JP4568124B2 - Air electrode and air secondary battery using the air electrode - Google Patents

Description

  The present invention relates to an air electrode having gas diffusibility and capable of both oxygen generation and oxygen reduction, an air secondary battery using the air electrode, and more specifically, an air electrode that does not require an auxiliary electrode other than a positive electrode and a negative electrode. Next battery.

  As is well known, a positive electrode comprising a combination of a conductive material such as carbon powder and an oxygen reduction catalyst, a negative electrode using any one of zinc, aluminum, iron, and hydrogen as an active material, and an electrolyte solution such as an alkaline aqueous solution. Has been put to practical use as an air primary battery capable of obtaining power by a reduction reaction of oxygen in the air. For example, when the reaction of the oxygen / hydroxide ion pair at the positive electrode and the reaction of the zinc / zinc oxide pair at the negative electrode are combined, an air battery having an electromotive force of about 1.5 V can be obtained.

  Air batteries currently in practical use are primary batteries that can only be discharged. In this case, the positive electrode has a gas diffusibility that allows oxygen to penetrate into the positive electrode, and an oxygen reduction catalyst that can reduce oxygen with as little energy loss as possible, that is, with a smaller polarization is required. . For this purpose, as a conventional positive electrode material, carbon powder for imparting conductivity and holding an oxygen reduction catalyst, platinum as an oxygen reduction catalyst, and further imparting gas diffusibility and using the positive electrode as a molded body A fluororesin such as polytetrafluoroethylene, which plays the role of a binder to maintain, is used, and those molded and sintered are generally well known.

  However, the air primary battery can only be discharged as its name suggests, and does not have a function that can be recycled by charging. In order to allow charging, both the oxidation reaction and the reduction reaction must be able to proceed at each of the positive electrode and the negative electrode. The negative electrode used in the air primary battery mentioned above should constitute a negative electrode that can be oxidized and reduced in any active material such as zinc, aluminum, iron, and hydrogen, that is, can be used for charging and discharging. Is possible. In fact, in the case of zinc, there is a zinc electrode that is used as a negative electrode of a nickel-zinc secondary battery, and in the case of hydrogen, there is a hydrogen storage alloy electrode that is used as a negative electrode of a nickel-hydrogen secondary battery.

  On the other hand, in the case of the positive electrode, various materials used as an oxygen reduction catalyst have a low catalytic ability for oxygen generation, and charging is practically impossible with the positive electrode for air primary batteries currently used. In addition, when a carbon material is used for the positive electrode, if an oxygen generation reaction is caused on the positive electrode by charging, the carbon is simultaneously oxidized and finally reaches carbon dioxide. Will be worn out and become unusable. In other words, the positive electrode used in the conventional primary air battery can be charged by simply supplying electricity from an external circuit, or the negative electrode can respond, but the positive electrode causes a corresponding reaction. It was impossible to use it as a secondary battery.

  On the other hand, attempts have been made to apply air batteries as secondary batteries. For example, in Patent Document 1, an air battery is constituted by a photoelectric conversion part and a battery part, and the battery part is composed of a metal electrode, an electrolyte, an air electrode, and an auxiliary electrode, and the air electrode is exposed to the air and the electrolyte. The metal electrode and the auxiliary electrode are disposed in the electrolyte, and the output of the photoelectric conversion unit is connected between the metal electrode and the auxiliary electrode so that the metal electrode is charged. A rechargeable air battery capable of charging a metal electrode consumed by discharge is disclosed.

  Patent Document 2 discloses an alkaline secondary battery including a gas diffusion electrode as a positive electrode, a hydrogen storage alloy as a negative electrode, and a catalytic electrode body as an auxiliary electrode for negative electrode charging, and the gas diffusion electrode as an air electrode. A certain alkaline secondary battery and a method for producing the catalytic electrode body are disclosed.

Further, Patent Document 3 includes nickel powder, iridium and / or iridium oxide supported on the nickel powder, an oxygen reduction catalyst supported on the nickel powder, and a binder. And an air secondary battery including a negative electrode using the air electrode as a positive electrode and any one of zinc, iron, aluminum, and hydrogen as an active material.
JP 2000-133328 A JP-A-7-282860 JP 2002-158013 A

  In the rechargeable air battery and alkaline secondary battery disclosed in Patent Documents 1 and 2 above, a third electrode for charging called an auxiliary electrode or an auxiliary electrode for negative electrode charging is required in addition to the positive electrode and the negative electrode. It is. Therefore, the structure of the battery is more complicated than that of an air primary battery consisting only of a positive electrode and a negative electrode, there are many battery components, the manufacturing process is complicated, and there are many steps, and the third electrode is an essential requirement. Therefore, when the volume and weight of this electrode are taken into account, there is a drawback that the energy density and output density per unit volume or unit weight, which is a great merit of the air battery, is reduced. Further, when the third electrode is required, there is a drawback that it is extremely difficult to increase the size of the positive electrode and the negative electrode by simply laminating them and to further increase the energy density and output density.

  In other words, when applying an air battery as a secondary battery, a so-called dual function that can perform oxygen generation (during charging) and oxygen reduction (during discharge) at the positive electrode without using the third electrode. It is desirable to use an air electrode with a dual function, in order to improve various characteristics such as weight reduction, large capacity, high energy density, and high power density. It is. On the other hand, the air electrode having such a dual function is based on the same structure as the air electrode used in the air primary battery so far, and the oxygen reduction catalyst and the oxygen generation catalyst are mixed together with the carbon powder. However, since carbon powder is used, it is consumed by charging, and when the charge / discharge cycle is repeated, there is a drawback that it becomes unusable early due to the consumption.

  In contrast, the air electrode disclosed in Patent Document 3 uses nickel powder instead of carbon powder, and further includes a catalyst for oxygen generation and oxygen reduction supported on the nickel powder. Therefore, it is said that there is no consumption by charge like carbon powder, and it has high durability with respect to the charge / discharge cycle.

  However, since two types of catalysts are used, the structure and manufacturing method are complicated, and since each catalyst has only a single function, the polarization of oxygen reduction and oxygen generation, particularly the polarization of oxygen reduction is large. was there. Furthermore, since the oxygen reduction catalyst has low durability against oxygen generation, there is a drawback that this becomes a factor of deteriorating charge / discharge cycle characteristics. Furthermore, in the method of directly supporting the oxygen generating catalyst or oxygen reduction catalyst on the nickel powder, the nickel powder is oxidized in order to perform the heat treatment of the nickel powder at a high temperature, thereby reducing the conductivity of the nickel powder. When this nickel oxide reacts in an alkaline aqueous solution that is an electrolytic solution, there is a drawback that this may hinder conduction between nickel powders and may deteriorate charge / discharge cycle characteristics.

  In response to the above problems, the present invention has a dual function capable of generating oxygen and reducing oxygen with gas diffusibility, having low polarization during oxygen reduction, and having high durability against oxygen generation / reduction cycles. The purpose is to provide a positive air electrode.

  In addition, the present invention has a simple configuration capable of charging / discharging with only the positive electrode and the negative electrode, has a high energy density, a high output density, a high durability, and can easily increase the capacity by stacking. An object is to provide a secondary battery.

  In response to the above problems, the present inventors have developed a catalyst material having a new dual function, and at the same time, studied a new air electrode configuration, manufacturing method, manufacturing conditions, and characteristic evaluation using nickel powder. At the same time, the present invention has been made based on the knowledge obtained from the results of various studies on the production and evaluation of the secondary battery using the air electrode.

That is, the present invention is an air electrode formed by mixing nickel powder, pyrochlore oxide containing iridium, and a binder. Here, the pyrochlore type oxide containing iridium is a B site in A ₂ B ₂ O _7-x (where −1 ≦ x ≦ 1), which is a general expression representing the molar composition of the pyrochlore type oxide. Is an oxide in which the element is iridium, and examples of the A site element include bismuth and lead. The binder is water-repellent and allows the diffusion of gas into the gap while binding nickel powder to each other, and is a fluororesin such as polytetrafluoroethylene. A system material is used, but the material is not particularly limited as long as the above conditions are satisfied.

  The mixing ratio of the nickel powder, the pyrochlore-type oxide containing iridium, and the binder is preferably 98.9 to 20: 0.1 to 60: 1 to 20 in terms of mass ratio. If the amount of pyrochlore oxide containing iridium is less than 0.1% by mass, the catalyst cannot be sufficiently distributed in the air electrode, and the catalyst function cannot be sufficiently obtained in the entire air electrode. If the amount is more than the upper limit, the ratio of the oxide having a lower conductivity than that of nickel in the air electrode is increased, so that the electric resistance of the entire air electrode is increased, which is not preferable. Further, if the binder is less than 1% by mass, water repellency cannot be sufficiently imparted in the air electrode, the gas diffusibility is lowered and the oxygen reduction polarization is increased, and the electrolyte is used for the air electrode. It is not preferable because it penetrates to the atmosphere side and leaks the electrolyte and cannot function as an air electrode. When the amount exceeds 20% by mass, the water repellency in the air electrode becomes too strong and the electrolyte becomes air. It is difficult to penetrate into the electrode, and the area where the electrolyte solution contacts with the nickel powder and the catalyst inside the air electrode during oxygen generation is reduced, which increases the polarization of oxygen generation. For these reasons, the nickel powder ratio is preferably 98.9 to 20% by mass.

  The present inventors have shown that an air electrode comprising pyrochlore oxide containing iridium and nickel powder exhibits high catalytic properties for oxygen generation and oxygen reduction in an alkaline aqueous solution as an electrolyte. I found it. Here, the pyrochlore type oxide containing iridium is supported on the nickel powder and / or is in contact with both the alkaline aqueous solution and air together with the nickel powder (the pyrochlore type oxide is mixed with the nickel powder). And acts as a catalyst for both oxygen reduction and oxygen generation. In particular, although the details are not clear, the present inventors have developed oxygen and oxygen reduction compared to the conventional air electrode due to electronic and chemical interaction between the pyrochlore oxide containing iridium and the nickel powder. It has been found that it exhibits a high catalytic ability for. Furthermore, by such an action, both oxygen generation and oxygen reduction inside the air electrode proceed smoothly, and the oxidation and reduction of the nickel powder itself, which is a side reaction, is suppressed, thereby reducing the consumption of the nickel powder. Compared with conventional air electrodes using carbon powder and air electrodes having a combination of nickel powder and other metal-based and / or oxide-based catalysts, the oxygen generation / reduction cycle is higher. It has been found that durability can be realized.

Further, the present invention is the air electrode, wherein the pyrochlore oxide containing iridium is bismuth iridium oxide. Here, the bismuth iridium oxide is an oxide represented by Bi ₂ Ir ₂ O _7-x in the composition formula of the pyrochlore oxide described above. This oxide is a pyrochlore type oxide containing iridium, especially in combination with nickel powder, and has low polarization with respect to oxygen generation and oxygen reduction, and can be charged and discharged even at high current density and high temperature operation. On the other hand, high durability can be realized.

  Further, the present invention is an air secondary battery including a negative electrode using the air electrode as a positive electrode and any one of zinc, iron, aluminum, and hydrogen as an active material. Here, as a negative electrode using each element of zinc, iron, and aluminum as an active material, a negative electrode used in a conventional zinc-air battery, iron-air battery, or aluminum-air battery can be used. . Moreover, about the negative electrode which uses hydrogen as an active material, La-Ni system alloy, La-Nd-Ni system alloy, La-Gd-Ni system alloy, La-Y-Ni system alloy, La-Co-Ni system alloy, La-Ce-Ni alloy, La-Ni-Ag alloy, La-Ni-Fe alloy, La-Ni-Cr alloy, La-Ni-Pd alloy, La-Ni-Cu alloy, La- Ni-Al alloy, La-Ni-Mn alloy, La-Ni-In alloy, La-Ni-Sn alloy, La-Ni-Ga alloy, La-Ni-Si alloy, La-Ni- Ge-based alloy, La-Ni-Al-Co-based alloy, La-Ni-Al-Mn-based alloy, La-Ni-Al-Cr-based alloy, La-Ni-Al-Cu-based alloy, La-Ni-Al- Si-based alloy, La-Ni-Al-Ti-based alloy, La-Ni-Al-Zr Alloy, La-Ni-Mn-Zr alloy, La-Ni-Mn-Ti alloy, La-Ni-Mn-V alloy, La-Ni-Cr-Mn alloy, La-Ni-Cr-Zr alloy Alloys, La-Ni-Fe-Zr alloys, La-Ni-Cu-Zr alloys, alloys in which the La element in the above alloys is replaced by misch metal, Ti-Zr-Mn-Mo alloys, Zr-Fe-Mn alloys, Mg-Ni alloys, etc. Alloys composed of combinations of two or more of Ti, Fe, Mn, Al, Ce, Ca, Mg, Zr, Nb, V, Co, Ni, Cr elements Further, a metal that forms a hydride such as Ti, V, Zr, La, Pd, and Pt (having hydrogen storage properties), or a hydride of the above alloy or metal (a substance that stores hydrogen) ) Etc., but occlusion of hydrogen If out material possible, it is not particularly limited to the above composition.

  The air secondary battery of the present invention has a high energy density, a high output density, and a high durability with a simple configuration capable of charging and discharging only with a positive electrode and a negative electrode without the need for a third electrode, In addition, it is possible to provide an air secondary battery that can be easily increased in capacity by stacking.

  Moreover, this invention is an air secondary battery whose said negative electrode is a hydrogen storage alloy. Compared to zinc negative electrode, iron negative electrode, and aluminum negative electrode, the hydrogen storage alloy is superior in durability to charge / discharge cycles and response characteristics to sudden load fluctuations, so it has higher charge / discharge cycle performance and load response characteristics. By being excellent, it is possible to provide a secondary battery with a wide application range.

  As described above, the present invention has the following effects.

(1) Providing an air electrode that has a dual function capable of generating oxygen and reducing oxygen as well as gas diffusivity, has high oxygen generation / reduction catalytic ability, and has high durability against oxygen generation / reduction cycles. As a result, the electrode resistance of the air electrode, the polarization accompanying oxygen generation / reduction reactions are reduced, energy loss in the air electrode can be reduced, the output can be improved, and the life of the air electrode can be extended. .

(2) Since an air secondary battery using an air electrode having the above-described excellent characteristics and effects can be provided, a large capacity and light weight can be achieved by stacking with a simple structure that does not require the third electrode. It becomes feasible, the energy density and the output density are improved, and the durability of the air electrode is high, so that the secondary battery has an extremely long life.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example and a comparative example, this invention is not limited to a following example.

Example 1
0.6020 g of Bi (NO ₃ ) ₃ .5H ₂ O and 0.6378 g of H ₂ IrCl ₆ .6H ₂ O were dissolved in 300 cm ³ of distilled water at 75 ° C., stirred and mixed, and then 2 mol / dm ³ Of aqueous NaOH was added. At that time, the bath temperature was 75 ° C., and the mixture was stirred for 3 days while carrying out oxygen bubbling. The solution containing the precipitate formed thereby was kept at 85 ° C. and evaporated to dryness to obtain a paste. The paste-like material was transferred to an evaporating dish, dried at 120 ° C. for 12 hours, pulverized in a mortar, and then baked in an air atmosphere at 600 ° C. for 2 hours. Next, in order to remove by-products contained in the fired product, suction filtration was performed using distilled water at 70 ° C. to isolate pyrochlore-type bismuth iridium oxide. Furthermore, after drying this at 120 degreeC for 12 hours, it grind | pulverized using the mortar and obtained the bismuth iridium oxide powder. The structure was confirmed to be a pyrochlore type by X-ray diffraction.

The thus obtained bismuth iridium oxide powder, nickel powder (purity 99.8%, particle size 3 to 7 μm), and commercially available PTFE (polytetrafluoroethylene) particle suspension were stirred and mixed to form a clay. did. At this time, the mass ratio of bismuth iridium oxide powder, nickel powder, and PTFE particles was 10:80:10. The clay-like material was dried at room temperature for about 30 minutes, pressed into a disk shape at 100 kg / cm ² on a nickel mesh as a current collector, and then heat-treated at 370 ° C. for 12 minutes in a nitrogen atmosphere. An air electrode was produced.

(Comparative Example 1)
The air electrode was produced as follows. A mixed solution of about 5 g of nickel powder (purity 99.8%, particle size 3-7 μm) containing iridium acid containing 1 mg / cm ^{3 in} terms of metal iridium and chloroplatinic acid containing 1 mg / cm ^{3 in} terms of metal platinum 50 cm ³ After being immersed therein for about 60 minutes, it was heated at 470 ° C. for 2 minutes in an electric furnace in an air atmosphere (powder 1). As a result of analyzing powder 1 by XPS and EDX, it was confirmed that iridium oxide and platinum were supported on the surface of powder 1. Powder 1 and nickel powder (purity 99.8%, particle size 3 to 7 μm) and commercially available PTFE (polytetrafluoroethylene) particle suspension were mixed by stirring to form a clay, and then dried at room temperature for about 30 minutes. It was. At this time, the mass ratio of powder 1, nickel powder, and PTFE particles was set to 30:60:10. The dried product was pressed into a disk shape at 100 kg / cm ² on a nickel net, and then heat-treated at 370 ° C. for 12 minutes in a nitrogen atmosphere to produce an air electrode.

For each air electrode obtained in Example 1 and Comparative Example 1, a constant current using a platinum plate (14 cm ² ) as a counter electrode, a mercury-mercury oxide electrode as a reference electrode, and a 7 mol / dm ³ KOH aqueous solution as an electrolyte. A polarization curve was created by the method. The measuring method is in accordance with a standard method. The counter electrode is immersed in the electrolytic solution, the electrolytic solution and the reference electrode are connected with a liquid junction, and the air electrode is used as the electrolytic solution with a Teflon (registered trademark) holder. Was configured to be in contact with air. The respective polarization characteristics of the oxygen generation reaction (anode polarization) and the oxygen reduction reaction (cathode polarization) are shown in FIG. In addition, with the same configuration, a pulse current that periodically reverses the polarity was applied to the air electrode at a current density of ± 50 mA / cm ² , a current application time of 10 minutes, and a rest time of 1 minute, and the change in potential at that time was measured. . The characteristic evaluation was performed at 60 ° C.

  As shown in FIG. 1, it was found that the air electrode (Example 1) of the present invention had a very high catalytic ability because the polarization during oxygen reduction was smaller than that of the air electrode of Comparative Example 1. In particular, it was found that oxygen can be generated and reduced at a high current density, and that an air secondary battery capable of obtaining a high output density can be produced by using this air electrode.

  Further, FIG. 2 shows a continuous positive current applied to each air electrode when a positive current is applied (oxygen generation) and a potential immediately before the current interruption is applied and when a negative current is applied (oxygen reduction). The change with respect to the number of cycles is shown with the negative current applied as one cycle. As is clear from FIG. 2, compared with Comparative Example 1, the air electrode of Example 1 had a higher potential during oxygen reduction, and polarization associated with discharge was suppressed. Furthermore, in the air electrode of Comparative Example 1, the potential for oxygen reduction suddenly decreased after about 500 cycles, and the current could not be supplied in 680 cycles, whereas in the air electrode of Example 1, the change in potential with respect to the number of cycles. Was small for both oxygen generation and oxygen reduction, and it was found that energization exceeding 2000 cycles was possible. That is, it became clear that the air electrode of the present invention has extremely high durability.

(Example 2)
FIG. 3 is a schematic configuration diagram of the air secondary battery of the present invention, in which 1 is an air electrode, 2 is a negative electrode, 3 is an electrolyte, 4 is a case, 5 is a positive electrode terminal, and 6 is a negative electrode terminal. .

The air electrode of Example 1 was used as the positive electrode, LaNi _5- based hydrogen storage alloy (15 mm × 15 mm × 3 mm) was used as the negative electrode, and 7 mol / dm ³ KOH aqueous solution was used as the electrolytic solution. A secondary battery was prepared using a Teflon (registered trademark) container. In addition, the nickel wire was connected to each as a terminal of a positive electrode and a negative electrode. The electromotive force of this battery was about 1 V, and the current efficiency was almost 100% with respect to charging / discharging at 50 mA / cm ² (per positive electrode surface area). Moreover, in charging / discharging more than 100 cycles, a change was not recognized by the charging / discharging voltage, and it turned out that it has high durability.

  The present invention can be used for mobile devices, personal computers, memory backup batteries, small electronic devices, hearing aids, hybrid vehicles, electric vehicles, distributed household power sources, distributed business power sources, power storage batteries, and the like.

The polarization curve of the air electrode of Example 1 and Comparative Example 1 is shown. The cycle characteristics of the charge / discharge potential of Example 1 and Comparative Example 1 are shown. The schematic structure of the air secondary battery of this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air electrode 2 Negative electrode 3 Electrolytic solution 4 Case 5 Positive electrode terminal 6 Negative electrode terminal

Claims (4)

An air electrode formed by mixing nickel powder, pyrochlore oxide containing iridium, and a binder.   The air electrode according to claim 1, wherein the pyrochlore oxide containing iridium is bismuth iridium oxide.   An air secondary battery comprising a negative electrode having the air electrode according to claim 1 as a positive electrode and any one of zinc, iron, aluminum, and hydrogen as an active material.   The air secondary battery according to claim 3, wherein the negative electrode is a hydrogen storage alloy.

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