JP2847750B2 - Hydrogen storage electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydrogen storage electrode used for a negative electrode of an alkaline battery.

Conventional technology A hydrogen storage electrode uses a hydrogen storage alloy that can reversibly store and release hydrogen, and uses the electrochemical oxidation-reduction reaction of hydrogen for the electromotive reaction of the negative electrode of an alkaline storage battery. I do. The hydrogen storage alloy used in the hydrogen storage electrode, TiNi, Ti ₂ Ni, and LaNi ₅ and TiMn ₂ such intermetallic compound, and is used obtained by replacing the constituent elements of these intermetallic compounds with other elements I have. If these hydrogen storage alloys have different compositions, the hydrogen storage amount, the equilibrium hydrogen pressure,
Since properties such as storage capacity characteristics when charge and discharge are repeated in an alkaline electrolyte change, attempts have been made to improve the performance of the hydrogen storage electrode by changing the composition of the alloy.

Conventional hydrogen-absorbing electrodes for batteries have been manufactured by filling a foamed metal with the powder of the hydrogen-absorbing alloy, bonding with an alkali-resistant polymer, or sintering at a high temperature. And, with these hydrogen storage electrodes,
No. 273, acetylene black is added, as disclosed in JP-B-58-468273, metal nickel is added and sintered, or as described in JP-A-63-110553, a metal short fiber is added. As described in JP-A-61-64069 and JP-A-61-101957, a self-catalytic wet electroless plating of metallic nickel or metallic copper is applied to the surface of a powder of a hydrogen storage alloy to form an electrode. The conductivity was high.

Problems to be Solved by the Invention As described above, a conventional hydrogen storage electrode has been added with a conductive aid composed of a staple fiber such as acetylene black or metal nickel, or a plating layer of metal copper or the like. These conductive aids have the function of increasing the conductivity of the electrode and promoting the discharge reaction of the hydrogen storage alloy, but do not discharge themselves. Therefore, when increasing the discharge capacity of the hydrogen storage alloy, it is necessary to reduce the amount of the conductive additive, increase the content of the hydrogen storage alloy, and increase the discharge capacity per weight of the hydrogen storage electrode. There is.

Therefore, the inventor of the present invention added metal nickel powder as a conductive auxiliary agent, or performed autocatalytic electroless plating of metallic copper on the surface of the hydrogen storage alloy powder to make the hydrogen storage alloy powder highly alkaline resistant. Hydrogen storage electrodes bound by molecules were fabricated, and the discharge performance of the hydrogen storage electrodes was examined by changing the addition rate of these conductive assistants. As a result, it was found that when the content of these conductive additives was small, there was a problem that the discharge capacity per weight of the hydrogen storage alloy was significantly reduced.

The present invention provides a hydrogen storage electrode comprising a powder of a hydrogen storage alloy and a binder of an alkali-resistant polymer latex, in which the discharge capacity per weight of the hydrogen storage alloy is significantly reduced when the addition rate of a conductive additive is small. To do so is to solve the problem.

Means for Solving the Problems The present invention contains at least one powder of cuprous oxide, cupric oxide or bismuth oxide, a powder of a hydrogen storage alloy, and a binder of an alkali-resistant polymer latex. It is an object of the present invention to solve the above-mentioned problem by using a hydrogen storage electrode in which the mixture is held on a conductive support.

The hydrogen storage electrode of the present invention includes at least one powder of cuprous oxide, cupric oxide, or bismuth oxide, a powder of a hydrogen storage alloy, and a binder of an alkali-resistant polymer latex. . This electrode is obtained by pressing these mixtures onto a conductive core such as punched metal or expanded metal, or dispersing these mixtures in water or the like, and adjusting the paste-like mixture to a conductive core. It is coated on a sintered body of foamed metal or metal fiber, dried, and pressed to be held on a conductive support.

When the hydrogen storage electrode of the present invention is charged and discharged, the discharge capacity decreases as the amount of cuprous oxide, cupric oxide or bismuth oxide added decreases. However, in the electrode of the present invention, such a decrease in the discharge capacity is due to the fact that instead of these oxides used in the electrode of the present invention, a conductive additive such as metallic nickel powder or acetylene black is used at the same addition rate. Compared with the added hydrogen storage electrode or the hydrogen storage electrode in which the surface of the powder of the hydrogen storage alloy is electrocatalytically plated with metallic copper or metallic nickel, especially when the addition rate is small, it is effectively suppressed. You.

The reason for the phenomenon that the discharge capacity of the hydrogen storage electrode of the present invention is larger than that of the conventional hydrogen storage electrode is that, as described below, the added oxide is reduced to a metal and effectively acts as a conduction aid. It is presumed that it is in doing.

That is, the first oxidation used for the hydrogen storage electrode of the present invention.
Copper, cupric oxide, or bismuth oxide has an equilibrium potential for a reduction reaction to a metal that is more noble than a potential at which a charging reaction of a hydrogen storage electrode occurs. These oxides partially dissolve in the alkaline electrolyte.

Therefore, when the cuprous oxide, cupric oxide or bismuth oxide is first charged by immersing the hydrogen storage electrode in an alkaline electrolyte, the metal is eluted in the alkaline electrolyte in the pores of the electrode and then charged. It is reduced to copper or metallic bismuth and precipitates in the vicinity of the hydrogen storage alloy, forming a fine conductive network. Then, the charging reaction of the hydrogen storage alloy proceeds thereafter. Since these oxides are once dissolved and then precipitated as a metal, this conductive fine network can be effectively formed even if the addition ratio of the above oxides is small.

The potential at which metallic copper or metallic bismuth is oxidized is
Since the hydrogen storage alloy is more noble than the potential at which the hydrogen storage alloy discharges, these metals are not oxidized when the electrode is discharged until the discharge reaction of the hydrogen storage alloy ends. Therefore, the fine conductive network of these metals
Until the discharge of the hydrogen storage alloy is completed, the hydrogen storage alloy effectively acts as a conductive additive, and a decrease in the discharge capacity of the hydrogen storage alloy is suppressed.

On the other hand, in the case of a conventional hydrogen storage electrode, a dissolution reaction does not occur because the metal or graphite powder or the metal plating layer is added to the electrode. Therefore, it is difficult to effectively form a conductive network, and the distribution of the conductive auxiliary is not always efficient. When the addition rate of the conductive auxiliary is small, the discharge of the hydrogen storage alloy is hindered, and the discharge capacity thereof is reduced. Decrease.

Examples Hereinafter, the present invention will be described in detail using preferred examples.

[Hydrogen storage electrode a] (Example of the present invention) A commercially available electrolytic nickel and sponge titanium were weighed and blended in an equimolar amount, were lined with calcium oxide, and kept in an argon atmosphere in a high-frequency induction furnace. This mixture was melted. The melt was pressurized and sprayed in argon gas to obtain a TiNi alloy powder. And this
The TiNi alloy powder was sieved, and a powder having a particle size of 300 μm or less was used for the electrode.

Next, the powder of this TiNi alloy and the powder of cuprous oxide (chemical formula: Cu ₂ O), a special-grade reagent manufactured by Nacalai Tesque, Inc., were mixed, and the mixture was wetted with water. A polymer latex in which an acryl-styrene copolymer as a binder for a molecular latex was dispersed was added to prepare a paste-like mixture. This pasty mixture is
The mixing ratio of solid content was adjusted to five types of 10 parts by weight, 20 parts by weight, 30 parts by weight, 40 parts by weight, and 50 parts by weight of cuprous oxide powder with respect to 100 parts by weight of TiNi powder. . The polymer latex was blended so that its solid content was 8 parts by weight based on 100 parts by weight of the total of the TiNi alloy powder and the cuprous oxide powder.

Then, the paste-like mixture was applied to a conductive core body plated with nickel on a perforated steel sheet having a thickness of 0.09 mm, and dried with hot air at 80 ° C. to express the binding force of the polymer latex. Pressing with a roll produced the hydrogen storage electrode a of the present invention. The dimensions of this electrode are about 40mm x 20mm x 1.4m
m, and one electrode contained about 3.4 g of the hydrogen storage alloy.

[Hydrogen storage electrode b] (Example of the present invention) Instead of cuprous oxide in the hydrogen storage electrode a of the present invention, powder of cupric oxide (chemical formula: CuO) of a special grade reagent manufactured by Nacalai Tesque, Inc. was used. The hydrogen storage electrode b of the present invention was manufactured in the same manner as the electrode a except that the hydrogen storage electrode b was used.

[Hydrogen storage electrode c] (Example of the present invention) Powder of bismuth oxide (chemical formula: Bi ₂ O ₃ ) of Nacalai Tesque Co., Ltd. instead of cuprous oxide in the hydrogen storage electrode a of the present invention. The hydrogen storage electrode c of the present invention was manufactured in the same manner as the electrode a except for the above.

[Hydrogen storage electrode d] (conventional example) Carbonyl nickel type 255 manufactured by INCO was used in place of cuprous oxide in the hydrogen storage electrode a of the present invention, and the other hydrogen was used in the same manner as the electrode a. An occlusion electrode d was manufactured.

[Hydrogen storage electrode e] (conventional example) In the hydrogen storage electrode a of the present invention, instead of adding the cuprous oxide powder, electroless plating of metallic copper is performed on TiNi alloy powder, and the other components are the same as those of the electrode a. Thus, a conventional hydrogen storage electrode e for comparison was manufactured. The weight of electroless plating of metallic copper is 5 parts by weight, 10 parts by weight for 100 parts by weight of TiNi alloy powder.
Five kinds, that is, 15 parts by weight, 20 parts by weight, and 25 parts by weight were used.

[Hydrogen Storage Electrode f] (Conventional Example) A conventional hydrogen storage electrode f for comparison was manufactured in the same manner as the electrode a without using cuprous oxide in the hydrogen storage electrode a of the present invention.

Next, in order to clarify the discharge performance of the hydrogen storage alloy when these hydrogen storage electrodes a, b, c, d, e and f were used in an alkaline battery, these hydrogen storage electrodes were used as negative electrodes. Then, test open-type alkaline batteries A, B, C, D, E and F were constructed so that the discharge of the battery was regulated by the discharge capacity of the negative electrode.

These batteries were manufactured as follows. That is,
One hydrogen-absorbing electrode was placed at the center to form a negative electrode, and two sintered nickel hydroxide electrodes were placed on both sides of a separator made of a nonwoven fabric made of nylon to form a positive electrode.

The nickel hydroxide electrode used as the above positive electrode was manufactured as follows. That is, using a sintered nickel substrate having a porosity of about 85%, the vacuum impregnation is performed by the ordinary vacuum impregnation method.
By repeating this process, nickel hydroxide and cobalt hydroxide were co-precipitated in the pores of the sintered substrate to produce a sintered nickel hydroxide electrode. The size of this electrode is 400mm x 40mm
× 0.85 mm, and the total amount of nickel hydroxide and cobalt hydroxide filled in one electrode was about 2.4 g. The content of cobalt hydroxide was about 95% by molar ratio based on the total amount of nickel hydroxide and cobalt hydroxide. The discharge capacity of the positive electrode used in this battery is 1.39 Ah when the discharge follows a one-electron reaction. The electrolyte is 5.
An 8 M KOH aqueous solution was used. Battery case is 45mm x 45mm x 3m
m alkaline resin was used.

These batteries were then run at 25 ° C at 0.7A
A charge / discharge test was performed under the condition that the battery was charged for 1.5 hours and discharged at a current of 0.2 A to 1.0 V. FIG. 1 shows the discharge capacity of the battery in the third cycle in this case.

In FIG. 1, the horizontal axis represents the weight of the conductive assistant with respect to 100 parts by weight of the hydrogen storage alloy contained in the hydrogen storage electrode. , Cupric oxide powder, bismuth oxide powder, metallic nickel powder or plated metallic copper. The vertical axis represents the discharge capacity of the battery per 1 g of the hydrogen storage alloy contained in the hydrogen storage electrode of each battery.

The following is clear from FIG. That is, in any case of the hydrogen storage electrode, when the rate of addition of the conductive auxiliary decreases, the discharge capacity of the battery tends to decrease, and when using the conventional hydrogen storage electrode f to which the conductive auxiliary is not added,
Almost no discharge capacity is obtained.

When the amount of the conductive assistant per 100 parts by weight of the hydrogen storage alloy is in the range of 10 parts by weight or more and 50 parts by weight or less, the discharge capacity of the battery is significantly different if the hydrogen storage electrode is different.
That is, the discharge capacities of the batteries A, B and C using the hydrogen storage electrode of the present invention are as follows.
It is larger than batteries D and E using the conventional hydrogen storage electrode.

Therefore, it can be said that the hydrogen storage electrode of the present invention effectively suppresses the decrease in the discharge capacity of the hydrogen storage alloy when the addition ratio of the conductive additive is as small as 50 parts by weight or less.

In the above-described embodiment, the case where a TiNi alloy manufactured by a gas atomization method is used as the hydrogen storage alloy powder has been described, but instead of this alloy powder, a hydrogen storage alloy having a composition of LaNi ₄ Co or Ti ₂ Ni is mechanically used. The same results as in the above-described test were obtained also when the powder prepared by pulverizing into a powder was used.

Further, in the above-described embodiment, the case where the paste-like mixture is applied to the punching metal to hold the hydrogen-absorbing alloy is described. However, instead of applying the paste to the punching metal, a foam made by Sumitomo Electric The same results as in the above test were obtained when nickel was filled with the paste-like mixture to retain the hydrogen storage alloy.

Further, in the above embodiment, a polymer latex made of an acryl-styrene copolymer was used as a binder for the alkali-resistant polymer latex.
When a polymer latex composed of fine particles of polytetrafluoroethylene resin was used, the same result as in the above test was obtained.

When two or more oxides of cuprous oxide, cupric oxide or bismuth oxide are used together (any combination may be used), or three kinds of oxides are used together. In this case, almost the same results were obtained as when these oxides were used alone.

Effect of the Invention The hydrogen storage electrode of the present invention has the effect of suppressing a decrease in the discharge capacity of the hydrogen storage alloy when the conductive tablet contained in the hydrogen storage electrode has a low addition rate.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the addition rate of a conductive auxiliary agent of a hydrogen storage electrode and the discharge capacity of a battery using the hydrogen storage electrode of the present invention and a battery using a conventional hydrogen storage electrode. . A, B, C: Batteries using the hydrogen storage electrode of the present invention D, E, F ... Batteries using the conventional hydrogen storage electrode

Claims (1)

(57) [Claims] 1. A mixture containing at least one powder of cuprous oxide, cupric oxide or bismuth oxide, a powder of a hydrogen storage alloy, and a binder of an alkali-resistant polymer latex, is electrically conductive. A hydrogen storage electrode which is held on a support.