JP3596148B2 - Method for producing sintered positive electrode plate for alkaline storage battery - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sintered positive electrode plate for an alkaline storage battery using cadmium, a hydrogen storage alloy, zinc, iron, or the like for a negative electrode, and a method for producing the same.
[0002]
[Prior art]
With the spread of various small portable devices such as mobile phones, video cameras, and headphone stereos in recent years, alkaline storage batteries play an important role as a power source for these devices. Generally, a sintered positive electrode plate used for an alkaline storage battery is obtained by impregnating a solution mainly composed of an acidic nickel salt into a sintered nickel substrate (hereinafter referred to as a sintered substrate) which is a support obtained by sintering nickel powder into a perforated steel plate. Then, the operation of converting the hydroxide to hydroxide by the action of an alkali, washing and drying is repeated several times, thereby producing an active material mainly composed of nickel hydroxide.
[0003]
In connection with the improvement of the performance of the sintered substrate used in the sintered positive electrode plate, a sintered substrate as disclosed in JP-A-59-96659 is heated in an oxygen atmosphere to form an oxide film. Methods for improving discharge characteristics have been proposed. Also, a method of forming a solid solution layer having a molar ratio of nickel hydroxide to cobalt hydroxide of 7: 3 to 5: 5 on a sintered substrate as disclosed in JP-A-63-48747, Cobalt hydroxide is formed on the surface of a sintered substrate as disclosed in JP-A-62-37875 and JP-A-62-58566, and then the cobalt hydroxide is converted to cobalt oxide or oxywater using anodizing or an oxidizing agent. Means for preventing corrosion of a sintered substrate when performing an active material filling operation, such as a method of performing an active material filling operation involving impregnation with an acidic nickel salt after changing to cobalt oxide, have been proposed.
[0004]
[Problems to be solved by the invention]
In general, it is known that when an alkaline storage battery is left unused for a long period of time, the aging phenomenon of the positive electrode active material, that is, the regularization of nickel hydroxide crystals proceeds, and the charging efficiency decreases. Therefore, the discharge capacity before recovery is not recovered unless the charge and discharge are repeated several cycles after the storage. In this case, although the open circuit voltage of the battery is reduced, if the degree is large, irreversible capacity reduction occurs, and there is a problem in that the capacity before being left cannot be obtained even after repeated charging and discharging.
[0005]
Also, recently, in consideration of safety in use, some chargers have been provided with a protection circuit such as controlling the battery charging not to start unless the battery voltage falls below a set value of about 1 V, for example. Was. This is intended to prevent, for example, a fire due to abnormal heating or the like when the battery whose open-circuit voltage is reduced due to a minute short circuit is charged, and charging or reverse charging in a state where the battery is not correctly set. . Therefore, there is also a problem that a battery that has been left for a long time and has an open circuit voltage lower than the set value cannot be charged by this type of charger. Therefore, effective solutions to these problems that occur when the alkaline storage battery is left for a long time have been demanded.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a passive nickel oxide film on a nickel sintered body of a sintered nickel substrate, and then applies a cobalt: nickel molar ratio of 20:80 to 97: 3 on the surface. The present invention provides a method for producing a sintered positive electrode plate for an alkaline storage battery in which a nickel mixed hydroxide is formed and then an active material mainly composed of nickel hydroxide is retained after oxidizing the mixed hydroxide. is there. It is desirable that the mixed hydroxide be contained in an amount of 1 to 15% by weight based on the active material mainly containing nickel hydroxide.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, a passive oxide film is provided on a nickel sintered body of a sintered nickel substrate as a support. Next, a cobalt / nickel mixed hydroxide having a molar ratio of cobalt to nickel of 20:80 to 97: 3 is formed on the surface. Further, after oxidizing the mixed hydroxide, a sintered positive electrode plate for an alkaline storage battery is manufactured by holding an active material mainly composed of nickel hydroxide. The alkaline storage battery using the sintered positive electrode plate having such a configuration is characterized in that the open-circuit voltage and the irreversible discharge capacity are less reduced even when left for a long time. In addition, when the ratio of the mixed hydroxide to the active material mainly composed of the nickel hydroxide is 1 to 15% by weight, it is particularly effective and practical for improvement of performance degradation during long-term storage.
[0008]
【Example】
Hereinafter, the details of the present invention will be described using examples.
[0009]
A sintered substrate having a porosity of about 85% was heated in air at 400 ° C. for 20 minutes to give a dense passive oxide film of nickel oxide. This was impregnated with an aqueous 2.5 M nitrate solution having a molar ratio of cobalt to nickel of 70:30 and then immersed in an alkaline aqueous solution, followed by washing with hot water and drying. An oxide formed. Then, the mixed hydroxide was oxidized by immersing it in a 0.5 M aqueous potassium permanganate solution for 1 hour, followed by washing with hot water and drying. Further, an operation of impregnating a 5.5 M nitrate aqueous solution containing nickel nitrate as a main component under reduced pressure, immersing the same in an alkaline aqueous solution, followed by washing with hot water and drying is repeated several times to obtain an active material mainly containing nickel hydroxide. To prepare a sintered positive electrode plate for an alkaline storage battery according to the present invention. At this time, the ratio of the cobalt / nickel mixed hydroxide on the surface of the sintered substrate to the active material mainly composed of nickel hydroxide was about 10 wt%.
[0010]
This positive electrode plate, and a known sintered cadmium negative electrode plate having a capacity sufficiently larger than the positive electrode and partially charged by a chemical conversion treatment, are spirally wound via a polypropylene separator imparting hydrophilicity, and used as an electrolyte. A KR-SC size sealed nickel-cadmium battery A (hereinafter, battery A of the present invention) having a nominal capacity of 1600 mAh and a nominal capacity of 1600 mAh was prepared using a 7M aqueous potassium hydroxide solution.
[0011]
As a comparison, a comparative battery B and a positive electrode plate which were the same as the battery A of the present invention except that a positive electrode plate filled with an active material without performing oxidation treatment after forming a cobalt / nickel mixed hydroxide were used. Comparative Battery C, which was the same as Battery A of the present invention except that a sintered substrate not performing the above process was used, without forming the mixed hydroxide, the surface of the heat-treated sintered substrate was mainly made of nickel hydroxide. Battery D similar to Battery A of the present invention except that a positive electrode plate filled with an active material was used, and Comparative Battery D similar to Comparative Battery D except that a sintered substrate not subjected to heat treatment was used for the positive electrode plate. A comparative battery E was manufactured.
[0012]
These batteries were initially charged at 25 ° C. at 0.1 CmA (160 mA) for 15 hours and then discharged at 1 CmA (1600 mA) to 1V. Further, the battery was charged and discharged at 1 CmA for 1.2 hours and discharged at 0.2 CmA (320 mA) for 5 cycles. The battery in the discharged state was left in a constant temperature room at 45 ° C. for 90 days. After standing, the battery was returned to an atmosphere of 25 ° C., and after 3 hours, charging and discharging were repeated 5 cycles under the same conditions as before standing.
[0013]
FIG. 1 shows a change in open circuit voltage of each battery during standing at 45 ° C. After forming a cobalt-nickel mixed hydroxide on a nickel sintered body of a sintered substrate provided with a passive oxide film, the open-circuit voltage of the battery A of the present invention using the positive electrode plate subjected to the oxidation treatment was measured. The decrease was small and a high value of 1 V or more was shown even after 90 days of standing.
[0014]
On the other hand, the open circuit voltage of the comparative battery B using the positive electrode plate not subjected to the oxidation treatment of the mixed hydroxide was 1 V or more on the 90th day of standing, but was lower than that of the battery A of the present invention. The open circuit voltage of the comparative battery C using the positive electrode plate in which the mixed hydroxide was formed on the surface of the nickel sintered body of the sintered substrate to which the passive oxide film was not applied was significantly reduced around the 50th day of standing. Then, the voltage became about 0.2 V on the 90th day of standing. In addition, the open-circuit voltages of the comparative batteries D and E using the positive electrode plate in which the mixed hydroxide was not formed on the surface of the nickel sintered body of the sintered substrate significantly decreased from around the 20th day of standing, The eye value was about 0.6 V in Comparative Battery D in which only the passive oxide film was applied to the nickel sintered body, and about 0 V in Comparative Battery E in which neither the passive oxide film nor the mixed hydroxide was formed. 0.2V.
[0015]
That is, the effect of suppressing the decrease in the open-circuit voltage during standing by only applying the passive oxide film to the nickel sintered body of the positive electrode sintered substrate is small, and the cobalt / nickel mixed hydroxide Even when a product was formed, the voltage drop could not be suppressed unless the passive oxide film was provided. Further, even when a positive electrode plate which does not undergo oxidation treatment even when the mixed hydroxide is formed on the surface of the nickel sintered body provided with the passive oxide film is used, the effect of suppressing the voltage drop is insufficient. Was. On the other hand, after forming a cobalt-nickel mixed hydroxide on the surface of the nickel sintered body of the sintered substrate provided with the passivation oxide film, the oxidation-treated positive electrode plate is used for the first time during standing. Can be suppressed over a long period of time.
[0016]
When the oxidation treatment of the mixed hydroxide was not performed, a part of the mixed hydroxide was eluted in the impregnating liquid as an acidic solution in the step of impregnating the active material. This causes a change in the composition and the concentration of the impregnating solution, and thus causes a problem that it is difficult to control the formation amount of the mixed hydroxide and the concentration of the impregnating solution. The method for manufacturing a positive electrode plate according to the present invention can solve these problems.
[0017]
Next, in order to examine the effect of the composition of the cobalt / nickel mixed hydroxide on the standing performance, the cobalt / nickel mixed hydroxide having various compositions was used using a 2.5M nitrate aqueous solution in which the molar ratio of cobalt and nickel was appropriately adjusted. Various batteries were manufactured in the same manner as the battery A of the present invention except that a hydroxide was formed. FIG. 2 shows the open circuit voltage of each battery after being left at 45 ° C. for 90 days when the same experiment as described above was performed using these batteries.
[0018]
When the compound formed on the surface of the nickel sintered body of the positive electrode sintered substrate was nickel or cobalt alone, the open circuit voltages after standing were as low as about 0.55 V and about 0.80 V, respectively. On the other hand, when the cobalt / nickel mixed hydroxide is formed, the voltage drop is suppressed, and particularly when the molar ratio of cobalt to nickel in the mixed hydroxide is 20:80 to 97: 3, the voltage drop is 45%. A remarkable effect was obtained in that the open-circuit voltage after standing at 90 ° C. for 90 days showed 1 V or more. The reason for this is not clear, but it is considered that the addition of nickel to the compound on the surface of the nickel sintered body amplifies the effect of the so-called cobalt oxyhydroxide to form a network.
[0019]
FIG. 3 shows the relationship between the composition of the cobalt / nickel mixed hydroxide formed on the surface of the nickel sintered body of the sintered substrate and the capacity recovery rate in this test. Here, the capacity recovery rate of each battery was defined as capacity recovery rate (%) = {discharge capacity at 5th cycle after standing (mAh) / discharge capacity before standing (mAh)} × 100. When the proportion of cobalt in the mixed hydroxide was 20 mol% or more, the capacity recovery rate showed a high value exceeding 95%, and a battery with a small irreversible capacity decrease upon standing could be obtained.
[0020]
Furthermore, in order to investigate the effect of the amount of cobalt / nickel mixed hydroxide formed on the surface of the nickel sintered body on the standing performance, the molar ratio of cobalt to nickel was fixed at 70:30 and adjusted to various concentrations. Various batteries having different amounts of cobalt / nickel mixed hydroxide formed on the surface of the nickel sintered body of the positive electrode sintered substrate were manufactured in the same manner as the battery A of the present invention except for using the nitrate aqueous solution thus prepared. In addition, the number of times of impregnation was appropriately adjusted so that the theoretical capacity of the active material mainly composed of nickel hydroxide in each battery was approximately equal.
[0021]
FIG. 4 shows the open-circuit voltage of each battery after being left at 45 ° C. for 90 days when the same experiment as described above was performed using these batteries. In this case, when the ratio of the mixed hydroxide on the surface of the nickel sintered body to the active material mainly composed of nickel hydroxide was 1 wt% or more, the open circuit voltage after standing showed a high value of 1 V or more. However, if the amount of the mixed hydroxide formed is too large, the residual porosity of the positive electrode plate is reduced, so that there is a problem that an active material for obtaining a sufficient discharge capacity cannot be filled, which is not practical. Therefore, the ratio of the cobalt / nickel mixed hydroxide formed on the surface of the nickel sintered body to the active material mainly containing nickel hydroxide is practically limited to 1 to 15 wt%.
[0022]
In the positive electrode plate according to the present invention shown in the examples, a method of applying heat treatment in air as a method of applying a passive oxide film to a nickel sintered body of a sintered substrate has been described. Metal nickel may be oxidized using a conventional method, or a method of attaching an oxide is also effective. The method of chemically oxidizing cobalt-nickel mixed hydroxide formed on the surface of sintered nickel body using potassium permanganate aqueous solution was shown, but electrochemical anodic oxidation in alkaline aqueous solution was performed. The same effect was obtained by the method of (1). As a method for filling the active material, not only a chemical impregnation method but also an electrochemical impregnation method can be used.
[0023]
Needless to say, the effects of the present invention are not limited to nickel-cadmium batteries, but are also effective in alkaline storage batteries using a hydrogen storage alloy, zinc, iron, or the like for the negative electrode.
[0024]
【The invention's effect】
The sintered positive electrode plate for an alkaline storage battery according to the present invention can suppress a decrease in the open circuit voltage of the battery due to long-term storage, and provides a battery excellent in storage performance with small irreversible capacity reduction. The target value is extremely large.
[Brief description of the drawings]
FIG. 1 is a diagram showing a change in open circuit voltage when each battery is left. FIG. 2 is a diagram showing a relationship between the composition of a cobalt / nickel mixed hydroxide in a positive electrode plate and the open circuit voltage after the battery is left. FIG. 3 is a diagram showing the relationship between the composition of the cobalt / nickel mixed hydroxide in the positive electrode plate and the capacity recovery rate after standing. FIG. Diagram showing the relationship between the ratio and the open circuit voltage after leaving the battery

Claims (2)

After applying a passive oxide film to the nickel sintered body of the sintered nickel substrate, a cobalt / nickel mixed hydroxide having a molar ratio of cobalt to nickel of 20:80 to 97: 3 is formed. A method for producing a sintered positive electrode plate for an alkaline storage battery, comprising impregnating an active material mainly composed of nickel hydroxide after an oxidation treatment. 2. The method for producing a sintered positive electrode plate for an alkaline storage battery according to claim 1, wherein a ratio of the cobalt / nickel mixed hydroxide to the active material mainly containing the nickel hydroxide is 1 to 15 wt%. .

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