JP7122946B2 - Air electrode catalyst for air secondary battery, method for producing air electrode catalyst, and air secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air electrode catalyst for an air secondary battery, a method for producing the air electrode catalyst, and an air secondary battery.

In recent years, an air battery using oxygen in the atmosphere as a positive electrode active material has been attracting attention because of its high energy density and ease of miniaturization and weight reduction. Among such air batteries, zinc-air primary batteries have been put to practical use as power sources for hearing aids.

In addition, as a rechargeable air battery, an air secondary battery using Li, Zn, Al, Mg, or the like as a negative electrode metal has been researched, and such an air secondary battery is a lithium ion secondary battery. It is expected as a new secondary battery with an energy density exceeding that of .

However, in the air secondary battery using the negative electrode metal as described above, the dissolution and deposition reaction of the negative electrode metal is repeated with the chemical reaction (hereinafter referred to as the battery reaction) during charging and discharging of the battery. There are problems such as so-called dendrite growth, in which metal precipitates in a dendrite pattern, which leads to internal short circuits, and battery capacity decreases due to changes in the shape of the negative electrode due to shape change. Not yet.

As a type of air secondary battery, research has been conducted on an air-hydrogen secondary battery that uses an alkaline aqueous solution (alkaline electrolyte) as an electrolyte and hydrogen as a negative electrode active material (see, for example, Patent Document 1). An air-hydrogen secondary battery as typified by Patent Document 1 uses a hydrogen storage alloy as a negative electrode metal. Since it is hydrogen, the dissolution and deposition reaction of the hydrogen storage alloy itself does not occur with the cell reaction. Therefore, in the air-hydrogen secondary battery, the above-described problems of internal short circuit due to dendrite growth and decrease in battery capacity due to shape change do not occur.

In an air secondary battery that uses an alkaline electrolyte, such as the air-hydrogen secondary battery, the following charging and discharging reactions occur at the positive electrode (hereinafter referred to as the air electrode).

Charging (oxygen evolution reaction): 4OH ⁻ →O ₂ +2H ₂ O+4e ⁻ (I)
Discharge (oxygen reduction reaction): O ₂ +2H ₂ O+4e ⁻ →4OH ⁻ (II)
The air electrode of an air secondary battery produces oxygen and water as represented by Reaction Formula (I) during charging, and reduces oxygen to hydroxide as represented by Reaction Formula (II) during discharge. generate ions. Oxygen generated at the air electrode is released into the atmosphere from a portion of the air electrode that is open to the atmosphere.

Japanese Patent No. 4568124

By the way, in the above-described air secondary battery, the energy efficiency has not yet reached a sufficient value, and high output has not yet been sufficiently achieved. Therefore, in order to put air secondary batteries into practical use, further improvements in energy efficiency and higher output are required.

One of the factors that hinder the improvement in energy efficiency and the increase in output as described above is the large overvoltage of the discharge reaction, that is, the oxygen reduction reaction, at the air electrode.

The present invention has been made based on the above circumstances, and its object is to manufacture an air electrode catalyst for an air secondary battery that contributes to reducing the overvoltage in the discharge reaction, and the manufacture of this air electrode catalyst. An object of the present invention is to provide a method and an air secondary battery that includes this air electrode catalyst and is capable of reducing overvoltage in the discharge reaction.

To achieve the above object, according to the present invention, the general formula: A _2-x (Ru _α B _1-α ) _2-y O _7-z , where x, y, z and α are 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < α ≤ 1, and A is Bi, Pb, Tb, La, Ce, Pr, Nd, Pm, Sm, Eu , Gd, Dy, Ho, Er, Tm, Yb, Lu, Mn, Y, Zn and Al, B represents Ir, Si, Ge, Ta, Sn, Hf, Zr, represents at least one element selected from Ti, Nb, V, Sb, Rh, Cr, Re, Sc, Co, Cu, In, Ga, Cd, Fe, Ni, W and Mo.) and a ruthenium oxide present on the surface of the pyrochlore-type composite oxide.

The peak intensity in the (110) plane of the X-ray diffraction pattern of the ruthenium oxide is 1.7% or more with respect to the peak intensity in the (222) plane of the X-ray diffraction pattern of the pyrochlore-type composite oxide. It is preferable to

Further, according to the present invention, the general formula: A _2-x (Ru _α B _1-α ) _2-y O _7-z (where x, y, z, and α are 0≦x≦1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < α ≤ 1, and A is Bi, Pb, Tb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho , Er, Tm, Yb, Lu, Mn, Y, Zn and Al, B represents Ir, Si, Ge, Ta, Sn, Hf, Zr, Ti, Nb, V, represents at least one element selected from Sb, Rh, Cr, Re, Sc, Co, Cu, In, Ga, Cd, Fe, Ni, W and Mo.) A precursor preparation step of preparing a precursor of a pyrochlore-type composite oxide, a primary heat treatment step of subjecting the precursor to a first heat treatment to form the pyrochlore-type composite oxide, and a primary heat treatment step obtained by the primary heat treatment step an acid treatment step of immersing the pyrochlore-type composite oxide in an acidic aqueous solution for acid treatment; and a secondary heat treatment step of subjecting the pyrochlore-type composite oxide that has undergone the acid treatment step to a second heat treatment. A method for producing an air electrode catalyst for an air secondary battery is provided.

The first heat treatment is preferably performed at 400° C. or higher and 700° C. or lower.

The second heat treatment is preferably performed at 400° C. or higher.

Further, according to the present invention, an electrode group including an air electrode and a negative electrode superimposed with a separator interposed therebetween, and a container housing the electrode group together with an alkaline electrolyte are provided, and the air electrode is the above-described An air secondary battery is provided that includes an air electrode catalyst for an air secondary battery.

The negative electrode preferably contains a hydrogen storage alloy.

The air electrode catalyst for an air secondary battery according to the present invention has the general formula: A _2-x (Ru _α B _1-α ) _2-y O _7-z (where x, y, z, and α are , 0≦x≦1, 0≦y≦1, 0≦z≦1, and 0<α≦1, and A is Bi, Pb, Tb, La, Ce, Pr, Nd, Pm, Sm, represents at least one element selected from Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Mn, Y, Zn and Al, and B is Ir, Si, Ge, Ta, Sn, Hf, Zr , Ti, Nb, V, Sb, Rh, Cr, Re, Sc, Co, Cu, In, Ga, Cd, Fe, Ni, W and Mo.) and the ruthenium oxide present on the surface of the pyrochlore-type composite oxide contribute to reducing the overvoltage in the discharge reaction. Therefore, in the air secondary battery containing such an air electrode catalyst, the overvoltage in the discharge reaction is reduced, so the energy efficiency is improved and the output is also increased. Therefore, according to the present invention, an air electrode catalyst for an air secondary battery that contributes to reducing overvoltage in the discharge reaction, a method for producing the air electrode catalyst, and a discharge reaction including the air electrode catalyst An air secondary battery that can reduce overvoltage can be provided.

1 is a plan view schematically showing an air-hydrogen secondary battery according to an embodiment of the present invention; FIG. FIG. 2 is a cross-sectional view showing a cross section taken along line II-II in FIG. 1; 1 shows XRD profiles of air electrode catalysts of Example 1, Example 2, Comparative Example 1 and Comparative Example 2. FIG. It is an XRD profile obtained by enlarging the range of 2θ to 45 degrees in FIG. 2 is a drawing-substituting photograph showing an SEM image of the air electrode catalyst of Example 1. FIG. 4 is a drawing-substituting photograph showing an SEM image of the air electrode catalyst of Example 2. FIG. 4 is a graph showing discharge characteristic curves of air-hydrogen secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2. FIG.

Hereinafter, an air-hydrogen secondary battery 1 (hereinafter referred to as battery 1) containing an air electrode catalyst according to the present invention will be described with reference to the drawings.

The battery 1 has a battery case 10 as a container, as shown in FIG. The battery case 10 includes an air electrode side case half 12 and a negative electrode side case half 14, as shown in FIG. Together, a box-shaped battery case 10 is formed as a whole. The battery case 10 is made of acrylic resin, for example.

The air electrode side case half 12 includes an air electrode facing wall 16 facing the air electrode 23 and an air electrode side outer peripheral wall 18 provided on the peripheral edge of the air electrode facing wall 16 and surrounding the air electrode 23. there is

The negative electrode-side case half 14 includes a negative electrode-side facing wall 26 in contact with the negative electrode 21 , and a negative electrode-side outer peripheral wall 28 that surrounds the negative electrode 21 and is provided on the periphery of the negative electrode-side facing wall 26 .

The electrode group 20 is accommodated together with the alkaline electrolyte 32 inside the battery case 10 .
The electrode group 20 is formed by stacking an air electrode (positive electrode) 23 and a negative electrode 21 with a separator 22 interposed therebetween.

The negative electrode 21 includes a conductive negative electrode base material having a porous structure and a large number of pores, and a negative electrode mixture supported in the pores and on the surface of the negative electrode base material. Foamed nickel, for example, can be used as the negative electrode substrate as described above.

The negative electrode mixture contains hydrogen-absorbing alloy powder, which is an aggregate of hydrogen-absorbing alloy particles capable of absorbing and releasing hydrogen as a negative electrode active material, a conductive material, and a binder. Here, graphite, carbon black, or the like can be used as the conductive material.

The hydrogen storage alloy forming the hydrogen storage alloy particles is not particularly limited, but a rare earth-Mg-Ni hydrogen storage alloy is used. The composition of this rare earth-Mg-Ni hydrogen storage alloy can be freely selected.
Ln _1-a Mg _a Ni _b-c-d Al _c M _d (III)
It is preferable to use what is represented by.

However, in general formula (III), Ln is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Zr and Ti represents at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P and B The subscripts a, b, c, and d represent at least one element selected from the group, and 0.01≦a≦0.30, 2.8≦b≦3.9, and 0.05≦c≦, respectively. It represents a number that satisfies 0.30 and 0≤d≤0.50.

Here, the hydrogen-absorbing alloy particles are obtained, for example, as follows.
First, metal raw materials are weighed and mixed so as to have a predetermined composition, and this mixture is melted in, for example, a high-frequency induction melting furnace under an inert gas atmosphere to form an ingot. The obtained ingot is homogenized by heating to 900 to 1200° C. in an inert gas atmosphere and holding at that temperature for 5 to 24 hours. Thereafter, the ingot is pulverized and sieved to obtain hydrogen-absorbing alloy powder, which is an aggregate of hydrogen-absorbing alloy particles having a desired particle size.

Examples of binders that can be used include sodium polyacrylate, carboxymethylcellulose, styrene-butadiene rubber, and the like.

The negative electrode 21 can be manufactured, for example, as follows.
First, a negative electrode mixture paste is prepared by kneading a hydrogen-absorbing alloy powder, which is an aggregate of hydrogen-absorbing alloy particles, a conductive material, a binder, and water. The obtained negative electrode mixture paste is filled in a negative electrode substrate and dried. After drying, the negative electrode base material to which the hydrogen-absorbing alloy particles and the like are adhered is roll-rolled to increase the alloy content per volume, and then cut to manufacture the negative electrode 21 . The negative electrode 21 has a plate shape as a whole.

Next, the air electrode 23 is composed of a conductive air electrode base material having a porous structure and a large number of pores, and an air electrode mixture (positive electrode material) supported in the pores and on the surface of the air electrode base material. combination drug) and Foamed nickel or nickel mesh, for example, can be used as the air electrode substrate as described above.

The air electrode mixture contains an air electrode catalyst for an air secondary battery, a conductive material, and a binder.
As an air electrode catalyst for an air secondary battery, one comprising a pyrochlore-type composite oxide and a ruthenium oxide present on the surface of the pyrochlore-type composite oxide is used.

The pyrochlore-type composite oxide has the general formula: A _2-x (Ru _α B _1-α ) _2-y O _7-z (where x, y, z, and α are 0≦x≦1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < α ≤ 1, and A is Bi, Pb, Tb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho , Er, Tm, Yb, Lu, Mn, Y, Zn and Al, B represents Ir, Si, Ge, Ta, Sn, Hf, Zr, Ti, Nb, V, represents at least one element selected from Sb, Rh, Cr, Re, Sc, Co, Cu, In, Ga, Cd, Fe, Ni, W and Mo.) A pyrochlore-type composite oxide is used.

The composite oxide has dual functions of oxygen reduction and oxygen generation, and the catalyst having such dual functions contributes to reducing the overvoltage of the battery during both the charging process and the discharging process. The pyrochlore-type composite oxide used in the present invention is also one of the catalysts having a dual function.

Here, it is known that characteristics such as the oxygen defect structure greatly contribute to the oxygen reduction activity of the composite oxide catalyst. Therefore, it is considered that the oxygen reduction activity can be affected by changing the properties of the composite oxide, such as the amount of oxygen defects, the valence state, and the binding energy between the metal element and oxygen. In addition, it is considered important for oxygen to be adsorbed on the catalyst side-on in order to efficiently cut the bonds of oxygen molecules, and the spacing between adsorption points and the surface condition are also considered to be important factors. be done.

The inventors of the present invention have conducted various studies in consideration of the above matters, and as a result, have found that a pyrochlore-type composite oxide exhibits excellent catalytic activity when ruthenium oxide is present on its surface. . When ruthenium oxide is present on the surface of the pyrochlore-type composite oxide, the interaction with oxygen changes, and the bonding strength between oxygen and the surface of the air electrode catalyst changes. It is thought that the decomposition of hydrogen peroxide ion (HO ₂ ⁻ ), which is an intermediate produced in the process of , is accelerated, and the multifunctionality of the catalyst is caused.

Here, the electrochemical reduction mechanism of oxygen in the alkaline electrolyte includes, in addition to the four-electron reduction pathway as shown in the above formula (II), the two-electron reduction mechanism as shown in the following formula (IV) An electron reduction pathway exists. This two-electron reduction pathway yields hydrogen peroxide ion (HO ₂ ⁻ ) as an intermediate.
O ₂ +H ₂ O+2e ⁻ →HO ₂ ⁻ +OH ⁻ (IV)

HO ₂ ⁻ is adsorbed on the electrode surface, inhibits the reaction, adversely affects the battery reaction, and causes an increase in the overvoltage of the battery. However, the air electrode catalyst containing the pyrochlore-type composite oxide and ruthenium oxide according to the present invention is believed to promote the decomposition of HO ₂ ^- , and is believed to promote the reaction of formula (V) below. .
2HO ₂ ⁻ →2OH ⁻ +O ₂ (V)
From the formulas (IV) and (V) above, the overall reaction is the same as the formula (II).

Bismuth ruthenium oxide is preferably used as the pyrochlore-type composite oxide used in the present invention. Specifically, it is preferable to use a bismuth ruthenium oxide represented by Bi ₂ Ru ₂ O ₇ . Bismuth ruthenium oxide is one of pyrochlore-type composite oxides, and is a catalyst having dual functions of oxygen evolution and oxygen reduction.

Here, ruthenium can take various oxidation states such as trivalent, tetravalent, pentavalent, heptavalent and octavalent, and RuO ₂ and RuO ₄ exist.

The amount of ruthenium oxide is considered necessary to the extent that the peak of the X-ray diffraction pattern can be confirmed, and in the present invention, in relation to the pyrochlore type composite oxide, 2θ = The peak intensity of the (110) plane, which is the strongest line at 28 degrees, is 1.74% or more of the peak intensity of the (222) plane at 2θ = 30 degrees, which is the strongest line in the X-ray diffraction pattern of the pyrochlore-type composite oxide. It is preferable that the amount of ruthenium oxide corresponding to the amount is present on the surface of the pyrochlore-type composite oxide. More preferably, it is 2.1% or more.

Next, a method for producing an air electrode catalyst for an air secondary battery will be specifically described below, taking as an example a pyrochlore-type bismuth ruthenium oxide having ruthenium oxide on its surface.

First, Bi(NO ₃ ) 3.5H ₂ O and RuCl _{3.3H 2} O were put into distilled water so as to have the same concentration, and stirred to obtain Bi ₍ NO ₃ ) _{3.5H 2} O and RuCl ₃ . • Prepare a mixed aqueous solution of _3H2O . At this time, the temperature of the distilled water should be 60° C. or higher and 90° C. or lower. Then, a NaOH aqueous solution of 1 mol/L or more and 3 mol/L or less is added to this mixed aqueous solution. At this time, the bath temperature is maintained at 60° C. or higher and 90° C. or lower, and the mixture is stirred while oxygen bubbling is performed. The solution containing the precipitate produced by this operation is held at 80° C. or higher and 100° C. or lower to evaporate part of the water to form a paste. This paste is transferred to an evaporating dish, heated to 100° C. or more and 150° C. or less, and kept in that state for 10 hours or more and 20 hours or less for drying to obtain a dried paste product. Then, after pulverizing this dried product in a mortar, it is heated to a temperature of 400° C. or higher and 700° C. or lower in an air atmosphere and held for 0.5 hours or more and 24 hours or less for primary heat treatment, followed by first firing. get things

Here, if the temperature of the primary heat treatment is less than 400° C., the pyrochlore-type composite oxide cannot be formed. On the other hand, if the temperature of the primary heat treatment exceeds 700° C., the structure of the pyrochlore-type composite oxide changes and the particles are sintered to reduce the surface area of the first fired product. Therefore, the temperature of the primary heat treatment is preferably 400° C. or higher and 700° C. or lower.

The above-described first fired product has become a pyrochlore-type composite oxide by the above-described primary heat treatment, but a by-product is formed on a part of the surface. Although this by-product contains ruthenium oxide, it also contains unnecessary single oxides, amorphous oxides, amorphous hydroxides, and the like. In order to remove such unnecessary oxides and the like, as the next step, the obtained first fired product is subjected to an acid treatment. By applying this acid treatment, only the ruthenium oxide which is insoluble in acid is left, and other oxides can be removed.

As the acid treatment step, the first baked product is immersed in an aqueous nitric acid solution. Specifically, it is as follows.

First, an aqueous nitric acid solution is prepared. Here, the concentration of the nitric acid aqueous solution is preferably 1 mol/L or more and 3 mol/L or less, and the amount of the nitric acid aqueous solution is preferably prepared at a rate of 20 mL with respect to 1 g of the first fired product. , the temperature of the nitric acid aqueous solution is preferably set to 20°C or higher and 25°C or lower.

Then, the first baked product is immersed in the prepared nitric acid aqueous solution and stirred for 0.5 hours or more and 24 hours or less. After a predetermined time has elapsed, the first baked product is suction-filtered from the nitric acid aqueous solution. The filtered first baked product is put into ion-exchanged water set at 60° C. or higher and 80° C. or lower and washed.

The washed first baked product is held in an environment of 100° C. or higher and 120° C. or lower for 1 hour or longer and 2 hours or shorter and dried.

As described above, the first baked product subjected to the acid treatment is obtained. By performing acid treatment in this way, unnecessary by-products generated in the process of manufacturing bismuth ruthenium oxide (pyrochlore type composite oxide) can be removed, leaving only ruthenium oxide. The acidic aqueous solution used for the acid treatment is not limited to the nitric acid aqueous solution, and besides the nitric acid aqueous solution, a hydrochloric acid aqueous solution and a sulfuric acid aqueous solution can be used. These aqueous solutions of hydrochloric acid and sulfuric acid also have the same effect of removing unnecessary by-products as the aqueous nitric acid solution.

Next, secondary heat treatment is applied to the acid-treated first baked product. Specifically, the first calcined product after the acid treatment is heated to a temperature of 400° C. or higher in an air atmosphere and held for 0.5 hours or more and 24 hours or less to perform secondary heat treatment, and the second calcination is performed. get things

By performing this secondary heat treatment, crystallization of the ruthenium oxide remaining on the surface of the bismuth ruthenium oxide (pyrochlore-type composite oxide) is promoted, and excellent catalytic activity can be obtained.

Here, if the temperature of the secondary heat treatment is less than 400° C., crystallization of the ruthenium oxide is difficult to progress. In order to promote crystal growth of the ruthenium oxide, the heat treatment temperature is preferably 400° C. or higher, more preferably 500° C. or higher. On the other hand, if the temperature of the secondary heat treatment is too high, the crystal structure of the ruthenium oxide will change, and the crystal structure of the base pyrochlore-type composite oxide will also change. In order to avoid such problems, the temperature of the secondary heat treatment is preferably 700° C. or less.

As a result, a pyrochlore-type bismuth ruthenium oxide having ruthenium oxide present on its surface, that is, an air electrode catalyst is obtained.

Next, the conductive material will be explained. This conductive material is used to reduce the internal resistance in order to increase the output of the air secondary battery and as a support for the above-described catalyst. As such a conductive material, it is preferable to use nickel powder, which is an aggregate of nickel particles, for example. As the nickel particles described above, for example, particles having an average particle size of 0.1 μm to 10 μm are preferably used. Here, in the present invention, the average particle size is obtained by measuring the particle size distribution on a volume basis using a laser diffraction/scattering particle size distribution measuring device for a powder that is an aggregate of target particles. shall refer to the volume-average particle size obtained.

The nickel powder described above is preferably contained in the air electrode mixture in an amount of 60% by mass or more. The upper limit of the nickel powder content is preferably 80% by mass or less in view of the relationship with other constituent materials in the air electrode mixture.

Moreover, the conductive material is not limited to the nickel powder described above, and a metal-coated conductive filler in which a core material is coated with a metal material can also be used. This metal-coated conductive filler is lighter than metal particles made entirely of metal, and contributes to weight reduction of the air electrode as a whole. The above-described core material is not particularly limited, and examples thereof include silica particles. It is preferable to employ nickel as the metal coating layer. The metal-coated conductive filler powder, which is an aggregate of such metal-coated conductive fillers, is preferably contained in an air electrode mixture in an amount of 30% by mass or more.

The binder functions to bind the constituent materials of the air electrode mixture and to impart appropriate water repellency to the air electrode 23 . Here, the binder is not particularly limited, and for example, a fluororesin is used. As a preferable fluororesin, polytetrafluoroethylene (PTFE) is used, for example.

The air electrode 23 can be manufactured, for example, as follows.
First, an air electrode mixture paste containing an air electrode catalyst, a conductive material, a binder and water is prepared.

The obtained air electrode mixture paste is formed into a sheet, and then press-bonded to a nickel mesh (air electrode base material). This yields an intermediate cathode product.

Next, the obtained intermediate product is put into a sintering furnace and sintered. This firing treatment is performed in an inert gas atmosphere. Nitrogen gas and argon gas, for example, are used as this inert gas. The conditions for the firing treatment are heating to a temperature of 300° C. or more and less than 400° C., and maintaining this state for 10 minutes or more and 20 minutes or less. After that, the intermediate product is naturally cooled in the kiln, and when the temperature of the intermediate product reaches 150° C. or lower, it is taken out into the atmosphere. As a result, an intermediate product that has undergone a firing treatment is obtained. The air electrode 23 is obtained by cutting the intermediate product after the baking treatment into a predetermined shape.

The air electrode 23 and the negative electrode 21 obtained as described above are stacked with the separator 22 interposed therebetween to form the electrode group 20 . The separator 22 is arranged to avoid a short circuit between the air electrode 23 and the negative electrode 21, and is made of an electrically insulating material. As the material used for the separator 22, for example, a polyamide fiber nonwoven fabric to which a hydrophilic functional group is added, or a polyolefin fiber nonwoven fabric such as polyethylene or polypropylene to which a hydrophilic functional group is added can be used. can. Here, the separator 22 has a rectangular shape as a whole. It is preferable that the planar view shape of the separator 22 is larger than the planar view shape of the air electrode 23 and the planar view shape of the negative electrode 21 described above.

When forming the electrode group 20 , the electrode group 20 is assembled so that the four ends of the separator 22 protrude more than the four ends of the air electrode 23 and the negative electrode 21 .

It is preferable to further place a water-repellent ventilation member 50 on the air electrode 23 of the obtained electrode group 20 . The water-repellent ventilation member 50 is not particularly limited as long as it has a function of permeating air and preventing permeation of an alkaline electrolyte. As such a water-repellent air-permeable member 50, for example, it is preferable to use a fluororesin porous film. More preferably, a PTFE porous membrane is used. Furthermore, as the water-repellent air-permeable member 50, it is preferable to use a composite of a fluororesin porous membrane and a non-woven fabric diffusion paper superimposed thereon.

The electrode group 20 on which the water-repellent ventilation member 50 is placed is arranged inside the battery case 10 . More specifically, as shown in FIG. 2, the electrode group 20 on which the water-repellent ventilation member 50 is placed is located between the air electrode facing wall 16 of the air electrode side case half 12 and the negative electrode side facing wall 16 of the negative electrode side case half 14 . The separator 22 is sandwiched between the wall 26 and the four ends of the separator 22 are connected to the tip 19 of the air electrode side outer peripheral wall 18 of the air electrode side case half 12 and the negative electrode side outer peripheral wall of the negative electrode side case half 14. 28 and the distal end portion 29 thereof. The battery 1 is thus formed.

Here, the distance between the tip 19 of the air electrode-side outer peripheral wall 18 of the air electrode-side case half 12 and the tip 29 of the negative electrode-side outer peripheral wall 28 of the negative electrode-side case half 14 is from the end of the separator 22 . It is sealed with a packing 34 so that the alkaline electrolyte 32 does not leak to the outside.

As shown in FIGS. 1 and 2, the negative electrode side case half 14 includes an electrolytic solution reservoir 30 attached to a portion of the negative electrode side outer peripheral wall 28 via a connecting portion 40 . The electrolyte storage unit 30 is a container that stores an alkaline electrolyte 32 . The connection part 40 is a channel for the alkaline electrolyte 32 that communicates between the inside of the battery case 10 and the electrolyte storage part 30 . Since the interior of the battery case 10 and the electrolyte storage section 30 are thus in communication, the alkaline electrolyte 32 can move between the interior of the battery case 10 and the electrolyte storage section 30 . Therefore, when the amount of the alkaline electrolyte 32 increases due to the generation of water by the air electrode 23 during charging, excess alkaline electrolyte 32 inside the battery case 10 moves to the electrolyte storage section 30. stored in When the air electrode 23 decomposes water during discharge and the alkaline electrolyte 32 decreases, the alkaline electrolyte 32 stored in the electrolyte storage unit 30 moves into the battery case 10 and the air electrode 23 can make up for the shortage of the alkaline electrolyte 32 in . By having the electrolytic solution storage unit 30 in this way, leakage and depletion of the alkaline electrolytic solution 32 can be suppressed.

As the alkaline electrolyte described above, a general alkaline electrolyte used in alkaline secondary batteries is preferably used. Specifically, an aqueous solution containing at least one of NaOH, KOH and LiOH as a solute. is used.

In addition, the air electrode side case half 12 has an air passage 60 . The air passage 60 supplies oxygen in the air to the air electrode 23 during discharging and discharges oxygen generated from the air electrode 23 during charging to the outside. The shape of the air passage 60 is not particularly limited. A preferred shape of the air passage 60 includes, for example, the shapes shown in FIGS. 1 and 2 . That is, the air passage 60 includes a groove 63 as an air electrode opening provided in the inner wall surface 17 of the air electrode facing wall 16 on the air electrode side, and a first air vent 61 provided at one end of the groove 63. and a second vent 62 provided at the other end of the groove 63 .

As is apparent from FIG. 1, the concave groove 63 has a single serpentine shape in plan view as a whole, and as apparent from FIG. It opens toward the side (the side of the water-repellent ventilation member 50). Note that the number of folds of the serpentine shape is not particularly limited.

The first vent 61 is a through-hole penetrating from the inside to the outside of the cathode facing wall 16 at one end of the recessed groove 63 . A part of the inner peripheral surface of the first vent 61 communicates with the groove 63 .

The second vent 62 is a through-hole penetrating from the inside of the cathode facing wall 16 to the outside at the other end portion of the recessed groove 63 . A part of the inner peripheral surface of the second vent 62 communicates with the concave groove 63 .

The water-repellent ventilation member 50 described above is interposed between the air electrode facing wall 16 and the air electrode 23 and is in close contact with both the air electrode facing wall 16 and the air electrode 23 . The water-repellent ventilation member 50 has a size that covers the groove 63 , the first ventilation port 61 and the second ventilation port 62 entirely.

Air flows through the air passage 60 in the battery 1 having the configuration described above. The air flowing through the ventilation path 60 diffuses inside the water-repellent ventilation member 50 facing the concave groove 63 of the ventilation path 60 . Then, the water-repellent air-permeable member 50 allows the diffused air to permeate the air electrode 23 directly below and in contact therewith. That is, the water-repellent ventilation member 50 functions as a gas diffusion layer. Further, the water-repellent ventilation member 50 allows oxygen generated from the air electrode 23 to permeate the concave groove 63 . Oxygen that has reached the groove 63 is released into the atmosphere outside the battery case 10 through the vent.

Further, the water-repellent ventilation member 50 prevents the alkaline electrolyte 32 inside the battery case 10 from permeating the ventilation path 60 . Therefore, when the pressure of the alkaline electrolyte 32 inside the battery case 10 increases, the leakage of the alkaline electrolyte 32 to the outside through the vent can be suppressed.

Here, in the battery 1 according to the present invention, a compressing pump 74 as a compressing device is attached to the first vent 61 via a piping member 72 . By driving the pressure-feeding pump 74 , air can be sent from the first vent 61 to the concave groove 63 .

In this embodiment, although illustration is omitted, an air electrode lead is electrically connected to the air electrode 23, and a negative electrode lead is electrically connected to the negative electrode 21, respectively. appropriately extends from the inside to the outside of the battery case 10 while maintaining airtightness and watertightness of the battery case 10 . An air electrode terminal is attached to the tip of the air electrode lead, and a negative electrode terminal is attached to the tip of the negative electrode lead. Therefore, in the battery 1, these air and negative terminals are used to input and output current during charging and discharging.
Further, in FIG. 1, illustration of the compressing pump 74 is omitted.

Here, in the battery 1 , the concave groove 63 of the air electrode side case half 12 faces the water-repellent ventilation member 50 . The water-repellent ventilation member 50 allows air to pass through but blocks moisture, so the air electrode 23 is open to the atmosphere through the water-repellent ventilation member 50, the groove 63, the first ventilation port 61 and the second ventilation port 62. It will be. In other words, the air electrode 23 is in contact with the atmosphere through the water-repellent ventilation member 50 .

Since the air electrode catalyst for the air secondary battery as described above can contribute to reducing the overvoltage in the discharge reaction, the air secondary battery containing such an air electrode catalyst reduces the overvoltage in the discharge reaction. It is possible to improve the energy efficiency and increase the power output.

[Example]
1. Manufacture of battery (Example 1)
(1) Synthesis of air electrode catalyst As a first step, a predetermined amount of Bi(NO ₃ ) 3.5H ₂ O and RuCl _{3.3H 2 O is prepared, and these Bi(NO 3 ) 3.5H 2 O and RuCl 3 are prepared} . * _{3H 2} O was put into distilled water at 75°C so as to have the same concentration, and stirred to prepare a mixed aqueous solution of Bi(NO ₃ ) _{3.5H 2} O and RuCl 3.3H ₂ O. Then, a 2 mol/L NaOH aqueous solution was added to this mixed aqueous solution. At this time, the bath temperature was 75° C., and the mixture was stirred while oxygen bubbling was performed. The precipitate-containing solution resulting from this operation was held at 85° C. to evaporate some of the water to form a paste. This paste was transferred to an evaporating dish, heated to 120° C., and held in that state for 12 hours for drying to obtain a dried paste (precursor).

As a second step, the obtained dried product was pulverized in a mortar, then subjected to primary heat treatment by heating to 600° C. in an air atmosphere and held for 1 hour to obtain a fired product. The obtained baked product was washed with distilled water at 70°C, filtered by suction, and dried at 120°C. Thus, a first fired product was obtained.

The obtained first fired product was pulverized using a mortar to obtain a powder of the first fired product, which is an aggregate of particles having a predetermined particle size. As a result of observing a secondary electron image of the powder of the first fired product with a scanning electron microscope, the particle size of the first fired product was 0.1 μm or less.

As a third step, 1 g of the powder of the first fired product was placed in a stirring tank of a stirrer together with 20 mL of an aqueous nitric acid solution, and stirred for 1 hour while maintaining the temperature of the aqueous nitric acid solution at 25°C. Here, the concentration of the nitric acid aqueous solution was set to 2 mol/L.

After the stirring was completed, the powder of the first baked product was taken out from the nitric acid aqueous solution by suction filtration. The powder of the first fired product taken out was washed with 1 liter of ion-exchanged water heated to 70°C. After washing, the powder of the first fired product was dried by heating to 120°C.

As a fourth step, the first calcined product, which had been treated with nitric acid, was subjected to secondary heat treatment by heating to 500° C. in an air atmosphere and held for 1 hour to obtain a calcined product. As a result, a second fired product, that is, an air electrode catalyst for an air secondary battery was obtained. Here, part of the obtained air electrode catalyst was set aside as a sample for analysis, and the rest was used for manufacturing the air electrode.

(2) Manufacture of Air Electrode A nickel powder, which is an aggregate of nickel particles, was prepared. The nickel particles had an average particle size of 2 to 3 μm.

Furthermore, polytetrafluoroethylene (PTFE) dispersion and deionized water were prepared.

Nickel powder, polytetrafluoroethylene (PTFE) dispersion, and ion-exchanged water were mixed with the air electrode catalyst powder obtained as described above. At this time, 20 parts by mass of the air electrode catalyst powder, 70 parts by mass of the nickel powder, 10 parts by mass of the PTFE dispersion, and 30 parts by mass of the ion-exchanged water were uniformly mixed to form an air electrode mixture paste. manufactured.

The obtained air electrode mixture paste was molded into a sheet and dried in an atmosphere of 25° C., and then the sheet-like air electrode mixture paste was passed through a mesh having a mesh number of 60, a wire diameter of 0.08 mm, and an aperture ratio. It was press crimped onto a 60% nickel mesh.

The air electrode mixture paste pressure-bonded to the nickel mesh was heated to 340° C. in a nitrogen gas atmosphere, held at this temperature for 13 minutes, and fired. The sintered air electrode mixture sheet was cut into a length of 40 mm and a width of 40 mm to obtain an air electrode 23 . The thickness of this air electrode 23 was 0.23 mm. In addition, in the obtained air electrode 23, the amount of the air electrode catalyst was 0.23 g.

(3) Production of Negative Electrode After mixing metal materials such as Nd, Mg, Ni, and Al in a predetermined molar ratio, the resulting molten metal is put into a high-frequency induction melting furnace and melted in an argon gas atmosphere. was poured into a mold and cooled to room temperature of 25°C to produce an ingot.

Next, the ingot is subjected to heat treatment at a temperature of 1000° C. in an argon gas atmosphere for 10 hours, and then mechanically pulverized in an argon gas atmosphere to obtain a rare earth-Mg-Ni hydrogen-absorbing alloy powder. Obtained. The volume average particle diameter (MV) of the obtained rare earth-Mg-Ni hydrogen-absorbing alloy powder was measured by a laser diffraction/scattering particle size distribution analyzer. As a result, the volume average particle diameter (MV) was 60 μm.

The composition of this hydrogen-absorbing alloy powder was analyzed by high-frequency plasma spectrometry (ICP) and found to be Nd _0.89 Mg _0.11 Ni _3.33 Al _0.17 .

Based on 100 parts by mass of the obtained hydrogen-absorbing alloy powder, 0.2 parts by mass of sodium polyacrylate powder, 0.04 parts by mass of carboxymethyl cellulose powder, 3.0 parts by mass of styrene-butadiene rubber dispersion, and carbon black. and 22.4 parts by mass of water were added and kneaded in an environment of 25° C. to prepare a negative electrode mixture paste.

This negative electrode mixture paste was filled in a foamed nickel sheet having a surface density (basis weight) of about 250 g/m ² and a thickness of about 0.6 mm. Then, the negative electrode mixture paste was dried to obtain a foamed nickel sheet filled with the negative electrode mixture. The obtained sheet was rolled to increase the alloy content per volume, and then cut into a length of 40 mm and a width of 40 mm to obtain the negative electrode 21 . The thickness of the negative electrode 21 was 0.25 mm.

Next, the obtained negative electrode 21 was subjected to activation treatment. The procedure for this activation process is shown below.
First, a general sintered nickel hydroxide positive electrode was prepared. As this nickel hydroxide positive electrode, one having a positive electrode capacity sufficiently larger than the negative electrode capacity of the negative electrode 21 was prepared. Then, this nickel hydroxide positive electrode and the obtained negative electrode 21 were stacked with a separator made of polyethylene nonwoven fabric interposed therebetween to form an electrode group for activation treatment. This electrode group for activation treatment was placed in a container made of acrylic resin together with a predetermined amount of alkaline electrolyte. Thus, a monopolar cell of a nickel-metal hydride secondary battery was formed.

As the initial charging and discharging operation, the monopolar cell was left to stand for 5 hours in an environment at a temperature of 25 ° C., and then charged at 0.1 It for 14 hours. It was discharged to 0.70V. Next, as the second charging and discharging operation, after charging at 0.5 It for 2.8 hours in an environment at a temperature of 25 ° C., discharging at 0.5 It until the battery voltage reaches 0.70 V. did After the second charge/discharge cycle, the charge/discharge cycle was repeated a plurality of times, thereby activating the negative electrode 21 . In addition, the capacity of the monopolar cell was determined for each charge/discharge cycle. Then, the maximum value of the obtained capacity was taken as the capacity of the negative electrode. Incidentally, the capacity of the negative electrode was 640 mAh.

Then, after charging at 0.5 It for 2.8 hours, the negative electrode 21 was removed from the single-polar cell. Thus, the negative electrode 21 that had been activated and charged was obtained.

(4) Manufacture of air-hydrogen secondary battery The obtained air electrode 23 and negative electrode 21 were stacked with the separator 22 interposed therebetween to manufacture the electrode group 20 . The separator 22 used in the production of this electrode group 20 was made of polypropylene fiber non-woven fabric having a sulfone group, and had a thickness of 0.1 mm (basis weight of 53 g/m ² ).

On the other hand, as the water-repellent air-permeable member 50, a composite was prepared by laminating non-woven fabric diffusion paper on a PTFE porous membrane. Here, the dimensions of the PTFE porous membrane were 45 mm long, 45 mm wide, and 0.1 mm thick. The dimensions of the non-woven fabric diffusion paper were 40 mm long, 40 mm wide, and 0.2 mm thick.

The composite as the water-repellent ventilation member 50 was placed on the air electrode 23 in the electrode group 20 and accommodated in the battery case 10 . Specifically, the electrode group 20 on which the composite as the water-repellent ventilation member 50 is placed is divided into the air electrode facing wall 16 of the air electrode side case half 12 and the negative electrode side facing wall 26 of the negative electrode side case half 14. While being sandwiched between the four ends of the separator 22, the ends 19 of the air electrode side outer peripheral wall 18 of the air electrode side case half 12 and the tip portions of the negative electrode side outer peripheral wall 28 of the negative electrode side case half 14 29 and fixed. Here, the distance between the tip 19 of the air electrode-side outer peripheral wall 18 of the air electrode-side case half 12 and the tip 29 of the negative electrode-side outer peripheral wall 28 of the negative electrode-side case half 14 is from the end of the separator 22 . It was sealed with a packing 34 to prevent the alkaline electrolyte 32 from leaking to the outside.

A serpentine-shaped recessed groove 63 having a width of 1 mm, a depth of 1 mm, and a peak width of 1 mm is provided in the air electrode facing wall 16 of the air electrode side case half 12 as the recessed groove 63 . The total length of this concave groove 63 is 720 mm. A first vent 61 is provided at one end of the groove 63, and a second vent 62 is provided at the other end. The concave groove 63 is open on the water-repellent ventilation member 50 side. Furthermore, a compressing pump 74 was attached to the first vent port 61 via a piping member 72 .

An electrolytic solution storage part 30 is attached to a part of the negative electrode side outer peripheral wall 28 of the negative electrode side case half 14 via a connecting part 40 . A 5 mol/L KOH aqueous solution was injected as the alkaline electrolyte 32 into the electrolyte storage unit 30 . The amount of the KOH aqueous solution injected at this time was 50 mL.

As described above, the battery 1 as shown in FIGS. 1 and 2 was manufactured. The resulting battery 1 was allowed to stand in an environment of 25° C. for 1 hour to permeate the electrode group 20 with the alkaline electrolyte.

An air electrode lead (not shown) is electrically connected to the air electrode 23, and a negative electrode lead (not shown) is electrically connected to the negative electrode 21, respectively. It appropriately extends from the inside to the outside of the battery case 10 while maintaining the airtightness and watertightness of the battery case 10 . An air electrode terminal (not shown) is attached to the tip of the air electrode lead, and a negative electrode terminal (not shown) is attached to the tip of the negative electrode lead.

(Example 2)
As a fourth step, the first baked product that had been treated with nitric acid was heated to 400 ° C. in an air atmosphere and subjected to a secondary heat treatment of holding for 1 hour to obtain a baked product. An air-hydrogen secondary battery was produced in the same manner as above.

(Comparative example 1)
As a fourth step, the first baked product that had been treated with nitric acid was heated to 300 ° C. in an air atmosphere and subjected to a secondary heat treatment of holding for 1 hour to obtain a baked product. An air-hydrogen secondary battery was produced in the same manner as above.

(Comparative example 2)
Air hydrogen secondary battery in the same manner as in Example 1, except that the secondary heat treatment in the fourth step was omitted, and the first baked product that had been treated with nitric acid was used as the air electrode catalyst for the air secondary battery. manufactured.

2. Evaluation of Air-Hydrogen Secondary Battery (1) Analysis of Air Electrode Catalyst X-ray diffraction (XRD) analysis was performed on the analysis samples of the air electrode catalysts of Examples 1, 2, Comparative Examples 1 and 2. A parallel beam X-ray diffractometer was used for the XRD analysis. The analysis conditions here were as follows: X-ray source: CuKα; tube voltage: 40 kV; tube current: 15 mA; scan speed: 1 degree/min; step width: 0.01 degree. Profiles of the analysis results are shown in FIGS. 3 and 4. FIG. Here, FIG. 3 shows an overall profile, and FIG. 4 shows a partially enlarged profile.

The phase composition was confirmed from the XRD profiles of FIGS. 3 and 4. FIG.

Further, the samples for analysis of the air electrode catalysts of Examples 1 and 2 were observed with a scanning electron microscope (SEM) and subjected to elemental analysis with an energy dispersive X-ray spectrometer (EDS), so-called SEM/EDS. Analysis was carried out. A photograph of an SEM image (magnification: 5000 times) of the analysis results of Example 1 is shown in FIG. 5, and a photograph of an SEM image (magnification: 5000 times) of the analysis results of Example 2 is shown in FIG.

EDS analysis was performed on the measurement spots numbered 1 to 6 in each SEM image. At each measurement spot, the intensity (number of counts) of characteristic X-rays of C, O, Na, Al, Ru and Bi was measured to examine the concentration (atomic %) of each element. The results are shown in Table 1 for Example 1 and Table 2 for Example 2. The ratio of Bi to Ru is also shown in Tables 1 and 2 as Bi/Ru.

(2) Discharge Test The air-hydrogen secondary batteries of Examples 1, 2, Comparative Examples 1 and 2 were charged at 0.5 It for 1.2 hours through the air electrode terminal and the negative electrode terminal. One cycle consisted of discharging at 0.5 It until the battery voltage reached 0.4 V, and such charging and discharging were repeated 10 cycles. At this time, regardless of charging/discharging, air was sent from the first ventilation port 61 by the pressure pump 74, and the air was always supplied to the ventilation path 60 at a rate of 53 mL/min. Note that the negative electrode capacity (640 mAh) was set to 1 It.

Then, in each cycle, the discharge capacity and battery voltage were measured.
FIG. 7 shows the relationship (discharge characteristic curve) between the discharge capacity and the battery voltage at 10 cycles when the battery characteristics are stable.

Table 3 shows the battery voltage when the discharge capacity reaches half of the total discharge capacity at this time as the discharge intermediate voltage.

(3) Consideration FIG. 3 shows peak position data of Bi ₂ Ru ₂ O ₇ and RuO ₂ in ICDD (registered trademark) (International Center for Diffraction Data). As a result of comparing the peak positions of these Bi ₂ Ru ₂ O ₇ and RuO ₂ with the XRD profiles of Example 1, Example 2, Comparative Example 1 and Comparative Example 2, Example 1, Example 2, Comparative Example 1 and It was confirmed that all the air electrode catalysts of Comparative Example 2 had a Bi ₂ Ru ₂ O ₇ peak. Further, in Examples 1 and 2, it was confirmed that there was a peak corresponding to RuO ₂ . However, in Comparative Examples 1 and 2, no peak corresponding to RuO ₂ could be confirmed. From this, the air electrode catalysts of Comparative Examples 1 and 2 hardly contain RuO ₂ , but in Examples 1 and 2, Bi ₂ Ru ₂ O ₇ and RuO ₂ coexist. I understand.

Further, from the SEM/EDS analysis results of FIGS. 5, 6, Tables 1 and 2, in Example 1, the portion of the measurement spot 1 has an extremely small amount of Bi and a large amount of Ru. In Example 2, it was confirmed that the portion of the measurement spot 4 had an extremely small amount of Bi and a large amount of Ru. It is believed that these portions are crystals corresponding to RuO ₂ containing almost no Bi. That is, in the air electrode catalysts of Examples 1 and 2, it was confirmed that RuO ₂ was present on the surface of the main phase of Bi ₂ Ru ₂ O ₇ .

In addition, regarding Examples 1 and 2, based on the results of the XRD profile, the (110) plane, which is the strongest line of RuO ₂ , with respect to the peak intensity of the (222) plane, which is the strongest line of Bi ₂ Ru ₂ O ₇ When the peak intensity ratio of was obtained, it was 2.1% in Example 1 and 1.74% in Example 2.

Next, from the results of FIG. 7 showing the discharge characteristic curves of Example 1, Example 2, Comparative Example 1 and Comparative Example 2, the discharge characteristic curves of Comparative Example 1 and Comparative Example 2 are compared with the discharge characteristic curves of Example 1 and Example 2. The discharge characteristic curve of No. 2 shifts toward higher discharge voltages, and it can be seen that in Examples 1 and 2, the overvoltage on the discharge side was reduced.

Further, from the results of Table 3 showing the intermediate discharge voltage, the intermediate discharge voltage of Example 1 was improved by 0.08 V compared to Comparative Examples 1 and 2, and the intermediate discharge voltage of Example 2 was improved by 0.08V. 03 V, and it can be seen that the overvoltage on the discharge side has been reduced.

As described above, the presence of ruthenium oxide on the surface of Bi ₂ Ru ₂ O ₇ (pyrochlore-type composite oxide) increased the discharge voltage. This is probably because the charge transfer resistance decreased due to the improvement in oxygen reduction activity. Ruthenium oxide has a RuO ₂ phase from the XRD profile, but RuO ₂ has activity in oxygen generation (charging side), and it is difficult to think that oxygen reduction (discharging side) activity can be improved by itself. . Therefore, it is considered that a catalyst having high catalytic activity could be produced by combining it with a pyrochlore-type composite oxide. In other words, the coexistence of pyrochlore-type composite oxides and ruthenium oxides makes the catalyst multi-functional, such as changes in interaction with oxygen and promotion of catalytic decomposition of hydrogen peroxide ions, which are intermediates in the two-electron reduction process. It is presumed that the overvoltage in the discharge reaction could be reduced because of the occurrence of

Further, from the above results, in order to make ruthenium oxide exist on the surface of Bi ₂ Ru ₂ O ₇ (pyrochlore type composite oxide), it is preferable to perform secondary heat treatment at 400 ° C. or higher, and more excellent overvoltage can be obtained. In order to obtain the reduction effect, it can be said that it is preferable to perform the secondary heat treatment at 500° C. or higher. Furthermore, the ratio of the peak intensity in the (110) plane of the ruthenium oxide X-ray diffraction pattern to the peak intensity in the (222) plane of the X-ray diffraction pattern of the pyrochlore-type composite oxide is set to 1.7% or more. In order to obtain an overvoltage reduction effect, and to obtain a more excellent overvoltage reduction effect, it is preferable to set the ratio to 2.1% or more.

The present invention is not limited to the above-described embodiments and examples, and as an air electrode catalyst for an air secondary battery, in addition to the bismuth ruthenium oxide, the composition of the pyrochlore-type composite oxide described above can be used. Examples include oxides of the selectable elements listed in the general formula represented. Moreover, the present invention is not limited to the air-hydrogen secondary battery, and may be other air secondary batteries using Zn, Al, Mg, Li, or the like as the metal used for the negative electrode. These other air secondary batteries can also obtain the same effect as the above-described air-hydrogen secondary battery.

Also, in the present invention, an XRD profile attributed to RuO ₂ was confirmed, but ruthenium oxide is not limited to RuO ₂ because the oxidation state may well change during the battery reaction.

<Aspect of the present invention>
A first aspect of the present invention is represented by the general formula: A _2-x (Ru _α B _1-α ) _2-y O _7-z (where x, y, z, and α are , 0≦y≦1, 0≦z≦1, and 0<α≦1, and A is Bi, Pb, Tb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, represents at least one element selected from Ho, Er, Tm, Yb, Lu, Mn, Y, Zn and Al, and B is Ir, Si, Ge, Ta, Sn, Hf, Zr, Ti, Nb, V , Sb, Rh, Cr, Re, Sc, Co, Cu, In, Ga, Cd, Fe, Ni, W, and Mo.) and a ruthenium oxide present on the surface of the pyrochlore-type composite oxide.

In a second aspect of the present invention, in the first aspect of the present invention described above, the peak intensity in the (110) plane of the X-ray diffraction pattern of the ruthenium oxide is the X-ray diffraction pattern of the pyrochlore type composite oxide. is 1.7% or more of the peak intensity on the (222) plane of the air electrode catalyst for an air secondary battery.

A third aspect of the present invention is represented by the general formula: A _2-x (Ru _α B _1-α ) _2-y O _7-z (where x, y, z, and α are , 0≦y≦1, 0≦z≦1, and 0<α≦1, and A is Bi, Pb, Tb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, represents at least one element selected from Ho, Er, Tm, Yb, Lu, Mn, Y, Zn and Al, and B is Ir, Si, Ge, Ta, Sn, Hf, Zr, Ti, Nb, V , Sb, Rh, Cr, Re, Sc, Co, Cu, In, Ga, Cd, Fe, Ni, W, and Mo.) a precursor preparation step of preparing a pyrochlore-type composite oxide precursor, a primary heat treatment step of subjecting the precursor to a first heat treatment to form the pyrochlore-type composite oxide, and the primary heat treatment step. an acid treatment step of immersing the obtained pyrochlore-type composite oxide in an acidic aqueous solution for acid treatment, and a secondary heat treatment step of subjecting the pyrochlore-type composite oxide that has undergone the acid treatment step to a second heat treatment. It is a method for producing an air electrode catalyst for an air secondary battery.

A fourth aspect of the present invention is a method for producing an air electrode catalyst for an air secondary battery according to the third aspect of the present invention, wherein the first heat treatment is performed at 400 ° C. or higher and 700 ° C. or lower. be.

A fifth aspect of the present invention is a method for producing an air electrode catalyst for an air secondary battery according to the third aspect or the fourth aspect of the present invention, wherein the second heat treatment is performed at 400 ° C. or higher. is.

A sixth aspect of the present invention comprises an electrode group including an air electrode and a negative electrode superimposed with a separator interposed therebetween, and a container housing the electrode group together with an alkaline electrolyte. Item 3. An air secondary battery comprising the air electrode catalyst for an air secondary battery according to Item 1 or 2.

A seventh aspect of the present invention is the air secondary battery according to the sixth aspect of the present invention, wherein the negative electrode contains a hydrogen storage alloy.

1 Air secondary battery (air hydrogen secondary battery)
REFERENCE SIGNS LIST 10 battery case 20 electrode group 21 negative electrode 22 separator 23 air electrode 30 electrolyte storage unit 50 water-repellent ventilation member 60 ventilation path 61 first ventilation port 62 second ventilation port 63 recessed groove 74 pumping pump

Claims (5)

General formula: A _2-x (Ru _α B _1-α ) _2-y O _7-z (where x, y, z, and α are 0≦x≦1, 0≦y≦1, and 0≦ Satisfying the relationship of z ≤ 1, 0 < α ≤ 1, A is Bi, Pb, Tb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu , Mn, Y, Zn and Al, B represents Ir, Si, Ge, Ta, Sn, Hf, Zr, Ti, Nb, V, Sb, Rh, Cr, Re, represents at least one element selected from Sc, Co, Cu, In, Ga, Cd, Fe, Ni, W and Mo.) and a pyrochlore-type composite oxide having a composition represented by
and a ruthenium oxide present on the surface of the pyrochlore-type composite oxide. The peak intensity in the (110) plane of the X-ray diffraction pattern of the ruthenium oxide is 1.7% or more with respect to the peak intensity in the (222) plane of the X-ray diffraction pattern of the pyrochlore-type composite oxide. The air electrode catalyst for an air secondary battery according to claim 1. General formula: A _2-x (Ru _α B _1-α ) _2-y O _7-z (where x, y, z, and α are 0≦x≦1, 0≦y≦1, and 0≦ Satisfying the relationship of z ≤ 1, 0 < α ≤ 1, A is Bi, Pb, Tb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu , Mn, Y, Zn and Al, B represents Ir, Si, Ge, Ta, Sn, Hf, Zr, Ti, Nb, V, Sb, Rh, Cr, Re, represents at least one element selected from Sc, Co, Cu, In, Ga, Cd, Fe, Ni, W, and Mo.). a precursor preparation step of preparing a body;
a primary heat treatment step of subjecting the precursor to a first heat treatment to form the pyrochlore-type composite oxide;
an acid treatment step of immersing the pyrochlore-type composite oxide obtained in the primary heat treatment step in an acidic aqueous solution for acid treatment;
a secondary heat treatment step of subjecting the pyrochlore-type composite oxide that has undergone the acid treatment step to a second heat treatment;
and
The first heat treatment is performed at 400° C. or higher and 700° C. or lower,
The second heat treatment is performed at 400 ° C. or higher and 700 ° C. or lower,
A method for producing an air electrode catalyst for an air secondary battery. an electrode group including an air electrode and a negative electrode superimposed with a separator interposed therebetween;
and a container housing the electrode group together with an alkaline electrolyte,
The air secondary battery, wherein the air electrode contains the air electrode catalyst for an air secondary battery according to claim 1 or 2. 5. The air secondary battery according to claim 4 , wherein said negative electrode contains a hydrogen storage alloy.

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