JP2021093260A - Air electrode and metal-air battery - Google Patents

Abstract

To provide an air electrode capable of obtaining an excellent battery characteristic.SOLUTION: A metal-air battery 1 comprises an air electrode 10 having a collector 13, a catalyst layer 12, and a water-repellent film 11. An air permeability of the water-repellent film 11 is set to 1900 to 9000 seconds/100 cc. The air permeability of the catalyst layer 12 is set to 400 seconds/100 cc or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to an air electrode and a metal-air battery provided with a current collector, a catalyst layer, and a water repellent film.

In recent years, various batteries using the chemical reaction of metal for electrodes have been put into practical use, and one of them is a metal-air battery. A metal-air battery is composed of an air electrode (positive electrode), a fuel electrode (negative electrode), an electrolyte (or an electrolyte), etc., and is subjected to an electrochemical reaction to produce zinc, iron, magnesium, aluminum, sodium, calcium, etc. And, the electrical energy obtained in the process of converting a metal such as lithium into a metal oxide is extracted and used.

In an air electrode provided with a current collector, a catalyst layer, and a water-repellent film, an oxygen reduction reaction proceeds inside the catalyst layer. The oxygen reduction reaction inside the catalyst layer is considered to proceed at the interface (three-phase interface) where the three-phase surfaces of the catalyst, which is the solid phase, the electrolytic solution, which is the liquid phase, and the air, which is the gas phase, are in contact with each other. ing. Therefore, considering that the progress of the oxygen reduction reaction at the three-phase interface affects the output characteristics of the air electrode, the water repellency of the catalyst layer is improved, and the good storage characteristics and heavy load discharge characteristics in the metal-air battery are obtained. (See, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2008-41521

The air battery described in Patent Document 1 includes an air electrode composed of a catalyst layer, a current collector, and a water-repellent film, and the surface contact angle of the catalyst layer with respect to water is 90 ° or more. In the above-mentioned air battery, the water repellency of the catalyst layer is improved to obtain excellent storage characteristics and heavy load discharge characteristics. However, if the water repellency becomes too high, the rate at which the electrolytic solution permeates into the catalyst layer. There is a problem that is significantly reduced.

The present invention has been made to solve the above problems, and an air electrode and a metal-air battery capable of obtaining good battery characteristics by appropriately setting the air permeability of the water-repellent film and the catalyst layer can be obtained. The purpose is to provide.

The air electrode according to the present invention is an air electrode provided with a current collector, a catalyst layer, and a water-repellent film, and the air permeability of the water-repellent film is 1900 to 9000 seconds / 100 cc. The air permeability is 400 seconds / 100 cc or less.

In the air electrode according to the present invention, the catalyst layer and the water-repellent film may be laminated so as to be adjacent to each other.

In the air electrode according to the present invention, the catalyst layer may be configured such that the contact angle with water is 132 ° or less.

In the air electrode according to the present invention, the water-repellent film may have a thickness of 30 to 500 μm.

In the air electrode according to the present invention, the catalyst layer may have a thickness of 100 to 1000 μm.

In the air electrode according to the present invention, the catalyst layer may contain at least a metal oxide, carbon and a fluororesin, and at least one of the metal oxide and the carbon may have a hydrophilic structure. ..

In the air electrode according to the present invention, the catalyst layer may contain at least two or more of the carbons, and one of the carbons may be activated carbon.

The metal-air battery according to the present invention is characterized by including an air electrode, a metal electrode, and an electrolyte according to the present invention.

According to the present invention, good battery characteristics can be obtained by appropriately setting the air permeability of the water-repellent film and the catalyst layer. That is, the air permeability of the water-repellent membrane can be prevented from leaking from the surface of the water-repellent membrane by setting it to 1900 seconds / 100 cc or more, and by setting it to 9000 seconds / 100 cc or less, it can be passed through the water-repellent membrane. Therefore, a sufficient amount of oxygen to be taken into the catalyst layer can be secured. Further, by setting the air permeability of the catalyst layer to 400 seconds / 100 cc or less, water can easily move in the catalyst layer, and oxygen is supplied due to a liquid pool generated between the water-repellent membrane and the catalyst layer. Can eliminate the inhibition of.

It is the schematic sectional drawing which shows the metal-air battery which concerns on embodiment of this invention. It is a characteristic chart which shows the result of the characteristic evaluation in an air electrode and a metal-air battery.

Hereinafter, the metal-air battery according to the embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing a metal-air battery according to an embodiment of the present invention.

The metal-air battery 1 according to the embodiment of the present invention is a battery in which the metal pole 15 is the negative electrode (cathode) and the air electrode 10 is the positive electrode (cathode), and is, for example, a zinc air battery, a lithium air battery, or sodium. These include air batteries, calcium-air batteries, magnesium-air batteries, aluminum-air batteries, and iron-air batteries. The air electrode 10 is formed by laminating a water-repellent film 11, a catalyst layer 12, and a current collector 13.

The metal-air battery 1 includes a housing 14 that houses a metal pole 15 and an air pole 10, and an electrolytic solution 16 is injected into the housing 14. A plurality of ventilation holes 14a penetrating from the outside to the inside space are provided on one side surface of the housing 14. The air pole 10 is held inside the housing 14 along the side surface having the ventilation holes 14a. Of the air poles 10, the surface provided with the water repellent film 11 faces the ventilation hole 14a, and the surface provided with the current collector 13 faces the inside of the housing 14. That is, since the ventilation hole 14a is closed by the air electrode 10, only the air can pass through without the electrolytic solution 16 flowing out from the ventilation hole 14a.

The metal pole 15 is held in the housing 14 so as to be in contact with the electrolytic solution 16, and in order to improve battery performance, it is preferable that the metal pole 15 and the electrolytic solution 16 have a large area in contact with each other. Among those described above as an example of the metal-air battery 1, for example, in the case of a zinc-air battery, metallic zinc can be used as the material of the metal electrode 15, and potassium hydroxide aqueous solution is used as the electrolytic solution 16. Can be done. The metal electrode 15 is not limited to this, and other materials may be used, and the electrolytic solution 16 may be appropriately selected depending on the combination with the metal electrode 15.

A part of the metal pole 15 and the air pole 10 may protrude from the housing 14 for connection with wiring or the like, and the air pole 10 may have a structure in which only the current collector 13 protrudes.

Next, the method of manufacturing the metal-air battery 1 will be described in detail together with the material of each member of the air electrode 10.

The water-repellent film 11 is preferably a water-repellent porous sheet such as PTFE (polytetrafluoroethylene) or PE (polyethylene). The thickness of the water-repellent film 11 is preferably 30 to 500 μm. If the water-repellent film 11 is too thin, problems may occur in durability and handleability, and if it is too thick, liquid pooling may be induced due to a decrease in adhesion to the catalyst layer 12. Therefore, the above-mentioned problem can be solved by setting the water-repellent film 11 to an appropriate thickness.

The catalyst layer 12 contains a metal oxide as a catalyst, carbon having conductive and catalytic functions, and a fluororesin that binds them, and at least one of these materials may have hydrophilicity. preferable. That is, by imparting hydrophilicity to the constituent material of the catalyst layer 12, the flow of the electrolytic solution 16 (water) in the catalyst layer 12 becomes good, and the electrolytic solution is between the catalyst layer 12 and the water-repellent film 11. 16 is less likely to accumulate. Further, the effect of lowering the contact angle of water due to hydrophilicity can be sufficiently exhibited.

In producing the catalyst layer 12, MnO ₂ powder (manufactured by Chuo Denki Kogyo Co., Ltd., trade name: CMD-K200) as catalyst particles and carbon particles were mixed. Two carbon particles were used: carbon black (manufactured by Denka Co., Ltd., trade name: Denka Black) and activated carbon (manufactured by Darco Co., Ltd., G-60) from the viewpoint of imparting hydrophilicity. That is, activated carbon has high hydrophilicity as compared with other carbon particles.

Then, this mixed powder was mixed with a binder (manufactured by Daikin Industries, Ltd., PTFE dispersion "D-210C", solvent: water, solid content concentration: 60 wt%) in an amount of 25% by weight with respect to the total solid content. An amount of water having a total solid content concentration of 50 wt% was added and mixed with a planetary mixer to prepare a mixture A. Further, this mixture A was placed in a mortar and kneaded to prepare a dumpling-shaped kneaded product B. After that, the catalyst layer 12 is produced by forming the kneaded product B into a sheet shape by a roll rolling mill. The thickness of the catalyst layer 12 is preferably 100 to 1000 μm. If the catalyst layer 12 is too thin, there are problems that it is difficult to manufacture the catalyst sheet itself and that the handleability is deteriorated. Further, if it is too thick, there is a risk that the adhesion to the current collector 13 may be deteriorated and the performance may be deteriorated due to damage to the water repellent film 11. Therefore, the above-mentioned problem can be solved by setting the catalyst layer 12 to an appropriate thickness.

In the step of producing the air electrode 10, the water-repellent film 11, the catalyst layer 12, and the current collector 13 (Ni mesh manufactured by Nirako Co., Ltd., opening # 20) are stacked in this order and pressed at room temperature to integrate them. .. A zinc-air battery is produced by combining the above-mentioned air electrode 10 with a 7 M KOH aqueous solution which is an electrolytic solution 16 and a zinc plate which is a metal electrode 15.

Next, the characteristic evaluation of the created air electrode 10 and the metal-air battery 1 will be described.

FIG. 2 is a characteristic chart showing the results of characteristic evaluation of the air electrode and the metal-air battery.

The air permeability of the water repellent film 11 and the catalyst layer 12 was measured. The air permeability is measured by No. The measurement was performed using a 323 Garley type densometer (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) under measurement conditions conforming to "JIS P 8117".

Further, the contact angle was measured with respect to the catalyst layer 12. In the contact angle measurement, a portable contact angle meter PCA-1 (manufactured by Kyowa Interface Science Co., Ltd.) is used to drop a droplet of water (approximately 10 μL) on the sample surface, and the static contact angle 1 second after the drop is measured. did. The contact angle is measured based on the equation "θ / 2 = arctan (h / r)" in the θ / 2 method. In this equation, θ indicates the contact angle and r indicates the radius of the droplet. Shown, h indicates the height of the droplet. The contact angle is measured at three points for each sample and is taken as the average value thereof.

Further, the air electrode 10 was subjected to a continuous energization test to evaluate its characteristics. In the continuous energization test, a battery tester (Battery test system PFX2011 manufactured by Kikusui Electronics Co., Ltd.) is used, and the measurement condition is 30 mA / cm ² . In addition, during the energization test, the presence or absence of liquid leakage from the surface of the water-repellent film 11 and the presence or absence of liquid pooling between the water-repellent film 11 and the catalyst layer 12 (floating or swelling of the water-repellent film 11) are also checked. evaluated. Leakage of the alkaline solution (electrolyte solution 16) from the surface of the water-repellent film 11 is a serious problem in terms of safety, and the liquid pool between the water-repellent film 11 and the catalyst layer 12 is the surface of the water-repellent film 11. Since it hinders the intake of air from the air, the battery characteristics are greatly deteriorated.

In the evaluation result items shown in FIG. 2, the initial output indicates whether or not the specified output was obtained in the energization test, and if the specified output is possible, it is marked with "○", and if the specified output is not possible, it is marked as "○". It is marked as "x".

The liquid leakage indicates whether or not the liquid leakage from the surface of the water-repellent film 11 can be visually confirmed. If there is no liquid leakage, it is marked with “◯”, and if there is a liquid leak, it is marked with “x”.

The liquid pool indicates whether or not a liquid pool has been confirmed between the water-repellent membrane 11 and the catalyst layer 12, and if no liquid pool is observed by visual evaluation and there is no decrease in the output from the metal-air battery 1, " ◎ ”. Further, although no liquid pool is observed in the visual evaluation, when the output from the metal-air battery 1 is slightly reduced, it is marked with "◯". In addition, here, it is limited to the case where the specified output is maintained. On the other hand, if the occurrence of liquid pool can be confirmed by visual evaluation and the specified output is not possible, it is marked with "x".

In the evaluation of the air electrode 10, five types of samples having different air permeability of the water repellent film 11 were prepared. Regarding the catalyst layer 12, activated carbon is used in combination as carbon, and the contact angles of the catalyst layer 12 are adjusted by changing the weight ratio of the activated carbon in the total carbon to adjust the contact angles of 137 °, 132 °, and 100 °. , And four types of samples at 80 ° were prepared. Regarding the contact angle, the surface of the catalyst layer 12 on the side in contact with the water-repellent film 11 was measured.

Further, with respect to the catalyst layer 12, three types of samples were prepared in which the sheet air permeability after the completion of the roll rolling treatment was adjusted by adjusting the above-mentioned mixture A and changing the conditions for kneading the kneaded product B.

The above-mentioned sample of the water-repellent film 11 and the sample of the catalyst layer 12 were combined to prepare a plurality of evaluation air electrodes (Examples 1 to 12 and Comparative Examples 1 to 18 shown in FIG. 2). Next, the details of the plurality of evaluation air electrodes will be described. In addition, for the sake of explanation below, the unit of air permeability may be abbreviated. For example, when the air permeability is "1900 seconds / 100 cc", it is abbreviated as "air permeability 1900".

<Comparative Examples 1 to 4>
In Comparative Examples 1 to 4, a water-repellent film 11 having an air permeability of 10 and four types of catalyst layers 12 having different characteristics are combined. In Comparative Examples 1 to 4, the water-repellent film 11 had a small air permeability (easily allows air to pass through) regardless of the characteristics of the catalyst layer 12, so that liquid leakage occurred from the surface of the water-repellent film 11.

<Comparative Examples 5 to 8>
In Comparative Examples 5 to 8, a water-repellent film 11 having an air permeability of 800 and four types of catalyst layers 12 having different characteristics are combined. In Comparative Examples 5 to 8, liquid leakage occurred from the surface of the water-repellent film 11 regardless of the characteristics of the catalyst layer 12, as in Comparative Examples 1 to 4.

<Comparative Examples 9 to 11 and Examples 1 to 6>
In Comparative Examples 9 to 11 and Examples 1 to 6, a water-repellent film 11 having an air permeability of 1900 and nine types of catalyst layers 12 having different characteristics are combined.

According to the results of Examples 1 to 6, liquid leakage from the surface of the water-repellent film 11 is suppressed by setting the water-repellent film 11 to have an air permeability of 1900 or more. Further, by setting the catalyst layer 12 to have an air permeability of 400 or less, the electrolytic solution 16 (water) can easily flow in and out of the catalyst layer 12, and a liquid pool between the water-repellent film 11 and the catalyst layer 12 can be easily collected. Good battery characteristics were obtained for a long period of time. Further, when the contact angle of the catalyst layer 12 is 132 ° or less, the water uptake performance into the catalyst layer 12 is improved, and the liquid pool between the water repellent film 11 and the catalyst layer 12 is further improved. It can be suppressed, the loss of battery performance is eliminated, and the life performance is further improved.

On the other hand, according to the results of Comparative Examples 9 to 11, even when the water-repellent membrane 11 has an air permeability of 1900, when the air permeability of the catalyst layer 12 becomes large, the electrolytic solution 16 and water are passed through the catalyst layer 12. It cannot be returned, and liquid pools occur between the water-repellent film 11 and the catalyst layer 12, or liquid leaks from the surface of the water-repellent film 11. As a result, the battery performance gradually deteriorated, and finally it became impossible to output.

<Comparative Examples 12 to 14 and Examples 7 to 12>
In Comparative Examples 12 to 14 and Examples 7 to 12, a water-repellent film 11 having an air permeability of 9000 and nine types of catalyst layers 12 having different characteristics are combined. In Examples 7 to 12, as in Examples 1 to 6, no liquid leakage or liquid pool was confirmed, and good battery characteristics were obtained. On the other hand, in Comparative Examples 12 to 14, as in Comparative Examples 9 to 11, the catalyst layer 12 had a large air permeability, so that liquid pooling occurred and the battery performance deteriorated.

<Comparative Examples 15-18>
In Comparative Examples 15 to 18, a water-repellent film 11 having an air permeability of 10500 and four types of catalyst layers 12 having different characteristics are combined. In Comparative Examples 15 to 18, regardless of the characteristics of the catalyst layer 12, the water-repellent film 11 has a high air permeability, so that oxygen is insufficiently taken in through the water-repellent film 11, and the battery characteristics cannot be obtained from the initial stage of energization. The result was.

As described above, good battery characteristics can be obtained by appropriately setting the air permeability of the water repellent film 11 and the catalyst layer 12. That is, the air permeability of the water-repellent membrane 11 can be prevented from leaking from the surface of the water-repellent membrane 11 by setting it to 1900 seconds / 100 cc or more, and by setting it to 9000 seconds / 100 cc or less, the water-repellent membrane 11 can be prevented from leaking. A sufficient amount of oxygen to be taken into the catalyst layer 12 can be secured. Further, by setting the air permeability of the catalyst layer 12 to 400 seconds / 100 cc or less, water can easily move in the catalyst layer 12, and a liquid pool generated between the water repellent film 11 and the catalyst layer 12 is generated. Can be resolved.

Further, by reducing the contact angle of water on the surface of the catalyst layer 12, the performance of taking in water into the catalyst layer 12 is improved, and the liquid accumulation between the water repellent film 11 and the catalyst layer 12 can be further suppressed. , The loss of battery function can be eliminated and the life performance can be improved.

It should be noted that the embodiments disclosed this time are examples in all respects and do not serve as a basis for limited interpretation. Therefore, the technical scope of the present invention is not construed solely by the embodiments described above, but is defined based on the description of the claims. It also includes all changes within the meaning and scope of the claims.

1 Metal-air battery 10 Air electrode 11 Water-repellent film 12 Catalyst layer 13 Current collector 14 Housing 14a Vent 15 Metal electrode 16 Electrolyte

Claims (8)

An air electrode with a current collector, a catalyst layer, and a water repellent membrane.
The air permeability of the water-repellent membrane is 1900 to 9000 seconds / 100 cc.
An air electrode characterized in that the air permeability of the catalyst layer is 400 seconds / 100 cc or less. The air electrode according to claim 1.
An air electrode characterized in that the catalyst layer and the water-repellent film are laminated adjacent to each other. The air electrode according to claim 1 or 2.
The catalyst layer is an air electrode characterized by having a contact angle with water of 132 ° or less. The air electrode according to any one of claims 1 to 3.
The water-repellent film is an air electrode having a thickness of 30 to 500 μm. The air electrode according to any one of claims 1 to 4.
The catalyst layer is an air electrode having a thickness of 100 to 1000 μm. The air electrode according to any one of claims 1 to 5.
The catalyst layer contains at least a metal oxide, carbon, and a fluororesin.
An air electrode characterized in that at least one of the metal oxide and the carbon has hydrophilicity. The air electrode according to claim 6.
An air electrode characterized in that the catalyst layer contains at least two or more of the carbons, one of which is activated carbon. A metal-air battery comprising the air electrode, the metal electrode, and the electrolyte according to any one of claims 1 to 7.

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