JPH10199519A - Nickel electrode and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain uniform closest packing in an electrode plate and reduce the quantity of an additive so as to obtain an electrode of a low price and high energy density by specifying the ratio of the cobalt compound powder particle diameter to the nickel hydroxide powder particle diameter of an electrode that are filled in an alkali resistant metallic porous body. SOLUTION: A nickel electrode composed of nickel hydroxide powder and a cobalt compound additive agent is left, as it is, in an alkali electrolytic liquid before formation so as to resolve the cobalt compound as a bivalent complex ion, and to be uniformly dispersed in the electrode, to be changed in CoOOH during the initial discharging time, and thus conductivity between active material particles is secured. Then, any cobalt compound left out of alteration can not be changed to CoOOH regardless of its repetition of cycles. Although an excessive quantity of cobalt compound is added so as to effectively use active material, since the nickel hydroxide powder made to have high density has a spherical shape, high density filling is limited to some extent, the cobalt compound particle diameter is set to be less than 1/10 of the nickel hydroxide particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nickel electrode and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, as portable electronic devices have become smaller and lighter, it has been desired to increase the energy density of batteries as power sources. The nickel electrode of a conventional alkaline battery is called a sintering electrode. A nickel substrate is impregnated with a nickel nitrate solution on a porous substrate obtained by sintering nickel powder on a core metal such as a perforated steel sheet, and then an alkaline aqueous solution is used. It is manufactured by a so-called solution impregnation method in which a hydroxide is filled in the solution, and filling is performed. However, the energy density of the nickel positive electrode was limited to about 400 mAh / cc. In addition, in order to secure a required capacity, a sintered electrode needs to repeat a complicated step of filling an active material many times, and there is a problem that a long time is required and a manufacturing cost is high.

On the other hand, at present, for the purpose of increasing the capacity,
Past-type electrodes which control the growth of internal pores of nickel hydroxide powder particles, which had conventionally been low-density, to increase the density thereof, and achieve high-density filling of the electrodes are becoming mainstream. The paste-type electrode is one in which an alkali-resistant metal substrate having a higher porosity than that of the sintered electrode is directly filled with nickel hydroxide powder which is made into a paste with water or the like. In this paste type electrode, the filling space of the substrate is increased in order to secure the active material filling amount. Therefore, the paste type electrode has a lower current collecting property for the active material than the substrate of the sintered type electrode, and therefore, for example, metal cobalt, a cobalt compound or the like is indispensable as an additive for imparting conductivity.

[0004]

Here, the cobalt compound changes to stable CoOOH by an irreversible reaction at the time of initial charge, and the CoOOH achieves conduction between the nickel hydroxide particles. However, since the metal cobalt powder undergoes a three-electron reaction with Co → CoOOH + 3e ⁻ when changing to CoOOH, a large amount of electricity is required, and the capacity balance between the positive electrode and the negative electrode is lost, and the battery life is shortened. there were. Therefore, it was found that the addition of a cobalt compound that forms divalent cobalt ions having a small number of reactive electrons as described below, in particular, the addition of CoO having a higher alkali solubility than the others, is effective, for example, in place of metal cobalt. It has been proposed in Japanese Patent Publication No. 7-77129.

[0005] Co ²⁺ ions → CoOOH + e ^- The high energy density of the nickel hydride batteries or nickel-cadmium batteries have been recently developed practical Co
O addition is essential. By the way, the high-density nickel hydroxide powder in which the internal pore growth of the nickel hydroxide powder particles is controlled is different from the low-density nickel hydroxide having a conventional amorphous shape, in that the particle morphology develops into a spherical shape. For this reason, although the filling property of the powder is better than the case where amorphous nickel hydroxide is used, a certain amount of filling gap occurs even if the powder is filled to the highest density because of its spherical shape. Therefore, in order to secure a sufficient positive electrode utilization rate, it is necessary to add CoO as much as 8 to 12% by weight based on the whole active material, thereby increasing the cost of the battery material, or increasing the amount of nickel hydroxide as the active material itself. Was also limited.

[0006]

The first object of the present invention is to provide an alkali-resistant metal which is obtained by adding a nickel compound powder and a cobalt compound powder which is dissolved in an alkaline electrolyte to form a divalent cobalt complex ion. In a nickel electrode filled in a porous body, the particle diameter of the cobalt compound powder is set to 1/10 or less of the particle diameter of the nickel hydroxide powder.

A second aspect of the present invention is that the cobalt compound is
2. The nickel electrode according to claim 1, wherein said nickel electrode is added to nickel hydroxide in a range of 2 to 6 wt% in terms of metal Co.

[0008] A third aspect of the present invention is to provide nickel hydroxide powder with:
In a method for manufacturing a nickel electrode using an active material to which a cobalt compound powder that dissolves in an alkaline electrolyte to form a divalent cobalt complex ion is added, the particle size of the cobalt compound powder is set to 10 times the particle size of the nickel hydroxide powder. A step 1 of classifying the cobalt compound into one part or less, a step 2 of adding nickel hydroxide powder to the cobalt compound to form a battery active material paste, and a step 3 of filling the paste into an alkali-resistant porous metal.
And a method for producing a nickel electrode.

[0009]

A nickel electrode comprising nickel hydroxide powder and a cobalt compound additive is immersed in an alkaline electrolyte before chemical formation to dissolve the cobalt compound as a divalent complex ion and uniformly disperse it in the electrode. After that, it is changed to stable CoOOH at the time of initial charging, and the conductivity between the active material particles is secured by CoOOH.

However, since the cobalt compound has low solubility in alkali and CoOOH covers the active material very densely, the cobalt compound which is not changed to CoOOH during the first charge and is left as a divalent complex ion It cannot be diffused between the active material particles, and does not change to CoOOH even if the cycle is repeated. For this reason, it is necessary to add an excessive amount of a cobalt compound in advance to sufficiently utilize the active material effectively, and to sufficiently diffuse the divalent cobalt complex ion between the active material particles.

Also, since the densified nickel hydroxide powder has a spherical shape, there is a limit in filling the powder at a high density.

The present invention achieves uniform close packing in the electrode by reducing the particle size of the cobalt compound to be added to at least one-tenth of the particle size of the nickel hydroxide particles, and at the same time reduces the amount of addition. , High energy density and reduction in battery cost.

[0013]

The present invention will be described below with reference to examples. A commercially available CoO obtained by wet classification to a particle size of 0.1 to 0.5 μm is mixed with a high-density nickel hydroxide powder having a particle size of 5 to 50 μm at a ratio of 5 parts by weight to 95 parts by weight to form a paste. The nickel electrode of the present invention was obtained by filling an alkali-resistant metal substrate. On the other hand, for comparison, a comparative electrode 1 in which a paste obtained by mixing CoO and high-density nickel hydroxide powder in a ratio of 10 parts by weight to 90 parts by weight without wet classification of CoO into an alkali-resistant metal substrate, Also, a comparative electrode 2 was prepared by filling a paste mixed with CoO and high-density nickel hydroxide powder in a ratio of 5 parts by weight to 95 parts by weight without wet classification in an alkali-resistant metal substrate. Using these nickel electrodes as a counter electrode of a normal cadmium electrode, an open-type battery with excess liquid was prepared and charged and discharged. Table 1 shows the results.

[0014]

[Table 1]

In Table 1, the discharge utilization rate is obtained by dividing the discharge capacity at the third cycle when the theoretical capacity of nickel hydroxide is 290 mAh per gram by the theoretical capacity and multiplying by 100. As is clear from Table 1, the nickel electrode of the present invention can obtain a sufficient capacity even when the addition amount of CoO is Ｃｏ.

The X-ray diffraction diagrams of the electrode of the present invention and the comparative electrode 2 after the above-mentioned charge / discharge test are shown in FIGS. Despite the same amount of CoO added to nickel hydroxide, the characteristic diffraction peak of CoO was observed at around 36.6 degrees and 42.2 degrees in the comparative electrode 2 of FIG. 2, indicating that CoO remained. . On the other hand, no diffraction peak of CoO was observed in the electrode of the present invention shown in FIG. 1, indicating that CoO was completely dissolved.

FIG. 3 is a schematic view showing the formation of a conductive network of CoOOH of the electrode of the present invention. The electrode of the present invention is C
Since the particle size of oO is classified into one-tenth or less of the particle size of nickel hydroxide, it is considered that the particles of CoO are uniformly dispersed in the gaps between the densely packed nickel hydroxide particles. . In addition, the specific surface area increases due to the small particle size,
It is considered that the dissolution of CoO is promoted, and a uniform conductive network is formed with a smaller addition amount than before.

FIG. 4 is a schematic diagram showing the formation of a conductive network of CoOOH of the comparative electrode 2. In the comparative electrode 2, since the CoO particles are not classified, they are not uniformly dispersed, many undissolved portions remain, and the formation of the conductive network is considered to be insufficient.

In the above embodiment, only the case of CoO has been described, but other cobalt compounds which form divalent cobalt complex ions, for example, β-Co (OH) ₂ , α-C
A similar trend was observed with o (OH) ₂ .

Although a wet classifier is used in the embodiment, the same effect can be obtained by using another dry classifier.

[0021]

As described above, in the present invention, uniform close-packing in the electrode plate is achieved by setting the particle size of the cobalt compound to be added to 1/10 or less of the particle size of the nickel hydroxide particles. At the same time, it is possible to provide an inexpensive and high-energy-density nickel electrode for an alkaline storage battery and an alkaline storage battery using the same, the amount of which is reduced, and the industrial value thereof is extremely large.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of the electrode of the present invention.

FIG. 2 is an X-ray diffraction diagram of a comparative electrode 2.

FIG. 3 is a schematic view showing formation of a conductive network of CoOOH of the electrode of the present invention.

FIG. 4 is a schematic diagram showing the formation of a conductive network of CoOOH of a comparative electrode 2.

Claims (3)

[Claims] 1. A nickel electrode obtained by filling an alkali-resistant metal porous body with an active material obtained by adding a cobalt compound powder which dissolves in an alkaline electrolyte to form a divalent cobalt complex ion to nickel hydroxide powder, The particle size of the cobalt compound powder is set to 1/10 of the particle size of the nickel hydroxide powder.
A nickel electrode characterized by the following. 2. The nickel electrode according to claim 1, wherein said cobalt compound is added to nickel hydroxide in a range of 2 to 6 wt% in terms of metal Co. 3. A method for producing a nickel electrode using an active material obtained by adding a cobalt compound powder which dissolves in an alkaline electrolyte to form a divalent cobalt complex ion to nickel hydroxide powder, the method comprising: Step 1 of classifying the diameter to one-tenth or less of the particle diameter of the nickel hydroxide powder
And a step 2 of adding a nickel hydroxide powder to the cobalt compound to form a battery active material paste, and a step 3 of filling the paste into an alkali-resistant metal porous body.