Metal-air battery

Abstract

The present invention provides a metal-air battery which has good thermal efficiency. This metal-air battery 10 includes a solid electrolyte fuel cell 12, a heater 14, an airtight housing 16, a blower 18, and a heat exchanger 20. The heater 14 raises the temperature of the solid electrolyte fuel cell 12 to an operating temperature. The blower 18 is for blowing air into an air electrode 12a of the solid electrolyte fuel cell 12. The heat exchanger 20 heats the low-temperature air blown in by means of the high-temperature air to be discharged. The metal-air battery 10 is wrapped in a heat insulation layer 22 except for an entrance of air that contains a hydrogen gas and water vapor in an internal space 16a. The metal-air battery 10 includes a ceramic pipe 24. The ceramic pipe 24 is for supplying a hydrogen gas, water, or water vapor from the outside to the metal-air battery 10. The ceramic pipe 24 is connected to a tank 24b via an opening / closing valve 24a. The tank 24b contains water, water vapor, or hydrogen.

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 use of exhaust heat, and therefore has a problem of poor thermal efficiency.

[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 with good thermal efficiency.

[0007] Specifically, the present invention provides a metal-air battery comprising: a solid electrolyte fuel cell cell formed by laminating an air electrode capable of oxidizing and reducing oxygen in the air, a solid electrolyte membrane that conducts oxygen ions, and a hydrogen electrode capable of oxidizing and reducing hydrogen; a heater that heats the solid electrolyte fuel cell cell to an operating temperature; an airtight casing having the solid electrolyte fuel cell cell on its wall and having an internal space filled with a porous metal or metal powder made of iron, manganese, nickel, cobalt, or the like; a blower for blowing air into the air electrode of the solid electrolyte fuel cell cell; and a heat exchanger that heats the blown-in low-temperature air with the discharged high-temperature air, wherein the metal-air battery is surrounded by a thermal insulating layer except for an inlet and outlet for air containing hydrogen gas or water vapor, and the metal-air battery comprises a ceramic pipe for supplying hydrogen gas, water, or water vapor from the outside, and the ceramic pipe is connected to a tank containing water, water vapor, or hydrogen via an on-off valve.

[0008] Furthermore, the present invention preferably further comprises a temperature detection mechanism and a control device that controls the blower and heater in accordance with the temperature of the metal-air battery. It is also preferable that the present invention further comprises a pressure detection mechanism that measures the pressure in the internal space, and that the control device has a function of detecting a pressure drop in the internal space and opening and closing the on-off valve.

[0009] The metal-air battery of the present invention can improve thermal efficiency.

[0010] 1 is a cross-sectional view showing a fuel cell and its periphery that constitute the metal-air battery of the present invention.

[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 comprises a solid electrolyte fuel cell 12, a heater 14, an airtight housing 16, a blower 18, and a heat exchanger 20. The solid electrolyte fuel cell 12 is composed of a stack of an air electrode 12a, a solid electrolyte membrane 12b, and a hydrogen electrode 12c. The air electrode 12a can oxidize and reduce oxygen in the air. The solid electrolyte membrane 12b conducts oxygen ions. The hydrogen electrode 12c can oxidize and reduce hydrogen. The heater 14 heats the solid electrolyte fuel cell 12 to an operating temperature. The airtight housing 16 has the solid electrolyte fuel cell 12 on its wall and an internal space 16a filled with a porous metal body or metal powder (hereinafter referred to as fuel material 16b). The fuel material 16b is made of iron, manganese, nickel, or cobalt. The blower 18 blows air into the air electrode 12a of the solid electrolyte fuel cell 12. The heat exchanger 20 heats the incoming cold air with the outgoing hot air.

[0013] The metal-air battery 10 is surrounded by a thermal insulating layer 22, except for an inlet / outlet for air containing at least one of hydrogen gas and water vapor in the internal space 16a. The metal-air battery 10 is equipped with a ceramic pipe 24. The ceramic pipe 24 is used to supply hydrogen gas, water, or water vapor to the metal-air battery 10 from the outside. The ceramic pipe 24 is connected to a tank 24b via an open / close valve 24a. The tank 24b contains water, water vapor, or hydrogen. The junction 32 is disposed between the solid electrolyte fuel cell 12 and the airtight housing 16 to join them. This configuration allows the metal-air battery of the present invention to have improved thermal efficiency.

[0014] The metal-air battery 10 preferably further includes a temperature detection mechanism 26 and a control device 28. In this case, the control device 28 controls the blower 18 and the heater 14 according to the temperature of the metal-air battery 10. With this configuration, the metal-air battery of the present invention can maintain a constant operating temperature.

[0015] The metal-air battery 10 may further include a pressure detection mechanism 30. In this case, the pressure detection mechanism 30 measures the pressure in the internal space 16a, and the control device 28 has the function of detecting a drop in pressure in the internal space 16a and opening and closing the on-off valve 24a. With this configuration, the metal-air battery of the present invention can maintain charge and discharge performance for a long period of time by replenishing the fuel gas.

[0016] Next, the conditions for refilling hydrogen gas, etc. will be described. When refilling hydrogen gas, the metal-air battery 10 may be refilled during charging, after charging, or during discharging, or, if the metal-air battery 10 is mounted on a moving body, it may be refilled while the moving body is stopped. The same applies when refilling water vapor at the same time as hydrogen gas. On the other hand, when refilling only water vapor, the metal-air battery 10 may be refilled during charging or after charging, but it is not preferable to refill during discharging. Furthermore, when the metal-air battery 10 is mounted on a moving body, it is not preferable to refill only water vapor while the moving body is stopped.

[0017] Next, the fuel material constituting the metal-air battery of the present invention will be described. The fuel material 16b 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 16b is covered with the shape-retaining material, and the mass ratio of the shape-retaining material to the fuel material 16b is 0.1% or more and 5% or less. If this mass ratio is less than 0.1%, the surface of the fuel material 16b may sinter, preventing the oxidation-reduction reaction from occurring. If it is more than 5%, the oxidation-reduction 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 solid electrolyte fuel cell 12 may be 450 to 1000°C, and the temperature of the fuel material 16b may be 300 to 1000°C. That is, if the temperature of the solid electrolyte fuel cell 12 is below 450°C or the temperature of the fuel material 16b is below 300°C, the metal-air battery 10 may not operate. If the temperature of the solid electrolyte fuel cell 12 exceeds 1000°C or the temperature of the fuel material 16b exceeds 1000°C, a decrease in output due to aggregation of the fuel material 16b may occur. Furthermore, if the temperature of the internal space 16a increases from, for example, 22°C to 730°C, the volume does not change, and therefore the pressure increases by approximately 3.4 times according to Boyle's law. Therefore, for a given thickness of the solid electrolyte fuel cell 12, the larger the size of the solid electrolyte fuel cell 12, the more likely the solid electrolyte fuel cell 12 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 16b reacts with hydrogen gas to generate water vapor and becomes a pure metal, the hydrogen electrode 12c reduces the water vapor to hydrogen gas, the solid electrolyte membrane 12b conducts oxygen ions, and the air electrode 12a 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 12a reduces oxygen in the air to oxygen ions, the solid electrolyte membrane 12b conducts the oxygen ions, the hydrogen electrode 12c oxidizes hydrogen gas to water vapor, and the fuel material 16b reacts with 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 flat solid electrolyte fuel cells 12 are arranged vertically, it is necessary to prevent the assembly 32 (if liquid rather than solid) from moving downward due to gravity. On the other hand, when flat solid electrolyte fuel cells 12 are 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 16b during charging and water vapor during discharging, and to supply water vapor to the solid electrolyte fuel cells 12 during charging and hydrogen gas during discharging, it is preferable that the vertical length of the internal space 16a be as short as possible. Furthermore, if the temperature of the gas in the internal space 16a is not uniform, convection is likely to occur. Specifically, when a heater is placed above, convection is likely to occur only in the gas above, while when a heater is placed below, convection is likely to occur throughout the gas, not just the gas above. 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 improving thermal efficiency and is therefore industrially useful.

[0024] REFERENCE SIGNS LIST 10 Metal-air battery 12 Solid electrolyte fuel cell 12a Air electrode 12b Solid electrolyte membrane 12c Hydrogen electrode 14 Heater 16 Airtight housing 16a Internal space 16b Fuel material 18 Blower 20 Heat exchanger 22 Heat insulating layer 24 Ceramic pipe 24a Opening / closing valve 24b Tank 26 Temperature detection mechanism 28 Control device 30 Pressure detection mechanism 32 Joint

Claims

1. A metal-air battery comprising: a solid electrolyte fuel cell cell formed by laminating an air electrode capable of oxidizing and reducing oxygen in the air, a solid electrolyte membrane that conducts oxygen ions, and a hydrogen electrode capable of oxidizing and reducing hydrogen; a heater that heats the solid electrolyte fuel cell cell to its operating temperature; an airtight casing having the solid electrolyte fuel cell cell on its wall and having an internal space filled with a porous metal or metal powder made of iron, manganese, nickel, cobalt, or the like; a blower that blows air into the air electrode of the solid electrolyte fuel cell cell; and a heat exchanger that heats the internal space filled with high-temperature air by the discharged high-temperature air, wherein the internal space is surrounded by a thermal insulating layer except for an inlet and outlet for air containing hydrogen gas or water vapor, and the metal-air battery is provided with a ceramic pipe for supplying hydrogen gas, water, or water vapor from the outside, and the ceramic pipe is connected to a tank containing water, water vapor, or hydrogen via an on-off valve.

2. The metal-air battery according to claim 1, further comprising a temperature detection mechanism and a control device for controlling the blower and heater according to the temperature of the metal-air battery.

3. A metal-air battery as described in claim 2, further comprising a pressure detection mechanism for measuring the pressure in the internal space, and wherein the control device has the function of detecting a drop in pressure in the internal space and opening and closing the opening and closing valve.

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