JP2001085050A - Nickel hydrogen storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel-hydrogen storage battery with its positive electrode formed of paste nickel and a negative electrode of paste alloy, assuring improved high-temperature storing characteristics. SOLUTION: The nickel-hydrogen storage battery is composed of a positive electrode formed of paste nickel of such a structure that an electroconducting assistant consisting of metal cobalt or cobalt compound is dispersed in a binder together with nickel hydroxide, a negative electrode formed of a paste alloy in which a hydrogen storage alloy is dispersed in a binder, a separator interposed between the two electrodes, and an electrolytic solution consisting of alkaline aqueous solution, wherein the negative electrode contains nickel compound of two-valency or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel hydrogen storage battery using nickel hydroxide as a main active material for a positive electrode and a hydrogen storage alloy as a main active material for a negative electrode. Nickel hydrogen storage battery.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of portable electronic devices using a storage battery as a main power source, these electronic devices have been increasingly used in portable environments, and have been used in a wider environment than before. It has come. For this reason, secondary batteries are required to exhibit stable performance irrespective of environmental changes, particularly temperature changes.For example, when used in laptop computers and mobile phones, high temperature and low temperature are required at room temperature. A characteristic equivalent to that at the time is required, and the load on the battery is increasing. In particular, with regard to the nickel hydrogen storage battery that is frequently used in the above-described electronic devices, studies for further improving the temperature characteristics are being continued.

As the positive electrode of a nickel hydrogen storage battery, there are a sintered type and a paste type. In the latter type, nickel hydroxide, which is an active material, is used together with a binder, a thickener and the like as a solvent. The paste is formed by dispersing the paste into a paste and filling the paste into a conductive porous substrate. In this paste-type nickel electrode, there is a problem that the distance between the active material and the current collector is long and the utilization factor is inferior. Cobalt compounds such as cobalt oxide and cobalt hydroxide are added. These additives provide Co, CoO, Co (OH) ₂ for electrically connecting nickel hydroxide particles during charging.
→ It is known that a change in CoOOH occurs to form a cobalt network. On the other hand, as a negative electrode, a sintered alloy electrode in which a hydrogen storage alloy is held on a base material and then sintered, and a paste in which the hydrogen storage alloy powder is bound with a binder such as polytetrafluoroethylene or polypropylene Although there is a formula-type alloy electrode, the latter paste-type alloy electrode is generally used.

In a nickel hydrogen storage battery using such a positive electrode and a negative electrode, gas generation from the negative electrode at the end of charging and the end of discharging is suppressed by giving the negative electrode a capacity larger than that of the positive electrode. In other words, even after the positive electrode is fully charged or completely discharged during charging, there is an uncharged portion in the negative electrode, whereby oxygen gas can be preferentially generated from the positive electrode, preventing generation of hydrogen gas from the negative electrode. The configuration is such that it can be used. The excess capacity of the negative electrode during this discharge (discharge reserve) is not directly involved in the charge / discharge reaction, but is necessary to discharge the positive electrode capacity until the end of discharge. It is formed on the negative electrode as a counter reaction to the formation reaction of the cobalt network and other side reactions (such as alloy corrosion).

[0005]

However, a conventional nickel hydrogen storage battery having the above-mentioned paste-type nickel electrode as a positive electrode and the paste-type alloy electrode as a negative electrode,
When left in a high-temperature environment, it was clarified that the battery voltage was significantly reduced, the discharge capacity after storage was deteriorated, and the capacity recovery rate was small.

[0006] In view of such circumstances, the present invention has
In a nickel-metal hydride storage battery using a strike-type nickel electrode as a positive electrode and a paste-type alloy electrode as a negative electrode, voltage drop during high-temperature storage is suppressed, capacity recovery after high-temperature storage is large, and high-temperature storage characteristics are improved. It is intended to provide a nickel hydrogen storage battery.

[0007]

Means for Solving the Problems In order to achieve the above object, the present inventors first studied the cause of the voltage drop during high-temperature storage. As a result of the rise in the equilibrium dissociation pressure of hydrogen, the hydrogen absorbed as a discharge reserve formed on the negative electrode is released into the battery as hydrogen gas, and this reduces the voltage of the positive electrode. Was. Therefore, to suppress the voltage drop during storage, it was considered effective to reduce the amount of hydrogen in the discharge reserve, and for that purpose, an attempt was made to add a metal compound or the like to the negative electrode.

This is because, by adding a metal compound or the like to the negative electrode, a part of hydrogen in the discharge reserve is used for reduction of the metal compound or the like to metal, thereby preventing reduction of the positive electrode. This is because voltage drop can be suppressed. For the metal compound used for this purpose, it is necessary that the metal state be ensured within the normal operating potential range of the hydrogen storage electrode. Based on this idea, the present inventors have conducted various studies on the types of metal oxides and the like, and found that nickel compounds are effective, and among them, when a nickel compound having two or more valences is added to the negative electrode, In addition, they found that the voltage drop during high-temperature storage can be greatly suppressed, and completed the present invention.

That is, the present invention provides a paste-type nickel electrode obtained by dispersing a cobalt conductive additive composed of metallic cobalt or a cobalt compound together with nickel hydroxide in a binder, as a positive electrode, and binding a hydrogen storage alloy. In a nickel hydrogen storage battery having a paste-type alloy electrode dispersed in a dispersing agent as a negative electrode and having a separator interposed between the two electrodes and an electrolytic solution comprising an aqueous alkaline solution, the above-mentioned negative electrode has a divalent or higher valent nickel The present invention relates to a nickel hydrogen storage battery characterized by containing a compound.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In a nickel hydrogen storage battery, when a cobalt conductive auxiliary is added to a paste type positive electrode, it dissolves as divalent cobalt ions during a standing period after injection of an electrolytic solution or at the time of initial charging, and nickel hydroxide is used. It precipitates as cobalt hydroxide between the particles and on the current collector, and is then oxidized to cobalt oxyhydroxide having excellent conductivity when further charging proceeds.
At the negative electrode, hydrogen corresponding to a counter reaction such as the above-described cobalt oxidation reaction or alloy corrosion forms a discharge reserve. Hydrogen that functions as a discharge reserve is not discharged by normal charge / discharge reactions, but when the battery is stored in a high-temperature atmosphere, it is released from the hydrogen storage alloy as hydrogen gas as the equilibrium pressure of the hydrogen storage alloy increases. The conductive network of cobalt formed on the positive electrode is reduced, and a voltage drop occurs.

On the other hand, it is conceivable to reduce the amount of hydrogen stored as a discharge reserve in the negative electrode.
Since the discharge reserve contains not only the reaction for forming the conductive network formed on the positive electrode but also the amount of hydrogen corresponding to the reaction such as the corrosion reaction of the hydrogen storage alloy, the discharge reserve for the negative electrode is provided. Cannot be reduced alone. For this reason, in the present invention, as described above, by incorporating a nickel compound having a valency of 2 or more into the negative electrode, utilizing the reaction in which this is reduced to a metal at a more noble potential than the charge and discharge reaction of the hydrogen storage alloy, By replacing a part of the hydrogen in the discharge reserve with this metal, the amount of hydrogen in the discharge reserve is reduced.

In the present invention, the nickel compound having two or more valences used for such a purpose is not particularly limited as long as it is a compound which is added to the negative electrode to be reduced. Large amounts of NiO, Ni
It is preferably at least one selected from (OH) _{2 and} Ni ₂ O ₃ . In addition, as a nickel compound, as long as it is mainly a nickel compound having two or more valencies,
A composite metal compound in which a part of nickel is substituted by another metal, for example, cobalt or the like may be used. The use amount of these nickel compounds is usually 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight, based on 100 parts by weight of the hydrogen storage alloy.

In the present invention, the negative electrode comprises a hydrogen storage alloy, the above-mentioned nickel compound having a valence of 2 or more, and, if necessary, a conductive aid such as nickel powder, using a binder or a dispersant in the presence of water or a solvent. The paste-like material is applied to a suitable conductive porous substrate, filled, dried, compression-molded, and formed of a paste-type alloy electrode. A negative electrode can be manufactured by forming a negative electrode.

Examples of the hydrogen storage alloy include AB ₂ type alloy mainly composed of Zr, Ni, Mn, etc., and Mm (La, Ce, N
d, there is AB ₅ type alloys, such as Pr) -Ni system. Among them, a part of Ni in Mm-Ni based alloy is Mn, Co,
At least one selected from Al, Mg, Cu, and Cr
Alloys substituted by seeds are preferred, and these can be expected to have a high capacity at a low hydrogen equilibrium pressure, but are particularly useful in the present invention because they contain a large amount of transition metal and generate a large amount of hydrogen gas from the negative electrode. Among alloys having 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, other Ni, C
Hydrogen storage alloys having a total amount of o, Mn, Al and M of 5.02 to 5.45) are particularly useful in the present invention because a large amount of transition metal is present on the alloy surface and the amount of hydrogen gas generated is large. It is.

In the present invention, the positive electrode, together with nickel hydroxide as an active material, at least one kind of cobalt compound such as cobalt monoxide, α-cobalt hydroxide, β-cobalt hydroxide, and metallic cobalt. A cobalt conductive additive is used. In order to form a cobalt network of the positive electrode capable of reducing the amount of discharge reserve of the negative electrode and to form a strong cobalt network capable of suppressing reduction by hydrogen gas generated from the negative electrode, a cobalt compound, particularly a cobalt compound, is required. Preferably, cobalt hydroxide is used. When metallic cobalt is used, the formation of a network causes C
This is because a three-electron reaction of o → Co (OH) ₂ → CoOOH is required, and the amount of discharge reserve formed on the negative electrode tends to increase. The amount of the cobalt conductive additive used is 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight, in terms of cobalt, based on 100 parts by weight of nickel hydroxide, in order to achieve both the above effects and high capacity. Good to do.

As the nickel hydroxide, conventionally known ones can be used. Nickel hydroxide crystals in which 0.5 to 5% by weight of cobalt forms a solid solution are preferable because the charging rate at high temperatures can be improved. Also, zinc is 0.5 to 5
It is preferable to use a solid solution in which the weight percent is dissolved because the cycle life can be improved. Furthermore, the surface of the particles is cobalt monoxide, α
-Coated with at least one kind of divalent or more cobalt compound selected from cobalt hydroxide, β-cobalt hydroxide, and cobalt oxyhydroxide, the conductivity is reduced even if the amount of the cobalt conductive additive is reduced. Since the network can be formed effectively and the amount of discharge reserve for the reaction can be reduced,
preferable. Among the above-mentioned cobalt compounds, α-cobalt hydroxide and β-cobalt hydroxide, which can easily form a stronger conductive cobalt network, are preferable. The coating of the cobalt compound is zinc, calcium, yttrium,
A composite coating in which elements such as ytterbium are composited can also be used. The coating amount of the cobalt compound is usually 1 to 10% by weight, preferably 2 to 5% by weight of nickel hydroxide.
% By weight.

In the present invention, the positive electrode comprises the above-mentioned active material comprising nickel hydroxide, a cobalt conductive additive, and, if necessary, another conductive aid such as nickel powder having an average particle size of 3 μm or less. Using a binder such as ethylene or a thickener such as carboxymethyl cellulose, disperse in an organic solvent to form a paste, and paste
After the strike-like material is applied to a porous metal body such as a nickel foam or other suitable conductive porous substrate, filled, and dried,
It can be manufactured by compression molding to form a sheet-like positive electrode composed of a paste-type nickel electrode.

The nickel hydrogen storage battery of the present invention has the above-described negative electrode and positive electrode, a separator interposed between these two electrodes, and an electrolytic solution composed of an aqueous alkaline solution. The positive electrode can be produced by winding the positive electrode through a separator, inserting the positive electrode into a battery can, and then injecting the above-mentioned electrolytic solution. At that time, since the conductive network is formed by the cobalt conductive additive added to the positive electrode during the initial charge, both the positive and negative electrodes are assembled in a non-chemical state without any electrochemical charging or discharging. Can be That is, by combining the positive and negative electrodes which have not undergone any of charging and discharging, the cobalt conductive additive added to the positive electrode is oxidized by the initial charging (chemical formation) after assembling the battery. The discharged discharge reserve is formed on the negative electrode, and a positive electrode regulated battery can be obtained.

[0019]

Next, an embodiment of the present invention will be described in more detail. However, the present invention is not limited only 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 cobalt hydroxide was added 2.9 parts of cobalt monoxide powder as a cobalt conductive additive, and 2% by weight of carboxymethyl cellulose. 5 parts of an aqueous solution (hereinafter referred to as CMC) and 5 parts of a 60% by weight aqueous dispersion of polytetrafluoroethylene (hereinafter referred to as PTFE) were mixed to form a paste. A predetermined amount of this paste-like material is filled in a conductive porous base material made of a nickel foam, carried, dried, regulated in pressure (compression molding), cut into a predetermined size, and paste-type. A sheet-like positive electrode comprising a nickel pole was produced.

Separately, the composition is MmNi _4.05 Co
_0.45 Mn _0.5 Al _0.35 (Mm composition is La: 0.32 at%, Ce: 0.48 at%, Nd: 0.15 at%,
Pr: 0.04 atomic%, Ni, Co, Mml
1 part of NiO and 2 parts of nickel powder were added to 100 parts of a hydrogen storage alloy represented by the following formula (the total of Mn and Al was 5.35), and 20 parts of a 2% by weight aqueous CMC solution and 60 parts by weight of PTFE aqueous dispersion were further added. A paste was formed by adding 2 parts of the liquid. A predetermined amount of this paste-like material is applied to both surfaces of a conductive porous substrate made of a perforated iron nickel-plated steel sheet, dried, pressurized (compression molded), cut into predetermined dimensions, A sheet-like negative electrode composed of a strike type alloy electrode was produced.

Next, the sheet-shaped negative electrode and the sheet
An electrode body was produced by winding the cathode in a manner to face each other via a separator. This electrode body was inserted into a battery can, and a predetermined amount of an electrolytic solution composed of a 30% by weight aqueous solution of potassium hydroxide was injected and sealed, thereby producing a nickel hydrogen storage battery.

Comparative Example 1 A sheet-like negative electrode was produced in the same manner as in Example 1 except that NiO was not added to the hydrogen storage alloy. Also,
Using this sheet-shaped negative electrode, in the same manner as in Example 1,
A nickel hydrogen storage battery was manufactured.

In order to examine the performance of the nickel hydrogen storage batteries of Example 1 and Comparative Example 1 produced as described above, each of the batteries was maintained at 60 ° C. for 17 hours, and at 7 ° C. at 25 ° C. and 0.2 CA.
After two cycles of charging for 0.2 hours and discharging at 0.2 CA (final voltage: 1.0 V) were repeated, as a high temperature storage characteristic, a voltage change during high temperature storage and a capacity recovery rate after high temperature storage were examined by the following method. . The voltage change during high temperature storage is as shown in FIG. 1, and the capacity recovery rate after high temperature storage is shown in Table 1.
The results were as shown in FIG. In FIG. 1, 1a is the test result of Example 1, and 1b is the test result of Comparative Example 1.

<High temperature storage characteristics> 1 at 25 ° C. and 1.0 CA
After 20% charge, discharge at 1.0 CA (final voltage 1.0
The discharge capacity at the time of performing V) was measured, and this was defined as the discharge capacity before storage. Further, the battery discharged at 0.2 CA was stored at 85 ° C. for 14 days, and the voltage change during storage was measured. Also, the battery after the high-temperature storage is cooled to 25 ° C.
After charging at 120% with 1.0 CA, the discharge capacity was measured when discharging at 1.0 CA (final voltage: 1.0 V) was performed three times, and this was defined as the discharge capacity after high-temperature storage. The capacity recovery rate after high-temperature storage was determined as (discharge capacity before storage / discharge capacity after high-temperature storage) × 100.

[0026]

As is clear from the results shown in FIG. 1 and Table 1, the nickel hydrogen storage battery of Example 1 in which NiO was added to the negative electrode was the nickel hydrogen storage battery of Comparative Example 1 in which NiO was not added to the negative electrode. It can be seen that the voltage drop during high-temperature storage is significantly suppressed, and the capacity recovery rate after high-temperature storage is higher than in the case of.

The above embodiment is an example in which NiO is used. However, when NiO is replaced with another divalent or higher valent nickel compound, for example, Ni (OH) ₂ or Ni ₂ O _3. However, almost the same results as above were obtained. Further, it was also found that a compound in which part of nickel in these nickel compounds was substituted with another metal such as cobalt can obtain substantially the same results as described above.

[0029]

As described above, according to the present invention, there is provided a paste obtained by dispersing a cobalt conductive additive comprising metallic cobalt or a cobalt compound together with nickel hydroxide in a binder.
In a nickel hydrogen storage battery in which a strike-type nickel electrode is used as a positive electrode and a paste-type alloy electrode in which a hydrogen storage alloy is dispersed in a binder is used as a negative electrode, a nickel compound having two or more valences is contained in the negative electrode. With this configuration, it is possible to provide a nickel hydrogen storage battery in which a voltage drop during high-temperature storage is suppressed, a capacity recovery rate after high-temperature storage is large, and high-temperature storage characteristics are significantly improved.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing voltage changes during high-temperature storage for both nickel hydrogen storage batteries of Example 1 and Comparative Example 1.

[Explanation of symbols]

 1a Test result of nickel hydrogen storage battery of Example 1 1b Test result of nickel hydrogen storage battery of comparative example 1

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Masato Isogai 1-88 Ushitora, Ibaraki-shi, Osaka F-term within Hitachi Maxell Co., Ltd. 5H003 AA03 BA03 BB02 BB04 BB14 5H016 AA02 BB09 EE01 EE05 5H028 AA01 AA05 CC11 EE01 EE05

Claims (2)

[Claims] 1. A paste-type nickel electrode obtained by dispersing a cobalt conductive additive comprising metallic cobalt or a cobalt compound together with nickel hydroxide in a binder, and a positive electrode, and a hydrogen storage alloy dispersed in the binder. In a nickel hydrogen storage battery having a paste-type alloy electrode formed as a negative electrode and a separator interposed between the two electrodes and an electrolytic solution consisting of an alkaline aqueous solution, the negative electrode contains a divalent or higher valent nickel compound. A nickel hydrogen storage battery characterized by the above-mentioned. 2. The nickel compound having two or more valences is NiO,
Nickel hydride storage battery according to claim 1 is at least one selected from Ni (OH) ₂ or Ni ₂ O _3.