, and the temperature of the second element 12 is T B1 From T B0The voltage decreases to V. The first element 11 receives heat from the surroundings 16, and the electromotive force of the first element 11 is V A1 From V A0 It decreases to V. Meanwhile, the second element 12 releases heat to the surroundings 17, and the electromotive force of the second element 12 is V B1 From V B0 It rises.

[0027] The difference V in electromotive force before and after the temperature of the first element 11 changes. A1 -V A0 The difference V in electromotive force before and after the temperature of the second element 12 changes. B1 -V B0 Because these are different, when the switch 14 connects the electrical circuit and connects the first element 11 and the second element 12 in parallel, electrical energy proportional to the voltage difference ΔV between the first element 11 and the second element 12 can be supplied to the load 15. Therefore, the thermoelectric converter 10 changes from the state in Figure 1(a) to the state in Figure 1(b) and then to the state in Figure 1(c), and then returns to the state in Figure 1(a), and by connecting the first element 11 and the second element 12 in parallel, it can output electrical energy equivalent to the capacitance C·ΔV once again. By connecting and disconnecting the switch 14 each time the temperature of the first element 11 and the second element 12 changes, electrical energy can be repeatedly extracted to the outside.

[0028] When the signs of the slopes ΔS / nF of the temperature dependence of the electromotive force of the first element 11 and the second element 12 are the same (Figure 2), it is preferable for the absolute value of the slope of the temperature dependence of the electromotive force of the first element 11 and the second element 12 to be large. This is because a larger absolute value of the slope of the temperature dependence of the electromotive force results in a larger voltage difference between the first element 11 and the second element 12 due to temperature changes, and therefore a larger amount of energy that can be extracted externally by thermoelectric conversion.

[0029] The slope ΔS / nF of the temperature dependence of the electromotive force of the first element 11 and the second element 12 does not need to be calculated at the temperature between two specific points. For example, the electromotive force at each temperature of n points (where n is an integer greater than or equal to 3) can be plotted, and the slope can be calculated by approximating the result with a straight line using the least squares method.

[0030] In the embodiment, the case was described in which the signs of the temperature dependence slopes of the electromotive force of the first element 11 and the second element 12 are the same, and the slopes of the temperature dependence slopes of the electromotive force of the first element 11 and the second element 12 are different (Figure 2), but it is not limited to this. They may be the same. It is also possible that one of the first element 11 and the second element 12 has a zero slope in the temperature dependence of its electromotive force (i.e., its electromotive force does not change with temperature). This is because if the electromotive force of the other element 11 changes with temperature, a voltage difference will occur between the first element 11 and the second element 12.

[0031] Temperature change T of the first element 11 A1 -T A0 and the temperature change T of the second element 12 B1 -T B0 The values ​​may be the same or different. Temperature change T of the first element 11 A1 -T A0 and the temperature change T of the second element 12 B1 -T B0 One of the elements may be at 0°C (no temperature change). Also, when the temperature of the first element 11 or the second element 12 changes periodically, the first element 11 or the second element 12 do not need to return to the same temperature or voltage as before the temperature change.

[0032] The internal resistance, charging capacity, and discharging capacity of the first element 11 may be the same as or different from those of the second element 12. However, in order to reduce losses when the first element 11 and the second element 12 output electrical energy, it is preferable that the internal resistance of the first element 11 and the second element 12 be small. The first element 11 and the second element 12 with small internal resistance are garnet-type Li7La3Zr2O 12 An example is a lithium-ion secondary battery in which an oxide-based solid electrolyte doped with Mg and Sr in (LLZ) is mixed with the positive electrode active material.

[0033] When the voltage difference between the first element 11 and the second element 12 is output as a current, it is preferable that the current value be small in order to reduce voltage drop and increase the efficiency of thermoelectric conversion. Furthermore, it is preferable that the time required to release electrical energy by connecting the electrical circuit and using the voltage difference between the first element 11 and the second element 12 is shorter than the time required for the first element 11 and the second element 12 to reach equilibrium temperature and equilibrium voltage in response to temperature changes in the environment surrounding the thermoelectric converter 10. This is because, when the thermoelectric converter 10 is placed in an environment where periodic temperature changes occur, a large amount of electrical energy is released before the voltage difference between the first element 11 and the second element 12 decreases due to temperature changes in the next cycle following the cycle in which the voltage difference between the first element 11 and the second element 12 was created.

[0034] Electromotive force V of the first element 11 A0 and the electromotive force V of the second element 12 B0 They may be the same or they may be different. Electromotive force V of the first element 11 A0 ,V A1 and the electromotive force V of the second element 12 B0 ,V B1 It is preferable that the differential capacitance dQ / dV of the first element 11 and the second element 12 is in a region where it shows a large value. This is because a large amount of electrical energy can be extracted when the temperature of the first element 11 and the second element 12 is changed to create a voltage difference. The differential capacitance dQ / dV can be determined from the charge-discharge curve obtained by plotting the potential V of the electrodes of the first element 11 and the second element 12 against the capacitance Q of the first element 11 and the second element 12.

[0035] It is preferable that the first element 11 and the second element 12 have low self-discharge. This is because if the voltage of the first element 11 and the second element 12 decreases due to self-discharge during long-term use, the voltage of the first element 11 and the second element 12 may deviate from the desired voltage, which may reduce the electrical energy obtained by thermoelectric conversion or cause the voltage of the first element 11 and the second element 12 to fall below the rated voltage. To prevent a decrease in the voltage of the first element 11 and the second element 12, it is preferable that the thermoelectric converter 10 is equipped with a charging device (not shown) for charging the first element 11 and the second element 12.

[0036] Examples of first and second elements 11 and 12, which have low self-discharge, include lithium-ion secondary batteries. Lithium-ion secondary batteries are widely used and have the advantage of being readily available as inexpensive used products. Lithium-ion secondary batteries can be used without restriction, including batteries containing electrolyte, all-solid-state batteries, and semi-solid-state batteries.

[0037] The first element 11 and the second element 12 do not need to be unused. For example, even used electrochemical elements with reduced performance that cannot be used in electric vehicles can be used as long as their internal resistance and self-discharge characteristics have not deteriorated significantly, safety is maintained, and there is no problem when performing thermoelectric conversion.

[0038] A second embodiment will be described with reference to Figures 3 and 4. In the first embodiment, the case where the signs of the temperature dependence slopes of the electromotive forces of the first element 11 and the second element 12 are the same was described. In contrast, in the second embodiment, a thermoelectric converter 20 in which the signs of the temperature dependence slopes of the electromotive forces of the first element 21 and the second element 22 are different will be described. In the second embodiment, the same reference numerals are used for the same parts as in the first embodiment, and the description of the same parts is omitted.

[0039] Figure 3(a) is a schematic diagram of the thermoelectric converter 20 in the second embodiment. The thermoelectric converter 20 comprises a first element 21 and a second element 22, which are electrochemical elements. The thermoelectric converter 20 is placed in an environment where the temperature around the first element 21 and the second element 22 changes periodically due to diurnal or seasonal variations, such as outdoors.

[0040] Figure 4 shows the temperature dependence of the electromotive force of the first element 21 and the second element 22. The first element 21 and the second element 22 have different signs in the slope of the temperature dependence of their electromotive force. In this embodiment, the first element 21 has a temperature dependence of ΔS < 0, so the sign of the slope of the temperature dependence of its electromotive force is negative. The second element 22 has a temperature dependence of ΔS > 0, so the sign of the slope of the temperature dependence of its electromotive force is positive.

[0041] Let's return to Figure 3 for explanation. Figure 3(b) is a schematic diagram of the thermoelectric converter 20 when the ambient temperature changes. Compared to the state in Figure 3(a), the temperature of the area 23 surrounding the first element 21 is T A0 (For example, from room temperature) A1 The temperature drops to T, and the temperature of the area 23 around the second element 12 is T B0 (For example, at room temperature) B1 The voltage is decreasing. As the temperature of the surrounding area 23 changes, the first element 21 releases heat to the surrounding area 23, and since ΔS < 0, the electromotive force of the first element 21 is V A0 From V A1 It rises to the . The second element 22 also releases heat to the surroundings 23, and since ΔS>0, the electromotive force of the second element 22 is V B0 From V B1 It decreases.

[0042] When the switch 14 is in the state where the electrical circuit is closed (the first element 21 and the second element 22 are electrically insulated from each other), the temperature of the first element 21 is T A0 From T A1 The difference V in electromotive force before and after the change. A1 -V A0 Then, the temperature of the second element 22 is T B0 From T B1 The difference V in electromotive force before and after the change. B1 -VB0 And are different.

[0043] Figure 3(c) is a schematic diagram of the thermoelectric converter 20 when electrical energy is extracted. After a difference in electromotive force is created between the first element 21 and the second element 22, the switch 14 connects the electrical circuit and connects the first element 21 and the second element 22 in parallel, V A1 -V A0 ≠V B1 -V B0 Therefore, a voltage difference ΔV is generated between the first element 21 and the second element 22. This allows electrical energy proportional to the voltage difference ΔV, which depends on the capacitance C of the first element 21 and the second element 22, to be supplied to the load 15.

[0044] After electrical energy is extracted from the thermoelectric converter 20, the switch 14 turns off the electrical circuit, and the state changes from the state in Figure 3(c) to the state in Figure 3(a). At this point, the temperature of the first element 21 is T A1 From T A0 The temperature rises to T, and the temperature of the second element 22 is T B1 From T B0 It rises to V. The first element 21 receives heat from the surroundings 23, and the electromotive force of the first element 21 is V A1 From V A0 The voltage decreases to V. The second element 22 also receives heat from the surroundings 23, and the electromotive force of the second element 12 is V. B1 From V B0 It rises.

[0045] The difference V in electromotive force before and after the change in ambient temperature of the first element 21. A1 -V A0 And the difference V in electromotive force before and after the temperature of the second element 22 changes. B1 -V B0Because these are different, when the switch 14 connects the electrical circuit and connects the first element 21 and the second element 22 in parallel, electrical energy proportional to the voltage difference ΔV between the first element 21 and the second element 22 can be supplied to the load 15. Therefore, the thermoelectric converter 20 changes from the state in Figure 3(a) to the state in Figure 3(b) and then to the state in Figure 3(c), and then returns to the state in Figure 3(a), and can output electrical energy again by connecting the first element 21 and the second element 22 in parallel. By connecting and disconnecting the switch 14 each time the temperature of the first element 21 and the second element 22 changes, electrical energy can be repeatedly extracted to the outside.

[0046] A third embodiment will be described with reference to Figure 5. In the first embodiment, the case was described in which the temperature of the first element 11 is varied between room temperature and low temperature, and the temperature of the second element 12 is varied between room temperature and high temperature, when the sign of the slope of the temperature dependence of the electromotive force of the first element 11 and the second element 12 is the same. In the third embodiment, a thermoelectric converter 30 will be described in which the temperatures of the first element 11 and the second element 12 are varied between room temperature and low temperature, when the sign of the slope of the temperature dependence of the electromotive force of the first element 11 and the second element 12 is the same. In the third embodiment, the same reference numerals are used for the same parts as in the first embodiment, and the description of the same parts is omitted.

[0047] Figure 5(a) is a schematic diagram of the thermoelectric converter 30 in the third embodiment. The thermoelectric converter 30 is placed in an environment where the temperature around the first element 11 and the second element 12 changes periodically, for example, due to diurnal or seasonal variations. The first element 11 is covered with a member 31 that has a larger heat capacity than the heat capacity of the first element 11. The member 31 is provided to reduce the temperature change of the first element 11 in response to temperature changes around the first element 11, and to increase the temperature difference between the first element 11 and the second element 12.

[0048] The member 31 includes, for example, a heat insulating material typified by a foamed material, a porous body, or a fiber material made of a synthetic resin, a vacuum heat insulating material made of a metal or glass, a liquid typified by water, and soil. The first element 11 can be covered with a jacket containing a liquid or a heat insulating material, or the first element 11 can be submerged in a liquid while ensuring waterproofing of the first element 11. The first element 11 may be buried in the ground while ensuring electrical insulation between the terminals of the first element 11. A heat shielding material that reflects or blocks radiant heat from the outside to the first element 11, such as a material having a metallic luster, may be used in combination with the member 31.

[0049] FIG. 5(b) is a schematic diagram of the thermoelectric conversion device 30 when the ambient temperature changes. Compared with the state of FIG. 5(a), the temperature of the periphery 32 of the first element 11 and the second element 12 has decreased. Since the first element 11 is covered with the member 31, the temperature change of the first element 11 can be reduced compared to the temperature change of the second element 12. When the second element 12 reaches the equilibrium temperature and the temperature of the first element 11 is changing, the difference between the temperature of the first element 11 and the temperature of the second element 12 can be increased. As a result, compared with the case where the member 31 is not present, the difference in voltage between the first element 11 and the second element 12 can be increased, so that the electrical energy that can be taken out to the outside can be increased.

Example

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

[0051] (Fabrication of Electrochemical Element) As the positive electrode active material, LiNi 0.6 Mn 0.2 Co 0.2A slurry was prepared by mixing O2, acetylene black as a conductive additive, and polyvinylidene fluoride dissolved in N-methylpyrrolidone as a binder, so that the ratio of active material, conductive additive, and binder in the solid content was 94:3:3 (by weight). The slurry was coated onto one side of the aluminum foil current collector using a table coater, dried, and then punched out into a 46 mm square. A tab lead was welded to the current collector to create the positive electrode. The weight of the active material in the coated slurry after drying was 19 mg / cm³. 2 That was the case.

[0052] A slurry was prepared by mixing graphite as the negative electrode active material, acetylene black as a conductive additive, carboxymethylcellulose as a thickener, and styrene-butadiene rubber dispersed in pure water as a binder, so that the ratio of active material, conductive additive, thickener, and binder in the solid content was 97.7:0.3:1.0:0.1 (by weight). The slurry was coated onto one side of the copper foil of the current collector using a table coater, dried, and then punched out into a 50 mm square. Tab leads were welded to the current collector to create the negative electrode. The weight of the active material in the coated slurry after drying was 10 mg / cm³. 2 That was the case.

[0053] The positive electrode and negative electrode active material coated surfaces were facing each other, with a polypropylene separator sandwiched between them, and the laminated components were housed in a laminated outer casing. LiPF6, the electrolyte, was dissolved in a solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a 1:1:1 (volume ratio) ratio to a concentration of 1 mol / L, and 1 wt% vinylene carbonate was added to prepare the electrolyte solution, which was then injected into the separator. After reducing the pressure, the excess electrolyte was removed, and the outer casing was sealed to obtain the first element consisting of a lithium-ion battery. A second element consisting of a lithium-ion battery was obtained by fabricating it in the same manner as the first element.

[0054] The first and second elements were connected to a charge / discharge device, and charge / discharge tests were conducted at 25°C. The results showed that the discharge capacity during constant current discharge (hereinafter referred to as "CC discharge") at a current value of 0.2C was 63mAh for both elements.

[0055] Figure 6 is the dQ / dV curve of the first element during discharge at a constant current of 0.2C. The first element showed a maximum value around 3.6V.

[0056] (Measurement of temperature change of electromotive force) First, the voltage was adjusted by constant current - constant voltage charging (hereinafter referred to as "CCCV charging") or CC discharge at 25°C so that the first element and the second element reached a predetermined voltage. When adjusting the voltage by CCCV charging, constant current charging was performed at a current value of 6.3 mA (0.1C). When the first element and the second element reached the predetermined voltage, the charging was switched to constant voltage charging, and the cut-off current value for the constant voltage charging was set to 0.63 mA (0.01C). When adjusting the voltage by CC discharge, discharging was performed at a current value of 0.63 mA (0.01C), and when the predetermined voltage was reached, the discharge was terminated, and it was repeated as necessary. In both cases of CCCV charging and CC discharge, after storing the first element and the second element after voltage adjustment in an open circuit state at 25°C for 3 days or more to stabilize the voltage, the temperature change of the electromotive force was measured.

[0057] The measurement of the temperature change of the electromotive force was referred to the description in Transactions of the Institute of Electrical Engineers of Japan, Vol. 122, No. 11, p. 1192, 2002. After storing the first element and the second element adjusted to the predetermined voltage in a constant temperature bath set at 10°C, 20°C, 30°C or 40°C for 30 minutes, the electromotive force at each temperature was measured. After plotting the measurement results against the temperature, the slopes of the temperature dependence of the electromotive force (V A1 -V A0 ) / (T A1 -T A0 ) and (V B1 -V B0 ) / (T B1 -T B0 ) were calculated. The above measurements were performed at voltages of 2.69V, 2.99V, 3.29V, 3.67V, and 4.17V.

[0058] Figure 7 shows the relationship between the voltage of the first element and the slope of the temperature dependence of the electromotive force. The relationship between the voltage of the second element and the slope of the temperature dependence of the electromotive force was almost the same as the result for the first element shown in Figure 7. For both the first and second elements, the absolute value of the slope of the temperature dependence of the electromotive force was 4.2 × 10⁻⁶ when the voltage was approximately 3.3V. -4 It was found that the V / K ratio was relatively large. Therefore, thermoelectric conversion experiments were conducted using the first and second elements with the voltage adjusted to 3.3V.

[0059] (Example 1) First, at 25°C, the positive terminals of the first and second elements were electrically connected to each other, and the negative terminals of the first and second elements were electrically connected to each other, so that the voltages between the first and second elements would be as equal as possible. After disconnecting the parallel connection between the first and second elements, the electromotive force was measured in the open-circuit state, and the electromotive force of the first element was 3.2853V, and the electromotive force of the second element was 3.2854V.

[0060] Next, the temperature of the first element was changed to 40°C and the temperature of the second element to 10°C, and these temperatures were maintained for more than 30 minutes. At this time, the electromotive force of the first element was 3.2790V and the electromotive force of the second element was 3.2915V, resulting in a voltage difference of 12.5mV between the first and second elements. Then, with a charge / discharge device interposed between the first and second elements, the first and second elements were connected in parallel, and constant current discharge was performed between the first and second elements at a current of 0.1mA until the voltage difference between the first and second elements became 0V.

[0061] Figure 8 shows the change in the voltage difference between the first and second elements. It was revealed that 0.994 mJ of electrical energy was extracted to the outside by the constant current discharge at this time.

[0062] Next, the positive terminals of the first and second elements were electrically connected to each other, and the negative terminals of the first and second elements were electrically connected to each other, so that the voltages between the first and second elements were made as similar as possible. The parallel connection between the first and second elements was then removed, and the electromotive force was measured in the open-circuit state. The electromotive force of the first element was 3.2847V, and the electromotive force of the second element was 3.2848V.

[0063] Next, the temperatures of both the first and second elements were changed to 25°C and held for 30 minutes. At this time, the electromotive force of the first element was 3.2906V and the electromotive force of the second element was 3.2792V, resulting in a voltage difference of 11.4mV between the first and second elements. Then, with a charge / discharge device interposed between the first and second elements, the first and second elements were connected in parallel, and constant current discharge was performed between the first and second elements at a current of 0.1mA until the voltage difference between the first and second elements became 0V.

[0064] Figure 9 shows the change in the voltage difference between the first and second elements. It is clear that 0.850 mJ of electrical energy was extracted to the outside by the constant current discharge at this time.

[0065] In Example 1, the temperature of the first element changed from 25°C to 40°C and then to 25°C, and the temperature of the second element changed from 25°C to 10°C and then to 25°C. It became clear that a total of approximately 1.84 mJ of electrical energy was extracted to the outside through the two temperature changes that occurred in the first and second elements during this cyclical temperature change process.

[0066] (Example 2) Thermoelectric conversion experiments were conducted using the first and second elements, whose voltages were adjusted to approximately 3.6V, the largest dQ / dV value within the measurement range shown in Figure 6. First, at 25°C, the positive terminals of the first and second elements were electrically connected to each other, and the negative terminals of the first and second elements were electrically connected to each other, so that the voltages between the first and second elements were made as similar as possible by connecting them in parallel. After disconnecting the parallel connection between the first and second elements, the electromotive force was measured in the open-circuit state. The electromotive force of the first element was 3.6739V, and the electromotive force of the second element was 3.6738V.

[0067] Similar to Example 1, the temperature of the first element was changed from 25°C to 40°C and then to 25°C, and the temperature of the second element was changed from 25°C to 10°C and then to 25°C. According to Example 2, a total of approximately 1.21 mJ of electrical energy was extracted to the outside through the two temperature changes that occurred in the first and second elements during this cyclical temperature change process.

[0068] Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention.

[0069] In this embodiment, the electrical connection and disconnection between the first elements 11, 21 and the second elements 12, 22 was described using a switch 14, but this is not necessarily the only way to connect or disconnect the two elements. It is certainly possible to omit the switch 14 and connect or disconnect the two elements by connecting or disconnecting conductors that electrically connect the first elements 11, 21 and the second elements 12, 22. It is also certainly possible to perform the operations of connecting and disconnecting conductors and operating the switch 14 manually. [Explanation of symbols]

[0070] 10, 20, 30 Thermoelectric converter 11,21 First element 12,22 Second element 31 components

Claims

1. It comprises a first element and a second element that convert chemical energy into electrical energy, At least one of the first element and the second element has an electromotive force that changes with temperature. A thermoelectric converter in which, when the first element and the second element are electrically insulated from each other, the difference in electromotive force before and after a change in the temperature of the first element is different from the difference in electromotive force before and after a change in the temperature of the second element.

2. The thermoelectric converter according to claim 1, wherein the first element and the second element are connected in parallel after the temperature of at least one of the first element and the second element has changed, and the voltage difference between the first element and the second element is output as a current.

3. The thermoelectric converter according to claim 1, wherein the first element and the second element have the same sign in the slope of the temperature dependence of their electromotive force.

4. The thermoelectric converter according to claim 1, wherein the first element and the second element have different signs in the slope of the temperature dependence of the electromotive force.

5. The thermoelectric conversion device according to any one of claims 1 to 4, wherein at least one of the first element and the second element is placed in an environment in which the ambient temperature changes cyclically.

6. The thermoelectric conversion device according to any one of claims 1 to 4, wherein at least one of the first element and the second element is covered with a material whose heat capacity is greater than the internal heat capacity.

7. The thermoelectric conversion device according to any one of claims 1 to 4, wherein at least one of the first element and the second element is a lithium-ion secondary battery.

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