JPH0577148B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a nickel positive electrode plate for an alkaline storage battery.

Conventional technology and its problems Conventionally, there are two types of nickel positive electrode plates for alkaline storage batteries: pocket type and sintered type, but the proportion of sintered type plates, which have excellent performance, is increasing year by year. There is.

Recently, foamed nickel type positive electrode plates, in which a sponge-like nickel porous material is physically filled with a positive electrode active material, are being commercialized with the main purpose of reducing costs.
Furthermore, a method called a paste method, in which an active material is simply applied to a metal core serving as a current collector, is also being developed.

Demand for alkaline storage batteries, particularly nickel-cadmium storage batteries, has been increasing in recent years, and there is a strong demand in the market for improved energy density in terms of performance. The main methods for increasing energy density include improving the active material utilization rate or discharge potential of the positive electrode plate, which is the capacity-limiting electrode. While current products have almost reached their limits in improving the active material utilization rate, no effective means have been found to improve the discharge potential.

On the other hand, since the main active material of an unformed nickel positive electrode plate is divalent nickel hydroxide, which has low conductivity, the polarization during the first charge is greater than that during subsequent cycles, and the competitive reaction of oxygen gas generation occurs. In particular, in paste-type positive electrode plates, collapse of the electrode plate due to oxygen gas generation from the early stage of charging has become a major problem.

In addition, in a sealed battery using a positive electrode plate where oxygen gas is generated from the early stage of charging as described above, the charge of the negative electrode plate has not progressed sufficiently, and the internal pressure increases without enough metal cadmium, which is effective for gas absorption, being generated. As a result, the safety valve is activated, causing a decrease in electrolyte and leakage, which poses a risk of deteriorating battery performance and life.

The present invention aims to solve the problems of the prior art described above.

Means for Solving the Problems The present invention provides a method for manufacturing a nickel positive electrode plate for an alkaline storage battery, in which the substrate or electrode plate is impregnated with a solution containing nickel salt or cobalt salt as a main component by a chemical impregnation method, and then It performs alkaline treatment and oxidation treatment simultaneously by immersing it in a mixed solution of caustic alkali and oxidizing agent, and retains the active material of higher oxides with more than two valences. It is characterized by having salt as its main component. When the reaction is described using sodium hydroxide as the caustic alkali and sodium chlorite as the oxidizing agent, it becomes equations 1 and 2.

4Ni(NO ₃ ) ₂ +8NaOH+NaClO ₂ →4NiOOH+
8NaNO ₃ +NaCl+2H ₂ O...1 set 4Co(No ₃ ) ₂ +8NaOH+NaClO ₂ →4CoOOH+
8NaNO ₃ + NaCl + 2H ₂ O...2 type action The divalent active materials Ni(OH) ₂ and Co(OH) ₂ have low conductivity as mentioned above, but in comparison, higher oxides with more than 2 valence, For example, NiOOH and CoOOH have extremely high conductivity. As a result of repeated studies on this issue, we applied the treatment according to the present invention to paste-type positive electrode plates that tend to generate oxygen gas from the early stage of charging. It was discovered that oxygen gas generation does not occur from the initial stage of charging even under high rate charging conditions. Further investigation revealed that the above effect was influenced by the distribution of higher oxides.
If it is uniformly distributed throughout the electrode plate, the amount of higher oxide required to obtain the above effect will be large, but in the present invention, the higher oxide forms a three-dimensional network structure. In such a case, the amount required would be very small. Figure 1 shows the internal pressure rise at the end of charging of a sealed nickel-cadmium storage battery using a paste-type positive electrode plate to which the present invention is applied. You'll know what to do if you do.

As mentioned above, the present invention was originally devised for the purpose of improving paste-type positive electrode plates, but in the process, unexpected new effects were discovered. In other words, the positive electrode plate to which the present invention is applied, regardless of whether it is a sintered type, a foamed type, or a paste type, has a nobler discharge potential than a positive electrode plate manufactured by a conventional method, and this tendency increases as the discharge current increases. , the deeper the discharge depth, the more remarkable it becomes. Furthermore, it was found that this effect was not temporary but continued.

The cause of the above is not yet well understood, but it can be inferred from the fact that the discharge potential is becoming nobler that higher oxides with more than two valences form a three-dimensional network structure inside the electrode plate when subjected to the treatment according to the present invention. This is thought to form a very good current collecting property inside the electrode plate, making it easier for the active material to be charged, and most of the charging products have a lower discharge potential than γ-NiOOH. It is thought that it has become a noble β-NiOOH.

There are conventionally known techniques for producing higher nickel oxides, particularly γ-NiOOH. This was a method for producing the active material itself, in which a mixture of caustic alkali and an oxidizing agent was charged in a reaction tank, and nickel hydroxide or nickel salt was added thereto to produce a higher oxide of nickel. , this method has several drawbacks.

First, because extra manufacturing equipment, purification equipment, washing water, labor costs, etc. are required to carry out the above reaction, the final manufacturing cost of the electrode plate will be considerably higher than the current cost.

Second, a facility is required to store the manufactured higher nickel oxide, and since the higher oxide of nickel gradually decomposes during storage, quality control must be carried out periodically.

Thirdly, it cannot be applied to a sintered nickel positive electrode plate.

Fourth, when applied to a paste-type or foam-type positive electrode plate, the higher oxide of nickel is uniformly dispersed in the electrode plate, so the minimum amount necessary to obtain the same effect as that of the present invention is required. For example, the amount of higher oxide added to nickel increases.

On the other hand, since the present invention relates to a method for manufacturing a nickel positive electrode plate, it is fundamentally different from the above-mentioned known techniques, and the present invention has almost no drawbacks that exist in the above-mentioned known techniques.
In other words, in the case of the present invention, it can be applied to sintered positive electrode plates, the cost increase is small compared to the current manufacturing method, and the time from the electrode plate manufacturing process to the battery assembly process is short, so high-grade oxidation Although the decomposition of the material is negligible and the higher oxides are thought to come into contact with each other in the electrode plate to form a three-dimensional network structure, the current collection property is good. First, the amount of higher oxides can be reduced.

The present invention is also different from a method of oxidizing using an oxidizing agent alone. In other words, in addition to the fact that the effects of the present invention cannot be obtained when oxidizing with an oxidizing agent alone,
In addition to the active material, its metal support, such as nickel or iron, is also oxidized, reducing the mechanical strength of the electrode plate, whereas in the case of the present invention, the solution used for oxidation treatment is strongly alkaline. Therefore, it does not affect the metal support in any way.

Example Examples of the present invention will be described in detail below.

Example 1 A sintered nickel substrate with a porosity of 85% was impregnated with a mixed solution of nickel nitrate and cobalt nitrate, and then the usual chemical impregnation process was repeated five times, in which the substrate was treated with an alkali solution of sodium hydroxide. The substrate is filled with active materials of nickel hydroxide and cobalt hydroxide. In the sixth chemical impregnation process,
Using an aqueous sodium hydroxide solution containing 2.0% sodium chlorite and a specific gravity of 1.20, the active material was filled in the same manner as before, except that the alkali treatment and the oxidation treatment were performed at the same time, to produce a positive electrode plate. This is designated as sample A.

Example 2 A positive electrode plate was produced in the same manner as in Example 1 except that potassium peroxodisulfate was used instead of sodium chlorite in the sixth chemical impregnation step. This is designated as sample B.

Example 3 A positive electrode plate was produced in the same manner as in Example 1 except that sodium hypochlorite was used instead of sodium chlorite in the sixth chemical impregnation step of Example 1. This is designated as sample C.

Example 4 For comparison, everything was the same as in Example 1, except that the alkali treatment in the sixth chemical impregnation step of Example 1 was performed solely with an aqueous sodium hydroxide solution with a specific gravity of 1.20.
A positive electrode plate was prepared in the same manner as above. This is designated as sample D.

Specific gravity of the sample positive electrode plate prepared as above
1.250 (20℃) Discharge characteristics in KOH aqueous solution
As shown in the figure. Samples A and B treated according to the present invention have a higher discharge potential than sample D prepared by the conventional method, and the intermediate potential is about 20 mV nobler. Further, the discharge potential of Sample C using sodium hypochlorite was not significantly different from that of Sample D, a conventional product, and no effect of increasing the discharge potential was observed.

Next, an example of a paste type positive electrode plate will be described.

Example 5 100 parts of nickel hydroxide powder, 5 parts of metallic cobalt powder, and 15 parts of carbonyl nickel powder were kneaded with 50 parts of 1% methylcellulose solution, and then the solid content was 50%.
An active material paste was prepared by adding 5 parts of the epoxy resin latex and a curing agent for epoxy resin. This active material paste was applied to a core made of a perforated steel plate plated with nickel, and then dried at 90°C to produce a base positive electrode plate. Next, this base positive electrode plate was impregnated with an aqueous solution of nickel nitrate, and then treated with alkali in an aqueous sodium hydroxide solution with a specific gravity of 1200 (20°C) to prepare a positive electrode plate. This is designated as sample E.

Example 6 The alkali treatment in Example 5 was carried out in an aqueous sodium hydroxide solution containing 2.0% sodium chlorite with a specific gravity of 1200 (20°C), and the alkali treatment and oxidation treatment were simultaneously carried out to produce a positive electrode plate. This is designated as sample F.

Example 7 A positive electrode plate was produced in the same manner as in Example 6 except that cobalt nitrate was used instead of nickel nitrate and potassium peroxodisulfate was used instead of sodium chlorite. This is designated as sample G.

Example 8 A positive electrode plate was produced in the same manner as in Example 6 except that sodium hypochlorite was used instead of sodium chlorite in Example 6. This is designated as sample H.

A cylindrical sealed battery was produced by combining the sample positive electrode plate prepared as described above with a sintered cadmium negative electrode plate prepared by a normal chemical impregnation method.
Figure 3 shows the internal pressure when charging at the nominal capacity of 1 hour. As is clear from the figure, in the conventional sample E, oxygen gas generation occurred from the early stage of charging, whereas in samples F and G treated according to the present invention, oxygen gas generation did not occur from the early stage of charging. , there is no risk of electrolyte loss or leakage due to an abnormal increase in internal pressure. In Sample H, which used sodium hypochlorite for oxidation treatment, the internal pressure started to rise somewhat later than in the conventional product, but when compared with Samples F and G, which were treated according to the present invention. is clearly bad. Also, for confirmation, a sample electrode plate of 4cm x 4cm
The treatment according to the present invention was performed as a result of cutting the cadmium negative electrode plates into the same size and charging them at a rate of 1 hour to the theoretical capacity in a large amount of alkaline electrode solution using two sintered cadmium negative electrode plates of the same size. Samples F and G are
Although there was no change in shape even after charging to 150%,
Sample E, a conventional product, had a charge of about 30%, and sample H, which used sodium hypochlorite, had a charge of about 60%, resulting in all the active material falling off the core.

From the above, the effects of the present invention are clear.

Effects of the Invention As described above, based on the present invention, after a positive electrode plate or substrate is impregnated with a solution mainly composed of nickel salt or cobalt salt, a mixed solution of a chlorite or peroxoninitrate oxidizing agent and caustic alkali is added. A nickel positive electrode plate with a high discharge potential can be obtained by immersing the nickel in a liquid and performing an alkali treatment and an oxidation treatment at the same time. Furthermore, in the case of a paste-type nickel positive electrode plate, collapse of the electrode plate during charging can be suppressed and charging efficiency can be improved.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between the content of higher oxides exceeding divalence in the positive electrode plate immediately before the first charge and the battery internal pressure, and Figure 2 is a characteristic diagram showing the relationship between the battery internal pressure and the content of higher oxides exceeding divalence in the positive electrode plate, and Figure 2 is the positive electrode plate produced by the method of the present invention and the conventional method. A characteristic diagram showing a comparison of the discharge potential of
FIG. 3 is a characteristic diagram showing a comparison of internal pressure rise during charging of cylindrical sealed batteries using positive electrode plates produced by the method of the present invention and the conventional method.

Claims (1)

[Scope of Claims] 1. A porous metal substrate or a nickel positive electrode plate holding an active material mainly composed of nickel hydroxide is impregnated with a solution mainly composed of nickel salt or cobalt salt, and then a caustic alkali and an oxidizing agent are impregnated with a solution mainly composed of nickel salt or cobalt salt. This process involves immersing the product in a mixed solution of and performing alkaline treatment to retain the active material of a higher oxide with a valence of more than 2, and the oxidizing agent is mainly composed of peroxonisulfate or chlorite. A method for producing a nickel positive electrode plate for an alkaline storage battery, characterized by: 2. The method for producing a nickel positive electrode plate for an alkaline storage battery according to claim 1, wherein 3% or more of the retained active material is changed into a higher oxide with a valence exceeding divalence.