JP2017021924A - Positive electrode for metal-air battery and metal-air battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode for a metal-air battery with which a metal-air battery sufficiently high in voltage and capable of being discharged over a long period of time can be obtained, and also to provide a metal-air battery including the positive electrode for a metal-air battery.SOLUTION: A positive electrode 20 for a metal-air battery included in a metal-air battery that includes a negative electrode containing a negative electrode active material comprising metal or an alloy is used. The positive electrode 20 for a metal-air battery is characterized to include a metal layer 22 including a plurality of pores formed therein, and a coat 23 covering a surface of the metal layer 22.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a positive electrode for a metal-air battery and a metal-air battery.

  Batteries used in electronic devices and the like are required to have high performance such as high voltage and high capacity. As such a battery, a battery using lithium, such as a lithium ion secondary battery, is widely used, and development thereof is underway.

  However, lithium is a metal with a relatively low crustal abundance of about 20 ppm, and belongs to the so-called rare metal class. Lithium is a relatively expensive metal because of its low crustal abundance, and is a major factor in increasing the cost of raw materials when manufacturing batteries using lithium and increasing the manufacturing cost. It has also been pointed out that lithium may be depleted depending on the future development status.

  For these reasons, as a battery with a small amount of use of lithium, studies have been promoted for improving various performances of conventionally proposed batteries and batteries that have been put into practical use. .

  One of conventionally known batteries is an air battery. The air battery uses oxygen in the air as a positive electrode active material. That is, the air battery has a structure in which oxygen in the air is used as an oxidant and a reducing agent that is a substance that emits electrons during a discharge reaction is contained in the battery as a negative electrode active material. In the air battery, in discharging, electrons are transferred by an oxygen reduction reaction and a reducing agent oxidation reaction, and an electric current is taken out to the outside. For this reason, since it is not necessary to provide the area | region which a positive electrode active material occupies for the air battery in the structure, since a large amount of negative electrode active materials can be put in a battery compared with other primary batteries, high energy density Is obtained.

  In addition, as such an air battery, for example, an electrode made of carbon fiber or the like made porous to increase the surface area is used as an air electrode that is a positive electrode, and zinc (Zn) or aluminum (Al) is used as a negative electrode. And a metal-air battery using a metal electrode made of a metal such as magnesium (Mg) or an alloy thereof. As such a metal-air battery, since a raw material having a relatively high crust presence as described above can be used as the negative electrode, an inexpensive battery can be realized.

  Also, for example, aluminum is a resource-rich metal and is much cheaper than lithium. Furthermore, aluminum has a large energy capacity per unit volume and a higher energy density than lithium. From this, it is considered that a metal-air battery such as an air battery using aluminum or an aluminum alloy as the negative electrode can realize a sufficiently high capacity even if it is a downsized battery.

  As such a metal air battery, the battery of patent document 1 and patent document 2 is mentioned, for example.

  Patent Document 1 includes a negative electrode made of magnesium, and a liquid holding part capable of holding an aqueous electrolyte solution that elutes magnesium ions from the negative electrode, and the liquid holding part contains an aqueous solution of a polyvalent carboxylate. A magnesium battery retained as an aqueous electrolyte is described.

  Patent Document 2 discloses an aluminum-air battery using an air electrode as a positive electrode and aluminum or an aluminum alloy as a negative electrode, wherein an electrolyte interposed between the positive electrode and the negative electrode is placed in contact with the negative electrode. An aluminum air battery including an ionic conductor is described.

JP 2010-182435 A JP 2006-147442 A

  Batteries using metal electrodes, such as magnesium batteries, generally generate electrons when the metal contained in the negative electrode dissolves in the electrolyte solution, and reacts with hydrogen ions in the electrolyte solution to generate hydrogen. It is known that a phenomenon called self-discharge occurs in which electrons generated in the negative electrode do not sufficiently move to the positive electrode and current does not flow sufficiently. For this reason, a battery using a metal electrode sometimes fails to obtain a theoretical discharge capacity stably.

  Since this self-discharge tends to be more prominent as the hydrogen ion concentration is higher, it is conceivable to neutralize the electrolyte in order to suppress self-discharge.

  However, when the electrolyte is neutral, metal hydroxide such as magnesium hydroxide may be deposited on the surface of the positive electrode, and a suitable discharge may not be maintained.

  In this regard, according to Patent Document 1, the polyvalent carboxylate ions and the magnesium ions eluted from the negative electrode are complexed to increase the solubility of magnesium hydroxide, thereby suppressing the precipitation of magnesium oxide and maintaining the magnesium. It is disclosed that the electrolysis can be performed and the negative electrode capacity of the magnesium battery can be continuously increased.

  Further, according to Patent Document 2, in an aluminum air battery using an air electrode as a positive electrode and aluminum or an aluminum alloy as a negative electrode, an aluminum ion in which an electrolyte interposed between the positive electrode and the negative electrode is placed in contact with the negative electrode Including a conductor suppresses the discharge inhibition by aluminum hydroxide of the discharge product when using a neutral aqueous solution, and suppresses the discharge inhibition by aluminum hydroxide of the discharge product when using an alkaline aqueous solution. In addition to this, it is disclosed that an aluminum-air battery having a long battery life can be provided by suppressing the corrosion of the negative electrode in an open circuit state and increasing the utilization rate of aluminum or aluminum alloy used as the negative electrode. Has been.

  However, even the batteries disclosed in Patent Document 1 and Patent Document 2 may not be able to flow a current stably over a long period of time. Specifically, when an electrode made of a metal such as iron, copper, and nickel is used as the positive electrode, there is a problem that the positive electrode is corroded by the electrolytic solution. Further, when an electrode made of carbon powder is used as the positive electrode, the resistance of the positive electrode is high and the current collecting property is low. From these things, in order to improve the performance of the battery using metal electrodes, such as a magnesium battery and an aluminum battery, the further examination of the positive electrode to be used was required.

  In addition, as a metal foil that can be used as a metal electrode, for example, an aluminum foil is provided at a price that can be effectively used as a negative electrode of a metal-air battery because there is a great demand for food packaging materials and the like. Providing a battery that can effectively use such inexpensively available metal foil is expected to be extremely effective as an emergency power supply source.

  This invention is made | formed in view of this situation, Comprising: It aims at providing the positive electrode for metal air batteries which can obtain the metal air battery whose voltage is high enough and can discharge over a long period of time. Moreover, it aims at providing the metal air battery provided with the said positive electrode for metal air batteries.

  As a result of various studies, the present inventor has found that the above object is achieved by the present invention described below.

  A positive electrode for a metal-air battery according to an aspect of the present invention is a positive electrode for a metal-air battery provided in a metal-air battery including a negative electrode containing a negative electrode active material made of a metal or an alloy, and a metal having a large number of holes formed A layer and a film covering the surface of the metal layer.

  According to such a configuration, it is possible to provide a positive electrode for a metal-air battery that can obtain a metal-air battery that has a sufficiently high voltage and can be discharged over a long period of time.

  This is considered to be due to the following.

  First, as described above, since the metal layer provided in the positive electrode for metal-air batteries has a large number of holes, the contact area with oxygen in the air as the positive electrode active material can be increased, that is, It is considered that oxygen in the air can be taken in efficiently. Therefore, it is thought that the positive electrode for metal air batteries provided with the said metal layer works suitably as a positive electrode of a metal air battery.

  Next, the surface of the metal layer provided in the positive electrode for the metal-air battery is covered with the coating film. Therefore, even when the metal-air battery positive electrode is used as the positive electrode of the metal-air battery, the metal-air battery electrolyte is prevented from coming into contact with the metal layer, and the metal layer is corroded by the electrolyte. It is thought that it can be suppressed. Furthermore, with such a positive electrode for a metal-air battery, even if a metal hydroxide that can be generated from metal ions eluted from the negative electrode is deposited on the surface of the positive electrode, this deposition reduces the contact area with air. It is thought that it can be suppressed. From these things, it is thought that the fall of the performance as a positive electrode of a metal air battery can fully be suppressed over a long period irrespective of the kind of electrolyte solution of a metal air battery.

  From the above, it is considered that a metal-air battery having a sufficiently high voltage and capable of discharging over a long period of time can be obtained by using the positive electrode for a metal-air battery according to one embodiment of the present invention.

  In the positive electrode for a metal-air battery, the coating is preferably an oxide coating or a carbon coating.

  According to such a configuration, a more suitable discharge can be maintained over a long period of time.

  This is because if the coating for coating the metal layer is an oxide coating or a carbon coating, it is possible to further suppress the occurrence of corrosion of the metal layer by the electrolytic solution, the precipitation of metal hydroxide on the positive electrode surface, and the like. it is conceivable that.

  In the positive electrode for a metal-air battery, the metal layer preferably has the hole formed over the entire metal layer.

  According to such a configuration, a more suitable discharge can be maintained over a long period of time.

  This is considered to be because oxygen in the air, which is a positive electrode active material, can be efficiently taken in by the metal layer.

  The positive electrode for a metal-air battery preferably includes a porous body containing carbon, and the porous body is laminated on the coating film.

  According to such a configuration, a more suitable discharge can be maintained over a long period of time.

  This is considered to be due to the fact that the porous body laminated on the coating can suppress the occurrence of corrosion of the metal layer by the electrolytic solution, the precipitation of the metal hydroxide on the positive electrode surface, and the like.

  In the metal-air battery positive electrode, the metal layer coated with the coating is preferably disposed so as to be sandwiched between two porous bodies.

  According to such a configuration, a more suitable discharge can be maintained over a long period of time.

  This is because the metal layer covered with the coating is sandwiched between the porous bodies, and as described above, the corrosion of the metal layer due to the electrolytic solution and the deposition of the metal hydroxide on the surface of the positive electrode are performed. This is considered to be due to the fact that it can be further suppressed.

  A metal-air battery according to another embodiment of the present invention includes a positive electrode using oxygen as a positive electrode active material, a negative electrode including a negative electrode active material made of a metal or an alloy, and an electrolyte solution for eluting metal ions from the negative electrode. And a separator interposed between the positive electrode and the negative electrode and holding the electrolytic solution, wherein the positive electrode is the positive electrode for a metal-air battery.

  According to such a configuration, since the positive electrode for metal-air batteries is used as the positive electrode, a metal-air battery having a sufficiently high voltage and capable of discharging over a long period of time can be provided.

  In the metal-air battery, the electrolyte solution is preferably a neutral electrolyte solution or a weakly basic electrolyte solution.

  According to such a structure, the safety | security at the time of leak can be improved. Therefore, it is possible to provide a metal-air battery having a sufficiently high voltage, capable of discharging over a long period of time, and having high safety at the time of leakage.

  This is considered to be due to the following. First, as described above, the positive electrode for a metal-air battery according to one embodiment of the present invention has a reduced contact area with air due to the occurrence of corrosion of the metal layer due to the electrolytic solution or precipitation of metal hydroxide on the positive electrode surface. Regardless of the type of the electrolyte of the metal-air battery, it is considered that the deterioration of the performance of the metal-air battery as the positive electrode can be sufficiently suppressed over a long period of time. From this, it is considered that a metal-air battery having a sufficiently high voltage and capable of discharging over a long period of time can be obtained even when the above-described electrolyte solution having high safety at the time of leakage is used as the electrolyte solution. Therefore, it is considered that a metal-air battery having a sufficiently high voltage and capable of discharging over a long period of time and having high safety at the time of leakage is obtained.

  In the metal-air battery, it is preferable that the electrolyte contains at least one selected from the group consisting of halides, phosphates, organic acid salts, carbonates, and hydrogen carbonates.

  According to such a structure, the safety | security at the time of leak can be improved. Therefore, it is possible to provide a metal-air battery having a sufficiently high voltage, capable of discharging over a long period of time, and having high safety at the time of leakage.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode for metal air batteries which can obtain the metal air battery whose voltage is high enough and can discharge over a long period of time can be provided. Moreover, the metal air battery provided with the said positive electrode for metal air batteries is provided.

FIG. 1 is a schematic cross-sectional view showing an example of a configuration of a metal-air battery including a positive electrode for a metal-air battery according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the positive electrode for a metal-air battery according to one embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing another example of the configuration of the positive electrode for a metal-air battery according to one embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing another example of the configuration of the positive electrode for a metal-air battery according to one embodiment of the present invention.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  The positive electrode for metal air batteries which concerns on one Embodiment of this invention is a positive electrode for metal air batteries with which the negative electrode containing the negative electrode active material which consists of a metal or an alloy is provided. The positive electrode for a metal-air battery includes a metal layer in which a large number of holes are formed and a coating that covers the surface of the metal layer.

  First, the metal-air battery to which the positive electrode for the metal-air battery is applied is not particularly limited as long as it is a metal-air battery including a negative electrode including a negative electrode active material made of a metal or an alloy. In this specification, a “metal-air battery” is a battery in which oxygen in the air is a positive electrode active material (a substance that receives electrons) and a metal or an alloy is a negative electrode active material (a substance that emits electrons). The metal-air battery is also called a metal fuel cell.

  Moreover, an electromotive force is generated in the metal-air battery as follows. Specifically, an explanation will be given by taking an aluminum-air battery using aluminum as a metal as an example.

Aluminum contained in the negative electrode emits electrons and becomes aluminum ions and is eluted in the electrolytic solution. On the other hand, in the positive electrode, oxygen and water receive electrons and become hydroxide ions. When the battery is viewed as a whole, aluminum hydroxide (Al (OH) ₃ ) is generated from aluminum, oxygen, and water, so that an electromotive force is generated between both electrodes.

  The respective reaction formulas at the positive electrode and the negative electrode are as follows.

Positive electrode: 3O ₂ + 6H ₂ O + 12e ⁻ → 12OH ⁻
Negative electrode: 4Al → 4Al ³⁺ + 12e ⁻
Overall: 4Al + O ₂ + 6H ₂ O → 4Al (OH) ₃
As a metal air battery, a metal air battery as shown in FIG. 1 is mentioned, for example. FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a metal-air battery including a positive electrode for a metal-air battery according to an embodiment of the present invention. As shown in FIG. 1, the metal-air battery 10 includes a positive electrode 20, a negative electrode 30, and a separator 40 that is interposed between the positive electrode 20 and the negative electrode 30 and holds an electrolytic solution. That is, the positive electrode 20, the separator 40, and the negative electrode 30 are laminated in this order. The metal-air battery 10 can be discharged, for example, by electrically connecting the positive electrode 20 and the negative electrode 30 via the wattmeter 50 or the like. The wattmeter 50 can measure the voltage and current of electricity that has flowed through this discharge. And as this positive electrode 20, the positive electrode for metal air batteries which concerns on one Embodiment of this invention can be used. In addition, a positive electrode, a negative electrode, a separator, and electrolyte solution are mentioned later.

  In addition, the metal-air battery is not limited to the case where the positive electrode 20, the separator 40, and the negative electrode 30 are stacked in this order, as shown in FIG. Specifically, the metal-air battery may have a configuration in which a positive electrode and a negative electrode are opposed to each other through a separator and wound in a spiral shape. The structure which wound the positive electrode in order may be sufficient.

  Moreover, the positive electrode for metal air batteries which concerns on one Embodiment of this invention is equipped with the said metal layer and the said film as mentioned above. Moreover, the positive electrode for metal air batteries should just be provided with the said metal layer and the said film, and may be provided with the other layer.

  First, as the metal-air battery positive electrode 20, as shown in FIG. 2, a positive electrode composed of a metal layer 22 and a coating 23 can be mentioned. In the case of such a positive electrode, the metal layer 22 on which the coating film 23 is formed serves as a positive electrode, so other layers are unnecessary, which is advantageous in terms of price, and the battery weight is reduced by thinning the electrode. It is also advantageous in terms of reducing the number of parts. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the positive electrode for a metal-air battery according to one embodiment of the present invention.

  The metal layer has a large number of holes. That is, the metal layer is a porous metal layer. The metal layer can increase the contact area with oxygen by the large number of holes, and can realize a suitable battery reaction. Further, the hole may be formed on one surface of the metal layer, may be formed on both surfaces, or is formed entirely from one surface to the other surface. May be. Among these, it is preferable that the said metal layer has the said hole formed over the whole metal layer. Such a metal layer in which holes are formed throughout can be considered to be able to take in oxygen in the air more efficiently and maintain a more favorable discharge over a long period of time.

  Further, the method for obtaining the porous metal layer is not particularly limited as long as it is a method (a method for making a porous structure) in which a metal layer in which a large number of holes are not formed is subjected to a treatment for forming a large number of holes. Examples of this method include physical methods such as cutting, polishing, and sand blasting, and chemical methods such as electrolytic etching and electroless etching using an etching solution such as acid and base. Moreover, as a method of making it porous, each said method may be performed independently and may be performed in combination of 2 or more type. Further, as a method for making the pores, a chemical method is preferable from the viewpoint of increasing the surface area, in order to form pores (pores) to be formed more densely.

  Further, the material of the metal layer is not particularly limited as long as it can be used as a positive electrode current collector, and examples thereof include aluminum, copper, iron, titanium, tungsten, nickel, and alloys thereof. It is done. Among these, the material of the metal layer is preferably aluminum from the viewpoint of cost and workability. The metal layer is preferably a so-called aluminum foil.

  The thickness of the metal layer is not particularly limited, but is preferably 0.01 to 5 mm, more preferably 0.1 to 3.5 mm, and 0.15 to 3 mm, for example. Is more preferable. If the metal layer is too thin, current collection efficiency and strength tend to decrease, and contact points with oxygen in the air and contact points with the electrolyte solution decrease, and the battery output tends to decrease. Moreover, when the said metal layer is too thick, there exists a tendency which inhibits size reduction of the metal air battery finally obtained. From these things, if the thickness of the said metal layer is in the said range, it will become the thing which was excellent in current collection efficiency and intensity | strength, without making it unnecessarily thick.

  Moreover, the shape of the said metal layer is not specifically limited, For example, flat plate shape, corrugated plate shape, a punching metal, an expanded metal, etc. are mentioned. Among these, from the viewpoint of workability as a positive electrode current collector, a flat plate shape or a punching metal is preferable. In order to facilitate application to the metal layer, it is preferable to provide a terminal (lead).

  Moreover, the said film is a layer which coat | covers the surface of the said metal layer. This coating exhibits an effect of suppressing the occurrence of corrosion of the positive electrode by the electrolytic solution and the precipitation of metal hydroxide on the surface of the positive electrode current collector. Moreover, this film will not be specifically limited if it is a film formed on the surface of the said metal layer, For example, an oxide film, a carbon film, etc. are mentioned.

  The oxide film is not particularly limited, and examples thereof include an oxide layer formed by oxidizing the surface of the metal layer. As the oxide film. Specifically, an oxide film formed by heating a metal layer in the presence of oxygen and oxidizing the surface of the metal layer, or an oxide oxidized by a method of electrically oxidizing the surface of the metal layer A film etc. are mentioned. Among these, the film is preferably an oxide film oxidized by a method of electrically oxidizing the surface of the metal layer from the viewpoint of strength and oxidation homogeneity.

  Moreover, the said carbon film is not specifically limited, For example, the carbon film etc. which were formed with the following method are mentioned. First, examples of the carbon coating include a carbon coating directly formed on the surface of the metal layer by a method such as chemical vapor deposition (CVD). In addition, a coating film containing a thermosetting resin containing carbon such as phenol resin, epoxy resin, fiber reinforced plastic (FRP), and unsaturated polyester resin is applied to the surface of the metal layer and cured by heat treatment. And so on. Moreover, the carbon film which apply | coated petroleum pitch, coal pitch, etc. to the metal layer surface, and was heat-condensed and made into a film | membrane is also mentioned. Among these, from the viewpoints of productivity, economy, and the like, a method of applying a coating liquid containing a thermosetting resin or petroleum pitch is preferable.

  The thickness of the coating is not particularly limited, but is preferably 2 μm or less, more preferably 0.1 to 2 μm, and even more preferably 0.2 to 1 μm. If the coating is too thin, the effect of increasing the corrosion resistance tends to decrease. Moreover, when the said film is too thick, the electroconductivity of a positive electrode falls with the said film, and there exists a tendency for current collection efficiency to fall. For these reasons, when the thickness of the coating is within the above range, it is possible to more appropriately realize discharge over a long period of time.

In addition, the BET specific surface area of the metal layer on which the film is formed is not particularly limited, but is preferably 0.5 to 50 m ² / g, for example, 0.7 to 40 m ² / g. More preferably, it is 1-30 m < ² > / g. If the BET specific surface area of the metal layer is too small, the contact area with oxygen becomes narrow, and the battery reaction tends to be inhibited. Moreover, when the BET specific surface area of the said metal layer is too large, there exists a tendency for the inhibitory effects, such as precipitation of a metal hydroxide, on the surface of this metal layer to fall. For these reasons, if the BET specific surface area of the metal layer on which the coating film is formed is within the above range, it is possible to more appropriately realize discharge over a long period of time. The BET specific surface area is a specific surface area measured by the BET method and can be measured by a known method. Examples of the method for measuring the BET specific surface area include a method of performing nitrogen adsorption isotherm measurement and calculating from the obtained adsorption isotherm.

  Further, the metal-air battery positive electrode 20 may be a positive electrode including the metal layer 22 and the coating film 23 as shown in FIG. Such a positive electrode composed of the metal layer 22 and the coating film 23 exhibits performance as an oxygen adsorbent that comes into contact with oxygen and also functions as a positive electrode current collector. Therefore, the metal layer 22 and the coating film 23 The laminate composed of is also simply referred to as the positive electrode current collector 25. Moreover, the positive electrode for metal air batteries should just be provided with the said metal layer and the said film, and may be provided with the other layer. Specifically, in the metal-air battery positive electrode 20, as shown in FIGS. 3 and 4, the porous body 21 is laminated on the positive electrode current collector 25 including the metal layer 22 and the coating 23. It is preferable. That is, a laminate in which a porous body 21 containing carbon is laminated on the coating 23 is preferable. Such a porous body 21 laminated on the coating 23 is considered to be able to further suppress the occurrence of corrosion of the metal layer due to the electrolytic solution and the precipitation of metal hydroxide on the positive electrode surface. A more favorable discharge can be maintained.

  The porous body is more preferably laminated so as to be in close contact with the positive electrode current collector. That is, it is more preferable that the positive electrode current collector and the porous body are integrated. By doing so, it is thought that generation | occurrence | production of the corrosion of the metal layer by electrolyte solution, precipitation of the metal hydroxide on the positive electrode surface, etc. can be suppressed further.

  Moreover, the positive electrode 20 for metal air batteries may be arrange | positioned so that the positive electrode electrical power collector 25 may be pinched | interposed with two porous bodies 21, as shown in FIG. 3, for example, as shown in FIG. Alternatively, the porous body 21 and the positive electrode current collector 25 may be laminated using one each. 3 and 4 are schematic cross-sectional views showing another example of the configuration of the positive electrode for a metal-air battery according to one embodiment of the present invention. Moreover, as a positive electrode for metal air batteries, as shown in FIG. 3, it is preferable to have a configuration in which a positive electrode current collector is sandwiched between two porous bodies. With such a configuration, it is considered that the occurrence of corrosion of the metal layer by the electrolytic solution and the precipitation of metal hydroxide on the surface of the positive electrode current collector can be further suppressed. For this reason, the obtained metal air battery can maintain a more suitable discharge over a long period of time.

  First, the positive electrode current collector includes the metal layer 22 and the coating film 23 described above.

  Next, the porous body is not particularly limited as long as it is a porous body containing carbon. Since this porous body supplies electrons to oxygen in the air, which is a positive electrode active material, a porous body having a large contact area with oxygen in the air is preferable. That is, the porous body here is a porous body that contains carbon, has conductivity that does not hinder the movement of electrons, has excellent air permeability, and can act as an oxygen adsorbent. preferable. Specifically, a porous body containing carbon as a main component or a porous body made of carbon may be used. Specific examples of the carbon contained in the porous body include carbonaceous materials such as activated carbon, activated carbon fiber, and carbon fiber. The carbon is preferably activated carbon or activated carbon fiber from the viewpoint of corrosion resistance and specific surface area. Moreover, as this carbon, various carbonaceous materials may be used independently and may be used in combination of 2 or more type. Specifically, the porous body containing carbon is preferably a cloth-like or felt-like one made of the carbonaceous material. Such a porous body is excellent in corrosion resistance and air permeability. And the said positive electrode for metal air batteries can take in oxygen in the air which is a positive electrode active material efficiently by providing the above porous bodies as a porous body. It is thought that it works suitably as a positive electrode.

  Moreover, the thickness of the porous body is not particularly limited, but is preferably 0.1 to 10 mm, more preferably 0.2 to 9 mm, and more preferably 0.25 to 8 mm. More preferred. When the porous body is too thin, the contact point with oxygen in the air and the contact point with the electrolyte solution are decreased, and the battery output tends to be lowered. On the other hand, when the porous body is too thick, the resistance in the thickness direction of the porous body increases, and the battery output tends to decrease. From these things, if the thickness of the said porous body is in the said range, battery output can fully be raised.

Further, BET specific surface area of the porous body are not particularly limited, for example, is preferably 100~4000m ² / g, more preferably 150~3000m ² / g, 200~2500m ² / More preferably, it is g. If the BET specific surface area of the porous body is too small, the contact area with oxygen tends to be narrow, and the battery reaction tends to be inhibited. Moreover, when the BET specific surface area of the said porous body is too large, there exists a tendency for suppression effects, such as generation | occurrence | production of the corrosion of the metal layer by electrolyte solution, and precipitation of a metal hydroxide on the positive electrode collector surface. From these things, if the BET specific surface area of the said porous body is in the said range, it can implement | achieve discharge more suitably over a long period of time.

  The positive electrode current collector and the porous body may be integrated as long as the positive electrode current collector and the porous body are stacked in close contact with each other. The positive electrode current collector is used as a positive electrode of a metal-air battery, and the positive electrode current collector is in close contact with the electrolyte so that contact with the electrolyte can be suppressed by the porous material. Is preferred. By adhering in this manner, it is considered that the occurrence of corrosion of the positive electrode due to the electrolytic solution and the precipitation of metal hydroxide on the surface of the positive electrode current collector can be suppressed. From this, it is considered that the deterioration of the performance as the positive electrode of the metal-air battery can be sufficiently suppressed over a long period regardless of the type of the electrolyte of the metal-air battery. Therefore, even if the positive electrode for metal-air batteries is used as a positive electrode of a metal-air battery for a long period of time, it can maintain suitable performance as a positive electrode. Therefore, by using this positive electrode, the voltage is sufficiently high. It is considered that a metal-air battery that can be discharged over a long period of time can be obtained. Further, by integrating the positive electrode current collector and the porous body, the current collection efficiency of the obtained positive electrode can be increased, and further, the strength, corrosion resistance, air permeability, etc. are improved. be able to.

  The integration method is not particularly limited. Specifically, the positive electrode current collector and the porous body may be pressed and integrated by pressure, or the positive electrode current collector and the porous material may be integrated using a conductive tape or a conductive adhesive. The porous body may be bonded and integrated. Further, if sufficient conductivity can be secured between the positive electrode current collector and the porous body, the positive electrode current collector and the porous body are cured and bonded using a thermosetting resin. Also good. Among these, a method of adhering the porous body and the positive electrode current collector with a conductive adhesive is preferable. If it is the method of adhere | attaching with a conductive adhesive, it is thought that the said positive electrode collector and the said porous body can be closely contact | adhered in a positive electrode, without inhibiting the movement of the electron in a positive electrode. . For this reason, the obtained positive electrode for metal-air batteries can realize a metal-air battery that can maintain a more suitable discharge over a long period of time.

  In addition, the conductive adhesive is not particularly limited as long as it is an adhesive that can realize electrical conduction at the interface between bonded objects after bonding. Examples of the conductive adhesive include a carbon-based conductive filler dispersed in an adhesive. Moreover, as an adhesive agent contained in a conductive adhesive agent, it is preferable that it is a thermosetting resin from a non-corrosive point. Therefore, as the conductive adhesive, for example, a material obtained by dispersing a carbon-based filler in a thermosetting resin is preferably used.

  The thickness of the positive electrode for a metal-air battery is not particularly limited, but is preferably 0.11 to 15 mm, more preferably 0.3 to 12.5 mm, and 0.4 to 11 mm, for example. It is more preferable that When the positive electrode for metal-air batteries is too thin, there is a tendency that the performances of the positive electrode current collector and the porous body cannot be fully exhibited. Moreover, when the said positive electrode for metal air batteries is too thick, there exists a tendency which inhibits size reduction of the metal air battery finally obtained. For these reasons, if the thickness of the positive electrode for metal-air batteries is within the above range, it is possible to more appropriately realize discharge over a long period of time without making it thicker than necessary.

  Moreover, the said positive electrode for metal air batteries can be utilized as a positive electrode with which a metal air battery is equipped as mentioned above. When the positive electrode for a metal-air battery is used as a positive electrode provided in a metal-air battery, as shown in FIGS. 3 and 4, the porous body 21 provided in the positive electrode 20 for metal-air battery includes the separator. Preferably, the metal-air battery positive electrode 20 and the separator 40 are disposed so as to be in contact with 40. By arranging in this way, it is considered that the metal hydroxide derived from the metal ions eluted from the negative electrode can be further suppressed from precipitating on the surface of the positive electrode current collector, and a more suitable discharge can be maintained over a long period of time. A metal-air battery is obtained.

  Moreover, the said negative electrode will not be specifically limited if it is used as a negative electrode of a metal air battery. Specifically, the negative electrode includes a negative electrode active material made of a metal or an alloy. The metal is not particularly limited as long as it can be used as a negative electrode active material in a metal-air battery. Examples of the metal include zinc (Zn), aluminum (Al), magnesium (Mg), and calcium. The alloy is not particularly limited as long as it is an alloy that can be used as a negative electrode active material in a metal-air battery. Examples of the alloy include an alloy containing the metal. Specific examples include alloys including zinc alloys, aluminum alloys, magnesium alloys, calcium alloys, and the like. In addition, for example, an aluminum alloy is an alloy containing aluminum and generally refers to an alloy containing aluminum as a main component, and examples thereof include an alloy containing 50% by mass or more of aluminum. Moreover, a magnesium alloy is an alloy containing magnesium, and generally refers to an alloy containing magnesium as a main component. Examples thereof include an alloy containing magnesium in an amount of 50% by mass or more.

  Further, the negative electrode only needs to contain the negative electrode active material, and may be made of the negative electrode active material. Specific examples of the negative electrode include magnesium foil, magnesium alloy foil, aluminum foil, and aluminum alloy foil.

  Further, the thickness of the negative electrode is not particularly limited, but is preferably 0.001 to 5 mm, more preferably 0.005 to 4 mm, and more preferably 0.008 to 3 mm. . If the negative electrode is too thin, the battery capacity tends to be small. Moreover, when the said negative electrode is too thick, there exists a tendency which inhibits size reduction of the metal air battery finally obtained. For these reasons, when the thickness of the negative electrode is within the above range, it is possible to more appropriately achieve discharge over a long period of time without increasing the thickness more than necessary.

  Moreover, the said separator will not be specifically limited if it can be used as a separator of a metal air battery. That is, a separator is arrange | positioned between a negative electrode and a positive electrode, the electrical short circuit between a negative electrode and a positive electrode is prevented, and electrolyte solution is hold | maintained. The shape of the separator is not particularly limited, and examples thereof include a film shape, a woven fabric shape, and a nonwoven fabric shape. From the viewpoint of liquid retention, which is the performance of retaining the electrolytic solution, it is preferable to have voids, and specifically, a nonwoven fabric is preferable. Moreover, it does not specifically limit as a material of a separator, For example, resin, such as polyethylene and a polypropylene, glass, etc. are mentioned. That is, as a separator, the woven fabric which consists of these resin fibers and glass fibers, the nonwoven fabric using these resins and glass, etc. are mentioned. Moreover, a filter paper etc. are used as a separator.

  The thickness of the separator is not particularly limited, but is preferably 0.01 to 3 mm, more preferably 0.05 to 2 mm, and more preferably 0.1 to 1 mm. . If the separator is too thin, there is a tendency that an electrical short circuit between the negative electrode and the positive electrode cannot be sufficiently prevented, or the amount of electrolyte retained is reduced and a suitable battery reaction cannot be realized. On the other hand, if the separator is too thick, the metal-air battery finally obtained tends to be downsized or the battery reaction tends to be hindered. For these reasons, if the thickness of the separator is within the above range, it is possible to more appropriately realize discharge over a long period without increasing the thickness more than necessary.

Moreover, the said electrolyte solution will not be specifically limited if it can be used as an electrolyte solution of a metal air battery. That is, the electrolytic solution elutes metal from the negative electrode and supplies water (H ₂ O) that reacts with oxygen to the positive electrode. The pH of the electrolytic solution is not particularly limited and may be an acidic electrolytic solution, a neutral electrolytic solution, or a basic electrolytic solution. Among these, the electrolytic solution is preferably a neutral electrolytic solution or a weakly basic electrolytic solution from the viewpoint of safety during leakage.

  Examples of the electrolyte contained in the electrolytic solution include halides, sulfates, nitrates, phosphates, carbonates, bicarbonates, and organic acid salts. Examples of the halide include lithium chloride, sodium chloride, potassium chloride, calcium chloride, lithium bromide, sodium bromide, potassium bromide, lithium iodide, sodium iodide, and potassium iodide. Examples of the sulfate include lithium sulfate, sodium sulfate, and potassium sulfate. Examples of the nitrate include lithium nitrate, sodium nitrate, and potassium nitrate. Examples of the phosphate include lithium phosphate, sodium phosphate, and potassium phosphate. Examples of the carbonate include lithium carbonate, sodium carbonate, and potassium carbonate. Examples of the hydrogen carbonate include lithium hydrogen carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate. Examples of the organic acid salt include sodium acetate and potassium acetate. As the electrolyte, each of the above electrolytes may be used alone or in combination of two or more. Among the electrolytes, halides, phosphates, carbonates, hydrogen carbonates, and organic acid salts are preferable from the viewpoint of safety and electrolyte solubility, and lithium chloride, sodium chloride, potassium chloride, and calcium chloride are preferable. More preferred are chlorides such as sodium chloride and potassium chloride. That is, the electrolyte solution is preferably an electrolyte solution containing chloride ions (chloride ion electrolyte solution). Moreover, as this chloride ion electrolyte solution, sodium chloride aqueous solution, potassium chloride aqueous solution, magnesium chloride aqueous solution, calcium chloride aqueous solution etc. are used preferably, for example. Therefore, the electrolytic solution is more preferably an electrolytic solution using each of the chloride ion electrolytic solutions alone or an electrolytic solution using a combination of two or more.

  Further, the electrolytic solution is held by the separator. The method for holding the electrolytic solution in the separator is not particularly limited. For example, the method of immersing a separator in electrolyte solution etc. are mentioned. In addition, for example, the electrolyte solution may be stored in an electrolyte tank provided with the metal-air battery, and the electrolyte solution may be supplied to the separator. There are no particular limitations on the shape, material, and the like of such an electrolyte bath, as long as the electrolyte can be stored. Examples of the electrolyte bath include a container formed of a synthetic resin such as polypropylene.

  The present invention will be described more specifically with reference to the following examples. However, the scope of the present invention is not limited to these examples.

[Reference Example 1]
(Preparation of porous metal layer)
First, an aluminum foil having a thickness of 100 μm and a purity of 99.9% was formed on the surface by opening holes with a diameter of 0.5 mm at intervals of 3 mm and immersing in a 1 wt% sulfuric acid aqueous solution at 80 ° C. for 60 seconds. The natural oxide film is removed.

Next, the aluminum foil from which the natural oxide film was removed was immersed in a 90 ° C. aqueous solution having a phosphoric acid concentration of 1.0 mass% for 60 seconds. Thereafter, an aqueous solution (temperature of 30 ° C.) prepared so as to be 5% by mass of hydrochloric acid, 2% by mass of aluminum chloride, 0.1% by mass of sulfuric acid, 0.5% by mass of phosphoric acid, and 0.2% by mass of nitric acid. The aluminum foil is immersed in an aluminum concentration of 0.1% by mass), and 5 V, a current density of 0.5 A / cm ² , a sine wave current of 40 Hz in frequency is applied to the aluminum foil, and etching is performed for 300 seconds. A plurality of tunnel-like holes called pits having a width of 1 μm and a depth of 1 to 10 μm were formed.

  Next, in order to enlarge the formed pit holes, the obtained aluminum foil was immersed in a 10% by mass sulfuric acid aqueous solution at 60 ° C. for 5 minutes, followed by 0.1% by mass ethanolamine at 50 ° C. After hydration treatment with an aqueous solution, heat treatment was performed for 3 minutes at 250 ° C. in the atmosphere.

As described above, an aluminum foil subjected to the etching treatment was obtained. The aluminum foil subjected to this etching treatment had a large number of holes formed from one side to the other side. The obtained aluminum foil is a metal layer (porous metal layer) in which a large number of holes are formed. Moreover, the thickness of this metal foil was 0.2 mm. Moreover, the BET specific surface area of this metal foil was 5.1 m < ² > / g.

[Reference Example 2]
(Formation of oxide film)
By immersing the aluminum foil obtained in Reference Example 1 above in an aqueous solution of ammonium adipate having a concentration of 200 g / L at 80 ° C. and applying a voltage of 15 V at a low current density of 25 mA / cm ² , Chemical conversion treatment was applied to the aluminum foil that had been subjected to the etching treatment. By doing so, the film by anodic oxidation was formed on the surface of the aluminum foil. When this aluminum foil was cut and the cross section was observed with an electron microscope, the film thickness of the oxide film was 0.6 μm. Moreover, when the specific surface area (BET specific surface area) of the aluminum foil which formed this oxide film was measured using the vapor | steam adsorption amount measuring apparatus (BELSORP-18PLUS) by Nippon Bell Co., Ltd., it was 4.6 m < ² > /. g.

[Reference Example 3]
(Formation of carbon coating)
The aluminum foil obtained in Reference Example 1 was immersed in an aqueous resol phenolic resin solution at 80 ° C. and a concentration of 20 g / L, pulled up, dried for 12 hours with a hot air dryer at 80 ° C., and then The carbon film was formed on the aluminum foil by heating at 500 ° C. for 3 hours. When this aluminum foil was cut and the cross section was observed with an electron microscope, the film thickness of the carbon film was 0.4 μm. Moreover, it was 3.2 m < ² > / g when the specific surface area (BET specific surface area) of the aluminum foil in which this carbon film was formed was measured by the method similar to the reference example 2. FIG.

[Example 1]
(Metal air battery: Aluminum air battery)
First, as the positive electrode, an aluminum foil produced in Reference Example 2 and having an oxide film formed thereon was cut into 100 mm ² .

  Moreover, the aluminum foil was used as a negative electrode.

  Further, a saturated sodium chloride aqueous solution was used as the electrolytic solution.

As the separator, 120 mm ² filter paper (5C manufactured by Advantech Toyo Co., Ltd.) was used.

  Next, as shown in FIG. 1, a separator immediately after impregnating 10 mL of a saturated sodium chloride aqueous solution as an electrolytic solution is placed on the positive electrode, and further, a negative electrode is placed thereon, thereby placing aluminum. An air battery was produced.

[Example 2]
As the positive electrode, the same as Example 1 except that the aluminum foil produced in Reference Example 3 and having the carbon coating formed thereon was cut into 100 mm ² .

[Example 3]
Instead of using a separator immediately after impregnating with 10 mL of a saturated sodium chloride aqueous solution as an electrolytic solution, the separator was impregnated with 10 mL of a saturated sodium chloride aqueous solution as an electrolytic solution, and then left on the positive electrode for 5 hours. Example 1 is the same as in Example 1.

[Example 4]
Instead of using a separator immediately after impregnating with 10 mL of a saturated sodium chloride aqueous solution as an electrolytic solution, the separator was impregnated with 10 mL of a saturated sodium chloride aqueous solution as an electrolytic solution, and then left on the positive electrode for 5 hours. Example 2 is the same as in Example 2.

[Example 5]
(Positive electrode)
First, as the porous body, an activated carbon sheet (Kuraray Chemical Corporation Kurasheet CH900, thickness: 3 mm, BET specific surface area: 1200 m ² / g) cut to 100 mm ² was used.

Next, as the positive electrode current collector, an aluminum foil produced in Reference Example 2 on which an oxide film was formed and cut into 100 mm ² was used.

  A conductive adhesive in which a carbon-based filler was dispersed in an acrylic resin (Dotite XC-12 manufactured by Fujikura Kasei Co., Ltd.) was applied on both surfaces of the positive electrode current collector to a thickness of 200 μm. As shown in FIG. 3, heating is performed at 80 ° C. for 2 hours in a state where the two porous bodies are placed on both sides of the positive electrode current collector coated with a conductive adhesive on both sides. Thus, an integrated positive electrode was obtained in which the positive electrode current collector and the porous body were laminated in close contact. The thickness of this positive electrode was 6.2 mm.

(Metal air battery: Aluminum air battery)
As the positive electrode, the positive electrode obtained by the above production method was used.

  Moreover, the aluminum foil was used as a negative electrode.

  Further, a saturated sodium chloride aqueous solution was used as the electrolytic solution.

As the separator, 120 mm ² filter paper (5C manufactured by Advantech Toyo Co., Ltd.) was used.

  Next, as shown in FIG. 1, a separator immediately after impregnating 10 mL of a saturated sodium chloride aqueous solution as an electrolytic solution is placed on the positive electrode, and further, a negative electrode is placed thereon, thereby placing aluminum. An air battery was produced. At this time, the separator is disposed so as to contact the porous body provided in the positive electrode.

[Example 6]
The conductive adhesive is applied only to one surface of the positive electrode current collector, and as shown in FIG. 4, the porous body is laminated on one surface of the positive electrode current collector, The same as in the fifth embodiment. The thickness of this positive electrode was 3.2 mm. In this case as well, the separator is disposed so that the porous body provided in the positive electrode is in contact therewith.

[Example 7]
Example 6 is the same as Example 6 except that the separator is disposed so that the positive electrode current collector in the positive electrode is in contact with the separator. Specifically, the oxide film of the metal layer on which the oxide film is formed, which is a positive electrode current collector, is disposed so as to be in contact with the separator.

[Comparative Example 1]
Example 1 is the same as Example 1 except that the aluminum foil produced in Reference Example 1 and subjected to the etching treatment is cut into 100 mm ² as the positive electrode. That is, it is the same as in Example 1 except that a metal layer on which neither an oxide film nor a carbon film is formed is used.

[Comparative Example 2]
As the positive electrode, the same as in Example 1 except that the aluminum foil in Reference Example 1 before being etched was cut to 100 mm ² . That is, it is the same as that of Example 1 except that a metal layer on which neither an oxide film nor a carbon film is formed and an etching process is used is used.

[Comparative Example 3]
Instead of using a separator immediately after impregnating 10 mL of a saturated aqueous sodium chloride solution as an electrolytic solution, the separator was impregnated with 10 mL of a saturated aqueous sodium chloride solution as an electrolytic solution and then left on the positive electrode for 5 hours. It is the same as that of the comparative example 1 except using.

[Comparative Example 4]
Instead of using a separator immediately after impregnating with 10 mL of a saturated sodium chloride aqueous solution as an electrolytic solution, the separator was impregnated with 10 mL of a saturated sodium chloride aqueous solution as an electrolytic solution, and then left on the positive electrode for 5 hours. It is the same as that of the comparative example 2 except using this.

  The voltage and current immediately after production of each aluminum air battery obtained as described above, and the current after 5 hours from production were measured.

  As can be seen from Table 1, when using a positive electrode for an aluminum air battery comprising a metal layer in which a large number of holes are formed and a coating covering the surface of the metal layer (Examples 1 to 7), other than this As compared with the case of using the positive electrode, a larger amount of high voltage current was allowed to flow. That is, it can be seen that a suitable discharge could be maintained over a long period of time.

  From this, it can be seen that by using a positive electrode for an aluminum air battery comprising a metal layer in which a large number of holes are formed and a coating covering the surface of the metal layer, the resistance decreased and the extraction current increased. It can be seen that the durability is further maintained. It can be seen that such a positive electrode for an aluminum-air battery can have current collection efficiency, strength, corrosion resistance, and air permeability required for the positive electrode.

  The above can also be seen from a comparison between Examples 3 and 4 and Comparative Examples 3 and 4 in which the positive electrode and a separator impregnated with an electrolytic solution were previously contacted for 5 hours. That is, in the case of using the positive electrode on which the film was formed (Examples 3 and 4), the metal layer was not corroded by the electrolytic solution even after the contact for 5 hours in advance, but the film was formed. In the case of using a positive electrode that was not used (Comparative Examples 3 and 4), it can also be seen from the fact that the metal layer is corroded by the electrolytic solution even if the contact is made in advance for 5 hours, and a suitable discharge cannot be maintained. That is, when the positive electrode for an aluminum air battery in which the surface of the metal layer having a large number of pores is coated with a film is used (Examples 3 and 4), neither an oxide film nor a carbon film is provided (Comparative Example) By comparing with 3 and 4), it can be seen that a suitable discharge could be realized even if the electrolyte solution was kept in contact for a long time. In the case of the positive electrode for an aluminum air battery according to the example, the corrosion of the positive electrode by the electrolytic solution was sufficiently suppressed, whereas in the case of the positive electrode for an aluminum air battery according to the comparative example, the positive electrode was used by the electrolytic solution. This is probably because the corrosion of the positive electrode could not be sufficiently suppressed.

  Moreover, the case where the porous body is further laminated (Examples 5 to 7) is longer than the case where the metal layer on which the film is formed is used for the positive electrode (Examples 1 to 4). It was found that it can be maintained over a period of time.

DESCRIPTION OF SYMBOLS 10 Metal-air battery 20 Positive electrode 21 Porous body 22 Metal layer 23 Coating 25 Positive electrode collector 30 Negative electrode 40 Separator 50 Wattmeter

Claims (8)

A metal-air battery positive electrode provided in a metal-air battery including a negative electrode containing a negative electrode active material made of a metal or an alloy,
A metal layer with a large number of holes,
A positive electrode for a metal-air battery, comprising: a coating that covers the surface of the metal layer.   The positive electrode for a metal-air battery according to claim 1, wherein the coating is an oxide coating or a carbon coating.   3. The positive electrode for a metal-air battery according to claim 1, wherein the hole of the metal layer is formed over the entire metal layer. Comprising a porous body containing carbon;
The positive electrode for a metal-air battery according to any one of claims 1 to 3, wherein the porous body is laminated on the coating.   The positive electrode for a metal-air battery according to claim 4, wherein the metal layer coated with the coating is disposed so as to be sandwiched between two porous bodies. A positive electrode using oxygen as a positive electrode active material;
A negative electrode including a negative electrode active material made of a metal or an alloy;
An electrolytic solution for eluting metal ions from the negative electrode;
A separator interposed between the positive electrode and the negative electrode and holding the electrolytic solution;
The said positive electrode is a positive electrode for metal air batteries of any one of Claims 1-5, The metal air battery characterized by the above-mentioned.   The metal-air battery according to claim 6, wherein the electrolytic solution is a neutral electrolytic solution or a weakly basic electrolytic solution.   The metal-air battery according to claim 6 or 7, wherein the electrolytic solution is at least one selected from the group consisting of halides, phosphates, organic acid salts, carbonates and bicarbonates.

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