JPS61281460A - Alkaline zinc storage battery - Google Patents

Abstract

PURPOSE:To prevent both the eduction of zinc and the coming-off of an active material, by making an active material layer of a plurality of layers, and causing the outer active material layer of a zinc electrode to contain calcium hydroxide. CONSTITUTION:A zinc electrode comprises a current collector 1 and active material layers provided on the surface of the current collector and each consisting of a plurality of layers such as an inner and an outer layers 2, 3. The outer layer 3 contains calcium hydroxide so that zinc dissolved in the form of zincic ion is prevented from being electrodeposited or educed somewhere else. The growth of zinc dendrite and the closure of pores as ion passages in the zinc electrode are thus prevented. Since the inner layer 2 contains no calcium hydroxide, the active material layers are kept from separating or coming off due to the contact of calcium hydroxide with the current collector 1.

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.

(b) Conventional alkaline zinc storage batteries have advantages such as high energy density per unit weight, high operating voltage, and excellent economy and safety, but they have short cycle life. There are drawbacks. There are two reasons why this defect occurs. The first is that zinc repeatedly undergoes dissolution and precipitation during the charge-discharge reaction, so the zinc eluted as zincate ions during discharge is deposited on the surface of the zinc electrode, and the deposited zinc grows in a dendritic manner and forms the positive electrode. In addition, zinc precipitates at a high density near the surface of the zinc electrode, which is a porous electrode, and blocks the pores that serve as ion paths, resulting in an insufficient supply of water-dispersed ions inside the electrode. This means that the reactivity decreases. The second problem is that hydrogen gas is generated from the surface of the current collector due to self-discharge of zinc, causing the active material to peel off from the current collector.

In order to improve these properties, it has been proposed to use various metal oxides as additives in zinc electrodes. One of them is calcium hydroxide; Japanese Patent Publication No. 48-16104 discloses a zinc electrode made by coating a current collector with a mixed powder of zinc and calcium hydroxide; shows a hexagonal zinc electrode in which a calcium hydroxide layer is provided on the surface of the zinc electrode via an ion-permeable separation membrane. However, in the former case, since calcium hydroxide exists near the current collector, the adhesion between the active material and the current collector is poor, and the electronic conductivity between the active material and the current collector decreases. It may also cause the active material to fall off. Although the latter can suppress the elution of zincate ions from the surface of the zinc electrode, there is a problem in that zinc is deposited at a high density near the surface of the zinc electrode, resulting in insufficient fx supply of hydroxide ions into the electrode.

e→ Problems to be Solved by the Invention The present invention reduces the cycle life by suppressing the growth of zinc dendrites in the zinc electrode and high-density precipitation near the electrode surface, as well as preventing the active material from falling off. The alkaline zinc storage battery of the present invention, which attempts to obtain an improved alkaline zinc storage battery, is equipped with a zinc electrode formed by forming a zinc active material layer on the surface of a current collector. It is composed of layers, and except for the inner active material layer in contact with the surface of the current collector, at least the active material layer on the surface portion located on the surface of the zinc electrode contains calcium hydroxide.

(e) Function It is known that the charging reaction of zinc proceeds by the mechanism of dissolution and precipitation. Calcium hydroxide converts the zincate ion produced in this reaction into calcium zincate ((3azB(OIII)4
) to prevent it from dissolving and escaping into the electrolyte.

On the other hand, since calcium hydroxide reacts with water and zinc and solidifies, it reduces the Ia adhesion between the active material layer and the current collector.

According to the above method, the active material layer in the surface area, which is located near the surface of the zinc electrode where an electrolytic solution is abundant and dissolution and precipitation reactions of zinc easily occur, contains calcium hydroxide and zincate ions. This prevents the dissolved and dissipated zinc from being electrodeposited or precipitated elsewhere, which effectively prevents the growth of zinc dendrites and the blockage of the pores that serve as routes for zinc electrode ions. Can be suppressed. Mar. 6, the inner active material layer that comes into contact with the current collector does not contain calcium hydroxide, so the part of the active material layer that comes into contact with the current collector will solidify, which would occur if it contained calcium hydroxide. , it is possible to prevent the active material layer from peeling off or falling off from the current collector. Furthermore, by increasing the hydrogen overvoltage and suppressing hydrogen gas generation from the current collector,
If the internal active material layer contains indium or tin that maintains sufficient adhesion between the current collector and the active material layer, peeling or falling off of the active material layer from the current collector can be more effectively prevented. .

In addition, the zinc active material layer formed on the current collector surface of the zinc electrode generally has a uniform composition of the active material from the contact surface with the current collector to the surface, and the surface area where there is a large amount of electrolyte is particularly reactive. However, if the active material layer has a multilayer structure such as an internal active material layer and a surface active material layer,
If the discharge overvoltage of the active material layer inside the zinc electrode is smaller than that of the active material layer on the surface, it is possible to discharge deeply to the active material layer inside the zinc electrode where there is less electrolyte. In addition, the discharge capacity of the zinc electrode increases as well.

(f) Example: 90 parts by weight of strict zinc, 10 parts by weight of zinc. A mixed powder prepared by mixing 5 parts by weight of calcium hydroxide, 2.5 parts by weight of thallium oxide and 2.5 parts by weight of indium hydroxide as a KmZJl agent. , polytetrafluoroethylene as a binder and water were added, kneaded and rolled to prepare an active material sheet a, and at the same time, thallium oxide was added as an additive to 90 parts by weight of zinc oxide and 10 parts by weight of zinc powder. An active material sheet b was prepared using a mixed powder prepared by mixing 2.5 parts by weight and 25 parts by weight of indium hydroxide. These active material sheets
The sheets were pressed together so that both sides of the punched metal sheet (2) b was in contact with the current collector and the sheet a was on the front side, and dried to form a current collector (1) as shown in Figure 1. ) was obtained, which had two layers of active material on both surfaces: an internal active material layer (2) and a surface active material layer (3).

The dimensions of the zinc electrode obtained in this way are thickness Q and 7Qa+.

The width is 4Q1m+, the length is 200ff, and the ratio of the thickness of the internal active material layer to the surface active material layer is 1:1.

Let this zinc electrode be a person.

In addition, in the same manner, only the additives contained in the internal active material layer and the surface active material layer were changed as shown in the table, and 8 more types of zinc electrodes were fabricated, resulting in a total of 9 types of zinc electrodes A to A. I got a job. In addition, the amount of additives added in the table is 9% of zinc oxide.
It is expressed as a weight ratio with zinc as 0 and zinc as 10.

Next, each of these zinc electrodes A to I was combined with a sintered nickel electrode to produce an AA type nickel-zinc storage battery. A cross-sectional view of the battery thus produced is shown in FIG. Second
In the figure, (4) is a zinc electrode, (5) is a nickel electrode, (6) is a separator, (7) is a battery case, (8) is a sealing plate, (9)
) is an insulating backing. In addition, these batteries were subjected to cycle tests, and the cycle lives obtained are also shown in the table. The cycle test was performed after charging at 450mA for 4 hours and 30 minutes. [Then, the operation of discharging at 45 QmA for 4 hours was repeated and continued, and the battery life was defined as the point at which the battery voltage of 1.4 V could not be maintained for more than 3 hours during discharging. In addition, the cycle life shown in the table is expressed as the average of the remaining 4 cells after manufacturing 5 cells of the same battery and carrying out a cycle test, excluding the 1 cell with the poorest performance.

Batteries with zinc electrodes A to G that do not contain calcium hydroxide in the active material layer inside the surface have a longer cycle life than batteries with zinc electrodes R and I that contain calcium hydroxide in the inner active material layer. Significantly improved, especially zinc, E
The improvement in cycle life of and F is remarkable.

Calcium hydroxide reacts with water and zinc oxide or zinc as an active material during electrode production, and the water is consumed in this reaction, causing the active material layer to dry, shrink, and solidify. In addition to the surface active material layer, the internal active material layer also contains calcium hydroxide.In the case of zinc electrodes, the active material layer cracks before being incorporated into the battery), and the active material layer has already been removed from the current collector. The layers peel off,
It was in a state where it was easy to fall off. On the other hand, zinc electrodes A to G, which do not contain calcium hydroxide in the internal active material layer, maintain sufficient adhesion between the internal active material layer and the current collector.
In the case where the active material layer in the 1fC surface area contained calcium hydroxide, the active material layer in the outer surface area was retained by the internal active material layer, and no cracks were observed in the active material layer. In addition, it is preferable that the zinc electrode, which is a porous electrode, maintain sufficient ohmic contact between the current collector and the active material to enable deep charging and discharging, but if calcium hydroxide is present near the current collector, , there is originally little electrolyte inside the electrode, and
Calcium hydroxide fixes zinc ions, making it difficult for zinc to electrodeposit on the current collector during charging), which is thought to reduce the adhesion between the current collector and the active material layer. From these facts, it is inferred that the cycle life of the battery equipped with the zinc electrodes R and I was extremely short compared to the battery equipped with the zinc electrodes A to G.

In order to maintain the adhesion between the current collector and the active material layer, additives are used that eutectoid with zinc to form dense crystals and increase the hydrogen overvoltage to suppress hydrogen generation from the current collector. It is effective to include it in the internal active material layer in contact with the current collector. Examples of materials having such properties include indium hydroxide or oxide and tin oxide. K, indium, and tin may be used alone or in combination so that the effect is seen in all batteries equipped with zinc poles, E, and F.

Through repeated charging and discharging, it becomes zincate ions and dissolves.
Calcium hydroxide and thallium oxide are used as additives to suppress the dendritic growth of zinc that occurs when the escaped zinc is electrodeposited or precipitated elsewhere, and the clogging of the pores that serve as ion paths in the porous tW zinc electrode. , indium hydroxide and indium oxide.

Calcium hydroxide fixes zincate ions as calcium zincate and prevents the elution of zinc, and since calcium zincate is charged and returns to zinc, it prevents zinc from depositing in a high density and blocking the ion path. Can be suppressed. The effect of adding calcium hydroxide is significant when comparing the cycle life of batteries with zinc electrodes A and G. This is evident from the fact that ponds have a longer cycle life. There is also a method of forming a single layer of calcium hydroxide only on the surface of the zinc electrode, but in this case it is possible to suppress the elution of zincate ions from the surface of the zinc electrode, but the electrolyte is relatively abundant. This effect does not extend to the inside of the active material layer near the surface of the zinc electrode, and zinc is deposited in a high density near the surface of the zinc electrode, blocking the ion path and preventing charge/discharge reactions inside the active material layer. This is not desirable. Therefore, it is necessary to add calcium hydroxide so that it is contained within the active material layer.

Thallium oxide has a reduction potential much higher than that of zinc, so once it is charged it remains as metallic thallium, and remains as metallic thallium as long as it does not overcharge even after repeated charging and discharging. -! Therefore, the interdiffusion constant between zinc and thallium is very large, and some of the zinc electrodeposited on thallium diffuses into thallium to form an alloy and is stabilized. As a result, thallium acts as a nucleus for zinc electrodeposition during the charging reaction, and as long as thallium is not unevenly distributed, the particle size of zinc will not change even after repeated charging and discharging, and zinc will precipitate at a high density. This can prevent the ion path from being blocked. In this way, both calcium hydroxide and thallium have the function of suppressing group closure of the ion path caused by the dense precipitation of zinc, but when comparing the cycle lives of batteries equipped with batteries C and D, As is clear from the above, further effects can be obtained by adding thallium oxide in addition to calcium hydroxide to the active material layer.

In addition, indium suppresses the growth of zinc dendrites extending from the surface of the zinc electrode and increases the hydrogen overvoltage to suppress zinc self-discharge. As is clear from the comparison of the ponds, even if the active materials MK calcium hydroxide and thallium are added, the cycle life is significantly extended if indium is further added. This improvement in cycle life is also related to the addition of both indium and thallium to the surface active material layer. This K will be explained below.

Normally, the composition of the active material layer formed on the current collector surface of a zinc electrode is uniform from the surface in close contact with the current collector to the surface, and when this zinc electrode is used, the electrolyte is abundant. The existing surface area reacts particularly strongly, and during discharge, the surface area is covered with zinc oxide in the discharged state while leaving undischarged zinc inside where there is less electrolyte. Because the diameter is large, the electrolyte does not reach the inside of the zinc electrode, which is a porous electrode, and the zinc inside the electrode does not discharge.

If the active material on the surface is intensively used for charging and discharging in this way, the cycle life of the stain pond will be shortened, as dendritic growth of zinc on the surface of the zinc electrode and blockage of ion paths will progress rapidly. In the zinc iD, both indium and thallium are added to the surface active material layer, and only indium is added to the inner active material layer.When both indium and thallium are added to the active material layer, indium The discharge overvoltage of zinc increases by 60 to 7 QmV compared to the case where thallium and thallium are respectively added to the active material alone. This is thought to be because the addition of thallium stabilizes zinc by turning it into a thallium-zinc alloy, and the addition of indium makes the zinc crystals denser, making it difficult to discharge. In this way, if the discharge overvoltage is lower in the inner active material layer than in the surface active material layer, the discharge will occur deeper into the zinc electrode where there is less electrolyte, and as a result, the unbalanced charge/discharge reaction will be eliminated. As a result, the rate of deterioration of the zinc electrode is slowed down, and the discharge capacity of the zinc electrode is also increased. In addition, in the table, those in which the discharge overvoltage is smaller in the inner active material layer than in the surface active material layer are zinc poles, E, F, and I. The discharge overvoltages of the material layer and the internal active material layer are approximately the same. As is clear from the table, the life cycle life of the batteries with zinc WiD, E, and r is significantly improved compared to other batteries. However, although the cycle life of batteries equipped with zinc electrodes is longer than that of batteries with zinc electrodes H, it is considerably shorter than that of other batteries. This is because, since the active material layer contains calcium hydroxide, the active material layer peels off and falls off from the aggregate at an early stage, so that a sufficient effect could not be obtained.

In the above example, the case was described in which the active material layer formed on the surface of the current collector was two layers, but the active material layer may be three or more layers. Even if the material layer does not contain calcium hydroxide and all the remaining active material layers contain calcium hydroxide, the same effect is produced, at least for current collectors that are susceptible to peeling and falling off of the active material layer. The active material layer in contact with the zinc electrode does not contain calcium hydroxide, and the active material 111 on the surface of the zinc electrode, which tends to cause dendritic growth of zinc and blockage of pores in the zinc electrode that serve as ion routes, does not contain hydroxide. It is necessary to contain calcium. It is preferable to configure the discharge overvoltage so that it gradually decreases from the active material layer on the surface of the zinc electrode toward the active material in contact with the current collector, so that the discharge progresses uniformly in the zinc electrode.

In addition, as a result of individually examining and researching the effects of each additive, the addition I of additives to be included in the active material was found to be 1 to 5% for indium hydroxide and 1 to 5% for thallium oxide.
When the active material layer is composed of two layers, the thickness of the surface active material layer and the inner active material layer is It was confirmed that a similar effect was obtained when the ratio was between 2:1 and 1:2.

(G) Effects of the Invention The alkaline zinc storage battery of the present invention has a zinc electrode in which an active material layer is formed on the surface of a current collector, the active material layer is composed of a plurality of layers, and the current collector Except for the internal active material layer in contact with the surface of the electrode, at least the surface active material layer located on the surface of the zinc electrode contains calcium hydroxide, so the adhesion between the current collector and the active material layer can be improved. It is possible to improve the cycle life by maintaining a sufficient amount of zinc and suppressing the dendritic growth of zinc on the surface of the zinc electrode and the clogging of pores in the zinc electrode that serve as ion paths. Furthermore, when the internal active material layer contains indium hydroxide, indium oxide, or tin oxide, peeling and falling off of the active material layer from the aggregate is further suppressed, and the discharge overvoltage of the internal active material layer is further suppressed. When the discharge overvoltage of the active material layer in the surface portion is made smaller than that of the active material layer in the surface portion, the charging/discharging reaction of the zinc electrode sufficiently proceeds to the inside, increasing the discharge capacity and suppressing deterioration of the zinc electrode. Furthermore, if the surface active material layer contains calcium hydroxide, indium hydroxide or indium oxide, and thallium oxide, the deterioration of the zinc electrode can be further suppressed. It is also effective in reducing the discharge overvoltage of the layer.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the zinc electrode of the present invention, and FIG. 2 is a sectional view of the zinc electrode of the present invention. It is a longitudinal cross-sectional view of an alkaline zinc storage battery in an example. (1) -------・Current collector, (2)・Old...Inner active material layer, (3)...Active material layer on the surface, (4)
・・・・・・Zinc electrode, (51 towns・-Niracle electrode, (6)
Separator, (7) Battery exterior can, (8) Sealing plate, (9) Insulating backing.

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 multiple layers, and the active material layer inside the current collector is in contact with the surface of the current collector. excluding the material layer,
An alkaline zinc storage battery characterized by containing calcium hydroxide in the active material layer of the surface portion located at least on the surface of the zinc electrode. (2) The alkaline zinc storage battery according to claim (1), wherein the internal active material layer contains indium hydroxide, indium oxide, or tin oxide. (3) The alkaline zinc storage battery according to claim (1), wherein the internal active material layer has a lower discharge overvoltage than the surface active material layer. (4) The alkaline zinc storage battery according to claim (1) or (3), wherein the active material layer in the surface portion contains indium hydroxide or indium oxide and thallium oxide.