Metal-air battery

Abstract

Provided is a metal-air battery which is continuously operable over a long period of time. A metal-air battery 10 comprises a fuel cell 12, a fuel material 14, a joint body 16, and a supply device 18. An air electrode 12b reduces oxygen in the air to oxygen ions during discharge. A fuel electrode 12c oxidizes a hydrogen gas with the oxygen ions to water vapor during discharge. The fuel material 14 reacts with the water vapor to generate a hydrogen gas, and the fuel material 14 itself forms an oxide. The joint body 16 is disposed between the fuel cell 12 and an airtight container 16a to join the fuel cell 12 and the airtight container 16a together, and includes glass. The airtight container 16a hermetically contains the fuel material 14, and the air electrode 12b of the fuel cell 12 is hermetically fixed to a portion of the wall of the airtight container 16a with the air electrode 12b exposed to the outside. The fuel cell 12 and the fuel material 14 are heated to be maintained at respective prescribed temperatures. The supply device 18 is connected to the airtight container 16a, and supplies at least one selected from among hydrogen gas, water, and water vapor.

Description

Metal-air battery

[0001] The present invention relates to a metal-air battery that can be charged as well as discharged, and more particularly to a metal-air battery that uses metal powder or particles such as iron powder to regenerate fuel gas within the system.

[0002] Fuel cells are a means of generating electricity by supplying fuel gas to a power generator. Among fuel cells, solid oxide fuel cells (SOFCs), which use an inorganic solid electrolyte with oxygen ion conductivity, are known to be clean, highly efficient, and excellent power generation devices. In addition, metal-air batteries have been developed that can be used as secondary batteries by restoring the fuel gas consumed by the discharge of the fuel cell.

[0003] Patent Document 1 describes a metal-air battery having a solid electrolyte body, an anode, a cathode, an anode fuel material body, a heating portion, and a sealing portion.

[0004] Patent No. 5210450

[0005] However, Patent Document 1 does not take into consideration a method for replenishing hydrogen in the event that hydrogen leaks from the sealed space to the outside, and therefore has the problem of being unable to operate continuously for long periods of time.

[0006] The present invention has been made in view of the above-mentioned problems in the prior art, and an object of the present invention is to provide a metal-air battery that can be operated continuously for a long period of time.

[0007] That is, a first aspect of the present invention provides a metal-air battery comprising: a fuel cell having an air electrode, on one surface of a solid oxide membrane that conducts oxygen ions, that reduces oxygen in the air to oxygen ions during discharge, and an anode, on the other surface, that oxidizes hydrogen gas to water vapor by the oxygen ions during discharge; a fuel material that reacts with water vapor to produce hydrogen gas and becomes an oxide itself; and an airtight container in which the fuel material is airtightly contained, the airtight container having the air electrode of the fuel cell airtightly fixed to a part of its wall with the air electrode of the fuel cell exposed to the outside, and a joint including glass disposed between the fuel cell and the airtight container to join the fuel cell and the airtight container, the fuel cell and the fuel material being heated and maintained at their respective predetermined temperatures; and further comprising a supply device connected to the sealed container to supply at least one of hydrogen gas, water, and water vapor.

[0008] In addition, a second aspect of the present invention provides a metal-air battery comprising: a flat fuel cell having an air electrode, on one surface of an oxygen ion-conducting solid oxide membrane, that reduces oxygen in the air to oxygen ions during discharge, and an anode, on the other surface, that oxidizes hydrogen gas to water vapor by the oxygen ions during discharge; a fuel material that reacts with water vapor to produce hydrogen gas and itself becomes an oxide; a detachable fuel section having a first internal space in which the fuel material is airtightly contained; a main body section having a second internal space within which the main body section has an airtightly fixed air electrode of the fuel cell exposed to the outside in a part of its wall; and a joining body including glass, arranged between the fuel cell and the main body section to join them; and further comprising: a flow path arranged between the first internal space and the second internal space to communicate them; and a supply device connected to the first internal space, the second internal space, or the flow path, for supplying at least one of hydrogen gas, water, and water vapor.

[0009] Furthermore, in the first and second embodiments of the present invention, it is preferable that the supply device has a function of determining the timing for hydrogen gas replenishment based on a decrease in pressure inside the sealed container, a decrease in discharge capacity, a decrease in charge capacity, or an increase in overvoltage during charge and discharge, and then replenishes hydrogen.

[0010] The metal-air battery of the present invention can be operated continuously for a long period of time.

[0011] Fig. 1 is a cross-sectional view showing a first embodiment of a metal-air battery of the present invention. Fig. 2 is a cross-sectional view showing a fuel cell constituting the metal-air battery of Fig. 1 and its periphery. Fig. 3 is a cross-sectional view showing a second embodiment of a metal-air battery of the present invention. Fig. 4 is a cross-sectional view showing a first modified example of the metal-air battery of Fig. 3. Fig. 5 is a cross-sectional view showing a second modified example of the metal-air battery of Fig. 3.

[0012] The metal-air battery of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. First, a first embodiment of the metal-air battery of the present invention will be described. Fig. 1 is a cross-sectional view showing the first embodiment of the metal-air battery of the present invention, and Fig. 2 is a cross-sectional view showing a fuel cell and its periphery that constitute the metal-air battery of Fig. 1.

[0013] The metal-air battery 10 includes a fuel cell 12, a fuel material 14, a joint 16, and a supply device 18. The fuel cell 12 has a solid oxide membrane 12a that conducts oxygen ions, an air electrode 12b on one surface, and an anode 12c on the other surface. The air electrode 12b reduces oxygen in the air to oxygen ions during discharge. The anode 12c oxidizes hydrogen gas to water vapor using the oxygen ions during discharge. The fuel material 14 reacts with water vapor to produce hydrogen gas and becomes an oxide itself. The joint 16, which includes glass, is disposed between the fuel cell 12 and an airtight container 16a to join them. The airtight container 16a airtightly houses the fuel material 14, and the air electrode 12b of the fuel cell 12 is airtightly fixed to a portion of its wall while being exposed to the outside. The fuel cell 12 and the fuel material 14 are heated and maintained at their respective predetermined temperatures. The supply device 18 is connected to the airtight container 16a and supplies at least one of hydrogen gas, water, and water vapor. The cover 16b is preferably disposed between the outer surface of the airtight container 16a and the external environment to provide thermal insulation between them. With this configuration, the metal-air battery of the present invention can operate continuously for a long period of time.

[0014] Next, a second embodiment of the metal-air battery of the present invention will be described. FIG. 3 is a cross-sectional view showing the second embodiment of the metal-air battery of the present invention. The metal-air battery 30 includes a flat fuel cell 12, a fuel material 14, a joint 16, a detachable fuel section 32, a flow path 36, and a supply device 18. The fuel cell 12 includes a solid oxide membrane 12a that conducts oxygen ions, an air electrode 12b on one surface thereof, and an anode 12c on the other surface thereof. The air electrode 12b reduces oxygen in the air to oxygen ions during discharge. The anode 12c oxidizes hydrogen gas to water vapor using the oxygen ions during discharge. The fuel material 14 reacts with water vapor to produce hydrogen gas and then becomes an oxide. The fuel section 32 includes a first internal space 32a in which the fuel material 14 is hermetically housed. The joint 16 is disposed between the fuel cell 12 and the main body 34 to join them, and includes glass. The main body 34 has a second internal space 34a therein, and the air electrode 12b of the fuel cell 12 is airtightly fixed to a part of its wall while being exposed to the outside. The flow path 36 is arranged between the first internal space 32a and the second internal space 34a to communicate with each other. The supply device 18 is connected to the first internal space 32a and supplies at least one of hydrogen gas, water, and water vapor.

[0015] It is preferable that the first covering 32b be placed between the outer surface of the fuel section 32 and the external environment, the second covering 34b be placed between the outer surface of the main body section 34 and the external environment, and the flow path covering 36a be placed between the outer surfaces of each component constituting the flow path 36 and the external environment.

[0016] Next, a first modified example of the second embodiment of the metal-air battery of the present invention will be described. FIG. 4 is a cross-sectional view showing the first modified example of the metal-air battery of FIG. 3. The metal-air battery 40 differs from the metal-air battery 30 in that the shapes of the fuel portion 42, first internal space 42a, main body portion 44, and second internal space 44a are different from those of the fuel portion 32, first internal space 32a, main body portion 34, and second internal space 34a. However, the other aspects are the same, and therefore a description thereof will be omitted. The supply device 18 is connected to the second internal space 44a and supplies at least one of hydrogen gas, water, and water vapor. The first covering body 42b is preferably disposed between the outer surface of the fuel portion 42 and the external environment to provide thermal insulation, and the second covering body 44b is preferably disposed between the outer surface of the main body portion 44 and the external environment to provide thermal insulation.

[0017] Next, we will explain Modification 2 of the second embodiment of the metal-air battery of the present invention. FIG. 5 is a cross-sectional view showing Modification 2 of the metal-air battery of FIG. 3. Metal-air battery 50 differs from metal-air battery 30 in that the shapes of fuel section 42, first internal space 42a, and flow path 56 are different from those of fuel section 32, first internal space 32a, and flow path 36. However, since the fuel section 42 and first internal space 42a are identical to those of metal-air battery 40 and the rest of the battery is the same, a description thereof will be omitted. A supply device 18 is connected to flow path 56 and supplies at least one of hydrogen gas, water, and water vapor. A flow path covering 56a is preferably disposed between the outer surfaces of each component constituting flow path 56 and the external environment to insulate them from each other. This configuration allows the metal-air battery of the present invention to operate continuously for extended periods of time.

[0018] The supply device 18 has a function of determining the timing for hydrogen gas replenishment based on a decrease in pressure inside the airtight container 16a, a decrease in discharge capacity, a decrease in charge capacity, or an increase in overvoltage during charge and discharge, and then replenishes hydrogen. With this configuration, the metal-air battery of the present invention can operate continuously for a long period of time.

[0019] Next, the conditions for replenishing hydrogen gas and the like will be described. When replenishing hydrogen gas, the metal-air batteries 10, 30, 40, and 50 may be replenishing during charging, after charging, or during discharging. If the metal-air batteries 10, 30, 40, and 50 are mounted on a moving vehicle, the replenishing may be performed while the moving vehicle is stopped. The same applies when replenishing water vapor simultaneously with hydrogen gas. On the other hand, when replenishing only water vapor, the metal-air batteries 10, 30, 40, and 50 may be replenishing during charging or after charging, but it is not preferable to replenishing during discharging. Furthermore, when the metal-air batteries 10, 30, 40, and 50 are mounted on a moving vehicle, it is not preferable to replenishing only water vapor while the moving vehicle is stopped.

[0020] Next, the fuel material constituting the metal-air battery of the present invention will be described. The fuel material 14 is not particularly limited as long as it reacts with water vapor to produce hydrogen gas and becomes an oxide itself. However, it is preferably a pellet-shaped material composed of iron particles or iron powder and a shape-retaining material. The shape-retaining material is a sinter-resistant material or a mixture thereof. Examples of sinter-resistant materials include aluminum oxide, silicon dioxide, magnesium oxide, and zirconium oxide. At least a portion of the surface of the fuel material 14 is covered with the shape-retaining material, and the mass ratio of the shape-retaining material to the fuel material 14 is 0.1% or more and 5% or less. If this mass ratio is less than 0.1%, the surface of the fuel material 14 may sinter, preventing the redox reaction from occurring. If it is more than 5%, the redox rate may be excessively suppressed. The pellet diameter is, for example, 2 to 10 mm.

[0021] Next, the operating temperature of the metal-air battery of the present invention will be described. The temperature of the fuel cell 12 may be 450 to 1000°C, and the temperature of the fuel material 14 may be 300 to 1000°C. That is, if the temperature of the fuel cell 12 is below 450°C or the temperature of the fuel material 14 is below 300°C, the metal-air batteries 10, 30, 40, and 50 may not operate. If the temperature of the fuel cell 12 exceeds 1000°C or the temperature of the fuel material 14 exceeds 1000°C, a decrease in output due to aggregation of the fuel material 14 may occur. Note that if the temperature inside the airtight container 16a increases from, for example, 22°C to 730°C, the volume does not change, and therefore the internal pressure increases by approximately 3.4 times according to Boyle's law. Therefore, for a given thickness of the fuel cell 12, the larger the size of the fuel cell 12, the more likely the fuel cell 12 is to be damaged. The same applies to the first internal space 32a and the second internal space 34a that are in communication with each other, and to the first internal space 42a and the second internal space 44a that are in communication with each other.

[0022] Next, the state of the metal-air battery of the present invention during charging will be described. During charging, the fuel material 14 reacts with hydrogen gas to generate water vapor and becomes a pure metal, the fuel electrode 12c reduces the water vapor to hydrogen gas, the solid oxide film 12a conducts oxygen ions, and the air electrode 12b oxidizes the oxygen ions to oxygen and releases it into the air.

[0023] Next, the state of the metal-air battery of the present invention during discharge will be described. During discharge, the air electrode 12b reduces oxygen in the air to oxygen ions, the solid oxide film 12a conducts the oxygen ions, the fuel electrode 12c oxidizes hydrogen gas to water vapor, and the fuel material 14 reacts with water vapor to produce hydrogen gas and becomes an oxide itself.

[0024] Next, we will explain the effect of gravity on the metal-air battery of the present invention. When the flat fuel cell 12 is vertically arranged, it is necessary to prevent the assembly 16 (if it is liquid rather than solid) from moving downward due to gravity. On the other hand, when the flat fuel cell 12 is horizontally arranged, gravity tends to cause hydrogen gas, water vapor, and nitrogen to gather from the top, and over a long period of time, the gas molecules gradually become separated into layers. Therefore, in order to supply hydrogen gas to the fuel material 14 during charging and water vapor during discharging, and to supply water vapor during charging and hydrogen gas to the fuel cell 12 during discharging, it is preferable that the vertical lengths of the internal space of the airtight container 16a, the first internal space 32a, 42a, and the second internal space 34a, 44a, are as short as possible. Furthermore, it is preferable that the first internal space 32a, 42a and the second internal space 34a, 44a be positioned at the same vertical position (height) as possible. Because of the generation of conduit resistance, the flow paths 36, 56 are preferably as wide and short as possible, and are preferably positioned horizontally without tilting. Furthermore, if the temperature of the gas in each space is not uniform, convection is likely to occur. Specifically, if the heater is placed above, convection is likely to occur only in the gas above, but if the heater is placed below, convection is likely to occur not only in the gas above but also in the entire gas. The metal-air battery of the present invention is basically configured as described above.

[0025] The metal-air battery of the present invention has been described in detail above, but the present invention is not limited to the above description, and various improvements and modifications may be made without departing from the spirit and scope of the present invention.

[0026] The metal-air battery of the present invention has the advantage of being capable of continuous operation for a long period of time, and is therefore industrially useful.

[0027] 10, 30, 40, 50 Metal-air battery 12 Fuel cell 12a Solid oxide membrane 12b Air electrode 12c Anode 14 Fuel material body 16 Assembly 16a Airtight container 16b Cover 18 Supply device 32, 42 Fuel section 32a, 42a First internal space 32b, 42b First cover 34, 44 Main body section 34a, 44a Second internal space 34b, 44b Second cover 36, 56 Flow path 36a, 56a Flow path cover

Claims

1. A metal-air battery comprising: a fuel cell having an air electrode, on one surface of a solid oxide film that conducts oxygen ions, that reduces oxygen in the air to oxygen ions during discharge, and an anode, on the other surface, that oxidizes hydrogen gas to water vapor by the oxygen ions during discharge; a fuel material that reacts with the water vapor to produce the hydrogen gas and becomes an oxide itself; an airtight container in which the fuel material is airtightly contained, the airtight container having the air electrode of the fuel cell airtightly fixed to a part of its wall with the air electrode of the fuel cell exposed to the outside, and a joining body including glass arranged between the fuel cell and the airtight container to join the fuel cell and the airtight container; wherein the fuel cell and the fuel material are heated and maintained at their respective predetermined temperatures; and a supply device connected to the sealed container to supply at least one of hydrogen gas, water, and water vapor.

2. A metal-air battery comprising: a flat fuel cell having an air electrode, on one surface of an oxygen ion-conducting solid oxide membrane, that reduces oxygen in the air to oxygen ions during discharge, and an anode, on the other surface, that oxidizes hydrogen gas to water vapor by the oxygen ions during discharge; a fuel material that reacts with the water vapor to produce the hydrogen gas and becomes an oxide itself; a detachable fuel section having a first internal space in which the fuel material is airtightly contained; a main body section having a second internal space within which the air electrode of the fuel cell is airtightly fixed to a part of its wall with the air electrode exposed to the outside, and a joining body including glass arranged between the fuel cell and the main body section to join them; and further comprising: a flow path arranged between the first internal space and the second internal space to communicate them; and a supply device connected to the first internal space, the second internal space, or the flow path, for supplying at least one of hydrogen gas, water, and water vapor.

3. The metal-air battery according to claim 1 or 2, wherein the supply device has the function of determining the timing for hydrogen gas replenishment based on a drop in pressure inside the sealed container, a drop in discharge capacity, a drop in charge capacity, or an increase in overvoltage during charge and discharge, and then replenishes hydrogen.

Images