JP2015170400A - metal-air battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal-air battery combining the functions of a secondary battery and a fuel battery, and functioning as a secondary battery during normal time capable of receiving system power supply, and as a fuel battery when system power supply cannot be received.SOLUTION: A metal-air battery of three-pole system has a structure capable of supplying fuel metal to an auxiliary pole, and plays the fuel battery function by causing power generation reaction between the auxiliary pole and an air pole. The auxiliary pole has a cylindrical holding structure so that the fuel metal can be fed equally.

Description

  The present invention relates to a rechargeable three-electrode metal-air secondary battery that can also be used as a fuel cell capable of supplying fuel with an auxiliary electrode as a third electrode.

  Metal-air batteries are batteries that can extract electrical energy obtained in the process of changing metals represented by zinc, iron, magnesium, aluminum, sodium, calcium, and lithium into metal oxides by electrochemical reactions. It is. The metal-air battery is composed of an air electrode, a metal electrode (hereinafter, metal is also referred to as a fuel electrode), an electrolyte such as an electrolyte, and the like.

  For example, in the case of a zinc metal-air battery, the following reaction occurs at the fuel electrode and the air electrode during discharge.

  At the fuel electrode, zinc and hydroxide ions react to generate zinc hydroxide, and electrons are emitted and flow to the air electrode. Zinc hydroxide is further decomposed into zinc oxide and water, and the water returns to the electrolyte.

  At the air electrode, oxygen contained in the air and electrons received from the fuel electrode react with water by the air electrode catalyst and change into hydroxide ions. Hydroxide ions conduct ions in the electrolyte and reach the fuel electrode.

  By these cycles, oxygen taken from the air electrode is utilized, and zinc in the fuel electrode is used as a fuel to realize continuous power extraction while forming zinc oxide. By utilizing this principle, button batteries (primary batteries) for hearing aids have already been put into practical use.

  On the other hand, various researches have been made on making the metal-air battery into a secondary battery, but in the case of the bipolar type, although the metal electrode (fuel electrode) is regenerated by charging, the air electrode is oxidized and consumed. In general, it is known that the lifetime is shortened, and it has not been put into practical use due to problems such as difficulty in realizing an inexpensive air electrode suitable for both charge and discharge reactions.

  In order to solve the above-described charging problem, for example, a three-electrode type or mechanical charge (mechanical charge) metal-air secondary battery has been proposed.

  The three-electrode system is a system that uses the third electrode without using the air electrode during charging in order to solve the problem of air electrode degradation in the two-electrode system. For example, in Patent Document 1, a cylindrical metal-air battery is proposed as a secondary battery using a three-electrode system.

  Patent Document 1 will be specifically described with reference to FIG. FIG. 5 shows a simplified metal-air battery of Patent Document 1. (A) is a vertical sectional view, and (b) is a plan view. Electric power is supplied by a discharge reaction between the positive electrode layer 902 and the negative electrode layer 903 disposed on the first electrolyte layer 911. In addition, charging is performed by applying a voltage to the negative electrode layer 903 and the auxiliary electrode layer 904 disposed in the second electrolyte layer 912 to cause a charging reaction, and depositing a metal on the negative electrode layer 903.

  As another method, a demonstration experiment of an electric vehicle (such as a large bus) by mechanical charging (mechanical charging) in which the entire fuel electrode is replaced has been performed in the past. As an example of mechanical charge, Patent Document 2 proposes a method of safely replacing a metal part (metal electrode) that is a negative electrode.

JP2012-209020 (released on October 25, 2012) JP 2004-362869 (released on June 3, 2003)

  However, for example, in a power storage device represented by a secondary battery such as Patent Document 1, the device itself does not have a power generation function, and can be charged and charged by receiving power supply from outside the device. Yes. That is, in an emergency in which the supply of system power cannot be received, there is a problem that if the pre-charged power is used up, it will not function as a power supply device.

  In addition, in the power generation apparatus such as Patent Document 2, it can be used as a power supply apparatus by consuming fuel in an emergency in which power supply from the system cannot be received, but charging is performed by using inexpensive system power. Therefore, it is necessary to purchase a dedicated fuel each time, and there are problems that the running cost is high and it is difficult to recover the device cost.

  That is, a device having both functions of a power storage device and a power generation device has not been proposed.

  The present invention has been made in view of the above problems, and is intended to provide a system that can be used as a secondary battery in normal times and can continuously generate power even when power supply from the system is lost. And

  In order to solve the above-described problems, a metal-air battery according to the present invention is a metal-air battery comprising a three-electrode battery cell composed of three electrodes, a fuel electrode, an air electrode, and an auxiliary electrode. The pole has a cylindrical shape with a holding structure, and has electrolyte permeability. The holding structure holds a metal material that is a fuel for power generation.

  In the metal-air battery of the present invention, the fuel electrode is disposed at the center of the metal-air battery, the auxiliary electrode is disposed so as to surround the fuel electrode, and the air electrode is disposed so as to surround the auxiliary electrode. Is preferred.

  In the metal-air battery of the present invention, it is preferable that the fuel electrode, the auxiliary electrode, and the air electrode each have a coaxial cylindrical shape having a common central axis.

  Moreover, it is preferable that the metal air battery of the present invention further includes a charging mechanism for evenly distributing the metal material to the holding structure.

  In the metal-air battery of the present invention, the metal material is preferably zinc.

  The present invention has been made in view of the above problems. In other words, by combining the functions of a power storage device and the power generation device, it is normally used as a secondary battery, and is used for peak shift to depreciate the main unit price. By using the polar fuel, it is possible to realize a system capable of continuous power generation even when power supply from the grid is lost.

BRIEF DESCRIPTION OF THE DRAWINGS It is Example 1 which shows Example 1 and shows a metal air battery typically. FIG. 1 is a diagram illustrating Example 1 and schematically illustrating a state in which fuel is charged into a metal-air battery. It is a perspective view for comparing the shape of the auxiliary electrode of a metal air cell, and the state which injected the fuel. It is sectional drawing which shows the example of the mechanism which throws in a fuel into a metal air cell. It is a figure which shows typically the example of a conventional structure of the metal air battery using a 3 pole system.

  The metal-air battery of Example 1 according to the embodiment of the present invention will be described below with reference to the drawings.

  The metal-air battery of the present invention is composed of a battery cell and an electrode switching device, but the electrode switching device is not shown in the drawing because there is no structural difference from the conventional three-pole metal-air secondary battery, and only the battery cell is shown. And

  In FIG. 1, the schematic of the metal air battery of Example 1 is shown. (A) is a vertical sectional view, and (b) is a plan view.

  The metal-air battery of Example 1 is a triode-type metal-air secondary battery cell composed of three electrodes, a fuel electrode 12, an auxiliary electrode 13, and an air electrode 14 that are immersed in the electrolyte 11. Become. These electrodes are arranged in a cylindrical shape from the center toward the outer edge in the order of the fuel electrode 12, the auxiliary electrode 13, and the air electrode 14. The auxiliary electrode 13 is surrounded by concentric cylindrical wall surfaces having different diameters (coaxial double cylinder), and the wall surface is made of a porous shape such as a metal mesh. The air electrode 14 side is a mesh 13a, and the fuel electrode side is a mesh 13b. This mesh structure realizes electrolyte permeability that allows the electrolyte 11 to move back and forth inside the mesh structure. Due to the electrolyte permeability, the space between the mesh 13a and the mesh 13b is actually filled with the electrolyte 11, but in FIG. 1, both (a) and (b) are left blank for convenience of explanation. The bottom surface of the auxiliary electrode 13 has a structure for holding the fuel metal, and may be any of a plate shape or a porous shape such as a metal mesh similar to the wall surface. In FIG. 1A, the upper portion of the auxiliary electrode 13 has an opening shape for charging the fuel metal. However, in practice, a lid may be provided so that unnecessary objects do not enter during normal use. .

  Details of each electrode will be described.

  For example, stainless steel, copper, iron, nickel, and aluminum can be used for the fuel electrode 12. Moreover, it can use as a fuel electrode for discharge by having zinc which is a fuel metal on the surface. Moreover, zinc may be previously provided to the surface by plating or the like, or a fuel metal (referred to as zinc in Example 1) may be deposited on the surface by charging.

  The auxiliary electrode 13 is made of a non-oxidizing porous metal material or the like as an auxiliary electrode of a tripolar metal-air secondary battery. For example, a nickel porous body or nickel / nickel alloy / SUS may be used.

  The air electrode 14 is made of, for example, a porous carbon material as a base material, and a surface thereof is coated with a catalyst for activating the reaction and a fluorine-based water repellent material for preventing leakage of the electrolyte. Then, one side is in contact with the air and the other side is in contact with the electrolyte 11.

  As the electrolyte 11, an aqueous potassium hydroxide solution or the like can be used.

  Next, the secondary battery operation of the metal-air battery of Example 1 will be described in detail with reference to FIG.

  Here, the electrode switching device is electrically connected to the positive electrode / negative electrode of the external load and the positive electrode / negative electrode of the external power source, the fuel electrode 12, the auxiliary electrode 13, and the air electrode 14 through the wiring, and is controlled by the control of the control unit. It has a function of switching the connection between each electrode of the external load / external power source and each electrode of the battery cell. This control may be realized by either manual operation or automatic determination.

  Charging as a secondary battery will be described. Charging is performed using the fuel electrode 12 and the auxiliary electrode 13. Specifically, the auxiliary electrode 13 and the positive electrode of the external power supply are connected, the fuel electrode 12 and the negative electrode of the external power supply are connected, and a voltage is applied from the external power supply. As a result, electrolysis occurs inside the metal-air battery, and the fuel electrode 12 is charged with fuel metal (zinc in the first embodiment) being deposited. Thereby, for example, if charging is performed when it is a time zone for inexpensive nighttime electric power, it is possible to charge at low cost.

  The discharge as a secondary battery will be described. Discharging is performed using the fuel electrode 12 and the air electrode 14 on which zinc is deposited by charging. Specifically, the air electrode 14 and the positive electrode of the external load are connected, and the fuel electrode 12 is connected to the negative electrode of the external load. Thereby, electric power is supplied as a battery of an air electrode (+) fuel electrode (-).

  The operation of the secondary battery of Example 1 has been described above based on FIG. Next, the fuel cell operation of the first embodiment will be described with reference to FIG.

  FIG. 2 shows a state in which fuel for operating the fuel cell is supplied to the metal-air battery of Example 1. As in FIG. 1, (a) shows a vertical sectional view and (b) shows a plan view. A state is shown in which zinc pellets 13c as a fuel metal are introduced into the space surrounded by the auxiliary electrode 13 described in FIG. 1, specifically, the meshes 13a and 13b. The zinc pellets 13c are processed and formed into pellets having a diameter larger than the hole diameters of the meshes 13a and 13b, and are supplied to the auxiliary electrode 13 from a pellet storage container (not shown) by a transport device (for example, a screw).

  Power generation as a fuel cell is performed using the auxiliary electrode 13 holding the zinc pellet 13c and the air electrode 14 as shown in FIG. Specifically, the air electrode 14 and the positive electrode of the external load are connected, and the auxiliary electrode 13 is connected to the negative electrode of the external load. Thereby, electric power is supplied as a battery of an air electrode (+) auxiliary electrode (-). In power generation as a fuel cell, the auxiliary electrode 13, which is the third electrode, is used instead of the original fuel electrode 12 when the previously accumulated power is used up in the secondary battery operation described so far. The zinc pellets 13c are supplied to generate electricity.

  In the conventional example described in Patent Document 1 shown in FIG. 5, the negative electrode layer 903 (the fuel electrode in the present application) is located between the auxiliary electrode layer 904 (the same auxiliary electrode) and the positive electrode layer 902 (the same air electrode). The second electrolyte layer 912 between the negative electrode layer 903 and the auxiliary electrode layer 904 is different from the first electrolyte layer 911 between the negative electrode layer 903 and the positive electrode layer 902. The auxiliary electrode layer 904 does not have a fuel metal holding structure. The difference is that it is not involved in power generation. In the arrangement of FIG. 5, when the secondary battery is discharged, discharge is performed by the positive electrode layer 902 and the negative electrode layer 903, and the surface of the negative electrode layer 903 facing the positive electrode layer 902 forms the auxiliary electrode layer 904. Because it is more active than the facing surface, it is easier to consume metal. On the other hand, when the secondary battery is charged, the auxiliary electrode layer 904 and the negative electrode layer 903 are charged, but the surface of the negative electrode layer 903 facing the auxiliary electrode layer 904 is more active than the surface facing the positive electrode layer 902, and the auxiliary electrode The surface facing the layer 904 tends to deposit metal more easily. Therefore, when viewed comprehensively, the metal tends to decrease on the surface facing the positive electrode layer 902 of the negative electrode layer 903, and forms an environment where the surface facing the auxiliary electrode layer 904 tends to increase, making control difficult and cycle life. There was a problem of shortening.

  In contrast, in the metal-air battery of Example 1, an auxiliary electrode 13 having electrolyte permeability is disposed between the air electrode 14 and the fuel electrode 12, as shown in FIG. Thereby, when the secondary battery is discharged, the discharge between the air electrode 14 and the fuel electrode 12 is performed without being disturbed by the auxiliary electrode 13, and at the time of charging, the auxiliary electrode 13 and the fuel electrode 12 are charged without any obstruction factor. It can be carried out. Therefore, both charge and discharge in the fuel electrode 12 are an equal reaction and are easy to control, and the cycle life can be extended.

  Further, in the case of emergency power generation, even if a part of the fuel metal remains in the fuel electrode 12, it is not between the air electrode 14 and the auxiliary electrode 13 where a power generation reaction occurs, and therefore power generation can be performed with minimal influence. . Further, if the auxiliary electrode 13 is used, it is easy to handle, and the fuel metal can be supplied efficiently even in the case of multiple cells.

  As described above, as the metal-air battery constituting the present invention, the positional relationship between the fuel electrode 12, the auxiliary electrode 13, and the air electrode 14 and the outline of the reaction of each electrode of charge / discharge / power generation have been described. Next, the effect of making the fuel metal holding structure of the auxiliary electrode 13 cylindrical will be described with reference to FIGS.

  FIG. 3A is a perspective view including a vertical cross section in a state where the zinc pellets 13c are put into the auxiliary electrode 13 of the first embodiment. FIG. 3B shows a case in which a holding structure of a flat space is applied to the auxiliary electrode as a comparative example.

  If the auxiliary electrode 13 has a cylindrical shape and the input space has a cylindrical shape as in the case of Example 1 in FIG. 3A, when the zinc pellet 13c is supplied from the pellet storage container to the auxiliary electrode 13, for example, a screw It can be input by a conveying device such as. As a result, the zinc pellets 13c can be thrown evenly in the horizontal direction, that is, at a uniform height.

  On the other hand, when the input space is a flat plate shape as in the comparative example of FIG. 3B, it is difficult to input the zinc pellets 13c evenly in the horizontal direction, that is, at a uniform height. As shown in FIG. 3B, it becomes non-uniform, such as being piled up high near the center. In this way, when the charging conditions are not uniform, the electric field at the time of power generation becomes uneven and the power generation characteristics are also deteriorated.

  FIG. 4 shows an example of the charging mechanism of the zinc pellet 13c. FIG. 4A shows an example of a charging mechanism applicable to the first embodiment, and FIG. 4B shows an example of a charging mechanism applicable to the comparative example. In any case, the zinc pellets 13c are conveyed onto the metal-air battery by rotating the conveying screw 15 for conveyance, and are charged into the auxiliary electrode 13 by the charging mechanism. The introduction mechanism 17 according to the first embodiment is further provided with a conical drop control member 18, so that the zinc pellets 13 c introduced from the conveying screw 15 are made to have an annular entire circumference that is an upper opening portion of the auxiliary electrode 13. Distribute evenly while spreading. With the simple configuration as described above, in the first embodiment, as shown in FIG. 3A, the input height of the zinc pellets 13c in the auxiliary electrode 13 is substantially uniform over the entire circumference in the horizontal direction.

  On the other hand, when only the conveying screw 15 is used in the comparative example of FIG. 4B, the conveying screw 15 can be introduced only from one position of the opening 16. As a result, as shown in FIG. 4 (b), it is piled up mainly at one location directly below the opening 16. Even if the opening 16 is made larger, the situation that it is introduced from one point of the end of the opening 16 does not change, so in the comparative example, the introduction height is not uniform in the horizontal direction.

  For example, when only the conveying screw 15 is applied to the first embodiment as in the comparative example of FIG. 4B, it is piled up at one place just below the opening 16 as in the comparative example. However, since the upper opening portion and the cross section of the auxiliary pole 13 are annular and have a continuous and continuous shape as in the first embodiment, for example, the charging mechanism 17 shown in FIG. 4A can be used. The zinc pellets 13c can be charged almost evenly. In the comparative example, the depth direction in FIG. 3B is narrower and lower in symmetry than in the first embodiment, and has no continuity. Therefore, the feeding mechanism 17 as shown in FIG. 4A may be used. It is difficult, and it is difficult to uniformly charge the zinc pellets 13c.

  The purpose of the input mechanism 17 in FIG. 4A is to supply the zinc pellets 13c substantially evenly during the fuel cell power generation of the metal-air battery, and the attachment / detachment thereof is not particularly limited. That is, it may be fixed to the auxiliary electrode or may be removable. Alternatively, it may be integrated with the auxiliary electrode. Further, the drop control member 18 has its conical center axis coincided with the center axis of the input mechanism 17 and the center axis of the auxiliary electrode 13 in order to evenly distribute the zinc pellets 13c to the holding structure of the auxiliary electrode 13. It is preferable.

  As described above, according to the configuration of the first embodiment, the zinc pellets 13c can be introduced into the auxiliary electrode 13 so as to be substantially spatially uniform, so that good power generation characteristics can be obtained.

  In addition, other effects of Example 1 other than the input height of the zinc pellet 13c will be described. For example, consider the case where the auxiliary electrode 13 and the air electrode 14 have a hollow rectangular parallelepiped shape. In such a configuration, the distance between the electrodes varies depending on the location, so that the deterioration is considered to be accelerated. Further, the presence of a portion where the distance between the electrodes is short or an edge portion causes concentration of the electric field, which may cause dendrite. On the other hand, in the configuration of the first embodiment, since the fuel electrode 12, the auxiliary electrode 13, and the air electrode 14 are all coaxial cylindrical shapes, the distance between the electrodes is substantially equal over the entire surface of each electrode. The above problems are unlikely to occur.

  That is, in the configuration of the first embodiment, the auxiliary electrode 13 has a cylindrical shape (or a coaxial cylindrical shape). The electric field during power generation becomes uniform, and good power generation characteristics can be obtained. 2. The zinc pellets 13c can be charged to a substantially uniform height, and as a result, the electric field during power generation becomes uniform and good power generation characteristics can be obtained. There is the above synergistic effect.

  In Example 1, the fuel electrode 12, the auxiliary electrode 13, and the air electrode 14 are all expressed as a cylindrical shape. Actually, the fuel electrode 12 has a columnar shape, and the auxiliary electrode 13 has a coaxial double cylindrical shape, but the above-described effects can be substantially obtained in any shape based on the columnar / cylindrical shape. Can do. That is, the cylindrical shape in the present invention includes various shapes based on a column / cylinder, such as a column, a cylinder, a double cylinder, and a hollow cylinder. Depending on the positional relationship of the electrodes and the role of holding the fuel metal, it may be appropriately designed and applied including the presence or absence of the bottom surface. If the cylindrical shape of each electrode is coaxial as described above, the distance between the electrodes is preferably equal.

In the second embodiment, the following may be considered as a modification of the auxiliary electrode 13 described in the first embodiment.
(A) A cylindrical type, that is, a structure of “electrode height> electrode diameter”.
(A) Disc type, that is, “electrode height <electrode diameter”.
(C) A mesh placed on all cylindrical walls.
(D) A mesh placed on a part of a cylindrical wall.

  As a specific example of (d), when viewed from above, meshes are arranged at 1-5 o'clock and 7-11 o'clock in terms of timepieces, and a supporting frame is provided between the meshes. There is. By providing the support frame, the strength is ensured, and both the electrolyte permeability and strength of the auxiliary electrode 13 can be realized.

The metal-air battery according to the present invention is a metal-air battery comprising a three-electrode battery cell composed of three electrodes, a fuel electrode, an air electrode, and an auxiliary electrode, and the auxiliary electrode has a cylindrical shape having a holding structure. The holding structure having electrolyte permeability is characterized by holding a metal material which is a fuel for power generation.

  The conventional secondary battery has a problem that it cannot supply power if the power stored in advance is used up. For this reason, when it is desired to secure sufficient power even in an emergency, it is necessary to pay attention to the remaining amount of the secondary battery and use it within the constraints, or prepare another power source as a backup.

  In addition, when power supply from the grid power is stopped, in order to use more power, a power generation device such as an internal combustion engine may be used. There is also a problem that it cannot be used indoors.

  On the other hand, the metal-air battery is also a fuel cell that can generate electricity by supplying a substance such as zinc as a fuel. However, when used in this form on a daily basis, sufficient cost merit cannot be obtained when compared with system power. Therefore, there is a problem that it can only be used as an emergency power source and it is difficult to recover the device cost.

  According to the above configuration, in the three-electrode type metal-air secondary battery, even when the material of the fuel electrode decreases and sufficient electric power cannot be obtained or when the material of the fuel electrode is used up, the power generation unit is switched. By supplying fuel metal to the holding structure provided on the auxiliary electrode, power can be generated continuously, and stable power supply can be achieved without paying attention to the remaining amount unlike a secondary battery.

  In addition, by making the auxiliary electrode into a shape with good electrolyte permeability, it is possible to suppress a decrease in power generation efficiency when used as a secondary battery and to realize a battery cell with high power generation efficiency.

  In addition, since the auxiliary electrode has a cylindrical holding structure, the fuel metal can be introduced spatially and uniformly, so that good power generation characteristics can be obtained.

  Further, it is not necessary to separately prepare a secondary battery or a power generation device as a backup, and the number of devices can be reduced because one device combines the functions of the secondary battery and the fuel cell.

  In addition, low-cost nighttime power supplied from the grid is routinely peak-shifted using the secondary battery function to depreciate the equipment cost, while injecting fuel metal into the auxiliary electrode in an emergency There is an effect that it becomes possible to supply the power.

  In the metal-air battery of the present invention, the fuel electrode is disposed at the center of the metal-air battery, the auxiliary electrode is disposed so as to surround the fuel electrode, and the air electrode is disposed so as to surround the auxiliary electrode. Is preferred.

  According to the above configuration, when used as a secondary battery, the consumption / precipitation surface of the fuel electrode can be made the same regardless of whether it reacts with the air electrode and the fuel electrode or the auxiliary electrode and the fuel electrode. It becomes easier to control. In addition, since there is no other electrode between the auxiliary electrode where the power generation reaction occurs and the air electrode in emergency power generation, there is no hindrance factor and the power generation efficiency is high. Even if a part of the fuel remains in the fuel electrode, it is not between the air electrode and the auxiliary electrode in which a power generation reaction takes place, so that it is possible to generate power with minimal influence.

  In the metal-air battery of the present invention, it is preferable that the fuel electrode, the auxiliary electrode, and the air electrode all have a coaxial cylindrical shape having a common central axis.

  According to the above configuration, since the distance between the electrodes is substantially equal over the entire surface of each electrode, electric field concentration hardly occurs, dendrite hardly occurs, and deterioration can be suppressed.

  In the metal-air battery of the present invention, it is preferable that the metal-air battery further includes a charging mechanism for evenly distributing the metal material to the holding structure.

  According to the above configuration, the fuel metal can be introduced evenly spatially, so that good power generation characteristics can be obtained. There is an effect that can be.

  In the metal-air battery of the present invention, the metal material is preferably zinc.

  According to the above configuration, by using inexpensive zinc that is suitable for a metal-air battery and widely used as a fuel metal material, the battery cell of the present invention can be easily designed, and a desired battery cell can be easily realized. it can.

  The metal-air secondary battery according to the present invention can be widely applied to all uses used as a power supply device.

DESCRIPTION OF SYMBOLS 11 Electrolyte 12 Fuel electrode 13 Auxiliary electrode 13a Mesh 13b Mesh 13c Zinc pellet 14 Air electrode 15 Carrying screw 16 Opening part 17 Input mechanism 18 Drop control member

Claims (5)

A metal-air battery comprising a three-electrode battery cell comprising three electrodes, a fuel electrode, an air electrode, and an auxiliary electrode,
The auxiliary electrode has a cylindrical shape having a holding structure, has electrolyte permeability, and the holding structure holds a metal material that serves as a fuel for power generation. The fuel electrode is disposed in the center of the metal-air battery,
The auxiliary electrode is arranged so as to surround the fuel electrode,
The metal-air battery according to claim 1, wherein the air electrode is disposed so as to surround the auxiliary electrode.   3. The metal-air battery according to claim 1, wherein the fuel electrode, the auxiliary electrode, and the air electrode each have a coaxial cylindrical shape having a common central axis.   The metal-air battery according to any one of claims 1 to 3, wherein the metal-air battery further includes a charging mechanism for evenly distributing the metal material to the holding structure.   The metal-air battery according to any one of claims 1 to 4, wherein the metal material is zinc.