JPS58218775A - Air cell - Google Patents

Abstract

PURPOSE:To keep off a concentration variation in an electrolyte as well as to make a specified discharge capacity maintainable for a long period of time, by applying a porous body consisting of a hydrophobic high polymer and a hydrophilic high polymer to the air side surface of an air pole. CONSTITUTION:In case of an air cell whose electrolyte comprises an alkaline aqueous solution, a porous body consisting in a structure that incorporates a hydrophilic high polymer such as polyvinyl alcohol, etc., dispersively into a matrix composed of a hydrophobic high polymer such as polyvinyl chloride is applied to the air side surface of an air pole. That is to say, this porous body is either charged in an air room or installed on the air side surface of the air pole. Each bore of this porous body is preferable to a minute opening of 1mum or less and formed so as to distribute these minute bores as many as 10-70% or so. Since this porous body effectively absorbs moisture in the air flowing in from outside or moisture flowing in from the electrolyte after turning to vapor, dilution or concentration in the electrolyte is thus checked.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an air battery with excellent long-term usage characteristics and storage performance.

[Technical background of the invention and its problems]

An air battery is a battery that uses oxygen gas in the air as a depolarizer, metals such as zinc or iron as the negative electrode active material, and an aqueous alkaline solution as the electrolyte. A typical structural example of a titanium air battery is schematically shown in FIG. 1. The figure is a partially cutaway vertical cross-sectional view. A porous gas electrode 3 (for example, a porous molded body of activated carbon) having an ability to reduce oxygen gas is laminated with a porous gas electrode 3 (for example, a porous molded body of activated carbon) interposed therebetween (for example, a nonwoven fabric made of polyglopylene) to constitute a power generation element as a whole.

A sealing plate 4 which also serves as a cathode terminal is attached to each of these power generation elements, and is airtightly arranged in an outer can 6 which also serves as an anode terminal via a gasket 5.

An air chamber 7 of arbitrary volume is provided between the bottom of the outer can 6 and the gas electrode 3.
is formed, and a plurality of holes are bored in the bottom surface of the outer can 6.

Oxygen gas in the air flows into the air chamber 7 through the air intake 8 and comes into contact with the gas electrode, where it is activated (ionized).

However, in an air battery with such a structure,
Since air can freely enter and exit the air chamber 7, for example, when the humidity of the air is higher than the humidity of the electrolyte, the air chamber 7
The electrolyte is diluted by the moisture in the air that has entered the chamber, resulting in a decrease in the concentration of the electrolyte. Conversely, when the air humidity is low, the water in the electrolyte evaporates into the air chamber 7, and as a result, the electrolyte concentration increases, reducing the ionic conductivity of the electrolyte and reducing the overall Internal resistance increases.

Therefore, an inconvenient situation arises in the conventionally structured air battery in that it is unable to maintain a predetermined discharge capacity during long-term use or storage.

In order to overcome these drawbacks of air batteries, it has been proposed to press, for example, a porous thin film of water-repellent fluororesin to the surface of the gas electrode on the air chamber side. However, although this porous thin film exhibits an effective function against electrolyte leakage, it does not have the function to sufficiently prevent moisture (water vapor) from entering and exiting the atmosphere, so it cannot prevent the above-mentioned disadvantages. It's not a solution.

[Object of the Invention] An object of the present invention is to provide an air battery that can prevent changes in the concentration of an electrolytic solution, maintain a predetermined discharge capacity over a long period of time, and has high long-term usage characteristics and storage performance.

[Summary of the decoy]

As a result of extensive research to solve the above-mentioned problems, the present inventors have discovered a porous material obtained by foaming an emulsion of a certain kind of hydrophobic polymer and a hydrophilic polymer and then curing the emulsion. When it is filled into the air chamber of an air battery, the body absorbs moisture from the air flowing in from the outside to prevent dilution of the electrolyte, and conversely also absorbs moisture that evaporates from the electrolyte and flows out. The inventors discovered that the air cell functions as a kind of buffer material capable of preventing undesirable concentration of the electrolytic solution and keeping the concentration of the electrolytic solution constant, leading to the completion of the air battery of the present invention.

That is, the air battery of the present invention is characterized in that it has a structure in which a porous body made of a hydrophobic polymer and a hydrophilic polymer is brought into contact with the air side surface of the gas electrode.

The porous body according to the present invention is made of a hydrophobic polymer matrix.
It has a structure in which hydrophilic polymers are dispersed and incorporated into Trix. In order for the porous body to effectively absorb moisture in the air flowing in from the outside or moisture evaporating and flowing out from the electrolyte, it is necessary to have 10 to 7 fine pores with a pore diameter of 1 μm or less.
Preferably, the distribution is 0%. When the pore size exceeds 1 μm, the water absorption ability decreases. Furthermore, if the distribution is less than 10 inches, the moisture absorption capacity of the porous body decreases, resulting in a shortened service life. If it exceeds 70 degrees, an inconvenient situation will occur in which the absorbed moisture will connect with each other, the liquid film will spread laterally, and the absorption capacity will decrease.

Examples of the hydrophobic polymer constituting the matrix of the porous body include one or a combination of two or more of polyvinyl chloride, polyethylene, propylene, polystyrene, and the like. Examples of the hydrophilic polymer include polyvinyl alcohol, sodium polyacrylate, cellulose 7 acetate, ethyl cellulose, and the like, or a suitable combination of two or more thereof.

The porous body according to the present invention is manufactured as follows.

That is, a low degree of polymerization (usually a degree of polymerization of 3000 to 7000)
) of the above-mentioned hydrophobic polymer resin solution with a low degree of polymerization (degree of polymerization 250) dissolved in a solvent such as 1 water and ethyl alcohol.
A hydrophilic polymer of o to 5ooo) is added to prepare an emulsion in which the hydrophilic polymer is dispersed in a core hydrophobic polymer. At this time, the hydrophilic polymer is compared to the hydrophobic polymer,
When added in an amount of 5 to 35% by weight, preferably 10 to 25%, the resulting porous body will have an appropriate moisture absorption ability.

Then, the obtained emulsion bottle is heat-treated in an inert gas flow with a nitrogen ring at a temperature of 100 to 250° C. for a time of 0.5 to 8 hours. At this time, the emulsion seal is thermally cured, but at the same time, the solvent that dissolves the hydrophilic polymer evaporates, and the escape holes are cured as they are, resulting in a porous structure as a whole.

The porous body thus produced is applied in the following manner to obtain the air battery of the present invention. In other words, first
In this embodiment, the above-mentioned emulsion mesh is impregnated into cellulose nonwoven fabric, nylon paper, a foamed polystyrene resin plate having minute ventilation holes, a porous molded body made of activated carbon powder bound with PTFE, a mat made of various synthetic fibers, etc. The whole is heated to foam the emulsilon, and the resulting porous body is filled into the air chamber. In the second embodiment, the emulsilon is applied to the air side surface of the gas electrode to a predetermined thickness and then foamed. In a third embodiment, the emulsilon is applied to a smooth surface such as a nickel plate or a hard chrome-plated copper plate, and then foamed.
This is peeled off, and the resulting porous membrane is attached to a gas plate or filled into an air chamber. In any case, in the air battery of the present invention, the porous body of the present invention must be in contact with the air side surface of the gas electrode.

Although the above explanation takes a butane type air battery as an example, the present invention is not limited to this, but can be applied to a cylindrical type battery such as LR-8,
Needless to say, it can also be applied to square air batteries.

[Embodiments of the invention]

Emulsilon having the specifications shown in Table 1 was prepared.

An activated carbon-PTFE sheet with 20 micropores with a pore diameter of 15 μm was immersed in the above four types of Emulsilon, and 1O
The impregnation treatment was carried out under reduced pressure of Torr. The obtained sheet was heat-treated at 120° C. for 6 hours in a nitrogen stream. The weight of the seat has increased by approximately 15 inches.

These sheets were then attached to the air side surface of the gas electrode to assemble four air cells as shown in FIG. For comparison, PT with a thickness of 0 or 1 arm was placed on the air side surface of the gas electrode.
A battery with an FE membrane attached was also assembled.

These five batteries were left in air at a temperature of 25°C and a relative humidity of 50°C, and the discharge capacity was measured according to a conventional method, and the relationship between the number of days left and the rate of deterioration of the discharge capacity was investigated. The results are shown in Figure 2 and circled.

In addition, the weight of the battery was measured at each point in time when the battery was left unattended, and the change in weight was investigated. Both weights decreased. The weight loss (■) is shown in Table 2.

〔Effect of the invention〕

As is clear from the above explanation, the air battery of the present invention suppresses the dilution and concentration of the electrolyte, and as a result, maintains its discharge characteristics over a long period of time, and its storage characteristics are also significantly improved, making it useful. be.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway vertical cross-sectional view of a typical alkaline-air battery, and FIG. 2 is a diagram showing changes over time in the discharge capacity deterioration rate of the battery of the present invention and a comparative battery. 1... Cathode mixture, 2... Senotarator, 3... Gas electrode, 4... Sealing plate, 5... Gasket, 6...
Outer can, 7...air chamber, 8...air intake. Figure 1 Figure 2 Our III (+3)

Claims (1)

[Claims] 1. An air battery having a structure in which a porous body made of a hydrophobic polymer and a hydrophilic polymer is in contact with the air side surface of a gas electrode. 2. The porous body has 10 fine pores with a pore diameter of 1 μm or less.
The air battery according to claim 1, which has a distribution of .about.70 times.