JPH0622116B2 - Zinc alkaline battery - Google Patents

Description

The present invention relates to a zinc-alkaline battery using zinc as a negative electrode active material, an alkaline aqueous solution as an electrolyte, and manganese dioxide, silver oxide, mercury oxide, oxygen, etc. as a positive electrode active material. It is about improvement.

2. Description of the Related Art A common problem of zinc alkaline batteries is corrosion of a zinc negative electrode during storage due to an electrolytic solution. Heretofore, it has been adopted as an industrial method to increase hydrogen overvoltage by using zinc fluoride powder obtained by adding about 5 to 10% by weight of mercury to zinc to suppress corrosion to such an extent that there is no practical problem. .
However, in recent years, reducing the amount of mercury contained in a battery has become a social need for reducing pollution, and various studies have been made. For example, a method has been proposed in which an alloy powder in which lead, gallium, indium, etc. are added to zinc is used to improve corrosion resistance and reduce the rate of conversion. Although this is effective in suppressing corrosion, there is an adverse effect that the strong discharge performance deteriorates by reducing the rate of conversion. In these proposals, it is unclear why the low discharge rate deteriorates the strong discharge performance, but the discharge product covers the active zinc surface, and the zinc surface of the hydroxide ion necessary for the discharge reaction is covered. It is considered that this is because the degree of hindrance to the supply to the anode is large compared to the case where the mercury content is high, and establishment of a low-degradation zinc anode having both corrosion resistance and strong discharge performance is an important issue for the future.

In addition, there is a proposal that the use of zinc or a zinc alloy in which indium is added to a zinc alloy for a negative electrode has a great effect on corrosion, mainly for the purpose of improving a manganese dry battery.
(Japanese Examined Patent Publication No. 33-3204).

In the above proposal, as elements in the zinc alloy, in addition to indium, Fe, Cd, Cr, Pb, Ca, Hg, Bi, Sb, Al, Ag, M
Although it is described to include one or two or more of g, Si, Ni, Mn, etc. as impurities or additives, in addition to the effectiveness of using indium and lead as additive elements, the above No distinction is made as to whether each of the miscellaneous elements described above is included as an impurity or added as an effective element, and it is not clear which element is effective for anticorrosion, let alone indium and lead. There is no description other than. It is still left as a future subject to investigate the effect of the combination of these elements and to investigate the effect in a zinc alkaline battery to obtain an effective alloy composition.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, there is a demand for a zinc negative electrode for alkaline batteries, which has both a low reduction rate and corrosion resistance and strong discharge performance.

INDUSTRIAL APPLICABILITY The present invention reduces the corrosion rate of the negative electrode zinc without degrading the discharge performance, the discharge performance, the storability, and the low pollution.
It is an object of the present invention to provide a zinc alkaline battery having excellent performance such as liquid leakage resistance.

MEANS FOR SOLVING THE PROBLEMS The present invention is directed to an alkaline aqueous solution containing caustic potash, caustic soda, etc. as an electrolyte, zinc as a negative electrode active material, manganese dioxide, silver oxide, mercury oxide as a positive electrode active material, Indium (In) is added to the negative electrode of a zinc-alkaline battery that uses oxygen, etc.
1 to 0.5% by weight, 0.01 to 0.5% by weight in total of one or more elements of lead (Pb), cadmium (Cd), tin (Sn) and calcium (Ca). A zinc alloy containing 005 to 0.15% by weight is used.

Action The present invention first of all, the discharge reaction product covers the active zinc surface, inhibits the supply of hydroxide ions, and the discharge reaction at a large current tends not to proceed smoothly. The problem that appears remarkably when used for is solved by alloying by adding an appropriate amount of Ca and further adding In, which is said to have a great effect for improving the corrosion resistance of the zinc alloy, at the same time. By adding an appropriate amount of an element selected from the group consisting of Pb, Cd, and Sn to further synergistically enhance the anticorrosion effect of In, a zinc negative electrode with low corrosion rate and excellent discharge performance can be obtained. It was realized.

The above Ca addition effect is effective at an appropriate addition amount, as shown in Examples described later, but its action mechanism has not been sufficiently clarified. It is presumed that Ca contained in the zinc alloy of the negative electrode has a base potential lower than that of zinc and discharges together with zinc, and the discharge product accelerates the dissolution of the discharge product of zinc in the electrolytic solution. Or plays a role in mitigating the passivation of the zinc surface due to the densification of the layer of undissolved product, and the state in which hydroxide ions are abundantly supplied to the active surface of zinc is consumed until the end of discharge when zinc is consumed. It is considered that this will be maintained continuously and the discharge utilization rate of zinc will be increased.

In addition, In is known as one of the most effective anti-corrosion additive elements among all elements, but the anti-corrosion effect can be further enhanced by the combined effect with other additive elements.

In addition to having the effect of increasing the hydrogen overvoltage of the zinc alloy, the addition effect of In has a large affinity with mercury, so the mercury added for grading is fixed on the surface and grain boundaries of the zinc alloy, and It is considered that a large anticorrosion effect can be obtained by suppressing the inward diffusion of the zinc alloy and maintaining a high mercury concentration on the surface and grain boundaries with the addition of a small amount of mercury. In the present invention, Pb, Cd, and Since Sn has a relatively low affinity for mercury, it suppresses the diffusion of mercury in the zinc alloy, which has been selected from the surface where these elements exist at the grain boundaries of the zinc alloy, from the surface layer to the grain boundaries. It is presumed that it exhibits a synergistic anticorrosion effect with In because it is effective in maintaining a high surface concentration of mercury.

The main effect of the addition of Ca in the present invention is to improve the discharge performance, but depending on the addition amount, it has some effect in enhancing the anticorrosion effect of the other elements described above. When the zinc negative electrode is corroded by the electrolytic solution during the storage period, it is a metal that is less base than zinc and is therefore easily oxidized preferentially to zinc, forming an oxide film that inactivates the active points on the surface of the zinc alloy. It is thought that there is an effect of suppressing corrosion, but if added in an amount more than that required for forming the above oxide film, excessive addition elements will corrode preferentially over zinc, so rather increase the generation of hydrogen gas. It is thought that the result will be obtained.

As described above, the present invention has experimentally examined the combination of the additive elements and the addition amount of the zinc alloy used for the negative electrode, and has realized a zinc negative electrode having both a discharge performance and a corrosion resistance and a low reduction rate.

Example Various zinc alloys were prepared by adding various elements to a zinc metal having a purity of 99.997% or more, as shown in the table below,
It is melted at 00 ℃ and sprayed with compressed air to make powder. 5
It was sieved to a particle size range of 0 to 150 mesh. Then, the above powder was put into a 10% by weight aqueous solution of caustic potash, and a predetermined amount of mercury was added dropwise while stirring to effect hydration. Then, it was washed with water, replaced with acetone and dried to prepare a zinc hydride alloy powder. Further, zinc fluorinated alloy powders other than the examples of the present invention were prepared by the same method as comparative examples.

A cylindrical alkaline manganese battery shown in the figure was manufactured using these selected powders. In the figure, 1 is a positive electrode case in which iron is plated with nickel, and a positive electrode 2 in which manganese dioxide is mixed with graphite and pressure-molded therein, a separator 3 made of polypropylene non-woven fabric, a cellulose bottom plate 4, and carboxymethyl cellulose are shown. A gelled negative electrode 5 in which various zinc hydride alloys are dispersed in an electrolytic solution of a gelled potassium caustic solution is housed. Reference numeral 6 denotes a polypropylene sealing plate that seals the opening of the case 1, and has a brass negative electrode current collector 7 fixed to the center thereof. 8 is a negative terminal plate, 9 is a positive terminal plate,
10 and 11 are insulating rings, 12 is a heat-shrinkable resin tube, and 13 is a metal outer can.

The prototype battery was an AA alkaline manganese battery. The weight of the zinc hydride alloy powder used for the negative electrode was unified to 2.80 g, and the amount of mercury added (rate of conversion) was 1% of the zinc alloy powder. It was set to% by weight. After storing the prototype battery at 60 ° C for 1 month, 2
The continuous discharge performance of 10Ω at 0 ° C, the resistance to liquid leakage, and the degree of expansion were evaluated. The following table shows the breakdown of the zinc alloy for the negative electrode and the test results.

As can be seen from this table, in the case of adding only In in the conventional example (No. 1), the appropriate amount of Pb, Cd or Sn is set to In.
When added together (No. 3), 5, 6), the expansion of the battery is smaller and the synergistic effect improves the corrosion resistance. However, it is clear from the comparison between No. 2 and No. 3, for example, that the element that strongly controls the corrosion resistance is In. Also,
If elements added to improve corrosion resistance such as Nos. 4, 7, and 8 become excessive, the opposite effect will occur. Among these conventional examples, the battery whose expansion is remarkable has poor discharge performance. Also,
Sufficient corrosion resistance and little swelling or liquid leakage, eg No. 3,
In 5 and 6, the duration of heavy load discharge of 10Ω is shorter than that of the product of the present invention.

On the other hand, in order to improve the drawbacks of these conventional examples, when Ca is added at the same time for the purpose of facilitating the discharge reaction of the negative electrode as well as enhancing the corrosion resistance by the combined effect of the above-mentioned additional elements (No. 9 to 28), the discharge performance and corrosion resistance are good and the battery expansion is small, and it is judged that it is improved from the conventional example, 0.01 to 0.5% by weight of In, one of Pb, Cd, and Sn. Alternatively, when a zinc alloy containing 0.01 to 0.3% by weight of two or more elements in total and 0.005 to 0.15% by weight of Ca is used (No. 10, 11, 12, 15, 16) , 1
8,19,20,21,22,23,26,27), and the amount of added element is insufficient or excessive (No. 9, 13,
14, 17, 24, 25, 28), some combined effects are recognized, but there is little difference from the comparatively good one of the conventional examples, or inferior on the contrary, there is an appropriate addition amount range as described above. A remarkable effect is recognized in.

As described above, the present invention, by using a zinc alloy containing a combination of additional elements having a large corrosion resistance effect and an element mainly aiming at smoothing of the discharge reaction in an appropriate range at the same time in the negative electrode, It is a pollution-free zinc-alkaline battery with excellent practical performance.

In the examples, a battery using a zinc negative electrode having a conversion rate of 1% by weight has been described. However, in an air battery provided with an exhaust mechanism, a zinc alkaline battery provided with a hydrogen absorption mechanism, etc. Since the allowable generation amount is relatively large,
When the present invention is applied to such a battery, it can be carried out with a low reduction rate and, in some cases, without reduction.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to reduce the conversion rate of negative electrode zinc and obtain a low-pollution zinc alkaline battery.

[Brief description of drawings]

The figure is a side view in which a part of the alkaline manganese battery used in the embodiment of the present invention is omitted. 2 ... Positive electrode, 3 ... Separator, 5 ... Zinc negative electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ryoji Okazaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 652-15 Takehara-cho, Takehara-shi, Hiroshima Prefecture

Claims (1)

[Claims] 1. 0.01 to 0.5% by weight of indium,
0.01 to 1 or more of lead, cadmium and tin
A zinc alkaline battery using a zinc alloy containing 0.5% by weight and 0.005 to 0.15% by weight of calcium as a negative electrode active material.