JPS59101768A - Manufacture of negative electrode for alkaline battery - Google Patents

Abstract

PURPOSE:To provide a negative electrode for an alkaline battery having uniform filling amount and increased discharge capacity by coating one side of porous synthetic resin film with a gelled negative electrode prepared by dispersing amalgamated zinc powder in a water soluble high molecule solution. CONSTITUTION:A gelled negative electrode prepared by mixing amalgamated zinc powder in a gelled solution of a water soluble high molecule is spreaded on the one side of a porous synthetic resin film, or a woven or nonwoven sheet, and it is dried and cutted in a desired shape to form a negative electrode for an alkaline battery. When this negative electrode is used, the scattering of the filling amount of the negative active material is decreased, and the filling amount is uniform. Thereby, discharge capacity of a small battery is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a negative electrode for use in alkaline batteries such as silver oxide batteries and alkaline manganese batteries, particularly thin batteries.

Conventional configuration and problems This type of alkaline battery is widely used as a power source for cameras, calculators, electronic watches, hearing aids, etc. In recent years, with the rapid diversification and increased production of these consumer devices,
Demand has increased significantly, and products of various sizes are being produced. The above-mentioned consumer equipment includes ICs and LS that make up the circuit.
Due to the continuous progress in integrated circuit technology such as I, it has become possible to make devices smaller and thinner, so smaller and thinner batteries have come to be used as power sources.

Most of the above-mentioned small and thin consumer devices are required to be able to be used for a long period of one year or more with one battery charge, so the battery used as a power source must be discharged as much as possible. Something with capacity is required.

Various attempts have been made in the past to meet the above-mentioned requirements for small, thin alkaline batteries. For example, a button-type alkaline battery needs to be of a specified outer diameter and height, but in order to make the most of its limited volume, the battery's positive position must be adjusted to make the most of its limited volume.

Attempts have been made to increase the filling rate of the active material by reducing the thickness of the container that houses the negative electrode active material to increase its internal volume, or by changing the shape of the container.

Although these methods improve the battery's discharge capacity to a certain extent, thin containers have a poor yield in the parts manufacturing process, and if too strong external force is applied during the battery manufacturing process, they may become deformed. problems are likely to occur. In addition, the method of changing the shape of the container uses a mechanical caulking seal to prevent leakage of the electrolyte inside the battery, so in order to change the shape, it is necessary to drastically change the sealing process.
There are disadvantages in that it is expensive and requires a long period of time because sufficient confirmation of leakage resistance is required.

In other words, although the increase in discharge capacity due to shape change was small, it was not a practical improvement method considering the cost and time required.

In addition, attempts have been made to increase the discharge capacity by reducing the thickness of the separator and liquid-containing material that separate the positive and negative electrodes to increase the amount of positive and negative electrode active materials filled.
With this method, a problem sometimes occurs in which the open circuit voltage of the battery decreases after long-term storage, so it was not an acceptable method.

On the other hand, in this type of -alkaline battery, the electric capacity of the positive electrode active material is designed to be larger than that of the negative electrode active material in order to prevent the generation of hydrogen crabs due to the withdrawal tK. To explain in more detail, the design is such that the maximum capacitance, taking into account the variation in the filling of the negative electrode active material, is less than the minimum capacitance, taking into account the variation in the filling of the cathode active material. In other words, the discharge capacity of this type of alkaline battery is controlled by the filling amount of the negative electrode, and the discharge capacity of the battery can be improved by reducing the filling variation of the positive and negative electrode active materials. silver oxide.

The positive electrode active material such as manganese dioxide is normally used as a fine powder, so the filling variation is almost negligible. 200~ alloyed with metallic mercury
In this method, a negative electrode powder of 48 mesh size is mixed with water-soluble polymer powder, and only the amount to be filled into a certain volume of space is mechanically measured and filled using a mass cutting method.

Therefore, due to the shape and particle size distribution of the frozen zinc powder, the particle size distribution of the water-soluble polymer powder, the bulk specific gravity, etc., the filling variation of the mixed negative electrode powder negative electrode active material, which is a mixture of the frozen zinc powder and the water-soluble polymer powder, may be caused in the battery. This results in variations in discharge capacity. In addition, in order to account for the above-mentioned variations in the positive and negative electrode capacities, the average negative electrode filling amount was reduced, and the discharge capacity of the battery had to be reduced at the design stage. In particular, as the battery size becomes smaller and thinner, the variation in negative electrode filling capacity increases significantly.For example, tJfJIs product number 5R44 and 5R62.
Comparing the filling capacity variation of 1, it is about 5 times more ±5R62
The variation in 1 becomes large.

For this reason, several attempts have been made to reduce the variation width using the negative electrode powder weighing method described above. For example, one method is to make the frozen zinc powder into a certain shape such as a sphere to make the particle size distribution uniform, the other is to make the water-soluble polymer retain some moisture so that it is difficult to separate from the frozen zinc powder. Furthermore, attempts were made to improve the weighing equipment. However, even if the above improvement methods are combined, according to the square measurement method, the above-mentioned 5R
It was impossible to reduce the variation in negative electrode filling amount in 621 to 4@ or less compared to the conventional product 8R44.

OBJECTS OF THE INVENTION In view of the above, an object of the present invention is to provide a method for obtaining a negative electrode with a constant filling amount in order to improve the discharge capacity of a small battery.

Structure of the Invention The present invention does not use the above-mentioned negative electrode filling method using the mass cutting method, but instead uses a porous synthetic resin to fill a gel negative electrode in which frozen zinc powder, which is a negative electrode active material, is uniformly dispersed in an aqueous solution of a water-soluble polymer. It is characterized by applying it to one side of a film, woven fabric, or non-woven fabric, drying it, and then cutting it into a certain shape.

According to the present invention, it is possible to reduce the filling variation width of the negative electrode, thereby reducing the variation in the discharge capacity of the battery, and in particular, it is possible to improve the discharge capacity of a small thin alkaline battery.

The illustrative drawings of the embodiments show button-type silver oxide batteries. 1 is a metal sealing plate that also serves as a negative electrode terminal, 2 is a gas sealing plate, and 3 is a cylindrical gold case with a bottom.A mixed powder of silver oxide and graphite is preformed into a tablet shape on the inner bottom of the case 3. The mixed material 4 is press-bonded together with the positive electrode ring 6. Reference numeral 6 denotes a separator made of a porous synthetic resin film, such as a porous polypropylene film or acrylic kraft polyethylene.

7 is a negative electrode, which is made of a porous synthetic resin film, or a woven or nonwoven fabric 7a of synthetic resin fibers, with a layer 7b containing frozen zinc on one side thereof.

To explain in more detail, a gel-like aqueous solution with a concentration of 0.6 to 8.0% by weight of an alkali metal salt of carboxymethylcellulose, an acrylic acid polymer or a copolymer is prepared, and this is sieved through a 100 mesh sieve. Add frozen zinc powder with a particle size that passes through the water so that the mixing ratio is 30 to 70% by weight, and then uniformly mix it on one side of a porous film or woven or nonwoven fabric made of polyethylene, polypropylene, nylon, etc. The material was applied to the surface, dried under reduced pressure at a temperature of 70 to 8°C, and then cut into a predetermined shape.
After inserting into the inner surface of the metal sealing plate 1, inject an alkaline electrolyte made into a thin gel with an alkali metal salt of carboxymethyl cellulose, an alkali metal salt of an acrylic acid polymer, or a copolymer, or only an alkaline electrolyte to absorb the liquid. This is what I did.

When creating the above negative electrode, the uniformity of the gelled negative electrode obtained by adding frozen zinc to the gelled water bath solution and the adhesion to the synthetic resin film, woven fabric, or nonwoven fabric are determined by the water-soluble polymer Although it depends on the material, if the concentration of the water-soluble polymer, the particle size of the frozen zinc powder, and the addition rate to the gelled aqueous solution are appropriately adjusted within the above range, a gelled negative electrode that can be applied uniformly can be created. can get. However, if the concentration of the water-soluble polymer is less than 0.5% by weight, a gel-like water bath liquid cannot be obtained;
- If it exceeds 0% by weight, the viscosity of the gel-like aqueous solution will be high, making it impossible to uniformly mix the frozen zinc. Furthermore, if the particle size of frozen zinc is too coarse to pass through a 10.0 mesh sieve, it will become an obstacle during cutting. Furthermore, the mixing ratio of frozen zinc powder to the gel-like aqueous solution is 70% by weight.
If it exceeds 30 wtcIbK, the adhesion is good, but if it is less than 30 wt cIbK, the presence rate of the negative electrode frozen zinc powder per certain area decreases, making it difficult to achieve the desired increase in filling capacity. It disappears.

Note that the time required for drying by heating under reduced pressure can be shortened by adding several grams of ethyl alcohol or the like that is compatible with water to the water-soluble polymer aqueous solution in advance. Further, the shape to be cut is usually circular, but it is also possible to cut it into a donut shape or a polygon.

The negative electrode 7 thus obtained is inserted into the sealing plate so that the layer 7& is on the separator side and the layer 7b is on the sealing plate side.

The filling capacity of the negative electrode obtained in this way varies slightly depending on the coating thickness and cutting shape of the gelled negative electrode.
5R6 against the variation of the conventional product 5R44 shown above
It is now possible to suppress the variation in 21 to within 1.6 times, and the 8R621
The discharge capacity can be improved by 10 to 15 inches. Furthermore, this negative electrode can be automatically manufactured in a nearly continuous process, making it possible to simplify the battery assembly process.

Next, specific examples will be shown. Add 60 parts by weight of 160 to 200 mesh frozen zinc powder to 1f4o parts by weight of an aqueous solution containing 2% by weight of sodium salt of carboxymethyl cellulose, and apply it to one side of a porous polypropylene film,
JIS product number 5 using the negative electrode obtained by cutting into circular shapes after drying.
We made a prototype R621-shaped battery man. In addition, as a comparative example, a battery B of the same size was prototyped in which the negative electrode was filled using the conventional powder mass cutting method. The following table shows the variation R in discharge capacity and the average discharge capacity of 10 of these battery cans when they are continuously discharged under a load of 30Ω until the discharge voltage drops to 1.2 volts.

As is clear from this table, the battery using the negative electrode according to the present invention has a discharge capacity variation of approximately 21 yen, and the average discharge capacity is approximately 19% higher than the conventional battery B. .

Effects of the Invention As described above, according to the present invention, it is possible to reduce the range of dispersion in discharge capacity, and thereby it is possible to particularly improve the discharge capacity of small and thin alkaline batteries.

[Brief explanation of the drawing]

The drawing is a cross-sectional side view of a main part of a button-type silver oxide battery according to an embodiment of the present invention. 4...Positive electrode, 6...-Separator, 7.
...Porous film, 7a...Porous film, 7
b...--Painting layer.

Claims (1)

[Claims] A gel-like negative electrode made by dispersing frozen zinc powder in an aqueous solution of a water-soluble polymer is applied uniformly to the surface of a porous synthetic resin film or woven or non-woven fabric, and after drying, it is cut into a certain shape. A method for producing a negative electrode for alkaline batteries characterized by the following.