JP2020080291A - Air electrode catalyst for air secondary battery, manufacturing method of air electrode catalyst, and air secondary battery - Google Patents

Abstract

To provide an air electrode catalyst for an air secondary battery that contributes to reducing an overvoltage in a discharge reaction, a method for manufacturing the air electrode catalyst, and an air secondary battery that includes the air electrode catalyst and can reduce an overvoltage in the discharge reaction.SOLUTION: A battery 1 includes an electrode group 20 including an air electrode 23 and a negative electrode 21 that are stacked via a separator 22, and a battery case 10 containing the electrode group 20 together with an alkaline electrolyte, and the air electrode 23 contains an air electrode catalyst in which RuOis present on the surface of BiRuOwhich is a pyrochlore type composite oxide.SELECTED DRAWING: Figure 2

Description

  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.

  2. Description of the Related Art In recent years, air batteries using oxygen in the atmosphere as a positive electrode active material have been attracting attention because of their high energy density, easy size, and light weight. In such an air battery, a zinc-air primary battery has been put into practical use as a power source for a hearing aid.

  Further, as a rechargeable air battery, research on an air secondary battery using Li, Zn, Al, Mg, or the like as a metal for a negative electrode has been carried out, and such an air secondary battery is a lithium ion secondary battery. Is expected as a new secondary battery that exceeds the energy density of

  However, in the air secondary battery using the metal for the negative electrode as described above, the dissolution and precipitation reaction of the metal for the negative electrode is repeated along with the chemical reaction during charging/discharging of the battery (hereinafter, referred to as battery reaction). There is a problem that so-called dendrite growth occurs in which metal deposits in a dendritic form, an internal short circuit occurs with it, and the shape of the negative electrode changes due to shape change, resulting in a decrease in battery capacity. I haven't arrived.

  By the way, as one kind of air secondary battery, an air-hydrogen secondary battery using an alkaline aqueous solution (alkali electrolytic solution) as an electrolyte and hydrogen as a negative electrode active material has been studied (for example, see Patent Document 1). The air-hydrogen secondary battery represented by Patent Document 1 uses a hydrogen storage alloy as the metal for the negative electrode, but the negative electrode active material in the air-hydrogen secondary battery is stored and released in the hydrogen storage alloy described above. Since it is hydrogen, the dissolution and precipitation reaction of the hydrogen storage alloy itself does not occur with the battery reaction. Therefore, in the air-hydrogen secondary battery, the above-mentioned problems of decrease in battery capacity due to internal short circuit due to dendrite growth and shape change do not occur.

  In an air secondary battery that uses an alkaline electrolyte, such as the above-described air-hydrogen secondary battery, the following charge/discharge reaction occurs 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 generates oxygen and water as shown in reaction formula (I) during charging, and reduces oxygen as shown in reaction formula (II) during discharge to reduce hydroxide. Generates ions. Oxygen generated at the air electrode is released into the atmosphere from the portion of the air electrode that is open to the atmosphere.

Japanese Patent No. 4568124

  By the way, in the above-mentioned air secondary battery, the energy efficiency has not yet reached a sufficient value, and the high output has not yet been sufficiently achieved. Therefore, in order to put the air secondary battery into practical use, further improvement 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 that the overvoltage of the discharge reaction at the air electrode, that is, the oxygen reduction reaction is large.

  The present invention has been made based on the above circumstances, and an object of the present invention is to manufacture an air electrode catalyst for an air secondary battery, which contributes to reducing an overvoltage in a discharge reaction, and to manufacture the air electrode catalyst. It is to provide a method and an air secondary battery including the air electrode catalyst, which can reduce an overvoltage in a discharge reaction.

In order to achieve the above object, according to the present invention, a general formula: A2 _-x (Ru[ _alpha] B1-[ _alpha] ) _{2-yO7 -z} (where x, y, z and [alpha] are, respectively, The relationship of 0≦x≦1, 0≦y≦1, 0≦z≦1, 0<α≦1 is satisfied, 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, and at least one element is selected, and B is Ir, Si, Ge, Ta, Sn, Hf, Zr, It 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.). There is provided an air electrode catalyst for an air secondary battery, comprising: a pyrochlore-type composite oxide having a composition according to claim 1, and 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 that

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 respectively 0≦x≦1, The relationship of 0≦y≦1, 0≦z≦1, 0<α≦1 is satisfied, 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, and at least one element is selected, 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 precursor of a pyrochlore-type composite oxide, a first heat treatment step of subjecting the precursor to a first heat treatment to form the pyrochlore-type composite oxide, and a first heat treatment step. And an acid treatment step of immersing the pyrochlore-type composite oxide in an acidic aqueous solution to perform an acid treatment, and a secondary heat treatment step of subjecting the pyrochlore-type composite oxide subjected to the acid treatment step to a second heat treatment. A method for manufacturing 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 stacked via a separator, and a container accommodating the electrode group together with an alkaline electrolyte, the air electrode is as described above. There is provided an air secondary battery including an air electrode catalyst for the air secondary battery.

  It is preferable that the negative electrode includes a hydrogen storage alloy.

The air electrode catalyst for an air secondary battery according to the present invention has a general formula: A2 _-x (Ru[ _alpha] B1-[ _alpha] ) _{2-yO7 -z} (where x, y, z and [alpha] are, respectively. , 0≦x≦1, 0≦y≦1, 0≦z≦1, 0<α≦1, and A is Bi, Pb, Tb, La, Ce, Pr, Nd, Pm, Sm, At least one element selected from Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Mn, Y, Zn and Al is represented, 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). Since the pyrochlore-type composite oxide having the above composition and the ruthenium oxide existing on the surface of the pyrochlore-type composite oxide are provided, it contributes to reducing the overvoltage in the discharge reaction. Therefore, in the air secondary battery including such an air electrode catalyst, since the overvoltage in the discharge reaction is reduced, the energy efficiency is improved and the output is increased. Therefore, according to the present invention, an air electrode catalyst for an air secondary battery that contributes to reducing an 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 capable of reducing overvoltage can be provided.

1 is a plan view schematically showing an air-hydrogen secondary battery according to an embodiment of the present invention. It is sectional drawing which showed the cross section along the II-II line in FIG. 3 is an XRD profile of air electrode catalysts of Example 1, Example 2, Comparative Example 1 and Comparative Example 2. FIG. 4 is an XRD profile in which 2θ in FIG. 3 is expanded in the range of 25 degrees to 45 degrees. 4 is a drawing-substituting photograph showing an SEM image of the air electrode catalyst of Example 1. 7 is a drawing-substituting photograph showing an SEM image of the air electrode catalyst of Example 2. 3 is a graph showing discharge characteristic curves of air-hydrogen secondary batteries of Examples 1 and 2, Comparative Example 1 and Comparative Example 2.

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

  The battery 1 includes a battery case 10 as a container, as shown in FIG. As shown in FIG. 2, the battery case 10 includes an air electrode side case half body 12 and a negative electrode side case half body 14, and the air electrode side case half body 12 and the negative electrode side case half body 14 are separated from each other. Combined, the battery case 10 having a box shape as a whole is formed. The battery case 10 is made of, for example, acrylic resin.

  The air electrode side case half 12 includes an air electrode facing wall 16 that faces the air electrode 23, and an air electrode side outer peripheral wall 18 that is provided in a peripheral portion of the air electrode facing wall 16 and surrounds the air electrode 23. There is.

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

Inside the battery case 10, the electrode group 20 is housed together with the alkaline electrolyte 32.
The electrode group 20 is formed by stacking an air electrode (positive electrode) 23 and a negative electrode 21 via a separator 22.

  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 carried in the pores and on the surface of the negative electrode base material. As the negative electrode base material as described above, for example, nickel foam can be used.

  The negative electrode mixture contains a hydrogen storage alloy powder, which is an aggregate of hydrogen storage alloy particles capable of storing 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 that constitutes the hydrogen storage alloy particles is not particularly limited, but a rare earth-Mg-Ni-based hydrogen storage alloy is used. Although the composition of this rare earth-Mg-Ni-based hydrogen storage alloy can be freely selected, for example, a general formula:
Ln _1-a Mg _a Ni _b-c-d Al _c M _d ... (III)
It is preferable to use the one represented by

  However, in the general formula (III), Ln is derived from 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. Represents at least one element selected from the group, and subscripts a, b, c, d are 0.01≦a≦0.30, 2.8≦b≦3.9, 0.05≦c≦, respectively. It represents a number satisfying 0.30 and 0≦d≦0.50.

Here, the hydrogen storage 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 an inert gas atmosphere, for example, in a high frequency induction melting furnace to form an ingot. The obtained ingot is heated to 900 to 1200° C. under an inert gas atmosphere and subjected to a heat treatment of holding at that temperature for 5 to 24 hours for homogenization. Then, the ingot is crushed and sieved to obtain a hydrogen storage alloy powder, which is an aggregate of hydrogen storage alloy particles having a desired particle size.

  As the binder, for example, sodium polyacrylate, carboxymethyl cellulose, styrene butadiene rubber or the like is used.

The negative electrode 21 can be manufactured, for example, as follows.
First, a hydrogen storage alloy powder, which is an aggregate of hydrogen storage alloy particles, a conductive material, a binder, and water are kneaded to prepare a negative electrode mixture paste. The obtained negative electrode mixture paste is filled in the negative electrode base material and dried. After drying, the negative electrode base material to which the hydrogen-absorbing alloy particles and the like are attached is rolled to increase the alloy amount per volume, and then cut, whereby the negative electrode 21 is manufactured. The negative electrode 21 has a plate shape as a whole.

  Next, the air electrode 23 includes a conductive air electrode base material having a porous structure and a large number of pores, and an air electrode mixture (a positive electrode) carried in the pores and on the surface of the air electrode base material. (Mixture). As the air electrode base material as described above, for example, foamed nickel or nickel mesh can be used.

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 provided with 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: A2 _-x (Ru[ _alpha] B1-[ _alpha] ) _{2-yO7 -z} (where x, y, z, and α are 0≤x≤1, respectively). The relationship of 0≦y≦1, 0≦z≦1, 0<α≦1 is satisfied, 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, and at least one element is selected, 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 pyrochlore type complex oxide is used.

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

  Here, it is known that properties such as an 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, the binding energy between the metal element and oxygen. In addition, it is considered that the side-on adsorption of oxygen on the catalyst is important in order to efficiently break the bond of oxygen molecules, and the interval between adsorption points and the surface condition are also important factors. Be done.

The present inventor, as a result of various studies in consideration of the above matters, has found that in the pyrochlore type composite oxide, when ruthenium oxide is present on the surface thereof, excellent catalytic activity is exhibited. .. When ruthenium oxide is present on the surface of the pyrochlore type composite oxide, the interaction with oxygen is changed, and the bond strength between oxygen and the surface of the air electrode catalyst is changed. It is considered that the decomposition of hydrogen peroxide ion (HO ₂ ⁻ ) which is an intermediate produced in the process of 1) is promoted, and the multi-functionality of the catalyst is caused.

Here, the electrochemical reduction mechanism of oxygen in the alkaline electrolyte is not limited to the four-electron reduction pathway as shown in the above formula (II), but as shown in the following formula (IV). There is an electron reduction pathway. This two-electron reduction pathway produces hydrogen peroxide ion (HO ₂ ⁻ ) as an intermediate.
_{O 2 + H 2 O + 2e} - → HO 2 - + OH - ··· (IV)

HO ₂ ⁻ is adsorbed on the surface of the electrode and inhibits the reaction, which 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 the ruthenium oxide according to the present invention is considered to promote the decomposition of HO ₂ ⁻ , and is considered to proceed the reaction of the following formula (V). .
^{_{2HO 2 - → 2OH - + O}} 2 ··· (V)
From the above formulas (IV) and (V), the entire reaction is the same as that of 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 the pyrochlore type composite oxides and is a catalyst having a dual function of oxygen generation and oxygen reduction.

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

  It is considered that the amount of ruthenium oxide is necessary to the extent that the peak of the X-ray diffraction pattern can be confirmed. In the present invention, in relation to the pyrochlore type composite oxide, 2θ= in the X-ray diffraction pattern of the ruthenium oxide The peak intensity of the (110) plane which is the strongest line of 28 degrees is 1.74% or more with respect to the peak intensity of the (222) plane of 2θ=30 degrees which is the strongest line in the X-ray diffraction pattern of the pyrochlore type composite oxide. It is preferable that an 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 by taking a pyrochlore-type bismuth ruthenium oxide having ruthenium oxide on the surface as an example.

First, Bi(NO ₃ ) ₃ .5H ₂ O and RuCl ₃ .3H ₂ O were poured into distilled water so as to have the same concentration, stirred, and then Bi(NO ₃ ) ₃ .5H ₂ O and RuCl ₃ were added. · 3H ₂ to prepare an O mixed aqueous solution of. At this time, the temperature of the distilled water is 60° C. or higher and 90° C. or lower. Then, 1 mol/L or more and 3 mol/L or less NaOH aqueous solution is added to this mixed aqueous solution. The bath temperature at this time is maintained at 60° C. or higher and 90° C. or lower, and stirring is performed while oxygen bubbling is performed. The solution containing the precipitate generated by this operation is kept at 80° C. or higher and 100° C. or lower to evaporate a part of the water to form a paste. This paste is transferred to an evaporating dish, heated to 100° C. or higher and 150° C. or lower, and kept in that state for 10 hours or more and 20 hours or less to dry to obtain a dried paste product. Then, after crushing 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 is held for 0.5 hours or longer and 24 hours or shorter to carry out a primary heat treatment to perform a 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, when the temperature of the primary heat treatment exceeds 700° C., the structure of the pyrochlore type complex oxide changes and the surface area of the first fired product decreases due to the sintering of the particles. Therefore, the temperature of the primary heat treatment is preferably 400° C. or higher and 700° C. or lower.

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

  In the acid treatment step, the first fired product is immersed in a nitric acid aqueous solution. Specifically, it is as follows.

  First, a nitric acid aqueous 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 20 mL with respect to 1 g of the first baked 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 fired product is immersed in the prepared nitric acid aqueous solution and stirred for 0.5 hours or more and 24 hours or less. After the lapse of a predetermined time, the first fired product is suction filtered from the aqueous nitric acid solution. The filtered first fired product is put into ion-exchanged water set at 60° C. or higher and 80° C. or lower and washed.

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

  As described above, the acid-treated first fired product is obtained. By performing the acid treatment in this way, unnecessary by-products generated in the manufacturing process of bismuth ruthenium oxide (pyrochlore type composite oxide) can be removed and only ruthenium oxide can be left. The acidic aqueous solution used for the acid treatment is not limited to the nitric acid aqueous solution, and a hydrochloric acid aqueous solution or a sulfuric acid aqueous solution can be used in addition to the nitric acid aqueous solution. Even in these hydrochloric acid aqueous solution and sulfuric acid aqueous solution, it is possible to obtain the effect that unnecessary by-products can be removed similarly to the nitric acid aqueous solution.

  Next, a secondary heat treatment is performed on the acid-treated first fired product. Specifically, the first fired 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 longer and 24 hours or shorter to perform a second heat treatment, and then the second firing. 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 brought out.

  Here, if the temperature of the secondary heat treatment is less than 400° C., crystallization of the ruthenium oxide is difficult to proceed. In order to promote the crystal growth of 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 changes and the crystal structure of the base pyrochlore type composite oxide also changes. In order to avoid such problems, the temperature of the secondary heat treatment is preferably 700°C or lower.

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

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

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

  Further, the conductive material is not limited to the above-mentioned nickel powder, and a metal-coated conductive filler having a core material coated with a metal material can also be used. This metal-coated conductive filler is lighter than the metal particles entirely formed of metal, and contributes to weight reduction of the air electrode as a whole. The core material described above is not particularly limited, and examples thereof include silica particles. Then, it is preferable to adopt 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 amount of 30% by mass or more based on the air electrode mixture.

  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. In addition, as a preferable fluororesin, for example, polytetrafluoroethylene (PTFE) is used.

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). Thereby, an intermediate product of the air electrode is obtained.

  Next, the obtained intermediate product is put into a firing furnace and subjected to a firing treatment. This firing process is performed in an inert gas atmosphere. As the inert gas, for example, nitrogen gas or argon gas is used. The conditions for the firing treatment are heating to a temperature of 300° C. or higher and lower than 400° C., and holding in this state for 10 minutes or longer and 20 minutes or shorter. Then, the intermediate product is naturally cooled in the firing furnace and taken out into the atmosphere when the temperature of the intermediate product becomes 150° C. or lower. As a result, an intermediate product that has been subjected to a baking 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 in between, and thus the electrode group 20 is formed. 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 a material adopted for the separator 22, for example, a polyamide fiber non-woven fabric to which a hydrophilic functional group is added, or a polyolefin fiber non-woven fabric such as polyethylene or polypropylene to which a hydrophilic functional group is added, is used. it can. Here, the separator 22 has a rectangular shape as a whole. The shape of the separator 22 in plan view is preferably larger than the shapes of the air electrode 23 and the negative electrode 21 in plan view described above.

  When the electrode group 20 is formed, the electrode group 20 is assembled so that the four end portions of the separator 22 project from the four end portions of the air electrode 23 and the negative electrode 21.

  In the obtained electrode group 20, it is preferable to further mount a water repellent ventilation member 50 on the air electrode 23. The water repellent ventilation member 50 is not particularly limited as long as it has a function of allowing air to permeate and preventing permeation of the alkaline electrolyte. As such a water repellent ventilation member 50, for example, a fluororesin porous film is preferably used. More preferably, a PTFE porous membrane is used. Further, as the water repellent and ventilation member 50, it is preferable to use a composite body in which a nonwoven fabric diffusion paper is laminated on a fluororesin porous film.

  The electrode group 20 on which the water repellent ventilation member 50 is placed is arranged in 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 faces the air electrode facing wall 16 of the air electrode side case half body 12 and the negative electrode side of the negative electrode side case half body 14. While being sandwiched between the wall 26 and the four ends of the separator 22, the four end portions of the separator 22 are provided at the tip end portion 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. It is sandwiched and fixed by the tip 29 of 28. Thereby, the battery 1 is formed.

  Here, between the tip portion 19 of the air electrode side outer peripheral wall 18 of the air electrode side case half 12 and the tip portion 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 packing 34 so that the alkaline electrolyte 32 does not leak outside.

  As shown in FIGS. 1 and 2, the negative electrode side case half 14 includes an electrolytic solution storage portion 30 attached to a part of the negative electrode side outer peripheral wall 28 via a connecting portion 40. The electrolytic solution storage unit 30 is a container that stores the alkaline electrolytic solution 32. The connection part 40 is a flow path of the alkaline electrolyte 32 that connects the inside of the battery case 10 and the electrolyte storage part 30. As described above, since the inside of the battery case 10 and the electrolytic solution storage unit 30 communicate with each other, the alkaline electrolytic solution 32 can move between the inside of the battery case 10 and the electrolytic solution storage unit 30. For this reason, when the amount of the alkaline electrolyte solution 32 increases due to the air electrode 23 generating water during charging, the excess alkaline electrolyte solution 32 inside the battery case 10 moves to the electrolyte solution storage unit 30. Stored. When the alkaline electrolyte 32 is reduced due to the air electrode 23 decomposing water at the time of discharge, the alkaline electrolyte 32 stored in the electrolytic solution storage unit 30 moves into the battery case 10 to move the air electrode 23. It is possible to make up for the shortage of the alkaline electrolyte 32. As described above, by including the electrolytic solution storage unit 30, it is possible to suppress leakage and depletion of the alkaline electrolytic solution 32.

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

  Further, the air electrode side case half 12 has a ventilation path 60. The ventilation 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 ventilation passage 60 is not particularly limited. As a preferable shape of the ventilation path 60, for example, the shapes shown in FIGS. 1 and 2 can be mentioned. That is, the ventilation path 60 includes the concave groove 63 as an air electrode opening provided on the inner wall surface 17 of the air electrode facing wall 16 on the air electrode side, and the first ventilation hole 61 provided at one end of the concave groove 63. And a second ventilation hole 62 provided at the other end of the groove 63.

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

  The first ventilation hole 61 is a through hole that penetrates from the inside of the air electrode facing wall 16 to the outside at the one end portion of the concave groove 63. A part of the inner peripheral surface of the first ventilation port 61 communicates with the concave groove 63.

  The second ventilation port 62 is a through hole that penetrates from the inside of the air electrode facing wall 16 to the outside at the other end portion of the concave groove 63. Then, a part of the inner peripheral surface of the second ventilation port 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 entire groove 63, the first ventilation hole 61, and the second ventilation hole 62.

  In the battery 1 having the above-described configuration, air flows through the ventilation path 60. The air flowing through the ventilation passage 60 diffuses into the water repellent ventilation member 50 facing the concave groove 63 of the ventilation passage 60. Then, the water repellent ventilation member 50 allows the air diffused inside to permeate the air electrode 23 which is in contact therewith immediately below. 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 into the concave groove 63. The oxygen that has reached the groove 63 is released into the atmosphere outside the battery case 10 through the vent hole.

  In addition, the water repellent ventilation member 50 prevents the alkaline electrolyte 32 in the battery case 10 from permeating the ventilation path 60. For this reason, when the pressure of the alkaline electrolyte solution 32 inside the battery case 10 rises, it is possible to prevent the alkaline electrolyte solution 32 from leaking to the outside through the vent hole.

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

In the present embodiment, although not shown, the air electrode lead is electrically connected to the air electrode 23, and the 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 the 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, the current is input and output at the time of charging/discharging by using the air electrode terminal and the negative electrode terminal.
Further, in FIG. 1, the pressure feed pump 74 is not shown.

  Here, in the battery 1, the concave groove 63 of the air electrode side case half body 12 faces the water repellent ventilation member 50. Since the water-repellent ventilation member 50 allows gas to pass through but blocks moisture, the air electrode 23 is opened 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. That is, the air electrode 23 comes into 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 including the air electrode catalyst reduces the overvoltage in the discharge reaction. It is possible to improve the energy efficiency and increase the output.

[Example]
1. Production of battery (Example 1)
(1) as a synthetic first step of air electrode _{catalyst, Bi (NO 3) 3 ·} 5H 2 O and RuCl ₃ · 3H ₂ O prepared a predetermined amount, these _{Bi (NO 3) 3 · 5H} 2 O and RuCl ₃ · 3H ₂ O is poured into distilled water so 75 ° C. the same concentration was prepared a mixed aqueous solution of stirring to _{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. The bath temperature at this time was 75° C., and stirring was performed while oxygen bubbling was performed. The solution containing the precipitate generated by this operation was kept at 85° C. to evaporate part of the water content to form a paste. This paste was transferred to an evaporation dish, heated to 120° C., and kept in that state for 12 hours to be dried to obtain a dried material (precursor) of the paste.

  As a second step, the obtained dried product was crushed in a mortar and then subjected to a primary heat treatment of heating at 600° C. in an air atmosphere and holding for 1 hour to obtain a fired product. The obtained fired product was washed with distilled water at 70° C., suction filtered, and dried at 120° C. Thereby, the 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 was an aggregate of particles having a predetermined particle size. As a result of observing a secondary electron image of the powder of the first baked product with a scanning electron microscope, the particle diameter of the first baked product was 0.1 μm or less.

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

  After the stirring was completed, the powder of the first baked product was taken out from the aqueous nitric acid 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 heated to 120° C. to be dried.

  As a fourth step, the first fired product that had been treated with nitric acid was heated to 500° C. in an air atmosphere and subjected to a secondary heat treatment of holding for 1 hour to obtain a fired product. As a result, the second fired product, that is, the air electrode catalyst for the air secondary battery was obtained. Here, a 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) Production of air electrode Nickel powder, which is an aggregate of nickel particles, was prepared. The nickel particles had an average particle size of 2 to 3 μm.

  Further, a polytetrafluoroethylene (PTFE) dispersion and ion-exchanged 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, the powder of the air electrode catalyst was 20 parts by mass, the nickel powder was 70 parts by mass, the PTFE dispersion was 10 parts by mass, and the ion-exchanged water was uniformly mixed at a ratio of 30 parts by mass to prepare 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 this sheet of air electrode mixture paste was used for mesh number 60, wire diameter 0.08 mm, opening ratio. It was press-bonded to 60% nickel mesh.

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

(3) Manufacture of Negative Electrode Nd, Mg, Ni, and Al metal materials were mixed in a predetermined molar ratio, and then charged into a high-frequency induction melting furnace and melted under an argon gas atmosphere to obtain a molten metal. Was poured into a mold and cooled to room temperature of 25° C. to produce an ingot.

  Then, this ingot was subjected to a heat treatment of holding it in an argon gas atmosphere at a temperature of 1000° C. for 10 hours, and then mechanically crushed in an argon gas atmosphere to obtain a rare earth-Mg—Ni-based hydrogen storage alloy powder. Obtained. The volume average particle diameter (MV) of the obtained rare earth-Mg-Ni hydrogen storage alloy powder was measured by a laser diffraction/scattering particle size distribution measuring device. As a result, the volume average particle diameter (MV) was 60 μm.

When the composition of this hydrogen storage alloy powder was analyzed by the high frequency plasma spectroscopy (ICP), the composition was Nd _0.89 Mg _0.11 Ni _3.33 Al _0.17 .

  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 100 parts by mass of carbon black based on 100 parts by mass of the obtained hydrogen storage alloy powder. 0.5 parts by mass of powder 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 material mixture paste was filled into a nickel foam sheet having an areal density (area 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 sheet of foamed nickel filled with the negative electrode mixture. The obtained sheet was rolled to increase the amount of alloy per volume, and then cut into a length of 40 mm and a width of 40 mm to obtain a 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 of this activation processing 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, the nickel hydroxide positive electrode and the obtained negative electrode 21 were overlapped with a separator made of a polyethylene nonwoven fabric interposed therebetween to form an activation treatment electrode group. This activation treatment electrode group was housed in a container made of acrylic resin together with a predetermined amount of alkaline electrolyte. As a result, a single electrode cell of a nickel hydrogen secondary battery was formed.

  As a first charge/discharge operation, this single electrode cell was left standing for 5 hours in an environment of a temperature of 25° C., charged at 0.1 It for 14 hours, and then at 0.5 It, the battery voltage was 0. It was discharged to 0.70V. Next, as a second charge/discharge operation, an operation of charging the battery at 0.5 It for 2.8 hours in an environment of a temperature of 25° C., and then discharging at 0.5 It until the battery voltage becomes 0.70 V. I went. After the second time, the negative electrode 21 was activated by performing a plurality of charge/discharge cycles in which the above-described second charge/discharge operation was one cycle. In addition, the capacity of the monopolar cell was obtained in each charge/discharge cycle. Then, the maximum value of the obtained capacities was taken as the capacity of the negative electrode. 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 electrode 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 sandwiched therebetween to manufacture the electrode group 20. The separator 22 used for manufacturing this electrode group 20 was formed of a polypropylene fiber non-woven fabric having a sulfone group and had a thickness of 0.1 mm (basis weight: 53 g/m ² ).

  On the other hand, as the water-repellent air-permeable member 50, a composite body formed by stacking a nonwoven fabric diffusion paper on a PTFE porous film was prepared. Here, the dimensions of the PTFE porous membrane were 45 mm in length, 45 mm in width, and 0.1 mm in thickness. The dimensions of the non-woven diffusion paper were 40 mm in length, 40 mm in width, and 0.2 mm in thickness.

  The composite body as the water repellent ventilation member 50 was placed on the air electrode 23 in the electrode group 20 and housed in the battery case 10. Specifically, the electrode group 20 on which the composite body as the water repellent ventilation member 50 is placed is provided with the air electrode facing wall 16 of the air electrode side case half 12 and the negative electrode facing wall 26 of the negative electrode side case half 14. And the four end portions of the separator 22 are attached to the front end portion 19 of the air electrode side outer peripheral wall 18 of the air electrode side case half body 12 and the negative electrode side outer peripheral wall 28 of the negative electrode side case half body 14. It was sandwiched by 29 and fixed. Here, between the tip portion 19 of the air electrode side outer peripheral wall 18 of the air electrode side case half 12 and the tip portion 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. The packing was sealed with packing 34 so that the alkaline electrolyte 32 did not leak outside.

  Here, the air electrode facing wall 16 of the air electrode side case half 12 is provided with a serpentine-shaped groove 63 having a width of 1 mm, a depth of 1 mm, and a mountain width of 1 mm as the groove 63. The total length of the groove 63 is 720 mm. The first vent 61 is provided at one end of the groove 63, and the second vent 62 is provided at the other end. The groove 63 is open on the side of the water repellent ventilation member 50. Further, a pressure feed pump 74 was attached to the above-mentioned first ventilation port 61 via a piping member 72.

  Further, in the negative electrode side case half body 14, an electrolytic solution storage portion 30 is attached to a part of the negative electrode side outer peripheral wall 28 via a connecting portion 40. A 5 mol/L KOH aqueous solution was injected as the alkaline electrolyte 32 into the electrolytic solution 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 obtained battery 1 was allowed to stand in an environment of 25° C. for 1 hour to allow the electrode group 20 to permeate 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. These air electrode lead and negative electrode lead are connected to the battery case. The battery case 10 appropriately extends from the inside to the outside while maintaining the airtightness and watertightness. 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 the fourth step, the first calcined 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, except that a calcined product was obtained. An air hydrogen secondary battery was manufactured in the same manner as in.

(Comparative Example 1)
As the fourth step, the first calcined product that had been treated with nitric acid was heated to 300° C. in an air atmosphere and subjected to a secondary heat treatment for holding for 1 hour, except that a calcined product was obtained, and Example 1 An air hydrogen secondary battery was manufactured in the same manner as in.

(Comparative example 2)
An air-hydrogen secondary battery was prepared in the same manner as in Example 1 except that the fourth step of the secondary heat treatment was omitted and the first calcined product after the treatment with nitric acid was used as the air electrode catalyst for the air secondary battery. Was manufactured.

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

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

  In addition, so-called SEM/EDS in which the analysis samples of the air electrode catalysts of Examples 1 and 2 are observed by a scanning electron microscope (SEM) and elemental analysis is performed by an energy dispersive X-ray spectrometer (EDS) Analysis was carried out. The SEM image (magnification: 5000 times) of the analysis result of Example 1 is shown in FIG. 5, and the SEM image (magnification: 5000 times) of the analysis result of Example 2 is shown in FIG.

  Then, EDS analysis was performed on the measurement spots of the portions numbered 1 to 6 in each SEM image. At each measurement spot, the intensity (count number) of the characteristic X-rays of C, O, Na, Al, Ru, and Bi was measured, and the concentration of each element (number of atoms %) was examined. The results are shown in Table 1 for Example 1 and Table 2 for Example 2. In addition, 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 Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were charged at 0.5 It for 1.2 hours through the air electrode terminal and the negative electrode terminal, Discharging at 0.5 It until the battery voltage reached 0.4 V was defined as one cycle, and such charging/discharging was repeated 10 cycles. At this time, regardless of charge and discharge, air was sent from the first ventilation port 61 by the pressure pump 74, and air was constantly supplied to the ventilation path 60 at a rate of 53 mL/min. The negative electrode capacity (640 mAh) was set to 1 It.

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

  In addition, the battery voltage when the discharge capacity is half the total discharge capacity at this time is shown in Table 3 as the discharge intermediate voltage.

(3) Consideration FIG. 3 shows data of peak positions of Bi ₂ Ru ₂ O ₇ and RuO ₂ in ICDD (registered trademark) (International Center for Diffraction Data). As a result of collating 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 the air electrode catalysts of Comparative Example 2 each had a peak of Bi ₂ Ru ₂ O ₇ . In addition, in Example 1 and Example 2, it was further confirmed that there was a peak corresponding to RuO ₂ . However, in Comparative Example 1 and Comparative Example 2, a peak corresponding to RuO ₂ could not be confirmed. From this, the air electrode catalysts of Comparative Example 1 and Comparative Example 2 hardly contain RuO ₂ , but in Example 1 and Example 2, Bi ₂ Ru ₂ O ₇ and RuO ₂ coexist. I understand.

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

Further, regarding Example 1 and Example 2, based on the result of the XRD profile, 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 is} the (110) plane. When the ratio of the peak intensities was calculated, 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, compared with the discharge characteristic curves of Comparative Example 1 and Comparative Example 2, Example 1 and Example The discharge characteristic curve of No. 2 shifts toward the higher discharge voltage, and it can be seen that in Examples 1 and 2, the overvoltage on the discharge side was reduced.

  Also, from the results of Table 3 showing the discharge intermediate voltage, the discharge intermediate voltage of Example 1 was improved by 0.08 V, and the discharge intermediate voltage of Example 2 was 0. It is improved by 03 V, and it can be seen that the overvoltage on the discharge side is reduced.

From the above, the discharge voltage was increased by allowing the ruthenium oxide to exist on the surface of Bi ₂ Ru ₂ O ₇ (pyrochlore type composite oxide). It is considered that this is because the charge transfer resistance decreased due to the improvement in oxygen reduction activity. Although ruthenium oxide has a phase of RuO ₂ from the XRD profile, RuO ₂ is active in oxygen generation (charge side), and it is unlikely to improve the activity of oxygen reduction (discharge side) by itself. . Therefore, it is considered that a catalyst having high catalytic activity could be produced by combining it with the pyrochlore type composite oxide. In other words, the coexistence of pyrochlore-type composite oxide and ruthenium oxide makes the catalyst multi-functional, such as the change in interaction with oxygen and the promotion of catalytic decomposition of hydrogen peroxide ion, which is an intermediate in the two-electron reduction process. It is presumed that the overvoltage in the discharge reaction could be reduced due to the occurrence of the phenomenon.

Further, from the above results, in order to allow the ruthenium oxide to be present on the surface of Bi ₂ Ru ₂ O ₇ (pyrochlore type composite oxide), it is preferable to carry out the secondary heat treatment at 400° C. or higher, which is more excellent in overvoltage. In order to obtain the reduction effect, it can be said that the secondary heat treatment is preferably performed at 500° C. or higher. Furthermore, by setting the ratio of the peak intensity at the (110) plane of the X-ray diffraction pattern of the ruthenium oxide to the peak intensity at the (222) plane of the X-ray diffraction pattern of the pyrochlore type composite oxide to 1.7% or more. In order to obtain the effect of reducing the overvoltage and to obtain the more excellent effect of reducing the overvoltage, it can be said that the ratio is preferably 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 bismuth ruthenium oxide, a composition of the above-mentioned pyrochlore-type composite oxide is used. Oxides of the selectable elements listed in the general formulas represented are included. Further, the present invention is not limited to the air-hydrogen secondary battery, and may be another air secondary battery using Zn, Al, Mg, Li or the like as the metal used for the negative electrode. These other air secondary batteries also have the same effects as those of the air hydrogen secondary battery described above.

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

<Aspect of the present invention>
A first aspect of the present invention have the general _{formula: A 2-x (Ru α} B 1-α) 2-y O 7-z ( however, x, y, z, alpha, respectively, 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 at least one element selected from Al, and B represents Ir, Si, Ge, Ta, Sn, Hf, Zr, Ti, Nb, and 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.

  A second aspect of the present invention is the above-mentioned first aspect of the present invention, wherein the peak intensity at the (110) plane of the X-ray diffraction pattern of the ruthenium oxide is the X-ray diffraction pattern of the pyrochlore type complex oxide. It is 1.7% or more with respect to 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 directed to a general formula: A2 _-x (Ru[ _alpha] B1-[ _alpha] ) _{2-yO7 -z} (where x, y, z and [alpha] are each 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 at least one element selected from Al, and B represents Ir, Si, Ge, Ta, Sn, Hf, Zr, Ti, Nb, and V. , 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 complex oxide, a first heat treatment step of subjecting the precursor to a first heat treatment to form the pyrochlore type complex oxide, and a first heat treatment step. An acid treatment step of dipping 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.

  A fourth aspect of the present invention is the 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. is there.

  A fifth aspect of the present invention is the 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 includes an electrode group including an air electrode and a negative electrode that are stacked via a separator, and a container that accommodates the electrode group together with an alkaline electrolyte. 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 rechargeable battery (air hydrogen rechargeable battery)
DESCRIPTION OF SYMBOLS 10 Battery case 20 Electrode group 21 Negative electrode 22 Separator 23 Air electrode 30 Electrolyte storage part 50 Water repellent ventilation member 60 Ventilation path 61 First ventilation hole 62 Second ventilation hole 63 Recessed groove 74 Pressure pump

Claims (7)

General _{formula: A 2-x (Ru α} B 1-α) 2-y O 7-z ( however, x, y, z, alpha, respectively, 0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ The relationship of z≦1, 0<α≦1 is satisfied, 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, and B represents 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 represents at least one element, and a pyrochlore type composite oxide having a composition represented by:
An air electrode catalyst for an air secondary battery, comprising: a ruthenium oxide present on the surface of the pyrochlore type composite oxide.   The peak intensity on the (110) plane of the X-ray diffraction pattern of the ruthenium oxide is 1.7% or more with respect to the peak intensity on the (222) plane of the X-ray diffraction pattern of the pyrochlore type composite oxide. An 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 ( however, x, y, z, alpha, respectively, 0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ The relationship of z≦1, 0<α≦1 is satisfied, 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, and B represents Ir, Si, Ge, Ta, Sn, Hf, Zr, Ti, Nb, V, Sb, Rh, Cr, Re, Which represents at least one element selected from Sc, Co, Cu, In, Ga, Cd, Fe, Ni, W and Mo.) A precursor of a pyrochlore type complex oxide having a composition represented by A precursor preparation step for preparing the body,
A first 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 by the primary heat treatment step in an acidic aqueous solution for acid treatment;
A second heat treatment step of performing a second heat treatment on the pyrochlore-type composite oxide that has undergone the acid treatment step;
A method for producing an air electrode catalyst for an air secondary battery, comprising:   The method for producing an air electrode catalyst for an air secondary battery according to claim 3, wherein the first heat treatment is performed at 400° C. or higher and 700° C. or lower.   The method for producing an air electrode catalyst for an air secondary battery according to claim 3, wherein the second heat treatment is performed at 400° C. or higher. An electrode group including an air electrode and a negative electrode superposed via a separator,
A container containing the electrode group together with an alkaline electrolyte,
An air secondary battery, wherein the air electrode includes the air electrode catalyst for an air secondary battery according to claim 1 or 2.   The air secondary battery according to claim 6, wherein the negative electrode contains a hydrogen storage alloy.