Power generation element

Abstract

The present invention provides a power generation element which is capable of achieving a larger electromotive force by utilizing humidity fluctuations in the environment. The present invention specifically provides a power generation element which generates electric power by utilizing humidity change due to water vapor in the environment. According to the present invention, a first chamber that is blocked from water vapor in the environment and a second chamber that is opened to water vapor in the environment are separated from each other by means of an ion permeable membrane, and are subsequently filled with an aqueous electrolyte that is composed of an aqueous solution of a deliquescent ionic compound, respectively. Meanwhile, the first chamber and the second chamber are respectively provided with electrodes. The ion permeable membrane is composed of an electrolyte which is capable of conducting ions which are not hydrated.

Description

Power generating element

[0001] The present invention relates to a power generating element that generates electricity or detects changes in humidity by utilizing electromotive force caused by humidity fluctuations in the environment.

[0002] Humidity fluctuation batteries as power generation elements are environmental power generation elements that generate electricity using changes in humidity in the environment, and are capable of operating in a wide range of environments where humidity fluctuations occur.Therefore, they are expected to be used, for example, as power sources for IoT-related devices that may be installed in large numbers in various locations.

[0003] For example, Patent Document 1 discloses one structure of such a humidity fluctuation battery. An aqueous solution of a deliquescent ionic compound is separated by an ion-permeable membrane, and electrodes are inserted on either side of the membrane. One side of the ion-permeable membrane is sealed and isolated from the outside air, while the other side is connected to the outside air. Humidity changes in the outside air can cause a difference in ion concentration resulting from the ionic compound in the aqueous solution sandwiched between the ion-permeable membrane, generating an electromotive force between the electrodes.

[0004] Japanese Patent Application Laid-Open No. 2022-99092

[0005] In commonly used batteries, self-discharge causes a voltage drop over time, and reducing this drop can achieve long-term operational stability. Typically, the timescale for this voltage drop is several months to several years. On the other hand, in humidity-fluctuating batteries, self-discharge acts to immediately reduce the concentration difference of ionic compounds in the aqueous solution sandwiched between the ion-permeable membrane due to humidity changes. In other words, the formation of a concentration difference due to humidity changes and the disappearance of the concentration difference due to self-discharge occur simultaneously, so the resulting voltage is not very high. Therefore, for use as a power source for IoT-related devices, it is necessary to obtain sufficient power for practical use. In other words, it is important to be able to generate a large electromotive force even with slight humidity fluctuations in the environment.

[0006] The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a power generating element that can generate a larger electromotive force when generating electricity or detecting a change in humidity by utilizing the electromotive force caused by humidity fluctuations in the environment.

[0007] The present inventors have conducted extensive research into the low electromotive force of existing power generating elements in practical use and have discovered that this is due to the movement of water in the ion-permeable membrane, leading to the present invention.

[0008] That is, the present invention is a power generation element that generates electricity by utilizing humidity changes due to water vapor in the environment, characterized in that a first chamber that is isolated from the water vapor in the environment and a second chamber that is open to the water vapor in the environment are separated by an ion-permeable membrane, and each chamber is filled with an aqueous electrolyte solution consisting of an aqueous solution of an ionic compound that has deliquescent properties, and each chamber is provided with an electrode, and the ion-permeable membrane is made of an electrolyte that can conduct unhydrated ions.

[0009] According to this feature, the movement of water in the ion-permeable membrane can be suppressed, and it becomes possible to generate a larger electromotive force than ever before as a power generating element that utilizes the humidity in the environment, i.e., fluctuations in water content.

[0010] In the above-described invention, the electrolyte may be made of a water-resistant ion-conductive glass-ceramic. The water-resistant ion-conductive glass-ceramic may be made of a LATP solid electrolyte having a LISICON-type crystal structure. This feature chemically stabilizes the ion-permeable membrane, enabling stable operation over a long period of time by utilizing humidity fluctuations in the environment.

[0011] In the above invention, the ion-permeable membrane may be a composite of a support made of a foam material and the electrolyte. The foam material may be made of foamed fluororubber. This feature physically stabilizes the ion-permeable membrane, enabling it to operate stably for a long period of time by utilizing humidity fluctuations in the environment.

[0012] In the above invention, the second chamber may be isolated from the environment by a moisture-permeable membrane that allows water vapor to pass through, and the area of ​​the moisture-permeable membrane exposed to the environment may be larger than the area of ​​the ion-permeable membrane that separates the first chamber and the second chamber. This feature improves the rate at which water vapor in the environment is absorbed and released into the environment, enabling the generation of an electromotive force that responds quickly to changes in humidity in the environment.

[0013] 1 is a cross-sectional view of a humidity fluctuation battery according to the present invention. 2 is an exploded perspective view of a humidity fluctuation battery used in a production test. 3 is a cross-sectional view showing the production process of the humidity fluctuation battery. 4 is a cross-sectional view showing the production process of the humidity fluctuation battery. 5 is a cross-sectional view showing the production process of the humidity fluctuation battery. 6 is a cross-sectional view showing the production process of the humidity fluctuation battery. 7 is a cross-sectional view showing the production process of the humidity fluctuation battery. 8 is a graph of the voltage generated when humidity fluctuations are applied to the humidity fluctuation battery.

[0014] Hereinafter, a power generating element according to one embodiment of the present invention will be described with reference to FIG.

[0015] As shown in Figure 1, the humidity fluctuating battery 10 serving as a power generation element includes a closed tank 1 serving as a first chamber filled with an aqueous electrolyte solution (aqueous electrolyte) 9a and isolated from water vapor in the environment, and an open tank 2 serving as a second chamber filled with an aqueous electrolyte solution 9b and open to water vapor in the environment. The closed tank 1 and the open tank 2 are separated from each other by an ion-permeable membrane 3. Electrodes 4a and 4b are inserted into the closed tank 1 and the open tank 2 so as to contact the electrolyte solutions 9a and 9b, respectively. The electrodes 4a and 4b are connected to wiring 5a and wiring 5b for extracting the electromotive force generated between them to the outside.

[0016] The electrolyte solutions 9a and 9b are aqueous solutions of deliquescent ionic compounds. Therefore, when exposed to water vapor in the open tank 2, the electrolyte solution 9b absorbs or releases moisture due to changes in the humidity of the outside air, changing the ion concentration. Furthermore, chlorides, for example, can be suitably used as the deliquescent ionic compound. The open tank 2 is isolated from the outside by, for example, a waterproof / breathable membrane to allow exchange of water vapor with the outside. This prevents leakage of the electrolyte solution 9b while leaving the open tank 2 exposed to water vapor in the environment. It is preferable that the area of ​​the waterproof / breathable membrane exposed to the environment is larger than the area of ​​the ion-permeable membrane 3 separating the closed tank 1 and the open tank 2, as this improves the rate of absorption of water vapor from the environment and release of water vapor into the environment.

[0017] By configuring as described above, the humidity-fluctuating battery 10 can change the ion concentration in the open tank 2 in response to fluctuations in humidity in the environment, and generate electricity by performing ion exchange between the open tank 2 and the closed tank 1 using the difference in ion concentration as a driving force.

[0018] In such humidity-fluctuating batteries, for example, an ion-exchange membrane that allows hydrated cations to pass through is used as the ion-permeable membrane. The electrostatic repulsion of the fixed negative charge within the membrane prevents anions from penetrating the membrane, allowing only cations to pass through selectively in a hydrated (solvated) state. However, such cation-exchange membranes have some water permeability due to the water contained within them. Osmotic pressure causes water to pass through in a direction that reduces the ion concentration difference between the open and closed compartments, resulting in self-discharge. Furthermore, such ion-exchange membranes that conduct hydrated cations exhibit reduced ion selectivity for electrolytes with concentrations exceeding the fixed negative charge density, allowing anions to pass through as well. In the case of humidity-fluctuating batteries, depending on the humidity, such electrolytes may become highly concentrated, resulting in reduced output.

[0019] Therefore, in the humidity fluctuation battery 10 of this embodiment, an electrolyte capable of conducting non-hydrated ions (non-hydrated ions) is used as the ion-permeable membrane 3. In other words, it is an ion-permeable membrane without water. With such an electrolyte, it is not necessary to contain water within the ion-permeable membrane 3, and water permeation due to osmotic pressure can be prevented. By suppressing water movement in the ion-permeable membrane 3, it is possible to suppress the decrease in concentration difference due to self-discharge and to generate a large electromotive force by utilizing humidity fluctuations in the environment. Furthermore, an electrolyte that conducts non-hydrated ions can exhibit high ion selectivity (cation transference number) regardless of the concentration of the electrolyte. This effect also allows the humidity fluctuation battery 10 to obtain higher voltage and higher output than humidity fluctuation batteries that use a cation exchange membrane that conducts hydrated ions.

[0020] Such an electrolyte may be, for example, a water-resistant ion-conductive glass ceramic. The water-resistant ion-conductive glass ceramic may be, in particular, a LATP (Li ion-conductive poly(trimethylsilyl phosphate)) having a LISICON (lithium superionic conductor) type crystal structure with high water resistance. １．４ Al ０．４ Ti １．６ (P.O. ４ ) ３ ) solid electrolytes can be preferably used, which can chemically stabilize the ion-permeable membrane 3.

[0021] The ion-permeable membrane 3 is fixed in the humidity fluctuating battery 10 by being sandwiched between a lower support 6a and an upper support 6b. It is preferable to use a foam material as the lower support 6a and the upper support 6b to form a composite containing an electrolyte, since this prevents damage to the ion-permeable membrane 3 made of a fragile, water-resistant, ion-conductive glass ceramic and physically stabilizes the ion-permeable membrane 3. The lower support 6a and the upper support 6b also serve as sealing materials for sealing in the electrolyte solutions 9a and 9b, respectively. For example, foamed fluororubber can be suitably used as such a foam material.

[0022] [Fabrication Test] Next, an example of fabricating the humidity fluctuating battery 10 according to this example will be described.

[0023] First, a method for fabricating the humidity fluctuating battery 10 will be described with reference to FIGS.

[0024] As shown in FIG. 2, the humidity fluctuating battery 10 can be fabricated by laminating a closed-chamber housing 11 and an open-chamber housing 12 made of resin together with other components, and welding them together.

[0025] Referring also to FIG. 3A , a rectangular annular lower support 6a with a 24 x 24 mm opening was placed inside the closed vessel housing 11, which was made of black ABS resin and had a dish-like shape with a roughly rectangular depression in the center. The lower support 6a was a fluororubber sponge with a hardness of 48 (type A durometer). 0.15 mL of a 20 wt % lithium chloride aqueous solution was poured into the opening of the lower support 6a, which became the closed vessel 1, and the electrode 4a was immersed in it. The electrode 4a was made by printing a mesh of silver paste on both sides of 23 x 23 mm filter paper, baking it, and anodizing it in an aqueous solution containing chloride ions to convert some of the silver to silver chloride. A gold-plated silver wire was then attached to the surface as the wiring 5a. A 1-inch square, 20 μm thick LATP solid electrolyte membrane was placed as the ion-permeable membrane 3 to close the opening. An upper support 6b with the same planar shape as the lower support 6a was then placed on top of it. The upper support 6b is a fluororubber sponge having a hardness of 12 (type A durometer).

[0026] As shown in Figure 3B, an open-tank housing 12 made of transparent polymethyl methacrylate resin was placed on top of the upper support 6b, and a load was applied from above. As a result, the open-tank housing 12 crushes the upper support 6b and the lower support 6a, and its outer periphery abuts against the closed-tank housing 11. The open-tank housing 12 has an opening on its lower side that is the same size as the opening of the upper support 6b, and an opening on its upper side that is wider. This allows the area of ​​the upper opening to be larger than the area of ​​the ion-permeable membrane 3 that separates the closed tank 1 and the open tank 2.

[0027] As shown in Figure 3C, the closed-tank housing 11 and the open-tank housing 12 were fixed together by laser welding while maintaining the load. Other methods of fixation may also be used, such as adhesives, double-sided tape, hot melt adhesives, and ultrasonic welding. The laser passes through the transparent open-tank housing 12 and is irradiated onto the black closed-tank housing 11, heating the surface of the closed-tank housing 11 that contacts the open-tank housing 12, thereby welding the two thermoplastic resins together. At this time, the wiring 5a was routed to the outside through the gap between the closed-tank housing 11 and the lower support 6a, and between the closed-tank housing 11 and the open-tank housing 12.

[0028] 3D, 0.225 mL of a 20 wt % aqueous solution of lithium chloride as electrolyte 9b was poured into the lower opening of open-tank casing 12, which would become open-tank 2, and the opening of upper support 6b, and electrode 4b was immersed in the electrolyte 9b. Electrode 4b was the same as electrode 4a.

[0029] Finally, as shown in Figure 3E, a waterproof / moisture-permeable membrane 13 made of a porous fluororesin film and a mesh sheet 14 made of a PET film with honeycomb-shaped openings were installed to cover the top opening of the open-chamber housing 12. The waterproof / moisture-permeable membrane 13 and mesh sheet 14 were attached to the open-chamber housing with double-sided tape. The waterproof / moisture-permeable membrane 13 prevents leakage of the electrolyte solution 9b and the intrusion of other liquids while leaving the open-chamber 2 open to water vapor in the environment. The mesh sheet 14 is installed to prevent the intrusion of solid matter from the outside. Mesh sheets can also be made of mesh bodies or perforated sheets made of various plastic or metal materials. Furthermore, the wiring 5b was routed to the outside through the gap between the waterproof / moisture-permeable membrane 13 and the open-chamber housing 12. This resulted in the production of a humidity-fluctuating battery 10.

[0030] Next, a test was conducted to examine the performance of the humidity fluctuating battery 10 thus fabricated, and the results will be described.

[0031] Figure 4 shows the results of measuring the open-circuit voltage when a humidity fluctuation battery 10 fabricated as an example was subjected to a humidity change. The humidity fluctuation battery 10 was placed in a constant-temperature, constant-humidity chamber and subjected to a humidity change that alternated between 30% and 90% every four hours. As a comparative example, a humidity fluctuation battery using a conventional cation exchange membrane (Nafion (registered trademark) 117) instead of the ion-permeable membrane 3 was also tested. As a result, the example obtained a higher voltage than the comparative example at both 30% and 90% humidity. The comparative example exhibited self-discharge behavior, in which the voltage gradually decreased after reaching a peak, whereas the example did not. In other words, the humidity fluctuation battery 10, which uses an electrolyte that conducts non-hydrated ions as the ion-permeable membrane 3, can suppress voltage drop due to self-discharge by preventing moisture penetration between the closed chamber 1 and the open chamber 2, and can be used as an energy-generating element for IoT-related devices and other devices that can generate a large electromotive force.

[0032] The humidity fluctuation battery 10 can also be used as a humidity fluctuation detection sensor, particularly as a humidity fluctuation detection sensor that operates without a power source. As shown in Figure 4, the output voltage changes slowly over time with respect to changes in humidity, and unlike, for example, a resistance change type humidity sensor, it is possible to directly output the average humidity fluctuation value in the environment without signal processing.

[0033] Although typical embodiments of the present invention have been described above, the present invention is not necessarily limited thereto, and those skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the appended claims.

[0034] 1 Closed tank (first chamber) 2 Open tank (second chamber) 3 Ion permeable membrane 4a, 4b Electrode 9a, 9b Electrolyte 10 Humidity variable battery

Claims

1. A power generation element that generates electricity by utilizing humidity changes caused by water vapor in the environment, The device comprises a first chamber isolated from the water vapor in the environment and a second chamber open to the water vapor in the environment, separated by an ion-permeable membrane, and each chamber filled with an aqueous electrolyte consisting of an aqueous solution of a deliquescent ionic compound, and electrodes provided in each chamber. The ion-permeable membrane is made of an electrolyte capable of conducting unhydrated ions, The power generation element is characterized in that the electrolyte is made of water-resistant ion-conducting glass ceramic.

2. The power generation element according to Claim 1, characterized in that the water-resistant ion-conducting glass ceramic is made of a LATP solid electrolyte having a LISICON-type crystal structure.

3. The power generation element according to claim 1, characterized in that the ion permeable membrane is a composite comprising the electrolyte on a support made of a foamed material.

4. The power generation element according to claim 3, characterized in that the foamed material is made of foamed fluororubber.

5. The power generation element according to claim 1, characterized in that the second chamber is separated from the environment by a moisture-permeable membrane that allows water vapor to pass through, and the area of ​​the moisture-permeable membrane exposed to the environment is larger than the area of ​​the ion-permeable membrane separating the first chamber and the second chamber.