JP2001313069A - Nickel hydrogen storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel hydrogen storage battery of which high temperature storage characteristics that a voltage drop at high temperature storage is small, and a capacity recovery factor after high temperature storage is large, are improved. SOLUTION: In the nickel hydrogen storage battery consists of a paste type nickel electrode as a positive electrode 1 containing a cobalt electric conduction assistant containing metal cobalt or a cobalt compound with water oxidation nickel, a negative electrode 2 consists of a rare earth group system alloy expressed by MmNi5-X+YMX (Mm expresses the rare earth group elements which contain La at least, and M expresses a metallic element containing Mn at least, and is 0<x<2, -0.2<y<0.6) as a hydrogen storage alloy of a negative electrode 2, a separator 3 which is intervened among these two electrodes, and an electrolyte consists of an alkaline aqueous solution, when quantity of electricity required to deoxidize cobalt oxide in a positive electrode to a valence of 2 is set to Cco(II) and quantity of electricity of a discharge reserve currently formed in the negative electrode is set to CH2, a relation of CH2/Cco(II)<=1.3 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nickel hydrogen storage battery, and more particularly to a nickel hydrogen storage battery having improved high-temperature storage characteristics.

[0002]

2. Description of the Related Art Along with the miniaturization of portable electronic devices, there is a demand for safe and higher capacity secondary batteries, and nickel hydrogen storage batteries using a hydrogen storage alloy as a negative electrode active material are also required to have higher capacities. Examination for is continuing. In such a nickel hydrogen storage battery, the hydrogen storage alloy as the negative electrode active material is a Labes alloy (AB ₂ type alloy) composed of Zr, Ni, V, Mn, or the like, or Mg, Ni, or the like. Mg-N
In addition to an i-based alloy (A ₂ B type alloy), a rare earth based alloy (AB ₅ type alloy) which is an alloy of a rare earth element and Ni is well known. Among them, Mm is a rare earth element.
Metal alloy (Mitsubishi Metal)
mNi ₅ -based alloy) is widely used as an electrode material because it has features such as easy activation and excellent hydrogen absorbing and releasing ability.

However, the hydrogen storage alloy is superior in hydrogen storage capacity, it is determined from the charge and discharge efficiency, while the hydrogen dissociation pressure at normal temperature normal 20~500kPa are said to correct, said MmNi ₅ Since the system alloy has a high hydrogen dissociation pressure of 1 MPa at room temperature, it is necessary to reduce this dissociation pressure. Further, this MmNi ₅ -based alloy also has a problem that, when charging and discharging are repeated in an alkaline electrolyte, it causes undesired changes such as a decrease in hydrogen storage capacity and a decrease in reactivity due to the occurrence of pulverization and composition change.

For this reason, in an MmNi ₅ alloy, N
MmNi ₅ -based alloys, in which a part of i is substituted with a metal such as Mn, have attracted attention because they have a low hydrogen equilibrium dissociation pressure, are excellent in hydrogen storage capacity, and can prolong the life of the alloy in charge / discharge reactions. This kind of mesh metal alloy is available in
No. 15774, Japanese Patent Publication No. 5-86029,
Nos. 162741 and the like, which are characterized in that they are alloys of almost stoichiometric composition containing a relatively large amount of Co in order to prevent pulverization and improve corrosion resistance to an electrolytic solution. ing. In addition to this stoichiometric composition, it has been proposed to use a non-stoichiometric metal alloy having a higher content on the B site side.

[0005]

By the way, with the miniaturization of portable electronic devices using a storage battery as a main power source, the chances of using the storage battery by hand increase, and the storage battery is used in a wider environment than before. It has come. For this reason, storage batteries are required to exhibit stable performance without being affected by environmental changes, particularly temperature changes.
For example, when used in laptop computers and mobile phones, the same characteristics are required at high and low temperatures as at room temperature, and the demand for batteries is increasing. Therefore, studies have been continued on further improving the temperature characteristics of the storage batteries used in such electronic devices.

However, in a nickel hydrogen storage battery using the above-mentioned metal alloy as a hydrogen storage alloy as a negative electrode active material and combining it with a paste-type nickel electrode as a non-sintering type positive electrode, this is considered as a problem. If left in a high temperature environment of 80 ° C, the battery voltage will drop significantly,
In particular, it has been found that the voltage drop in the high-temperature environment described above becomes remarkable in the case of using a multi-component metal-based alloy in which at least a part of Ni of MmNi ₅ is substituted with Mn. Since such a voltage drop during high-temperature storage has a great effect on the subsequent battery capacity, improving this high-temperature storage characteristic is extremely important for a nickel hydrogen storage battery.

In view of such circumstances, the present invention provides a nickel hydrogen using a rare earth alloy as a hydrogen storage alloy as a negative electrode active material and a paste nickel electrode as a non-sintered positive electrode. It is an object of the present invention to provide a nickel hydrogen storage battery having a small voltage drop during high-temperature storage, a large capacity recovery rate after high-temperature storage, and improved high-temperature storage characteristics.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors first prepared a non-sintered positive electrode comprising a paste-type nickel electrode having a cobalt conductive additive added to the positive electrode. A nickel hydrogen storage battery using an MmNi ₅ -based hydrogen storage alloy containing Mn for the negative electrode was examined for a phenomenon in which the voltage is reduced when the battery is stored in a high-temperature environment. -1b (Comparative Example 1 described later), it was found that the voltage dropped in two stages. As a result of studying the cause of the voltage drop, the first step, the voltage drop to around 0.9 V, is a phenomenon caused by hydrogen generated from the hydrogen storage alloy of the negative electrode due to the temperature rise reducing the positive electrode. It was also found that the voltage drop to 0 V in the second stage was a phenomenon caused by a slight short circuit in the battery.

Here, the voltage drop in the first stage should not be released originally because it was stored as a discharge reserve in the negative electrode due to an increase in the equilibrium dissociation pressure of the hydrogen storage alloy accompanying an increase in the ambient temperature during storage. Was released into the battery as hydrogen gas, and this reduced the positive electrode, and as a result, it was found that the high-temperature storage characteristics deteriorated. That is, the reason can be considered as follows.

The positive electrode of the nickel hydrogen storage battery includes a sintered positive electrode and a non-sintered positive electrode which is a paste nickel electrode. Among these, the non-sintered positive electrode is made by dispersing nickel hydroxide in water or a solvent together with a binder and a thickener, etc. to make a paste, and filling it into a conductive porous base material that serves as a current collector. However, in this case, the distance between the active material and the base material increases, and the utilization rate of the active material tends to decrease. In order to increase the utilization rate and achieve a higher capacity, metallic cobalt, cobalt monoxide, cobalt hydroxide, or the like is added to the positive electrode as a cobalt conductive additive. These cobalt conductive assistants are oxidized to higher-order cobalt oxides higher than divalent during charging, that is, Co, CoO, Co (O
H) ₂ → CoOOH, etc. change, and a conductive network of cobalt that electrically connects the nickel hydroxide particles.
It is known to form cracks.

In a nickel hydrogen storage battery, the negative electrode has a capacity greater than that of the positive electrode, thereby suppressing gas generation from the negative electrode at the end of charging or discharging, and absorbing oxygen gas generated from the positive electrode at the negative electrode. , Realizes hermetic sealing. In other words, even after the positive electrode has been fully charged or completely discharged during charging, there is an uncharged portion or an undischarged portion in the negative electrode, whereby oxygen gas can be preferentially generated from the positive electrode. Is configured to be able to prevent the occurrence of the problem. The excess capacity of the negative electrode during such discharge, that is, the amount of electricity in the discharge reserve, does not directly participate in the charge / discharge reaction, but is necessary to discharge the positive electrode capacity until the end of discharge. The negative electrode is formed on the negative electrode as a counter reaction to the formation reaction of the cobalt conductive network in the positive electrode.

However, when such a nickel hydrogen storage battery is stored at a high temperature after the end of discharge, the excess capacity of the negative electrode on the discharge side, that is, the hydrogen stored as the amount of electricity in the discharge reserve, is discharged from the negative electrode as the temperature rises. Evolved as hydrogen gas, which reduces the conductive network of cobalt in the positive electrode, resulting in lower battery voltage. As a result of studying this phenomenon, in the above-mentioned discharge reserve, the amount of electricity more than the reaction amount of the oxidation reaction of the cobalt conductive assistant for maintaining the conductivity of the positive electrode is formed in the paste nickel electrode. Further, it was found that the additional component was further increased by the corrosion reaction component of the hydrogen storage alloy as the negative electrode active material, and further increased.

[0013] Further, in the above-mentioned metal alloy in which a part of Ni is replaced by another metal, although the hydrogen equilibrium dissociation pressure can be reduced, the hydrogen storage capacity can be increased, and the alloy can have a longer life in the charge / discharge reaction, MmNi without substitution metal
₍₅₎ Compared to the alloy, the active surface of the alloy causes a large amount of corrosion reaction of the alloy in the electrolytic solution, thereby easily increasing the amount of hydrogen in the discharge reserve, and as a result, the voltage during high-temperature storage. The decrease is significant. In particular, for those containing Mn as an alloying element, Mn is easily eluted as Mn ions into the electrolytic solution upon storage, so that the reaction of the oxidation of Mn also accumulates in the negative electrode as a discharge reserve, and The amount of electricity in the reserve increases. Further, when the Mn ion moves to the positive electrode, the potential of the positive electrode is noble, so that the Mn ion is further oxidized to the positive electrode, thereby reducing the conductive network of cobalt.

Next, the voltage drop in the second stage is considered as follows. When a conductive network of cobalt for electrically connecting the nickel hydroxide particles is formed, cobalt ions generated by dissolution also precipitate on the separator on the side in contact with the nickel electrode of the positive electrode. It is considered that the oxide is oxidized to cobalt oxide by the first charge. However, at this point, since no precipitation has occurred up to the separator in contact with the hydrogen storage alloy electrode of the negative electrode, a slight short circuit does not occur.

However, as the battery is often left in a high temperature state after the end of discharge, as described above, as a first step, the positive electrode is formed by hydrogen gas generated from the hydrogen storage alloy as the temperature rises. It is considered that the higher-order cobalt oxide in the positive electrode is reduced and becomes a lower-order cobalt compound that can be dissolved in the alkaline electrolyte. The cobalt ions generated by this dissolution are at a high temperature and in a reducing atmosphere.
Although it is difficult to precipitate as a cobalt compound such as hydroxide even at a relatively high concentration, it gradually moves to the negative electrode during storage and is reduced to metallic cobalt here. As a result, metallic cobalt precipitates at the negative electrode during standing at high temperature, and a minute short circuit occurs due to this and the oxide of cobalt deposited on the separator from the positive electrode, resulting in a decrease in battery voltage. . That is, it is considered that the voltage drop in the second stage also occurs in correlation with the voltage drop in the first stage.

[0016] The present inventors have based on such knowledge,
In order to solve the above-mentioned problems, further studies have been continued. In particular, focusing on the relationship between the amount of electricity that reduces cobalt oxide in the positive electrode to divalent and the amount of electricity in the discharge reserve, A wide-ranging experiment was conducted to explore the above relationship that could suppress the decrease in battery voltage due to hydrogen. As a result, the amount of electricity that reduces cobalt oxide in the positive electrode to divalent was defined as C _{Co (II)} and formed on the negative electrode. Assuming that the amount of electricity of the discharged reserve is C _H2 , if the ratio of C _H2 / C _{Co (II)} is 1.3 or less, the high-temperature storage characteristics can be greatly improved, It has been found that a nickel hydrogen storage battery with a small voltage drop and a large capacity recovery rate after high-temperature storage can be obtained.
The present invention has been completed.

That is, according to the present invention, a paste-type nickel electrode containing cobalt hydroxide or a cobalt conductive additive comprising a cobalt compound together with nickel hydroxide is used as a positive electrode, and MmNi _{5-x + y} M is used as a hydrogen storage alloy for a negative electrode. _x (M
m represents a rare earth element containing at least La, M represents a metal element containing at least Mn, and 0 <x <2, −0.
2 <y <0.6), in a nickel hydrogen storage battery having a separator interposed between these two electrodes and an electrolytic solution composed of an alkaline aqueous solution, the cobalt oxide in the positive electrode When the amount of electricity required to reduce the substance to divalent is C _{Co (II),} and the amount of electricity of the discharge reserve formed on the negative electrode is C _H2 , C _H2 / C _{Co (II)}
The present invention relates to a nickel hydrogen storage battery characterized by satisfying a relationship of ≦ 1.3.

In the present specification, the amount of electricity [C required for the cobalt oxide in the positive electrode to be reduced to divalent
_{Co (II)} ] is an amount of electricity remaining after nickel hydroxide is discharged, as is clear from the above description.
Since cobalt has a low reduction rate and does not discharge under normal discharge conditions, it means the quantity of electricity when the discharged battery is discharged to 0 V with a very small current. The amount of electricity [C _H2 ] of the discharge reserve formed on the negative electrode is a value obtained by directly measuring the amount of hydrogen gas contained in the negative electrode of a certain battery at the end of discharge in terms of molar amount by a water-on-water replacement method. is there.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the positive electrode of the present invention, conventionally known powders can be used as nickel hydroxide. Among them, powder in which 0.5 to 5.0% by weight of cobalt is dissolved in nickel hydroxide crystal is preferably used because charging efficiency at high temperatures can be improved. Also,
A powder in which zinc is solid-dissolved at 0.5 to 5.0% by weight can also improve cycle life, and is also preferably used. Further, such nickel hydroxide powder is coated with at least one divalent or more cobalt compound selected from cobalt monoxide, α-cobalt hydroxide, β-cobalt hydroxide, cobalt oxyhydroxide and the like. It is preferably a powder that has been prepared.

When the surface of the nickel hydroxide is coated with the above-mentioned cobalt compound, the conductive network is more effective with a small amount of cobalt added as compared with the case where a cobalt conductive aid is added to the uncoated nickel hydroxide. And the amount of electricity in the discharge reserve for the reaction can be reduced. Among the cobalt compounds for coating, α-cobalt hydroxide and β-cobalt hydroxide, which are liable to form a stronger conductive network, are most preferable. In coating the cobalt compound, Zn, Ca, Y, Yb, Mg, Ti, Z
It may be a composite coating in which elements such as r are composited. Also,
The coating amount of the cobalt compound is usually 1 to 10 parts by weight, preferably 2 to 5 parts by weight, based on 100 parts by weight of the nickel hydroxide.

In the positive electrode of the present invention, a cobalt compound such as metallic cobalt or cobalt monoxide, α-cobalt hydroxide and β-cobalt hydroxide is used as the cobalt conductive additive. In order to reduce the amount of electricity in the discharge reserve of the negative electrode and to form a strong cobalt conductive network capable of suppressing hydrogen gas generated from the negative electrode, a cobalt compound, particularly cobalt monoxide, is preferable. Metallic cobalt is Co → Co (O) to form a conductive network.
H) → Three-electron reaction of CoOOH is necessary, and the amount of electricity in the discharge reserve increases accordingly. Therefore, when using metallic cobalt, it is desirable to carry out an alkali immersion treatment described later. The addition amount of the cobalt conductive additive is usually 0.5 to 10 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the nickel hydroxide, while maintaining the above performance and high capacity. .

The positive electrode of the present invention comprises the above-mentioned nickel hydroxide and a cobalt conductive additive together with a binder such as polytetrafluoroethylene (PTFE) and a thickener such as carboxymethyl cellulose (CMC). A positive electrode paste is prepared by mixing the mixture in a solvent, supporting the paste on a metal porous substrate such as a nickel foam, drying, and compression-molding a sheet. This is a non-sintered positive electrode composed of electrodes. At that time, in order to reduce the reduction amount of the cobalt oxide in the positive electrode, after the above-described compression molding, an oxidation treatment may be performed in advance by an alkali immersion treatment, a preliminary charge, or the like.

In the above alkali immersion treatment, the cobalt compound coated on the surface of the cobalt conductive additive and the nickel hydroxide is converted into a slightly more oxidized state in advance, whereby the discharge by the lower-order oxidation reaction of cobalt is caused. The temperature should be 35-100 to effectively reduce the amount of reserve.
° C, preferably 50 to 90 ° C, and the immersion time is 0.2 to
The time is 1.2 hours, preferably 0.25 to 0.8 hours. In addition, as a method of preliminary charging, for the same reason as described above, the capacity [C (A
h)], a current value of 0.001 to 0.1 C (A), preferably 0.005 to 0.05 C (A), and 1 to 1
It is good to pre-charge for 00 hours, preferably 2 to 50 hours.

In the negative electrode of the present invention, the hydrogen storage alloy includes MmNi _{5-x + y} M _x (Mm represents a rare earth element containing at least La, M represents a metal element containing at least Mn, and 0 <x < 2, -0.2 <y <0.6). As described above, those containing Mn in the substitution metal have the advantage that the hydrogen equilibrium dissociation pressure of the alloy can be reduced and the capacity can be increased.
n has a disadvantage that the corrosion reaction is large because the standard reduction potential has a low potential, and the corrosion reaction is more likely to proceed when the alloy is pulverized by the reaction and the surface area is increased. However, when this is applied to the present invention, the above disadvantages can be overcome and the above advantages can be utilized.

The metals other than Mn include Co, A
Examples thereof include l, Cu, Mg, Cr, Zn, Sn, and Fe. Among them, an alloy containing at least Co and Al is preferable. Also, among the alloys of the above composition,
A high-capacity non-stoichiometric hydrogen storage alloy having a higher content on the Ni side of the B site (for example, for Mm: 1,
In the case of a hydrogen storage alloy in which the total amount of other metals including Ni, Co, Mn and Al is 5.02 to 5.45), a transition metal is often present on the alloy surface, so that the amount of hydrogen gas generated is large. For the same reason as above, high-temperature storage characteristics are usually liable to decrease. However, the present invention is particularly preferably used because its properties can be effectively exhibited. Further, the hydrogen storage alloy of the present invention has a small amount of S
i, Mo, Sb, Nb, Ti, etc. may be included.

The negative electrode of the present invention preferably contains a metal oxide in order to adjust the ratio of C _H2 / C _{Co (II)} . Even when hydrogen gas is generated due to the corrosion reaction of the hydrogen storage alloy, it is used for the above-mentioned reaction to reduce the metal oxide to metal before it forms a discharge reserve, so that the discharge reserve can be reduced. An increase in the amount of electricity can be prevented. As such a metal oxide, those which can be reduced to a metal by charging and which can maintain a metal state in a normal operating potential region are preferable, and in particular, a divalent or higher valent metal which requires a large amount of hydrogen for a reduction reaction to a metal. The following oxides are preferred: For example,
α- (or β-) Co (OH) ₂ , Co ₂ O ₃ , Co
₃ O ₄ , NiO, Ni ₂ O ₃ , CuO, Cu ₂ O, Li
MO ₂ (M is at least one selected from Co and Ni)
And the like. Among these,
Co ₃ O ₄ , N with little effect of side reactions on the hydrogen storage alloy
iO and LiMO ₂ are most preferred. The addition amount of such a metal oxide varies depending on the type of metal, oxidation state, etc., but is usually 0.5 to 100 parts by weight of the hydrogen storage alloy.
It is preferable to use 5 parts by weight.

The negative electrode of the present invention is prepared by mixing the above-mentioned hydrogen storage alloy and preferably the above-mentioned metal oxide with water or a solvent together with an appropriate binder and a conductive additive to prepare a negative electrode paste. Then, apply this to the conductive substrate, after drying,
It is produced by compression molding into a sheet. At this time, in order to reduce the corrosion reaction of the hydrogen storage alloy, an alkali immersion treatment and an oxidation treatment can be performed in advance as in the case of the positive electrode. This treatment forms an oxide on the surface of the hydrogen storage alloy, which is reduced to a metal, which can contribute to a reduction in the amount of electricity in the discharge reserve. The conditions for the above alkali immersion treatment are as follows:
00 ° C., preferably 60 ° C. to 90 ° C., and the immersion time is 0.1 mm.
The time is preferably 2 to 2 hours, preferably 0.5 to 1 hour.

The nickel hydrogen storage battery of the present invention has the above-described positive electrode and negative electrode, a separator interposed between these two electrodes, and an electrolytic solution composed of an alkaline aqueous solution. The negative electrode can be manufactured by winding it through a separator, inserting the negative electrode into a battery can, and then injecting the above-mentioned electrolytic solution. At this time, since the conductive network is formed by the cobalt added to the positive electrode by the initial charge, both the positive and negative electrodes are assembled in a non-chemical state in which neither the charge nor the discharge has been performed electrochemically. That is, by combining the positive and negative electrodes which have not undergone charging or discharging, metal cobalt or a cobalt compound added to the positive electrode by aging or initial charging (chemical formation) after assembling the battery has a higher cobalt content. It is oxidized to an oxide, and the amount of electricity of the above-mentioned discharge reserve is formed in the negative electrode along with the reaction, so that a positive electrode regulated battery can be obtained.

The nickel-hydrogen storage battery of the present invention thus manufactured has the amount of electricity required for the higher-order cobalt oxide in the positive electrode after the chemical conversion to be reduced to divalent and the amount of electricity formed in the negative electrode. The ratio of the discharge reserve to the amount of electricity [ _CH2 / C
_{Co (II)} ] is 1.3 or less. That is, by setting the above ratio to 1.3 or less, preferably 1.1 or less, and more preferably 1.0 or less, the discharge
The amount of electricity in the cathode can be optimized in relation to the formation of the cobalt conductive network in the positive electrode, suppressing the generation of hydrogen gas from the negative electrode even during high-temperature storage, thereby reducing the reduction of cobalt oxide in the positive electrode And the battery voltage can be prevented from lowering. In particular, when the above ratio is 1.0 or less, even if hydrogen gas is generated from the negative electrode during high-temperature storage, the reducing power required to reduce the conductive network of cobalt of the positive electrode is inferior. In the case where a slight short-circuit occurs, a decrease in voltage can be suppressed.

The electric charge of the discharge reserve formed on the negative electrode is inevitably formed by oxidation of cobalt in the positive electrode, and in the paste type positive electrode, an organic substance such as a binder is used. Since the amount of the discharge reserve increases due to the decomposition reaction of the alloy and the corrosion reaction of the alloy, the above ratio is usually larger than 1.5 in a battery in which the discharge reserve is not adjusted. It is desired that the amount be 1.3 or less, and if possible, the amount of electricity in the discharge reserve is 1.0 or less with respect to the amount of electricity required for the cobalt reduction reaction. However, the ratio cannot be made too small because of the necessity of preventing deterioration of the negative electrode during overdischarge, and the discharge characteristics at low temperatures tend to improve as the ratio increases, so that the ratio is usually 1.3. What is necessary is just to make it as small as possible within the following ranges, and the lower limit is considered to be about 0.5.

Further, it is desirable that a zinc compound is contained in the electrolytic solution injected into the battery can. That is, when a zinc compound is contained in the electrolytic solution, part or all of the zinc compound becomes zinc ions, and the ions move in the battery by a charge / discharge reaction, and Mn dissolved in the electrolytic solution from the hydrogen storage alloy. The transfer of ions to the positive electrode is suppressed, and M
The formation of n-oxides is prevented and they work synergistically to improve discharge characteristics after high temperature storage. The concentration of the zinc compound in the electrolyte is preferably 30 to 65 g / liter, more preferably 40 to 55 g / liter, in terms of zinc oxide.

The separator used in the present invention is preferably a nonwoven fabric, a woven fabric, or the like, and the constituent fibers thereof are preferably heat fusion fibers. Examples of the fiber structure include a core-sheath type composite fiber, a side-by-side type composite fiber, and a single-component type fiber. From the viewpoint of strength, a core-sheath type composite fiber is preferable. As the type of fiber, a fiber whose surface is subjected to a hydrophilic treatment such as a sulfonation treatment is preferable because of high permeability of the electrolytic solution. With this hydrophilic treatment, the cobalt ions eluted from the positive electrode into the electrolytic solution can easily pass through the separator.
The present invention can cope with such a problem and can be effectively used as a separator.

In the present invention, the separator preferably contains at least one element selected from the group consisting of Y, Yb and Er.
That is, as described above, the voltage drop in the second stage during high temperature storage is due to the hydrogen gas generated from the negative electrode in the first stage reducing the cobalt conductive network of the positive electrode. By setting the relationship between the amount of reduction electricity of the oxide and the amount of discharge reserve of the negative electrode in the above range, the amount of cobalt ions eluted from the positive electrode and deposited on the negative electrode during high-temperature storage can be reduced. And the short circuit between the cobalt oxide on the separator and the metallic cobalt of the negative electrode can be reduced.

However, even in this case, it is more preferable to suppress the precipitation of cobalt oxide on the separator in contact with the positive electrode when forming the cobalt conductive network. From this point of view, as a result of various studies on substances capable of suppressing the deposition of cobalt ions on the separator, it has been found that it is effective to support the Y, Yb or Er species on the separator. Wakata. Here, Y is yttrium, Yb is ytterbium, Er is erbium, and the Y, Yb, or Er species refers to a simple substance of Y, Yb, or Er, an oxide, a complex, or the like of Y, Yb, or Er, respectively. This means that a mixture mainly composed of a mixture of these rare earth elements may be used.

The reason why the voltage drop during high-temperature storage can be further improved by including such elemental species in the separator is as follows.
Although it is not always clear, it is considered that the above element species suppress the cobalt ions eluted in the alkaline aqueous solution during storage at a high temperature from being precipitated on the separator. In addition, a cobalt compound such as a produced hydroxide of cobalt is hardly precipitated as a solid in a solution, but a separator plays a role of a tube wall as in a silver mirror reaction. The cobalt compound tends to precipitate on the separator, but when the above element species is present on the separator, the element species lowers the solubility of cobalt ions on the separator and causes It is thought to suppress the formation of cobalt compounds such as. When a metal oxide such as cobalt is added to the negative electrode in order to reduce the above-mentioned discharge reserve, a minute short-circuit easily occurs with the oxide of cobalt deposited on the separator described above. The above element species are particularly effective in avoiding them.

The above-mentioned elemental species have extremely low solubility in an aqueous alkali solution as compared with cobalt, and the oxide of cobalt is formed on a separator.
Even if it is contained in the electrolyte, the effect is reduced,
It has the property that it hardly moves from the place where it is added. Therefore, in order to suppress the deposition of cobalt oxide on the separator during formation of the conductive network without affecting the battery constituent materials other than the separator (especially, the positive electrode), it is necessary to use a separator. It is most effective to include the above-mentioned element types in the liquid crystal.

When the above-mentioned element species are contained in the separator, as described above, in addition to the simple substance of each element, the separator can be contained in the form of an oxide, a complex or the like. It is particularly preferable to use an oxide from the viewpoint of easiness in containing it. In addition, as a method of including in the separator, a method of directly spraying the above element species on the separator, a method of immersing the separator in an aqueous medium in which the above element species are dispersed and drying, Alternatively, an aqueous solution thereof may be applied to a separator and dried to allow the constituent elements of the separator to be supported on constituent fibers.

With respect to the content of the above element species in the separator, the oxide [A ₂ O] of each element is based on the area of the separator.
₃ (A is Y, Yb or Er)], 0.05 to 3
it is preferable to be mg / cm ^2, and more preferably, 0.1 to 2 mg / cm ^2. The reason for this is that by including the above element species in the separator within the above range, the precipitation of cobalt oxide on the separator can be appropriately suppressed.

[0039]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples. In the following, “parts” means “parts by weight”.

Example 1 To 100 parts of nickel hydroxide powder coated with 4.7% by weight of β-cobalt hydroxide (cobalt solid solution: 1.2% by weight, zinc solid solution: 2% by weight) 2.9 parts of cobalt monoxide powder as a cobalt conductive aid, 10 parts of a 2% by weight aqueous solution of carboxymethyl cellulose and 2 parts of a 60% by weight dispersion of polytetrafluoroethylene were added and mixed. did. The positive electrode paste was filled and supported on a metal porous substrate made of a nickel foam, dried, and then compression-molded into a sheet. 30% by weight of this sheet at 70 ° C
After immersion treatment in potassium hydroxide aqueous solution for 0.5 hour,
Drying, washing, and re-drying were sequentially performed, and finally, the resultant was cut into a predetermined size to produce a positive electrode made of a paste-type nickel electrode having a capacity of 700 mAh.

Separately, the composition is MmNi _4.28 Co
_0.4 Mn _0.37 Al _0.3 Mg _0.05 (Mm composition is La: 8
0 atomic%, Ce: 12 atomic%, Nd: 4 atomic%, Pr:
Hydrogen storage alloy 1 represented by the following formula: 4 atomic%, Mm: 1, the total of Ni, Co, Mn and Al is 5.4).
To 00 parts, 2 parts of nickel powder and 1 part of Co ₃ O ₄ powder were added, and an appropriate amount of an aqueous solution of carboxymethyl cellulose and a dispersion of polytetrafluoroethylene were added to make a paste. A predetermined amount of this negative electrode paste is applied to both surfaces of a substrate made of perforated iron nickel-plated steel, dried, compression-molded into a sheet, and finally cut into predetermined dimensions to produce a negative electrode. did.

The negative electrode and the positive electrode composed of the above-mentioned paste-type nickel electrode were wound so as to face each other via a sulfonated polypropylene separator to prepare an electrode body. This electrode body was inserted into a battery can, and a predetermined amount of an electrolytic solution obtained by dissolving 45 g / liter of zinc oxide in a 30% by weight aqueous solution of potassium hydroxide was injected and sealed, whereby a nickel having the structure shown in FIG. A hydrogen storage battery was manufactured.

In FIG. 1, reference numeral 1 denotes a non-sintered positive electrode comprising a paste-type nickel electrode using the above-mentioned nickel hydroxide as an active material, 2 denotes a negative electrode using the above-mentioned hydrogen storage alloy as an active material, Both poles 1 and 2 are shown as having a single configuration in which the base material and the like are omitted. As described above, the positive electrode 1 and the negative electrode 2 are overlapped with each other via the separator 3, spirally wound to form an electrode body 4, and inserted into the battery can 5. An insulator 14 is arranged on the upper part of the electrode body 4, and an insulator 13 is arranged on the bottom of the battery can 5 before the electrode body 4 is inserted.

6 is an annular gasket made of nylon 66;
Is a battery cover composed of a terminal plate 8, a sealing plate 9, a metal spring 10 and a valve body 11 arranged in an internal space formed by them, and an opening of the battery can 5 is sealed with the battery cover 7 or the like. ing. That is, the electrode body 4 and the insulator 1 are placed in the battery can 5.
3, 14 and the like are inserted, and an annular groove 5a having a bottom protruding inwardly is formed near the opening end of the battery can 5, and the groove 5a is formed.
The lower portion of the annular gasket 6 is supported by the inner peripheral side protruding portion a, and the annular gasket 6 and the battery cover 7 are arranged in the opening of the battery can 5. To close the opening of the battery can 5. Terminal plate 8
Has a gas discharge hole 8a, and a sealing plate 9 has a gas detection hole 9a.
A metal spring 10 and a valve body 11 are arranged between the terminal plate 8 and the sealing plate 9, and the outer peripheral portion of the sealing plate 9 is bent to sandwich the outer peripheral portion of the terminal plate 8. Thus, the terminal plate 8 and the sealing plate 9 are fixed.

In this nickel hydrogen storage battery, under normal circumstances, the valve body 11 closes the gas detection hole 9a by the pressing force of the metal spring 10, and the inside of the battery is kept in a sealed state. When the gas is generated and the pressure inside the battery rises abnormally, the metal spring 10 contracts to create a gap between the valve body 11 and the gas detection hole 9a, and the gas inside the battery is released from the gas detection hole 9a. When the internal pressure of the battery is reduced and the internal pressure of the battery returns to normal, the metal spring 10 is restored to its original state, and the valve body 11 is restored by the pressing force. Is the gas detection hole 9a again
To keep the inside of the battery sealed.

Reference numeral 12 denotes a nickel ribbon positive electrode lead.
One end is spot-welded to the exposed portion of the metal porous substrate at the outermost periphery of the positive electrode 2, and the other end is spot-welded to the lower end of the sealing plate 9. The terminal plate 8 can function as a positive electrode terminal by contact with the sealing plate 9. Further, a base made of perforated iron nickel-plated steel plate is exposed on the outer surface side of the outermost peripheral portion of the negative electrode 2, and this base is in contact with the inner wall of the battery can 5, whereby the battery can 5 Can function as a negative electrode terminal.

The nickel hydrogen storage battery thus manufactured is kept at 40.degree. C. for 6 hours, cooled to 25.degree.
5 cycles of charging at 0.14 A for 7 hours and discharging at 0.14 A (1.0 V throughout) at 5 ° C. are necessary for reducing the cobalt oxide in the positive electrode of the battery after these discharges to divalent. The amount of electricity [C _{Co (II)} ] and the amount of electricity [C _H2 ] of the discharge reserve formed on the negative electrode were measured by the following methods. From these two measured values, the ratio [C
_H2 / _{CCo (II)} ] was found to be 1.1.

<C_{Co (II)}And C_H2Measurement> 0.07A
After discharging the battery to 0.7V, disassemble the battery
Separate the positive and negative electrodes, and copy the
The amount of electricity [C
_{Co (II)}] And the amount of electricity of the negative electrode discharge reserve [C_H2]
I asked. That is, the positive electrode and the positive electrode
Precharged cadmium electrode with sufficient capacity
And the same composition as used in the battery fabrication.
A cell is prepared by immersion in an electrolytic solution.
By measuring the amount of electricity when discharged to V,
C_{Co (II)}I asked. In addition, the above-mentioned negative electrode is boiled pure
By immersing it in the air, a discharge reserve is provided in the negative electrode.
Release the stored hydrogen as hydrogen gas.
It was collected by the top displacement method, cooled to 20 ° C, and its volume was measured.
Converts the number of moles of hydrogen gas calculated from the volume of
And C _H2Value. It is used in Examples and Comparative Examples.
C_{Co (II)}And C_H2The value of
It is the average of the measured values of the battery.

[0049] In the preparation of Example 2 positive electrode, instead of cobalt monoxide 2.9 parts of a cobalt conductive additive, and a metal cobalt 1.2 parts, and in preparation of the negative electrode, Co ₃ O ₄ powder 1 A nickel hydrogen storage battery was produced in the same manner as in Example 1 except that 1.6 parts of β-Co (OH) ₂ powder was used instead of the parts. In this storage battery, the ratio of C _H2 / C _{Co (II)} measured and calculated in the same manner as in Example 1 was 1.3.

Example 3 A nickel hydrogen storage battery was produced in the same manner as in Example 2, except that a separator coated with Yb ₂ O ₃ powder at a rate of 1.5 mg / cm ² was used. This storage battery had a ratio of C _H2 / C _{Co (II)} of 1.2 as measured and calculated in the same manner as in Example 1.

Example 4 In the preparation of the positive electrode, after the sheet was compression-molded, it was charged with 0.035 A for 4 hours in a 30% by weight aqueous solution of potassium hydroxide instead of the alkali immersion treatment, and then washed and dried. A nickel hydrogen storage battery was fabricated in the same manner as in Example 3 except for the above. This storage battery had a ratio of C _H2 / C _{Co (II)} measured and converted in the same manner as in Example 1 of 0.9.

Comparative Example 1 In the preparation of the positive electrode, nickel hydroxide not coated with cobalt was used as nickel hydroxide, and instead of 2.9 parts of cobalt monoxide as a cobalt conductive additive, 2.2 metallic cobalt was used. In the same manner as in Example 1, except that the alkaline immersion treatment was not performed after the sheet-shaped compression molding and that the Co ₃ O ₄ powder was not included in the production of the negative electrode. A storage battery was manufactured. In this nickel hydrogen storage battery, the ratio of C _H2 / C _{Co (II)} measured and calculated in the same manner as in Example 1 was 2.4.

[0053] In the preparation of Comparative Example 2 positive electrode, shea - without the alkali immersion treatment after bets like compression molding, also in preparation of the negative electrode, Co ₃ O
₄ Example 1 except that the amount of powder used was changed to 0.6 part.
In the same manner as in the above, a nickel hydrogen storage battery was produced. This storage battery has C _H2 / C measured and calculated in the same manner as in Example 1.
The ratio of _{Co (II)} was 1.6.

Each of the nickel hydrogen storage batteries of Examples 1 to 4 and Comparative Examples 1 and 2 was stored at 80 ° C. for 14 days, and the voltage change during high-temperature storage was examined. The result was as shown in FIG. 2, 1a is the result of the nickel hydrogen storage battery of Example 1, 2a is the result of the nickel hydrogen storage battery of Example 2, 3a is the result of the nickel hydrogen storage battery of Example 3, and 4a is the result of the nickel hydrogen storage battery of Example 4. Result, 1b
Is the result of the nickel hydrogen storage battery of Comparative Example 1, and 2b is the result of the nickel hydrogen storage battery of Comparative Example 2.

For each of the nickel hydrogen storage batteries of Examples 1 to 4 and Comparative Examples 1 and 2, the initial (before storage) discharge capacity and the discharge capacity after high temperature storage (after storage at 80 ° C. for 14 days) were determined. The measurement was performed, and the ratio of the discharge capacity after high-temperature storage was determined based on the initial discharge capacity, and this was evaluated as the capacity recovery rate after high-temperature storage. This result is shown in Table 1 below.
The results were as shown in FIG. Incidentally, in the table, for reference, it is also shown the ratio of the nickel hydride storage battery _{C H2 / C Co (II)} .

[0056]

From the results shown in Table 1 and FIG. 2, each of the nickel hydrogen storage batteries of Examples 1 to 4 has a high temperature even when a nonstoichiometric metal alloy containing Mn is used as the hydrogen storage alloy. The voltage drop during storage was small, and the discharge capacity after high-temperature storage was almost equal to the initial level, indicating that the high-temperature storage characteristics were improved. In contrast, in the two-nickel hydrogen storage batteries of Comparative Examples 1 and 2, the cobalt oxide in the positive electrode was reduced, and the voltage drop during high-temperature storage was large.
Poor capacity recovery after high temperature storage.

[0058]

As described above, according to the present invention, a paste-type nickel electrode is used as a non-sintered type positive electrode, and MmNi _{5-x + y} M _x (Mm contains at least La) as a hydrogen storage alloy of a negative electrode. Represents a rare earth element, M represents a metal element containing at least Mn, and 0 <x <2, -0.2 <y <0.6)
In a nickel hydrogen storage battery using a rare earth alloy represented by the following formula, the amount of electricity [C _{Co (II)} ] required for the cobalt oxide in the positive electrode to be reduced to divalent and the discharge reservoir formed in the negative electrode -The ratio of the amount of electricity to the electric charge [C _H2 ] is 1.3 or less, so that the voltage drop during high-temperature storage is small, the capacity recovery rate after high-temperature storage is large, and the high-temperature storage characteristics are improved. A nickel hydrogen storage battery can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a nickel hydrogen storage battery manufactured in Example 1.

FIG. 2 is a characteristic diagram showing voltage changes during high-temperature storage for each of the nickel hydrogen storage batteries of Examples 1 to 4 and Comparative Examples 1 and 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode (paste type nickel pole) 2 Negative electrode 3 Separator 5 Battery can

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/38 H01M 4/38 A 4/52 4/52 (72) Inventor Masato Isogai Ushitora, Ibaraki-shi, Osaka 1-88, Hitachi Maxell Co., Ltd. (72) Inventor Ryu Nagai 1-1-88, Ushitora, Ibaraki City, Osaka Prefecture F-term, Hitachi Maxell Co., Ltd. 5H021 AA06 CC02 EE04 EE22 EE23 EE31 5H028 AA01 AA05 EE01 EE05 HH10 5H050 AA10 BA14 CA08 CB17 DA19 GA02 GA22 HA19

Claims (2)

[Claims] (1) Cobalt metal with nickel hydroxide.
Or a cobalt conductive additive consisting of a cobalt compound
The paste-type nickel electrode is used as a positive electrode, and the negative electrode absorbs hydrogen.
MmNi as gold_{5-x + y}M_x(Mm is at least La
Represents a rare earth element containing M, and M represents a metal containing at least Mn.
0 <x <2, -0.2 <y <0.6
Using a rare earth alloy represented by
Electrolyte consisting of a separated separator and an alkaline aqueous solution
In a nickel hydrogen storage battery with
The amount of electricity required for the oxide to be reduced to divalent is C
_{Co (II)}And the electricity of the discharge reserve formed on the negative electrode
Amount C_H2And C_H2/ C _{Co (II)}≤ 1.3
A nickel hydrogen storage battery characterized by satisfying. 2. The nickel hydrogen storage battery according to claim 1, wherein the separator contains at least one element selected from the group consisting of Y, Yb, and Er.