JPH09147904A - Paste type nickel electrode for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paste type nickel electrode for an alkaline storage battery, in which high conductivity can be maintained for a long time in a charge- discharge cycle, by using a composite grain, in which a coating layer made of a cobalt compound with a specific valence is formed on the surface of a nickel hydroxide grain possessing a specific physical properly, as an active material. SOLUTION: In a composite grain constituting the powder used as an active material, a coating layer made of a cobalt compound, whose mean valence is more than 2 and not more than 3, is formed on the surface of a nickel hydroxide grain with a half value width of 0.35-0.7 degree for an X-ray diffraction peak on a grating face 101. For the cobalt compound whose mean valence is more than 2 and not more than 3, a mixture of cobalt hydroxide and cobalt oxyhydroxide or cobalt oxyhydroxide is available. A ratio of cobalt to the composite grain is 1-10% by weight desirably.

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, it is an object of the present invention to provide a paste type nickel electrode capable of maintaining high conductivity for a long period of a charge / discharge cycle. , Improvement of active materials.

[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.

Therefore, in order to improve the conductivity of such a paste type nickel electrode, a nickel hydroxide powder (active material) having a half-value width of the X-ray diffraction peak of the lattice plane (101) of 0.8 degrees or more is used. , Metallic cobalt, or cobalt compounds such as cobalt hydroxide and cobalt monoxide having an average valence of 2 or less have been proposed (JP-A-4-3).
28257).

However, in this paste-type nickel electrode, the cobalt initially present on the surface of the nickel hydroxide particles diffuses inside the particles during repeated charge and discharge cycles, and the conductivity of the electrode plate deteriorates. Therefore, it was found that an alkaline storage battery having a sufficiently long charge / discharge cycle life cannot be obtained.

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 maintain high conductivity for a long period of charge / discharge cycle. It is possible to provide a paste type nickel electrode for alkaline storage batteries.

[0009]

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 has a half-value width of an X-ray diffraction peak of a lattice plane (101) plane. Powder having composite particles formed by forming a coating layer made of a cobalt compound having an average valence of cobalt of more than 2 and not more than 3 on the surface of nickel hydroxide particles of 0.35 to 0.7 degree. Use as active material.

In the electrode of the present invention, nickel hydroxide particles having a half-value width of the X-ray diffraction peak of the lattice plane (101) of 0.35 to 0.7 degrees are used as the nickel hydroxide particles. When the half-value width of the X-ray diffraction peak on the lattice plane (101) plane of the nickel hydroxide particles is less than 0.35 degrees (when the crystallinity of the nickel hydroxide particles is too high), diffusion of protons during charge / discharge Since the speed is reduced, the utilization rate of the active material is reduced and the charge / discharge cycle life is shortened. On the other hand, when the half-value width exceeds 0.7 degrees (when the crystallinity of the nickel hydroxide particles is too low), diffusion of the cobalt coating the surface of the nickel hydroxide particles into the particles easily occurs. Therefore, the conductivity of the surface of the nickel hydroxide particles is lowered, and as a result, the utilization rate of the active material is lowered and the charge / discharge cycle life is shortened.

In the electrode of the present invention, a cobalt compound having an average cobalt valence of more than 2 and not more than 3 is used as the cobalt compound for coating the nickel hydroxide particles. When the average valence of cobalt is 2 (in the case of cobalt hydroxide), the conductivity of the electrode plate cannot be sufficiently enhanced. The average valence of cobalt is regulated to 3 or less because there is no cobalt compound having an average valence of cobalt greater than 3. To increase the active material utilization rate,
It is preferable to coat with a cobalt compound having an average valence of 2.5 to 2.93.

Nickel hydroxide particles having a half-value width of 0.35 to 0.7 degrees of the X-ray diffraction peak of the lattice plane (101) plane are, for example, nickel sulfate aqueous solution and aqueous ammonia in water in a reaction vessel. In addition, the pH of the solution is adjusted by adding an alkaline aqueous solution, and then mixed by stirring for a predetermined time to obtain a precipitate. The higher the pH of the liquid during the reaction, the more
Nickel hydroxide particles having a large half-value width of the X-ray diffraction peak of the lattice plane (101) plane, that is, low crystallinity are obtained. The nickel hydroxide particles according to the present invention have a half-value width of 0.35 of the X-ray diffraction peak of the lattice plane (101) plane.
Solid solution particles in which cobalt, zinc, cadmium, calcium, manganese, magnesium, and the like are solid-dissolved in nickel hydroxide having a temperature of up to 0.7 degrees are also included.

The coating layer is formed on the surface of the nickel hydroxide particles by, for example, mixing nickel hydroxide powder and cobalt hydroxide powder, adding an alkaline aqueous solution thereto, and then heat-treating at a predetermined temperature for a predetermined time. Done by. Instead of the cobalt hydroxide powder, cobalt monoxide powder or metallic cobalt powder may be used. Concentration of alkaline aqueous solution,
By adjusting the heat treatment time or heat treatment temperature,
The average valence of cobalt in the cobalt compound can be adjusted to a range of 2 or more and 3 or less. The higher the concentration of the alkaline aqueous solution, the higher the heat treatment temperature, and the longer the heat treatment time, the more the coating layer having a large average valence of cobalt is formed. In addition to the above method, the coating layer can also be formed by a method in which nickel hydroxide powder is introduced into a cobalt salt aqueous solution and alkali is added to precipitate cobalt hydroxide on the surface of the nickel hydroxide particles.

Various cobalt compounds having an average cobalt valence of more than 2 and not more than 3 include cobalt hydroxide (cobalt valence: 2) and cobalt oxyhydroxide (cobalt valence: 3). Mixtures of ratio and cobalt oxyhydroxide are mentioned.

The weight ratio of cobalt to the composite particles in the coating layer is preferably 1 to 10%. This weight ratio is 1
If it is less than 10%, the conductivity of the active material is insufficient and the utilization rate of the active material is lowered, and the battery capacity is reduced. On the other hand, if this weight ratio exceeds 10%, the hydroxylation directly related to the battery capacity is achieved. This is because the amount of nickel decreases and the battery capacity decreases.

The electrode of the present invention comprises nickel hydroxide particles having appropriate crystallinity (nickel hydroxide particles having a half-value width of the X-ray diffraction peak of the lattice plane (101) plane of 0.35 to 0.7 degrees).
Since the composite particles obtained by coating the surface of the above with a cobalt compound having excellent conductivity (cobalt compound having an average valence of cobalt of more than 2 and not more than 3) are used as the active material, Excellent conductivity is maintained for a long time.

[0017]

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.

[0018]

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 4 [Preparation of Nickel Hydroxide Powder] Water containing 1 liter of a 30 wt% nickel sulfate aqueous solution and 0.1 liter of a 5 wt% ammonia water kept at 35 ° C. in a water tank. Was added to the solution, and the pH of the solution was adjusted to 10.5, 11.0, 11.25 or 11.5 with a 20% by weight aqueous sodium hydroxide solution with stirring, and then stirring was continued for 1 hour. The pH at this time was monitored by a glass electrode pH meter with automatic temperature compensation. Next, the generated precipitate was filtered, washed with water, and vacuum dried to obtain four kinds of nickel hydroxide powder. Then, the half-value width of the X-ray diffraction peak of the lattice plane (101) plane of each nickel hydroxide powder was determined from the X-ray diffraction diagram by the X-ray diffraction under the following conditions, and it was 0.35 degrees (pH 10.
5), 0.5 degree (pH 11.0), 0.6 degree (pH 1
1.25) and 0.7 degrees (pH 11.5).

<Conditions for X-ray Diffraction> Anti-cathode Cu filter Ni tube voltage 40 kV scanning speed 2.00 ° / min tube current 100 mA divergence slit 1 °

[Preparation of Composite Particle Powder] A mixed powder of 92 parts by weight of each nickel hydroxide powder and 8 parts by weight of cobalt hydroxide powder was added to a 40% by weight sodium hydroxide aqueous solution 5
0 parts by weight was added, and the mixture was heated and maintained at 80 ° C. for 48 minutes, washed with water, and dried in vacuum to form a coating layer made of a cobalt compound on the surface of each nickel hydroxide powder particle. A particle powder was produced.

Next, when the average valence of cobalt in the coating layer (cobalt compound) of each of the composite particle powders was determined by the method shown below, all were 2.93.

<How to obtain average valence of cobalt> A certain amount of a sample is weighed, dissolved in concentrated hydrochloric acid, and the amount of cobalt in the solution is quantified by an atomic absorption method. The amount of cobalt quantified at this time is the total amount of cobalt (total amount of divalent cobalt and trivalent cobalt) A contained in the coating layer. Next, the same amount of the same sample is separately weighed, dissolved in concentrated nitric acid, and the solution is filtered.
Since trivalent cobalt does not dissolve in nitric acid, a filtrate containing only divalent cobalt can be obtained by filtration. The amount of cobalt in this filtrate is quantified by an atomic absorption method. The amount of cobalt quantified at this time is the amount B of divalent cobalt contained in the coating layer. The average valence of cobalt of each sample is calculated by the following formula.

Average valence of cobalt = 3-B / A

[Preparation of Paste Type Nickel Electrode] 100 parts by weight of each composite particle powder described above and 20 parts by weight of a 1% by weight methylcellulose aqueous solution are kneaded to prepare a paste,
Porous body (substrate) made of foamed metal (porosity 95%, average pore size 200 μm) obtained by nickel-plating this paste
Were filled, dried and molded to prepare a paste type nickel electrode.

[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 700 mAh) A1 to A4 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) Examples 1 to 1 except that the pH of the liquid was kept at 10 when the nickel hydroxide powder was prepared.
A composite particle powder was prepared in the same manner as in 4. The half width of the lattice plane (101) plane of the nickel hydroxide powder was 0.30. Then, an AA-sized alkaline storage battery B1 was produced in the same manner as in Examples 1 to 4 except that this composite particle powder was used as the positive electrode active material.

(Comparative Example 2) Examples 1 to 1 except that the pH of the liquid was kept at 12 when the nickel hydroxide powder was prepared.
A composite particle powder was prepared in the same manner as in 4. The half width of the lattice plane (101) plane of the nickel hydroxide powder was 0.80. Next, an AA-sized alkaline storage battery B2 was produced in the same manner as in Examples 1 to 4 except that this composite particle powder was used as the positive electrode active material.

(Comparative Examples 3 to 9) The half-value widths of the X-ray diffraction peaks of the lattice plane (101) plane produced in the same manner as in Examples 1 to 4 were 0.35, 0.5, 0.6, 0. 0.7, 0.8 (pH 12 at the time of production), 0.9 (pH 12.5 at the time of production),
1.0 (pH 13 at the time of production) each nickel hydroxide powder 9
3.6 parts by weight, 6.4 parts by weight of cobalt monoxide powder,
A paste was prepared by kneading with 20 parts by weight of a 1% by weight methylcellulose aqueous solution, and the paste was filled in a porous body (substrate) made of nickel-plated foam metal (porosity 95%, average pore diameter 200 μm) and dried, It shape | molded and produced the paste type nickel electrode. Examples 1 to 4 except that each of these paste type nickel electrodes was used as the positive electrode
Similarly to, AA size alkaline storage batteries B3 to B9
Was prepared. The batteries B7 to B9 are described in JP-A-4-328.
257 is a conventional battery disclosed in 257.

<Activity Utilization Rate of Paste Type Nickel Electrode Used in Each Battery and Charge / Discharge Cycle Life of Each Battery> For each battery prepared in Examples 1 to 4 and Comparative Examples 1 to 9,
After charging 160% at 0.1 ° C at 25 ° C, 25 ° C
At 1C, a charge / discharge cycle test was conducted with one cycle consisting of discharging to 1.0V at 1C, and the active material utilization rate at the 10th cycle of the paste type nickel electrode used for each battery and the charge / discharge cycle life of each battery were determined. I asked. The active material utilization rate is
It was calculated based on the following formula.

Utilization rate of active material (%) = {discharge capacity at the 10th cycle (mAh) / (amount of nickel hydroxide (g) × 28)
8 (mAh / g)} × 100

The charge / discharge cycle life was evaluated by the number of charge / discharge cycles (times) until the discharge capacity reached 80% of the discharge capacity at the 10th cycle. Table 1 shows the active material utilization rate of the 10th cycle of the paste nickel electrode used for each battery and the charge / discharge cycle life of each battery. The active material utilization rate is indicated by an index when the 10th cycle active material utilization rate of the paste type nickel electrode used in the battery A2 is 100. Further, in Table 1, the weight ratio (%) of cobalt to the composite particles in the coating layer, the average valence of cobalt in the cobalt compound, and the half-value width (degree) of the nickel hydroxide particles are shown.
Are also shown.

[0033]

[Table 1]

As shown in Table 1, in the batteries A1 to A4, the paste nickel electrode has a high utilization rate of the active material and has a long charge / discharge cycle life, whereas the nickel hydroxide particles have a lattice plane (101) plane. Batteries B1 and B2 having a half width of the X-ray diffraction peak outside the regulation range of the present invention have a high utilization rate of the active material of the paste nickel electrode, but have a short charge / discharge cycle life. From this fact, in order to obtain an alkaline storage battery in which the active material utilization rate of the positive electrode is high and the charge / discharge cycle life is long, the half-value width of the X-ray diffraction peak of the lattice plane (101) plane is determined as nickel hydroxide particles. It can be seen that it is necessary to use the one of 0.35 to 0.7 degree. In addition, the batteries B7 to B9 in which the half width of nickel hydroxide particles is 0.8 degrees or more are compared with the batteries B3 to B6 in which the half width is 0.35 to 0.7 degrees.
Although the paste type nickel electrode has a high utilization rate of the active material and a long charge / discharge cycle life, compared to the batteries A1 to A4,
The active material utilization rate of the paste nickel electrode is low, and the charge / discharge cycle life is short.

[Relationship Between Average Valence of Cobalt of Cobalt Compound and Utilization Rate of Active Material] Water having a half-value width of 0.5 on the X-ray diffraction peak of the lattice plane (101) prepared in the same manner as in Example 2. The average valence of cobalt was 2.0, in the same manner as in Example 2 except that the heat treatment time for forming the coating layer on the surface of the nickel oxide particles was changed between 2 and 55 minutes.
1, 2.2, 2.3, 2.4, 2.45, 2.5, 2.
A coating layer made of cobalt compounds of 6, 2.7, 2.8, 2.9, 2.93, and 3.0 was formed to prepare 13 kinds of composite particle powder (included in each coating layer. The weight ratio of cobalt to composite particles is 5% in each case). Then, each composite particle powder was used as an active material of a paste-type nickel electrode to prepare an AA size alkaline storage battery.

A charge / discharge cycle test was conducted on each of the above batteries under the same conditions as above, and the utilization rate of the active material at the 10th cycle of the paste nickel electrode used for each battery was determined.
The results are shown in FIG. FIG. 1 is a graph showing the relationship between the average valence of cobalt of a cobalt compound and the utilization rate of the active material, with the vertical axis representing the utilization rate of the active material and the horizontal axis representing the average valence of cobalt. The active material utilization factor on the vertical axis is an index when the active substance utilization factor at the 10th cycle of the paste nickel electrode having an average valence of cobalt of 2.7 is 100.

As shown in FIG. 1, a battery having an average cobalt valence of more than 2 has a much higher utilization ratio of the active material of the paste nickel electrode than a battery having an average cobalt valence of 2. From this fact, in order to obtain a paste-type nickel electrode having a high active material utilization rate, it is necessary to use composite particles obtained by coating nickel hydroxide particles with a cobalt compound having an average cobalt valence of greater than 2. I understand. Also,
From FIG. 1, it can be seen that it is preferable to use the composite particle powder obtained by coating the nickel hydroxide particles with the cobalt compound having an average cobalt valence of 2.5 to 2.93.

[Relationship Between Weight Ratio of Cobalt to Composite Particles in Coating Layer, Utilization Rate of Active Material and Battery Capacity] Half value of X-ray diffraction peak of lattice plane (101) prepared in the same manner as in Example 2 The average valence of cobalt was 2.93 in the same manner as in Example 2 except that the amount of cobalt hydroxide used when forming the coating layer on the surface of the nickel hydroxide particles having a width of 0.5 was changed. A coating layer of various thicknesses made of a cobalt compound is formed, and the weight ratio of cobalt in the coating layer to the composite particles is 0.5%, 1%, 5%, 7.5%,
Six kinds of composite particle powders different from 10% and 11% were produced. Next, using each composite particle powder as an active material, a paste type nickel electrode and an AA size alkaline storage battery were produced.

A charge / discharge cycle test was conducted on each of the above batteries under the same conditions as described above, and the utilization ratio of the active material at the 10th cycle of the paste nickel electrode used for each battery and the battery capacity at the 10th cycle of each battery were measured. I asked. The results are shown in FIGS. 2 and 3, respectively. FIG. 2 shows the relationship between the weight ratio of cobalt in the coating layer to the composite particles and the active material utilization rate,
FIG. 3 is a graph in which the vertical axis represents the active material utilization rate and the horizontal axis represents the weight ratio (%). Further, FIG. 3 shows the relationship between the weight ratio and the battery capacity, and the vertical axis represents the active material utilization rate. (%)
Is a graph in which the horizontal axis represents the battery capacity. The active material utilization rate on the vertical axis of FIG. 2 and the battery capacity on the vertical axis of FIG. 3 are the active material utilization rate and the battery capacity at the 10th cycle of a battery in which the weight ratio of cobalt to the composite particles is 5%, respectively. It is shown as an index when 100 is set.

From FIG. 2, it can be seen that when the weight ratio of cobalt to the composite particles in the coating layer is 1% or more, the active material utilization rate is high. Also, from FIG.
The weight ratio of cobalt to the composite particles in the coating layer is 1
It can be seen that in the case of 10%, a battery having a large battery capacity can be obtained. From these results, it is understood that it is preferable to form the coating layer so that the weight ratio of cobalt to the composite particles in the coating layer is in the range of 1 to 10%.

[0041]

EFFECT OF THE INVENTION Since the electrode of the present invention maintains excellent conductivity at the beginning of the charge / discharge cycle for a long period of time, by using this as the positive electrode, the utilization rate of the active material of the positive electrode is high and the charge / discharge cycle life is long. It is possible to obtain an alkaline storage battery.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the average valence of cobalt in a cobalt compound and the active material utilization rate.

FIG. 2 is a graph showing the relationship between the weight ratio of cobalt in the coating layer to the composite particles and the active material utilization rate.

FIG. 3 is a graph showing the relationship between the weight ratio of cobalt in the coating layer to the composite particles and the battery capacity.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiroshi Watanabe 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. No. 5 Sanyo Electric Co., Ltd. (72) Inventor Kozo Nogami 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Pref. Sanyo Electric Co., Ltd. (72) Inventor Ikuro Yonezu 2 5-5-5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. An average valence of cobalt is greater than 2 and 3 on the surface of nickel hydroxide particles having a half-value width of an X-ray diffraction peak of a lattice plane (101) plane of 0.35 to 0.7 degrees. A paste-type nickel electrode for an alkaline storage battery, which uses as an active material a powder composed of composite particles formed by forming a coating layer composed of the following cobalt compound. 2. The paste type nickel electrode for an alkaline storage battery according to claim 1, wherein the cobalt compound is a mixture of cobalt hydroxide and cobalt oxyhydroxide or cobalt oxyhydroxide. 3. The paste-type nickel electrode for an alkaline storage battery according to claim 1, wherein the cobalt compound has an average valence of cobalt of 2.5 to 2.93. 4. The paste-type nickel electrode for an alkaline storage battery according to claim 1, wherein the weight ratio of cobalt in the coating layer to the composite particles is 1 to 10%.