JPS622453A - Hydrogen-occlusion alloy electrode - Google Patents

Abstract

PURPOSE:To heighten the capacity of a hydrogen battery, by setting the quantity ratios of a hydrogen-occlusion alloy and a binder for the body of an electrode and the void percentage of the body, within appropriate ranges. CONSTITUTION:In a hydrogen-occlusion alloy electrode, a current collector is integrally provided on the electrode body in which a hydrogen-occlusion alloy and a binder are provided as essential constituents. The volume ratios of the hydrogen-occlusion alloy and the binder to the electrode body are set at 40-85% and 5-40%, respectively. The void percentage of the electrode body is set at 10-50%. If the void percentage were less than 10%, an electrolyte would no effectively infiltrate into the electrode body. If the void percentage were more than 50%, the amount of the hydrogen-occlusion alloy for constituting the electrode body would be so small as to make it hard to heighten the capac ity of a battery. If the volume ratio of the binder were less than 5%, the elec trode body could not be molded. If the volume ratio of the binder were more than 40%, the relative amount of the hydrogen-occlusion alloy which is the other essential constituent would decrease.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a hydrogen storage alloy electrode used, for example, as a hydrogen electrode in a hydrogen battery, and more specifically, to a hydrogen storage alloy electrode that is effective in contributing to increasing the capacity of a hydrogen battery. In particular, it relates to the electrode body, which is a fundamental component of the electrode.

[Technical background of the invention and its problems] Hydrogen storage alloys are attracting attention as materials for hydrogen electrodes in hydrogen secondary batteries. This is because the hydrogen storage alloy has the property of storing and releasing a large amount of hydrogen under normal pressure.

The electrode of a hydrogen battery using this hydrogen storage alloy generally has the following structure. That is, an electrode body with a predetermined thickness made by binding hydrogen storage alloy powder with a predetermined particle size with a predetermined amount of binder, and a current collector integrally attached to at least one surface of the electrode body by pressure bonding. It consists of

In the case of a hydrogen battery incorporating this electrode, hydrogen is first generated on the surface of the hydrogen storage alloy in the electrode body by electrolysis of water during charging, and this hydrogen is stored in the hydrogen storage alloy, and also during discharge. Then, this absorbed hydrogen reacts with hydroxyl groups in the electrolyte to generate water.

Therefore, the hydrogen storage alloy must simultaneously satisfy the following two conditions: (1) electrical continuity with the external circuit of the battery is maintained, and (2) the electrolyte is in contact with the surface of the hydrogen storage alloy. If even one of these conditions is missing, the electrochemical reaction on the surface of the hydrogen storage alloy will not proceed smoothly and the electrical capacity of the battery will be significantly reduced.

By the way, the above two conditions can be easily satisfied in a relatively short period of time near the surface of the electrode body;
However, inside the electrode body, that is, in the center of the body, it takes a considerable amount of time for the electrolyte to permeate and come into contact with the hydrogen storage alloy in that area, so the hydrogen storage alloy inside should be used effectively. result in a situation where it is not possible to do so.

On the other hand, in order to increase the capacity of a battery, it is sufficient to ■increase the amount of hydrogen storage alloy per unit volume, which means that ■it is sufficient to reduce the amount of binder as much as possible when forming the electrode body. . Considering the need to increase the contact opportunities between the electrolytic solution and the surface of the hydrogen storage alloy mentioned above, it is sufficient to increase the porosity of the electrode body. However, the problems of These are clearly contradictory conditions.

In addition, the condition (2) is such that if the amount of binder is too small, it will prevent the collapse of the electrode body due to the expansion of the hydrogen storage alloy during hydrogen storage and the miniaturization of the hydrogen storage alloy due to repeated volume increases and decreases during hydrogen release. This is disadvantageous because the wearability is reduced.

However, proper characterization of hydrogen storage alloy electrodes that enable high capacity hydrogen batteries has not been carried out, and therefore knowledge regarding the conditions that should be kept in mind when manufacturing appropriate hydrogen storage alloy electrodes is still lacking. has not been found.

[Object of the Invention] An object of the present invention is to provide a hydrogen storage alloy electrode that enables high capacity hydrogen batteries.

[Summary of the Invention 1 In order to achieve the above object, the present inventors characterized a hydrogen storage alloy electrode, and as a result, found appropriate ranges of the hydrogen storage alloy, binder, and porosity in the electrode body. Based on these findings, we have developed the hydrogen storage alloy electrode of the present invention.

That is, the hydrogen storage alloy electrode of the present invention is a hydrogen storage alloy electrode in which a current collector is integrally attached to an electrode body containing a hydrogen storage alloy and a binder as essential components. Volume ratio occupied by alloy is 5-40%
and the volume ratio occupied by the binder is 40 to 85%
and the porosity of the electrode body is 10 to 50%.

The electrode of the present invention is an integral structure of an electrode body, which will be described later, and a current collector, such as a nickel net or a stainless steel net, attached thereto. Usually, the current collector is crimped onto at least one side of an electrode main body having a predetermined thickness.

The electrode body is composed of a hydrogen storage alloy and a binder as essential components. In order to increase the conductivity of the electrode body, in addition to the above essential components, conductive powders such as carbon black and graphite fine powder, and KOH that promotes permeation of the electrolyte into the electrode are added.
There is no problem in adding a predetermined amount of additives such as , LiOH.

The hydrogen storage alloy is not particularly limited as long as it can store hydrogen during charging in the electrolyte used and release the stored hydrogen during discharge.Specifically, LaNi 5° MmNi5 (however,
Mm stands for Mitsushmetal).

LaNi5 (where L+o represents La-rich Mitsushi metal) or a portion of Ni in these alloys.

Mn, Fe, Go, Ti, Cu, Zn, Z
Ternary or quaternary alloys substituted with metals such as r, Cr; Mg2Ni alloy HT1Ni alloy HTiF
An example is an e-based alloy. These hydrogen storage alloys are usually used in the form of powder with an average particle size of 100 μm or less.

Any binder may be used as long as it binds the hydrogen-absorbing alloy powder to form the electrode body, has resistance to the electrolyte, and has appropriate water repellency.
In particular, it is preferable to use a bonding force that allows the electrode body to maintain its shape even if the hydrogen storage alloy is pulverized due to absorption and release of hydrogen. Specifically, examples include polytetrafluoroethylene, polyethylene, polyvinyl alcohol, and the like.

The electrode body is manufactured by mixing a predetermined amount of the above two components and applying a roll forming method or the like to the resulting mixture to form a sheet with a predetermined thickness. In the electrode body according to the present invention, the porosity is first set within the range of 10 to 50%. If this porosity is less than 10%, the electrolyte will not be able to penetrate effectively into the electrode body, and as a result, the effective use of the hydrogen storage alloy will be inhibited, making it difficult to achieve the goal of increasing capacity. On the other hand, if the porosity is greater than 50%, it becomes difficult to achieve a high capacity because the amount of hydrogen storage alloy constituting the electrode body decreases. Preferably it is 20-45%.

Next, the amount of binder is set so that the volume percentage occupied within the electrode body is 5 to 40%. This ratio is 5v
If it is less than 1%, it is impossible to mold the electrode body, and conversely, if it is more than 40vo1%.

As the relative amount of hydrogen storage alloy, another essential component, decreases, the capacity of the battery is a guideline for increasing capacity:
This is disadvantageous since the value is much lower than 600mAh/cm3.

The volume ratio of the hydrogen storage alloy in the electrode body is 40 to 8
It is set within the range of 5%. The ratio is 4゜7015
If it is less than 600ra, the above-mentioned guideline value for increasing capacity is 600ra.
It is difficult to extract a capacity of Ah/cr1 or more,
If the amount is more than 85%, the porosity will be less than 10% and/or the binder amount will be less than 5%, making it difficult to achieve a high capacity battery for the reasons mentioned above.

In addition, in both the hydrogen storage alloy and the binder, the volume of each component, which is the basis for calculating the volume ratio in the present invention, is expressed as the value obtained by dividing the used weight of the hydrogen storage alloy and binder by the specific gravity of each.

[Effects of the Invention] As described above, the hydrogen storage alloy electrode of the present invention is constructed with an electrode body that has the quantitative ratio of hydrogen storage alloy and binder necessary for high capacity, and has an appropriate porosity. Therefore, it has great industrial utility in achieving high capacity hydrogen batteries. Moreover, the amount of hydrogen storage alloy and binder used during the manufacture of this electrode body is controlled by volume control, so even if the components used are different, the amount of each component to be blended will be the same as the above-mentioned volume ratio. All you have to do is configure it.

Actual quality control can be carried out stably.

[Embodiments of the invention] 1'
8mNi4 as a hydrogen storage alloy for and
．． 2Mno, B powder was selected (particle size 20g), polyethylene 71 (low density 9 particle size 5-20q) was selected as a binder.
, specific gravity 0.915. M % manufactured by IJ Tex), polyethylene 2 (product name: Frose 7LF-7. Low density 9 particle size approx. Made of monofluorochemical ■, specific gravity 2.2), polyolefin (product name:
Miperon 1 particle size 20%.

Specific gravity 0.94. An average molecular weight of 2 million: manufactured by Mikata Petrochemical Co., Ltd.) was selected.

Using these, various hydrogen storage alloy electrodes were manufactured. A hydrogen battery was manufactured by incorporating these electrodes. In addition, the electrolyte solution was 8NKOH in all cases.

The capacity Δill of these hydrogen batteries was determined by a conventional method, and the value was divided by the weight of the hydrogen storage alloy used to calculate the battery capacity (mAh/g) per unit weight of the hydrogen storage alloy.

These are shown in FIG. 1 as a relationship with the porosity of each electrode body.

In the figure, the binder is polyethylene l. This is mixed with a hydrogen storage alloy, the resulting mixture is put into a mold together with a current collector net, and the whole is press-molded at 3.25 tons/-. After that, the binder is polyethylene 1, which is heat-treated to 150'0, and the binder is polyethylene 1. This is mixed with a hydrogen storage alloy, the resulting mixture is put into a mold together with the current collector net, and the whole is molded. After heating to 150°C, 3.25t
On / Pressure molded with a fan, - Low mark / Heingu is polyethylene 2, molded in the same way as ÷ mark, -1 - mark is a binder of polytetrafluoroethylene.

The mixture obtained by mixing this with a hydrogen storage alloy was made into a sheet with a current collector net crimped on one side, -Δ
The binder marked - is Miperon, which is mixed with a hydrogen storage alloy, the resulting mixture is put into a mold together with a current collector net, and after heating to 220°C, it is heated to 3.25 ton/c.
711, respectively.

As is clear from the figure, there is a certain correlation between capacity and porosity, regardless of the type of binder used. That is, when the porosity is less than 10%, almost no capacity can be extracted from the battery, and when it exceeds 40%, the extractable capacity is almost saturated.

2. In the hydrogen battery used in (1) with - and l1 of the binder, Figure 2 shows the effects that the volume ratios and porosity of the hydrogen storage alloy and binder in the electrode body have on each other on the battery capacity. Ta. In the figure, each town represents the same thing as in case (1). The number written near each town is the value obtained by dividing the capacity of each battery by the volume of the electrode, and the capacity per unit volume of the electrode. (represents mAh/a().

In addition, both songs &1A-11 in Figure 1 are curves connecting the equal capacitance values per unit volume of the electrodes in each battery, and represent so-called equal capacitance lines, that is, A: 500+sAh/(
74, B: 800mAh/i, C: 700■A
h/cnt, D: 8o.

It represents the isocapacitance line of mAh/Ai.

As is clear from the figure, in order to obtain a battery with a battery capacity of 800 ■Ah/CrA (curve B) or higher, which is the standard value for increasing the capacity of the battery, the volume ratio of the hydrogen storage alloy must be 40 μF% or more. It was found that the binder should have a porosity of less than 40% and a porosity in the range of 10-50%.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the capacity of a hydrogen battery incorporating a hydrogen storage alloy electrode and the porosity of the electrode body. FIG. 2 is a ternary correlation diagram between the volume proportions of the hydrogen storage alloy and the binder, and the porosity. Motsugi Amendsho January 21, 1986

Claims (1)

[Scope of Claims] In a hydrogen storage alloy electrode formed by integrally attaching a current collector to an electrode body containing a hydrogen storage alloy and a binder as essential components, the volume ratio occupied by the hydrogen storage alloy in the electrode body is 5~
40%, and the volume ratio occupied by the binder is 40 to 40%.
85%, and the porosity of the electrode body is 10 to 50.
% hydrogen storage alloy electrode.