JPH06260166A - Nickel electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To provide a nickel electrode for alkaline storage battery which ensures a high rate of service, prevention of the electrode from wet swelling, prolongation of the lifetime, and enhancement of the high temp. performance by including copper, silver, or compound thereof in nickel hydroxide which is the main active material for the positive electrode, and also mixing cobalt compound with it. CONSTITUTION:Cobalt compound added to nickel hydroxide as main active material is dissolved and dispersed as cobalt complex ions in an alkaline electrolytic solution and re-educed as an active cobalt hydroxide film on the surfaces of nickel hydroxide particles. In charging thereafter, it is turned into electroconductive oxy cobalt hydroxide (CoOOH), and as a result, the active material particles and an electricity collector are connected microscopically through a conductive network of CoOOH, so that the discharge depth is as deep as near NiO1.0 to ensure an increased rate of service. Formation of the network disperse the discharge current uniformly, so that production of gamma-NiOOH resulting from unevenness of the current density can be suppressed effectively, and the electrode is prevented from wet swelling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel electrode for an alkaline storage battery used in a nickel-cadmium battery or a nickel metal hydride battery.

[0002]

2. Description of the Related Art The ideal charge / discharge reaction of a nickel electrode is a homogeneous solid-phase reaction in which the discharge product is nickel hydroxide Ni (OH) ₂ and the charge product is nickel oxyhydroxide NiOOH. The value is divalent (N
i0 ₁ . ₀₎ and trivalent (NiO _{1. 5)} varies between continuously. In addition, nickel oxyhydroxide has β-type (β-N
iOOH) and γ-type (γ-NiOOH) exist, and γ-type is an oxide having a lower density than β-type, so the generation of γ-type causes swelling of the nickel electrode (increased electrode thickness). It is known.

[0003] utilization of the active material of the nickel electrode, or nickel oxyhydroxide (NiO _{1. 5)} is how much discharge, that is, usually determined by the depth of discharge. The reason is that since nickel oxyhydroxide has some conductivity in the charging process, NiO ₁ . _In contrast to being oxidized up to ₅ , in the discharge process, since nickel hydroxide is an insulator, the conductivity drops sharply at the end of discharge. Ni
O ₁ . _This is because it becomes very difficult to discharge deeply to ₀ . In the conventional nickel electrode, in order to increase the depth of discharge, the addition of a conductive auxiliary agent such as nickel powder or carbon powder, or a metal powder sintered body substrate is used. However, even in the nickel powder sintered electrode, which has been said to have the most excellent conductivity and current collecting property, the depth of discharge is NiO ₁ . It remains at ₁ , and the utilization rate is 80%.
In addition, in a non-sintered electrode (paste electrode) in which a porous metal substrate having a high porosity is filled with an active material, the depth of discharge is further reduced and the utilization rate is as low as 50 to 60%. The utilization rate has been improved by adding a cobalt compound that is soluble in the solution.

The swelling of the nickel electrode causes a decrease in life, a short circuit between the electrodes, and a decrease in capacity due to uneven distribution of the electrolytic solution. The cause thereof is, as described above, the low density γ- produced at the end of charging. It is known to be in NiOOH. Conventionally, in order to prevent the production of this γ-NiOOH, cadmium has been added in a solid solution state in the crystals of nickel hydroxide, but recently, from the viewpoint of environmental protection, zinc is a harmless alternative element that replaces cadmium. It is mainly added as.

As described above, the important problems in the practical application of the nickel electrode are the development of a conductive auxiliary agent for improving the depth of discharge (improvement of utilization rate) and the prevention of electrode swelling, that is, γ-
The development of a pollution-free additive for preventing the generation of NiOOH (prolongation of the life) has been made, but conventionally, no effective additive has been found other than the combination of the cobalt compound and zinc.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a high utilization rate, a long life in which electrode swelling is prevented, and a nickel-free alkaline storage battery having excellent high-temperature performance. An electrode is provided.

[0007]

In the nickel electrode of the present invention, nickel hydroxide, which is the main active material, contains copper, silver or a compound thereof, which is a transition element of Group Ib, and is mixed with a cobalt compound. It is characterized by. The transition element has a content of 1 to 10% by weight,
It is in a solid solution state in the nickel hydroxide crystal. The compound is an oxide or hydroxide. Furthermore, Ib
In addition to the transition elements of group III, cobalt is in solid solution in the nickel hydroxide crystal.

[0008]

[Create a cobalt compound added to the nickel hydroxide is a main active material is the alkaline electrolyte cobalt complex ion HCoO ₂ - was dissolved and dispersed as ^1, the active cobalt hydroxide coating the nickel hydroxide particle surface And has the property of re-precipitating, and changes to conductive cobalt oxyhydroxide (CoOOH) in the subsequent charging. As a result, the active material particles and the current collector are microscopically connected by the conductive network of CoOOH, so that the discharge depth is NiO.
₁ . It becomes possible to be close to ₀ , which has the effect of significantly increasing the utilization rate.

Γ-NiOOH, which is the cause of electrode swelling, is
The higher the current density, the easier it is to generate. The formation of the conductive network by the cobalt monoxide additive not only improves the utilization factor but also uniformly disperses the charging current, so that the formation of γ-NiOOH due to the non-uniformity of the current density is effective. It has the effect of suppressing. However, in order to completely suppress the swelling of the electrode, modification of the active material itself is required. Conventionally, addition of a solid solution of a Group II element (zinc, cadmium, magnesium, etc.) to nickel hydroxide crystals has been known to suppress the production of γ-NiOOH in the active material itself. It was found that the same effect can be obtained by adding a solid solution or a compound thereof to the crystal of nickel hydroxide of copper or silver which is a transition element of the group.

As described above, according to the present invention, copper of Group Ib,
Γ-NiO by the synergistic action of silver and cobalt compounds
It becomes possible to obtain a nickel electrode which suppresses the generation of OH, effectively prevents electrode swelling, and has a high utilization rate of the active material and no pollution. Further, copper and silver may be deposited on the counter electrode if they are not in a completely solid solution state, but since the cobalt compound forms a film on the surface of the nickel hydroxide particles, there is no such fear.

[0011]

EXAMPLES Examples of the present invention will be described below. The nickel hydroxide of this example was added with ammonium sulfate to an aqueous solution of nickel sulfate to which a predetermined amount of copper sulfate or silver nitrate was added to form an ammine complex, and the aqueous sodium hydroxide solution was dropped with vigorous stirring to adjust the alkalinity to pH 11 to 11. By controlling the concentration to 13, nickel hydroxide particles in which copper or silver was solid-dissolved were deposited and grown to obtain nickel hydroxide powder having a tap density of about 2 g / ml. In this embodiment,
The contents of copper and silver were each set to 5% by weight. Similarly, as a comparative example, an additive-free nickel hydroxide powder was obtained.

10% by weight of cobalt monoxide powder (CoO) was mixed with these nickel hydroxide powders, and the mixture was made into a paste with a thickening solution of carboxymethyl cellulose.
A nickel fiber porous body substrate having a porosity of 5% was filled in a predetermined amount, dried and pressed to obtain a nickel electrode of the present invention.

Here, the nickel electrodes of the present invention filled with an active material prepared by mixing nickel hydroxide powder containing copper or silver as a solid solution with cobalt monoxide powder will be referred to as electrodes (A) and (B), respectively. Further, as a reference electrode, an electrode (C) filled with an active material obtained by mixing undoped nickel hydroxide powder with cobalt monoxide powder, and an electrode filled with only nickel hydroxide powder added with copper as a solid solution ( D), the electrode (E) is filled with only nickel hydroxide powder without any additive.

In order to examine the utilization rate of the active material and the electrode swelling of these various nickel electrodes, an open type cell is constructed with a cadmium electrode as a counter electrode through a separator,
Charging and discharging were performed in an electrolytic solution of a 6N potassium hydroxide aqueous solution. In order to form a uniform conductive network of cobalt monoxide, it was left in the electrolytic solution for 3 days and then initially charged. Charging is at a rate of 0.1C and is 1 of the nominal capacity
The discharge was performed up to 50%, and the discharge was performed at a rate of 0.2 C up to 0 V with respect to the mercury oxide reference electrode. In addition, overcharging was performed at a charge rate of 0.5 C at 5 ° C., and γ-NiO, which causes electrode swelling,
It was evaluated by the production rate of OH. The production rate of γ-NiOOH was measured by powder X-ray diffraction of the active material.

Table 1 shows the measurement results of the active material utilization rate of various nickel electrodes and the nickel oxidation value ( _X value of NiO _X formula) at the end of discharge. The utilization factor was calculated as the ratio of the actual discharge capacity value to the theoretical capacity value calculated from the filling amount of nickel hydroxide.

[0016]

The electrodes (A) and (B) and the comparative example (C) of the present invention have a high utilization rate with respect to the comparative examples (D) and (E), and the discharge depth is 1. 0-1.1
You can see that it has reached a deeper area. Further, in the measurement result of the nickel oxidation value at the end of charging, the electrodes (A) and (B) of the present invention were about 1.5, while the comparative examples (D) and (E) showed 1.6 or more. Γ- which is a high-order oxide
The production of NiOOH came. Even in Comparative Example (C), such a tendency was recognized. Thus, it is understood that the addition of the cobalt monoxide powder to the active material is indispensable for improving the utilization rate.

Next, γ-NiOO which is the cause of electrode swelling
FIG. 1 shows the relationship between the H generation rate and the charge amount. The electrode (A) of the present invention has a γ-value even in the overcharge region as compared with the comparative example.
It can be seen that the production of NiOOH is effectively suppressed. γ-
Regarding the effect of preventing the generation of NiOOH, the electrode (A) of the present invention is the most excellent, and the comparative example (C) in which the cobalt monoxide powder is added next, and then the comparative example in which only the nickel hydroxide powder to which copper is added as a solid solution is filled (D) and then Comparative Example (E) in which only nickel hydroxide powder was filled. The electrode (B) was similar to the electrode (A). In order to prevent the formation of γ-NiOOH, the fact that the active material itself is modified by adding a solid solution of a transition element of the Ib group to the nickel hydroxide crystal, and the addition of cobalt monoxide powder between active materials This means that it is important to form a conductive network in.

In this embodiment, the amount of the Ib group transition element added is 5% by weight, but it is effective in the range of 1 to 10% by weight. Further, instead of the nickel hydroxide powder to which the transition element of the Ib group is added as a solid solution, copper oxide or silver oxide, which is a compound thereof, may be added together with the cobalt monoxide powder to obtain the same effect as described above. .

Further, in the examples, C was used as the cobalt compound.
Although oO was used, other than α-Co (OH) ₂ or β-Co
The same effect can be obtained by using (OH) ₂ .

Further, the nickel electrode (F) of the present invention was prepared by adding cobalt monoxide powder to nickel hydroxide powder in which copper and cobalt were simultaneously added as a solid solution in nickel hydroxide crystals in the same manner as described above. Was produced. The content of cobalt was 3% by weight. The electrode (F) of the present invention showed a small decrease in the utilization factor in the high temperature region of 45 ° C., and thus the comparative example (C)
Of 63% (ratio to capacity at 20 ° C) of 92
%, Which was a high value. It can be seen that nickel hydroxide powder in which a transition element of Group Ib and cobalt are simultaneously added as a solid solution is effective for improving the high temperature performance.

[0022]

As described above, according to the present invention, nickel hydroxide, which is the main active material, and copper, which is a transition element of the Ib group, are added.
A nickel electrode for a non-polluting alkaline storage battery, which contains silver or its compound or cobalt at the same time, and which is mixed with cobalt monoxide powder, has a high utilization rate, has a long service life that prevents electrode swelling, and has excellent high-temperature performance. , Its industrial value is extremely high.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a charge amount and a γ-NiOOH production ratio in nickel electrodes of the present invention and a comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Oshiya 6-6 Josaimachi, Takatsuki-shi, Osaka Yuasa Corporation

Claims (5)

[Claims] 1. A nickel electrode for an alkaline storage battery, characterized in that nickel hydroxide, which is a main active material of a positive electrode, contains copper, silver, or a compound thereof, which is a transition element of Group Ib, and is mixed with a cobalt compound. . 2. The cobalt compound is CoO or α-C.
The nickel electrode for an alkaline storage battery according to claim 1, which is o (OH) ₂ or β-Co (OH) ₂ . 3. The content of the transition element of Group Ib is 1 to
The nickel electrode for an alkaline storage battery according to claim 1, wherein the content is 10% by weight, and the element is in a solid solution state in the crystal of nickel hydroxide. 4. The nickel electrode for an alkaline storage battery according to claim 1, wherein the group Ib compound is an oxide or a hydroxide. 5. The nickel electrode for an alkaline storage battery according to claim 1, wherein cobalt other than the transition element of Group Ib is in a solid solution state in nickel hydroxide crystals.