JPH0348619B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a zinc negative electrode that is used at a low or zero rate in an alkaline electrolyte containing an alkali metal hydroxide as the main electrolyte. [Technical background of the invention] Zinc powder or zinc alloy powder, which is generally a negative electrode material for alkaline batteries, can be produced by various methods, but the most widely used is 4N (purity
Zinc powder consisting of a group of irregularly shaped particles obtained by atomizing using high-purity electrolytic zinc (99.99%) or higher, with a particle diameter (minor axis) of about 60 μm to 350 μm, and a shape index of 2.0 to 2.3. The zinc oxide content is about 0.2% to 0.3% by weight. [Problems in the background art] Such zinc powder has a low hydrogen overvoltage in an alkaline electrolyte, and also has a relatively low chemical polarization when discharged in a battery where the amount of electrolyte is actually extremely limited. Because of their large size, they are usually amalgamated to various degrees depending on the type, structure, and intended use of the battery.
In this case, the filtration rate is in the range of 5% to 25% by weight as a weight ratio of the bulk zinc filtrate powder, and in particular, a ratio of 6% to 12% by weight is often used. Further, the zinc oxide content is often about 0.4% by weight to 0.9% by weight. The presence of a large amount of mercury in the negative electrode is undesirable because it inevitably leads to a decrease in the amount of active material within the volume that the negative electrode is designed to occupy within the battery, resulting in a decrease in battery capacity. Furthermore, as is well known, mercury is a pollution control substance, and reducing its usage has become a particularly strong social demand in recent years. Research has been widely conducted to reduce the amount of mercury added in negative electrode zinc, and the main methods of improvement include zinc alloy composition, surface treatment of zinc particles, and addition of corrosion inhibitors to alkaline electrolytes. It is about addition. Among these, one of the most basic methods is the addition of a third metal element that increases the hydrogen overvoltage by alloying with zinc and does not impede the discharge characteristics. Most of the elements proposed as such are metallic elements belonging to groups b, b, b, b, b, and b of the periodic table. Zinc alloys for this purpose are being obtained to a certain level through research, but these zinc alloys cannot be pulverized and made into a non-oxidized state, or at least with a lower percentage of oxidation than before. When used, it has not been found to have a hydrogen gas generation suppressing effect comparable to that of conventional zinc oxide powder with a high oxidation rate, and has not been put to practical use as a negative electrode active material for commercial alkaline batteries. [Objective of the Invention] The main object of the present invention is to improve the chemical composition and physical properties of negative electrode zinc powder or zinc alloy powder for alkaline batteries, thereby achieving significantly lower levels than those of the prior art. Even if it is used in a state of oxidation or no oxidation, it generates less hydrogen gas in the battery to the extent that it is comparable to the currently used zinc powder with a high oxidation ratio, and therefore has good storage characteristics. It is to provide a zinc battery. [Summary of the invention] That is, in the method of the present invention, by adding a small amount to zinc and alloying it, multiple types of metallic elements are added that provide a corrosion-preventing effect in an alkaline electrolyte and do not impede the polarization characteristics. When granulating the zinc alloy to a predetermined practical particle size or an average particle size, the atomized zinc alloy powder has a significantly larger bulk specific gravity than conventional products, and is used in alkaline batteries. By using it as a negative electrode active material, hydrogen gas generation within the battery can be suppressed to a practically sufficient level even when used at a significantly lower rate of oxidation or no oxidation compared to conventional products. This is what I did. [Examples of the Invention] The details of the present invention will be explained below using Examples.
Table 1 shows a comparison of the hydrogen gas generation rate, bulk specific gravity, average shape index, and zinc oxide content in an alkaline electrolyte between the sprayed zinc alloy powder according to the present invention and the sprayed zinc alloy powder according to the prior art. In Table 1, the hydrogen gas generation rate is determined by immersing 10 g of the test sample in 10 ml of a 35% KOH solution saturated with zinc oxide, degassing it for 30 minutes under a reduced pressure of several torr, and then cleaning the electrolyte surface with liquid paraffin. This is when the sample was filled and left at 60℃ for 174 hours. Also, the average shape index is
When the length of each particle in the maximum direction is l (major axis) and the maximum length in the direction perpendicular to the l axis is s (minor axis), l/s expresses the deformation degree of the particle in terms of slenderness. This is the shape index. Atomized zinc powder in practical use includes various shapes.
It is simplest and most practical to use the average shape index to indicate the degree of deformation of these particles. The shape index of the commonly used atomized zinc particles is that most of the particles are
The average shape index is about 1.8 to 3.6, and the average shape index is about 2.0 to 2.3. The particle size or particle size distribution shown by classifying a certain powder using a standard sieve and a shaker is approximately the particle size or particle size distribution of the short diameter s described above, if the classification conditions are appropriate. .

[Table] In Table 1, D and E are examples of the present invention, A is a conventional example, and B and C are comparative examples. That is, A in Table 1 is a typical conventional product, in which electrolytic zinc with a purity of 4N is granulated by the atomization method in the air, and then 100μ
This is an atomized zinc powder with a viscosity ratio of 6.5% by weight, which is obtained by classifying the zinc powder into particles in the range of 300 μm to 300 μm and atomizing it with metallic mercury in a dilute NaOH solution. The bulk specific gravity of this product is slightly large at 3.12 g cm ^-3 , but this is because the true specific gravity is increased due to the high mercury content. The specific gravity is usually around 2.5g·cm ^-3 to 2.8g·cm ^-3 . Next, B in Table 1 is a comparative product, in which a zinc alloy containing 0.20% by weight of lead, 0.18% by weight of gallium, and 0.06% by weight of tin is granulated by the atomization method in the air.
After classification, a rare product containing the required amount of mercuric chloride
This is a low-fragility atomized zinc alloy powder with a viscosity rate of 1.37% by weight, obtained by treatment in a CH ₃ COOH solution and viscosity. C in Table 1 is also a comparative product with 0.15% lead by weight.
This is an atomized atomized zinc alloy powder obtained by atomizing a zinc alloy containing 0.13% by weight of gallium and 0.025% by weight indium in the atmosphere, and then classifying it into particles in the range of 100 μm to 300 μm. In Table 1, D and E each represent an example of the present invention, and D has the same composition as B above.
A Ga-Sn based quaternary alloy is granulated by an atomization method in a nitrogen atmosphere, then classified to have a particle size of 100 μm to 300 μm, and then treated in a dilute CH ₃ COOH solution containing the required amount of mercuric chloride. Obtained conversion rate
It is a 1.34% by weight low-fragility zinc alloy powder. Also E
is an aqueous atomized zinc alloy powder in which a Zn-Pb-Ga-In quaternary alloy having the same composition as C is granulated by the atomization method in a nitrogen gas atmosphere and then classified to have a grain size in the range of 100 μm to 300 μm. It is. As can be seen from the hydrogen gas generation rates in Table 1 B and C, multiple metallic elements selected from the group of elements belonging to Group b, Group b, Group b, Group b, and Group b of the Periodic Table. Even when the atomized zinc alloy powder to which an effective combination of the following is added is used at a lower rate of oxidation or no oxidation than conventional products, hydrogen gas generation is greatly reduced. In other words, with atomized zinc powder made in the same way from electrolytic zinc with a purity of 4N, for example, in the case of non-grading, even at a test temperature of 45°C, the 60% in Table 1 C is
This is because the hydrogen gas generation rate is several tens of times higher than the value at ℃. However, it can be seen that the amount of hydrogen gas generated is still large compared to the conventional products with a high conversion rate shown in Table 1A. On the other hand, in the case of the zinc spray alloy powder of the present invention shown in Table 1 D and E, which has a large bulk specific gravity, even if it is used with a low viscosity rate of 1.34% by weight or with no viscosity, the It can be seen that the hydrogen gas generation rate is halved compared to B and C, and the hydrogen gas generation rate is close to that of conventional example A, which has a high hydrogenation rate. The reason why the atomized zinc alloy particles having a large bulk specific gravity in the present invention generate less hydrogen gas in an alkaline electrolyte when the particle size is approximately the same has not been fully elucidated. However, according to SEM, differences in particle shape as shown in the drawings are observed. FIG. 1 shows a particle shape model of the atomized zinc alloy powder according to the present invention, and FIG. 2 shows a particle shape model of the conventional powder. In each figure, a is a shape model of a particle with a large diameter, and b is a shape model of a particle with a small breadth. The atomized zinc alloy particles of the present invention shown in Fig. 1 have significantly fewer sharp parts in the particle shape than the conventional product shown in Fig. 2, and the particle ends are rounded as a whole. Almost no wrinkle-like pattern is observed on the surface. In addition, the smaller the particle size, the more spherical it is compared to the conventional product, and there are many particles with a shape index close to 1.0. Corresponding to this change in shape, the average graininess index is also 1.6 to 1.0 in the case of the present invention, compared to about 2.0 to 2.3 in the conventional case. These changes in shape are thought to be the main reason for increasing the bulk specific gravity, but at the same time, it has been recognized that the powder fluidity (flow rate) is also improved because it reduces the friction between particles and makes it difficult to form bridges. There is. Further, as shown in Table 1, the zinc oxide content of the atomized zinc alloy powder having a large bulk specific gravity is extremely small. The zinc oxide content does not significantly affect the hydrogen gas generation rate if it is not excessive, but it tends to cause variations in the amount of hydrogen gas generated, and especially when used in alkaline batteries, the characteristics under harsh usage conditions, such as rapid discharge characteristics at low temperatures. This may deteriorate the pulse discharge characteristics. In addition, zinc oxide is a reaction product of batteries, and excessive inclusion means a decrease in the amount of active material.
It is desirable that the content thereof be as small as possible. [Effects of the Invention] From the above observations, the effects of the present invention can be considered as follows. In other words, from a transient phenomenon point of view, in the conventional case, molten zinc or molten zinc alloy extruded from a nozzle rapidly forms single molecules on the surface of clean droplet-shaped metal particles immediately after being atomized by air blow. An oxide film with a thickness of 1 to 30 mm or more is produced. The formation of an oxide film changes the interfacial tension of the liquid metal particles, and the individual particle shapes cool and solidify below the melting point before they are sufficiently affected by agglomeration due to the interfacial tension. Particles with various irregular shapes are produced depending on the acceleration, direction, gravity, etc., and sharp edges are likely to be formed at the ends of the particles. In addition, the formation of wrinkle-like patterns on the surface of metal particles occurs because the liquid metal particles with an oxide film formed on the surface change shape every moment as they move until they cool and solidify. It is thought that it was produced by repeatedly exposing a surface and reoxidizing that part. On the other hand, in the case shown in the embodiment of the present invention, molten zinc or molten zinc alloy extruded from a nozzle is sprayed into an inert gas atmosphere with high-pressure nitrogen gas, and when granulated, a liquid alloy is formed. Because the particle surface undergoes little or no oxidation, it is more susceptible to agglomeration and spheroidization due to interfacial tension, and the finer particles are less affected by acceleration and gravity until they are cooled below their melting point and solidified. It is thought that it easily becomes spherical. For particles with a large radius, the shape of the particle as a whole is difficult to become spherical and tends to become irregular due to the influence of gravity, etc., but locally the edges of the particle become rounded and the sharp edges are reduced, so the shape index is small. becomes. Furthermore, the particle surface is not affected by the oxide film, so it becomes a relatively smooth surface. From these results, it seems that the average shape index becomes smaller, the friction between particles decreases, improving fluidity and increasing the bulk specific gravity. In addition, these changes bring about some changes in the state of alloy crystals and grain boundaries, as well as in the segregation behavior of unavoidably contained impurity elements and effective additive elements in grain boundaries, and as a result, the hydrogen overvoltage of the sprayed zinc alloy powder according to the present invention increases. It seems that it is getting bigger. In any case, such favorable changes in characteristics are
It was found that by correlating with changes in the bulk specific gravity, it is possible to perform collective management based on the bulk specific gravity. As described above, the present invention is a quaternary alloy in which tin or indium is added to a ternary alloy of zinc-lead-gallium, and the atomized zinc alloy powder formed to have a bulk specific gravity of 3.8 gcm ^-3 or more is used to activate the negative electrode. By using it as a substance, hydrogen gas generation in the alkaline electrolyte is extremely small when used at a low or non-grading rate with a mercury content of 2% by weight or less, and therefore it has good storage characteristics and is environmentally friendly. A preferred alkaline battery can be provided. In addition, by using powder with a large bulk density in this way, the amount of active material in the same negative electrode volume can be increased,
In addition to improving rapid discharge characteristics at low temperatures, it is also possible to obtain gelled zinc negative electrodes that are easy to handle and have little variation in battery filling weight during volumetric measurement in the battery manufacturing process. It's big. The zinc alloy powder of the present invention which has low or no gradient has a so-called gel method in which a gelled zinc mixed with an alkaline electrolyte and an arbitrary gelling agent is used as a negative electrode, and a gelling agent is mainly provided on the surface of the zinc alloy particles. It can be applied to any of the so-called Powder With Gel methods in which a thin layer is formed and then gelled by injecting an alkaline electrolyte into the negative electrode container. The technology of the present invention also applies to various structures (cylindrical, button-shaped, coin-shaped, super It is effective when applied to alkaline batteries (flat type, etc.).

[Brief explanation of drawings]

FIG. 1 is a particle shape model of particles constituting the atomized zinc powder of the present invention, and FIG. 2 is a particle shape model of particles constituting the conventional atomized zinc alloy powder. In each figure, a indicates the particle shape of a large particle, and b indicates a particle shape of a small particle.

Claims (1)

[Claims] 1. In an alkaline battery using a zinc alloy powder with a mercury conversion rate of 2% by weight or less and a particle size of 100 to 300 μm as a negative electrode active material, the zinc alloy powder is a zinc-lead-gallium powder. It is a quaternary zinc alloy made by adding tin or indium to ^a ternary alloy of An alkaline zinc battery characterized by a content of 0.15% by weight or less.