JPH11339865A - Air electrode and air cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the rise of stress in a cell and improve an anti-leakage characteristic during preservation for a long period by forming a catalyst layer containing catalyst reducing oxygen and containing a specific quantity of silver oxide on a current collector made of a metal material. SOLUTION: A catalyst layer 9 preferably contains silver oxide 1-50 wt.%. An air electrode 2 is constituted of a current collector 8, the catalyst layers 9 applied to both faces of it, and a porous film 10 stuck to one catalyst layer 9. The catalyst layer 9 contains a catalyst reducing the oxygen in the air, a carbon material carrying the catalyst, and a fluororesin binding the catalyst and the carbon material. An air cell introduces air from the outside, the cell cannot be formed into a sealed structure, therefore an electrolyte is leaked when the cell internal pressure is increased by the hydrogen gas generated by a cell reaction. The catalyst layer 9 contains silver oxide to convert the hydrogen into water, and the electrolyte is prevented from being leaked to the outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air electrode and an air battery using oxygen in the air as a positive electrode active material.

[0002]

2. Description of the Related Art With the spread of portable electronic devices in recent years, demands for portable power supplies are only increasing. In particular, the emergence of lighter, stronger, and longer-life batteries, that is, high energy density batteries, is expected.

An air battery is a battery that does not fill the battery with a positive electrode active material and uses oxygen in the air as the positive electrode active material. A special porous electrode (hereinafter, air electrode) for reacting oxygen in the air is used as a positive electrode of the air battery. The thickness of the air electrode is extremely thin as compared with a general positive electrode for an alkaline battery, and therefore, the volume for charging the negative electrode is much larger than that of other battery systems. For this reason, the air battery is a high energy density battery having about twice the energy density of other alkaline batteries. That is, an air battery is an ideal primary battery as a portable power source, and a demand for a button-type air battery as a power source for a hearing aid or a pager is increasing.

[0004]

However, since the air battery utilizes oxygen in the air for the reaction, the air battery has an air hole for taking air into the inside of the battery. for that reason,
The air battery cannot have a sealed structure. Therefore, when the internal pressure of the battery rises due to a gas such as hydrogen generated by the battery reaction, a problem arises in that the electrolyte or the like contained in the battery leaks out.

[0005] As a method for preventing liquid leakage, a method is generally employed in which mercury is added to a negative electrode active material made of zinc or the like to prevent corrosion of the negative electrode active material. However, mercury has a great influence on the environment, and it is extremely difficult to effectively suppress gas generation in the current trend of low mercury, mercury-free, and lead-free. When a battery is made mercury-free, it has low leakage resistance characteristics over a long period of storage as compared with other alkaline batteries, and cannot ensure a high level of reliability.

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned conventional circumstances, and has a high reliability in which an increase in stress inside a battery is suppressed, and a liquid leakage resistance characteristic during long-term storage is improved. An object is to provide an air electrode and an air battery.

[0007]

An air electrode according to the present invention has a current collector made of a metal material, and a catalyst layer formed on the current collector and containing a catalyst for reducing oxygen. The catalyst layer is characterized by containing silver oxide in a ratio of 1% by weight to 50% by weight.

In the above-described air electrode according to the present invention, since the catalyst layer contains silver oxide at a ratio of 1% by weight to 50% by weight, hydrogen gas generated by the reaction is converted into water by the silver oxide. Can be

An air battery according to the present invention includes an air electrode having a current collector made of a metal material and a catalyst layer formed on the current collector and containing a catalyst for reducing oxygen. And silver oxide in a ratio of 1% by weight to 50% by weight.

In the air battery according to the present invention as described above, the catalyst layer of the air electrode contains 1% by weight to 50% by weight of silver oxide.
, The hydrogen gas generated by the battery reaction is changed to water by silver oxide, thereby suppressing an increase in the internal pressure of the battery.

[0011]

Embodiments of the present invention will be described below.

FIG. 1 is a sectional view of an air battery to which the present invention is applied. The air battery 1 includes an air electrode 2 as a positive electrode, and a positive electrode case 4 in which an air hole 3 and an air electrode 2 are provided and a negative electrode case 6 filled with a negative electrode mixture 5 are caulked via an insulating gasket 7. It is composed.

As shown in FIG. 2, the air electrode 2 is coated on a current collector 8, a catalyst layer 9 coated on both sides of the current collector 8, and a catalyst layer 9 coated on both sides of the current collector 8. And a porous film 10 attached to one of the catalyst layers 9.

The current collector 8 is made of a material such as a flat metal wire mesh or expanded metal, which has holes penetrating on the front and back sides and has conductivity. The material of the current collector 8 is not particularly limited, but a material having high mechanical strength and excellent corrosion resistance is preferable. For example,
Fe-Ni-Cr-based stainless steel, Fe-Cr-based stainless steel, Fe-Ni-based stainless steel, nickel and iron, their alloys, clad materials, and the like. Fe-Ni-C
As r-type stainless steel, there is SUS304 (trade name).

The current collector 8 is plated on its surface. By plating the surface of the current collector 8, both the mechanical strength and the electric conductivity of the current collector 8 can be compatible. As such a plating material, a material having high conductivity and high conductivity is used, and examples thereof include nickel and tin.

The catalyst layer 9 is coated on the current collector 8 and has a catalyst for reducing oxygen in the air, a carbon material supporting the catalyst, and a fluorine-based material for bonding the catalyst and the carbon material. And a resin. For example, manganese oxide is used as the catalyst. Activated carbon such as carbon black is used as the carbon material. Further, as the fluororesin, for example, polytetrafluoroethylene (hereinafter, PTF)
E) is used.

In this catalyst layer 9, oxygen in the air is used as a positive electrode active material. However, this air battery 1
However, the battery cannot be hermetically sealed because air is taken in from the outside. Therefore, when the internal pressure of the battery increases due to a gas such as hydrogen generated by the battery reaction, the electrolyte or the like leaks.

Therefore, in the air battery 1, the catalyst layer 9 contains silver oxide (Ag ₂ O). Silver oxide reacts with hydrogen (H ₂ ) to form silver (Ag) and water (H
₂ O).

Ag ₂ O + H ₂ → Ag + H ₂ O As described above, by containing silver oxide in the catalyst layer 9, hydrogen gas is changed to water to prevent the internal pressure of the battery from rising due to the hydrogen gas, and the electrolyte leaks to the outside. Can be prevented.

The content of silver oxide is preferably 1% by weight to 50% by weight with respect to the catalyst layer 9. If the content of silver oxide is less than 1% by weight, the effect of converting hydrogen into water by the above-described reaction and preventing the increase in the internal pressure of the battery due to hydrogen gas is not sufficient. On the other hand, if the content of silver oxide is more than 50% by weight, the characteristics of the air battery 1 deteriorate during long-term storage. Therefore, by setting the content of silver oxide to 1% by weight to 50% by weight of the catalyst layer 9, it is possible to obtain the air battery 1 having excellent liquid leakage resistance and long-term storage characteristics.

The porous membrane 10 serves as an oxygen supply port for the air electrode 2. Air is taken in from the outside of the material of the porous membrane 10, but at the same time, it is necessary that the internal electrolytic solution is not leaked. For example, a fluorine-based resin such as PTFE is used.

The positive electrode case 4 is formed, for example, by applying nickel plating to iron and serves as an external positive electrode terminal of the air battery 1.
An air hole 3 for taking in air is drilled at the bottom, and when not in use, it can be stored by closing the outside with a seal 11. In the center of the bottom inside the positive electrode case 4,
The air diffusing material 12, the water repellent film 13, the air electrode 2, the separator 14, and the electrolyte holding material 15 in this order from the bottom in the positive electrode case 4.
Are placed one on top of the other.

The air diffusing material 12 is for uniformly supplying the air taken in from the air holes 3 to the air electrode 2. The water-repellent film 13 is for preventing liquid leakage, and for example, a PTFE film or the like is used. The air electrode 2
Are arranged such that the porous membrane 10 serving as an oxygen supply port is on the lower side. The separator 14 and the electrolyte holding material 15 are for closing the negative electrode mixture 5 filled in the negative electrode case 6. The separator 14 is made of, for example, a microporous polypropylene film. The electrolyte holding material 15 is made of, for example, a natural pulp material.

The negative electrode case 6 is made of, for example, a clad material of copper, stainless steel and nickel, and serves as an external negative electrode terminal of the air battery 1. The negative electrode case 6 is filled in the negative electrode case 6. The negative electrode mixture 5 is composed of granular zinc as a negative electrode active material, an electrolytic solution using an aqueous potassium hydroxide solution, and a gelling agent for preventing liquid leakage in a gel state. As the gelling agent, for example, carboxymethyl cellulose is used.

The insulating gasket 7 is incorporated in the negative electrode case 6 and integrated. The insulating gasket 7 is for preventing the negative electrode mixture 5 filled in the negative electrode case 6 from leaking. This insulating gasket 7 is made of, for example, nylon or the like.

In such an air battery 1, the catalyst layer 9 contains silver oxide as a generated gas absorbing substance in an amount of 1% by weight to 50% by weight. Since silver oxide reacts with hydrogen gas to form silver and water, the internal pressure of the battery that has increased due to the generation of hydrogen gas can be reduced. Therefore, in the air battery 1, it is possible to prevent the electrolyte solution from leaking while suppressing an increase in the internal pressure.

In the above-described embodiment, a button-type air battery has been described as an example. However, the present invention is not limited to this, and the present invention is not limited to this. The invention is also applicable to batteries and air electrodes used therein.

[0028]

EXAMPLE An air electrode having the above-described structure was manufactured, and an air battery was manufactured using the air electrode.

<Example 1> First, an air electrode was manufactured as follows.

As a catalyst, β-manganese oxide powder (Mn
And O _2), the activated carbon and carbon black as a conductive material 1: a mixture in 1 (AC + CB), as a fluorine-based resin binder water repellent solids 60 wt% of polytetrafluoroethylene (PTFE) The aqueous dispersion and silver oxide (Ag ₂ O) were mixed at a ratio (% by weight) as shown in Table 1 to obtain a paste-like catalyst layer composition. The ratio of silver oxide at this time is 1% by weight.

The catalyst layer composition was coated on both sides of a stainless steel (SUS304) mesh plated with nickel so that the surface roughness Ra was 10 μm.
It was applied to a thickness of 2 mm and dried to form a catalyst layer sheet.

Next, a porous PTFE film having a thickness of 0.1 mm was pressure-bonded to one surface of the obtained catalyst layer sheet.
This was punched out into a circle having a diameter of 22.5 mm to obtain an air electrode.

Next, using the obtained air electrode, an air battery was manufactured as follows.

An air diffusion material was provided at the center of the bottom of the positive electrode case which also served as the positive electrode terminal. A polytetrafluoroethylene porous film serving as a water-repellent film was punched out and inserted into a circular shape, and the air electrode described above was inserted thereon with the porous film facing down. Separately, a polypropylene separator and a nonwoven fabric electrolyte retaining material made of natural pulp fiber were punched out and inserted into a circular shape.

An insulating gasket is incorporated into and integrated with a negative electrode case also serving as a negative electrode terminal, and a negative electrode mixture obtained by gelling a negative electrode active material and an electrolytic solution with a gelling agent is provided inside the integrated body of the negative electrode case and the insulating gasket. Injected. Here, as a negative electrode active material, a mixture of bismuth, indium, and a granular zinc alloy was used. Further, an aqueous solution of potassium hydroxide was used as an electrolytic solution.

The negative electrode mixture filled with the negative electrode case and the insulating gasket are covered with the positive electrode case inserted up to the electrolyte holding material, and the entire periphery of the opening of the positive electrode case is mechanically bent to the negative electrode case side to remove air. The battery was sealed. Finally, a seal was attached to the air hole at the bottom of the positive electrode case to complete a button-type air battery having a diameter of 23 mm and a height of 3 mm.

Table 1 shows the mixing ratio of the materials constituting the catalyst layers of the air batteries of Example 1, the following Examples 2 to 4, and Comparative Examples 1 to 3.

[0038]

[Table 1]

Example 2 An air electrode catalyst layer was prepared in the same manner as in Example 1 except that the mixing ratio of the materials constituting the catalyst layer was changed as shown in Table 1. A battery was manufactured. In this case, the content of silver oxide in the catalyst layer was 30% by weight.

Example 3 An air electrode was prepared in the same manner as in Example 1 except that the mixing ratio of the materials constituting the catalyst layer was as shown in Table 1 when producing the catalyst layer. A battery was manufactured. At this time, the content of silver oxide in the catalyst layer was 50% by weight.

Example 4 An air electrode catalyst layer was produced in the same manner as in Example 1 except that the mixing ratio of the materials constituting the catalyst layer was as shown in Table 1. A battery was manufactured. The content of silver oxide in the catalyst layer at this time was 40% by weight.

Comparative Example 1 Air was prepared in the same manner as in Example 1 except that the mixing ratio of the materials constituting the catalyst layer was as shown in Table 1 when the catalyst layer for the air electrode was produced. A battery was manufactured. At this time, the catalyst layer does not contain silver oxide.

<Comparative Example 2> An air electrode was prepared in the same manner as in Example 1 except that the mixing ratio of the materials constituting the catalyst layer was as shown in Table 1 when producing the catalyst layer. A battery was manufactured. In this case, the content of silver oxide in the catalyst layer was 0.5% by weight.

Comparative Example 3 Air was prepared in the same manner as in Example 1 except that the mixing ratio of the materials constituting the catalyst layer was changed as shown in Table 1 when producing the catalyst layer of the air electrode. A battery was manufactured. The content of silver oxide in the catalyst layer at this time was 55% by weight.

The air battery manufactured as described above was aged at room temperature for 2 weeks, and a characteristic evaluation test was performed on heavy load closed circuit voltage characteristics, internal resistance characteristics, and heavy load discharge characteristics. Further, after storing these batteries at 60 ° C. for 40 days, the same property evaluation test was performed, and further, a liquid leakage resistance test was performed.

As a heavy load closed circuit voltage characteristic test, a battery was loaded with a 20 Ω load resistance 10 minutes after the seal was opened.
For 2 seconds, and the closing voltage (V) at that time was measured. In this case, the higher the battery voltage, the better.

As an internal resistance characteristic test, an AC current of 1 μA and 1 kHz was applied to the battery 10 minutes after opening the seal, and the AC resistance (mΩ) at that time was measured. In this case, the smaller the resistance value, the better.

As a heavy load discharge characteristic test, a load resistance of 42 Ω was connected to the battery 10 minutes after the seal was opened.
Discharge capacity (mAh) until battery voltage falls below 0.9V
Was measured. In this case, the larger the numerical value, the larger the discharge capacity, which is preferable.

In the leak resistance test, the seal was stuck and left in a 60 ° C. air bath for 100 days, and after 100 days, the electrolyte leaked from the air hole was confirmed as a leak. It was confirmed. In this case, the smaller the number of leaked liquids, the better.

Table 2 shows the results of the characteristic evaluation tests performed on the batteries of Examples 1 to 4 and Comparative Examples 1 to 3 before and after storage.

[0051]

[Table 2]

According to Table 2, the content of silver oxide was from 1% by weight to 5% by weight.
In the air batteries of Examples 1 to 4 in which the content was 0% by weight, excellent characteristics were obtained in all of the discharge capacity, internal resistance, and closed circuit voltage before storage. And it turned out that these excellent characteristics are fully maintained even after storage. Furthermore, in these air batteries, no liquid leakage was observed even during long-term storage, and the long-term storage characteristics and the leakage resistance characteristics could be dramatically improved.

On the other hand, Comparative Example 1, in which no silver oxide was added,
In addition, in the air battery of Comparative Example 2 in which the amount of silver oxide added was 1% by weight or less, the result that the internal resistance was large before storage was obtained. Then, after storage, all the characteristics were greatly deteriorated. Then, in long-term storage, 10 out of 1000 liquid leaks were observed. Comparative Example 3 in which the addition amount of silver oxide was 55% by weight.
Although the characteristics of the air battery are excellent before storage, the characteristics are significantly deteriorated after storage. In long-term storage, 5 out of 1000 leaked liquids were observed.

From the above results, it was found that by containing silver oxide in a proportion of 1% by weight to 50% by weight with respect to the catalyst layer,
It was found that an air battery having excellent long-term storage characteristics, especially excellent liquid leakage resistance, can be obtained.

[0055]

According to the present invention, since the catalyst layer of the air electrode contains silver oxide in a ratio of 1% by weight to 50% by weight, it reacts with the hydrogen gas generated by the battery reaction to convert the hydrogen gas into water. Thus, an increase in the internal pressure of the battery can be suppressed. Therefore,
According to the present invention, it is possible to realize an air battery excellent in liquid leakage resistance.

Further, according to the present invention, liquid leakage can be prevented even if mercury is not contained in the electrode active material.
An air battery excellent in environmental friendliness and safety can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one configuration example of an air battery according to the present invention.

FIG. 2 is a cross-sectional view showing one configuration example of an air electrode according to the present invention.

[Explanation of symbols]

1 air battery, 2 air electrode, 3 air hole, 4
Positive electrode case, 5 Negative electrode mixture, 6 Negative electrode case, 7
Insulating gasket, 8 current collector, 9 catalyst layer, 1
0 Porous membrane

Claims (2)

[Claims] 1. A current collector comprising a metal material, and a catalyst layer formed on the current collector and containing a catalyst for reducing oxygen, wherein the catalyst layer contains 1% by weight of silver oxide. An air electrode containing 50% by weight. 2. An air electrode comprising: a current collector made of a metal material; and a catalyst layer formed on the current collector and containing a catalyst for reducing oxygen, wherein the catalyst layer is formed of silver oxide. An air battery characterized in that it is contained at a ratio of from 50% by weight to 50% by weight.