JPH09190827A - Air electrode for air battery - Google Patents

Abstract

(57) Abstract: An air electrode for an air battery that does not deteriorate the heavy load discharge characteristics of the air battery can be provided at low cost. SOLUTION: In an air electrode for an air battery in which a catalyst composition containing an oxygen reduction catalyst, a conductive material and a fluororesin binder is supported on a conductive core, a silver-nickel composite oxide is used as an oxygen reduction catalyst. use. Further, it is preferable to use manganese oxide together as an oxygen reduction catalyst.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an air diffusion type air electrode of an air battery. More specifically, it relates to an air electrode capable of improving the heavy load discharge characteristics of an air battery.

[0002]

2. Description of the Related Art Conventionally, various air batteries using an air electrode as a positive electrode have been known, but in recent years, the production amount of electronic devices using the air battery, such as hearing aids, pagers, and pagers. Has increased dramatically.

By the way, as an air electrode of an air battery, a catalyst composition is prepared by kneading platinum having very high oxygen reduction catalytic activity adhered to activated carbon with a water-repellent fluororesin binder, and It is known that a sheet is fixedly carried on a conductive core such as a nickel net, and an oxygen-permeable water-repellent fluororesin film is integrally formed on one surface of the sheet. The air electrode using platinum can realize good heavy load discharge characteristics in an air battery. However, since platinum is a very expensive metal, it is practically impossible to apply the air electrode using it to a general-purpose air battery in terms of manufacturing cost.

Therefore, as an oxygen reduction catalyst for an air electrode for an air battery, a metal chelate compound such as cobalt phthalocyanine (Japanese Patent Publication No. 2-30142) or β is used instead of platinum.
Manganese oxides such as —MnO ₂ and γ-MnO ₂ have come to be used.

[0005]

However, in the case of an air electrode using a metal chelate compound, the metal chelate compound tends to drop off from the surface of the activated carbon during long-term storage or long-term discharge, which results in stable battery characteristics. There is a problem that it becomes very difficult to maintain.

On the other hand, in the case of the air electrode using manganese oxide, the manufacturing cost of manganese oxide itself is low,
It has a relatively stable discharge characteristic. However, an air battery equipped with an air electrode using manganese oxide requires a large current (for example, a large current required by devices such as alarms and vibrations).
There was a problem that heavy current discharge characteristics were insufficient because a stable current of about 20 mA / cm ² (per electrode area) could not be flowed.

Therefore, when the air electrode is produced, the amount of the manganese oxide used is increased, while the amount of the water-repellent fluororesin binder to be kneaded with the manganese oxide is conventionally used in the catalyst composition. Relative to 1 when it was 30% by weight or more
Attempts have been made to suppress the content to about 0 to 20% by weight. However, in this attempt, since the amount of the water-repellent fluororesin binder used was too small, the electrolyte penetrated into the air electrode during long-term storage of the air battery or during heavy load discharge, and the air flowed into the air electrode. It is not preferable because it interferes with the diffusion, which deteriorates the discharge characteristics.

The present invention is intended to solve the above-mentioned problems of the prior art, in particular, an platinum-based air battery which is superior in heavy load discharge characteristics to an air electrode using manganese oxide as an oxygen reduction catalyst. An object of the present invention is to provide an air electrode for an air battery which can be constructed at a lower cost than when used as an oxygen reduction catalyst.

[0009]

The present inventors have found that the silver-nickel composite oxide has an excellent oxygen reduction catalytic ability and has sufficient conductivity as an oxygen reduction catalyst for an air electrode for an air battery. Therefore, by using a silver-nickel composite oxide as an oxygen reduction catalyst for the air electrode of an air battery, an excellent heavy load discharge characteristic can be achieved in the air battery even when the amount of catalyst and the amount of conductive material are relatively reduced compared to conventional ones. In addition, since the amount of the water-repellent fluororesin binder used can be relatively increased at the same time, the permeation of the electrolyte into the air electrode can be suppressed, and the long-term storage characteristics and the discharge life can be stabilized. The inventors have found that the above can be realized and have completed the present invention.

That is, the present invention provides an air electrode for an air battery, which contains a silver-nickel composite oxide as an oxygen reduction catalyst.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The air electrode for an air battery of the present invention will be described in detail below.

The air electrode for an air battery of the present invention is characterized by containing a silver-nickel composite oxide as an oxygen reduction catalyst. This silver-nickel composite oxide has high oxygen reduction catalytic ability and good conductivity. Moreover, the manufacturing cost is much lower than that of platinum. Therefore, by using this silver-nickel composite oxide, an air battery having good battery characteristics can be manufactured at low cost. Here, the silver-nickel composite oxide is represented by the formula (1) in terms of chemical structure.

[0013]

## STR1 ## is a compound represented by AgNiO ₂ (1).

This compound can be produced by various methods, for example nickel oxyhydroxide (NiOO).
It can be easily produced by reacting H) with silver nitrate (AgNO ₃ ) in an alkaline aqueous solution, and washing the resulting precipitate with water and then drying with hot air.

An air electrode for an air battery containing the silver-nickel composite oxide comprises a catalyst composition prepared by kneading the silver-nickel composite oxide, a conductive material and a water-repellent fluororesin binder. Similar to the conventional air electrode, it is preferable to have a structure supported on a known conductive core body such as a nickel mesh.

When the content of the silver-nickel composite oxide in the catalyst composition is too small, the oxygen reducing ability of the air electrode as a whole becomes insufficient, and when it is too large, the amount of the water-repellent fluororesin binder used becomes relatively large. Is decreased, and there is a concern that the inflow and diffusion obstacles of the air may occur due to the permeation of the electrolytic solution into the air electrode. Particularly, when only the silver-nickel composite oxide is used as the oxygen reduction catalyst, the heavy load discharge characteristics can be further improved by setting the content to 10 to 30% by weight.

In the air electrode for an air battery of the present invention, a silver-nickel composite oxide is used as an oxygen reduction catalyst, but the production cost of this silver-nickel composite oxide is much lower than that of a platinum catalyst. , Still higher than manganese oxide. Therefore, in order to reduce the amount of silver-nickel composite oxide used without degrading battery characteristics such as heavy load discharge characteristics of an air battery, it is possible to use manganese oxide in combination with silver-nickel composite oxide as an oxygen reduction catalyst. preferable.

As the manganese oxide, α-MnO ₂ and β-, which are used in conventional air electrodes for air batteries, are used.
MnO ₂ , γ-MnO ₂ , Mn ₂ 0 ₃ , Mn ₃ 0 ₄ , Mn
₅ 0 _8, the thermal decomposition product of manganese oxide (JP 59-139
570) and the like can be used alone or in combination.

If the amount of manganese oxide used is too small, the effect obtained cannot be obtained. If the amount of manganese oxide is too large, the amount of the water-repellent fluororesin binder relatively decreases, and the inside of the air electrode of the electrolytic solution is reduced. Since there is a concern that air inflow and diffusion obstacles may occur due to the permeation into the air, it is preferably 10 to 30% by weight.

When silver-nickel composite oxide and manganese oxide are used together as an oxygen reduction catalyst, the amount of silver-nickel composite oxide used can be reduced as compared with the case where manganese oxide is not used. It can be used, and the preferable amount thereof is 3 to 10% by weight in the catalyst composition.

As the conductive material that can be used in the air electrode for an air battery of the present invention, a carbonaceous material used in conventional air electrodes, for example, powder of carbon black, acetylene black, activated carbon, graphite or the like is used. You can The amount used is usually 30 to 4 in the catalyst composition.
0% by weight.

As the water-repellent fluororesin binder, those similar to those used in conventional air batteries can be used. For example, polytetrafluoroethylene is preferably used. it can. The fluororesin binder is preferably used in the state of aqueous dispersion due to the action of the surfactant.

The amount of the water-repellent fluororesin binder used is determined by considering the coatability of the catalyst composition, the shape retention after drying, the content of the oxygen reduction catalyst, etc. However, if it is too small, there is a concern that an air inflow diffusion obstacle may occur, so the content is preferably 30% by weight or more in the catalyst composition.

When manganese oxide is also used as the oxygen reduction catalyst, if the amount of the water-repellent fluororesin binder used is too large, the amounts of the oxygen reduction catalyst and the conductive material relatively decrease. Since there is a possibility that the characteristics of the air electrode itself may deteriorate, it is preferably 50% by weight or less in the catalyst composition.

As the conductive core used in the air electrode for an air battery of the present invention, a known conductive core such as nickel net can be used.

The air electrode for an air battery of the present invention can be produced by a conventional method. For example, a silver-nickel composite catalyst powder and, if necessary, manganese oxide powder are added to an aqueous dispersion of a fluororesin binder. A paste-like catalyst composition is prepared by dispersing it in water or alcohol, and the conductive core is coated with a known coating method by a known coating method, for example, a transfer roller method. It can be prepared by drying at 100 to 150 ° C. and, if necessary, heat treatment at 250 to 350 ° C. in order to improve the water repellency of the fluororesin binder.

The air electrode for an air battery of the present invention can be preferably applied to a conventional air diffusion type air battery. In this case, it is preferable to dispose a known water-repellent porous fluororesin film that prevents leakage of the electrolytic solution and allows oxygen to pass through on at least one surface of the air electrode. Other configurations of the air battery may be the same as those of the conventionally known air battery.

[0028]

The present invention will be described below in more detail with reference to examples.

Examples 1 to 20 and Comparative Example 1 (Preparation of silver-nickel composite oxide) 100 g of nickel oxyhydroxide (NiOOH) was added to 3 liters of a potassium hydroxide aqueous solution having a concentration of 5 mol / l and stirred sufficiently. did. Into this, a 1 mol / l concentration silver nitrate aqueous solution (1N-
1 liter of AgNO ₃ ) was added and stirring was continued at 60 ° C. for 16 hours. Then, the produced precipitate was collected by filtration, washed with water and dried at 110 ° C. to obtain a silver-nickel composite oxide.

(Production of air electrode) The obtained silver-nickel composite oxide (AgNiO ₂ ) or β-manganese oxide powder (MnO ₂ ) or both of them and a conductive material (activated carbon and carbon black 1: 1). The mixture (AC + CB)) and an aqueous dispersion of polytetrafluoroethylene (PTFE) having a solid content of 60% by weight as a water-repellent fluororesin binder are mixed so as to have the composition shown in Table 1, A pasty catalyst composition was obtained.

This composition was applied to a sheet-like nickel net in a thickness of 0.5 mm, dried at 120 ° C., and then 30
A catalyst sheet was obtained by heat treatment at 0 ° C. next,
The obtained sheet was further added with a porous PTF having a thickness of 0.1 mm.
After the E film was pressure-bonded, it was punched into a circle having a diameter of 11.0 mm to obtain an air electrode for an air battery.

Incidentally, Examples 1 to 10 are examples in which only the silver-nickel composite oxide is used as the oxygen reduction catalyst, and Examples 11 to 20 are the silver-nickel composite oxide and the manganese oxide (β- MnO ₂₎ and a combination with an example, Comparative example 1 is an example of using only manganese oxide (β-MnO ₂₎ without using a silver-nickel composite oxide as an oxygen reduction catalyst.

(Prototype Air Battery) Using the obtained air electrode, a button type air battery shown in FIG. 1 having a diameter of 11.6 mm and a height of 5.4 mm was produced. Here, the air battery of FIG. 1 includes a positive electrode case 1 made of Ni plated with iron, an air hole 2 formed in the positive electrode case 1, an air diffusion material 3 for diffusing air, and an air electrode 4 (compression bonding to the air electrode 4). Porous PTFE membrane (not shown) provided on the side of the air diffusion material 3), the air diffusion material 3
Between the air electrode 4 and the porous PTFE membrane 5, a separator 6 made of a microporous polypropylene film, an electrolyte holding material 7 made of natural pulp material, a gasket 8 made of nylon, and copper. / SUS / Ni
The negative electrode cup 9 made of the clad material, the negative electrode mixture 10 made of a mixture of zinc iodide particles, the gelling material and the potassium hydroxide solution, and the air hole seal 11 were assembled in the same manner as in the conventional air battery. It is a thing.

(Evaluation of Performance of Air Battery) Next, the obtained air battery was aged at room temperature for 2 weeks, and a heavy load closed-circuit voltage characteristic test for confirming the heavy load current characteristic when the battery was used Heavy load discharge characteristic test to confirm the discharge level of the oxygen reduction catalyst used for the electrode, and heavy load after storage to confirm the discharge level of the oxygen reduction catalyst after long-term storage (storage at 60 ° C for 40 days) The discharge characteristic test was evaluated as shown below.

(1) Heavy load closed circuit voltage characteristic test After aging for 2 weeks, the air hole seal of the battery was opened.
Ten minutes after the seal was opened, a load resistance of 70Ω was connected to the battery for 5 seconds, and the closed circuit voltage (V) at that time was measured. The results are shown in Table 1 (item of closed circuit voltage (V)). In this case, the higher the battery voltage, the more preferable.

(2) Heavy Load Discharge Characteristic Test After aging for 2 weeks, the air hole seal of the battery was opened.
Ten minutes after the seal was opened, a load resistance of 150Ω was connected to the battery, and the discharge capacity (mAh) until the battery voltage fell below 0.9V was measured. The results are shown in Table 1 (Heavy load discharge capacity (mAh) item). The larger the value, the larger the discharge capacity, which is preferable.

(3) Heavy load discharge characteristic test after storage After aging for 2 weeks, the sample was further stored at 60 ° C. for 40 days, and the heavy load discharge capacity (mAh) at the end of storage was the same as the above heavy load discharge characteristic test. Went to. Table 1 shows the results.
(Item of discharge capacity after storage (mAh)). Also in this case, the larger the value, the larger the discharge capacity, which is preferable.

[0038]

[Table 1] AgNiO2 MnO2 AC + CB PTFE Closed circuit voltage Heavy load discharge Discharge after storage (wt%) (wt%) (wt%) (wt%) (V) Capacity (mAh) Capacity (mAh) Comparative example 1 0 40 40 20 1.10 460 430 Example 1 5 0 40 55 1.06 510 490 2 10 0 40 50 1.12 510 490 3 20 0 40 40 1.16 500 485 4 30 0 40 30 1.17 480 470 5 40 0 40 20 1.18 465 435 6 5 0 30 65 1.04 510 490 7 10 0 30 60 1.10 510 490 8 20 0 30 50 1.15 500 485 9 30 0 30 40 1.15 485 470 10 40 0 30 30 1.12 480 465 11 3 15 40 42 1.08 505 490 12 12 6 15 40 39 1.12 490 480 13 10 15 40 35 1.18 485 470 14 15 15 40 30 1.18 480 470 15 3 25 40 32 1.12 485 470 16 6 25 40 29 1.16 480 470 17 10 25 40 25 1.20 470 450 18 18 15 25 40 20 1.25 460 430 193 3 15 30 52 1.06 510 490 20 6 15 30 49 1.10 510 490

From Table 1, the batteries of Examples 1 to 10 using the silver-nickel composite oxide as the oxygen reduction catalyst were compared with the batteries using only the manganese oxide as the oxygen reduction catalyst in the heavy load discharge characteristics and storage. Later heavy load discharge characteristics showed favorable results. Among them, from the viewpoint of closed-circuit voltage, heavy load discharge characteristics and heavy load discharge characteristics after storage, it is preferable that the catalyst composition contains 10 to 30% by weight of the silver-nickel composite oxide.

Further, from Table 1, the batteries of Examples 11 to 20 in which the silver-nickel composite oxide and the manganese oxide were used together as the oxygen reduction catalyst were compared with the batteries of Examples 1 to 10 in the silver-nickel composite oxide. Despite the small amount of
Similar to the batteries of Examples 1 to 10, excellent battery characteristics were exhibited. In this case, it is understood that the preferable amount of the silver nickel composite oxide used in the catalyst composition is 3 to 10% by weight.

From the results of Examples 1 to 10, it is understood that preferable battery characteristics are obtained by using the water-repellent fluororesin binder in an amount of 30% by weight or more. Further, from the results of Examples 11 to 20, when the silver-nickel composite oxide and the manganese oxide were used together as the oxygen reduction catalyst, the amount of the water-repellent fluororesin binder used was 3%.
It can be seen that it is preferable that the content is 0% by weight or more and 50% by weight or less.

[0042]

According to the air electrode for an air battery of the present invention, an air battery having excellent heavy load discharge characteristics can be obtained at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of an air battery using an air electrode for an air battery of the present invention.

[Explanation of symbols]

 1 Positive electrode case 2 Air hole 3 Air diffusion material 4 Air electrode 5 Porous polytetrafluoroethylene film 6 Separator 7 Electrolyte holding material 8 Gasket 9 Negative electrode cup 10 Negative electrode mixture 11 Air hole seal

Front page continued (72) Inventor Tomoyuki Kanai, Takakura character, Hiwada-cho, Koriyama city, Fukushima Prefecture 1 of 1 Shimosugishita, Sony Energy Tech Co., Ltd. (72) Kuniyasu Oya Takakura character, Hiwada-cho, Koriyama city, Fukushima Prefecture No. 1 in Shimosugishita, Sony Energy Tech Inc.

Claims (8)

[Claims] 1. An air electrode for an air battery, which contains a silver-nickel composite oxide as an oxygen reduction catalyst. 2. The air electrode for an air battery according to claim 1, wherein a catalyst composition containing an oxygen reduction catalyst, a conductive material, and a fluororesin binder is supported on a conductive core body. 3. The air electrode for an air battery according to claim 1, wherein the content of the silver-nickel composite oxide in the catalyst composition is 2 to 45% by weight. 4. The air electrode for an air battery according to claim 1, wherein the content of the silver-nickel composite oxide in the catalyst composition is 10 to 30% by weight. 5. The air electrode for an air battery according to claim 1, further comprising a manganese oxide as an oxygen reduction catalyst. 6. The air electrode for an air battery according to claim 5, wherein the content of the silver-nickel composite oxide in the catalyst composition is 3 to 10% by weight. 7. The air electrode for an air battery according to claim 2, wherein the content of the fluororesin binder in the catalyst composition is 30% by weight or more. 8. An air battery comprising the air electrode for an air battery according to claim 1.