JPS6164078A - Alkaline zinc storage battery - Google Patents

Abstract

PURPOSE:To maintain zinc used as the negative active material in adequately close contact with the current collector by performing tin plating on a base plate consisting of either a nickel plate or a nickel-plated iron plate to prepare the current collector. CONSTITUTION:A current collector is prepared by performing nickel plating on an iron plate and then performing tin plating on the nickel layer. Since the tin layer constituting the surface of the thus prepared current collector closely adheres to zinc used as the active material and also has high hydrogen overvoltage, it is possible to prevent the generation of hydrogen gas from the surface of the current collector. Even when a minute amount of tin is dissolved, there is no possibility that an oxidized film of nickel located under the tin layer is formed similarly to iron resulting in increased electric resistance. Accordingly, the current collector can be maintained in close contact with the negative active material over a long period, thereby obtaining awn alkaline storage battery with longer life.

Description

Detailed Description of the Invention (a) Field of Industrial Application The present invention relates to alkaline zinc storage batteries, such as silver-zinc batteries and nickel-zinc batteries, which use a zinc electrode as a negative electrode and use an alkaline aqueous solution for solution. In particular, it relates to improvements in zinc electrode current collectors.

In conventional alkaline zinc storage batteries, zinc as a negative electrode active material has the advantages of high energy density per unit cell and low cost. However, during discharge, zinc is eluted into the alkaline electrolyte and becomes zincate ions, and during charging, a charge-discharge reaction occurs in which these zincate ions are deposited on the surface of the zinc electrode.

Since the electrodeposition potential of this zinc electrode is electrochemically less noble than the hydrogen generation potential, there is a drawback that hydrogen is generated from the negative electrode during charging or when left unused, increasing the internal pressure of the battery.

As a method of suppressing hydrogen generation from the active material, a method of adding a substance that increases the hydrogen overvoltage, such as mercury or cadmium, to the zinc active material has been proposed. Although this considerably suppresses hydrogen generation from above the active material, hydrogen generation from above the current collector supporting the active material cannot be suppressed. In particular, the generation of hydrogen from above the current collector not only increases the internal pressure of the battery, but also causes the active material to fall off from the current collector and cause iq*t- to shorten the cycle life of the storage battery.

In JP-A-48-15850, in order to prevent self-discharge due to the use of a current collector with a low hydrogen overvoltage, cadmium has a relatively high hydrogen overvoltage.

A nine-zinc electrode has been proposed in which the upper electrode is plated with mercury, lead, tin, etc. and a zinc active material is applied, and this K suppresses hydrogen generation from above the current collector. However, as the charge/discharge cycle progresses, the plating dissolves into the electrolyte, exposing the core material of the current collector. At this time, if an iron plate or the like is used for the core or material, the iron will change to iron oxide at the end of the discharge, producing iron oxide, increasing the electrical resistance of the nine parts and causing volumetric expansion, which causes the current collector to Falling off of active material and j
This caused H1 separation, and it was not possible to maintain sufficient adhesion between zinc as a negative $i active material and the current collector for a long period of time.

(c) Problems to be Solved by the Invention The present invention aims at solving the problem that the shedding and performance of the negative bridge active material of the current collector leads to a decrease in the cycle life.

The purpose of this invention is to maintain sufficient adhesion between zinc, which is a negative 4+% active material, and a single bottle over a long period of time, and to obtain an alkaline zinc storage battery that has a longer cycle life.

In order to solve this problem, the present invention uses a nickel plate as a zinc electrode current collector or a substrate such as an iron plate plated with nickel plated with tin plating. A collection of nine bodies is used.

(e) Effects Since tin has a high hydrogen overvoltage, hydrogen generation from the current collector can be suppressed by plating tin on the surface of the current collector, and zinc electrodeposited on tin is extremely Since the zinc active material becomes dense, the adhesion between the zinc active material and the zinc active material is good. However, since the tin on the surface of the current collector detaches and dissolves at the end of the discharge of the ff battery, the core material of the current collector becomes exposed as the charge/discharge cycle progresses. At this time, if the tin plating is applied to a substrate covered with nickel, even if the tin melts and some of the nickel is exposed, the nickel may form an oxidized film like iron. There is no increase in electrical resistance. Also, since the tiny amount of tin that has eluted will precipitate again, the nickel surface exposed on the current collector will not suddenly spread.

(f) Example An example of the present invention will be described below, and a comparison with a comparative example will be mentioned.

Depending on the type of plating, a 3μ thick nickel plating is applied to the iron plate using the plating bath, temperature and current density conditions shown in Table 1, and then a 3μ thick tin plating is applied to the surface of the nickel plating layer. The electric conductor and part water are added and kneaded to turn the fluororesin into fibers and then rolled to obtain a sheet.This sheet is attached to both sides of the current collector and pressure molded to form *SC++t, 4-width zinc electrodes. get. The four zinc electrodes thus obtained and six nickel electrodes of the same size were stacked on top of each other through a separator made of a combination of a microporous film and a nylon nonwoven fabric, and the nickel-zinc 1? ■(4) was produced.

In addition, for comparison, five types of assemblies were prepared by applying lead plating, cadmium plating, and tin plating to a thickness of 3μ on an iron plate under the conditions shown in Table 1 according to the type of plating as described above, and these were used as assemblies of zinc electrodes. Comparative batteries ('B) to (D)t? used as electric bodies and otherwise the same as in the examples were used. Created.

Table 1 A charge/discharge cycle test was conducted on the battery cells (CDs to CDs) thus prepared. Cycle conditions are 5QQmA
After charging for 5 hours with a charging current of
It discharges with a discharge current of 500mA,
Charging and discharging were repeated until the discharge capacity dropped to 70 inches of the initial discharge capacity of each battery, and the cycle life was determined by the number of cycles. The results are shown in Table 2.

Table 2 Good results have been obtained with Yuki 1ike (1)mΦ with tin plating in B1 to ('D), which uses a negative electrode mass made by completely plating only one type of metal on an iron plate. The reason for this can be considered as follows. Lead, cadmium, and tin all have a high hydrogen overvoltage, and when used as a coating on a current collector, they all work to collect current and suppress hydrogen generation from the body, so they become active materials due to hydrogen generation from the current collector. There is no falling off.

However, when we examine the morphology of zinc deposited on the surface of the current collector, we find that zinc deposited on tin is very dense, whereas zinc deposited on lead or cadmium is very coarsely crystalline. It became. For this reason, the adhesion of the active material to zinc is better for a single aggregate plated with tin than for a single aggregate plated with lead or cadmium.
It is thought that the separation was suppressed and a longer cycle was achieved.

In addition, from the results in Table 1 and 2, a battery using a current collector with a nickel plated iron plate and tin plated on its surface is better than a battery using a current collector with a nickel plated iron plate and tin plated on its surface. It can be seen that this shows a better cycle life. The negative electrode current collectors of these batteries are both plated with tin on the surface and have the same surface condition, so good adhesion to the active material can be obtained as described above, but a small amount of tin dissolves at the end of discharge. As the charge/discharge cycle progresses, a portion of the surface beneath the tin plating becomes exposed. At this time, tin is applied directly (in the case of a current collector plated on an iron plate, if the iron located on the bottom surface of the tin plating is exposed, the iron becomes iron oxide at the end of discharge, causing volume expansion, which causes the active material to be removed from the current collector). Where peeling occurs and an iron oxide film is formed, electrical resistance increases, resulting in a decrease in battery capacity.

On the other hand, if nickel is placed on the bottom surface of the tin plating, even if a portion of the nickel surface is exposed, the nickel remains stable in the alkaline electrolyte, so it does not form an oxide film like iron, and the active material There is no increase in the electrical resistance of the contact surface. In addition, since the small amount of tin eluted replaces metallic zinc and precipitates again, the exposed nickel surface does not suddenly expand and can be retained for a long period of time, which is thought to extend the cycle life. It will be done. In addition, from the results of this example, when nickel is electrodeposited on an iron plate, a thickness of 3 μm is sufficient for the thickness of the nickel resin.

(G) Effects of the Invention The alkaline zinc storage battery of the present invention has a zinc electrode with a current collector formed by tin-plating a substrate whose surface is covered with nickel, and the tin on the surface of the current collector is an active material. Since it has good adhesion with zinc and has a high hydrogen overvoltage, it is possible to prevent the generation of hydrogen gas from the surface of the current collector.Also, even if a small amount of tin dissolves, the nickel located on the underside of the tin plating Unlike iron, it does not form an oxide film and increase electrical resistance, so it can maintain adhesion between the current collector and the negative electrode active material over a long period of time, providing an alkaline storage battery with a longer life.

Claims (1)

[Claims] (1) An alkaline zinc storage battery having a zinc electrode and a current collector made of a substrate whose surface is covered with nickel and plated with tin.