JP3229800B2 - Non-sintered nickel electrode for alkaline storage batteries - Google Patents

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 for an alkaline storage battery such as a nickel-hydrogen storage battery or a nickel-cadmium storage battery, and more particularly, to a non-sintered nickel electrode for an alkaline storage battery having a high active material utilization rate. The present invention relates to improvement of an active material powder for the purpose of providing a nickel electrode.

[0002]

2. Description of the Related Art Conventionally, as a nickel electrode of an alkaline storage battery such as a nickel-hydrogen storage battery or a nickel-cadmium storage battery, a sintered substrate obtained by sintering nickel powder on a perforated steel plate or the like is impregnated with an active material (nickel hydroxide). Sintered nickel electrodes are 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 increased to more than 80%, and therefore, the sintered nickel electrode has a problem that the active material filling amount is small. In addition, since the pore size of a sintered body of nickel powder is generally as small as 10 μm or less, the active material must be filled into a substrate (sintered body) by a solution impregnation method in which a complicated impregnation step is repeated several times. There is also a problem.

[0004] Under such circumstances, a non-sintered nickel electrode has recently been proposed. Non-sintered nickel electrodes are prepared by mixing a kneaded product (paste) of an active material (nickel hydroxide) and a binder solution (methylcellulose solution) with a highly porous substrate (foam metal plated with an alkali-resistant metal, etc.). 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 the active material can be increased. Can be easily filled into the substrate.

[0005] 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 nickel electrode. As a result, the active material utilization rate decreases.

Therefore, in order to increase the conductivity of the non-sintered nickel electrode, a powder composed of composite particles in which the surface of nickel hydroxide particles is coated with cobalt hydroxide has been used as the active material powder (Japanese Patent Laid-Open No. Sho 62-62). JP-A No. 234867), a powder composed of composite particles in which the surface of particles mainly composed of nickel hydroxide is coated with cobalt oxyhydroxide, or
3-78965).

However, the present inventors have studied and found that
It has been found that even with these improvements, it is difficult to obtain a non-sintered nickel electrode having a sufficiently high active material utilization rate.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a non-sintered nickel electrode for an alkaline storage battery having a high utilization rate of an active material. To provide.

[0009]

In order to achieve the above object, a non-sintered nickel electrode for an alkaline storage battery according to the present invention comprises:
A powder comprising a composite particle obtained by forming a conductive layer composed of a lithium-containing cobalt compound on the surface of nickel hydroxide particles or particles containing nickel hydroxide as a main component, wherein the lithium is used as an active material. In the contained cobalt compound, the ratio of the lithium weight converted to atoms, that is, the lithium content is 0.1% by weight to 10% by weight based on the total weight of the lithium-containing cobalt compound.

If the lithium content is out of this range, a conductive agent having sufficiently high conductivity cannot be obtained. In addition, the calculation of the lithium content is calculated according to the following equation.

Lithium content (% by weight) = (weight of lithium converted to atoms / total weight of lithium-containing cobalt compound) × 100 Particles containing nickel hydroxide as a main component include cobalt, zinc, cadmium and calcium. , Manganese, magnesium and the like having an effect of suppressing the expansion of the nickel electrode are dissolved in nickel hydroxide.

The chemical structure of the lithium-containing cobalt compound constituting the conductive layer is not known at present, but since the active material of the present invention has extremely high conductivity,
It is presumed that this is not a mere mixture of a cobalt compound (such as cobalt oxyhydroxide) and lithium, but an intercalation compound in which lithium is incorporated in crystals of the cobalt compound.

The active material powder according to the present invention is, for example, a powder comprising nickel hydroxide particles or composite particles formed by forming a cobalt compound layer on the surface of particles containing nickel hydroxide as a main component. It can be manufactured by performing a heat treatment at 50 ° C. to 200 ° C. with a lithium aqueous solution added. The cobalt compound layer may be in the form of cobalt hydroxide or cobalt oxide.
For example, it is formed by charging nickel hydroxide into an aqueous solution of cobalt sulfate, adding an aqueous solution of sodium hydroxide, and chemically depositing a cobalt compound on the surface of the nickel hydroxide particles. The cobalt compound layer can also be formed on the surface of the nickel hydroxide particles by a mechanical charge method in which the nickel hydroxide powder is kneaded with cobalt oxide, cobalt hydroxide or metal cobalt. Instead of the powder composed of the composite particles, a powder composed of nickel hydroxide particles or a powder composed mainly of nickel hydroxide, and a mixed powder such as a cobalt hydroxide powder, a cobalt monoxide powder or a metal cobalt powder is used. However, the former method is preferable because a conductive layer (coating) is hardly formed by this method.

In the present invention, the heat treatment temperature is from 50 ° C.
Regulated to 200 ° C. If the heat treatment temperature is outside this range, it is difficult to form a conductive layer having high conductivity. This is considered for the following reasons.

That is, the conductive layer in the present invention is formed by the following reaction route when, for example, cobalt hydroxide is used as a starting material.

[0016]

Embedded image

However, if the heat treatment temperature is lower than 50 ° C., the reaction from CoHO ₂ to the Li-containing cobalt compound becomes difficult to proceed sufficiently, so that a large amount of CoHO ₂ having low conductivity is generated. On the other hand, when the heating temperature exceeds 200 ° C., a large amount of tricobalt tetroxide (Co ₃ O ₄ ) having low conductivity is generated. It is considered that these are the reasons why a conductive layer having high conductivity is difficult to be formed when the heat treatment temperature is out of 50 ° C to 200 ° C.

The heat treatment time varies depending on the amount and concentration of the aqueous lithium hydroxide solution, the heat treatment temperature and the like, but is generally 0.5 to 10 hours.

The lithium content of the lithium-containing cobalt compound is restricted to 0.1% by weight to 10% by weight. If the lithium content is outside this range, a conductive layer having a sufficiently high conductivity will not be formed, and a non-sintered nickel electrode having an extremely high active material utilization rate cannot be obtained.

The composite particles constituting the active material powder according to the present invention may include, in the composite particles, nickel hydroxide particles or particles containing nickel hydroxide as a main component in the lithium-containing cobalt compound. 1% by weight of cobalt atom in terms of cobalt
It is characterized by containing 10% by weight. This value is defined as the content of the lithium-containing cobalt compound in this specification. This value was calculated as follows.

Content of lithium-containing cobalt compound (% by weight) = (weight of cobalt converted to atoms in lithium-containing cobalt compound / weight of nickel hydroxide particles or particles containing nickel hydroxide as a main component) × 100 When the content of the lithium-containing cobalt compound is less than 1% by weight, the conductivity of the active material powder is not sufficiently improved, so that a sufficient electrode capacity cannot be obtained. On the other hand,
If it exceeds 10% by weight, the amount of nickel hydroxide as an active material is reduced, so that sufficient electrode capacity cannot be obtained.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. However, the present invention is not limited to the following embodiments, and the present invention is implemented by appropriately changing the scope of the invention. Is possible. (Preliminary Experiment 1) Cobalt hydroxide and 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, or 8% by weight of lithium hydroxide aqueous solution The mixture was mixed at a weight ratio of 1:10 and heated at 80 ° C. for 8 hours. After the heat treatment, the product was washed with water and dried at 60 ° C. to produce a lithium-containing cobalt compound. When the lithium content of this lithium-containing cobalt compound was analyzed by atomic absorption spectroscopy, it was found that 0.05% by weight, 0.1% by weight, 0.5% by weight, 1% by weight, 5% by weight, 10% by weight, 12% by weight, and 15% by weight in that order. Met. The lithium content of the lithium-containing cobalt compound shown below is
It is a value estimated from the concentration of the used lithium hydroxide aqueous solution based on the above analysis results. (Example 1) An aqueous solution obtained by dissolving 13.1 g of cobalt sulfate in water.
100 g of nickel hydroxide powder was added to 1000 ml, and then a 1 M aqueous sodium hydroxide solution was added dropwise with stirring until the pH of the solution reached 11, and stirring was continued thereafter. The pH of the solution was constantly maintained at 11 by appropriately adding an aqueous solution of sodium oxide, and the reaction was carried out for 1 hour. Monitoring of pH used a glass electrode with autofocus.
Next, the precipitate was separated by filtration and washed with water to obtain a powder composed of composite particles obtained by coating the surface of nickel hydroxide with cobalt hydroxide. Next, this powder and a 4% by weight aqueous solution of lithium hydroxide are mixed at a weight ratio of 1:10, and heat-treated at 80 ° C. for 8 hours, washed with water, dried at 60 ° C., and applied to the surface of the nickel hydroxide particles. An active material powder composed of composite particles obtained by forming a conductive layer composed of a lithium-containing cobalt compound was obtained. When the content of the lithium-containing cobalt compound in the composite particles was analyzed by an atomic absorption method, it was 5% by weight. The lithium content of this lithium-containing cobalt compound is 1% by weight (estimated value from preliminary experiment 1).

The above active material powder (average particle size: 10 μm) 100
By weight, a paste was prepared by kneading 20 parts by weight of a 1% by weight aqueous solution of methylcellulose as a binder. This paste is applied to a nickel-plated foam metal (porosity
A non-sintered nickel electrode A1 according to the present invention was prepared by filling a porous substrate having a pore size of 95% and an average pore diameter of 200 μm), drying and pressing. (Comparative Example 1) A powder composed of composite particles obtained by coating the surface of nickel hydroxide particles with cobalt hydroxide, obtained in the middle of the production process of the active material powder of Example 1, was used as the active material powder. A non-sintered nickel electrode (comparative electrode) B1 was produced in the same manner as in Example 1 except that the electrode was used.

The method adopted here is similar to the technique described in Japanese Patent Application Laid-Open No. 62-234867, which is a prior art. (Comparative Example 2) Powder composed of composite particles obtained by coating the surface of nickel hydroxide particles with cobalt hydroxide, which was obtained in the middle of the step of preparing the active material powder of Example 1, was replaced by 40
By reacting with 30% by weight aqueous hydrogen peroxide heated to ℃, the cobalt hydroxide on the surface was oxidized to β-CoOOH. A non-sintered nickel electrode (reference electrode) B2 was produced in the same manner as in Example 1, except that this powder was used as the active material powder.

The method adopted here is similar to the technique described in Japanese Patent Application Laid-Open No. 3-78965, which is a prior art. [Preparation of alkaline storage battery] The above-mentioned non-sintered nickel electrode (positive electrode), a conventionally known paste-type cadmium electrode (negative electrode) having a larger electrochemical capacity than this positive electrode, a polyamide nonwoven fabric (separator), 30% by weight hydroxylation An AA size alkaline storage battery was manufactured using a potassium aqueous solution (alkaline electrolyte), a metal battery can, a metal battery cover, and the like. <Active Material Utilization Rate of Non-Sintered Nickel Electrode> After charging the above alkaline storage battery by 160% at 25 ° C. and 0.1 C,
10 cycles of charging / discharging were performed with the step of discharging at 1.0 ° C. to 1.0 V at 1 ° C. being 10 cycles, and the active material utilization of the positive electrode at the 10th cycle defined by the following equation was determined.

Active material utilization rate (%) = ｛discharge capacity at 10th cycle (mAh) / (amount of nickel hydroxide (g) × 288 (mAh /
g))｝ × 100 The results are shown in Table 1. The active material utilization in Table 1 is an index when the active material utilization of the non-sintered nickel electrode A1 is 100.

[0027]

[Table 1]

As shown in Table 1, the non-sintered nickel electrode A
No. 1 has a higher active material utilization rate than the non-sintered nickel electrodes B1 and B2. <Relationship between lithium content and active material utilization rate of lithium-containing cobalt compound> 1% by weight, 2% by weight, 3% by weight, 5% by weight, 6% by weight, and 7% by weight of aqueous lithium hydroxide solution during heat treatment Alternatively, a lithium-containing cobalt compound was produced in the same manner as in Example 1, except that an aqueous 8% by weight lithium hydroxide solution was used. The lithium content of these lithium-containing compounds is 0.05% by weight, 0.1% by weight,
0.5 wt%, 5 wt%, 10 wt%, 12 wt%, 15 wt%
Met. Next, non-sintered nickel electrodes A to G were produced in the same manner as in Example 1 except that these lithium-containing cobalt compounds were used, and then an alkaline storage battery was produced.

The manufactured alkaline storage battery was subjected to 10 cycles of charge and discharge under the same conditions as above, and the active material utilization of the non-sintered nickel electrode at the 10th cycle was determined. Investigated the relationship. The results are shown in Table 2 and FIG. FIG. 1 is a graph showing the relationship between the lithium content of the lithium-containing cobalt compound (conductive layer) and the active material. In FIG. 1, the horizontal axis represents the lithium content (% by weight) of the lithium-containing cobalt compound, and the vertical axis represents the utilization rate of the active material. FIG. 1 also shows the results of the non-sintered nickel electrode A1 (lithium content: 1% by weight) manufactured in Example 1 above. The active material utilization on the vertical axis in FIG. 1 is relatively expressed by an index when the active material utilization of the non-sintered nickel electrode A1 is 100.

[0030]

[Table 2]

As shown in Table 2 and FIG. 1, when the lithium content of the lithium-containing cobalt compound is 0.1 to 10% by weight, a non-sintered nickel electrode having an extremely high active material utilization rate can be obtained. . <Relationship between lithium-containing cobalt content of composite particles and active material utilization rate> The lithium-containing cobalt compound (conductive layer) was converted to cobalt atoms in the same manner as in Example 1 except that the concentration of the aqueous cobalt sulfate solution was changed. , 0.5% by weight, 1% by weight, 10% by weight, 12% by weight, or 15% by weight of the active material powder was prepared. Each powder has a lithium content of 1 in the lithium-containing cobalt compound.
Adjusted to% by weight. Next, non-sintered nickel electrodes a to e were produced in the same manner as in Example 1 except that each of these active material powders was used, and then an alkaline storage battery was produced.

The prepared alkaline storage battery was subjected to 10 charge / discharge cycles under the same conditions as above, and the active material utilization rate of the non-sintered nickel electrode at the 10th cycle was determined. The relationship between the rate and the active material utilization rate was investigated. Table 3 shows the results. Table 3 also shows the results of the non-sintered nickel electrode A1 (content of lithium-containing cobalt compound: 5% by weight) produced in Example 1 above. The active material utilization in Table 3 is an index when the active material utilization of the non-sintered nickel electrode A1 is 100.

[0033]

[Table 3]

From Table 3, it can be seen that when the lithium-containing cobalt compound content of the composite particles is 1% by weight or more, a non-sintered nickel electrode having a high active material utilization rate can be obtained.

FIG. 2 shows the relationship between the content of the lithium-containing cobalt compound in the composite particles and the battery capacity. In FIG. 2, the abscissa plots the content (% by weight) of the lithium-containing cobalt compound, and the ordinate plots the battery capacity. The battery capacity in FIG. 2 is the battery capacity of the nickel-cadmium storage battery using the non-sintered nickel electrode A1.
It is relatively expressed by an index when 100 is assumed.

FIG. 2 shows that when the content of the lithium-containing cobalt compound in the composite particles exceeds 10% by weight, the amount of nickel hydroxide as an active material decreases, and the battery capacity sharply decreases. I understand. When the results of Table 3 and FIG. 2 are combined, in order to obtain a non-sintered nickel electrode having a high active material utilization rate and a large capacity, the content of the lithium-containing cobalt compound in the composite particles must be 1% by weight. It is understood that the content is preferably set to 10% by weight. (Experiment 3) The following experiment was performed as preliminary experiment 2. That is, cobalt hydroxide and a 4% by weight aqueous solution of lithium hydroxide are mixed at a weight ratio of 1:10, and are mixed at 45 ° C., 50 ° C., 60 ° C., 10
0 ℃, 150 ℃, 200 ℃, 220 ℃ or 250 ℃, each 8
Heat treatment was performed for a time. After the heat treatment, the product was washed with water and dried at 60 ° C. to produce a lithium-containing cobalt compound. The lithium content of this lithium-containing cobalt compound was analyzed by atomic absorption spectroscopy.
% By weight (50 ° C), 1% by weight (60 ° C), 1% by weight (100 ° C), 1%
Wt% (150 ° C), 1 wt% (200 ° C), 0.05 wt% (220
° C) and 0.02% by weight (250 ° C).

The lithium content of the lithium-containing cobalt compound used below is a value estimated from the heat treatment temperature in the above analysis results.

In the preparation of the lithium-containing cobalt compound, the heat treatment temperature was set at 45 ° C., 50 ° C., 60 ° C., 10 ° C.
Except that the temperature was set at 0 ° C., 150 ° C., 200 ° C., 220 ° C. or 250 ° C., the same procedure as in Experiment 1 was performed, that is, a lithium-containing cobalt compound was prepared using a 4% by weight aqueous solution of lithium hydroxide. The lithium content of these lithium-containing cobalt compounds was determined to be 0.01% by weight, 1% by weight, 1% by weight, 1% by weight, 1% by weight, 1% by weight,
% By weight and 0.02% by weight. Next, Experiment 1 was performed except that each of these lithium-containing cobalt compounds was used.
In the same manner as in the above, alkaline storage batteries T1 to T8 were sequentially manufactured.

For these alkaline storage batteries T1 to T8, 10 cycles of charge / discharge under the same conditions as in Experiment 1 were performed to determine the active material utilization rate of the positive electrode at the 10th cycle. Investigated the relationship. This result
As shown in FIG. FIG. 3 shows the relationship between the heat treatment temperature and the active material utilization when synthesizing a lithium-containing cobalt compound. In FIG. 3, the abscissa plots the heat treatment temperature (° C.), and the ordinate plots the active material utilization rate. FIG. 3 also shows the results for the alkaline storage battery A1 produced in the above-mentioned experiment 1. The active material utilization rate on the vertical axis in FIG. 3 is relatively expressed by an index when the active material utilization rate of the alkaline storage battery A1 is 100.

As shown in FIG. 3, the alkaline storage batteries A1, T
Since the active material utilization rate of T2 to T6 is extremely high, 50 to 20
It can be seen that the lithium-containing cobalt compound (the conductive agent of the present invention) produced by heat treatment at 0 ° C. has an extremely high electrical conductivity.

[0041]

As described above, according to the present invention, a non-sintered nickel electrode for an alkaline storage battery having an improved utilization ratio of an active material and high conductivity can be obtained, and a battery having a large battery capacity can be provided. The industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a lithium content of a lithium-containing cobalt compound (conductive layer) and an active material utilization rate.

FIG. 2 is a graph showing the relationship between the lithium-containing cobalt compound of the composite particles and the battery capacity.

FIG. 3 is a graph showing the relationship between the heat treatment temperature and the active material utilization when synthesizing a lithium-containing cobalt compound.

──────────────────────────────────────────────────続 き Continued on the front page (72) Kozo Nogami 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Ikuo Yonezu 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-8-203516 (JP, A) JP Hei 9-129224 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 4/24-4/62 H01M 10/24-10/34

Claims (3)

(57) [Claims] An alkaline storage battery comprising, as an active material, a powder comprising composite particles formed by forming a conductive layer comprising a lithium-containing cobalt compound on the surfaces of nickel hydroxide particles or particles containing nickel hydroxide as a main component. A non-sintered nickel electrode for use, wherein in the lithium-containing cobalt compound, a ratio of lithium weight converted into atoms to the total weight of the lithium-containing cobalt compound is 0.1% by weight to 10% by weight. A non-sintered nickel electrode for an alkaline storage battery. 2. A powder comprising a composite particle obtained by forming a cobalt compound layer on the surface of nickel hydroxide particles or particles containing nickel hydroxide as a main component. 50 ° C ~ 200
2. The non-sintered nickel electrode for an alkaline storage battery according to claim 1, wherein the non-sintered nickel electrode is manufactured by heat treatment at a temperature of ℃. 3. The composite particles, wherein the weight of cobalt in the lithium-containing cobalt compound is 1 weight per weight of cobalt in the lithium-containing cobalt compound with respect to the weight of nickel hydroxide particles or particles containing nickel hydroxide as a main component. The non-sintered nickel electrode for an alkaline storage battery according to claim 1, wherein the non-sintered nickel electrode contains 0.1% to 10% by weight.