JP3500030B2 - Method for producing non-sintered cadmium negative electrode and method for producing nickel-cadmium storage battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a non-sintered cadmium negative electrode and a method for producing a nickel-cadmium storage battery using the negative electrode produced by this method.

[0002]

2. Description of the Related Art A cadmium negative electrode used in a nickel-cadmium storage battery has a sintering type in which a porous base material made by sintering nickel powder holds an active material, and a synthetic material, a paste, etc. There is a non-sintering method typified by a method of kneading together to form a paste or slurry, and applying this to a conductive core body such as punching metal, but it is low cost and has a high energy density. Good paste formulas are widely used.

However, since the non-sintered cadmium negative electrode does not have a conductive base such as that of the sintered type, there is a problem that the conductivity between the active materials is extremely low. Therefore, in order to solve this problem, a method of forming a conductive matrix in the active material by performing electrochemical formation is known. At this time, in order to uniformly form the matrix, a chemical conversion method of performing complete charge / discharge is desirable.

On the other hand, it is known to add metal cadmium as a precharge product to a non-sintered cadmium negative electrode. This metal cadmium plays a role as a conductive agent by itself, and it is described in JP-A-4-355054 that the battery performance can be further improved by performing chemical conversion in a state where the metal cadmium is added. There is.

Here, as the above-mentioned chemical conversion method, the following method has been proposed. A method of continuous processing using an apparatus equipped with a large number of charging and discharging rollers. A method of energizing the negative electrode and the negative electrode in a laminated state by using a counter electrode and a separator. A method of energizing a sheet-shaped negative electrode plate, a separator, and a counter electrode by spirally winding them. Among the above three methods, the method (1) is excellent as a chemical conversion method for performing complete charging / discharging because mass production is possible with a relatively small facility.

[0006]

However, in the above method, the distribution of the current distribution during energization is likely to occur, so that the amount of remaining metal cadmium in the charged state is large and small, especially at the end of discharging. Occurs. When such a non-sintered cadmium negative electrode is incorporated into a battery, the charging reserve is reduced in places where there is a large amount of metallic cadmium, and hydrogen gas is easily generated, which may result in disruption of the battery closed system. .

The present invention has been made in consideration of the above-mentioned conventional problems, and is a non-sintered cadmium negative electrode capable of improving the performance and reliability of a battery or an electrode without breaking the closed system of the battery. And a method for manufacturing a nickel-cadmium storage battery.

[0008]

In order to achieve the above-mentioned object, the invention according to claim 1 of the present invention provides a negative electrode precursor containing cadmium oxide or cadmium hydroxide and metal cadmium as a counter electrode plate. And, after being spirally wound with the separator, in the method for producing a non-sintered cadmium negative electrode prepared by undergoing a charge / discharge step of performing complete charge / discharge in sodium hydroxide, the discharge step in the charge / discharge step is After the completion and the reversal, the over-discharge is further performed for a predetermined time, and then the pre-charge is performed.

In the chemical formation in which the negative electrode is spirally wound with the counter electrode and the separator, usually, in order to prevent over discharge,
Discharge is terminated at a final voltage of 1.5 to 2.0 V with respect to the counter electrode. However, in this case, it is difficult to make the current distribution uniform as described in the related art, and the amount of metal cadmium tends to vary in the length direction and the width direction of the sheet-shaped negative electrode plate. One of the problems in this variation is the case where a part that is not fully discharged remains after the end of discharge, and this part inevitably has a state where the charge reserve is insufficient. In this case, hydrogen gas may be generated and the closed system may be broken.

In contrast to this problem, in the present invention, since over-discharging is performed in the discharge during formation, it is possible to forcibly discharge the undischarged portion, and it is possible to avoid a state in which the charge reserve is insufficient. . Therefore, when the battery is used, generation of hydrogen gas can be suppressed, and the closed system of the battery can be maintained.

Further, in the above method, since sodium hydroxide is used as the electrolytic solution at the time of chemical conversion, the form of the active material after discharge becomes γ-Cd (OH) ₂ having high activity, and the active material caused by over-discharge is formed. Can be suppressed, that is, deterioration of charge acceptability can be suppressed. When potassium hydroxide is used as the electrolytic solution at the time of chemical conversion, the form of the active material after discharging is β-Cd (OH) ₂ having a low activity, so that the charge acceptability deteriorates.

Furthermore, since the residual metal cadmium powder can be used as a precharge active material, the amount of electricity in precharging can be reduced, and since it acts as a conductive agent in precharging, variations in precharging can be suppressed. Exert an effect on.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the current value in over-discharging is regulated to be smaller than the average discharge current value until the polarity is changed. If the current value when performing over-discharge is higher than the current value before performing over-discharge, metal cadmium cannot be sufficiently discharged and is likely to remain, but the current value when performing over-discharge is higher than that before performing over-discharge. If the current value is lower than the current value, the metal cadmium is satisfactorily discharged and the variation can be suppressed.
Therefore, it is necessary to set the current value for overdischarging to be lower than the current value before overdischarging. However, if the current value is too low, the chemical conversion treatment will take a long time. Therefore, it is usually preferable that the theoretical capacity is 0.01 C or more.

The invention according to claim 3 is the same as the invention according to claim 1, wherein the average particle size of the metal cadmium is 0.8.
It is characterized in that it is ˜2.0 μm. According to this definition, when charging / discharging in chemical conversion treatment, metal cadmium can sufficiently act as a conductive agent, so that the conductivity of the negative electrode is sufficiently ensured, and the negative electrode of the negative electrode when incorporated in a battery is ensured. Deterioration can be suppressed.

In the invention according to claim 4, a pole plate containing cadmium oxide or cadmium hydroxide and metal cadmium is spirally wound together with a counter electrode plate and a separator and then completely charged and discharged in sodium hydroxide. The first step of producing a non-sintered cadmium negative electrode through a charging / discharging process to be performed, and the non-sintered cadmium negative electrode is wound with a positive electrode and a separator to produce a power generating element, which is then inserted into a battery can. In a method for manufacturing a nickel-cadmium storage battery, which further comprises a second step of sealing the battery can after injecting an electrolytic solution into the battery can, in the first step, after the discharging process is completed and the polarity is changed, Further, the battery is over-discharged for a predetermined time and then pre-charged, and potassium hydroxide is used as an electrolyte used in the second step. That.

As described above, when sodium hydroxide having a discharge property slightly inferior to that of potassium hydroxide is used as the chemical conversion liquid, most of the metal cadmium does not become cadmium hydroxide and remains, and it is hardly affected by overdischarge. Therefore, metal cadmium maintains the charge acceptability as a conductive agent even after over-discharging, and has a degree of activity that is involved in the charge-discharge reaction in potassium hydroxide. As a result,
If a battery electrolyte containing mainly potassium hydroxide is used, it will be used as a pre-charging active material, and like the above-mentioned γ-Cd (OH) ₂ formation, suppression of inactivation due to over-discharge will be suppressed. it can. Since this cadmium metal has been uniformly mixed in advance, even if it remains during chemical formation, it does not cause variation.

The invention according to claim 5 is characterized in that, in the invention according to claim 4, the current value in over-discharging is regulated so as to be smaller than the average discharge current value until the polarity is changed. With such a method, the above-mentioned claim 2
The same effect as the described invention is obtained.

The invention according to claim 6 is the same as the invention according to claim 4, wherein the average particle diameter of the metal cadmium is 0.8.
It is characterized in that it is ˜2.0 μm. In this way, if the average particle size of metal cadmium is less than 0.8 μm, it changes to cadmium hydroxide even in sodium hydroxide, and while the metal cadmium is less likely to remain,
When it exceeds 2.0 μm, sufficient reactivity cannot be obtained even in potassium hydroxide, the effect due to the presence of the metal cadmium is lost, and the energy density of the battery decreases.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. First, an active material paste was prepared by adding 80 parts by weight of cadmium oxide and 20 parts by weight of metallic cadmium to a nylon fiber and a paste solution in which sodium hydrogen phosphate as a hydration inhibitor was dissolved, and kneading these. Was produced. Next, this active material paste is used as a conductive core (thickness:
0.08 mm) on both surfaces to prepare a sheet-shaped negative electrode precursor. The metal cadmium used had an average particle size (Fisher subsieve sizer) of 1.5 μm.

Then, the sheet-shaped negative electrode precursor (length: 300 m) was wound with a counter electrode made of a nickel plate through a separator made of polypropylene woven fabric,
In a 20% by weight aqueous solution of sodium hydroxide, which is a chemical solution, this was heated at a theoretical capacity of 0.2 C at a theoretical capacity of 150
%, And then discharged with the same current as above to 1.6 V against the counter electrode. After this, the theoretical capacity of 0.
A negative electrode was manufactured through an over-discharging step of discharging at a current of 05 C until completely polarized and further discharging at the same current for 1 hour.

Then, after precharging to 5% of the theoretical capacity, it was washed with water, dried, and cut into a predetermined length.
Then, after winding with a known nickel positive electrode through a separator to produce a power generation element, the power generation element was inserted into a battery can. Next, after injecting 30 wt% potassium hydroxide as an electrolytic solution into the battery can, the battery was sealed with a sealing plate to prepare a nickel-cadmium battery (nominal capacity 1100 mAh).

In the embodiment of the invention described above, pure potassium hydroxide is used as the electrolytic solution. However, the electrolytic solution is not limited to this, and the main component is potassium hydroxide, which is mixed with sodium hydroxide. It is also possible to use the one as described above. Further, when the current value of the discharge that is performed until the polarity is changed is not constant (for example, when the current value is changed stepwise to perform discharge), these average current values (the average current value is It has been confirmed by experiments that the effect of the present invention can be obtained by discharging at a current value smaller than a value obtained by dividing the total amount of electricity supplied by the total amount of time supplied. Furthermore, the active material is not limited to cadmium oxide, but cadmium hydroxide can be used.

[0023]

【Example】

[First Example] (Example) A negative electrode was produced in the same manner as in the embodiment of the present invention. The negative electrode manufactured in this manner is hereinafter referred to as a negative electrode A of the present invention.

(Comparative Example 1) Except that over-discharge was not performed,
A negative electrode was produced in the same manner as in the above example. The negative electrode thus manufactured is hereinafter referred to as comparative negative electrode B1.

(Comparative Example 2) A negative electrode was produced in the same manner as in the above-mentioned example except that 20% aqueous potassium hydroxide solution was used as the chemical conversion solution instead of 20% aqueous sodium hydroxide solution. The negative electrode thus manufactured is hereinafter referred to as comparative negative electrode B2.

Comparative Example 3 A negative electrode was prepared in the same manner as in Comparative Example 2 except that 20% potassium hydroxide aqueous solution was used as the chemical conversion liquid instead of 20% sodium hydroxide aqueous solution. The negative electrode thus manufactured is hereinafter referred to as comparative negative electrode B3. Table 1 below shows the difference in the manufacturing method of each of the negative electrodes.

[0027]

[Table 1]

(Experiment 1) With respect to the above-mentioned negative electrode A of the present invention and comparative negative electrodes B1 to B3, samples were randomly drawn in the length direction of the electrode plate, and the undischarged metal cadmium content at each site was examined. Is shown in FIG.
In addition, all the negative electrodes were measured in a state where they were not precharged.

As is clear from FIG. 1, the negative electrode A of the present invention and the comparative negative electrode B2 which have undergone the over-discharging step have an undischarged metal cadmium content as compared with the comparative negative electrodes B1 and B3 which have not undergone the over-discharging step. It can be seen that the variation of is small. Therefore, in order to reduce the variation in the undischarged metal cadmium content, it is desirable to perform over-discharge after passing through a normal discharge process.

(Experiment 2) The charge and discharge efficiencies of the present invention negative electrode A and comparative negative electrodes B1 to B3 were examined, and the results are shown in Table 2. The experiment was conducted in a 20 wt% potassium hydroxide solution using a nickel electrode as the counter electrode. The charging / discharging conditions are such that each negative electrode is charged at a theoretical capacity of 0.15 C for 2.4 hours and discharged at the same current value to 1.5 V with respect to the nickel electrode.

[0031]

[Table 2]

As is clear from Table 2 above, the negative electrode A of the present invention and the comparative negative electrode B1 which were subjected to the chemical conversion treatment with the sodium hydroxide aqueous solution were the same as the comparative negative electrode B2 and the comparative negative electrode B3 which were subjected to the chemical conversion treatment with the aqueous potassium hydroxide solution. In comparison, it can be seen that the charge / discharge efficiency is higher. Therefore, in order to improve the charge / discharge efficiency, it is desirable to perform the chemical conversion treatment with an aqueous sodium hydroxide solution.

From Experiments 1 and 2 described above, in order to reduce the variation in the undischarged metal cadmium content and improve the charge / discharge efficiency, a chemical conversion treatment with an aqueous sodium hydroxide solution was carried out, and the usual discharge step was performed. It can be understood that it is desirable to perform over-discharge after a certain period.

(Experiment 3) A negative electrode was prepared in the same manner as in the negative electrode A of the present invention except that the current value during overdischarge was changed (0.05 to 0.4 C). The content of undischarged metal cadmium in these negative electrodes was examined, and the results are shown in Table 3. In addition, all the negative electrodes were measured in a state where they were not precharged, and for reference, those having no overdischarge were similarly examined.

[0035]

[Table 3]

As is clear from Table 3, when the current value during over-discharge is smaller than the current value during normal discharge (0.2 C in this example), the variation of the undischarged metal cadmium content (maximum value) However, if the current value during overdischarge is equal to or greater than the current value during normal discharge, the variation in the undischarged cadmium metal content will increase. Is recognized. Therefore, in order to reduce the variation in the undischarged metal cadmium content, it is necessary to set the current value during overdischarge to be smaller than the current value during normal discharge. It should be noted that, in the case of no over-discharge at all, it is recognized that the variation of the undischarged metal cadmium content becomes very large.

(Experiment 4) A negative electrode was prepared in the same manner as the negative electrode A of the present invention, except that the average particle diameter (Fisher subsieve sizer) of the metal cadmium to be added was changed (0.8 to 2.4 μm). The undischarged metal cadmium content and charge / discharge efficiency of these negative electrodes were examined by the same method as in Experiments 1 and 2 above, and the results are shown in Table 4.
In addition, the content of undischarged metal cadmium was measured in a state where it was not precharged in any of the negative electrodes.

[0038]

[Equation 1]

[0039]

[Table 4]

As is clear from Table 4, the amount of metal cadmium remaining decreases as the particle size of metal cadmium increases. This is because the smaller the particle size, the higher the reactivity and the easier the discharge is during the chemical conversion treatment. Also,
It is recognized that the charging / discharging efficiency becomes low when the particle size of metal cadmium is too small or too large. It is considered that this is due to the following reasons.

That is, when the particle size of the metal cadmium becomes small, most of the metal cadmium is discharged during the chemical conversion. Therefore, when a battery is constructed, most of the metal cadmium that contributes to charge and discharge remains in potassium hydroxide. As a result, the charge / discharge efficiency is reduced.

At this time, it is possible to increase the amount of precharge power in order to obtain the required amount of precharge active material. However, in this method, the amount of precharge power is increased, so that the production efficiency is reduced. Then, the manufacturing cost of the battery rises, and since the amount of metal cadmium acting as a conductive agent is small, the reactivity at the time of precharging is low,
A new problem arises that causes variation in precharge.

On the other hand, when the particle size of the metal cadmium becomes large, a large amount of the metal cadmium remains after the chemical conversion treatment, but when the particle size of the metal cadmium becomes too large, the reactivity becomes low, so that the charge / discharge efficiency also decreases. To do.

At this time, in order to obtain a necessary amount of the precharge active material, it is conceivable to increase the amount of power for precharge as in the above case. In this case, since a large amount of metal cadmium acting as a conductive agent is present, variations in precharge are reduced. However, even with this method, there is a problem in that the amount of power for precharge increases, the production efficiency decreases, and the manufacturing cost of the battery rises, and moreover, the active material that does not contribute to the charge / discharge reaction increases, so that the battery The problem arises that the energy density decreases. Considering these things, it is desirable that the particle diameter of the metal cadmium be in the range of 0.8 to 2.0 μm.

Second Example (Example) A battery was manufactured in the same manner as in the above-described embodiment of the present invention. The battery thus manufactured is hereinafter referred to as a battery a of the invention.

(Comparative Example 1) A battery was prepared in the same manner as in the above-mentioned example except that 30% sodium hydroxide was used as the electrolytic solution. The battery thus produced is
It is referred to as comparative battery b1.

(Comparative Example 2) A battery was produced in the same manner as in the above-mentioned Example except that the negative electrode produced by the method of Comparative Example 2 of the first example was used as the negative electrode. The battery thus manufactured is hereinafter referred to as comparative battery b2.

Comparative Example 3 A battery was prepared in the same manner as in Comparative Example 2 except that 30% sodium hydroxide was used as the electrolytic solution. The battery thus manufactured is hereinafter referred to as comparative battery b3. The following Table 5 shows the difference in the manufacturing method of each of the above batteries.

[0049]

[Table 5]

(Experiment) The above battery a of the present invention and comparative battery b
The cycle characteristics in 1 to 3 were examined, and the results are shown in FIG. The experimental condition is that the cycle of charging for 16 hours at a current of 0.1 C of theoretical capacity, resting for 1 hour, discharging for a current of 1 C of theoretical capacity, and resting for 1 hour is repeated. is there. As is apparent from FIG. 2, the battery a of the present invention has improved cycle characteristics as compared with the comparative batteries b1 to b3.

[0051]

As described above, the negative electrode produced by the production method of the present invention can avoid a state in which the charge reserve is insufficient. Therefore, when a battery is produced using this negative electrode, hydrogen gas is generated. Can be suppressed and the closed system of the battery can be maintained. Further, since the form of the active material after discharging is γ-Cd (OH) ₂ having high activity, deterioration of charge acceptability can be suppressed. Further, in the battery using the negative electrode manufactured by the manufacturing method of the present invention, since metal cadmium is used as a precharge active material, inactivation due to overdischarge can be suppressed. From these facts, there is an excellent effect that the performance and reliability of the battery and the electrode such as cycle characteristics can be improved without breaking the closed system of the battery.

[Brief description of drawings]

FIG. 1 shows the negative electrodes A of the present invention and comparative negative electrodes B1 to B3.
It is a graph which shows the relationship between each point of the length direction, and the content of undischarged metal cadmium.

FIG. 2 is a graph showing cycle characteristics of the battery a of the present invention and the comparative batteries b1 to b3.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Kambayashi 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Masahiro Okubo 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 within Sanyo Electric Co., Ltd. (56) Reference JP-A-54-53232 (JP, A) JP-A-4-355054 (JP, A) JP-A 60-250556 (JP, A) JP-A 61- 7565 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 10/28 H01M 4/26

Claims (6)

(57) [Claims] 1. A negative electrode precursor containing cadmium oxide or cadmium hydroxide and metal cadmium is spirally wound together with a counter electrode plate and a separator and then subjected to a charging / discharging step of performing complete charging / discharging in sodium hydroxide. In the method for producing a non-sintered cadmium negative electrode manufactured by the above, after the discharge step in the charge / discharge step is completed and the polarity is changed, over-discharge is further performed for a predetermined time, and then precharge is performed. A method for producing a sintered cadmium negative electrode. 2. The method for producing a non-sintered cadmium negative electrode according to claim 1, wherein the current value in the over-discharging is regulated to be smaller than the average discharge current value until the polarity is changed. 3. The average particle size of the metal cadmium is 0.
The method for producing a non-sintered cadmium negative electrode according to claim 1, which has a thickness of 8 to 2.0 μm. 4. An electrode plate containing cadmium oxide or cadmium hydroxide and metal cadmium is spirally wound together with a counter electrode plate and a separator and then subjected to a charging / discharging step of performing complete charging / discharging in sodium hydroxide. The first step of producing a sintered cadmium negative electrode, and by winding the non-sintered cadmium negative electrode together with a positive electrode and a separator to produce a power generating element, insert this into a battery can, and further electrolyze into the battery can. A second step of sealing the battery can after injecting the liquid, and a method for manufacturing a nickel-cadmium storage battery comprising: Nickel-cadmium characterized by carrying out and then precharging and using potassium hydroxide as the electrolyte used in the second step. Method for manufacturing a storage battery. 5. The method for manufacturing a nickel-cadmium storage battery according to claim 4, wherein the current value in the over-discharge is regulated to be smaller than the average discharge current value until the polarity is changed. 6. The average particle diameter of the metal cadmium is 0.
The method for producing a nickel-cadmium storage battery according to claim 4, which has a thickness of 8 to 2.0 μm.