JP3070081B2 - Sealed alkaline storage battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sealed alkaline storage battery.

2. Description of the Related Art A hydrogen storage electrode used as a negative electrode of an alkaline storage battery includes a hydrogen storage alloy. This hydrogen storage alloy contains LaNi ₅
And there are intermetallic compounds such as TiMn _2, a part of the component elements of these alloys, and be replaced by other elements, by varying the stoichiometry number, changing the hydrogen storage capacity of these alloys It has been used for electrodes by changing the equilibrium hydrogen pressure of these metal hydrides and improving the corrosion resistance of alloys in alkaline electrolytes.

As one of the conventional manufacturing methods of this electrode, a powder of the above-mentioned hydrogen storage alloy is held on a conductive support such as punched metal or foamed nickel, and polyvinyl alcohol,
Some are bonded with an alkali-resistant polymer such as a fluororesin or an acrylic-styrene resin.

The negative electrode, a positive electrode such as a nickel hydroxide electrode, and an alkaline electrolyte such as potassium hydroxide constitute an alkaline storage battery.

In an alkaline storage battery using a hydrogen storage electrode, the discharge capacity of the hydrogen storage electrode reaches about twice that of a cadmium electrode having the same volume. Therefore, for example, so that the capacity of the hydrogen storage electrode is about 1.5 times the capacity of the cadmium electrode,
In the case of a nickel metal hydride battery, the capacity of the nickel-metal hydride battery is reduced by reducing the volume of the hydrogen storage electrode, increasing the volume of the positive electrode by the reduced volume, and increasing the capacity of the positive electrode by about 1.5 times. However, it can be increased to about 1.5 times that of nickel-cadmium batteries of the same volume.

When an alkaline storage battery is configured using a hydrogen storage electrode as a negative electrode, the battery is configured as follows to achieve hermetic sealing.

First, the case of overcharging is as follows. That is, the chargeable capacity of the positive electrode is made smaller than the chargeable capacity of the negative electrode so that the charge of the positive electrode ends earlier than the charge of the negative electrode. When this sealed battery is overcharged, water is electrolyzed, and oxygen gas generated from the positive electrode is electrochemically reduced on the surface of the negative electrode to generate water. Does not change. And in the negative electrode,
Since a reduction reaction of oxygen gas occurs during overcharging and charging of the negative electrode is stopped, generation of hydrogen gas after charging of the negative electrode is prevented, and accumulation of hydrogen gas in the battery does not occur. Therefore, even if the battery is overcharged, the gas does not accumulate in the battery and the internal pressure does not increase significantly, and the closed system of the battery is maintained. Conversely, if the battery is configured so that the charging of the negative electrode ends earlier than the positive electrode, hydrogen gas is generated from the negative electrode during overcharge, but the rate at which hydrogen gas is electrolytically oxidized at the positive electrode is extremely small. It is difficult to effectively prevent accumulation of hydrogen gas in the battery. Therefore, in a practical sealed battery, charging of the positive electrode is completed before charging of the negative electrode.

The principle of sealing during overcharging is the same as that of a sealed nickel-cadmium battery. This battery configuration can be realized by making the chargeable capacity of the positive electrode smaller than the chargeable capacity of the negative electrode.

Next, overdischarge is as follows. That is,
The dischargeable capacity of the positive electrode active material is made smaller than the dischargeable capacity of the negative electrode, so that the discharge of the positive electrode ends before the negative electrode. When the sealed battery is over-discharged, water is electrolyzed and hydrogen gas generated from the positive electrode is electrochemically oxidized on the surface of the negative electrode to generate water. Does not change. At the negative electrode, the oxidation reaction of the hydrogen gas occurs at the time of overdischarge, and the discharge of the negative electrode stops. Therefore, the discharge of the negative electrode is stopped and the generation of oxygen gas is prevented, and the accumulation of oxygen gas in the battery occurs. Absent. Therefore, even if the battery is over-discharged, the gas does not accumulate in the battery and the internal pressure does not increase significantly, and the closed system of the battery is maintained. Conversely, if the battery is configured such that the discharge of the negative electrode ends earlier than the positive electrode, oxygen gas is generated from the negative electrode during overdischarge, but the rate at which oxygen gas is electrolytically reduced at the positive electrode is extremely small. It is difficult to effectively prevent accumulation of oxygen gas in the battery. Accordingly, in a practical sealed battery, the discharge of the positive electrode is configured to end before the discharge of the negative electrode.

If the gas absorption reaction does not occur at a sufficiently high rate during overcharge or overdischarge, gas generated by electrolysis of water in the alkaline electrolyte accumulates in the battery,
The internal pressure of the battery rises significantly, the safety valve operates, and the gas in the battery is released. If this is repeated, the gas generated by the electrolysis of water will leave the battery system, so the amount of electrolyte in the battery will decrease significantly, making it difficult to charge and discharge the battery. Discharge cycle life is significantly shortened. In particular, such a principle of hermetic sealing during overdischarge is peculiar to a sealed alkaline storage battery using a hydrogen storage electrode or a hydrogen gas diffusion electrode as a negative electrode.

In the case of a hydrogen storage electrode, the amount of hydrogen that is difficult to discharge at high-rate discharge or low-temperature discharge increases, and the discharge capacity decreases. In such a case, when the discharge of the negative electrode ends earlier than the positive electrode and the hydrogen storage electrode of the negative electrode is over-discharged and oxygen gas is generated, the surface of the hydrogen storage alloy is anodized and becomes inactive. The inconvenience that charging / discharging thereafter becomes difficult occurs. Accordingly, it is useful to prevent this inconvenience by enclosing the sealed alkaline storage battery provided with the hydrogen storage electrode on the negative electrode and limiting the discharge of the battery by the positive electrode so that the negative electrode is not over-discharged. .

Problems to be Solved by the Invention In a sealed alkaline storage battery using a hydrogen storage electrode as a negative electrode, as described above, means for configuring the battery so that discharge of the positive electrode ends before discharge of the negative electrode include the following. Some methods have been proposed, but each has its own problems.

The first means is a method in which the hydrogen storage electrode is charged in advance before forming the battery. Specifically, a fixed amount of gaseous hydrogen gas is supplied to the hydrogen storage alloy of the hydrogen storage electrode. This is a method in which occlusion is performed or a hydrogen storage electrode is partially charged in an electrolytic solution. These methods have the following problems. That is, when hydrogen gas in the gas phase is occluded, it is difficult to uniformly store the hydrogen gas in the hydrogen storage electrode, and it is necessary to pressurize and heat the hydrogen gas at the time of occlusion. With Also, when partially charging the hydrogen storage electrode, it is necessary to wash and dry the electrode before assembling the battery. At that time, the hydrogen in the electrode is released, and the storage amount is controlled. Is difficult to do.

The second means is to add a reducing agent to the alkaline electrolyte,
This is a method utilizing the phenomenon that the negative electrode is charged as the reducing agent is oxidized. Specifically, there is a method in which hydrazine or alcohol is added. These methods are excellent in that the amount of the reducing agent to be added can be controlled to easily control the excess discharge amount of the negative electrode, but the oxidation products of the reducing agent have various adverse effects on the battery. That is, the nitrogen compound, which is an oxidation product of hydrazine, promotes self-discharge by the “shuttle mechanism” similar to the nickel-cadmium battery. In addition, alcohol is oxidized to generate a large amount of carbonate, which promotes corrosion of metallic nickel, which is a conductive skeleton of the nickel hydroxide electrode of the positive electrode, and causes inactivation of nickel hydroxide. .

The third means is to support a metal that is electrochemically lower than the hydrogen electrode potential in the aqueous alkaline solution in the hydrogen storage electrode, and oxidize the base metal when the hydrogen storage electrode comes into contact with the alkaline electrolyte. With the reaction, the hydrogen storage electrode is partially charged by the local battery mechanism. Specifically, it has been proposed to support a base metal such as zinc. This method has the following disadvantages. In other words, the hydrogen storage alloy has a low hydrogen overvoltage, and the overcharge of the hydrogen storage alloy that has not been charged / discharged has a high overvoltage. Therefore, when the hydrogen storage electrode supporting the base metal comes into contact with the alkaline electrolyte, the hydrogen storage alloy has a low hydrogen overvoltage. Not only the charging reaction, but also the generation of hydrogen gas from the hydrogen storage electrode makes it impossible to accurately control the amount of electricity to be partially charged.

A fourth means is to use a non-sintered nickel hydroxide electrode provided with metal cobalt or cobalt hydroxide for the positive electrode. When charging the battery, the metal cobalt or cobalt hydroxide of the positive electrode becomes trivalent cobalt oxide. This utilizes the phenomenon of irreversibly oxidizing a substance, in which case the negative electrode is partially charged without charging the active material of the positive electrode. This method is excellent in that it is easy to control the partial charge amount of the negative electrode. However, since cobalt metal or cobalt hydroxide is easily oxidized in the active material impregnation step of the sintered nickel hydroxide electrode, this method cannot be applied when the sintered nickel hydroxide electrode is used for the positive electrode. There are drawbacks.

The fifth means is to make the capacity of the negative electrode larger than the capacity of the positive electrode, charge the battery while the battery is open until oxygen gas is generated from the positive electrode, and then seal the battery. In this case, the positive electrode is overcharged while the battery is open, and at least a portion of the oxygen gas generated from the positive electrode is released outside the battery system without being electrolytically reduced by the negative electrode. It is charged more than the positive electrode by the amount of electricity required to reduce the released oxygen. Therefore, the discharge capacity of the positive electrode can be made smaller than the discharge capacity of the negative electrode. This method is advantageous in that it does not require any additives and can be applied regardless of the type of electrode.However, when overcharging the battery in an open state, it is necessary to control the efficiency of the oxygen gas reduction reaction at the negative electrode. Therefore, it is difficult to control the oxygen gas discharged outside the battery system, and it is difficult to control the excessive discharge amount of the negative electrode.

As described above, in the sealed alkaline storage battery using the hydrogen storage electrode as the negative electrode, when the discharge of the positive electrode is configured to end before the discharge of the negative electrode, it is easy to control the excess discharge amount of the negative electrode, There has been a demand for a means that does not pose a danger to the work, does not generate impurities that cause self-discharge or inactivates battery components, and can be applied even when a sintered nickel hydroxide electrode is used for the positive electrode. .

Means for Solving the Problems In the present invention, in order to solve the above problems, in a sealed alkaline storage battery in which a hydrogen storage electrode is used for a negative electrode and the discharge capacity of the negative electrode is made larger than the discharge capacity of the positive electrode, A metal cadmium or metal cobalt powder whose utilization is increased by making the diameter less than 5 μm is mixed with a hydrogen storage alloy powder and held on a conductive support of a negative electrode, and the metal cadmium or metal cobalt powder is mixed. Wherein the excess discharge capacity of the negative electrode is adjusted by the average particle size and the mixing amount of the negative electrode.

Effect When the fine metal cadmium or metal cobalt powder is provided in the hydrogen storage electrode in which the powder of the hydrogen storage alloy is bonded to the conductive support with an alkali-resistant polymer, the following effects are obtained.

That is, since the potential at which metal cadmium and metal cobalt are oxidized in the alkaline electrolyte is more noble than the equilibrium potential of hydrogen, even if this hydrogen storage electrode comes into contact with the alkaline electrolyte, hydrogen gas is spontaneously generated. Does not occur.

Then, the metal cadmium powder provided in the hydrogen storage electrode can be charged and discharged at the same potential as the hydrogen stored in the hydrogen storage alloy. Therefore, when discharging the hydrogen storage electrode provided with metal cadmium powder, firstly, the stored hydrogen whose discharge potential is lower than the discharge potential of the metal cadmium powder is discharged, then the metal cadmium powder is discharged, and when the discharge is further continued, The stored hydrogen whose discharge potential is more noble than metal cadmium powder is discharged. Therefore, compared to the hydrogen storage electrode without metal cadmium, this negative electrode is in a state equivalent to the case where the discharge capacity of the metal cadmium powder is excessively charged in advance, and the discharge capacity of the negative electrode is larger than the discharge capacity of the positive electrode. Can be increased.

Since the potential at which metal cobalt is electrolytically oxidized to cobalt hydroxide is about 100 mV noble than the equilibrium potential of hydrogen, the electrolytic oxidation reaction of the metal cobalt powder, that is, the discharge reaction, occurs after the discharge of the hydrogen storage alloy is almost completed. Happens. Therefore, even in the case of this electrode, as compared with the hydrogen storage electrode without the metal cobalt powder, only the discharge capacity of the metal cobalt powder is equivalent to the case where the battery is excessively charged in advance, and the discharge capacity of the positive electrode is smaller than that of the positive electrode. Also, the discharge capacity of the negative electrode can be increased.

In the case of a hydrogen storage electrode provided with a powder of metal cadmium or metal cobalt, the process of oxidizing these metals to hydroxide is a two-electron reaction. It is oxidized from divalent cobalt hydroxide to a trivalent compound. This reaction in which cobalt is oxidized from divalent to trivalent occurs at a potential which is more noble than the potential at which oxygen gas is generated. Therefore, when the metal cobalt powder is provided, the three-electron reaction can be used until the hydrogen storage electrode is discharged and oxygen gas is generated, so that the excess discharge capacity is larger than when the metal cadmium powder is provided. Is advantageous.

When discharging and charging the hydrogen storage electrode including metal cadmium, cadmium hydroxide of the discharge product is charged to generate metal cadmium, and the metal cadmium discharges this electrode next. In such a case, the effect of the negative electrode having an excessive discharge capacity is maintained even after repeated charging and discharging.

On the other hand, the rate at which cobalt hydroxide is reduced to metallic cobalt and the rate at which a trivalent compound of cobalt is reduced to cobalt hydroxide are extremely low. Therefore, when the high-rate discharge of the sealed alkaline storage battery of the present invention including the hydrogen storage electrode including metal cobalt is performed, and the discharge of the negative electrode metal cobalt occurs, the metal cobalt is discharged during the subsequent charging. There is almost no generation, and instead, the amount of charge of the hydrogen storage alloy increases by the amount of electricity required for the discharge reaction of metallic cobalt. As a result, in the subsequent charging and discharging, the state becomes equivalent to the case where the hydrogen storage electrode is excessively charged, so that the state in which the discharge capacity of the negative electrode is larger than the discharge capacity of the positive electrode is maintained.

In order to obtain the above-mentioned effects in the present invention, it is necessary that an electrochemical discharge reaction of metal cadmium or metal cobalt occurs efficiently. Otherwise, a large amount of these metal powders must be added, the packing density of the hydrogen storage alloy decreases, and the high capacity density of the hydrogen storage electrode is lost. In the case of a hydrogen storage electrode comprising a metal cadmium or metal cobalt powder on a hydrogen storage electrode in which a powder of a hydrogen storage alloy is bonded to a conductive support with an alkali-resistant polymer, the discharge of these metal powders Of the active material decreases as the particle size of these metals increases, and decreases significantly when the average particle size is 5 μm or more. Therefore, the average particle size of these metal powders is 5
Preferably less than μm.

In the sealed alkaline storage battery of the present invention, in order to obtain the above-mentioned effects, it is necessary that the metal cadmium and metal cobalt of the negative electrode have not undergone significant oxidation when constituting the battery. The metal cadmium and metal cobalt powders tend to be oxidized more easily as the average particle size is smaller. However, as in the case of manufacturing a sintered nickel hydroxide electrode, unless it is a severe oxidizing condition such as prolonged exposure to a high temperature nitric acid nickel salt solution,
Its oxidation does not occur rapidly. That is, a powder of a hydrogen storage alloy is mixed with an alkali-resistant polymer binder such as polyvinyl alcohol, a fluorine resin, and an acryl-styrene resin, and a paste-like mixture prepared by adding a dispersant such as water to a punched metal or foamed metal. Hydrogen storage electrodes that are held on a conductive support such as nickel, dried, and pressed do not require any significant oxidation of metal cadmium or metal cobalt because the manufacturing process is mild, and the above-mentioned effects are effective. Is obtained.

Since the potential at which metal cadmium and metal cobalt are oxidized in the alkaline electrolyte is more noble than the equilibrium potential of hydrogen, even when this hydrogen storage electrode comes into contact with the alkaline electrolyte, hydrogen gas is spontaneously generated. Does not occur. Therefore, the excess discharge capacity of the negative electrode can be easily controlled only by changing the amount of the metal cadmium or metal cobalt powder. In addition, high-temperature and high-pressure hydrogen gas is not used during this control, so that there is little danger in work. further,
Since the oxide or hydroxide of cobalt or cadmium is already used as an additive for the nickel hydroxide electrode of the positive electrode, the metal cadmium or metal cobalt provided on the negative electrode is oxidized, and the product is generated in the battery. Does not adversely affect the performance of the battery. Further, in the battery of the present invention, in order to increase the discharge capacity of the negative electrode more than that of the positive electrode, the negative electrode is provided with metal cadmium or metal cobalt to obtain the effect. The same effect can be obtained not only when using a nickel oxide electrode but also when using a sintered nickel hydroxide electrode.

Examples The present invention will be described in detail with reference to examples.

Experiment 1 First, the results of an experiment in which the effect of the particle size of the metal cadmium and metal cobalt powders provided for the hydrogen storage electrode on the utilization of these metal powders when discharging the hydrogen storage electrode will be described.

[Hydrogen storage electrode A] (Example of the present invention) In the hydrogen storage alloy, La in LaNi ₅ was replaced with misch metal (raw material is bastnaesite) Mm, and Ni was replaced with a mixture of nickel, cobalt, aluminum and manganese. hand,
In a high-frequency induction furnace in an argon atmosphere, the constituent elements were melted in a high-frequency induction furnace so that the chemical formula became MmNi _3.55 Co _0.75 Al _0.4 Mn _0.3 , poured into an iron mold and cast, and the casting was roughly crushed with a jaw crusher. , Sift,
A coarse powder having a particle size of 1 mm or less was obtained.

Next, this coarse powder was wet with ethanol, and ball milled using an alumina pot and balls. Then, this powder was vacuum-dried and then classified to obtain a fine powder of a hydrogen storage alloy that passed through a 30-mesh sieve.

Then, 100 parts by weight of the hydrogen storage alloy powder, 3 parts by weight of metal cadmium powder, 2 parts by weight of furnace black as a conductive additive, and 2 parts by weight (solid content) of a synthetic latex comprising an acryl-styrene copolymer as a binder Water is added to prepare a paste-like mixture, and this paste-like mixture is applied to both surfaces of a nickel-plated iron punching metal having a thickness of 0.09 mm as a conductive support and an aperture ratio of about 0.5, and then dried. , Pressed and cut to produce a hydrogen storage electrode A.

Average particle size of metal cadmium powder is 1μm or more and 10μm
It was changed in the following range.

The size of one hydrogen storage electrode A is such that the portion where the hydrogen storage alloy is attached is 55 mm in height and 15 mm in width, and the thickness of the electrode is 0.4 mm. The weight of the hydrogen storage alloy contained in one electrode was about 1.25 g.

[Hydrogen storage electrode B] (Example of the present invention) Hydrogen storage electrode B was manufactured in the same manner as hydrogen storage electrode A except that 3 parts by weight of metal cobalt powder was used instead of metal cadmium powder in hydrogen storage electrode A. did. The average particle size of the metal cobalt powder was changed in the range of 1 μm or more and 10 μm or less. The dimensions of the electrode and the amount of the hydrogen storage alloy carried were almost the same as those of the hydrogen storage electrode A. Note that the metal cobalt powder used in this experiment has a chain structure, and thus the particle size in this case represents the minor axis.

[Hydrogen Storage Electrode C] (Conventional Example) A hydrogen storage electrode C was manufactured in the same manner as the hydrogen storage electrode A without using metal cadmium powder in the hydrogen storage electrode A. The dimensions of the electrode and the amount of the hydrogen storage alloy carried were almost the same as those of the hydrogen storage electrode A.

[Hydrogen Storage Electrode D] (Conventional Example) A hydrogen storage electrode D was manufactured in the same manner as the hydrogen storage electrode A except that metal zinc powder was used instead of the metal cadmium powder in the hydrogen storage electrode A. The dimensions of the electrode and the amount of the hydrogen storage alloy carried were almost the same as those of the hydrogen storage electrode A.

When the above four types of hydrogen storage electrodes were immersed in a 5.8 M potassium hydroxide electrolyte and observed, hydrogen gas bubbles were actively generated only with the hydrogen storage electrode D including zinc powder. From this, it can be seen that in the hydrogen storage electrode including the zinc powder, the hydrogen gas leaves the battery system and it is difficult to control the excess discharge capacity of the negative electrode. Therefore, the hydrogen storage electrode D was not used in the following tests.

Next, when the hydrogen storage electrodes A, B, and C are over-discharged, the metal cadmium and metal cobalt powders contained in these electrodes are discharged in a state where they are provided in the hydrogen storage electrode, and oxygen is discharged from this electrode. The larger the discharge capacity until the gas is generated, the more the excess discharge capacity is given to the negative electrode.

Then, in order to investigate the influence of the average particle diameter of these metal powders on this discharge capacity, these hydrogen storage electrodes were discharged without charging, and their discharge capacities were examined.

The test conditions are as follows. That is, one hydrogen storage electrode was used as a test electrode, and nickel plates were arranged on both sides of the hydrogen storage electrode so that the distance between the test electrode and the test electrode was 2.5 cm. , A flooded open test cell was constructed using a potassium hydroxide electrolyte having a concentration of To measure the potential of the test electrode,
A mercury electrode was used as a reference electrode.

Then, these test electrodes are charged at 25 ° C without charging.
, With a current of 45 mA, +0.
Discharge to 25 V (Equilibrium potential of oxygen gas generation reaction is +0.3
Since it is 03V, no oxygen gas is generated at + 0.25V. ), Metal cadmium and metal cobalt utilization were measured. The theoretical capacity was calculated on the assumption that the discharge reaction of metal cadmium followed a two-electron reaction and the discharge reaction of metal cobalt followed a three-electron reaction. Further, the hydrogen storage electrode C could not be discharged, and an oxygen gas generation reaction occurred immediately after the start of discharge.

FIG. 1 shows the relationship between the utilization of metal cadmium powder in the hydrogen storage electrode A and the utilization of metal cobalt powder in the hydrogen storage electrode B obtained from this test, and the average particle size of these metal powders.

The following can be seen from FIG. That is, when the average particle diameter of both the metal cadmium powder and the metal cobalt powder is less than 5 μm, the utilization factor is significantly increased and the discharge capacity is increased. Therefore, when a metal cadmium powder or a metal cobalt powder having an average particle size of less than 5 μm is added to the hydrogen storage electrode, in a sealed alkaline storage battery,
It can be seen that it is effective to make the discharge capacity of the hydrogen storage electrode larger than the discharge capacity of the positive electrode.

Experiment 2 Next, the sealed alkaline storage battery was continuously over-discharged,
The battery internal pressure was measured and the remaining capacity of the negative electrode was measured. In the battery of the present invention, it was experimentally demonstrated that the negative electrode was prevented from being noblely polarized in the event of overdischarge, and the internal pressure of the battery was prevented from rising. The results are explained below.

[Sealed alkaline storage battery] (Battery according to the present invention) The sealed alkaline storage battery was configured as follows.

As the negative electrode, four hydrogen storage electrodes A containing metal cadmium powder having an average particle size of about 1 μm were used. For the positive electrode, the dimensions of the active material holding part were 54 mm in height, 14.5 mm in width, and 0.82 in thickness.
Three well-known sintered nickel hydroxide electrodes having a discharge capacity of 340 mAh assuming that the charge / discharge reaction of nickel hydroxide follows a one-electron reaction in mm. Since this positive electrode plate is formed by charging and discharging in an alkaline electrolyte by a conventional method, nickel positive oxide which is difficult to discharge when charged is already contained in the positive electrode plate. For the separator, a polysulfone nonwoven fabric having a thickness of 0.12 mm was used, and one positive electrode plate was wrapped with one separator, and the positive electrode plate and the negative electrode plate were alternately laminated. This electrode plate group was inserted into the battery case, and a solution prepared by dissolving 15 g of lithium hydroxide in a 6 M aqueous potassium hydroxide solution 1 was used as an electrolytic solution. A sealed alkaline storage battery was manufactured. This battery has a prismatic shape having an outer dimension of 66.2 mm in height, 16.4 mm in width, and 5.6 mm in thickness, including a safety valve that operates at an internal pressure of about 5 kg / cm ² . The nominal capacity of this battery is 900 mAh.

[Sealed Alkaline Storage Battery A] (Battery According to the Present Invention) The sealed alkaline storage battery A uses a hydrogen storage electrode B instead of the negative electrode hydrogen storage electrode A in the sealed alkaline storage battery A, and the metal cobalt powder has an average particle size. The other configuration was the same as that of the sealed alkaline storage battery A, with a size of about 1.5 μm.

[Sealed Alkaline Battery C] (Battery according to Comparative Example) The sealed alkaline storage battery C has an average particle diameter of the hydrogen storage electrode A of the negative electrode in the sealed alkaline storage battery A instead of the metal cadmium powder having an average particle diameter of about 1 μm. Was about 10 μm, and the other configuration was the same as that of the sealed alkaline storage battery.

[Sealed alkaline storage battery d] (Battery according to comparative example) The sealed alkaline storage battery d has an average particle diameter of about 1.5 μm in the negative electrode hydrogen storage electrode B in the sealed alkaline storage battery d.
In place of the metallic cobalt powder, a powder having an average particle size of about 10 μm was used, and the other configuration was the same as that of the sealed alkaline storage battery A.

[Sealed Alkaline Battery B] (Battery of Conventional Example) The sealed alkaline battery B uses a hydrogen storage electrode C instead of the negative electrode hydrogen storage electrode A in the sealed alkaline storage battery A, and the other configuration is a sealed alkaline storage battery. The same configuration as a.

In the first cycle, after charging the above five sealed alkaline storage batteries with a current of 90 mA for 15 hours, with a current of 180 mA,
Discharge was performed until the terminal voltage of each battery reached 0.8 V.
Next, the battery was charged with a current of 180 mA for 6 hours, discharged at a current of 180 mA until the terminal voltage became 0 V, and overcharged for another 1 hour with the current as it was, and 10 charge / discharge cycles were performed. At the last overdischarge, the internal pressure of the battery was measured. These charging and discharging were performed at 25 ° C.

FIG. 2 shows the change over time of the internal pressure of the battery during this overdischarge. The following can be seen from FIG.

That is, the sealed alkaline storage batteries A and B each having the hydrogen storage electrode of the present invention holding the metal cadmium powder and the metal cobalt powder having a small average particle size, respectively, have an internal pressure during overdischarge suppressed to a small value and have a safety valve. The working pressure of 5 kg / cm ² was not reached, and the battery was hermetically sealed. On the other hand, the sealed alkaline storage batteries C and D each having the hydrogen storage electrode of Comparative Example holding the metal cadmium powder and the metal cobalt powder having large average particle diameters respectively, and the hydrogen storage of the conventional example not holding the metal cadmium or metal cobalt powder. The internal pressure of the sealed alkaline storage battery E having the electrodes increases with the progress of overdischarge, and the internal pressure reaches the operating pressure of the safety valve.

In addition, disassemble these five batteries after overdischarge,
The negative electrode plate was taken out and used as a test electrode. Under the same conditions as in Experiment 1, the negative electrode plate was discharged to +0.25 V with respect to a mercuric oxide electrode, and the discharge capacity was examined. Table 1 shows the results.

From Table 1, it can be seen that in the sealed alkaline storage batteries A and A each having the hydrogen storage electrode of the present invention, the discharge was limited by the capacity of the positive electrode, since the remaining capacity of the negative electrode was obtained. On the other hand, in the sealed alkaline storage batteries c and d using the hydrogen storage electrode of the comparative example and the sealed alkaline storage battery e provided with the hydrogen storage electrode of the conventional example, since the remaining capacity of the negative electrode cannot be obtained, the discharge is limited by the capacity of the positive electrode. It turns out that it is difficult.

In the above embodiment, the description has been made using a specific composition as the hydrogen storage alloy. However, not only this alloy, but also an alloy in which the component elements are changed or a hydrogen storage alloy belonging to the Laves phase is used. In this case, the present invention can be similarly applied.

Further, in the above-described embodiment, the case where a synthetic latex made of an actyl-styrene copolymer is used as the alkali-resistant polymer acting as a binder has been described, but it is not limited to this alkali-resistant polymer, and a polyolefin resin is used. The present invention can also be applied to the case where fluorinated resin, methyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol and the like are used.

Further, in the above embodiment, the case where the punching metal is used as the conductive support has been described.
The present invention can be applied to the case where a metal net, an expanded metal, a conductive porous body such as a metal foam or a metal fiber sintered body is used.

In the above-described embodiment, the case where a powder having a chain structure was used as the metal cobalt powder was described. However, the effect is not limited to the case where the powder having the chain structure is used, Similar effects can be obtained even if the average particle size is less than 5 μm, even if the shape is other than the above.

Advantageous Effects of the Invention The present invention provides a sealed alkaline storage battery using a hydrogen storage electrode as a negative electrode, in which the discharge of the positive electrode is completed before the discharge of the negative electrode, thereby effectively suppressing an increase in the internal pressure of the battery during overdischarge. Has the effect of doing In addition, at that time, it is not necessary to work in a dangerous state such as a high-temperature and high-pressure hydrogen gas atmosphere, and since solid metal powder that does not generate hydrogen gas in the alkaline electrolyte is added, the amount of excessive discharge of the negative electrode can be controlled. It is easy and does not generate nitrogen compounds or carbonates which are harmful to the performance of the battery such as self-discharge, and has the effect of being applicable to the case where a sintered nickel hydroxide electrode is used for the positive electrode.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the utilization rate of metal powder and the average particle size of metal powder when a hydrogen storage electrode provided with metal powder is overdischarged. A: Electrode provided with metal cadmium powder B: Electrode provided with metal cobalt powder FIG. 2: A diagram showing the change over time of the internal pressure of a sealed alkaline storage battery with the progress of overdischarge. A, B: Battery according to the present invention C, D: Battery according to comparative example E: Battery according to conventional example

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/34 H01M 10/24 H01M 4/24

Claims (1)

(57) [Claims] In a sealed alkaline storage battery in which a hydrogen storage electrode is used as a negative electrode and the discharge capacity of the negative electrode is made larger than the discharge capacity of the positive electrode, metal cadmium whose utilization factor is increased by setting the average particle size to less than 5 μm. Alternatively, the metal cobalt powder is mixed with the hydrogen storage alloy powder and held on the conductive support of the negative electrode, and the excess discharge capacity of the negative electrode is adjusted by the average particle size and the mixing amount of the metal cadmium or metal cobalt powder. A sealed alkaline storage battery characterized by being made.