Metal-air battery

Abstract

Provided is a metal-air battery that makes it possible to shorten an apparent charging time. The metal-air battery 10 has a fuel material body 12, a first internal space 14, and a second internal space 16. The fuel material body 12 reacts with water vapor to generate hydrogen gas, and becomes an oxide. The fuel material body 12 is hermetically accommodated in the first internal space 14. The second internal space 16 is provided with a tabular fuel cell 18. The tabular fuel cell 18 is provided with an air electrode 18b on one surface of a solid oxide film 18a for conducting oxygen ions, and a fuel electrode 18c on the other surface. The air electrode 18b reduces oxygen in air to oxygen ions during discharge. The fuel electrode 18c oxidizes hydrogen gas into water vapor by use of oxygen ions during discharge. The first internal space 14 is detachable.

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 the replacement of a fully discharged anode fuel material with a fully charged anode fuel material, and therefore has the problem that the charging time cannot be shortened.

[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 shorten the apparent charging time.

[0007] That is, the present invention provides a metal-air battery having a fuel material that reacts with water vapor to produce hydrogen gas and becomes an oxide itself, a first internal space in which the fuel material is hermetically contained, and a second internal space provided with a flat fuel cell cell that has, on one surface of a solid oxide membrane that conducts oxygen ions, an air electrode that reduces oxygen in the air to oxygen ions during discharge, and a fuel electrode that oxidizes hydrogen gas to water vapor by the oxygen ions during discharge, on the other surface, wherein the first internal space is detachable.

[0008] Furthermore, in the present invention, it is preferable to further include a cooling gas introducing device for introducing and discharging cooling gas into the first internal space.

[0009] The metal-air battery of the present invention can reduce the apparent charging time.

[0010] Fig. 1 is a cross-sectional view showing a metal-air battery of the present invention. Fig. 2 is a cross-sectional view showing a fuel cell and its periphery that constitute the metal-air battery of Fig. 1. Fig. 3 is a cross-sectional view showing a fuel exchange system for a mobile body equipped with the metal-air battery of Fig. 1.

[0011] The metal-air battery of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. Fig. 1 is a cross-sectional view showing 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.

[0012] The metal-air battery 10 has a fuel material body 12, a first internal space 14, and a second internal space 16. The fuel material body 12 reacts with water vapor to produce hydrogen gas and then becomes an oxide. The first internal space 14 accommodates the fuel material body 12 in an airtight manner. The second internal space 16 contains a flat fuel cell 18. The flat fuel cell 18 has an air electrode 18b on one surface of an oxygen ion-conducting solid oxide membrane 18a, and an anode 18c on the other surface. The air electrode 18b reduces oxygen in the air to oxygen ions during discharge. The anode 18c oxidizes hydrogen gas to water vapor using the oxygen ions during discharge. The first internal space 14 is detachable. This configuration allows the metal-air battery of the present invention to shorten the apparent charging time.

[0013] The metal-air battery 10 may further include a cooling gas introduction device 20. In this case, the cooling gas introduction device 20 introduces and exhausts cooling gas into the first internal space 14. When the metal-air battery 10 is mounted on a vehicle, it is preferable that the cooling gas introduction device 20 is installed on the ground rather than on the vehicle. With this configuration, the metal-air battery of the present invention allows safe installation and removal of the first internal space 14.

[0014] The fuel container 22 defines a first internal space 14 therein. The first covering body 24 is preferably disposed between the outer surface of the fuel container 22 and the external environment to provide thermal insulation between them. The main container 26 defines a second internal space 16 therein. The second covering body 28 is preferably disposed between the outer surface of the main container 26 and the external environment to provide thermal insulation between them. The connecting body 30 is preferably disposed between the fuel cell 18 and the main container 26 to connect them. The flow path 32 is a part of the first internal space 14 or the second internal space 16, and connects the two. The flow path opening / closing device 34 opens and closes the flow path 32. To prevent gas from escaping from the second internal space 16 and cooling gas from entering the second internal space 16, the flow path 32 is preferably closed before starting the fuel material 12 replacement operation and opened after the replacement operation is completed.

[0015] Next, a fuel exchange system will be described. FIG. 3 is a cross-sectional view showing a fuel exchange system for the mobile body equipped with the metal-air battery of FIG. 1. The fuel exchange system 40 includes a mobile body 42 equipped with the metal-air battery 10 and an elevator device 44. The elevator device 44 is disposed on or below the floor surface on which the mobile body 42 moves, and is a device for moving the fuel container 22 and the first enclosure 24 disposed on its outer surface in a direction perpendicular to the floor surface on which the mobile body 42 moves. The first enclosure 24a represents a first enclosure that has been removed from the mobile body 42 because the remaining amount of fuel is low, and the first enclosure 24b represents a fully charged first enclosure to be installed in the mobile body 42.

[0016] The cooling gas introduction device 20 preferably includes a nitrogen gas container 20a, a water container 20b, and water 20c. The nitrogen gas container 20a is a container of nitrogen gas for cooling the fuel container 22, and the water container 20b is a container of water 20c for generating water vapor. The cooling gas introduction device 20 has the function of supplying and discharging nitrogen gas for cooling to the first internal space 14 of the metal-air battery 10 mounted on the mobile object 42, and the function of supplying water vapor together with the nitrogen gas to replenish the first internal space 14 instead of hydrogen gas. The replenishment of water vapor may occur either during or after charging the metal-air battery 10.

[0017] Next, the fuel material constituting the metal-air battery of the present invention will be described. The fuel material 12 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 12 is covered with the shape-retaining material, and the mass ratio of the shape-retaining material to the fuel material 12 is 0.1% or more and 5% or less. If this mass ratio is less than 0.1%, the surface of the fuel material 12 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.

[0018] Next, the operating temperature of the metal-air battery of the present invention will be described. The temperature of the fuel cell 18 may be 450 to 1000°C, and the temperature of the fuel material body 12 may be 300 to 1000°C. That is, if the temperature of the fuel cell 18 is below 450°C or the temperature of the fuel material body 12 is below 300°C, the metal-air battery 10 may not operate. If the temperature of the fuel cell 18 exceeds 1000°C or the temperature of the fuel material body 12 exceeds 1000°C, a decrease in output due to the aggregation of the fuel material body 12 may occur. Furthermore, if the temperature of the interconnected first and second internal spaces 14 and 16 increases, for example, from 22°C to 730°C, the volume does not change, and the pressure increases by approximately 3.4 times according to Boyle's law. Therefore, for a given thickness of the fuel cell 18, the larger the size of the fuel cell 18, the more likely the fuel cell 18 is to be damaged.

[0019] Next, the state of the metal-air battery of the present invention during charging will be described. During charging, the fuel material 12 reacts with hydrogen gas to generate water vapor and becomes a pure metal, the fuel electrode 18c reduces the water vapor to hydrogen gas, the solid oxide film 18a conducts oxygen ions, and the air electrode 18b oxidizes the oxygen ions to oxygen and releases it into the air.

[0020] Next, the state of the metal-air battery of the present invention during discharge will be described. During discharge, the air electrode 18b reduces oxygen in the air to oxygen ions, the solid oxide film 18a conducts the oxygen ions, the fuel electrode 18c oxidizes hydrogen gas to water vapor, and the fuel material 12 reacts with the water vapor to produce hydrogen gas and becomes an oxide itself.

[0021] Next, we will explain the effect of gravity on the metal-air battery of the present invention. When the flat fuel cell 18 is arranged vertically, it is necessary to prevent the assembly 30 (if it is liquid rather than solid) from moving downward due to gravity. On the other hand, when the flat fuel cell 18 is arranged horizontally, 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 12 during charging and water vapor during discharging, and to supply water vapor to the fuel cell 18 during charging and hydrogen gas during discharging, it is preferable that the vertical lengths of the first internal space 14 and the second internal space 16 be as short as possible. Furthermore, it is preferable that the first internal space 14 and the second internal space 16 be arranged at the same vertical position (height) as much as possible. Because of the generation of pipe resistance, the flow path 32 is preferably as wide and short as possible, and is preferably arranged horizontally without tilting. Furthermore, convection is more likely to occur if the gas temperature within each space is not uniform. Specifically, when the heater is placed above, convection tends to occur only in the gas above, but when the heater is placed below, convection tends 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.

[0022] 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.

[0023] The metal-air battery of the present invention has the effect of shortening the apparent charging time, and is therefore industrially useful.

[0024] REFERENCE SIGNS LIST 10 Metal-air battery 12 Fuel material body 14 First internal space 16 Second internal space 18 Fuel cell 18a Solid oxide membrane 18b Air electrode 18c Anode 20 Cooling gas introduction device 20a Nitrogen gas container 20b Water container 20c Water 22 Fuel container 24 First covering body 24a First covering body (after replacement) 24b First covering body (before replacement) 26 Main container 28 Second covering body 30 Joint 32 Flow path 34 Flow path opening / closing device 40 Fuel exchange system 42 Mobile body 44 Lifting device

Claims

1. A metal-air battery comprising: a fuel material that reacts with water vapor to produce hydrogen gas and becomes an oxide itself; a first internal space in which the fuel material is hermetically contained; and a second internal space containing a flat fuel cell having an air electrode on one surface of a solid oxide film that conducts oxygen ions, which reduces oxygen in the air to oxygen ions during discharge, and a fuel electrode on the other surface, which oxidizes hydrogen gas to water vapor by the oxygen ions during discharge, wherein the first internal space is detachable.

2. The metal-air battery according to claim 1, further comprising a cooling gas introducing device for introducing and discharging cooling gas into said first internal space.

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