JP3250840B2 - Paste electrode for alkaline secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste type electrode for an alkaline secondary battery.

[0002]

2. Description of the Related Art A sintered positive electrode has conventionally been used as an electrode for an alkaline secondary battery, for example, a positive electrode (the negative electrode is almost the same, so the positive electrode will be described below). This sintered positive electrode, for example, by sintering nickel powder on a core metal such as a perforated steel plate or nickel net, impregnating the pores of more than ten microns with a nickel salt aqueous solution, and then subjecting this to alkali treatment, It was obtained by changing the impregnated nickel salt to nickel hydroxide. However, this sintered type positive electrode requires complicated operations such as nickel salt impregnation and alkali treatment at the time of production, and the above operation is usually performed about 4 to 10 times to impregnate a predetermined amount of active material. Since it has to be repeated, 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, a nickel hydroxide powder is mixed with a conductive powder, a binder and water to form a paste, and then has an average porosity of 95% or more and an average pore size of several tens to A method has been proposed in which a positive electrode is manufactured by directly filling the paste into an alkali-resistant metal porous material such as a three-dimensional sponge-like metal porous material or a metal fiber mat of several hundred microns. This method is called a non-sintering method or a paste method as opposed to a sintering method.

[0004] Since the paste type electrode has a large porosity and an average pore diameter of the porous metal body, it has an advantage 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 current collecting property is degraded depending on the distance from the active material to the current collector bulk. It was as low as about 60% for 95% of the formula electrodes, 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 cobalt compounds such as cobalt oxide and cobalt hydroxide and metallic cobalt is used. There is a method of adding it in the paste. However, even with the addition of the cobalt compound or the like, the active material utilization rate is at most about 85%, and there is a variation of about 10%, so that the active material utilization rate of the sintered electrode has not been reached.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems, and it is intended to improve the active material utilization and to stabilize the active material utilization with little variation. It is an object of the present invention to provide a paste type electrode for an alkaline secondary battery, which is capable of being used.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a paste type electrode for an alkaline secondary battery in which an alkali-resistant porous metal is filled with an active material mixture.
It is to contain a positive electrode active material or negative electrode active material, a Co ₂ O ₃
CoO powder (hereinafter referred to as cobalt oxide powder).
Measured according to the method specified in JIS M8233.4.
The Co ₂ O ₃ content in the obtained CoO powder is 6% by weight.
It is a paste type electrode for an alkaline secondary battery characterized by the following.

[0008] Examples of the alkali-resistant porous metal include those having a porous structure such as a net, sponge, fiber, and felt. Examples of the material thereof include nickel or a metal such as stainless steel or a resin plated with nickel. Examples of the positive electrode active material include nickel hydroxide. Examples of the negative electrode active material include Cd (OH) ₂ , metal cadmium, CdO, and the like.

The amount of Co ₂ O ₃ in the above-mentioned cobalt oxide powder is measured by a method specified in JIS M8233.4. The measurement of the amount of Co ₂ O ₃ in the cobalt oxide powder by such a method is performed according to the following principle. That is, the cobalt oxide powder is converted to sulfuric acid-acidic iron sulfate (I
I) When dissolved in an aqueous solution, Co (II) ions due to CoO and Co (III) ions due to Co ₂ O ₃ are generated,
As shown in the following formula (1), the Co (III) ion is Fe
(II) reduced by ions; Fe ²⁺ + Co ³⁺ → Fe ³⁺ + Co ²⁺ (1)

By quantifying the Fe (III) ion generated at this time with an aqueous potassium permanganate solution, C
Since o (III) ions are indirectly quantified, the amount of Co ₂ O _{3 in} cobalt oxide can be measured. In the conventional paste type electrode, the presence of Co ₂ O ₃ in the cobalt oxide powder was confirmed by an X-ray diffraction method or the like.
Cobalt oxide powder was used without knowing the amount of ₂ O ₃ .

The above-mentioned cobalt oxide powder can be produced as follows. That is, a cobalt hydroxide (Co (OH) ₂ ) powder having a particle size of 0.5 to 20 μm is fired at a firing temperature of 300 to 600 ° C.
By firing under the conditions of firing time 5 to 48 hours,
Manufacture cobalt oxide powder. This firing step is preferably performed in an inert gas atmosphere so as not to promote the oxidation reaction more than necessary. In some cases, the firing step may be performed in a reducing atmosphere to further suppress the acceleration of the oxidation reaction. Since the method of producing a cobalt oxide powder by firing such a cobalt hydroxide powder is based on a simple dehydration reaction, there is an advantage that it is easy to estimate physical properties such as a particle diameter and a surface area of the obtained cobalt oxide powder. .

In the active material mixture mainly composed of the positive electrode active material or the negative electrode active material, a thickener and the like may be blended as required in addition to the cobalt oxide powder. Examples of the thickener include carboxymethylcellulose, methylcellulose, and sodium polyacrylate.

The above-mentioned paste type electrode can be manufactured, for example, as follows. First, cobalt oxide powder is added to the positive electrode active material or the negative electrode active material, and kneaded with a thickener and water to form a paste. Next, the paste-type nickel electrode is manufactured by filling the paste into the alkali-resistant metal porous body, drying and molding the paste. Next, the operation of the paste electrode of the present invention will be described.

In the past, it has been known that the addition of a cobalt compound to the active material mixture can improve the utilization rate of the active material. One of the reasons that the electrode does not reach that is that the cobalt compound itself is unstable and the oxidation reaction proceeds during storage, resulting in a slightly different cobalt compound. In general, the mechanism for improving the active material utilization rate by adding a cobalt compound is that the cobalt compound dissolves in an alkaline electrolyte and a divalent so-called blue complex ion (HCoO ₂ ⁻ ), And
After that, it is adsorbed as cobalt hydroxide (Co (OH) ₂ ) so as to cling to the surface of the active material, and cobalt oxyhydroxide (CoOOH) having high conductivity at a more noble potential.
To coat 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 the alkaline electrolyte. Further, when the paste mainly composed of the active material is prepared, the cobalt compound particles are activated. It must be well mixed with the material particles. As described above, the cobalt compound reduced the active material utilization rate of the electrode for an alkaline secondary battery by the conventional (8).
In order to improve and stabilize, the cobalt compound is mainly (1) rapidly dissolved in the alkaline electrolyte, (2) well mixed with the active material at the time of paste preparation, (3) It is important to satisfy the three points of excellent storage stability.

According to the paste type electrode of the present invention, Co is contained in the active material mixture mainly composed of the positive electrode active material or the negative electrode active material.
By adding a cobalt oxide powder having an amount of ₂ O ₃ of 6% by weight or less and a balance of CoO, the utilization rate of the active material can be improved to the same level as or higher than that of the sintered electrode. This is because CoO and Co ₂ O ₃ are more effective as additives for improving the active material utilization rate than other cobalt compounds such as metallic cobalt and cobalt hydroxide. Further, the reason why the amount of Co ₂ O ₃ in the cobalt oxide powder is limited will be described below.

That is, as the cobalt oxide, CoO,
There are Co ₂ O ₃ and Co ₃ O ₄ . Co ₃ O
₄ is extremely stable, so 2
Value of the blue complex ion (HCoO ₂ ^- ) Is not produced and conductive CoOOH cannot be obtained, so that the utilization rate of the active material cannot be improved.

It is said that it is difficult to obtain any one of these cobalt oxides in a completely pure state. For example, by heating Co (OH) ₂ in an inert gas, CoO having the lowest oxygen content can be obtained.
Can be synthesized, but contains a small amount of Co ₂ O ₃ and Co ₃ O ₄ instead of completely pure CoO. The ratio of Co ₂ O ₃ and Co ₃ O _{4 in} this cobalt oxide is
Co ₂ O ₃ is the majority and Co ₃ O ₄ is very small.

[0018] The Co ₂ O ₃ is dissolved in an alkaline electrolyte as with CoO, 2 divalent blue complex ion (HCoO ₂ ^- ) To obtain conductive CoOOH to improve the utilization of the active material.
Has a lower solubility in an alkaline electrolyte. For this reason, when the Co ₂ O ₃ content of the added cobalt oxide increases, the cobalt oxide does not completely change to CoOOH, which leads to a decrease in the active material utilization rate. Therefore, increase the active material utilization rate,
In addition, in order to reduce the variation in the utilization rate of the active material, it is very important to control the amount of Co ₂ O ₃ in the cobalt oxide.

The paste-type electrode of the present invention has been found based on such a viewpoint. By limiting the amount of Co ₂ O ₃ in the cobalt oxide powder to 6% by weight or less, the paste-type electrode of the cobalt oxide powder has Since it is possible to prevent a decrease in the utilization rate of the active material due to solubility in the electrolytic solution, the utilization rate of the active material is improved to the same level as or higher than that of the sintered electrode, and the utilization rate of the active material is small. It becomes possible to be stable.

[0020]

Embodiments of the present invention will be described below in detail.

First, after dissolving metallic cobalt (m-Co) in an aqueous sulfuric acid solution, an aqueous solution of sodium hydroxide is gradually added to neutralize the solution to obtain α-cobalt hydroxide (α-Co).
A crystal of Co (OH) ₂ ) was obtained. By further aging, it was converted to β-cobalt hydroxide (β-Co (OH) ₂ ) which is relatively stable even in air.

Next, the β-cobalt hydroxide is placed in an inert gas atmosphere (in some cases, in a reducing atmosphere) for 20 minutes.
By sintering each at an arbitrary temperature of 0 to 600 ° C. for 20 hours, various cobalt oxide powders containing Co ₂ O ₃ and the balance being CoO were obtained. The amount of Co ₂ O ₃ in each cobalt oxide powder thus obtained was determined according to JIS M8233.
It measured by the method prescribed | regulated in 4.

Each of the obtained cobalt oxide powders was added in an amount of 10 parts by weight based on 100 parts by weight of the nickel hydroxide powder, and kneaded with a thickener such as carboxymethyl cellulose and water to form a paste. Subsequently, the paste was filled into a nickel-plated metal porous body (alkali-resistant metal porous body) having a porosity of 95% and an average pore diameter of 200 μm, dried, and then molded to obtain a paste-type nickel positive electrode.

The paste-type nickel positive electrode thus obtained is combined with a paste-type cadmium negative electrode, a separator made of nylon nonwoven fabric, an alkaline electrolyte mainly composed of potassium hydroxide, a metal battery container, and a metal lid. , A nickel-cadmium secondary battery was assembled. The aging conditions from battery assembly to first charge were 25 ° C. and 19 hours.

Each of the batteries was charged at a current of 0.5 C to a depth of 150% and discharged at a current of 1 C repeatedly for 10 cycles, and the activity of the paste-type nickel positive electrode at the 10th cycle having a sufficiently stable discharge capacity was repeated. Material utilization was investigated.
The result is shown in FIG. FIG. 1 shows the JISM823.
FIG. 6 is a characteristic diagram showing a change in the active material utilization rate of the paste nickel positive electrode with respect to the amount of Co ₂ O ₃ in the cobalt oxide powder measured by the method specified in 3.4.

As is apparent from FIG. 1, when the amount of Co ₂ O ₃ in the cobalt oxide powder is 6% by weight or less, the active material utilization of the paste nickel positive electrode is sufficiently high.

Therefore, by adding a cobalt oxide powder having a Co ₂ O ₃ content of 6% by weight or less and a balance of CoO, the active material utilization of the paste-type nickel electrode can be improved and the active material utilization can be improved. It was confirmed that the rate could be made stable with little variation.

[0028]

As described above in detail, according to the present invention, a paste for an alkaline secondary battery capable of improving the active material utilization rate and stabilizing the active material utilization rate with less variation. A formula electrode can be provided.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a change in the active material utilization rate of a paste nickel positive electrode with respect to the amount of Co ₂ O ₃ in a cobalt oxide powder.

Claims (1)

(57) [Claims] 1. A paste-type electrode for an alkaline secondary battery in which an alkali-resistant metal porous body is filled with an active material mixture , wherein the active material mixture comprises : a positive electrode active material or a negative electrode active material;
CoO powder containing o ₂ O ₃ and JIS M823.
The CoO powder measured by the method specified in 3.4.
A paste electrode for an alkaline secondary battery , wherein the content of Co ₂ O ₃ therein is 6% by weight or less .