Metal-air battery

Abstract

Provided is a metal-air battery that is capable of maintaining charge / discharge performance for a long period of time with a simpler configuration and less manufacturing labor. A metal-air battery 10 has a fuel cell 12, a fuel material body 14, and a bonding body 16. The bonding body 16 contains glass and is disposed between the fuel cell 12 and an airtight container 16a in order to join the fuel cell 12 and the airtight container 16a together. The airtight container 16a accommodates the fuel material body 14 in an airtight manner, and an air electrode 12b of the fuel cell 12 is fixed in an airtight manner to a portion of a wall of the airtight container in a state where the air electrode 12b is exposed to the outside. The fuel cell 12 and the fuel material body 14 are heated and maintained at respective prescribed temperatures. The crystallization temperature of the glass in the glass-containing bonding body 16 is higher than the prescribed temperature of the fuel cell 12. The metal-air battery 10 is manufactured such that the glass-containing bonding body 16 does not exceed the crystallization temperature, and is used in a temperature region where crystallization of the glass-containing bonding body 16 is not promoted.

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. Metal-air batteries have also been developed that can be used as secondary batteries by restoring the fuel gas consumed by the fuel cell's discharge. Furthermore, technology has been developed to prevent fuel gas leakage, preventing a decline in charge / discharge performance when the fuel gas is consumed and restored repeatedly over a long period of time.

[0003] Patent Document 1 describes that in a metal-air battery having a flat electrode composite, a negative electrode fuel material, and a metal sealed container, a glass film is provided to cover an oxide layer formed on at least one of the outer and inner surfaces of the sealed container in order to improve hydrogen permeation suppression performance.

[0004] Patent No. 6865993

[0005] However, Patent Document 1 has the problem that the structure becomes complicated because an oxide layer must be formed between the surface of the sealed container and the glass film, and also the problem that the sealed container must be fired in air to form the oxide layer, which increases the number of manufacturing steps.

[0006] The present invention has been made in consideration of the above-mentioned problems of the prior art, and an object of the present invention is to provide a metal-air battery that has a simpler configuration and requires fewer manufacturing steps, and is capable of maintaining charge-discharge performance 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 comprising, on one surface of a solid oxide film that conducts oxygen ions, an air electrode that reduces oxygen in the air to oxygen ions during discharge, and, on the other surface, a fuel electrode 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, on a part of its wall, the air electrode of the fuel cell airtightly fixed in a state where it is exposed to the outside, and an assembly 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; the glass of the glass-containing assembly has a crystallization temperature higher than the predetermined temperature of the fuel cell; the metal-air battery is manufactured so that the glass-containing assembly does not exceed the crystallization temperature; and the metal-air battery is characterized in that it is used mainly in a temperature range in which crystallization of the glass-containing assembly is not promoted.

[0008] In addition, a second aspect of the present invention provides 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; a second internal space constituted by a main body and flat fuel cells each 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; the fuel cells and the main body being hermetically joined by a glass-containing bonded body disposed between them; and a flow path disposed between them to communicate the first internal space with the second internal space; the metal-air battery is manufactured so that the glass-containing bonded body does not exceed its crystallization temperature; and the metal-air battery is characterized in that it is used mainly in a temperature range in which crystallization of the glass-containing bonded body is not promoted.

[0009] Furthermore, in the first and second aspects of the present invention, it is preferable that the predetermined temperature of the fuel cell is 450 to 800°C and the crystallization temperature of the glass is 820 to 900°C.

[0010] The metal-air battery of the present invention can maintain charge / discharge performance for a long period of time with a simpler configuration and fewer manufacturing steps.

[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 and its periphery constituting the metal-air battery of Fig. 1. Fig. 3 is a cross-sectional view showing a second embodiment of a metal-air battery of the present invention.

[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, and a joint 16. The fuel cell 12 has an air electrode 12b on one surface of an oxygen ion-conducting solid oxide membrane 12a, 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 glass of the glass-containing assembly 16 has a crystallization temperature higher than the predetermined temperature of the fuel cell 12. The metal-air battery 10 is manufactured so that the glass-containing assembly 16 does not exceed its crystallization temperature, and is used in a temperature range in which crystallization of the glass-containing assembly 16 is not promoted. 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 maintain long-term charge / discharge performance with a simpler configuration and fewer manufacturing steps.

[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 comprises a fuel material body 14, a first internal space 32, and a second internal space 34. The fuel material body 14 reacts with water vapor to produce hydrogen gas and then becomes an oxide. The first internal space 32 accommodates the fuel material body 14 in an airtight manner. The second internal space 34 is composed of a flat fuel cell 12 and a main body 34a. 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 cell 12 and the main body 34a are airtightly joined by a glass-containing joining body 16 disposed between them. The metal-air battery 30 further has a flow path 36. The flow path 36 is disposed between the first internal space 32 and the second internal space 34 to allow them to communicate with each other. The metal-air battery 30 is manufactured so that the temperature of the glass-containing joined body 16 does not exceed the crystallization temperature, and is used in a temperature range in which crystallization of the glass-containing joined body 16 is not promoted.

[0015] The fuel section 32a has a first internal space 32 therein. It is preferable that the first covering 32b be disposed between the outer surface of the fuel section 32a and the external environment, the second covering 34b be disposed between the outer surface of the main body 34a and the external environment, and the flow path covering 36a be disposed between the outer surfaces of the members constituting the flow path 36 and the external environment. With this configuration, the metal-air battery of the present invention can maintain long-term charge / discharge performance with a simpler configuration and fewer manufacturing steps.

[0016] 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.

[0017] Next, the operating temperature of the metal-air battery of the present invention will be described. The crystallization temperature of the glass may be 820 to 900°C. In this case, the temperature of the fuel cell 12 may be 450 to 800°C, and the temperature of the fuel material body 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 body 14 is below 300°C, the metal-air batteries 10 and 30 may not operate. If the temperature of the fuel cell 12 exceeds 800°C or the temperature of the fuel material body 14 exceeds 1000°C, a decrease in output due to the aggregation of the fuel material body 14 may occur. Note that if the internal temperature of 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 32 and the second internal space 34 which are in communication with each other.

[0018] 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.

[0019] 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.

[0020] 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 to the fuel cell 12 during charging and hydrogen gas during discharging, it is preferable that the vertical lengths of the internal spaces of the airtight container 16a, the first internal space 32, and the second internal space 34, be as short as possible. Furthermore, it is preferable that the first internal space 32 and the second internal space 34 be positioned at the same vertical position (height) as possible. Because of the generation of pipe resistance, the flow path 36 is preferably as wide and short as possible, and is preferably positioned 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.

[0021] Next, the present invention will be described in more detail with reference to specific examples. First, in Example 1, a metal-air battery A was fabricated using glass A. Glass A has a crystallization temperature of 800 to 900°C and a thermal expansion coefficient of 105 to 115×10 －７ Next, as Example 2, a metal-air battery B was fabricated using glass B. Glass B has a crystallization temperature of 800 to 900°C and a thermal expansion coefficient of 95 to 105 × 10 －７ / ℃.

[0022] Next, as Comparative Example 1, a metal-air battery C was fabricated using Glass C. Glass C has a crystallization temperature of 700 to 800°C and a thermal expansion coefficient of 110 to 120 × 10 －７ Next, as Comparative Example 2, a metal-air battery D was fabricated using Glass D. Glass D has a crystallization temperature of 700 to 800°C and a thermal expansion coefficient of 90 to 100 × 10 －７ / ℃.

[0023] <Discharge Capacity Measurement> As an indicator of long-term charge / discharge performance, the number of charge / discharge cycles under conditions where a discharge capacity of 90% or more was maintained was set, with a target range of 10 or more charge / discharge cycles. First, metal-air battery A was charged and discharged in a furnace at 730°C, cooled to room temperature, and then reheated and charged / discharged repeatedly, and the discharge capacity at each cycle was measured. As a result, metal-air battery A maintained 100% discharge capacity up to the 30th charge / discharge cycle, which was within the preset target range. Similarly, metal-air battery B was measured, and as a result, metal-air battery B maintained 100% discharge capacity up to the 10th charge / discharge cycle, which was within the preset target range.

[0024] In contrast, similar measurements were performed on metal-air battery C, which showed a discharge capacity of 0% after the sixth charge / discharge, thus falling outside the preset target range. Similarly, similar measurements were performed on metal-air battery D, which showed a discharge capacity of 0% after the third charge / discharge, thus falling outside the preset target range. These results clearly demonstrate that by constructing a metal-air battery in the same manner as in Examples 1 and 2, it is possible to maintain long-term charge / discharge performance with a simpler configuration and fewer manufacturing steps.

[0025] The metal-air battery of the present invention has been described in detail above with reference to Examples 1 and 2. However, 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 effect of being able to maintain charge / discharge performance for a long period of time with a simpler configuration and fewer manufacturing steps, and is therefore industrially useful.

[0027] 10, 30 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 32 First internal space 32a Fuel portion 32b First cover 34 Second internal space 34a Main body 34b Second cover 36 Flow path 36a Flow path cover

Claims

1. A metal-air battery comprising: a fuel cell comprising an air electrode, on one surface of an oxygen ion-conducting solid oxide film, 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 portion of its wall with the air electrode of the fuel cell exposed to the outside, and an assembly including glass disposed 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; the glass of the glass-containing assembly has a crystallization temperature higher than the predetermined temperature of the fuel cell; and the metal-air battery is manufactured so that the glass-containing assembly does not exceed the crystallization temperature, and the metal-air battery is mainly used in a temperature range in which crystallization of the glass-containing assembly is not promoted.

2. 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 composed of a main body and flat fuel cell cells each having an air electrode, on one surface of an oxygen ion-conducting solid oxide film, 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; wherein the fuel cell cells and the main body are hermetically joined by a glass-containing bonded body disposed between them, and further comprising a flow path disposed between them to communicate the first internal space with the second internal space; wherein the metal-air battery is manufactured so that the glass-containing bonded body does not exceed its crystallization temperature, and the metal-air battery is mainly used in a temperature range in which crystallization of the glass-containing bonded body is not promoted.

3. A metal-air battery according to claim 1 or 2, wherein the predetermined temperature of the fuel cell is 450 to 800°C, and the crystallization temperature of the glass is 820 to 900°C.

Images