JPS6235453A - Alkaline-zinc storage battery - Google Patents

Abstract

PURPOSE:To suppress inactivity in the vicinity of surface of zinc electrode due to shortage of electrolyte and to prevent elution of active substance by forming the active substance layer with the surface layer and internal layer, causing both layers to include the wetting agent and the surface layer to include said moistening agent in the higher rate than that of internal layer. CONSTITUTION:Water is added to mixed powder consisting of zinc oxide powder, metal zinc powder, mercury oxide, silicon oxide, for example, as the wetting agent and a binding agent and these are kneaded and is then rolled into a sheet A by a roller. In the same way, a rate of inclusion of the wetting agent is increased more than that in the sheet A and the active substance is reduced as much as increment of the wetting agent to form a sheet B. The sheet A and sheet B are stacked in both sides of a collector material and adhered. Thereafter, these are pressurized for molding and is then dried. The zinc electrode 1 may be obtained by providing the internal layer 2 consisting of the sheet A and the surface layer 3 consisting of the sheet B to the surface. Thereby, the inclusion property of electrolyte in the vicinity of the surface of zinc electrode which may easily generate shortage of electrolyte and resultant inactivity may be improved and elution of active substance due to reduction in amount of active substance within the zinc electrode and inclusion in large amount of electrolyte may be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of industrial application The present invention relates to an alkaline zinc storage battery using zinc as a negative electrode active material, such as a nickel-zinc storage battery or a silver-zinc storage battery.

Conventional Technology Zinc, which is used as a negative electrode active material in alkaline storage batteries, has a high energy density per unit of electricity and is inexpensive, but on the other hand, zinc dissolves in the electrolyte during discharge and becomes zincate ions.
During charging, these zincate ions are deposited in a spongy or dendritic form, so when charge and discharge cycles are repeated, these deposited zinc grow and penetrate the separator, causing internal short circuits and shortening the cycle life. It has nine.

In order to solve this problem, a method is generally adopted in which the amount of electrolyte is regulated, free electrolyte is eliminated, and elution of zincate ions is suppressed.

However, in batteries in which electrolytic [M] is regulated, the charging and discharging reactions of the zinc active material do not proceed smoothly during high-rate discharge or low-temperature discharge. This is because in high-rate discharge, the reaction speed is fast and a large amount of electrolyte is required at the same time, resulting in a shortage of electrolyte, and at low temperatures, the movement of ions is slow, resulting in an actual shortage of electrolyte. It is. In addition, if the discharge reaction progresses in a state where the electrolyte is insufficient, the surface of the active material layer of the zinc electrode will be covered with dense zinc oxide, which is a discharge product, and the diffusion of the electrolyte into the active material matrix will be inhibited. Since the zinc oxide is inert and has low electronic conductivity, the reactivity of the zinc electrode is extremely reduced.

One possible method for suppressing the formation of such inert zinc oxide is to increase the amount of electrolyte retained in the active material layer. For example, JP-A-58-165162 proposes a zinc electrode containing titanium oxide as a wetting agent in the active material, thereby improving the electrolyte impregnation of the zinc electrode.

The production of inactive zinc oxide due to lack of electric wIg is suppressed.

(c) Problems to be solved by the invention However, even in the case of a zinc electrode with a wetting agent added, the wetting agent is uniformly added to the active material layer as shown in JP-A-58-163162. In the case of a zinc electrode, if the amount of wetting agent added is small, it was not possible to sufficiently suppress the inactivation of the surface of the zinc electrode when performing high rate discharge or the like. It is also possible to prevent the surface of the zinc electrode from being inactivated by increasing the amount of wetting agent added, but in this case, the amount of active material decreases significantly, resulting in a decrease in electrode plate capacity.

There was a problem in that the liquid impregnation of the zinc electrode became too large and the active material was eluted into the electrolyte.

B) Means for Solving the Problems In view of the fact that the zinc electrode in an alkaline zinc storage battery is significantly deactivated near the surface of the zinc electrode, the present invention provides an active material layer formed on the surface of the current collector of the zinc electrode. consists of a surface layer and an internal layer.1
Both the surface layer and the internal layer contain a wetting agent such as oxide or hydroxide such as titanium or zirconium, and carbon, and the content ratio of the wetting agent is greater in the inner layer than in the surface layer, thereby solving the above problem. This solves the problem.

Further, the content ratio of the wetting agent is set at the surface t in the surface layer.

5-1'Wk% of the layer, 5-fold t of the inner layer in the inner layer
% or less is even more effective.

(e) Effect: By the above means, it is possible to improve the liquid retentivity of the electrolyte near the surface of the zinc electrode where electrolyte shortage occurs and deactivation is likely to occur, and the zinc It is possible to prevent the elution of the active material due to a decrease in the amount of active material inside the electrode and the inclusion of a large amount of electrolyte.

(f) Example The present invention will be explained in detail below.

Zinc oxide powder 45 weight tS, metal zinc powder 45 weight %, oxidized water 4 weight % as an additive, silicon oxide 1 tft% as a wetting agent, and fluororesin powder 5 weight as a binder.
Water was added to a mixed powder consisting of Sk% by weight, kneaded, and rolled with rollers to produce a sheet. Similarly to sheet (4), the content ratio of the wetting agent was varied and increased as shown in Table 1, and the amount of the active material consisting of zinc oxide and zinc oxide was decreased by the amount increased. ) was created.

Table 1 The thus prepared sheet (4)) is adhered to both sides of a current collector made of copper or the like in the order of sheet holder and sheet (6), and after pressure molding, it is dried and the surface of the current collector is has an inner layer made of a sheet and a surface layer made of a sheet Φ), and the inner layer and the surface IY1w! A zinc electrode is obtained in which the thickness of j4 is 1:1. This zinc electrode was combined with a known sintered nickel electrode to produce a nickel-zinc storage battery (IL). The symbols given to the batteries correspond to the symbols (a) to Φ) shown in Table 1, depending on the content of silicon oxide in the surface layer of the zinc electrode used.

Figure 1 shows a cross-sectional view of this nickel-zinc storage battery. In the figure, (1) is a zinc electrode, (2) is an internal layer, (3) is a surface layer, and (4) is a current collector. (5) is a nickel electrode, (
6) is a separator, (7) is a liquid holding e, (81 is a battery case, (
9) is the container lid, and t101αD is the positive and negative terminals.

For comparison, the sheet (4) was adhered to double the thickness on both sides of the current collector, and the sheet (4) was pressure-molded and dried to uniformly add the wetting agent to one surface and the internal active material layer. Obtain the pole,
Except for using this zinc electrode.

A comparative battery (1) was prepared which was otherwise the same as in the above example.

Using these batteries (a) to (1), after charging at a current of 0.20 for 5 hours, the battery voltage became 1. O
The cycle life was measured by repeating charging and discharging under the cycle condition of discharging until the voltage reached V, and determining the cycle life when the iE battery capacity reached 50% of the initial capacity. The results are shown in FIG. Also.

Change the wetting agent added to the zinc electrode to acetylene black,
The third factor shows the results obtained by performing the same measurements with the rest being the same.

As is clear from FIG. 2 and the third factor, when the content of the wetting agent in the surface layer of the zinc electrode is 5 to 60% by weight of the surface layer, the wetting agent is uniformly added and the wetting agent in the surface layer is The cycle life is improved compared to the one in which the content of the wetting agent in the surface layer is 1 dc of the surface layer, and particularly good cycle characteristics are obtained when the content of the wetting agent in the surface layer is 5 to 50 dc of the surface layer. I know that there is. This means that the wetting agent content in the surface layer η is 5% by weight.
If the content of the wetting agent in the surface layer exceeds 60% by weight, the liquid impregnation of the surface of the zinc electrode will not improve much and passivation of the active material cannot be suppressed. However, the liquid receptivity of

It is thought that the amount of active material A decreases, the effective amount of active material in the zinc electrode decreases, and deterioration accelerates. In this type of zinc electrode, where the active material layer is composed of an inner layer and a surface layer, and the surface layer is formed on the surface of the inner layer, the zinc in the surface (!TI layer) is electrodeposited on the inner layer and the inner layer and surface layer are Although the adhesion of the layers is improved,
Add a wetting agent to the mix.

When the zinc content in the surface layer decreases due to

As the amount of zinc electrodeposited on the inner layer decreases, the adhesion between the inner layer and the surface layer decreases, making it impossible to fully exhibit the effect of adding a wetting agent.

Next, batteries were prepared in the same manner as in battery (+1) by varying the wetting agent content with the same zinc and other components.
) to (S).

Table 2 The f′df ponds of the present invention (jl to (1
1) and ((1) and the comparative battery (1) were used to measure cycle characteristics.

Figure 4 is a cycle characteristic diagram when charging and discharging are repeated under the above-mentioned cycle conditions, and Figure 5 shows that after charging at a current of 0.20 for 5 hours, the battery voltage is tO
It is a cycle characteristic diagram when charging and discharging are repeatedly performed under cycle conditions of discharging until v. Note that the shaded areas in the vJA diagram and FIG. 5 indicate that the characteristics of batteries (j) to (13) and (a) were concentrated within this range.

As is clear from FIGS. 4 and 5, the battery of the present invention (j)
The cycle life of batteries (8) to (8) and (a) is improved compared to comparative battery (1). This is because in the battery of the present invention, the content of the wetting agent in the surface layer of the zinc electrode has increased significantly, which improves the electrolyte receptivity on the surface of the zinc electrode. Since the electrolyte contained inside is supplied to the surface of the zinc electrode during discharge, it is possible to prevent inactivation due to lack of electrolyte near the surface of the zinc electrode, and also to prevent deactivation due to excessive liquid impregnation of the zinc electrode. This is thought to be because elution of the active material could be effectively suppressed by suppressing the content of the wetting agent inside the zinc electrode.

Also, although it is not clear in FIGS. 4 and 5.

Among the batteries of the present invention, battery (g)) had the best characteristics, followed by battery (j) with almost no difference, and then battery (n). It was showing. The reason why zirconium oxide and titanium oxide are superior in specific ion conductivity compared to other wetting agents is thought to be why zirconium oxide and titanium oxide are superior to batteries) and (j), and the reason why battery (n) is superior is because acetylene black is high. This is thought to be because the redox reaction of zinc within the zinc electrode was carried out smoothly because it had good electron conductivity in addition to having liquid-retaining properties.

In addition to those shown in the above examples, oxides or hydroxides of strontium, baricum, yttrium, germanium, and tin are also effective as the moisturizer used in the present invention.

(G) Effects of the Invention The alkaline zinc storage battery of the present invention is equipped with a zinc electrode formed by forming an active material layer on the surface of a current collector, and the active material layer is composed of a surface layer and an inner layer. 1. Since both the surface layer and the internal layer contain a wetting agent, and the content of the wetting agent is greater in the surface layer than in the internal layer, the zinc electrode is Inactivation due to insufficient electrolyte near the surface can be suppressed, and elution of the active material due to excessive improvement in liquid impregnation of the zinc electrode can be suppressed, and cycle life can be improved.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the battery of the present invention, Figures 2 and 3 are diagrams showing the relationship between the wetting agent content in the surface layer of the zinc electrode and the cycle life, and Figures 4 and 5 are the batteries of the present invention. FIG. 2 is a cycle characteristic diagram of a comparative battery. (,11...zinc electrode, (2)...internal j-ring, (3)
...Surface M, (51...nickel electrode, (6)...
Separator, (7)...Liquid retention gloss, (81...Battery container,
(9)...Battery case i, α0) (IIJ...Positive and negative terminals.

Claims (4)

[Claims] (1) A battery equipped with a zinc electrode formed with an active material layer formed on the surface of a current collector, wherein the active material layer is composed of a surface layer and an internal layer, and both the surface layer and the internal layer are An alkaline zinc storage battery characterized in that the battery also contains a wetting agent, and the content of the wetting agent is greater in the surface layer than in the inner layer. (2) The surface layer contains a wetting agent in an amount of 5 to 50% by weight of the surface layer, and the inner layer contains a wetting agent in an amount of 5% by weight or less of the inner layer. The alkaline zinc storage battery described in item 1). (3) A patent characterized in that the wetting agent is at least one oxide or hydroxide selected from the group consisting of silicon, zirconium, titanium, magnesium, strontium, barium, aluminum, yttrium, germanium, and tin. An alkaline zinc storage battery according to claim (1). (4) The alkaline zinc storage battery according to claim (1), wherein the wetting agent is carbon.