JPH03179664A - Hydrogen storage electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To increase cycle life by using specific carbonyl nickel powder as a conductive material mixed with hydrogen storage material powder. CONSTITUTION:Carbonyl nickel powder having three-dimensional chain structure and a particle size of 1mum or less is used as a conductive material mixed with hydrogen storage material powder comprising a hydrogen storage alloy and/or a hydride. Since particles of the hydrogen storage material powder are covered with the carbonyl nickel powder mixed, conductivity is increased, and stress applied to a whole electrode caused by expansion and shrinkage of each particle of the hydrogen storage material powder attendant on repeated chargedischarge is eased by the existence of the carbonyl nickel powder covering the particle, and the breakage of the particle and that of the electrode as a whole are prevented. The cycle life of the electrode is increased.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a hydrogen storage electrode for alkaline storage batteries.

[Conventional technology]

Conventional hydrogen storage electrodes for alkaline storage batteries are made by mixing a conductive material and a binder with hydrogen storage powder made of a hydrogen storage alloy or hydride that has the property of electrochemically absorbing and releasing hydrogen repeatedly. The mixture is then pressure-molded onto a current collector.

[Problem to be solved by the invention]

The conventional hydrogen storage electrode described above is used as the negative electrode of an alkaline storage battery, and as the battery is repeatedly charged and discharged,
Due to repeated engraving and shrinkage, the hydrogen-absorbing alloy element produces minute cracks, and even cracks occur in the entire electrode, which impairs the conductivity of the electrode, increases internal resistance, and reduces capacity. This resulted in inconveniences such as a shortened cycle life.

In order to solve this problem, it has been considered to coat the surface of the hydrogen storage alloy particles with an electroless plating film, but the plating process is complicated, and it is necessary to solve the above-mentioned disadvantages with a simpler method. That's it! ! , twist.

[Means to solve the problem]

The present invention provides an alkaline storage battery that can be easily manufactured without any prior treatment such as complicated plating on the hydrogen storage powder, eliminates the above-mentioned conventional disadvantages, and has an improved cycle life. Carbonyl nickel, which has a three-dimensional chain structure and has a diameter of 1 μm or less, is used as a conductive material mixed with a hydrogen storage powder made of a hydrogen storage alloy or/and a hydride. It is characterized by the use of powder.

[For production]

Effects of the present invention (Although it is not clearly understood, as mentioned above, the particles of hydrogen storage powder are surrounded by the carbonyl nickel powder having the above-mentioned characteristics, which increases the conductivity. However, due to the engraving and contraction of the particles of the hydrogen storage powder due to repeated charging and discharging, the stress is relaxed without being applied to the entire electrode due to the presence of the powder that encapsulates the particles, and the stress of the hydrogen storage powder is It is believed that cracks in the particles and in the entire electrode are effectively prevented, and as a result, the cycle life of the electrode is improved.

In this case, the carbonyl nickel powder preferably contains about 5 to 30 wt of the hydrogen storage powder in the range of χ.

〔Example〕

Next, examples of the present invention will be described.

Commercially available La, Ni, and AI were weighed and mixed at a constant composition ratio, and heated and melted using an arc melting method. At 1pA, a hydrogen storage alloy is prepared so that the alloy composition is 1aNI*, y^1o3, this alloy is made into a fine powder of 400 mesh or less, and a fluororesin and conductive resin are added to this hydrogen storage alloy powder as a binder. Carbonyl nickel powder, which will be described in detail later, was added as a material and mixed until the fluororesin was sufficiently fiberized. The mixture thus obtained was placed on a current collector, for example, a nickel wire gauze, and press-molded to form an electrode plate.

As the carbonyl nickel powder, for example,
lNC0 Ultra Fine Nickel Powder ($210
) is used. This nickel powder has countless branches in the three-dimensional direction, and the average diameter of the chain-like parts is 0.3~
It has a bulk density of approximately 0.3 t/cc and a specific surface area of approximately 2-/g"'C".

Therefore, in manufacturing the above electrode plate, the amount of nickel powder added was changed to 10 g (2.5^) of hydrogen storage alloy powder.
(equivalent to H), a number of electrode plates with different contents were fabricated.

Thus, each of the electrode plates made of these hydrogen storage alloys was used as a negative electrode, combined with a known sintered 2.7 gel electrode plate, and a cycle life test cell was constructed using caustic potassium water M solution as the electrolyte. Created. In this case, in order to understand the cycle life of the negative electrode, the negative electrode capacity was made smaller than the positive electrode capacity, and a negative electrode rule was adopted. Each cell was charged under the charging and discharging conditions at 0.5C for 2.5 hours (125% charge) and then discharged at 0.5C. Under these charging and discharging conditions, the discharge capacity of each cell after 10 charging and discharging cycles was measured. Thus, the amount of the carbonyl nickel powder used as the exclusive material of the present invention added to the hydrogen storage alloy powder, that is, the relationship between the content and the cell capacity is as shown in the relationship curve A in FIG. Ta. As is clear from this, in order to take out the original capacity of the hydrogen storage alloy in the negative electrode of the cell, it is preferable to contain about 5 wt.
Although some increase in capacity is observed as the content increases up to around 0vt, It can be seen that this results in a decrease in the energy density of the electrode. Therefore, in general, in the electrode of the present invention, the characteristic amount of the conductive material added, that is,
The content is preferably in the range of about 5 to 30 wt, 'X.

For comparison, carbonyl nickel powder lNC0I255 was used instead of the carbonyl nickel powder described above, and electrode plates made of hydrogen storage alloys with different contents were prepared by changing the amount added in the same manner as above. Cells were prepared in the same manner as above using each electrode plate as a negative electrode, and charge and discharge cycles were performed in the same manner as above, and the capacity after 10 cycles was measured. The relationship between its content and capacity is as shown in relationship curve B in FIG.

The average diameter of the chain portion of lNC01255 is 1.5
~3μm, bulk density is 0.5g/CC1 specific surface area is 0.5
rrf/g.

As shown in curve B, even if carbonyl nickel powder is used, if the diameter of the chain portion is 1.5 to 3 μm, which is much larger than 1 μm, even if the content is varied, Unable to obtain sufficient capacity, 30Wt,
However, it turned out that it was not possible to extract the original capacity of the hydrogen storage alloy.

Figure 2 shows the cycle life test conducted under the above charge/discharge cycle conditions using 10 wt of the above lNC01210 as a conductive material.
, a cell equipped with an electrode of the present invention containing X;
The respective characteristic curve holes and B' are shown for the results of comparing NC01255 with a cell equipped with a reference electrode containing the same 20 wt.

As is clear from this, comparison 1! The cell using the electrode had a significantly lower initial capacity than the cell using the electrode of the present invention, and also experienced a rapid capacity drop after 100 cycles. In contrast, the cell using the electrode of the present invention has a
Retains high capacity even after cycling.

For further comparison, the above-mentioned hydrogen-absorbing alloy powder was subjected to electroless plating in advance and coated with towt% plating. Similarly, a fluororesin is added and mixed, and the resin is mixed until it is sufficiently fiberized, and the obtained mixture is used to prepare a hydrogen storage electrode plate in the same manner as above, and this is used as a 1L electrode. A cell was prepared in the same manner as above, and a cycle life test was conducted on this cell under the same charging and discharging conditions as described above. The results were as shown in characteristic curve C in FIG.

Cycle life characteristic curve of a cell equipped with the electrode of the present invention +1!
Comparing characteristic curve A with characteristic curve C, it can be seen that they have equivalent performance.

In the above embodiments, a hydrogen storage alloy was used as the main material in the construction of the electrode, but the above object can be similarly achieved by using the hydrogen storage alloy as a hydride.

In addition, in the above embodiments of the present invention, fluororesin was used as the binder, but similar results can be obtained using polyethylene resin or other suitable synthetic resin, and foamed nickel plates or the like may be used as the current collector. Similar results can be obtained by using

〔Effect of the invention〕

As described above, a conductive material with a diameter of 1
By using carbonyl nickel powder, in which chain portions smaller than μm are branched into countless three-dimensional directions, an electrode with a large battery capacity and a long cycle life, and thus a battery, can be obtained, and it is easy to manufacture. In particular, the powder has an effect of about 5 to
When the content is in the range of 30 wtJ, it is possible to reliably obtain an electrode having characteristics of high energy density and long cycle life.

Claims (1)

[Claims] 1. Carbonyl nickel powder having a three-dimensional chain structure and having a diameter of 1 μm or less is used as a conductive material mixed with a hydrogen storage powder made of a hydrogen storage alloy or/and a hydride. 2. A hydrogen storage electrode for an alkaline storage battery characterized by
wt. The hydrogen storage electrode for an alkaline storage battery according to claim 1, wherein the hydrogen storage electrode contains %.