JP2986816B2 - Hydrogen storage electrode and its manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydrogen storage electrode used as a negative electrode of an alkaline storage battery.

[Conventional technology]

Conventionally, hydrogen storage alloys or their hydrides can electrochemically store and release hydrogen, so they are mainly made of powder, mixed with a conductive material and a binder, and formed by pressure molding. And is used as a negative electrode of an alkaline storage battery.

[Problems to be solved by the invention]

The above-mentioned hydrogen storage electrode, along with the repetition of charge and discharge, the hydrogen storage alloy powder, that is, each particle thereof expands and contracts repeatedly, so that the particles are cracked and subdivided,
It is easy to fall off, eventually causing phenomena such as cracking of the electrodes, and therefore, increasing the internal resistance and reducing the capacity,
This leads to inconveniences such as a shortened cycle life.

Conventionally, in order to solve such inconveniences, before mixing the hydrogen storage alloy powder with a conductive material and a binder, an electroless plating process was used to prepare a nickel storage coating of the hydrogen storage alloy powder particles, and this was mainly used. Although it has been proposed to produce a hydrogen storage electrode having the following characteristics, depending on the composition of the hydrogen storage alloy, an electrode having insufficient bonding between the plating and the hydrogen storage alloy particles can be obtained. The cycle life of an alkaline storage battery that results from the disadvantage of being as short as 50 to 60 cycles.

[Means for solving the problem]

The present invention solves the above-mentioned drawbacks of the hydrogen storage electrode mainly made of the above-mentioned conventional nickel-plated hydrogen storage alloy powder, and has a remarkably long life regardless of the type of the hydrogen storage alloy. The hydrogen storage electrode is composed of a composite powder composed of a hydrogen storage alloy powder and a carbonyl nickel powder having a chain structure which is innumerably branched in a three-dimensional direction and coated with the particles. Become the subject.

The production method is a method of firing a mixture of hydrogen storage alloy powder and carbonyl nickel powder having a chain structure innumerably branched in three dimensions in a vacuum heating furnace and pulverizing the composite sintered body to obtain a composite. The method is characterized in that body powder is mixed with a binder, and the mixture is pressure-formed on a current collector.

(Operation)

Although the effect of the composite powder of the present invention is not sufficiently clear, the structure is such that the hydrogen storage alloy powder particles are firmly covered with carbonyl nickel powder having a fine and three-dimensional chain structure,
In addition, since these composite powders have a three-dimensional chain structure of the carbonyl nickel powder and are continuous with each other in a three-dimensional structure, the conductivity as an electrode is increased, and the hydrogen storage alloy powder accompanying the repetition of charging and discharging is added. The carbonyl nickel powder intervenes to reduce the stress exerted by the expansion and contraction of the particles on the entire electrode, thereby preventing cracking and fragmentation of the hydrogen storage alloy powder particles as much as possible. As a result, the cycle life of the electrode is improved. I do. Thus, since the composite powder is manufactured by firing the hydrogen storage alloy powder and the carbonyl nickel powder and pulverizing the composite sintered body, the alloy powder is firmly mixed with the carbonyl nickel powder. A binder-coated product is obtained, which prevents cracking due to expansion and contraction of the alloy powder, falling off due to fragmentation, and cracking of the electrode.

In this case, by adding at least 5% by weight of the carbonyl nickel powder to the hydrogen storage alloy powder, a sufficiently good coating and binding state can be obtained.

〔Example〕

 Next, embodiments of the present invention will be described in detail.

Commercially available La and Ni are weighed and mixed so as to have a fixed composition ratio, and heated and melted by an arc melting method to obtain a hydrogen storage alloy. As an example, the alloy composition was weighed and mixed so that the alloy composition was LaNi ₅ , and heated and melted to produce a hydrogen storage alloy having the LaNi ₅ composition, and this was pulverized to produce a hydrogen storage alloy powder of 250 mesh or less. Carbonyl nickel powder having a chain structure that is fine and countlessly branched in a three-dimensional direction is added to and mixed with the hydrogen storage alloy powder. This amount is at least 5% by weight so as to sufficiently cover the hydrogen storage alloy powder particles.

For example, with respect to 10 g of the hydrogen storage alloy powder, 10% by weight, that is, 1 g, of commercially available INCO # 255 is added and mixed as carbonyl nickel powder composed of fine particles of about 2.5 μm in thickness, and the mixture is placed in a vacuum heating furnace Sintered at 1000 ° C. for 1 hour. Next, this composite sintered body was pulverized to produce a composite powder having a mesh size of 250 mesh or less.

To this composite powder, a fluororesin powder was added as a binder in an amount of 5% by weight based on the composite powder.
For example, 5% by weight of copper powder having an average particle size of 2 μm is added, and the mixture is stirred well until the binder is sufficiently fiberized to obtain a mixture thereof. Next, the mixture was placed on a nickel wire net to a uniform thickness and pressed to produce a hydrogen storage electrode made of a thin circular plate-like molded body. As the current collector, a nickel foam, a foamed nickel plate or the like can be used.

The hydrogen storage electrode of the present invention thus produced was used as a negative electrode, and in accordance with a conventional method, combined with a known sintered nickel electrode, using an aqueous caustic potassium solution as an electrolytic solution, to constitute an alkaline storage battery. In order to make the cycle life understandable, the negative electrode capacity was made smaller than the positive electrode capacity, and the negative electrode rule was set. The cell was charged at 0.5 C for 2.5 hours (125% charge), and then repeatedly charged and discharged at 0.5 C to a final voltage of 1.0 V in order to conduct a cycle life test.

For comparison, a hydrogen storage alloy powder having the same composition as described above, a copper powder having an average particle diameter of 2 μm as a conductive material was added to the carbonyl nickel powder in the composite powder used in the present invention and the added copper powder. A mixture prepared by adding the same amount of the above-mentioned fluororesin powder to the above-mentioned fluororesin powder and adding the same amount of 15% by weight to the nickel wire netting in the same manner as above to a uniform thickness as above. It was mounted and pressurized to form a hydrogen storage electrode. Using this as a negative electrode, a cell was manufactured in the same manner as described above.
(Hereinafter, this is referred to as comparison cell No. 1.) This cell No. 1
Was subjected to a cycle life test in the same manner as described above. Further, for comparison, a hydrogen storage alloy powder having the same composition as described above was prepared in advance by electroless plating to prepare a nickel storage coating hydrogen storage alloy powder, and the same amount as when preparing the electrode of the present invention as a conductive material. Copper powder having an average particle size of 2 μm and the same amount of fluororesin powder as described above were added, a hydrogen storage electrode was produced by the same means as described above, and a cell was produced by using this as a negative electrode by the same means as described above. (Hereinafter referred to as cell No. 2 for comparison)
This cell No. 2 was subjected to a cycle life test in the same manner as described above.

FIG. 1 shows the test results. As is clear from this figure, the comparative cell No. 2 using the nickel-plated coated hydrogen storage alloy powder as the negative electrode was the comparative cell No. 2 using the bare hydrogen storage alloy powder mixed with the copper powder as the negative electrode. The cycle life was slightly longer than that of .1, but only about 60 cycles. On the other hand, when the electrode of the present invention was used, a long-life cell whose cycle life easily exceeded 150 cycles or more was provided.

Incidentally, even if the hydride powder is used as a raw material instead of the hydrogen storage alloy powder, the operation and effect are essentially the same. The term "alloy" is used in a sense that also includes "its hydride". Therefore, the hydride examples were omitted.

Conductive material, as in the above example, in the production of the electrode,
It is common to add and mix the three components of the composite powder, the conductive material and the binder, but depending on the amount of the carbonyl nickel powder that is also the conductive material in the composite powder, the binder may be used. And a mixture of the above-mentioned components and a conductive material need not be separately added. Generally, the conductive material is preferably added in a range of 10 to 30% by weight based on the hydrogen storage alloy powder.

〔The invention's effect〕

As described above, according to the present invention, hydrogen storage mainly comprising a composite powder composed of a hydrogen storage alloy powder and a carbonyl nickel powder having a chain structure that is innumerably branched in a three-dimensional direction and coated with the particles is mainly used. Since the electrodes are formed, the carbonyl nickel powder particles form a three-dimensional chain between each other, thereby providing an electrode having good conductivity and an electrode using a conventional hydrogen-absorbing alloy powder mixed with copper powder or nickel. Compared to an electrode using a hydrogen-absorbing alloy powder coated with a plating, the present invention has an effect of providing an electrode having a significantly improved cycle life and a cell using the electrode as a negative electrode.

Further, according to the present invention, when the composite powder is produced integrally by sintering the hydrogen storage alloy powder and the carbonyl nickel powder, cracks and fragmentation accompanying expansion and contraction of the hydrogen storage alloy powder particles are provided. Dropout, cracking of the electrode, and the like are prevented by the carbonyl nickel powder coated thereon, which also has the effect of prolonging the life of the cell.

In this case, in the preparation of the composite powder, when at least 5% by weight of the carbonyl nickel powder is added to the hydrogen storage alloy powder, it is sufficient to coat the particles of the alloy powder and the conductivity is good. This has the effect of reliably providing an electrode with an improved life.

[Brief description of the drawings]

FIG. 1 shows a comparison graph of cycle life of a cell using the electrode of the present invention and a cell using a comparative electrode.

Claims (4)

(57) [Claims] 1. A hydrogen storage electrode mainly comprising a composite powder composed of a hydrogen storage alloy powder and a carbonyl nickel powder having a chain structure which is innumerably branched in a three-dimensional direction and is coated with the powder. 2. A mixture of a hydrogen storage alloy powder and a carbonyl nickel powder having a chain structure innumerably branched in a three-dimensional direction as a conductive material is fired in a vacuum heating furnace, and the composite sintered body is pulverized. A method for producing a hydrogen storage electrode, comprising: mixing the composite powder obtained as described above with at least a binder, and pressing the mixture onto a current collector. 3. The method for producing a hydrogen storage electrode according to claim 2, wherein at least 5% by weight of said carbonyl nickel powder is added to and mixed with said hydrogen storage alloy powder. 4. The method for producing a hydrogen storage electrode according to claim 2, wherein the composite powder is mixed with a binder and a conductive material, and the mixture is pressure-formed on a current collector. .