JPH0365620B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to improvement of the negative electrode of a zinc-alkaline battery using zinc as the negative electrode active material, an alkaline aqueous solution as the electrolyte, and manganese dioxide, silver oxide, mercury oxide, oxygen, nickel hydroxide, etc. as the positive electrode active material. It is something. Prior Art A common problem with zinc-alkaline batteries is corrosion caused by the negative electrode zinc electrolyte during storage.
Conventionally, an industrial method has been used to increase the hydrogen overvoltage by using zinc chloride powder containing 5 to 10% by weight of mercury to suppress corrosion to a level that poses no practical problems. . However, in recent years, there has been an increasing social need to reduce the amount of mercury contained in batteries in order to reduce pollution, and various studies have been conducted. For example, lead, cadmium,
A method has been proposed in which alloy powder containing indium, gallium, etc. is added to improve corrosion resistance and reduce the corrosion rate. These corrosion inhibiting effects are
In addition to the effect of a single additive element, the combined effect of multiple additive elements is also large, and systems such as indium and lead or those with gallium added to them, and zinc alloys with gallium and lead added have been proposed as promising systems. has been done. Although all of these can be expected to have a certain degree of corrosion resistance and to reduce the degree of corrosion to some extent, it is necessary to search for an alloy system with even better corrosion resistance. In addition, we mainly aim to improve manganese dry batteries.
There is a proposal that using zinc or a zinc alloy with indium added to the zinc alloy for the negative electrode has a great anticorrosion effect ((Japanese Patent Publication No. 33-3204). Problems to be Solved by the Invention The above proposal As an element in zinc alloys,
In addition to indium, Fe, Cd, Cr, Pb, Ca, Hg,
The description includes cases where one or more of Bi, Sb, Al, Ag, Mg, Si, Ni, Mn, etc. are included as impurities or additives, but when indium and lead are used together as additive elements. Other than the effectiveness of corrosion prevention, there is no clear distinction as to whether each of the miscellaneous elements listed above is added as an impurity or as an effective element, and it is not even clear which elements are effective for corrosion prevention. There is no description of the amount of addition other than indium and lead. It remains a challenge for the future to study the effects of the combination of these elements in zinc-alkaline batteries and to find an effective alloy composition. The present invention aims to provide a zinc-alkaline battery with low pollution and excellent overall performance such as discharge performance, storage performance, and leakage resistance, by reducing the corrosion resistance and discharge performance of the negative electrode zinc. purpose. Means for Solving the Problems The present invention uses an aqueous alkaline solution containing caustic potash, caustic soda, etc. as the main components in the electrolyte, zinc as the negative electrode active material, manganese dioxide, silver oxide, mercury oxide, etc. as the positive electrode active material, The negative electrode of a so-called zinc-alkaline battery that uses oxygen etc. is made mainly of zinc, 0.01 to 0.5% by weight of nickel (Ni), and aluminum (Al).
0.005-0.2% by weight, one or both of indium (In) and thallium (Tl) in a total amount of 0.01-0.5% by weight
It is characterized by using a zinc alloy containing zinc. The present invention focuses on the fact that, among the additive elements or impurities in the conventional zinc alloys, Ni and Al are inexpensive and have no concerns about environmental pollution, but the effects of their addition have hardly been investigated. We conducted experiments on the combined effect of the addition of Al and In and Tl, which have traditionally been considered effective additive elements, and found that with the appropriate combination and content of the additive elements as described above, an extremely remarkable combined anticorrosion effect was achieved. It was completed after discovering what could be achieved. Effect The mechanism of action regarding the anticorrosive effect of adding Ni, Al, In, or Tl alone, and the combined effect of these elements is unclear, but it is inferred as follows. First, although the solubility of Ni in zinc is small, the cooling rate during powderization by the injection method is extremely high, on the order of 10 ³ °C/sec, so the zinc alloy with an appropriate content in the examples described below In powder, Ni may become solution with zinc. Therefore, when a zinc alloy is oxidized from the surface, it is thought that Ni, which has a low affinity for mercury, suppresses the diffusion of mercury into the crystal and contributes to maintaining a high mercury concentration on the surface of the zinc alloy. . On the other hand, there is a concern that the adhesion of mercury to the surface of the zinc alloy may become worse. Also,
Like Al and Ni, it has a low affinity for mercury, so
It is thought that this contributes to suppressing the diffusion of mercury into the interior of the zinc alloy. Furthermore, it has been confirmed that the surface of zinc alloy particles pulverized by the injection method tends to be smoothed by the addition of Al, and the effect of inhibiting corrosion by reducing the reaction surface area is also expected. but
Since Al is a metal that is more base than zinc, it is more likely to corrode than zinc in an electrolytic solution, and it is thought that it is necessary to consider the balance with the anti-corrosion effect mentioned above, and in particular, excessive addition should be avoided. It has been confirmed that corrosion resistance is impaired. In addition, In and Tl increase the hydrogen overvoltage of zinc alloys and are easily compatible with mercury, so when a zinc alloy is made into a grain, it is effective in making the surface uniform by making it into a grain. It is also expected to play a role in fixing mercury at grain boundaries. As mentioned above, each additive element is expected to have a different effect, so the present invention increases the hydrogen overvoltage of the zinc alloy by the combined effect of these elements, and also reduces the mercury on the surface by using a small amount of mercury. We have discovered a zinc alloy composition that maintains a high concentration, has a uniform surface condition, has a small surface area, and has extremely excellent corrosion resistance. In other words, the coexistence of Ni and Al strengthens the ability to suppress the diffusion of mercury into crystal grains, and
In, Tl
By integrating the expected effects of each additive element, we have achieved a significantly improved combined effect of increasing the hydrogen overvoltage of the zinc alloy, making the surface of the zinc chloride alloy uniform, and fixing mercury on the surface and grain boundaries. That's what I got. As described above, the present invention significantly improves the corrosion resistance of the zinc alloy used for the negative electrode, realizes a corrosion-resistant zinc negative electrode with a low rate of deterioration, and provides a low-pollution zinc-alkaline battery with excellent discharge performance and storage stability. It is. Hereinafter, it will be explained in detail using examples. Example: Various zinc alloys were created by adding various elements shown in the following table to zinc ingot with a purity of 99.997% or more.
It was melted at 500°C, pulverized by blasting with compressed air, and sieved to a particle size range of 50-150 mesh. Next, the powder was put into a 10% by weight aqueous solution of caustic potash, and a predetermined amount of mercury was added dropwise to the solution while stirring. Thereafter, it was washed with water, substituted with acetone, and dried to produce a zinc chloride alloy powder. Further, zinc chloride powder or zinc chloride alloy powder other than the examples of the present invention were also prepared in the same manner as comparative examples. The button-shaped silver oxide battery shown in the figure was manufactured using these oxidized powders. In the figure, reference numeral 1 denotes a sealing plate made of stainless steel, the inner surface of which is plated with copper 1'. 2 is a zinc negative electrode prepared by gelling an electrolytic solution of a 40% by weight aqueous solution of caustic potassium saturated with zinc oxide with carboxymethylcellulose, and dispersing zinc oxide alloy powder in this gel. 3 is a cellulose-based liquid retaining material, 4 is a separator made of porous polypropylene, 5 is a positive electrode made of a mixture of silver oxide and graphite and pressure molded, 6 is a positive electrode ring made of nickel-plated iron, and 7 is made of stainless steel. With the positive electrode can,
Its inner and outer surfaces are decorated with nickel metal.
A polypropylene gasket 8 is compressed between the positive electrode can and the sealing plate by bending the positive electrode can. The prototype battery has a diameter of 11.6 mm and a height of 5.4 mm.
The weight of the oxidized powder of the negative electrode was unified to 193 mg, and the amount of mercury added (the oxidized ratio) was 1% by weight based on the zinc alloy powder. The following table shows the composition of the zinc alloy of the prototype battery, and the changes in discharge performance and total battery height after storage at 60°C for one month. The discharge performance is 510Ω at 20℃.
It is expressed as the discharge duration when discharge is performed with a final voltage of 0.9V.

【table】

[Table] Regarding changes in total battery height in this table,
After the battery is sealed, the total height of the battery typically decreases during the period until the stress relationship between the battery components becomes stable over time. However, in a battery where a large amount of hydrogen gas is generated due to corrosion of the zinc negative electrode, there is a strong tendency to increase the total battery height due to an increase in battery internal pressure that counteracts the above-described force for decreasing the total battery height. Therefore, the corrosion resistance of the zinc negative electrode can be evaluated based on the change in total battery height due to storage. In addition, batteries with insufficient corrosion resistance will not only increase the total height of the battery, but also deteriorate leakage resistance due to an increase in battery internal pressure, as well as depletion of zinc due to corrosion, formation of an oxide film on the surface of zinc, and the presence of hydrogen gas. The discharge performance is significantly deteriorated due to inhibition of the discharge reaction by the zinc negative electrode, and the discharge duration also largely depends on the corrosion resistance of the zinc negative electrode. In the table, No. 1 listed as a comparative example of the present invention
~7, when the additive element is added alone (No.
Both the corrosion resistance and discharge performance of the zinc negative electrode were somewhat improved in the cases where two types of elements were added (Nos. 5, 6, and 7) compared to those in Nos. 1, 2, 3, and 4). However, Ni,
Examples of the present invention (No. 9,
In the case of 10, 11, 14, 15, 18, 19, 22, 23, 25, 26,), the corrosion resistance and discharge performance are even better than in the above comparative example, and the combined effect of the added elements is clearly demonstrated. . On the other hand, even when the above three elements coexist, there is an excess or deficiency in their content (No. 8, 12, 13,
16, 17, 20, 21, 24) are not much different from the comparative examples, and the combined effect is poor. As mentioned above, the present invention has succeeded in reducing the rate of reduction by properly combining the above three or four elements and using a zinc alloy in the negative electrode in an appropriate content. The amount of Ni
It is appropriate that the total amount (sum) of one or both of In and Tl be 0.01 to 0.5% by weight, and that Al be 0.005 to 0.2% by weight. As described above, the present invention has discovered that the corrosion resistance of the zinc alloy used for the negative electrode is improved due to the synergistic effect of the combination of the above-mentioned additive elements, and has determined the appropriate content to create a zinc-alkaline alloy with low pollution and excellent practical performance. This is the realization of a battery. In addition, in the examples, a battery using a zinc chloride negative electrode was explained, but in an open air battery or a sealed zinc alkaline battery equipped with a hydrogen absorption mechanism,
Since the permissible amount of hydrogen gas to be generated is relatively large, when the present invention is applied to such a case, it can be carried out with a lower rate of hydrogenation, or in some cases, with no rate of hydrogenation. Effects of the Invention As described above, the present invention can reduce the oxidation rate of negative electrode zinc, and is extremely effective in obtaining a low-pollution zinc-alkaline battery.

[Brief explanation of drawings]

The figure is a partially sectional side view of a button-shaped silver oxide battery used in an example of the present invention. 2... Zinc negative electrode, 4... Separator, 5... Silver oxide positive electrode.

Claims (1)

[Claims] 1 0.01 to 0.5% by weight of nickel, 0.005 to 0.2% by weight of aluminum, 1 of indium and thallium.
A zinc-alkaline battery using a zinc alloy containing 0.01 to 0.5% by weight of one or both species as a negative electrode active material.