JPH07201325A - Nickel electrode for alkaline storage battery and manufacture of the electrode - Google Patents

Abstract

PURPOSE:To increase the filling density of an active material and heighten the use efficiency of the active material. CONSTITUTION:A conductive substrate having a three dimensional porous structure is filled with active material particles composed of a solid solution of nickel hydroxide and calcium hydroxide and having 7-13mum Fisher size as average particle size. Consequently, a battery can have high capacity by using the resulting electrode as a positive electrode for an alkaline storage battery. The electrode can be manufactured within a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel electrode used in alkaline storage batteries such as nickel-hydrogen storage batteries and nickel-cadmium storage batteries, and a method for producing the same.

[0002]

2. Description of the Related Art Sintered or non-sintered nickel electrodes using nickel hydroxide as an active material have been put to practical use as positive electrodes for alkaline storage batteries. Since the diffusion rate is low, there is a problem that the utilization rate of the active material of the nickel electrode is low and the battery capacity is small.

In order to solve this problem, an aqueous solution of nickel nitrate containing 0.5% by weight of calcium nitrate (pH =
It has been proposed that a solid solution of nickel hydroxide and calcium hydroxide, which is obtained by adding 2) to a sodium hydroxide aqueous solution and coprecipitating nickel hydroxide and calcium hydroxide, as active material particles (precipitation) is used. Method) (JP-A-63
(See JP-A-228567).

However, the active material particles produced by the precipitation method have a particle size smaller than that of nickel hydroxide (usually having a particle size of about 6 μm or more) produced by the conventional method of simultaneously adding nickel hydroxide. Since the particle size is as small as 2-3 μm and the bulk density is small, the non-sintered nickel electrode using this as an active material has a problem that the packing density of the active material is low.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a nickel electrode for an alkaline storage battery having a high packing density of the active material and a high utilization rate of the active material, and the same. It is to provide a manufacturing method.

[0006]

A nickel electrode for an alkaline storage battery (hereinafter, referred to as "the electrode of the present invention") according to the invention of claim 1 for achieving the above object is nickel hydroxide and hydroxide. An active material particle having a three-dimensional porous structure is filled with active material particles having a mean particle size of 7 to 13 μm, which is made of a solid solution with calcium and has a Fisher size.

The average particle size of the active material particles is regulated to 7 to 13 μm by the Fisher size when the average particle size is 7 μm.
If it is less than 3, it becomes difficult to fill the conductive material having a three-dimensional porous structure with the active material, and the bulk density of the active material becomes small, so that the packing density of the active material becomes small, while the average particle diameter is 13 μm. This is because if it exceeds, it becomes difficult to charge the inside of the active material particles, and the utilization rate of the active material decreases.

The electrode of the present invention is, for example, any one selected from nickel nitrate aqueous solution or nickel sulfate aqueous solution, calcium nitrate aqueous solution or calcium sulfate aqueous solution, sodium hydroxide, potassium hydroxide, and lithium hydroxide. After mixing with a buffer solution containing an alkali, an active material particle consisting of a solid solution of nickel hydroxide and calcium hydroxide and having an average particle size of 7 to 13 μm in Fisher size is obtained. The production method according to claim 4, wherein the slurry is prepared by mixing with a solvent containing a viscous agent, and the conductive substrate having a three-dimensional porous structure is filled with the slurry (hereinafter, referred to as "the method of the present invention"). It is produced by.

According to the method of the present invention, a spherical active material particle composed of a solid solution of nickel hydroxide and calcium hydroxide and having a large average particle size and bulk density is filled in a conductive substrate having a three-dimensional porous structure. The invention electrode can be manufactured in a short time.

The preferred calcium content of the active material particles is 0.1 to 3% by weight. If it is less than 0.1% by weight, the utilization rate of the active material is not sufficiently improved, while if it exceeds 3% by weight, the amount of nickel hydroxide as the active material is relatively small, resulting in a decrease in capacity. Invite.

The crystallite size of the active material particles in the direction perpendicular to the lattice plane (101) measured by X-ray diffraction is 1
It is preferably 25 Å or less. Crystallite size is 1
When it exceeds 25 Å, the utilization rate of the active material decreases.
It is considered that this is because when the crystallite size exceeds 125 Å, the strain of the crystal becomes small and the reaction area of the active material particles involved in charging / discharging becomes small.

The preferred pH of the buffer solution used in the method of the present invention is 11 ± 0.1. If the pH is out of this range, it tends to take a long time to prepare the active material particles, or spherical active material particles having a high packing density cannot be obtained. Specific examples of the buffer solution include an aqueous solution containing a strong base such as sodium hydroxide, potassium hydroxide and lithium hydroxide and a weak alkali such as ammonia.

[0013]

In the electrode of the present invention, since the active material particles having a predetermined average particle diameter are used, the utilization rate and packing density of the active material are increased.

In the method of the present invention, a nickel nitrate aqueous solution or a sulfate aqueous solution and a calcium nitrate aqueous solution or a sulfate aqueous solution are brought to a predetermined pH, preferably pH 11.
When added to a buffer solution of ± 0.1, spherical active material particles having a large average particle size and bulk density are obtained as a coprecipitate. By filling the active material particles in a conductive substrate having a three-dimensional porous structure, the electrode of the present invention having a high utilization ratio of the active material and a high packing density can be produced in a short time.

[0015]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the examples described below, and various modifications may be made without departing from the scope of the invention. Is possible.

(Reference Examples 1 to 7)
PH 11 ± 0.1 with sodium hydroxide and ammonia
The resulting mixture was added to the aqueous solution prepared as above and mixed with stirring to obtain α-type nickel hydroxide spherical powder. During this stirring and mixing, the stirring speed and the mixing time are changed so that the average particle size is 5 μm, 7 μm, 9 μm, 11 μm, 13 μm in Fisher size.
Seven kinds of spherical powders of 15 μm and 20 μm were obtained. Next, each spherical powder was immersed in a 20% by weight aqueous solution of sodium hydroxide kept at 100 ° C for 30 minutes, washed with water and dried to give β.
A spherical nickel hydroxide powder (active material particles) was obtained.

Next, 70 parts by weight of each spherical powder, 9 parts by weight of cobalt hydroxide, and 21 parts by weight of a 1% by weight aqueous solution of methylcellulose are kneaded to form a slurry, and the slurry is filled in a foam metal and dried. , Electrode (non-sintered nickel electrode) ER1 (average particle diameter of active material particles: 5 μm),
ER2 (average particle size of active material particles: 7 μm), ER3 (average particle size of active material particles: 9 μm), ER4 (average particle size of active material particles: 11 μm) and ER5 (average particle size of active material particles: 13 μm) ), ER6 (average particle size of active material particles: 15
μm) and ER7 (average particle size of active material particles: 20 μm)
Was produced.

In Reference Examples 1 to 7, the stirring speed was set to 300 to 900 rpm and the mixing time was set to 5 to 50 hours. In addition, as the stirring speed is increased,
Further, as the mixing time is lengthened, the average particle size of the obtained active material particles increases.

[Relationship Between Average Particle Size of Active Material Particles and Packing Density of Active Material] The packing density of the active materials of the electrodes ER1 to ER7 was investigated, and the relationship between the average particle size of the active material particles and the packing density of the active material was investigated. I checked. The results are shown in Fig. 1.

FIG. 1 shows the relationship between the average particle size of the active material particles and the packing density of the active material, the vertical axis being the packing density of the active material (g / c).
c) and the abscissa the average particle size (μm) of the active material particles. As shown in the figure, when the average particle size of the active material particles is 7 μm or more, the packing density of the active material is Is as large as about 2.8 g / cc, whereas when the average particle size of the active material particles is 5 μm, the packing density of the active material is about 2.5 g / cc.
And small. From this, from the viewpoint of the packing density of the active material, it is understood that the average particle diameter of the active material particles needs to be regulated to 7 μm or more.

[Relationship Between Average Particle Size of Active Material Particles and Utilization Rate of Active Material] Using electrodes ER1 to ER7, a test cell was assembled as described below, and this test cell was subjected to a current of 1 C for 1.6 hours. After charging, a discharge end voltage of 0.
The discharge capacity of each test cell was measured by discharging to 8 V, and the utilization rate of the active material of the positive electrode of each test cell was determined based on the calculation formula described below. The results are shown in Figure 2.

<Assembly of Test Cell> The electrodes ER1 to ER7 are used as test electrodes (positive electrodes), and a paste-type cadmium electrode having a sufficiently large electrochemical capacity is used as a counter electrode so that they are completely opposed to each other via a nylon separator. Overlap with. This is put in a polyethylene bag and a constitutional pressure (40 Kgf) is applied from both sides. A 1.23 KOH aqueous solution having a specific gravity was put into this to prepare an open type unipolar cell.

<Calculation formula of utilization rate of active material> Utilization rate of active material (%) = discharge capacity of test cell (mAh)
X 100 / {active material weight (g) x theoretical capacity per unit active material weight (mAh / g)} theoretical capacity per unit active material weight (mAh / g) = theory of constituent substance 1 (Ni (OH) ₂ Capacity x weight of constituent substance 1 per 1 g of active material (wt%) + constituent substance 2 (Co (O
H) ₂ ) theoretical capacity x weight of constituent substance 2 per 1 g of active material (wt%) + theoretical capacity of constituent substance 3 (Ca (OH) ₂ ) x weight of constituent substance 3 per 1 g of active material (wt%) )

For example, Ni (OH) ₂ 289.0 mAh /
g, Co (OH) ₂ 288.3 mAh / g, Ca (O
H) ₂ 723.4 mAh / g.

In FIG. 2, the relationship between the average particle diameter of the active material particles and the utilization rate of the active material is shown, the vertical axis represents the utilization rate (%) of the active material, and the horizontal axis represents the average particle diameter of the active material particles ( μm), and as shown in the figure, when the average particle size of the active material particles is 13 μm or less, the utilization rate of the active material is as high as about 89%, while the average of the active material particles is Particle size is 15 μm and 20
At μm, the utilization rates of the active material are low at 86% and 83%, respectively. Therefore, in terms of the utilization rate of the active material, it is necessary to regulate the average particle diameter of the active material particles to 13 μm or less.

(Examples 1 to 5) An aqueous solution of nickel nitrate and an aqueous solution of calcium nitrate were added to an aqueous solution adjusted to pH 11 ± 0.1 with sodium hydroxide and ammonia and mixed by stirring to contain calcium hydroxide as a solid solution. To α
A spherical nickel hydroxide powder (active material particles) was obtained. During the stirring and mixing, the stirring speed was 600 rpm, the mixing time was 48 hours, and the amount of the calcium nitrate aqueous solution used was changed for each example to obtain five types of spherical powders having different calcium contents. Then, the electrode EA1 of the present invention was prepared in the same manner as in Reference Examples 1 to 4 except that these spherical powders were used.
[Calcium content of active material particles (hereinafter abbreviated as "calcium content"): 0.1 wt%], electrode EA2 of the present invention [calcium content: 0.5 wt%], electrode EA3 of the present invention [ Calcium content: 1.0 wt%], electrode EA4 of the present invention [calcium content: 2.0 wt%] and electrode EA5 of the present invention [calcium content: 3.0 wt%] were produced.

(Comparative Example 1) A spherical powder was obtained in the same manner as in Examples 1 to 5 except that the calcium nitrate aqueous solution was not used. Then, in the same manner as in Examples 1 to 5 except that this spherical powder was used, the comparison electrode EC1 [average particle size: 1
1.5 μm, calcium content: 0% by weight].

(Comparative Examples 2 and 3) Two kinds of spherical powders were obtained in the same manner as in Examples 1 to 5 except that the amount of the calcium nitrate aqueous solution used was changed. Then, in the same manner as in Example 1 except that these spherical powders were used, the reference electrode EC2
[Average particle size: 6.0 μm, calcium content: 4.0% by weight] and comparative electrode EC3 [average particle size: 4.5 μm, calcium content: 5.0% by weight] were prepared.

Comparative Example 4 Nickel nitrate aqueous solution containing 0.5% by weight of calcium nitrate (specific gravity 1.25, pH =
2) was added to a sodium hydroxide aqueous solution having a specific gravity of 1.20,
A spherical powder was obtained in the same manner as in Examples 1 to 5 except that the mixture was stirred and mixed at 600 rpm for 48 hours. Then, a comparative electrode EC4 [average particle diameter: 2.5 μm, calcium content: 0.5% by weight] was produced in the same manner as in Examples 1 to 5 except that this spherical powder was used.

[Relationship Between Calcium Content of Active Material Particles, Average Particle Diameter of Active Material Particles, Crystallite Size, Tap Bulk Density, and Utilization Rate of Active Material] Electrodes EA1 to EA5 of the present invention and comparative electrode EC1 To the average particle size of the active material particles used in the preparation of EC4 in Fisher size, the size of the crystallite, the tap bulk density, and the active materials of the electrodes EA1 to EA5 of the present invention and the comparative electrodes EC1 to EC4 I checked the utilization rate.
The average particle size of the active material in Fisher size, the size of the crystallite, the tap bulk density and the utilization rate of the active material are shown in Table 1, and the utilization rates of the active material of the electrodes EA1 to EA5 of the present invention and the comparative electrodes EC1 to EC3 are shown. Is shown in FIG.

[0031]

[Table 1]

The calcium content of the active material particles was analyzed by ICP. The utilization rate of the active material is measured by the electrode E of the present invention.
A test cell was assembled in the same manner as above using A1 to EA5 and the reference electrodes EC1 to EC4, charged and discharged under the same conditions as above, and calculated from the above-described calculation formula. Regarding the size of the crystallite, the tube voltage is 30 kV, the tube current is 12.5 mA,
X-rays obtained by irradiating X-rays at a scanning speed of 5 deg / min
From the line diffraction pattern, the peak (2
(θ = 38.5 °) was obtained, and this value was calculated by substituting this value into the Scherrer's formula shown below.

<Scherrer's Formula> Dhkl = 0.9λ / βcosθ Dhkl (Å): Crystallite size in the direction perpendicular to the (hkl) plane λ (Å): Wavelength (λ = of measured X-ray (Cukα line))
1.5448 Å) β (radian): full width at half maximum θ (°): Bragg angle of diffraction peak

FIG. 3 shows the relationship between the calcium content of the active material particles and the utilization rate of the active material, the vertical axis represents the utilization rate (%) of the active material, and the horizontal axis represents the calcium content of the active material particles ( As shown in the figure, when the calcium content is 0.1 to 3% by weight, the utilization rate of the active material is as high as 95% or more, while calcium is included. When it is not present, the utilization rate of the active material is as low as about 85%, and when the calcium content is 4 to 5% by weight, the utilization rate of the active material is as low as about 93%. Therefore, the preferable calcium content of the active material particles is 0.1 to 3% by weight.

Further, as shown in Table 1, the electrode EA of the present invention
The average particle diameter of the active material particles used in 1 to EA5 is 8.0 to 1
It is as large as 1.6 μm, and the tap bulk density is 2.0 to 2.
It is as large as 5 g / cc. On the other hand, the comparison electrodes EC2 to
The average particle size of the active material particles used for EC4 is as small as 6.0 μm or less, the tap bulk density is 1.8 g / cc or less, and the average particle size of the active material particles used for the reference electrode EC1 is 11. Large as 5 μm, and tap bulk density is 2.5
Although it is as large as g / cc, since the active material particles do not contain calcium hydroxide, the utilization rate of the active material of the comparison electrode EC1 is as low as 84.8%.

[Crystallite size (hereinafter abbreviated as "crystallite size") in the direction perpendicular to the lattice plane (101) plane of the active material particles measured by X-ray diffraction, and the utilization rate of the active material. Relationship] The crystallite size was 50Å, 75 in the same manner as in Examples 1 to 5 except that the stirring speed and the mixing time were changed.
Six types of spherical powders different from Å, 100 Å, 125 Å, 130 Å and 150 Å were obtained. Next, an electrode of the present invention and a comparative electrode were produced in the same manner as in Examples 1 to 5 except that these spherical powders were used. Then, using these electrodes of the present invention and the reference electrode, a test cell was assembled in the same manner as above. Next, charge and discharge were performed under the same conditions as above to obtain the utilization rate of the active material from the above-described calculation formula, and the relationship between the crystallite size of the active material particles and the utilization rate of the active material was investigated. The results are shown in Fig. 4.

FIG. 4 shows the relationship between the crystallite size of the active material particles and the utilization rate of the active material, and the vertical axis represents the utilization rate (%) of the active material.
Is a graph showing the crystallite size (Å) on the horizontal axis. As shown in the same figure, the crystallite size is 125
If it is less than Å, the utilization rate of the active material can be increased.

[0038]

The electrode of the present invention has a high packing density of the active material and a high utilization rate of the active material. Therefore, by using the electrode of the present invention as the positive electrode of an alkaline storage battery, it is possible to increase the capacity. Further, according to the method of the present invention, the electrode of the present invention can be produced in a short time.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average particle size of active material particles and the packing density of active material.

FIG. 2 is a graph showing the relationship between the average particle size of active material particles and the utilization rate of active material.

FIG. 3 is a graph showing the relationship between the calcium content of the active material particles and the utilization rate of the active material.

FIG. 4 is a graph showing the relationship between the crystallite size and the utilization rate of the active material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Saito 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (7)

[Claims] 1. A solid solution of nickel hydroxide and calcium hydroxide, having an average particle size of 7-1 in Fisher size.
A nickel electrode for an alkaline storage battery, characterized in that a conductive substrate having a three-dimensional porous structure is filled with 3 μm active material particles. 2. The active material particles contain calcium in an amount of 0.1 to 0.1.
The nickel electrode for an alkaline storage battery according to claim 1, containing 3% by weight. 3. The crystallite size of the active material particles in the direction perpendicular to the lattice plane (101) measured by X-ray diffraction is 125Å
The nickel electrode for an alkaline storage battery according to claim 1, wherein: 4. A buffer solution containing an aqueous solution of nickel nitrate or an aqueous solution of nickel sulfate, an aqueous solution of calcium nitrate or an aqueous solution of calcium sulfate, and any one alkali selected from sodium hydroxide, potassium hydroxide and lithium hydroxide. Are mixed to obtain active material particles composed of a solid solution of nickel hydroxide and calcium hydroxide and having an average particle size of 7 to 13 μm in Fisher size, and then a solvent containing the active material particles and a thickener. To prepare a slurry,
A method for producing a nickel electrode for an alkaline storage battery, which comprises filling a conductive substrate having a three-dimensional porous structure with this slurry. 5. The method for producing a nickel electrode for an alkaline storage battery according to claim 4, wherein the buffer solution is an aqueous solution containing the alkali and ammonia and having a pH of 11 ± 0.1. 6. The active material particles contain calcium in an amount of 0.1 to 0.1.
The method for producing a nickel electrode for an alkaline storage battery according to claim 4, which contains 3% by weight. 7. The crystallite size of the active material particles in the direction perpendicular to the lattice plane (101) measured by X-ray diffraction is 125Å
The method for producing a nickel electrode for an alkaline storage battery according to claim 4, wherein: