JP3454274B2 - Nickel electrode for alkaline storage battery and alkaline storage battery using the same - Google Patents

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 and an alkaline storage battery using the same, and more particularly to a nickel electrode for an alkaline storage battery which is mechanically filled with an active material and an alkaline storage battery using the same. Is.

[0002]

2. Description of the Related Art Generally, there are two types of nickel electrodes: one that is chemically impregnated with an active material and one that is mechanically filled with an active material. The former, that is, one that is chemically impregnated with an active material is called a sinter-type electrode, and nickel hydroxide is chemically added to a special substrate that has fine pores obtained by sintering nickel powder on the surface of a perforated steel sheet. It is made by impregnating. The latter, that is, those that mechanically fill the active material, include pocket type electrodes, button type electrodes,
There is a paste type electrode and the like, and an electrode called a cored bar type electrode, which is obtained by pressing an active material layer on the surface of the cored bar, is being developed.

[0003]

In each of the above-mentioned electrodes of the type in which the active material is mechanically filled, the active material filling step is extremely simple as compared with the sinter type electrode in which the active material is chemically impregnated. In addition, there is an advantage that waste liquid is not generated from the active material filling step. However, these electrodes have a drawback that the utilization rate of the active material is lower than that of the sinter type electrode except for the paste type electrode. A large distance between the nickel hydroxide powder and the current collector is one of the causes of the low utilization rate of the active material in the nickel electrode that is mechanically filled with the active material. That is, in the sinter type electrode or the paste type electrode, the nickel hydroxide powder is filled in the pores, so the distance to the current collector is as short as 100 μm or less, while on the other hand, the nickel electrode using the core metal as the current collector. Then, the nickel hydroxide powder farthest from the current collector is separated from the current collector by the thickness of the active material layer. By the way, the electrode reaction of the nickel electrode in a normal state is represented by the equation (1). _{β-Ni (OH) 2 +} OH - = β-NiOOH + H 2 O + e - ········· (1) nickel hydroxide in the charge-discharge reaction process as shown in equation (1) The number of oxidations of nickel hydroxide changes, and as a result, the conductivity of nickel hydroxide changes due to this charge-discharge reaction. Explaining this point in a practical and strict sense, the oxidation number is 2 when the discharge is complete.
It is not reduced to a valence, continuously changes in the range of 2.2 to 3.0, and the conductivity also changes in the range of 10 ^-4 to 10 ^-2 . On the other hand, as described above, when the distance between the nickel hydroxide powder and the current collector is large, a resistance component is generated by the amount of the active material between the nickel hydroxide powder and the current collector. In the discharge reaction, nickel hydroxide powder whose oxidation number is close to divalent and whose conductivity is lowered is present between them. As a result, the resistance component becomes very large. As a function of such a resistance component, the utilization factor of the active material of the nickel electrode using the core metal as a current collector becomes low,
The discharge curve also results in a lack of flatness. Therefore, in order to improve the utilization rate of the active material of this electrode, it is essential to reduce this resistance component. As a countermeasure from this viewpoint, it is conceivable to control the decrease in the conductivity of nickel hydroxide with the progress of the discharge reaction, but such a decrease in the conductivity cannot be controlled. Therefore, the conductivity of the active material powder is usually improved by mixing a nickel hydroxide powder with a conductive material powder such as graphite or nickel powder. However, there is usually a large contact resistance between the conductive material powder and the nickel hydroxide powder, and simply mixing the conductive material powder with the nickel hydroxide powder does not necessarily lead to a dramatic improvement in the utilization rate. . Therefore, it is necessary to take measures to reduce the contact resistance between the conductive material powder and the nickel hydroxide powder. As such a countermeasure, for example, when graphite powder is used as the conductive material powder, there is a method of reducing the contact resistance by mixing the graphite powder with nickel hydroxide powder and then kneading. However, graphite does not exist stably in an oxidizing atmosphere in an alkaline solution to which the nickel electrode is exposed, and gradually decomposes to form carbonate radicals, which causes a phenomenon of contaminating the electrolytic solution. In particular, fine particle graphite has a strong effect of reducing the contact resistance, and at the same time has a drawback that it is easily decomposed, so that the effect does not last for a long time, the utilization rate of the active material decreases with time, and the decomposition of such a conductive material is Is the most significant cause of deterioration of the discharge characteristics. The present invention has been made in view of the above problems of the prior art, eliminates the disadvantages of the nickel electrode that mechanically fills the active material, and activates the electrode of the method that mechanically fills the active material. An object of the present invention is to provide a nickel electrode for an alkaline storage battery, which can be manufactured inexpensively and easily by improving the material utilization rate, and has a high utilization rate of an active material, and an alkaline storage battery using the same.

[0004]

Means for Solving the Problems The present inventor has conducted various studies to solve the above problems, and freely uses a cobalt compound to reduce the contact resistance between the conductive material powder and the nickel hydroxide powder. Since the material that can be selected and is used as the conductive material is not limited to graphite, the inventors have found that the conventional problem of deterioration of discharge characteristics due to decomposition of graphite can be solved and have created the present invention. That alkaline storage battery of nickel electrodes of the present invention, in the alkaline storage battery of nickel electrodes were mechanically filling the active material, nickel hydroxide powder as an active material, a conductive material powder, flour is a mixture of cobalt compound powder
Nickel battery for alkaline storage battery mechanically filled with powder
In the pole, the conductive material powder is scale-like nickel powder.
Ri, said cobalt compound has the property of precipitating as once dissolved after cobalt hydroxide as a cobalt complex ion in alkaline electrolyte, a mixed amount of the cobalt compound is pre
It is characterized in that it is 2.0 to 10.0 wt% of the powder material . Examples of nickel electrodes for alkaline storage batteries that are mechanically filled with an active material as referred to in the present invention include pocket-type electrodes, button-type electrodes, and core metal-type electrodes. It is preferable that the cobalt compound has a property of being once dissolved as a cobalt complex ion in an alkaline electrolyte and then deposited. As a result, it dissolves once and precipitates as cobalt hydroxide on the surface of the conductive material powder or nickel hydroxide powder, and the conductive material powder and nickel hydroxide powder are connected very firmly to improve the conductivity of the active material. is there. Examples of such cobalt compounds include C
oO, β-Co (OH) ₂ , α-Co (OH) _{2 and the} like. The amount of the cobalt compound mixed is based on the total powder material.
On the other hand, it is 2.0 to 10.0 wt%. If the amount of the cobalt compound mixed is less than 2.0 wt% with respect to the total powder material, the contact resistance of the conductive material powder and / or nickel hydroxide powder is not sufficiently reduced, and the utilization rate of the active material is reduced. 90%
Less than On the other hand, if it exceeds 10.0 wt%, the amount of the conductive material powder and / or the nickel hydroxide powder added is relatively decreased, and the capacity of the electrode is decreased as a whole. The electric conductivity of the material powder is preferably 10 ⁻² S · cm ⁻¹ or more, more preferably 2 × 10 ⁻² S · cm ⁻¹ or more. The conductive material powder to be added is required to have a shape that is alkali resistant and has a contact resistance as small as possible from the viewpoint of preventing deterioration of discharge characteristics due to nickel electrode cycles. From this viewpoint, in the present invention
Applies scale-like nickel powder as the conductive material powder.
The amount of conductive material powder added is such that the conductivity of the powder material is 10 ^-2 S.
-It is desirable to set it to be cm- ¹ or more. If the amount of addition is small, even if the cobalt compound is added to reduce the contact resistance, the conductivity of the active material layer is not sufficient, and a dramatic improvement in the active material utilization cannot be obtained.

[0005]

The cobalt compound, which has the property of being dissolved once in an alkaline electrolyte, passing through cobalt ions, and then precipitated, has the effect of lowering the contact resistance between the conductive material powder and the nickel hydroxide powder. That is, the cobalt compound mixed with the nickel hydroxide powder together with the conductive material powder dissolves once after the alkali injection, and is deposited as cobalt hydroxide on the surfaces of the conductive material powder and the nickel hydroxide powder. Such cobalt hydroxide is changed to irreversible cobalt oxyhydroxide having high conductivity by the first charge, and such cobalt oxyhydroxide connects the conductive material powder and the nickel hydroxide powder very firmly to form the active material. Improves conductivity and dramatically improves active material utilization.

[0006]

EXAMPLES Examples of the present invention will be described below. There are pocket type electrodes, button type electrodes, core metal type electrodes, etc. as the nickel electrodes to be mechanically filled, but the core metal has the most remarkable effect on the active material utilization rate and high rate discharge characteristics. Formula electrodes were selected and implemented. Example 1 Production of nickel electrode Nickel hydroxide powder (92-b) wt% to cobalt monoxide powder bwt
% And graphite powder 8 wt% were mixed to obtain an active material. Here, b was variously set in the range of 0.0 to 2.5 wt%. Polytetrafluoroethylene (3 wt%) was added to the active material as a binder, and processed into a sheet having a thickness of 300 μm. The active material sheet was pressed on both sides of the nickel mesh to form a nickel electrode having a thickness of 0.7 mm. Production of storage battery By combining the nickel electrode obtained above with a paste type cadmium electrode as a counter electrode, inject a potassium hydroxide aqueous solution with a specific gravity of 1.26 and leave it for 24 hours after injecting the electrolyte to dissolve and re-precipitate cobalt monoxide. A battery having a flowable electrolyte was obtained. Charge / Discharge Test Temperature 20 ℃, Charge 0.1CA × 15 hours, Discharge 0.2CA (End voltage 1.
00V) was repeated. Figure 1 shows the relationship between the amount of cobalt monoxide powder added and the active material utilization rate. As shown in the figure, by adding 0.5 wt% or more of cobalt monoxide powder, the active material utilization rate exceeds 85%, and particularly when 2.0% or more is added, the utilization rate is further improved to 90%. The above utilization rate is achieved. In such an example, the cobalt monoxide powder changes to a stable and irreversible cobalt oxyhydroxide upon initial charging.

Example 2 Nickel powder was used as a conductive material instead of graphite powder, and nickel hydroxide powder (70 _-c ) wt%, cobalt monoxide powder cw% and nickel powder 30 wt% were mixed to obtain an active material. . A nickel electrode and a storage battery were produced in the same manner as in Example 1 except that this active material was used. In the above, c is
Various settings were made within the range of 2 to 10 wt%. The reason why the amount of cobalt monoxide added is wide in this example is that nickel powder has a larger contact resistance than graphite powder.
The nickel powder 30 wt% has almost the same volume as the above graphite powder 8 wt%. In addition, in this embodiment, nickel powder having three different shapes was used. Figure 2 shows an electron micrograph of the nickel powder used. Fig. 3 shows the relationship between the amount of cobalt monoxide powder added and the active material utilization rate for nickel powder of various shapes shown in Fig. 4. As shown in FIGS. 2 and 3, the utilization ratio of the active material is improved by adding the cobalt monoxide powder in the range of 2 to 10 wt% regardless of the shape of the nickel powder. However, as shown in FIG. 3, the degree of improvement in the utilization rate of the active material varies depending on the type of nickel powder, and when the scale-like nickel powder shown in FIG. It is found that the utilization rate of the active material is improved by the smallest amount of the cobalt monoxide powder added. This example shows that the addition of the cobalt monoxide powder can improve the utilization rate of the active material for the conductive materials other than the graphite powder. In addition, it can be seen that a remarkable effect can be obtained particularly when the conductive material has a scaly shape.

Comparative Example 1 Nickel hydroxide powder (100 _-a ) wt% graphite powder awt%
Were mixed as an active material, and otherwise a nickel electrode and a storage battery were prepared in the same manner as in Example 1. Note that a is 5 to 20 wt%
Various settings were made within the range. The storage battery obtained as described above was repeatedly charged and discharged at a temperature of 20 ° C. for 0.1 CA × 15 hours and discharged at 0.2 CA (final voltage 1.00 V). Figure 4 shows the relationship between the amount of graphite powder added and the conductivity of the active material in that case. Fig. 5 shows the relationship between the amount of graphite powder added and the active material utilization rate in that case. It can be seen from FIGS. 4 and 5 that there is a correlation between the active material utilization rate and the active material conductivity. The active material utilization rate and the active material electrical conductivity initially improve with an increase in the amount of graphite powder added. However, the addition amount
It reaches the ceiling around 8wt%, and the active material utilization rate does not exceed 85%. Therefore, it can be said that the addition of 8 wt% or more of graphite powder is invalid. Comparing this result with the result of Example 1 described above, it can be seen that the cobalt monoxide powder has the effect of further improving the utilization rate of the active material, which has reached the ceiling.

Comparative Example 2 A nickel electrode and a storage battery were manufactured in the same manner as in Example 1 except that an active material containing cobalt oxyhydroxide powder added in place of the cobalt monoxide powder was used, and a charge / discharge test was conducted. . As a result, in this case, the utilization factor of the active material was about the same as b = 0.0 in Example 1, that is, the same as when cobalt hydroxide was not added (FIG. 1). From this result, it can be seen that the effect of adding the cobalt monoxide powder is obtained by the dissolution and reprecipitation process. Although cobalt monoxide was used as an additive in the above examples, the object of the present invention can be achieved as long as it is a cobalt compound having the property of being once dissolved as a cobalt complex ion in an alkaline solution electrolyte and then precipitated. It is possible to obtain the same effects as those of the first and second embodiments.

[0010]

As described above, according to the present invention, in the nickel electrode that is mechanically filled with the active material, the nickel electrode powder, the conductive material powder, and the cobalt compound that produces the cobalt complex ion in the alkaline electrolyte are used as the active material. By using the substance, it is possible to provide an inexpensive nickel electrode for an alkaline storage battery having a high utilization rate of an active material and an alkaline storage battery using the same.

[Brief description of drawings]

[1] relates to the battery embodiment of the present invention, is a diagram showing the relationship between cobalt monoxide powder addition amount and the utilization of the active material in the case of using the graphite powder as a conductive material.

FIG. 2 shows various nickel powders used for carrying out the present invention.
It is an electron micrograph which shows a particle structure .

FIG. 3 is a graph showing the relationship between the amount of cobalt monoxide powder added and the active material utilization rate when the present invention is carried out using various nickel powders as conductive materials.

FIG. 4 is a diagram showing the relationship between the amount of graphite powder added and the electrical conductivity of the active material.

FIG. 5 is a graph showing the relationship between the amount of graphite powder added and the active material utilization rate.

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01M 4/24-4/32 H01M 4/62

Claims (2)

(57) [Claims] 1. A nickel electrode for an alkaline storage battery in which a powder material consisting of nickel hydroxide powder, conductive material powder and cobalt compound powder is mechanically filled, wherein the conductive material powder is scale-like nickel powder and the cobalt compound is It has the property of once dissolving as cobalt complex ions in an alkaline electrolyte and then precipitating as cobalt hydroxide, and the mixing amount of the cobalt compound is 2.0 to 10.
Nickel electrode for alkaline storage battery, characterized in that it is 0 wt%. 2. An alkaline storage battery using a nickel electrode for alkaline storage battery mechanically filled with nickel hydroxide powder as an active material, wherein the nickel electrode for alkaline storage battery is the nickel for alkaline storage battery according to claim 1. An alkaline storage battery characterized by being an electrode.