JPH0622113B2 - Nickel positive electrode for alkaline storage battery and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nickel positive electrode for an alkaline storage battery and a method for producing the same, in which nickel hydroxide powder is used as a main active material, and the nickel hydroxide powder is directly filled inside a support. Alternatively, it is generally applicable to the positive electrode coated on the support plate.

Structure of Conventional Example and Problems Thereof The nickel positive electrode is roughly classified into a sintered body of metal powder as a support, a sintering type in which a nickel salt is impregnated therein, and an active material mixture mainly composed of nickel hydroxide powder. It is classified as a non-sintered type that is filled in the support or applied to the support plate. The former generally has relatively excellent charge and discharge characteristics, but is somewhat expensive. On the other hand, the latter generally has the possibility of relatively high capacity density and low cost, but on the other hand, it is slightly inferior in characteristics as an electrode for charging and discharging. Further, here, a foamed metal type nickel positive electrode in which a foamed metal which is commercially available recently is used as a support, and a powder mainly containing nickel hydroxide is filled therein is also included in the latter.

As described above, the non-sintered nickel positive electrode is usually slightly inferior to the sintered nickel positive electrode in various electrode characteristics, but among them, the foam metal nickel positive electrode is relatively characteristic of the sintered nickel positive electrode. Close to. Moreover, the packing density of the active material is as high as the advantage of the non-sintering type, and is about 1.3-
I have 1.5 times.

However, regarding the utilization rate of the active material, the foam metal type shows a low value as compared with 95% to 100% of the sintering type similarly to other non-sintering types. The value is roughly 60 to 70% with nickel hydroxide powder alone, and 85 to 95% at present even if various additives and conductive materials are added. Further, the numerical values have variations, and in order to increase the capacity and density, which is a characteristic of the non-sintering type, it is necessary to improve and stabilize the utilization rate of the active material.

A foam metal nickel positive electrode will be described in more detail as a typical nickel positive electrode using nickel hydroxide powder as a starting material. To improve the utilization rate of the active material of this electrode, nickel hydroxide powder has been conventionally used. There has been proposed a method of adding cobalt powder or nickel powder when filling the inside, a method of leaving the electrode in a water-containing state to promote the effects of those additives and conductive materials, and the like. However, even if these methods are used, the improvement of the active material utilization rate of the commercially available nickel hydroxide powder is about 85 to 95%, and the value is still low compared with the sintering type, and the variation is somewhat large.

The active material utilization rate of this electrode also has a causal relationship with the packing density. What has been described so far is approximately 400 to 5 when the active material packing density is approximately the same as the maximum value of the sintering formula, that is, 289 mAh per 1 g of nickel hydroxide.
Although it is the case of 00 mAh / cc, at an active material packing density of 500 mAh / cc or more, the active material utilization rate decreases as the value increases, and even if the utilization rate is improved by the conventional method, it becomes 550
At about mAh / cc, it tends to decrease to 80 to 90%. In order to realize the high capacity density, which is an advantage of the non-sintered electrode, it is also extremely important to improve the utilization rate of the active material during high density filling.

OBJECT OF THE INVENTION It is an object of the present invention to improve the active material utilization rate of a nickel positive electrode and stabilize it by improving nickel hydroxide powder which is an active material powder.

The nickel positive electrode of the present invention is one in which an active material mixture mainly composed of nickel hydroxide is filled in or coated on a support, and nickel hydroxide which is a main component of the active material is present inside the particles. It is characterized by containing fine cobalt particles.

In addition, the above nickel hydroxide particles are produced by an aging step of neutralizing a nickel salt solution with an alkali to grow the nickel hydroxide particles produced, a water washing step, a drying step, and a step of crushing as necessary, It is obtained as one containing cobalt fine particles by dispersing the cobalt fine particles in the solution at the stage from the neutralization to the aging step.

As the nickel salt, nickel sulfate or nickel nitrate is used, and since the aqueous solution of these is acidic, there is a disadvantage that the surface is oxidized if cobalt is added before neutralization.

Description of Examples FIG. 1 shows a schematic structure in which a part of nickel hydroxide particles obtained by the method of the present invention is shown in cross section. The particle size of this particle 1 is about 60 μm. The particles are aggregated during growth. Therefore, the space portion indicated by 2 exists in the inside of the particle 1 in a mesh shape. Conventionally, the powder is in such a state, but in the present invention, cobalt fine particles are added as shown by 3 in the process of forming an aggregate of nickel hydroxide, and this is included in the particle 1. The cobalt fine particles 3 are inside the particles 1 and most of them are in contact with the space.

Example 1 13 kg of nickel sulfate having water of crystallization of hexahydrate is dissolved in water to make the total volume 40. This is maintained at about 25 ° C., and 8 kg of caustic soda powder is added as an alkali with sufficient stirring. Next, 0.3 kg of carbonyl cobalt powder having a particle size of 0.1 to 10 μm was immediately added, and the mixture was stirred at about 50 ° C. for 1 hour.
Leave for hours. The precipitate formed by forming aggregates of elementary particles is passed over, dried, and then pulverized to obtain a desired particle size. Then, it is thoroughly washed with water and dried to obtain about 5 kg of nickel hydroxide powder.

Nickel hydroxide 8 having a particle size of 0.1 to 150 μm thus obtained
10 parts by weight of carbonyl nickel powder and 2 parts by weight of carbonyl cobalt powder are mixed with 8 parts by weight, and water is added thereto and kneaded into a paste form. The kneaded product has a porosity of 95%,
It is filled in a foamed nickel porous plate having an average pore diameter of 200 μm and a thickness of 1.3 mm, dried and pressed to obtain an electrode having a thickness of about 0.7 mm and a packing density of nickel hydroxide powder of 500 to 550 mAh / cc.

Example 2 In the same manner as in Example 1, an aqueous solution of nickel sulfate, caustic soda powder and carbonyl cobalt powder were prepared, these were mixed at the same time, and stirring was continued while maintaining the temperature at about 50 ° C. to obtain nickel hydroxide particles. When the particles grow to 1 μm or more, the particles are taken out, and a nickel positive electrode is obtained in the same manner as in Example 1.

Example 3 In Example 1, a mixture of 5 kg of lithium hydroxide and 4 kg of caustic soda was used in place of caustic soda.
A nickel positive electrode is obtained in the same manner as in. The nickel hydroxide obtained here contains cobalt powder and lithium hydroxide.

Example 4 In Example 1, 0.5 kg of carbonyl nickel powder was added together with the carbonyl cobalt powder, and a nickel positive electrode was obtained in the same manner as in Example 1 below.

The nickel hydroxide obtained here contains nickel powder as well as cobalt powder.

A sealed nickel-cadmium storage battery KR-C was prototyped by combining the nickel positive electrode obtained in Example 1 and a general-purpose cadmium load having a larger capacity than the positive electrode, and the discharge capacity thereof was measured to examine the active material utilization rate.

Packing density of nickel positive electrode is about 450,500,550mA
The cells were adjusted to h / cc and the above-mentioned batteries were manufactured as prototypes for each of 20 sheets (20 cells for each). Charging was performed at 250 mA for 16 hours, and discharging was performed at 500 mA to a final voltage of 1.0V. All tests were carried out at 20 ° C, and the amount of discharge electricity at the stable third cycle was measured. 1 g of a powder mainly composed of nickel hydroxide
The amount of electricity per unit was calculated as 289 mAh to obtain the active material utilization rate. The remaining maximum value and minimum value excluding one cell for the maximum value and the minimum value are shown by a and a'in FIG. As a comparative example, the same results are shown by b (maximum value) and b ′ (minimum value) in the case of using a commercially available nickel hydroxide powder as a comparative example.

Although the example using the nickel positive electrode of Example 1 is given here, the use of the electrodes of Examples 2 to 4 also improves the utilization factor of the active material to some extent, but the results are almost the same as in Example 1.

As is clear from the above results, the nickel positive electrode according to the present invention has a higher utilization ratio of the active material than that of the conventional one, and a small variation.

The reason for this is that in an electrode using a nickel hydroxide powder having a diameter of 10 to 100 times as large as a starting material, as compared with the case of adding with a nickel salt as in a sintering method,
It seems that there is a limit to the effect of adding cobalt, which is currently most effective in improving the utilization rate of the active material. In other words, it is considered that the inside of the nickel hydroxide particles is unlikely to be affected. Therefore, it is considered that by adding cobalt to the inside of the nickel hydroxide particles in advance as in the present invention, the effect of adding cobalt is enhanced and the utilization rate of the active material is improved.

Further, the smaller the particle size of the cobalt particles in the nickel hydroxide particles is, the more uniformly they are dispersed, and the effect on the utilization rate of the active material tends to appear. Therefore, it is preferable to use carbonyl cobalt having a particle size of 0.1 to 10 μm.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a nickel positive electrode having a high utilization rate of the active material and having a constant quality.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the structure of nickel hydroxide according to an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between nickel hydroxide packing density and active material utilization rate. 1 ... Nickel hydroxide particles, 3 ... Cobalt powder.

Claims (4)

[Claims] 1. A nickel positive electrode containing nickel hydroxide powder as a main active material, wherein the nickel hydroxide contains at least metal cobalt fine particles inside the nickel positive electrode for an alkaline storage battery. . 2. The particle size of the metal cobalt fine particles in the nickel hydroxide is 0.1 to 10 μm.
The nickel positive electrode for alkaline storage batteries according to the item. 3. The nickel positive electrode for an alkaline storage battery according to claim 1, wherein the nickel hydroxide further contains nickel fine particles or a hydroxide of lithium. 4. A nickel salt solution is neutralized with an alkali,
A step of obtaining a nickel hydroxide containing cobalt fine particles by dispersing the cobalt fine particles in the solution at a stage from the neutralization to the aging step, which has an aging step of growing nickel hydroxide particles to be generated. Of manufacturing a nickel positive electrode for an alkaline storage battery having the same.