JPH08213011A - Nickel paste electrode and alkaline storage battery using this nickel electrode - Google Patents

Abstract

PURPOSE: To enhance charging efficiency at high temperature in spite of a small amount of additive, and lengthen life. CONSTITUTION: Nickel hydroxide powder, a small amount of calcium zincate powder, and cobalt hydroxide powder are mixed, then the mixture is kneaded together with carboxymethylcellulose to prepare slurry. The slurry is filled in a foamed nickel substrate, dried, pressed, then the nickel substrate is cut to produce a nickel paste electrode. A hydrogen storage alloy electrode serving as an anode and the nickel electrode are wound together with a nonwoven fabric separator so as to position the hydrogen storage alloy electrode in the outer periphery to form an electrode group. The electrode group is put into a cylindrical battery can, and 31 wt.% potassium hydroxide aqueous solution is poured into the can to manufacture a sealed nickel hydrogen storage battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste type nickel electrode and an alkaline storage battery using the same.
In particular, it relates to improvement of the characteristics of the paste type nickel electrode.

[0002]

2. Description of the Related Art Conventionally, alkaline storage batteries such as nickel-cadmium storage batteries and nickel-hydrogen storage batteries have been widely used in portable equipment as rechargeable secondary batteries. With the remarkable development of electronic parts such as ICs, downsizing and weight reduction of portable devices are progressing, and there is a strong demand for higher capacity of these alkaline storage batteries. As a means for increasing the capacity of the nickel electrode, a paste nickel electrode has been proposed instead of the sintered nickel electrode. The paste-type nickel electrode is manufactured by using a felt made of sponge-like nickel porous material or nickel fiber as a current collector, and filling it with a slurry-like active material containing nickel hydroxide as a main component. A cobalt compound is added to the slurry-like active material to supplement conductivity.
Furthermore, in order to (1) increase the charging efficiency at high temperature, and (2) suppress the formation of γ-type nickel oxyhydroxide during overcharging or charging with a large current density, a mixed hydroxide of zinc is used. Nickel is used as an active material (Japanese Patent Application Laid-Open No. 2-30
061), and the use of an active material in which an oxide or hydroxide of calcium or zinc is mixed with nickel hydroxide (JP-A-5-101825).
The reason why it is necessary to suppress the production of γ-type nickel oxyhydroxide is that it has a lower density than that of β-type nickel oxyhydroxide that is normally produced, which causes the expansion of the nickel electrode and the loss of the active material, and causes the internal short circuit. Because it will be. further,
This is because γ-type nickel oxyhydroxide absorbs a large amount of the electrolytic solution, which increases the internal resistance of the battery and shortens the battery life.

[0003]

However, in the technique disclosed in the above publication, in order to achieve the objects of the above (1) and (2), the mixed crystal amount of zinc, calcium or zinc oxide or water is used. It is necessary to increase the mixing amount of each oxide. Since these do not participate in the charge / discharge reaction, the significance of adopting the paste nickel electrode in order to increase the capacity of the nickel electrode is diminished. The problem to be solved by the present invention is to improve the charging efficiency at high temperature with a small amount of additives, and further to provide a paste-type nickel positive electrode capable of improving the life characteristics, and an alkaline storage battery exhibiting those characteristics. It is a thing.

[0004]

In order to solve the above-mentioned problems, the paste type nickel electrode according to the present invention (hereinafter referred to as the nickel electrode only) is characterized in that the active material contains calcium zincate. An alkaline storage battery according to the present invention is characterized by using the nickel electrode.

[0005]

[Function] Calcium zincate is added in a smaller amount or mixed crystal than in the prior art in which a zinc compound and a calcium compound are individually added to the nickel electrode or a zinc compound is mixed with nickel hydroxide. The amount can suppress the decrease of the oxygen overvoltage in the high temperature atmosphere of the nickel electrode, and can improve the acceptability of charging. Furthermore, it is possible to suppress the generation of γ-type nickel oxyhydroxide during charging at a high current density such as overcharging or high potential, and it is possible to improve the life characteristics. Since calcium zincate is obtained in the form of powder, it is difficult to incorporate it into the nickel electrode by the impregnation operation in the production of the sintered nickel electrode. In that respect, the paste nickel electrode is
Since the slurry containing the active material can be directly filled in the current collector (base), calcium zincate can be easily contained in the nickel electrode. By using the above nickel electrode, the acceptability of charging under a high temperature atmosphere is good,
Moreover, an alkaline storage battery having improved life characteristics can be obtained.

[0006]

EXAMPLES Examples of the present invention and conventional examples will be described below. (Preparation of calcium zincate in Examples) The calcium zincate used in this Example was prepared as follows. First, calcium hydroxide (Ca (OH) ₂ ) powder is mixed in water at 10 ° C. and stirred to form a saturated solution of calcium compound. Next, zinc oxide (ZnO) powder was added at 60 ° C. and 35 wt% N
Mix in an aOH aqueous solution and stir to form a saturated solution of zinc compound. A precipitate forms when these saturated solutions are mixed. This is calcium zincate.

(Preparation of Nickel Electrode of Example) A nickel electrode constituted by the weight ratio shown in Table 1 using the above-mentioned calcium zincate, nickel hydroxide as an active material, and cobalt hydroxide as a conductive material ( A1 to A4) were produced. At this time, the weight ratio of cobalt hydroxide was 5 wt% in all the electrodes. The electrode preparation conditions are shown below. Mix nickel hydroxide powder, calcium zincate powder, and cobalt hydroxide powder. This is carboxymethyl cellulose 2w
Knead with a t% aqueous solution to form a slurry. This slurry was filled in a foamed nickel substrate having a thickness of 1.2 mm and a porosity of 94%, dried, pressed and cut to give a width of 40 m.
A nickel electrode having m, a length of 74 mm and a thickness of 0.65 mm was produced. Table 1 also shows the theoretical capacities of the nickel electrodes of the examples and conventional examples.

(Preparation of Nickel Electrode of Conventional Example B) 95 wt% of nickel hydroxide powder without using calcium zincate,
A nickel electrode was prepared in the same manner as in the above-described example using only 5 wt% of cobalt hydroxide powder. This is referred to as a conventional electrode B.

(Preparation of Nickel Electrode of Conventional Example C) Ca (OH) ₂ powder or CaO was used without using calcium zincate.
Table 1 shows the powder and Zn (OH) ₂ powder or ZnO powder.
90% by weight of nickel hydroxide powder and 5% by weight of cobalt hydroxide powder were mixed in the weight ratio shown in (1), and the other electrodes (C1 to C4) of the comparative example were manufactured in the same manner as in the above example.

[0010]

[Table 1]

(Production of Battery) As the cathode, a hydrogen storage alloy having a composition of Mm-Ni-Co-Al-Mn prepared by a conventional method is used, and this hydrogen storage alloy is crushed by a mechanical crusher such as a ball mill. Then, the particles having a particle diameter of about 60 to 100 μm were kneaded with hydroxypropylmethyl cellulose as a binder and filled in a foamed nickel substrate,
What was dried and pressed was used. The capacity density of each of the examples and the conventional example was adjusted to 1.4 times the capacity of the nickel electrode. The electrode plate size is 40 mm wide,
The length is 106 mm and the thickness is 0.35 mm. The nickel electrodes of Examples, Conventional Examples and Comparative Examples and the cathode were wound using a known nylon non-woven fabric separator so that the outermost periphery was the cathode. After inserting this electrode group into a cylindrical battery can,
Inject a predetermined amount of 31 wt% potassium hydroxide aqueous solution,
A sealed nickel-metal hydride storage battery of A type was produced.

(Experimental Conditions) As an evaluation of batteries using these nickel electrodes, a charging efficiency test at high temperature and a cycle life test were conducted. Before the test, activation treatment was carried out by a conventional method. The charging efficiency test at high temperature was conducted by charging at 0.1 CmA for 900 minutes in each atmosphere of 25 ° C and 45 ° C.
Final voltage 1.0V at 0.2CmA in 25 ℃ atmosphere
It was discharged up to and the discharge capacity was examined. The ratio of the discharge capacity after charging at 45 ° C. and the discharge capacity after charging at 25 ° C. was calculated. This capacity ratio is the charging efficiency at high temperature. The cycle life test was carried out at an ambient temperature of 20 ° C., at a charging temperature of 1 CmA, and at −ΔV = 10 mV (at the end of charging, when oxygen gas absorption occurred and the charging voltage dropped 10 mV from the peak voltage) until the battery was discharged at 1 CmA. Final voltage 1.0V
Was repeatedly charged and discharged up to, and the life was reached when the active material utilization rate became 70% or less.

(Experimental Results) Table 2 shows the charging efficiency at 45 ° C./25° C. of the batteries (A1 to A4) using the nickel electrode according to the present invention, the conventional battery B and the batteries (C1 to C4). The charging efficiency of the conventional battery (B) at a high temperature is extremely poor at about 65%, and the charging efficiency of the conventional example (C1 to 4) is 86 to 88%.
However, the batteries (A1 to A4) of this example have 90
It can be seen that a charging efficiency of up to 96% is exhibited. From this, the effect of improving the charging efficiency at high temperature of the present invention is clear. Moreover, the effect was obtained even when the amount of the additive (calcium zincate) to the nickel electrode was extremely small. Similarly, Table 2 shows the cycle life frequency. According to this, the battery B of the conventional example
In comparison with the battery of this example, the batteries (A1 to A4) of the present example dramatically extend to 1000 cycles or more, and
It can be seen that it is clearly superior to 4). Therefore, the effect of improving the cycle life characteristics of the present invention is clear.
Moreover, the effect was obtained even when the amount of the additive (calcium zincate) to the nickel electrode was extremely small.

[0014]

[Table 2]

In the present example, calcium zincate was prepared by the method described above, but the present invention is not limited to this. Further, although the nickel electrode of the present invention is applied to the cylindrical nickel-hydrogen battery in the present embodiment, it can be applied to other alkaline storage batteries such as nickel-cadmium battery and nickel-zinc battery. Further, naturally, the shape of the battery is not limited. Further, in this embodiment, the current collector (base) of the nickel electrode is used.
Although a foamed nickel substrate was used as the substrate, any other substrate may be used as long as it can directly fill the slurry containing the active material and calcium zincate.

[0016]

As described above, according to the present invention, it is possible to improve the charging efficiency at high temperature with a small amount of additives and further improve the life characteristics, and the alkaline storage battery exhibiting those characteristics. Could be provided.

Claims (2)

[Claims] 1. A paste-type nickel electrode containing calcium zincate in an active material. 2. An alkaline storage battery using the paste-type nickel electrode according to claim 1.