JPH02253573A - Air battery - Google Patents

Abstract

PURPOSE:To decrease variation in performance and to increase electrolyte leakage resistance by forming a separator with a laminate of a porous film and a oven fabric or a nonwoven fabric. CONSTITUTION:A separator 6 is formed with a laminate of a porous film stable in an electrolyte and a woven fabric or a nonwoven fabric. The woven fabric or the nonwoven fabric is made of polypropylene, polyethylene, polyamine, or cotton. As the porous film, a film having a mean pore size of 10mum or less and a porosity of 20% or more is preferable. An adhesive for bonding separator 6 to an air electrode 5 consists of a material insoluble in the electrolyte and a material lyophilic to but insoluble in the electrolyte. By forming the separator with a laminate, transfer of electrolyte exceeding necessary amount toward the electrode is retarded, and decrease in performance and electrolyte leakage can be prevented.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention relates to an air battery, and more specifically, the present invention relates to an air battery having an air electrode to which a separator is integrally attached. Related to air batteries that have small fluctuations, large current discharge, excellent leakage resistance, and stable performance (conventional technology) Air batteries are batteries that use oxygen in the air as a positive electrode active material. Based on their shape, they are classified as button-shaped air batteries, prismatic air batteries, or cylindrical air batteries.

The air battery will be explained based on a button-type zinc-air battery illustrated as an example of a longitudinal cross-sectional view.

In the figure, reference numeral 1 denotes a positive electrode can with air holes 2 formed on its bottom, which includes an air diffusion layer 3 made of nonwoven fabric such as cellulose or polypropylene, a water repellent layer 4 made of porous fluororesin, etc. An air electrode 5 and a separator 6 are stacked and housed in this order. Furthermore, separator 6
A negative electrode mixture 7 consisting of a negative electrode active material and an electrolyte is filled on the top, and a negative electrode can 8 which also serves as a negative electrode terminal is fitted into the opening of the positive electrode can 1 via a gasket 9. The periphery of the opening is caulked inward to seal the entire battery.

In an air battery having such a structure, the air electrode 5 is made by mixing particles of activated carbon and manganese oxide supporting catalyst components such as platinum, palladium, and nickel with a fluorine-based resin binder, and passing this mixture through a nickel wire mesh and an expander. It is supported on a positive electrode current collector such as dead metal.

The separator 6 has the function of separating the air electrode 5 and the negative electrode mixture 7 while maintaining liquid contact between them, and is generally made of a porous material with communicating pores distributed, such as nonwoven fabric, microporous film, or cellophane. Constructed of quality materials.

When manufacturing such an air battery, an air diffusion layer 3, a water-repellent layer 4, an air electrode 5, and a separator 6 are sequentially housed inside a positive electrode can 1, and then a negative electrode mixture 7 is filled thereon. The negative electrode can 8 is fitted into the positive electrode can 1 and then sealed. Due to this pressing force during sealing, the peripheral edge of the separator 6 is pressed against the air electrode 5.
It is fixed by pressure contact.

(Problem B to be Solved by the Invention) However, in the case of a battery manufactured by the method described above, the electrolyte tends to move more easily than necessary to the air electrode side through the communication hole of the separator 6. The air electrode gets wet in a relatively short period of time, leading to a decline in the battery's discharge characteristics, which in turn causes the electrolyte to leak out of the battery.
The adhesion between the air electrode 5 and the separator 6 is not sufficient, and a gap may occur between them. Therefore, when the viscosity of the electrolytic solution is high, the liquid junction between the negative electrode mixture 7 and the air electrode 5 cannot be sufficiently maintained, resulting in an increase in the internal resistance of the battery and an increase in its variation. Battery performance becomes unstable.

Therefore, in order to solve this problem, an air cell with a structure in which a water-soluble adhesive such as carboxymethyl cellulose, sodium polyacrylate, or polyvinyl alcohol is applied to a nonwoven fabric and is attached to the air electrode as a separator has been developed. It has been proposed (Japanese Unexamined Patent Publication No. 57-17266)
In the case of this battery, the adhesion between the air electrode and the separator is improved. If polyvinyl alcohol is used, it will form a strong insoluble film when it comes into contact with the electrolyte, and will instead damage the inside of the battery. This results in increased resistance.

Furthermore, JP-A No. 60-41763 discloses an air electrode and a separator that are fixed and integrated in advance with a resin adhesive, but this method has problems with the adhesion between the air electrode and the separator. However, the disadvantage is that the internal resistance of the battery increases due to the resistance of the adhesive itself interposed between the two.

The present invention solves the above-mentioned problems and aims to provide an air battery in which the air electrode and the separator are tightly adhered, the internal resistance of the battery is small, the variation is small, and the battery performance is stable.

[Structure of the Invention] (Means for Solving the Problem) In the course of intensive research to achieve the above object, the present inventors developed a material for bonding the air electrode and the separate electrode.
It goes without saying that it has a high adhesion ability, and if you use a material that forms a porous film when it comes into contact with the electrolyte, it is possible to maintain a liquid junction between the air electrode and the negative electrode mixture while also forming a porous film when it comes into contact with the electrolyte. After getting the idea that it would be possible to firmly adhere the separator to the separator, we conducted studies to find such a substance, and as a result, we discovered that a mixture of two types of substances having the properties described below is effective, and we have invented the present invention. This led to the development of an air battery. - In other words, the air battery of the present invention is an air battery comprising an air electrode and a separator attached to the air electrode via an adhesive substance, in which the separator is a laminate of a porous film and a woven or nonwoven fabric. The adhesive material is a mixture of a first component soluble in the electrolyte and a second component lyophilic and insoluble in the electrolyte.

As described above, the air battery of the present invention is characterized by the structure of the separator and the substance that bonds the air electrode and the separator, and other elements and structure are the same as the conventional battery described above. .

First, the separator used in the battery of the present invention is a laminate of a porous film and a woven or nonwoven fabric. The material of the porous film is not particularly limited as long as it is stable in the electrolytic solution, but it is preferably made of, for example, polytetrafluoroethylene, polypropylene, polyethylene, polyamide, ceraphane, or the like. Further, it is preferable that the film has micropores with an average pore diameter of 1OLLm or less, particularly preferably 5 μm or less, distributed such that the porosity is 20% or more, particularly preferably 25% or more. The thickness may be about 30 to 100 μm.

The woven fabric or nonwoven fabric laminated on the above porous film is! It retains enough electrolyte to prevent excess electrolyte from moving through the porous film to the air electrode, thereby preventing deterioration of battery performance and leakage over a long period of time. .

Examples of such woven or nonwoven fabrics include those made of polypropylene, polyethylene, polyamide, cotton, and the like. Also, its thickness is usually 0
．． It may be about 3 to 1.0+ nm.

Next, the first component constituting the adhesive substance is a substance soluble in the electrolytic solution, such as carboxymethyl cellulose,
Examples include sodium polyacrylate, and each of these may be used alone, or two or more types may be used in an appropriate combination.

On the other hand, the second component is a substance that is lyophilic but insoluble in the electrolytic solution, such as polyvinyl alcohol. These can be used alone or in appropriate combination.

The adhesive material according to the present invention can be prepared by mixing aqueous solutions of each of the above-mentioned components.
It is sufficient to prepare an aqueous solution with a concentration of 5 to 8% by weight and mix the two. The mixing ratio of the two at this time is not particularly limited, but the weight ratio of the first component and the second component is 1: 15
The ratio may be set to 0 to 150:1.

In addition, if a boron compound such as boric acid or borax is further added to this mixture in an amount of about 0.1 to 2.0% by weight,
This boron compound is suitable because it captures zinc ions that diffuse into the air electrode from the electrolytic solution and promotes the crosslinking reaction of the second component to stabilize battery performance.

The air electrode and separator are attached as follows. That is, the adhesive material according to the present invention is prepared as described above. Next, the adhesive substance is applied to the air electrode and the separator, and the two are bonded to be integrated. At this time, it is preferable to apply an adhesive substance to the porous film side of the separator and stick it to the air electrode.
After drying at ~80°C, it is punched into a predetermined shape and assembled into an air battery.

(Function) In the air battery of the present invention assembled by a conventional method, the adhesive substance described above behaves as follows, thereby contributing to improvement and stabilization of battery performance. That is, when the layer of adhesive material interposed between the separator and the air electrode comes into contact with the electrolyte, some of the components in the adhesive material, such as polyvinyl alcohol, which are lyophilic to the electrolyte but are insoluble. The second component solidifies to form a film, which firmly fixes the separator and the air electrode. On the other hand, other ingredients,
In other words, the first component that is soluble in the electrolyte, such as carboxymethyl cellulose and sodium polyacrylate, becomes a colloid in the film and gradually dissolves in the electrolyte, resulting in the formation of communicating pores in the film, making it porous. Qualification progresses.

Therefore, since the electrolytic solution on the negative electrode mixture side permeates through the communication holes formed in the film, the liquid junction between the air electrode and the electrolytic solution is maintained well and stably. That is, even though the air electrode and the separator are in close contact with each other, the liquid junction is sufficient, so the internal resistance of the battery does not increase and the variation is small, making it possible to extract a large current.

(Example) Examples 1 to 8 A polypropylene porous film with an average pore diameter of 1 μm, a porosity of 30%, and a thickness of 50 μm and a polypropylene nonwoven fabric with a thickness of 0.5 mm were immersed in an aqueous solution of the adhesive substance shown in the table. Then I took it out.

The porous film was first attached to one side of an air electrode made of a layered mixture of activated carbon and fluororesin supported on a nickel wire mesh, and then the nonwoven fabric was attached thereon. After drying the obtained laminate, it is punched and used to form a PH10 type button air battery (diameter 11
．． 6mm, total height 5.4mm).

For comparison, when the polypropylene nonwoven fabric used in the example was simply placed on the air electrode without adhesion (Comparative Example 1), the average pore diameter was 50 μm, the porosity was 10%, and the thickness was 10
Case in which a porous film of 0 μm polypropylene was placed on air and electrodes without adhesion (Comparative Example 2)
, P for each of the cases where the above-mentioned nonwoven fabric was adhered to the air electrode with the adhesive shown in the table (Comparative Example 3, Comparative Example 4)
An H10 type button battery was manufactured.

For each of these 200 batteries, immediately after battery manufacture and 2
The internal resistance value was measured after storage at 5°C for 3 months,
The average value and its variation width: a (n=50) were calculated, and the results are shown in the table.

In addition, we measured the initial maximum discharge current of these batteries immediately after manufacture, the temperature, 25°C, and the number of leaking batteries after storing them for 3 months in an atmosphere of 95% relative humidity, and compared the results with those of Comparative Example 1. It is shown in the table as a relative value with 1.

Example 9 0.3% by weight of boric acid was added to the adhesive material used in Example 1, and a PR44 type air battery was manufactured in the same manner as in Example 1 using this.

After storing 50 of these batteries at 45°C for 3 months, we measured the self-discharge rate and compared the results with those without the addition of boric acid. The discharge rate was about 60% of that of the cell using the boric acid-added adhesive.

[Effects of the Invention] As is clear from the above description, the air battery of the present invention has an extremely small internal resistance and small variation in internal resistance compared to conventional ones, and therefore can draw a large current. It also has good leakage resistance.

Although the present invention has been described with respect to a button-type air battery, 1
The present invention is not limited to this, and it goes without saying that the same effect can be obtained with, for example, prismatic or cylindrical batteries. Similar effects can be obtained with other types of air batteries such as iron.

[Brief explanation of drawings]

The figure is a longitudinal cross-sectional view showing the structure of a button-type air battery. 1... Positive electrode can 2... Air hole 3... Air diffusion layer 4... Water repellent layer 5... Air electrode
6...Separate lake 7...Negative electrode mixture
8...Negative pole element 9...Gasket

Claims (1)

[Claims] An air battery comprising an air electrode and a separator attached to the air electrode via an adhesive, wherein the separator is a laminate of a porous film and a woven or nonwoven fabric; An air cell characterized in that the adhesive substance is a mixture of a first component soluble in an electrolytic solution and a second component lyophilic and insoluble in the electrolytic solution.