JP2015216109A - Negative electrode for air battery, and solid electrolyte air battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a negative electrode for an air battery, which is high in capacity and superior in charge and discharge cycle characteristics; and a solid electrolyte air battery using such a negative electrode.SOLUTION: A negative electrode for an air battery comprises an active material layer including: an active material including a first metal element and capable of occluding and releasing oxygen; and a compound 5 including a second metal element and chemically more stable than the active material. A solid electrolyte air battery comprises: a negative electrode 2 composed of the negative electrode for an air battery; a positive electrode 1; and a solid electrolyte 3 between the positive electrode 1 and the negative electrode 2. In the solid electrolyte air battery arranged in this way, the grain growth and sintering of its active material are suppressed even at a high operation temperature and therefore, a high capacity and superior charge and discharge cycle characteristics are achieved.

Description

  The present invention relates to a negative electrode for an air battery and a solid electrolyte air battery using the same.

  Increasing demand for stationary large-scale storage batteries, such as storing electricity generated by natural energy such as wind power generation and solar power generation, and leveling power load by supplying power stored at night during the day Yes.

  In the metal-air battery, since the active material on the positive electrode side is oxygen, it is not necessary to fill the inside of the battery container with the positive electrode active material. That is, the active material filled in the battery container is only the negative electrode active material, so that the discharge capacity can be increased and the capacity can be increased (for example, see Patent Document 1). On the other hand, air batteries are considered to be difficult to make secondary batteries because the chemical properties of the negative electrode active material become unstable during charging or the metal of the negative electrode produces dendrites.

  Air batteries using iron for the negative electrode are promising as secondary batteries because dendrites are not generated during charging. For example, Patent Document 2 proposes an electrochemical energy conversion storage device using iron (iron oxide) as an energy storage medium capable of storing and recovering electrical energy.

JP 2012-043569 A Japanese National Patent Publication No. 11-501448

  However, in the electrochemical energy conversion storage device described in Patent Document 1, since an energy storage reaction bed using iron (iron oxide) is operated at a high temperature, iron (iron oxide) grows and sinters. However, the rate of the oxidation-reduction reaction decreases, the charge / discharge rate decreases, the reversibility of the oxidation-reduction reaction is impaired, the battery output density and capacity decrease due to the charge / discharge cycle, and the Coulomb efficiency is low. It was.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a negative electrode for an air battery having a high capacity and excellent charge / discharge cycle characteristics, and a solid electrolyte type air battery using the same.

  The negative electrode for an air battery of the present invention includes a first metal element, an active material capable of occluding and desorbing oxygen, a second metal element, and a compound that is chemically more stable than the active material. , Comprising an active material layer.

  The solid electrolyte type air battery of the present invention includes a solid electrolyte having oxygen ion conductivity between a positive electrode and a negative electrode, and the negative electrode is the above-described negative electrode for an air battery.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode for air batteries excellent in the charge / discharge cycle characteristic with high capacity | capacitance, and a solid electrolyte type air battery using the same can be provided.

It is sectional drawing which shows typically the structure of the solid electrolyte type air battery which is 1st Embodiment of this invention. (A) is sectional drawing which shows an example, (b) is sectional drawing which shows another example, (c) is sectional drawing which shows another example of the active material layer in this invention. It is a cross-sectional view of a cylindrical solid electrolyte type air battery which is an example of the first embodiment. It is sectional drawing which shows typically the structure of the solid electrolyte type air battery which is 2nd Embodiment of this invention. (A) of a solid electrolyte type air battery provided with a cylindrical battery cell as an example of the second embodiment is an overall view, and (b) is a cross-sectional view taken along line AA of (a). Sample No. 3 is a charge / discharge profile in the first cycle of the air battery of No. 3. Sample No. It is a graph which shows the behavior of the discharge capacity with respect to the discharge time of the 1st cycle of 1, 3, 8, and 10. FIG. Sample No. It is a graph which shows the behavior of the discharge capacity with respect to discharge time of the 5th cycle of 1, 3, 8 and 10. FIG.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

<First Embodiment>
A solid electrolyte type air battery (hereinafter also simply referred to as an air battery) according to a first embodiment of the present invention will be described with reference to FIG. The solid electrolyte type air battery of this embodiment includes a solid electrolyte 3 between a positive electrode 1 and a negative electrode 2.

The positive electrode 1 is the cathode, together with an oxygen reduction catalyst to reduce oxygen to oxide ions (O ^2-), guided by transmitting oxide ion (O ^2-) to the solid electrolyte 3. Examples of the oxygen reduction catalyst include lanthanum strontium cobalt ferrite ((La, Sr) (Co, Fe) O ₃ , LSCF), lanthanum strontium cobaltite ((La, Sr) CoO ₃ , LSC), samarium strontium cobaltite ((Sm , Sr) CoO ₃ , SSC) and the like. The positive electrode 1 is preferably a porous body of the oxygen reduction catalyst as described above, or the above-described oxygen reduction catalyst supported on a porous substrate. As the positive electrode 1, it is preferable to use LSC because of its high activity for oxygen reduction reaction and high electrical conductivity.

The solid electrolyte 3 is an inorganic solid electrolyte having oxygen ion conductivity such as a solid oxide. Examples of the material of the solid electrolyte 3 include rare earth stabilized zirconia (for example, yttrium stabilized zirconia (YSZ) and scandium) which are zirconia-based materials. Stabilized zirconia (ScSZ) and the like), gadolinium-doped ceria (GDC) that is a ceria-based material, and (La, Sr) (Ga, Mg) O ₃ (hereinafter, LSGM) that is a gallate-based material. As the solid electrolyte 3, it is preferable to use rare earth stabilized zirconia because of its high oxygen ion conductivity and excellent long-term stability in the operating environment of the air battery.

The oxide ions (O ²⁻ ) reduced by the positive electrode 1 move to the negative electrode 2 through the solid electrolyte 3 having oxygen ion conductivity.

The negative electrode 2 includes an active material layer 2a containing an active material. The active material is a material capable of occluding and desorbing oxygen, and the active material contained in the active material layer 2a is oxygenated by oxide ions (O ²⁻ ) that have moved to the negative electrode 2 through the solid electrolyte 3. Occludes (oxidizes). An electromotive force is generated when the active material occludes oxygen in the negative electrode 2, and the air battery is discharged.

  The active material is, for example, a metal such as zinc, iron, aluminum, magnesium, lithium, and the active material layer 2a is formed by layering a metal foil made of these metals, or a powdered or particulate active material. is there. In addition, when an active material is a powder form or a particulate form, the active material layer 2a may contain an electroconductive material, a binder, etc. as needed, and may have several pores.

  In the present embodiment, the active material layer 2a preferably contains a porous body of the active material, or a particulate active material 4 as shown in FIG. When a dense material such as a metal foil is used as the active material layer 2a, an oxide film may be formed on the surface depending on the type of the active material, which may reduce the reaction rate.

  In the air battery of this embodiment, the solid electrolyte 3 having oxygen ion conductivity is used. For example, when an electrolyte or a solid electrolyte 3 having metal ion conductivity is used as the electrolyte, the metal ions of the active material constituting the negative electrode 2 move from the negative electrode 2 side to the positive electrode 1 side through the electrolyte, and the positive electrode 1 Metal ions react with oxygen or the like on the surface, and a reaction product is deposited. And the oxygen reduction reaction in the positive electrode 1 is suppressed by the reaction product deposited on the surface of the positive electrode 1.

  On the other hand, in the present embodiment, since the solid electrolyte 3 having oxygen ion conductivity is used, no reaction product is deposited on the positive electrode 1 and the oxygen reduction reaction is not suppressed on the positive electrode 1. Moreover, in the air battery using the solid electrolyte 3, since the operating temperature is as high as 600 ° C. or higher, for example, the resistance of the electrode and the electrolyte material itself is reduced, and the performance of the battery is improved.

  On the other hand, since it operates at such a high temperature, in the case of an air battery using the solid electrolyte 3, the active material contained in the active material layer 2 a during the operation of the air battery, in particular, the particulate active material 4 is sintered. Knotting and grain growth are likely to occur. When the active material particles 4 are sintered or grain-grown, the surface area of the active material particles 4 is reduced, so that the rate of the oxidation-reduction reaction of the active material particles 4 gradually decreases, and the energy density of the air battery also decreases. To do.

  In the present embodiment, the active material layer 2a includes, in addition to the active material, a compound 5 (hereinafter referred to as a stable compound or simply a compound) that is a chemically stable material at the operating temperature of the air battery. The active material contains a first metal element that can occlude and desorb oxygen, that is, easily undergoes a redox reaction. On the other hand, the stable compound 5 contains the second metal element and is chemically more stable than the active material. The second metal element is mainly contained only in the stable compound 5 and is not substantially contained in the active material.

  As described above, the active material layer 2a includes the active material containing the first metal element and the compound 5 containing the second metal element and chemically stable at the operating temperature of the air battery. Sintering and grain growth of the active material are suppressed, the decrease in the redox reaction rate of the active material is suppressed, and the discharge (charging) rate of the air battery is improved, and the energy density of the air battery is decreased. It is suppressed. Moreover, the reversibility of the redox reaction of the active material is improved, the capacity of the air battery can be increased, and the coulomb efficiency and charge / discharge cycle characteristics are also improved.

The shape of the active material in the present embodiment is preferably a particulate active material 4 as shown in FIG. The active material is in the form of particles, and the active material particles 4 are compression-molded, or the active material layer 2a is formed as a mixture containing a binder, whereby an oxide ion (O ²⁻ ) or a mediator described later is obtained. And an air battery having a high reaction area and a high rate of redox reaction of the active material, that is, an air battery having a high output density and a high capacity.

And the stable compound 5 exists between the active material particles 4, that is, the stable compound 5 particles exist between the active material particles 4 as shown in FIG. 2A, or FIG. As shown in (b), at least a part of the surface of the active material particles 4 is coated with the stable compound 5, so that the active material particles 4 grow or sinter at the operating temperature of the air battery. It can suppress more reliably.

  As shown in FIG. 2C, the active material layer 2a may further contain metal particles 6 that have a catalytic action on the reduction of water vapor. The metal particles 6 promote the oxidation reaction of the active material in a form provided with a mediator described later.

Here, the particles 4 of the active material preferably have an average particle diameter of 0.1 to 20 μm. Since the active material particles 4 have such an average particle size, the reaction area with the oxide ions (O ²⁻ ) and a mediator described later is increased, and the active material particles 4 are grown and sintered. Performance degradation can be suppressed. Moreover, when the stable compound 5 is a particulate form, it is preferable that the average particle diameter is 0.1-2.0 micrometers. Since the stable compound 5 particles have such an average particle size, the compound 5 particles are dispersed between the active material particles 4 to suppress grain growth and sintering of the active material particles 4, and the compound 5 5 particle | grains themselves can be suppressed.

When the stable compound 5 covers the surface of the active material particles 4, 60 to 100% of the surface of the active material particles 4 is preferably covered with the stable compound 5. The compound 5 covers the surface of the active material particles 4 by 60% or more, thereby obtaining an effect of suppressing the sintering between the active material particles 4. The thickness of the compound 5 covering the surfaces of the active material particles 4 is preferably 10 to 200 nm. By setting the thickness of the compound 5 covering the surface of the active material particles 4 to 10 nm or more, grain growth and sintering of the active material particles 4 can be more reliably suppressed. Further, by setting the thickness of the compound 5 covering the surface of the active material particles 4 to 200 nm or less, the oxide ions (O ²⁻ ) can easily pass through the coating of the compound 5, and the active material particles 4 Easier to reach.

  For the shape, structure, and dimensions of the active material and the compound 5, for example, the cross section of the active material layer 2a is observed using a scanning electron microscope (SEM), and at the same time, the active material is analyzed by energy dispersive X-ray spectroscopy (EDS) analysis. And Compound 5 can be confirmed. The average particle diameter of the active material particles 4 and the compound 5 and the thickness of the coating layer may be obtained, for example, by image analysis of a cross-sectional SEM photograph of the active material layer 2a. Further, when the surface of the active material particles 4 is coated with the compound 5, in this specification, the coverage is defined as a ratio in which the contour of the cross section of the active material particles 4 is covered with the compound 5.

Examples of the material of the active material include metals such as zinc, iron, aluminum, magnesium, and lithium, and oxides of these metals. These materials are substances capable of storing oxygen, and among them, zinc, iron, magnesium and lithium can be desorbed in addition to storing oxygen, and can be expected to be used as secondary batteries. Preferred as a metal element. In particular, iron is particularly preferable as the first metal element because it can take various compositions such as FeO, Fe ₂ O ₃ , and Fe ₃ O ₄ when oxidized to iron oxide. As the active material of the present embodiment, any of iron metal, FeO, Fe ₂ O ₃ , and Fe ₃ O ₄ can be used. Further, when iron is used as the first metal element constituting the active material, no dendrite is generated during charging, and it can be suitably used as a secondary battery.

When an air battery using iron as the first metal element is charged as a secondary battery, the reaction opposite to the above-described discharge, that is, iron oxide as an active material is reduced in the negative electrode 2 and generated oxide ions ( O ²⁻ ) moves to the positive electrode 1 through the solid electrolyte 3, and the oxide ions (O ²⁻ ) moved to the positive electrode 1 are oxidized there, thereby charging the air battery.

  Aluminum occludes (oxidizes) oxygen to form very stable alumina, and once alumina is formed, it is difficult to desorb oxygen, so it is mainly used as a primary battery.

  The type of active material contained in the active material layer 2a can be confirmed by elemental analysis such as energy dispersive X-ray spectroscopy (EDS) analysis, fluorescent X-ray (XRF) analysis, high frequency inductively coupled plasma (ICP) emission spectroscopy, or the like. . Further, the crystal phase may be identified by X-ray diffraction (XRD) measurement.

The second metal element is included only in the stable compound 5 and is not included in the active material. The second metal element is preferably at least one of, for example, zirconium and aluminum. These oxides and composite oxides are chemically very stable. Specific examples of the stable compound 5 include rare earth elements as composite oxides containing zirconium in addition to oxides of individual metal elements. And complex oxides thereof, zirconates (such as BaZrO ₃ and Ba (Zr, Ti) O ₃ ), and zirconium silicate (ZrSiO ₄ ). Examples of the complex oxide containing aluminum include complex oxides with rare earths (such as Y ₃ Al ₅ O ₁₂ ) and spinels (such as MgAlO ₄ and FeAlO ₄ ). Among these, when an oxide or composite oxide containing aluminum, particularly alumina or FeAlO ₄ is contained as the compound 5, the active material layer 2a having excellent discharge rate and discharge capacity stability is preferable.

  For the stable compound 5 contained in the active material layer 2a, for example, a cross-section of the active material layer 2a for identifying the crystal phase from the XRD pattern obtained by X-ray diffraction (XRD) measurement of the active material layer 2a is SEM. It can be confirmed by a method such as observing and elemental analysis by EDS.

The content ratio X of the stable compound 5 in the active material layer 2a is preferably 5% by mass or more and 20% by mass or less when expressed by the following calculation formula.
X = B / (A + B)
Here, A is the oxide equivalent amount of the first metal element contained in the active material layer 2a, and B is the oxide equivalent amount of the second metal element contained in the active material layer 2a. Note that the first metal element not only constitutes the active material but may be contained in the stable compound 5, but may be evaluated as the total amount contained in the active material layer 2a.

For example, when the active material is iron and the stable compound 5 is FeAlO ₄ , the calculation is performed by comparing A which is the total amount of Fe contained in the active material and the compound 5 with the amount B of Al contained in the compound 5 Good. The ratio of each metal element contained in the active material layer 2a is obtained by elemental analysis such as fluorescent X-ray (XRF) analysis, high frequency inductively coupled plasma (ICP) emission spectroscopic analysis, or the like.

  An example is shown about the manufacturing method of the air battery (refer FIG. 3) of this embodiment. In addition, the manufacturing method shown below is an example and it does not limit at all about the manufacturing method, shape, and material of the air battery of this embodiment.

  The active material layer 2a of the negative electrode 2 is, for example, an iron oxide powder having an average particle size of 0.5 to 1.0 μm (for example, a purity of 98% or more), which is an active material, and a stable compound 5 (or a precursor thereof). What is necessary is just to produce using the alumina powder (for example, purity 95% or more) or the rare earth stabilized zirconia powder (for example, YSZ with purity 95% or more) of an average particle diameter of 0.1-0.5 micrometer as a raw material. A predetermined amount of these raw materials are blended, and mixed with a dispersing agent, a pore-forming agent, a binder, a solvent and the like as necessary to prepare a clay.

The kneaded material of the obtained active material layer 2a is extrusion-molded to obtain a cylindrical molded body. For example, a lanthanum chromite paste that becomes the interconnector 7 and a yttrium stabilized zirconia (YSZ) paste that becomes the solid electrolyte 3 are applied to the outer surface and dried. Thereafter, the molded body of the active material layer 2a coated with lanthanum chromite and YSZ is fired at, for example, 1200 ° C. or higher to obtain the active material layer 2a with the solid electrolyte 3. The interconnector 7 is formed on the surface of the active material layer 2a and functions as a current collector.

  A paste of, for example, lanthanum strontium cobalt ferrite (LSCF) to be the positive electrode 1 is applied to the surface of the solid electrolyte 3 of the fired active material layer 2 a with the solid electrolyte 3. After firing the active material layer 2a with the solid electrolyte 3 coated with LSCF at 1000 ° C. or higher, a platinum paste as a current collector is printed and baked on the surfaces of the positive electrode 1 and the interconnector 7, respectively. The air battery of this embodiment as shown in FIG.

  A positive electrode terminal is electrically connected to the current collector on the positive electrode 1 side of the air battery, and a negative electrode terminal is electrically connected to the interconnector 7 to charge and discharge the air battery.

Second Embodiment
A solid electrolyte type air battery according to a second embodiment of the present invention will be described with reference to FIG. Since the positive electrode 1 and the solid electrolyte 3 are the same as those in the first embodiment, further explanation is omitted.

  In the present embodiment, the negative electrode 2 further includes a catalyst 2b and a mediator (redox mediator, redox mediator) 2c in addition to the active material layer 2a. The catalyst 2b is disposed in contact with the solid electrolyte 3, and the mediator 2c is interposed between the active material layer 2a and the catalyst 2b. Unlike the oxygen reduction catalyst used for the positive electrode 1, the catalyst 2b promotes the oxidation-reduction reaction of the mediator 2c (for example, a mixture of hydrogen and water vapor).

Thus, in the air battery of this embodiment, the negative electrode 2 has a structure in which the active material layer 2a that is an energy storage unit and the catalyst 2b that is a part of the battery cell are separated via the mediator 2c. In the active material layer 2a, the active material expands / contracts, that is, changes in volume, along with the redox reaction of the active material. When the active material layer 2a is in direct contact with the solid electrolyte 3 as in the first embodiment, peeling or the like is performed at the interface between the negative electrode 2 (active material layer 2a) and the solid electrolyte 3 as the active material layer 2a expands and contracts. There is a concern that this problem will occur. On the other hand, when the catalyst 2b is in direct contact with the solid electrolyte 3 and the mediator 2c is interposed between the active material layer 2a and the catalyst 2b as in this embodiment, at the interface between the solid electrolyte 3 and the negative electrode 2 The occurrence of defects such as peeling can be suppressed and the reliability can be improved. Furthermore, by separating the active material layer 2a and the catalyst 2b, the operating conditions of the active material layer 2a and the operating conditions of the battery cell including the positive electrode 1, the solid electrolyte 3 and the catalyst 2b are suitable for each. The entropy loss when operating the air battery can be reduced. Therefore, long-term stability and energy efficiency of the air battery can be improved.

  In the present embodiment, for example, when YSZ is used as the solid electrolyte 3 and iron is used as the first metal element constituting the active material, the operating temperature in the active material layer 2a is about 700 ° C. The operating temperature of the battery cell including the electrolyte 3 and the catalyst 2b can be about 500 ° C.

  As the catalyst 2b in the present embodiment, for example, a noble metal such as platinum or palladium, nickel, copper, or the like may be used. From the viewpoint of heat resistance and cost, it is preferable to use a cermet containing nickel and rare earth stabilized zirconia. .

The mediator 2c plays a role of mediating the redox reaction between the catalyst 2b and the active material layer 2a, but does not change as a whole. For example, when a mixed gas (H ₂ / H ₂ O gas) of hydrogen (H ₂ ) and water (H ₂ O, water vapor) is used as the mediator 2c, hydrogen (H ₂ ) is oxidized on the surface of the catalyst 2b during discharge. It reacts with product ions (O ²⁻ ) to produce water (H ₂ O). In the active material layer 2a, water (H ₂ O) reacts with the active material (oxidizes the active material), and the active material absorbs oxygen to generate hydrogen (H ₂ ). During charging, water (H ₂ O) is electrolyzed on the surface of the catalyst 2b to generate hydrogen (H ₂ ). In the active material layer 2a, hydrogen (H ₂ ) reacts with the active material (reducing the active material), and the active material desorbs oxygen to generate water (H ₂ O).

As the mediator 2c, in addition to the aforementioned H ₂ / H ₂ O gas, a molten salt or the like can be used. However, since the molten salt is highly corrosive, the reliability of the electrode material and the active material is ensured. Therefore, it is preferable to use H ₂ / H ₂ O gas as the mediator 2c.

When H ₂ / H ₂ O gas is used as the mediator 2c, it is preferable that the active material layer 2a further contains metal particles 6 that have a catalytic action on the reduction of water vapor, as shown in FIG. The oxidation rate of the active material particles 4 can be improved by the metal particles 6, and as a result, the output density of the battery is improved.

  As shown in FIG. 2C, the presence of the metal particles 6 having a catalytic action for the reduction of water vapor in the gaps between the active material 4 and the compound 5 promotes the reduction reaction of the water vapor, that is, the oxidation reaction of the active material. can do.

  The metal particles 6 having a catalytic action for the reduction of water vapor preferably have an average particle diameter of 0.01 to 1.0 μm. By setting the average particle size of the metal particles 6 in such a range, the contact area between the metal particles 6 and water vapor or the active material is increased, and the oxidation reaction of the active material can be further promoted. In addition, by setting the average particle diameter of the metal particles 6 to 0.01 μm or more, sintering of the metal particles 6 itself during operation of the battery cell is suppressed, and the specific surface area of the metal particles 6 is maintained in the active material layer 2a. As a result, it is possible to suppress the performance degradation of the catalytic action (promoting the oxidation reaction of the active material).

  As the metal particles 6, for example, platinum, palladium, copper, nickel and the like can be used, and it is particularly preferable to use a noble metal such as palladium and platinum. These noble metals are chemically stable to other materials constituting the active material layer 2a, such as iron and iron oxide, alumina, and zirconia, and have a very high reactivity with respect to the reduction of water vapor. Although these noble metals have very high resource costs and the amount of use is limited, an effect as a catalyst can be expected with addition of a small amount. In particular, when iron or the like is used as an active material, the oxidation / reduction cycle progresses and the particle growth and sintering of the active material particles 4 progress and the reactivity with water vapor decreases. It is desirable to promote the oxidation reaction by the presence of the particles 6.

  The content ratio of the metal particles 6 contained in the active material layer 2a is preferably 0.1% by mass or more and 5% by mass or less as a ratio with respect to the total amount of metal elements contained in the active material layer 2a. When the content ratio of the metal particles 6 is 0.1% by mass or more, the effect of promoting the reduction reaction of water vapor is sufficiently obtained, and when the content ratio is 5% by mass or less, a sufficient battery capacity can be secured. In addition, when palladium or platinum is used as the metal particles 6, the material cost can be suppressed by minimizing the content ratio of the metal particles 6. The content ratio of the metal particles 6 can be confirmed by elemental analysis such as fluorescent X-ray (XRF) analysis and high frequency inductively coupled plasma (ICP) emission spectroscopic analysis.

  The shape, structure, and dimensions of the metal particles 6 are determined by, for example, observing the cross section of the active material layer 2a using a scanning electron microscope (SEM) and simultaneously analyzing the active material or compound by energy dispersive X-ray spectroscopy (EDS) analysis. 5. It can be confirmed by discriminating the metal particles 6. The average particle diameter of the metal particles 6 may be obtained by image analysis of a cross-sectional SEM photograph of the active material layer 2a, for example.

What is necessary is just to produce the air battery (refer FIG. 5) of this embodiment as follows, for example. First,
The active material layer 2a is produced. A predetermined amount of the raw material of the active material layer 2a shown in the first embodiment and, if necessary, palladium powder having an average particle size of 0.01 to 0.05 μm, which is metal particles 6 having high reactivity to reduction of water vapor, are blended. And after press-molding the raw material powder mixed similarly to 1st Embodiment, the press-molding body of this active material layer 2a is baked independently. The firing temperature may be, for example, 800 to 1000 ° C. In the present embodiment, a mixed powder obtained by mixing an active material powder and a stable compound 5 powder may be used as the active material layer 2a as it is or after being molded.

  The catalyst 2b is produced as follows. For example, nickel powder (average particle size 1.0 μm, purity 98%) and yttrium-stabilized zirconia powder (YSZ, average particle size 0.5 μm, purity 98% or more) are mixed by a kneader with a binder and a solvent as necessary. Make the clay.

  The clay of the obtained catalyst 2b is extrusion molded to obtain a cylindrical molded body. For example, a lanthanum chromite paste that becomes the interconnector 7 and a yttrium stabilized zirconia (YSZ) paste that becomes the solid electrolyte 3 are applied to the outer surface and dried. Thereafter, the molded body of the catalyst 2b coated with YSZ is fired at, for example, 1200 ° C. or higher to obtain the catalyst 2b with the solid electrolyte 3. The interconnector 7 is formed on the surface of the catalyst 2b and functions as a current collector.

  For example, lanthanum strontium cobalt ferrite (LSCF) paste to be the positive electrode 1 is applied to the surface of the solid electrolyte 3 of the calcined catalyst 2b with the solid electrolyte 3. By baking the catalyst 2b with the solid electrolyte 3 coated with LSCF at 800 ° C. or more, a battery cell as shown in FIG. 5B is obtained. In addition, the exposed part of the catalyst 2b and the solid electrolyte 3 exists in the outer surface of the both ends of a battery cell.

  A platinum paste as a current collector is printed and baked on the surfaces of the positive electrode 1 and the interconnector 7 of the obtained battery cell.

  The part where the catalyst 2b located at both ends of the produced battery cell is exposed is inserted into the opening of the container 8 and fixed as shown in FIG. 5A, and the solid electrolyte of the opening of the container 8 and the battery cell is fixed. 3 is sealed with glass. An active material layer 2 a is accommodated inside the container 8. As the container 8, for example, a metal or ceramic made of a heat-resistant alloy such as stainless steel, nickel-base alloy, or chromium-base alloy is used. In FIG. 5A, the positions of the catalyst 2b and the active material layer 2a inside the container 8 are indicated by broken lines for easy explanation.

  By introducing hydrogen into the space between the active material layer 2a and the catalyst 2b inside the container 8 and sealing the space, the air battery of this embodiment is obtained.

  A positive electrode terminal is electrically connected to the current collector on the positive electrode 1 side of the air battery, and a negative electrode terminal is electrically connected to the interconnector 7 to charge and discharge the air battery. In addition, as shown to Fig.5 (a), you may install the pump which circulates gas (mediator 2c) between the active material layer 2a and the catalyst 2b. When charging / discharging the air battery, the reaction may not proceed due to a bias in the constituent components of the gas (mediator 2c) in the vicinity of the active material layer 2a and the catalyst 2b due to the reaction as described above. By promoting the movement of the gas (mediator 2c), it is possible to eliminate the bias of the constituent components, and to suppress the decrease in the output of the air battery, the oxidation of the catalyst 2b, and the like.

The air battery of the first embodiment and the second embodiment may further include a heat storage material. The negative electrode for an air battery of the present invention has a property of generating heat during discharging and absorbing heat during charging. For example, it is possible to further increase energy efficiency by accumulating the amount of heat generated during discharging using a heat storage material and charging using the heat stored during charging.

  Hereinafter, the negative electrode for an air battery of the present invention and the air battery using the same will be described in detail based on examples. An air battery equipped with a mediator was produced as follows.

  First, 70% by mass of NiO powder (average particle size 0.5 μm) and 30% by mass of yttria-stabilized zirconia (YSZ) fine powder (purity 98%, average particle size 0.1 μm) were mixed. Additives such as a binder, a dispersant and a plasticizer were added and kneaded to prepare a clay. The produced clay was formed into a cylindrical shape having a diameter of 2 mm and a length of 100 mm by extrusion molding, and was fired at 800 to 1000 ° C. to obtain a cylindrical catalyst sintered body.

  Next, a solid electrolyte paste using a fine powder of YSZ (purity 98%, average particle size 0.1 μm) and an interconnector paste using a fine powder of lanthanum chromite (average particle size 1.0 μm) are prepared. did. These pastes were applied to the outer surface of a cylindrical catalyst sintered body and fired at 1200 ° C.

  Further, a positive electrode paste was prepared using fine powder of lanthanum strontium cobalt ferrite (LSCF) (average particle size 0.5 μm), applied to the surface of the solid electrolyte formed on the cylindrical catalyst sintered body, and 1000 ° C. To obtain a battery cell. Platinum paste was printed and baked as a current collector on the surface of the positive electrode and the interconnector of the obtained battery cell, respectively.

  The active material layer uses iron oxide powder (purity 98%) as an active material, alumina powder (purity 98%) and YSZ powder (purity 98%) as stable compounds, and a metal having a catalytic action for reduction of water vapor It was produced using palladium powder (purity 98%) as particles. A predetermined amount of each powder was blended, a dispersant and a solvent were added, ball mill mixing was performed, and the mixed powder obtained by drying was stored in an alumina container to form an active material layer. Table 1 shows the blending amount and average particle diameter of each material constituting the active material layer.

  One end of the cylindrical catalyst sintered body (battery cell) provided with the positive electrode and the solid electrolyte, where the catalyst is exposed, is inserted into the opening of the container containing the active material layer therein, and the opening of the container And the solid electrolyte of the battery cell were sealed with glass. At this time, it arrange | positioned so that a predetermined | prescribed space may exist between an active material layer and a catalyst. Thereafter, hydrogen was introduced into the space inside the container, and the other end of the battery cell was inserted into another container and sealed to obtain an air battery.

  A charge / discharge test was performed using this air battery. The charge / discharge test was performed by constant current charge / discharge with a charge / discharge rate of 1C. The cut-off voltage during charging / discharging was 0.7 V (during discharging) and 1.3 V (during charging), and the test temperature was 700 ° C.

  6 is a charge / discharge profile of the first cycle obtained by a charge / discharge test of an air battery (sample No. 3) using an active material layer containing 10% by mass of zirconia. According to FIG. 6, there is a portion where the potential change becomes flat near 0.9 V during discharging, and there is a portion where the potential change becomes flat near 1.2 V during charging. The discharge capacity was about 700 mAh / g based on the mass of iron oxide (FeO), and had a capacity about 7 times that of the lithium ion battery.

After the first discharge stop and after the charge stop, X-ray diffraction (XRD) measurement of the active material layer was performed and the crystal phase contained in the active material layer was identified from the obtained XRD profile. Most of the iron contained in the active material layer was in the state of iron oxide (FeO), and most of the iron contained in the active material layer after the charge was stopped was in the state of metallic iron. At that time, FeAl ₂ O ₄ was also detected from the active material layer to which alumina was added. When the active material layer was analyzed by a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), Fe ( A layer containing Al was confirmed on the surface of the (FeO) particles.

  Table 1 shows compound crystal phases other than iron oxide contained in the active material layer of each sample, which were confirmed by X-ray diffraction (XRD) measurement after charge and discharge.

  Sample No. containing a stable compound in the active material layer. Nos. 2 to 10 are data Nos. That do not contain a stable compound. The ratio of the discharge capacity at the fifth cycle to the initial (first cycle) discharge capacity was 85% or more with respect to 1, and the capacity retention rate, that is, the Coulomb efficiency was high.

  Sample No. For 1, 3, 8, and 10, the discharge capacity and discharge rate were compared. 7 and 8 show the behavior of the discharge capacity with respect to the discharge time when a constant voltage is applied to the air battery in the charge / discharge test. The discharge capacity is a relative value when the theoretical capacity is 100, and FIG. 7 shows the behavior at the first cycle and FIG. 8 shows the behavior at the fifth cycle.

  7 and 8, sample No. 1 containing 10% by mass of zirconia (YSZ) or alumina which is a stable compound in the active material layer in the initial discharge was obtained. Nos. 3 and 8 are sample Nos. 1 and 2 containing only the active material (iron and iron oxide) in the active material layer. It can be seen that the discharge rate is faster than 1. Sample No. No. 10 shows that the discharge rate is improved by containing palladium as metal particles having a catalytic action on the reduction of water vapor in the active material layer.

  In addition, from FIG. In Sample No. 1, the discharge capacity is lower than that in the initial stage. 3, 8, and 10 show that the decrease in the discharge capacity is suppressed compared to the initial stage.

DESCRIPTION OF SYMBOLS 1: Positive electrode 2: Negative electrode 2a: Active material layer 2b: Catalyst 2c: Mediator 3: Solid electrolyte 4: Active material particle 5: Stable compound 6: Metal particle | grains with water-vapor reduction catalytic action 7: Interconnector 8: Container

Claims (16)

  Provided with an active material layer containing an active material containing a first metal element and capable of occluding and desorbing oxygen, and a compound containing a second metal element and chemically more stable than the active material. A negative electrode for an air battery.   2. The negative electrode for an air battery according to claim 1, wherein the active material is in the form of particles having an average particle diameter of 0.1 to 20 μm, and the compound is present between the particles of the active material.   The negative electrode for an air battery according to claim 1, wherein the compound is in the form of particles having an average particle size of 0.1 to 2.0 μm.   The negative electrode for an air battery according to any one of claims 1 to 3, wherein the compound covers at least a part of the surface of the active material.   The negative electrode for an air battery according to any one of claims 1 to 4, wherein the first metal element is iron.   The negative electrode for an air battery according to any one of claims 1 to 5, wherein the second metal element is at least one of aluminum and zirconium.   In the active material layer, the content of the second metal element is 5% by mass or more and 20% by mass in terms of oxide with respect to the total amount of the first metal element and the second metal element. The negative electrode for an air battery according to any one of claims 1 to 6, wherein: A solid electrolyte having oxygen ion conductivity is provided between the positive electrode and the negative electrode,
A solid electrolyte air battery, wherein the negative electrode is the negative electrode for an air battery according to any one of claims 1 to 7.   The solid electrolyte type air battery according to claim 8, wherein the positive electrode is lanthanum strontium cobaltite.   The solid electrolyte type air battery according to claim 8 or 9, wherein the solid electrolyte is rare earth stabilized zirconia. The negative electrode further comprises a catalyst and a mediator,
The solid electrolyte type air battery according to any one of claims 8 to 10, wherein the catalyst is in contact with the solid electrolyte, and the mediator is interposed between the active material layer and the catalyst.   The solid electrolyte type air battery according to claim 11, wherein the catalyst is a cermet containing nickel and rare earth stabilized zirconia.   The solid electrolyte type air battery according to claim 11 or 12, wherein the mediator is a mixture of hydrogen and water.   The solid oxide air battery according to claim 13, wherein the active material layer further contains metal particles having a catalytic action for reduction of water vapor. The solid oxide air battery according to claim 14, wherein the metal particles are at least one of palladium and platinum.   The content ratio of the metal particles is 0.1% by mass or more and 5% by mass or less as a ratio to the total amount of metal elements contained in the active material layer. Solid electrolyte type air battery.

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