JPH01289068A - Zinc active material for alkaline storage battery and its manufacture and zinc electrode using same active material - Google Patents

Abstract

PURPOSE:To make the zinc electrode for an alkaline storage battery and the charge-discharge reactions of the battery uniform so as to improve the cycle characteristics by covering the surface of metallic zinc grains of zinc active material with specified two kinds of additives effectively and uniformly, and producing a mixture layer with the both additives. CONSTITUTION:The 1st additive is selected from metals or their compounds nobler than zinc such as indium, thallium, gallium and cadmium, and the 2nd additive is composed of alkali earth metal hydroxides or oxides, and the both additives produce a mixture layer to cover the surface of metallic zinc powder. The 1st additive makes the electro-precipitation of zinc acid ions onto the zinc surface slow and uniform, and effectively prevents the growth of dendrite zinc or the growth of inactive oxide film. The 2nd additive prevents the enlargement or the dissolution of zinc grains and the deformation of the zinc electrode 1. By the synergistic effect of the two additives, a zinc electrode of little variation with time due to the progress of the number of cycles can be obtained to improve the cycle characteristics.

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a zinc active material for alkaline storage batteries, which is used as a negative electrode active material in 2.7 keel zinc storage batteries, silver-zinc storage batteries, etc., and a method for producing the same. This invention relates to a zinc electrode using an active material.

(b) Conventional technology Zinc active materials used as negative electrode active materials are on the rise! li
- Research and development is being carried out because it has a high energy density per unit, is inexpensive, and is non-polluting.

And because this zinc electrode is a soluble electrode,
There are the following problems. That is, during discharge, zinc is eluted into the alkaline electrolyte and becomes zincate ions, and during charging, these zincate ions are deposited on the surface of the zinc electrode in a dendritic or spongy form. Due to repeated charging and discharging reactions, the deposited zinc penetrates the separator and causes an internal short circuit.The metal zinc surface is covered with an electrochemically inactive oxide film, reducing the reaction surface quality and deteriorating the battery characteristics. occurs.

Therefore, as a conventional technique for improving the cycle characteristics of this type of battery, Japanese Patent Publication No. 54-9696 discloses that 2 to 30% by weight of one or more metals or oxides selected from cadmium, lead, indium, and tin. discloses that cycle characteristics can be improved by adding 5 to 20% by weight of calcium hydroxide to a zinc active material. According to this method, metal oxides such as cadmium oxide are reduced as the charge/discharge cycle progresses, forming a porous skeleton that serves as an electron conduction path, and the addition of calcium hydroxide allows the active material to be removed from the electrode. It has the effect of reducing dissolution and release, and as a result, it becomes possible to improve cycle life.

However, if these additives are simply added, they will be unevenly distributed in the zinc electrode, and the effect as an additive will not be obtained to a large extent.Additionally, these additives will be reduced, and as the number of cycles progresses, the metal By covering the zinc surface, metal zinc is inhibited from becoming a dendritic zinc generation nucleus, and an electrochemically inactive oxide film is prevented from being generated.

However, at the beginning of the charge/discharge cycle, the surface of the metal zinc is not covered with the additive, and the metal zinc becomes a nucleus for the formation of dendritic zinc, or electrochemically inactive zinc is formed. If such inert zinc is produced, even if the additive is present, the electrochemically inert zinc will not react and will not function as an active material, and the growth of dendritic zinc cannot be effectively inhibited.

(c) Problems to be Solved by the Invention The present invention has been made in view of the above-mentioned problems, and aims to improve the dispersibility of additives in zinc electrodes for alkaline storage batteries, and to improve the dispersibility of additives in zinc electrodes for alkaline storage batteries. This paper proposes a zinc active material that can suppress the growth of dendritic zinc, a method for producing the same, and a zinc electrode. The objective is to provide an alkaline storage battery with excellent cycle characteristics.

(d) Means for Solving the Problems The zinc active material for alkaline storage batteries of the present invention comprises a first additive, a second additive, and metal zinc powder, and the first additive comprises: The second additive is made of a metal nobler than zinc, such as indium, thallium, gallium, or cadmium, or a compound thereof, and the second additive is made of an alkaline earth metal hydroxide or an oxide thereof. The first additive and the second additive form a mixed layer, and the mixed layer covers the surface of the metal zinc powder.

The active material is prepared by wet mixing the first additive, the second additive, and the metal zinc powder, or by mixing the first additive and the second additive by wet mixing. It can be manufactured by adhering it to the metal zinc powder by sputtering or vapor deposition.

Further, a zinc electrode is constituted by the zinc active material for an alkaline storage battery, zinc oxide, and a binder.

(E) Effect By using the surface-modified metal zinc powder as an active material, cycle characteristics can be improved. This is because the metal zinc surface is covered with a mixed layer in which the second additive, alkaline earth metal hydroxide or oxide, and the first additive coexist, so the metal zinc and the additive are simply mixed. The concentration of the additive on the metal zinc surface is higher than in the case where the zinc metal is used, and the effect as an additive appears efficiently from the beginning of the charge/discharge cycle.

The first additive increases the overvoltage of the zincate ion electrodeposition reaction, and as a result, the zincate ions are slowly and uniformly deposited on the metal zinc surface. Therefore, metallic zinc can serve as a nucleus for dendritic zinc growth, and dendritic zinc growth from the zinc electrode is effectively inhibited. Furthermore, on the metal zinc surface,
It also prevents the formation of an electrochemically inert fermentation film. In addition, alkaline earth metal hydroxides or oxides are
Prevents coarsening or elution of zinc particles and prevents deformation of zinc electrodes.

Due to the synergistic effect of these two, a zinc electrode with little change over time is obtained even as the number of cycles progresses, and the cycle characteristics are improved.

(f) Example Hereinafter, examples of the present invention will be referred to and explained in detail.

(Example 1) Metallic zinc powder (average particle size 3 to 7 scales) and indium hydroxide 10 as a first additive to the metal zinc powder
% by weight and 10% by weight of barium hydroxide as a second additive, 501i% by weight of water was added, and wet mixing was performed. The conditions at this time were to knead for 30 minutes at room temperature using a mulch machine. As for the amount of water added at this time, various studies have shown that 30 to 200% by weight is suitable. In this way, the zinc active material (surface-modified zinc) of the present invention was obtained.

Here, the first additive is indium hydroxide [In(O
H) sl, calcium hydroxide (Ca
Zinc active material obtained by wet mixing using (OH)tl (
X-ray diffraction analysis was performed using the zinc active material obtained by dry mixing (used in the battery F of the present invention) and the zinc active material obtained by dry mixing (used in the comparative battery F) described below. The results are shown in Figures 1 and 2. Note that the peaks of metal zinc, zinc oxide, etc. are much larger than the peaks of the first additive and the second additive, so their illustrations are not shown here. is omitted. It is understood from the X-ray diffraction analysis shown in FIG. 1 that this surface-modified zinc has indium present in a metallic state on its surface. The weight of this indium coating is approximately 3jl%
It is. In detail, from the results shown in Figure 1, the first additive, indium (marked in the figure), exists in a metallic state on the surface of the gold-zinc particles, and this is ion-exchanged with metallic zinc. It was generated. In addition, calcium zincate Ca[Zn(0)1)ah 2H* is present on the surface of the metal zinc particles.
O (O mark in the figure) is generated, and the indium (In
) can be seen to coexist.

On the other hand, from the results shown in Figure 2, the first additive, indium hydroxide [In(OH>=] (inside the figure), and the second additive, calcium hydroxide [Ca(OH)]. ,
] (marked with △ in the figure), C1 calcium zincate was not confirmed because each of them was simply present, and the surface of the metal zinc particles formed a mixed layer with the first additive and the second additive. I can't confirm that there is.

To the thus obtained mixed powder consisting of 35% by weight of surface-modified zinc, 60% by weight of zinc oxide, and 5% by weight of fluororesin, water is added and kneaded to obtain a paste. And so. The thus produced zinc electrode was combined with a known bridle-type two-layer electrode to obtain a cylindrical sealed nickel-zinc battery, which was designated as the battery A1 of the present invention.

Similarly, batteries of the present invention B5, C+, D+, El, F+SG+, H2, ■3, containing the additives shown in Table 6,
I got Jl.

FIG. 3 shows a cross-sectional view of the battery of the present invention. In the figure, 1 is a zinc electrode, 2 is a nickel electrode, and 3 is a separator. These are wound up, wrapped around a heat shrink tube 8, and inserted into an outer can 4. do. 6 is a conductive tab for the positive electrode, which is connected to the sealing body 5; and 7 is a conductive tab for the negative electrode, which is connected to the outer can 4. Then, the sealing body 5 is attached to the outer can 4 via the backing 9.
is attached to the opening of the

(Example 2) A mixture of barium oxide and metallic indium with a weight ratio of 1=1 was placed in a tungsten boat, and the boat was vibrated while electron beam evaporation was performed at an accelerating current of 200 A and a distance of evaporation R source of 8.0σ. , a deposition rate of 700 people/sin, and a vacuum level of 1 G-' Torr) to coat the surface of the metallic zinc powder.
Calcium oxide (second additive), and indium (
(first additive) to obtain surface-modified zinc. The weight of the film at this time is about 10% of the weight of zinc! It was 1%. A zinc electrode was prepared from this surface-modified zinc in the same manner as in Example 1, and a battery was assembled in the same manner to form a battery A of the present invention.

Batteries B, C8, Dl, and E* of the present invention containing the additives shown in Table 6 were also prepared using the same electron beam evaporation method.

Fl,G,,H8,Il,J, were obtained.

Note that the acceleration current is preferably 100 to 300 mA, the distance to the vapor deposition source is 5 to 10 cm, and the degree of vacuum is preferably about 10-1 to 10-'.

(Comparative Example 1) Wet mixing was carried out in the same manner as in Example 1 by adding only the first additive without adding the second additive, the hydroxide and oxide of alkaline earth metal. , an active material was obtained, a battery was produced in the same manner, and comparative batteries a1, l)1. shown in Table 6 were obtained. el
, d7, els fl, g3, hl.

11, obtained j+.

(Comparative Example 2) Although the first additive and the second additive were used, wet mixing was not performed and active materials mixed by dry mixing were obtained. Comparative battery a8 shown in Table 10)
,el,fl,j, were obtained.

These invention batteries A1 to J+, invention batteries A, to J1
, Comparative battery @ t-j +, Comparative battery a3, C18, f
The cycle life was compared using 1 and j8.

The charging/discharging cycle conditions were as follows: After charging at 1/4c current for 4.6 hours, discharging at 1/4cllj current, and the battery voltage was 1. Discharging was terminated when Ov was reached, and the number of cycles at which the battery capacity became 50% or less of the initial capacity was defined as the cycle life.

The results are shown in the table for each addition open side. Tables 1 through 10 show the first additive, second additive, and cycle life.

As is clear from the margin table below, it can be seen that the use of the surface-modified zinc of the present invention is superior to the case of dry mixing with additives. Figure 4 shows batteries E3 and E shown in Table 5.
1, e3, and e are comparison diagrams of charge/discharge cycle characteristics. From the results shown in Tables 1 to 10, the effect is particularly remarkable in barium hydroxide-indium-thallium-gallium, and the cycle characteristics are excellent. This is because the surface of metallic zinc is covered with indium, thallium, or gallium efficiently and with good dispersion from the beginning of the charge/discharge cycle, and the synergistic effect of these three metal elements causes the overvoltage of the zincate ion electrodeposition reaction. It is thought that this is because the electrodeposition reaction of zincate ions occurs slowly and uniformly due to the increase in the number of zinc oxides, resulting in a state in which dendritic zinc growth is less likely to occur.

In addition, since this surface-modified zinc is uniformly coated with alkaline earth metal aqueous substances or oxides, it effectively prevents the elution of zincate ions during discharge, and even as the Nicle number progresses, zinc It is thought that changes in the shape of rights will be prevented. still,
In Example 1, barium hydroxide and calcium hydroxide were used alone as the alkaline earth metal hydroxide as the second additive, but other alkaline earth metal hydroxides were used as the second additive. , or a combination of two or more of these, similar effects can be obtained. In addition, the amount of alkaline earth metal hydroxide as the second additive or the first additive was all 10311%, but the amount of alkaline earth metal hydroxide as the second additive was 1 to 1%. 20% by weight,
The same effect can be obtained as long as the amount of the first additive is within the range of 5 to 201i%. Also in Example 2, the second additive is an alkaline earth metal oxide, other forms,
Alternatively, a combination of 211 or more may be used, and the same effect can be obtained as long as the coating weight is within the range of 2 to 20% by weight.

(G) Effects of the Invention According to the present invention, the surface of metal zinc particles, which is a zinc active material, is efficiently and uniformly covered with the first additive, and the alkaline earth particles, which are the second additive, Covered with metal hydroxide or oxide, the first additive and the second additive form a mixed layer, so the charge/discharge reaction is uniform, and the cycle is maintained over a long period of time with little change in shape. Zinc electrodes and batteries for alkaline storage batteries with excellent properties can be obtained, and their industrial value is extremely large.

4. An hour wheel explanation of rxJ plane No. 1150 is an X-ray diffraction result diagram of the zinc active material according to the present invention, and Fig. 2 is an x! 1 is a diffraction result diagram, FIG. 3 is a vertical cross-sectional view of the battery of the present invention, and FIG. 4 is a comparison diagram of cycle characteristics of the batteries.

1... Zinc electrode (negative electrode), 2... Nickel electrode (positive electrode)
, 3... Separator, 4... Exterior can, 5... Sealing body, 6... Conductive dove for positive electrode, 7... Conductive tab for negative electrode, 8... Heat shrink tube, 9...・Backing E, , E,...Battery of the present invention, e, lam...
・Comparison battery.

Claims (4)

[Claims] (1) Consists of a first additive, a second additive, and metal zinc powder, and the first additive is a metal nobler than zinc, such as indium, thallium, gallium, cadmium, or a compound thereof. The second additive is made of an alkaline earth metal hydroxide or an oxide thereof, and the first additive and the second additive form a mixed layer. A zinc active material for an alkaline storage battery, wherein the mixed layer covers the surface of the metal zinc powder. (2) The method for producing a zinc active material for an alkaline storage battery according to claim (1), characterized in that the first additive, the second additive, and the metal zinc powder are wet-mixed. (3) The first additive and the second additive are attached to the metal zinc powder by sputtering or vapor deposition, Production method. (4) A zinc electrode for an alkaline storage battery, comprising the zinc active material for an alkaline storage battery, zinc oxide, and a binder.