JPH0259587B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for manufacturing an anode plate for an alkaline storage battery having a layer in which cobalt hydroxide exists alone on the surface of an active material.

(b) Prior art The anode plate of a conventional alkaline storage battery is made by coating a core with a slurry mainly composed of carbonyl nickel powder and sintering this in a reducing atmosphere. The substrate is manufactured using a manufacturing method in which the active material is filled into the pores of the substrate by impregnating the substrate with an impregnating liquid containing as the main component, and then immersing it in an alkaline solution. However, recent market demands cannot be satisfied with alkaline storage batteries using anode plates obtained by the above-mentioned manufacturing method, and there is a strong desire for increased battery capacity. It is necessary to develop an anode plate with a large energy density and a large volumetric energy density. The basic method to increase the capacity of the electrode plate is to increase the utilization rate of the active material, and generally cobalt nitrate is added to the impregnating solution and cobalt is added to uniformly disperse the cobalt in the active material. is being carried out. Although the addition of cobalt is effective in improving the utilization rate and high-temperature characteristics, the utilization rate of the active material in the anode plate was not sufficient.

(c) Purpose of the Invention In view of the above, the present invention provides an anode plate that improves the capacity of the electrode plate by improving the utilization rate of the anode active material, and suppresses capacity deterioration due to an increase in charge/discharge cycles. The purpose is to

(d) Structure of the Invention The method for manufacturing an anode plate for an alkaline storage battery of the present invention is to replace a porous metal substrate holding an anode active material mainly composed of nickel hydroxide or only nickel hydroxide with cobalt nitrate. The active material is immersed in an aqueous nitrate solution containing 75% or more of cobalt hydroxide, and then subjected to alkali treatment to form a layer in which cobalt hydroxide exists alone on the surface of the active material. By oxidizing the cobalt hydroxide using a chemical agent to make cobalt trivalent, it is possible to prevent capacity deterioration and improve capacity through charging and discharging cycles of an anode plate with cobalt added to the surface layer of the active material.

Further, the cobalt hydroxide is 0.5 to 5% by weight based on the nickel hydroxide, and the porous metal substrate is immersed in the nitrate aqueous solution for an impregnation time of
(minutes), and when the impregnating liquid temperature is Y (°C), by setting it in the range of be.

(e) Examples Experiments and examples related to the present invention are shown below.
This will be explained using drawings.

Experiment 1 Using an impregnating liquid containing nickel nitrate as the main component,
An electrode plate with a utilization rate of 76% is made by holding a nickel anode active material on a sintered nickel substrate using a chemical impregnation method.
After being immersed for 5 minutes in a nitrate impregnating solution with a specific gravity of 1 and 4, which was made by varying the content of nickel and cobalt, the anode plates were then treated with alkali, washed with water, and dried to create anode plates, and the utilization rate was measured. . FIG. 1 is a drawing showing the relationship between the composition of nickel and cobalt in the nitrate impregnation solution and the utilization rate. As is clear from the drawings, the utilization rate is greatly affected by the composition of the impregnating liquid, and the higher the proportion of cobalt, the higher the utilization rate. That is, the higher the cobalt content in the surface layer of the active material, the better, and a high utilization rate can be obtained when the impregnating liquid composition contains at least 75% cobalt, preferably 100%.

Experiment 2 An electrode plate with a utilization rate of 76% as in Experiment 1 was used at a liquid temperature of 20%.
℃, 45℃, and 70℃ in a cobalt nitrate impregnating solution with a specific gravity of 1 and 4, respectively, for an arbitrary period of time, and then immersed in an alkaline aqueous solution to convert it into cobalt hydroxide, followed by washing with water,
After drying, cobalt was deposited on the surface layer of the active material to prepare an anode plate. Figure 2 is a diagram showing the relationship between impregnation time and utilization rate with cobalt nitrate impregnating solution, and Figure 3 is a diagram showing the relationship between impregnation time and impregnating solution temperature to obtain a high utilization rate. be. From FIG. 2, it can be seen that the utilization rate decreased despite the increase in the impregnation time. This is thought to be because by immersing the electrode plate in the impregnating liquid for a long time, the active material nickel dissolves and mixes with cobalt, causing the content of cobalt hydroxide in the surface layer of the active material to decrease.
The reason for this is that the higher the temperature of the impregnating liquid, the faster the decrease in utilization rate occurs, and the higher the temperature, the more dissolution and mixing of nickel into cobalt progresses. It can also be seen that if the impregnation time is within 30 minutes at an impregnating solution temperature of 20°C, within 20 minutes at 45°C, and within 10 minutes at 70°C, a significant improvement in the utilization rate can be expected. In other words, this is the shaded area in Figure 3, and the temperature of the impregnating liquid is Y.
(°C) and the impregnation time is X (minutes), generally a good effect can be obtained when X≦(95-Y)/2.5.

Experiment 3 An electrode plate with a utilization rate of 76% as in Experiment 1 was used at a liquid temperature of 20℃.
After being immersed in cobalt nitrate aqueous solutions with different specific gravity for 5 minutes, anode plates were then treated with alkali, washed with water, and dried to create anode plates with varying amounts of cobalt added to the surface layer of the active material, and the utilization rates were evaluated. FIG. 4 is a drawing showing the relationship between the specific gravity of the cobalt nitrate impregnation liquid and the cobalt addition rate (ratio of cobalt hydroxide in the surface layer of the active material to nickel hydroxide in the active material).
The figure is a diagram showing the relationship between cobalt addition rate and utilization rate. It can be seen from FIG. 4 that the amount of cobalt added can be changed by changing the specific gravity of the cobalt nitrate impregnation liquid. One possible way to change the amount of cobalt added is to use an impregnating liquid of the same specific gravity and change the impregnation time, but as mentioned above, long-term immersion in an aqueous cobalt nitrate solution is undesirable because it reduces the utilization rate. Furthermore, as can be seen from Figure 5, when the amount of cobalt added is small, it can be seen that the utilization rate improves due to the addition of cobalt, but the utilization rate is still not sufficient and at the same time, the deterioration during charge/discharge cycles increases. (described later). If too much cobalt is added, the utilization rate will decrease due to the addition of cobalt, and partial peeling of the electrode plate will occur due to gas generation, and the movement of cobalt to the separator will be significant. involves the risk of If too much cobalt is added, the utilization rate decreases because some of the pores in the electrode plates are closed by cobalt, and the cobalt layer on the surface of the active material becomes too thick, causing electrolyte diffusion and
This is presumed to be due to limited penetration. As mentioned above, the amount of cobalt added to the surface layer of the active material has an optimum value, and is preferably 0.5 to 5.0% by weight.

Experiment 4 Considering the results of Experiments 1 to 3, electrode plates A to F were created and their cycle characteristics were investigated.

Electrode plate A The electrode plate with a utilization rate of 76% used in Experiment 1 was used as a base electrode plate, and this base electrode plate was immersed in a cobalt nitrate aqueous solution with a specific gravity of 1.4 at room temperature for 5 minutes, followed by drying, alkali treatment, water washing, and drying. By doing this, the amount of cobalt hydroxide added to the active material was about 3.0%, and the anode plate was made.

Plate B Among the conditions for making Plate A, the immersion time is 60 minutes.
The anode plate was prepared under the same conditions except that the amount of cobalt hydroxide added was about 3.5% based on the active material.

Electrode plate C was prepared under the same conditions as electrode plate A, with the specific gravity of the cobalt nitrate aqueous solution being 1.1, and the other conditions being the same.
The amount of cobalt hydroxide added is approximately 0.5 to the active material.
% anode plate.

Electrode Plate D The base electrode plate is immersed in a nitrate aqueous solution with a specific gravity of 1.4 and a molar ratio of cobalt and nickel of 3:1 at room temperature for 5 minutes, followed by drying, alkaline treatment, washing with water, drying, and immersion in water. This is an anode plate in which the amount of cobalt oxide added is approximately 2.8% based on the active material.

Electrode plate E Electrode plate D was prepared under the conditions that the molar ratio of cobalt and nickel in a nitrate aqueous solution with a specific gravity of 1 and 4 was 1:3, and the other conditions were the same, and the amount of cobalt hydroxide added to the active material was For the anode plate, it was about 1.6%.

Note that the base electrode plate is referred to as electrode plate F.

A cycle test of these electrode plates was carried out using a nickel plate as a counter electrode and applying a specific gravity of 1,23 to the electrolyte under an excess of electrolyte.
Using KOH, charging is the theoretical capacity of 0.1C x 16 hours.
Further, the discharge was performed at 0.2C. FIG. 6 shows the relationship between the number of cycles and capacity obtained by this test.
From Figure 6, all of the plates A to E are the base plate F.
It is seen that the capacity has increased compared to the plate D.
Since the amount of active material and E is increased by 4 to 8% compared to other electrode plates, the utilization rate of active material is lower, and in electrode plate C with less cobalt addition, the cycle deterioration is higher than that of other electrode plates. It has become extremely large. Next, we measured the volumetric efficiency of plates A and F and the valence of nickel during charging and discharging, and found that plate F had a volumetric efficiency of 430 mAH/cc, while plate A had a volumetric efficiency of 430 mAH/cc.
It can be seen that the valence has increased significantly to 540 mAH/cc, and the valence of Nickel is approximately 3.1 for both plates during charging, which is almost the same, but when discharging, plate A is discharged to a valence of approximately 2.1. On the other hand, the electrode plate F is discharged only to a valence of about 2.3, and it is thought that this difference in valence of 0.2 leads to an increase in capacity. This is because in the case of electrode plate F, the charged product NiOOH is Ni(OH), which has a lower conductivity than the active material surface layer during discharge _.
As the discharge progresses, the surface layer of the active material becomes covered with Ni(OH) ₂ , making it difficult for the reaction of NiOOH inside to proceed, whereas in the case of electrode plate A, it is difficult to discharge to the surface layer of the active material. CoOOH exists and this
This is thought to be because CoOOH has higher conductivity than Ni(OH) ₂ , so it is difficult to form a passive layer like Ni(OH) ₂ on the surface layer, and the NiOOH reaction progresses to the inside.

However, it has been found that the capacity of the electrode plate in which cobalt is added to the active material surface layer described above deteriorates as the charge/discharge cycle progresses. Examples of the present invention are shown below, and the electrode plate according to the present invention and the above-mentioned electrode plate A are shown below.
This will be explained by comparing and F.

Example: Plate A used in Experiment 4 was dissolved in 2% hydrogen peroxide solution for 30 minutes.
The cobalt on the surface layer of the active material was oxidized to trivalent by dipping for a minute. The active material surface layer of this electrode plate was formed by immersing it in a nitrate aqueous solution containing 75% or more of cobalt nitrate and then performing an alkali treatment, and as shown in Experiment 1, the utilization rate was high.
It is presumed that a layer in which cobalt hydroxide exists alone is formed on the surface of the active material. The electrode plate thus obtained is designated as G.

Comparative example 1 The above-mentioned electrode plate A was added to a 2% sodium hypochlorite solution for 30 minutes.
The sample was immersed for a minute to oxidize the cobalt on the surface of the active material.
Let this electrode plate be H.

Comparative Example 2 The operation of reducing the pressure and injecting air into the electrode plate A described above in a reduced pressure container was repeated several times to oxidize the cobalt on the surface layer of the active material. This electrode plate is designated as I. The electrode plates A and F are used as Comparative Examples 3 and 4.

The electrode plates A and F to I were subjected to the same conditions as in Experiment 4.
Figure 7 shows the relationship between discharge capacity and discharge voltage when discharging at 0.2C. Here, plate H and plate G showed the same curve, and plate I and plate A also showed the same curve. Next, a cycle test was conducted under the same conditions as in Experiment 4, and the relationship between the number of cycles and the plate capacity was determined in the 8th experiment.
As shown in the figure.

It can be seen from FIG. 7 that the discharge voltage of plate A is slightly lower overall than that of plates F, G, and H, and that the discharge voltage is particularly low at the end of discharge, decreasing in a gentle curve. This is thought to be because a part of the cobalt, which has become a higher order oxide through charging, changes into divalent state through discharging, and the conductivity of the surface layer of the active material deteriorates. Further, from FIG. 8, it can be seen that the electrode plate A is good with almost no capacity deterioration up to about 30 cycles, but the capacity deterioration significantly occurs in subsequent cycles.

Next, looking at the electrode plates G of the embodiment of the present invention and the electrode plates A, F, H, and I of the comparative example, as can be seen from FIG. It has increased overall, albeit slightly. In addition, there is almost no drop in discharge voltage even at the end of discharge, and the electrode plate F
It draws almost the same curve. However, Plate I, which was oxidized with air, drew a curve similar to Plate A, and did not have the same effect as Plate G and H. This is thought to be because the cobalt added to the surface layer of the active material could not be completely oxidized. Further, from FIG. 8, it can be seen that the electrode plate G maintains a high capacity with almost no deterioration in capacity as a whole, and the effect of cobalt oxidation on the surface layer of the active material is manifested. On the other hand, the cycle deterioration of plate H oxidized with sodium hypochlorite was greater than that of plate A.
This is thought to be because using a strong oxidizing agent such as sodium hypochlorite not only oxidizes cobalt but also corrodes the electrode plate. As described above, when sodium hypochlorite is used as an oxidizing agent, it is difficult to use in the manufacturing process of electrode plates because it tends to corrode the electrode plates and it becomes difficult to set the conditions.

However, when ozone, which has a strong oxidizing power, was used as an oxidizing agent, an electrode plate was prepared in the same manner as in the comparative example and a cycle test was conducted, and the same tendency as that of the electrode plate G of the present invention was obtained. It can be seen that evaluation cannot be made simply by the strength or weakness of oxidizing power.

Therefore, when using an oxidizing agent, it is necessary to use a hydrogen peroxide solution or ozone in order to sufficiently oxidize cobalt under conditions that do not corrode the electrode plate.

These experiments revealed that the above-mentioned drawbacks due to the addition of cobalt to the surface layer of the active material can be overcome by oxidizing the cobalt on the surface of the electrode plate.
The reason for this is that the cobalt that is in direct contact with the active material nickel may be an active divalent cobalt, so if charging and discharging are performed in this state, a solid solution of nickel and cobalt is likely to be formed, and as the number of cycles increases, the cobalt It is thought that this is because the diffusion of cobalt also progresses, and by oxidizing cobalt to make it trivalent before charging and discharging, the formation of the solid solution is suppressed, and at the same time, the diffusion of cobalt is also suppressed, resulting in a good effect. .

(F) Effects of the Invention According to the method for manufacturing an anode plate for an alkaline storage battery of the present invention, a porous metal substrate holding an anode active material mainly composed of nickel hydroxide or only nickel hydroxide can be used. After immersing the active material in a nitrate aqueous solution containing 75% or more of cobalt nitrate, and then performing alkali treatment to form a layer in which cobalt hydroxide exists alone on the surface of the active material, at least one selected from hydrogen peroxide and ozone is added. The cobalt hydroxide is oxidized using 3 oxidizing agents to reduce cobalt to 3
By adding cobalt to the surface layer of the active material, it is possible to prevent capacity deterioration due to charge/discharge cycles of the anode plate and to improve the capacity of the plate.

Further, the cobalt hydroxide is 0.5 to 5% by weight based on the nickel hydroxide, and the porous metal substrate is immersed in the nitrate aqueous solution for an impregnation time of
(minutes), and when the impregnating liquid temperature is Y (°C), by setting it in the range of and its industrial value is extremely large.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the composition of cobalt and nickel in the impregnating solution and the utilization rate, Figure 2 is a diagram showing the relationship between the immersion time in the cobalt nitrate impregnating liquid and the utilization rate, and Figure 3 is a diagram showing the relationship between the utilization rate and the composition of cobalt and nickel in the impregnating solution. Figure 4 is a diagram showing the relationship between the impregnation time and impregnating liquid temperature to obtain the utilization rate; Figure 4 is a diagram showing the relationship between the specific gravity of the impregnating liquid and the cobalt addition rate;
The figure shows the relationship between cobalt addition rate and utilization rate, Figures 6 and 8 show the relationship between cycle number and plate capacity, and Figure 7 shows the relationship between discharge capacity and discharge voltage. FIG.

Claims (1)

[Claims] 1. A porous metal substrate holding an anode active material mainly composed of nickel hydroxide or only nickel hydroxide is immersed in a nitrate aqueous solution containing 75% or more of cobalt nitrate, and then After performing alkali treatment to form a layer in which cobalt hydroxide exists alone on the surface of the active material, the cobalt hydroxide is oxidized using at least one oxidizing agent selected from hydrogen peroxide and ozone. A method for producing an anode plate for an alkaline storage battery, characterized by making cobalt trivalent. 2. The method for producing an anode plate for an alkaline storage battery according to claim 1, wherein the cobalt hydroxide is 0.5 to 5% by weight based on the nickel hydroxide. 3 The porous metal substrate is immersed in the nitrate aqueous solution for an impregnation time of X (minutes) and an impregnation solution temperature of Y (°C).
Then, the first claim or the second claim has the relationship X≦(95-Y)/2.5.
A method for producing an anode plate for an alkaline storage battery as described in .