TW202315211A - Humidity variation battery - Google Patents

Abstract

The present disclosure provides a humidity variation battery in which decreasing of output voltage over time is suppressed and therefore stable operation is provided. The humidity variation battery obtains an electromotive force by using humidity variation in the environment. The present invention is characterized in that an electrode and an aqueous electrolyte are provided to two sides separated by an ion-permeable membrane containing a fluorine resin, and the one side that is the first side is exposed to the environment, while the other side that is the second side is isolated from the environment on the ion-permeable membrane, wherein the aqueous electrolyte is an aqueous solution containing an ionic compound with deliquescence; the aqueous electrolyte contains water-soluble polymers, and permeation of water via the ion-permeable membrane is inhibited.

Description

Humidity Variation Battery

The present invention relates to a humidity fluctuation battery utilizing humidity fluctuation in the atmosphere, and more particularly to a humidity fluctuation battery having a structure separated by an ion exchange membrane and provided with an aqueous electrolyte containing a deliquescent material.

The humidity fluctuation battery is a battery that generates electricity by utilizing changes in humidity in the atmosphere, and is composed of an open cell exposed to the atmosphere, a closed cell that is closed, an ion exchange membrane that separates the two cells, and electrodes. In addition, an aqueous electrolyte solution containing deliquescent material is applied to the open cell and the closed cell, the concentration of the electrolyte solution in the open cell is changed according to the humidity in the air, and the concentration difference generated between the open cell and the closed cell is used to generate electricity ( Non-Patent Document 1).

However, as described above, in the humidity swing battery having the structure of separating the ion exchange membrane and providing the aqueous electrolyte solution containing the deliquescent material, the fluorine resin ion composed of the linear polymer and having high chemical stability can be used An exchange membrane is used for the ion exchange membrane.

For example, Patent Document 1 discloses a moisture-sensitive dew condensation element, which is separated by a fluorine resin ion-exchange membrane produced by DuPont under the trade name of Naflon N-110 and attached with electrodes. In such a component, the resistance value measured between the electrodes will decrease monotonically with the increase of the relative humidity in the atmosphere, and from The change in resistance value at 100% humidity to the resistance value due to condensation is rapid and large, and it can function as a switching element.

(Prior Art Literature)

(patent documents)

Patent Document 1: Japanese Patent Laid-Open No. 56-14147

(non-patent literature)

Non-Patent Document 1: "Energy harvesting by ambient humidity variation with continuous milliampere current output and energy storage", Y. Komazaki et al., Sustain. Energy Fuels, 2021,5, pp.3570-3577

Humidity fluctuation batteries can generate electricity locally by using humidity fluctuations in the environment and can omit the wiring for power transmission. Therefore, it is expected to operate without maintenance for a long time, for example, as a power supply for small sensors for IoT (Internet of Things) . On the other hand, it was observed that the output voltage of the battery due to humidity fluctuation tended to decrease over time.

The present invention has been made in view of the above-mentioned situation, and an object of the present invention is to provide a humidity fluctuation battery that suppresses the drop in output voltage over time and provides stable operation.

The inventors of this case conducted intensive research on the tendency of the output voltage of the humidity-fluctuating battery to decrease over time, and found that this is caused by the decrease in the mobility of the ion-exchange membrane and the movement of water through the ion-exchange membrane. And complete the present invention.

That is, the humidity fluctuation battery of the present invention obtains electromotive force by utilizing the humidity fluctuation in the environment; and make the first side of one side exposed to the aforementioned environment, and the second side of the other side is isolated from the aforementioned environment on the aforementioned ion-permeable membrane, wherein the aforementioned aqueous electrolyte is composed of a deliquescent ionic compound Aqueous solution; the aforementioned aqueous electrolytic solution contains water-soluble polymers, and inhibits the permeation of water through the aforementioned ion-permeable membrane.

According to the above-mentioned features, in the process of extracting the electromotive force by generating an ion concentration difference by causing the ions derived from the ionic compound to migrate between the first side and the second side through the ion permeable membrane due to the humidity fluctuation in the environment, the The mobility of the ion permeation membrane is improved, and the voltage obtained by electromotive force is increased, and the temporal decrease of the voltage can be suppressed.

1: open slot

2: closed slot

3: Ion permeable membrane

4a, 4b: electrodes

9a, 9b: Aqueous electrolyte

10: Humidity change battery

11: The first plate body

12: Second plate body

14: Gasket

Fig. 1 is a sectional view of a humidity variable battery as an embodiment of the present invention.

FIG. 2 is a graph of open circuit voltage when a humidity fluctuation is applied to a humidity fluctuation battery using polyethylene glycol as a water-soluble polymer.

Fig. 3 is a graph showing the open circuit voltage when a humidity fluctuation is applied to a humidity fluctuation battery using (a) polyethylene glycol dimethyl ether and (b) 18-crown-6 ether as water-soluble polymers.

Fig. 4 is a graph of an open circuit voltage when a humidity fluctuation is applied to a humidity fluctuation voltage obtained by changing a water-soluble polymer.

Fig. 5 is a graph showing open circuit voltage when a humidity fluctuation is applied to a humidity fluctuation battery using a hydrocarbon-based cation exchange membrane as an ion permeable membrane.

Hereinafter, a humidity variable battery as an embodiment of the present invention will be described with reference to FIG. 1 .

As shown in FIG. 1 , in a humidity variable battery 10 , aqueous electrolytic solutions 9 a and 9 b are provided on both sides separated by an ion permeable membrane 3 . For the ion permeable membrane 3, a fluororesin which is a hydrophilic linear polymer not having a crosslinked structure is used. The aqueous electrolytic solution 9 a on one side partitioned by the ion permeable membrane 3 is accommodated in the open tank 1 and communicates with the outside of the humidity variable battery 10 . The aqueous electrolytic solution 9b on the other side is housed in the closed tank 2 and sealed from the outside. That is, the open tank 1 is exposed to the environment, while the closed tank 2 is isolated from the environment. In addition, as long as the open tank 1 can exchange water with the outside, a cover formed of a membrane or the like that allows water vapor to permeate but does not permeate the aqueous electrolytic solution 9a may be provided. Since the outflow of the aqueous electrolytic solution 9a in the open tank 1 to the outside can be suppressed, handling of the humidity fluctuation battery 10 can be facilitated.

Moreover, the open tank 1 is equipped with the electrode 4a, and is in contact with the aqueous electrolytic solution 9a. Likewise, the closed tank 2 is provided with an electrode 4b and is in contact with an aqueous electrolytic solution 9b. The electrodes 4a and 4b are connected to wiring for extracting an electromotive force generated between these electrodes to the outside.

The aqueous electrolytic solutions 9a and 9b are aqueous electrolytic solutions of deliquescent ionic compounds. By communicating with the outside in the open tank 1, moisture is absorbed or discharged according to humidity fluctuations in the environment to change the ion concentration of the aqueous electrolytic solution 9a. In addition, as an ionic compound having deliquescent properties, for example, halides such as chlorides and bromides can be suitably used. For example, when lithium chloride is used as the ionic compound, a higher voltage can be suitably obtained. In addition, when chlorides such as lithium chloride are used as the ionic compound, silver-silver chloride electrodes can be suitably used as the electrodes 4a, 4b. In this case, the internal resistance of the humidity variable battery 10 can be set to 10 ohms or less. Details will be stated later, the aqueous electrolyte solutions 9a and 9b contain water-soluble polymers.

Here, the second plate body 12 and the first plate body 11 are sequentially laminated to form a battery unit (cell) for obtaining the humidity variable battery 10 , the second plate body 12 is provided with a recess for forming the closed groove 2 , The first plate body 11 is provided with a through hole for forming the open groove 1 . The first plate 11 and the second plate 12 are sealed with a gasket 14 formed of adhesive, and the outer periphery of the ion permeable membrane 3 is fixed to the first plate 11 and the second plate 12 .

The humidity fluctuation battery 10 generates electricity as follows. For example, when a cation-exchange membrane is used as an ion-permeable membrane system, the cation-exchange membrane system has a porous structure and has a large number of negatively charged fixed-charge groups in the membrane. Due to the presence of negative fixed charge groups, cations derived from ionic compounds can easily penetrate into the membrane, but anions of the same polarity cannot penetrate into the membrane due to electrostatic repulsion, and ion permeability selectivity can be obtained.

Furthermore, when the external humidity of the humidity variable battery 10 is low, the aqueous electrolyte solution 9a in the open cell 1 discharges moisture into the environment, thereby increasing the concentration of cations obtained by dissolving the ionic compound. In this way, the cations will migrate towards the aqueous electrolyte solution 9b in the closed tank 2 with a relatively low concentration, using the concentration difference as the driving force to permeate the ion-permeable membrane 3 for migration.

As a result, in the open cell 1, the anions in the aqueous electrolytic solution 9a become excessive compared with the cations, react with the electrode 4a and generate electrons to obtain a balance. On the other hand, in the closed tank 2, the anions in the aqueous electrolytic solution 9b become less than the cations, and electrons are supplied to the electrode 4b and decomposed to generate anions to obtain balance. Thereby, electromotive force can be extracted in the external circuit which connects the electrode 4a and the electrode 4b. In other words, an electromotive force is obtained by causing a concentration difference of ions in the aqueous electrolyte solutions 9 a and 9 b (that is, a concentration difference of the electrolyte solutions) due to changes in humidity in the environment. In addition, when the external humidity of the humidity variable battery 10 is set to be high, contrary to the above, cations will permeate the ion permeable membrane 3 from the aqueous electrolyte solution 9b in the closed tank 2 toward the aqueous electrolyte solution 9a in the open tank 1, and the ion permeable membrane 3 can be obtained. electromotive force in the opposite direction.

When the electromotive force is obtained by using the concentration difference of the electrolyte as described above, when the concentration difference of the electrolyte decreases regardless of the battery operation other than discharging, that is, self-discharging, energy loss will be caused. Self-discharge as described above was also confirmed in the humidity fluctuation battery. In the humidity fluctuation battery, the reduction of the concentration difference of the electrolyte not caused by the battery operation caused by discharge is mainly caused by the migration of water from the lower ion concentration of the aqueous electrolyte to the higher one. In other words, water penetrates the ion-permeable membrane by means of osmotic pressure. As mentioned above, the ion permeable membrane system has permselectivity to ions, but the electrostatic force cannot be applied to the uncharged water molecules, but allows the migration through the porous pores. Therefore, moisture permeability is imparted to the ion permeable membrane, and the concentration difference of ions decreases irrespective of the battery operation of discharge. As a result, the output voltage of the battery due to humidity fluctuations tends to decrease over time.

Therefore, in the humidity variable battery 10 of this embodiment, the aqueous electrolytic solutions 9 a and 9 b contain water-soluble polymers as described above. The permeation of water through the ion permeable membrane can be inhibited by the water-soluble polymer. For example, it is speculated that adding water to water-soluble polymers increases the apparent molecular weight of water, increases the viscosity of the aqueous electrolyte, or uses water-soluble polymers to block the pores of the ion-permeable membrane to inhibit water penetration. Therefore, it is thought that the water-soluble polymer preferably has an appropriate size (molecular weight) corresponding to the pores of the ion permeable membrane.

Furthermore, since the ion permeable membrane 3 has permeation selectivity for ions by having a fixed charge, it is preferable that the water-soluble polymer does not affect the effect of the charge. Specifically, an electrically neutral polymer is preferable rather than a positively charged polycation or a negatively charged polyanion. As such a water-soluble polymer, for example, polyethylene glycols or crown ethers can be suitably used.

As described above, according to the humidity fluctuation battery 10, in the process of extracting electromotive force due to the difference in ion concentration generated between the open tank 1 and the closed tank 2 by utilizing the humidity fluctuation in the environment, it is possible to suppress water penetration and separation. The sub-permeable membrane 3 can increase the mobility of ions derived from ionic compounds. As a result, the voltage obtained by the electromotive force increases, and its voltage drop over time can be suppressed.

〔Manufacturing test〕

The results of actually manufacturing the above-mentioned humidity fluctuation battery and investigating its performance will be described using FIGS. 2 to 5 .

[Test 1]

As shown in Figure 2(a) to (d), a humidity fluctuation battery using PEG (polyethylene glycol) as a water-soluble polymer was produced, and the change in electromotive force obtained when the addition amount and molecular weight was changed was investigated.

Specifically, Nafion (registered trademark) 117, which is a membrane body made of fluororesin, was used as the ion permeable membrane, and lithium chloride aqueous solution was used as the aqueous electrolyte. Add 0.75mL of the above-mentioned aqueous electrolyte to the open tank and the closed tank individually, and add a water-soluble mass % polymer. The water-soluble polymer added, the average molecular weight is set to five kinds of 200 (PEG200), 400 (PEG400), 1000 (PEG1000), 2000 (PEG2000), 4000 (PEG4000), and the addition amount is calculated as 1% by mass %, 2%, 5%, and 10% (wt% in the figure is synonymous with mass%). A humidity fluctuation battery was manufactured as described above. These humidity fluctuation batteries were placed in a constant temperature and humidity chamber, and the humidity was alternately varied between 30% and 90% every four hours, and the open circuit voltage was measured.

When the molecular weight was 200, it was confirmed that it was substantially the same as that measured separately without adding the water-soluble polymer. In addition, as shown in the figure, it was confirmed that the voltage increases when the molecular weight is 400 or more, and the voltage increase becomes larger as the molecular weight increases. On the other hand, even if the addition amount of the water-soluble polymer was increased, the voltage increase range was only slightly. It is presumed that when the addition amount of the water-soluble polymer is 2% by mass, the voltage boosting effect is almost saturated.

[Test 2]

As shown in Figure 3, the water-soluble polymer system uses (a) polyethylene glycol dimethyl ether (PEGDME500; average molecular weight: 500), (b) 18-crown-6 ether (18-C-6; molecular weight: 264 ) to manufacture the humidity change battery, and measure the open circuit voltage in the same way. Both the water-soluble polymers (a) and (b) were added to the water-soluble electrolytic solution at 10% by mass. Other than that, it was the same as Experiment 1. As a result, the open circuit voltage of any of them was equal to or higher than that of PEG2000 or PEG4000 in Test 1. That is, with these polyethylene glycol derivatives, even if the molecular weight is lower than that of polyethylene glycol, a high voltage boosting effect can be obtained.

[Test 3]

As shown in Figure 4, for water-soluble polymers, 10 mass % of (a) polyethylene glycol (PEG20000; average molecular weight 20000) was added, and 2 mass % of (b) polyvinyl alcohol (PVA; average molecular weight 66000 ~79200), add 3.5% by mass of (c) polydiallyldimethylammonium chloride (PDDA; average molecular weight below 100,000), add 10% by mass of (d) polyacrylic acid (PAA; average molecular weight 5000 ) were manufactured in the same manner as the humidity fluctuation battery and measured the open circuit voltage. However, the humidity change was applied every 8 hours. In contrast to the voltage of 90 mV or higher obtained with PEG20000, only about 20 mV of voltage was obtained with PDDA, which is a polycation, and PAA, which is a polyanion. Even in PVA, which is generally not regarded as a polycation and has a large number of OH groups, only about 20 mV of voltage is obtained. In other words, it is presumed that the water-soluble polymer is preferably one that can obtain a higher voltage if it is an electrically neutral polymer.

[Test 4]

In the above test, the water-soluble polymer was changed, but in Test 4, the ion permeable membrane was Neosepta CSE (manufactured by Astom Co., Ltd.), which is a hydrocarbon-based cation exchange membrane. The other lines are the same as in Experiment 1.

As shown in FIG. 5 , only a voltage of about 30 mV was obtained in both cases where 10 mass % of (a) PEG2000 and 10 mass % of (b) PEG4000 were added to the water-soluble polymer system. in test In 1, a voltage of about 80~90mV can be obtained as long as fluorine resin is used for the ion permeable membrane. However, since the ion permeable membrane is changed to a hydrocarbon-based cation exchange membrane, the obtained voltage becomes lower. That is, it is advantageous to use a fluororesin for the ion permeable membrane.

Above, the representative embodiment of the present invention has been described, but the present invention is not necessarily limited thereto, as long as it is a person with common knowledge in the technical field of the present invention without departing from the gist of the present invention or the scope of the appended patent application. Various alternative embodiments and modifications are found.

1: open slot

2: closed slot

3: Ion permeable membrane

4a, 4b: electrodes

9a, 9b: Aqueous electrolyte

10: Humidity change battery

11: The first plate body

12: Second plate body

14: Gasket

Claims (6)

A humidity fluctuation battery, which obtains electromotive force by using the humidity fluctuation in the environment; in the humidity fluctuation battery, The electrode and the aqueous electrolyte are applied to both sides separated by the ion-permeable membrane containing fluororesin, and the first side of one is exposed to the aforementioned environment, and the second side of the other is exposed to the aforementioned ion-permeable membrane. isolated from the aforementioned environment, wherein the aforementioned aqueous electrolyte is an aqueous solution containing deliquescent ionic compounds; The aforementioned aqueous electrolyte contains water-soluble polymers to inhibit water from permeating through the aforementioned ion-permeable membrane. The humidity variable battery according to claim 1, wherein the water-soluble polymers are polyethylene glycols or crown ethers. The humidity fluctuation battery according to claim 1 or 2, wherein the ionic compound is chloride. The humidity fluctuation battery according to claim 3, wherein the chloride is lithium chloride. The humidity fluctuation battery according to claim 3 or 4, wherein the aforementioned electrode is a silver-silver chloride electrode. The humidity fluctuation battery according to any one of claims 3 to 5, wherein the internal resistance is 10 ohms or less.

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