JPH0766811B2 - Air battery - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an air battery having excellent electrolyte leakage resistance.

[Technical Background of the Invention and Problems Thereof] Various structures are known for an air battery using oxygen in the air as a positive electrode active material, and a typical one is a button structure. Further, since zinc is often used as the negative electrode active material, a button type air zinc battery will be described below.

A conventional button-type zinc-air battery has a structure generally shown in FIG. That is, in the figure, an air diffusion layer 3, an air electrode 4 composed of a porous catalyst layer having oxygen gas reducing ability and a current collector layer, and an air electrode 4 at the bottom of a positive electrode case 1 having air holes 2 formed at the bottom. For example, the separators 5 made of polypropylene non-woven fabric are stacked and stored in this order. On the other hand, the cap 7 also serving as the negative electrode terminal is fitted into the opening of the positive electrode case 1 through the gasket 6,
Moreover, the periphery of the opening of the positive electrode case 1 is bent inward to seal the entire battery. The space defined by the positive electrode case 1 and the cap 7 is filled with the negative electrode mixture 8. As the negative electrode mixture, a mixture of zinc powder, an alkaline electrolyte such as a KOH aqueous solution and an alkali resistant gelling agent is generally used. Then, in such a button-type zinc-air battery, oxygen gas in the air is introduced into the air diffusion layer 3 from the air holes 2, and thereafter,
Activation (ionization) by contact with the air electrode 4
Is performed.

In such a conventional button type zinc-air battery, as the air electrode 4, for example, a porous molded body of activated carbon is generally used. However, in the button-type zinc-air battery having such a structure, the air electrode 4 allows water vapor, which is inevitably introduced into the battery together with oxygen in the air, to pass therethrough. The water vapor reaching the mixture 8 causes the electrolyte to be diluted / increased. As a result, during long-term use or storage of the battery, the electrolytic solution in the negative electrode mixture 8 leaks out from the battery, resulting in damage to the device or deterioration of the function of the device. Further, on the contrary, the water content of the electrolytic solution inside the battery is diffused to the outside through the air electrode 4, so that the electrolytic solution is dried and solidified,
There are problems such as deterioration of battery characteristics.

Therefore, recently, a structure has been proposed in which a water-repellent film such as a porous thin film made of a fluororesin is pressure-bonded to the surface of the air electrode 4 on the air diffusion layer 3 side, that is, the lower surface in the drawing. It is put to practical use in some alkaline / air batteries. However, although such a thin film is effective for preventing leakage of the electrolytic solution, it does not have a sufficient function of preventing invasion of moisture (water vapor) in the air, and therefore the above-mentioned problems still exist.

[Object of the Invention] The present invention solves the above-mentioned conventional problems and effectively prevents the invasion of water vapor into the battery or the diffusion of water in the electrolytic solution, resulting in a change in the concentration of the electrolytic solution and the electrolytic solution. It is an object of the present invention to provide an air battery that does not leak and has little change in discharge characteristics during long-term discharge.

[Summary of the Invention] In order to solve the above-mentioned object, the inventors focused their attention on the structure of the air electrode and, as a result, conducted intensive studies. As a result, first, the air electrode was formed into a water-repellent layer, a catalyst layer, and a current collector layer. In order to complete the present invention, a three-layer one-body structure composed of and the total air permeability of the air electrode having the three-layer structure is limited to a predetermined range to be described later to confirm the effect. Arrived

That is, the air battery of the present invention has at least a water-repellent layer,
An air battery comprising an air electrode having a structure in which a catalyst layer and a current collector layer are laminated, and the total air permeability of the air electrode is 1,000 to 1,500,000 se in Gurley number.
It is characterized by c / 100cc · in ² .

Here, the Gurley number is the number of seconds required for permeation of 100 cc of air per square inch of the air electrode.

As described above, the air battery of the present invention is characterized in that the structure of the air electrode and its physical properties are limited, and the other constituent elements are not limited at all.

The air electrode of the air battery of the present invention will be described in detail below.

FIG. 1 shows a three-layer structure as an example.
Has a three-layer structure in which a water-repellent layer 14a, a catalyst layer 14b and a current collector layer 14c are laminated and integrated. Then, when assembling the battery, the water-repellent layer 14a is housed in the battery so that the water-repellent layer 14a faces the air diffusion layer side.

As a constituent material of the water-repellent layer, for example, a film made of porous polytetrafluoroethylene (PTFE), porous polyethylene, porous polypropylene or the like is suitable, and as the catalyst layer, platinum, palladium, silver, manganese oxide is used. It is preferable to use, for example, a catalyst obtained by supporting a catalyst having an oxygen reducing ability on activated carbon or the like. Then, as the current collector layer, for example, a porous current collector such as Ni net, Ni expanded metal, Ni punched metal, or Ni-plated steel wire mesh is suitable.

The air electrode having the three-layer structure is formed by stacking the above-mentioned layers and then pressurizing the entire body to press-contact each layer, or interposing an adhesive layer made of, for example, fluororesin powder between the layers to press the whole body. As a result, it is manufactured as an integrated structure.

The total air permeability of the air electrode of the three-layer integrated structure thus obtained is 1,000 to 1,500,000 se in Gurley number.
It is necessary to specify c / 100cc ・ in ² . Gurley number is 1,00
If it is less than 0 sec / 100 cc · in ² , that is, if the air permeability is larger than the range of the present invention, the discharge capacity, which is one of the characteristics of the air electrode itself, becomes large, but on the other hand, in the air together with oxygen gas. Since a large amount of water vapor of the electrolyte is transmitted, the above-mentioned dilution or dryness of the electrolytic solution is likely to occur inside the battery, and as a result, the performance of the battery may fluctuate greatly or the electrolytic solution may leak to the outside. Or, there is a problem that the power generation function of the entire battery is hindered.

On the contrary, when the Gurley number exceeds 1,500,000 sec / 100cc · in ² , that is, when the air permeability is smaller than the range of the present invention, the inflow of water vapor into the battery is prevented,
Although battery performance is stable and leakage resistance is improved,
On the other hand, since oxygen gas cannot be sufficiently taken in until it reaches the oxygen gas reduction action point of the catalyst layer, it is not preferable because sufficient current cannot be taken out to drive applied equipment such as a hearing aid.

In order to make the Gurley number of the air electrode of the present invention fall within the above range, firstly, the air permeability of each layer constituting the air electrode, particularly the lower water repellent layer and the catalyst layer is controlled. Secondly, the method of press-bonding or adhering each layer may be appropriately selected, that is, the type of adhesive to be used, the pressing force at the time of press-bonding, or the like may be appropriately selected.

Among the constituent layers of the air electrode, the lower water-repellent layer,
For example, if the pore size of the porous PTFE layer is too large, it will be difficult to keep the air permeability (Gurley number) of the air electrode as a whole in the above range even if the other conditions as described above are controlled, and The electrolytic solution inside the battery is also likely to leak, which is not preferable. Considering such points, it is preferable to set the maximum pore diameter of the water-repellent layer to 0.3 μm or less, and further to 0.2 μm or less. The porosity is set to 95% or less, preferably 60% or less, and more preferably 50% or less.

The layer structure of the air electrode according to the present invention is not limited to the above-mentioned three-layer structure. For example, the order of the catalyst layer and the current collector layer is reversed, or the water repellent layer-catalyst layer- A four-layer structure in which a current collector layer and a catalyst layer are laminated in this order is also effective.

[Examples of the Invention] Examples of the present invention will be described below with reference to button-type zinc-air batteries.

Porous PTFE membrane with maximum pore size 0.15μm and thickness 200μm, thickness 4
A catalyst layer of 00 μm and a porous current collector layer made of Ni net were laminated in this order, and an appropriate pressure (usually 50 to 100 kg / cm) was applied to the whole.
² ) was applied to produce an air electrode having a three-layer one-body structure. The catalyst layer used was a mixture of activated carbon having an average particle size of 80 μm and a PTFE binder. The total air permeability of the air electrode respectively Gurley number 7,000sec / 100cc · in ^2, was 20,000sec / 100cc · in ² and 1,000,000sec / 100cc · in ^2.

The air electrode thus obtained was housed in place of the air electrode 4 of the button type zinc-air battery shown in FIG. 2 to manufacture 100 air cells having an outer diameter of 11.5 mm and a height of 5.4 mm. In this button-type zinc-air battery, the negative electrode mixture 8 used was a mixture of zinc powder, an aqueous caustic potash solution and carboxymethyl cellulose.

The button type zinc-air battery was divided into two groups of 50 cells, and each group was subjected to the following evaluation tests.

(1) Discharge capacity Measure the discharge capacity at a temperature of 25 ℃ and an external load of 620Ω.
The average value was calculated.

(2) Leakage resistance characteristics The number of batteries in which leakage occurred when stored for 7 days in an atmosphere of temperature 45 ° C and relative humidity 90% was examined.

The above results are collectively shown in the table.

For comparison, the total Gurley number of the air electrode was 850 sec / 100 cc · in ² (Comparative Example 1) and 3,000,000 se.
A button type zinc-air battery was manufactured in the same manner as in the above-mentioned example except that the c / 100 cc · in ² (Comparative Example 2) was used, and the same evaluation test was performed. The results are also shown in the table.

In addition, although the button type air zinc battery is described as an example in the present embodiment, the present invention is not limited to this, and the same effect can be obtained for other types of zinc air batteries such as prismatic type and cylindrical type. Needless to say. Further, not only the air / zinc system, but also the air battery of other systems such as air / aluminum and air / iron can obtain the same effect.

[Effects of the Invention] As is clear from the above description, the air battery of the present invention is
Firstly, the air electrode has a three-layer, one-body structure, and secondly, the total air permeability of the air electrode is limited to the above range, so that it has a sufficient discharge capacity, that is, for driving the device. In addition to being able to take out a sufficient current, it has excellent liquid leakage resistance properties, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a battery used in an air battery according to an embodiment of the present invention.
The figure which shows the structure of the air electrode of a layer 1 structure, FIG. 2 is a longitudinal cross-sectional view which shows the structure of a normal button type zinc-air current. 4,14 ... Air electrode, 14a ... Water repellent layer, 14b ... Catalyst layer,
14c …… Current collector layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michio Watanabe 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo Within Toshiba Battery Co. (72) Inventor Hitomi Sato 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo Toshiba Battery Co., Ltd.

Claims (3)

[Claims] 1. An air battery comprising an air electrode having a structure in which at least a water repellent layer, a catalyst layer and a current collector layer are laminated, and the total air permeability of the air electrode is Gurley number. The air battery is characterized by 1,000 to 1,500,000 sec / 100cc in ² . 2. The total air permeability of the air electrode is 5,000 to 1,200,000 in terms of Gurley number.
The air battery according to the item. 3. The air battery according to claim 1, wherein the water repellent layer has a maximum pore size of 0.3 μm or less.