JPS5931184B2 - alkaline battery - Google Patents

Description

Detailed Description of the Invention The present invention relates to the improvement of zinc cathode bodies in alkaline batteries such as nickel-zinc batteries, silver-zinc batteries, and alkaline manganese batteries. The purpose is to measure improvement.

In the zinc cathode used in this type of battery, particles of the zinc cathode active material are conventionally bonded together using a water-soluble binder such as boxymethyl cellulose or polyacrylate, or a hydrophobic binder such as polyfluoroethylene or polypropylene. It is being used to integrate them.

A zinc cathode body molded with a water-soluble binder can effectively retain the electrolyte necessary for discharge near the zinc cathode active material, but on the other hand, the strength of the electrode plate decreases due to penetration of the electrolyte.
If the bond between each active material particle is poor, the electrode plate may collapse due to gas generation that occurs during discharging or charging, or the binder may dissolve in the electrolyte when the battery is stored at high temperatures. Due to deterioration, the function of the binder is reduced and the discharge efficiency of the zinc cathode active material is poor.

On the other hand, hydrophobic binders are stable against electrolytes and high temperatures, but the electrolyte does not permeate through the zinc cathode body molded using it, so most of the electrolyte injected during battery assembly is absorbed into the anode and separator. If the binder is not uniformly distributed in the cathode, the electrolyte will be distributed unevenly and a uniform discharge reaction will not occur.

In particular, the amount of hydrophobic binder added greatly affects the amount of electrolyte in the cathode and the state of its distribution, so strict work management is required. The present invention overcomes the above-mentioned drawbacks by using an ethylene-acrylic acid polymer as the binder in the zinc cathode body.

Polymers of ethylene, acrylic acid, and lylic acid are produced by adding about 0% acrylic acid to 100 parts by weight of ethyl in the presence of a polymerization initiator such as benzo peroxide, yl peroxide, and lauryl peroxide (tertiary butyl peracetate). It is obtained by reacting the polymer in a proportion of .1 to 1 part by weight, and this polymer is mixed with potassium hydroxide,
By adding it to a solution of sodium hydroxide, ammonia, etc. and stirring it, it becomes an emulsion. V) This solution maintains a stable emulsified state for a long period of time even without the use of an emulsion agent.

Next, embodiments of the present invention will be described with reference to the drawings.

An emulsion of a zinc active material and a copolymer prepared so that the solid content of the ethylene-acrylic acid polymer is about 0.3 parts by weight relative to about 15 parts by weight of zinc oxide powder (solid content of about 10 parts by weight).
~30% by weight) is applied to a cathode current collector 1 made of expanded metal, punched metal, wire mesh, etc., and dried at 60 to 90°C to form a binder made of the copolymer. A zinc cathode 2 is formed by bonding the particles of the cathode active material to each other. This zinc cathode 2 is bent into a U-shape, and its side surface is covered with a semipermeable membrane 3 made of polyvinyl alcohol, cellophane, etc. that does not allow zincate ions to pass through, and the outside thereof is made of a polypropylene nonwoven fabric treated with hydrophilic material to absorb electrolyte. Nickel anode 5 through body 4
and inject an alkaline electrolyte to assemble a nickel-zinc battery with a discharge capacity of 600 mAh.

Reference numeral 6 denotes a ventilation member made of a non-woven fabric of fluorine resin fibers inserted into the center of the zinc cathode 2, and is a spacer for guiding oxygen gas generated from the anode 5 to the side surface of the cathode 2 during charging so that it disappears.

The addition range of ethylene-acrylic acid polymer is zinc oxide 1
The amount is about 0.5 to 15 parts by weight, preferably about 1 to 10 parts by weight, based on 00 parts by weight.

A nickel-zinc battery A according to the above example, a battery B of the same shape with a zinc cathode molded with a binder made of carboxymethyl cellulose, and a battery C of the same shape with a zinc cathode molded with a binder of polyfluoroethylene. , 45
Figure 2 shows the rate of deterioration of the discharge capacity of the battery when it is repeatedly charged and discharged at ℃.

As is clear from this, in battery B using a water-soluble binder, the zinc cathode collapses significantly under high temperature and gas generation conditions, and in battery C using a hydrophobic binder, the zinc cathode collapses significantly. Because the amount of electrolyte held is small and the distribution of the electrolyte is not uniform, the performance deteriorates due to repeated charging and discharging. Compared to these, the battery according to the present invention has
As will be described later, since it has a stable binding function and good ionic conductivity, there is little deterioration in discharge capacity and the performance is stable. The present invention is configured as described above.
, the binder made of ethylene-acrylic acid polymer does not undergo deterioration when dissolved in the electrolytic solution even at high temperatures.
Since it has the property of agglomerating when mixed with the cathode active material powder, the binding between the active materials is stable.

Furthermore, the polymer is hydrophilic, but when it contains an electrolyte, it has ionic conductivity and is lyophilic, so the electrolyte has good permeability to the negative electrode, allowing the electrolyte necessary for discharge to enter the negative electrode. Since it can be held well and the distribution of the electrolytic solution is uniform, it is possible to increase the discharge efficiency of the zinc negative electrode active material and improve the discharge performance. Additionally, when a small amount of alkaline earth metal hydroxide such as calcium hydroxide is added to the zinc active material,
The binding force of the ethylene-acrylic acid polymer as a binder increases, and the charging/discharging efficiency of the zinc electrode increases.

At this time, the addition range of the hydroxide is preferably 0.5 to 4 parts by weight per 15 parts by weight of zinc oxide. Furthermore, in a battery of the type in which oxygen gas generated from the anode during charging is guided to the cathode and disappears as in the example, the binder made of ethylene-acrylic acid polymer has excellent oxidation resistance. There is no risk of deterioration due to generated oxygen gas.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a battery according to the present invention, and FIG. 2 is a diagram showing the charging and discharging characteristics of the battery. 2...Zinc cathode.

Claims (1)

[Claims] 1. An alkaline battery characterized by using a zinc cathode body in which particles of zinc cathode active material are integrated with each other using a binder made of ethylene-acrylic acid polymer.