JP2975130B2 - Electrodes for alkaline storage batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a paste type electrode for an alkaline storage battery.

[0002]

2. Description of the Related Art Conventionally, a sintered positive electrode is used as an electrode for an alkaline storage battery, for example, a positive electrode (the same applies to a negative electrode. This sintered positive electrode is obtained by sintering nickel powder on a core metal such as a perforated steel plate or a nickel net, impregnating a 10 μm or more hole with a nickel salt aqueous solution, and then subjecting the impregnated nickel to an alkali treatment. It was obtained by changing the salt to nickel hydroxide. However, this sintered type positive electrode requires a complicated operation such as impregnation of a nickel salt or alkali treatment at the time of production, and the above operation is usually repeated about 4 to 10 times to impregnate a predetermined amount of active material. Since it has to be performed, there is a problem that the manufacturing cost is increased. Furthermore, since the porosity at which the mechanical strength of the nickel powder sintered body can be maintained is limited to about 80%, there is also a problem that the amount of the active material itself is limited.

In order to solve these problems, nickel hydroxide powder is mixed with a conductive powder, a binder and water to form a paste, and has an average porosity of 95% or more and an average pore diameter of several tens to
There has been proposed a method of manufacturing a positive electrode by directly filling a three-dimensional sponge-like metal porous body or a metal fiber mat of several hundred μm with the material. This method is called a non-sintering method or a paste method as opposed to a sintering method.

[0004] This paste method is very excellent in that the porosity and average pore diameter of the porous metal body are large, so that the active material filling step is easy and the filling amount can be increased. However, since the pores of the porous metal body are larger than in the case of the sintering method, the distance between the active material and the current collector bulk deteriorates the current collecting property. It was as low as about 60% against 95%, and did not reach practical use.

As a means for improving the utilization rate of the active material of the paste type electrode, generally, a combination of two or more of three kinds of cobalt compounds of metal cobalt, cobalt oxide and cobalt hydroxide is used. There is a method of adding to the substance paste. However, even with the addition of this cobalt compound, the active material utilization rate is about 85%, and there is a variation of about 10%, so that it does not reach the level of the sintering active material utilization rate.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made to improve the utilization rate of an active material in a paste type electrode of an alkaline storage battery to about the same or higher than that of a sintered type electrode. Further, the object is to improve the stability.

[0007]

According to the present invention, there is provided an electrode for an alkaline storage battery comprising a porous alkali-resistant metal body filled with a paste containing a positive electrode active material as a main component and a cobalt oxide powder added thereto. , The chemical formula of CoO
Or at least one of Co ₂ O ₃ having a specific surface area of 5 to 50 m ² / g and a tap density of
The present invention relates to an electrode for an alkaline storage battery, which has an amount of 0.5 to 1.5 g / cm ³ .

[0008]

According to the conventional method, it is known that adding a cobalt compound to the active material can increase the utilization of the active material. One is that the cobalt compound itself is unstable and the oxidation reaction proceeds during storage, resulting in a slightly different cobalt compound. Generally, the mechanism of improving the utilization rate of an active material by adding a cobalt compound is that the cobalt compound dissolves in an alkaline electrolyte and a so-called divalent blue complex ion (HCoO ₂ ⁻ ) is formed.
And then adsorbed as cobalt hydroxide (Co (OH) ₂ ) so as to cling to the surface of the active material.
OOH) and coats the surface of the active material. Based on this, it is an absolute condition that the cobalt compound is such that it rapidly dissolves in an alkaline solution, and further, when the paste containing mainly the active material is prepared, the cobalt compound particles become active material particles. Must be well mixed.

As described above, in order for the cobalt compound to further improve and stabilize the utilization rate of the active material of the electrode for an alkaline storage battery beyond the conventional one (about 85%), the cobalt compound must be dissolved in (1) an alkaline solution promptly. It is important to satisfy the following three points: (2) good mixing with the active material during paste preparation, and (3) excellent storage stability.

The cobalt compound used in the present invention is
At least one of those represented by the chemical formula CoO or Co ₂ O ₃ , having a specific surface area of 5 to 50 m ² / g;
Tap density of 0.5 to 1.5 g / cm ^3. By using these, the active material utilization of the electrode can be improved, and can be made equal to or higher than the sintering active material utilization.

In this case, among the many cobalt compounds, at least one of cobalt oxide CoO and CO ₂ O ₃ is limited because the additive for improving the utilization factor is more than m-cobalt and cobalt hydroxide. Is that cobalt oxide is more effective. Also,
In particular, CoO or Co ₂ O ₃ is suitable for mass production in terms of battery production, because it is excellent in storage stability (in air) of the above (3).

That is, CoO has a well-balanced Co atom and O atom, a low chemical potential in air, and a crystallographically stable orthorhombic system. Therefore, for example, the oxidation reaction does not proceed very much even when left in the air. However, when immersed in an alkaline solution, the chemical potential of the hydration of Co ²⁺ and O ²⁻ is much lower than the chemical potential of the lattice of CoO, so that the dissolution reaction as HCo ₂ ⁻ Occur. Co ₂ O ₃ has a hexagonal system in crystallography and is more stable in air than CoO, so that there is almost no deterioration due to storage. Further, although the alkaline solution is slightly less soluble than CoO, the effect on the battery characteristics is not so large.

For example, it is assumed here that, among the cobalt compounds, cobalt hydroxide (α, β-Co (OH) ₂ is generally considered to be good) is directly added to a paste mainly composed of an active material. Then, a question arises when asked about the storage stability during the mass production of cobalt hydroxide. That is, if cobalt hydroxide is stored in the air, a part of it always changes to cobalt oxide during storage. Moreover, the cobalt oxide is not limited to the above-mentioned CoO and Co ₂ O _3, and if storage conditions are poor, extremely stable and useless Co ₃ O ₄ may be produced. Further, the oxidation degree, Co ₃ O ₄ from when viewed in batch scale Co (OH) ₂
This has an extremely wide range, which is not preferable because it leads to a wide range in the utilization rate of the active material itself. In order to stably store cobalt hydroxide, it is conceivable to store it in an alkaline solution whose pH is controlled, but in this case, the handling of the alkaline solution is relatively difficult, so the cost of equipment is high. This is not desirable either. On the other hand, even if it is assumed that m-Co is added to the paste mainly composed of the active material, the oxidation reaction proceeds similarly, and a slight difference in the degree of oxidation occurs unless stored in an inert gas atmosphere. Is not preferable because it gives a difference in the utilization rate of the active material.

[0014]

EXAMPLES Examples of the present invention will be described below with reference to Experiments 1 and 2.

<Experiment 1> Cobalt oxide in this experiment was CoO. The tap density was limited to 0.75 to 1.25 g / cm ³ , and the optimum range of the specific surface area and the amount of addition were examined.

First, after dissolving metallic cobalt (m-Co) in an aqueous sulfuric acid solution, an aqueous sodium hydroxide solution is gradually added to neutralize the solution, and α-cobalt hydroxide (α-Co (O
H) The crystals of ₂ ) are obtained. This is further aged to make β-cobalt hydroxide (β-Co (O
H) Convert to ₂ ). The size of the crystals of cobalt hydroxide should be increased by controlling the pH so that the components are used for crystal growth so as not to form too many crystal nuclei when neutralizing with sodium hydroxide aqueous solution. Can be. Conversely, in order to produce small crystals, the pH may be controlled so that a large number of crystal nuclei of cobalt hydroxide are formed.

The thus obtained β of various sizes
-Cobalt hydroxide was fired at an arbitrary temperature and an arbitrary time under an inert gas atmosphere to obtain cobalt oxide having an arbitrary tap density and an arbitrary specific surface area. The confirmation that cobalt oxide is CoO is as follows.
Performed by X-ray powder diffraction. The specific surface area was measured by a known nitrogen adsorption method, and the tap density was measured by a known tapping method.

Any specific surface area of 2 to 60 m ² obtained above
/ G, a cobalt oxide having a tap density of 0.75 to 1.25 g / cm ³ was left in air at 25 ° C. for 2 weeks intentionally to check the storage stability.
5 to 30% by weight, and kneaded with a thickener such as carboxymethyl cellulose and water to form a paste,
This was filled into a nickel-plated metal porous body having a porosity of 95% and an average pore diameter of 200 μm, and dried and molded to obtain a nickel positive electrode plate.

A nickel-cadmium battery was fabricated by combining the thus obtained positive electrode with a known paste-type cadmium electrode, a nylon nonwoven fabric separator, an electrolyte mainly composed of potassium hydroxide, a metal battery container, and a metal lid. . The aging conditions from battery production to first charge were 25 ° C. and 19 hours.

This battery was charged to a depth of 150% with a current of 0.5c and discharged at a rate of 1c, which was repeated 10 cycles.
The utilization rate at the 10th cycle when the discharge capacity was sufficiently stable was examined. The results are shown in FIG.

FIG. 1 shows that the specific surface area of CoO is 5 to 50 m ^2.
/ G, the addition amount is (nickel hydroxide powder 90% by weight
In the case of 5% by weight or more, it can be seen that the utilization rate exceeds 95%. This can be considered to be equal to or greater than the 95% nickel electrode utilization rate of the sintering method described above. This indicates that, when the surface area of CoO is in this range, CoO does not deteriorate when left in air at 25 ° C. for 2 weeks, and that the dissolution in the alkaline electrolyte is sufficiently performed during aging. I have. But,
The usage rate of CoO having such a specific surface area and having an addition amount of 30% by weight is the same as that of 20% by weight, indicating that the addition is excessive.

On the other hand, those having a specific surface area of less than 5 m ² / g and those having a specific surface area of more than 50 m ² / g, even at 5% by weight, reach a peak at a utilization rate of at most about 80 to 85%. Even if we increased the number, the utilization rate only decreased. That is, those having a specific surface area of less than 5 m ² / g are:
Since the surface area is small, the dissolution rate with respect to the alkaline electrolyte is low, and CoO with respect to aging for the same time after injection
The absolute amount of dissolution is small. This is probably because a sufficient conductive film (CoOOH) was not formed on the surface of the nickel hydroxide particles. With respect to those having a specific surface area of more than 50 m ² / g, even if the surface area is too large and CoO is relatively stable in the air, the oxidation reaction proceeds during the storage, and the vicinity of the surface is not stable such as Co ₃ O _4. It is considered that the same phenomenon as that having a specific surface area of less than 5 m ² / g was caused as a result of the change to the conductor. Co ₃ O ₄ has a crystal structure called a spinel type and is extremely stable and hardly soluble in an alkaline solution. Also, in any case, the usage rate decreases with the addition of 5% by weight or more.
This is probably because cobalt oxide, which could not be dissolved in the alkaline electrolyte during aging, worked as insulation resistance.

In summary, in summary, cobalt oxide is CoO
When the tap density is 0.75 to 1.25 g / cm ³ , C
The oO having a specific surface area of 5 to 50 m ² / g is excellent in storage stability in air, and the addition amount of CoO is 5 to 20% by weight with respect to 100% by weight of nickel hydroxide. The rate can be increased to the same level as or higher than that of a conventional sintered nickel electrode.

<Experiment 2> In this experiment, cobalt oxide was CoO, the specific surface area was limited to 10 to 40 m ² / g, and the amount of cobalt oxide was limited to 15% with respect to 100% by weight of nickel hydroxide powder. Above, the optimal range of the tap density was examined.

The specific surface area is 10 to 40 m ² / g, and the amount of cobalt oxide added is 15 to 100% by weight of nickel hydroxide powder.
% And a tap density of 0.3 to 2.0 g / cm ³ , a battery was assembled in exactly the same manner as in Experiment 1, and evaluated under the same charge / discharge conditions. FIG. 2 shows the relationship between the tap density and the nickel pole utilization rate in this experiment.

FIG. 2 shows that the tap density is 0.5 to 1.5 g / cm ^3.
In the case of, the utilization rate is 95%, and when less than 0.5 g / cm ³ , the utilization rate is about 85%. Further, when the tap density exceeds 1.5 g / cm ³ , it is reduced to about 80%. From this, the tap density is 0.3-1.5g /
In the case of cm ³ , it is considered that the formation of the conductive film CoOOH (at the time of the first charge) is quickly and smoothly caused by the dissolution of CoO on the surface of the nickel hydroxide particles during the preparation of the paste of the CoO particles. .

On the other hand, CoO having a tap density of less than 0.5 g / cm ³ has poor dispersibility with nickel hydroxide particles at the time of preparing the paste of CoO particles. It is considered that the current collection efficiency did not increase because the CoOOH conductive film was not sufficiently formed on the surface of the nickel oxide particles, and the utilization rate was limited to about 85%. In addition, since the conductive film of CoOOH is not uniform, current is concentrated on a part of nickel hydroxide at the time of charging, and γ is considered to be difficult to discharge.
Since nickel oxyhydroxide (γ-NiOOH) has been formed, it is considered that the utilization factor is low. Furthermore, the reason why the utilization rate dropped to about 80% although the tap density exceeded 1.5 g / cm ³ was due to the contradictory physical properties of the tap density and the specific surface area. That is, an increase in the tap density means that the crystal itself is small and easily clogged, which means that the specific surface area of the crystal becomes small. By the way, only those having a specific surface area of about 2 m ² / g could be produced with a tap density of 2.0 g / cm ³ . In other words, the reason for the low utilization rate is that
Similar to that described in Experiment 1, which results in solubility of CoO.

From the above results, when the cobalt oxide was CoO, the specific surface area was 5 to 50 m ² / g, and the amount of CoO added was limited to 15% by weight with respect to 100% by weight of nickel hydroxide powder, the tap density was It was found that when the value was 0.3 to 1.5 g / cm ³ , the utilization rate of the nickel electrode could be increased to the same level as or higher than that of the conventional sintered nickel electrode.

As described above, in Experiments 1 and 2, the case where the cobalt oxide synthesized from cobalt hydroxide was CoO was described. Instead of CoO, Co ₂ O ₃ or C ₂ O _{3 was used.}
It was confirmed that similar results were obtained even with a mixture with oO.

In addition to Experiments 1 and 2, CoO
Alternatively, at least one of Co ₂ O ₃ is added in an amount of 5 to 100% by weight of the nickel hydroxide powder.
20 wt%, and the specific surface area and tap density of cobalt oxide are 3 to 50 m ² / g and 0.5 to 1.5 g / cm, respectively.
It was confirmed that by setting ³ , the utilization rate of the nickel electrode can be improved to 95% or more.

Although the active material has been described as nickel hydroxide, the present invention is not limited to this, and examples thereof include Cd (OH) ₂ , metal Cd, and CdO as negative electrode active materials. Further, the alkali-resistant metal porous body filled with the active material paste is not limited to the nickel-plated metal porous body.

[0032]

As described above, according to the present invention,
The utilization rate of the paste-type alkaline storage battery electrode can be improved to the same level as or higher than that of the sintered type.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the specific surface area of cobalt oxide, the amount of cobalt oxide added, and the nickel electrode utilization rate when the tap density of cobalt oxide is constant.

FIG. 2 is a diagram showing the relationship between the tap density of cobalt oxide and the nickel electrode utilization rate when the specific surface area of cobalt oxide and the amount of cobalt oxide added are constant.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuyuki Hata Inventor Toshiba Battery Co., Ltd., 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo (58) Field surveyed (Int. Cl. ⁶ , DB name) H01M 4 / 62 H01M 4/24-4/32

Claims (1)

(57) [Claims] 1. An alkaline storage battery electrode comprising an alkali-resistant metal porous body filled with a paste mainly composed of a positive electrode active material and a cobalt oxide powder added thereto, wherein the cobalt oxide has a chemical formula of CoO or At least one of Co ₂ O ₃ , whose specific surface area is 5
~ 50m ² / g, the alkaline storage battery electrode tap density, characterized in that a 0.5 to 1.5 g / cm ^3.