JPH10270037A - Non-sintered nickel electrode for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the long-term availability of active substance and to decrease the availability after over-discharging, by adding a rare earth element and/or its compound to active substance powder which consists of composition particles in which a coating layer made of Na-containing cobalt compound on the surface of nickel hydroxide particles. SOLUTION: A coating layer made of Na-containing cobalt compound is produced, by adding sodium hydroxide aqueous solution to the powder consisting of composition particles in which a metallic cobalt layer or a cobalt hydroxide layer is formed on the surface of nickel hydroxide particles, and by heating them under oxidizing atmosphere. Preferable contents of the coating layer in each composition particle is 3-15 wt.%. Preferable contents of Na in the coating layer is 0.1-10 wt.%. The compound of a rare earth element, which is added to active substance powder, is oxide, hydroxide, fluoride and carbonate salt. The adding ratio of the rare earth element or its compound is 0.05-5 pts.wt. of rare earth elements to 100 pts.wt. of active substance powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-sintered nickel electrode used as a positive electrode of an alkaline storage battery such as a nickel-zinc storage battery, a nickel-cadmium storage battery, and a nickel-hydrogen storage battery.

[0002]

2. Description of the Related Art
As a nickel electrode of 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. Further, since the pore diameter of the sintered body of nickel powder is generally as small as 10 μm or less, the active material must be filled into the substrate (sintered body) by a solution impregnation method which requires a complicated impregnation step to be repeated several times. There is also the problem that it must be done.

[0004] Under such circumstances, a non-sintered nickel electrode has recently been proposed. A non-sintered nickel electrode is made by mixing a kneaded product (paste) of an active material (nickel hydroxide) and a binder solution (methylcellulose aqueous solution) with a highly porous substrate (foamed metal plated with an alkali-resistant metal).
It is made by directly filling the In the non-sintered nickel electrode, a substrate having a high porosity can be used (a substrate having a porosity of 95% or more can be used), so that the packing density of the active material can be increased and Can be easily filled into the substrate.

However, when a non-sintered nickel electrode having a large porosity is used to increase the packing density of the active material, the current collecting capability of the substrate is lower than that of the sintered substrate used in the sintered nickel electrode. As a result, the conductivity becomes worse as compared with the sintered nickel electrode, and the active material utilization decreases.

Therefore, in order to enhance the conductivity of the non-sintered nickel electrode, it is necessary to use, as the active material powder, a powder composed of composite particles in which a coating layer composed of cobalt hydroxide is formed on the surface of nickel hydroxide particles. It has been proposed (see JP-A-62-234867).

[0007] However, this non-sintered nickel electrode has a problem that, when overdischarged, the subsequent utilization of the active material is greatly reduced.

The present invention has been made in view of the above circumstances, and is an alkali which has a high active material utilization rate over a long period of time as well as at the beginning of a charge / discharge cycle, and a small decrease in the active material utilization rate after overdischarge. An object is to provide a non-sintered nickel electrode for a storage battery.

[0009]

The non-sintered nickel electrode for an alkaline storage battery according to the present invention (electrode of the present invention) is a composite in which a coating layer comprising a sodium-containing cobalt compound is formed on the surface of nickel hydroxide particles. It is characterized in that a rare earth element and / or a compound thereof is added to an active material powder composed of particles.

[0010] The active material powder of the electrode of the present invention comprises composite particles in which a coating layer made of a sodium-containing cobalt compound is formed on the surfaces of nickel hydroxide particles. By forming the coating layer having high conductivity, the conductivity of the active material particle surface is increased. Nickel hydroxide particles include, in addition to particles consisting of nickel hydroxide only, nickel hydroxide, zinc, cobalt, calcium, manganese, aluminum,
Examples include particles in which at least one element selected from the group consisting of magnesium, yttrium, bismuth, scandium, lanthanoid, and cadmium is dissolved.
By dissolving each of the above elements in nickel hydroxide, expansion of the non-sintered nickel electrode during charging is suppressed.

The coating layer comprising a sodium-containing cobalt compound is a composite in which a cobalt compound layer such as a metal cobalt layer, a cobalt hydroxide layer, a cobalt monoxide layer and a cobalt oxyhydroxide layer is formed on the surface of nickel hydroxide particles. Sodium hydroxide aqueous solution is added to the powder consisting of particles,
It is formed by performing a heat treatment in an oxidizing atmosphere.

As a method for forming a cobalt hydroxide layer on the surface of nickel hydroxide particles, for example, nickel hydroxide powder is added to a cobalt salt aqueous solution (such as cobalt sulfate aqueous solution), and an alkaline aqueous solution is added dropwise with stirring. After adjusting the pH to about 11, after the pH is lowered, an alkaline aqueous solution is appropriately added dropwise and the mixture is stirred for a predetermined time while constantly maintaining the pH at about 11 to precipitate cobalt hydroxide on the surface of the nickel hydroxide particles. Method. The cobalt hydroxide layer can also be formed by a mechanical charge method in which nickel hydroxide powder and cobalt hydroxide powder are dry-mixed in an inert gas using a compression grinding mill. In this mechanical charge method, if a cobalt monoxide powder and a metal cobalt powder are used instead of the cobalt hydroxide powder, a cobalt monoxide layer and a metal cobalt layer can be formed, respectively.

The cobalt oxyhydroxide layer is formed, for example, by forming a cobalt hydroxide layer on the surface of nickel hydroxide particles and then oxidizing the cobalt hydroxide layer on the surface with a hydrogen peroxide solution heated to about 40 ° C. Can be formed.

The coating layer made of a sodium-containing cobalt compound is prepared by adding an aqueous solution of sodium hydroxide to a powder consisting of composite particles having a cobalt compound layer formed on the particle surface,
It is formed by performing a heat treatment in an oxidizing atmosphere. Simply adding an aqueous solution of sodium hydroxide does not allow the cobalt compound layer to contain sodium, but requires heat treatment in an oxidizing atmosphere. The heat treatment temperature at this time is preferably 50 to 200 ° C.
When the heat treatment temperature is lower than 50 ° C., C
oHO ₂ precipitates a lot, while heat treatment temperature is 200 ° C
Is exceeded, tricobalt tetroxide (Co) having low conductivity is used.
₃ O ₄ ) is largely precipitated. The heat treatment time depends on the amount and concentration of the aqueous sodium hydroxide solution, the heat treatment temperature, and the like. Generally, it is 0.5 to 10 hours.

The preferred coating layer content (sodium-containing cobalt compound content) of the composite particles is 3 to 15% by weight. When the content of the coating layer is less than 3% by weight, the conductivity of the surface of the active material particles is not sufficiently improved, so that it is difficult to obtain a non-sintered nickel electrode having a high active material utilization rate. On the other hand, when the ratio exceeds 15% by weight, the specific capacity (capacity per unit volume and unit weight) of the electrode decreases because the amount of the active material charged decreases. The preferable sodium content of the coating layer made of the sodium-containing cobalt compound is 0.1 to 10% by weight. If the sodium content is out of this range, the conductivity of the coating layer will deteriorate, and it will be difficult to obtain a non-sintered nickel electrode having a high active material utilization rate.

The chemical structure of the sodium-containing cobalt compound constituting the coating layer is not yet known by the present inventors, but since it has an extremely high electric conductivity, it is not a mere mixture of the cobalt compound and sodium. It is presumed that the compound has a special crystal structure in which sodium is incorporated in the crystal of the cobalt compound.

In the electrode of the present invention, a rare earth element and / or a compound thereof is added to the above-mentioned active material powder. These may be used alone or in combination of two or more as needed. Rare earth elements include La,
Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, D
y, Ho, Er, Tm, Yb and Lu. Examples of the rare earth compound include oxides, hydroxides, fluorides, and carbonates. The preferable addition ratio of the rare earth element and / or the compound thereof to the active material powder is 0.05 to 500 parts by weight of the active material powder as the rare earth element.
5 parts by weight. When the addition ratio of the rare earth element and / or the compound thereof is less than 0.05 parts by weight as the rare earth element, it is difficult to sufficiently suppress the decrease in the active material utilization rate after overdischarge. 5 as an element
If the amount exceeds the weight part, the packing density of nickel hydroxide decreases, and the capacity of the electrode decreases.

Specific examples of the electrode of the present invention include a paste-type nickel electrode obtained by applying a paste containing an active material powder and a rare earth element and / or a compound thereof to a conductive core and drying the paste. Examples of the conductive core at this time include a foamed metal, a sintered metal fiber, a metal mesh, and a punching metal. In addition to the paste nickel electrode, the present invention provides a tubular nickel electrode for filling an active material in a tubular metal conductor, a pocket nickel electrode for filling an active material in a pocket-shaped metal conductor, The present invention can also be applied to a nickel electrode for a button type battery formed by pressing a substance together with a mesh-shaped metal conductor under pressure.

When the active material powder in which the surface of the nickel hydroxide particles is coated with the sodium-containing cobalt compound alone is used, the over-discharge reduces the sodium-containing cobalt compound in the coating layer, and a part of the reduction product is hydroxylated. Since it diffuses into the nickel particles and the electron conductivity of the surface of the active material particles decreases, the active material utilization after overdischarge decreases. On the other hand, in the electrode of the present invention, since the rare earth element and / or the compound thereof is added to the active material powder, the sodium-containing cobalt compound in the coating layer is not easily reduced,
Even after overdischarge, the electron conductivity of the surface of the active material particles does not easily decrease. For this reason, the electrode of the present invention has a high active material utilization over the initial and long periods of the charge / discharge cycle, and the active material utilization is unlikely to decrease even after overdischarge.

[0020]

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.

(Preliminary Experiment 1) Cobalt hydroxide powder, 5
%, 10%, 15%, 25%, 35%, 40%, 45% or 50% by weight of an aqueous sodium hydroxide solution at a weight ratio of 1:10, And heat-treated at 85 ° C. for 8 hours. After heat treatment,
After washing with water and drying at 60 ° C., a sodium-containing cobalt compound was prepared. When the sodium content of the sodium-containing cobalt compound was determined by an atomic absorption method,
In order, 0.05% by weight, 0.1% by weight, 0.5% by weight,
1%, 5%, 10%, 12% and 15% by weight
% By weight.

(Preliminary Experiment 2) Cobalt hydroxide powder and 2
5% by weight aqueous solution of sodium hydroxide was added at a weight ratio of 1:10
45 ° C, 50 ° C, 100 ° C, 150 °
C, 200 ° C, 220 ° C or 250 ° C for 8 hours. After the heat treatment, it was washed with water and dried at 60 ° C. to produce a sodium-containing cobalt compound. When the sodium content of the sodium-containing cobalt compound was determined by an atomic absorption method, the weight was 0.05% by weight,
%, 1%, 1%, 1%, 0.05% and 0.02% by weight.

(Experiment 1) The characteristics of the electrode of the present invention and the conventional electrode were compared.

[Preparation of Electrodes A to R of the Present Invention] In 1,000 ml of an aqueous solution obtained by dissolving 13.1 g of cobalt sulfate powder in water,
100 g of nickel hydroxide powder is charged, and then 1 mol /
One liter of an aqueous sodium hydroxide solution was added dropwise with stirring to adjust the pH of the solution to 11, and then stirred for 1 hour. During this time, the pH of the solution was monitored with a glass electrode (pH meter) with automatic temperature compensation, and the pH of the solution was constantly maintained at approximately 11 by dropping an aqueous solution of sodium hydroxide as needed.

Next, the resulting precipitate was separated by filtration, washed with water, and dried under vacuum to obtain a powder composed of composite particles having a coating layer composed of cobalt hydroxide formed on the surface of nickel hydroxide particles.

The powder comprising the composite particles and a 25% by weight aqueous sodium hydroxide solution are mixed at a weight ratio of 1:10, and heated in air at 85 ° C. for 8 hours, and then washed with water. After drying at 65 ° C., an active material powder composed of composite particles having a coating layer composed of a sodium-containing cobalt compound formed on the surface of nickel hydroxide particles was obtained. The coating layer content of the composite particles was 5% by weight. The sodium content of the sodium-containing cobalt compound constituting the coating layer is estimated to be 1% by weight from the preliminary experiment 1 described above.

The above active material powder (average particle size: 10 μm) 1
00 parts by weight, 2 parts by weight of a rare earth element or a rare earth element compound shown in Table 1 as a rare earth element, and 1 part as a binder.
A paste is prepared by kneading 20 parts by weight of an aqueous solution of 20% by weight of methylcellulose, and the paste is filled in the pores of a nickel foam (porosity: 95%; average pore diameter: 200 μm), dried, and pressure-formed. And non-sintered nickel electrodes (electrodes of the present invention) A to R were produced.

[Preparation of Conventional Electrode X] Cobalt sulfate powder 1
100 g of nickel hydroxide powder was added to 1000 ml of an aqueous solution in which 3.1 g was dissolved in water, and then a 1 mol / l aqueous solution of sodium hydroxide was added dropwise with stirring to adjust the pH of the solution to 11, and then 1 hour. Stirred. During this time,
PH of liquid with glass electrode (pH meter) with automatic temperature compensation
Was monitored, and the pH of the solution was constantly maintained at about 11 by dropwise addition of an aqueous sodium hydroxide solution as needed.

Next, the resulting precipitate was separated by filtration, washed with water, and dried under vacuum to obtain a powder composed of composite particles having a coating layer composed of cobalt hydroxide formed on the surface of nickel hydroxide particles. The content of the coating layer of the composite particles as determined by atomic absorption spectrometry was 5% by weight.

A non-sintered nickel electrode (conventional electrode) X was produced in the same manner as in the production of the electrodes A to R of the present invention except that the above-mentioned powder was used as the active material powder. This electrode is
A powder composed of composite particles in which a coating layer composed of cobalt hydroxide is formed on the surface of nickel hydroxide particles is used as an active material powder, and corresponds to an electrode disclosed in JP-A-62-234867. .

[Preparation of Conventional Electrode Y] Nickel sulfate 16
To 1000 ml of an aqueous solution of 6.9 g in water, 7.2 g of lanthanum nitrate (La (NO ₃ ) ₃ ) was added and mixed. After dropwise addition of aqueous ammonia, the mixture was vigorously stirred while adding an aqueous solution of sodium hydroxide. Separately, the powder was washed with water to prepare a powder composed of particles in which lanthanum was dissolved in nickel hydroxide. Incidentally, the lanthanum content of the solid solution particles was determined by emission spectroscopy and found to be 3% by weight based on nickel hydroxide. A paste is prepared by kneading 100 parts by weight of the solid solution particle powder, 2 parts by weight of cadmium hydroxide (Cd (OH) ₂ ) powder as a conductive agent, and 20 parts by weight of a 1% by weight aqueous solution of methylcellulose as a binder. Then, this paste was filled in pores of a nickel foam (porosity: 95%; average pore diameter: 200 μm), dried, and pressed to prepare a non-sintered nickel electrode (conventional electrode) Y. . This electrode uses, as an active material powder, a powder composed of solid solution particles on which a coating layer is not formed.
This corresponds to the electrode disclosed in Japanese Patent Publication No. 508.

[Preparation of Comparative Electrode Z] A non-sintered nickel electrode (reference electrode) was prepared in the same manner as in the preparation of the electrodes A to R of the present invention except that no rare earth element or rare earth compound was added to the active material powder. ) Z was prepared.

[Preparation of Battery] Each of the above-mentioned non-sintered nickel electrodes (positive electrodes), a conventionally known paste-type cadmium electrode (anode) having an electrochemical capacity 1.6 times that of the above, a polyamide nonwoven fabric (separator), AA size nickel-cadmium storage batteries A to R, X, Y, and Z were produced using a 30% by weight aqueous solution of potassium hydroxide (alkaline electrolyte), a metal battery can, a metal battery cover, and the like. The reference number of the battery matches the reference number of the electrode of the non-sintered nickel electrode used as the positive electrode.

[Characteristics of Non-Sintered Nickel Electrode Used in Each Battery] For the batteries A to R, X, Y, and Z, they were charged at 25 ° C. at 0.1 C at 160%, and then charged at 25 ° C. A charge / discharge cycle test was performed in which the process of discharging to 1.0 V at 1 C was defined as one cycle, and the active material utilization D0 in the first cycle and the active material utilization in the 100th cycle of the non-sintered nickel electrode used for each battery were used. The rate D1 was determined. D0 and D1 were calculated based on the following equation. Next, a 1 Ω resistor was connected to each battery in the discharge state at the 100th cycle,
And let it discharge for 7 days, remove the resistor,
The charge / discharge was performed 5 times at C, and the active material utilization rate D2 at the 5th cycle was obtained, and the ratio Q of D2 to D1 [Q =
(D2 / D1) × 100] was obtained. D2 was calculated based on the following equation. The ratio Q is an index indicating the level of the active material utilization rate after overdischarge, and the electrode having a larger value indicates a smaller decrease in the active material utilization rate after overdischarge. Table 1 shows the results
Shown in D0, D1 and D2 in Table 1 are the electrodes A
Is a relative index when the active material utilization rate D0 in the first cycle is 100.

Active material utilization rate (%) = {discharge capacity (mAh) at the first or 100th cycle / [amount of nickel hydroxide (g) × 288 (mAh / g)]} × 100

[0036]

[Table 1]

As shown in Table 1, the electrodes A to R of the present invention
Compared to the conventional electrodes X and Y and the comparative electrode Z, the active material utilization D0 in the first cycle and the active material utilization D1 in the 100th cycle are higher, and the ratio Q is larger. The reason why the active material utilization D0 in the first cycle of the electrode X is low is that the electron conductivity on the surface of the active material particles is not sufficiently high.
The reason why the active material utilization D1 in the cycle is low is that the cobalt hydroxide in the coating layer diffused into the nickel hydroxide particles during repeated charge / discharge cycles, and the electron conductivity on the surface of the active material particles decreased. It depends. Also, the electrodes Y,
The active material utilization D0 in the first cycle of Z and the active material utilization D1 in the 100th cycle are considerably high, but the ratio Q is small, that is, the decrease in the active material utilization after overdischarge is large.

From these results, by adding a rare earth element and / or a lanthanum compound to an active material powder composed of composite particles having a coating layer composed of a sodium-containing cobalt compound formed on the surface of nickel hydroxide particles, It can be seen that a non-sintered nickel electrode having a high active material utilization rate over a long period of time as well as at the beginning of the charge / discharge cycle and a small decrease in the active material utilization rate after overdischarge can be obtained.

In the preparation of the electrode of the present invention in Experiment 1, lanthanum oxide (La ₂ O ₃ ), lanthanum fluoride (LaF ₃ ) or lanthanum carbonate (La ₂ (CO ₂ )
_{3) 3)} was added, the hydroxide or oxide of other rare earth elements, hydroxides, even if the addition of fluoride or carbonate, non-sintered nickel electrode having similar excellent properties Was separately confirmed.

(Experiment 2) The relationship between the coating amount and the active material utilization was examined.

The amount of cobalt sulfate powder used was 13.1 g.
In place of 1.31 g, 5.25 g, 7.88 g, 2
Except that 6.3 g, 39.4 g, 44.7 g, or 52.5 g was used, non-sintered nickel electrodes B1 to B7 were sequentially manufactured in the same manner as the method of manufacturing electrode B of the present invention, and each of these electrodes was manufactured. , Nickel-cadmium storage batteries B1 to B7 of AA size were manufactured in order. The coating layer content of the composite particles constituting the active material powder was 0.5% by weight,
%, 3%, 10%, 15%, 17% and 20% by weight. From the preliminary experiment 1, the sodium content of the sodium-containing cobalt compound constituting the coating layer is estimated to be 1% by weight in each case.

A charge / discharge cycle test was performed on each of the above batteries under the same conditions as above, and the discharge capacity at the 300th cycle of the non-sintered nickel electrode used for each battery was determined. The results are shown in FIG. FIG. 1 shows the coating layer content of the composite particles and 3
5 is a graph showing the relationship between the discharge capacity at the 00th cycle, the discharge capacity at the 300th cycle on the vertical axis, and the coating layer content (% by weight) on the horizontal axis. FIG. 1 also shows the discharge capacity at the 300th cycle of the electrode B of the present invention.
This is a relative index when the discharge capacity at the cycle is 100.

As shown in FIG. 1, the electrodes B, B3 to
The discharge capacity at the 300th cycle of B5 is particularly large. From this fact, it is understood that the coating layer content of the composite particles is preferably 3 to 15% by weight.

(Experiment 3) The relationship between the sodium content of the sodium-containing cobalt compound constituting the coating layer and the active material utilization was examined.

In place of the 30% by weight aqueous sodium hydroxide solution, 0.1% by weight, 5% by weight, 10% by weight, 20% by weight, 35% by weight, 40% by weight, 45% by weight and 50% by weight were added respectively. Other than that, non-sintered nickel electrodes f to m were sequentially manufactured in the same manner as the method of manufacturing electrode B of the present invention, and AA-size nickel-cadmium storage batteries f to m were sequentially manufactured using these electrodes. Was prepared. The coating layer content of each of the composite particles was 5% by weight. Also,
The sodium content of the sodium-containing cobalt compound constituting the coating layer was 0.00
Wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 5 wt%, 10 wt%, 12 wt% and 15 wt%
It is estimated to be.

A charge / discharge cycle test was performed on each of the above batteries under the same conditions as above, and the active material utilization rate of the 10th cycle of the non-sintered nickel electrode used for each battery was determined. The results are shown in FIG. FIG. 2 shows the relationship between the sodium content of the sodium-containing cobalt compound constituting the coating layer and the active material utilization, the ordinate represents the active material utilization at the tenth cycle, and the abscissa represents the sodium content of the sodium-containing cobalt compound. It is the graph shown by taking (%). FIG. 2 also shows the active material utilization at the 10th cycle of the electrode B of the present invention (sodium content: 1% by weight). It is a relative index when the active material utilization rate at the 10th cycle of No. is 100.

As shown in FIG. 2, the electrodes B, h to k of the present invention
The active material utilization rate at the 10th cycle is particularly high. From this fact, it is understood that the sodium content of the sodium-containing cobalt compound constituting the coating layer is preferably 0.1 to 10% by weight.

(Experiment 4) The relationship between the heat treatment temperature and the active material utilization when forming a coating layer comprising a sodium-containing cobalt compound was examined.

When the heat treatment temperature is 45 ° C., 50 ° C., 1
00 ° C, 150 ° C, 200 ° C, 220 ° C or 2
Except that the temperature was set to 50 ° C., non-sintered nickel electrodes n to t were sequentially manufactured by the same manufacturing method as the manufacturing method of the electrode B of the present invention, and an AA size nickel electrode was sequentially manufactured using these electrodes. Cadmium storage batteries n to t were produced. The coating layer content of each of the composite particles was 5% by weight. Also,
From the preliminary experiment 2, the sodium content of the sodium-containing cobalt compound constituting the coating layer was 0.05
% By weight, 1% by weight, 1% by weight, 1% by weight, 1% by weight,
It is estimated to be 0.05% and 0.02% by weight.

A charge / discharge cycle test was performed on each of the above batteries under the same conditions as above, and the active material utilization of the non-sintered nickel electrode used in each battery at the tenth cycle was determined. The results are shown in FIG. FIG. 3 shows the relationship between the heat treatment temperature and the active material utilization rate when forming a coating layer made of a sodium-containing cobalt compound, the vertical axis represents the active material utilization rate at the tenth cycle, and the horizontal axis represents the heat treatment temperature (° C.). It is the graph shown by taking C). FIG. 3 shows the electrode B of the present invention (heat treatment temperature of 8).
The active material utilization rate at the 10th cycle at 5 ° C.) is also shown, and the active material utilization rate at the 10th cycle on the vertical axis is a relative index with the active material utilization rate at the 10th cycle of the electrode B of the present invention being 100. It is.

As shown in FIG. 3, the electrodes B, or
The active material utilization rate in the cycle is particularly high. From this fact,
It is understood that the heat treatment temperature when forming the coating layer made of the sodium-containing cobalt compound is preferably 50 to 200 ° C.

(Experiment 5) The relationship between the addition ratio of lanthanum oxide to the active material powder and the utilization rate of the active material was examined.

The addition ratio of lanthanum oxide as lanthanum atom to 100 parts by weight of the active material powder is 0.01 part by weight, 0.05 part by weight, 0.1 part by weight, 0.5 part by weight,
The same method as the method for producing the electrode B of the present invention (addition ratio of lanthanum oxide as lanthanum atom: 2 parts by weight) except that the parts were 3 parts by weight, 5 parts by weight, 6 parts by weight, or 7 parts by weight, Non-sintered nickel electrodes (1) to (9) were manufactured in order, and AA size nickel-cadmium storage batteries (1) to (9) were manufactured in order using these electrodes. The coating layer content of each of the composite particles was 5% by weight. Further, the sodium content of the sodium-containing cobalt compound constituting the coating layer is estimated to be 1% by weight in each of the preliminary experiments 1.

A charge / discharge cycle test and an overdischarge test under the same conditions as described above were performed on each of the above batteries, and the discharge capacity and ratio Q of the 100th cycle of the non-sintered nickel electrode used for each battery were determined. Table 2 shows the results. Table 2 also shows the results for the electrode B of the present invention and the comparative electrode Z.

[0055]

[Table 2]

As shown in Table 2, batteries B, (2) to
In (7), the discharge capacity at the 100th cycle is large, and the ratio Q is large. Therefore, it can be seen that the addition ratio of lanthanum oxide to 100 parts by weight of the active material powder is preferably 0.05 to 5 parts by weight in terms of lanthanum atoms.

In Experiments 2 to 5, lanthanum oxide was used as the rare earth element compound, but it was separately confirmed that similar results could be obtained when other rare earth element compounds or rare earth elements specified in the present invention were added. did.

[0058]

According to the present invention, there is provided a non-sintered nickel electrode for an alkaline storage battery having a high active material utilization rate over a long period of time as well as at the beginning of a charge / discharge cycle, and a small decrease in the active material utilization rate after overdischarge. Is done.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the coating layer content of composite particles and the discharge capacity at the 300th cycle.

FIG. 2 is a graph showing a relationship between a sodium content of a sodium-containing cobalt compound constituting a coating layer and an active material utilization rate.

FIG. 3 is a graph showing a relationship between a heat treatment temperature and an active material utilization rate when forming a coating layer.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shin Fujitani 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Koji Nishio 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd.

Claims (7)

[Claims] A rare earth element and / or a compound thereof is added to an active material powder composed of composite particles having a coating layer composed of a sodium-containing cobalt compound formed on the surface of nickel hydroxide particles. Non-sintered nickel electrode for alkaline storage batteries. 2. The nickel hydroxide particles according to claim 1, wherein the nickel hydroxide contains at least one element selected from the group consisting of zinc, cobalt, calcium, manganese, aluminum, magnesium, yttrium, bismuth, scandium, lanthanoid and cadmium. The non-sintered nickel electrode for an alkaline storage battery according to claim 1, which is a solid-solution particle. 3. A method according to claim 1, wherein said coating layer comprising said sodium-containing cobalt compound is prepared by adding an aqueous solution of sodium hydroxide to powder comprising composite particles having a metal cobalt layer or a cobalt compound layer formed on the surface of nickel hydroxide particles; 3. The non-sintered nickel electrode for an alkaline storage battery according to claim 1, wherein the non-sintered nickel electrode is formed by heat treatment in an oxidizing atmosphere. 4. The rare earth element compound is a rare earth element oxide, hydroxide, fluoride or carbonate.
A non-sintered nickel electrode for an alkaline storage battery according to any one of claims 1 to 3. 5. The non-sintered nickel electrode for an alkaline storage battery according to claim 1, wherein said sodium-containing cobalt compound contains 0.1 to 10% by weight of sodium. 6. The non-sintered nickel electrode for an alkaline storage battery according to claim 1, wherein the composite particles contain 3 to 15% by weight of a coating layer made of the sodium-containing cobalt compound. 7. The rare earth element and / or a compound thereof,
The non-sintered nickel electrode for an alkaline storage battery according to any one of claims 1 to 6, wherein 0.05 to 5 parts by weight of a rare earth element is added to 100 parts by weight of the active material powder.