JPH09219198A - Conductive agent for alkaline storage battery and non-sintered nickel electrode for alkaline storage battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve utilization of an active material by adding a conductive agent having an high electric conductivity to an active material of a non-sintered nickel electrode while sodium is contained in a conductive agent for alkaline storage battery. SOLUTION: This conductive agent for alkaline storage battery is obtained by a heat treatment of cobalt or cobalt compound adding a sodium hydroxide aqueous solution thereto at 50 to 200 deg.C, and contains sodium of 0.1 to 10wt.%. In this non-sintered nickel electrode for alkaline storage battery, the conductive agent for alkaline storage battery is added to an active material powder composed of nickel hydroxide particles or particles mainly containing nickel hydroxide in the proportion of 1 to 20 weight parts to 100 weight parts nickel hydroxide in the active material powder.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive agent for alkaline storage batteries and a non-sintered nickel electrode for alkaline storage batteries using the same.

[0002]

2. Description of the Related Art
As a nickel electrode of an alkaline storage battery such as a nickel-cadmium storage battery or a nickel-hydrogen storage battery, a sintering method in which a sintered substrate obtained by sintering nickel powder on a perforated steel plate or the like is impregnated with an active material (nickel hydroxide). The nickel pole 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.

Under these circumstances, recently, a non-sintered nickel electrode has been newly proposed. The non-sintered nickel electrode directly mixes a kneaded material (paste) of an active material (nickel hydroxide) and a binder solution (aqueous solution of methylcellulose, etc.) onto a substrate with high porosity (foamed metal plated with alkali resistant metal, etc.). It is made by filling. In the non-sintered nickel electrode, since a substrate having a high porosity can be used (a substrate having a porosity of 95% or more can be used), the packing density of the active material can be increased and the active material can be used. Can be filled into the substrate once.

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, cobalt hydroxide powder may be added to nickel hydroxide powder (see Japanese Patent Laid-Open No. 61-74261).
It has been proposed to add graphite powder (see Japanese Patent Application Laid-Open No. 7-212316).

However, as a result of studies by the present inventors, it has been found that it is difficult to obtain a non-sintered nickel electrode having a sufficiently high utilization ratio of the active material even if cobalt hydroxide powder or graphite powder is added. It was

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a conductive agent for an alkaline storage battery having a high electric conductivity and a non-use for an alkaline storage battery having a high utilization rate of an active material using the same. To provide a sintered nickel electrode.

[0009]

A conductive agent for an alkaline storage battery according to the present invention (a conductive agent of the present invention) according to the present invention for achieving the above object is a cobalt or cobalt compound in a state in which an aqueous sodium hydroxide solution is added thereto. , Sodium at 50 to 200 ° C., and sodium at 0.
1 to 10% by weight is contained. If the sodium content is out of this range, a conductive agent having a sufficiently high conductivity cannot be obtained.

Examples of the cobalt compound include cobalt hydroxide and cobalt oxide.

Although the chemical structure of the conductive agent of the present invention is not known at present, since the conductive agent of the present invention has an extremely high electric conductivity, it is not a simple mixture of a cobalt compound (cobalt oxyhydroxide, etc.) and sodium. It is speculated that it may be an intercalation compound in which sodium is incorporated in the crystal of the cobalt compound.

The heat treatment temperature for producing the conductive agent of the present invention is 50 to 200 ° C. If the heat treatment temperature is out of this range, a conductive agent having a high electric conductivity cannot be obtained.

That is, the conductive agent of the present invention is considered to be synthesized by the following reaction route when, for example, cobalt hydroxide is used as a starting material. However, the heat treatment temperature is 50
If the temperature is lower than ° C, the reaction of CoHO ₂ ⇒ Na-containing cobalt compound is difficult to proceed sufficiently, and a large amount of CoHO ₂ having a low electric conductivity is produced. On the other hand, the heat treatment temperature is 20
When it exceeds 0 ° C, a large amount of tricobalt tetroxide (Co ₃ O ₄ ) having a low electric conductivity is produced. For the above reason, when the heat treatment temperature deviates from 50 to 200 ° C, it is considered that a conductive agent having a high electric conductivity cannot be obtained.

Co (OH) ₂ ⇔ HCoO ₂ ^- ⇔ Co
HO ₂ ⇒ Na-containing cobalt compound (conducting agent of the present invention)

The heat treatment time for producing the conductive agent of the present invention varies depending on the amount and concentration of the aqueous sodium hydroxide solution, the heat treatment temperature, etc., but is generally 0.5 to 10 hours.

The non-sintered nickel electrode for an alkaline storage battery according to the present invention (the electrode of the present invention) uses the above-mentioned conductive agent of the present invention having a high electric conductivity as a non-sintered nickel electrode conductive agent. 1 to 20 parts by weight of the conductive agent of the present invention is contained in an active material powder composed of nickel hydroxide particles or particles containing nickel hydroxide as a main component, relative to 100 parts by weight of nickel hydroxide in the active material powder. It has been added.
If the amount of the conductive agent added is less than 1 part by weight, a non-sintered nickel electrode having a sufficiently high utilization ratio of the active material cannot be obtained. on the other hand,
When the addition ratio of the conductive agent exceeds 20 parts by weight, the filling amount of nickel hydroxide as the active material decreases, so that the electrode capacity decreases.

As the particles containing nickel hydroxide as a main component, particles in which an element having an action of suppressing expansion of the nickel electrode such as cobalt, zinc, cadmium, calcium, manganese, magnesium, etc. is dissolved in nickel hydroxide. It is illustrated.

[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.

(Experiment 1) [Preparation of Conducting Agent] Cobalt hydroxide and a 25 wt% aqueous solution of sodium hydroxide were mixed at a weight ratio of 1:10 to prepare 8
Heat treatment was performed at 0 ° C for 8 hours. After heat treatment, wash with water, 6
It was dried at 0 ° C to prepare a sodium-containing cobalt compound which is a conductive agent of the present invention. When the sodium content of this sodium-containing cobalt compound was analyzed by an atomic absorption method, it was 1% by weight.

[Preparation of Non-Sintered Nickel Electrode] 100 parts by weight of nickel hydroxide as an active material, 10 parts by weight of the above-mentioned sodium-containing cobalt compound as a conductive agent, and a 1% by weight aqueous solution of methylcellulose as a binder. 20 parts by weight was kneaded to prepare a paste, and this paste was nickel-plated foam metal (porosity 95%; average pore diameter 2
(00 μm) was filled into a porous substrate, dried, and pressure-molded to produce a non-sintered nickel electrode according to the present invention.

[Preparation of alkaline storage battery] The non-sintered nickel electrode (positive electrode) described above, a known paste type cadmium electrode (negative electrode) having a larger electrochemical capacity than this positive electrode, polyamide nonwoven fabric (separator), 30% by weight An alkaline storage battery A1 was produced using a potassium hydroxide aqueous solution (alkali electrolyte solution), a metal battery can, a metal battery lid, and the like.

Separately, in the above-mentioned preparation of the non-sintered nickel electrode, the sodium-containing cobalt compound 1 was used as a conductive agent.
Cobalt hydroxide 10 parts by weight or graphite 1 instead of 0 parts by weight
Alkaline storage batteries A2 and A3 were produced in the same manner except that 0 part by weight was used.

<Active material utilization rate> Alkaline storage battery A described above
For 1 to A3, after charging 160% at 0.1C at 25 ° C and then discharging to 1.0V at 1C at 25 ° C, 10 cycles of charging / discharging are performed. The active material utilization rate of the positive electrode at the 10th cycle defined was determined. The results are shown in Table 1. The active material utilization rate in Table 1 is
It is an index when the active material utilization rate of the alkaline storage battery A1 is 100.

Utilization rate of active material (%) = {discharge capacity at the 10th cycle (mAh) / (amount of nickel hydroxide (g) × 2)
88 (mAh / g)} x 100

[0025]

[Table 1]

As shown in Table 1, the alkaline storage battery A2,
The positive electrode active material utilization rates of A3 are 90 and 85, respectively, lower than those of the alkaline storage battery A1. From these results, it can be seen that the conductive agent (sodium-containing cobalt compound) according to the present invention has significantly higher conductivity than cobalt hydroxide and graphite. In Example 1, cobalt hydroxide was used as the cobalt raw material when synthesizing the sodium-containing cobalt compound. However, when metallic cobalt, cobalt oxide, or the like was used, the conductivity was the same as when cobalt hydroxide was used. It has been confirmed that a high content sodium-containing cobalt compound can be obtained.

(Experiment 2) In the preparation of the sodium-containing cobalt compound, 5 wt%, 10 wt%, 15 wt%, 35 wt%, 40 wt%, 45 wt% or 25 wt% sodium hydroxide aqueous solution was used. In the same manner as in Experiment 1 except that a 50 wt% sodium hydroxide aqueous solution was used,
Sodium-containing cobalt compounds with different sodium contents were prepared. When the sodium content of these sodium-containing cobalt compounds was analyzed by an atomic absorption method, 0.05% by weight, 0.1% by weight, 0.5% by weight, 5% by weight, 10% by weight, 12% by weight, It was 15% by weight. Next, alkaline storage batteries A4 to A10 were sequentially manufactured in the same manner as in Experiment 1 except that each of these sodium-containing cobalt compounds was used.

These alkaline storage batteries A4 to A10 were charged and discharged under the same conditions as in Experiment 1 for 10 cycles to obtain the active material utilization rate of the positive electrode at the 10th cycle, to determine the sodium content of the sodium-containing cobalt compound and the active material. I investigated the relationship of utilization rates. The results are shown in FIG. FIG. 1 shows the relationship between the sodium content rate of a sodium-containing cobalt compound and the active material utilization rate, the vertical axis represents the active material utilization rate, and the horizontal axis represents the sodium content rate (% by weight) of the sodium-containing cobalt compound. It is a graph. In FIG. 1,
The results for the alkaline storage battery A1 produced in Experiment 1 above are also shown. The active material utilization rate on the vertical axis of FIG. 1 is
It is an index when the active material utilization rate of the alkaline storage battery A1 is 100.

As shown in FIG. 1, alkaline storage batteries A1, A
Since the active material utilization rate of 5 to A8 is extremely high, it is understood that the sodium-containing cobalt compound (conducting agent of the present invention) having a sodium content of 0.1 to 10 wt% has an extremely high electrical conductivity.

(Experiment 3) In the production of a non-sintered nickel electrode, the amount of the sodium-containing cobalt compound added to 100 parts by weight of nickel hydroxide was 0.5 parts by weight, 1 part by weight, 5 parts by weight, 15 parts by weight. , 20 parts by weight, 22.5 parts by weight, or 25 parts by weight, in the same manner as in Experiment 1 to prepare non-sintered nickel electrodes having different amounts of the sodium-containing cobalt compound (conductive agent) added. However, as the sodium-containing cobalt compound, the sodium content is 1
The thing of the weight% was used. Next, alkaline storage batteries A11 to A17 were sequentially manufactured in the same manner as in Experiment 1 except that these non-sintered nickel electrodes were used.

Each of these alkaline storage batteries A11 to A17 was charged and discharged under the same conditions as in Experiment 1 for 10 cycles, and the active material utilization rate of the positive electrode at the 10th cycle was determined. I investigated the relationship between the rates. Table 2 shows the results. Table 2 shows the previous experiment 1
The results for the alkaline storage battery A1 manufactured in 1. are also shown.

[0032]

[Table 2]

It can be seen from Table 2 that when a sodium-containing cobalt compound is added in an amount of 1 part by weight or more relative to 100 parts by weight of nickel hydroxide, a non-sintered nickel electrode having a high utilization ratio of the active material can be obtained.

FIG. 2 shows the relationship between the amount of sodium-containing cobalt compound added and the battery capacity, the vertical axis represents battery capacity, and the horizontal axis the amount of sodium-containing cobalt compound added (parts by weight relative to 100 parts by weight of nickel hydroxide). It is the graph which took and showed. Note that FIG. 2 also shows the results for the alkaline storage battery A1 manufactured in Experiment 1 above. The battery capacity on the vertical axis in FIG. 2 is an index when the battery capacity of the alkaline storage battery A1 is 100.

As shown in FIG. 2, alkaline storage batteries A1, A
Since the battery capacity of 12 to A15 is extremely high, the non-sintered nickel electrode (the electrode of the present invention) in which the amount of the sodium-containing cobalt compound added to 100 parts by weight of nickel hydroxide is 1 to 20 parts by weight is an extremely high electrode. It turns out that it has a capacity.

(Experiment 4) In the preparation of the sodium-containing cobalt compound, the heat treatment temperature was 45 ° C and 50 ° C.
C, 60 ° C, 100 ° C, 150 ° C, 200 ° C,
A sodium-containing cobalt compound was produced in the same manner as in Experiment 1 except that the temperature was 220 ° C. or 250 ° C.
When the sodium content of these sodium-containing cobalt compounds was analyzed by the atomic absorption method, it was found to be 0.05
% By weight, 1% by weight, 1% by weight, 1% by weight, 1% by weight, 1
%, 0.05% by weight, 0.02% by weight. Then, alkaline storage batteries A18 to A25 were sequentially manufactured in the same manner as in Experiment 1 except that each of these sodium-containing cobalt compounds was used.

Each of these alkaline storage batteries A18 to A25 was charged and discharged under the same conditions as in Experiment 1 for 10 cycles and the active material utilization rate of the positive electrode at the 10th cycle was determined to find the relationship between the heat treatment temperature and the active material utilization rate. Examined. The results are shown in FIG. FIG. 3 shows the relationship between the heat treatment temperature and the active material utilization rate when synthesizing a sodium-containing cobalt compound, with the vertical axis representing the active material utilization rate and the horizontal axis representing the heat treatment temperature (° C). It is a graph. Note that FIG. 3 also shows the results for the alkaline storage battery A1 manufactured in Experiment 1 above. The active material utilization rate on the vertical axis of FIG. 3 is an index when the active material utilization rate of the alkaline storage battery A1 is 100.

As shown in FIG. 3, alkaline storage batteries A1, A
Since the active material utilization rates of 19 to A23 are extremely high, 5
It can be seen that the sodium-containing cobalt compound (conducting agent of the present invention) produced by heat treatment at 0 to 200 ° C. has extremely high electric conductivity.

Although nickel hydroxide was used as the active material in the above examples, the present invention is also applicable to the case where nickel hydroxide is used as a solid solution with cobalt, zinc, cadmium, calcium, manganese, magnesium or the like. It has been confirmed that a non-sintered nickel electrode having a high utilization rate of the active material can be obtained by adding a predetermined amount of the inventive conductive agent.

[0040]

Since the conductive agent of the present invention contains sodium, it has a high electric conductivity. Further, the electrode of the present invention has a high utilization ratio of the active material because a conductive agent having a high conductivity is added to the active material.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a sodium content rate of a sodium-containing cobalt compound and an active material utilization rate.

FIG. 2 is a graph showing the relationship between the amount of sodium-containing cobalt compound added and the battery capacity.

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masao Inoue 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Hiroshi Watanabe 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd. (72) Inventor Rezo Maeda 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Denki Co., Ltd. (72) Inventor Ikuro Yonezu Keihan Hondori, Moriguchi City, Osaka Prefecture 2-5-5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. Cobalt or a cobalt compound in a state of being added with an aqueous sodium hydroxide solution at 50 to 200 °.
A conductive agent for alkaline storage batteries, which is obtained by heat treatment with C and contains 0.1 to 10% by weight of sodium. 2. A conductive material for an alkaline storage battery according to claim 1, wherein the active material powder consisting of nickel hydroxide particles or particles containing nickel hydroxide as a main component is added to 100 parts by weight of nickel hydroxide in the active material powder. 1 to 20 parts by weight is added to the non-sintered nickel electrode for alkaline storage batteries.