JPS5935360A - Zinc electrode - Google Patents

Abstract

PURPOSE:To increase cycle life by forming a zinc electrode of an alkaline electrode with an active material prepared by adding hydrophilic short fiber, an additive, and a binder to zinc oxide powder and metal zinc powder both having a specified particle size. CONSTITUTION:Zinc oxide powder having a particle size of 0.1-0.5mu, and metal zinc powder having a particle size of 1-6mu and rayon short fiber are mixed. Polytetrafluoroethylene dispersion and water are added to above mixture and they are kneaded. A paste sheet made of the kneaded material is kept in contact with an anode current collector to form a zinc electrode 1. The zinc electrode 1 is combined with a sintered nickel electrode 2 with an electrolyte absorbing layer 4 and a separator 3 interposed, and they are accommodated in a container 5 to form a nickel-zinc storage battery. Crystal growth of an active material and deformation of an electrode plate are prevented, and electrolyte is supplied smoothly and cycle life is increased.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a zinc electrode that can be applied to alkaline storage batteries that use silver oxide, nickel oxide, etc. as a positive electrode active material and an alkaline solution as an electrolyte. By controlling the particle size of the substances metal zinc and zinc oxide and adding hydrophilic short fibers, we prevent the crystal size of the negative electrode active material from becoming coarser due to charge and discharge cycles, and suppress the deformation of the zinc electrode plate. At the same time, the purpose is to smoothly supply the electrolyte into the zinc electrode, to minimize the decrease in battery capacity, and to improve the cycle life of the battery.

[Background technology]

Conventionally, zinc storage batteries that use metallic zinc as an active material in the negative electrode have high energy density and are less polluting because zinc is cheap and has a lower rank in alkaline electrolytes than cadmium electrodes. Since there is little to worry about, many practical applications have been abandoned.

However, there are drawbacks such as a lack of reliability due to a short circuit phenomenon between the positive and negative electrodes due to zinc tendrite during the charge/discharge cycle, and difficulty in obtaining a long cycle life due to significant deformation of the zinc electrode during the charge/discharge cycle. be. This is due to the fact that zinc is an electrode that is soluble in an alkaline electrolyte.

Thus, it is known to use a mixture of metallic zinc and zinc oxide as a zinc active material. However, conventionally used metallic zinc has a particle size of several tens of micrometers to several hundred micrometers, and practical zinc has a particle size of several tenths of a micrometer, which is 2 times smaller than that of metallic zinc.
The particle size is three orders of magnitude smaller. As described above, the particle size of conventional metallic zinc is particularly large compared to the particle size of zinc oxide, resulting in the following drawbacks. First, since the difference in particle size is as large as two to three orders of magnitude, metallic zinc and zinc oxide are not mixed uniformly. Second, because the particle size is large, even if the same amount of metallic zinc is mixed, there are fewer rice grains than the number of grains that can form the nucleus of electrodeposition, so the zincate ions, which are discharge products, will be absorbed during the next charging. It becomes difficult to electrodeposit in the original position.

Thirdly, since the particle size of the original metal zinc is large, it quickly grows into coarse zinc particles that become the core of dendrite generation.

In order to deal with this problem, a patent application was filed in 1983 to regulate the particles of metal zinc powder and zinc oxide powder, which are active materials.
It was proposed in No.-41843. That is, the particle size of the metal zinc powder is 1 to 6 μm, and the particle size of the zinc oxide powder is 0°1 to 0.5 μm. By regulating the particle size in this way,
It is possible to prevent the crystal size of the active material from becoming coarser due to charging and discharging cycles, suppress deformation of the electrode plate, minimize capacity decrease, and improve the cycle life of the battery.

However, when charge and discharge cycles are repeated over a longer period of time, the regulated zinc particles gradually become coarser and denser, and the number of cleaved zinc particles, which form the core of zinc electrodeposition, decreases. do. As a result, non-uniform electrodeposition occurs, reducing the active area of the zinc electrode and reducing its porosity, which impedes the supply and diffusion of the electrolyte inside the zinc electrode, resulting in a decrease in discharge capacity. It becomes noticeable.

[Disclosure of the invention]

The present invention has been devised in view of these points, and is intended to alleviate the above-mentioned problems and improve the cycle life of a storage battery when applied to a storage battery. That is, the present invention uses zinc oxide powder having a particle size of 01 to 0.5μ and zinc oxide powder having a particle size of 1 to 6μ.
The zinc electrode is composed of a zinc active material of metallic zinc powder having a particle size of , hydrophilic short fibers, additives, and a binder. As is clear from this configuration, the present invention suppresses deformation of the zinc electrode and improves the cycle life of the battery by regulating the particle size of the active materials, metal zinc powder and zinc oxide powder. Due to the presence of short fibers,
The purpose is to further improve cycle life by smoothing the supply and diffusion of electrolyte into the zinc electrode.

〔Example〕

A comparative example will be explained below along with a detailed explanation of the present invention.

Example: 100% by weight of zinc oxide powder with a diameter of 0.1 to 0.5μ, 10% by weight of metallic zinc powder with a particle size of 1 to 6μ, 2% by weight of mercury oxide, and 1% by mass of short It fibers of rayon were mixed. Add 5% by weight of polyfluoroethylene at a concentration of 60% and 50% by weight of water to the mixed powder, and knead while applying strength. The obtained kneaded material is rolled using a rolling roller. The paste sheet was rolled to a thickness of Qmm, and the paste sheet was brought into contact with both sides of the cathode current collector, and the paste sheet was rolled and crimped to obtain a zinc electrode with a thickness of 1.5 m.

A nickel-zinc storage battery (A>) with a capacity of 2AH was created using five of these zinc negative electrodes and four well-known sintered nickel electrodes.

In addition, conventional metallic zinc powder with a size of several tens of microns to several hundred microns can be produced by melting the metallic zinc once in a reducing atmosphere and blowing it off in the form of a spray from a nozzle, but with the present invention. The metal zinc powder used has a size of 1 to 6 microns and is obtained by melting metal zinc in a reducing atmosphere, evaporating it, and condensing it.

Figure 1 is a cross-sectional view of this M battery (A>. In this drawing, (1) is a zinc electrode, (2) is a nickel electrode, and (3) is a nickel electrode.
is a separator, (4> is a liquid retaining layer, (5) is a battery case, (6)
is the battery case lid, and (7) and (8) are the positive and negative terminals.

Comparative Example For comparison, a storage battery (B) was prepared which was the same as the storage battery/It2 (A>) of the example except that short fibers were not used.

Figure 2 shows a storage battery (A) using zinc electrodes according to the present invention and a comparative battery 7'II! (B) is a charge/discharge cycle characteristic diagram. The charging and discharging conditions are: After charging at 400mA for 5 hours,
At 500mA, the battery voltage is 1. Discharging is performed until it reaches OV. Figure 2 shows the initial capacity as 100 as the discharge capacity.
Shown as

It can be seen from FIG. 2 that the cycle characteristics of the storage battery (A) using the zinc electrode according to the present invention are improved compared to the cycle characteristics of the comparative battery (B).

The reason for this improvement is thought to be that since the short fibers made of rayon are hydrophilic, they facilitate the supply and diffusion of the electrolyte to the zinc electrode where the electrolyte is insufficient. Examples
Although we have shown examples of short fibers, other hydrophilic short fibers, such as natural fibers such as cotton linters, hemp, and conotons, can be used as long as they are hydrophilic and do not adversely affect the charge/discharge reaction. Synthetic fibers such as nylon, polypropylene, and polyethylene treated with parent wood, or a blend thereof can be used. In addition, the fiber length is 5 for uniform mixing.
It is desirable that the thickness be less than mm. If the short fiber content is less than 0.1% by weight, it has almost no effect, and if it is more than 25% by weight, it reduces the filling amount of the zinc active material and causes an increase in the internal resistance of the zinc electrode. It is preferably about 25 to 25% by weight, preferably 0.3 to 10% by weight.

〔effect〕

As described above, the present invention regulates the particles of metal zinc powder and zinc oxide powder, which are the active materials of the zinc electrode, and also adds hydrophilic short fibers to the negative electrode active material during charge and discharge cycles. It not only prevents the crystal diameter from becoming coarser, but also suppresses the deformation of the zinc electrode, and also facilitates the supply of electrolyte inside the zinc electrode, thereby extending the cycle life of a storage battery using this zinc electrode. It is of great value to the T industry, such as being able to reduce

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an alkaline zinc storage battery using the zinc electrode according to the present invention, and FIG. 2 is a cycle characteristic diagram of an alkaline zinc storage battery using the zinc electrode according to the invention and a comparative battery. ＼－Stopichi・′

Claims (1)

[Claims] (ljo, zinc active material of zinc oxide powder with a particle size of 1 to 0.5 μ and metal zinc powder with a particle size of 1 to 6 μ;
A zinc electrode consisting of hydrophilic short fibers, additives, and a binder.