JPH09147907A - Paste type nickel electrode for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paste type nickel electrode, in which discharging capacity is hardly reduced after over discharge, by using active material powder consisting of composite grains in each of which a coating layer of magnesium hydroxide or zinc hydroxide covering the surface of nickel hydroxide grain is covered with a cobalt hydroxide layer. SOLUTION: In a paste type nickel electrode, active material powder consisting of composite grains, in each of which the surface of nickel hydroxide grain is covered with a magnesium hydroxide layer or a zinc hydroxide layer and this coating layer is covered with a cobalt hydroxide layer, is used. In this composite grain, 0.05-3% by weight of the magnesium hydroxide layer or the zinc hydroxide layer are container desirably. Meanwhile, the composite grain contains 1-20% by weight of the cobalt hydroxide layer feasibly.

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 for an alkaline storage battery, and more specifically, for suppressing a decrease in discharge capacity due to a decrease in conductivity after over-discharging,
The present invention relates to improvement of active material powder.

[0002]

2. Description of the Related Art
As a nickel electrode for an alkaline storage battery, a sintered nickel electrode obtained by impregnating a sintered substrate obtained by sintering nickel powder on a perforated steel plate or the like with an active material (nickel hydroxide) is well known.

[0003] In order to increase the packing density of the active material in the sintered nickel electrode, it is necessary to use a sintered substrate having a high porosity. However, the bond between the nickel particles due to sintering is weak, and if the porosity of the sintered substrate is increased, the nickel powder tends to fall off the sintered substrate. Therefore, in practice, the porosity of the sintered substrate cannot be made larger than 80%, and the sintered nickel electrode has a problem that the packing density of the active material is small. Moreover, since the pore size of the sintered body of nickel powder is as small as 10 μm or less, the filling of the active material into the substrate (sintered body) must be performed by the solution impregnation method, which requires repeated complicated impregnation steps several times. There is also the problem of not becoming.

Under these circumstances, a paste type nickel electrode has recently been proposed. The paste nickel electrode is
It is prepared by directly filling a kneaded material (paste) of an active material (nickel hydroxide) and a binder solution (aqueous solution of methyl cellulose, etc.) into a substrate (foamed metal, etc.) having a high porosity. Since the paste nickel electrode can use a substrate having a large porosity (the paste nickel electrode can use a substrate having a porosity of 95% or more), it is possible to increase the packing density of the active material. The active material can be charged into the substrate once.

However, when a substrate having a high porosity is used in order to increase the packing density of the active material in the paste type nickel electrode, the current collecting ability of the substrate becomes worse than that of the sintered substrate. In comparison, the conductivity becomes worse. Such poor conductivity leads to a reduction in utilization rate of the active material and a shortening of charge / discharge cycle life.

In order to improve the conductivity of such a paste type nickel electrode, the surface of the nickel hydroxide particles may be coated with cobalt hydroxide to increase the conductivity of the surface of the active material particles. Cobalt hydroxide is dissolved in the alkaline electrolyte to form monovalent HCoO ₂ ⁻ , and this HCoO ₂ ⁻ becomes highly conductive CoOOH (cobalt oxyhydroxide) at a noble potential and nickel hydroxide. This is because they are deposited on the surface of the particles. A method for coating the surface of such nickel hydroxide particles with cobalt hydroxide is disclosed in JP-A-62-23.
It is disclosed in Japanese Patent No. 4867 and Japanese Patent Laid-Open No. 62-237667. In addition, JP-A-3-62457 proposes a method of coating the surface of nickel hydroxide particles with a solid solution coating of nickel hydroxide and cobalt hydroxide.

However, in these paste type nickel electrodes, the cobalt oxyhydroxide existing on the surface of the nickel hydroxide particles diffuses inside the particles during repeated charge and discharge cycles, and the nickel hydroxide particle surface It has been found that there is a problem that the conductivity is lowered, and as a result, the discharge capacity is lowered. In particular, the decrease in discharge capacity after overdischarge was remarkable. This is because cobalt oxyhydroxide (the cobalt hydroxide layer is oxidized to cobalt oxyhydroxide at the time of charging) does not change in normal discharge, but cobalt oxyhydroxide is reduced in the case of overdischarge. Is converted to cobalt hydroxide [CoOOH + H ₂ O + e ^- ⇒
This is because it is more likely to diffuse into the nickel hydroxide particles than Co (OH) ₂ + OH ⁻ ], nickel oxyhydroxide.

The present invention has been made to solve the above-mentioned problems of the conventional paste type nickel electrode, and an object thereof is to provide an alkaline storage battery whose discharge capacity does not easily decrease even after over-discharge. Providing a pasted nickel electrode.

[0009]

In a paste type nickel electrode for an alkaline storage battery (electrode of the present invention) according to the present invention for achieving the above object, the surface of the nickel hydroxide particles is replaced by a magnesium hydroxide layer or water. An active material powder composed of composite particles coated with a zinc oxide layer and coated with the magnesium hydroxide layer or the zinc hydroxide layer with a cobalt hydroxide layer is used.

The electrode of the present invention is produced by filling a non-sintering type porous substrate with a kneaded material (paste) of an active material powder and a binder solution (such as an aqueous solution of methylcellulose), drying, and press-molding. It

The nickel hydroxide particles in the present invention include
Solid solution particles in which cobalt, zinc, cadmium, calcium, manganese, magnesium, and the like are solid-dissolved in nickel hydroxide are also included.

The formation of the two coating layers on the surface of the nickel hydroxide particles is carried out, for example, as follows. First, nickel hydroxide powder is placed in a zinc sulfate aqueous solution or a magnesium sulfate aqueous solution, an alkaline aqueous solution (sodium hydroxide aqueous solution, etc.) is added dropwise with stirring, and the formed precipitate is filtered off,
Vacuum drying is performed to obtain a powder composed of composite particles in which the surface of nickel hydroxide particles is coated with zinc hydroxide or magnesium hydroxide. Then, put this powder in an aqueous cobalt sulfate solution (if necessary, an aqueous cobalt sulfate solution to which magnesium sulfate or zinc sulfate has been added may be used), add an alkaline aqueous solution with stirring, and filter the formed precipitate. Then, by vacuum drying, active material powder composed of composite particles in which two coating layers are formed on the surface of nickel hydroxide particles is obtained.

The above composite particles have a magnesium hydroxide layer or zinc hydroxide layer content of 0.05 to 3% by weight.
Are preferred. If the content is less than 0.05% by weight, the diffusion of cobalt hydroxide into the nickel hydroxide particles is not sufficiently suppressed because the amount of magnesium hydroxide or zinc hydroxide is too small. On the other hand, when the content exceeds 3% by weight, the conductivity of the surface of the nickel hydroxide particles is not sufficiently improved because the intermediate layer is too thick, and the amount of nickel hydroxide directly related to the capacity decreases. Therefore, the battery capacity becomes small.

The composite particles preferably have a cobalt hydroxide layer content of 1 to 20% by weight.
If the content is less than 1% by weight, the conductivity of the nickel hydroxide particles cannot be sufficiently improved because the amount of cobalt hydroxide as the conductivity-imparting agent is too small. On the other hand, if the content exceeds 20% by weight, the amount of nickel hydroxide, which is directly related to the capacity, decreases, and the battery capacity decreases. The cobalt hydroxide layer may be a layer formed of a solid solution in which magnesium hydroxide or zinc hydroxide is solid-dissolved in cobalt hydroxide. In this case, the preferred weight ratio of cobalt hydroxide to magnesium hydroxide or zinc hydroxide is 5 or more.

In the electrode of the present invention, the cobalt hydroxide produced by over-discharging becomes a solid solution with magnesium hydroxide or zinc hydroxide and changes into a solid solution (mixed crystal) which is difficult to diffuse into the nickel hydroxide particles. Even after over-discharging, the excellent conductivity of the surface of the nickel hydroxide particles does not easily deteriorate.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is widely applicable to a paste type nickel electrode used as a positive electrode of an alkaline storage battery such as a nickel-cadmium storage battery or a nickel-hydrogen storage battery.

[0017]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

(Examples 1 to 10) [Preparation of powder consisting of composite particles] 100 g of nickel hydroxide powder was mixed with a predetermined weight% of zinc sulfate aqueous solution (0.008 weight% in the case of A4) or magnesium sulfate aqueous solution ( A
1% (0.01% by weight in the case of 1) was added to 1 liter, 1N-sodium hydroxide aqueous solution was added dropwise to the mixture with stirring until the pH reached 12, and the formed precipitate was filtered off and dried in vacuum.
A powder composed of composite particles in which the surface of nickel hydroxide particles was coated with zinc hydroxide or magnesium hydroxide was obtained. The coating amount at this time was adjusted by the concentration of zinc sulfate or magnesium sulfate. As the nickel hydroxide powder, a powder composed of solid solution particles in which cobalt hydroxide and calcium hydroxide were solid-dissolved in nickel hydroxide was used (weight of Co / (weight of Ni + weight of Co) × 100 = 1%; C
Weight of a / (weight of Ni + weight of Ca) × 100 = 1
%).

Next, 100 g of this powder was added to a 0.8 wt% cobalt sulfate aqueous solution (in Example 9, a magnesium sulfate-added cobalt sulfate aqueous solution, and in Example 10 a zinc sulfate-added cobalt sulfate aqueous solution, respectively). (1) used, and 1N-sodium hydroxide aqueous solution was added dropwise with stirring until the pH reached 12, and the formed precipitate was separated by filtration and vacuum dried to form a double layer on the surface of the nickel hydroxide particles. An active material powder composed of composite particles having a coating layer formed was obtained. The outer layer of the composite particles prepared in Example 9 was composed of a solid solution having a weight ratio of cobalt hydroxide to magnesium hydroxide of 9: 1, and the outer layer of the composite particles prepared in Example 10 was water. It consisted of a solid solution with a weight ratio of cobalt oxide to zinc hydroxide of 9: 1.

[Preparation of Paste Type Nickel Electrode] 80 parts by weight of each active material powder described above and 20 parts by weight of a 1% by weight methylcellulose aqueous solution are kneaded to prepare a paste, and this paste is nickel-plated foam metal (porous metal). 95 degrees
%, An average pore diameter of 200 μm) was filled, dried and pressure-molded to prepare 10 kinds of paste nickel electrodes (electrodes of the present invention).

[Preparation of Alkaline Storage Battery] Each of the above-mentioned paste type nickel electrodes (positive electrode), a known paste type cadmium electrode (negative electrode) having a larger electrochemical capacity than the positive electrode, polyamide nonwoven fabric (separator), 30 wt% water AA size alkaline storage batteries (battery capacity: about 1200 mAh) A1 to A10 were produced using a potassium oxide aqueous solution (alkali electrolyte solution), a metal battery can, a metal battery lid, and the like.

Comparative Example 1 100 g of nickel hydroxide powder
Was added to 1 liter of a 0.8 wt% cobalt sulfate aqueous solution, and the pH of the 1N-sodium hydroxide aqueous solution was adjusted with stirring.
The resulting precipitate was filtered off and dried under vacuum to obtain a powder consisting of composite particles in which the surface of nickel hydroxide particles was coated with cobalt hydroxide. Next, a paste type nickel electrode (reference electrode) and an alkaline storage battery B1 were produced in the same manner as in Examples 1 to 10 except that this powder was used as the active material powder.

(Comparative Example 2) 100 g of nickel hydroxide powder
To cobalt sulfate and magnesium sulfate respectively.
8% by weight and 0.1% by weight of an aqueous solution of 0.1% by weight were added to 1 liter, and 1N-sodium hydroxide aqueous solution was added while stirring.
It was added dropwise until H12, the precipitate formed was filtered off, and dried in vacuum to form a solid solution (mixed crystal) of nickel hydroxide particles on the surface of which the weight ratio of cobalt hydroxide and magnesium hydroxide was 9: 1. A powder consisting of the coated composite particles was obtained. Next, a paste type nickel electrode (reference electrode) and an alkaline storage battery B2 were produced in the same manner as in Examples 1 to 10 except that this powder was used as the active material powder.

(Comparative Example 3) Nickel hydroxide powder 100 g
0.8 wt% of cobalt sulfate and zinc sulfate
And 1 liter of 0.08% by weight solution,
With stirring, 1N-sodium hydroxide aqueous solution was added to pH 12
The resulting precipitate is filtered off and dried under vacuum to coat the surface of the nickel hydroxide particles with a solid solution (mixed crystal) of cobalt hydroxide and zinc hydroxide in a weight ratio of 9: 1. A powder consisting of the composite particles was obtained. Next, a paste type nickel electrode (reference electrode) and an alkaline storage battery B3 were produced in the same manner as in Examples 1 to 10 except that this powder was used as the active material powder.

<Discharge capacity maintenance rate after over-discharging of each battery> After each battery was charged at 160% at 120 mA, 1.
A charging / discharging cycle test in which the step of discharging to 1.0 V at 2 A was set as one cycle was performed, and the discharge capacity C1 at the 10th cycle of the paste nickel electrode used for each battery was obtained.
Next, after the 10th cycle of discharging, each battery was further over-discharged at 120 mA by 20%, charged at 120 mA by 160%, and then discharged at 1.2 A to 1.0 V to obtain a discharge capacity C2. The ratio P of C2 to C1 was calculated by the following formula, and the over-discharge resistance characteristics of each battery were evaluated. The larger P indicates that the paste-type nickel electrode that can be used is an electrode in which the diffusion of cobalt hydroxide into the nickel hydroxide particles does not easily occur during overdischarge. Table 1 shows the results.

P (%) = (C2 / C1) × 100

[0027]

[Table 1]

As shown in Table 1, the batteries A1 to A10 are P
Is large, whereas batteries B1 to B3 have small P. From this fact, a composite obtained by coating the surface of nickel hydroxide particles with a magnesium hydroxide layer or a zinc hydroxide layer, and further coating the magnesium hydroxide layer or the zinc hydroxide layer with a cobalt hydroxide layer. It can be seen that by using the powder made of particles, a paste-type nickel electrode in which the conductivity is less likely to decrease even after over-discharging can be obtained.

[0029]

EFFECT OF THE INVENTION The electrode of the present invention is less likely to decrease in conductivity even after overdischarge.

Front page continued (72) Inventor Reizou Maeda 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (72) Inventor Katsuhiko Niiyama 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Denki Co., Ltd. (72) Inventor Masao Inoue 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Denki Co., Ltd. (72) Inventor Ikuo Yonezu 2-chome, Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A composite obtained by coating the surface of nickel hydroxide particles with a magnesium hydroxide layer or a zinc hydroxide layer, and coating the magnesium hydroxide layer or the zinc hydroxide layer with a cobalt hydroxide layer. A paste-type nickel electrode for alkaline storage batteries that uses active material powder consisting of particles. 2. The paste-type nickel electrode for an alkaline storage battery according to claim 1, wherein the composite particles contain 0.05 to 3% by weight of the magnesium hydroxide layer or the zinc hydroxide layer. 3. The paste type nickel electrode for an alkaline storage battery according to claim 1, wherein the composite particles contain the cobalt hydroxide layer in an amount of 1 to 20% by weight. 4. The paste-type nickel electrode for an alkaline storage battery according to claim 1, wherein the cobalt hydroxide layer is made of a solid solution of cobalt hydroxide and magnesium hydroxide or zinc hydroxide.