JP2000223146A - Nickel hydrogen storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a storage battery which is low in capacity degradation after over discharge and good in cycle life characteristic by performing initial charge at a specific battery temperature. SOLUTION: Initial charge is performed at battery temperature 40-80 deg.C. Preferably, in this nickel hydrogen storage battery, electrolyte is composed of potassium hydroxide, lithium hydroxide, and sodium hydroxide. Preferable electrolyte contains 25-45 pts.wt. potassium hydroxide, 0.5-12 pts.wt. lithium hydroxide, and 1-5 pts.wt. sodium hydroxide. Higher-order cobalt oxide formed by using alkaline aqueous solution containing a plurality of alkaline metal ions as the electrolyte and performing the initial charge in a temperature range of 40-80 deg.C does not receive reduction even in an over discharge state and keeps a strong conductive network. Thus, reduction of availability of a nickel electrode is prevented, corrosion of surfaces of negative electrode hydrogen storage alloy is restrained, and therefore, this nickel hydrogen lead-acid battery is provided which is good in capacity recovery characteristic after over discharge and cycle life characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a positive electrode and a negative electrode used for a nickel-metal hydride storage battery.

[0002]

2. Description of the Related Art In recent years, nickel-metal hydride storage batteries having a high energy density have been used in portable telephones, power tools and small personal computers. Conventionally, nickel-metal hydride batteries were said to be unsuitable for high-power applications,
Improvements in high-rate discharge characteristics have begun to be used in applications to hybrid vehicles that run on both electricity and gasoline as energy sources. Against this background, development of a nickel-metal hydride storage battery with higher performance is expected.

At present, in a nickel-metal hydride storage battery, a hydrogen storage alloy capable of storing and releasing hydrogen is used for a negative electrode, nickel hydroxide is used for a positive electrode, and an alkaline aqueous solution is used for an electrolyte.

The positive electrodes are roughly classified into two types: a sintered nickel electrode and a paste nickel electrode. The sintered nickel electrode is prepared by depositing and growing nickel hydroxide in a hole of a porous substrate obtained by sintering a metal powder using a neutralization reaction.
Since the porous substrate used here has a role of maintaining the strength of the electrode, it is difficult to increase the porosity, and there is a problem that a high capacity cannot be expected. On the other hand, the paste-type nickel electrode is prepared by mixing nickel hydroxide, a conductive agent, a binder, and the like, forming a paste, applying the paste to a porous metal substrate, and then drying. In this case, even if the porosity of the porous metal substrate is increased, the binder serves as a reinforcing agent to maintain the electrode strength, and the addition of a conductive agent can maintain the current collection effect and increase the capacity. There is an advantage that there is.

However, β-Co (OH) ₂ or α-Co (OH) _{2 is used as} the active material of the paste-type nickel electrode.
When nickel hydroxide coated on the surface is used, the conductive path of β-CoOOH formed at the time of initial charging is decomposed by overdischarge, and the conductive path cannot be maintained, and electronic isolation of the active material proceeds. For this reason, there is a problem that the discharge capacity is smaller than before the overdischarge and the capacity cannot be recovered. Thus, by using an electrolytic solution obtained by adding sodium hydroxide, lithium hydroxide, or the like to an aqueous potassium hydroxide solution, this problem is slightly improved, but it has not been solved.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a nickel-metal hydride storage battery having a small capacity deterioration after overdischarge and excellent cycle life characteristics. And

[0007]

SUMMARY OF THE INVENTION According to the present invention, a battery is heated at the time of initial charging, and a plurality of alkali metal hydroxides are contained in an electrolyte to form a stronger .beta.-CoOOH conductive path. Thus, it is possible to provide a secondary battery having excellent capacity recovery after overdischarge and excellent cycle life characteristics.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A hydrogen storage alloy capable of storing and releasing hydrogen in a negative electrode, β-Co (OH) ₂ or α-Co (O
H) Using nickel hydroxide coated on the surface with ₂ and an alkaline aqueous solution containing a plurality of alkali metal hydroxides in the electrolytic solution, the battery temperature during the initial sealed formation was set to 40 to 80.
Charge the battery while maintaining the temperature at ℃.

The charging current during the initial charging is 1/20 CmA
In the case described above, the conversion efficiency of cobalt hydroxide to cobalt oxyhydroxide decreases, the formation of the conductive network becomes incomplete, and a high active material utilization cannot be obtained. Therefore, it is necessary to perform initial charging at 1/20 CmA or less, and preferably, perform initial charging at 1/20 CmA or less.

The electrolytic solution comprises potassium hydroxide, lithium hydroxide and sodium hydroxide. The potassium hydroxide is 25 to 45 parts by weight, the lithium hydroxide is 0.5 to 12 parts by weight and the sodium hydroxide is 1 to 25 parts by weight. It is preferable that 5 are parts by weight.

[0011]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

(Invention 1) An alkaline aqueous solution containing 34 parts by weight of potassium hydroxide, 2.5 parts by weight of lithium hydroxide, and 4 parts by weight of sodium hydroxide was used as an electrolytic solution.

The positive electrode is made of a nickel porous material as a current collector obtained by mixing 80 parts by weight of nickel hydroxide coated on the surface with β-Co (OH) ₂ and 20 parts by weight of an aqueous solution containing carboxymethylcellulose as a binder. It was applied to a substrate and dried.
Thereafter, pressing was performed to reduce the electrode thickness to 0.5 mm. The positive electrode capacity was 500 mAh.

The negative electrode is composed of MmNi _3.6 as a hydrogen storage alloy.
An alloy having a composition of Co _0.6 Mn _0.35 Al _0.3 was used. M
m means a misch metal which is a mixture of rare earth elements. A thickener was added to this sample to form a paste, which was applied to a perforated steel plate, dried and pressed to produce a hydrogen storage alloy electrode. The negative electrode capacity was 1000 mAh.

These were combined with a positive electrode, a negative electrode and an electrolytic solution to prepare an open-type battery, and thereafter, an initial charge was performed in a temperature range of 40 to 80 ° C.

(Invention 2) An alkaline aqueous solution containing 28 parts by weight of potassium hydroxide, 6 parts by weight of lithium hydroxide, and 4 parts by weight of sodium hydroxide was used as the electrolytic solution.

The positive electrode is a nickel porous material as a current collector obtained by mixing 80 parts by weight of nickel hydroxide coated on the surface with β-Co (OH) ₂ and 20 parts by weight of an aqueous solution containing a carboxymethyl cellulose binder. It was applied to a substrate and dried.
Thereafter, pressing was performed to reduce the electrode thickness to 0.5 mm. The positive electrode capacity was 500 mAh.

The negative electrode is made of MmNi _3.6 as a hydrogen storage alloy.
An alloy having a composition of Co _0.6 Mn _0.35 Al _0.3 was used.
Mm means a misch metal which is a mixture of rare earth elements as described above. A thickener was added to this sample to form a paste, which was applied to a perforated steel plate, dried and pressed to produce a hydrogen storage alloy electrode. The negative electrode capacity was 1000 mAh.

These were combined with a positive electrode, a negative electrode and an electrolytic solution to prepare an open-type battery, and thereafter, an initial charge was performed in a temperature range of 40 to 80 ° C.

Comparative Example 1 An alkaline aqueous solution containing 34 parts by weight of potassium hydroxide, 2.5 parts by weight of lithium hydroxide, and 4 parts by weight of sodium hydroxide was used as an electrolytic solution.

The positive electrode is a nickel porous material serving as a current collector obtained by mixing 80 parts by weight of nickel hydroxide coated on the surface with β-Co (OH) ₂ and 20 parts by weight of an aqueous solution containing a carboxymethyl cellulose binder. It was applied to a substrate and dried.
Thereafter, pressing was performed to reduce the electrode thickness to 0.5 mm. The positive electrode capacity was 500 mAh.

The negative electrode was made of MmNi _3.6 as a hydrogen storage alloy.
An alloy having a composition of Co _0.6 Mn _0.35 Al _0.3 was used. A thickener was added to this sample to form a paste, which was applied to a perforated steel plate, dried and pressed to produce a hydrogen storage alloy electrode.
The negative electrode capacity was 1000 mAh.

These were combined with a positive electrode, a negative electrode and an electrolytic solution to produce an open-type battery, after which initial charging was performed at 20 ° C.

Comparative Example 2 An alkaline aqueous solution containing 28 parts by weight of potassium hydroxide, 6 parts by weight of lithium hydroxide, and 4 parts by weight of sodium hydroxide was used as an electrolytic solution.

The positive electrode is a nickel porous material as a current collector obtained by mixing 80 parts by weight of nickel hydroxide coated on the surface with β-Co (OH) ₂ and 20 parts by weight of an aqueous solution containing a carboxymethyl cellulose binder. It was applied to a substrate and dried.
Thereafter, pressing was performed to reduce the electrode thickness to 0.5 mm. The positive electrode capacity was 500 mAh.

The negative electrode was made of MmNi _3.6 as a hydrogen storage alloy.
An alloy having a composition of Co _0.6 Mn _0.35 Al _0.3 was used.
A thickener was added to this sample to form a paste, which was applied to a perforated steel plate, dried and pressed to produce a hydrogen storage alloy electrode. The negative electrode capacity was 1000 mAh.

These were combined with a positive electrode, a negative electrode and an electrolytic solution to produce an open-type battery, after which initial charging was performed at 20 ° C.

Comparative Example 3 An alkaline aqueous solution containing 39 parts by weight of potassium hydroxide and 3 parts by weight of lithium hydroxide was used as an electrolytic solution.

The positive electrode is a nickel porous material as a current collector obtained by mixing 80 parts by weight of nickel hydroxide coated on the surface with β-Co (OH) ₂ and 20 parts by weight of an aqueous solution containing a carboxymethyl cellulose binder. It was applied to a substrate and dried.
Thereafter, pressing was performed to reduce the electrode thickness to 0.5 mm. The positive electrode capacity was 500 mAh.

The negative electrode was made of MmNi _3.6 as a hydrogen storage alloy.
An alloy having a composition of Co _0.6 Mn _0.35 Al _0.3 was used. A thickener was added to this sample to form a paste, which was applied to a perforated steel plate, dried and pressed to produce a hydrogen storage alloy electrode.
The negative electrode capacity was 1000 mAh.

These were combined with a positive electrode, a negative electrode and an electrolytic solution to produce an open-type battery, which was then initially charged in a temperature range of 20 to 80 ° C.

(Comparative Example 4) As an electrolytic solution, an alkaline aqueous solution containing 28 parts by weight of potassium hydroxide and 8 parts by weight of sodium hydroxide was used.

The positive electrode is a nickel porous material as a current collector obtained by mixing 80 parts by weight of nickel hydroxide coated on the surface with β-Co (OH) ₂ and 20 parts by weight of an aqueous solution containing a carboxymethyl cellulose binder. It was applied to a substrate and dried.
Thereafter, pressing was performed to reduce the electrode thickness to 0.5 mm. The positive electrode capacity was 500 mAh.

The negative electrode was made of MmNi _3.6 as a hydrogen storage alloy.
An alloy having a composition of Co _0.6 Mn _0.35 Al _0.3 was used.
A thickener was added to this sample to form a paste, which was applied to a perforated steel plate, dried and pressed to produce a hydrogen storage alloy electrode. The negative electrode capacity was 1000 mAh.

The positive electrode, the negative electrode, and the electrolytic solution were combined to form an open-type battery, and thereafter, an initial charge was performed in a temperature range of 20 to 80 ° C.

The batteries according to the present invention 1, the present invention 2, the comparative examples 1, 2, 3, and 4 were subjected to 20 to 80.
In the temperature range of ° C., the charging condition in the first cycle is 1
/ Constant current charging at 50 CmA for 10 hours, and 0.1 C
The battery was charged at a constant current of 10 hours at mA. Discharge condition is 0.2C
The battery was discharged at a constant current of 0.6 V at mA. After the second cycle, the battery is charged at a constant current of 0.1 CmA for 15 hours,
The battery was discharged at a constant current of 1.0 A to 1.0 V. After repeating this operation for 4 cycles, in order to overdischarge,
It was short-circuited for 8 hours. To study the recovery rate after overdischarge,
The charge and discharge were repeated again under the same conditions as the second cycle.

FIG. 1 shows the capacity recovery characteristics of the batteries of Invention 1, Invention 2, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 after the overdischarge test. It can be seen that the capacity recovery rate after overdischarge is improved by about 5% in the present invention by performing the initial charging by heating to 40 ° C. or higher as compared with Comparative Examples 1 and 2. In addition, it can be seen that the capacity recovery rate after overdischarge is improved by about 5% when the three kinds of mixed alkaline aqueous solutions of the present invention are used for the electrolytic solution as compared with the two kinds of mixed alkaline aqueous solutions shown in Comparative Examples 3 and 4. .

The reason for this is that the electrochemical oxidation of cobalt hydroxide to a higher-order cobalt oxide such as cobalt oxyhydroxide at the time of initial charging is carried out at a high temperature and in the electrolysis of an aqueous potassium hydroxide solution in which sodium and lithium coexist. By performing in a liquid, a strong conductive network is maintained without being reduced even in an overdischarged (low potential) state.
This is considered to be because the reduction in the utilization rate of the nickel electrode was prevented.

FIG. 2 is an electron micrograph of the surface of the negative electrode hydrogen storage alloy after 300 cycles of the batteries of Invention 2 and Comparative Examples 2 and 4. It can be seen that in the present invention, needle-like products of rare earth hydroxides are significantly suppressed as compared with Comparative Examples.
In addition, as a result of analyzing each electrolytic solution, it was found that in the present invention, the amount of rare earth ions was significantly larger than that of the comparative example. Therefore, the rare earth is ionized and eluted into the electrolyte by heating the electrolyte to a three-component system by heating to 40 ° C. or more at the time of initial charging, and the precipitation of rare earth hydroxide on the surface of the negative electrode hydrogen storage alloy is suppressed. it is conceivable that.

If the temperature exceeds 80 ° C. at the time of initial charging, the evaporation of the electrolytic solution becomes active and corrosion of the surface of the hydrogen storage alloy of the negative electrode proceeds, which is not preferable.

[0041]

According to the battery of the present invention, the capacity recovery characteristic after overdischarge is remarkably improved, and the corrosion of the surface of the negative electrode hydrogen storage alloy is suppressed. Unlike the comparative example, by using a mixture of a plurality of alkaline aqueous solutions in the electrolytic solution and heating at the time of initial charging, it is possible to form a stronger conductive network and suppress corrosion of the negative electrode hydrogen storage alloy surface. It has become possible.

As is apparent from the above description, according to the present invention, as described above, an initial aqueous charge is performed in a temperature range of 40 to 80 ° C. using an alkaline aqueous solution containing a plurality of alkali metal ions as an electrolytic solution. The high-order cobalt oxide thus formed does not undergo reduction even in an overdischarge (low potential) state and maintains a strong conductive network, so that a decrease in the utilization rate of the nickel electrode is prevented, and Since the corrosion of the hydrogen storage alloy surface is suppressed, it is possible to provide a nickel-metal hydride storage battery having excellent capacity recovery characteristics after overdischarge and excellent cycle life characteristics.

[Brief description of the drawings]

FIG. 1 shows the capacity recovery characteristics after overdischarge of the nickel-metal hydride storage batteries of the present inventions 1, 2, and Comparative Examples 1, 2, 3, and 4.

FIG. 2 shows electron micrographs of the surfaces of the negative electrode hydrogen storage alloys of Invention 2 and Comparative Examples 2 and 4.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Minoru Kuzukatsubara 6-6 Josaicho, Takatsuki-shi, Osaka F-term in Yuasa Corporation (reference) 5H028 AA01 AA06 EE05 FF04 HH08

Claims (2)

[Claims] 1. A nickel-metal hydride storage battery using an alkaline aqueous solution containing a plurality of alkali metal hydroxides in an electrolytic solution, wherein initial charging is performed at a battery temperature of 40 to 80 ° C. 2. The nickel-metal hydride storage battery according to claim 1, wherein said electrolyte comprises potassium hydroxide, lithium hydroxide and sodium hydroxide.