Catalyst for air electrode, air electrode including the catalyst for air electrode, and air secondary battery including the air electrode

Abstract

To provide an air electrode catalyst, an air electrode containing the air electrode catalyst, and an air secondary battery containing the air electrode, which can contribute to an increase in discharge voltage more than before.SOLUTION: A battery 2 includes: an electrode group 10 including an air electrode 16 and a negative electrode 12 superimposed via a separator 14; and a container 4 containing the electrode group 10 together with an alkaline electrolyte 82. The air electrode 16 includes an air electrode catalyst, and the air electrode catalyst is an air electrode catalyst including an oxide containing at least bismuth, ruthenium, sodium, and oxygen, and Na / (Ru+Bi+Na) representing the atomic ratio of sodium to the total of bismuth, ruthenium, and sodium is 0.126 or more and 0.145 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a catalyst for an air electrode, an air electrode including the catalyst for an air electrode, and an air secondary battery including the air electrode.

Background Art

[0002] In recent years, air batteries using oxygen in the atmosphere as a positive electrode active material have attracted attention because of their high energy density, easy miniaturization, and weight reduction. Among such air batteries, zinc-air primary batteries have been put into practical use as power sources for hearing aids.

[0003] In addition, as a rechargeable air battery, research has been conducted on an air secondary battery using Li, Zn, Al, Mg, etc. as the metal for the negative electrode. Such an air secondary battery is expected as a new secondary battery that may exceed the energy density of lithium-ion secondary batteries.

[0004] As one type of such an air secondary battery, an air hydrogen secondary battery using an alkaline aqueous solution (hereinafter also referred to as an alkaline electrolyte) as an electrolyte and hydrogen as a negative electrode active material is known (see, for example, 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. However, since the negative electrode active material in the air hydrogen secondary battery is hydrogen occluded and released in the above-described hydrogen storage alloy, a dissolution and precipitation reaction of the hydrogen storage alloy itself does not occur during charge and discharge in the battery (hereinafter also referred to as a battery reaction). For this reason, the air hydrogen secondary battery has the merit that problems such as the occurrence of internal short circuit due to so-called dendrite growth in which the metal for the negative electrode precipitates dendritically and the decrease in battery capacity due to shape change do not occur.

[0005] In an air secondary battery using an alkaline electrolyte such as the above-described air hydrogen secondary battery, the following charge and discharge reactions occur at the positive electrode (hereinafter also referred to as an air electrode).

[0006] Charge (oxygen generation reaction): 4OH -→ O2 + 2H2O + 4e - ···(I) Discharge (oxygen reduction reaction): O2 + 2H2O + 4e - → 4OH - ···(II)

[0007] As shown in reaction formula (I), in the air secondary battery, oxygen is generated at the air electrode during charging. This oxygen is released into the atmosphere from the portion of the air electrode that is open to the atmosphere through the voids inside the air electrode. On the other hand, during discharge, the oxygen taken in from the atmosphere is reduced as represented by reaction formula (II) to generate hydroxide ions.

[0008] As the air electrode, which is the positive electrode of the air secondary battery described above, a catalyst that promotes the above-described charge and discharge reactions is used. In an air secondary battery, in order to improve energy efficiency and increase the output power, it is desired to reduce the overvoltage in the charge and discharge reactions of the air electrode. For this reason, regarding the material that becomes the catalyst used for the air electrode, studies have been made on materials effective for reducing the overvoltage. As materials effective for reducing such overvoltage, various metal oxides are promising. Among such metal oxides, pyrochlore-type bismuth ruthenium composite oxides have a "dual function" of oxygen reduction and oxygen generation, and can reduce the overvoltage in both the charging reaction and the discharging reaction, and thus are considered to be particularly effective as a catalyst for the air electrode.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] By the way, in the air secondary battery, since it is expected to be applied to various uses, further increase in output power is desired. In order to further increase the output power, it is particularly necessary to increase the discharge voltage compared to the current situation.

[0011] The present invention has been made based on the above circumstances, and an object thereof is to provide a catalyst for an air electrode that can contribute to increasing the discharge voltage compared to the prior art, an air electrode including this catalyst for an air electrode, and an air secondary battery including this air electrode.

Means for Solving the Problems

[0012] In order to achieve the above object, according to the present invention, there is provided a catalyst for an air electrode comprising an oxide containing at least bismuth, ruthenium, sodium and oxygen, wherein the atomic ratio of sodium to the total of the bismuth, the ruthenium and the sodium, represented by Na / (Ru + Bi + Na), is 0.126 or more and 0.145 or less.

Effects of the Invention

[0013] The catalyst for an air electrode according to the present invention is a catalyst for an air electrode comprising an oxide containing at least bismuth, ruthenium, sodium and oxygen, wherein the atomic ratio of sodium to the total of the bismuth, the ruthenium and the sodium, represented by Na / (Ru + Bi + Na), is 0.126 or more and 0.145 or less. When Na / (Ru + Bi + Na) is 0.126 or more and 0.145 or less, the catalytic ability of the catalyst for an air electrode is improved. Therefore, an air secondary battery using an air electrode including the catalyst for an air electrode according to the present invention has an improved discharge voltage compared to a conventional air secondary battery. Thus, according to the present invention, it is possible to provide a catalyst for an air electrode that can contribute to increasing the discharge voltage compared to the prior art, an air electrode including this catalyst for an air electrode, and an air secondary battery including this air electrode.

Brief Description of the Drawings

[0014]

Figure 1

Modes for Carrying Out the Invention

[0015] Hereinafter, an air-hydrogen secondary battery (hereinafter also referred to as a battery) 2 including an air electrode catalyst for an air secondary battery according to an embodiment will be described with reference to the drawings.

[0016] As shown in FIG. 1, the battery 2 includes a container 4 and an electrode group 10 placed in the container 4 together with an alkaline electrolyte 82.

[0017] The electrode group 10 is formed by laminating a negative electrode 12 and an air electrode (positive electrode) 16 with a separator 14 interposed therebetween.

[0018] The negative electrode 12 includes a conductive negative electrode substrate 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 substrate. As the negative electrode substrate as described above, for example, foamed nickel can be used.

[0019] The negative electrode mixture includes a hydrogen storage alloy powder which is an aggregate of hydrogen storage alloy particles capable of occluding and releasing hydrogen as a negative electrode active material, a conductive material, and a binder. Here, as the conductive material, graphite powder which is an aggregate of graphite particles, carbon black powder which is an aggregate of carbon black particles, etc. can be used.

[0020] The hydrogen storage alloy constituting the hydrogen storage alloy particles is not particularly limited, but for example, it is preferable to use a rare earth-Mg-Ni based hydrogen storage alloy. The composition of this rare earth-Mg-Ni based hydrogen storage alloy can be freely selected. For example, General formula: Ln 1-a Mg a Ni b-c-d Al c M d ···(III) It is preferable to use those represented by.

[0021] However, in the general formula (III), Ln represents at least one element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Zr, and Ti; M 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; and the subscripts a, b, c, and d each represent a number satisfying the relationships of 0.01 ≦ a ≦ 0.30, 2.8 ≦ b ≦ 3.9, 0.05 ≦ c ≦ 0.30, and 0 ≦ d ≦ 0.50.

[0022] Here, the hydrogen storage alloy particles can be obtained, for example, as follows. First, metal raw materials are weighed and mixed to have a predetermined composition, and this mixture is melted in an inert gas atmosphere, for example, in a high-frequency induction melting furnace, and then cooled to form an ingot. The obtained ingot is heated to 900 to 1200 °C in an inert gas atmosphere and subjected to a heat treatment of holding at that temperature for 5 to 24 hours to be homogenized. After that, the ingot is crushed and sieved to obtain hydrogen storage alloy powder, which is an aggregate of hydrogen storage alloy particles having a desired particle size.

[0023] As the binder, for example, sodium polyacrylate, carboxymethyl cellulose, styrene-butadiene rubber, etc. are used.

[0024] Here, the negative electrode 12 can be manufactured, for example, as follows. First, 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 into a negative electrode substrate, and then a drying treatment is performed. After drying, the negative electrode substrate with hydrogen storage alloy particles etc. attached is roll-pressed to increase the alloy amount per unit volume, and then cut, whereby the negative electrode 12 is obtained. This negative electrode 12 has a plate shape as a whole. Since the negative electrode mixture layer contained in the negative electrode 12 is formed by particles of a hydrogen storage alloy, particles of a conductive material, etc., there are gaps between the particles, and it has a porous structure as a whole.

[0025] Next, the air electrode 16 includes a conductive air electrode substrate having a mesh structure and an air electrode composite layer (positive electrode composite layer) formed of an air electrode composite (positive electrode composite) supported on the above-described air electrode substrate. As the air electrode substrate as described above, for example, a nickel mesh can be used.

[0026] The air electrode composite includes a redox catalyst (catalyst for air electrode), a conductive material, and a binder. As the redox catalyst, one having a dual function of oxidation-reduction is used. Such a catalyst having a dual function contributes to reducing the overvoltage of the battery during both the charging process and the discharging process. As such a redox catalyst, for example, a pyrochlore-type bismuth ruthenium composite oxide is used. This bismuth ruthenium composite oxide has a dual function of oxygen generation and oxygen reduction.

[0027] The bismuth ruthenium composite oxide in the present embodiment contains at least bismuth, ruthenium, sodium, and oxygen. And Na / (Ru + Bi + Na) representing the atomic ratio of sodium to the whole of bismuth, ruthenium, and sodium is 0.126 or more and 0.145 or less.

[0028] Here, the inventor of the present application has intensively studied the improvement of the catalytic ability in the catalyst for air electrode, and has discovered that sodium contained in the bismuth ruthenium composite oxide affects the catalytic ability. The inventor of the present application believes that if the catalytic ability is improved, the performance of the air secondary battery is improved, and more specifically, has studied the relationship between the discharge voltage and sodium in the air secondary battery. As a result, there is a relationship between the amount of sodium contained in the bismuth ruthenium composite oxide and the discharge voltage, and by setting Na / (Ru + Bi + Na) representing the atomic ratio of sodium to the whole of bismuth, ruthenium, and sodium in the bismuth ruthenium composite oxide to 0.126 or more, it has been found that a remarkable discharge voltage improvement effect can be obtained. In the process of this research, it has been confirmed that the discharge voltage improvement effect can be obtained until the aspect where Na / (Ru + Bi + Na) becomes 0.145.

[0029] The pyrochlore-type bismuth ruthenium composite oxide as described above can be produced, for example, as follows.

[0030] Prepare Bi(NO3)3·5H2O and RuCl3·3H2O. Then, weigh Bi(NO3)3·5H2O and RuCl3·3H2O so that each has a predetermined amount. Here, it is preferable to weigh Bi(NO3)3·5H2O and RuCl3·3H2O such that the atomic ratio of Ru is 1.000, and Bi is 0.780 or more and 0.815 or less.

[0031] Next, the measured Bi(NO3)3·5H2O and RuCl3·3H2O are put into distilled water and stirred to prepare a mixed aqueous solution of Bi(NO3)3·5H2O and RuCl3·3H2O. At this time, the temperature of the distilled water is set to be 60°C or higher and 90°C or lower. Then, a NaOH aqueous solution with a concentration of 1 mol / L or higher and 3 mol / L or lower is added to this mixed aqueous solution to precipitate a precursor. After the precursor has precipitated, the mixed aqueous solution is stirred. This stirring operation is carried out for 12 hours to 48 hours with oxygen bubbling. Here, while the stirring operation is being performed, for the mixed aqueous solution, the pH is maintained at 11, and the temperature is maintained at 60°C or higher and 90°C or lower. After the stirring operation is completed, the mixed aqueous solution is allowed to stand for 12 hours to 48 hours. After standing, the resulting precipitate is collected by suction filtration. The collected precipitate is kept at 80°C or higher and 100°C or lower to evaporate a part of the moisture to form a paste. This paste is transferred to an evaporating dish and heated at 100°C or higher and 150°C or lower, and held in this state for 1 hour or more and 5 hours or less to be dried, obtaining a dried product of the paste. The obtained dried product of the paste is put into a mortar and ground with a pestle to be pulverized, obtaining a powder. Then, this powder is heated at a temperature of 400°C or higher and 700°C or lower in an air atmosphere and held for 0.5 hour or more and 4 hours or less to perform a firing treatment. The powder after the firing treatment is washed with distilled water at 60°C or higher and 90°C or lower and then subjected to a drying treatment. Thereby, a pyrochlore-type bismuth ruthenium composite oxide is obtained. This bismuth ruthenium composite oxide is Bi 2-x Ru2O 7-z (However, x satisfies the relationship of 0 ≤ x ≤ 1, and z satisfies the relationship of 0 ≤ z ≤ 1.) and is represented by, and a part of Bi is substituted by Na. This Na mainly originates from the NaOH aqueous solution used in the above-mentioned catalyst production process.

[0032] Next, it is preferable to immerse the obtained bismuth ruthenium composite oxide in a nitric acid aqueous solution and perform an acid treatment. Specifically, it is as follows.

[0033] First, prepare an aqueous nitric acid solution. Here, the concentration of the aqueous nitric acid solution is preferably 5 mol / L or less. More preferably, it is 2 mol / L or less. The amount of the aqueous nitric acid solution is preferably prepared in an amount such that the ratio is 20 mL per 1 g of the bismuth ruthenium composite oxide. The temperature of the aqueous nitric acid solution is preferably set at 20°C or higher.

[0034] Then, immerse the bismuth ruthenium composite oxide in the prepared aqueous nitric acid solution and stir for 1 hour or more and 6 hours or less. After a predetermined time has elapsed, suction filter the bismuth ruthenium composite oxide from the aqueous nitric acid solution. The filtered bismuth ruthenium composite oxide is washed with distilled water set at 60°C or higher and 80°C or lower.

[0035] The washed bismuth ruthenium composite oxide is held for 1 hour or more and 4 hours or less in an environment of 100°C or higher and 130°C or lower, and a drying treatment is performed.

[0036] In the above manner, a bismuth ruthenium composite oxide subjected to an acid treatment is obtained. By performing the acid treatment in this way, by-products generated in the production process of the bismuth ruthenium composite oxide can be removed. Note that the acidic aqueous solution used for the acid treatment is not limited to the aqueous nitric acid solution, and an aqueous hydrochloric acid solution or an aqueous sulfuric acid solution can be used in addition to the aqueous nitric acid solution. In these aqueous hydrochloric acid solution and aqueous sulfuric acid solution, an effect of being able to remove by-products in the same manner as the aqueous nitric acid solution can be obtained.

[0037] In the above manner, a powder of the bismuth ruthenium composite oxide, which is an aggregate of particles of the bismuth ruthenium composite oxide from which by-products have been removed, is obtained.

[0038] Next, the conductive material will be described. The conductive material is used to reduce the internal resistance in order to increase the high output of the air secondary battery, and as a carrier for the above-described redox catalyst.

[0039] As such a conductive material, for example, it is preferable to use nickel powder composed of nickel particles. The average particle size of the nickel particles described above is not particularly limited, and it is preferably set to a size that can impart a desired conductivity to the air electrode.

[0040] The nickel powder described above is preferably contained in an amount of 60% by mass or more in the air electrode composition. The upper limit of the content of this nickel powder is preferably 80% by mass or less in relation to other constituent materials in the air electrode composition.

[0041] The binder functions to bind the constituent materials of the air electrode composition and impart appropriate water repellency to the air electrode 16. Here, the binder is not particularly limited, and for example, a fluororesin is used. As a preferable fluororesin, for example, polytetrafluoroethylene (hereinafter also referred to as PTFE) is used.

[0042] The air electrode 16 can be manufactured, for example, as follows. First, prepare catalyst powder which is an aggregate of bismuth ruthenium composite oxide particles, conductive material powder which is an aggregate of Ni particles as a conductive material, a binder, and water. Then, knead these catalyst powder, conductive material powder, binder, and water to prepare an air electrode composition paste.

[0043] The obtained air electrode composition paste is formed into a sheet shape, for example, by applying a roller press, thereby obtaining an air electrode composition sheet. Thereafter, the air electrode composition sheet is press-bonded to a nickel mesh (air electrode base material). Thereby, an intermediate product of the air electrode is obtained.

[0044] Next, the obtained intermediate product is charged into a firing furnace for firing. This firing process is carried out in an inert gas atmosphere. As this inert gas, for example, nitrogen gas or argon gas is used. As the conditions for the firing process, it is heated to a temperature of 200°C or higher and 400°C or lower, and held in this state for 10 minutes or more and 40 minutes or less. Then, the intermediate product is naturally cooled in the firing furnace and taken out into the atmosphere when the temperature of the intermediate product reaches 150°C or lower. Thereby, an intermediate product subjected to the firing process is obtained. By cutting the intermediate product after this firing process into a predetermined shape, the air electrode 16 is obtained. This air electrode 16 includes an air electrode binder layer formed by an air electrode binder. Since the air electrode binder contains particles of bismuth ruthenium composite oxide and the like, the air electrode binder layer formed of such an air electrode binder has a porous structure containing a large number of pores as a whole and is excellent in gas diffusibility.

[0045] The air electrode 16 and the negative electrode 12 obtained as described above are laminated via the separator 14, thereby forming the electrode group 10. This separator 14 is disposed to avoid a short circuit between the air electrode 16 and the negative electrode 12, and a material with electrical insulation properties is adopted. As the material adopted for this separator 14, for example, a material obtained by imparting a hydrophilic functional group to a non-woven fabric made of polyamide fiber, a material obtained by imparting a hydrophilic functional group to a non-woven fabric made of polyolefin fiber such as polyethylene or polypropylene, etc. can be used.

[0046] The formed electrode group 10 is placed in the container 4 together with the alkaline electrolyte. The container 4 is not particularly limited as long as it can accommodate the electrode group 10 and the alkaline electrolyte. For example, a box-shaped container 4 made of acrylic is used. This container 4 includes, for example, as shown in FIG. 1, a container body 6 and a lid 8.

[0047] The container body 6 has a box shape with a bottom wall 18 and side walls 20 extending upward from the peripheral edge of the bottom wall 18. The portion surrounded by the upper end edge 21 of the side walls 20 is open. That is, an opening 22 is provided on the side opposite to the bottom wall 18. Further, in the side walls 20, through holes are provided at predetermined positions of the right side wall 20R and the left side wall 20L, and these through holes serve as lead wire outlets 24 and 26 described later.

[0048] Furthermore, an electrolyte storage portion 80 is attached to the container body 6. This electrolyte storage portion 80 is a container that stores an alkaline electrolyte 82, and is attached, for example, via a connecting portion 84 that communicates with a through hole 19 provided in the bottom wall 18. The connecting portion 84 is a flow path of the alkaline electrolyte 82 that communicates between the inside of the container 4 and the electrolyte storage portion 80. Since the inside of the container 4 and the electrolyte storage portion 80 communicate with each other in this way, the alkaline electrolyte 82 can move between the inside of the container 4 and the electrolyte storage portion 80.

[0049] The lid 8 has the same planar shape as the container body 6 in plan view, is placed on the upper part of the container body 6, and closes the opening 22. A liquid-tight seal is provided between the lid 8 and the upper end edge 21 of the side walls 20.

[0050] In the lid 8, a ventilation path 30 is provided on the inner surface portion 28 facing the inside of the container body 6. The ventilation path 30 has a portion facing the inside of the container body 6 open, and has an overall serpentine shape. Further, an inlet ventilation hole 32 and an outlet ventilation hole 34 penetrating in the thickness direction are provided at predetermined positions of the lid 8. The inlet ventilation hole 32 communicates with one end of the ventilation path 30, and the outlet ventilation hole 34 communicates with the other end of the ventilation path 30. That is, the ventilation path 30 is open to the atmosphere via the inlet ventilation hole 32 and the outlet ventilation hole 34. It is preferable to attach a pressure pump (not shown) to the inlet ventilation hole 32. By driving this pressure pump, air can be sent into the ventilation path 30 from the inlet ventilation hole 32.

[0051] On the bottom wall 18 of the container body 6, an adjustment member 36 is disposed as needed. The adjustment member 36 is used for aligning the height direction of the electrode group 10 in the container 4. As the adjustment member 36, for example, a nickel foam sheet is used.

[0052] The electrode group 10 is disposed on the adjustment member 36. At this time, the negative electrode 12 of the electrode group 10 is disposed so as to be in contact with the adjustment member 36.

[0053] On the other hand, on the side of the air electrode 16 of the electrode group 10, a water-repellent breathable member 40 is disposed so as to be in contact with the air electrode 16. This water-repellent breathable member 40 is a combination of a PTFE porous membrane 42 and a non-woven diffusion paper 44. The water-repellent breathable member 40 exhibits a water-repellent effect by PTFE and allows the passage of gas. The water-repellent breathable member 40 is interposed between the lid 8 and the air electrode 16 and is in close contact with both the lid 8 and the air electrode 16. This water-repellent breathable member 40 has a size that covers the entire ventilation path 30, the inlet ventilation hole 32, and the outlet ventilation hole 34 of the lid 8.

[0054] The lid 8 is placed on the container body 6 that houses the electrode group 10, the adjustment member 36, and the water-repellent breathable member 40 as described above. Then, as schematically depicted in FIG. 1, the peripheral edge portions 46, 48 of the container 4 (the container body 6 and the lid 8) are clamped from above and below by the connectors 50, 52. Thereafter, a predetermined amount of the alkaline electrolyte 82 is injected from the electrolyte storage portion 80, and the container 4 is filled with the alkaline electrolyte 82. In this way, the battery 2 is formed.

[0055] Note that as the above-described alkaline electrolyte 82, a general alkaline electrolyte used for an alkaline secondary battery is preferably used. Specifically, an aqueous solution containing at least one of NaOH, KOH, and LiOH as a solute is used.

[0056] Here, in the battery 2, the ventilation path 30 of the lid 8 faces the water-repellent ventilation member 40. Since the water-repellent ventilation member 40 allows gas to pass through but blocks moisture, the air electrode 16 will be open to the atmosphere via the water-repellent ventilation member 40, the ventilation path 30, the inlet ventilation hole 32, and the outlet ventilation hole 34. That is, the air electrode 16 will be in contact with the atmosphere through the water-repellent ventilation member 40.

[0057] Also, in this battery 2, an air electrode lead (positive electrode lead) 54 is electrically connected to the air electrode (positive electrode) 16, and a negative electrode lead 56 is electrically connected to the negative electrode 12. Although these air electrode lead 54 and negative electrode lead 56 are schematically depicted in FIG. 1, they are drawn out of the container 4 from the lead-out ports 24, 26 while maintaining airtightness and liquid tightness. And an air electrode terminal (positive electrode terminal) 58 is provided at the tip of the air electrode lead 54, and a negative electrode terminal 60 is provided at the tip of the negative electrode lead 56. Therefore, in the battery 2, the input and output of current during charge and discharge are performed using these air electrode terminal 58 and negative electrode terminal 60.

[0058] [Embodiment] 1. Manufacture of Battery (Example 1) (1) Synthesis of Catalyst for Air Electrode 1) Coprecipitation Process Bi(NO3)3·5H2O and RuCl3·3H2O were prepared. Then, Bi(NO3)3·5H2O and RuCl3·3H2O were weighed respectively so that the content of Bi was 14.2 atomic percent, the content of Ru was 17.4 atomic percent, and the atomic ratio of Bi was 0.815 with respect to 1.000 of Ru. The weighed Bi(NO3)3·5H2O and RuCl3·3H2O were put into distilled water at 70 °C and stirred to prepare a mixed aqueous solution of Bi(NO3)3·5H2O and RuCl3·3H2O. In addition, 2 L of distilled water was prepared. Then, a 2 mol / L NaOH aqueous solution was gradually added to the obtained mixed aqueous solution to precipitate a precursor. After the precursor precipitated, the mixed aqueous solution was stirred. This stirring operation was carried out for 24 hours while performing oxygen bubbling. During this stirring operation, the pH of the mixed aqueous solution was maintained at 11 and the temperature was maintained at 70 °C. After the stirring operation was completed, the mixed aqueous solution was allowed to stand for 24 hours. After standing, the resulting precipitate was collected by suction filtration. The collected precipitate was kept at 85 °C to evaporate part of the water to make it into a paste. The obtained paste was transferred to an evaporating dish, heated to 120 °C, and kept in that state for 3 hours for drying treatment to obtain a dried product of the precursor.

[0059] 2) Firing process The dried product of the obtained precursor was put into a mortar and ground with a pestle to make it into a powder. The obtained precursor powder was subjected to a firing treatment of heating to 500 °C and holding for 3 hours in an air atmosphere. After the firing treatment was completed, the precursor was washed with distilled water at 70 °C, then suction filtered, and kept at 120 °C for 3 hours for drying treatment. Thereby, a bismuth ruthenium composite oxide (catalyst for air electrode) was obtained.

[0060] 3) Acid treatment process The bismuth ruthenium composite oxide was put into a stirring tank of a stirrer together with a nitric acid aqueous solution, and acid treatment was carried out by stirring for 1 hour while maintaining the temperature of the nitric acid aqueous solution at 25 °C. At this time, the amount of the nitric acid aqueous solution was set to a ratio of 20 mL per 1 g of the powder of the bismuth ruthenium composite oxide. Also, the concentration of the nitric acid aqueous solution was 2 mol / L.

[0061] After the stirring was completed, the powder of bismuth ruthenium composite oxide was taken out from the aqueous nitric acid solution by suction filtration. The taken-out powder of bismuth ruthenium composite oxide was washed with distilled water heated to 70 °C. After washing, the powder of bismuth ruthenium composite oxide was dried by holding it in an atmosphere of 120 °C for 3 hours.

[0062] In the above manner, the powder of the acid-treated bismuth ruthenium composite oxide, that is, the powder of the catalyst for the air electrode, was obtained.

[0063] (2) Manufacture of air electrode Ni powder, which is an aggregate of Ni particles, was prepared. These Ni particles were filamentous and had an average particle size of 10 to 20 μm.

[0064] Furthermore, polytetrafluoroethylene (PTFE) dispersion and ion-exchanged water were prepared.

[0065] To the powder of the bismuth ruthenium composite oxide (catalyst for the air electrode) obtained as described above, nickel powder, polytetrafluoroethylene (PTFE) dispersion, and ion-exchanged water were added and mixed. At this time, the powder of the bismuth ruthenium composite oxide was uniformly mixed at a ratio of 20 parts by weight, nickel powder was 70 parts by weight, PTFE dispersion was 10 parts by weight, and ion-exchanged water was 10 parts by weight to produce a paste of the air electrode binder.

[0066] The obtained paste of the air electrode binder was formed into a sheet shape and dried by holding it in a room temperature environment of 25 °C to obtain a sheet of the air electrode binder. The obtained sheet of the air electrode binder was press-bonded to a nickel mesh with a mesh number of 60, a wire diameter of 0.08 mm, and an opening ratio of 60%. Thereby, an intermediate product of the air electrode was obtained.

[0067] Next, the intermediate product of the air electrode was subjected to a firing process. The conditions of the firing process were as follows: the intermediate product of the air electrode was heated to a firing temperature of 340°C in a nitrogen gas atmosphere and held at this temperature for 13 minutes. The fired intermediate product was cut into a size of 40 mm in length and 40 mm in width, thereby obtaining the air electrode 16. The thickness of this air electrode 16 was 0.23 mm. In addition, in the obtained air electrode 16, the amount of the bismuth ruthenium composite oxide powder (catalyst for the air electrode) was 0.24 g.

[0068] (3) Manufacture of the negative electrode After mixing the metal materials of Nd, Mg, Ni, and Al so as to have a predetermined molar ratio, they were put into a high-frequency induction melting furnace and melted in an argon gas atmosphere. The obtained molten metal was poured into a mold and cooled to room temperature of 25°C to manufacture an ingot.

[0069] Next, the ingot was heat-treated by holding it in an argon gas atmosphere at a temperature of 1000°C for 10 hours and then cooled to room temperature of 25°C. After cooling, the ingot was mechanically crushed in an argon gas atmosphere to obtain a rare earth-Mg-Ni-based hydrogen storage alloy powder. For the obtained rare earth-Mg-Ni-based hydrogen storage alloy powder, the volume average particle diameter (MV) was measured by a laser diffraction / scattering type particle size distribution measuring device. As a result, the volume average particle diameter (MV) was 60 μm.

[0070] When the composition of this hydrogen storage alloy powder was analyzed by high-frequency inductively coupled plasma atomic emission spectrometry (ICP-AES), the composition was Nd 0.89 Mg 0.11 Ni 3.33 Al 0.17 as follows.

[0071] Here, for the obtained hydrogen storage alloy, an electrochemical alloy capacity measurement was performed. Specifically, a measurement sample set aside from a part of the hydrogen storage alloy powder obtained as described above and nickel powder were prepared. Then, 0.25 g of the hydrogen storage alloy powder as the measurement sample and 0.75 g of nickel powder were mixed to prepare a mixed powder, and the mixed powder was formed into a circular pellet electrode with a diameter of 10 mm.

[0072] Next, 100 mL of an 8 mol / L KOH aqueous solution was poured into a cylindrical resin container, and a pellet electrode and a mercury oxide reference electrode were disposed in the center of the container and within the KOH aqueous solution. Further, a nickel hydroxide counter electrode with a sufficiently large capacitance was disposed at the edge of the container with respect to the negative electrode (pellet electrode). In this way, a battery with regulated negative electrode capacitance was formed. In this battery, a charge-discharge test was carried out, which included a charging operation of charging at 0.5 It for 200 minutes and a discharging operation of discharging at 0.5 It until the negative electrode potential reached -0.3 V with respect to the mercury oxide reference electrode, and the electrochemically alloy capacity was determined. In the charge-discharge operation regarding the above-mentioned pellet electrode, the negative electrode capacity calculated assuming an alloy capacity of 300 mAh / g was taken as 1 It.

[0073] To 100 parts by weight of the obtained hydrogen storage alloy powder, 0.2 parts by weight of sodium polyacrylate powder, 0.04 parts by weight of carboxymethyl cellulose powder, 1.0 part by weight of a styrene-butadiene rubber dispersion, 0.3 parts by weight of carbon black powder, and 22.4 parts by weight of water were added and kneaded in an environment at 25°C to prepare a negative electrode mixture paste.

[0074] This negative electrode mixture paste was filled into a foamed nickel sheet with a surface density (basis weight) of about 300 g / m 2 and a thickness of about 1.7 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 amount per unit volume and then cut into a size of 40 mm in length and 40 mm in width. In this way, the negative electrode 12 was obtained. The thickness of the negative electrode 12 was 0.75 mm. Also, the negative electrode capacity calculated from the above-mentioned electrochemically alloy capacity was 2500 mAh.

[0075] Next, the obtained negative electrode 12 was subjected to an activation treatment. The procedure of this activation treatment is shown below. First, a general sintered nickel hydroxide positive electrode was prepared. Note that as this nickel hydroxide positive electrode, one with a positive electrode capacity sufficiently larger than the negative electrode capacity of the negative electrode 12 was prepared. Then, this nickel hydroxide positive electrode and the obtained negative electrode 12 were overlapped with a separator formed of a polyethylene nonwoven fabric interposed therebetween to form an electrode group for activation treatment. This electrode group for activation treatment was housed in an acrylic resin container together with a predetermined amount of an alkaline electrolyte. Thereby, a single cell of a nickel-hydrogen secondary battery with regulated negative electrode capacity was formed.

[0076] With respect to this single cell, after standing still for 5 hours in an environment at a temperature of 25°C, charging was performed at 0.5It for 2.8 hours, and then discharging was performed at 0.5It until the battery voltage reached 0.70V. The activation treatment of the negative electrode 12 was performed by repeating this charge-discharge cycle 5 times.

[0077] Thereafter, after charging at 0.5It for 2.8 hours, the negative electrode 12 was removed from the single cell. In this way, the negative electrode 12 that had undergone activation treatment and charging was obtained.

[0078] (4) Manufacture of an air-hydrogen secondary battery The obtained air electrode 16 and negative electrode 12 were overlapped with the separator 14 sandwiched therebetween to manufacture an electrode group 10. The separator 14 used in the manufacture of this electrode group 10 was formed of a nonwoven fabric made of polypropylene fibers having a sulfone group, and its thickness was 0.2 mm (basis weight 100 g / m 2 ).

[0079] Next, a container body 6 was prepared, and the above-described electrode group 10 was housed in this container body 6. At this time, a nickel foam sheet as an adjusting member 36 was disposed on the bottom wall 18 of the container body 6, and the electrode group 10 was placed on this adjusting member 36. Here, the nickel foam sheet had a thickness of 1 mm and had a square shape with a length of 40 mm and a width of 40 mm.

[0080] Next, a water-repellent and breathable member 40 was disposed on top of the electrode group 10 (on top of the air electrode 16). Here, the water-repellent and breathable member 40 is formed by combining a PTFE porous membrane 42 having a length of 45 mm, a width of 45 mm, and a thickness of 0.1 mm, and a nonwoven diffusion paper 44 having a length of 40 mm, a width of 40 mm, and a thickness of 0.2 mm.

[0081] Next, a lid 8 was placed so as to close the opening 22 of the container body 6. At this time, the area including the ventilation path 30, the inlet ventilation hole 32, and the outlet ventilation hole 34 on the inner surface portion 28 of the lid 8 is brought into close contact with the water-repellent and breathable member 40 so that the entire area is covered with the water-repellent and breathable member 40. Here, the ventilation path 30 as a whole has a single serpentine shape. The cross-section of the ventilation path 30 is rectangular, and the vertical dimension of the rectangle is 1 mm and the horizontal dimension is 1 mm. The ventilation path 30 is open on the side of the water-repellent and breathable member 40.

[0082] Regarding the container 4 formed by combining the container body 6 and the lid 8, its peripheral edge portions 46, 48 are sandwiched from above and below by connecting tools 50, 52. Note that a resin packing (not shown) is disposed at the contact portion between the container body 6 and the lid 8 to prevent leakage of the alkaline electrolyte.

[0083] Next, a 5 mol / L KOH aqueous solution was injected into the electrolyte storage portion 80 as the alkaline electrolyte 82. The amount of the KOH aqueous solution injected at this time was 50 mL. As described above, the battery 2 as shown in FIG. 1 was manufactured.

[0084] Note that an air electrode lead 54 is electrically connected to the air electrode 16, and a negative electrode lead 56 is electrically connected to the negative electrode 12. These air electrode lead 54 and negative electrode lead 56 appropriately extend outside the container 4 from the lead wire outlets 24, 26 while maintaining the airtightness and liquid tightness of the container 4. Further, an air electrode terminal 58 is attached to the tip of the air electrode lead 54, and a negative electrode terminal 60 is attached to the tip of the negative electrode lead 56.

[0085] (Example 2) An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that Bi(NO3)3·5H2O and RuCl3·3H2O were weighed such that the content of Bi was 15.3 atomic percent and the content of Ru was 19.0 atomic percent, and the atomic ratio of Bi was 0.806 with respect to 1.000 of Ru.

[0086] (Example 3) An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that Bi(NO3)3·5H2O and RuCl3·3H2O were weighed such that the content of Bi was 15.6 atomic percent and the content of Ru was 19.4 atomic percent, and the atomic ratio of Bi was 0.806 with respect to 1.000 of Ru.

[0087] (Example 4) An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that Bi(NO3)3·5H2O and RuCl3·3H2O were weighed such that the content of Bi was 15.6 atomic percent and the content of Ru was 19.4 atomic percent, and the atomic ratio of Bi was 0.805 with respect to 1.000 of Ru.

[0088] (Example 5) An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that Bi(NO3)3·5H2O and RuCl3·3H2O were weighed such that the content of Bi was 13.7 atomic percent and the content of Ru was 17.0 atomic percent, and the atomic ratio of Bi was 0.802 with respect to 1.000 of Ru.

[0089] (Example 6) An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that Bi(NO3)3·5H2O and RuCl3·3H2O were weighed such that the content of Bi was 15.4 atomic percent and the content of Ru was 19.8 atomic percent, and the atomic ratio of Bi was 0.780 with respect to 1.000 of Ru.

[0090] (Example 7) An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that Bi(NO3)3·5H2O and RuCl3·3H2O were weighed so that the content of Bi was 16.2 atomic percent and the content of Ru was 20.2 atomic percent, and the atomic ratio of Bi was 0.801 with respect to 1.000 of Ru.

[0091] (Comparative Example 1) An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that Bi(NO3)3·5H2O and RuCl3·3H2O were weighed so that the content of Bi was 16.4 atomic percent and the content of Ru was 19.1 atomic percent, and the atomic ratio of Bi was 0.861 with respect to 1.000 of Ru, and the firing temperature was 600 °C in the firing process.

[0092] (Comparative Example 2) An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that Bi(NO3)3·5H2O and RuCl3·3H2O were weighed so that the content of Bi was 19.2 atomic percent and the content of Ru was 21.6 atomic percent, and the atomic ratio of Bi was 0.890 with respect to 1.000 of Ru, and the temperature of the nitric acid aqueous solution was 60 °C and the concentration of the nitric acid aqueous solution was 5 mol / L in the acid treatment process.

[0093] (Comparative Example 3) An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that Bi(NO3)3·5H2O and RuCl3·3H2O were weighed so that the content of Bi was 15.9 atomic percent and the content of Ru was 18.1 atomic percent, and the atomic ratio of Bi was 0.879 with respect to 1.000 of Ru, and the firing temperature was 600 °C in the firing process.

[0094] (Comparative Example 4) Bi(NO3)3·5H2O and RuCl3·3H2O were weighed respectively such that the content of Bi was 17.5 atomic percent and the content of Ru was 20.1 atomic percent, and the atomic ratio of Bi was 0.867 with respect to 1.000 of Ru. An air-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that the firing temperature was 600 °C in the firing process.

[0095] Here, the firing temperatures and the conditions of the acid treatment process (conditions during nitric acid treatment) in the synthesis of the catalysts for air electrodes in Examples 1 to 7 and Comparative Examples 1 to 4 described above are summarized in Table 1.

[0096]

Table 1

[0097] 2. Analysis of the catalyst for air electrode Regarding the analysis samples of the powders of the catalysts for air electrodes obtained in Examples 1 to 7 and Comparative Examples 1 to 4, analysis was performed by X-ray diffraction method (XRD). A parallel beam X-ray diffractometer was used for the XRD analysis. The conditions of the analysis here were: X-ray source was CuKα, tube voltage was 15 kV, tube current was 15 mA, scan speed was 1 degree / min, and step width was 0.01 degree. As a result of the analysis, it was confirmed from the obtained diffraction chart pattern that the catalyst for air electrode has a pyrochlore-type crystal structure and a Bi crystal structure similar thereto 2-x Ru2O 7-z (where x satisfies the relationship 0 ≦ x ≦ 1 and z satisfies the relationship 0 ≦ z ≦ 1).

[0098] Furthermore, regarding the analysis samples of the powders of the catalysts for air electrodes obtained in Examples 1 to 7 and Comparative Examples 1 to 4, so-called SEM / EDS analysis was performed in which the secondary electron image was observed with a scanning electron microscope (SEM) and elemental analysis was performed by energy dispersive X-ray spectroscopy (EDS). As the analysis apparatus for SEM / EDS analysis, a scanning electron microscope (JSM-6510) and an energy dispersive X-ray analyzer (JED-2300) manufactured by JEOL Ltd. were used.

[0099] First, as a result of observing a secondary electron image using a scanning electron microscope, the particle size of the bismuth ruthenium composite oxide was 0.1 μm or less.

[0100] Next, elemental analysis was performed. Elemental analysis can be divided into two cases: analyzing the elemental composition of the particle surface and analyzing the elemental composition inside the particle, i.e., the bulk. For analyzing the elemental composition of the particle surface, a Rutherford backscattering spectrometer (RBS), which can directly measure the depth distribution of the elemental composition in the vicinity of the surface (within about 1 μm from the outermost surface), is a powerful technique. However, since the atomic percentage of Na, which is the main analysis target of this application, easily changes depending on the cleaning condition of the catalyst on the particle surface, analysis of the particle surface by RBS was not performed, and bulk elemental analysis was carried out.

[0101] As a specific analysis procedure, first, the powders of the air electrode catalysts, which are the analysis samples of Examples 1 to 7 and Comparative Examples 1 to 4, were each embedded in resin, and the resin was cured. A predetermined portion of the cured resin was cut to expose the cross-section (bulk portion) of the particles of the air electrode catalyst. Then, the cut surface of the resin containing the exposed cross-section of the particles of the air electrode catalyst was buffed. Next, using an energy-dispersive X-ray analyzer, an electron beam was irradiated onto the cross-section of the particles of the air electrode catalyst after polishing, and characteristic X-rays generated at that time were spectroscopically analyzed to perform quantitative analysis of Bi, Ru, O, and Na. Specifically, quantitative analysis was performed in the first field of view and a second field of view different from the first field of view under the conditions of an acceleration voltage of 15 keV, a measurement magnification of 2000 times, and an integration number of 50 times. Then, the contents of Bi, Ru, O, and Na were determined from the average value of the analysis results in the first field of view and the analysis results in the second field of view. These results are shown in Table 2. Furthermore, based on the obtained contents of Bi, Ru, O, and Na, the atomic ratio of Na to the total of Bi, Ru, and Na, represented by Na / (Ru + Bi + Na), and the atomic ratio of Bi to Ru, represented by Bi / Ru, were determined. These results are also shown in Table 2.

[0102] 3. Battery performance evaluation Regarding the air-hydrogen secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 4, in an atmosphere of 25 °C, charging was performed at 0.1 It for 10 hours via the air electrode terminal 58 and the negative electrode terminal 60, and discharging was performed at 0.2 It until the battery voltage reached 0.4 V, and this charge-discharge cycle was repeated. In the charge-discharge operation of the above-described air-hydrogen secondary battery, 2.0 Ah corresponding to 80% of the negative electrode capacity was taken as 1.0 It.

[0103] In the above-described charge-discharge operation, a 10-minute rest period was provided between charging and discharging, and between discharging and charging, respectively.

[0104] The intermediate voltage during discharging at the third cycle of the above-described charge-discharge was shown in Table 2 as the discharge intermediate voltage.

[0105] In the above-described charge-discharge operation, regardless of charge and discharge, air was introduced from the inlet vent hole 32 and discharged from the outlet vent hole 34, and air was continuously supplied to the ventilation path 30 at a rate of 33 mL / min. As the air supplied to the ventilation path 30, air (CO2 concentration of about 100 ppm) obtained by bubbling through an aqueous KOH solution was used.

[0106]

Table 2

[0107] 4. Discussion From Table 2, the discharge intermediate voltages of the batteries of Examples 1 to 7 are 0.726 V to 0.750 V, while the discharge intermediate voltages of the batteries of Comparative Examples 1 to 4 are 0.689 V to 0.717 V. It can be seen that the batteries of Examples 1 to 7 have higher discharge voltages and improved discharge characteristics compared to the batteries of Comparative Examples 1 to 4. For the batteries of Examples 1 to 7, the value of Na / (Bi + Ru + Na) is 0.126 to 0.145, while for the batteries of Comparative Examples 1 to 4, the value of Na / (Bi + Ru + Na) is 0.102 to 0.108. That is, the batteries of Examples 1 to 7 contain a catalyst for air electrodes with a larger amount of Na relative to the total amount of Bi, Ru, and Na compared to the batteries of Comparative Examples 1 to 4. From this, it can be said that increasing the proportion of the amount of Na contained in the catalyst for air electrodes can increase the discharge voltage.

[0108] In Examples 1 to 7, by adjusting the composition ratio of the mixed aqueous solution of bismuth and ruthenium during catalyst production and adjusting the firing conditions and acid treatment conditions, the amount of sodium contained in the bulk of the bismuth ruthenium composite oxide is increased. As a result, a part of bismuth in the pyrochlore-type crystal structure is substituted by sodium. When such substitution by sodium occurs, the crystal structure of the bismuth ruthenium composite oxide deviates from the general Bi2Ru2O7. As a result, the movement of oxygen within the crystal lattice becomes easier, so it is speculated that the catalytic activity involving the movement of oxygen within the crystal lattice is improved and the discharge voltage increases. It is also considered that the improvement in conductivity due to the inclusion of sodium in the bulk of the bismuth ruthenium composite oxide also contributes.

[0109] <Aspects of the present invention> A first aspect of the present invention is a catalyst for an air electrode comprising an oxide containing at least bismuth, ruthenium, sodium, and oxygen, wherein Na / (Ru + Bi + Na), which represents the atomic ratio of sodium to the total amount of the bismuth, the ruthenium, and the sodium, is 0.126 or more and 0.145 or less.

[0110] According to this first aspect, by increasing the content ratio of Na in the bismuth ruthenium composite oxide, a part of bismuth in the pyrochlore-type crystal structure is substituted by sodium, improving the catalytic ability. As a result, it can contribute to the improvement of the discharge voltage of the battery.

[0111] A second aspect of the present invention relates to a catalyst for an air electrode, in the first aspect of the present invention described above, wherein Bi / Ru, which represents the atomic ratio of the bismuth to the ruthenium, is 0.780 or more and 0.815 or less.

[0112] According to this second aspect, the catalytic ability of the bismuth ruthenium composite oxide becomes higher.

[0113] A third aspect of the present invention relates to an air electrode, comprising a substrate for an air electrode and an air electrode mixture held on the substrate for an air electrode, wherein the air electrode mixture contains the catalyst for an air electrode according to claim 1 or 2.

[0114] According to this third aspect, an air electrode can be obtained that contributes to the improvement of the discharge characteristics of the battery more than a conventional air electrode.

[0115] A fourth aspect of the present invention is an air secondary battery, comprising a container, an electrode group disposed in the container, and an alkaline electrolyte injected into the container, wherein the electrode group includes an air electrode and a negative electrode stacked via a separator, and the air electrode includes the air electrode according to the third aspect described above.

[0116] According to this fourth aspect, an air secondary battery with improved discharge characteristics compared to a conventional air secondary battery can be obtained.

[0117] A fifth aspect of the present invention is the air secondary battery according to the fourth aspect described above, wherein the negative electrode contains a hydrogen storage alloy.

[0118] According to this fifth aspect, an air hydrogen secondary battery with excellent discharge characteristics can be obtained.

[0119] Note that the present invention is not limited to the above-described embodiments and examples. For example, the present invention is not limited to an air-hydrogen secondary battery, and other air secondary batteries using Zn, Al, Mg, Li, etc. as the metal used for the negative electrode may be used. In these other air secondary batteries, the reaction at the air electrode is the same as that of the air-hydrogen secondary battery of the present embodiment, and the effect of improving the discharge voltage of the battery can be obtained similarly.

Explanation of Reference Numerals

[0120] 2 Battery (air-hydrogen secondary battery) 4 Container 6 Container body 8 Lid 10 Electrode group 12 Negative electrode 14 Separator 16 Air electrode (positive electrode) 30 Ventilation path 40 Water-repellent ventilation member

Claims

1. A catalyst for an air electrode made of an oxide containing at least bismuth, ruthenium, sodium and oxygen, wherein Na / (Ru + Bi + Na), representing the atomic ratio of sodium to the whole of said bismuth, said ruthenium and said sodium, is 0.126 or more and 0.145 or less, and Bi / Ru, representing the atomic ratio of said bismuth to said ruthenium, is 0.780 or more and 0.815 or less. A catalyst for an air electrode.

2. An air electrode substrate, and an air electrode mixture held on said air electrode substrate. An air electrode, wherein said air electrode mixture contains the catalyst for an air electrode according to Claim 1.

3. A container, an electrode group disposed in said container, and an alkaline electrolyte injected into said container. An air secondary battery, wherein said electrode group includes an air electrode and a negative electrode superposed via a separator, and said air electrode is the air electrode according to Claim 2.

4. The air secondary battery according to Claim 3, wherein said negative electrode contains a hydrogen storage alloy.

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